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question about what drives auto focus

auto focus

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4 replies to this topic

#1
pelha

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I have a D7100 & the 18 -140mm kit lens. When I try to auto focus on a low light or low dynamic range scene, using single point focusing, nothing is in focus. Is this a lens issue, or a camera issue? This image was taken yesterday. It and the other 2 from this location have this problem. All the other shots are beautiful.

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#2
nsomnac

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Hard to tell - can't check the exif data for your settings. And not quite sure what you focused on in this shot.

The D7100 focuses using contrast and sharpness. That scene - with all the twigs and sticks - could be difficult for that camera to focus. FWIW: the posted photo looks like plenty of light to focus. I'd be curious if you had stabilization on and if you had a bit of shake.

If you question the fine focus. Try running through Dot Tune. https://youtu.be/7zE50jCUPhM

Jim

#3
hatman

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You mentioned it was taken in low light which might mean a slow shutter speed was used with a wide aperture. Test again with an aperture in the lenses mid-range like f8.  Mid-range values are usually sharper than wide open or completely stopped down. It might also be possible the image is not sharp due to slight camera movement during the exposure. To rule out camera movement use a tripod or place the camera on a stable surface then make the exposure with the self timer. Using the self timer will eliminate the possibility of jiggling the camera a bit when the shutter button is pressed. Its also possible wind might have caused some movement in the branches. Lots of reasons an image might not be sharp with no fault to the equipment. As mentioned knowing the exif data would help.



#4
dem

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 Is this a lens issue, or a camera issue?

If other images are sharp, the camera and the lens are probably fine. I am guessing it is just camera shake but might be many other things:

 

10 reasons why your photos are blurry | TechRadar



#5
Nikon Shooter

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All auto focus have a contrast based operation… no matter if

there is low or enough light. One can't focus on a white wall

but get a twig in there and it will react.







Also tagged with one or more of these keywords: auto focus