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Sigma 18-250 problems
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Feb 28, 2016 10:41:23   #
rogerl
 
I have a Nikon D7100 9Used mainly with Sigma 150-500 for wildlife). For walkabout, I bought this Sigma 18-250 but am not happy with sharpness. I tried AF-Fine TUne at -5 & -8 but this made no difference. Here are three photos - each staright out of the camera except reduced for uploading. In each case VR /OS was on.

I would welcome advice, please
Programmed Auto f5.6 1/500 ISO 400
Programmed Auto f5.6 1/500 ISO 400...
(Download)
Programmed Auto f6.3 1/1000 ISO 400
Programmed Auto f6.3 1/1000 ISO 400...
(Download)
Aperture Priority f16 1/50 ISO 500
Aperture Priority f16 1/50 ISO 500...
(Download)
 
Feb 28, 2016 11:02:06   #
Rongnongno (a regular here)
 
1) Grass is in focus
2) Pine tree in front of the tower is in focus
3) Foreground purple flowers are in focus.

The problem is not the lens but your focusing choice(s)
Feb 28, 2016 11:17:43   #
Mike D.
 
You might want to check where the camera thinks it needs to focus. I have the same camera and lens and mh problems stem from not paying attention to where the camera wants to focus.

http://www.uglyhedgehog.com/t-368410-1.html

Check this post to see what I mean.
Feb 28, 2016 12:45:33   #
Ol' Frank
 
Rongnongno wrote:
1) Grass is in focus
2) Pine tree in front of the tower is in focus
3) Foreground purple flowers are in focus.

The problem is not the lens but your focusing choice(s)


I agree, I have the same lens on my D7000 and it works fine for me.
Mar 1, 2016 12:00:50   #
R.G. (a regular here)
 
Ditto to watching your focus point. To that I'd add that you seem to prefer lowish f-stops. #2 shows that even with a fairly distant focus point, f/6.3 can still give a restrictively shallow DOF.

My own very general rule of thumb is that I don't come below f/8 unless there's a very specific reason to do so.

In all of these shots there was plenty light and you weren't using much zoom, so you didn't have to keep your shutter speed up. Using a higher f-stop wouldn't have been problematic.
 
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