# Question RE EF Lenses on EOS M and other APSC Cameras



## mvrbnsn (Jul 23, 2016)

I want to buy the EF 35mm f/2.0 IS lens to go with my EOS M. Currently I use the 50 f/1.8 via adapter and the native 22mm f/2.0 and 18-55.

My inclination towards EF lenses is in the interest of obtaining maximum image quality, and because I may want to pick up a full frame second body at some point, likely a 6D. 

BUT I ran across an article recommending against full lenses on APSC cameras. The argument made sense but I had never heard this before.
The rationale was that the amount of light reaching the sensor is greatly reduced on a crop body camera such that an f/2.0 lens ends up being almost an f/4.0!

Is this a valid argument with an adapter, on a mirror less such as the M? Would I be negating the advantage of a good EF lens by using it on a crop body? Or does the adapter itself help recover some of that light loss?

I'd appreciate the opinion of some of you with more expertise than I?

Thanks!


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## candc (Jul 23, 2016)

An f/2 lens is its aperture/focal length ratio. It does not change regardless of what it is mounted on. An image recorded by a crop sensor is the same as one taken on ff and later cropped to the same size. (as long as pixel size is the same) Ef lenses are not inherently better. I would stick with ef-m lenses on your m.


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## neuroanatomist (Jul 23, 2016)

mvrbnsn said:


> The rationale was that the amount of light reaching the sensor is greatly reduced on a crop body camera such that an f/2.0 lens ends up being almost an f/4.0!



Whoever wrote that is clueless. The smaller sensor means an f/2 lens gives the DoF of f/3.2 on FF, for the same framing.


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## mvrbnsn (Jul 23, 2016)

Thanks. What I gathered from the article (by Tony Northrup), and I hope I didn't misrepresent his point, was that a full frame lens on a crop body wouldn't deliver the same amount of light to the sensor meaning that the seeming advantage of the lens wouldn't be so great on a crop body.

So by way of example, if I were using the EF 35mm f/2.0 on the EOS M would it be less bright at a given aperture than the native EFM 22mm f/2.0?

Thanks!


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## neuroanatomist (Jul 23, 2016)

mvrbnsn said:


> Thanks. What I gathered from the article (by Tony Northrup),



From a technical standpoint, I'd trust advice from a bowling ball more than advice from Northrup. 




mvrbnsn said:


> I was thinking that by using a good quality EF lens I would be gaining image quality. Right or wrong?



Right, because you're using only the center of a larger-than-necessary image circle, and lens IQ drops at the periphery of the image circle.


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## Etienne (Jul 23, 2016)

I use the 35 f/2 IS on both my EOS-M3 and 5DIII. It works great on both and I highly recommend this lens.


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## rs (Jul 23, 2016)

mvrbnsn said:


> So by way of example, if I were using the EF 35mm f/2.0 on the EOS M would it be less bright at a given aperture than the native EFM 22mm f/2.0?



f2 is f2. So both lenses would have equal brightness on an EOS M.

The somewhat misguided point TN was attempting to make is that a FF f2 lens is capable of transmitting more total light (and a wider field of view) than a crop sensor behind the lens can capture.

However if you have a crop body and currently use an f2 lens, this new f2 lens will not fall short of your expectations. And it will only get better if used on FF.


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## sunnyVan (Jul 23, 2016)

It's a good move to get the 35 f2 IS especially when you know you want to go full frame eventually. There is no down side to it other than higher cost and awkward ergonomics on m3. Very high grade full frame lenses have great image quality from center to the outer edge of the image circle. Mediocre full frame lenses have decent IQ in the center but the outer edge sucks. If you use a high grade L lens on a cropped sensor you're wasting the outer edge and you're kind of carrying extra weight for nothing. 

Tony's youtube channel is not that terrible but you always have to take his advice with a grain of salt.


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## jd7 (Jul 24, 2016)

OP, if you want to get a good understanding of shooting with full frame versus crop, I suggest having a look at this website:
http://www.josephjamesphotography.com/equivalence/
It takes a bit of time to digest it all (and I haven't worked through all of the maths in detail), but I found it very useful.

In practical terms

f2 is f2 in terms of allowing light density (brightness) to build up on the sensor. That means the exposure time for a given brightness will be the same whether you use crop of full frame. (The crop sensor will gather less total light though, simply because it's smaller.)

You need to multiply the focal length by the crop factor to work out the "equivalent" focal length.

If you assume the same framing, you need to multiply the focal length by the crop factor to work out the "equivalent" depth of field.

If you use crop, it crops off the outer regions of the image circle of a full frame lens, which are often the weakest area.

I shot with a Sigma 24-70 2.8 on crop for years before I got a 17-55 2.8, and I really regret it. The 17-55 focal length was much more useful/versatile for me than 24-70, when using a crop sensor. And the 17-55 was lighter, had IS, and longer zoom range.

Building a lens kit of EF lenses when you have a crop sensor camera doesn't necessarily help you as much as you might expect when you jump to full frame, as the way the lens performs and hence what you want to use it for will change. Of course, sometimes a lens can be very good and useful on both full frame and crop, albeit you are likely to use it differently. (And the exception to that is long lenses when you are going for maximum reach - then you will use it for the same things.)

In my view, the ability to use EF-S lens is an advantage of having a crop sensor which should not be overlooked (especially for wide angle and normal focal lengths).

That said, if you are looking for a 50 or 55 mm equivalent, fairly fast aperture lens for your M, the 35 IS will be a good a choice.


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## Sporgon (Jul 24, 2016)

Definitely recommend using the EF prime lenses on the M3 via the adapter. Three points: firstly their use allows you to benefit from the much misunderstood "disadvantage" of crop, that is the greater dof for a given aperture. This means you can shoot at wider apertures and benefit from more volume of light, less defraction for the small pixel pitch, faster shutter speeds, lower ISO etc. The M zooms are generally too slow to use in this way. 

Secondly the flange to sensor distance on the M lenses is very shallow but those lenses are not tele-centric, so the light falling on the outer part of the sensor is coming in a one hell of an angle. There have been suggestions that the sensor has not actually been designed for this but rather been lifted straight from a dslr design. By using EF lenses with both a larger image circle and greater distance away, the light angle is much more acceptable, and the IQ is better, in fact it can be top notch in reasonable light. 

Thirdly, a negative: the EF lenses via adapter don't focus or track as well, a you lose some other minor functions.


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## justmy2cents (Jul 24, 2016)

mvrbnsn said:


> Thanks. What I gathered from the article (by Tony Northrup), and I hope I didn't misrepresent his point, was that a full frame lens on a crop body wouldn't deliver the same amount of light to the sensor meaning that the seeming advantage of the lens wouldn't be so great on a crop body.
> 
> So by way of example, if I were using the EF 35mm f/2.0 on the EOS M would it be less bright at a given aperture than the native EFM 22mm f/2.0?
> Thanks!



A APS-C sensor has less than half the size of a FF sensor, so you'd have to use a larger aperture because the pixels are smaller. Or you could crank up ISO, but that would increase noise.

I think the baseline of what TN is saying is: if you spent a lot of money on FF lenses, you better get a FF body as well to make full use of them. And if you don't plan on going FF, buy crop lenses - if there are any good.


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## Sporgon (Jul 24, 2016)

justmy2cents said:


> And if you don't plan on going FF, buy crop lenses - if there are any good.



I think he is wrong, or at least out of date. The crop sensors are now so good you can actually benefit from FF EF lenses as I outlined in my post on the previous page.


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## mvrbnsn (Jul 24, 2016)

*Re: Question RE EF Lenses on EOS M--THANKS TO ALL!*

Wow! A big thanks to each and every one of you for your thoughtful and informative responses.
I really appreciate you taking the time to enlighten me with your knowledge and experience.

This is a great forum. Much appreciated.


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## Rocky (Jul 24, 2016)

There is another catch on using FF lens on the APSC. The APSC sensor has a multiplication factor of 1.61 linear or 2.59 area. In order to fully utilize the resolution power of the APSC sensor, the FF lens must have 1.61 more resolution power than what is needed for the FF sensor. M3 has a resolution of 24.2 MP. It needs a FF lens with 62.79 MP resolution to fully utilize the resolution power of the M3. How many FF lens can make that claim?? It is unfortunate that Canon does not make a 35mm f2.0 IS EF-M lens.


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## privatebydesign (Jul 24, 2016)

Rocky said:


> There is another catch on using FF lens on the APSC. The APSC sensor has a multiplication factor of 1.61 linear or 2.59 area. In order to fully utilize the resolution power of the APSC sensor, the FF lens must have 1.61 more resolution power than what is needed for the FF sensor. M3 has a resolution of 24.2 MP. It needs a FF lens with 62.79 MP resolution to fully utilize the resolution power of the M3. How many FF lens can make that claim?? It is unfortunate that Canon does not make a 35mm f2.0 IS EF-M lens.



You need to learn how system resolution works before making patently inaccurate comments like that.

Here is a start: http://www.canonrumors.com/forum/index.php?topic=26938.msg595091#msg595091


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## Rocky (Jul 24, 2016)

privatebydesign said:


> Rocky said:
> 
> 
> > There is another catch on using FF lens on the APSC. The APSC sensor has a multiplication factor of 1.61 linear or 2.59 area. In order to fully utilize the resolution power of the APSC sensor, the FF lens must have 1.61 more resolution power than what is needed for the FF sensor. M3 has a resolution of 24.2 MP. It needs a FF lens with 62.79 MP resolution to fully utilize the resolution power of the M3. How many FF lens can make that claim?? It is unfortunate that Canon does not make a 35mm f2.0 IS EF-M lens.
> ...


\
Thanks for pointing it out. I am fully aware of that. As per your quote says. When both sensor and lens resolution are matched. the end resolution is only 71%. If the lens resolution is only 66% of the sensor. The end resolution becomes only 55% of the sensor. That is 21 % reduction from the potential resolution. This is not fully utilize the resolution of the sensor. We spend money to buy expensive equipment, we want to get the most out of it.


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## neuroanatomist (Jul 24, 2016)

Rocky said:


> privatebydesign said:
> 
> 
> > Rocky said:
> ...



How is it that, as you imply, your argument applies to FF lenses used on APS-C cameras, but not APS-C lenses used on APS-C cameras? Or do you believe that APS-C lenses intrinsically deliver higher resolution? Sorry, but I can't really see any relevance to your point in this discussion of using FF lenses on APS-C cameras. Yes, smaller pixels benefit more from higher resolution lenses, but the pixels of the M3 aren't all that much smaller than those on the 5DsR (same density as a 20 MP APS-C sensor). 

If anything, since lens resolving power is generally highest in the center and drops toward the periphery, the benefit from using only the center of the FF image circle is quite significant – a glance at the 35/2 IS MTF chart shows resolution remains quite high through area of the APS-C sensor.


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## dougkerr (Jul 25, 2016)

mvrbnsn said:


> The rationale was that the amount of light reaching the sensor is greatly reduced on a crop body camera such that an f/2.0 lens ends up being almost an f/4.0!



The _illuminance_ on the sensor (for a given scene luminance), which (along with the shutter speed) is the factor that determines the _photometric exposure_, the quantity to which the sensor responds, is determined by the f-number of the lens. Period.

Best regards,

Doug


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## privatebydesign (Jul 25, 2016)

dougkerr said:


> mvrbnsn said:
> 
> 
> > The rationale was that the amount of light reaching the sensor is greatly reduced on a crop body camera such that an f/2.0 lens ends up being almost an f/4.0!
> ...



The point is the sensor receives photons as a function of area, ergo a sensor that is less than half the size receives less than half the photons. That is why FF cameras are at least one stop better in ISO noise performance for any given exposure and output size.


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## Fleetie (Jul 26, 2016)

dougkerr said:


> mvrbnsn said:
> 
> 
> > The rationale was that the amount of light reaching the sensor is greatly reduced on a crop body camera such that an f/2.0 lens ends up being almost an f/4.0!
> ...


And the T-stop.


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## jolyonralph (Jul 27, 2016)

You already use the 50mm f/1.8 with an adaptor, so that should tell you the article is nonsense as presumably you're happy with the results!

The 35mm f/2.0 would be a nice partner for the EOS-M - I'm considering getting one myself


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## mb66energy (Jul 27, 2016)

neuroanatomist said:


> Rocky said:
> 
> 
> > privatebydesign said:
> ...



I see a better resolution of my EF-S 60 compared to the EF 100 (non-IS) in my images. I am shure that isn't intrinsical but a result of lens optimization for the use case.

A FF lens must have reasonable quality for an image circle of ~43mm while the APS-Lens only needs ~26mm image circle of reasonable IQ.

Classic FF lenses are too optimized for the center region where most subjects in standard compositions are located (e.g. the 24mm 2.8 non-IS) but I am shure that there is some co-optimization in newer lenses for both, FF and APS-C. The 35mm 2.0 is - in my opinion - a good example for a dual use lens with extraordinary resolution within the APS-C image circle and very good res. for the rest of the area.

My conclusion is that an EF-S or a newer EF lens should work optimally on APS-C sensors. Older lenses (pre APS-C era) should be checked.


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## AE-1Burnham (Jul 27, 2016)

Wouldn't it be cool if Canon made a Speedbooster for EF to APSC sensor?! Or if Metabones made a EF to "APSC" or "EF-M" adaptor. God that would make me so happy.  (I imagine Canon Corporate would get quite angry at Metabones and out would come lawyers and such...) If this existed I would buy an M series camera immediately.


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## psychilles (Jun 17, 2018)

AE-1Burnham said:


> Wouldn't it be cool if Canon made a Speedbooster for EF to APSC sensor?! Or if Metabones made a EF to "APSC" or "EF-M" adaptor. God that would make me so happy.  (I imagine Canon Corporate would get quite angry at Metabones and out would come lawyers and such...) If this existed I would buy an M series camera immediately.



Kinotika says Viltrox is coming out with a EF to EF-M speedbooster
https://www.youtube.com/watch?v=cIcbU6aznNk


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