Galilean telescope

A Galilean telescope is a refracting telescope of the type used famously by Galileo, with a convex objective lens and a concave lens as an eyepiece, separated by the difference of their focal lengths. Galilean telescopes are shorter than equivalent Keplerian telescopes and give bright, upright images, but they suffer from a limited field of view, spherical and chromatic aberration, and, except at low magnification (about 30× or less), poor eye relief.