Quote Originally Posted by Monito View Post
The article is a good read and has much good information. However, I think it makes a common error and confuses "telephoto" with "long focus" (long focal length). All telephoto lenses are long focus, but not all long focus lenses are telephoto.

The telephoto concept is a long focus lens that has the optics arranged to shorten the overall length of the barrel to about two-thirds the size it would be if it were a simple long focal length design (without resorting to catadiatropic (mirror) lens designs).
A great explanation is nontechnical terms. Well done.