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?
Thanks to all who have replied to my post. Unfortunately I have been suffering from Covid and only just felt like doing further tests. Bazsl's comment on manual focus got me thinking. So using a Bob Atkins chart on a 45 degree angle, I shot the lens in manual on a tripod. It was perfect. Then came tests using servo and single shots with varying types of focussing points on tripod and hand held. Spot focus on one shot, on tripod and hand held were extremely sharp, using servo took more care to get a sharp shot. My Nikon 105 f4 is much slower to focus than the Canon 100 f2.8 but tends to be accurate most of the time whereas, as mentioned, although much faster, the 100mm in servo needs a little more care. So another example of not the lens but the idiot behind it! I know this post is on the lens, but I must mention how brilliant a camera the R5 is, in particular the ability to set the AF-ON button to AF eye and also set the AE lock button to AF servo and set any focussing point. With that combination you are set for any focussing challenge. I wished my Nikon Z7ii could do the same, but then the R5 is almost twice the price. As regards my Nikon 105, I'm going to sell it along with my d850 and Nikon EF 70-200 f2.8 and buy the canon RF 70-200 f2.8, which will be, I hope, a more practical solution to photographing my daughter's wedding and other situations.
Thanks again for all the advice,
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
04/20/2023: New firmware version 1.4.1 is available for EOS R3
03/30/2023: New firmware updates are available.
2/07/2023: New product announcements!EOS R8 EOS R50RF-S55-210mm F5-7.1 IS STMRF24-50mm F4.5-6.3 IS STMRF15-30mm F4.5-6.3 IS STM