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?
If the EF 100mm f/2.8L IS USM has focus shift, then I have never noticed it. More times than not, I am manually focusing from a tripod. When I do shoot handheld AF, then I am almost always using a crop sensor camera body, shooting at around f/4.
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".
"(I) never knew this "problem" existed until I read this post and followed John's link."
This is the bottom line Newton. Is it really a problem? I say, no, not actually. This phenomenon has been around ever since lenses have been.
" I typically shoot between f/6.3 and f/16, mostly hand held but also some on tripod,..."
The problem isn't the final aperture you shoot at. It is the way most lenses work. You AF at wide open aperture and when you take the shoot at whatever aperture, the camera stops down. There is a slight difference in critical focus point between wide open, f2.8 and f8 lets say. Your flower is very nice and proves it really isn't a problem. If a person feels it is a problem, I suppose they can buy the EF version which I understand has less focus shift. I have the EF 100mm f2.8L and I never noticed the issue with it.
I am a Nikon and Canon shooter based in the UK. I bought the 100mm with the hope that I could sell my Nikon Z 105mm f4, as the Canon not only seemed a great macro lens but lighter than the Nikon to use as a portrait lens. However, I have found the Canon has a large degree of back focusing and cannot be used as an autofocus, run and gun, lens. The lens is as sharp as my Nikon 105 and I've done lots of testing, but the canon simply does not focus on the focussing point, with the area just behind the focussing point being in sharp focus. I have updated the firmware on my R5, but with no change to the lens performance. I will keep the lens, using manual focus for macro work. If anyone on this forum has a solution to using the lens, handheld and in autofocus mode, I would be very grateful, as I wanted to use it at my daughters upcoming wedding.
I don't think manual focus will help since the problem, as described online, is that the focus shifts when the lens stops down at the time the photo is taken. The problem is not "back focus" as with a DSLR where a lens may not focus on the sensor plane. With mirrorless cameras the focus is always on the sensor plane since the focus detecting elements are built into the sensor.
Sorry you are having this problem and I wish I knew exactly what I am doing to avoid it. As I mentioned earlier in this post, I don't notice it in my day to day. I own the EF version as well and used it on the R5, then went straight from it to the RF with very few changes, mostly in post where I use a bit more unsharp masking. I hand hold and "run and gun" as you say, but do use a tripod on occasion. In fact, I shot several stacks today, 160 total shots in four stacks, and all of my starting points were dead on using AF at f/3.2, which in theory should show very little shift anyway. Generally when I'm shooting hand held, I use apertures ranging from f/8 to f/16. At f/16 it starts to get soft due to diffraction I'm sure. I also use high shutter speeds and higher than normal (for others) ISO. I do this (ISO) to keep my shutter up (I shake). For whatever reason, I don't notice focus shift. Since I own the EF version, I took my time researching this lens and bought it because of the outstanding reviews, sample images, and videos, none of which mentioned focus shift. Not that I doubt it exists, it's just that there seem to be lots of folks besides me who don't see it as an issue, or a deal breaker for that matter.
Once again, sorry you are having this issue. If you want, I have posted many shots with this lens and the R5 in the users photo section of this forum with EXIF info, so you may be able to glean some info from them that will help.
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