Related posts on this issue:
- Nikon D850: the Focusing Distance Issues Stem from a Sensor that is not Parallel to the Lens Mount (Nikon quality control issue)
- Nikon D850: Apparent Build Tolerance Error in Flange Focal Distance vs Optical Viewfinder, Causes Major Focus Error with Manual Focus Lenses and Focus Confirmation
- Nikon D850: Misaligned Sensor Example Images
- Testing for a Misaligned Sensor
Flange focal distance = distance from the lens mount to the sensor. It should be the distance at which lenses focus to infinity at normal temperature.
When I received my very own Nikon D850 from B&H after the lost and found UPS episode, I tested it for asymmetry and it looked good. However, it had/has the same problem with infinity focus: to focus all of my Zeiss lenses (and the Nikon 14-24), the lens has to be focused way past the infinity mark. Every one of them.
This was never an issue with the D800, D800E, D810. Just swapping lenses between the D850 and D810 shows that the D850 is out of spec; every lens has to go quite a ways beyond the infinity mark, most of them using up 3/4 of the range from the mark to the hard mechanical stop.
Put the same lenses on my trusty D810 and the focus position is normal for all of them, right on or very close to the infinity mark.
My camera is not the only one. The one I borrowed had this problem (and asymmetry too). One reader returned his because it had the same problem. I bet there are many of them out there with this issue, but since most users shoot Nikon zooms with autofocus, no one pays any attention to it.
The flange focal distance was perfect on my D800, D800E, and D810. It is now wrong on the Nikon D850. Is this sloppy quality control, or some deliberate (and destructive) decision by Nikon?
Some lenses cannot focus past a hard mechanical infinity focus. I’m in the mountains and so I cannot test 20 or so other lenses including old Nikkors. But all my Zeiss glass is now “past infinity” on the D850, as is the Nikon 14-24mm f/2.8G. With the 14-24, I had to dial in +20 to get autofocus right—seems like a symptom of the same disease.
Today, in the 50°F range, the Zeiss Milvus 18/2.8 was already way past the infinity mark, with very little mechanical focusing range to spare. By the time it was 28°F (it cools off fast at 11,500'), there was no range left. I wonder what would happen at 15°F or 0°F? Plenty of people shoot in the winter.
I’ve asked Nikon PR for an official statement on this matter. The D850 flange focal distance error is unacceptable, and I want an answer. It is a serious problem for shooters like me, shooting Nikon, Sigma, Zeiss and other brand lenses. The loaner camera I had showed the same issue. Another user wrote to report the same issue. This is not a one-off “bad sample”: Nikon has something seriously wrong with D850 production tolerances.
Craig H writes:
I read your blog articles on this matter with great interest. Although I am not in the market for a D850 (I now shoot Sony), I am a former Nikon shooter. I wonder whether other symptoms of this issue may arise in a similar vein to what you may experience if you use a lens adapter with bad tolerances on a Sony.
I tried using my old F-mount Tamron 15-30 2.8 VC on my A7RII with an adapter that evidently was not properly calibrated (too thin). Not only was infinity focus reached on all my Nikon glass before the infinity marker (including on lenses that had a perfectly calibrated hard stop on my D810) but I found that this flange focal length inaccuracy introduced severe field curvature on the 15-30 that was not present on the D810.
I later learned this can manifest itself with certain lenses if the adapter is not of the correct thickness - I wonder if this lens (or indeed others) may have a similar problem on the D850, or at least on those samples of which have this inaccuracy present? The 15-30 is an excellent lens, and if I was a D850 buyer I would be quite annoyed if it did not work properly on my camera. The field curvature I experienced with this too-thin adapter rendered the lens essentially unusable at any aperture for landscape work.
DIGLLOYD: in the case of lens adapters, it is better to have a little slop that tends to reach infinity focus before (marked) infinity focus on the lens. This is because lenses have variation; if the adapter fixed a position that is nominallly correct and/or it was out of spec just a little then a lens could not reach infinity. So it is a good idea for a lens adapter to allow a bit of slop unless the build tolerances are extremely tight.
There is variation between camera bodie on flange focal distance even of the same model: I owned two Canon 5D bodies some years back. One of them would focus at infinity right at the hard limit, the other would reach infinity focus just before that. Same lens—two of the same brand/model camera bodies.
As for field curvature being exacerbated by flange focal distance, I know of no technical reason that could change field curvature behavior unless an adapter has glass in it, and I would never buy that type of adapter, excepting the Metabones SpeedBooster. If the lens is at infinity focus and the distance to the sensor is correct, the lens care not what the flange focal offset is. That’s why I can still work with my Zeiss lenses on the D850 (barely)—because they have some mechanical focusing range beyond the infinity mark.