While trying to determine my next lens purchase I decided to rent Canon's 17-40mm f/4 wide-angle zoom lens this week to test it out in the field. I went for an extremely cold walk along the Chicago River and around Michigan Ave getting a feel how it performs. It did great wide open at 17mm and was tack sharp at f/10 with no noticeable issues. I would love to try something in the neighborhood of 14mm, but this is a great general purpose wide-angle. This was my favorite from the walk this week - the river was frozen over and the lights were just starting to come on as the sun disappeared behind the camera. Its tough shooting so wide because of the vertical distortion from the buildings, but if you keep that in mind while shooting you can give yourself some room to fix in post.