Came across this 3-part primer. Good for newbies like me!
http://vimeo.com/videoschool/lesson/114/behind-the-glass-part-1-an-introduction-to-lenses
http://vimeo.com/videoschool/lesson/113/behind-the-glass-part-2-focal-length
http://vimeo.com/videoschool/lesson/112/behind-the-glass-part-3-depth-of-field
http://vimeo.com/videoschool/lesson/114/behind-the-glass-part-1-an-introduction-to-lenses
http://vimeo.com/videoschool/lesson/113/behind-the-glass-part-2-focal-length
http://vimeo.com/videoschool/lesson/112/behind-the-glass-part-3-depth-of-field