Focus shift with RF 100mm f2.8L macro lens

[Bazsl]

I have read a number of articles that discuss the focus shift problem with this lens. The only response I have seen from Canon was extremely brief and said that it was a design decision. I must be missing something because I cannot imagine any reason to buy any lens that exhibits focus shift as the lens is stopped down. The only work around that I have seen is to take a photo and, if it is out of focus, then manually focus in front of the desired focus point and use focus bracketing to take a series of photos and pick the one that has the desired point in focus. Why would I (or anyone) buy this lens instead of keeping their EF-100mm macro and sticking an adapter on the back. What am I missing?

[ebiggs1]

All lenses have a focus shift to some degree. It affects lens with faster maximum apertures the most. All lense are a compromise between physical lens factors and manufacturing abilities.

[Bazsl]

All of which has nothing to do with the question. I have never read a review or article about the original EF 100MM f2.8 macro lens or the EF 100mm f2.8L macro lens that mentioned focus shift. However, there are numerous articles about the RF 100mm f2.8L macros lens that describe the focus shift problem with sample images. To me this suggests the focus shift of the RF 100mm f2.8L macro lens is severe enough to be very obvious and, therefore, a problem that no one would want to deal with. I certainly would  not. I cannot understand why Canon would think anyone would want this lens given the reviews I have read. Clearly Canon engineers could have designed a lens without obvous focus shift since they have done so in the past. Please understand that I am not trying to troll the forum. I am a serious photographer looking for a factual answer.

[rs-eos]

I'm not following.  Are you saying you are acquiring focus at some aperture, then while that focus is locked in place, you are changing the aperture before you take the shot?

Or are you speaking to the lens back or forwards-focusing?

If the latter, does your camera allow for AF micro adjustments?

[Bazsl]

I am shooting a R5. I do not own the RF 100mm f2.8L macro but considered buying it until I read several articles complaining about focus shift. According to my reading the problem is that the camera focuses with the lens wide open, in this case at f2.8. As always, when you trip the shutter release the lens stops down to the aperature set either by the automatic exposure system or by the user in manual mode. The problem accourding to the articles I have read is that when the the lens stops down the focus point shifts to a point behind the original focus point. This is more common at small f-stops (f8.0 and smaller) and high magnifications (close focusing distances). If you want more information do a search for "Canon RF 100mm macro focus shift" (without the quotes) and you will find serveral articles describing the phenomenon. 

[jrhoffman75]

Discussed here:

https://www.the-digital-picture.com/Reviews/Canon-RF-100mm-F2.8-L-Macro-IS-USM-Lens.aspx

[Bazsl]

Thanks jr. The article you referenced provides an excellent description of the problem.

[ebiggs1]

"All lenses have a focus shift to some degree."  "... which has nothing to do with the question."

Ah, but it does. It explains why and what is happening. The original EF version has focus shift. Apparently it isn't as bad as the the new lens but it's there. Lenses that are prone to focus shift problems have more faster maximum apertures.  Prime lenses with uncorrected spherical aberration will always have focus shift problems.  All fast lens with aberration problems will exhibit some focus shift at different apertures. This is not new nor is it solely an issue with the lens in reference. Most, or I might say, all of the time the focus still lies in the acceptable focus range although perhaps not at the critical focus point.

[FloridaDrafter]

I've been using the RF 100mm f/2.8 L IS USM on an R5 and R6 since September, 2021, with outstanding results, and never knew this "problem" existed until I read this post and followed John's link. When doing research, I didn’t look at extensive lab results, but rather images/videos taken with this lens by pros who shoot similar subjects and technique as me. I'm glad I bought it, it is a wonderful lens and I haven’t noticed the problem. I typically shoot between f/6.3 and f/16, mostly hand held but also some on tripod, AF hand held and MF on tripod for “posed” flowers. I also use this lens to stack.

Shot 1.4:1, cropped 50%, f/9, 1/500th, ISO 3200, slight editing in DPP. These orchids are 1/16".

Newton

[jrhoffman75]

Great shot Newton.