Telescope Buying Guide
It’s a fascinating time to be in amateur astronomy! There are a lot of telescopes and accessories available at affordable prices. Choosing a telescope may seem a little daunting at first because of all the technical jargon, features and options. But with just a little bit of basic understanding, it’s easier than you might think to choose the best telescope for you.
There’s no one simple answer to the question, “what’s the best telescope to buy,” just like there isn’t one for “what’s the best car to buy.” This guide will make it easy to choose the best telescope for you, with your own personal reasons.
Consideration 1 – What Do You Want to Observe With Your Telescope?
The first step is to ask yourself what you want to do with the telescope. Deciding what you want to look at with a telescope makes it easy to narrow down your choices.
So think about what’s important to you. What do you most want to look at with your telescope? How dark is the sky where you live? How experienced of an observer are you? What fits in your budget? How much storage space do you have, and how much weight do you want to carry when you move your telescope around?
Consideration 2 – Aperture. The Most Important Feature of a Telescope
The most important feature of any telescope is its aperture. Aperture means the diameter of the telescope’s main optical component, which can be either a lens or a mirror. The size of your telescope’s aperture determines both how much light it can capture, and how sharp the image will be.
The more light that is captured, the more objects you can see in the night sky. The best recommendation is to buy as much aperture as you can afford (or can lift, since large-aperture telescopes get quite heavy).
With a 6-inch telescope you’ll be able to see craters on the Moon as small as a mile across. Pretty amazing, right? In turn, with a 3-inch scope, you’d only be able to discern craters that are 2 miles across (under the same conditions, and with the same magnification).
The same two instruments looking at a faint galaxy on a night without a moon would show an even more dramatic difference. Because the surface area of a 6-inch mirror is four times that of a 3-inch mirror, it collects four times as much light. This means that the galaxy would appear four times brighter!
Another way to think about aperture is that from a dark location, you can spot dozens of galaxies beyond our own Milky Way through a scope with an aperture of 3 inches. But you’d probably need a 6- or 8-inch aperture to see those same galaxies from a typical suburban backyard due to light pollution. And regardless of how bright or dark your sky is, the view through a telescope with more aperture will be more impressive than the view of the same object through less aperture.
Consideration 3 – Magnification. It’s Great, But it Isn’t Everything.
A telescope’s aperture doesn’t determine its magnification. Any telescope can provide almost any magnification. The magnification of a telescope is determined by the eyepiece you use. So you can change your magnification just by swapping your existing eyepiece with one that has a higher magnification.
But high magnifications alone won’t do you any good. The two main factors that limit the effectiveness of magnification without giving you a blurry image are: aperture (again) and atmospheric conditions.
There is only a limited amount of detail a telescopes main mirror or lens can create. So you need to find the optimum magnification to show the most detail without spreading out the light too much, making a dim object too dim to see, or turning a bright object into a big blur.
Good observers generally use low powers for looking at faint things like galaxies and nebulae, and no more than medium-high powers to look at bright things such as the Moon and planets. To help understand this, think about what happens when you enlarge a digital photograph too much. It looks pixelated and blurry. Excess magnification on a telescope does the same thing, just making the object you’re viewing more blurry.
So how much power is too much? The simple rule to find the top useful magnification is to multiply you telescope’s aperture in inches by 50 (assuming perfect optics and steady night air).
Another way to think of this is that a high-quality 4-inch telescope should not be pushed beyond about 200x. Even a small telescope with good optics will show you Saturn’s rings or the principal cloud belts on Jupiter, since these can be seen at a magnification of 75x. On the other hand, if you see a small, 2.5-inch telescope scope advertising “300X power,” you’ll know it’s just hype and you may want to look elsewhere.
Consideration 4 – Types of Telescopes
There are three standard telescope types, or optical designs: Refractor, Reflector, and Compound (or Catadioptric). Which one you choose will depend on the observing priorities you have. Each type is suited best to a different application, and some are more versatile than others.
Refracting telescopes, or refractors, are probably the most common telescope around, and fit the stereotype of how a telescope “looks” — a long tube with a large lens in front and an eyepiece at the back. The front lens (the objective) focuses light to form an image in the back. The eyepiece is a little magnifying glass which you look at the image through.
- Easy to use due to the simplicity of design.
- Excellent for lunar, planetary and binary stargazing, especially with larger apertures.
- Sealed tube protects optics and reduces image degrading air currents.
- Rugged. Needs little or no maintenance.
- Generally have smaller apertures, typically 3 to 5 inches.
- Smaller apertures mean less clear viewing of distant galaxies and nebulae.
- Heavier, longer and bulkier than reflector and cassegrain telescopes with the same aperture.
- Good-quality refractors cost more per inch of aperture than any other kind of telescope.
If you want to look at terrestrial objects (wildlife, etc.) as well as stars, a refractor is a good choice. If you’re only going to be stargazing, a Reflector will get you more bang for the buck.
Reflecting telescopes use mirrors instead of lenses. The eyepiece is located at the side of the main tube, up near the top. There are a variety of reflecting telescope designs, but the most common is the Newtonian.
If you want the most aperture for your money, you’ll want to strongly consider a reflector. Good quality reflectors can provide sharp, high contrast images of every kind of celestial object at a much lower cost than with an equal-aperture refractor.
For the best value, you may want to consider a particular design of reflector known as the Dobsonian. A Dobsonian is a Newtonian on a very simple, rugged mount. These popular telescopes are available with apertures from 4 inches to more than 30 inches, and might be the best in convenience for the casual viewer.
- Usually have larger apertures which mean excellent viewing of faint deep sky objects (remote galaxies, nebulae and star clusters).
- Low in optical irregularities, with very bright images.
- A reflector costs the least per inch of aperture compared to other types of telescopes, because mirrors can be produced at a lower cost than lenses.
- Generally, not suited for terrestrial applications.
- The tube is open to the air, which means dust will get on the optics, even if the tube is kept covered.
- Reflectors may require a little more care and maintenance.
A Newtonian reflector is hard to beat. If you don’t need to view terrestrial subjects, and don’t plan on doing much astrophotography, there isn’t a better telescope for the money.
Compound (or Catadioptric)
Compound telescopes use a combination of both lenses and mirrors. They offer compact tubes and are relatively light weight. Two popular designs are the Schmidt-Cassegrains and the Maksutov-Cassegrains.
Many people looking for a highly versatile, highly portable (for the aperture) telescope that can be used for viewing anything in the sky and for astrophotography will tend to choose some form of compound instrument. Telescopes of this type also tend to be the most highly “technologized,” with a lot of options for computerized pointing and photographic adaptations. In short, they’re excellent general-purpose scopes that can use a wide variety of accessories.
- Most versatile type of telescope with excellent lunar, planetary and deep space observing, plus terrestrial viewing and photography.
- Best near focus capability of any type telescope.
- First-rate for deep sky observing or astrophotography with fast films or CCD’s.
- Closed tube design reduces image degrading air currents.
- Compact and durable.
- More expensive than reflectors with the same aperture.
- Their appearance may not be to everybody’s taste.
If you want a little bit of everything, from deep-sky to planetary viewing and photography, as well as portability, a Compound telescope is a great choice. It’s the one telescope that can be used for almost any application. That, and its moderate price, make the catadioptric one of the most popular telescope designs on the market today.
Consideration 5 – Telescope Mounts
There are two basic types of telescope mounts: equatorial and alt-azimuth. Which one you choose depends on the application of the telescope, as well as portability and setup considerations. A good mount is important for stabilizing your telescope and permits it to be directed to part of the sky you’re interested in, and to follow celestial objects smoothly and precisely as the Earth turns beneath it.
An alt-az mount works like a tripod’s pan-and-tilt head, moving the scope up-down (in altitude) and left-right (in azimuth). Equatorial mounts also possess two axes, but they’re tilted so that one can be aligned with the rotational axis of the Earth.
A “stable” mount is one that won’t wiggle the telescope too much when you hold the focus knob, so you can see when you’ve found the sharpest focus. Also, when you let go of the telescope after finding and focusing, the aim shouldn’t jump to one side.
Some telescope mounts have small motors to move them around the sky. In the more advanced models of this type, often called “Go To” telescopes, a computer controls the movement. After you’ve entered the current date, time, and your location (and many newer models don’t even require you to do that), the telescope can point itself and track thousands of objects in the sky. Some “Go To”s let you choose a guided tour of the best celestial showpieces, complete with descriptions of what’s known about each object.
Consideration 6 – Your Budget For a Telescope
Deciding how much to invest in your telescope is the final consideration. Pick the telescope with the biggest aperture you can afford that meets your precise needs in the hobby. Sometimes spending a little more on a telescope ensures that you get a better one that will last you longer and that you will use more often.
The Best Telescope?
In conclusion, any telescope can literally open your eyes to a universe of delights in the sky. With a little care and though in selecting the right telescope for you personally, you’ll be ready for a lifetime of exploring the night sky. So, is there a perfect telescope out there? Actually, there is for you. It’s the one that meets your own individual needs, and the one you’ll use the most often!