Maksutov telescope - Invention and Design, Applications, Derivative Designs

An optical telescope in which the principal image-forming lens and mirror surfaces are spherical, and therefore easy to make. The design was published by the Russian optician D D Maksutov (1896–1964) in 1944.

The Maksutov is a catadioptric (mirror-lens) telescope that is designed to minimize off-axis aberrations such as coma.

Invention and Design

Invented by the Russian optician Dmitri Maksutov in 1944, the design uses a spherical primary mirror in conjunction with a "meniscus corrector shell" at the entrance pupil in order to correct spherical aberration, which is a significant problem in other types of reflecting telescopes. The chief disadvantage of the Maksutov design is that it does not scale up well to large apertures (>250mm/10 inches), since the corrector plate rapidly becomes prohibitively large, heavy and expensive as the aperture increases.

Applications

At the time of his invention, Maksutov himself hinted at the possibility of a 'folded' Cassegrain-type construction. Gregory later published his landmark design for two f/15 and f/23 Maksutov-Cassegrain telescopes in a 1957 issue of Sky and Telescope.

Light path in a Maksutov-Cassegrain

Most Maksutovs manufactured today are this type of 'Cassegrain' design (sometimes called a Spot-Maksutov) that use, as secondary, a small aluminized spot on the inner face of the corrector. Gregory himself, in a second, faster (f/15) design resorted to aspherization of the front corrector surface (or the primary mirror) in order to reduce aberrations.

Astronomical uses

The focal ratio of the Maksutov-Cassegrain design provides high powers and a narrower field of view. Today the design has become a popular choice for the amateur astronomer, if not a 'telescope for the masses', something unthinkable in the 60s when even a small Maksutov-Cassegrains such as the 'Questar 3.5' were quite expensive and within the reach of deep pockets only.

Industrial/Aerospace uses

The Maksutov design has been used extensively in military, industrial, and Aerospace applications. Since all of the optical elements can be permanently fixed in alignment and the tube assembly can be environmentally sealed the design is extremely rugged.

Derivative Designs

The Klevtsov-Cassegrain

A variation on the Maksutov is the Klevtsov-Cassegrain.