Telescope Magnification Calculator
Calculate Magnification
M = objective focal length / eyepiece focal length
Find Eyepiece for Target Magnification
Formula
Magnification = Objective Focal Length / Eyepiece Focal Length
Frequently Asked Questions
How is telescope magnification calculated?
Divide the objective focal length by the eyepiece focal length. A 1200mm scope with a 25mm eyepiece gives 48x.
What is the maximum useful magnification?
About 2x the aperture in mm. Beyond this the image becomes dim and blurry.
What is exit pupil?
Exit pupil is aperture divided by magnification. 5 to 7mm is ideal for dark sky viewing.
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