These reviews are always interesting as is the wide variety of comments and experiences.
I had a choice between this and the 16-35 l and I went for 17-40 for reasons of price.
I wouldn't say the lens is the greatest ever but I think it's pretty good.
You can take very fine photographs with it. It's so a wide field of view that lack of sharpness in the corner isn't the end of the world. You can take a pretty sharp looking photograph with it.
Alot of photos nowadays are seen on an iPhone from Flickr and Facebook and you definately won't show up flaws then. It takes filters and this is very important for me for landscape photography. The fact it's 77mm is handy in terms of adapters (and lost lens caps).
Maybe my version is better than others (or more compatible with the tolerances in my camera (5D MIII).
I would have to say I am fairly happy with it.
I have a 24 TSE II and I can use that to combine 3 shots for a fairly wide angle view with shift but it's much more convenient to do it with a 17-40mm straight off. The 17-40mm may not be as sharp as the 24 TSE II but for me it's sharp enough and with Live view I can ensure what I definately want in focus is in focus.
I have the Sigma 10-20mm for an APS-C camera. I loved this when I got it first. I just loved Wide Angle at the time. I think I'm not so wide angly any more. The 17-40 was an attempt to replicate this.
I also have the Samyang 14mm which I've used very successfully for Wide Field Astrophotography. It's great for this. It gives me Super Wide Angle if needs be. It's pretty sharp. I have the Samyang 8mm Fisheye. I thought that was great fun on a APS-C camera.
I think now I'm more taking landscapes at 24mm. It's less distorted and I have to think harder about composition rather than fitting it all in.
Anyway a thumbs up from for the 17-40mm. Don't use it too often but it works for me when I do.
If you want to see what I do with this gear here is my Flickr Page.
I wouldn't claim to be the world's greatest photographer or anywhere near that.
I do enjoy it alot and I find Canon Rumors very interesting.
The technical knowledge here is remarkable.www.flickr.com/fergalocallaghan