Is my Sigma OK?

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bulb763

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Jon
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Just got a new Sigma 70-200 f2.8. Did a quick test and I'm slightly concerned that it might have a focusing problem. Can you guys give me your opinion please :)

I have auto-focused on the word "on" in the middle of the image
_DSC00360001-01.jpg


Settings used were 200mm f2.8. Camera (D50) was approx 5feet away from the subject, so well outside the minimum focusing distance (~1m). I would expect the in-focus part of the image to stretch approx 2x as far away from the word "on" as it does towards me. As you can see it doesn't really do that :S

Here is the subject in its natural surroundings, for a sense of scale (if it makes a difference :shrug:)

_DSC00370001-01.jpg


Any thoughts? Is it something I should worry about? Is there a better test I can do to check this?

Thanks for your help :)
 
f2.8 @ 200mm produces quite a shallow DOF. Chances are, in the bad light you took the shot the D50 stuggled to get the focus right.

I would be inclined to take it for a walk and get some good bright daylight shots in and examine the images from there.

King.
 
F2.8 is an extremely narrow DOF, have you tried at other apertures?
 
Thanks King.

The light actually wasn't as bad is that shot makes it look (I guess the camera is trying to expose for 18% grey). I had the booklet set on top of the gold box you can see, directly under a tube light. I used f2.8 to try to emphasise the shallow dof and highlight any small focus inaccuracies. I shall try the lens outside and try some smaller apertures when I get back.

ETA thanks Les too :)
 
My sigma will produce images like that indoors at f2.8

Take it outside and try it, then have a look at what it does.
 
Focussing on a single word on a page of text will give very hit & miss results as the focus point will cover more area that the word.

The way I test a lens is twofold. I go out and shoot with it for a couple of days. If all seems well and my shots are as sharp as I would expect then that is it.

On the couple of occasions I have had to measurebate then my methos is to draw a thick black line across a page of white a4. I then lay a ruler perpendicular to the line. Focus on the line and it gives the AF nothing else to get confused by - the ruler shows how much the lens gives before and after the focus point :)
 
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