How to Calculate Telescope Magnification
Whether you're gazing at the moon, Saturn, the Orion Nebula or a distant object, the magnification of the telescope plays an important role in your experience. Calculating magnification is relatively easy, and it can help in decision-making when purchasing and using your telescope and eyepieces.
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Things You'll Need
- Focal length of the telescope
- Focal length of the eyepiece
- Calculator or pencil and paper
Instructions
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1
Find the focal length of the telescope. Focal length is the distance light travels from the telescope's lens or primary mirror to where it is focused as an image. You can find this number on the telescope or in the accompanying manual.
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Find the focal length of the eyepiece. That number, usually in millimeters (mm), is located on the eyepiece.
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3
Divide the focal length of the eyepiece into the focal length of the telescope. For instance, if the telescope's focal length is 1000mm and the eyepiece's focal length is 25mm, then the magnification is 1000/25, or 40x.
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Tips & Warnings
Make sure both numbers are in the same unit of measurement (most likely millimeters).
Higher magnification is not always desirable, since you sacrifice sharpness of focus. Also, some less expensive telescopes don't have lenses that are wide enough to properly handle high magnifications, so beware if an inexpensive model boasts of very high power.
