Canon has a Virtual Lens Plant in which you can see how lenses are manufactured.
It's a fascinating documentary video, and worth watching if you have any interest in camera equipment.
Image © Canon, Inc.
There's a long process involved in just making even one piece of glass. When you consider that many lenses contain between 10-18 pieces of glass with various coatings, and with precision being of the utmost importance... you can certainly begin to understand why good camera lenses are so expensive.
Image © Canon, Inc.
You can find more geeky camera goodness in the Canon Camera Museum.
