UKC

I’m having problems with back focus on my Nikon D810, this only manifests itself on prime lenses.

its rather frustrating as I want to start using a couple of primes more, 85mm and was thinking of trading in some old gear for a second hand 20mm

Does anyone have any experience of this and what did they do?

i know you can calibrate the camera which I did with the 50 mm but it didn’t seem a 100% across the focus range

Hi Jethro. 

Do you think it’s a hardware issue?

Could it be a communication error on the mounting ring(s) maybe? 

Or else - and I know you know what you’re doing - are you sure you’re not just getting used to the fast primes still and have muzzed up a couple of shots, or is it really across the board?

Across the board, the D810 is very unforgiving so I did a couple of tripod tests, I’m perplexed as to why the zooms aren’t affected but the primes are.

Ah weird. I shoot on Canon’s so don’t know the ins and outs of that body, but - and again, probably too obvious but - you don’t have some servo function turned on in the autofocus which is overriding your intended focus do you? 

Jethro, are you the only owner of the camera? I had issues with two lenses on a D810 and it was because a previous owner had applied custom settings when they owned it. When I put my lenses on the camera, it picked up their settings as, coincidentally, we used the same model of lenses (24mm prime and 85mm prime).

Easily solved - stick with the zooms !

Fixed that for both of you

Ah good suggestion, I’ll check 

1) Did you try AF fine tune with each and every one of your lenses (not just the 50mm)? It's lens specific, after all. I think the newer Nikons can even automate the process (although the 810 probably not). Get a good lighting, large enough AF target perpendicular to the camera and a ruler at 45degrees next to it (or one of those pre-made AF calibration targets). Distance matters as well.

2) The AF (not in live view) always focuses wide open - thus if your primes are faster than the zooms, any misalignment will be more pronounced with them (even if you shoot them stopped down)

3) What CH wrote, check the AF fine tune settings with every lens, there might have been settings set by a previous owner for their lenses messing you up.

4) Remember, you have two variables that need to match - the lens and the camera (used to be just the camera, but nowadays the lenses are so full of electronics, distance sensors etc that it matters). If your camera is say -5 from correct (meaningless units, just as an example), your zooms +5 and your primes -1, the zooms will seem to be ok even when they are actually much more out of alignment than the primes... Especially if the primes are faster, even one stop can make a big difference.

You could finally let Nikon check at least the body with their reference lens or an optical bench or whatever they use (at best with all your lenses), but that could be pretty long and costly wait unless you are a member of NPS.

What FrankR said.  Read this:-  https://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths/

Thanks guys