Free Image Resolution Calculator
Calculate the angular resolution of a telescope from its aperture using the Dawes limit: theta = 116 / D arcseconds, where D is in mm.
mm
Dawes Limit
0.5800 arcsec
Rayleigh Limit (550nm)0.6920 arcsec
Dawes Limit vs Aperture Diameter
Telescope Image Resolution
The resolving power of a telescope is limited by diffraction at the aperture.
Dawes Limit
theta = 116 / D
where D is in mm. This empirical limit gives the smallest angular separation at which two equal stars can be distinguished.
Rayleigh Criterion
theta = 1.22 * lambda / D
At 550 nm this is 138.4 / D arcseconds.
Example Calculation
200 mm aperture telescope.
- 01Dawes limit = 116 / 200 = 0.58 arcsec
- 02Rayleigh limit = 138.4 / 200 = 0.692 arcsec