A Galilean telescope (ray diagram)

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The eyepiece is placed so that the ray which crosses the axis passes through the center of the lens and is undeflected. The other ray is deflected and the virtual image is upright and formed some distance to the left. For relaxed viewing the image is formed 'at infinity'.

A Galilean telescope is an unusual instrument. It has a concave lens for an eyepiece. A ray diagram for a Galilean telescope is awkward to draw. The small inverted real image formed by the objective forms a virtual object close to the focal length of the concave eyepiece. The magnification is given by M = fo/fe.

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