Auto Focus 75-300 issue

Discussion in 'Nikon' started by orourke, Sep 3, 2011.

  1. Got a quick question. I have a Nikon push/pull 75-300 4.5 AF. Lately I've noticed it is not autofocusing from about 75-150ish. From there out to 300 it works like a champ. I hang it on an F4 and the green focus dot works throughout the range. I popped on a 28 to 85AF and that lens snaps in focus throughout it's range with no problem. In focus indicator also works on all my manual lenses.
    As a qualifier, I have tried in different lighting conditions, bold contrast and varying distances to subject. I have also tried in single or continuous focus mode. Seems to be an issue with the lens rather than the camera.
    Oh, and I've also chastised it with a wide range of adjectives to no avail.
    Any ideas?
    Thanks in advance...................
     
  2. Check the focus limit switch - depending on where the focus ring is when it is set to "Limit", it will cut the focus ring's range in half.
    I'm not sure if this has an effect on the fact that you say AF is not working from 75-150mm, but it's the first thing I came up with when checking my own AF 75-300mm lens.
     
  3. Thanks Eric. Yeah, I forgot to mention that. The limit switch, and fresh batteries, were the first two things I checked. I switched it back and forth a few times thinking that if there was oxidation on the contacts of the switch (if there even is such a thing) it might help. But I don't think the limit switch is set up to function as a cut off mid zoom. I also checked/cleaned the pin contacts on the lens and they appear, at least aestetically, to be ok. Not sure about the internal ends though.
     
  4. Do you mean that it doesn't even attempt to focus, i.e., the focus motor doesn't turn at all, or that it tries and fails? Also does the shutter/speed aperture display correctly in the range where it won't focus?
     
  5. Professopr K,
    It doesn't even try. Depressing the shutter release doesn't initiate any response in auto focus until you slide the zoom out to about 150. All other functions read normally. Aperture obviously is an anolog window in the viewfinder but the shutter speed and focus indicator light work throughout the full 75-300 range.
    At first I thought I may not be depressing the shutter release far enough. As a result I now have a few impressionist images I didn't know I was capable of.
     
  6. Your 75 to 300 zoom has an internal slider that moves along a circuit as you zoom. If the contacts are out of alignment, the camera may not 'know' that the lens is attached over some part of the zoom range. Happened to my copy of the 75-300, except it worked only at the short end of the zoom. Suggest you try the lens on a body that requires you to control the aperture from the body, i.e., try it on a Nikon which requires the lens to be set to minimum aperture. If the problem is internal, you'll get the 'FEE' display over part of the zoom range.
     
  7. Interesting. I just set the F4 in shutter priority. It will set the aperture, at least what appears to be correctly, again, from about 150-300. Nothing below 300. There is no FEE displayed in the viewfinder. Instead, it just displays "A" below 150. Above that focal length it will show changing aperture when passing through a light source. There is an "FEE" display, however that is only on if the lens isn't stopped down all the way. So, I can shoot the lens in aperture priority throughout the range by manually focusing under 150mm. Shutter speed changes throughout the 75-300 so that isn't an issue. However, I cannot shoot shutter priority under 150mm and expect the right aperture.
    Is this internal slider you mentioned a still serviceable part through Nikon or are there any tricks to realign it?
     
  8. If it is just a matter of alignment, any competent repair shop ought to be able to fix it - the stationary part of the circuit, which may have come loose, is just cemented to an internal barrel. If anything has to be replaced, Nikon may no longer have parts. And if Nikon no longer has parts, they may no longer accept it for repair.
     
  9. Thanks Professor, I appreciate the response. I suppose I'll send it in....somewhere.
    And thank you again to Eric.
    Regards,
    Bill
     
  10. Thanks for the link Robert.
     
  11. sorry, double post.
     

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