The focus shift issue with the Canon RF 100mm f/2.8L IS USM Macro revisited in revised review

Del Paso

M3 Singlestroke
Aug 9, 2018
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1,442
Along with the RF 14mm TS, this is the RF lens I wanted to buy.
Since I'm often, when trekking, doing hand-held macro , AF can sometimes be very useful. But focus-shift killed it!
Unless Canon fixes this issue, I'll keep using my EF version.
 

Del Paso

M3 Singlestroke
Aug 9, 2018
1,316
1,442
That's a weird reply from Canon, focus-shift is something the firmware could very well compensate for since it knows the actual position of the focus motors and hence the exact focus distance.
And did Canon just imply that their AF should be avoided?
Wonderful new world, an AF lens that shall be used in manual mode if you need sharp pictures...:mad:
 

FrenchFry

Wildlife enthusiast!
Jun 14, 2020
459
574
Bryan @ TDP posted the information he received from Canon's engineers:

"...due to its 1.4x magnification (1.4:1 reproduction ratio) capability, a magnification far exceeding 1.0x, the RF 100mm F2.8 L Macro IS Lens's optical design exhibits some focus shift.

The focus shift is not sample dependent and is not related to the SA control ring. As focus shift is characteristic of this lens, no production changes to the lens or lens/camera firmware updates are anticipated. Correction, when necessary, is accomplished by focusing slightly in front of the subject.
"

Is the focus shift Canon is acknowledging at all magnifications or only when the lens is above 1:1 and approaching 1.4x magnification?
If given the choice between a lens limited to 1x and no focus breathing or a lens that goes to 1.4x but has focus breathing through the entire range, I think many would choose the former. It seems weird to introduce a lens that has a special feature that compromises the utility of the lens for the whole range, not just when the feature is being used.
Hopefully they will address it as much as feasible in firmware in spite of this statement.
 
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stevelee

FT-QL
CR Pro
Jul 6, 2017
2,176
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Davidson, NC
At macro levels, the focus mostly a matter of choosing magnification. So if I am using a tripod, I use the focus dial for setting size, and the rail to focus. The added bonus (besides not driving one’s self crazy) is you are already set up to do focus stacking if you want it.

Chasing around insects is a whole ‘nother matter. Even then I have better luck moving the camera to focus rather than twisting a dial. And if someone can do that at 1.4x, he’s a better man than I.
 

Viggo

EOS R5
Dec 13, 2010
4,790
1,470
At macro levels, the focus mostly a matter of choosing magnification. So if I am using a tripod, I use the focus dial for setting size, and the rail to focus. The added bonus (besides not driving one’s self crazy) is you are already set up to do focus stacking if you want it.

Chasing around insects is a whole ‘nother matter. Even then I have better luck moving the camera to focus rather than twisting a dial. And if someone can do that at 1.4x, he’s a better man than I.
Focus shift makes no difference in MF or AF, it happens as the aperture closes during exposure, so it will still be a problem. Not sure if you can use dof-preview and dial in focus based on that preview.
 

neuroanatomist

I post too Much on Here!!
CR Pro
Jul 21, 2010
26,051
4,615
Focus shift makes no difference in MF or AF, it happens as the aperture closes during exposure, so it will still be a problem. Not sure if you can use dof-preview and dial in focus based on that preview.
Correct. If you’re shooting at f/2.8 (with macro, unlikely), there’s no focus shift. If you stop down, there will be backfocus that goes away narrower than ~f/11, because at that point the DoF is sufficiently deep to encompass the backfocus. So if you usually shoot at f/14, focus shift is a non-issue. If you focus stack it’s also a non-issue even if you shoot wider than f/11 to avoid any softening from diffraction, provided you collect a deep enough stack.
 
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stevelee

FT-QL
CR Pro
Jul 6, 2017
2,176
882
Davidson, NC
Focus shift makes no difference in MF or AF, it happens as the aperture closes during exposure, so it will still be a problem. Not sure if you can use dof-preview and dial in focus based on that preview.
Yes,I realized later that my post somewhat missed the point. Otherwise, I meant what I said, for what that’s worth. I’ve never experienced focus shift as far as I could tell in macro situations, so it is not something I related to. I would think DOF preview should help on a mirrorless camera. On my DSLR, looking through a glass darkly is not likely to tell me much.
 
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