Calculate the magnification and exit pupil of your telescope with different eyepieces.
Telescope & Eyepiece Details
mm
mm
mm
Calculation Results
Enter telescope and eyepiece specs
About this calculator
Quick Reference
MagnificationPrimary ratio
Exit PupilAperture / Magnification
Focal Ratio (f/)Focal Length / Aperture
Overview
Telescope magnification is determined by the ratio of the telescope's focal length to the eyepiece's focal length. The exit pupil indicates the diameter of the light beam exiting the eyepiece.
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Pro Tips
Highest useful magnification is usually about 2x per mm of aperture (50x per inch).
Lower magnification provides a brighter image and wider field of view.
An exit pupil between 2mm and 4mm is often ideal for many deep-sky objects.
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Fun Facts
"The largest optical telescope in the world has an aperture of over 10 meters."
"Most astronomical viewing is limited by the atmosphere to about 200x-300x magnification."
"Magnification doesn't always reveal more detail; aperture is the key to resolution."
