David Oatley posted:

what is prime focus
and how do you get it

Prime focus is the location of the main focal point for the light gathered by
a telescope without any eyepiece or other optical device being involved. If
you place the film in a camera at that point, it is said to be operating at
"prime focus", and the telescope will act as a sort of big telephoto lens
rather than as an instrument for the eye to look into. Some telescope
focusers will not allow the camera go low enough to get the film to prime
focus, so prime focus may not be accessable (unless you move the objective
closer). Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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