Free Telescope Resolution Calculator
Compute the angular resolution (Dawes limit) of a telescope from its aperture: theta = 116 / D (arcseconds, D in mm).
mm
Dawes Limit
0.580 arcsec
Rayleigh Limit0.690 arcsec
Dawes Limit vs Aperture Diameter
Telescope Angular Resolution
Dawes Limit (empirical, for equal-brightness stars)
theta = 116 / D arcseconds (D in mm)
Rayleigh Criterion (diffraction-limited at 550 nm)
theta = 138 / D arcseconds
Smaller is better. A 200 mm telescope resolves about 0.58 arcsec. Atmospheric seeing typically limits ground-based resolution to about 1-2 arcsec.
Example Calculation
A 200 mm (8-inch) telescope.
- 01Dawes: 116 / 200 = 0.58 arcsec
- 02Rayleigh: 138 / 200 = 0.69 arcsec
- 03This can split double stars separated by 0.6 arcsec on a steady night.