Whether you are a beginner or a hobbyist looking for an upgrade, a good telescope gives you the chance to observe the heavens and discover distant stars and planets. It engages you in an adventure of discovery by uncovering tiny details you cannot see with the naked eye. With several brands and models available, you need to know which one is right for you.
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This guide looks at various types of telescopes, features, peculiarities, and uses so that you will have the best stargazing experience and intense exploration of the larger universe.
When browsing for telescopes, you'll likely find three popular styles — refractors, reflectors, and catadioptric telescopes. While all of these telescopes will zoom in on elements, their features and designs differ.
A refractor is the most common telescope you’ll find. It has an extended gleaming tube and a large lens at the front, with an eyepiece at the back. This type of telescope delivers brighter and sharper images as the aperture increases because there’s no mirror in front to block incoming light.
While a refractor telescope is available in various categories and is relatively affordable, be prepared to spend more with each advanced aperture. With a top-quality, 40-inch refractor, you will quickly see objects deep in the sky, including surface details on Jupiter, Saturn, and Mars. Also, refractors are generally rugged, with lenses that hardly fall out of alignment. They are also lightweight and portable, making viewings of darker skies enjoyable.
To minimize false color, such as when a bright star looks like a rainbow-tinted blur, you’ll need to get special glasses or use long focal ratios. You can also buy a tripod to support the pivot point above the head as you embark on a thrilling stargazing experience.
Unlike the refractor type, a reflector telescope has an inbuilt mirror at the end of the tube. The mirror gathers and focuses light to send to another mirror before hitting the eyepiece. The most common model is the Newtonian reflector with a dish-shaped mirror at the telescope’s end and a diagonal secondary mirror directing light from the primary mirror to the side of the telescope tube.
You can find a reflector with an aperture that’s good enough to provide you with sharp images of celestial objects for a small fraction of what its refractor counterpart costs. A reflector is the best option for anyone looking to view faint objects, and its image quality supersedes that of a refractor telescope.
A reflector telescope is more expensive than the refractor kind, though, and requires periodic collimation or adjustment. Its mirrors sometimes fall out of alignment, especially when moved around, so you’ll need to adjust for peak performance. Also, its tube is open, which means regular maintenance is required if you want to keep it from gathering dust.
Also known as a compound telescope, the catadioptric variety combines the best features of refractors and reflectors by utilizing mirrors and lenses to form clear images. It has a mirror in the front and another at the back, working together to produce high-quality images.
The common ones are Schmidt-Cassegrains and Maksutov-Cassegrains, with focal ratios preventing the production of wide, low-power fields of view. You can buy a focal reducer to fix this, though.
Catadioptric telescopes are best for astrophotography and work well for faint and earth objects, but they are bulkier and often more expensive than other telescopes. Also, the additional mirror reduces image brightness, and they take longer to cool down and adjust to the night air temperature, which is required for high-power imaging. So you might need to leave your catadioptric telescope outdoors for pre-cooling ahead of use.
To get the best value from a telescope, you must understand the basic components of one. Here are a few features you should focus on when you're looking to buy a telescope.
The main component of a telescope is the aperture, which represents a mirror in the scope or the diameter of the lens. Generally, a bigger aperture is better for more visibility. A telescope with a larger aperture will allow more light in the eyepiece, with deeper sight into space and better image quality even for faint objects.
The diameter of the lens is called the objective and is often measured in millimeters. You’ll find a telescope’s specifications near the focuser at the front of the telescope’s tube or its box. It should read at least 70 mm or 2.8 inches.
The larger an aperture, the more impressive the imaging you’ll get. So a larger aperture size will give you finer, detailed images and allow you to see faint objects from afar. Planets, for instance, look clearer and objects like nebulae and galaxies seem bolder. Bear in mind, though, that telescopes with bigger lenses or mirrors are heavier and often challenging to move around.
Magnification refers to the number of times an object appears in size compared to when viewed with the naked eye. You can calculate magnification by dividing the eyepiece's focal length into the telescope’s focal length. For example, a telescope with a mm focal length that uses a 25mm eyepiece produces a magnification of 60x. This specification implies that you’ll achieve a higher magnification with a longer telescope focal length and shorter eyepiece focal length.
Beginners should note that while a higher magnification setting may mean more power, it often comes with issues such as decreased image brightness, vibrations, shortened eye relief, and a diminished exit pupil that makes it difficult to see anything in the dark. So, for beginners, lower magnifications are typically better.
The optimum magnification for most objects is between 8× and 40× per inch of aperture for deep-sky objects, like galaxies, nebulae, and clusters. A good rule of thumb for anyone using a telescope is to go for a magnification that's twice the telescope’s aperture in millimeters.
While every telescope can magnify objects in the sky, the eyepiece and focal length determine the magnification level. Focal length is the total distance between your telescope’s focal point and lens or mirror. More focal length makes objects appear bigger.
Measured in millimeters, the focal length is that number engraved on the front or back of your scope, and it’s often between 400 millimeters and 3,000 millimeters. When you divide the telescope’s focal length by its aperture, you’ll get the focal ratio written as “f/” and followed by a number. Most telescope focal ratios fall between f/4 and f/15.
Those between f/10 and f/15 usually work well for planetary observation since they cannot provide wide-field, low-power views that many deep-sky observers prefer. On the other hand, telescopes with focal ratios of f/4 to f/4.5 provide great low-power views and work best with complex eyepieces. They can hardly focus at high power, though, unless you equip the scope with a precision focuser. For a compromise between both preferences, focal ratios f/5 to f/8 come highly recommended as they typically provide a decent wide-field capability.
For effective usage, you need something solid to support your telescope. While some telescopes come with mounts or tripods, others only have the mounting block for easy attachment to a tripod. This hardly-appreciated component is responsible for the alignment, movement, and tracking of celestial objects, and its two major types are Alt-Azimuth and German Equatorial.
The Alt-Azimuth allows you to move the scope up and down, left and right. Next is the equatorial mount that tracks celestial objects through one-axis turns you can motorize. They are often larger and heavier, and you’ll need to align the mount to Polaris if you want to enjoy it.
With different types of telescopes to choose from and varying maintenance options and price ranges, you must consider a few things when choosing a telescope for kids or adults.
Before deciding on whether to buy a reflector, refractor, or catadioptric telescope, you need to understand what’s important to you. What do you want to do with the telescope? You can get a refractor or reflector telescope if you’re just getting started with the hobby. For astrophotography, you will need a compound scope.
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If you want to avoid regular maintenance, choose a refractor telescope. A reflector or compound telescope is the best option for observing birds and viewing objects far up in the sky.
Most modern telescopes come as complete sets, so they don’t require additional purchases. But some high-end optics do not come with a mount, finder, or other accessories. Checking what is included before buying is a good idea to be sure you will not need to buy an accessory.
For example, do not buy a refractor telescope if you would rather not buy accessories — like the star diagonal for bending light away from a target object.
Telescopes vary in price. They can cost as low as $150 to upwards of thousands of dollars. So it is good to set your budget from the beginning and go for products within your stipulated budget. Meanwhile, make sure that you do not go for subpar products to save some money. This will only lead to more expenses on repairs or entirely new purchases.
Consider the weight and collapsibility of the telescope when buying, especially if the purpose of purchase involves transporting it from one site to another.
Many telescopes are now designed to automatically locate objects in the sky. While not every astronomy hobbyist needs this feature, you should consider buying an electronic telescope with a built-in computer if you're considering astrophotography.
To achieve the best results and be able to use your telescope for an extended period, here are a few tips.
The universe is full of wonders, but they are hard to notice without a telescope. The right one can unlock fine details that are hidden to the naked eye. To properly observe these celestial objects and gain the right view of the Earth, you need a telescope you can rely on to function properly without having to break the bank.
Whether you choose a reflector, refractor, or catadioptric telescope, you should consider buying one from a reliable online retailer like AmScope. We can answer all the questions you have about buying the right telescope, whether you are an avid hobbyist or a beginner in the world of astronomy.
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Note: please also check out our Youtube video on How to Buy a Telescope.
Amateur Astronomy is one of the most fascinating hobbies in the world, but to get really into it, you probably will want to get a telescope either for yourself or perhaps for a son or daughter who is showing an interest in the wonders of the universe. Somehow, you will have to find your way through the maze of ads, catalogs, claims and counterclaims about which telescope is best or the least expensive. You may be asking yourself questions like “What type should it be?”, or “Just what should I believe when I read the ads?”. Finally, you will have to lay out the cold hard cash needed to purchase what you hope will be the best instrument your money can buy. If you are a bit confused or frustrated at this point, don’t worry. We of the Prairie Astronomy Club know exactly how you feel, because we have all gone through this many times before. This article should help answer many of the questions you may have about purchasing a telescope as well as clearing up some of the mysteries about astronomical telescopes in general. It was assembled by our club members using the many years of experience they have in selecting, buying, building, and using telescopes. They all had to buy that “first telescope”, and hopefully, you can benefit from their hindsight.
TELESCOPES IN GENERAL: A telescope has two main functions: (1) to gather and focus a large amount of light from an object (much more than the eye alone can) to form an image of the object, and (2) to magnify that image so that distant objects can be better seen. There are many different designs of telescope that will accomplish these functions but only two designs are practical for small inexpensive telescopes: the refractor and the Newtonian Reflector. A refractor (figure A) focuses light by “refracting” or bending it through a special two element glass lens. A reflector (figure B) focuses light by reflecting it off a curved mirror. A set of lenses known as the Eyepiece then magnifies the focused image in each design.
Telescope performance depends primarily on the diameter of the main lens or curved mirror, whichever is used. This diameter is commonly known as the APERTURE. The larger the aperture is, the more light is gathered and the better the image will be. Aperture is usually measured in inches, with commonly available sizes being 2.4 and 3 inch refractors and 4.25, 6 and 8 inch reflectors. Another term used in describing telescopes is the FOCAL LENGTH. It is simply the distance from the lens or the main mirror’s surface to the point where the light comes to a focus. The two terms (aperture and focal length) are sometimes combined into the F-RATIO, which is just the focal length divided by the aperture. Thus if a telescope has a 6-inch mirror and a focal length of 48 inches, its f-ratio (or f/) is f/8. The f-ratio is often quoted instead of the focal length since it is a useful way of quickly stating what the focal length is regardless of the units of measurement for the aperture. The focal length of a telescope also helps determine another useful item, the MAGNIFICATION, or “power” of a telescope. The magnification of a telescope increases the apparent size of an object to a point where the human eye or camera can easily view it. Magnification is changed by changing the eyepiece being used. The “power” of a telescope is determined by dividing the focal length of the telescope by the focal length of the eyepiece, which is usually marked on the eyepiece barrel in millimeters. Thus if you had a telescope with a focal length of 48 inches ( mm) and were using an eyepiece with a 9 mm focal length, you would be using about 135x, and the object being viewed would look 135 times larger than it does to the unaided eye.There is a catch to using high power! Higher magnification, while making the object appear larger, spreads out the light gathered by the telescope over a larger area resulting in a fainter image. Also, because of the restrictions imposed on eyepiece design, you may only see part of that big image due to the smaller “field of view” high powers give you. Very long f-ratio telescopes can give you higher power with a given eyepiece, but you may not be getting much out of those powers if the light is too spread out. You have to compromise to get the best results.
At this time we must cover a very important point:– Do not be fooled by an advertiser’s claims of a “high-power” telescope!!! There is no theoretical limit on power, but there is a practical limit beyond which the images obtained are worthless. Because of the way light behaves, the MAXIMUM USABLE POWER is about 50 times the diameter of the main mirror or lens in inches or 50 POWER PER INCH of aperture. Using magnifications much beyond this will make the picture dim and very very fuzzy, like using a microscope on a newspaper picture or blowing up a photograph too much. For example, a common 2.4 inch refractor has a maximum usable power of about 120x, but we frequently see ads in major catalogs or retail chain stores advertising this same telescope as having “over 400 power !!!”. You would have trouble seeing anything at 400x in such a small instrument, although it might perform well at low magnification. Most astronomical objects except the moon and planets require very low powers to be seen at all, so the so-called “high power” would do you little good. In short: don’t buy a telescope just because it is advertised as having “high power”. Aperture and quality in a telescope are worth much more than power any day.
Telescope Types: Which is Best? The least expensive types of telescopes (small refractors and Newtonian reflectors) both have many advantages and disadvantages. The Refractor is probably the first type of astronomical telescope most people encounter so we will deal with it first. Because different colors of light are bent differently, a refracting telescope must use a special compound main lens which consists of at least two lenses of different shape and glass type to correct for this unequal bending (known as Chromatic Aberration). In addition, all of the glass surfaces must be coated with a thin layer of material which enhances contrast and reduces unwanted reflections. The main lens is mounted firmly at the front of the telescope tube, and when the eyepiece is in place, the tube is closed, keeping dust or air currents out. Refractors require little maintenance, although they must be handled with care to prevent scratching or damaging the delicate coatings on all the glass surfaces. They provide good high-contrast images, and are fairly popular with those who observe the moon and the planets exclusively. Their major good and bad points are summarized in the following chart.
A refractor may give slightly better high power views than a reflector, but the refractor can cost well over three times as much as a reflector of the same size! It is for this reason that most amateurs prefer the Newtonian reflector over the refractor for apertures larger than four inches.
Other Telescope Designs: A newer design which has a price somewhere between that of a refractor and a reflector is the so-called CATADIOPTRIC, or “mirror-lens” telescope. It uses a curved main mirror, an oppositely curved secondary mirror, and a special large correcting lens out front to obtain sharp images over a wide field of view. Catadioptric telescopes offer large aperture performance in a package that in some cases is small enough to sit on a table top! Their portability makes them popular with those advanced amateurs who don’t have room for a large Newtonian or refractor, but their price usually makes them out of reach of most beginners’ pocketbooks. You may see them listed under the names “Schmidt-Cassegrain”, or “Maksutov”, each of which uses a somewhat different optical design to do the same thing.
Telescope Mountings: Most astronomical telescopes cannot be hand-held like binoculars, so some sort of mount or stand must be used to hold the instrument and allow it to be pointed at any object in the sky. There is nothing more frustrating than having a good telescope on a mount that makes the images jiggle and dance every time the wind blows, so a good solid steady mount is a must. Many cheap telescopes found in stores have small metal tripods with thin legs and small screw-tightened pivot points for bearings. We call these “pillar and claw” mounts and they are the worst possible way to mount a telescope. The single tiny support bearings are so small that the telescope vibrates like a tuning fork when touched. Most camera tripods are almost as bad. The mount must be designed to support the telescope well and to damp out vibration while at the same time make the instrument easy to point. There are two basic types of mountings: the Altazimuth (figure C), and the Equatorial (figure D). The altazimuth is a good simple design that allows the telescope to tip up and down and to rotate around in a circle somewhat like a gun turret on a ship. It can point at any area in the sky and is easy to use especially for the beginner. The equatorial mount is the design favored by serious amateurs because it allows the instrument to follow the motion of the stars using movement around one axis instead of two. If equipped with a device called a clock drive, it will follow the stars automatically without the user’s help. This is a real convenience at high powers where the earth’s rotation causes many objects to drift out of the field of view in only a few seconds. The equatorial is heavier, a bit more expensive, and somewhat harder for the beginner to get used to than the altazimuth. Both mounts will work well if the bearings are large enough and the tripod or pedestal used with the mount is sturdy.
Binoculars: Binoculars are really two small refractors mounted side by side that use special prisms to “fold” the optical path of the light and make the instrument very short. They are described by two numbers (ie: 7 x 35), the first giving the magnification and the second giving the diameter of the main objective lenses in millimeters. In astronomy, binoculars can be used to see many more stars than the eye alone can, revealing many faint star clusters, nebulae, and even a few galaxies. Camera tripod mounts for binoculars are also available, and they help make the view steadier and more comfortable during longer viewing sessions. Binoculars will show many of the larger craters on the moon, as well as the four brightest moons of Jupiter. Their wide field and low power make binoculars an excellent choice for studying the brighter comets that occasionally appear. They also have the advantage of a right-side up image, something most astronomical telescopes don’t have. For astronomy work, we suggest the 7 x 50 wide-angle binoculars available for as low as $90. Binoculars can’t show you as much as a telescope, but they are an excellent way to get your feet wet in the hobby of amateur astronomy.
Refractors: There are basically two sizes of refractors that are suitable for beginners: the 2.4-inch (60mm) refractor, and the 3.1 inch (80mm) refractor. The 2.4-inch is the most common and is available in various focal lengths and on both types of mounts. The 2.4-inch runs from about $170 for an altazimuthly mounted 700mm focal length, to about $350 for a 900mm focal length equatorially mounted instrument. The 3.1 inch is considered an instrument for serious amateurs and is usually mounted equatorially for about $450 to $600. Many refractors smaller than 2.4 inches are often poorly made and generally not worth the money, except as small spotting or finder telescopes. Refractors larger than 3.1 inches are also available, but they are rather expensive. Most of the small refractors are made in Japan and come with a small telescope or “finder” mounted on the side of the refractor, as well as with one or two eyepieces.Finders are a must since the main telescope frequently has a fairly small field of view making pointing it at anything without using the finder very difficult. A 60mm refractor with a 20x to 60x zoom feature may also a good buy since it uses fewer eyepieces.
Reflectors: The two most popular sizes for the beginner are the 4.5 inch and 6 inch reflectors. The 4.5 inch size comes in a variety of focal lengths from 17 inches (f/4 “rich field” telescope) to 45 inches (planetary scope), and most are in the $250 to $500 price range. The good ones come with a finder and several eyepieces along with a Barlow or “booster” lens for higher powers. Newtonian reflecting telescopes are generally impractical in sizes under 3 inches and we know of few quality reflectors on the market under 4 inches in aperture (most are just junk mounted on the infamous “pillar and claw” mount, so beware of them). If you are at all handy with tools, you can buy the optics for the 4.5 inch scope in a kit and build the telescope using wood, plumbing fixtures, and a few spare weekends of time. Your total cost can be fairly low, and plans or parts sources can be found on many Internet sites or in Sky and Telescope and ASTRONOMY magazines.
One of the most popular telescopes among amateurs is the 6 inch Newtonian. It offers good light grasp and allows a wide range of powers at a fairly reasonable cost ($400 bare bones to $800 for one fully equipped, equatorially mounted and clock driven). These telescopes can be home built for under $300 and hold their resale value well. Large altazimuthly mounted short focus Newtonians commonly known as “Dobsonians” are also inexpensive with many 8 inch models selling for as low as $500. Their short f-ratio means they must use somewhat more expensive eyepieces. Also, many do not come with finders.
Buying Telescopes: Some camera or hobby stores have in stock or can order some of the more popular telescopes and accessories. However, there are no “telescope stores” in this area where you can go to see the full range of products from a variety of manufacturers. Some department stores sell a few 2.4 inch refractors, but be very careful when buying one of these. You should beware of any retailer making exaggerated performance claims (ie: over 120x for a 2.4 inch refractor). Check to see whether it has a good sturdy mount and clear crisp images at high power. Excessive color fringes around bright objects can mean poor optics, so look through the telescope before you buy it (the main lens should be called an “achromat” by the manufacturer). Also, make sure the finder gives good images and is mounted securely with metal, rather than plastic.Most amateur astronomers in this area buy from mail order companies that advertise in magazines such as Sky and Telescope or ASTRONOMY (available at local libraries and bookstores). Most of these firms are reputable and sell quality instruments, parts, or accessories. These magazines also have classified ad sections where used equipment is advertised, often with much lower prices than new instruments. The local Astronomy club is also a good source of information on new as well as used equipment. Occasionally, newspaper ads or garage sales can prove fruitful in the search for used telescopes.
Some Recommendations: For a young student or a beginner who is not sure of his/her interest in astronomy or who doesn’t want to spend much money, we recommend a short focal length (700mm or so) 2.4 inch (60mm) refractor on a good sturdy altazimuth mount. Also, binoculars are a good choice for stargazing as well as for other more down-to-earth uses.For the older child or for someone interested in astronomy as a part-time hobby, the 4.5 inch reflecting telescope is a good choice (from f/4 for wide angle views to f/10 for higher power lunar and planetary viewing). For the person with a serious interest in astronomy who wants to start seeing the sights immediately, we recommend a 6 inch “Dobsonian” Newtonian reflector on an altazimuth mount. The person who likes building things may want to build their own telescope from scratch or from parts and optics that are commercially made. A great deal of money can be saved by building, and the builder can take real pride in a customized instrument of his own making. A monthly column on telescope making appears in Sky and Telescope and there is even a magazine that deals with telescope making only. About a third of all telescope owners make their own instruments. The local Astronomy club can show you the many different approaches people have to instrument design and construction.
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