Masz jakies uwagi co do wykonania Sigmy EX? Jezeli chodzi o ostrosc 15-30, to bardzo dobre szklo za bardzo dobra cene (jak sie trafi na dobra kopie). Generalnie jak sie wie jak uzywac to jest to cudne szklo.
Co do porownania z 17-40 dosc popularne jest tu:
http://www.16-9.net/ultrawides/
"The Sigma 15-30mm matches or maybe even outresolves the Zeiss 21mm in the frame centre,
though it can't compare to the Zeiss' edge performance."
"In conclusion, I am hugely disappointed by the second 17-40mm L I have tested in this way, and hugely impressed by the Sigma 15-30mm"
http://www.16-9.net/lens_tests/best19_21.html