So you have decided to take the plunge and invest in a telescope. Congratulations! That alone is a huge step. But unlike a television, you cannot just walk into a mall and randomly buy a telescope. There is a lot more involved in this process and if salespeople were honest, they’d tell you that they don’t always understand the needs of aspiring astronomers. This telescope buying guide provides all the information you need to ensure that invest in the right telescope for you.
The number one rule when in the market for astronomical equipment is to shun the flimsy department stores that offer cheap telescope. While there are affordable scopes for kids and beginners, it’s always vital to make sure that you purchase a quality telescope. What you want is something that meets two criteria – steady, smoothly working mount and high quality optics. You may also want something that is large and nice, but don’t forget about convenience and portability.
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Types of Telescopes
Depending on what you are looking for and budget, you will come across three types of telescopes:
The reflector telescope was invented by James Gregory and its description was published for the first time in 1663. Sir Isaac Newton was, however, the one who constructed the first reflector telescope in 1668. It was 6 inches long and had a mirror of 1.3 inches.
Modern Newtonian reflector telescopes come with two mirrors – a large, curved one at the bottom of the tube known as the primary and a small flat one near the top called the secondary. When light enters, it travels down the tube and hits the primary mirror then reflects to the secondary before being reflected to the eyepiece. Reflector telescopes are the cheapest and hence a great option for those on a budget.
It's worth nothing that reflector scopes are the biggest in size of the amateur telescopes. Because of how the mirror attaches to the tube, reflectors are prone to jostling or bumping during transportation. In addition, they suffer from a defect that causes celestial objects at the edge of the field of view to look thin and long like comets. Reflectors don’t show excess color and as such, you will not see any color fringes around the brightest objects.
Refracting telescopes utilize specially designed lenses that ensure the light comes into focus. The first refractor was made by Hans Lipperhey, a Dutch eyeglass-maker, in 1608. Galileo Galilei was the first person to used the 3x tube to view celestial objects and his experience helped revolutionize astronomy. Two terms you will come across when reading about modern refractors are apochromat and achromat.
Both describe a lens system that combines different types of light. An achromat lens has two pieces of glass and brings all colors of light into two wavelengths, blue and red, into visual focus on the same plane. Apochromat lenses, on the other hand, combine three wavelengths, red, blue and green, and are top of the line. They can combine up to four mirrors. Nothing blocks the light that passes through the lenses and as such, refractor telescopes produce images with better contrast.
The main advantage of these telescopes are that they are low maintenance as lenses don’t need coating or adjustment. Because they have a closed tube, they need time to adjust to the outside temperature when moved from a cooler or warmer location.
These are a hybrid of reflector and refractor telescopes. Bernhard Schmidt, a German astronomer, constructed the first compound telescope in 1930. It had a glass corrector plate on the front and a spherical primary mirror at the back.
This telescope served as the precursor of the modern Schmidt-Cassegrain telescope in which light enters through the corrector plate before hitting the primary plate then reflecting to the secondary mirror. The compact design is the number one advantage of compound telescopes. They come with closed tubes and as such need time to adjust to outside temperature.
Aperture is the Most Important Telescope Feature
Whether big or small, all telescopes are designed to brighten as well as magnify views of celestial objects. The different types, i.e. compound, reflector and refractor telescopes, each have their own way of achieving this. Regardless of the type, the aperture is the most important spec. The aperture refers to the diameter of the main mirror or lens that gathers light.
The lens or mirror is called the objective. Generally, bigger apertures produce sharper and brighter images. Your telescope should have at least 2.8 inch aperture, preferably more. A larger aperture will allow you to see finer details and more distant objects better than a small aperture. Stay clear of telescopes that are primarily advertised on the basis of their magnification.
This is particularly true if they have implausible powers like 600x. The reason is that the maximum telescope magnification that’s useful is 50 times its aperture.
A bigger aperture allows for use of higher magnification. However, changing the eyepieces enables one to use any preferred magnification regardless of what telescope they use. It’s important to note that without a large aperture, high magnification will be worthless.
In addition, telescopes will only magnify objects up to a power of 50x before the Rings of Saturn, Moons of the Jupiter and other celestial objects start to appear blurry. Expect to get anywhere from 20x to 50x useful magnification depending on the observing conditions as well as the optical quality.
You need to think twice about a product whose package advertising super-high power. A big aperture is different from high magnification in that the former allows one to view fainter objects.
This is important as the main problem with viewing celestial objects is that many of them are faint, not too small. Seeing such objects requires more light or, in other words, more aperture.
Telescope Mounts and Drives
Just as a car can’t do without wheels and a chassis, so can’t a telescope do without a mount. The optical tube only makes half the telescope while the mount makes the other half. An unstable mount will lead to poor quality images and if it is too light, the wind will not be your friend. The popular types of telescope mounts include:
- Alt-azimuth mounts: The name is coined from altitude and azimuth. It's the simplest type of mount and moves right and left (azimuth) as well as up and down (altitude). The photo tripod is a good example of an alt-azimuth mount. These mounts are generally lighter compared to equatorial mounts, partially because they don’t require counterweights to balance the scope.
- Dobsonian mounts: The history of these mounts can be traced to the 1960s when John Dobson made a special type of alt-azimuth mount that now bears his name. These mounts are the cheapest and are often combined with a reflector. As the tube sits loosely in the mount, carrying the two parts is easy.
- Equatorial mounts: An alt-azimuth mouth would be all we needed if the Earth didn’t move around the sun. However, we must deal with the fact that it does spin and that’s where the equatorial mount comes in. Its origin dates to the early 19th century when Joseph von Fraunhofer, a German optician, invented it in the hopes of tracking the stars.
He aligned one of the axes parallel to the Earth’s axis and utilized a weight-driven clock drive to move it at the same rate as the Earth’s spin. Modern equatorial mounts incorporate a motor that moves them, thus allowing the telescope to follow the stars as they move across the sky.
- Go-to mounts and drives: This is a recent development whose creation involves attaching motors to the altitude and azimuth axes. The motors are also connected to an onboard computer. The go-to drive finds and tracks celestial objects as long as it’s been set up properly. Mounts that incorporate this system are very accurate, hence their popularity among astronomers. Many modern go-to mounts have databases with information on thousands of objects that they have been tracking.
Understanding the Eyepieces
Eyepieces are like stereo equipment. You want a sound system that produces music as close to the original as possible. The same concept applies when it comes to eyepieces. The best ones contain several highly polished and coated lenses made from specialised glass, hence they are expensive.
Manufacturers often apply ultra-thin layers to lenses in a bid to reduce stray light and increase the amount that passes through. Many astronomers don’t understand why one has to spend so much on eyepieces, but truth be told, this is a long-term investment as you won’t be required to buy new ones when upgrading your telescope.
One of the most important factors to consider when buying eyepieces is their weight. As ridiculous as it sounds, some weigh as much as 2lbs. Go for lighter pieces if your telescope is small or medium. The field of view is also crucial. You will come across two numbers – the true field of view and the apparent field view.
The latter describes the angle at which light enters the eyepiece and can be anything from 24 degrees to 84 degrees. The former refers to the amount of sky seen when looking through the eyepiece and this changes from one telescope to another.
Barlow lenses are an optical accessory that helps improve the magnification of an eyepiece. They go between the eyepiece and the focuser. They can magnify 2x, 3x, 4x and so on. If you use a 2x Barlow lens in a telescope whose eyepiece is 18mm and gives a magnification of 100x, then it will produce a 200x magnification.
What Accessories Will You Need?
We have covered a lot of ground but hopefully, the tech talk you get from sales representatives now makes more sense. Needless to say, we still have to discuss a few more topics before we set you loose on your hunt for a new telescope. Many people make the mistake of thinking about the big things they see in catalogues. They forget that just as you need keys to drive a car, there are other essentials required to use a telescope. Such include:
- Finder scopes: The best telescope in the world will be useless if one cannot find anything with it. The reason is that high magnification limits the field of view. Even with a go-to mount and drive, a high quality finder scope is important when using a telescope.
Go for one whose front lens has a minimum diameter of 2 inches (50mm). This allows enough light in and eliminates the frustration of trying to find faint objects. The magnification should range from 7x to 9x.
- Power supplies: Consider yourself lucky if you observe from a place that has access to electicity. If you don’t fit within that category, you will need some form of portable power. You can use your car battery if you have the right adapter. A dedicated power supply is also a good option.
The Celestron Power-Tank 17 is one of the best dedicated power supplies. It comes with two 12-volt DC car-style outlets, 17 amp/hour battery, a siren, white spotlight, an AM/FM radio and a red-filtered flashlight.
- Lights: This is particularly important if you plan on using star chart while observing in the night. Red light is best recommended as it affects night vision the least. Keep in mind that even red light will interfere with how well you see through the telescope as your eyes will have to re-adjust to the light. With that in mind, a flashlight that lets you adjust the brightness is probably best.
- Star charts: You need a road map to find your way when you fire up the engine and hit the road in a car, especially if you are in a new territory. The same is true when you purchase a telescope. Expert astronomers use the biggest and most detailed sky charts they can find. You may already own a planisphere, a rotating wheel that helps identify constellations.
Basic knowledge about how to use such a wide-constellation map is crucial when embarking on telescopic astronomy. However, it’s important to note that you will need more than just a planisphere if you want to mine the sky’s riches. An 8th magnitude atlas will suffice.
- Filters: These help you observe more details. Astronomical filters are available in two varieties; light pollution reduction filters, which reduce artificial light so that you can see the nebule better, and color filters, which enhance viewing of objects.
- Light pollution reduction filters (LPR): They are effective because outdoor lights produce only a few distinct colors. For example, mercury vapor lamps give off blue and green light while high-pressure sodium vapor streetlights shine yellow. However, these filters are not a solve-all.
They do little to reduce the impact of incandescent and car lights as they give off all kinds of visible colors. This means you should choose your observing site carefully.
- Color filters: These are designed to improve clarity even when using lower quality telescopes. They work by boosting the contrast between areas on the surface or atmosphere of the planets. They work best when used with large telescopes because then the only thing that matters is natural light. Light blue filters let 73% of the light pass through, hence best for small scopes.
- Moon filters: Otherwise known as the neutral density filters, these reduce amount of light by absorbing it rather than changing or filtering the color. They let up to 80% light pass through, making them ideal for observing the moon and planets.
The fact that some new discovery in the night sky is always making the news is one of the things that makes astronomy exciting. But just because you are an amateur astronomer doesn’t mean that you can’t participate. But how do you start observing the sky? While learning the sky in a general sense helps, choosing the right telescope also matters a great deal.
There are many factors that you will need to think about when choosing your telescope, ranging from optics quality to mounts and accessories. Understanding the types of telescopes is something one has to do and so is choosing the right observation location. All of these are discussed in this one stop telescope buying guide. Other sources that might be of help include, Extended Telescope for Beginners Guide, What To Know Before You Buy, Guide to Buying Your First Telescope.
We hope that this has lessened the stress of shopping for a telescope. Feel like we have left out anything? Let us know in the comment section.