Nikon 24-70 f2.8 (non VR) - AF fine-tune not stable.

Discussion in 'Nikon' started by kevin_beretta, Sep 16, 2021.

  1. I played with the Df and the 24-70 f2.8 today and noticed it was not taking sharp pics like it used to. Onto the tripod it went, AF fine tune adjustment with all the right tools showed I needed +20 as it was massively front-focusing. Surprised to say the least. But I set it at +20 and took a bunch of test shots, real hand-held shots of cats and books, tripod shots and what not. A few faces. All seemed sharp as a tack. Fast forward a few hours. Now, the camera is back focusing like crazy. Why would it suddenly vary so much? Have not tried it on a second body yet.

    Any ideas welcome...
     
  2. It sounds like there is something broken in the camera's AF system. Take it to service.
     
  3. There is a time variable change in the physical distance of the optical path, so something is moving somewhere that shouldn't be....:eek:

    Whether it's in the lens or body, I guess you could check by substitution.

    I'm guessing LV shooting is perfect?
     
  4. Like Nikon's wobbly secondary-mirror AF system?
     
  5. It could be a problem in the mirror assembly, yes. Or the mounting of the AF sensor itself. The Df uses the same AF system as the D7000, or some variant of it, and there was a recall (in some countries quiet, in others the users were informed of this) on the D7000 where Nikon would replace components of the AF system for free as they determined there was a flaw.

    More recent cameras such as the D810, D850 etc. seem much more accurate and reproducible in AF (it helps to have a recent lens as well). I never owned the Df though. I don't know whether this issue is an isolated case. But I think Nikon will be able to resolve it in service.
     
    Last edited: Sep 16, 2021
  6. Lighting variation?
     
  7. Fine tuning is intended to manage consistent focusing errors. If one or more of the internal cams is worn, you won't get consistent results with or without tuning. With Nikon, focusing is based on feed-forward control, which in turn relies on a chip which can be reprogrammed.

    You've done what you can on your own. Take it to an authorized Nikon service agency for an estimate. In the last 20 years, I've had three Nikon zooms repaired by replacing the cams and reprogramming - about $500. That's still a lot cheaper than a new lens.
     
  8. But it should be OK on LV focussing right?
     
  9. Ok so I did a bunch more work on this today. I tried the 24-70 on the D850, forced it to back and front focus etc. to make sure it was not the lens that was at fault. That all seemed to work. I reviewed my historical shots with the D850 and the 24-70 and they all seemed tack sharp. Also reviewed the pics with the Df and the 24-70 from a few months ago and those too seemed all spot on. However, I ended up setting the lens to +12 on the D850. Maybe I never saw the lack of sharpness due to earlier pics being not at f2.8 but smaller. At +12, the focus with the D850 is great, as is sharpness etc. Still a bit puzzled to have to set it there because I did a big lens tune and test back in January over a 2 days period with all 10 lenses and both cameras.

    The Df ended up with +13 in the end for the 24-70 and that seemed to be fine. I did notice that at 24 and 50 it slightly front focused a bit still at +10 but that was gone at +13. For now, I am going to try that on for size.

    I also plopped the 85 1.4G on the Df and tinkered with it, forced front and back focus and ended up with +3 for the Df and 0 for the D850. I may never have tuned that lens on the Df as I use it on the D850 only.

    Also tested with a 50 1.8G that came with the Df and both on the D850 and Df it was fine. I had earlier set the 50 1.8G at +3 on the Df and did not change it now.

    I guess shooting with manual primes mostly on the Df lately I have not used AF at all really. My plan is to take the Df and 24-70 to Nepal for 2 months (leaving on the 30th) so I really only ran into this issue the other day when I was checking things out. I hope I don't see another aberration in focus in the next few days.

    Lots of test shots I think in nature in the next few days .... The equipment for the trip (since I have to carry it all..) will be the Df 24-70, 50 1.8 G and a Canon G5X-Mark II
     
  10. I got a (really) bad sample of D7200 first time round. The kit 18-140 lens needed the full amount of AF 'fine tune' and even then wasn't consistent from wide-to-tele. About 2 weeks into ownership the shutter developed a fault and, eventually, the D7200 body was replaced. Not only did that fix the shutter error, but the same lens then focused perfectly from end to end.

    So IME and opinion, the body is more likely to be at fault than the lens. Get the position and tightness of the AF module in the Df checked, and adjusted if necessary. AF fine-tune is just a fudge to overcome lack of accuracy in the AF module position IMO.
    Reprogramming?
    But AF fine-tune data are stored in the camera body for each lens surely. Otherwise how would you be able to swap lenses between bodies, and have the appropriate focus fudge applied?
     
    Last edited: Sep 17, 2021
  11. Although I mostly use a Z these days, I recently decided that I should have a higher resolution DSLR than my D3s available if needed. Did not want to spend much $, so I found a very cheap deal on a high mileage D800. The D800 I had a while back when they were current needed some fine tune for about every lens I tried. Same lenses on the D810 that replaced the D800 did not need much if any tuning.

    The new to me but well worn D800 surprisingly seems accurate without tuning with the lenses I have tried, including a 105@1.4, up close. So there does seem to be body to body AF accuracy differences within the same model. The D800 I had previously was bought new and was later than the early series with the AF issue. I certainly don't miss doing the AF fine tune routine.
     
  12. Yes. More or less the same experience here.
    I bought a D800 after I thought the 'bad AF' dust had settled, but the first sample I was given proved to have dodgy AF. Took it back to the store a day later and was given an exchange that proved more satisfactory. However I noticed the box of the exchange body had a 'CIPA award' sticker that wasn't present on the previous box.

    Was I attempted to be fobbed off with old stock or a previous return? Who knows? It's all water under an ancient bridge now.
     

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