Yo creo que ese Sigma es unicamente para cámaras con recorte, para full frame no te vale.
http://www.kenrockwell.com/sigma/30mm-f14.htm"The Sigma 30mm f/1.4 is not a wide-angle and it doesn't work on film, FX or full-frame cameras. I tried it, and the corners go black on full-frame. It easily covers 1.6x format Canon and Nikons"
Un saludo.
Pascual