Tamron 10-24 compared to Sigma 10-20

I did some quick test shots yesterday, indoors as weather sucked. Before I say anything, I have to say, I know I got a good copy of Sigma. Probably the best one there is in stock. I got it straight from the distributer here in Slovenia and he told me himself he checked it.
As for the Tamron, I got the only copy available in the country.
We all know that quality control is not that great with "3rd party lenses" as we like to call them, so margin for error in this kind of comparison test is wide. I'd probably have to compare 3 or more same lenses to get some accurate/average results.
But anyhow, first comparison done, to put it in one sentence: Sigma wins in sharpness hands down.
Sun is out, I'm packing my gear, so check back in few hours for comparison shots and final words.

Update #1:

Ok, I did manage to get some shots, despite the fact the weather is against me and it started to rain again.
All shots done on D300, aperiture mode & matrix metering. Shot in NEF, imported into Lightroom, comparison view for same show of both lenses, screenshot, saved in Photoshop CS3, quality level 10. It's for show, not trying to get the best out of the images. Same process for all of them, so post process in not a factor.

10mm, Tamron f3.5 vs Sigma f4, border


10mm, Tamron f5.6 vs Sigma f5.6, border


10mm, Tamron f8 vs Sigma f8, border


10mm, Tamron f11 vs Sigma f11, border


I guess no comment needed, right?

10mm, Tamron f3.5 vs Sigma f4, center


10mm, Tamron f5.6 vs Sigma f5.6, center


10mm, Tamron f8 vs Sigma f8, center


10mm, Tamron f11 vs Sigma f11, center


20mm, Tamron f5.6 vs Sigma f5.6, border


20mm, Tamron f8 vs Sigma f8, border


20mm, Tamron f5.6 vs Sigma f5.6, center


20mm, Tamron f8 vs Sigma f8, center


I noticed that on almost all the shots Tamron appears to be one stop brighter. Just did a quick controlled test in a closed environment and this is not the case at it appears. Both lenses produced virtually the same exposure data on all apertures and focal lenghts. So it must have been the weather again..


Close up shots..
Tried some shots from the minimum focusing distance.

10mm, Tamron f4 vs Sigma f4, border


10mm, Tamron f5.6 vs Sigma f5.6, border


10mm, Tamron f8 vs Sigma f8, border


10mm, Tamron f4 vs Sigma f4, center


10mm, Tamron f5.6 vs Sigma f5.6, center


10mm, Tamron f8 vs Sigma f8, center



Some CA tests. All 1:1 crops from the edge of the images.

Tamron f5.6 CA sample:


Sigma f5.6 CA sample:


Tamron f8 CA sample:


Sigma f8 CA sample:



Update #2:

Vignette test shots:


Another handling observation: Sigma has about 1.5cm space between the rings (plus some extruded lines on both sides), so it's easy to get a good grip when you're replacing lenses. Tamron has only around 0.5cm and it's a lot harder to hold it and replace it. Especially if you're in a hurry.


Conclusion:
Judging by my two copies, Sigma is a clear winner. It's overall sharpness is better then Tamrons, far better on corners and better in the center. CA appears to be similar, but Sigma is still ahead slightly. Tamron is brighter, has less vignette and has easier distortion to fix. Tamron has a bit longer range, is a bit brighter, costs less, weights less, but I'm not sure those factors overpower the clear image quality advantage Sigma showed? Not for me anyhow.. If you're thinking about buying one of these wide lenses, or any lens for that matter, try to test and compare your copies yourself if you can. One copy can really be totally different then another.

UPDATE (03.12.2008):
I've received some images from a friend overseas, who has tested his copy of the Tamron lens. His results were A LOT better. I talked with our distributer and we have concluded the copy they got is a really bad one. So, I'm awaiting a new copy and as soon as it arrives I'll do another test and comparison with Sigma. Stay tuned.