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On occasion, the auto-focus system in my camera and/or lens just stops working. I'll be holding down the shutter release halfway and tracking a subject and I can feel/hear the auto-focus system making adjustments, and then it just stops. If I release the button and try to re-activate, nothing happens. Essentially, auto-focus is dead until I turn the camera off, and then turn it back on again.

I am using a Nikon D90 with a Sigma 70-200mm F2.8. Is the problem likely to be in the camera or the lens? I also have a Nikon 18-105mm lens, but don't use it enough that I can recall experiencing the same problem. I have taken over 10,000 shots with the D90/Sigma combo, and have had this problem occur 10-15 times.

There might be a correlation with how long I've been shooting. Often I will be at an event where I might shoot 500-800 shots in a day of shooting (say 6-8 hours), and it seems like maybe this happens more often later in the day than earlier.

Both the camera and lens are still under warranty, but I'm not sure whether it is the camera or the lens, and don't want Nikon and Sigma pointing fingers at each other, and don't know who to contact first.

Has anybody experienced a similar problem? or have any suggestions on a course of action?

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3 Answers 3

up vote 2 down vote accepted

Everything I've read in the past and a quick Google indicates it's been known to happen with some specific Sigma lenses, yours in particular. But it's nothing more than anecdotal.

If it only happens with that lens and internet anecdotes suggest it's the lens, send the lens in under warranty while you still can.

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autofocus froze on my D7000 whilst using a defocus lens, it was still locked when changed to another fixed lens but worked when I put on the 18-200 zoom. After a lot of trial and error I got the defocus lens to autofocus again by playing with the AEL/AFL button. Hope this works for you

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IIRC the D90 AF motor is in the body, but the motor is only one possible cause. If it works immediately after turning the camera off and on again, it could be a problem with the connection between the lens and the body.

Ideally you need to try it with your other lens to narrow it down; if it doesn't happen at all with the 18-105, it's the lens. If it does happen, it's the body. Perhaps, rather than turning the camera off, try just disconnecting the lens (i.e. twist it without taking it right off) and reconnecting, to reestablish the CPU connection.

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While the D90 has an in body focus motor - I highly doubt its actually used for this lens, so thats not really pertinent. –  rfusca Mar 12 '11 at 17:28
    
Hence my statement that it was only one possible cause... –  ElendilTheTall Mar 12 '11 at 22:04

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