Maksutov telescope

Lore & Background

Dmitri Maksutov may have been working on pairing a spherical primary mirror with a negative meniscus lens as far back as 1936. His notes from that time on Mangin mirrors include a sketch of a Mangin mirror with the mirror and negative lens separated. Maksutov claimed to have conceived the idea of replacing the complex Schmidt corrector plate with an all-spherical 'meniscus corrector plate' while riding in a train of refugees from Leningrad. He patented his design in May, August, or October 1941 and built a 'Maksutov–Gregorian'-style prototype in October 1941. Similar independent meniscus telescope designs were also patented in 1941 by Albert Bouwers, K. Penning, and Dennis Gabor, but wartime secrecy kept these inventors from knowing about each other's work.

The Maksutov design is most commonly seen in a Cassegrain variation with an integrated secondary. The 'spot Maksutov–Cassegrain' uses a small aluminized spot on the inner face of the corrector as the secondary, simplifying construction and eliminating diffraction spikes from a spider. This type typically requires focal ratios above f/15 to avoid aberrations. The Rutten Maksutov–Cassegrain (Rumak) uses a separate secondary mounted on the corrector, providing extra freedom for aberration correction. Sub-aperture corrector designs place a small corrector in the converging light cone to reduce mass and cool-down time, but require a spider assembly.

Reader's Guide

The Maksutov telescope's significance lies in its practical combination of spherical surfaces, which simplifies fabrication compared to the Schmidt camera's aspheric corrector. Its Cassegrain variations, particularly the spot Maksutov, became popular in amateur astronomy from the 1950s, with the Questar telescope appearing commercially in 1954. The design's ruggedness—allowing all optical elements to be permanently fixed and the tube sealed—made it ideal for military, industrial, and aerospace applications, including tracking and radar calibration. Mass-produced models entered the market in the mid-1970s, and low-cost Russian and Chinese production later drove price competition. The Maksutov–Cassegrain's high focal ratio and narrow field of view make it suitable for lunar, planetary, and double-star observing. Derivative designs include Maksutov–Newtonians and Maksutov cameras, the latter having a curved focal plane like the Schmidt camera.

Did You Know?

• Maksutov claimed to have conceived the meniscus corrector while riding in a train of refugees from Leningrad.
• The Maksutov design has been used in military and aerospace applications due to its rugged, sealable construction.