Sigma 10-20mm f4-5.6

I recently borrowed a Sigma 10-20mm from a friend for a few days.  I've been thinking about purchasing an ultra wide lens (check out this review of four models by Ken Rockwell for more info) so I was excited to try out the Sigma.  Unfortunately I didn't have this lens long enough to do an extensive review, but I will say this: it's worth the money ($500).  Rockwell complains that the lens is cheaply built, but I disagree-- it seems very robust to me, solid and heavy.  Of course, I don't use the professional caliber lenses that he uses, so my basis of comparison is different.  I also thought the focus of the Sigma was excellent, quick and completely silent (this lens uses one of Sigma's HSM motors).

My only complaint with the Sigma (and this whole selection of lenses) is that the zoom feels unnecessary.  I already have lenses that cover 20mm, so really, if I'm putting this on my camera, it's for the 10mm and little else.  And no one makes a 10mm lens with the same properties as the 10mm length on the Sigma.  Nikon, for example, has a 10.5mm lens, but it's a fisheye lens, and the fisheye look has never appealed to me. 

Photo details: Nikon D50 with Sigma 10-20mm, handheld at 10mm, 1/50sec at f4, iso800.  This is the Madonna della Strada Chapel on Loyola University Chicago's campus, shortly after a wedding that I attending.  I had to compose and shoot this fairly quickly, as they were ushering us out of the church at the time, and I wanted to capture some people in the shot.