Primary Focus Telescopes


Primary Focus Telescope ray diagram

A ray diagram of a Primary Focus Telescope

The light enters the telescope from the left and is focussed by reflecting off the large Concave Mirror.

Since the focus is inside the telescope, it is diffcult to see the result or put an instrument there.

Normally telescopes use another mirror to move the focus somewhere else
(see the ray diagrams for Newtonian and Cassegrain telescopes).

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