If you want to see far away, you need a big powerful lens. Unfortunately, a big lens is very heavy. Heavy lenses are hard to make and difficult to hold in the right place. Also, as they get thicker the glass stops more of the light passing through them.
Because the light is passing through the lens, the surface of the lens has to be extremely smooth. Any flaws in the lens will change the image. It would be like looking through a dirty window.
Unlike a lens, a mirror can be very thin. A bigger mirror does not also have to be thicker. Light is concentrated by bouncing off of the mirror. So the mirror just has to have the right curved shape. It is much easier to make a large, near-perfect mirror than to make a large, near-perfect lens. Also, since mirrors are one-sided, they are easier than lenses to clean and polish. Will you want to bother dragging it out into the backyard each time you want to use it?
Will you be okay transporting it to your favorite dark area or to a stargazing event? Do you want it to be something small children can use? But the aperture determines how much detail you will be able to see even if you have a large magnification. Having a small telescope with a large magnification will only zoom in on a blurry image because your telescope can't collect enough light to allow you to see any more detail. Atmospheric conditions can also limit the detail you see. Even with the clearest skies, our atmosphere causes detail to be lost, so magnification only goes so far.
The upshot of this is that magnification isn't everything! You can calculate magnification on your own by dividing the focal length of the telescope by the focal length of the eye piece. Both numbers should be readily available from the manufacturer. Another aspect of a telescope you need to consider is its mount.
This is what keeps the telescope steady and allows you to smoothly turn it to view different parts of the sky. APOs are also particularly good for wide-field astrophotography. Apochromats used to be extremely expensive, but prices have come down significantly in recent years. The cheaper but still excellent! An ED refractor is now a plausible choice for a beginner who wants a rugged, portable, highly versatile telescope and is willing to accept the limited image brightness and resolution that are inevitable consequences of small aperture.
The second type of telescope, the reflector , uses a mirror to gather and focus light. Its most common form is the Newtonian reflector invented by Isaac Newton , with a specially curved concave dish-shaped primary mirror at the bottom end of the telescope. Near the top, a small, flat, diagonal secondary mirror directs the light from the primary to the side of the tube, where it's met by a conveniently placed eyepiece. If you want the most aperture for your money, the reflector is the scope for you.
When well made and maintained, a reflector can provide sharp, contrasty images of all manner of celestial objects at a small fraction of the cost of an equal-aperture refractor. Newtonians have two additional important advantages. And the eyepiece is at the top of the tube, meaning that the pivot point is well below your head.
That allows them to be used with low tripods or, in the case of the popular Dobsonian design, with no tripod at all. In general, a Newtonian on a Dobsonian mount delivers by far the brightest and most detailed images possible per dollar.
Newtonians do require occasional maintenance. Unlike a refractor's solidly mounted lens, a reflector's mirrors can get out of alignment and hence need periodic collimation adjustment to ensure peak performance, particularly if the telescope is moved frequently. The mirrors of the average Newtonian may not require tweaking for months at a time. But for those not mechanically inclined, having to collimate a Newtonian reflector even occasionally may be frustrating.
Then there's the third type of telescope, the catadioptric or compound telescope. These were invented in the s out of a desire to marry the best characteristics of refractors and reflectors: they employ both lenses and mirrors to form an image. The greatest appeal of these instruments is that, in their commonly encountered forms the Schmidt-Cassegrain and Maksutov-Cassegrain , they are very compact. Their tubes are just two to three times as long as wide, an arrangement allowed by "optical folding" of the light.
The smaller tube can use a lighter and thus more manageable mounting. The upshot is that you can obtain a large-aperture, long-focus telescope that's very transportable. But here too there are caveats. That means that they are unable to produce genuinely wide, low-power fields of view. Like the Newtonian, the Schmidt-Cassegrain telescope needs occasional optical collimation that lessens its appeal to those disinclined to tinker. In terms of cost, aperture for aperture, the catadioptric lies midway between the reflector and the refractor.
Like a Newtonian, the popular forms of compound telescopes have a secondary mirror in the light path, and this slightly degrades performance for high-magnification lunar and planetary observing. Even so, when well made, a Schmidt-Cassegrain or Maksutov will deliver very fine images of a wide variety of celestial objects. If you live in an area where dew occurs which is almost everywhere , some sort of tube extension is a must to prevent dew from forming on the exposed corrector plate at the front of the tube.
Many people in humid climates also use electric dew heaters. Catadioptrics also take longer than any other design to cool down to the temperature of the night air, which is necessary to produce pristine high-power images.
So unless you can leave your scope outside to pre-cool, catadioptrics are a poor choice for quick, casual looks at the planets. Low-quality mounts are by far the most common problem with budget-priced telescopes. That can make observing painful at best and impossible at worst. And when you let go, the aim must not jump to one side. All telescope mounts fit into a few broad categories. The oldest and simplest design is the manually adjusted altitude-azimuth mount, often referred to as an alt-az.
These work like the pan-and-tilt heads on photo tripods, moving the scope up-down in altitude and left-right in azimuth. In fact, robust photo tripods work fine for small telescopes at low and medium magnifications. If you intend to use a small telescope for casual sky viewing or daytime use say, birdwatching , you'll find an alt-az mounts preferable because of its simplicity, compactness, and light weight. Alt-az mounts designed for high-power use often have finely threaded slow-motion controls that enable the scope to be moved smoothly by tiny amounts.
The Dobsonian mount dispenses with the tripod and places the pan-tilt head directly on the ground. Dobsonian mounts are typically built of wood or particleboard, and the large, stable bearings are usually constructed with Teflon. On the one hand, it seems quite easy: unlike with, for example skating or golf, no specific skills or long workouts are needed. Some even think that as soon as they point their telescope at the night sky, multicolored planets the size of a soccer ball as well as star clusters and even whole galaxies will start popping up out of nowhere.
Like in the movies. Or maybe a comet will fly before you and wave its shining tail? Alas, no. The smartest of you probably have already guessed that the reality is somewhat more prosaic.
Nevertheless, using a telescope properly will allow you to see countless space objects that have a good chance of leaving you completely speechless. First, the magnification power — the ability to zoom in on distant objects — has actually little to do with the quality of the picture you see in the telescope.
The main characteristic of a telescope is its resolution, or the ability to draw two closely located details in focus. Imagine a phone camera, for example. Do you remember the old Nokia phones with 1—2 megapixel cameras? And now compare them with IPhone 7 cameras. Both cameras look pretty much the same; can zoom in and zoom out. But the pictures you take are completely different: one is dull and blurry, without any details. The other one is beautiful and bright; you can even see the tips of your eyelashes.
The same principle works for telescopes. Imagine that the telescope is the "camera" fitted into your eye. If you buy a cheap and simple "camera", you can clearly see objects magnified 70 times.
If you magnify further, objects will become dim and fuzzy. But if you have a good, expensive camera, you can get a magnification of up to times, without losing the quality of the picture, while the sizes of the objects on the pictures will be same.
The larger the diameter of the lens, the better the resolution; hence the more distant objects can be seen. Ideally, for the best image quality the magnification should be no more than the diameter of the lens in millimeters.
For example, a mm lens will be perfect for a x magnification. Some increase the magnification up to 1. We are ready to share it with you. First, let's dispel a few popular myths:. If you have high hopes to examine the stellar disks in detail and find out how the stars in the Ursa Major constellation differ from the stars in the Little Dipper — slow your roll here.
The closest star to us, Proxima Centauri, is 7 times smaller than the Sun and is 4 light years away. In order to see it, you would need a telescope with a lens m in diameter, which is impossible in terrestrial conditions. The largest of the currently existing optical telescopes, the Grand Canary Telescope Gran Telescopio Canarias , has a mirror of only Therefore, in the nearest future, we will only be able to see the stars as glowing blurred spots, surrounded by concentric rings.
No, no and no again.
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