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I have a Nikon 35mm f/1.8G AF-S DX I bought for my Nikon D5100, it's only a couple months old, never been dropped or anything, and it all of a sudden won't auto focus. Anyone know if this is a simple fix or if I should take it in to be repaired?

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    \$\begingroup\$ This may be a stupid question, but do you have the autofocus switch turned off on the lens? \$\endgroup\$
    – ElendilTheTall
    Feb 26, 2012 at 18:49
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    \$\begingroup\$ LOL....No, It's turned on. I even tried turning off auto then turning it back on. Nothing:/ \$\endgroup\$
    – Jayme
    Feb 26, 2012 at 19:07

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First, check the AF/M switch on the D5100 camera body. This is at the left-hand side of the camera (from the photographer's point of view) near the bottom, below the lens release button. Make sure it's set to "AF". Similarly check the "M/A - M" focus mode switch on the lens. Make sure it's set to set to "M/A".

Beyond that, see if you can narrow the problem down to just the lens, just the body, or just this particular combination, by trying a different AF lens with the same body, and a different AF body with the same lens.

If you've taken care of those checks and eliminated those problems, and you're sure the lens is correctly seated on the camera body, then the most frequent remaining cause is poor electrical connections between the camera body and the lens.

If you suspect this problem, you can try wiping those connections gently with a lens cloth or a tissue without any coatings. But when doing this it's vitally important not to get foreign matter into the camera body. So using an eraser or something like that to clean the connections is quite dangerous (if you have bits of rubber somewhere inside the mirror cavity, that's not going to be good for image quality).

This last bit won't apply to your D5100 camera, but if you were using a different body that will autofocus with AF and AF-D lenses also, you could do an additional diagnostic step: see if one of those lenses (i.e. autofocus, but not AF-S) will autofocus on your camera body. When that happens it can be a hint that there is a problem with either the electrical connections in the lens mount. Or, for those camera bodies that have them, a problem with the aperture coupling ring.

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  • \$\begingroup\$ I have the D5100, not the D90:) All my other lenses work fine, it's just this lens. I went ahead and took it in to the store today and exchanged it for a new one. Hopefully It was just a defective lens and I won't have this problem again. Thanks! \$\endgroup\$
    – Jayme
    Feb 27, 2012 at 2:06
  • \$\begingroup\$ Sorry I didn't read your question carefully enough. I have updated the answer to be more consistent with the question in order to better help anybody coming across the question later. Meanwhile, I'm glad that you have managed to resolve your problem. Happy shooting! \$\endgroup\$
    – James Youngman
    Feb 27, 2012 at 14:49
  • \$\begingroup\$ That's ok. Thank you for the advice. I'll keep it in mind in case this happens again in the future! \$\endgroup\$
    – Jayme
    Feb 28, 2012 at 21:12
  • \$\begingroup\$ I can't believe I didn't look at the switch... feel like an idiot, but a thankful one. \$\endgroup\$
    – user25329
    Jan 12, 2014 at 5:29
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Try taking off the lens and cleaning the metal contacts. Take a piece of cloth dip it into rubbing alcohol and gently wipe the contacts.

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  • \$\begingroup\$ Thank you! I went ahead and exchanged it for a new one today:) It will be in, in a week, hopefully I don't have this problem again! \$\endgroup\$
    – Jayme
    Feb 27, 2012 at 2:07
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I found out something by chance about AF issues I have been having with my Nikon: When you put the lens cover on - if you push it on too hard and the lens turns in a little, it will go into a lock position.

To fix: hold on to the very end of your lens and the camera base. Give the lens a little twist - you will feel it unlock. DO NOT twist it hard. It will release.

After I release my lenses, auto focus seems to work as it should.

I hope this works for others. It could be just an isolated incident with my own lenses, but that little twist has unlocked all my lenses.

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Check your camera settings if autofocus is set for the AE-L/AF-L Button. You can check this in the "Setup Menu" -> "Buttons" -> "Assign AE-l/AF-L button"

Set the settings back to AE/AF lock so that autofocus is set to the shutter button only.

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