Selection of astronomical telescope for teaching equipment
There are three types of astronomical telescopes: refraction, reflection and catadioptric:
The refraction type is more convenient to use, has a larger field of view, and the star image is bright, but there is chromatic aberration, which reduces the resolution. The objective of a high-quality refracting lens is two double-separated achromatic objectives or three apochromatic objectives. However, achromatic or apochromatic cannot completely eliminate chromatic aberration.
The advantage of the mirror is that there is no chromatic aberration, but the coma and astigmatism of the mirror are large, which makes the image quality at the edge of the field of view worse. Commonly used mirrors are Newtonian and Cassegrain. The optical system of the former is simple and cheap. The spherical reflector is at the back and the eyepieces are on the side of the front. The main and secondary lenses of the latter are aspherical, with both the primary and eyepieces at the back. The image quality is better and the price is more expensive. .
The catadioptric mirror takes into account the advantages of a refractor and a mirror: large field of view, good image quality, short lens barrel, and convenient carrying. Compared with a refracting telescope of equal focal length and the same aperture, the price is less than one-third. There are two types of catadioptric mirrors: Schmidt-Cassegrain and Maksutov-Cassegrain, the latter is also known as horse-card mirror. There are two types of horse-card mirrors and three types. For example, Bosma’s BOSMA1800150 and BOSMA2400200 are both three-slice type. Because the image quality is better than two-slice type, they are very popular among astronomy enthusiasts at home and abroad.