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I have a Nikon D5100 and a used Nikkor 300mm AF-S f/2.8D IF-ED II, where the two usually work great together. However, if I use autofocus a few times in a row (usually when the change in focus distance is small), I hear this funky motor noise that sounds like a motor is winding up, and my autofocus stops working until I switch to Manual and back to Autofocus mode (A or M/A). Here's a sound clip of me focusing a few times, the motor noise, me switching from Manual focus and back, and successfully focusing again:

https://dl.dropboxusercontent.com/u/4979266/focus_noise.mp3

Any idea why this could be happening? I'm hoping my autofocus isn't going out.

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    I'm guessing (hoping) the sound is very loud because of the proximity of the mic, right? That is, the AF isn't actually that loud, right? If it is, I'd say almost definitely the AF is dying! – Dan Wolfgang Jan 15 '14 at 12:24
  • I amplified the volume a bit so that it was easier to hear, though I'd say the actual volume was around whisper to soft voice volume. – Ampp3 Jan 15 '14 at 16:19
  • Does this happen no matter where the subject is? Also, what mode of auto-focus are you using on your D5100? – Muhammad Usman Nov 18 '14 at 19:40
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Try giving the focus ring a little nudge when the autofocus gets stuck. I have a Tamron 18-270 which has the same issue when zoomed at 150mm or more. It seems that due to the small change in focus required, the camera does not power the motor enough to get it moving, resulting in the noises.

I don't know if you have this exact issue, it could be that the motor is slipping/struggling for some reason.

  • Thanks! My final deduction was indeed that the motor wasn't getting enough power, and the issue was solved when I switched to a full frame body that had a built in motor. Thanks again! – Ampp3 Apr 6 '15 at 17:46

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