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The fratio is the focal length divided by the
diameter of the telescope. Magnification is the
focal length of the telescope divided by the focal length of
the eyepiece.
Example:
To find the fratio of a telescope 10 " in diameter with
a 45" focal length:
 Divide 45 " F.L. by10" D. to get an fratio of
4.5.
To compute magnification:
First, convert focal length to mm: 45" = 1146 mm, then:
 1146 mm focal length divided by 35 mm eyepiece equals 33
magnification.
