🔭
Stargazing Auxiliary
Telescope Magnification Calculator
Magnification, true field of view, resolution and exit pupil.
Try the tool
Magnification: 40.0×
True field of view: 1.250°
Resolution (Dawes): 0.58″
Exit pupil: 5.00 mm
Tool principle
Magnification = telescope focal length ÷ eyepiece focal length. True FOV = apparent FOV ÷ magnification. Resolution uses Dawes' limit (116″ ÷ aperture in mm). Exit pupil = eyepiece focal length ÷ focal ratio.
Data source: Native optical formulas.
User guide
- 1Enter telescope focal length and aperture (mm).
- 2Enter eyepiece focal length (mm) and apparent field of view (°).
- 3Choose an eyepiece that keeps exit pupil between 0.5 mm and 7 mm.
Frequently asked questions
What's a useful magnification range?＋
Roughly 0.2× to 2× per mm of aperture; more is diminishing returns.
Related tools
⭐
Star Magnitude Calculator
Convert between apparent magnitude, absolute magnitude and luminosity.
🧭Latitude & Longitude Stargazing Calibrator
Best aim angle and astronomical twilight window for your location.
🎨Starry Sky Color Calibrator
Adjust brightness, contrast, saturation and hue on stargazing photos.