How to choose a Telescope? Ultimate beginner guide from EDISLA

How to choose a Telescope? Ultimate beginner guide from EDISLA


Stargazing is a fascinating hobby. It allows people to admire the beauty of the night sky and explore the mysteries of the universe. Humans aren't the only ones who watch the sky. Many animals, from dung beetles to seals, use the stars to navigate. By looking up at the night sky, they can determine where to go in order to migrate, find food, or search for mates.

There's never been a better time to become an amateur astronomer. This is because of advances in technology over the past few decades. Telescopes are now more powerful, more affordable, and easier to use than ever before. With the right telescope and accessories, amateur astronomers can now observe distant galaxies, nebulae, and other celestial objects. 

Whether you're looking to buy your first telescope or just thinking about it, this guide will help. Here's an overview of the basic features of all telescopes, followed by some specifics. There are advantages and disadvantages to every instrument, so let's talk about those too.

You must decide what's important to you before you buy anything. 

  1. What do you want to see most?

  2. Is your sky dark?

  3. Are you an experienced observer?

  4. What is your budget?

  5. Would you be able to carry the weight of your telescope, and where will you store it?

You'll find a telescope that will satisfy you for a long time by answering these key questions. 

The focus of this guide is on visual observation rather than astrophotography.

A telescope can take snapshots of the Moon, but long-exposure images of galaxies and nebulae require patience, time, and specialized equipment. Beginners should gain a thorough grounding in visual astronomy before tackling astrophotography. If you want to do both visual and astrophotography, buying separate scopes is often cheaper than buying one scope that is suitable for both.

Understanding how telescopes work is important before choosing one.


In any telescope, the aperture, or the diameter of the optical component, is of utmost importance. In addition to determining how bright an image appears, an aperture also determines how sharp an image is. A beginner telescope's aperture typically ranges between 2.8 and 10 inches (70 to 250 mm).

Telescopes with larger apertures make any given object appear more impressive. Through a 10-inch scope, small objects like planets appear sharp and detailed, while faint objects like galaxies and nebulae appear bolder. Given the large aperture's ability to gather nearly 13 times more light than a 2.8-inch aperture, it shouldn't be surprising.

So should you buy the biggest telescope you can afford? Definitely not.

Big lenses or mirrors tend to make a telescope heavy and bulky. That might not be a problem if you keep your telescope in a shed and roll it out when you want to use it, but a big telescope could be a deal-breaker if you have to carry it up and down many flights of stairs, want to take it on an aeroplane, or live in a small apartment.

Your eyes have a maximum aperture of 7 mm (0.28 inches), which is much smaller than the smallest telescope. In other words, a 70-mm scope can collect 100 times more light than your eyes can. The telescope can show you incredible details on the Moon, as well as hundreds of star clusters, nebulae, and galaxies.


Newcomers often ask, "How much does it magnify?" "Any amount you want," is the answer. With the right eyepiece, any telescope can produce an endless range of magnifications. The aperture of an instrument and the weather are the two main factors that limit how much power you can use effectively.

There is a limit to how much detail a telescope can show, so you need to find the right magnification to see the target's detail without losing too much light, becoming too dim to see, or looking blurry.

Is there a limit to how much magnification power is too much? If the telescope has superior optics and the night air is particularly stable, a telescope can magnify 50 times its aperture in inches, or twice its aperture in millimetres. As a result, a good 4 inch (100 mm) scope should not be able to exceed 200X. You should avoid department-store telescope scopes labelled "300 power!," which are promotional hype. But if you think department-store scopes are impressive, just wait until you try out the new "1000 power!" scopes, they'll have you seeing even the craters on the moon's dark side!

The Moon, planets, and the vast majority of deep-sky objects (star clusters, nebulae, and galaxies) are best observed at 8X to 40X per inch of aperture. Observers of the deep sky often use magnifications of 4X per inch or lower to maximize their field of view. You need that when you're looking at massive objects like the Pleiades Cluster and Andromeda Galaxy or exploring fields of galaxies, star clusters, and nebulae.

Realistic magnifications range from 4X to 50X per inch of aperture, with 8X–40X being the most useful. 


You now know the useful magnification range for each instrument. But how do you get them? What do the small numbers on the eyepiece mean?

A scope's focal length is the distance between the main lens or mirror and the image it produces. As we'll see later, some telescopes fold the light path internally, so focal length isn't always the same as tube length. Focal length is usually written on the front or back of the scope. It usually ranges from 400 to 3,000 millimetres. Most telescopes display the focal length on their front or back.

The focal length of an eyepiece is also determined by its focal length, such as 25mm or 10mm. Dividing the scope's focal length by the eyepiece's focal length will give you the magnification for any combination of telescope and eyepiece. Using a 25-mm eyepiece on a 1,000-mm scope, for example, gives 40 power (or 40). Use a shorter focal length lens if you want higher magnification: a 10-mm eyepiece on the same scope makes 1,000 / 25 = 100. There's no connection between magnification and the size of the telescope's main mirror or lens; only its focal length matters.

Traditionally, the focal ratio is expressed as "f/" followed by a number, that's focal length divided by aperture. For example, a 6-inch f/8 telescope has a 6-inch aperture and an f/8 focal ratio. So its focal length is about 1,200 mm. A mass-market telescope usually has a focal ratio around f/4 to f/15.

For visual observing, you should choose eyepieces based on their focal ratio. The theoretical maximum aperture of a telescope is 50 per inch, so you need an eyepiece with a focal length half that. This is 2 mm for an f/4 scope, and 7.5 mm for an f/15 scope. An f/4 scope requires a 25 mm eyepiece, while an f/15 scope requires a 95 mm eyepiece.

Currently, there is no eyepiece on the market with a focal length of 95 mm. A typical telescope's focuser tube is too small to accommodate an eyepiece with such a long focal length. For planetary observations, telescopes with focal ratios between f/10 and f/15 are well suited. However, they cannot deliver the wide-field, low-power views that deep-sky enthusiasts desire. 

Low-power telescopes with focal ratios of f/4 and f/4.5 provide excellent views, but can be difficult to focus at high power without a precision focuser unless they are compatible with more complex and therefore more expensive eyepieces. Focus ratios between f/5 and f/8 provide excellent ocular comfort and wide-field performance.

Look for a telescope that can accommodate larger eyepieces if you want a wider field of view. Generally, modern eyepieces have a barrel diameter of 1 3/4 inches or 2 inches. Most high-quality scopes accept both sizes, but most low-priced telescopes only accept the smaller size. This allows them to use long-focal-length eyepieces, which offer low magnifications and big fields of view.


In bad atmospheric conditions, even the greatest telescope cannot provide clear images. 

You can see more detail in the moon or on the planets with the best telescope on certain evenings. Even between individual seconds, the clarity of the vision changes. High magnification typically blurs and shimmers planets and stars. This is not because of a lack of focus, but rather because of Earth's wavy atmosphere and sometimes very local factors like hot air rising from an asphalt driveway. An astronomical term for a stormy night is bad "seeing.".

It is easier to see dim objects and fine detail on the Moon and planets when the aperture is large. However, the better the weather, regardless of the aperture, the better the view. In the absence of stable air, even 10-inch telescopes are frequently limited to 250X or 300X on all but the most stable evenings.

Patience and fair expectations are essential. People are familiar with photographs taken by spacecraft that circle close to the surface of planets. As Earth's dense layer of air impairs image quality, it is impossible to observe this level of detail across interplanetary space.

If you practice, you will notice more detail in an image — not only because you gain experience, but also because the longer you gaze, the better your chances of catching a few minutes of particularly steady atmospheric vision. 

I am unable to see the Andromeda galaxy, why is that?

Even in poor sky conditions, Saturn's beautiful rings awe everyone who sees them for the first time. However, many people are underwhelmed by their first sighting of a galaxy, no matter how bright it is. There are some beginners who can't even tell galaxies apart.

Light pollution, unrealistic expectations, and inexperience are the main culprits.

You can't deny that galaxies are faint. One of the best examples is the Milky Way. On a clear moonless night away from city lights, its mellow radiance sweeping across the sky is one of nature's most beautiful sights. There is nothing quite like it. It is the stuff of legends, a sight that was known to all humanity before the invention of the electric light. Most people in the industrialized world have never seen our galaxy, despite its majesty. Light pollution overwhelms the Milky Way's delicate glow.

Under dark skies, the Andromeda Galaxy, Messier 31, looks seven moon-widths across, pushing the wide-field capabilities of any telescope to their limits. It is difficult to discern the long, dark dust lanes in pictures using a telescope's eyepiece, as shown in the rural-sky sketch. Under suburban skies, only the innermost dust lane is visible, and from the city center, only the brilliant core is visible.

This cannot be corrected by telescopes. Although they magnify celestial objects, they cannot intensify their light. No matter how big the telescope is, you won't be able to see the dim, outer portions of any other galaxy if your backyard is too bright. A galaxy's compact, relatively intense core is the only part that shines through light pollution. Milky Way's center is obscured by interstellar dust, so we can't see it.

It's good news for urban and suburban astronomers that many deep-sky objects are bright enough to see through light pollution, though you may need a bigger aperture to see them. Some examples of urban-friendly deep-sky objects are star clusters, double stars, and planetary nebulae. There's nothing like the Ring Nebula to catch the eye of a stargazer in the city or suburbs.

You can still see the bright center of galaxies from the heart of a big city even with modest binoculars. Remember what you're looking at: a system of around one trillion stars, likely orbited by many planets, and home to many sentient species. Over 2.5 million years, its light has traveled intergalactic distances. Don't you think it'd be a shame to miss it? Seeing a distant galaxy is akin to discovering buried treasure after a long and arduous quest — the feeling of accomplishment and awe is worth the effort.


So now we know a few things about telescopes, let's look at the different kinds. You'd think there are endless options from the ads. Although telescopes come in all shapes and sizes, they can be divided into three classes: refractors, reflectors, and catadioptrics.

Types of Telescopes: Refractors

Most people think of a refractor when they think of a telescope: a long, shiny tube with a big lens at the front and an eyepiece at the back.

Refractors usually give sharper, brighter images per inch of aperture than anything else. Lenses work better than mirrors, and most other designs have a secondary mirror in front that blocks some light. Refractors do about as well on deep-sky objects as 5-inch reflectors or catadioptrics, and they might even do better on planets.

Usually telescopes with 80mm or less openings are refractor types. That's because small lenses are cheap and easy to make, and the refractor's performance advantage is most noticeable at small apertures. As a result, refractors are the most popular both at the low and high ends of the market, where people want high-performance telescopes that are portable.

Refractors have another advantage: their lenses are less likely to get out of alignment than other types of scopes. Refractors work almost immediately when you take them outside, while large reflectors and catadioptrics don't work well until their mirrors get the same temperature as the air outside, which can take an hour or more. If you don't want to mess with the optics or want an easy-to-grab instrument, small refractors are good.

There are a few reasons why refractors don't scale well. As the aperture increases, the cost of making a high-quality lens shoots up dramatically - much more than mirrors. Therefore, there aren't that many amateurs with refractors much larger than 6 inches. As opposed to beginners, skilled observers own reflectors with mirrors ranging from 12 to 30 inches in diameter.

False color is a problem with refractors, which can lead to bright stars looking like rainbows instead of points of light. If you're looking at the Moon and planets at high magnification, false color can be a big issue. However, you can reduce it with long focal ratios or special glasses.

Achromats, with lenses made from traditional flint and crown glass, are essentially colorless unless the focal ratio is three times the aperture. Therefore, a 3-inch achromat with a focal length of 27 inches needs to be f/9 for optimal planetary views. That's a pretty manageable tube size. A 6-inch achromat would need to be f/18 to work at high power, so the tube would be 108 inches, or 9 feet long!

For refractors, long tubes are especially problematic because the eyepiece is at the bottom. To accomplish this, you need a tripod that is tall, heavy, and expensive.

Recently, achromats with focal ratios between f/4 and f/6 have been really popular. They're called short-tube achromats, and they sacrifice a bit of power for portability and a wide field of view. You can't see the Moon or planets with them, but they're great for star clusters, the Milky Way, and terrestrial subjects like birds and distant ships.

The good news is that modern technology lets you combine the benefits of short-tube and long-tube refractors. APOs, or apochromats, use extra-low dispersion (ED) glasses and other materials to reduce false color. So you can build a refractor that's color-free and short focal ratio. This not only eliminates the problem of overlong tubes, but also gives these scopes gorgeous wide-field views at low magnifications and flawless high-power ones. In addition to astrophotography, APOs are great for wide-field shots.

In recent years, apochromatic lenses have become more affordable. Cheaper, but still great, ED refractors are often marketed as refractors rather than as APOs. For a beginner who wants a rugged, portable, highly versatile telescope and is willing to accept the limited image brightness and resolution that come with small apertures, an ED refractor is a goodchoice.


You can't beat the price of a reflector. Regularly cleaning and adjusting the optics may lessen its appeal to some users. A reflector telescope uses a mirror to gather and focus light. Most telescopes use Newtonian reflectors, with their curved concave primary mirrors at the bottom.

Light is guided from the primary mirror to an eyepiece on the side of the tube by a small, flat, diagonal secondary mirror near the top. If you want the maximum aperture for your money, you should use the reflector. 

For a fraction of the price of an equal-aperture refractor, a reflector can produce clear, contrasty images of celestial objects. There are two additional benefits to Newtonians. They offer large fields of view for their aperture at focal ratios ranging from f/4 to f/8. The pivot point is below your head because the eyepiece is near the top of the tube. Due to this, they can be used with low-profile tripods or, in the case of the popular Dobsonian design, without any tripods. We'll talk more about Dobsonian mounts later; suffice it to say, they're easy, affordable, and easy to use.

For the money, Newtonians on Dobsonian mounts produce the best views. Dobsonian telescopes have become extremely popular because of their low cost, ease of use, and mobility. There are times when Newtonians need repair. In contrast to refractor lenses that are solidly installed, reflector mirrors can become misaligned and require periodic collimation (correction) to keep performing well. This won't be a problem once you get used to it. It is possible for a Newtonian's mirrors to not need adjustment for months at a time. People who are not mechanically inclined may find it unpleasant to collimate a Newtonian reflector even rarely.


In addition to being compact and easy to upgrade, catadioptrics are roughly priced between Newtonians and refractors. The third type of telescope is the catadioptric or compound telescope.

In the 1930s, they were designed to combine the most desirable features of refractors and reflectors. The most appealing thing about these instruments is their small size, especially in their most common configurations, Schmidt-Cassegrain and Maksutov-Cassegrain.

Optical folding makes their tubes two to three times longer than they are wide. With a smaller tube, you can mount it lighter and more easily. It means you can make a large-aperture, long-focus telescope that's still relatively portable.

It's not without caveats, though. In most Schmidt-Cassegrains, the focal ratio is f/10, and Maksutov-Cassegrains are even longer. Because of this, they can't give you really wide, low-power fields of view. Most versions allow attachment of a focal reducer so the effective focal ratio can be dropped to f/6 or so, which helps a lot.

The Schmidt-Cassegrain telescope needs periodic optical collimation like the Newtonian, so it's not for those who don't like to tinker. A catadioptric falls between a reflector and a refractor in terms of cost. Many compound telescopes, like Newtonian telescopes, have a secondary mirror in the light path, which lowers their performance for viewing planetary and lunar objects at high magnifications. In spite of that, well-made Schmidt-Cassegrains and Maksutovs will take great photos of astronomical objects. Almost everywhere has dew-prone environments, so a tube extension is required to avoid dew accumulating on the exposed corrector plate at its front. In humid climates, electric dew heaters are also popular.

Also, catadioptrics take longer to cool to night air temperature, which is required to produce clean high-power images. Unless you can let your telescope pre-cool outside, catadioptrics are not the best choice for casual planet-watching.


 It is worth noting that the Dobsonian telescope is an excellent example of an instrument mounted on an alt-azimuth mount. In height and azimuth, the tube moves up and down. Other alt-az mounts may be able to track better at high power with slow-motion controls.

No telescope is worth anything unless it's mounted on a smooth, solid mount. This is because we need to orient it and follow a celestial object as the Earth rotates and moves your target through the field of view.

Low-cost telescopes are most commonly plagued by low-quality mounts. Even reputable suppliers sometimes combine perfectly functional optical tubes with undersized mounts to save money, especially on "toy" telescopes. This makes observing hard, if not impossible.

When you tap the tube, a stable mount doesn't vibrate for more than a second or two. When you touch the focus knob, you should be able to tell when you have found the sharpest image, since the view should not fluctuate so much. It is critical that the goal does not shift when you let go.

All telescope mounts fall into one of several categories.

A manual altitude-azimuth mount, or alt-az, is the oldest and simplest type. The scope can be moved up and down (in altitude) as well as left and right (in azimuth) using these heads. Despite their small size, sturdy photo tripods can be used for tiny telescopes of modest magnification. The simplicity, compactness, and light weight of an alt-az mount make it ideal for recreational sky viewing or daytime use such as birdwatching.

The slow-motion controls on alt-az mounts designed for high power are often precisely threaded so that the scope can be moved smoothly in small increments. Dobsonian mounts eliminate the need for tripods by mounting a pan-tilt head directly to the ground. Most Dobsonian mounts are made of wood or particleboard, with Teflon bearings. This results in a highly effective, low-cost mount that glides smoothly along both axes. Newtonian reflectors installed this way aren't just easy to set up, but they're also cheap.

A tabletop alt-az mount was used for Galileo's 1610 telescope, which was designed to be placed on a sturdy surface. In recent years, tabletop mounts have made a comeback, with Dobsonian styles being included with many of the most popular scopes.

Equatorial mounts are basically alt-az mounts with the azimuth axis parallel to Earth's spin axis and rotate in a plane parallel to the equator instead of the ground. In this way, celestial objects appear to move as the Earth spins under you as they traverse the sky. Keeping the scope directed at your objective is as simple as rotating the polar axis in the opposite direction to the Earth's rotation.

Tracking can be accomplished with a few quick twists of a slow-motion knob, or by attaching an equatorial mount with a motor. A motorized tracking system is particularly useful at high power levels. Due to the rotation of the Earth, an equatorial mount makes tracking celestial objects easier. To track an object across the sky, the scope only needs to be rotated about one axis - and a drive motor can do this automatically. 

There are two major limitations to equatorial mounts. These mounts are heavier and thicker than equivalent alt-az mounts, and they place the telescope's eyepiece in uncomfortable positions. They remained indispensable until the motorized Dobsonian mount and computed alt-az were introduced.

Let's go to the GOTO mount. Using the Go To mount, you enter the name of the object. It will search for its celestial coordinates, determine when and where it will appear, and direct the telescope there.

You can save a great deal of time in light-polluted environments when there are few reference stars to help you spot objects. By recalculating their position every second or so, Go To mounts can track moving objects in the sky. This enables alt-az mounts to combine mechanical and ergonomic benefits with autonomous tracking, which was previously impossible.

Using a Go To telescope is easy because it contains a computer and database to make finding things easier. The disadvantage is that you need to know your naked-eye stars before you use most designs. You should keep a few things in mind when working with GoTo technology.

The first thing you have to do is initialize your Go To mount so it knows the time, location, and orientation. More expensive models can do this automatically, but most entry-level GoTo scopes require you to point them at specific stars.

With a little experience, beginners who are unfamiliar with constellations will find it simple and easy to use. GoTo mounts are not cheap. Instead of allocating half your budget to GoTo capabilities, you might be better off investing it entirely in superb optics and a sturdy manual mount. 

Last but not least, most GoTo mounts require large batteries or grid connectivity. An alternative to GoTo is PushTotechnology, which works like GoTo but does not require motors. By calculating the target's location, this mount tells you where to push the scope to reach it instead of moving the scope.

The most significant disadvantage is that you lose automatic tracking; after the scope has detected the object, it is up to you to maintain it in view. Dobsonians are easy to push because of the leverage offered by their long tubes, but hard to motorize for the same reason. push-to-scope is cheaper and lighter than a comparable go-to scope, and it can run for a long time on a small battery.


There is usually a sighting device included with most telescopes. Low-power finderscopes and red-dot finders are the most common types. 

Using a telescope at medium to high power only shows you a tiny bit of the sky. If the scope does not come with some kind of sighting device, or finder, aiming becomes frustrating.

A finderscope, a miniature telescope with crosshairs like a gunsight, is the traditional solution.

Red-dot finders and red-circle finders are two popular alternatives, which project patterns onto a transparent window. Centering an object on the dot, circle, or crosshairs aligns the finder with the main scope.

5X finderscopes at the lower end of the market tend to be of poor quality. Otherwise, you shouldn't worry too much about what finder is included with your scope. At a fairly modest cost, you can switch to another one if you don't like it. In many cases, findingerscopes combined with red-circle finders are the best of all possible worlds.


Despite the temptation, do not buy the cheapest telescope you can find. Optically, mechanically, or both, most will disappoint you due to their poor quality. When you shop carefully, you can find a decent telescope for a good price. You'll still get a very modest aperture scope. Among the cheapest scopes that make no serious compromises would be the 6- or 8-inch Dob. 

Don't buy the largest, most expensive telescope you can afford just yet, even if you have a lot of money to spend. Make it easier to manage by starting small. Most serious observers have two or more telescopes. Start with a cheaper one until you figure out what you want in the long run. This is like taking small steps when learning to swim. You may want to jump into the deep end, but it's better to begin by slowly getting used to the water. This is done by taking classes or diving in the shallow end.

Save some money for eyepieces to expand the scope's magnification range, a detailed sky atlas, helpful guidebooks, and anything else you need. People often find adjustable-height chairs to be worth their weight in gold. And, of course, don't forget to invest in space food for the long nights of stargazing - freeze-dried ice cream may be a bit of a stretch, but it's worth it for the experience!


No matter who you are or where you live, there is a telescope that's right for you. You can share the wonders of the universe through your scope - and it's never too late to start!

Do you think there's a perfect telescope out there for you? Yes, of course. Experienced observers are fond of saying that the right telescope is the one you use most often.

With our advice, you'll end up with an instrument you'll want to use every clear night.

Additionally, you can try various scopes and talk to their owners at observing nights hosted by your local astronomy club. Feel free to ask.

Thanks for reading this far. You'll have a lot of fun stargazing. Don't forget to check for aliens! ;)

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