Introduction to Ritchey Chrétien Telescope
The Ritchey–Chrétien telescope is a type of reflecting telescope that belongs to the Cassegrain optical system. It was designed by George Ritchey and Henri Chrétien in 1910, and is named after the initials of both men’s names. The Ritchey Chrétien telescope configuration is a specialized variant of the Cassegrain telescope that uses a primary hyperbolic mirror (primary mirror) and a second hyperbolic mirror (secondary mirror) designed to eliminate off-axis optical errors (coma). The Ritchey Chrétien telescope has a wider field of view and fewer optical errors than that of traditional reflecting telescopes. This telescope design also eliminates chromatic aberration, which is a natural advantage over refracting telescopes.
Additionally, reflective telescopes are usually metal-coated, allowing for the use of wavelengths across both visible and infrared bands. As a result, the vast majority of astronomical telescopes use a reflective design. The Ritchey-Chrétien telescope design is well-known for its application in the Hubble Space Telescope, where it has enabled groundbreaking observations of the cosmos.
Reflecting Telescope
Newton’s first reflective telescope used a spherical mirror. However, spherical mirrors are well known to have spherical aberration, which is proportional to the third power of the aperture size, limiting both the F-number and the level of image quality. Spherical mirrors offer numerous rotational symmetry axes, resulting in uniform image quality across the field of view. They are particularly suitable for systems with small relative aperture and low image quality requirements. The spot pattern of the Newton telescope with F=8.3 is presented below. However, due to spherical aberration, the image quality of the entire field of view is not ideal.
