Nikkor 500mm P backfocus?

Discussion in 'Nikon' started by dilom_ski, Jan 26, 2015.

  1. Hello,
    I bought an used Nikkor 500mm f4 P 2 months ago.I must say its a fantastic lens and when I nail the focus is sharp, very sharp on my D7000.Anyway, the one thing thats bothering me is the backfocus issue.It seems like on greater distances - above 30m and more to see the bird sharp in the viewfinder, but on the photo the birds is out of focus and the focus area is just behind the bird.Happened many, many times.I am talking wading, relaxed birds, not fast birds in flight.So I made a diy microadjustment focus tool and tested the lens from the minimal distance of 5m.It seems that its slighty backfocused a bit, but I aint 100% sure about it.Anyway I dialed -8 on the AF fine tune to get the dot (manual focus assist) correct and I will test it in field.
    But anyway, have you expirienced something like this, or is it just me?If it is really an issue, can it be adjusted from Nikons side, or it will be pretty expensive?
    I already have many keepers with this lens, its just that the procent of the good ones is very low.I am using a monopod.
     
  2. AF Fine tune is really for calibrating your camera's viewfinder focus to your lens, and unless you can't dial in enough units of correction on the camera to focus accurately, the lens doesn't need to be adjusted. You can also check AF fine tune versus the Live View focusing to confirm that -8 AF FT units works for your lens at typical subjects' distances, though of course you're the focus motor and judge of focus, but the Live View will bypass small errors introduced by the prism viewfinder and focus on the actual sensor. Live View is not affected by AF Fine Tune.

    Be aware that AF fine tuning optimized at a close focus target may not work well for long telephotos at large distances. You may want to find a static target in the wild to use as an AF Fine tune target. Pick something that will be close to your anticipated targets for the subjects you're interested in.
     
  3. ShunCheung

    ShunCheung Administrator

    I bought an used Nikkor 500mm f4 P​
    Are we talking about the manual focus, 500mm/f4 AI-P lens, introduced around 1988 or so? I.e. first one on this list: http://www.photosynthesis.co.nz/nikon/lenses.html#500
    If it is possible, it is best to manual focus through live view.
     
  4. Yes Shun, its exactly the manual focus AI-P lens.I really saw the difference between liveview focusing and through the viewfinder - liveview is sharper.Too bad, that is not appropriate for every situation, but at least for perched or static birds is great - the best situation actually is the bitterns alarm stance - the bird doesn move at all :)
     
  5. In your case the AF fine tune may be of help. Allthough the view finder image may seem to be a bit unsharp, the calibrated AF-indicator may help getting the right focusing distance. As Steven said, tune the AF correction to suit your normal shooting distances. When you know the behaviour of your system, you can adapt.
    Good shooting.
     
  6. The focusing screen alignment/position can be adjusted to make it match the live view image. Of course it is still not as good as zoomed in live view can be, but this kind of systematic error is likely a result of a slightly incorrect position of the screen. Does the same problem affect your other lenses when focused manually using the matte screen?
     
  7. Ilkka, I havent tested it with other lenses.I have also a 300mm AF f4 (non AFS) and I havent got that many difficulties with manual focusing it as with the 500mm.
     
  8. But anyway, have you experienced something like this, or is it just me?If it is really an issue, can it be adjusted from Nikons side, or it will be pretty expensive?​
    Yes they can, it is probably not very expensive, as the operation is a simple one. But to get that right, you'd be better to send in the lens and the body.
    The operation is described in here: http://leongoodman.tripod.com/d70focuspart3.html and the tools are inexpensive.
    I have an old F100 that had back focus with all lenses. The camera had visual focus and AF in sync so they were focusing the same way - both back focusing. - If I had known earlier how easy the fix was.
    A week ago I did a minor tuning for my F100. First on the view finder focusing (outer hex). When that seemed to be fine, I tuned the AF helper mirror (inner hex) to get the af in proper tune.
    Note: if you change the resting position of the main mirror, you are changing the af-helper mirror position too, as the af-helper mirror is hanging on the main mirror. In the end you might need do the AF-fine tune for the rest of your lenses, even if you tune only the visual focusing.
    For a DSLR the tuning should be very straightforward as there is the LiveView for checking the current result.
    A good tripod, a good focus chart (e.g. siemens star), proper lighting will help. Also it might be of help to fix the focus ring with a tape if needed.
     
  9. I use to own a Nikkor 500/4 P and while it's a fantastic lens, my understanding is that the AF fine tuning feature only works of AF lenses (possibly only AF-S). The P lens series whether a 500/4 P or 45/2.8 P (one I still own) are basically MF lenses "chipped" for all possible AE options. The fix in your case is to have the body checked/adjusted to make certain the AF sensor plane, digital sensor plane and focus screen plane all match to factory spec.
     

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