So I've borrowed this lens for the weekend and I'm using it on a Rebel T4i I've also borrowed.
This is a delightful lens when it nails the focus, sharp from f/1.8 etc, but this combination of lens and camera I have needs a serious adjustment for front focus, of my shots at 18mm/infinity I'm lucky if 1/3 of them is in focus.
I'm not even referring to shots at f/1.8 either, it is off enough that shots taken at f/4 or f/5.6 supposedly focused at infinity are out of focus. It's unacceptable.
The T4i cannot be adjusted for focus in camera, and I don't have a USB dock to borrow with the lens, so I've taken to auto-focusing then turning the focus ring back in the right direction after AF has locked. This also wouldn't be such an issue if the lens didn't focus past infinity.
I think the camera body is mostly to blame, but I'm truly hoping the Pentax version will work better out of the box. If not, then at least I will be able to dial in a focus adjustment on my K-5.
I'll likely take the Nikon version for a spin too, when it is available.
btw: Flare is as bad as lenstip describes. I like to shoot towards the sun...haven't decided whether this is a deal-breaker yet, the lens does everything else right. :/
Here are some photos I've taken with it:
Sigma 18-35mm f/1.8 - a set on Flickr