The size of the camera lens affects a lot of things.
In this video you will learn about focal length, depth of field, lens compression and distortion among other things.
If you have ever taken a selfie and thought you looked really weird. You will understand why after watching this lesson.
(You might just look weird, but the chances are it was lens distortion making your face look strange)
Here is the link for the handy dof-utils add-on created by 'p2or'. Please note, CGCookie does not maintain this add-on.