What are the advantages and disadvantages of refractive, reflective and folding telescopes?

Advantages of refractive telescope 1. The imaging is stable, and the lens barrel of the refraction telescope is sealed to avoid air convection. Different lens combinations are used to correct coma. 3. Maintain the shortcomings of the refracting telescope 1. The chromatic aberration of light waves with different wavelengths is imaged near the focus, so the telescope images a colored halo. Correcting chromatic aberration requires adding a lens with different refractive index, but it is not easy to correct a lens with large aperture. 2. Length of the lens barrel In order to eliminate chromatic aberration, when designing a telescope, it is necessary to increase the focal length as much as possible, which is about 15 times of the aperture of the main mirror, which is inconvenient to use. It is difficult to build such a long and stable tripod. 3. It is expensive. Light passes through the lens, so it is much more expensive to use high-definition and good-quality glass. After completion, the price is several times to ten times more expensive than that of mirrors with the same caliber. The advantages of reflecting telescope. Any visible light is focused on one point. 2. The lens barrel is short. Usually, the length of the lens barrel is only eight times the diameter of the main mirror, so it is about two times shorter than the refractive lens barrel. The short lens barrel is easy to operate and it is easy to manufacture a tripod with high stability. 3. Cheap light is only reflected on the surface of the main mirror, and the mirror maker can buy more economical ordinary glass to make the main part of the mirror. Reflecting telescope shortcomings 1. The shading diagonal mirror is placed in front of the main mirror to block part of the incident light, and the diagonal mirror bracket generates diffraction, and three or four brackets will form six or four rays emitted by the light star. The focal ratio design of eight to ten can be used to reduce the shading rate. 2. Convection often occurs in the open lens barrel with unstable image, so it is difficult to solve the problem satisfactorily. Therefore, it is not easy to see the subtle parts of the planet's surface at high magnification. 3. The main mirror is deformed due to temperature change and mechanical factors, and the focus changes accordingly? Plot? Spherical aberration is formed, that is, the parallel rays near the edge of the main mirror and the optical axis are focused in different places, but the small aperture mirror is not a problem. 4. Keep the surface of the primary mirror plated with aluminum or silver. Due to air pollution, it needs to be re-plated once every six months. However, a good vacuum coating mirror can be used for several years. On the problem of turning back the lens

This kind of telescope can be used as an astronomical telescope and a photographic lens for observation, and some astronomical telescopes can also be connected to a camera for photography (some have designed a switching device, others have to be modified by themselves), and the effect is good. This kind of mirror is cheap because the manufacturing cost of metal reflector is much lower than that of glass lens.

Advantages:

1, low price and simple structure.

2. The lens is light and easy to carry.

3. Because the structure of the main imaging lens is a retroreflective cambered surface, there is no chromatic aberration caused by light passing through the glass, which makes this structure especially suitable for telephoto lenses. Generally, it is necessary to correct chromatic aberration when the lens exceeds 300 mm, but it is difficult to eliminate this chromatic aberration without special glass and aspheric structure, which is also the main reason why apochromatic lens (as some people call it) is expensive.