I'm looking for a new general purpose walk around lenses for my Canon XTI Rebel. Right now I have a the original Sigma 17-70 f/2.4-4.5 that does not have image stabilization, and looking to upgrade to a lens that does. I'd like to stick with a lens the can open up to a 2.8 aperture, and a wide focal length (15mm-20mm)
I've been reading a lot of reviews and have narrowed my choices down to the Canon EF-S 17-55 or the new Sigma 17-70 that has IS (or what sigma calls OS).
On B&H the 17-55 goes for $1099 and the 17-70 goes for $449. That's almost a 150% increase in price.
In comparison spec wise the 17-55 has a shorter zoom length, but also a constant 2.8 aperture and full time manual focus.
I've also been looking at the comparison shots on the-the-digital-picture.com, which seem to show that the 17-55 is a little sharper then the 17-70, but I'm really no expert at looking at these test shots, but they don't seem that different to me.
So what I'm trying to figure out is if the Canon is really worth the extra $650 over the Sigma? Both have image stabilization but is the Sigma version as good as the canon version? What about the Sigma USM auto focus? Is it as good as Canon's? The difference in focal length is not a big deal to me, but I would appreciate the constant 2.8 aperture and FTMF of the Canon although I'm not sure if that's worth and extra $650 to me.
Here's a few graphs I generated by running ExposurePlot on my photos folder. As you can see most of my photos are wide angle, and wide aperture. Yet I also end up using a high ISO like 1600 a lot. I was hoping a lens with IS would allow me to handhold at slower shutter speeds and thus lower ISO.
From the answers so far it sounds like the Canon 17-55 might be worth the money over the Sigma. I've also been considering an L including the 24-70 and 24-105. But I honestly have no plans to upgrade to a full frame any time soon, nor require the build quality of an L.