Why does my Nikon D3100 autofocus work in Live View but not through the viewfinder?

Asked 3/27/2012

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2 answers

My Nikon D3100 suddenly stopped autofocusing correctly when I shoot through the optical viewfinder. The focus motor runs to the end of travel (toward infinity) and never locks, so the shutter will not release. I tested multiple AF-S lenses and see the same behavior.

Autofocus works normally in Live View on the LCD, so the lenses and focus motor seem OK. I already tried single-point AF, resetting the camera, re-seating/cleaning lens contacts, and checking focus settings.

What could cause autofocus to fail only through the viewfinder, and is there anything else I should try before sending it for repair?

nikon autofocus d3100 repair viewfinder

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

14y ago

2 Answers

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.

Originally by user9279. Source · Licensed CC BY-SA 4.0

user9279

14y ago

AI Answer

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If autofocus works in Live View but not through the optical viewfinder with multiple AF-S lenses, the problem is likely in the camera’s phase-detect AF system, not the lenses.

Likely causes:

Dust or debris blocking the AF sensor under the mirror
A setting/button assignment affecting viewfinder AF behavior
A hardware fault in the viewfinder AF module or related mechanism

Things to try:

Check that neither the lens nor camera is set to manual focus.
Re-seat the lens and confirm contacts are clean.
Review button assignments, especially the Fn button, in case autofocus was reassigned or limited in viewfinder shooting.
Inspect for dust/debris around the mirror/AF sensor area.

Since Live View autofocus works, that strongly suggests the camera can still focus, but the separate AF system used for viewfinder shooting is not functioning correctly. If settings and cleaning do not fix it, the most likely next step is to contact Nikon or a repair center.

Why does my Nikon D3100 autofocus work in Live View but not through the viewfinder?

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