Telescope Magnification Calculator
Enter your telescope and eyepiece details to see what each eyepiece really does, and whether you are pushing past what the optics can show.
Result
- Magnification
- 75x
- Exit pupil
- 2 mm
- True field of view
- 0.69° (Moon is about 0.5°)
- Max useful magnification
- 300x
- Focal ratio
- f/5
Most nights the atmosphere limits useful magnification to about 200-300x regardless of aperture.
How this calculator works
Magnification = telescope focal length x Barlow / eyepiece focal length. Exit pupil = aperture / magnification. True field = apparent field / magnification. Maximum useful magnification is about 2x per millimetre of aperture.