Reply To: Practice Makes Better, Misc. Questions, Etc.

[stupido]

The scientific answer ain’t too bad. The F-stop is the ratio of the focal to the diameter of the opening. If you double the focal length (zoom in) you double the F-stop. Wiki has an nice article:

http://en.wikipedia.org/wiki/F-number

But really, just remember, as zoom in, you cut the amount of light you are receiving and thus the F-stop number increases.