Telescope Resolving Power Calculator
Fill in the values and the answer updates as you type.
How the Telescope Resolving Power Calculator works
The Dawes limit, 116 ÷ aperture in mm, is the closest pair of equal stars an observer can split. The Rayleigh criterion is 1.22 × wavelength ÷ aperture in radians, converted to arcseconds. Multiplying the angle in radians by the Moon distance of 384,400 km gives the smallest lunar feature the optics can in theory resolve. Poor seeing usually limits real views to about 1 arcsecond. Example: with Telescope aperture 200 mm and Light wavelength 550 nm, the result is Dawes limit (arcseconds) = 0.58; Rayleigh limit (arcseconds) = 0.69; Smallest Moon feature (km) = 1.29.
Inputs and results
The Telescope Resolving Power Calculator takes 2 inputs and gives 3 results.
What you enter
- Telescope aperture (mm) — starts at 200.
- Light wavelength (nm) — starts at 550.
What you get
- Dawes limit (arcseconds)
- Rayleigh limit (arcseconds)
- Smallest Moon feature (km)
Example: Telescope Resolving Power Calculator with the starting values
With telescope aperture 200 mm and light wavelength 550 nm, the calculator returns:
| Dawes limit (arcseconds) | 0.58 |
|---|---|
| Rayleigh limit (arcseconds) | 0.69 |
| Smallest Moon feature (km) | 1.29 |
Change any value above and the results update straight away.
Telescope Resolving Power Calculator FAQ
How do I use the Telescope Resolving Power Calculator?
Enter telescope aperture and light wavelength in the fields, then read dawes limit (arcseconds), rayleigh limit (arcseconds) and smallest moon feature (km) in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Telescope Resolving Power Calculator calculate?
Dawes and Rayleigh resolution limits and the smallest Moon feature visible. It returns dawes limit (arcseconds), rayleigh limit (arcseconds) and smallest moon feature (km) from the 2 values you provide.
What values does the Telescope Resolving Power Calculator start with?
It opens with telescope aperture 200 mm and light wavelength 550 nm so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Telescope Resolving Power Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Telescope Resolving Power Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.