Why Does Everyone Forget the Sigma 8-16?

Exactly as the title says, why do people never mention the 8-16mm when discussing ultra wide angles for APS-C? It was one of my favorite lenses when I was on crop. The colors, sharpness, and contrast were at least as good as the L lenses I own. The build quality and autofocus were also great. It is no more expensive than the Tokina 11-16 or Canon 10-22.

Is it because it is Sigma? Is it because of the variable aperture? How many people actually use f/2.8 on UWA's anyways?

People are missing out on a gem of a lens. If it had a red ring around the end it would sell like mad. It is the lens I really miss after moving to the 5D2.

I think it's because it's such an extreme lens and has pretty strong wide angle distortion. That can be fun, but isn't always what people want. Slightly milder focal lengths show less WA distortion, i.e. are "better corrected"... For example Canon 10-22, and my choice, Tokina 12-24.

Maybe you should pick up a Sigma 12-24 for your full frame camera. It's effectively the FF version of the 8-16mm. Short of a fisheye, these two Sigmas are the widest available lenses for FF and crop, respectively.

The Sigma 8-16 was the lens I missed the most when I sold my 60D and moved to FF. I ended up with it's FF FOV counterpart, the Sigma 12-24 II, which is a decent lens. I think that most people don't like these lenses because they don't like the extra barrel distortion, or because it is so slow, neither of which concerned me.

I guess the distortion never bothered me too much since I shot mostly nature and landscapes with it. The reviews of that 12-24 II aren't terribly favorable. With a Canon 14-24 likely coming sometime this year or next, I may wait to see what it looks like before investing in a UWA for full frame.

I think the bug-eye front element, odd lens cap and f/5.6 aperture put some people off, but I agree with you. I had the 10-22, Tok 12-24, 11-16 and Sig 8-16 and found the latter to be the best overall UWA of the bunch, assuming you want an ultra wide angle lens that lets you do true UWA photography.

I miss mine now that I'm on 1.3 crop and FF.

I'm with the lot of ya'. I upgraded to a 5D3 from a 7D, and, seeing as how I had to sell the 7D body to offset the cost of the new camera, I've got an 8-16mm up on Craiglist. I loved that lens

I mount my Sigma 8-16mm on my 5DMkII by using a Kenko TC between the lens and body. Effectively this gives me a 11-22mm, slow (f/6.3-f/8) wide angle. I don't usually use it at a setting wider than 10mm (which is effectively 14mm).
The slow aperture isn't a problem in some applications, and the combination seems to have less distortion than my Canon 17-40mm when set to produce an effective focal length of around 14 to 20mm.
Attached image shot with 5DMkII and Sigma 8-16/Kenko 1.4x combination, lens set at 13mm (effectively 18mm).

Lack of filters. At least, that is my reason for never recommending it.