Trouble with autofocus.

nickzou

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I'm not sure what the problem is. I don't know if it is my lens, I'm using the wrong mode or what. So I was playing some Settlers of Catan with my friends and we were sitting around and as per my usual habit, I'll snap a few pics here and there. Granted it is kinda dark in my basement but it's not even close to how dark some restaurants are and I'm told that the D7000 has great autofocus. I was using my 50 1.4 D. Does that lens have autofocus issues? How autofocus mode should I be using? I feel like I'm missing a key component to understanding how I should be using autofocus.
 
I'm not sure what the problem is. I don't know if it is my lens, I'm using the wrong mode or what. So I was playing some Settlers of Catan with my friends and we were sitting around and as per my usual habit, I'll snap a few pics here and there. Granted it is kinda dark in my basement but it's not even close to how dark some restaurants are and I'm told that the D7000 has great autofocus. I was using my 50 1.4 D. Does that lens have autofocus issues? How autofocus mode should I be using? I feel like I'm missing a key component to understanding how I should be using autofocus.

post an example with settings please! :)
 
Well the shots I kept are the good ones. And when the autofocus works, it works fine. But it only seems to lock on 1 in 4 tries in the "auto" setting for AF-C. If I just use the focus points it's a lot better, but sometimes I don't want to be pressing on the D-pad at the back to set the focus point . Especially if I'm in just taking a quick shot in between turns of a game.
 
Yep! Does that matter when I set AF-C to "auto"? Usually when I use the focus points, I set it to AF11 not AF39.
 
I just changed mine to AF-C, focus points to Auto, and it appears that under this setting the camera will pick the focus points automatically. The 9 cross-type focus points on your D7000 are in the middle, so if the computer picks an area that's outside of these focus points it will take a bit longer to focus. You can test it out for your self and see how quick cross type focuses compare to contrast detection. I typically do focus and recompose, and give it enough DOF and watch your distance.
 
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Autofocus is not the be-all / do-all tool that we would like it to be. There are instances where it just will not lock onto something with enough contrast for it to work. There is a section of the owner's manual that covers instances where autofocus may not work.
 
SCraig said:
Autofocus is not the be-all / do-all tool that we would like it to be. There are instances where it just will not lock onto something with enough contrast for it to work. There is a section of the owner's manual that covers instances where autofocus may not work.

I understand the basics of autofocus limitations. I know without the assist light it is pretty bad in the dark and if I'm just focusing at a white wall it will try and try all day and not get it but these are people, faces(!). Though while not sufficiently lit the room was by no means dark.
 
Only 1/2 of the light the lens gathers gets transmitted to the auto focus module in the bottom of the camera.

The other 1/2 of the light gets transmitted to the viewfinder.

The auto focus module relies on edge contrast to determine when focus has been achieved. If there is little or no edge contrast auto focus cannot work well.

Faces don't have sharp edges, so there is little edge contrast.
 
Edge contrast. Like, the contrast between the skin tone, the eyelash, and the sclera of the eye?
 

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