Astronomy is one of the most interesting hobbies. At the same time, a person experiences special happiness if he observes the moon, planets, nebulae and other astronomical objects through a telescope created with his own hands. One of the most important things to consider when building a telescope is the choice of lens.
Optical telescopes are divided into two main types - refractors and reflectors. In the first case, the objective is a lens or lens system, in the second, a concave mirror. A large mirror is much easier to make than a lens of the same size, which is why mirror telescopes are cheaper. Currently, most amateur astronomers focus on mirror telescopes. However, refractors also have their advantages; telescopes with a lens objective are also widely used.
Choosing a lens for a refractor telescope
In practice, when choosing a lens, one has to look for an optimal combination of several parameters, first of all, the lens diameter and its cost. The larger the lens, the higher its aperture, the fainter objects can be seen. For a beginner astronomy lover, a lens with a diameter of 80-100 mm is quite suitable. The 150mm lens will allow you to perform almost the entire range of observations, and the 200mm lens is suitable for serious professional astronomical research.
What magnification does the telescope have? You can roughly estimate its capabilities by multiplying the diameter of the lens by 2. For example, a 100mm lens can magnify up to 200x. For qualitative observations, an increase of 150-200 times is quite sufficient.
An important parameter of the lens is the relative aperture, it determines the ratio of the lens diameter to its focal length. For example, if the aperture ratio is 1:10, then the focal length is 10 times the lens diameter. For a lens with a diameter of 100 mm, for example, with such a relative aperture, the focal length will be 1 meter. The larger the focal length (respectively, the smaller the relative aperture), the less distortion, but the larger the telescope.
The quality of the lens optics is very important, depending on the manufacturer. The better the optics, the less the image is distorted, the finer details can be seen. Most of the telescopes currently offered are made in China. With the purchase of such a telescope, you can get both excellent optics and very poor ones. The quality varies greatly from sample to sample, so it is better to purchase a telescope in person in a store, and not via the Internet - the chance of getting a telescope with a bad lens will be much less.
Choosing a lens for a reflector telescope
All the main points discussed for refractors are also true for reflectors. In terms of its capabilities, a reflector with a mirror with a diameter of 120 mm is approximately equal to a 100 mm refractor.
Nowadays, astronomy lovers have the opportunity to order the manufacture of a mirror of the desired size via the Internet. Companies specializing in custom-made mirrors provide quite acceptable quality. A mirror with a diameter of 200 mm will cost around 10-12 thousand rubles. Of course, prices may differ slightly from manufacturer to manufacturer. Having made a pipe and a pry bar yourself, you can get a very good tool for a very reasonable price.
