Nikon D300 Mechanical Body Misalignment (Result Front Focus)

Discussion in 'Nikon' started by andre_noble|5, Mar 9, 2013.

  1. Hello, I put a thread many months back about a problem I was having with focus error after I had a Nikon 300 2.8 afs serviced.

    However the issue appears to be due to the Nikon D300 body's discrepancy between the lens flange-sensor distance and the lens flange-
    focusing screen distance.: for example, carefully manually focusing my new Nokton 58 SLII @ f1.4 on my Nikon D300 reveals a serious
    front focus issue in the resulting images. This repeats itself over a variety of focusing distances.

    Its a mechanical issue since AF is not involved. Furthermore, the green focus assist dot is agreeing with my eyes, so its not a human focus
    error.

    Has anyone else had similar lens flange to sensor distance misalignment? Was Nikon able to fix it to your satisfaction? At what charge?

    Thanks in advance.
     
  2. You have three things that need to be in alignment.
    1. Sensor to f-mount distance - is adjusted with shims on the mount or by tightening/loosening the screws that hold the front and back parts of the camera together. This distance can be measured but the camera needs to be partly disassembled. Should be 46.00 mm.
    2. Focusing screen alignment - is adjusted by shims and mirror adjustment. Verified optically.
    3. AF sensor alignment - is adjusted with special software, similar to AF fine tune.
    Since your manual focus and AF agree we can only be certain that number 2 and number 3 are set the same. You can't know if number 1 is correct or not.
    Nikons course of action will likely be to adjust your focusing screen and then readjust your AF.
    I've had it done on several cameras but can't really remember the cost, maybe $80 or so.
     
  3. I currently have this with my D2X, but as I hardly use that body anymore won't call it a problem.
    Basically the lens mount is no longer parallel with the sensor (one time when shooting surf I had put the body and a lens with TC on the ground, and someone stepped on it, the stupid girl). The (very cheap) TC was bent and consequently broken and lens mount slightly misaligned. But I never noticed it though as I always shot with AF, and that compensated for the misalignment and potential wrong focus.
    Only discovered it a few years ago when I decided to have all my bodies (2x D3, D2x and D1H) have a standard clean and service run. As it had not influenced the several tens of thousands of surf shots I had taken, and I used the D3's for main bodies I decided to spend my money on something else and left it unrepaired as it does not hinder me.
    Theoretically it will show up as front focus when shooting close up with limited DoF, ea when shooting portraits with a 1.4/85mm. Tried that for fun, as said I now mainly use my D3 and also D800, so no need to have it fixed for the limited use I'm giving the D2X.
     
  4. Solved (for now)
    The fix is called "Mirror stop adjustment". There is a 1.5 mm hex screw close to the manual focus mirror. Its a trial and error adjsutment that took me 2+ hours as a newbie to it to get it right. That was just for the main mirror. I have not yet adjusted the rear auto focus mirror.
    info here http://leongoodman.tripod.com/d70focuspart3.html
    There is some guy on another blog that advocates opening camera bottom plate and fiddling with the set screws that control the sensor plane. However I think the first "go to" fix is not this, but rather adjusting the mirror.
     
  5. I just needed to adjust my D300. It was out by a lot. 40 cm at 3m on a 50mm f:1.4D lens.
    There was not enough room to insert the Allen key again after I maxed it out.
    What I did was use two Allen keys. I twisted the end of one so that it now has a ridge where the the other has a flat. This way one of the two keys will always fit, no matter what the position of the set screw is.
     

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