The optical portion of the camera was built as a Cassegrain telescope.

This subsystem consisted of 4 parts, a Cassegrain telescope with a 1. 05 ° by 1. 05 ° field of view, a shutter and red / green filter assembly with 0. 08s and 0. 20s exposure times, a slow scan vidicon tube which translated the optical image into an electrical video signal, and the electronic systems required to convert the analogue signal into a digital bitstream for transmission.

The Cassegrain antenna design was adapted from the Cassegrain telescope, a type of reflecting telescope developed around 1672 and attributed to French priest Laurent Cassegrain.

* 1672-Laurent Cassegrain designs the Cassegrain telescope

– Much earlier than Laurent Cassegrain, he found the fundamental arrangement of the two-mirrors telescope combination, a concave primary mirror associated with a convex secondary mirror and discovered the telephoto effect that is critical in reflecting telescopes, although it is obvious that he was far from having understood all the implications of that discovery.

The telescope assembly was designed as a Cassegrain reflector with hyperbolic mirror polished to be diffraction limited ; the primary mirror had a diameter of 2. 4 m ( 95 in ).

File: Thomas Bresson-Sud-lune -- 2008-05-14 ( by ). JPG | Image of the moon taken with a Nikon Coolpix P5000 digital camera via Afocal projection through an 8 inch Schmidt – Cassegrain telescope

File: Gibbous Moon. jpg | A composite of several Digital-SLR photos compiled in Photoshop taken via eyepiece projection from an 8 inch Schmidt Cassegrain telescope.

Asteroid ( 3200 ) Phaethon, parent body of the Geminids, imaged on 25 Dec 2010 with the 37 cm F14 Cassegrain telescope of Winer Observatory, Sonoita ( MPC 857 )

Instruments can be mounted at a Cassegrain focus below the primary mirror, in enclosures on either of two Nasmyth focal points on the sides of the telescope mount, to which light can be directed with a tertiary mirror, or, in an arrangement rare on large telescopes, at the prime focus, in lieu of a secondary mirror, to provide a wide field of view suited to deep wide-field surveys.

Wide-field takes some 60 % of the telescope ; the other 40 % is devoted to operations with the Cassegrain instrumentation.

A Ritchey – Chrétien telescope ( or RCT ) is a specialized Cassegrain telescope invented in the early 20th century that has a hyperbolic primary mirror and a hyperbolic secondary mirror designed to eliminate optical errors ( coma ).

* Schmidt – Cassegrain telescope

The designs of some specific types of parabolic antenna, such as the Cassegrain and Gregorian, come from similarly named analogous types of reflecting telescope, which were invented by astronomers during the 15th century.

These may be integral part of the optical design ( Newtonian telescope, Cassegrain reflector or similar types ), or may simply be used to place the eyepiece or detector at a more convenient position.

24 inch convertible Newtonian / Cassegrain reflecting telescope on display at the Franklin Institute.

Light path in a Cassegrain telescope.

Later satellites had larger mirrors, with a diameter of around 2. 9 – 3. 1 m. Jane's Defence Weekly indicates that the secondary mirror in the Cassegrain reflecting telescope system could be moved, allowing images to be taken from angles unusual for a satellite.

Ultraviolet spectrograms of thousands of stars to as faint as 13th magnitude were obtained by a wide-angle meniscus telescope of the Cassegrain system, with an aperture diameter of 240 mm, an equivalent focal length of 1, 000 mm, and a 4-grade quartz prism objective.

They were first produced in 90 mm ( 3-1 / 2 ") Maksutov Cassegrain telescope in 1996.

The KAO's telescope was a conventional Cassegrain reflector with a 36-inch ( 91. 5 cm ) aperture, designed primarily for observations in the 1 to 500 μm spectral range.

Amongst the latter were a Dollond 46-inch achromatic, aperture 3¾ inches, and the one Cassegrain reflector constructed by Short, of 24 inches focus and 6 aperture, known among opticians as ' Short's Dumpy.

The IRTF is a 3. 0 m ( 118 " effective aperture ) classical Cassegrain telescope.

The Schmidt – Cassegrain design is very popular with consumer telescope manufacturers because it combines easy to manufacture spherical optical surfaces to create an instrument with the long focal length of a refracting telescope with the lower cost per aperture of a reflecting telescope.

Vixen produces an 8 inch aperture modified Cassegrain design ( VC200L ) they refer to as a VISAC ( Vixen Sixth-Order Aspheric Cassegrain ) that is based on a Cassegrain design with a primary mirror that is " sixth order aspheric "-somewhat like a hyperbolic mirror but able to be manufactured using mass-production techniques.

Laurent Cassegrain in 1672 described the design of a reflector with a small convex secondary mirror to reflect light through a central hole in the main mirror.

The Nasmyth design is similar to the Cassegrain except no hole is drilled in the primary mirror ; instead, a third mirror reflects the light to the side.

They are also used to re-direct and extend the light path and modify the final image in designs such as Cassegrain reflectors.

In a symmetrical Cassegrain both mirrors are aligned about the optical axis, and the primary mirror usually contains a hole in the centre thus permitting the light to reach an eyepiece, a camera, or a light detector.

The " Classic " Cassegrain has a parabolic primary mirror, and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary.

In more complex designs, such as the Cassegrain and Gregorian, a secondary reflector is used to direct the energy into the parabolic reflector from a feed antenna located away from the primary focal point.

Andrew Ainslie Common figured a mirror in 1885 ( and another in 1890 ) for a Newtonian reflecting telescope ( later converted to a Cassegrain ), but the telescope fell into disuse and was bought by the Harvard College Observatory from Common's estate.

The Schmidt – Cassegrain was developed from the wide-field Schmidt camera, although the Cassegrain configuration gives it a much narrower field of view.

Cassegrain designs are also utilized in satellite telecommunications earth station antennas and radio telescopes, ranging in size from 2. 4 metres to 70 metres.

To avoid blockage from the sub-reflector asymmetric designs such as the open Cassegrain can be employed.

In telecommunications and radar, a Cassegrain antenna is a parabolic antenna in which the feed radiator is mounted at or behind the surface of the concave main parabolic reflector dish and is aimed at a smaller convex secondary reflector suspended in front of the primary reflector.

However in offset Cassegrain configurations, the primary dish reflector is asymmetric, and its focus, and the secondary reflector, are located to one side of the dish, so that the secondary reflector does not partially obstruct the beam.

* Another reason for using the Cassegrain design is to increase the focal length of the antenna, to improve the field of view Parabolic reflectors used in dish antennas have a large curvature and short focal length, to locate the focal point near the mouth of the dish, to reduce the length of the supports required to hold the feed structure or secondary reflector.

The convex secondary reflector of the Cassegrain increases the focal length, and thus the field of view, so these antennas usually use a Cassegrain design.

A beam waveguide antenna, a type of Cassegrain design, showing the complicated signal path.

A disadvantage of the Cassegrain is that the feed horn ( s ) must have a narrower beamwidth ( higher gain ) to focus its radiation on the smaller secondary reflector, instead of the wider primary reflector as in front-fed dishes.

A beam waveguide antenna is a type of complicated Cassegrain antenna with a long radio wave path to allow the feed electronics to be located at ground level.

The first Cassegrain antenna was invented and built in Japan in 1963 by NTT, KDDI and Mitsubishi Electric.

Both bands use the dish antenna with prime-focus feeds, unlike the Cassegrain feeds of most other spacecraft dishes.