I noticed the EOS R sometimes stops down lenses during focusing, what's the deal with that?

Nov 12, 2016
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#1
I just noticed when using both an EF 50mm 1.2L and an EF 50mm 1.0L on the EOS R that the camera actually stops down the lens while it's attempting to autofocus in moderately bright conditions. If you have the aperture set wide open, it opens back up to actually take the photo. It will even stop down the lens when you aren't trying to focus by just pointing it at a bright source of light. If you focus under pretty dim lighting, the lens doesn't stop down. This seems kind of weird. I wonder why this happens. Apparently under some conditions there's just too much light hitting the sensor for it to focus properly? I do wonder how it can possibly nail focus at a wide aperture if it's not actually at the wide aperture when it's autofocusing.
 

Larsskv

Enthusiast with Canon related GAS
Jun 12, 2015
721
131
#2
One theory I have is that the EF 50L is so soft at f1.2 that it the dual pixel AF doesn´t focus very well at that aperture... It could therefore be programmed to stop down, in order to focus better. On the other hand though, I found the EF 50L + the EOS R to focus very badly at f3.5, not compensating for the focus shift on the 50L. Before that I had used the EF 50L on the 1DXII and 5DIV, and never experienced the focus shift issue. It seems to me that the 1DXII and 5DIV compensates for it, while the EOS R doesn't. This was just an impression I got. I didn't test this very thoroughly because I sold the EF50L as soon as I got the RF50L...
 
Nov 12, 2016
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#3
I don't know that I buy what you're saying about the camera not being able to focus wide open. After all, it will focus wide open in low light. But in a well lit room, then it stops down.

Also, your experience with the EOS R not focusing accurately is absolutely opposite of my own, and most other peoples' that I've read. The EOS R is focusing using the image on the sensor itself, not a separate autofocus sensor like DSLRs. Why would the supposed "focus shift" of a lens even matter on a mirrorless? The camera is just going to move the focus until the actual image is in focus. That's why Canon has done away with the AFMA settings on the EOS R. (And also why I'm very confused that Sony still has those settings on their cameras.) There's really no point to them any more. If your EOS R isn't focusing accurately, there's something really wrong with your camera or lens.
 

Mt Spokane Photography

I post too Much on Here!!
Mar 25, 2011
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#4
I don't know that I buy what you're saying about the camera not being able to focus wide open. After all, it will focus wide open in low light. But in a well lit room, then it stops down.

Also, your experience with the EOS R not focusing accurately is absolutely opposite of my own, and most other peoples' that I've read. The EOS R is focusing using the image on the sensor itself, not a separate autofocus sensor like DSLRs. Why would the supposed "focus shift" of a lens even matter on a mirrorless? The camera is just going to move the focus until the actual image is in focus. That's why Canon has done away with the AFMA settings on the EOS R. (And also why I'm very confused that Sony still has those settings on their cameras.) There's really no point to them any more. If your EOS R isn't focusing accurately, there's something really wrong with your camera or lens.

Focus shift is a concern if a camera focuses wide open and then stops the lens down. Being mirrorless does not change that. If the camera focuses at the same aperture as the shot, then focus shift is not a issue.

I have not tried to determine if my R focuses stopped down, or wide open just before stopping down, I'd have to do some experiments to see and try to figure out what its doing.
 
Nov 12, 2016
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#5
I did not realize focusing shifts at different apertures.

I can definitely confirm that with wide aperture primes, the lens actually stops down to focus, then opens back up to take the shot under fairly bright lighting conditions. (A well lit room, indoors.) When I discovered this, I was taking photos with the aperture set wide open, so I thought it was strange that it was stopping down at all.
 

Mt Spokane Photography

I post too Much on Here!!
Mar 25, 2011
15,037
409
#6
I did not realize focusing shifts at different apertures.

I can definitely confirm that with wide aperture primes, the lens actually stops down to focus, then opens back up to take the shot under fairly bright lighting conditions. (A well lit room, indoors.) When I discovered this, I was taking photos with the aperture set wide open, so I thought it was strange that it was stopping down at all.
Only lenses with a lot of spherical aberration are a significant issue, and only when a large change of aperture is involved. The Canon EF 50mm f/1.2 is a example. The Canon RF 50mm f/1.2 has much less spherical aberration and does not show the issue as being significant, but a little is still there.

https://photographylife.com/what-is-focus-shift
 

Larsskv

Enthusiast with Canon related GAS
Jun 12, 2015
721
131
#7
I did not realize focusing shifts at different apertures.

I can definitely confirm that with wide aperture primes, the lens actually stops down to focus, then opens back up to take the shot under fairly bright lighting conditions. (A well lit room, indoors.) When I discovered this, I was taking photos with the aperture set wide open, so I thought it was strange that it was stopping down at all.
Focus shift means that the plane of focus moves when the lens stops down. Therefore, if not corrected for, an EF 50 L (which has focus shift issues) which is in perfect focus at f1.2 will miss focus at approximately f2.8-f4.

Please, also note that few forum members has praised the EOS R focus accuracy with large aperture lenses more than I have.
 
Nov 12, 2016
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#8
Ok, I'll note that, but you just said that you found the EF 50L + the EOS R to focus very badly at f3.5.

So you're saying that the EOS R has good focus accuracy with large aperture lenses when used wide open, but sometimes not when those large aperture lenses are stopped down?
 

Larsskv

Enthusiast with Canon related GAS
Jun 12, 2015
721
131
#9
Ok, I'll note that, but you just said that you found the EF 50L + the EOS R to focus very badly at f3.5.

So you're saying that the EOS R has good focus accuracy with large aperture lenses when used wide open, but sometimes not when those large aperture lenses are stopped down?
It is the EF50L that suffers from focus shift. I am not aware of any other L prime that has focus shift issues.

Another lens that has focus shift is the EF24-70 f4, but you will rarely notice it because of the smaller apertures.

As I stated, when using 1DXII and 5DIV I never had focus shift issues with the EF50L. I believe those bodies compensates for it during AF. But the focus shift issue is real and has been used for bashing the EF50L for many years.
 

Larsskv

Enthusiast with Canon related GAS
Jun 12, 2015
721
131
#10
Ok, I'll note that, but you just said that you found the EF 50L + the EOS R to focus very badly at f3.5.

So you're saying that the EOS R has good focus accuracy with large aperture lenses when used wide open, but sometimes not when those large aperture lenses are stopped down?
By the way, I never tried the EF50L and the EOS R in good daylight, so it can very well be so that in good light it stops down when focusing, and therefore doesn’t change aperture when it takes the shot. If so, there will be no focus shift.
 

Mt Spokane Photography

I post too Much on Here!!
Mar 25, 2011
15,037
409
#11
By the way, I never tried the EF50L and the EOS R in good daylight, so it can very well be so that in good light it stops down when focusing, and therefore doesn’t change aperture when it takes the shot. If so, there will be no focus shift.
If you focus the lens at f/5.6 and then shoot at f/1.2, the focus point will change with the 50L. The same happens with a DSLR, but in reverse, they focus wide open, and then if you have it set to shoot at f/5.6 the focus point will shift.

One of the reasons to buy a 50L is the wide aperture, if you focus it with a DSLR and then shoot at f/1.2, there is no focus shift, but because the "R" stops down to focus, shooting a 50L at a wide aperture will result in focus issues. I'd highly recommend selling any 50L you own and getting the RF 50 1.2 if you plan to do a lot of photos at fast apertures. The lens is very good, there are very few mirrorless lenses to compete with it, so in its class, it stands out. We'll see how the new Nikon lens does when it hits the streets, it may be even more exceptional.
 

jd7

EOS 7D MK II
Feb 3, 2013
685
74
#12
For what it's worth, everything else I've read on the internet is that the EF 50 1.2L focuses very accurately on the EOS R.

This Steve Huff webpage is one example of the sort of thing I've read
http://www.stevehuffphoto.com/2018/10/21/that-old-canon-50-f-1-2-ef-rocks-on-the-eos-r/

If the EOS R is stopping down to AF and then opening the aperture to shoot, and that's causing focus shift, I'm surprised at the number of times I've read how well the EF 50 1.2L works with it.

Anyone here got an EOS R and an EF 50L to do some testing?
 
Aug 26, 2012
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#13
I have been using EF 50 1.2 with my R. I think it does tend to have soft focus as it stops down. I never realized till I read this thread. I have to check my files again, but I remember I took a bunch of shots of my 1.5 year old son at fast shutter speed and wide open. The focus acquiring seemed fast but pictures looked ever so slightly out of focus. It doesn’t appear that way at first unless you are really looking for it. It seems either the focal plane shifted a tad or the AF point that was used was slightly off target (due to user error maybe).
 

Larsskv

Enthusiast with Canon related GAS
Jun 12, 2015
721
131
#14
If you focus the lens at f/5.6 and then shoot at f/1.2, the focus point will change with the 50L. The same happens with a DSLR, but in reverse, they focus wide open, and then if you have it set to shoot at f/5.6 the focus point will shift.

One of the reasons to buy a 50L is the wide aperture, if you focus it with a DSLR and then shoot at f/1.2, there is no focus shift, but because the "R" stops down to focus, shooting a 50L at a wide aperture will result in focus issues. I'd highly recommend selling any 50L you own and getting the RF 50 1.2 if you plan to do a lot of photos at fast apertures. The lens is very good, there are very few mirrorless lenses to compete with it, so in its class, it stands out. We'll see how the new Nikon lens does when it hits the streets, it may be even more exceptional.
I thought it was obvious that if the R stops down to focus, then it stops down to the intended aperture you shoot with, and that it wouldn’t open up again to take the shot.

Btw, I own the RF50L. It is amazing.
 

Viggo

EOS 5D SR
Dec 13, 2010
3,764
337
#15
One might think the EF 50 L doesn’t have focus shift, and it was also some talk years ago that a 2010 version, and perhaps later were actually better etc. All not true, it lacks floating elements like the 85 f1.2 L does have so every single copy shows the exact same focus shift between f2.0-f4, better faster than f2 and from 5.6. It may also Show more or less depending on focusing distance.

The reason it might show better with the R, is that it stops down to focus when shooting wide open. And the other is that the AF with the R is incredibly precise showing ANY issues better than any other DSLR . Miscalibrate the EF 50 L slightly and it hides this issue to a certain degree. With the R being 100% accurate it will show. Combine those two things and the R will reveal focus shift a lot more, but it’s always there. One copy of the lens is not better than another one.
 
Nov 12, 2016
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#16
Well, now I've noticed that its behavior when focusing seems totally random. Sometimes it stops down, sometimes it doesn't. Sometimes it does or doesn't under similar circumstances. Is anyone else seeing this? I'm perplexed.
 

Mt Spokane Photography

I post too Much on Here!!
Mar 25, 2011
15,037
409
#17
I have my camera here, set to Fv with a f/8 aperture, ISO 100, servo AF and face det AF. With those settings, it focuses wide open and stops down to shoot. I then put it in the P position and it does the same. I have a very old 50mm f/2.5 lens mounted on it right now, my other lenses are not here with me, well, my 100mm L is around here, I guess.
I could try other lenses and settings, maybe another day. I no longer use fast primes, so I can't check them.
 

Viggo

EOS 5D SR
Dec 13, 2010
3,764
337
#18
I was trying something in M mode and noticed something I don’t get ; when shooting with a dark frame and Exp.Sim on it won’t open the aperture to focus, so when for example I choose f11 1/4000s indoors it just hunts. When I turn exp.sim off, it focuses normally. How is that not a bug?
 
Nov 12, 2016
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#20
Seems very random when it does. I've seen it a few times with fast primes, but then I also saw it the other day using a Tamron 24-70 2.8. Although, I was shooting towards the direction of the sun when it did this, so that's kind of understandable. I just sort of wonder why it's doing this.