Here's a link that does good job of explaining focal length..it also does a good job of explaining about digital sensors versus film..that's why I have more reach on the digital bodies with my zooms than I do on the film cameras...

http://www.photoxels.com/tutorial_focal_length.html

??????????

Erm, I don't see a link?

Well here I was already to learn about this and nothing.

ooops...
http://www.photoxels.com/tutorial_focal_length.html