D7100 Focusing Issue

Hi all,

Having a slight issue with my Nikon D7100. I have it set up for back button focusing, single AF point, continuous focus mode (AFC). When I use the centre AF point, the camera is now starting to struggle to lock on to the subject - the lens seems to briefly lock on, then just starts to hunt backwards and forwards randomly.

After a bit of testing tonight (tried different lenses, AFS mode, 9 AF points, cleaned the lens contact points, etc.), it appears that using any other AF point apart form the centre one, the camera focus works fine. But then resetting back to the centre point, it just wont 'lock' and hunts.

Any ideas?? Can an AF Point go 'bad' or is it likely to be some dust on the sensor or something (I had the camera professionally cleaned a few weeks ago, and it certainly never had an issue before that - maybe that is something to do with it ??).

Thanks, Richard.

Are you hand holding or fixed to a tripod? (it'll only take the slightest movement to lose focus)

Once locked on to focus, if you release BB does it stay focussed?

Thanks for the reply. I can replicate the issue, no problem. Hand holding the camera, centre AF point selected, press BBF button and it hunts all over the place. As soon as I change the AF point to a point adjacent (or indeed any other point except the centre), the focus locks on just fine. So it is nothing to do with hand hold/tripod, or the subject matter (e.g. lack of subject contrast), it just seems like the centre point doesn't work properly whereas the other point work?? (The focus does not change when releasing the BB - it either stays focused when using the surrounding AF points, or not focused when using the centre).

Some more tests :-

Tried *not* using BBF - just with the standard shutter release button...no different (centre AF point will not lock focus)

Tried complete manual focus - with the centre AF point selected, the little circle in the bottom left of the viewfinder will not appear - just get the arrow either side. With any other AF point selected, the circle will appear (indicating a good lock).

So......it is definitely something wrong with the centre AF point

No1 in this link would be my first call (could be a chance when camera was cleaned some dust got onto the focusing sensor in the mirror box)

http://www.bythom.com/autofocus.htm

Maybe try a factory re-set by pressing both green buttons whilst turning camera on:

View: https://www.youtube.com/watch?v=NtK3uAe4_iQ&vl=en

Does it focus using live view on the centre focusing point as this uses contrast detect rather than phase detect of the viewfinder?

Fras.

Update - I believe I have fixed it

I think there must have been some dust or something on the AF sensor panel. I locked the main mirror up then, with my little air blaster thingy, blew across the AF sensor (which, after a bit of Google-ing is found is at the bottom of the main 'chamber'). The centre AF point (along with all the ohers) is now is working fine

Thanks for your help everyone (and to answer Fras' questions - Liveview worked fine and I did try the 'Factory Reset' last weekend when we were out and about, but it didn't make any difference - I am pretty sure it is not a full reset anyway as my User defined presets (U1, U2, etc.) were still 'set'. Thanks again.

Great News!