9 out of 10 points and recommendedSilent, fast auto focus, image quality at wide end, build, handling, low distortion for a fish eye, constant aperture essential for videoWeight
SLR Gear gave an accurate review regarding image quality. A little soft around the edges at the 20mm end, otherwise excellent. Most of the time you're at the wide end of this lens anyway and that's where it excels. Nice to have the versatility at the narrow end, it's there when you need it, and worth the extra weight.reviewed September 24th, 2013 (purchased for $649)
This focal range is so much fun to work with and play with! Beautiful dramatic shots, and I never tire of the perspective, unlike a circular fish eye which is kind of a gimmick after so long. This is a lens you can shoot all day, and not be like Okay enough of the fish eye already!
Focusing is fast, so quiet I can barely hear it, and the feel of it in the hands is really great. Heavy but worth it's weight. I have an excellent 15mm prime lens that is super sharp, small and light, but still bring the sigma on all my trips.
The 3.5 version of this lens is worth full retail price of $650 I have no regrets. It produces the shots people love, more often than any other lens I have and that's saying a lot.
If you think you might someday shoot video with your SLR then the constant aperture of this lens is worth the price difference over the cheaper version. Or if you shoot often in low light settings like around here winters are dark, or night shots, or sports, really nice to have the extra f-stop.
So happy with this lens. I hope it lasts forever and it looks like it will.