For a long time there were simply no real options for Canon photographers using crop sensor digital SLRs if they wanted to shoot with fisheye lenses. Tokina was the first to address this with their Tokina 10-17mm f/3.5-4.5
. I considered buying this lens, but it seemed to have some image quality issues, particularly with regard to chromatic aberrations.
When I heard about the Sigma offering I was really excited, a prime fish eye which can shoot at f/2.8, now that sounded tempting. It has been a lot of fun so far.
I thought I would include a couple of sample photos of the lens in action, shooting sports photography. Firstly is a skate photo, shot just before it rained, shot with 1 Sunpak 555 and a 1 Vivitar 285 both off camera and set to half power triggered by Elinchrom Skyports.
[All pictures link to higher resolution Flickr ones]

First impressions
I thought my Sigma 10-20mm f4-5.6
was wide at 10mm, the fisheye is on another level! Very strange being able to see your feet or tripod legs in photos. The lens feels well built, a little heavier than I expected, which is no bad thing in my opinion. There is a small lens hood to protect from glare and comes with Sigma’s standard soft carrying case.
Although you cannot place regular filters on this lens, there is a small gelatin type holder on the rear of the lens for this purpose. The lens comes with the usual neat Sigma soft case.
The next sample photo is a BMX shot again using 2 flashes, one on camera and one to camera left.
Autofocus
Autofocus is provided by Sigma’s HSM which means it is quick and quiet, no problems there. It is worth noting though that because the lens’s DOF is so shallow for most photos the lens will be set to infinity anyway.

Image quality samples
These are crops, please click on the image to see a 100% un-cropped image.
Advice
This lens is so wide that you must be careful not to get tripod legs, or your own legs into the photos. Generally speaking onboard flash will not cover the scene, especially up close! An external Speedlite, a Canon 430ex in my case, fairs much better and will cover fairly well when set to 14mm wide mode.

Summary
Pros
- f/2.8 so great for low light photography
- Very sharp once stopped down to f/4.5 and beyond
- Well controlled CA
- Gelatine filter holder
- Cheaper than a 5D/1DS + 15mm (full frame option)
Cons
- Not as sharp as I would like wide open (but still usable)

A club on medium length exposure, a tripod was used. Colours are beautifully reproduced. Note the curvature of the roof due to the fisheye distortion.
Conclusion

This lens is not for everyone, but it’s a lot of fun and when used in moderation can add a unique aspect to your work which other lenses simply cannot achieve. The fisheye look can be overdone, but when used in the right situation some stunning results can be achieved. The lens is very sharp once stopped down down to f/4.5 and I am very impressed with the image quality in general.