James,
back in January 2011, the D7000 was just released, I used the new camera with the then current generation of fast lenses (AFS 24mm/1.4G, AFS 35mm/1.4G, AFS 85mm/1.4G). Much to my disappointment, the AF was way off for longer distance when shooting with an open aperture. What started as a seemingly simple issue to just correct a misaligned AF module in the D7000, became a much broader effort. Over the course of a few months the error "extended" to many more combinations in my gear set.
Ultimately,
the following camera's made the trip to Nikon's main service center for Central Europe multiple times: D7000, D3, D3s, D3x, plus the following lenses: AFS 24mm/1.4G, AFS 35mm/1.4G, AFS 85mm/1.4G, AFS 24-70mm/2.8, AFS 200mm/2 VR, AFS 70-200mm VR1, AF 85mm/1.4D. (many more lenses were impacted, but I didn't sent all. The lenses above represented a good sample). Some of the gear made the trip 3 or 4 times. As the backfocus/frontfocus pattern had so many variations (camera/lens/type of light/focus distance combinations), I sent in the whole gear set to allow the Nikon technicans to check their desired combinations as well. I spent many hours to use a similar lens cal device like you (lenscal) to check AF precision and had many phone conversations with the Nikon staff in the service facility in Düsseldorf (their main facility in Central Europe). Sent Nikon extensive test protocols and pictures to support their work finding the "pattern" of the errors.
I documented many of my findings in a thread in the german NFF forum. Sorry, it is in german, but anyway, here is the link for those who can read german, or use machine translation:
http://www.nikon-fotografie.de/vbulletin/nikon-d7000/151532-fokusprobleme-mit-neuen-lichtstarken-objektiven.htmlIn hindsight, a few things I remember (almost 5 years already passed by):
1) First check should always be if your lens is decentered. Particular important if you use an AF cross sensor on the testpattern. Makes your AF measurement random.
2) AF adjustment in the camera is distance related. Adjusting the focus at 3m right is no guarantee that it is equally precise at 10m.
3) Faster lenses are more affected (due to shallower focus). Only f2.8 or faster lenses are impacted. Focal length doesn't make a difference if a lens would be impacted or not.
4) Most affected where the generation of cameras between 2007 and 2010. With the D800/D4, quick checks didn't produce this erratic behavior of the previous generation.
5) Quality of light definitely impacted AF test results (incandescent, outdoor, daylight bulbs, ...).
6) Nikon's factory error margin for the D7000 AF was outside my understanding what infocus or back/front focus means (The D7000 was the first 16MP DX Camera and my camera came early - don't know if the QA process was later adjusted)). FYI, Nikon's guidelines prescribed a 50mm with f2.8 to calibrate the AF
7) Lower cost cameras as well as higher priced cameras where affected
8.) One lens (AFS 24mm/1.4G) was replaced by Nikon
9) After 2 months focussing on AF focus issues, the situation improved to a state, that it was sufficient for me.
10) The D2X and D2Xs where not affected, the D300 and D300s to a smaller degree
11) I learned a lot about potential AF errors.
12) It was my first needed engagement with Nikon's service organisation - until then, things worked fine
13) I am now much more relaxed about AF systems
(but I am still curious about the performance of the D5 and D500 AF systems
)
Please let me know if you have any further question, happy to try to answer it. Good luck with your gear.
rgds,
Andy
PS:
I can't find the info anymore but I believe I've read years later, that the randomization in the AF systems were due to IR sensitivity in the AF module. But as said, just a memory snippet.
