Telescope calculators — TelescopeTo
14 calculators for telescope optics, eyepieces, cameras and field power.
Telescope magnification
Calculate telescope–eyepiece magnification with a Barlow or reducer.
Exit pupil
Check image brightness and practicality for a chosen eyepiece.
True field of view — approximation
Estimate sky coverage from apparent field and magnification.
True field from field stop
Calculate a more accurate field when the field-stop diameter is known.
Telescope focal ratio
Calculate the focal ratio before and after an optical factor.
Barlow or focal reducer
Compare effective focal length, magnification and focal ratio.
Telescope resolving power
Compare Dawes and diffraction-limited Rayleigh resolution.
Light-gathering power
Compare the apertures of two instruments and the human pupil.
Estimated limiting magnitude
Estimate visual limiting magnitude with a sky-condition penalty.
Useful magnification range
Find a range from wide-field viewing to an aperture-based upper guide.
Astrophotography image scale
Calculate arcseconds per pixel for a telescope-camera system.
Camera field of view
Calculate angular sensor field horizontally and vertically.
Compare two eyepieces
Compare magnification spacing, exit pupils and possible duplication.
Field battery runtime
Estimate runtime for mount, dew heaters, camera and accessories.