This should be ideally carried out each time you observe or start an astrophotography session.įinally, reflector telescopes are first choice instruments when you want to collect the most light as possible. This procedure allows you to perfectly adjust the alignment of the telescope and must be done before each observation or astrophotography session. To this point, the cleaning of the mirror is highly recommended, paying extreme attention to the fragile optical parts while dismounting the telescope.Ī key element not to be forgotten with a newtonian-like telescope is the necessity to collimate it. For example, a mirror frequently exposed to this harsh environment could be less reflective within years, or put it in a different way, its ability to reflect light decreases. This is why they require to be manipulated with precision and attention. Reflector telescopes are mainly open telescopes, meaning that the mirrors are exposed to the air, humidity and dust. With such a geometry, you will never manage to focus perfectly the image of a star with your reflector, because of spherical aberration a delicate situation considering that astronomy requires to observe and photograph faint and diffuse celestial objects. More often, the low-cost manufacturers do not use nor a hyperbolic neither a parabolic mirror but a spherical mirror. However, a parabolic mirror is facing a defect: the coma aberration which deforms and elongates the star around the fields of view. In fact, such a mirror is relatively expensive and telescopes manufacturers choose rather a parabolic mirror instead, far simpler to build. Theoretically, getting a perfect round dot of a star requires having a newtonian reflector made with a hyperbolic primary mirror. However, a big mirror could quickly emphasize the optical aberrations of the telescope. The bigger the mirror is, the brighter the objects appear in the eyepiece. ![]() The asset of a reflector is its primary mirror’s very large size. Therefore, a secondary mirror is installed next to the front aperture of the telescope, enabling beams to be deviated on the side of the telescope, and so, to observe an image. Here, it is necessary to find a way to make the light beams going out of the tube. It has to collect and make the light beams converging towards the eyepiece holder, the element where we put our eyes. This primary mirror is the master piece of the reflector. The light coming from a star goes inside the optical tube and is first reflected on the primary mirror, located at the extremity. The newton telescopes are the most widespread reflectors in the market because of their easy building process and their low cost. Reflector telescopes Principle of a reflector They are a lot of differences between both of these categories, in terms of performances, durability and especially optical quality. The reflector telescopes are composed of mirrors whereas the refractor telescopes are only made of lenses. A short presentation of Refracting telescope is available here.What is a telescope? This question could seem trivial but behind this universal word, we find two main types of instruments to observe the tremendous objects of our starry sky. This type of telescope produces high-contrast images that are great for observing the Moon and planets, but there is not enough light-gathering power for observing the “deep-sky objects” such as nebulas and galaxies. Refracting telescopes are great for lunar and planetary observations. In a modern refracting telescope, an a chromatic or apochromatic lens is added to reduce chromatic aberration. In the 17 th century, they used to build telescopes with very long tubes - a very long focal length of a telescope diminishes chromatic aberration. Available from: ) There are several ways to reduce chromatic aberration in a telescope (Source: Synthesis of high refractive index materials for manufacturing apochromatic lens by 3D printing - Scientific Figure on ResearchGate. The result is disconcerting for astronomers and astrophotographers.Ĭhromatic aberration in a regular lens - refracting telescope This effect is seen as a rainbow of colors around the image. When passing through the lens, every color refracts at different angles.Ĭhromatic aberration occurs because the lens of a telescope is unable to focus all colors on a single point. One of the most well-known is an effect called chromatic aberration. There are also some disadvantages of refracting telescopes. ![]() ![]() Secondly, the image is steadier and sharper than on other types of telescopes because the effects of changing temperatures are eliminated. ![]() A significant advantage of a refracting telescope is its closed tube - this is good for two reasons:įirstly, the glass surface of a telescope is air sealed, which means that it is protected against dust, dirt, and humidity - because of that the lens doesn't need much cleaning.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |