I was looking at the Leitz Hektor and Ken Rockwell says
"This is a conventional long lens design, not a telephoto. Its diaphragm sits right at 135mm from the image plane.
The Nikkor lens shown above is a telephoto design, and is much shorter."
But I am not certain of what the difference is
I noticed that some old Russian lenses are very long too, above 80mm
I read in Why is there no apparent relation between focal length and physical lens size? that "Telephoto lenses are by definition lenses which are shorter than their focal-length."
I deduct that there are probably more elements, or magnifying lenses to allow telephoto lenses to be shorter
Otherwise, what is the difference ? are there advantages to long lenses, such as fewer elements?