Telescopes for Beginning Astronomers
Although telescopes are the first thought for sky gazers, binoculars may be the ideal choice. Being portable, they are more convenient and inexpenseve compared with telescopes. It’s wiser to buy a cheap pair of binoculars instead of a cheap telescope. 7 X 35 binoculars are a good choice because the size is light and easy to hold. The number 7 stands for the magnification produced by the binocular eyepiece, and the other number stands for the aperature in millimeters.
If you are considering a telescope there are essentially three types available to the amateur astronomer.
Refractors consist of lenses at both ends, and the most recognized type of telescope. They generally cost more per aperture inch than other telescopes, but their size makes them ideal beginner telescopes. It’s best to avoid cheap department store models, as these quote large magnifications but have small, useless apertures. The job of a telescope is to collect an images light, not magnify it, so large magnifications actually make things worse and can alter data. Earthly telescopes usually have extra lenses to make an image appear right side up, but this extra lense can cut down the amount of light that reaches the eye. Therefore, the extra lense is left out of astronomical telescopes, which leaves images upside down. Since lenses can create false rainbow images around really bright objects, it’s best to buy a filter to help correct the problem.
The second type of telescope is the reflector. Light travels down a tube before reflecting off a couple of mirrors and through an eyepiece on the side of the tube. Reflectors need to be larger than a refractor to be equally useful. They do not suffer chromatic aberration, but the main mirror may occasionally need repolishing or realigning (collimating). There are kits available for this. Reflectors are often the most comfortable telescopes to use because of the eyepiece position. You don’t have to kneel and possess an elastic neck to look straight upwards as you would with a reflector. A popular type of reflector is the Dobsonian, which has a mount near the ground rather than a tripod.
Finally, there is the Schmidt-Cassegrain telescope. This telescope uses both lenses and mirrors to fold light back onto itself inside a compact tube. These cost less than refractors and are dearer than reflectors, and are overall more portable and easier to handle.
Sometimes telescope specifications quote numbers which will not affect the image you see. However, they can affect the exposure you need if you start into astrophotography. It is wise to get familiar with your telescope and the sky before you look into astrophotography though.
By joining a local astonomy club or checking a library, you can evaluate different types of instruments. Also, astronomy magazines have reviews as well as advertising for good telescopes.
Although you should buy the biggest aperture you can afford, don’t get a large telescope if you will have to carry it a long way. A smaller telescope would be easier to set up and therefore more likely to be used. You will also be wasting your money on a large telescope if light pollution and atmospheric turbulence in your area are high, as you won’t be getting the best from the instrument.
The general rule for calculating the maximum practical magnification a telescope can achieve is to double the aperture in millimeters, e.g. a 100mm aperture telescope should have a maximum magnification of 200x. So spend the majority of your budget on getting a larger aperture, not more accessories. Do not be tempted to buy an eyepiece that will allegedly stretch magnification beyond the maximum value calculated from the aperture. If given a choice of eyepieces start off simple. A Kellner is a good general-purpose eyepiece and a Barlow lens placed between a focuser and eyepiece can triple magnification.
Along with finding celestial objects, telescopes also follow the movement of those objects. The instrument must be moved repeatedly to keep the object in focus, and different mounts and drives make this possible. Electronic drives will point a telescope in the right direction, but the sturdiness of the mount is the most important thing.
It may be saddening to know that many textbook photos have false colors and are long exposures. The eye is not sensitive enough to see color in dim objects, and stars will always look like tiny light points.
So, let’s talk about what you will see with a beginner telescope. With just a 75mm refractor or 150mm reflector, you can see nebulae, galaxies, moon craters, Saturn’s rings, and even some of Jupiter’s moons. All of these are amazing objects to view as you learn about the night sky.
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