cool.

Parting with $750 always hurts. But with this lens, the pain was much less than I expected. I took a trip to Death Valley just after buying this lens, and got a huge number of stunning landscapes, closeups, panoramas, etc. Although owners of full-frame cameras have many excellent superwide options, similarly wide options for DSLR cameras with a 1.5x or 1.6x crop factor are very limited. As I write this, the Canon and the Sigma 12-24 (full frame) are the two widest options, although the Tamron 11-18 and Tokina 12-24 are starting to be available, and the Sigma 10-20 is promised soon.

If you are not in a hurry to get a superwide lens, then it might be best to wait for the Sigma, Tokina, and Tamron options, which will be much cheaper than the Canon lens. The specifications of all four lenses are pretty similar in their focal length, aperture, and close focusing distance..

At the wide end, all of these lenses show considerable distortion in the corners, which is an inherent property of this kind of lens. The corners will be highly elongated, which I like in some scenes (makes clouds look very dramatic), but not others (makes human figures look very odd).

Close focusing: One thing I really like about this lens is its closest focusing distance of 9.5". This is actually the distance to the sensor, so you can actually focus within 4-5" of the lens' front element. This makes for nice macro effects that combine highly magnified foregrounds with superwide backgrounds.

Filters: Depending on where you buy this lens, the salesperson may try to sell you expensive thin filters, supposedly to avoid vignetting on wide lenses. Don't buy the thin UV filter - a standard 77mm UV filter works fine with no vignetting. However, you will need a thin circular polarizer, as a standard CP will cut the corners at 10mm. The vignetting isn't actually too bad, and even if you don't own a thin CP, you can probably trim the edges of your 10mm shots without affecting the appearance of your photos too much. And zooming in just a tiny bit, e.g. to 11mm or 12mm, eliminates the vignetting.

Optics: Optically, this lens is very sharp at 10mm, even wide open, although there is moderate softness and light falloff at wide open aperture. At 22mm, the corners are often a bit soft. There is also some chromatic aberration at all focal lengths, although this is correctable in software. These shortcomings make this lens fall short of "L" designation. However, the chromatic aberration is less severe than other wide consumer-level lenses I've seen - it is considerably milder than the 18-55 kit lens at 18mm, or the 17-85 IS lens at 17mm. However, it is much greater than you will see in a Canon "L" lens.

Build quality: Build quality is passable, but not what I'd like to see at this price. This lens is all plastic, except for a metal mount, and the plastic seems a bit soft. In one week of moderate use, the body already has more visible bruises and nicks than my older plastic lenses that have taken much more lifetime abuse. The front filter threads are made of the same soft plastic, and seem prone to being re-threaded by my metal filters. The lettering on the front of the lens is painted on thinly, and seems to be rubbing off at an alarming rate.

Flare, or lack thereof: Superwide lenses have a bad reputation for flare, but this lens is astonishingly flare-resistant. I have many shots with the sun in the frame, yet relatively few internal reflections. Flare is worst if the sun is exactly on the edge of the picture, but even then it generally consists of just a few colored circles. This is not too bad, and is much less than the 18-55 kit lens in the same situation. This is easily eliminated by reframing to wholly exclude or include the sun.

Incidentally, a hood is not included. Canon wants $30 extra for that. Given the minimal problems with flare, I didn't buy the hood, and haven't really felt the need to.

High price: This lens' current price (between $700 and $800) is much higher than it should be. Although an EF-S lens should theoretically be cheaper to manufacture than its full-frame counterpart, this lens is much costlier than its full-frame cousins. Theoretically, the 10-22mm range would be a cheaper, smaller-scale version of a 16-35mm lens on a full-frame camera. Yet it costs more than Canon's revered 17-40 f/4L lens which has better optics, better build quality, a larger aperture for most of its range, and slightly longer zoom range. Sigma and Tamron both make superwide full-frame lenses that are even cheaper. But for a digital SLR with a 1.6x crop factor, those lenses become much less wide. Interestingly, the Canon lens even costs more than the Sigma 12-24, which also works on a full-frame camera where it is freakishly wide. However, that lens is significantly larger and heavier, and anecdotally there seem to be a lot of bad copies of it around, suggesting it is a difficult lens to manufacture properly. So the Canon's high price is arguably justifiable, but it's probably worth checking out the Sigma 10-22, Tokina 12-24, and Tamron 11-18 lenses in addition to this one.