Summary: Great buy for the money. Very usable and performs like a more expensive lense. I would recommend this for those looking for a good multipurpose wide angle lense without the super heavy pricetag.
Summary: Start with the Pros: Cheap - I got mine used for $180, with signs of usage but still perfectly functional. Sharp - Even wide open at F2.8, this lens is very sharp. Portable - It's very light, it's a bit lighter than 50mm F1.4 I think. It's small, it fits in small camera bag with my 5D MKII. Cons: Loud Focus - It doesn't have USM. Poor Built - Comparing it to 50mm 1.4 (which costs about the same), it doesn't have as good built quality and it has an old design.
Summary: This lens is a great compact lens. If you wanted to travel as light as possible, this is a great choice. It is wide enough for scenic shots, and great for street and distorted people shots. I wish this version had an Ultrasonic motor, but for the price, I can live with the buzzy motor. It also gives you an extra stop of useable light. The sharpness is still good wide open, but stopped down to f5.6 it is great.
Summary: Great high speed lens to use when space doesn't allow me to go with my 50mm F1.8 which is my favorite low light lens. This 24mm is a little better build quality, but not as sharp as the 50mm. But you still can't go wrong.
Summary: I have an EOS 7D that I bought with the Canon 60mm 2.8 Macro lens. I am very happy with that lens so naturally that is what I compare other lenses to since it is my only point of reference. I quickly realized that I needed a wider angle lens but did not like the quality of all the zoom lenses so I quickly settled on buying a prime. After reading some poor reviews of the 24 and 28mm Canon lenses I went with the Sigma 24mm 1.8 lens.
Summary: This is a great prime lens for a camera that accepts FD mount lenses. 24mm works great for indoor and group photos as well as fun handheld self ports. ƒ2.8 is fast enough to take decent shots in lower light.
Summary: I was on the lookout for a good-quality autofocus wide angle lens for my Canon 5D MkII, and this seemed to be the best option. Canon's telephoto lenses are generally superb and they make some good zooms, but the company has traditionally had trouble with the wider focal lengths. I can't justify the expense of a 24-70mm f/2.8 or the 24mm f/1.4, and the 17-40mm and 16-35mm seem either underwhelming or too specialised for what they are.
Summary: So far I have gotten great results with this lens on my 20D. I have a 50mm 1.8, a Nikon manual 100mm 2.8 with an EOS adapter, and the older (non-IS) 18-55mm kit lens. The 24mm was the perfect complement to my setup, rounding out my prime lenses, and making up for the kit lens. I've gone back and forth about whether or not the 28mm would have been a better value (20-30% cheaper), but I think the wider angle, especially on a cropped sensor, was worth it.
Summary: I did quite a bit of research on this lens before buying it. I must have read fifty reviews. In the end I came to the conclusion that hypercritical people who have enough money to fill their bag with L lenses can find something bad to say about any lens that doesn't have a red ring around it. This lens seems to have a great balance of features with minimal discrepancies for a great price.