Well, some of them are more than good. Some of them are total
c-r-a-p (Nikon has that too). Some of them are pure gem ...
Wide Angle: Sigma EX 15-30 (compares in optical quality to Nikon
17-35 2.8 but not in quality built aklthough very well built)
Mid range Zoom: Sigma EX 28-70 2.8 APO ... Pretty good ...
Mid tele range Zoom: Sigma EX 70-200 2.8 APO HSM. As sharp as the
Nikon VR 70-200 2.8 and even sharper @ 2.8. Doesn't have the VR
function but this is truely an amazing lens. That is the one some
report to be trouble making with occasional focus lock. Mine has
the updated chip and never locks ... It is my favorite all around
lens. Focus is ultra fast (in the same range as the Nikon AF-S VR
70-200), ultra sharp lens with superb contrast.
These lenses are like 1/3 of the Nikon equivalent. No contest, the
Nikon have superior built ... Are you shooting in a professional
environment ? If yes, the Nikon are just built like tanks ...
Yves P.
http://www.pbase.com/kafrifelle
and
http://www.pbase.com/yves_p