Canon 50D + 17-40mm f4.0 L USM

Because it is a very high quality but moderately-priced ultra wide angle zoom lens, the Canon EF 17-40mm f/4.0 L USM Lens is one of Canon's best selling lenses. 

The 17-40 f/4 L fills out the bottom focal length range of Canon's f/4 L zoom lens series. It is the lightest L lens currently made (1.1 lbs / 475g) and is the smallest L zoom lens currently produced (3.3" x 3.8" / 83.5mm x 96.8mm - DxL). 




As indicated by the "ultra wide angle" designation, the 17-40mm focal length is ultra wide on a full-frame DSLR. Let's take a look at a focal length comparison.

Although the Canon EF 17-40mm f/4.0 L USM Lens can be a good people lens, it is not a good short-distance people lens. A head shot from this lens will emphasize the subject's nose more than the subject will want. The 17-40mm focal length range is great for group pictures, environmental portraits and full body pictures. Stand back and make a person part of a wide landscape shot. If tighter portraits are your interest, look for a lens that gives you at least an 85mm - 135mm equivalent focal length. The captures of your important subject will be more pleasing. 

Wide landscape photography is a very popular use for this lens Use wide angles toemphasize an object in the foreground against an attractive (and mostly in-focus) background. Or use it to simply take in a very wide field of view. Shoot your garden landscape, the lake, large mountains ...
 
Architecture and real estate photography often have large subjects that require wide angle lenses. These are more good uses for the Canon EF 17-40mm f/4.0 L USM Lens. You may need to remove the barrel distortion from 17mm shots during post-processing if straight lines are present near the edges of the frame.


Of course, that close-up wide angle portrait look is fun to use sometimes. Just don't overdo it.