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How to Find the Magnification of a Telescope Lens

The key to determining the magnification of a telescope lens is the focal length of the telescope. Telescopes don't have just one focal length though. Two focal lengths determine the magnification. Both the magnification of the telescope and the eyepiece must be considered. If your telescope has a replaceable eyepiece, this can be used to either increase or decrease the overall magnification based on a simple formula.

Instructions

- 1
  Locate the specifications for the telescope's focal length and the focal length of the eyepiece. These will be listed under the specifications of the telescope if you are making a purchase online, or on the label of the telescope on the box in the score.
- 2
  Write down the focal length of both the telescope and the eyepiece. For this example let's assume the telescope has a focal length of 1,000 centimeters and the eyepiece has a focal length of 20 centimeters (the focal length of the eyepiece is equal it its diameter).
- 3
  Divide the focal length of the telescope by the focal length of the eyepiece. In this example, 1,000 centimeters would be divided by 20 centimeters, resulting in a total of 50. This means your total magnification of your telescope lens is 50 times.

Astronomy