How to choose your first astronomical telescope

Lead: When choosing a telescope, you will see many advertisements. But as long as you know the most basic principle described in this paper, you can choose a telescope that suits your observation interest, lifestyle and budget.

How to choose your first astronomical telescope This article is a quick guide, which can help you understand the various telescopes available today. After understanding these basics, you can establish a good concept and know what to choose (and what to avoid) when searching for new telescopes in the market.

Many (probably most) high-quality entry-level telescopes cost more than $400, but there are also some excellent options that cost less than $250. But first, please read this article, so that you will understand the relevant terms and the type of telescope that suits you best.

The telescope you want has two important aspects: a high-quality optical system and a stable and smooth bracket. As we will see below, other things are equally important. Compared with small telescopes, large telescopes will show more details and be easier to use. But don't ignore portability and comfort? The best telescope for you is the one you can really use.

Aperture: the most important index of telescope

The most important index of a telescope is the aperture, that is, the diameter of a lens or mirror (usually called an objective lens) that collects light. Please find the parameters of the telescope near the focusing ring in front of the telescope tube or on the box. Caliber (d) is expressed in millimeters or inches (1 inch is equivalent to 25.4 millimeters), but the latter case is less common. According to experience, your telescope should be at least 2.8 inches (70 mm) in diameter, and the bigger the better.

Compared with small caliber, large caliber allows you to see darker celestial bodies and finer details. However, a high-quality small telescope can still let you see a lot of details, especially in an environment far from the city lights. For example, at a dark observation site, you can see dozens of extragalactic galaxies outside the Milky Way with an 80 mm (3. 1 inch) telescope. But if you want to see these small galaxies from the backyard observation point in the suburbs, you may need a 6-to 8-inch telescope, as shown in the picture below. No matter how dark or how bright the sky is at your observation point, the landscape seen through a large-aperture telescope is more spectacular than the same celestial body seen through a small telescope.

Dobson telescope can have a large aperture and the price is relatively low. (Image courtesy of S&; Craig Michael Ott)

Please avoid those telescopes that advertise their magnification, especially those with unreasonable magnification, such as 600 times. In most cases, the actual maximum magnification of a telescope is the aperture measured in inches multiplied by 50, that is, the aperture measured in millimeters multiplied by 2. Therefore, a telescope with a diameter of 12 inch is needed to obtain excellent imaging with a magnification of 600 times. Even so, you need to wait until the night with excellent observation conditions.

Type of telescope

You will encounter three basic types of telescopes.

-Refractive telescope is equipped with a lens group at the front end of the lens barrel. This is probably the most familiar kind of telescope. Although they are usually easy to maintain, the price of such telescopes will increase rapidly when the aperture increases. Click to watch an animated demonstration of light passing through a refractor.

-Reflective telescopes use mirrors mounted at the rear end of the lens barrel to focus light. For a telescope with a given aperture, the price of reflection is usually low, but you need to adjust the collimation of the optical path regularly, especially when the telescope is often bumped. Click to watch the animation demonstration of light passing through the mirror.

Integrated (or catadioptric) telescopes combine lenses and mirrors to achieve a compact lens barrel structure and relatively light weight. Two common optical paths are called Schmidt-Ka seglin telescope and Maksutov-Ka seglin telescope. For a telescope with a given aperture, the price of reflection is usually low, but you need to adjust the collimation of the optical path regularly, especially when the telescope is often bumped. Click to watch an animated demonstration of light passing through a catadioptric telescope.

The three basic types of telescopes use different optical systems and achieve the same result: making distant celestial bodies look bigger and brighter than those seen by the naked eye. Please refer to the text for the animation link of light through three light paths. (Image courtesy of S&; (Greg Dindman)

The focal length of the objective lens (denoted by the letter F or FL) is used to determine the magnification of the telescope. Multiplication? ) is the key. Magnification is equal to the focal length of the objective divided by the focal length of the eyepiece (this parameter can be found on the eyepiece barrel). For example, if a telescope has a focal length of 500 mm and an eyepiece with a focal length of 25 mm is used, its magnification is 500 divided by 25, which is 20 times. Most telescopes provide one or two eyepieces together. The magnification can be changed by changing the eyepieces with different focal lengths.

Bracket: the most neglected part of telescope

Telescopes need some solid parts to support them. Most telescopes conveniently provide tripods or brackets, but the lens barrel of small telescopes often only provides an adapter block, so that it can be connected to a standard photographic tripod with a screw. Warning: A tripod big enough to take a family photo may not be strong enough for astronomical observation. ) A bracket specially designed for telescopes usually does not use a single screw as a connection, but prefers to use a larger and stronger retaining ring or plate.

Some brackets allow the telescope to move up and down, left and right, just like a photographic tripod. These are elevation angles? Azimuth (abbreviated as alt-az) brackets. Many mirrors come with an elegant and simple wooden platform, called Dobson bracket, which is also a kind of alt-az bracket. More advanced supports can track the movement of stars by moving the rotating shaft. They are equatorial supports. Equatorial stent is bigger and heavier than alt-az stent. In order to use the equatorial support correctly, you need to aim it at the North Star in the northern sky? Polaris.

No matter how many patterns there are in appearance, telescope brackets can be divided into two basic types. Elevation? The azimuth bracket (left) allows the telescope to rotate up and down, left and right. It is easier to set up and can be used intuitively. The equatorial support (right) can track the movement of celestial bodies only by rotating one axis, and it is easier to drive by motor. But in order to work correctly, you must aim at the North Star in the northern sky? Polaris. (Image courtesy of S&; Craig Michael Ott)

Some telescopes are equipped with small motors, and you can patrol all day by pressing a button on the keyboard. Among these telescopes, the more advanced one is usually called. Automatic star guide? The telescope is equipped with a small computer in a hand-held control device. When you enter the current date, time and place, the telescope can rotate by itself and track thousands of celestial bodies. Some automatic star guiding telescopes allow you to choose the best celestial guide, and there are also digital displays to describe the known situation of each celestial body.

But not everyone has an automatic guided telescope? If you don't know how to find a bright calibration star in the sky, the erection process may be very chaotic. Moreover, compared with the entry-level non-electronic control telescope with the same price, the cheap automatic star guide telescope has a smaller caliber.

Please remember?

Any telescope can show you the beauty of the universe. When choosing a telescope that suits you, you only need a little care to explore the night sky all your life!