Fig. 4: Path of a ray in the microscope.
3.3 Telescope after Kepler
A convex lens of long focal length ƒ1 (+300 mm, for example),
and one of short focal length ƒ2 (e.g. +50 mm) are secured to
the optical bench at a distance of ƒ1 + ƒ2 (Fig. 5).
Fig. 5: Path of a ray in a Kepler telescope.
If we look through the lens of short focal length, we can see
an inverted, magnified image of a distant object.