Kellner eyepiece

Kellner eyepiece - The simplest and least costly of all the color corrected eyepieces. It typically has slightly more false color than other more expensive eyepieces and a fair amount of astigmatism.

lanthanum - A rare earth element used in certain state-of-the-art eyepieces to increase the eye relief of the ocular and also to correct for various optical aberrations.

light bucket - A Newtonian telescope of very large aperture on a Dobsonian mount.

Maksutov - In its purest form, an astrographic camera whose objective is a spherical mirror and whose optical defects are corrected by a meniscus. The Maksutov-Cassegrainian telescope is sometimes imprecisely referred to by the name Maksutov.

Maksutov-Cassegrainian - A hybrid telescope. It is essentially a Cassegrainian reflector whose steeply curved objective is corrected by a meniscus.

Maksutov-Newtonian - A hybrid telescope. It is essentially a Newtonian reflector whose steeply curved objective mirror is corrected by a Maksutov style meniscus.

meniscus - A lens with two curved surfaces, one of which is convex while the other is concave. Such a lens in the front of a Maksutov telescope cancels out optical defects in the objective mirror.

Newtonian reflector - A telescope whose objective is a concave mirror and whose flat secondary mirror is tilted 45 to the telescope’s longitudinal axis. This tilt causes the light to enter the eyepiece at the side of the telescope’s tube.

objective - The large lens or mirror in a telescope which collects and focuses light from the object to be viewed.

optics - All of the lenses and/or mirrors in a telescope.

ocular - See eyepiece.