I think its much better lens than what people let you think

Rock and Rollei wrote:

The only real issue with it is the amount of distortion, which certainly isn't reduced by stopping down. But I think it's a really decent lens, for me by far the best choice for APS-C. Plenty sharp enough, and a great range. It also performs brilliantly for IR shooting - no hotspots.

IMHO the biggest problem of this lens is that a majority of them are decentered, causing a soft/blurry corner or side. And that is not cured by stopping down either (although it becomes less obvious than at full open). Another known issue is frontfocus in the WA range on most older Rebel bodies. But I still use this lens because there is no better alternative on APS-C (a good quality zoom that starts at 24mm equiv.).

Agree about IR shooting, very little hotspot compared to most other current Canon lenses; probably a trait carried over from the 17-85. But corner sharpness at 15-24mm in IR leaves a lot to be desired, at least on my copy. I still have to do some controlled tests, but my impression is that a Sony dsc-f717 (from ten years ago) plus a good wide converter offers better corner sharpness at 24-35mm equiv. or so than this Canon lens

Unfortunately, in IR there are no obvious alternatives either, except maybe using the 10-22 for wider shots (10-22 is supposedly quite good at the tele end in IR, but also has corner smearing towards the widest setting).