So let's say a guy has a Canon 60D with a kit 18-135, a 70-200 f4 L and a 50mm f1.8 mark 2, and he's thinking about getting a wide angle lens for... Just to have something wider than 18mm, what would be a good choice?
I have thought about ditching the 18-135 for a 15-85, but I'm not sure this would really be that much wider than the 18-135 (though potentially fairly cost efficient). I have heard about the Sigma 10-20, and I know Tokina makes something similar, and of course Canon makes a few choices.
So the obvious question is, what would It be used for? I guess some landscape and some creative options.
Any references to threads already discussing this would be appreciated too. I did a search for 'wide angle lens' and didn't get a whole lot.