Recently I had a business trip to Kingston, ON; so I decided to take the Nikon D90 with the Sigma 20mm f1.8 and the Nikon 50mm f1.4D to do some night street shooting in the downtown area. Interestingly I didn’t even take the 50mm out of my pocket, and shot the whole time with the Sigma.
The Sigma is a bit of a funny lens on the D90. Sometimes the camera underexposes the shot significantly, and at f1.8 it isn’t particularly sharp. Beyond about a metre, the wide angle nature of the lens makes it hard to render objects out of focus, even at the fast wide open aperture. Obviously if you use the very close focus nature of the lens, it is quite easy to render backgrounds out of focus, but rarely are you shooting and object 10cm away in street shots.
Still, its not a bad combination for street shooting, the right amount of wide angle combined with the right amount of speed.