Auto-Focusing Problem on Nikon D3100

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donkey_kong

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Hi all,

I was out taking some photos at the weekend of various things. I had my trusty 35mm f1.8 lens on my D3100.

At one point, I was taking photos of some still life objects using AF and it would not pick up where to focus. It would focus out then focus in without focusing on the point I wanted to. Eventually, I had to give up AF and manually focus.

In addition, sometimes when it did AF, I pressed the shutter, nothing happened. Only after 2 or 3 seconds, when I finger was still on the shutter did it take.

This has happened before on my lens kit, but don't quite know why. Has anyone else had this problem and why does it happen?

Thanks,

DK
 
Are you using single point or one of the other have a guess focus modes? The camera might be getting confused.
 
donkey_kong said:
I would still expect it to focus on a selected point no matter what mode it would be in?
Click to expand...

Expect the unexpected :D What were you trying to focus on? And how close were you to it. Thinking you were on a certain mode is not exactly helpful for people giving replies.
 
More info needed

Were you shooting at wide apeture , f1.8 ? And how close to the subject ? Hunting can cause the symptoms you mention, as the DOF at f1.8 is pretty miniscule, and worse if you are trying to get real close

Also, i dont know the 3100, but on my D300 you can set the shutter to either Focus or Release, or in other words, the shutter wont fire till the camera has achieved what it thinks is properly in focus, and Release will fire anytime, regardless. Check the 3100 menu
 
Whether on Auto, 3D Tracking, Single Point or Dynamic focusing mode if I am pointing the camera at a subject, I would expect the camera to focus on the selected point.

I was focusing on a tealight holder on a table at f1.8. Light was moderate but wouldn't class it a low light. As for distance, I was approx. 3 feet from the subject - well within the minimum focusing distance.
 
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Tonto said:
More info needed
Also, i dont know the 3100, but on my D300 you can set the shutter to either Focus or Release, or in other words, the shutter wont fire till the camera has achieved what it thinks is properly in focus, and Release will fire anytime, regardless. Check the 3100 menu
Click to expand...

Thanks Peter, that probably explains the shutter delay problem. I'll take a look tonight - hopefully this should solve it.
 
donkey_kong said:
In addition, sometimes when it did AF, I pressed the shutter, nothing happened. Only after 2 or 3 seconds, when I finger was still on the shutter did it take.
Click to expand...

this also happened to me a few times, never on 35/1.8G though, only on 18-55mm and 18-200mm, i thought it was to wait for VR to stabilize.

i've never experienced AF hunting like you described, might just be you were too close to the subject? or there wasn't enough contrast on the AF dot?

try AF-S, single centre point, it should focus more consistently. 3D is hit/miss on slower AF lenses like kit and 35/1.8G.
 
Hi, I've had the same thing happen to me, always when using auto focus. It seems to struggle to lock on to some things, switching to manual focus is the only way I've found to get round it
 
heavens the coincidence I was having the same kid of trouble with my Canon 550 with the 18-55 kit lens over the weekend.. probably not a useless piece of junk after all
 
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