# Crop sensors need cropped lenes



## Skulker (Aug 9, 2013)

I used to have a 7D. A camera I took many pictures with and really enjoyed. But I was using it mainly behind L series lenses because I wanted the quality that those lenses provide. This has proved to be a good investment as I now have a 5D3 and a 1Dx and the lenses work with them.

I don't want more megapixels, I've got more than I uses almost always. And before anyone suggests it I certainly don't want more just so I can crop them away. 

One of my main problems with all this kit is the weight, carrying 40Kg on a trek to a wild life photo opertunity can be a pain. 

When the 7D2 comes out the thing that would get me to buy one would be if light weight lens were available with similar quality to the L series but making use of the reduced diameter needed for the smaller sensor. (While they are at it they can reduce the price as the elements aren't as big.  )

I know its not going to happen but it would be nice if it did. ------- Just think a nice quality 200-400 with built in 1.4x at about 1/2 the weight and cost in front of a crop sensor giving equivalent view to a 300 to 900 on a FF. 8)

( BTW There can be little doubt that someone who thinks they know better will ridicule this idea. If they convince me that they are right I will claim I was being sarcastic ;D )


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## wsmith96 (Aug 9, 2013)

I would think that there is a market for what you are describing, but I suspect the camera manufacturers are not inclined to do this as it could cost them sales on full frame equivalents. This is where what Sigma is doing with their new lens lines is so interesting to me. They are bringing high lens quality down to the price points that mainstream customers, like myself, are willing to pay, and they appear to be targeting the consumer market.

my .$02


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## Drizzt321 (Aug 9, 2013)

wsmith96 said:


> I would think that there is a market for what you are describing, but I suspect the camera manufacturers are not inclined to do this as it could cost them sales on full frame equivalents. This is where what Sigma is doing with their new lens lines is so interesting to me. They are bringing high lens quality down to the price points that mainstream customers, like myself, are willing to pay, and they appear to be targeting the consumer market.
> 
> my .$02



Partially agree, I think the problem is that the 1st party (Canon/Nikon/etc) view the crop bodies as consumer oriented, and so people won't spend $1+K on a lens when they can be one that looks similar for $300. Consumer mentality. So they figure target the audience who will buy such expensive lenses, which is invariably the "pro" market which is generally FF/1D body people. With the 7D2, if it's basically a crop/mini 1DX with associated capabilities, I see that there definitely would be a pretty decent market for a very high quality/durability super-wide zoom and normal zoom (24-70 equivalent). Otherwise, once you get much beyond those 2 areas, you might as well keep your lens lineup consolidated because people are buying the telephoto/super-telephoto for the reach, and the crop will give you narrower FoV which extends the apparent focal length of those lenses. Besides, even if you make a 500mm for a crop, it's still going to be pretty big and heavy and you'll want a tripod anyway. Much cheaper and easier to not split the product lines like that.


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## schill (Aug 9, 2013)

Would a 300/2.8 (or anything else for that matter) be any smaller if it was made for a crop camera?

300/2.8 is 300/2.8. Unlike smaller cameras, we don't usually talk FF-equivalent with crop DSLRs so the lenses are the same.

I'm very happy with a 70-200/2.8 and 300/4 on my 7D. I like the focal lengths and I like the apertures. These would be more or less the same size if they were redesigned for crop, wouldn't they?

Also, I think Canon is probably aware that there are plenty of people buying L lenses for crop cameras. Maybe not a lot of 600mm lenses, but plenty of 300s and 70-200s based on what I've seen in use.


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## wsmith96 (Aug 9, 2013)

Drizzt321 said:


> Partially agree, I think the problem is that the 1st party (Canon/Nikon/etc) view the crop bodies as consumer oriented, and so people won't spend $1+K on a lens when they can be one that looks similar for $300. Consumer mentality.



I see your point and agree. What I was meaning to say is that typically the same quality of lens is not found specifically designed for the crop cameras. That doesn't mean you can't buy a 70-200L and use it. I consider the 17-55, 15-85, and 10-22 to be "higher-end" EF-S lenses, though they don't have the L badge. But, for example, Sigma's 18-35 that's coming out - it appears to be at an L level (or above) in image quality per what I've read. I don't think that canon will make a EF-S L lens, but if they did, I do think the lens would sell. This is where I think what sigma is doing is interesting - making higher quality lenses targeted for crop cameras. 

On the zooms that go over 100mm, I agree - makes no sense to not buy an EF L lens at this point in time.


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## pharp (Aug 9, 2013)

schill said:


> Would a 300/2.8 (or anything else for that matter) be any smaller if it was made for a crop camera?
> 
> 300/2.8 is 300/2.8. Unlike smaller cameras, we don't usually talk FF-equivalent with crop DSLRs so the lenses are the same.
> 
> I'm very happy with a 70-200/2.8 and 300/4 on my 7D. I like the focal lengths and I like the apertures. These would be more or less the same size if they were redesigned for crop, wouldn't they?



A 300 on a crop sensor could of course be smaller, and really smaller on a short back plane mirrorless - e.g. Olympus 75-300 is tiny (relatively) - just compare to Canon 70-300.


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## CanonOregon (Aug 9, 2013)

That's very interesting as I've had the same 'dream' as well! With every new Canon lens in the $10,000+ US range, it really prices out the advanced amateur. Canon already makes some near 'L grade' EF-S lenses. A kit with a lighter, say, 400mm f4 or a 200-400 f5,6 would be absolutely fantastic for 'soccer moms and dads', weekend birders, etc. If I won a big lottery I'd put out a bounty for someone to build a lens like that if Canon didn't take it up.


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## schill (Aug 10, 2013)

pharp said:


> schill said:
> 
> 
> > Would a 300/2.8 (or anything else for that matter) be any smaller if it was made for a crop camera?
> ...



How can the front element of a true 300/2.8 or 300/4 be any smaller than they are now? I thought the focal length and aperture of a telephoto lens pretty much determined that.

The Canon 70-300 4-5.6 is 3.0" D and 5.6" L.
The Olympus 75-300 4.6-6.7 is 2.7" D and 4.56" L.

So yes, the Olympus is smaller, but only about an inch shorter. Hardly "tiny" relative to the Canon. The Canon is also a faster lens (although they both use the same size filter, 58mm). The Canon also needs to have the IS mechanism inside (but that's a different discussion).

Based on size, I don't see a huge benefit from one to the other.


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## Drizzt321 (Aug 10, 2013)

schill said:


> pharp said:
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Yes, the f-stop is related to the length of the lens and the aperture, but when a lens has to cover a smaller image circle it can be made with smaller optical elements. Can't be made really much shorter. 300mm is 300mm after all (excepting DO optics). But the elements themselves can be made smaller, which means the lens can be smaller in diameter and lighter and cheaper.


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## Don Haines (Aug 10, 2013)

So now we do a little experiment....

Take a full frame lens and mount it on an APSC camera. Point it at a constant light source.... Something like a white wall under constant illumination.... You don't want something that requires precise positioning to get the same exposure... Set the camera to manual and adjust settings for the proper exposure.....

Now cut out a circle in a piece of dark paper with a hole in the center about 60 percent of the radius of your lens filter.... Place it over the end of the lens and see what happens to the light meter reading.... It drops.....about 1 stop....

This is what happens if you make the lens elements smaller.... It is light from the whole lens surface that gets focused onto the sensor, not just the center part of the lens surface... This is why a 300mm F2.8 lens is the same size no matter what size the sensor is.... Try this yourself if you do not believe me.

A crop sensor does not change the properties of a lens.... What is does is to sample a smaller area of the image circle and thereby reducing the field of view, but at the gain of a higher sampling density. The effect is the same field of view as if the lens was 1.6 times longer. A 300mm lens on a crop sensor would have the same field of view as a 480mm lens on a ff camera would have.... And yes, a 300mm F2.8 lens is a lot smaller and cheaper than a 480mm F 2.8 lens


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## Pi (Aug 10, 2013)

Skulker said:


> When the 7D2 comes out the thing that would get me to buy one would be if light weight lens were available with similar quality to the L series but making use of the reduced diameter needed for the smaller sensor. (While they are at it they can reduce the price as the elements aren't as big.  )



The smaller sensor (for telephoto lenses) is a problem, not a benefit. Additional glass is needed to focus the image on a smaller sensor, assuming you want the same light gathering ability. The m43 have some absurd f/2 zooms of that sort, they are monsters. 

Not that there is no benefit of designing lenses for crop sensors - they can be optimized differently, and be sharper. But equivalent lenses will not be smaller of cheaper.


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## Pi (Aug 10, 2013)

Drizzt321 said:


> Yes, the f-stop is related to the length of the lens and the aperture, but when a lens has to cover a smaller image circle it can be made with smaller optical elements. Can't be made really much shorter. 300mm is 300mm after all (excepting DO optics). But the elements themselves can be made smaller, which means the lens can be smaller in diameter and lighter and cheaper.



If you want equivalent lens, it can't. It can be actually larger because it needs more or thicker elements to focus to a smaller and closer sensor. 

With loss of light, it can be made smaller but then you can use slower EF lenses on your crop body.


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## TexPhoto (Aug 10, 2013)

The closest comparison I can find is:

Crop - Sigma 50-150mm DC OS 76 x 135 mm 1340g - $949
FF - Sigma 70-200mm OS 87 x 184mm 1390g - $1,249


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## schill (Aug 10, 2013)

TexPhoto said:


> The closest comparison I can find is:
> 
> Crop - Sigma 50-150mm DC OS 76 x 135 mm 1340g - $949
> FF - Sigma 70-200mm OS 87 x 184mm 1390g - $1,249



150 to 200 is a pretty big difference.


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## Mt Spokane Photography (Aug 10, 2013)

Skulker said:


> I used to have a 7D. A camera I took many pictures with and really enjoyed. But I was using it mainly behind L series lenses because I wanted the quality that those lenses provide. This has proved to be a good investment as I now have a 5D3 and a 1Dx and the lenses work with them.
> 
> I don't want more megapixels, I've got more than I uses almost always. And before anyone suggests it I certainly don't want more just so I can crop them away.
> 
> ...


 
You must have quite a outfit to weigh 40KG (88 lbs). Most bodies and lenses are in the 2-3 lb category, the big whites weigh more, so if you used a lot of lenses like the 400mm f/2.8, the weight would add up. 

You are asking for "L" quality, the 17-55mm IS is close. Its also big and heavy. As the focal lengths get longer, the ability to save any significant amount of weight due to smaller image circle diminishes.


A "L" quality 70-200mm f/2.8 EF-s will be smaller, but the "L" treatment with high density glass and fluorite elements will add weight. It takes more and stronger material to hold those heavy elements securely, and soon there is little weight savings and no cost savings. 

IMHO, I really doubt that there is a market for a $1800 70-200mm f/2.8 EF-s lens. Most would pay the $400 extra for a FF, because they intend to get FF in the future.

Get EF-S lenses like the 10-22. and 17-55, and hope for a L treatment for a 55-250 f/4 IS lens. Any longer focal length is not very likely to happen, but up to 300mm at f/5.6 could happen.


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## TexPhoto (Aug 10, 2013)

schill said:


> TexPhoto said:
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> > The closest comparison I can find is:
> ...



150 on a 1.5 crop is 225. on a 1.6 it's 240. 
The lens was actually created and marketed as a way to get a similar range on a crop that a 70-200 provides. If you have some better examples, tell me.


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## Pi (Aug 10, 2013)

TexPhoto said:


> schill said:
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Also, it is f/4.5 ( eq. to 80-240/4.5). As such, the closest comparison is the 70-200/4 IS, which is $1,150, 760 g, and well, shorter than 240mm but can take some cropping on FF and still be much better that the 50-150 on crop. 

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=404&Camera=453&Sample=0&FLI=4&API=0&LensComp=804&CameraComp=736&SampleComp=0&FLIComp=3&APIComp=0


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## Skulker (Aug 10, 2013)

Mt Spokane Photography said:


> Skulker said:
> 
> 
> > I used to have a 7D. A camera I took many pictures with and really enjoyed. But I was using it mainly behind L series lenses because I wanted the quality that those lenses provide. This has proved to be a good investment as I now have a 5D3 and a 1Dx and the lenses work with them.
> ...



I agree with much of what your saying and don't expect it to happen.

But although I would expect the saving in money would not be much I do think the saving in weight could be significant, and in size as well come to that.


Also forgot to say, yes I'm carrying a couple of ff bodies and several big whites plus tripods flashes a hide a chair, it all adds up.


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## Skulker (Aug 10, 2013)

Don Haines said:


> So now we do a little experiment....
> 
> Take a full frame lens and mount it on an APSC camera. Point it at a constant light source.... Something like a white wall under constant illumination.... You don't want something that requires precise positioning to get the same exposure... Set the camera to manual and adjust settings for the proper exposure.....
> 
> ...



Sorry Don but I don't think your experiment makes sense. All you are doing is reducing the efficency of the lens.
How about a different approach. Think of a magnifying glass. The smaller you make the images the brighter it becomes. This is the opposite of what we see with converters. They magnify the image so even more photons miss the sensor.

The way I would look at it is that of all the photons that enter a big white a fairly high percentage hit a full frame sensor. Just a few are lost as we use rectangular sensors behind a round lens. But when that sensor is cropped to 1/1.6 of the size then only about 40perecent of the original photons are captured. (that's 1/1.6 squared for the mathematically inclined)


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## schill (Aug 10, 2013)

TexPhoto said:


> schill said:
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But I don't want the equivalent of a FF 200 on my 7D, I want to use a 70-200/2.8 (real numbers) which gives me an "effective" 320. A crop specific true 70-200/2.8 will not be much smaller than a FF lens.


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## rs (Aug 10, 2013)

The size and weight of all telephoto lenses is largely driven by their physical length, and the size of the front element. Those two factors are driven purely by focal length and aperture. For instance, get a 300/4, and with a simple bit of mathematics you can calculate the front element will be a quarter of 300mm - and the filter size is a very close match at 77mm. The 85/1.2 should have a theoretical 71mm front element, and it's filter size is 72mm. And so on.

This formula holds true for most lenses until the angle of view gets wider than about 45 degrees. At that point, the aperture is no longer dictates the size of the front element. Otherwise we would have a 14/2.8 with a 5mm diameter front element (entirely possible in a compact where the AoV is narrower than 45', but not possible on a FF DSLR).

It is with lenses wider than about 45 degrees AoV that they can be made smaller for these smaller imaging circles. Which is why normal zooms and ultrawides are typically made for crop sensor DSLR's, and no-one to my knowledge makes a crop only telephoto lens who's angle of view is (at its widest setting) much narrower than 45 degrees.


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## Sporgon (Aug 10, 2013)

The OP's got a point, and there are systems out there that fit the bill. Look at the Pentax 50-135 f2.8. It is much smaller and lighter than the FF equivalent 70-200 f2.8. The FF producers don't seem inclined to produce this kind of kit, probably for the reasons others have mentioned.


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## Skulker (Aug 10, 2013)

Sporgon said:


> The OP's got a point, and there are systems out there that fit the bill. Look at the Pentax 50-135 f2.8. It is much smaller and lighter than the FF equivalent 70-200 f2.8. The FF producers don't seem inclined to produce this kind of kit, probably for the reasons others have mentioned.



Thanks Sporting. That's what I was thinking of, it's half the weight for an equivalent image, I guess I really mean field of view. The quality may not be big white equivalent but nor is the price.

This example makes me think it would be possible to have much lighter systems that were close in quality.

I still don't think it will happen but I would like to see this more than a high megapixel camera.


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## rs (Aug 10, 2013)

Skulker said:


> Sporgon said:
> 
> 
> > The OP's got a point, and there are systems out there that fit the bill. Look at the Pentax 50-135 f2.8. It is much smaller and lighter than the FF equivalent 70-200 f2.8. The FF producers don't seem inclined to produce this kind of kit, probably for the reasons others have mentioned.
> ...


That Pentax lens, mounted to a Pentax body with its 1.5x crop factor is the direct equivalent of a 75-202/4.2 lens. Canon have the 70-200/4 L lens, which shares the same size filter size, is less than 3% heavier, and is 38% cheaper here in the UK. Admittedly the FF Canon lens is 26% longer, but the OP is mostly interested in weight saving. 3% more weight for 10% more light gathering is a good deal in my eyes, especially when you throw in the huge cost saving.

Also, if you're just after lightweight reach, the 70-200/4 when used on a crop camera is much a better compromise than a 50-135/2.8, even when you count the extra 3% weight.


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## Sporgon (Aug 10, 2013)

You'll open a whole can of worms with the 2.8 on APS is equal to 4.2 FF thing. 

A 2.8 lens is just that: 2.8. Yes due to the different COC the depth of field equivalent is 'slower' on the smaller format in resulting dof. ( I believe it's more like 3.2-3.6 depending on exact format). But the difference is really over stated here on CR IMO. 

You are still getting the fundamental benefits of a 2.8 lens. 

At Building Panoramics we've used FF since 2005, but I'm sure we could use APS to achieve the same thing.However with present technology certainly prefer the results from the less dense sensors such as the 1100D to say a 7D. 

You're quite right on the price of the Pentax lenses. They look very poor value next to Canon, and the 70-200 f4 L is much more substantially built.


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## Skulker (Aug 10, 2013)

The issue of a cropped 2.8 and equivalence to 4.2 FF is sure to get some folks wound up and may well produce some long posts. ;D

My view would be that with any lens designed to be used on a crop sensor, most of the photons entering the lens will hit the sensor, subject of course to the rectangular sensor reading a round lens. In contrast only 40% of the photons that would have hit the sensor on a full frame body will be used in a crop body (assuming a 1.6 crop) with a FF lens.

I'm getting more convinced that long lenses specifically designed for crop bodies would have a weight benefit. I still can't see Canon or Nikon making them. But maybe someone like Sigma might just do it to give themselves a USP.


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## rs (Aug 10, 2013)

Skulker said:


> The issue of a cropped 2.8 and equivalence to 4.2 FF is sure to get some folks wound up and may well produce some long posts. ;D


I'm keeping my mouth shut about that one from now on :-X


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## Pi (Aug 10, 2013)

Sporgon said:


> You'll open a whole can of worms with the 2.8 on APS is equal to 4.2 FF thing.
> 
> A 2.8 lens is just that: 2.8.



http://www.josephjamesphotography.com/equivalence/#1

2.8 is a denominator in a ratio, actually. You are forgetting the numerator. What you really mean, is, say, 50/2.8 is 80/2.8, and that is wrong.


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## neuroanatomist (Aug 10, 2013)

Pi said:


> Sporgon said:
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> > You'll open a whole can of worms with the 2.8 on APS is equal to 4.2 FF thing.
> ...



So you're saying the sensor size changes the numerator (focal length), and that's wrong, too. Focal length and max aperture are intrinsic properties of a lens, the sensor doesn't change them.


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## Pi (Aug 10, 2013)

neuroanatomist said:


> Pi said:
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> > Sporgon said:
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No, the sensor size does not change the FL. You are changing it, to get the same picture.

How often do you shoot with your smartphone at 200mm?


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## neuroanatomist (Aug 10, 2013)

Pi said:


> neuroanatomist said:
> 
> 
> > So you're saying the sensor size changes the numerator (focal length), and that's wrong, too. Focal length and max aperture are intrinsic properties of a lens, the sensor doesn't change them.
> ...



Maybe I'm not changing focal length, just moving forward or back... Or maybe I'm taking a different picture. 



Pi said:


> How often do you shoot with your smartphone at 200mm?



Just once, when I mounted my 70-200 II on my iPhone with an iPhone-to-EF Mount Adaptor that I borrowed from a friend.


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## Mt Spokane Photography (Aug 10, 2013)

Skulker said:


> Mt Spokane Photography said:
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## Pi (Aug 10, 2013)

neuroanatomist said:


> Pi said:
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Are we still talking about the Pentax 35-70 on crop vs. the 70-200 on FF? If you are taking a different picture, then this would be a different conversation. You can take different pictures with the same combo, as well.




> Pi said:
> 
> 
> > How often do you shoot with your smartphone at 200mm?
> ...




Would you post the result? That wold be interesting to see!


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## moreorless (Aug 10, 2013)

The discussion really seems to be focused on two different things...

1.Making a smaller/cheaper lens for ASPC with the same focal length.

2.Making a smaller/cheaper lens for ASPC with the same field of view.

The second clearly being possible while the first probably isn't.

My guess is that with crop cameras the market for a lens with 70-200mm FOV isn't that great, that range seems to be well suited for things like event photography and I'm guessing most pro's are going to be using FF. On ASPC I think the demand is much more long longer fast lenses for wildlife/sports use.


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## neuroanatomist (Aug 10, 2013)

Pi said:


> Are we still talking about the Pentax 35-70 on crop vs. the 70-200 on FF? If you are taking a different picture, then this would be a different conversation. You can take different pictures with the same combo, as well.



I wasn't, ever. Sprogon stated that f/2.8 is f/2.8, and you apparently disagreed. 



Pi said:


> How often do you shoot with your smartphone at 200mm?
> 
> 
> > Just once, when I mounted my 70-200 II on my iPhone with an iPhone-to-EF Mount Adaptor that I borrowed from a friend.
> ...



It really wouldn't - I just used it out the window of my 8th floor office.

However, what was I actually using? 

1) 70-200mm f/2.8,
2) 535-1528mm f/2.8, or
3) 535-1528mm f/21? 

Sounds like I'd say #1, you'd say #3, and Panasonic would print #2 on the side of their lens barrel, like they do on the Lumix FZ200. :


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## Etienne (Aug 10, 2013)

I have a Tokina 50-135 f/2.8 equiv to 80-112 mm.
It's a great lens. Much smaller than my 70-200L 2.8 IS II. BONUS: It is par-focal and that makes a big difference in video.
Pair that with a Tokina 11-16 f/2.8 and it is a great light-weight package for crop.
You could also add Sigma 30 1.4 and/or Canon 50 1.4.


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## Daniel Flather (Aug 10, 2013)

CanonOregon said:


> If I won a big lottery I'd put out a bounty for someone to build a lens like that if Canon didn't take it up.



Or just buy what's current and hire a assistant to haul your sh*t around.


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## Pi (Aug 10, 2013)

neuroanatomist said:


> However, what was I actually using?
> 
> 1) 70-200mm f/2.8,
> 2) 535-1528mm f/2.8, or
> ...



You were shooting (1), which was _equivalent _to (3); and (2) is wrong any way you look at it.


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## neuroanatomist (Aug 10, 2013)

Pi said:


> neuroanatomist said:
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> > However, what was I actually using?
> ...



Someone should tell Panasonic...


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## Pi (Aug 10, 2013)

neuroanatomist said:


> Pi said:
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A good lawyer?


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## carlh (Aug 10, 2013)

Skulker said:


> The issue of a cropped 2.8 and equivalence to 4.2 FF is sure to get some folks wound up and may well produce some long posts. ;D



Certainly 

A FF lens being used with an APS-C sensor results in a slower system, lens+sensor. Since the APS-C sensor only captures 40% of the light projected by the lens on the image plane, the combination is slower than if the same lens had been used with a FF sensor. The lens is of course the same and doesn't know what sensor you place behind. But a lens on its own will not produce any pictures. You need a sensor as well. Really, I cannot see the controversy. 



> My view would be that with any lens designed to be used on a crop sensor, most of the photons entering the lens will hit the sensor, subject of course to the rectangular sensor reading a round lens. In contrast only 40% of the photons that would have hit the sensor on a full frame body will be used in a crop body (assuming a 1.6 crop) with a FF lens.
> 
> I'm getting more convinced that long lenses specifically designed for crop bodies would have a weight benefit. I still can't see Canon or Nikon making them. But maybe someone like Sigma might just do it to give themselves a USP.



What you are describing is called a speed booster, and it is available today for mirror less cameras. 

http://www.metabones.com/buy-speed-booster

If, as you suggest above, you take, say, a 300 mm f/4 lens and project the otherwise wasted FF-photons onto the smaller APS-C sensor, the smaller sensor would still record the same FOV and the same amount of light as the FF sensor. This is because the aperture still has the same absolute size 300/4=75 mm.

However, by doing this you also decrease the focal length of the lens by a factor 1.6. So, while the absolute size of the aperture stays constant, its relative size increases to about f/2.5.

So, there you have it. The same FOV and the same amount of light captured by APS-C and FF. But, you have to decrease the FL with the crop sensor and keep the absolute aperture the same. This of course increases the relative size of the aperture. Hence the f/4 on FF is equivalent to f/2.5 on APS-C.

Unfortunately, if you want to capture a certain amount of light from a distant object the optics need to be of a certain size. You cannot fool the laws of physics just by cropping the sensor. Otherwise, why would e.g. the astronomers keep building larger and larger telescopes if they could just achieve the same thing by cropping their imaging sensors.

This is why its rather pointless to design APS-C only tele lenses. For WA lenses on the other hand its a different story as you can position the lens elements closer to the sensor due to the smaller mirror. Or lack of a mirror.


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## Skulker (Aug 10, 2013)

Well Carl that was a long post ;D

however you seem to have misunderstood my meaning.

I was not describing or promoting a speed booster, although that would, be one way of making use of the photons that are wasted when you put a bigger than needed lens (such as FF) on a smaller sensor (such as APS)

I would redesign the lens so it did not collect light that was not used. So it would be either lighter or brighter. Or maybe a bit of both.

Please don't try to imply that I'm thinking to break, fool, or in any way mess with the laws of physics. 8) cos I ain't. If you think that is what I'm trying to do then you are misunderstanding me. 

The main reason that I'm not talking about this or that f stop or focal length is that as an engineer is that to me it is irrelevant what sensor is behind a lens, when it comes to describing its physical properties.


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## Pi (Aug 10, 2013)

Skulker said:


> I would redesign the lens so it did not collect light that was not used. So it would be either lighter or brighter. Or maybe a bit of both.



The way to do this is to make the front glass element less curved, with all the implications of this on the rest or them. An EF, say, 70-200/2.8 lens has actually a wider FOV than a hypothetical EF-S 70-200/2.8. By doing so, you will get better performance - a good enough reason to design such a lens, IMO. But ... it would not be smaller, really. The front element will be more or less of the same diameter, approximately equal to 200/2.8 The back one would not be smaller but the size of the back is fixed by the mount anyway.


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## dougkerr (Aug 10, 2013)

> A FF lens being used with an APS-C sensor results in a slower system, lens+sensor. Since the APS-C sensor only captures 40% of the light projected by the lens on the image plane, the combination is slower than if the same lens had been used with a FF sensor. The lens is of course the same and doesn't know what sensor you place behind. But a lens on its own will not produce any pictures. You need a sensor as well. Really, I cannot see the controversy.



Not so.

The effect of a lens on exposure depends on its f-number. For, say, an f/4.0 lens, the luminance on the sensor for some part of the scene of course does not depend on the sensor overall size.

If we have two cameras, one with a larger sensor that the other, both with sensor systems that we operate at an ISO SOS of ISO 400, then for a given scene, the same exposure result will be obtained with the same shutter speed and f-number.

Indeed, the total amount of light captured across the entire sensor is less for a smaller sensor than for a larger one. But the light per unit area (the property to which the sensor responds, for any given ISO sensitivity) will remain the same.

Best regards,

Doug





> My view would be that with any lens designed to be used on a crop sensor, most of the photons entering the lens will hit the sensor, subject of course to the rectangular sensor reading a round lens. In contrast only 40% of the photons that would have hit the sensor on a full frame body will be used in a crop body (assuming a 1.6 crop) with a FF lens.
> 
> I'm getting more convinced that long lenses specifically designed for crop bodies would have a weight benefit. I still can't see Canon or Nikon making them. But maybe someone like Sigma might just do it to give themselves a USP.



What you are describing is called a speed booster, and it is available today for mirror less cameras. 

http://www.metabones.com/buy-speed-booster

If, as you suggest above, you take, say, a 300 mm f/4 lens and project the otherwise wasted FF-photons onto the smaller APS-C sensor, the smaller sensor would still record the same FOV and the same amount of light as the FF sensor. This is because the aperture still has the same absolute size 300/4=75 mm.

However, by doing this you also decrease the focal length of the lens by a factor 1.6. So, while the absolute size of the aperture stays constant, its relative size increases to about f/2.5.

So, there you have it. The same FOV and the same amount of light captured by APS-C and FF. But, you have to decrease the FL with the crop sensor and keep the absolute aperture the same. This of course increases the relative size of the aperture. Hence the f/4 on FF is equivalent to f/2.5 on APS-C.

Unfortunately, if you want to capture a certain amount of light from a distant object the optics need to be of a certain size. You cannot fool the laws of physics just by cropping the sensor. Otherwise, why would e.g. the astronomers keep building larger and larger telescopes if they could just achieve the same thing by cropping their imaging sensors.

This is why its rather pointless to design APS-C only tele lenses. For WA lenses on the other hand its a different story as you can position the lens elements closer to the sensor due to the smaller mirror. Or lack of a mirror.
[/quote]


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## jrista (Aug 10, 2013)

Pi said:


> neuroanatomist said:
> 
> 
> > However, what was I actually using?
> ...



It would be equivalent to #2. *Lenses focus light.* Aperture affects the amount of light _focused_ at any given point resolved at the sensor plane. Cropping out the center doesn't change the fact that an f/2.8 lens focuses the same amount of light on the center point of an APS-C sensor as on an FF sensor. Yes, total quantity of light imaged is less, but the amount of light focused anywhere on the sensor is the same. Therefor, an f/2.8 lens is an f/2.8 lens, regardless of the size of the sensor (even the microscopic iPhone sensor will still receive the same amount of light at the center as an APS-C or FF.)


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## Pi (Aug 10, 2013)

jrista said:


> Cropping out the center doesn't change the fact that an f/2.8 lens focuses the same amount of light on the center point of an APS-C lens as on an FF lens.



Right, and that amount is zero.


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## Pi (Aug 10, 2013)

dougkerr said:


> If we have two cameras, one with a larger sensor that the other, both with sensor systems that we operate at an ISO SOS of ISO 400, [...]



Why the same ISO?


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## jrista (Aug 10, 2013)

Pi said:


> jrista said:
> 
> 
> > Cropping out the center doesn't change the fact that an f/2.8 lens focuses the same amount of light on the center point of an APS-C lens as on an FF lens.
> ...



Why is it zero?


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## Pi (Aug 10, 2013)

jrista said:


> Pi said:
> 
> 
> > jrista said:
> ...



You integrate the intensity (modeled by a continuous function) over a set consisting of one point. Another way to say it - a point has area zero, and receives zero light.


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## jrista (Aug 11, 2013)

Pi said:


> jrista said:
> 
> 
> > Pi said:
> ...



Alright, now your just playing games.  You know what I mean. Lets call it a "spot", if you want to get that technical. 

Anyway, assuming two point light sources of equal intensity, they both focus a spot of light on the sensor plane of identical intensity, regardless of whether that spot is focused on an APS-C or FF sensor. In the little diagram below, the red represents a focused point light source that resolves to a spot on both the APS-C and FF sensors. The aperture blocks some light from the right-hand side of the lens, and the amount of light blocked is the same for both FF and APS-C. 

The blue is simply for demonstration. It is a point of light focused outside of the range of the APS-C sensor. It only falls on the FF sensor, however that does not change the fact that it is the lens and aperture that determines the amount of light that is actually focused at that spot, same as with the red. Total volume of light passing through the aperture that is actually imaged by the FF sensor is higher, however for any given spot, it is the same, regardless of sensor size. (I could have thrown a tiny little sensor in there for the iPhone...if I located it under the resolved spot of light for the red sample, it would be receiving the exact same amount of light as the APS-C and FF.)


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## Pi (Aug 11, 2013)

jrista said:


> Total volume of light passing through the aperture that is actually imaged by the FF sensor is higher, however for any given spot, it is the same, regardless of sensor size.



OK, you are talking about intensity. It is the same, indeed. So what? Why is intensity of light, on sensors of different sizes, a factor we have to worry about?


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## jrista (Aug 11, 2013)

Pi said:


> jrista said:
> 
> 
> > Total volume of light passing through the aperture that is actually imaged by the FF sensor is higher, however for any given spot, it is the same, regardless of sensor size.
> ...



Well, if you go back to the original post I replied to, you stated that using a 70-200 f/2.8 on an iPhone was actually like using a 535-1528mm f/21. *Given the fact that aperture affects the intensity of any given spot of focused light*, it really *is* like using a 535-1528mm f/2.8. I am just disputing the notion that would become an f/21 lens, and stating that an f/2.8 lens is an f/2.8 lens regardless of the size of the sensor it is used on. Sensor size has no impact on aperture. You may be trying to say something else, but the terms you used in the original post I responded to is rather misleading about the relationship between aperture and sensor size. 

For further evidence...the use of a focal reducer changes the optical nature _of the lens_, which is why on a mirrorless you can focal reduce an f/4 lens to f/2.5 (as noted by _dougkerr_). However it should be noted that the change in relative aperture has nothing to do with the fact that the sensor is smaller than the image circle was originally designed for...it has to do with the fact that the focal length of the lens was shortened while the entrance pupil remained the same size.


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## neuroanatomist (Aug 11, 2013)

Pi said:


> dougkerr said:
> 
> 
> > If we have two cameras, one with a larger sensor that the other, both with sensor systems that we operate at an ISO SOS of ISO 400, [...]
> ...



Because that gives the same exposure. Of course, since total light gathered is different, image noise at the same ISO is not equal...


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## jrista (Aug 11, 2013)

Skulker said:


> I used to have a 7D. A camera I took many pictures with and really enjoyed. But I was using it mainly behind L series lenses because I wanted the quality that those lenses provide. This has proved to be a good investment as I now have a 5D3 and a 1Dx and the lenses work with them.
> 
> I don't want more megapixels, I've got more than I uses almost always. And before anyone suggests it I certainly don't want more just so I can crop them away.
> 
> ...



It seems to me that this is pretty much what the micro4/3rds manufacturers have done. They took a smaller sensor, and designed a whole range of small, compact lenses in just the right way to provide optimal performance for that smaller sensor. Those smaller sensors have smaller pixels, and consequently a similar change in performance relative to the big pixels of a FF sensor.

I doubt Canon or Nikon would ever support the micro4/3 sensor, at least not in their DSLR products. I would say that if you don't care about having an OVF, then mirrorless is really what you are looking for. The Canon EOS-M is an APS-C system that should eventually get a whole range of lenses explicitly designed for that particular sensor. Not only can the lenses be smaller, the whole entire package is smaller, and if size and weight is your greatest concern, then you could save yourself a lot of hassle by using an EOS-M setup (albeit with a more limited range of lenses as of today...i.e. if you need 600mm, your just kind of out of luck at the moment in the Canon world.)


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## Pi (Aug 11, 2013)

jrista said:


> Pi said:
> 
> 
> > OK, you are talking about intensity. It is the same, indeed. So what? Why is intensity of light, on sensors of different sizes, a factor we have to worry about?
> ...



This does not answer my question. What is so sacred about _the same intensity_? Why is that of such a big concern?


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## Pi (Aug 11, 2013)

neuroanatomist said:


> Pi said:
> 
> 
> > dougkerr said:
> ...



... which confirms that the APS-C system in this scenario is "slower", and that was the reason for my remark.


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## jrista (Aug 11, 2013)

Pi said:


> neuroanatomist said:
> 
> 
> > Pi said:
> ...



It isn't slower. The total light over the area of the sensor MAY be more finely divided (there is no reason an APS-C sensor couldn't have the same pixel pitch as an FF, or for that matter, larger pixels), but that does not change how fast the whole area saturates at a given EV. If the APS-C sensor was _slower_, the *exposure value* at a given aperture and shutter speed would be different, yet that is not the case. For any given aperture and shutter speed, exposure value is always the same, as it doesn't have anything to do with sensor area. 

The noise increases because the pixels are smaller, not because the sensor, or he lens, is "slower." Back to the same old argument, but shoot the same subject with the same lens at the same distance, crop the FF, and scale the APS-C image to the same size as the cropped FF image. Noise and EV will be the same. Frame the two identically with the same lens, noise will be lower on the FF, while EV will still be the same. The only thing that changed when framing identically is _pixels on the subject_...the *speed *of the exposure remains the same.


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## Sporgon (Aug 11, 2013)

Sporgon said:


> You'll open a whole can of worms with the 2.8 on APS is equal to 4.2 FF thing.




Told you


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## jrista (Aug 11, 2013)

Sporgon said:


> Sporgon said:
> 
> 
> > You'll open a whole can of worms with the 2.8 on APS is equal to 4.2 FF thing.
> ...



 Sorry.


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## Pi (Aug 11, 2013)

jrista said:


> It isn't slower. The total light over the area of the sensor MAY be more finely divided (there is no reason an APS-C sensor couldn't have the same pixel pitch as an FF, or for that matter, larger pixels), but that does not change how fast the whole area saturates at a given EV. If the APS-C sensor was _slower_, the *exposure value* at a given aperture and shutter speed would be different, yet that is not the case. For any given aperture and shutter speed, exposure value is always the same, as it doesn't have anything to do with sensor area.
> 
> The noise increases because the pixels are smaller, not because the sensor, or he lens, is "slower." Back to the same old argument, but shoot the same subject with the same lens at the same distance, crop the FF, and scale the APS-C image to the same size as the cropped FF image. Noise and EV will be the same. Frame the two identically with the same lens, noise will be lower on the FF, while EV will still be the same. The only thing that changed when framing identically is _pixels on the subject_...the *speed *of the exposure remains the same.



Totally wrong, sorry. The shot noise is dependent on the total light. Intensity if irrelevant. 

*EDIT*: _"Exposure Value" is a vague term you just invented. Pixel size is largely irrelevant._* I was wrong with that. Consider it withdrawn. *
Read this, again:

http://www.josephjamesphotography.com/equivalence/

The source of the (photon) noise is not the pixels, it is the photon nature of light. 

http://www.josephjamesphotography.com/equivalence/#shot

Please, read something before you reply.


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## neuroanatomist (Aug 11, 2013)

Pi said:


> "Exposure Value" is a vague term you just invented.
> 
> Please, read something before you reply.



Lol, sorry but you lost a big quotient of credibility there. Might want to follow your advice and do a little reading yourself. :


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## jrista (Aug 11, 2013)

Pi said:


> "Exposure Value" is a vague term you just invented.





> Please, read something before you reply.



Umm...*seriously?* Why not read a little first yourself before replying: Exposure Value.

I don't know why I am debating with you if you do not even know about exposure value... ???



Pi said:


> The source of the (photon) noise is not the pixels, it is the photon nature of light.
> 
> http://www.josephjamesphotography.com/equivalence/#shot



I never said anything about the source of photon shot noise. Only that it is higher with smaller pixels due to their reduced full well capacity (maximum signal strength, which has a direct impact on per-pixel SNR, and therefor a direct impact on poisson, or shot, noise, which is the square root of the signal strength). If you have an APS-C sensor with pixels half the pitch of an FF sensor, averaging four of them together will result in the same amount of noise as a single FF pixel. Total amount of light is the same...it is just more finely delineated.


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## Ellen Schmidtee (Aug 11, 2013)

schill said:


> Would a 300/2.8 (or anything else for that matter) be any smaller if it was made for a crop camera?



No, but a photographer who has a crop camera would take a 180mm or 200mm lens to get the same angle of view as 300mm on FF, and that one would (or at least could) be smaller.

If he would also like to have the same DoF, the lens would have to be 1+ stop faster, which would offset much of the weight & size saving. E.g. the 200mm f/2 & the 300mm f/2.8 lenses have practically the same weight & length, the 200mm saves ~4cm in length - not a big difference.


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## rs (Aug 11, 2013)

Sporgon said:


> Sporgon said:
> 
> 
> > You'll open a whole can of worms with the 2.8 on APS is equal to 4.2 FF thing.
> ...


Next time, I'm saying nothing!


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## dgatwood (Aug 11, 2013)

Ellen Schmidtee said:


> schill said:
> 
> 
> > Would a 300/2.8 (or anything else for that matter) be any smaller if it was made for a crop camera?
> ...



Size, perhaps not, but unless I'm missing something, the weight difference could be considerable. The exit pupil would be the same size, and the length of the lens might be similar if it had the same number of elements, but all other things being equal, the diameter of the elements should be smaller because you need less glass to make a smaller image circle.

Now I know that the difference in lens diameter between EF and EF-S is not as extreme with longer lenses as it is for wide-angle lenses, but because the area (and thus, the volume) of a lens element falls off with the square of the diameter, even small changes could make a big difference in weight. For example, suppose an EF-S version of a 300mm f/2.4 were able to shave three millimeters off the diameter of the lens, from ~127mm to ~124mm. (That second number is entirely made up, BTW.) By my quick and dirty math, that tiny change in diameter would likely translate to almost a 5% reduction in lens element weight, which is not an insignificant difference.


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## Hillsilly (Aug 11, 2013)

In my opinion, if Canon made an EF-S 200mm f/2.8 which sold for around $500-$600 or a 300mm f/4 for around $800 and they were both high image quality, image stabilized, weather sealed, fast focusing lenses, many soccer mums (and dads) would want one...even if the size and weight savings were minimal.


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## rs (Aug 11, 2013)

dgatwood said:


> Size, perhaps not, but unless I'm missing something, the weight difference could be considerable. The exit pupil would be the same size, and the length of the lens might be similar if it had the same number of elements, but all other things being equal, the diameter of the elements should be smaller because you need less glass to make a smaller image circle.
> 
> Now I know that the difference in lens diameter between EF and EF-S is not as extreme with longer lenses as it is for wide-angle lenses, but because the area (and thus, the volume) of a lens element falls off with the square of the diameter, even small changes could make a big difference in weight. For example, suppose an EF-S version of a 300mm f/2.4 were able to shave three millimeters off the diameter of the lens, from ~127mm to ~124mm. (That second number is entirely made up, BTW.) By my quick and dirty math, that tiny change in diameter would likely translate to almost a 5% reduction in lens element weight, which is not an insignificant difference.


The physical diameter of the aperture of the lens can be worked out by a simple formula, and imaging circle has nothing to do with it:

*focal length divided by aperture*

The front element simply cannot get any smaller than that, otherwise either the focal length or the aperture is smaller than reported. When the AoV gets wider, the front element does get a lot bigger than the aperture. However, if the AoV is narrower than about 45º (which is a combination of focal length _and_ imaging circle size), there are many examples of EF lenses whose filter size is almost identical to their focal length divided by aperture:

EF 85/1.2 - Aperture size: 71mm - Filter size: 72mm
EF 200/2.8 - Aperture size: 71mm - Filter size: 72mm
EF 300/4 - Aperture size: 75mm - Filter size: 77mm

If any of these were to be remade as an EF-S lens of the same focal length and aperture, how could the smaller imaging circle make them any smaller/lighter? Bear in mind the physical length is dictated by focal length, the filter size is already as small as it could be, and the physical diameter and flange distance of the EF-S mount is identical to the EF mount. The extra depth that the rear elements can protrude into the body due to the smaller mirror doesn't help telephoto lenses as they're not retrofocus designs.

Canon _could_ make a lens such as an EF-S 300/4 lens, but I see no room to make it smaller or lighter than its EF counterpart, other than the use of new materials and fewer/thinner/DO elements, which of course they could apply to an EF lens too.

I still believe any lens which is telephoto (narrower AoV than about 45º) has no advantage being made for crop only - especially when the EF-S mount shares so much in common with EF.


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## Hillsilly (Aug 11, 2013)

I think dgatwood is referring to the internal elements. While you might not be able to change the front element size, ultimately an EF-S lens only needs to cover an APS-C sized imaging circle with a sharp image. What's that? A quarter of a FF image circle? Surely you wouldn't need the same sized internal elements for that? Or, if you do go with similar sized elements, you might be able to introduce manufacturing efficiencies to keep costs down (as you only need the centre of the element to be of high quality). Either way, I'm sure an APS-C lens could be made cheaper or lighter. How much? Maybe not much. Maybe a lot. Dgatwood guesses a 5% weight reduction. That seems pretty conservative.

However, given that EF lenses exist in the most likely focal lengths and apertures, I think they would have to sell for a noticeable discount on the EF lens price to have any market success. Maybe they could also be part of a new lens mount. These will mount on FF cameras, but work in "crop mode" only.


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## Sporgon (Aug 11, 2013)

Pi said:


> "Exposure Value" is a vague term you just invented.



;D

Old CR proverb say:

He who say Neuro make up stories before doing google search look like very silly fellow

( And you've got such a sophisticated nick name ! )


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## Etienne (Aug 11, 2013)

Hillsilly said:


> I think dgatwood is referring to the internal elements. While you might not be able to change the front element size, ultimately an EF-S lens only needs to cover an APS-C sized imaging circle with a sharp image. What's that? A quarter of a FF image circle? Surely you wouldn't need the same sized internal elements for that? Or, if you do go with similar sized elements, you might be able to introduce manufacturing efficiencies to keep costs down (as you only need the centre of the element to be of high quality). Either way, I'm sure an APS-C lens could be made cheaper or lighter. How much? Maybe not much. Maybe a lot. Dgatwood guesses a 5% weight reduction. That seems pretty conservative.
> 
> However, given that EF lenses exist in the most likely focal lengths and apertures, I think they would have to sell for a noticeable discount on the EF lens price to have any market success. Maybe they could also be part of a new lens mount. These will mount on FF cameras, but work in "crop mode" only.



Real life example, and I have both of these sharp lenses:

Tokina 50-135 f/2.8 (FF equiv 80-212mm) 845g, 135mm long, uses 67mm filter
Canon 70-200 2.8 IS II 1490g, 199mm long, uses 77mm filter

I don't think the front element size is linearly connected to the aperture and focal length either. Look at the Canon 50 1.4 vs Sigma 50 1.4


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## neuroanatomist (Aug 11, 2013)

Etienne said:


> Real life example, and I have both of these sharp lenses:
> 
> Tokina 50-135 f/2.8 (FF equiv 80-212mm) 845g, 135mm long, uses 67mm filter
> Canon 70-200 2.8 IS II 1490g, 199mm long, uses 77mm filter
> ...



Those dimensions make sense - 200mm/2.8 = 71mm, 135mm/2.8 = 48mm. The Canon 135mm f/2.8 Soft Focus takes a 52mm filter. A 135mm lens is going to be a lot smaller and lighter than a 200mm lens with the same max aperture, and that's what is really accounting for the size difference, not the fact that the Tokina zoom has a smaller image circle. Of course you can make a shorter focal length lens smaller/lighter - but the point is that for a tele lens or telezoom lens, a smaller image circle doesn't significantly help. 

Zoom lenses generally have a larger front element than a comparable prime, to reduce vignetting. Worth noting that the 70-200/2.8L IS II is right on the edge - a fair bit of native vignetting and adding a standard F-Pro filter causes increased vignetting (it's unusual with a tele lens, prime or zoom, to need a slim filter). 

The relationship between front element size and focal length / aperture applies to telephoto lens designs, not normal or wide lenses, so there's no reason to expect the relationship to hold for 50mm lenses.


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## jrista (Aug 11, 2013)

Sporgon said:


> Pi said:
> 
> 
> > "Exposure Value" is a vague term you just invented.
> ...



Hah. Actually, it was me he said made up the term "Exposure Value", so maybe the proverb doesn't apply. ;P I appreciate the photo, though!


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## Pi (Aug 11, 2013)

jrista said:


> I never said anything about the source of photon shot noise. Only that it is higher with smaller pixels due to their reduced full well capacity (maximum signal strength, which has a direct impact on per-pixel SNR, and therefor a direct impact on poisson, or shot, noise, which is the square root of the signal strength). If you have an APS-C sensor with pixels half the pitch of an FF sensor, averaging four of them together will result in the same amount of noise as a single FF pixel. Total amount of light is the same...it is just more finely delineated.



You are too much fixated on the pixels and fail to see the big picture. Replace the sensor by a piece of paper. The photon noise is still there. No pixels but photon noise. 

There is a huge difference between noise per pixel and noise on image level. 

Again, read it. It is all over the web.


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## Pi (Aug 11, 2013)

neuroanatomist said:


> Pi said:
> 
> 
> > "Exposure Value" is a vague term you just invented.
> ...



I was wrong, I admit. Somebody else invented it before. But it is semantics anyway. What you call it does not matter, it matters what you mean by it and what consequences you draw. 

Aside from that, do you agree with what I say, or you just act as a spell-checker? Do you agree that the (shot) noise is determined by the total light (same QE), and not by the total light per area? Do you agree that f/2.8 on FF and f/2.8 on crop would generate different photon noise, SS the same? Don't you find things in jrista's posts that you disagree with?


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## Sporgon (Aug 11, 2013)

jrista said:


> Sporgon said:
> 
> 
> > Pi said:
> ...



ooopps

Proverb probably similar,
Sporgon doesn't know his neuro from his rista


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## neuroanatomist (Aug 11, 2013)

Pi said:


> neuroanatomist said:
> 
> 
> > Pi said:
> ...



Big of you to admit your mistake, then shrug it off as irrelevant. 

Your mistake wasn't a spelling error (but thanks for the insult). Your statement was a factual error resulting from a lack of knowledge about one of the most basic principles of photography, expressed in commonly-known terminology for the field. A post like that on a photography forum sounds about as intelligent as a post on a math forum thread about the ratio of a circle's circumference to its diameter, asking if the discussion was about apple pie or pumpkin pie, and accusing people of inventing a new spelling for the word 'pie'.


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## Pi (Aug 11, 2013)

neuroanatomist said:


> Pi said:
> 
> 
> > neuroanatomist said:
> ...



It is not a principle of photography, it is a term. It escaped me that EV is the same as exposure value. I am used to seeing it as EV. If you really want to go to analogies in math, this is like a Russian mathematician saying "I do not know what a distribution is, you just invented that". Because Russians call distributions "generalized functions". This does not make that mathematician sound as not intelligent. 

And yes, it is irrelevant. It does not change what I meant a bit. I added a remark to my original post. Do you agree with the way it is now or not?

Let us see if you can add something of substance to the thread. You have a crop camera and an FF one, you take shots with the same EV. Is the photon noise the same? Assume same QE. This is what my opponent is missing, perhaps you can be the judge?


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## Sporgon (Aug 11, 2013)

Pi said:


> It is not a principle of photography, it is a term.



I think you're on real shaky ground here. Exposure Value is the combination of shutter speed, aperture and ISO; in other words - exposure. Without exposure you have no picture.

If that isn't a fundamental principal of photography I don't know what is.


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## Pi (Aug 11, 2013)

Sporgon said:


> Pi said:
> 
> 
> > It is not a principle of photography, it is a term.
> ...



Principle is a statement/rule; term is a convention how to call something. 

BTW, the convention what EV means does not involve ISO at all. Not that it matters because EV is just a term. I am fine with you not knowing what it is, after all, I did not until today.  

Let us go back to the main topic, shall we? Here is the question I asked twice, now reformulated in a way the public wants. What does EV (when comparing different formats) has to do with anything? I already explained why _total light_ is important - it determines the shot noise of the image projected on the sensor. What does _the same EV_ mean about the image captured?


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## neuroanatomist (Aug 11, 2013)

Pi said:


> Here is the question I asked twice, now reformulated in a way the public wants. What does EV (when comparing different formats) has to do with anything? I already explained why _total light_ is important - it determines the shot noise of the image projected on the sensor. What does _the same EV_ mean about the image captured?



Nothing at all, really. Aperture and shutter speed - it's not like they're important. We should compare the same total light. If the slower shutter speed used on FF to match DoF for _equivalence_ (have you used that terminology before? no matter, it's just semantics anyway) means the shot is ruined by subject motion blur, who cares? Exposure value, it's just more semantics with no relevance to the image captured.


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## Pi (Aug 11, 2013)

neuroanatomist said:


> Pi said:
> 
> 
> > Here is the question I asked twice, now reformulated in a way the public wants. What does EV (when comparing different formats) has to do with anything? I already explained why _total light_ is important - it determines the shot noise of the image projected on the sensor. What does _the same EV_ mean about the image captured?
> ...



Sometimes you are right without even knowing it.


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## Sporgon (Aug 11, 2013)

Pi said:


> BTW, the convention what EV means does not involve ISO at all. Not that it matters because EV is just a term. I am fine with you not knowing what it is, after all, I did not until today.



oh dear oh dear. Have you been reading up on EV when taking a break from digging this hole ?

I shoot at 250 / f5.6 / ISO 100 for 'correct' exposure. The EV is............ 13

I shoot at 250 / f11 / ISO 400 for the same 'correct' exposure. The EV is..............15

No it has nothing to do with ISO at all

<sarcasm>


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## Pi (Aug 11, 2013)

Since this discussion generated too much, I want to copy and paste a quote from Joe's essay, boldface mine:

http://www.josephjamesphotography.com/equivalence/#1

I only disagree with his mentioning of DR but I know that he knows about read noise, etc. 

_
1) f/2 = f/2 = f/2


This is perhaps the single most misunderstood concept when comparing formats. Saying "f/2 = f/2 = f/2" is like saying "50mm = 50mm = 50mm". Just as the effect of 50mm is not the same on different formats, the effect of f/2 is not the same on different formats.

Everyone knows what the effect of the focal length is -- in combination with the sensor size, it tells us the AOV (diagonal angle-of-view). Many are also aware that f-ratio affects both DOF and exposure. It is important, however, to understand that the exposure (the density of light falling on the sensor -- photons / mm²) is merely a component of the total amount of light falling on the sensor (photons): *Total Light = Exposure x Effective Sensor Area, and it is the total amount of light falling on the sensor, as opposed to the exposure, which is the relevant measure.*

Within a format, the same exposure results in the same total light, so the two terms can be used interchangeably, much like mass and weight when measuring in the same acceleration field. For example, it makes no difference whether I say weigh 180 pounds or have a mass of 82 kg, as long as all comparisons are done on Earth. But if makes no sense at all to say that, since I weigh 180 lbs on Earth, that I'm more massive than an astronaut who weighs 30 lbs on the moon, since we both have a mass of 82 kg.

*The reason that the total amount of light falling on the sensor, as opposed to the density of light falling on the sensor (exposure), is the relevant measure is because the total amount of light falling on the sensor, combined with the sensor efficiency, determines the amount of noise* and DR (dynamic range) of the photo.

For a given scene, perspective (subject-camera distance), framing (AOV), and shutter speed, both the DOF and the total amount of light falling on the sensor are determined by the diameter of the aperture. For example, 80mm on FF, 50mm on 1.6x, and 40mm on 4/3 will have the same AOV (40mm x 2 = 50mm x 1.6 = 80mm). Likewise, 80mm f/4, 50mm f/2.5, and 40mm f/2 will have the same aperture diameter (80mm / 4 = 50mm / 2.5 = 40mm / 2 = 20mm). Thus, if we took a pic of the same scene from the same position with those settings, all three systems would produce a photo with the same perspective, framing, DOF, and put the same total amount of light on the sensor, which would result in the same total noise for equally efficient sensors (the role of the ISO in all this is simply to adjust the brightness of the LCD playback and/or OOC jpg).

Thus, settings that have the same AOV and aperture diameter are called "Equivalent" since they result in Equivalent photos. Hence, saying f/2 on one format is the same as f/2 on another format is just like saying that 50mm on one format is the same as 50mm on another format.
_


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## Pi (Aug 11, 2013)

Sporgon said:


> Pi said:
> 
> 
> > BTW, the convention what EV means does not involve ISO at all. Not that it matters because EV is just a term. I am fine with you not knowing what it is, after all, I did not until today.
> ...



What if you shoot at 250 / f11 / ISO *200*?

Hint: now is the time to google it.


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## jrista (Aug 11, 2013)

Pi said:


> Since this discussion generated too much, I want to copy and paste a quote from Joe's essay, boldface mine:
> 
> http://www.josephjamesphotography.com/equivalence/#1
> 
> ...



Alright. I understand what this is saying, and it makes sense, but it is somewhat of an incomplete explanation. _Exposure_, which in his article is the same as *Exposure Value* (the amount of light allowed onto the sensor for a given aperture and shutter speed), IS identical across formats. Assuming you ignore ISO (which is what actual _exposure _does...ISO does not change exposure, it simply amplifies the result), an f/2 lens will always produce the _same _exposure.

What this article is explaining is that _total noise_ is the same when photographing* the same subject, at the same distance, with the same AoV.* Total noise is the same because the total amount of light on the sensor is the same. _Even though it is spread out more (<-- important point!!), and ISO is used to compensate!_

What this article does not fully explain is that an 80mm lens at f/4 is not equivalent to a 50mm f/2.5 lens *because of the inverse square falloff of light.* Light will spread out more and lose energy more over the 80mm distance to the sensor than over the 50mm distance to the sensor, despite an identical entrance pupil diameter. The use of an f/4 aperture will result in an EXPOSURE that one and a third stops *darker *than on the APS-C sensor. In order to produce the same final outcome, ISO must be increased by an equivalent amount, one and a third stops, to compensate for the LOWER exposure.

So, assuming the following:

A) APS-C, 50mm, f/2.5, ISO 100
B) FF, 80mm, f/4, ISO 320

The images from both will have the same final appearance. Same DoF, same AoV, same amount of image noise. True point. I think that is a point that is a little different than everyone else has been trying to make...equivalence requires complete equalization of EVERY SINGLE factor, including an increase in ISO, so therefor it is not actually discussing exposure (as in exposure value, which is usually what arguments about aperture and/or shutter speed "equivalence" pertain to). 

The point Pi is trying to make is that assuming equivalence (as explained in his linked article), then the final outcome of any sensor size would be identical.

I think the point everyone else has been trying to make is assuming an identical subject distance and lens, an f/2 aperture is an f/2 aperture regardless of sensor size. 

Technically speaking, both points are correct. Everyone has been debating oblique points.


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## jrista (Aug 11, 2013)

I would also point out that if you read the entire site Pi has linked to, his arguments (not just in this thread) make more sense. The core, critical point that Joseph James makes is that the only truly fair way to compare camera systems is to do so *at the same entrance pupil diameter and AoV*. I think in a general sense, that is probably quite true, and will indeed produce more useful comparisons in any situation that is not focal length limited.

I guess I would note that normalizing entrance pupil and AoV is not always possible in all forms of photography. I tend to shoot subjects that are difficult to get close to, so my "normal mode" of thinking about such problems is from a focal length limited standpoint, which relies on a few different rules than Joseph James's article assumes.


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## Efka76 (Aug 11, 2013)

I just read few last posts and understood that all you guys are so smart and that I need to learn a lot  I thought that I know photography quite well, however, I was not able to fully understand some of posts. I am wondering whether everybody in this forum are so smart or this just me alone


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## Sporgon (Aug 11, 2013)

OK I hold my hand up. Unlike some I didn't learn my photography from wiki. 

Obviously when you alter the ISO you alter the shutter/aperture combo - hence EV. 

The EV scale was developed years before digital, and I believe ( not from wiki ) that it was primarily for cine film. In those days you couldn't chop and change your ISO ( or even ASA ) like you can now, so in practice ISO effects EV, though I agree not in the definition of the term. 

For anyone who argues the technicalities of photography but believes 'exposure value' has just been made up is quite funny. 

The only photographic technicalities I do use wiki for is to decipher some of the forum slang such as in this case:
ROFLMFAO


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## Pi (Aug 11, 2013)

jrista said:


> Alright. I understand what this is saying, and it makes sense, but it is somewhat of an incomplete explanation. _Exposure_, which in his article is the same as *Exposure Value* (the amount of light allowed onto the sensor for a given aperture and shutter speed), IS identical across formats. Assuming you ignore ISO (which is what actual _exposure _does...ISO does not change exposure, it simply amplifies the result), an f/2 lens will always produce the _same _exposure.



Right, but, as Joe says, ... exposure ... is [not] the relevant measure. Total light is. 

Too many mistakes in the rest you wrote. F/2 will result in the same intensity (assuming a uniformly lit and fixed scene) no matter what the FL is. The inverse square law does not hold for focused light (even if you do not believe me, do not hold you hand under a bare lens in bright sunshine!) Anyway there is no point arguing this, we all know how this works in reality, if not in theory. You do not need faster f-stops with longer lenses. 

To summarize, f/2 on crop vs. f/2 on FF, _regardless of FL_, gives you same intensity, same EV (with the same SS) but this is an irrelevant measure of photon noise, and to a large extent of anything IQ related aside from resolution (a different discussion). Total light, in contrast, is relevant. In terms of total light, f/2 on crop "is not" f/2 on FF. Of course, this depends on what the meaning of the word "is" is.

If the outcome of this discussion is your reading of Joe's essay, I consider my job done. Joe writes well, and shoots even better - check out his galleries. BTW, he is in math, too...


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## neuroanatomist (Aug 11, 2013)

Sporgon said:


> For anyone who argues the technicalities of photography but believes 'exposure value' has just been made up is quite funny.



Indeed. It's also amusing when someone obtusely fails to acknowledge acute sarcasm. Whatever....arguing with someone who repeats the same statements over and over becomes pointless after a very short while.


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## jrista (Aug 11, 2013)

Pi said:


> jrista said:
> 
> 
> > Alright. I understand what this is saying, and it makes sense, but it is somewhat of an incomplete explanation. _Exposure_, which in his article is the same as *Exposure Value* (the amount of light allowed onto the sensor for a given aperture and shutter speed), IS identical across formats. Assuming you ignore ISO (which is what actual _exposure _does...ISO does not change exposure, it simply amplifies the result), an f/2 lens will always produce the _same _exposure.
> ...



I still think your being a little incomplete. No, you do not need a faster "f-stop" (relative aperture) with longer lenses, but that is because it is a _relative _measure. Just to be complete and clear, a 400mm f/4 lens has a much larger entrance pupil diameter than a 40mm f/4 lens. The longer lens has a 100mm diameter entrance pupil, while the 40mm has a 10mm diameter entrance pupil. The reason for the larger diameter on the longer lens is because of the inverse square law...falloff is greater over the greater distance to sensor with the 400mm lens. 

On a FF sensor, you could use a 400mm f/4, where as on APS-C, to achieve the same IQ at an equivalent AoV as you put it, you would need a 250mm f/2.5 lens. I don't disagree about that point, however if we conform to Joe's approach of entrance pupil diameter matters here, the statement "You do not need faster f-stops with longer lenses." is incomplete. Same f-stop, but longer lenses still do initially let through more light (considerably more, actually), which then falls off to produce the same intensity at the sensor as a shorter lens at the same f-stop. A 400mm f/4 lens has an entrance pupil area of 7850mm^2, where as the 40mm f/4 lens has a 78.5mm^2 entrance pupil area. Applying inverse square just to the aperture areas, we get the same result for both:


```
7850 * (1/400^2) = 0.05
 78.5 * (1/40^2) = 0.05
```

This may be entirely irrelevant in terms of measuring photon noise. That doesn't really matter either, though. Not everyone is solely concerned with noise. Sometimes sharpness is what matters, and in focal length limited situations, comparing equipment at the same AoV and entrance pupil diameter is not only irrelevant, it is also often impossible. ;P 

There are different goals in photography, and not all of them can be discussed or compared in the same way. I will happily concede that the point you were arguing from the angle you were arguing it was valid. I came at the problem from a different, and still wholly valid, angle, as I believe most of the other members of the discussion did. Different relevance for different situations...a point you might try to recognize sometime.


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## joseph james (Aug 11, 2013)

Joseph James here (Great Bustard on DPR). Been following the discussion. You may find the following links useful, as they discuss some of the points being raised:


http://www.josephjamesphotography.com/equivalence/#introduction

_A 50mm f/1.4 lens is a 50mm f/1.4 lens regardless of the sensor that sits behind it. However, the effect of 50mm f/1.4, in terms of the visual properties of the recorded photo, depend very much on the sensor that sits behind the lens:

25mm f/1.4 on mFT (4/3) is equivalent to 31mm f/1.8 on 1.6x (Canon APS-C), 33mm f/1.9 on 1.5x (APS-C for everyone else), and 50mm f/2.8 on FF (FX), where "equivalent to" means:

• The photos all have the same AOV (diagonal angle of view) and aperture (entrance pupil) diameter: 25mm / 1.4 = 31mm / 1.8 = 33mm / 1.9 = 50mm / 2.8 = 18mm. 

• The photos all have the same DOF (as well as diffraction softening) when they have same perspective (subject-camera distance), AOV, aperture diameter, and display size.

• The photos all have the same motion blur and the same total amount of light falls on the sensor when the aperture diameter and shutter speed are the same. which means the larger the sensor, the lower the exposure (same total light over a larger area) and thus a higher ISO setting for a given brightness.

• The photos all have the same same noise when the same total amount of light falls on the sensor if the sensors are equally efficient (less noise if the sensor is more efficient, more noise if the sensor is less efficient).

• Other elements of IQ, such as resolution, bokeh, color, etc., as well as elements of operation, such as AF speed/accuracy, size, weight, etc., are not covered in this use of the term "equivalent". _ 


http://www.josephjamesphotography.com/equivalence/#aperture

_The term "aperture", by itself, is vague -- we need a qualifying adjective to be clear. There are three different terms using "aperture":

1. The physical aperture (iris) is the smallest opening within a lens.
2. The virtual aperture (entrance pupil) is the image of the physical aperture when looking through the FE (front element).
3. The relative aperture (f-ratio) is the quotient of the focal length and the virtual aperture.

Thus, the "f" in an f-ratio stands for focal length. For example f/2 on a 50mm lens means the diameter of the virtual aperture (entrance pupil) is 50mm / 2 = 25mm. Likewise, a 50mm lens with a 25mm virtual aperture has an f-ratio of 50mm / 25mm = 2._


http://www.josephjamesphotography.com/equivalence/#exposure

_The exposure is the density of light (total light per area -- photons / mm²) that falls on the sensor during the exposure, which is usually expressed as the product of the illuminance of the sensor and the time the shutter is open (lux · seconds, where 1 lux · second = 4.1 billion photons / mm² for green light -- 555 nm). The only factors in the exposure are the scene luminance, t-stop (where the f-ratio is often a good approximation for the t-stop), and the shutter speed (note that neither sensor size nor ISO are factors in exposure).

For example, two pics of the same scene, one at f/2.8 1/200 ISO 100 and another at f/2.8 1/200 ISO 400 (on any system, regardless of format) will both have the same exposure, since the same number of photons per unit area will fall on the sensor, but the ISO 400 photo will appear 4x (2 stops) brighter than the ISO 100 photo since the signal is amplified by a factor of four due to the higher ISO setting.

The brightness, then, is the brightness of the final image after an amplification is applied to the exposure either by adjusting the ISO and/or a push/pull in the RAW conversion, and is often what people mean when they say "exposure". For example, pics of the same scene at f/2.8 1/200 ISO 100 and f/5.6 1/200 ISO 400 will be processed to have the same brightness, even though the f/2.8 photo has 4x (two stops greater) exposure than the f/5.6 photo.

The role of the ISO setting in exposure is in how the setting indirectly results in the camera choosing a different f-ratio, shutter speed, and/or flash power, any and all of which will change the exposure. For example, changing the ISO from 100 to 400 may result in the camera choosing f/5.6 instead of f/2.8, 1/200 instead of 1/50, f/4 1/100 instead of f/2.8 1/50, etc. Aside from that, the ISO control on the camera will apply an analog gain (which results in less read noise for higher ISOs with cameras that use non-ISOless sensors) and/or a digital push/pull (usually for intermediate ISO settings).

The total light is the total amount of light that falls on the portion of the sensor used to for the photo during the exposure: Total Light = Exposure · Effective Sensor Area. The same total amount of light will fall on the sensor for equivalent photos but, for different formats, this will necessarily result in a different exposure on each format, since the same total light distributed over sensors with different areas will result in a lower density of light on the larger sensor. Using the same example above, pics of the same scene at f/2.8 1/200 on mFT (4/3) and f/5.6 1/200 on FF will result in the same total light falling on each sensor, but the exposure will be 4x (2 stops) greater for the mFT photo, and thus the FF photographer would usually use a 4x (2 stops) higher ISO setting to get the same brightness for the LCD playback and/or OOC (out-of-the-camera) jpg.

Lastly, the Total Light Collected is the amount of light used to make the photo, which is the product of the Total Light that falls on the sensor during the exposure and the QE (Quantum Efficiency of the sensor -- the proportion of light falling on the sensor that is recorded). For example, if QE = 1, then all the light falling on the sensor is recorded. For reference, the Olympus EM5, Canon 5D3, and Nikon D800 all have a QE of approximately 0.5 (50%).

In terms of IQ, the total light collected is the relevant measure, because both the noise and DR (dynamic range) of a photo are a function of the total amount of light that falls on the sensor (along with the sensor efficiency, all discussed, in detail, in the next section). That is, noise is determined by the total amount of light falling on the sensor and the sensor efficiency, not the ISO setting on the camera, as is commonly believed (the ISO setting is simply a matter of processing the signal, discussed in more detail here). In other words, the less light that falls on the sensor, the more noisy and darker the photo will be. Increasing the ISO setting simply brightens the captured photo making the noise more visible.

For a given scene, perspective, and framing, the total light depends only on the aperture diameter and shutter speed (as opposed to the f-ratio and shutter speed for exposure). Fully equivalent images on different formats will have the same brightness and be created with the same total amount of light. Thus, the same total amount of light on sensors with different areas will necessarily result in different exposures on different formats, and it is for this reason that exposure is a meaningless measure in cross-format comparisons.

Mathematically, we can express these four quantities rather simply:

• Exposure (photons / mm²) = Sensor Illuminance (photons / mm² / s) · Time (s)

• Brightness (photons / mm²) = Exposure (photons / mm²) · Amplification (unitless)

• Total Light (photons) = Exposure (photons / mm²) · Effective Sensor Area (mm²)

• Total Light Collected (electrons) = Total Light (photons) · QE (electrons / photon)

The ISO setting on the camera determines the amplification applied to the signal. For example, at ISO 1600, the gain is 1600 / 100 = 16x for a camera with a base ISO of 100. The amplification can either be analog and/or digital, with analog gain resulting in less read noise for some cameras (see here for an example with the Canon 5D), but at the risk of more blown highlights (discussed in more detail here). It is important to note that not all cameras apply the same amount of amplification for the same ISO. For example, f/5.6 1/100 ISO 400 on one camera may not show the same brightness as f/5.6 1/100 ISO 400 on another camera. The ISO standards allow the manufacturers a lot of latitude in their definition of ISO._


http://www.josephjamesphotography.com/equivalence/#noise

_When people refer to noise in an image, what they mean is the density of the noise in an image (NSR -- noise-to-signal ratio) and is often represented as a percent. Often, we hear the term "SNR" (signal-to-noise ratio), which is the reciprocal of the NSR (SNR = 1 / NSR). For example, if the SNR = 5:1, then the NSR = 1/5 = 20%. However, since photo with high noise has a high NSR, and a photo with low noise has a low NSR, whereas it is exactly opposite for SNR, it is less confusing to think in terms of NSR than SNR.

There are two principle sources of noise in a photo: luminance noise and chroma (color) noise. Luminance noise is a function of the total amount of light falling on the sensor, and the efficiency of the sensor. The photon noise (often referred to as "shot" noise) is determined by how much light the sensor records. This, in turn, is determined by the total amount of light falling on the sensor (Total Light = Exposure x Effective Sensor Area) and the QE (Quantum Efficiency) of the sensor, which is the proportion of light falling on the sensor that is recorded (for example, a QE of 50% means half the light falling on the sensor is recorded). The other factor in luminance noise is the read noise, which is the additional noise added by the sensor and supporting hardware.

The chroma noise is the noise is a result of the color filters both blocking light which they are supposed to admit (AE -- Absorption Error), and admitting light they are supposed to block (TE -- Transmission Error). For example, if a red photon fails to make it through the red filter, this results in an Absorption Error, and if a red photon makes it through a green filter, this results in a Transmission Error.

The more transmissive the color filters (weaker color filter), the greater the QE, and thus the lesser the luminance noise, but the greater the chroma noise. The less transmissive the color filter (stronger color filter), the less the chroma noise, but lesser QE, and thus greater luminance noise. Different manufacturers choose a different balance in the transmissivity of their color filters resulting in a different balance between the luminance and chroma noise, which results is a different quality of noise in the photos, even if the quantity of noise remains the same.

The photon noise is the primary source of noise in the midtones and highlights of a photo. It is an inherent characteristic of incoherent light (the kind of light in almost all situations -- see the diagrams at the bottom of this page), and unavoidable -- one of those "Laws of Physics" things, as opposed to "an engineering challenge". Light has the properties of both a particle (photon) and wave, and the noise is measured in terms of its particle characteristics. The photons are collected and focused by the lens onto the sensor, where they are converted into electrons, and the signal is processed and recorded. The only role the sensor plays in the photon noise is what proportion of the photons falling on the sensor are converted into electrons (QE), since the electrons are the source of the electrical current that is processed by the hardware. The read noise, discussed in more detail further down, is how much noise is added when collecting and processing the signal produced by the photons.

The photon noise is proportional to the square root of the signal (N = sqrt S) so the photon noise density is inversely proportional to the square root of the signal (NSR = 1/ sqrt S). Thus, if we quadruple the signal (the total amount of light recorded), we halve the noise density.

There are, of course, other sources of noise, such as thermal noise, which plays a central role in long exposures, PRNU (Pixel Response Non-Uniformity) noise, which plays an important role in the highlights of the image, as well as other sources of noise. So, noise, is, of course, even more complicated than this essay makes it appear, and for some specific forms of photography (such as astrophotography) we may find that the noise is very different for equivalent images in some situations, much in the same way that corner sharpness is very different for equivalent images in some situations._

http://www.josephjamesphotography.com/equivalence/#fratio

_It is instructive to understand why the same f-ratio results in the same exposure for the same scene and framing, regardless of the focal length or format. There are six factors that determine how much light falls on the sensor:

• The luminance of the scene
• The amount of the scene that is recorded
• The distance from the scene
• The diameter of the aperture
• Transmissivity of the lens elements
• The shutter speed

The amount of light from the scene depends on how wide we frame -- the wider we frame, the more light we will capture, since we are gathering light from a larger scene. If we assume a scene with the same average luminance, framing twice as wide, for example, will result in collecting light from four times as much area, and thus four times as much light reaching the aperture.

The amount of light from the scene reaching the aperture also depends on how far we are from the scene -- the further away we are, the less of that light that reaches the lens. For example, if we are twice as far away, only 1/4 as much light will fall on the lens in any given time interval. It should be noted that the inverse square law is exact only for point sources, and becomes "less exact" the wider we frame. The reason is that the distance from the camera to the center of the focal plane is not the same as the distance to the other portions of the frame. So, when we increase the distance from the scene, the distance from the other portions of the frame do not increase in the same proportion as the center. However, for most situations, the difference is trivial.

Furthermore, the amount of light from the scene falling on the aperture is proportional to the area of the aperture. For example, if we double the diameter of the aperture, the area will quadruple, so four times as much light can pass through in any given time interval. However, some light is lost as it travels through the lens which depends greatly on the lens (click here for some examples). Lastly, the amount of the light passing through the aperture onto the sensor is proportional to the exposure time. That is, double the shutter speed, and you halve the amount of light falling on the sensor.

Let's work a few examples, ignoring the effects of light lost from the elements of the lens, keeping in mind that the exposure is the total light per area falling on the sensor, not the total amount of light. In other words, we can express the exposure as the quotient of the total amount of light falling on the sensor and the area of the sensor.

Say a photographer takes a "properly exposed" pic of a subject 10 ft away at 50mm f/2 1/100 (aperture diameter = 50mm / 2 = 25mm). If they step back to 20 ft away and use 100mm f/2 1/100, the aperture diameter has doubled (100mm / 2 = 50mm) and the aperture area has quadrupled (area is proportional to the square of the diameter). However, the amount of light from the scene reaching the lens is 1/4 as much since they're twice as far away. Since the aperture area is four times as much, it exactly compensates, and the same amount of light will pass through the aperture onto the sensor, and, since the sensor has not changed size, the exposure will also be the same.

Alternatively, let's say they don't step back, but instead remained at 10 ft and shot at 100mm f/2 1/100. At 100mm, the framing will be twice as tight, and thus record only 1/4 the light of the scene as they would at 50mm (assuming, of course, a uniformly lit scene). Thus, despite the fact that 1/4 as much light is reaching the lens, since the aperture area is four times as great, it exactly compensates once again. An excellent video on this can be seen here.

The above two examples demonstrate how the same f-ratio and shutter speed results in the same total light and exposure for a given scene and format regardless of focal length on the same format. However, for different formats, the same exposure does not result in the same total amount of light falling on the sensor.

Let's now consider a photographer using using 50mm f/2 1/100 on 4/3 and another photographer with FF shooting the same scene from the same distance at 100mm f/4 1/100. In both cases, the framing is the same (ignoring the minor differences in aspect ratio between the systems, which amounts to a mere 4% difference), the aperture diameters are the same (50mm / 2 = 100mm / 4 = 25mm), the distances from the scene are the same, and the shutter speeds are the same. Thus, the same amount of light will pass through the apertures onto the sensors.

On the other hand, if the FF photographer shot the same scene from the same position at 100mm f/2 1/100, the aperture diameter would now be 100mm / 2 = 50mm as opposed to 25mm. Since the aperture diameter is twice the size, the aperture area is four times as large, and four times as much light will fall on the sensor. But, since the sensor has four times the area, the density of the light on the sensor would be the same as the 4/3 sensor, so the exposures would be the same.

Thus, for a given scene, perspective, framing, aperture diameter, and shutters speed, the same amount of light will pass through the aperture onto the sensor for all systems. However, there are some exceptions. Some light is absorbed and/or scattered by the glass elements in the lens, and is quantified by noting the difference between the T-stop and the F-stop (f-ratio). Click here to see some examples of this differential for a few lenses for the Nikon system. It's helpful to note that a transmission of 79% represents a 1/3 stop loss of light, 63% represents a 2/3 stop loss of light, and 50% represents a one stop loss of light._


I hope these quotes make things more clear.


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## Pi (Aug 11, 2013)

Sporgon said:


> Obviously when you alter the ISO you alter the shutter/aperture combo - hence EV.



Obviously, you do not, unless you shoot in some kind of auto mode. Try it.


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## Pi (Aug 11, 2013)

neuroanatomist said:


> It's also amusing when someone obtusely fails to acknowledge acute sarcasm.



Agree. You are again right without knowing about it.


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## zim (Aug 11, 2013)

WTF  :-\ :'(
Thank the lord for P mode


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## neuroanatomist (Aug 11, 2013)

Wow, it's like ankorwatt calling in TheSuede for moral support. Fun times.


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## jrista (Aug 11, 2013)

joseph james said:


> jrista said:
> 
> 
> > Pi said:
> ...



If you had indeed read this thread, you would know that I have already read the entire page on equivalence. You would also know that I do not dispute its relevance in AoV/entrance pupil normalized situations.

However, I do believe there is a specific real-world circumstance where such a comparison is not possible. I regularly photograph birds and wildlife, which are generally considered reach-limited, or focal-length limited, circumstances. I own the EF 600mm f/4 L IS II and the EF 1.4x TC III. If I were to head out and photograph shorebirds, for example, I will usually find a spot near enough to the birds to get good shots, without being too near that I scare them all off.

In this situation, I could bring along a 5D III and a 7D, and swap them out for each photograph on my 840mm f/5.6 lens with the same shutter speed and ISO setting on both. The entrance pupil will remain the same 150mm regardless of the camera. I either have the option of taking a less detailed photo with less noise (5D III), or a more detailed photo with more noise (7D). If I aim to achieve as much parity between the results as possible, I have the option of cropping the 5D III image to the same AoV as the 7D and scaling the 7D image to the same dimensions as the 5D III. The result of that normalization is a reduction in noise in the 7D image such that it is roughly the same as the 5D III image, while concurrently increasing detail and sharpness. The exposure for both images would be the same.

As a side note, one could also attach a 2x teleconverter to the lens when using the 5D III. That would largely normalize effective focal length (1200mm f/8 for the FF, 1344mm f/5.6 for the APS-C), maintain an identical entrance pupil, and your equivalence framework would then apply. Your article does state that you ignored any additional factors that might affect IQ, however the addition of a 2x TC would very likely reduce the MTF of the lens and exacerbate optical aberrations to some degree (despite equivalence, although frankly I'd take the 5D III+600+2x over the 7D +600+1.4x if I had the option, if for nothing other than the superior AF and chance to pack more pixels on subject with a bit of extra sneaky technique to get closer to my shorebird subjects.) 

This is the world I usually live in when it comes to my photography. It is not the same situation that your article discusses, which quite clearly states that AoV must be the same. Nevertheless, it is a valid scenario that photographers DO encounter in the real world. Is it, then, invalid to compare cameras in such a scenario? Perhaps we are not talking about "equivalence" as you have defined it, but does that truly invalidate the comparison?

Your framework works beautifully to compare something like landscape photography or portraiture. As a landscape photographer myself, I have eagerly been awaiting Canon's _"Big Megapixel"_ body, however in the mean time I know that the 5D III will still produce better results with less noise and better dynamic range than my 7D, which with its crop sensor will never really compare. I just stand by my argument that there are different frames of reference that change how one might need to compare two cameras, and that it is not always possible to normalize AoV and entrance pupil.


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## joseph james (Aug 12, 2013)

jrista said:


> If you had indeed read this thread, you would know that I have already read the entire page on equivalence. You would also know that I do not dispute its relevance in AoV/entrance pupil normalized situations.
> 
> However, I do believe there is a specific real-world circumstance where such a comparison is not possible. I regularly photograph birds and wildlife, which are generally considered reach-limited, or focal-length limited, circumstances. I own the EF 600mm f/4 L IS II and the EF 1.4x TC III. If I were to head out and photograph shorebirds, for example, I will usually find a spot near enough to the birds to get good shots, without being too near that I scare them all off.
> 
> ...



In the case you are magnification or focal length limited, in terms of IQ, you are best served with the system that puts the greatest number of pixels on the subject and/or has the most efficient sensor.




> Your framework works beautifully to compare something like landscape photography or portraiture. As a landscape photographer myself, I have eagerly been awaiting Canon's _"Big Megapixel"_ body, however in the mean time I know that the 5D III will still produce better results with less noise and better dynamic range than my 7D, which with its crop sensor will never really compare. I just stand by my argument that there are different frames of reference that change how one might need to compare two cameras, and that it is not always possible to normalize AoV and entrance pupil.




Perhaps this section of the essay addresses that concern:

http://www.josephjamesphotography.com/equivalence/index.htm#purpose

_We can compare systems in many different ways. The five parameters of Equivalence are simply guidelines to comparing systems on the basis of the most similar visual properties of the final photo, and are certainly not a mandate that systems must be compared in such a fashion. Therefore, it is important to specify the purpose of the comparison, and then not artificially handicap one or the other system with the conditions of the comparison. In addition, it is important to interpret the results of the comparison in the context of the circumstances where the conditions of the comparison are valid.

The point of photography is making photos. As such, one doesn't choose the particular system to get images which are equivalent to another system. A person chooses a particular system for the best balance of the factors that matter to the them, such as price, size, weight, IQ, DOF range, available lenses, and/or operation. By understanding which settings on which system create equivalent images, the difference in their capabilities is more easily understood._


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## jrista (Aug 12, 2013)

joseph james said:


> Perhaps this section of the essay addresses that concern:
> 
> http://www.josephjamesphotography.com/equivalence/index.htm#purpose
> 
> ...



You are implying that the guy who cannot afford to spend eleven grand on a 500mm lens or thirteen grand on a 600mm lens is "artificially handicapping" the comparison when all he can use is his 400mm lens on both a FF and APS-C camera. I would call it a literal handicap, imposed not artificially, but by a real-world lack of funds. 

Your last paragraph there is a good one, and is entirely relevant in the case where someone has not yet already bought into a system, and has the option of determining up front which setup will best service their needs within their budget. I guess I am more concerned with the alternative case, where someone has already bought into a system, and is considering the most cost effective upgrade that will improve their results. If money is an object, reach is critical, and one cannot afford to buy the best telephoto lenses available for the system they already own, an upgrade from a 7D to a 7D II (assuming an increase in pixels and upgrade to AF performance and accuracy), for example, is probably better than an upgrade from a 7D to a 5D III. I am not sure your equivalence framework would help such an individual to make that determination.


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## jrista (Aug 12, 2013)

neuroanatomist said:


> Wow, it's like ankorwatt calling in TheSuede for moral support. Fun times.



Indeed. :


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## joseph james (Aug 12, 2013)

jrista said:


> joseph james said:
> 
> 
> > Perhaps this section of the essay addresses that concern:
> ...



Fair point. I have amended that portion of the Essay:

_We can compare systems in many different ways. The five parameters of Equivalence (same perspective, framing, DOF, shutter speed, and display size) are simply guidelines to comparing systems on the basis of the most similar visual properties of the final photo, and are certainly not a mandate that systems must be compared in such a fashion. Therefore, it is important to specify the purpose of the comparison, and then not artificially handicap one or the other system with the conditions of the comparison. Of course, this is not to say that there are not most certainly instances where a photographer is limited due to size, weight, and/or finances and would therefore compare systems within those constraints. However, it is important to interpret the results of the comparison in the context of the circumstances where the conditions of the comparison are valid._

Thanks for pointing that out!



> Your last paragraph there is a good one, and is entirely relevant in the case where someone has not yet already bought into a system, and has the option of determining up front which setup will best service their needs within their budget. I guess I am more concerned with the alternative case, where someone has already bought into a system, and is considering the most cost effective upgrade that will improve their results. If money is an object, and one cannot afford to buy the best lenses available for the system they already own, an upgrade from a 7D to a 7D II (assuming an increase in pixels and upgrade to AF performance and accuracy), for example, is probably better than an upgrade from a 7D to a 5D III. I am not sure your equivalence framework would help such an individual to make that determination.



Equivalence only applies when comparing systems. If you are not comparing systems, then there is no point in invoking Equivalence.


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## jrista (Aug 12, 2013)

joseph james said:


> jrista said:
> 
> 
> > joseph james said:
> ...



Glad to be of service.  Thanks for the amendment! 



joseph james said:


> > Your last paragraph there is a good one, and is entirely relevant in the case where someone has not yet already bought into a system, and has the option of determining up front which setup will best service their needs within their budget. I guess I am more concerned with the alternative case, where someone has already bought into a system, and is considering the most cost effective upgrade that will improve their results. If money is an object, and one cannot afford to buy the best lenses available for the system they already own, an upgrade from a 7D to a 7D II (assuming an increase in pixels and upgrade to AF performance and accuracy), for example, is probably better than an upgrade from a 7D to a 5D III. I am not sure your equivalence framework would help such an individual to make that determination.
> 
> 
> 
> Equivalence only applies when comparing systems. If you are not comparing systems, then there is no point in invoking Equivalence.



Ok, good to know there is an appropriate frame of reference. I do appreciate the details you've laid out. Once I fully read the article, it all made a lot of sense. I think it may be a bit _unconventional_, which is why it may not be as intuitive to the average photographer. Not that the conventional way of thinking about photography is correct (it is clearly not.)

For example, I think most photographers would most likely consider photographing at f/2.8, regardless of sensor size, if they had the option and wanted a thin depth of field. That they would have to photograph at a narrower aperture on a larger sensor in order to produce equivalent results with a smaller sensor is, I think, not generally how most photographers think. Even in the context of evaluating a camera system for purchase.


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## neuroanatomist (Aug 12, 2013)

jrista said:


> For example, I think most photographers would most likely consider photographing at f/2.8, regardless of sensor size, if they had the option and wanted a thin depth of field. That they would have to photograph at a narrower aperture on a larger sensor in order to produce equivalent results with a smaller sensor is, I think, not generally how most photographers think. Even in the context of evaluating a camera system for purchase.



I'd actually say _especially_ in the context of evaluating a FF purchase. I think there are quite a few people out there used to shooting wide open on APS-C, whether that's f/2.8, f/1.8, or even f/1.2, who then get a FF camera and slowly come to the realization that they need to stop down to get what they're used to having within the DoF to be in focus with the larger sensor.


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## Pi (Aug 12, 2013)

jrista said:


> For example, I think most photographers would most likely consider photographing at f/2.8, regardless of sensor size, if they had the option and wanted a thin depth of field. That they would have to photograph at a narrower aperture on a larger sensor in order to produce equivalent results with a smaller sensor is, I think, not generally how most photographers think. Even in the context of evaluating a camera system for purchase.



There is another side to it. Most crop camera photographers would shoot at f/2.8 (with the 17-55, or 70-200, etc.) not because they do not want to go get shallower DOF but because they cannot (say, with those zooms). When they try FF, they may discover that more than often, there is nothing wrong with the f/2.8 DOF on FF, and learn how to shoot and compose even then. This is something difficult to evaluate before you try. I am coming from film, so I did not need much convincing.


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## Rocky (Aug 12, 2013)

Pi said:


> jrista said:
> 
> 
> > For example, I think most photographers would most likely consider photographing at f/2.8, regardless of sensor size, if they had the option and wanted a thin depth of field. That they would have to photograph at a narrower aperture on a larger sensor in order to produce equivalent results with a smaller sensor is, I think, not generally how most photographers think. Even in the context of evaluating a camera system for purchase.
> ...



You are basically saying the same thing as Neuro in a oppsoite way.
For someone comming from film, I am surprised that you call "Exposure Value" as "a vague term you just invented"
Every half way decent phtographer will know the difference in DOF between APS-C and FF. They do not need to physically evaluate it. Please give us fellow photographer some credit.


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## Pi (Aug 12, 2013)

Rocky said:


> You are basically saying the same thing as Neuro in a oppsoite way.



No, I am saying the opposite thing. That you may find out that you do not need to stop down, very often at least. 

And not everybody is coming from film, many people started with crop cameras. Give some credit to the younger generation. 



> For someone comming from film, I am surprised that you call "Exposure Value" as "a vague term you just invented"



I explained that already.


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## Rocky (Aug 12, 2013)

Pi said:


> Rocky said:
> 
> 
> > You are basically saying the same thing as Neuro in a oppsoite way.
> ...


I did not say you say the opposite thing. I said you are saying the same thing as Nuero in an opposite way.
Understanding DOF has got nothing to do with film and has got nothing to do with the younger generation. You are just implying that people do not understand DOF without film back ground,. That is a very blunt and offending statement.
You did not explain why you call "Exposure Value" as "a vague term you just invented". You just admitted you do not know anything about "exposure value" even with your back ground on film.


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## Pi (Aug 12, 2013)

Rocky said:


> I did not say you say the opposite thing. I said you are saying the same thing as Nuero in an opposite way.



But I am not.



> Understanding DOF has got nothing to do with film and has got nothing to do with the younger generation. You are just implying that people do not understand DOF without film back ground,. That is a very blunt and offending statement.



Not really. Photography is a hobby. *EDIT: I stand corrected. For many, it is a profession.* Most people enjoy taking photos and do not or do not want to understand the technicalities. Nothing offending with saying that. Even when you understand it, you may not know what it actually means in practice if you have not tried it. For example, the myth that f/1.2 - f/1.4 on FF means razor thin DOF, is well and alive and is often cited as a reason not to go FF because who wants to shoot with such DOF. 



> You did not explain why you call "Exposure Value" as "a vague term you just invented". You just admitted you do not know anything about "exposure value" even with your back ground on film.



Wrong, read again. But feel free to beat on that drum as long as you want.


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## insanitybeard (Aug 12, 2013)

Pi said:


> For example, the myth that f/1.2 - f/1.4 on FF means razor thin DOF, is well and alive and is often cited as a reason not to go FF because who wants to shoot with such DOF.



Can you expand on this? Why is this a myth? I agree it depends on a number of variables, focal length, subject distance etc, but f1.2 *CAN* yield a very thin depth of field. Or is it the term 'razor' you find misleading?


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## neuroanatomist (Aug 12, 2013)

Pi said:


> For example, the myth that f/1.2 - f/1.4 on FF means razor thin DOF, is well and alive and is often cited as a reason not to go FF because who wants to shoot with such DOF.



Ahhh, so it's a _myth_ that you can get 'razor thin' DoF at f/1.2 - f/1.4 on FF. More semantics? Or are you merely stating that DoF thinner than the length of my 5 year old's button nose is technically thicker than a razor, so a ~1 cm DoF isn't razor thin? How about the MP-E 65mm at f/2.8 and 5x mag on FF, is that razor thin? (Oh, and by the way, that's another very valid scenario in which your favorite concept, equivalence, doesn't apply - macro shooting at max magnification, the lens' MFD doesn't change with sensor format, so the FoV isn't equivalent.)

As for citing thin DoF as a reason not to go FF, I guess you're saying the great unwashed masses of hobby photographers shooting APS-C are incapable of understanding that an f/1.2 lens can be stopped down, something easily understood by someone who comprehends the concept of exposure value so thoroughly that they fail to even recognize the term. :


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## daltech (Aug 12, 2013)

> One of my main problems with all this kit is the weight, carrying 40Kg on a trek to a wild life photo opertunity can be a pain.
> 
> When the 7D2 comes out the thing that would get me to buy one would be if light weight lens were available with similar quality to the L series but making use of the reduced diameter needed for the smaller sensor. (While they are at it they can reduce the price as the elements aren't as big.  )



The 7D is 820g, and the 5D Mark II, is 860g, not much differences !? The 1Dx at 1,340g I would notice the difference but the 7D and 5D, nope !?

If you're taking 40Kg of gears with you, perhaps you forgot to think of what you want vs. need on this outing !?


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## Don Haines (Aug 12, 2013)

Sporgon said:


> Pi said:
> 
> 
> > "Exposure Value" is a vague term you just invented.
> ...


Love it.... I've got an old light meter, probably 40 or so years old, and it's also marked in EV.... It's nice to know it was in widespread use for a half century or more before Neuro "made it up" yesterday.... This would imply that Neuro has a time machine, so I shall never doubt his predictions!


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## Don Haines (Aug 12, 2013)

Take a look at the EF 28-135 F5.6 lens and the EFS 18-135 F5.6 lens. They are the same width, the same length, within a few grams of the same weight. Surely if there was a size advantage of one format over the other, these two lenses would not be almost identical???


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## Pi (Aug 12, 2013)

insanitybeard said:


> Pi said:
> 
> 
> > For example, the myth that f/1.2 - f/1.4 on FF means razor thin DOF, is well and alive and is often cited as a reason not to go FF because who wants to shoot with such DOF.
> ...



Since the thread was cleaned up, for a good reason, I want to reply to you again. When you focus close, it is. When not, it is not. Check out Joe's gallery (who posted here yesterday), he has amazing shots with his 50L on FF, wide open; many of them with deep DOF. 

Of course, f/1.2 _can_ yield a razor thin DOF but it does not "mean" razor thin DOF.


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## Sporgon (Aug 12, 2013)

Pi said:


> Can you expand on this? Why is this a myth? I agree it depends on a number of variables, focal length, subject distance etc, but f1.2 *CAN* yield a very thin depth of field. Or is it the term 'razor' you find misleading?



Since the thread was cleaned up, for a good reason, I want to reply to you again. When you focus close, it is. When not, it is not. Check out Joe's gallery (who posted here yesterday), he has amazing shots with his 50L on FF, wide open; many of them with deep DOF. 

Of course, f/1.2 _can_ yield a razor thin DOF but it does not "mean" razor thin DOF.
[/quote]






If you focus a 50mm 1.2 wide open on FF at about 70 meters you'll get from around 40 m to infinity in focus. If you focus a 40mm at f11 at about 7 meters you'll get from about 3m to infinity in focus. So in this context the 50 1.2 would be very unforgiving wide open in comparison. 

I'm not sure what point you're trying to make really. The relationship between dof and magnification / distance is very old news and thoroughly documented. When an experienced photographer refers to 'razor thin' depth of field he's assuming the relationship between dof and distance is well understood. 

If you're trying to suggest that a larger format is just as easy to use as a smaller one you'd be wrong. Smaller is nearly always more forgiving of technique.


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## Don Haines (Aug 12, 2013)

> One of my main problems with all this kit is the weight, carrying 40Kg on a trek to a wild life photo opertunity can be a pain.


I can understand your problem, but APSC lenses are not going to save any weight.

I carry a LARGE pelican case and a carbon fibre tripod on canoe trips.... The reason I have stayed with APSC is that the field of view with a 400F5.6 on APSC is about the same as a 600F4 on FF, but is obviously a lot lighter. It's all about pixels on the target.... The only way the lens is going to get any lighter is if it goes to F6.3, and that means no autofocus on most Canon bodies....(that's why no current Canon lenses are slower than F5.6)

Several people in this thread have suggested that an APSC version of a lens would need smaller elements. While this is true for the last few elements, it is not for the first elements, and that means that the lens will be just as wide and almost as heavy as the FF version. Light from the entire surface of the biggest element gets focused on the APSC sensor, so making that element smaller means raising the F number.


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## rs (Aug 12, 2013)

Don Haines said:


> Take a look at the EF 28-135 F5.6 lens and the EFS 18-135 F5.6 lens. They are the same width, the same length, within a few grams of the same weight. Surely if there was a size advantage of one format over the other, these two lenses would not be almost identical???


There are many examples like that, such as these two similar angle of view zooms: The EF-S 18-55/3.5-5.6 kit lens has a virtually identical size/weight as the now discontinued EF 28-80/3.5-5.6.

Edit: the EF 28-90 is even lighter than the EF 28-80.


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## Pi (Aug 12, 2013)

Sporgon said:


> If you focus a 50mm 1.2 wide open on FF at about 70 meters you'll get from around 40 m to infinity in focus. If you focus a 40mm at f11 at about 7 meters you'll get from about 3m to infinity in focus. So in this context the 50 1.2 would be very unforgiving wide open in comparison.
> 
> I'm not sure what point you're trying to make really. The relationship between dof and magnification / distance is very old news and thoroughly documented. When an experienced photographer refers to 'razor thin' depth of field he's assuming the relationship between dof and distance is well understood.
> 
> If you're trying to suggest that a larger format is just as easy to use as a smaller one you'd be wrong. Smaller is nearly always more forgiving of technique.



The point I made is that the popular misconception about fast lenses on FF "meaning" razor thin DOF, one eye in focus only, etc., is, well, a misconception. I read this very often as an argument against FF. They do not say it is relative to something, they do not say how forgiving it is. The m43 forums, for example, are full of such statements. It does not help that the relationship between dof and distance is well understood. They are still saying it very often. I am pretty sure that they do not mean, say, 15m is razor thin compared to 100m, stopped down. EDIT: BTW, DOF grows non-linearly with distance, making in huge even in relative terms for large distances

Another point I made: you can play with DOF calculators all day but nothing replaces actual experience. Pushing the boundaries is fun and educational. A picture is worth ... well, more than a number in a DOF calculator.


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## schill (Aug 12, 2013)

Pi said:


> Another point I made: you can play with DOF calculators all day but nothing replaces actual experience. Pushing the boundaries is fun and educational. A picture is worth ... well, more than a number in a DOF calculator.



I think the line about experience ties in with how I think about lenses on a crop camera. I shoot with a 7D now and have been using a crop body for all of my digital "life" (starting with a D60). Before that, I shot film.

When I select a lens now, I never think in terms of "what is the crop equivalent of the FF lens that I want to use?" I select a lens based on my experience with lenses on a crop camera. I know what I'll get at 200mm or 300mm. I know the effects I'll see for f/2.8 or f/4, or f/8 or anything else for that matter.

Unless you are switching back and forth between ff and crop bodies and really find you need to think in terms of what you see with one on the other, I think it's mostly a non-issue. I know what a 70-200/2.8 is going to give me on my 7D.

This weekend, I shot with a 5DIII. This is the first time I've used a ff body since I put down my Elan II E for the D60. I never used the 70-200/2.8 with the Elan II E but it wasn't confusing at all. I didn't have to think about what it would show relative to the 7D. But, I did know that in familiar situations it would help to add a 1.4x teleconverter to get the reach.

Once you are actually shooting, the whole idea of equivalence and crop vs. ff lenses becomes a lot less important. A lens is a lens and a little experience makes everything pretty simple.


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