I asked Sigma to create a 10mm f:2.8, argueing that it would be cheaper to create than a zoom. They didn't respond yet, but when they do and I get, as "godfather" of the lens, my free copy, I'll send you my 10-20 zoom.

(Trying to be serious for a moment)

the 10-20 is a fine lens.  Yet I always use it at 10. as my main lens starts at 17 or so.

10, or 16 on the 350-400-40 etc , deforms a lot. All trees look like they are singing in close harmony when you tilt a bit upwards.

also, because of the enormous angle, a pola, being angle-dependant, is not always useable. It also has to be so thin that it's difficult to screw it off the lens.

you can also get bizarre light effects in a dark room with a light source in view. but that may well not be typical for this lens.

ahh...forgot: autofocus doesn't always work as everything becomes very small, excepting the forground object of course. This is no drama as you get a huge dof, but still...

There are no Borg. All resistance is fertile.