This is a continuation of a series of posts on the Sony a7RIII. You should be able to find all the posts about that camera in the Category List on the right sidebar, below the Articles widget. There’s a drop-down menu there that you can use to get to all the posts in this series; just look for “a7RIII”. I’ve also tagged this post for the a7RII.
In this post, I found that the Sony a7RIII in AF-S mode did not correct for focus shift caused by spherical aberration with the Zeiss Batis 85 mm f/1.8 lens. A few folks have asked if that’s true for the a7RII, which was the predecessor camera. You’re about to find out.
AF-S, spot, medium, AF-S, Setting Effect on, focus priority AF:
The dots are the samples, for each Adobe RGB color plane, with 10 shots per f-stop. The lines are the averages for all ten shots. Negative numbers indicate front-focusing. The image-plane shift in micrometers (um) increases fairly consistently. I wouldn’t trust the blue plane numbers at f/4 f/4.5, and f/5. Longitudinal chromatic aberration (LoCA) just doesn’t work like that.
Let’s look at the circles of confusion (CoCs) implied by the above misfocusing.
Ignoring the suspect blue samples, the worst-case average error is a bit over two pixels. This is pretty good, but it would be a lot better if the camera compensated properly for focus shift. Look at the tight clustering and low errors at f/1.8!
Net is that this behavior has been with us for a while; it’s not an a7RIII take-away.