Other RF 100 macro F2.8 L focus shift

[derekc23]

I have been trialing the RF 100mm macro L as a macro lens photographing butterflies, and the results are impressive. I also have the EF 100 macro 2.8 non L.
I'm interested in buying the RF, but I'm put off by the reports of focus shift. How to I know if I'm getting the best result? I've tried handheld focus bracketing, with variable results but some look good.
Should I stick with the EF (and save some money!!) or go with the RF with its 1.4 capability?

Derek Clements

 

[Archibald]

Hi, Derek.

Focus shift with aperture change is pretty normal, and I believe the EF 100mm also exhibits it. But maybe it is worse in the RF version (I don't know).

I love my RF 100 L, and never notice a problem. It's because I almost always shoot at f/11 or f/13. Any focus shift is small compared to the DOF at those apertures. If you shoot at wider apertures, then the error might be noticeable.

When doing stacks for focus stacking, it is common to shoot at wider apertures, because there is less diffraction at wider apertures. Then the focus plane will be slightly different than expected. But I suppose it doesn't matter in this case since the stacking will always select the sharpest part of each image.

So the use case where you might notice a focus error is when doing single frame shooting at intermediate apertures like f/5.6.

I shot with the EF version for years, and it was great. I used an extension ring to get better than 1x magnification. That worked pretty well, but AF was kind of balky with that tube.

Yes, I use AF for macro. It doesn't guarantee critically-sharp focus, but MF doesn't either, if you are hand-holding. And I'm almost always hand-holding. (When on a stand, I use MF.)

So the RF is way better, but also very expensive. I have no regrets about the switch.

 

[derekc23]

Hi, Derek.

Focus shift with aperture change is pretty normal, and I believe the EF 100mm also exhibits it. But maybe it is worse in the RF version (I don't know).

I love my RF 100 L, and never notice a problem. It's because I almost always shoot at f/11 or f/13. Any focus shift is small compared to the DOF at those apertures. If you shoot at wider apertures, then the error might be noticeable.

When doing stacks for focus stacking, it is common to shoot at wider apertures, because there is less diffraction at wider apertures. Then the focus plane will be slightly different than expected. But I suppose it doesn't matter in this case since the stacking will always select the sharpest part of each image.

So the use case where you might notice a focus error is when doing single frame shooting at intermediate apertures like f/5.6.

I shot with the EF version for years, and it was great. I used an extension ring to get better than 1x magnification. That worked pretty well, but AF was kind of balky with that tube.

Yes, I use AF for macro. It doesn't guarantee critically-sharp focus, but MF doesn't either, if you are hand-holding. And I'm almost always hand-holding. (When on a stand, I use MF.)

So the RF is way better, but also very expensive. I have no regrets about the switch.

 

[derekc23]

Thanks for informative answer. Am I wrong in thinking that at a given aperture the lens is focusing slightly back hence the suggestion in one review to focus slightly in front?

 

[Archibald]

Thanks for informative answer. Am I wrong in thinking that at a given aperture the lens is focusing slightly back hence the suggestion in one review to focus slightly in front?

As I understand it, the system focuses with the aperture wide open (usually). It focuses exactly right at that aperture. When it takes the picture it stops down to the selected aperture, and that causes the focus shift. The focus plane is slightly different at each aperture (because of spherical aberration). So that leads to the focus error. But the error is small.

I don't know what direction it moves, but if you shoot at apertures where it matters, I suppose you would find out from experience. It will vary with different apertures and distances.

I don't know if the RF 100 L can be focused stopped down. If so, then just focus with the aperture at the shooting aperture and there will be no error.

Another fix would be for Canon to incorporate algorithms in firmware to compensate the focus when shooting. I don't think that has been done, but maybe it will be in the future.

 

[Rhody]

I moved over to the RF 100 L this year and have not used the EF on the R5 since.
I still use the EF on my EOS film cameras though as I can't bring myself to get rid of either.
They are both superb lenses.