Telephoto lens and focal length being longer that single lens.

[copitlory8]

1. Why is a telephoto lens considered to have a longer focal length than that of a single convex lens?

A lens combination, such as a diverging and a convex lens, is referred to as a telephoto lens. Suggest why a telephoto lens is considered to have a longer focal length than that of a single convex lens.

 

[pantaz]

Wiki appears to have as good an explanation as any...
http://en.wikipedia.org/wiki/Telephoto_lens