Types of Telescopes


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 Telescope Types


 What are those numbers?

The f-ratio 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.


To find the f-ratio of a telescope 10 " in diameter with a 45" focal length:

    • Divide 45 " F.L. by10" D. to get an f-ratio 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.