Is Sigma 50-150mm f2.8 Really this Soft?

Started Jul 16, 2009 | Discussions thread
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Asif Tufal
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Is Sigma 50-150mm f2.8 Really this Soft?
Jul 16, 2009

I've just received this lens having bought it second-hand on ebay. Two things have worried me:

1. I'm shocked by how soft it is not only at f2.8 but also at f4. Things seem OK at f8 but only from a certain focal length. Please see the sample images below and let me know if this is typical or if there's something wrong with the lens. I certainly didn't buy an f2.8 lens only to use it at f8!

These are crops of the main area. Full size images (especially the original jpegs out-of-the-camera) which really show how soft it is at f2.8, can be downloaded at:

http://www.flickr.com/photos/tufal/sets/72157621551850324/

By the way, comparing these images with what I've achieved with the Tamron 17-50mm f2.8, tells me that something's got to be wrong with the Sigma:

http://www.flickr.com/photos/tufal/sets/72157621432199749/

2. The zoom rings rotates with very little resistance - hardly any at all. I've compared it with my Sigma 18-125mm DC OS HSM and Tamron 17-50mm f2.8 and their zoom rings are much firmer. Again, is this typical?

Here are the images, taken at various focal lengths (50mm, 68mm, 103mm and 150mm) and at three apertures each (f2.8, f4 and f8). To minimise the risk of user error, I used a tripod.

Is there something wrong with this lens? If so, how can it be fixed?

50mm f2.8

50mm f4

50mm f8

68mm f2.8

68mm f4

68mm f8

103mm f2.8

103mm f4

103mm f8

150mm f2.8

150mm f4

150mm f8

Is there something wrong with this lens? If so, how can it be fixed?

Regards,
Asif

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