ScopeCalc: Telescope Calc

Find out what any eyepiece does on your telescope, then see its field of view as a circle over the Moon, the planets and deep-sky objects.

• Magnification, true field of view, exit pupil and focal ratio from your telescope and eyepiece, with an optional field stop and a Barlow or focal reducer factor
• Limiting magnitude for your own sky, using a Bortle class or your naked-eye limit, plus Dawes and Rayleigh resolution, light grasp and the useful magnification range
• A field-of-view circle that shows how the Moon, Jupiter, Saturn, the Ring Nebula, the Hercules Cluster, the Orion Nebula, the Beehive, the Pleiades and the Andromeda Galaxy fit your eyepiece
• Compare a whole eyepiece set on one telescope, sorted by power, with nested field circles
• Best eyepieces for a target: your eyepieces, alone or behind a Barlow or reducer, ranked by exit pupil match and framing
• Camera imaging: image scale in arcseconds per pixel, field of view, image size and a sampling check for your sensor, pixel size and binning, plus how many pixels a target spans
• Back up your gear to a file and restore it later
• Keep your telescopes, eyepieces and Barlows or reducers in My Gear and apply them in one tap
• Quick-start setups for common refractors, Dobsonians, Schmidt-Cassegrains and Maksutovs
• Aperture and focal length in millimetres or inches
• Save scenarios and share a summary

All values are visual estimates for planning your observing session.