What's the difference?

[nightspidy]

I'm researching a new purchase for my Canon 30D and I'm already lost. Was looking at getting the Sigma 4.5mm 2.8 fisheye and discovered that there is a Sigma 8mm 3.5 fisheye. On B&H, both lens' are described as "a spherical fisheye lens that easily captures a full 180 degree view in all directions, in a circular image". So other than the obvious what's the diff? :dunno

[Tee Why]

The 4.5 is made for a cropped sensor like your Canon 30D.
The 8mm is made for a full frame body and if mounted on a 30D it would give you a image like this.
http://www.photozone.de/Reviews/Canon%20EOS%20Lens%20Tests/45-canon-eos-aps-c/254-peleng-8mm-f35-fisheye-converted-to-eos-mount-test-report--review

If you are looking for a circular fisheye, then the 4.5mm version would be for your body.

[nightspidy]

Thanks for clearing that up! Almost bought the wrong one! :D

[joshhuntnm]

The 4.5 is made for a cropped sensor like your Canon 30D.
The 8mm is made for a full frame body and if mounted on a 30D it would give you a image like this.
http://www.photozone.de/Reviews/Canon%20EOS%20Lens%20Tests/45-canon-eos-aps-c/254-peleng-8mm-f35-fisheye-converted-to-eos-mount-test-report--review

If you are looking for a circular fisheye, then the 4.5mm version would be for your body.

just to be clear--the full frame lense can work for both. the crop lens can only work on a crop body.