12/23/10

Just several comparison shots with a Canon 40D showing 17mm and 50mm/55mm center crops; edge performance is very close (not posted). I have used/tested over 30 copies of the Canon lens while owning 2 copies for several years. The Canon sample here is the best of 3 most recent copies, while the Sigma sample is the best of 4 copies I've recently had in-hand (2 of which had decentering issues).

3 Reviews:
*Lenstip's review is very consistent with my own findings and seems to me to be the most accurate of the online reviews as their copy looks to be solid with no decentering http://www.lenstip.com/256.11-Lens_review-Sigma_17-50_mm_f_2.8_EX_DC_OS_HSM_Summary.html

*Photozone's http://www.photozone.de/canon-eos/531-sigma1750f28os review is mostly on target but I can't help but think their copy had some sort of misaligment or decentering.

*Bob Atkins' review is also very good http://www.bobatkins.com/photography/reviews/Canon_EF-S_17-55_Sigma_17-50_review5.html but I do think his Canon bias does come through in his conclusion.