Telescope Resolving Power Calculator
Enter your telescope's aperture in millimeters.
Result
How to use
- Enter your values in the fields above.
- Press Calculate to see your result instantly.
- Use the Share button to copy a link to your result.
About this calculator
A telescope's resolving power is the smallest angular separation at which it can still distinguish two close objects, such as a tight double star. The Rayleigh criterion (θ = 1.22·λ/D) gives the diffraction-limited theoretical minimum, while the empirical Dawes limit (116/D, with D in mm, giving arcseconds) is a slightly tighter rule of thumb derived from real observations of equal-brightness double stars.
Both scale inversely with aperture D — bigger apertures resolve finer detail. Amateur and professional astronomers use this calculator to compare telescopes and predict what detail — lunar craters, planetary cloud bands, close binary star pairs — a given aperture can actually reveal before buying or setting up equipment.
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