How to use the telescope magnification calculator
Find the magnification and exit pupil of a refracting telescope. Enter objective focal length, eyepiece focal length, objective diameter in the fields above; the magnification, exit pupil are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “telescope power”, “telescope magnification”, “exit pupil size”, “calculate telescope magnification”, “find magnification”.
Formula
Variables
- fo — Objective focal length (mm)
- fe — Eyepiece focal length (mm)
- D — Objective diameter (mm)
Worked example
With objective focal length = 1000 mm, eyepiece focal length = 25 mm, objective diameter = 100 mm, the calculator gives magnification ≈ 40 ×; exit pupil ≈ 2.5 mm.
Frequently asked questions
What is the telescope magnification calculator used for?
Find the magnification and exit pupil of a refracting telescope. It helps with questions such as “telescope power”, “telescope magnification”, “exit pupil size”.
What is the formula for the telescope magnification calculation?
Magnification (×) = fo / fe. Exit pupil (mm) = D / [Magnification]. Here fo is objective focal length (mm), fe is eyepiece focal length (mm), D is objective diameter (mm).
What inputs do I need for the telescope magnification calculator?
You need objective focal length in mm, eyepiece focal length in mm, objective diameter in mm. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the telescope magnification calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the telescope magnification result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.