Summary: Why didn't I give this 5 stars? Because there is no "Perfect" lens. Hence, I'd never give anything 5. So, don't let the 4-star rating throw you. I love this lens. I got this when I decided to expand my photography business to also include landscape photography (my first love) to go with my weddings, events and portraits. Until then I used a Sigma 20mm f1.8, which was primarily for natural light shooting the insides of large churches and the occasional wedding group shot.
Pros: Consistent Output, Durable, Easily Interchangeable, Fast / accurate auto-focus, Rugged, Strong Construction
Summary: I went back and forth between this one and the other version with the 4-5.6f variable aperture, but I am glad i decided to spend a little extra for this lens. It produces consistently clear images with quick and accurate auto focus.
Pros: Consistent Output, Fast / accurate auto-focus, Strong Construction
Summary: I bought this lens instead of getting a fish eye to have a quality wide angle lens. After much research I found that for someone who loves to take pictures, but is by no means professional, the quality and value you get for the Sigma 10-20 3.5 fixed is unparalleled. The images produced are sharp and crisp all the way to the edges, through the full range of the camera's abilities, the auto focus is fast and accurate, and the low f stop makes this a great lens for night...
Summary: I feel this is a well made and durable piece of kit. It feels very solid, the minus side is that it feels heavy to me especially compared with my other lenses. In use it performs well for me, lovely clear and easy focus, and results have been good.
Pros: Durable, Quick Focus, Rugged, Sharp Focus, Strong Construction
Summary: Purchased this lens at the same time that I purchased a 70D. It fits the Canon 70D & 40D perfectly. Have tested the lens in low light with the images coming off a bit soft and also grainy (when upping the ISO). When used in daylight, the images produced are of good quality. There is the obvious distortion when not getting the angles right, but thats what you would expect from a wide angle.
Summary: Super wide angle with an impressive set of MTF curves this version (f3.5) of Sigma's wide angle zoom is an essential piece of serious kit. Perfect for opening up a scene this hefty piece of glass is reliable, quiet, reasonably fast for it's expansive field of view and offers excellent quality images for cropped sensor dslrs. It teams with my Sony SLT brilliantly. Well regarded by serious photographers, this lens is a must have.
Summary: I previously owned the slower version of this lens, and decided to upgrade to the f3.5 version. I've used the lens a couple of times so far (at Longleat taking shots of giraffes on the feeding platform from only inches away). I like the results, a rather quirky perspective but just what I was hoping for.