Canon EF 17-40 F4 L compared to Canon 17-55 2.8 IS USM lens

[Black_Dog]

Choosing the 17-55mm f/2.8 IS over the 17-40 f/4.0L was a no-brainer for me. In fact, I would have only considered the 17-40 if I shot with a FF body and needed it for a wide-angle zoom. On a crop sensor body, it is a comparatively poor standard zoom. The advantages of the EF-S include:

• The IS makes a big difference in delivering consistently sharp results from handheld shots at shutter speeds between 1/15-1/60 (sometimes even slower). This is especially handy if you are shooting with the camera held above your head or below eye level. I do both a lot to get unusual points of view at events such as dances at wedding receptions. This feature is undoubtedly what pushes the price of this lens over the 17-40, and it is worth every penny.
• The f/2.8 advantage over the f/4.0 gives you extra stop of light and helps with low-light focusing
• The f/2.8 opens up shallow DOF creative possibilities you can't get with the 'L'
• The extra length of 55mm vs. 40mm gives you a little more reach and allows for more flattering portrait shots.
• The 17-55mm is sharper edge-to-edge than the 17-40 at f/4.0

The only disadvantages are the lack of weather sealing / durability and the fact that the EF-S lens can't be used on a FF body. You've indicated that you shoot an 1100D and are thinking about upgrading to a 7D, so the latter should be of no particular concern for you. And the 17-55mm is hardly flimsy. I've even used it in some spritzing rains. I should think that unless you are a war correspondent on your way to Afghanistan, this isn't too much of a concern either.

My only regret with regard to the 17-55mm is that I waited so long to get it. I purchased it last October and it has hardly been off my primary body since.

+1 to btaylor regarding the 10-22mm if you want a wide-angle zoom for landscapes on a crop sensor body.