Hey guys,

I know that different lenses (telephoto vs. wideangle) have different focal lengths, and the telephoto lenses have large lengths. The longer the focal length, the greater the magnification (kind of like when you move a projector far from a screen, everything gets bigger).

But, what exactly is the measurement of? ie) 18mm-1000mm. Is it the distance between the outter lens and the film surface? If no film is used (i.e. digital), then what does the distance represent in this case?

Now, I also read that the correct definition of telephoto lens is: one in which the physical length of the lens is shorter than the focal length. How can this be possible? Perhaps I am confused because I always thought the focal length represents the distance between the lens and the film- if this is true, then focal length= physical length, so I am obviously mistaken.

I hope someone can clarify my problems!

Thanks,

Chris.