Summary: This lens captures extremely blurry photos and the depth of field is horrible. It is just impossible to have whole frame in focus (Or may be its an issue with the piece I received). I have just raised a return request to seller.
Excerpt: I've thought about buying this lens for a long time but felt I might not get enough use out of it. When the $ rebate was offered in early January, '15 I ordered it from B&H. While it is an $ investment, the quality of the lens and its casing is excellent.
Pros: Durable, Fast / accurate auto-focus, Lightweight, Rugged, Strong Construction
Excerpt: This Sigma 4.5mm was bought for night star shots, horizon to horizon, and it does that indeed. In other uses, if one can keep one's feet out of the frame, it is wonderful for cityscapes. A walk in the park can be almost magical with this real fisheye.
Pros: Consistent Output, Easily Interchangeable, Much Fun, Strong Construction
Excerpt: So I work a lot and photography is my tool for reminding I'm a much more interesting person outside of my work. I was a paid photographer at one point, maybe I might do it professionally in future. So I was interested in this lens since I could finally get this effect on my smaller sensor camera.
Pros: Consistent Output, Durable, Fast / accurate auto-focus, Rugged, Strong Construction
Summary: I picked this one out for my Sony Alpha 77 from all the other options, because this one has autofocus. I take a lot of self portraits and I needed autofocus for that purpose. It is exactly what I expected, works well in low light, sufficiently sharp, and fun to use.
Excerpt: This is the most extreme fish eye lens you can get for a APS-C camera. With a full 180º view, you get a full circular image, like the Sigma 8mm FE on a full frame câmera. Good lens quality. Luminous, fast and an excellent minimal distance of focus.
Pros: Clear Optics, Easy To Use, Firm Mount, Strong Construction
Summary: A nice, ultra wide angle lens. The HSM focus drive is fast and quiet. One great added feature is the adapter for the lens cap. It has 72mm threads, so unlike most ultra wide angle lenses this lens can be fitted with a protective filter, which is very important for valuable lens optics.
Summary: Perhaps I got a bad lens, but this lens is far too soft for my purposes. Remember, 180 degrees of vision is squeezed into a circle within the rectangular canvas of your camera's sensor (hence circular fisheye).