I recently bought a Canon 40D with this lens, and since I couldnt find any reviews of this Sigma here on the forum I decided to make one myself. In fact this is my first review on the Cameralabs forum, so if you think that I am missing something that would make a better review just let me know.
Here's the lens mounted on my 40D
Here's the lens at its shortest length(70mm)
Here's the lens at its longest length(24mm)
The lens feels really solid and well built all around. Since it has a constant 2.8 aperture, you would expect the lens to be quite heavy. In fact it is heavy but far from uncomfortable, at least to me. The filter thread is 82mm, quite huge and this also means that you will need to spend extra cash for CPL filters. The Manual Focus ring feels really smooth as well as the zoom ring but, it feels a bit harder to turn toward the widest focal lengths (around 35mm-24mm).Contrary to other zoom lenses, this one extends toward its widest focal length and retracts when you zoom in. There’s a handy MF/AF lock which is good if you are auto focusing on your subject and don’t want to accidentally turn the Manual Focus ring while holding the lens. To switch between AF/MF you need to move the Manual Focus ring to the front(towards the end of the barrel) to lock it into AF and backwards (towards the camera) to lock it into MF.My only complaint about the build quality is that the lens suffers a bit from lens creep. If you hold the camera with the lens facing up fully extended(24mm), it retracts under its own weight to around 35mm.It is good to know that if you like to shoot low light pictures, this lens does not feature image stabilization. So even though it has a wide aperture, a monopod or a tripod is a good accessory to have with you if you are using this lens under dim conditions.
I have yet to go out and actually test the lens but at least I have taken a few shots at home. This is my first 2.8 lens and I was amazed at the shallow depth of field that it produces. So far images taken at 2.8 are a bit soft, as you should expect, but stopping down to f 4 or f5.6 will improve the overall sharpness. I will update this review soon with samples at f2.8 to show the center and corners sharpness of this lens.
Here's a sample at f2.8
1/8sec f2.8 ISO 100 70mm
Here's another at f4
1/5sec f4 ISO 100 70mm