The question I get asked the most is "what telescope should I buy?" This usually comes from friends who are not amateur astronomers but who have a general interest in astronomy or just think it would be cool to have a telescope. Many have kids and want to nurture their curiosity with the gift of a telescope. Unfortunately, the question of what telescope to buy is nearly as complex as asking what automobile one should buy. We live in a time when there are hundreds of telescopes on the market, and thousands of accessories for them. There is also a huge range in prices for telescopes from about $50 on the low end to upwards of $100,000 on the high end! Even within the sensible range of prices most consumers could afford, there are many types of telescopes to choose from and it can be hard to know the relative merits of 2 telescopes at the same price. So how can one make sense of this complexity and zero in on what is the best telescope to buy?
Hopefully this blog entry can give some good advice on this topic. While there is no one, single telescope that is better than all others, there are certain considerations that hold true and can inform someone’s decision on what telescope they should buy. Firstly, if you are an experienced amateur astronomer, you are probably already beyond the advice in this blog entry. Astronomers debate for hours the relative merits of a new apochromatic refractor or a Newtonian astrograph. There are several good forums, such as Cloudy Nights, that have a wealth of information and opinions on these topics. This blog entry is for the complete novice who is looking to buy their first telescope and is just getting started in astronomy.
My first plea is to never buy a cheap “department store” telescope. These are typically found in the toy section of common big box stores and cost $100 or less. These telescopes usually have plastic lenses and long tubes. They are marketed towards young kids and, being cheap, many parents gravitate towards them. The problem is they are too cheap. Image quality is poor, there is no clock drive to follow objects, and the telescopes tend to be small and limited in their light gathering power. You can’t see much with them and they are more an exercise in frustration. The average kid will fumble with the telescope for a few minutes, get frustrated because it’s too hard to use, and then abandon it forever. Why waste $100 on such a telescope when a few hundred dollars more will buy a telescope your child will actually use?
If you are pressed for money, I recommend buying a pair of binoculars instead. A decent pair can be purchased for about the same cost as a “department store” telescope and is much more useful. For instance, binoculars can be used for daytime viewing such as sports events and birdwatching. Binoculars are specified by two numbers, their magnification and the size of their main lens. So a binocular specified as 10x50 has a magnification of 10 times and a main lens diameter (aperture) of 50mm. You might think the bigger aperture and higher magnification the better, and for enough money you can buy truly monstrous binoculars. However, bigger binoculars are heavier, and since you’ll be holding your binoculars while you scan the sky, your arms will get tired pretty quickly. On the other side, a too small pair of binoculars won’t gather much light and you won’t be able to see many astronomical objects. Similarly, higher magnification might sound better but it’ll make it that much harder to hold the binoculars steady enough to get a clear view. I have a pair of 16x50 binoculars and I can start to see that the magnification is getting high enough to make holding it steady a challenge. I’ve found that the best balance of magnification and aperture is about 10x50. A good 10x50 binocular can easily be had for less than $100, and maybe even less than $50. With such a pair you’ll easily be able to see brighter deep sky objects like the Orion Nebula and the Andromeda Galaxy as well as star clusters, the moon, and man-made satellites. Binoculars are intuitive, easy to use, and kids will love them.
If you or the person you’re buying for is ready to move beyond binoculars and wants to see more deep-sky objects, we’re back to the question of what telescope to buy. I suggest you are going to have to spend at least a few hundred dollars to get a decent telescope. The good news however is that the price of a decent telescope keeps coming down and the capabilities keep going up. I think an indispensable feature for any telescope is to have a motorized clock drive such that the telescope automatically follows an object as it moves across the sky. Astronomical objects, much like the sun, rise in the east and set in the west and move steadily across the sky. You might not think this is a big deal, but the small fields of view of most telescopes (after all telescopes magnify objects and this leads to small angular fields of view) means that the rotation of the Earth will, in just a few seconds, move objects out of your telescope’s field of view if you don’t have a clock drive. Also, if your telescope has the motors and gears needed for a clock drive, you’re halfway to what’s called a “Go-To” telescope. This feature utilizes a small computer in the telescope mount or hand-controller to allow the telescope to know where it is pointing and to be able to find and point to astronomical objects automatically. In the past, this feature was only in top-of-the-line telescopes costing thousands of dollars. Now it can be found in some of the cheapest telescopes costing just a few hundred dollars. And the advantage is profound, especially if you are new to astronomy and don’t know where many astronomical objects are or how to find them. With a Go-To telescope, you initially align the telescope by inputting your location, time, and date into the computerized hand-controller. Typically then the telescope will begin an alignment sequence whereby it points to a few bright stars to further refine its positioning. During this step you will have to know at least a little astronomy and be able to adjust the telescope’s initial “guess” and center up the bright alignment star in your telescope’s field of view. This alignment step literally takes just a few minutes, and once complete, you can point to any object in the telescope’s on-board database of thousands of objects without you having to be an expert on where it is located in the sky. Do you have no clue how to spot the Ring Nebula or the Hercules Globular Star Cluster? With a Go-To telescope, you just find the name of the object in the on-board menu and hit “Enter” and the telescope will automatically point to it. I’m old enough to remember the days before Go-To telescopes, where you had to remember the location of astronomical objects and little hints about how to find them. While that may have fostered a deeper connection with the sky, it did mean you spent more time trying to find objects than actually observing them. With a Go-To telescope, astronomy is more fun because you’ll have an easy time finding and observing astronomical objects.
So now we’ve concluded a telescope with a low cost Go-To mount and clock drive is best. But what about the actual type of telescope optics? There are two main categories of telescopes, “refractors” that use lenses and “reflectors” that use mirrors. Within these categories, there are tons of variations. Bigger telescopes like ones used by professional astronomers and advanced amateurs are almost all reflectors. They scale up better to larger sizes than refractors. That being said, I think the best type of telescope for someone starting out in astronomy is a refractor type telescope. Refractors are simple, lightweight, and don’t require you to adjust the alignment of the internal optics. Refractors are what people think about when you mention telescopes. A pirate’s spyglass and brass “harbor” telescopes are of the refractor type. They use lenses to gather light and focus it down a long tube to an eyepiece at the other end. Refractors, and indeed all telescopes, are specified by the size of their main light gathering optic (the aperture) and by their focal length. Much like with binoculars, bigger apertures gather more light, and longer focal lengths lead to greater magnification. Refractors tend to have their apertures specified in millimeters. Since you’ll have a mount for your telescope, the warning I gave about binocular apertures getting so big that your arms would get tired quickly doesn’t apply. But bigger apertures still lead to larger and more expensive telescopes, and with refractors, this trend grows quite quickly. A good sized amateur refractor is about 120 to 150 millimeters (about 5 to 6 inches). Going beyond that and the price climbs very quickly. I’ve seen 8-inch refractors before but they cost as much as a car, while an 8-inch reflector telescope can be had for less than $1000. So I recommend a refractor around 120 millimeters or less purely on cost grounds. Additionally, super long focal lengths (magnifications) sound nice but are not the way to go for a first telescope. For one thing, long focal lengths lead to long telescope tubes, which leads to heavier telescopes on heavier, more expensive mounts. Also, the field of view you’ll get will be smaller, and may challenge the accuracy of the Go-To mount to get astronomical objects in the middle of your telescope’s field of view. Finally, smaller focal lengths tend to smaller but brighter images, making it easier to see faint astronomical objects by eye. This all spells out what is called a “fast refractor”, that is a refractor type telescope with a relatively short focal length that is 5 to 7 times the size of the aperture. So for instance, a 120 millimeter fast refractor might have a focal length of 720 millimeters. With a standard 25 millimeter eyepiece, you’d get a magnification of about 29x, which will give nice views of larger astronomical objects like star clusters and the Orion Nebula. In comparison, our 10x50 binoculars only had a magnification of 10x, so we’re definitely going to see more detail with this telescope.
Great, so we’ve nearly narrowed down on the “ideal” first telescope. It would be a fast refractor type telescope with an aperture less than 150 millimeters, on a computerized Go-To mount that allows you to automatically point to and track astronomical objects. I haven’t talked about price too much yet but have implied that the reader is price conscious and maybe doesn’t want to spend a ton of money on a hobby they are not yet sure about. The good news is that an ideal first telescope can be had for a little more than $400. I don’t want to endorse any particular telescope, but some examples of telescopes that fit our requirements include the SmartStar R80 Computerized Telescope with GPS from Ioptron ($370). This is a Go-To mount with an refractor telescope with an 80mm aperture. The mount has built in GPS so the telescope always knows its location. Another possibility is the Nexstar 102 SLT Computerized Telescope from Celestron for $499.95. This has a fast refractor with 102 millimeters of aperture and a 660 millimeter focal length. Another exciting possibility is the Astro Fi 90mm Refractor Telescope also from Celestron. This telescope is soon to be released so we don’t know how good it is, but it will be controllable via a WiFi connection to a smartphone or tablet, and the price will be an affordable $399.95. There are a few other possibilities, but I'll leave it up to the reader to investigate some more to find a good fast refractor telescope within your budget. Paying more money should get you a nicer telescope, so if you can afford it, you can look to at greater than $500 telescopes, of which there are many. Some good online vendors of telescopes include:
Good luck and clear skies!
I have been excited about space since I was young, and have been involved in astronomy for over 20 years. I have built 4 of my own telescopes and continue to design and experiment with new instruments and accessories.