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My Nikon D3100 out of the blue cannot focus correctly.

It seem the that the focus motor always stops at the end of the run (Infinity) and cannot lock on the target, thus cannot release the shutter. I tried with two other AF-S lens but still the same.

This only happen when I use the viewfinder. The AF motor works fine and can focus on the target if I use the live view (LCD).

I tried the single point auto-focus, Reset to Factory Setting, and I tried cleaning the contacts but still cannot get the AF to focus on the target through the viewfinder.

What could be wrong and what can I do about it?

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  • \$\begingroup\$ Possible duplicate: photo.stackexchange.com/questions/16889/… \$\endgroup\$
    – Bharat B
    Mar 28, 2012 at 3:46
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    \$\begingroup\$ It may be a duplicate but it may be something else. A bit hard to tell. One thing that's worth noting is that live view and "normal" viewfinder mode use entirely different autofocus systems — live view uses contrast detection based on the data from the main sensor, as opposed to using the dedicated phase-detect sensors. So the symptoms here seem to indicate that's there's an issue with phase detect AF. \$\endgroup\$
    – mattdm
    Mar 28, 2012 at 12:36
  • \$\begingroup\$ Anything I can do to fix this problem or should I send it for repair? tks \$\endgroup\$
    – Qaz
    Mar 28, 2012 at 13:22
  • \$\begingroup\$ I have same issue , does Nikon charged for Sensor replacement ? , My camera is out of warranty? \$\endgroup\$
    – user10326
    Jun 24, 2012 at 17:42
  • \$\begingroup\$ Check on the lens. You will see an A/M switch - make sure it is on A for autofocus rather than M for Manual. \$\endgroup\$
    – user19990
    May 18, 2013 at 9:14

6 Answers 6

Reset to default
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If it won't focus in OVF mode with several lens, especially after checking all focus options and switches, switching in/out of manual focus, re-seating the lens, cleaning the contacts AND verifying that the live-view CDAF works in the very same situations, I would contact the vendor and/or Nikon and possibly send in for repairs.

Best of luck.

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    \$\begingroup\$ According to question, it's the phase-detect focusing that does not work; live view is fine. \$\endgroup\$
    – Imre
    Apr 3, 2012 at 22:15
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    \$\begingroup\$ Esssh, you are correct, not sure where the confusion came from... Anyway, reverse my comments, but the recommendation still stands. In fact, it goes double. If CDAF works, then there's likely something wrong with the multi-cam 1000 module (I believe that's the AF used in the 3100). \$\endgroup\$
    – Instantkamera
    Apr 3, 2012 at 22:45
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    \$\begingroup\$ I contacted NIKON Tech, and they asked me to bring the camera and have the tech look at it, most probable cause is the sensor, and need to be serviced. Can only do it next week. thanks for the advice \$\endgroup\$
    – Qaz
    Apr 5, 2012 at 1:23
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    \$\begingroup\$ updates: I sent my Nikon to be serviced, and the replaced the AF sensor. glad to have my 3100 back :) \$\endgroup\$
    – Qaz
    Apr 13, 2012 at 3:22
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In case it matters, a few sources I've seen say to check the AF sensor under the mirror for dust obscuring the AF sensor from getting a focus lock and keeping the camera from actuating the shutter.

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I have Nikon D5200 and had similar issue where it would auto-focus in 'live view mode' when shutter release button was pressed half-way but not in 'view finder mode'. Later found that I had assigned function key (Fn) to AF-C and it would only auto-focus by pressing function key (Fn) in 'viewfinder mode'.

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  • \$\begingroup\$ The OP sait that he tried "Reset to Factory Setting", so it's probably no a key assignment problem. \$\endgroup\$
    – Olivier
    Feb 8, 2016 at 10:45
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I have a Nikon D5300 and for some time have been really frustrated that my camera would only auto-focus in 'live view' mode. As the above answer said, I went int my menu and found that auto-focus was set to AF-C. I opened the menu, went to auto-focus and found it was set to 'focus' rather than 'release' and changing this sorted out my problem. I realise that this will be different from settings in different models but it solved a problem that had been driving me crazy for months!

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I just looked at this thread because I have a problem with my D3100. As I was going through the menus looking for the factory reset I saw that for some reason the Rangefinder was set to off. I set it to on and it seems to be fine now. How the heck that happened I don't know!

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I read this thread when I had the same problem (with live view). Turned the Rangefinder off, then back on and now it works.

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