The Best Thing to Do First Is to Not Buy a Telescope
Before rushing to buy a telescope or any other piece of astronomy gear, I strongly suggest you do three simple things.
First, simply look up! The simple act of first using the naked eye to observe the night sky can itself be a surprisingly instructive thing. I remember the time when I first started to pay attention to the sky at night and realized that what I thought was a bright star was in fact the planet Saturn. This epiphany fed my desire to learn more. You’ll get a feel for the rhythms of the lunar phases, and you’ll begin to identify various bright stars and some constellations.
Use the excellent star charts available for free at Skymaps.com to begin your visual naked eye journey.
Second, get your hands on a quality introductory book on astronomy. Perhaps it’s ironic of me to point this out on a website, but don’t depend exclusively on what you read on the internet. There is no substitute for a well-written and vetted piece of writing by an experienced amateur astronomer.
Terence Dickinson’s NightWatch: A Practical Guide to Viewing the Universe stands out as the very best introduction to the hobby. Be sure to get the latest edition, which at the time of this writing is the fourth edition and has content that is current until 2025. Dickinson offers valuable advice on gear, information on what you can see with that gear, basic star maps, and other practical and highly useful information. There is an especially helpful and straightforward chapter on telescopes. This was my first astronomy book, and I still reach for it after all these years. It was the best money I ever spent on the hobby.
An excellent supplement to NightWatch is Dickinson and Alan Dyer’s Backyard Astronomer’s Guide, which is jam-packed with useful insight and is also very much worth the money.
Your local library may very well have copies of both these books. Seek them out.
Try Before You Buy
Third, attend a star party put on by a local astronomy club or organization. Most will have some kind of ongoing public outreach effort. These events are great opportunities to have a first peak through different types of telescopes and to get a first-hand feel for them.
You’ll encounter many individuals who are eager to share the view through their scopes, and they are typically just as eager to share their opinions about them. They say that the problem is not getting amateur astronomers to talk about their telescopes, it’s getting them to shut up.
After seeing the night sky with the naked eye, learning more about the hobby by reading a good book or two, and interacting with experienced amateur astronomers and their telescopes, you’ll be in a far better position to make a selection that’s right for you.
When you finally arrive at the point when you’re ready to make a purchase, ask yourself three questions:
How Much Are You Willing to Spend?
Is your budget fifty dollars? Two hundred dollars? Two thousand dollars? Set your upper-most boundary. If you decide that $500 is your limit, I bet there will be a package available out there for $550 that is just a little bit better, so it’s important to have an idea about what dollar amount represents too much to spend on your first telescope setup.
When deciding on that amount, don’t forget to consider all of the gear you’ll need: telescope, mount, eyepieces, and a few other key accessories. Things can add up fast, so take it easy at first. Astronomy doesn’t have to be a pricey undertaking that requires a spending spree to get started.
But while “more expensive” doesn’t always translate into “better,” remember that you generally get what you pay for. Since the astronomy gear market is a highly competitive one, the price you pay often determines the quality you’ll get. Set your expectations realistically.
Generally speaking, packages that cost less than around $150 tend to have numerous serious drawbacks. There are some notable exceptions, but if the total setup is on the low end of the price range, the manufacturer has probably cut so many corners that it is fatally flawed in some critical way: flimsy mount, inferior optics, appalling eyepieces, dreadful accessories, etc. At around $300, your options for quality gear increases markedly, at $400 all the more so, and so forth. Again, you get what you pay for.
What Do You Want to Observe?
Are you mainly interested in observing the moon and planets? What about dimmer galaxies and nebulae? Some star clusters look great in smaller scopes, but others need more aperture in order to have that “wow” effect at the eyepiece. Different types of scopes are better for particular types of observing than others.
Where Are You Going to Observe?
This question is somewhat related to the previous one. Do you plan on doing most of your observing in the city under light-polluted skies, in the country under dark skies, or a combination of both? Some objects, namely the Moon and the planets, look just as good in the city as they do in the country. Other objects really need dark skies in order to be even visible in the eyepiece.
Just as different telescope designs excel at different types of objects, so too do different designs function better under light-polluted conditions in urban settings. I discuss this in greater detail below.
If one’s intention is to make frequent trips to sites under darker skies, an important consideration is the portability of a setup and how easy it is to assemble and disassemble. Don’t forget that, unless you stay up until dawn, you’ll be doing the latter in the dark. Make sure what you get is manageable.
Using Binoculars to Observe the Night Sky
Some say that binoculars are a great first “telescope” in that they provide a low-cost, easy-to-use set of optics for astronomical observing. Some love using their binoculars for taking in wide-field views in a simple, handheld instrument.
Personally speaking, sometimes I find myself grabbing the pair of 8 x 56 binoculars that I got during my early days in the hobby. But I’ve never really been drawn to observing with binoculars on a regular basis. My main objection is my inability to hold them steady when they’re pointed up and preventing the shaking that’s obvious when I’m using them to observe the heavens. You can get a binocular tripod, but at that point you’re getting beyond the realm of what a simple setup should be. Also, with a few exceptions, my preference is to observe most objects at a magnification higher than what handheld binoculars can offer.
If you already have an unused pair sitting in a closet, by all means get them out and point them up at the night sky. You’ll be shocked by how much you’re able to see even in the city. I know I was my first time.
The Three Mains Types of Gear
The three most important types of astronomy gear are the telescope, the mount, and the eyepiece.
This is really important: aperture is by far the most important characteristic to consider. A telescope’s main job is not to magnify but to gather light and bring it to a point of focus. The more a telescope gathers light, the brighter and better resolved it can render an object especially at higher magnifications.
A telescope’s ability to gather light is directly related to the aperture of the thing that gathers light (a lens or a mirror). Remember how to calculate the area of a circle? The area of a six-inch circle has an area that is over twice as large as that of a four-inch circle, so a six-inch aperture will gather that much more light than a four-inch aperture.
But the quality of your optics plays an important role, too. A telescope with smaller aperture and excellent optics is more of a pleasure to use than one with bigger aperture and second-rate optics. Some amateur astronomers I know will sacrifice aperture for optical quality if the choice is forced upon them.
Generally speaking, though, remember the most important thing: APERTURE, APERTURE, APERTURE.
The focal length of a telescope is the length (usually measured in millimeters) between the point at which the telescope begins to gather light and the point at which it brings it to a single point of focus. The longer the focal length of a telescope, the more it magnifies and the narrower its field of view.
A telescope’s focal ratio is simply its focal length divided by its aperture. For instance, a telescope with a focal length of 1200m and an aperture of 150mm will have a focal ratio of f/8.
Unlike in photography, where a lower or “faster” focal ratio results in a brighter exposure as compared to what a higher or “slower” ratio accomplishes using the same exposure speed, telescopes of the same aperture but different focal ratios will produce an image with the same brightness when used visually. The main effect that focal ratio has is by determining the lowest power that the telescope is capable of operating under. The lower the focal ratio for a given aperture, the higher that lowest magnification power is.
Also, telescopes with a higher focal ratio—a “slower” scope, to borrow photography language—tend to be more forgiving on eyepiece performance since the cone of focused light entering the eyepiece is less steep. When used in “faster” scopes with a lower focal ratio, simpler and less expensive eyepieces will exhibit visual aberrations especially around the edge of the field of view.
Another consideration to take into account is that making well-figured optics for telescope with a higher focal ratio can also be a very difficult and thus a rather expensive undertaking. Telescopes with a higher focal ratio tend to have optics that are easier to make well and are thus less expensive than scopes with a lower focal ratio but equal optical quality.
Unfortunately, there is no such thing as the perfect telescope for all applications. It’s important to note that all telescope designs represent compromises among various factors: aperture, the length of the telescope’s tube, portability, optical quality, and price. If you get some benefits here, you lose some other benefits there.
Here’s a brief comparison of the most common telescope types:
|Type||Brief Description||Advantages||Disadvantages||Best Uses|
|Refractors||A group of lenses spanning the front of the telescope brings light to focus at the back.||Unobstructed optics provide sharp, high-contrast views. Simple, rugged design. Relatively lightweight.||Smaller aperture limits how visible dimmer objects are. Achromatic refractors can show false color especially at lower focal ratios. Apochromatic refractors reduce or altogether eliminate false color but carry a very high price relative to aperture.||Lunar, planetary, and double-star observing. Refractors with lower focal ratios offer wide-field observing opportunities.|
|Reflectors||A concave primary mirror at the back of the telescope brings light to a focus as it reflects it back to the front. A secondary mirror near the front reflects light up to the user.||Largest aperture and best light grasp for the money. Simple design. Well suited to tinkerers.||Bulky and cumbersome, especially 8-inch scopes and larger. Secondary mirror obstruction reduces sharpness and contrast especially in faster scopes. Requires collimation, which can be harder to achieve in scopes with a lower focal ratio.||Observing fainter deep space objects under darker skies. Reflectors with lower focal ratios offer wide-field observing opportunities.|
|Catadioptrics||A combination of a correcting lens in the front of the telescope, a concave primary mirror at the back, and a secondary mirror in the front work together to focus light in a compact tube.||Very compact and easy to handle. Perhaps the most versatile design.||Somewhat higher price relative to aperture compared to reflectors. Schmidt-Cassegrains may require infrequent collimation. Secondary mirror obstruction reduces sharpness and contrast. Narrower field of view.||Situations where a jack of all trades is best. Catadioptrics are all-around instruments that are often satisfyingly good at everything, but not truly excellent at anything. A favorite of urban observers.|
Refractors are what would come to mind for most people when they imagine a telescope. And perhaps for a good reason: they’ve been around at least since the seventeenth century. In 1608, Dutch spectacle maker Hans Lippershey attempted to patent a design for a refracting telescope. The next year, Galileo Galilei learned of the design and built his own refractor, which he used to make a number of astronomical discoveries.
Quite simply, modern refractors are usually comprised of two or three lenses that are mounted in the front of the telescope. Light enters the front of the telescope, and those lenses bring light to a focus on the other end of the tube, where the observer looks into the eyepiece.
The following diagram illustrates a basic refractor figured at f/7 (i.e., the focal length is seven times as long as the aperture):
Generally speaking, refractors provide one with a crisp, high-contrast visual observing experience. But inexpensive refractors can also suffer from a problem known as chromatic aberration.
The problem of chromatic aberration or false color arises from the nature of how different colors in the spectrum of light come to focus at different points after it passes through some lenses:
Here is an illustration of an extreme case of what false color looks like in a very crude single-lens homemade refractor that I cobbled together using spare parts I had on hand:
Note the blue, purple, and yellow fringing around the edges of the cross member of this utility pole and the power lines. Also notice how out-of-focus this image appears. This is due partly to the fact that it’s impossible to achieve focus because different colors of light are coming to focus at different points. What a disaster.
By contrast, this is a photograph of the same pole that I took using my good-quality 4-inch Maksutov-Cassegrain telescope, which, to be sure, is not a refractor but which nonetheless demonstrates what one would rather see at the eyepiece:
Some types of refractors handle this problem better than others. Amateur astronomers typically use two basic types of refractors: achromats (or achromatic refractors) and apochromats (or apochromatic refractors). Each type handles chromatic aberration differently.
Achromats (pronounced “ACK-row-mats”) bring some colors to focus at the same point but bring other colors to focus at different points. To compensate for this, the higher the focal ratio of the telescope (that is, the longer the focal length relative to the aperture), the less apparent this effect is. Generally speaking, achromatic refractors whose focal ratio is f/10 or higher have less noticeable false color. In the middle of the twentieth century, it was not uncommon for amateurs to use long-tube achromatic refractors whose focal ratio was f/15 or even more.
After having shown you the above photo of what is an extreme case of chromatic aberration, I don’t want to leave you with the impression that achromats are completely incapable telescopes. In my experience, even inexpensive achromats can perform well as long as their focal ratio is f/10 or greater—that is, as long as the telescope tube is long. One of my favorite telescopes is my 90mm f/11 Meade Series 390 achromatic refractor. I’ve spent many hours at the eyepiece with this telescope. I reach for it whenever I do lunar observing in particular. It does show some false color, but it’s negligible.
All in all, long-focus achromatic refractors with focal ratios of f/10 and higher can be ideal telescopes for use in observing the Moon, the planets, and double stars.
Apochromats (pronounced “uh-PAH-chro-mats”) appeared as a viable option in the amateur astronomy market in the last decades of the twentieth century. When they’re well made, they have negligible if any false color. As one might expect, apochromatic refractors can be very expensive especially relative to the aperture size they offer. Those amateur astronomers who have a taste for the very best of the best will spend thousands of dollars in pursuit of the perfect apochromat.
While refractors use lenses to gather light and bring it to a focus, reflectors do the same thing by using mirrors. Sir Isaac Newton built the first reflecting telescope in 1668.
Light enters the front of the telescope, reflects off the concave primary mirror, reflects again off of a secondary mirror positioned near the front of the telescope, and goes into the eyepiece.
The following illustration of a basic reflector figured at f/7 shows how this works:
Reflectors offer the cheapest way to get the most aperture. They also typically have the simplest design of any other type of telescope. I can’t count how many times I’ve completely disassembled a reflector and put it back together again with absolutely no ill effect on the telescope’s performance. They are well suited to folks who like to tinker with things. If you’re mainly interested in using a simple setup to observe faint galaxies and nebulae, then a reflector with a generous aperture is definitely the way to go.
In spite of their advantages, reflectors can suffer from some drawbacks. One optical aberration that can sometimes turn up in reflectors is called coma, a type of aberration that makes stars at the edge of the field of view appear like drawn-out points of light.
Reflectors also require periodic collimation, which involves fine-tuning the alignment of the primary and secondary mirrors so that the path of focused light goes straight and squarely into the eyepiece without deviating to one side or another. It’s not hard to do, but it does need to be done, and it requires the use of a simple collimating tool.
Additionally, the secondary mirror creates a central obstruction that, while not obvious when your using the telescope, does have the effect of reducing the contrast of bright objects like the planets and introducing diffraction spikes.
Cheaper reflectors will often have primary mirrors whose curve is spherical in shape. One way to compensate for this is to figure the mirror with a long and thus more forgiving focal length. If you encounter an inexpensive reflector with a long tube, chances are it has a spherical mirror.
More expensive ones will typically have a parabolically-shaped primary mirror. The latter helps keep stars sharp towards the edge of the field of view. But the more complex a primary mirror’s figuring is, the more expensive it will make the telescope. Generally speaking, a reflector with a parabolic mirror is one important indication of its quality particularly in the case of those with a short focal length.
Catadioptric telescopes combine lenses and mirrors to fold a path of focused light back and forth inside a compact tube.
Catadioptric telescopes made their debut on the commercial market with the venerable Questar telescope in 1954. Their design stems from work that Russian optician Dimtri Maksutov did around the time of the Second World War.
Light first passes through a relatively thick meniscus corrector lens at the front of the scope, reflects off of a concave primary mirror at the back of the scope, reflects again off of a silvered secondary mirror spot usually positioned on the inside surface of the corrector lens, and passes out of a central hole in the primary mirror to the eyepiece. The following illustration demonstrates this design figured at f/15:
It’s an ingenious design that fits what would otherwise be an extremely long focal length into a compact telescope. If the focal length of an f/15 Maksutov-Cassegrain telescope were implemented as a refractor of equal aperture and focal ratio, this is how the two would compare:
Note how the width of the telescope tubes and cones of focused light exiting the back of both designs are the same proportion, but the Maksutov-Cassegrain is significantly shorter in length.
Since Maksutov-Cassegrains have a long focal length packed into a short tube, they are excellent performers for observing objects that require high magnification, particularly the planets. They are often the favorite design of urban astronomers who often observe under light polluted skies and who most commonly go for objects that don’t necessarily require dark skies to see well (again, the planets as well as the Moon and, when properly filtered, the Sun).
But because of the thickness of both the primary mirror and corrector lens coupled with the closed-tube nature of the design, longer cooldown times can sometimes be an issue especially when you’re taking your telescope from inside a warm house to the cold outdoors. Convection currents radiating off of the optics may cause a boiling visual effect at the eyepiece until the telescope comes to thermal equilibrium.
The central obstruction, while typically smaller than either reflectors (discussed above) or Schmidt-Cassegrains (discussed below), can still reduce the contrast of an object. Out of all the telescope designs that have an obstructed aperture, however, Maksutov-Cassegrains have the smallest obstruction and thus offer the best contrast.
And since the corrector lens is so thick, producing apertures larger than five inches involves figuring a large and thick lens blank, often an expensive undertaking.
Starizona has an excellent discussion of Maksutov-Cassegrain telescopes.
Schmidt-Cassegrain telescopes use the same basic principles as Maksutov-Cassegrains but with a slightly different design. Like with Mak-Casses, light enters the telescope through a corrector lens, although an SCT’s corrector lens is significantly thinner. Light then reflects off a concave primary mirror back toward the front of the scope, reflects again off a secondary mirror mounted into a hole in the lens, and finally makes its way to the back of the scope and to the eyepiece. The following illustration demonstrates this design figured at f/10, which is the most common focal ratio for SCTs:
It’s another clever design that squeezes a long focal length in a short tube. If this f/10 SCT were a refractor of equal aperture and focal ratio, this is how they would compare in size:
Like the Maksutov-Cassegrain above, note how the width of the telescope tubes and the cones of light exiting the back of both designs are the same proportion, but the SCT is significantly shorter in length.
Many of the same advantages and disadvantages of the Maksutov-Cassegrain design apply also to Schmidt-Cassegrains. SCTs pack a long focal length into a short tube. They are a favorite for urban observers. Cooldown times can be a problem just like with Maks. But the thin corrector lens of SCTs makes their weight more manageable especially in larger apertures. The eight-inch SCT is a staple of the amateur astronomy world and is not an uncommon sight on the observing field, but I have never encountered heavy Maksutov-Cassegrains larger than five inches at star parties. Any SCT that is eleven inches or larger is starting to get big and cumbersome. Schmidt-Cassegrains have a larger secondary mirror obstruction than the ones found in Maks, and so the contrast they offer is somewhat diminished than that of that other catadioptric design. And unlike the secondary mirror of Maksutov-Cassegrains, which are most commonly affixed directly to the back of the corrector lens as a mirrored spot, the secondary mirror of SCTs are mounted in a housing that can require periodic collimation especially if the telescope is transported frequently and/or is jostled about.
All in all, though, I really like the Schmidt-Cassegrain design especially in its eight-inch form. It does most everything I ask of it with a reasonable level of ability.
For an interesting commentary on Celestron’s Schmidt-Cassegrain telescopes, visit Ed Ting’s Celestron Schmidt-Cassegrain overview.
When I was first getting started in the hobby, I endlessly wrung my hands over what type of telescope to get. Once I finally got over my analysis paralysis and made a decision, the mount was an afterthought. I went for a relatively inexpensive, lightweight mount. It was a big mistake.
Don’t underestimate the importance of the mount. It will make or break an observing experience. A good scope sitting on a cheap, flimsy mount makes for a very frustrating experience. If you’re considering the purchase of a telescope that doesn’t include the mount, make sure the mount can adequately handle the scope. If the telescope already includes the mount, pay attention to whether the mount can in fact do its job. Especially in the case of the cheapest packages, many manufacturers include mounts that are not really up to the task of steadily holding the telescopes they come with.
Just like there are different types of telescopes, so, too, are there different types of mounts.
Alt-az (i.e., altitude-azimuth) mounts represent simply. The movement is up-down and side-to-side. Simplicity itself. They tend to sit on tripods, are most commonly found with smaller short-tube refractors and reflectors, and are very good choices for casual scanning or grab-and-go setups.
Equally simple are Dobsonian mounts, named after their chief proponent John Dobson. They are most common with moderate to large reflectors that have two-armed swivel bases that sit on the ground. One can also think of Dobsonians as a large version of an alt-az mount.
Equatorial mounts represent a more complex mount design. Because they have one of their axes of movement pointed at the north pole and thus enable a telescope’s movement to mimic the rotation of the Earth, they are well-suited for tracking objects especially at higher magnifications (e.g., the planets). But their counterweights make them a little more cumbersome to work with, and they can be tricky to figure out at first. But with a little thought and effort, they can be very intuitive mounts to work with.
An eyepiece is a set of small lenses one looks through when using a telescope. Since an eyepiece is the piece of gear that you are physically closest to when you use a telescope, they are indeed one of the most critical parts in the optical chain of a telescope.
In combination with the focal length of the telescope, the focal length of the eyepiece determines the magnification. The lower the eyepiece’s focal length, the higher the magnification.
Here is the critical formula:
Magnification = focal length of the telescope ÷ focal length of the eyepiece.
For example, using a 25mm eyepiece with a telescope whose focal length is 1200mm yields a magnification of 48x.
Field of View
When you look through an eyepiece, you’ll immediately notice how wide the field of view is. Some eyepieces have rather narrow and confining fields of view, which isn’t necessarily a bad thing if the object you’re observing doesn’t need a wide field of view to begin with (for example, planets). In fact, many high-end eyepieces have narrow fields of view but high-quality optics that feature high-grade materials. But generally speaking, a generously wide field of view can offer an expansive feeling at the eyepiece and, when well designed and executed, can often be the hallmark of a good, quality eyepiece. Many expensive eyepieces have several lens elements in several groups that, put together, offer a wide field of view with stars appearing sharp from edge to edge. The more glass is in an eyepiece, the heavier, bulkier, and more expensive it can get.
Eye relief is an expression of how close your eye needs to be to the eye lens (i.e., the top-most lens of an eyepiece) in order for you to be able to take in the entire field of view without having to move your eye around. Longer eye relief means that you can still take in the entire field of view with your eye being further from the eyepiece. Those who must wear glasses while observing (most frequently those who suffer from more than a minor amount of astigmatism) will look for eyepieces with generous eye relief.
I don’t wear my eyeglasses when I’m at the eyepiece. But given the particular shape of my eyebrow and my long eyelashes (I dislike the sensation of my lashes brushing up against the eye lens), I tend to look for eye relief no shorter than 18mm or so. Everyone is different, though. Some don’t mind shorter eye relief especially if the eyepiece’s field of view is wide. Many consider 20mm to be the standard for what constitutes long and comfortable eye relief especially for those who keep their eyeglasses on when observing.
Types of Eyepieces
Two types of eyepieces are typically included with beginner telescopes: Plossl and Kellner eyepieces. Plossl eyepieces feature two pairs of lenses and typically offer a moderately wide field of view. Kellner eyepieces are a somewhat simpler design that feature three lens and have roughly the same field of view size as Plossls. Both types at shorter focal lengths have tighter eye relief.
Beware of Huygens and Ramsden eyepieces—they tend to have narrow fields of view, tight eye relief, poor optical performance, and an overall level of quality that is truly awful. If a scope includes these eyepiece types and/or has eyepieces with 0.965-inch barrels as opposed to the more modern 1.25-inch standard, that’s one sign that the scope may suffer from inferior quality.
Edmund Optics has an excellent discussion of these and other eyepiece types.
Higher-end eyepieces often have 2-inch barrels that allow for wider fields of view and better performance than 1.25-inch eyepieces. Of course, your telescope will need to be able to accept these wider eyepieces.
Minimum and Maximum Magnifications
Where magnification is concerned, don’t go too low for your scope. Generally speaking, I’ve found that taking the focal ratio of a telescope and multiplying it by six will give me an idea of the highest eyepiece focal length and thus the lowest magnification that is useful for a telescope. If I had an f/5 telescope, for instance, I would not get an eyepiece whose focal length was higher than 30mm. For reasons having to do with the size of your eye’s dark-adapted pupil and the optical interaction between the telescope and eyepiece, lower magnifications may not be possible for a telescope with a given focal ratio.
Don’t push your magnification too high for your scope, either. Whatever your aperture will give you in terms of light gathering and resolution will really be apparent as you explore how high you can push magnification up. Making an object look bigger at the eyepiece means that whatever light the telescope gathers will be spread out more as that object appears larger. The object will thus appear dimmer, mushier, and less resolved.
Imagine aiming a flashlight against a wall. When the flashlight is close to the wall, the spot of light appears small and bright. As you pull the flashlight away from the wall, the spot of light grows bigger but also gets dimmer because the same amount of light becomes spread out across a larger area. Something like that happens at any telescope as you increase magnification.
Some say that 50x per inch of aperture is good rule of thumb to use. I’m somewhat more conservative. I find that a scope won’t yield useful magnifications beyond 30 or 35x per inch of aperture. Past that point, the telescope simply runs out of light. That is, a telescope’s aperture won’t gather enough light to resolve an object satisfactorily beyond a certain point.
I also find that anything above 200x is usually not possible no matter what the aperture is. Only on rare occasions am I able to push an 8-inch telescope up to 225x with anything approaching a well-resolved and pleasing image at the eyepiece. Turbulence in the atmosphere is usually the factor that imposes that 200x ceiling.
First, it’s important to note that different styles of equipment appeal to different people and different observing needs. There is no one telescope that is “the best” for all applications. The important thing to do when making a decision about what to get is to evaluate what is most important to you (aperture, performance, price, etc.) and find the gear that suits your needs best.
Generally speaking, I would avoid going below 3 inches (75mm) and above 10 inches (250mm) in aperture. Smaller scopes won’t give you the light grasp you need to have an overall satisfying observing experience, and larger scopes are simply a pain to lug around and won’t get used often. Within that range, 4 to 8 inches seems to be the sweet spot. Four-inch scopes are highly portable but lack the light grasp for that immersive experience of observing dim objects. Eight-inch instruments are far more likely give you that experience and are still small enough to be relatively easy to set up and take down. Where the perfect balance is between aperture size and managability is something you have to decide for yourself.
Perhaps one buying strategy when purchasing your first telescope is to seek out a smaller, reasonably priced, but still well-made instrument that will give you the opportunity to gain experience using a telescope and that will also continue to be useful as a complement to a possible larger-aperture scope that you may decide to get down the road. Small telescopes function well as convenient, grab-and-go instruments, but they also tend to induce a phenomenon known as aperture fever—at some point, you may find yourself craving for more aperture. If you get to that point and act on it after having first bought a quality small telescope, you can continue to use your smaller instrument when you want something for quick-look sessions while having a larger scope for those occasions when you really want to dig in and spend a number of hours observing.
My 4-inch (102mm) f/12.7 Orion Maksutov-Cassegrain telescope is very well suited for high-magnification planetary observing all in a lightweight and very convenient package. My manually-driven Orion AstroView mount carries this scope with no problem. This was my very first scope I ever bought, and I have a sentimental attachment to it. It’s a small scope that is highly transportable and has really crisp optics. Its focuser is smooth, and I have little problem achieving focus even at higher magnifications. Very much recommended.
A good choice for grab-and-go, higher-power observing under urban skies would be the ultra-portable Orion StarMax 90mm TableTop Maksutov-Cassegrain Telescope. If I didn’t have a sturdy table to hold it, I’d want to build or otherwise get a tripod for it. Like all Maksutov-Cassegrains, this scope offers a long focal length in a small, compact bundle. The higher magnification also helps with spreading out urban skyglow. And 90mm of aperture is good for quality views of the Moon and planets, which are just as well observed from the city as they are from the country. But its small aperture will limit the number of deep sky objects that are accessible with it.
Any Celestron Schmidt-Cassegrain is a good bet. The more aperture you get, the more satisfying of a view you’ll have. If you purchase an optical tube assembly (OTA) separately, remember to find an adequate mount.
My 3.5-inch (90mm) f/11 Meade Series 390 achromatic refractor punches above its weight. This was the first refractor I ever owned, and it introduced me to the crisp, high-contrast views that refractors are known to provide. It does suffer from some chromatic aberration, but it’s not bad at all especially considering that it’s an achromat and not an apochromat. I use it on my Orion AstroView equatorial mount. Because of the force of momentum its long length exerts on the mount, I am reluctant to go any bigger on that mount. I use this scope mostly for lunar observing and, with proper filters made for this purpose, solar observing. Unfortunately, this refractor is no longer sold new, but many other possibilities for long-tube, small-aperture refractors exist on the market.
If I were seeking out a good achromatic refractor, I would look for 80 or 90mm of aperture with a generous focal ratio (f/10 or above) to keep false color under control.
Reflectors on Alt-az Mounts
For absolute rock-bottom—and I really do mean rock-bottom—I would consider the Celestron Cometron FirstScope. If you have a steady table and want something uncomplicated, complete out of the box, and having a minimum level of quality for less than $60 to put into the hands of a young astronomer or to take with you on a camping trip for carefree use, this is a good choice. I once owned one of these scopes, and I bought it mainly as a project—I had it disassembled for parts within 15 minutes of it being out of the box. Out of all the variations of the FirstScope that are out there (and there are many), this version offers the best set of eyepieces. But its primary mirror is cheaply figured, its fast f/4 focal ratio is hard to get right at that focal ratio and price point, and its build quality is hit or miss. This little scope is good for getting your hands dirty with casual, low-magnification, wide-field views of the heavens. But don’t ask too much of it. Expect lots of distorted-looking stars at the edge of the field of view and a struggle to see the rings of Saturn.
For those occasions when I want a quick-grab scope or when I want to scan the sky at low power, my 4.5-inch (114mm) f/4 Zhumell Newtonian reflector telescope that I use on a home-built wooden mount fits the bill. Although I don’t believe that Zhumell-branded telescopes are still being sold, this particular offering appears under other brands. The Orion StarBlast 4.5, the Celestron Cometron 114AZ, and other variations of branding have appeared on (and disappeared from) the market. I am 99.9% certain that they all come out of the same factory in China. This scope has been around for years, and many serious amateur astronomers have one on hand for a convenient observing option. Orion sells an equatorially-mounted version of the StarBlast 4.5, but I would avoid this one considering that this scope operates best at low power and is most useful for scanning the sky in alt-az mode. It makes for a good, inexpensive, lightweight grab-and-go scope with decent optics that give me satisfying views at low power. This is a scope that really benefits from adding a Barlow lens (discussed below) when I want more than low magnification. But it’s not really well suited to be used for anything more than casual, spur-of-the-moment observing. And other scopes perform far better for planetary observing or high-magnification work. Its cheap focuser is its weakest link. When I operate anywhere above 50 or 60x, I struggle with achieving sharp focus. The focuser has a gooey, sloppy feeling that is the result of the infamous “glue grease” that the manufacturer uses to compensate for any loose play in the movement of the focuser tube. When I’m out with it for more than an hour or so, I start to want something with better light grasp, better hardware, and/or better optics.
Reflectors on Dobsonian Mounts
Small scopes are great for the convenience they offer. But there is simply no substitute for aperture, and there’s no better way to get that aperture for the least amount of money than Dobsonian-mounted reflectors. They may not have that classic telescope look, but they really deliver at the eyepiece.
For trips out to the country and darker skies, I use a 10-inch (254mm) f/4.7 Orion Dobsonian telescope whose navigation electronics had been stripped from it by a prior owner who also seems to have stripped it of other critical parts. I managed to restore the scope to functional condition using simple hardware store parts, and I don’t mind the fact that it’s missing its electronics for reasons I discuss below. This scope has excellent light grasp and shows me fine detail in faint objects. But a 10-inch telescope is perhaps the largest in the class of medium-sized scopes. Anything larger than that and you’re getting into big-scope territory and all of the encumbrances that come with it. Personally speaking, a 10-inch scope is definitely the limit for me in terms of how big I would want to go.
GSO’s 8- and 10-inch Dobs have great optics, excellent build quality, are very well accessorized, and generally stand out as an unbelievable value. They retail under a variety of brand names including Apertura (8-inch and 10-inch models) and SkyLine (8-inch and 10-inch models). I got a feel for a friend’s 10-inch GSO Dobsonian reflector a few years ago, and I was very impressed by the smooth movement of the scope on its mount, its focuser, and the overall quality of the package. If I ever needed to replace the 10-inch Dob I have, I’d go for either the 8- or 10-inch models depending on what level of physical ability I had at the time.
A debate has raged about computerized mounts since their introduction a number of decades ago. One camp argues that one is not a true astronomer without the ability to navigate the sky visually and that using a computerized mount is akin to having a bag over one’s head. The opposing group maintains that light pollution has gotten so insidious in recent decades that go-to technology is an essential addition to the hobby, one that enables the amateur astronomer to navigate the sky in spite of the increasing absence of dark skies.
I don’t have any computerized mounts. My preference is to tend towards simplicity and to put my money towards better optics rather than fussy electronics. A typical go-to system will add hundreds of dollars to the total cost of a setup—money that, in my mind, would be better spent on more aperture, better optics, quality eyepieces, or other accessories. Even in the city, I can make out at least the bright stars and, on good nights, some of the dimmer ones, too. It didn’t take me long to find that I didn’t need a computer to do the navigation for me and that the hobby was more enjoyable without one getting in the way.
Another argument against computerized mounts relates to convenience. A powered mount requires a battery, mostly likely a rechargeable one. A rechargeable battery requires charging, of course. Charging it requires you to remember to charge it, which itself requires forethought. If one night you see that it’s clear and that you’re in the mood for an observing session lasting a number of hours, what a disappointment it would be to discover that you forgot to charge the battery and thus were not able to run your mount. I’ve also seen friends arrive at a dark-sky site an hour’s drive from their home only to discover that they forgot their battery. Having to remember a power source is just one more complication for a hobby that can get pretty complicated in a hurry.
I’ve encountered countless individuals who struggle with their computerized mounts and ultimately give up on the hobby all because of a dumb computerized mount. What a shame.
Beyond pointing a camera into the eyepiece and taking pictures of the Moon, I’d advise against diving into the world of astrophotography before getting meaningful experience as a visual observer. Astrophotography is a complex and very expensive sub-area in amateur astronomy that can lead to a lot of aggravation especially for beginners. Take it easy at first and enjoy the view before even thinking about imaging what you see in the eyepiece.
I would start with whatever eyepiece(s) that came with your telescope when you bought it and maybe add one more. Take it easy at first. Don’t go overboard with buying eyepieces before you’ve had a chance to use your telescope. Eyepieces are important, but a little experience will quickly tell you what your preferences are. Spending some time working with what you have will put you in a better position to decide on additional eyepieces later on.
Pay attention to having an eyepiece set that gives you an even spread of magnifications. Roughly 30 or 40x between magnifications is a good place to start. If an 8-inch (200mm) telescope with 1200mm focal length came with a 25 and 10mm eyepiece, I’d consider adding a 14mm eyepiece. That set would give me 48x (25mm eyepiece), 86x (14mm eyepiece), and 120x (10mm eyepiece).
But if I had a small 4.5-inch telescope with 450mm focal length that came with a 17 and 8mm eyepiece, I’d live with that set for a while before thinking about getting something else. That pair of eyepieces would give me two magnifications: 26 and 56x. After a few nights with the scope, I’d assess what getting another eyepiece would do for me. Would an eyepiece that would give you more magnification be asking too much of the telescope? Would you want a better-quality eyepiece to replace the 8mm one that came with the scope? A little bit of experience will tell you right away.
As I discuss above, be careful about selecting eyepieces that give you a good range of magnifications, and don’t push magnification too high or too low.
Plossl eyepieces, which feature four lenses arranged in two pairs, work best at higher focal lengths (and lower magnifications), i.e., around 17mm and upward. I find that eye relief starts to get tight at eyepiece focal lengths of 15mm and lower. I still make regular use of my 32, 25, and 20mm Plossl eyepieces. Any GSO-built Plossl eyepiece at 15mm and longer is a good bet for additional relatively inexpensive starter eyepieces.
Starguider / Paradign Dual ED Eyepieces
The Starguider Dual ED (Agena) and Paradigm Dual ED (Astronomics) eyepiece lines, each of which come out of the same factory, represent one of the best values in the hobby. Priced at $60 each, they may seem expensive especially when you’re just getting started. But adding one whose focal length complements whatever other eyepieces you may have will substantially increase the satisfaction you get from observing. I own and recommend the 15, 12, and 8mm versions of the Starguider Dual ED sold by Agena, although, again, the Paradigms sold by Astronomics are identical. Especially at those shorter focal lengths (and higher magnifications), their comfortable eye relief, wider field of view, and excellent edge-of-field performance make them a significant step up from Plossls of equal focal length.
The additional of a Barlow lens, which doubles the magnification of an eyepiece by whatever factor is specified for it, is a possibility. But I go back and forth on whether to recommend this from the outset.
Adding that accessory increases the magnification of an eyepiece and also increases the effective focal length and focal ratio of a telescope. Some telescopes, particularly short-tube reflectors with rather unforgivingly low focal ratios around f/4, really benefit from the addition of a Barlow lens because it stretches out the scope’s focal length and increases its focal ratio.
But in certain other instances, adding more lenses into the path of light between the front of the telescope and your eye adds more opportunities for optical aberrations and other negative side effects to work their way in. The quality of the Barlow lens has a lot to do with how well it performs, too.
Barlow lenses can also change the optical behavior of an eyepiece. Particularly with eyepieces that have longer focal lengths and longer eye relief, the Barlow lens will lengthen that eye relief even further. You may find that you have to position your eye very far away from the eye lens and that the eyepiece will exhibit blackouts much more than if you used the eyepiece by itself.
Especially when observing the planets in a telescope that already has a long focal length, I find that using a well-made eyepiece with lower focal length yields a far superior view than using a longer focal length eyepiece with a Barlow lens. After buying a few Barlow lenses during my first few years in the hobby, I’ve since moved away from using them in most of my scopes.
At around $30, GSO’s 1.25” 2x Barlow lens won’t break the bank if you feel that trying one out might benefit you. This particular Barlow lens features a lens cell that unscrews from its barrel and attaches to the end of an eyepiece. Doing this increases the magnification of an eyepiece by 1.5x. That adds a whole other dimension of flexibility to one’s calculations: you’ll get three magnifications out of any one eyepiece. But remember the thoughts I expressed above about the negative side effects that Barlow lenses can introduce.
At bottom, it all depends on your setup. Wait until you have some experience with your particular telescope before making the decision to buy a Barlow lens.
A small number of other highly desirable accessories will enhance your observing experience.
During my first few weeks in the hobby, I picked up copies of the current issues of both Sky and Telescope and Astronomy magazine from the newsstand at my local grocery store. I found them to be an invaluable source of information, and I quickly subscribed to both publications.
In particular, Sky and Telescope is a thoughtfully-written publication. Published since 1941 after The Sky and The Telescope merged, the magazine is somewhat of an institution within amateur astronomy.
There are basic star maps in Dickinson’s NightWatch, but you’ll quickly outgrow them. When you reach this point, several other options exist for more detailed star charts.
I regularly use and highly recommend Sky and Telescope’s Pocket Sky Atlas in its regular size or jumbo size.
With a star atlas in hand, you’ll need a way to see and read it in the dark.
Any white-light flashlight will ruin your dark-adapted vision. Red light has the least effect, and red-light flashlights suited specifically to astronomy are readily available. There are tons of red-light flashlights out there—search the internet for “astronomy red light flashlight.”
An excellent value in a simple but effective red-light flashlight with a dimmer control is Celestron’s Night Vision Flashlight. Lots of other options exist out there. Nothing fancy is necessary.
Since a telescope’s main job is to gather light, looking at something as big and bright as the Moon in a telescope can be like looking at a car’s headlight. Having a way to cut down on that light will make for a much more comfortable lunar observing experience especially when the Moon reaches its full phase.
GSO’s green-tinted 18% transmission moon filter and their ND 0.3 50% transmission neutral density filter are both good buys. Both run around $11 at the time of writing.
When I first got started in the hobby, I made regular use of my Orion variable polarizing filter, but I’ve found lately that the dual filter creates annoying reflections of the Moon’s light off my eye. I haven’t been using it much lately.
I’m amazed how much my observing experience became more satisfying when I simply had a seat. I find that it’s far easier for me to hold my body steady when I’m seated at the eyepiece rather than when I had been standing up.
At the end of the day, a stool is a stool. Anything to sit on will aid with keeping your body steady at the eyepiece. It will help you concentrate more on what you’re observing and less on holding still. Numerous options exist for height-adjustable stools made specifically for astronomy. But at least from the outset, I would suggest just using anything you may already have on hand.
If you have a reflector, you’ll need some kind of tool to collimate it. Unless your reflector arrived in perfect collimation after shipment to your home (not likely), having the means to make the necessary adjustments to get the optics lined up for a first-rate observing experience is critical. These accessories can be as simple as a dust cap with a small hole and a reflective surface on the inside or as elaborate as a device featuring a laser. A good reflector will often include a collimation tool and instructions on how to use it.
I own two collimation tools: a Celestron Collimation Eyepiece, which I like for its simplicity and the fact that I don’t need to power it with batteries in order to use it, and a GSO Deluxe Laser Collimator III, which is nice to use in situations where I don’t have a light source (for example, when I arrive at an observing site at dusk). Both tools work well.
At some point, you may find that you’ve outgrown the set of accessories that came with your scope or that you bought when you first got it. This may especially happen when you get a feel for what upgrades would do for you after trying out a friend’s higher-end gear on the observing field at a star party.
This is probably the first upgrade I would suggest. My first telescope came with a small 6 x 26 finder scope (i.e., 6x magnification and 26mm aperture). Under urban skies, I struggled to find all but the brightest guide stars. Later, I upgraded to a 9 x 50 finder scope, and my ability to see guide stars as indicated in my star atlas increased substantially.
Just like different people prefer different telescopes, so, too, can eyepieces be a highly personal choice.
I began to introduce better eyepieces into my collection after being in the hobby for about a year or so after I had the chance to get my feet wet. That collection includes the following:
- Edmund Optics 28mm RKE eyepiece: This eyepiece has been around for decades and has somewhat of a legendary reputation. It produces a very distinctive floating image effect whereby the eyepiece’s long eye relief and thin housing combine to make the object you’re observing seem to be suspended in front of you with nothing around it. It’s a lot of fun to use.
- Explore Scientific 24mm 68° Series Argon-Purged Waterproof Eyepiece.
- APM 18mm 65° AFOV Ultra Flat Field Eyepiece.
- Orion Edge-On Planetary Eyepieces: I have the 14.5, 12.5, and 9mm versions. They have a field of view that is a bit narrow, and the price is a little high for what they offer, but their overall performance when observing bright planets is very good.
I really like all of these eyepieces and wouldn’t hesitate to recommend them to others. They are not the cheapest eyepieces out there, but, at $85-190 each, not the most expensive, either.
For truly high-end eyepieces at truly premium prices, check out the offerings from Tele Vue.
Another worthwhile upgrade in the case of refractors and catadioptrics is a better diagonal. The diagonal that manufacturers often package with a scope is a bottom-of-the-barrel model that may act as a weak link in your optical chain. An excellent telescope used with an excellent eyepiece will ultimately perform poorly if an inferior diagonal is placed between the two. When the time comes to upgrade your eyepieces, you may also consider upgrading your diagonal if your telescope requires one.
I also dislike how some diagonals (and some Barlow lenses, too) have set screws that dig into eyepiece barrels and leave a little nick in the metal. I look for models with either a compression ring or a twist-lock feature that I increasingly see available.
I use and recommend Orion’s 1.25-inch Dielectric Mirror Star Diagonal. At $100 at the time of writing, this may seem like a lot of money to pay for something as mundane as a diagonal, but it’s worth it. For $20 more, a version of this diagonal with a twist-lock mechanism is also available. Both are sourced from Long Perng, a manufacturer based in Taiwan. Astronomics sells a dielectric mirror star diagonal for $70 that is identical to the Orion-branded version.
An internet search for dielectric mirror star diagonals will reveal numerous other options.
At bottom, remember this where the acquisition of gear is concerned: keep it simple, and don’t go overboard! This is a hobby, not a spending spree for an expedition. The goal is to be outside, enjoy the stars, and experience the joy and serine beauty of nature and the heavens. The more bits and pieces you have to juggle, the more the observing experience becomes distracted by stuff. As much of a gear hound as I can be, I try to remember that the whole point of it all is to get out, observe, and enjoy the wonders of the night sky.
It’s true that you will need to lay some cash out at the beginning, and it’s also true that you generally get what you pay for. But there will never be an end to the gear you can buy. While you will learn best by getting your hands on some basic equipment and actually doing the hobby, you don’t need a ton of expensive gear to get your start. Once you’ve acquired a basic set of gear and have gotten some experience with it, you will be in a position to make better-informed decisions about buying those additional nice-to-have accessories. But at the beginning, get only what you need and enjoy what you have.