Vincent Laforet and the Vimeo staff put together a set of videos covering lenses and all of the issues and advantages that come with them. In the three part series they cover different lenses, depth of field and focal length.
They’re a pretty good primer for those who haven’t worked with lenses extensively. If you’re new to DSLRs and interested in learning more this series is a great place to start.
For more info check out Vincent Laforet’s blog and Vimeo Video School’s latest post.