Canon EOS R5 + any RF 35 mm = terrible back focus

[Chris.Chapterten]

I thought that the reviewing world had established that this RF 35/1.8 suffers from RSAs - focus shift, and what you're describing seems to fit with this. If so it's a normal characteristic of the lens and you'll have to learn to work around it just like those of us that have RSA effected lenses such as the EF 50/1.2 & Tamron 85/1.8 VC have to.

Very interesting. I had actually missed the focus shift issue in the reviews I had seen on YouTube. The digital picture has a good explanation of it in their review: https://www.the-digital-picture.com/Reviews/Canon-RF-35mm-f-1.8-IS-STM-Macro-Lens.aspx

In my first shoot with the lens I only used f2.0 and f2.5 so that would explain why I wasn’t really experiencing the focus shift issues. It seems most pronounced after 2.8 based on the digital picture review.

How does one compensate for this in real world shooting? I would imagine that adjusting manual focus and bringing the focus point forward would be extremely hit and miss? I’m honestly quite surprised that modern lenses still suffer from this.

It looks like I won’t be using my RF 35 f1.8 at the problem apertures... most likely will keep it at or below f2.5.

 

[Sporgon]

Very interesting. I had actually missed the focus shift issue in the reviews I had seen on YouTube. The digital picture has a good explanation of it in their review: https://www.the-digital-picture.com/Reviews/Canon-RF-35mm-f-1.8-IS-STM-Macro-Lens.aspx

In my first shoot with the lens I only used f2.0 and f2.5 so that would explain why I wasn’t really experiencing the focus shift issues. It seems most pronounced after 2.8 based on the digital picture review.

How does one compensate for this in real world shooting? I would imagine that adjusting manual focus and bringing the focus point forward would be extremely hit and miss? I’m honestly quite surprised that modern lenses still suffer from this.

It looks like I won’t be using my RF 35 f1.8 at the problem apertures... most likely will keep it at or below f2.5.

Well the only work around I have is when using apertures most effected, so those that are small enough to create the issue but not so small as to have enough dof to cover it up - like you say around the f/2.8 mark, is to focus on something that a little closer than I want. Obviously this is risky and not ideal.

Honestly I'm surprised that given the computing power of modern cameras, when using these lenses, like the EF 50/1.2 for instance, the camera can't be programmed to stop down when using the most effected apertures. Even in live view the EOS won't focus if you are holding the dof button in.

 

[Chris.Chapterten]

Well the only work around I have is when using apertures most effected, so those that are small enough to create the issue but not so small as to have enough dof to cover it up - like you say around the f/2.8 mark, is to focus on something that a little closer than I want. Obviously this is risky and not ideal.

Honestly I'm surprised that given the computing power of modern cameras, when using these lenses, like the EF 50/1.2 for instance, the camera can't be programmed to stop down when using the most effected apertures. Even in live view the EOS won't focus if you are holding the dof button in.

Thanks. Yeah, it really doesn’t sound like there is much you can do. I would be very reluctant to try and guess where the focus might land like that... very tricky to get right every time.

I have heard that Sony and Nikon mirrorless focus with the lens stopped down, so I’m not sure why canon can’t make this an option? It could even be automatic when an affected lens is detected by the camera.

I did actually just find a few images taken on my most recent shoot that were back focused at f2.5. (Ear instead of eye). These were at a slightly further distance (closer to full length body shots). It wasn’t an entirely consistent behaviour but all of the shots that did miss were slightly back focused (never front focused). I might have to do some tests to see how subject distance affects things with this lens..

 

[StoicalEtcher]

Well the only work around I have is when using apertures most effected, so those that are small enough to create the issue but not so small as to have enough dof to cover it up - like you say around the f/2.8 mark, is to focus on something that a little closer than I want. Obviously this is risky and not ideal.

Honestly I'm surprised that given the computing power of modern cameras, when using these lenses, like the EF 50/1.2 for instance, the camera can't be programmed to stop down when using the most effected apertures. Even in live view the EOS won't focus if you are holding the dof button in.

Just a thought: Could one use AFMA to counter-act this? i.e. check what adjustment works for you at the given/affected aperture and then in future dial that in when using the lens in question at that/those apertures?

 

[Joules]

Just a thought: Could one use AFMA to counter-act this? i.e. check what adjustment works for you at the given/affected aperture and then in future dial that in when using the lens in question at that/those apertures?

You probably could ... but as far as I'm aware, the RF bodies don't have any AFMA options

 

[StoicalEtcher]

You probably could ... but as far as I'm aware, the RF bodies don't have any AFMA options

Oh, of course - sorry, I'm still here in DSLR world, and not engaging what's left of my grey matter!
I was thinking of use cases for Ef50 f/1.2 ......
Ignore my post!

 

[Sporgon]

Just a thought: Could one use AFMA to counter-act this? i.e. check what adjustment works for you at the given/affected aperture and then in future dial that in when using the lens in question at that/those apertures?

On a DSLR possibly. The trouble is that for someone like me I'd forget to reset it and then I'd start a thread on CR titled "Terrible front focus of Canon EF 50/1.2"

 

[Chris.Chapterten]

Oh, of course - sorry, I'm still here in DSLR world, and not engaging what's left of my grey matter!
I was thinking of use cases for Ef50 f/1.2 ......
Ignore my post!

Unfortunately on a DSLR using the AFMA would only work for a specific subject distance at a specific aputure. It might be useful for a studio setting shooting still life. But for fashion etc. it would certainly ruin the mood of the shoot if the subject was unable to move from their mark.

I’ve done a little more reading on it and some people suggest to focus and then ‘lean back’. None of it sounds very scientific haha

 

[Chris.Chapterten]

Had another shoot today and was using the lens at f2.0, f2.2 and f2.5. With the subject at full body length distance there was quite a bit of focus inaccuracy. Every time it missed it was backfocused.

Strangely at closer distances like 3/4 length, 1/2 length and head and shoulder length, auto focus accuracy was very good. This seams counterintuitive, as I would have assumed the focus shift would be more obvious at closer distances, but the opposite was true for my copy of the lens.

Needless to say I’m going to have to learn some of the limitations of this lens and see if I can figure out the distance at which things go pear shaped with the autofocus. It’s such a shame as I love the image quality otherwise. I’ll be hanging out for the RF 35mm f1.2L... c’mon Canon!

 

[Dmitri_Kahm]

Had another shoot today and was using the lens at f2.0, f2.2 and f2.5. With the subject at full body length distance there was quite a bit of focus inaccuracy. Every time it missed it was backfocused.

Strangely at closer distances like 3/4 length, 1/2 length and head and shoulder length, auto focus accuracy was very good. This seams counterintuitive, as I would have assumed the focus shift would be more obvious at closer distances, but the opposite was true for my copy of the lens.

Needless to say I’m going to have to learn some of the limitations of this lens and see if I can figure out the distance at which things go pear shaped with the autofocus. It’s such a shame as I love the image quality otherwise. I’ll be hanging out for the RF 35mm f1.2L... c’mon Canon!

Well, up until 2,8 the backfocus is pretty tolerable. In the 2,8-5,0 range it is the worst, making these apertures almost unusable. That is very sad.
The only "good" point is that I was right after all when I started this topic despite the claims of some reputable forum members ;-)

The Canon EF 35 2.0 does not suffer from this issue and is still pretty light with similar IQ + it is not STM, but USM. You may try it + converter. I sold my RF and bought EF.

 

[Chris.Chapterten]

Well, up until 2,8 the backfocus is pretty tolerable. In the 2,8-5,0 range it is the worst, making these apertures almost unusable. That is very sad.
The only "good" point is that I was right after all when I started this topic despite the claims of some reputable forum members ;-)

The Canon EF 35 2.0 does not suffer from this issue and is still pretty light with similar IQ + it is not STM, but USM. You may try it + converter. I sold my RF and bought EF.

Yeah, I had no trouble with f2.0 - f2.5 at closer distances. Focus accuracy was very good. When I got a bit further out it wasn’t too happy. Funnily enough the lens actually reminds me of my old EF 50mm 1.4 in terms of focusing motor behaviour.

At a slightly further distance the RF 35mm f1.8 autofocus tends to jitter back and forth a bit while locking focus. With my L lenses once it has locked focus in single shot AF mode it just stays there. Even if I half press the shutter again, the L lens will only ever make the slightest of movement. I would assume this is because the initial acquisition of focus is more confident /accurate. With the RF 35mm 1.8 there are constant little movements all the way up until the focus locks. If I half press the shutter again without the subject moving it will start jittering back and forth a bit before locking focus. I would assume all of the missed focus were back focused because the lens tends to move in that direction when stopped down a bit anyway. So if the the focus is slightly off, the problem is made worse by using a slightly stopped down aputure?

Did you ever experience more focus motor movement like I described when trying to aquire focus from a slightly further distance?

EDIT: some further details after reviewing a batch of ‘problem images’ taken at a full length body distance at f2.0 and f2.2. Out of 62 photos 18 were backfocused to the point of being practically unusable. A further 5 were backfocused to the point were some sharpening made them acceptable. The remaining 39 were quite good and usable without the need for sharpening.

I should note that all 62 of these images were partially backlit. No direct sun or anything, just an open window with a partial sheer curtain covering. Contrast on the front of the subject was fairly low and settings ranged from ISO 400, f2.2, 1/200 to ISO 400, f2.0, 1/320. Just to give an idea of the light level. In essentially the same lighting conditions my RF 50mm 1.2L and RF 85mm 1.2L did perfectly fine with focus accuracy.

The frustrating thing with the AF inaccuracy on this lens in this particular situation is that I had 8 in a row that were backfocused to the point of being unusable. This meant I missed 3 different poses/expressions from the model (including one I was hoping to use as a final image).

 

[Dmitri_Kahm]

Yeah, I had no trouble with f2.0 - f2.5 at closer distances. Focus accuracy was very good. When I got a bit further out it wasn’t too happy. Funnily enough the lens actually reminds me of my old EF 50mm 1.4 in terms of focusing motor behaviour.

At a slightly further distance the RF 35mm f1.8 autofocus tends to jitter back and forth a bit while locking focus. With my L lenses once it has locked focus in single shot AF mode it just stays there. Even if I half press the shutter again, the L lens will only ever make the slightest of movement. I would assume this is because the initial acquisition of focus is more confident /accurate. With the RF 35mm 1.8 there are constant little movements all the way up until the focus locks. If I half press the shutter again without the subject moving it will start jittering back and forth a bit before locking focus. I would assume all of the missed focus were back focused because the lens tends to move in that direction when stopped down a bit anyway. So if the the focus is slightly off, the problem is made worse by using a slightly stopped down aputure?

Did you ever experience more focus motor movement like I described when trying to aquire focus from a slightly further distance?

EDIT: some further details after reviewing a batch of ‘problem images’ taken at a full length body distance at f2.0 and f2.2. Out of 62 photos 18 were backfocused to the point of being practically unusable. A further 5 were backfocused to the point were some sharpening made them acceptable. The remaining 39 were quite good and usable without the need for sharpening.

I should note that all 62 of these images were partially backlit. No direct sun or anything, just an open window with a partial sheer curtain covering. Contrast on the front of the subject was fairly low and settings ranged from ISO 400, f2.2, 1/200 to ISO 400, f2.0, 1/320. Just to give an idea of the light level. In essentially the same lighting conditions my RF 50mm 1.2L and RF 85mm 1.2L did perfectly fine with focus accuracy.

The frustrating thing with the AF inaccuracy on this lens in this particular situation is that I had 8 in a row that were backfocused to the point of being unusable. This meant I missed 3 different poses/expressions from the model (including one I was hoping to use as a final image).

Hello! Unfortunately I do not remember, how my RF 35 behaved in terms of "little movements" you mention. Probably, mine was behaving the same. But I feel that the USM focus motor the EF2.0 version has is anyway better and quicker than STM of RF 35. Moreover, there are no external moving parts is EF 2.0.