Telephoto vs. Zoom??

[dxqcanada]

I also found this:

"Most telephoto objectives contain a positive achromat in front and a negative achromat behind"

 

[table1349]

Alright, I want to know a basic answer to a basic question. What is the difference between a 70-210mm f/4.5-5.6 TELEPHOTO lens and a 55-200mm f/4-5.6 ZOOM lens (minus the differences in focal lengths, if I am trying to get in the 150-200mm range, as well as price)? I would like to know the difference in the to terms. If I can shoot a shot at 150mm, why should I pick one over the other?
Thanks,
Dave

OK, for that basic answer you asked for. One is 70-210mm and the other is 55-200mm. They are both zoom lenses. They are also both telephoto lenses.

Telephoto means longer focal length than 50mm. Zoom means variable focal lengths in the same lens. Both are technically telephoto-zoom lenses.

 

[dxqcanada]

Taken from my "The Manual of Photography" book:

"By placing a negative component behind a positive component, the transmitted beam of rays is made less convergent, as though it had been formed by a lens of much greater focal length; the nodal planes are in front of the lens."


FYI: this is a great old book (eighth edition) that covers a lot of technical stuff ... even film development.