Lurie–Houghton telescope

The Houghton telescope is a reflecting telescope with only spherical surfaces and in addition two or three corrective lenses that sit in front of the mirror. By the use of mirrors and lenses, it is a catadioptric telescope.

The telescope or lens type was filed by James Houghton, who worked for Kodak on 7 March 1941 in the UK for a patent. In the same year, on 30 August 1941 a similar system was developed by Robert Richter and Hermann Slevogt, both employed by Carl Zeiss, patented, which is why it is also referred to as judge - Slevogt lens.

Composed of the lens is afocal corrector, similar to the optical principle of the Schmidt plate of about ten years previously developed Schmidt camera and about the same time developed meniscus lens of the Maksutov telescope. There are afocal lens systems and therefore have a low chromatic aberration, but they cause coma and spherical aberration to compensate for the same spherical aberration of the primary mirror. In contrast to the other two variants mentioned there is a planar field of view and the lenses are easier to manufacture. Since they produce no chromatic aberration due to their geometry, they can be made from the same type of glass, although slightly different types of glass to improve the optical properties of some of the telescope. Likewise, the shape of the lens can be varied, they are symmetrical convex or concave and plano-convex and plano-concave lens, each with the same radii possible, and asymmetrical lenses slightly improve the optical properties, however. Another advantage of the corrector is in particular the simpler manufacturability, which makes it ideal for the amateur. The good correction of aberrations resulting compact telescopes with high aperture ratio and large picture angle, are typical values ​​of 1:3 and 2 ° at 200 mm lens and mirror diameter.

Development

The use of corrective lenses to the diameter of the telescope aperture makes the application for large telescopes not economical. However, the good optical properties inspired a number of other developments.

Newton and Cassegrain optical path

Already judge and Slevogt showed in their patent that these corrective lenses and spherical primary mirror are also suitable for the beam paths of Newton telescopes and similar to that of Cassegrain telescopes. The first arrangement is occasionally used in amateur telescopes; the last, mostly developed in catadioptric lenses for photographic purposes. Both versions have remarkable optical properties, since negative effects of the shift in position of the corrector along the optical axis by degrees of freedom in the lens system can be compensated.

Baker - Nunn camera

The Baker - Nunn camera uses the three-lens corrector at the Houghton had suggested in his patent application, and carries them out with aspheric and special types of glass. This image errors are further reduced and there is an aperture ratio of 1:1 at a field angle of 30 ° and 50 cm aperture possible.

Lurie - Houghton telescope

The Lurie - Houghton telescope is based on the principle of two corrective lenses LABEL FOR Houghton telescope, but with a beam path as in the Newtonian telescope. The position of the correction lenses is chosen so that they can serve as a mirror mount for the secondary mirror at the same time. Their geometry was optimized by Robert J. Lurie for this position with a parabolic primary mirror was used. However, are often telescopes with spherical primary mirror and corrector zweilinsigen - incorrect - also referred as.