How we worked it out
Updated as you change the numbers.
- Magnification = scope focal length × Barlow ÷ eyepiece. True field = apparent field ÷ magnification. Exit pupil = aperture ÷ magnification.
Method and assumptions
About 2× per millimeter of aperture (50× per inch) is a common practical limit set by the telescope’s resolving power and the atmosphere. Exit pupils larger than about 7 mm waste light for most eyes.
Questions
What magnification does a 25 mm eyepiece give on a 1,200 mm telescope?
48×, with a true field of about 1.08°.
Sources
Method and figures checked on . Every worked answer on this page is covered by an automated test. Found a mistake? Tell us.