lens test: are these results acceptable?

[astroskeptic]

I Just bought the Sigma 70-200mm f/2.8 DG MACRO HSM-II lens from B&H for my Nikon D300. I'd like to get advice regarding evaluating this lens. Is it good, or should it be RMA-ed for another copy?

Sadly, I don't have a full frame body so I can't evaluate performance at the edges. What I have tried to evaluate is general sharpness. Below I have an image showing 6 test shots I took at 3 apertures and the ends of the focal length range. I'd like help interpreting these results.

I took these images using a tripod and shutter timer to minimize vibration blur. I shot at 2 distances from the target in an effort to keep the image scale roughly constant across the 2 focal lengths.

What these results clearly show is softness at the wide (2.8) end with worse softness at 200mm than 70mm. From reading lens reviews at B&H I see it isn't unusual for lenses to be exchanged for reasons of softness at the wide aperture end ... does this look like a lens that should be exchanged?

I realize that some degree of softening is probably common at wider apertures and longer focal lengths and if this is true, the question I face is whether the degree of softening I see is more than I should expect for this lens. Obviously, this isn't a very high-end lens so it would be unreasonable to expect perfect performance but on the other hand, this is no kit lens either.

What do you think? Good ... bad ... average?

Thanks in advance.

 

[Petraio Prime]

Meh...

:meh:

 

[KmH]

Nope, no need to RMA it.

 

[Overread]

I've no experience of this lens to be able to say how its performance is - one tip I can give you though is to shoot test shots like this at an angle to the paper. When you shoot head on (especailly with wide apertures) there is always a chance that a slight missfocus (eg hand on the shutter, paper lifting a little etc..) might cause you to get a shot that is not soft, but where its out of focus.

Shooting at an angle means that each shot will for certain have at least one point which is very much in focus and this able to let you know what the sharpness is like without missed focus errors skewing your results.

 

[table1349]

Here is the test you want to do: Nikon D70 Focus Chart

 

[Derrel]

The camera to subject distance is probably VERY short, if this target is sheet music...the lens is probably not computed to be all "that" great at close distances--it's probably optimized for Infinity focusing, not close-range stuff. With that being said, the results are about what I'd expect from a Sigma 70-200/2.8 shot at close range...softness at 2.8, better at f/4, with contrast markedly improved at f/5.6. If you plan to photograph sheet music at close range in poor light, this might not be a very good lens, but for normal subjects at 200 times the focal length, the lens is probably pretty decent at f/4 on down to f/11 or so.

 

[astroskeptic]

Thanks for the responses. I tested at an angle with the recommended chart and the results seem reasonable. As Derrel suspected, my initial test was performed at close range and I hadn't considered that this constituted something of a "stress" test so there seems to be no strong evidence of a real problem.