Some lurid test results ...
Well ... I did some comparisons, using a tripod, against the TAMRON SP AF 17-50mm f/2.8
and I wasn't thrilled by the SIGMA 10-20mm f/4-5.6 in the comparison.
I set both lenses to 17mm (lens barrel indicated) @ f/5.6, which is the best the SIGMA can do at this focal length. I simply swapped the lenses ... and multifocused for the best shot.
I place the 100% crops side-by-side to compare them.
Here are the results:
SIGMA 10-20mm @ 17mm f/5.6 original image
SIGMA 10-20 100% crop
TAMRON 17-50 100% crop
TAMRON 17-50mm @ 17mm f/5.6 original image
Then I set the new SIGMA lens for 10mm ... at the same f/5.6 exposure ... just to be fair.
Then upped it f/8
Then finally f/11
I'm sorry, but 10mm is significantly softer at f/5.6. I'm shooting at the minimum focal length ... which is neither here nor there ... but demonstrates the truly nice close-up cabilities of these two lenses. Unfortunately, you have to crank down on the aperture, at 10mm, to sharpen your focus to a reasonable level with the SIGMA.
Is it me, or does the TAMRON seem a little better at color, also?
I'll look at distortion, later.