Thanks to reader David C for bringing this feature to my attention—compensation for focus shift is rare among cameras and a Very Good Thing, so long as the behavior is understood (it can work against you in some cases).
Apparently Nikon silently slipped in this upgrade a few years ago and made no mention of it. And yet it is a critical behavior that one must understand if focusing manually.
This test with the Nikon D810 suggests that it actively compensates for focus shift by modifying the point of focus to compensate, based on shooting aperture. That is, when conventional AF is used.
I’ll have to confirm this behavior with other lenses; at this point it’s unclear which cameras and lenses support focus shift compensation. Nikon is hiding their light under a bushel for some reason, which is very strange from a marketing standpoint.
Focus shift compensation is a super nice feature when applicable, but there are situations where it can degrade performance, nor not apply—any situation in which the AF system is used to prefocus at one aperture, but the image is exposed at another aperture. It could mean, for example, needing to focus at f/2.8 because of dim light but then shooting stopped down. Or pre-focusing at f/5.6 but then deciding to shoot at f/2.8. And so on. Presumably these are a small minority of cases. For myself, it means that shooting an aperture series is problematic because AF is prone to precision errors, focus shift compensation or not. And focusing in dim light is not feasible stopped down and DoF adds ambiguity as well.
Also, focus shift is not a simplistic behavior: it can be rearwar in the center and forward in the outer zones. Presumably the limited coverage of the focusing sensors in Nikon full-frame DSLRs cover too little of the frame for that to be an issue. Still, such differential behaviors mean that a full understanding of the behavior is essential for optimal results. For massive focus shift, see the Sigma 12-24mm f/4 Aperture Series @ 14mm: Two Aspen. I don’t know if such a lens takes advantage of focus shift compensation.
Finally, focusing in magnified Live View has long compensated for focus shift in this sense: the lens is stopped down to the shooting aperture by default. However, that often leads to serious errors in my own experience.
So I would say this: for conventional shooters (focus and shoot), focus shift compensation is a wonderful feature. For other usage scenarios, one still needs to understand what is happening. In particular, it’s problematic to shoot aperture series my usual way (by focusing wide open) and yet the AF system doesn’t always have enough precision for reliable results. This is the severe headache I ran into with the Fujifilm GFX. A lens without focus shift is always far, far preferable.
Markus H writes:
According to Marianne Oelund, focus shift correction has been added to bodies released in 2014 onwards. This includes for sure the D810, the D500 and the D5. Most likely also the D750 (released in 2014 but after the D810) and the D4s (released in 2014 but before the D810) as well as the 2015 D7200 and 2017 D7500.
If you don’t know Marianne Oelund, she is an engineer by trade and photographer by passion and when she says something, you’ll know it’s true because she has actually tested it herself.
Note that when a new lens gets released, bodies that can correct for focus shift need a firmware update to get the focus shift parameters for that lens to properly correct the focus shift.
DIGLLOYD: how non-Nikon AF lenses with severe focus shift behave is unclear to me.
I used the latest firmware on the D810 in my testing.
Firmware on the Nikon D810 + 70-200/2.8E reads:
C = 1.12
L = 2.015
David C writes:
I have just tested D500 for focus shift compensation with 70-200 2.8 FL. Bad news. It does not seem to compensate for focus shift.
DIGLLOYD: contradicts the claim above vs the D500. I can only speak directly to what I have personally tested and verified: the D810 compensates for focus shift. I should also do more extensive testing with the D810, but this will take time. Also, at dusk I found the AF system unable to cope with dim light, forcing use of f/2.8 in Live View, so there is no compensation viable under those conditions. I would not trust the AF system for critical work that I do in any case, moreover focus shift at distance looks to be not an issue with the 70-200/2.8E.