Telescope Field of View Calculator: Will the Target Fit?

A common surprise for beginners: the Andromeda Galaxy is six times wider than the full Moon, while a small galaxy is a tiny speck. This works out the true field of view your eyepiece shows, then tells you which popular targets fit inside it. The key formula is simple: true field of view equals the eyepiece's apparent field of view divided by the magnification.

The apparent field of view is a fixed property of the eyepiece design, printed in its specs (a plain Plossl is usually around 50 to 52 degrees, a wide-angle eyepiece 68 degrees or more). Dividing it by the magnification gives the true field, the actual patch of sky you see. For framing large objects like the Pleiades or the Andromeda Galaxy you want a wide true field, which means a long-focal-length eyepiece, ideally with a wide apparent field.