Klevtsov–Cassegrain telescope

The Klevtsov telescope is a reflecting telescope, which was constructed by the Russians Yuri A. Klewzow. As the Maksutov telescope ( and similar to the Cassegrain telescope ) it has a spherical primary mirror, which is pierced in the middle. Also Klevtsov telescope has a meniscus-shaped lens with the spherical aberration of the primary mirror is corrected. The combination of lenses and mirrors is a catadioptric system.

However, in contrast to the Maksutov and the Schmidt- Cassegrain telescope, the telescope Klevtsov is open in front ( like a Newtonian telescope ): The optical correction element is not located on the front tube opening, but is mounted on the inside of the secondary mirror. The secondary mirror is designed as Mangin secondary mirror. The correction lens has the same diameter as the secondary mirror, and is thus significantly smaller than in a Maksutov telescope.

The beam path runs from the primary mirror by the correction lens to Mangin secondary mirror, on the back of the light is reflected. The rays emerge from the glass of the Mangin secondary mirror from, pass through the correction lens and passed through the hole in the primary mirror to the eyepiece.

The Klevtsov telescope has, in principle, similar advantages like a Maksutov telescope. Because of the smaller correction lens, however, it is much easier ( and cheaper) than a Maksutov telescope of the same aperture and is therefore ideal for larger openings. An advantage over the Maksutov telescope and similar catadioptric systems is in the open at the front tube. This thermal problems (temperature adjustment of mirrors and corrector to the outside air, convection in the tube ) can be minimized. The disadvantage, however, is that the correction element must be made with extraordinary precision and adjusted, as optical errors due to the two-time ray passage and due to its small size have a greater impact. Another disadvantage is that the secondary mirror and corrector must be held by struts, as in the front part of the tube no glass element occupies the full opening; This leads to image artifacts due to light diffraction on the struts.

Similar variations

• Robert J. Magee has proposed a system in which the corrector consists of a cemented lens with the Mangin mirror.
• Ralph W. Field describes a telescope that sets a meniscus corrector before an ordinary secondary mirror.