Astronomy

Kellner eyepieces consist of three lenses and have an apparent field of view of around 45 degrees. Since the lenses are cemented together, thereby creating an achromat, colour defects are barely visible.

Kellner eyepieces can be used for higher magnifications on telescopes with an aperture ratio of 1:10. The limit for Newtonian reflectors is an aperture ratio of 1:5, beyond this you should instead use a Plössl eyepiece.