In my Canon EF-mount kit, one of my favorite lenses was the Canon EF 100mm f/2.8L Macro. It was solid and sharp, with snappy autofocus and good stabilization. So when I moved to an RF-mount system, I definitely wanted to pick up the new RF version, which is an improvement in just about every way: sharper, faster autofocus, better stabilization, and a shorter minimum focus distance enabling 1.4x magnification instead of the EF version’s 1.0x.

Recently, a friend let me know he was thinking of buying the lens, but was concerned about a reported focus-shift issue some reviewers and users mentioned. Focus shift is a phenomenon in which the plane of sharpest focus moves slightly as the aperture of the lens stops down. Since cameras generally focus at the widest aperture (f/2.8 in the case of this lens), focus shift can result in images that aren’t focused on the intended point, obviously a pretty big problem for a macro lens in particular. I hadn’t noticed the phenomenon myself–I tend to assume that missed-focus images are my fault! But I wanted to put the lens to the test a bit to confirm whether this was indeed an issue.

I’m not really one for focus charts and all that–I use my gear in the field, so I generally want to test it in the field. So yesterday I trekked out into the woods behind my home to find a good test subject. Focus shift is most evident and problematic at minimum focusing distance, where the the zone of sharpness is most narrow. Here’s my methodology.

I wanted a static subject, so I found a small mushroom growing from a fallen tree trunk. I set up with my R5 on a tripod, set the lens to manual focus at the minimum focus distance, and adjusted with my macro rail to where the front rim of the mushroom was in sharp focus. I used my small LED light panel to add illumination, so I could leave the ISO set at a reasonable 400. Starting at f/2.8, I then took shots at each full-stop aperture value, increasing the exposure time to compensate. I used 2-second delay and electronic shutter to minimize vibrations.

And here are the results! These are basically straight-out-of-camera CR3 files, exported from Lightroom with minimal sharpening and NR applied.

f/2.8, 1/640s, ISO 400
f/4, 1/320s, ISO 400
f/5.6, 1/160s, ISO 400
f/8, 1/80s, ISO 400
f/11, 1/40s, ISO 400
f/16, 1/20s, ISO 400
f/22, 1/10s, ISO 400
f/32, 1/5s, ISO 400

A slideshow of the above images for faster comparison:

I was pretty pleased with these results–to my eye it looks like focus remained right where it was supposed to be, with the depth of field increasing as I stopped down. Sharpness at the focus plane was very good through f/11, beginning to fall off due to diffraction from f/16 onwards.

To me, the proof of any lens is what I can get from it under normal use, which for me is generally handheld. Here are a few more handheld shots from this test outing, as well as from an excursion over the weekend.

I suppose it’s possible that different copies of the lens could have differences, and it could behave differently on different camera bodies. I’m not sure if Canon added any firmware tweaks to compensate for the focus shift since the initial reports came out. But as it stands, I see no problem and have no hesitation recommending this lens.

Drop me a line if you have any questions or suggestions!

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