# 50mm Lens Comparison Wide-Open & Does Canon Boost ISO Sneakily?



## Fleetie (Jul 12, 2013)

I did these tests this evening. I was as careful as possible to keep room lighting the same for each shot.

See the thread about "50mm lenses that don't suck wide-open", which made me get off my butt and do these tests.

Note that the aim for these tests was only to compare lens brightnesses (T-stop) and bokeh, with all lenses wide-open.
The scene is too dark to determine relative sharpnesses.

I tested the Canon 50mm f/1.4 wide-open, both connected and NOT CONNECTED electronically, by rotating lens in body while holding the lens-release button down. Mechanically it is still completely mounted, but the camera cannot communicate with the lens, so does not know what it is, so it cannot "decide" to sneakily increase the ISO.

Canon 5D Mark 3
Manual
t=1/15s, ISO400 (nominal)

Focus was on the same point on the lantern, using live view, magnified x10.


RESULTS:

Dude was right. The "CONNECTED" Canon 50mm f/1.4 image is noticeably brighter, and I took the picture both ways, several times, and the results were completely repeatable. So it seems that the 5D3 DOES sneakily SEEM TO boost ISO without telling you, if it detects that the 50mm f/1.4 lens is connected. When I review the images on the camera, they all say ISO400.

Dude was also right that the Olympus 50mm f/1.2 is significantly brighter than the Canon 50mm f/1.4 wide-open, EVEN brighter than the "CONNECTED" image. That makes me feel slightly better about having dropped just shy of £400 on this (perfect, mint, unmarked) example of this lens, back in Jan. 2010!


Here's the album on FB:

https://www.facebook.com/media/set/?set=a.4505135767033.1073741834.1849695638&type=1&l=7e5db91bd2

Here are the files on Dropbox, including raw files:

https://www.dropbox.com/sh/rhtr3k0ru902sbr/yMKl0KWANf?lst

The tests I did were:

Zuiko (Olympus) 50mm f/1.8 - Dimmest, as expected

Zuiko 50mm f/1.4 Silvernose

Zuiko 50mm f/1.4 Non-Silvernose (later model) VERY SLIGHTLY brighter than Silvernose

Zuiko 55mm f/1.2 - Has the "biggest" bokeh / OOF blur. NOTE! This is a 55mm lens, not a 50mm one.

Zuiko 50mm f/1.2 This is the brightest of them all

Canon 50mm f/1.4 NOT CONNECTED, because lens was rotated to disengage electronic contacts

Canon 50mm f/1.4 CONNECTED - Should be same, but IS BRIGHTER


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## Drizzt321 (Jul 12, 2013)

*Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?*

Do you have simulate exposure or whatever it's called turned on for LiveView? When it communicates with the lens it may get more information and so might also apply the peripheral correction information (which generally will affected the outer portions of the frame, not the overall frame).

As for Olympus f/1.2, it should be brighter than a f/1.4. You're talking a full stop there, no duh it'll be brighter.


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## Fleetie (Jul 12, 2013)

*Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?*



Drizzt321 said:


> Do you have simulate exposure or whatever it's called turned on for LiveView? When it communicates with the lens it may get more information and so might also apply the peripheral correction information (which generally will affected the outer portions of the frame, not the overall frame).
> 
> As for Olympus f/1.2, it should be brighter than a f/1.4. You're talking a full stop there, no duh it'll be brighter.



No, I never use "simulate exposure".

I know it should be brighter but last time I tested it, it came out looking slightly dimmer than the Canon 50/1.4 lens. but no, the results here are clear.

BTW, how on Earth do you get that f/1.2 is a FULL STOP wider than f/1.4?! No, it's not!


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## Drizzt321 (Jul 12, 2013)

*Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?*



Fleetie said:


> Drizzt321 said:
> 
> 
> > Do you have simulate exposure or whatever it's called turned on for LiveView? When it communicates with the lens it may get more information and so might also apply the peripheral correction information (which generally will affected the outer portions of the frame, not the overall frame).
> ...



Maybe send Roger over at LensRentals.com an email and see if he can find something. He loves figuring out mysteries like this.

Hmm...right, it's a 1/2 stop, sorry. I know it's a log scale so I went right to a full stop instead of really thinking. Anyway, just because it's a 1/2 stop doesn't say anything about how _transmissive_ the different lenses are. See T-stops. The Olympus might have a better efficiency than than Canon (or maybe vice-versa), which would account for more actual light than can be accounted for the 1/2 stop difference.


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## Fleetie (Jul 12, 2013)

Yes, I know about T-stops. That's partly what prompted this test. See the "50mm lenses that don't suck wide open" thread.

I'd been meaning to do a more scientific test of all my 50mm lenses like this for a while now, so tonight I finally got a round tuit.

Last time I did a similar but less rigorous test like this, the Canon f/1.4 seemed more transmissive, i.e. brighter, than the Zuiko 50/1.2.

But no, Zuiko 50/1.2 is much brighter, as you rightly say, one would expect.


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## noisejammer (Jul 12, 2013)

@Fleetie - thanks for doing the test.... I'll take a bow 

@Drizzt321 - wide open an f/1.2 lens collects (1.4/1.2)^2 = 1.39 times as much light as a f/1.4 lens. This corresponds to 0.47 stops (not 1 stop.)

Of course, you would expect the f/1.2 lens to be brighter than a f/1.4 lens but this is NOT what Fleetie observed. When the camera communicates with the lens, it boosts its internal ISO (without telling you) so that the f/1.4 image becomes brighter than the f/1.2.

(IMO) This is a swindle that's perpetrated to persuade people to continue buying fast glass.


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## Fleetie (Jul 12, 2013)

noisejammer said:


> Of course, you would expect the f/1.2 lens to be brighter than a f/1.4 lens but this is NOT what Fleetie observed. When the camera communicates with the lens, it boosts its internal ISO (without telling you) so that the f/1.4 image becomes brighter than the f/1.2.



No. That's not exactly what I am saying:

YES, the "connected" Canon image is definitely brighter.

But even the connected image is less bright than the Zuiko 50/1.2 image. That was not what I found last time, but this time I was more careful to keep lighting constant than last time.

The Zuiko 50/1.2 image is the brightest one I got (IMO).


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## Fleetie (Jul 13, 2013)

One day I might do another, similar test of the same lenses, but this time to compare their sharpness wide-open.

But don't hold your breaths; round tuits are scarce here.


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## comsense (Jul 13, 2013)

Fleetie said:


> I did these tests this evening. I was as careful as possible to keep room lighting the same for each shot.
> 
> See the thread about "50mm lenses that don't suck wide-open", which made me get off my butt and do these tests.
> 
> ...


Curb your enthusiasm!!!!
You need to care of these things:
1) Put the metering off and shoot in M mode
2) Put the tape (super thin one) over contacts and click it all the way. Rotating changes lens light entry and image plane to sensor angles and could effect light reaching sensor and hence brightness (not a perfect control - you are comparing apple with oranges)
3) Capture 5-10 photos with each condition and take an average


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## Fleetie (Jul 13, 2013)

I don't *need *to do anything of the sort.

I took several shots in both conditions, and the result was unambiguous.

Rotation does not change the angle of lens axis to plane of sensor. The lens is still mechanically mounted hard up against the flange, so no angular movement is possible. Clearly you have not tried this, or it would be obvious to you that mechanically, the mount is identical to the connected case.

You might "need" to. So please do.

In fact, let's have more people do this.


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## neuroanatomist (Jul 13, 2013)

The 'sneaky' ISO boost with fast primes it done to compensate for loss of light transmission through the microlenses over the sensor pixels that occurs at high incident angles of light. As such, it's specific to digital (vs. film), and more boost is needed for smaller pixels. The issue has been documented (and quantified) by DxOMark. It's not just Canon, by the way - Nikon and Sony do it, too. 

http://www.dxomark.com/index.php/Publications/DxOMark-Insights/F-stop-blues


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## Fleetie (Jul 13, 2013)

neuroanatomist said:


> The 'sneaky' ISO boost with fast primes it done to compensate for loss of light transmission through the microlenses over the sensor pixels that occurs at high incident angles of light. As such, it's specific to digital (vs. film), and more boost is needed for smaller pixels. The issue has been documented (and quantified) by DxOMark. It's not just Canon, by the way - Nikon and Sony do it, too.
> 
> http://www.dxomark.com/index.php/Publications/DxOMark-Insights/F-stop-blues



Thanks, Neuro.

I do remember years ago reading that the Leica M9 has special angled microlenses to mitigate this effect; I think it was the same effect.

It still does seem a little "sneaky" of the camera to not show the modified ISO used. 

I'm not going to lose sleep over it; it's something interesting I learned today. I still like my 5D3!


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## Mt Spokane Photography (Jul 13, 2013)

The 50mm 1.4 is a old lens (1993) designed for film, so the effects of light drop off at the edge of a digital sensor are not compensated for. Newer lenses do a better job of collimating the light so it comes in at a steeper angle, and the effect is less.

http://www.nikonians.org/html/resources/nikon_articles/body/FF_vs_DX_sized_sensors/

After I thinking about it, there would be no fixed distance to the sensor focal plane for collimated light, so this seems to be incorrect.


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## Etienne (Jul 13, 2013)

Mt Spokane Photography said:


> The 50mm 1.4 is a old lens (1993) designed for film, so the effects of light drop off at the edge of a digital sensor are not compensated for. Newer lenses do a better job of collimating the light so it comes in at a steeper angle, and the effect is less.
> 
> http://www.nikonians.org/html/resources/nikon_articles/body/FF_vs_DX_sized_sensors/



I don't think it's possible to collimate the light and still end up with a sharp image. There's urban-legend BS at work in that link.


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## WillThompson (Jul 13, 2013)

*Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?*



Drizzt321 said:


> Hmm...right, it's a 1/2 stop, sorry.



No it is 1/3 stop!

The 1/3 stop steps are: 1.0 1.1 1.2 1.4 1.6 1.8 2.0 .........


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## neuroanatomist (Jul 13, 2013)

*Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?*



WillThompson said:


> Drizzt321 said:
> 
> 
> > Hmm...right, it's a 1/2 stop, sorry.
> ...


No, it's both, or if you prefer, neither. On the half-stop scale, f/1.2 is 1/2-stop wider than f/1.4, but on the 1/3 stop scale, f/1.2 is 1/3-stop wider than f/1.4. See the wikipedia page on f/stops. 

Mathematically, f/1.2 really is closest to a 1/2-stop, since 21/2x0.5 = 1.1892), whereas 22/3x0.5 = 1.2599, which personally I'd round to f/1.3.


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## CharlieB (Jul 13, 2013)

Very good point about the sensor acceptance angles. I'm also wondering if periferal illumination correction also might have had an effect in this case.


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## Fleetie (Jul 13, 2013)

CharlieB said:


> Very good point about the sensor acceptance angles. I'm also wondering if periferal illumination correction also might have had an effect in this case.


No, because I always leave it switched off. And I just turned on the camera to double-check, and it was, and is, off.

The jpgs are SOOC, too.


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## Mt Spokane Photography (Jul 13, 2013)

Etienne said:


> Mt Spokane Photography said:
> 
> 
> > The 50mm 1.4 is a old lens (1993) designed for film, so the effects of light drop off at the edge of a digital sensor are not compensated for. Newer lenses do a better job of collimating the light so it comes in at a steeper angle, and the effect is less.
> ...


 
I think you are right, now that I think about it, its nonsense, there would be no fixed distance to the sensor focal plane for collimated light.

I've revised my post.


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## rs (Jul 13, 2013)

As higher pixel density sensors and faster lenses seem like a bad combination according to this, I wonder if it makes small sensor high MP bodies such as the OM-D E-M5 with lenses such as the SLR Magic 50/0.95 hyperprime not all as advertised?

With the pixel density of a 16MP m4/3 body (pixel pitch equal to a 64MP FF body) it is probably a long way off the f0.95 light capturing levels it claims. Could this effect make it nearer to f2.8?


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## Dylan777 (Jul 13, 2013)

*Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?*



neuroanatomist said:


> WillThompson said:
> 
> 
> > Drizzt321 said:
> ...



Thanks Fleetie for the data.

Thanks Neuro for providing the math formulas - I'm going to pretend that I know how to calculate those formulas and simplify the math so an ave Joe could understand:


(5D III - f2.8 or smaller) + (5D III + 50L @ f1.2) = amazing IQ in SUPER LOW LIGHT


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## WillThompson (Jul 13, 2013)

*Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?*



neuroanatomist said:


> WillThompson said:
> 
> 
> > Drizzt321 said:
> ...



Not on a canon camera that actually uses 1/6 stop increments, when setting exposure. The camera uses the standard 1/2 stop nomenclature but uses actuall 1/2 stop increments when set to 1/2 stop steps and the same goes for 1/3 stop steps so the steps will be exactly 1/3 or 1/2 depending on the camera setting.

This means that the difference between a setting of 1.2 and 1.4 will be different depending on camera settings.

In the real world there is 1/3 stop difference as apposed to the representational of 1/2 stop steps!


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## Aglet (Jul 13, 2013)

noisejammer said:


> @Fleetie - thanks for doing the test.... I'll take a bow
> (IMO) This is a swindle that's perpetrated to persuade people to continue buying fast glass.



Thanks guys, I've actually learned something. 
Knew about the acceptance angle issues of pixels but didn't know a sensitivity tweak was happening w-o me knowing about it when using a very wide aperture setting.
It's not a shooting scenario I often use, typically at f/2.0 or smaller aperture. But now I know about it if necessary.


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## neuroanatomist (Jul 13, 2013)

*Re: 50mm Lens Comparison Wide Open & Does Canon Boost ISO Sneakily?*



WillThompson said:


> Not on a canon camera that actually uses 1/6 stop increments, when setting exposure. The camera uses the standard 1/2 stop nomenclature but uses actuall 1/2 stop increments when set to 1/2 stop steps and the same goes for 1/3 stop steps so the steps will be exactly 1/3 or 1/2 depending on the camera setting.
> 
> This means that the difference between a setting of 1.2 and 1.4 will be different depending on camera settings.
> 
> In the real world there is 1/3 stop difference as apposed to the representational of 1/2 stop steps!



Fine, but that doesn't address the original issue, which was about the difference between an f/1.4 and an f/1.2 lens. 



> @Drizzt321 - wide open an f/1.2 lens collects (1.4/1.2)^2 = 1.39 times as much light as a f/1.4 lens. This corresponds to 0.47 stops (not 1 stop.)



That difference is best represented as 1/2-stop, whether or not the settings of the camera result in that complete 1/2-stop being used.


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## WillThompson (Jul 14, 2013)

*Still only 1/3 stop difference! (When using 1.3 stop steps)*



neuroanatomist said:


> That difference is best represented as 1/2-stop, whether or not the settings of the camera result in that complete 1/2-stop being used.



Still not correct.


With a 1/2 stop setting f1.2 is actually f1.1892.

With a 1/3 stop setting f1.2 is actually f1.2599.

With both a 1/2 & 1/3 stop setting f1.4 is actually f1.4142.


This difference is why the 1/2 stop setting between f1.4 & f2.0 is f1.7 not f1.6 or f1.8 as it is less confusing due to larger numbers allowing better numeric distinction between settings.

On a side note,

Is a f1.2 lens actually 1/6 stop wider when set to 1/2 stop increments when shot wide open???


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## neuroanatomist (Jul 14, 2013)

*Re: Still only 1/3 stop difference! (When using 1.3 stop steps)*



WillThompson said:


> neuroanatomist said:
> 
> 
> > That difference is best represented as 1/2-stop, whether or not the settings of the camera result in that complete 1/2-stop being used.
> ...



Who are you, DxOMark, unable to consider a lens independent of a camera?  Forget about the camera for a moment. Compare an f/1.4 lens vs. an f/1.2 lens, just the lens - how much faster is the f/1.2 lens? Well, neither exactly 1/2 nor exactly 1/3 stop, but 1/2 stop is a better approximation. 

To answer your question, 1D X with 85mm f/1.2L II, illumination constant, camera locked down, VF shutter closed, AV mode, ISO 100:

1/3 stop increments: f/1.2, f/1.4, f/1.6, f/1.8, f/2, metered shutter speed 1/50, 1/40, 1/30, 1/25, 1/20 s

1/2 stop increments: f/1.2, f/1.4, f/1.8, f/2, metered shutter speeds 1/45, 1/45 (no change from wide open), 1/30, 1/20 s

1 stop increments: f/1.2, f/1.4, f/2, metered shutter speeds 1/60 s, 1/30 s, 1/15 s


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## WillThompson (Jul 15, 2013)

*Re: Still only 1/3 stop difference! (When using 1.3 stop steps)*

A EOS lens is only functioning to specification when powered up with a body.

The aperture setting is not a passive but an active device!

Is that metered manual or auto exposure?

In auto the camera can skew both settings by 1/6 or is that multiple 1/10's of stops with no indication of f-stop or shutter speed change. (Not sure of the sub step values that Canon uses 1/10 vs 1/6, It has been a long time since I went to Canon school)

So answer me this, how many stops difference is f1.2599 from f1.4142??????


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