Telescope Resolving Power
Calculator
Results
- Dawes limit (arcseconds)
- 0.58
- Rayleigh limit at 550 nm (arcseconds)
- 0.692018
- Maximum useful magnification
- 400
Astronomy results
| Dawes limit (arcseconds) | 0.58 |
| Rayleigh limit at 550 nm (arcseconds) | 0.692018 |
| Maximum useful magnification | 400 |
formula-map diagram
- Dawes limit (arcseconds)
- 0.58
- Rayleigh limit at 550 nm (arcseconds)
- 0.692018
- Maximum useful magnification
- 400
Astronomical relationship
Formula
R = 116 / D(mm) (Dawes limit, arcseconds)= 0.58
Note
This result is a simplified model: it applies the displayed textbook formula to the values you entered, assuming ideal spherical bodies, circular orbits, blackbody radiation and perfect optics, and ignoring atmospheric seeing, relativistic corrections beyond those stated, cosmological models and measurement uncertainty. Use published ephemerides and catalogue data for real observations.
More in Astronomy and space
See all →Frequently asked questions
What does resolving power tell you about a telescope?+
Resolving power is the smallest angular separation between two points, like a close double star, that a telescope can distinguish as separate rather than a single blur. A smaller resolving-power value means finer detail can be seen.
How is resolving power calculated from aperture?+
The common approximation is the Dawes limit, resolving power (in arcseconds) equals 116 divided by the aperture in millimeters, or equivalently 4.56 divided by the aperture in inches. Because aperture is in the denominator, larger telescopes resolve finer detail.
Why does a bigger aperture always resolve more detail, regardless of magnification?+
Resolving power is fundamentally limited by diffraction, the bending of light waves around the telescope's aperture edge, and a larger aperture reduces this diffraction effect. No amount of magnification can reveal detail finer than the aperture's diffraction limit allows; it just enlarges the already-blurred image.
Does atmospheric seeing ever prevent a telescope from reaching its theoretical resolving power?+
Yes, this is a major real-world limitation — atmospheric turbulence typically blurs images to around 1-3 arcseconds even under good conditions, regardless of aperture. This is why large ground-based telescopes still can't resolve as finely as their aperture theoretically allows, unlike space telescopes free from atmosphere.
Why can a small telescope split some double stars but not others?+
A double star can only be resolved, seen as two separate points, if its angular separation exceeds the telescope's resolving power limit. Wide double stars are easy targets even for small scopes, while very close binary pairs require significantly larger apertures to split.