On Jul 19, 2006, at 11:37 AM, Kostas Kavoussanakis wrote: >> My testing of the Sigma 20/1.8 showed it to have poorer wide-open >> resolution and contrast than the Canon EF20/2.8. > > In addition to your point re contrast, we discussed T-stops the other > day too. I would be very interested to see the T-stop of the Sigma > (and not at all that of the Nocan :-)).
Not sure what a "Nocan" is. Here's the roster of elements in currently available Nikon, Canon, Pentax and Sigma fast 20mm lenses: Pentax FA20/2.8 - 10 in 9 groups Canon 20/2.8 - 11 in 9 groups Nikon 20/2.8 AIS or D-AF - 12 in 9 groups Sigma 20/1.8 - 13 in 11 groups The Sigma certainly has more lens elements in more groups and could therefore have more losses through absorbtion, but I don't know just how relevant that is. They're all pretty close, really, and they're all fairly complex designs. It's a faster lens than the other three and faster lenses usually do give up contrast and resolution compared against slower designs of similar quality. Godfrey -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
