Guide to Buying a First Telescope
Occasionally I am asked about how to select a telescope for a family, usually near the holidays. Although the decision on what telescope is right is very much dependent on the specifics of available budget, who is going to be using the telescope, and what the goal is for its use, this is an attempt to provide some overall ideas before we get into the details of your specific needs. Don't hesitate to contact me - I always enjoy helping navigate the confusing landscape of what is available to buy - but by reading this first you may save both of us a lot of keystrokes.
What Not To Buy
Let's get this out of the way first. There are two categories of telescope I would strongly advise against, no matter what your situation might be. The first are the very inexpensive telescopes, which I refer to as "department store refractors" because that is where they used to be sold. These are refractor telescopes (lens telescopes) on a tripod, usually 50mm or 75mm in diameter, and can be found for under $100. To be clear - I've owned one of these since childhood, and I keep it mostly for nostalgic reasons. Mine came from JC Penney. The optics in these cheap telescopes are at best "ok", and I fear that today's cheapest telescopes may be using plastic molded lenses, which are almost certainly going to give disappointing views. But the bigger issue is usually the tripod. Generally not much better than a camera tripod, not particularly stable, and may shift when you go to lock in a view, which can just drive you nuts. Your young astronomer is not likely to have the patience to put up with this, and most parents won't either. If you really are limited to $100 (which I can certainly understand), you are better off buying a nice pair of binoculars which will show you as much of the sky as these refractors, and are much, much easier to use.
The other category I would not want to see someone buy as a first telescope are the newest computerized camera telescopes (Vespera and ZWO Seestar are two examples). This would be like buying a Tesla to learn to drive. These systems are very flashy, undoubtedly "work" as advertised and produce nice photos of the brighter interesting objects, but cannot be used for visual observing at all, have very small apertures limiting what can be captured, and will teach you nothing about astronomy. They are also not particularly cheap, and that money (~$500) would be much better spent on a telescope you will actually use.
Budget
Unfortunately, a good telescope that is actually useful and not difficult to use is not inexpensive. And so your available budget is really the first thing to consider. The price of telescopes is constantly changing, almost always in the same direction, so the values in this article will need to be revisited every year or so. This is being written in the spring of 2024. As indicated above, if your budget is limited to under $100, don't buy a telescope (though see below about used telescopes), and consider a nice pair of binoculars instead. Even a 40 or 50mm binocular will show you a great deal more of the night sky than what your eye can see.
There are usually "breakpoints" in prices of telescopes. Under $300 you are looking at one set of instruments with very few choices to be made. Under $600 there are more options to be considered, depending on what you are trying to observe, and who is working with the telescope. Under $1500 those options are wider and the decisions to make more detailed (and more serious, given the expense). Over $1500 you are starting to look at very serious instruments and generally are leaving the realm of "first telescope". And there are many more rungs to this ladder - a $2500 level, a $3500 level, $7500, and then approaching the boundary between amateur and professional instruments. Obviously I would not recommend spending anywhere near these levels for a student's telescope. To put my own outlook on such things, the most expensive telescope I own was $1200 in 2007 (now about $2500), and I shudder to think about replacing it.
Aperture
The size of the hole through which light is collected by the telescope is the aperture. The larger the aperture, the more light is collected, meaning the dimmer the object that can be seen. The minimum reasonable aperture size is 50mm (for most uses), and with a 50mm telescope the Moon and brighter/bigger planets (Venus, Mars, Jupiter, Saturn), and a handful of star clusters can be observed. Nebulae will generally need 117mm (4.5 inches), the brighter galaxies 150mm (6"). But as aperture increases, cost goes up dramatically, and so does weight.
Let's talk weight for a minute. A child or young teen cannot be expected to be setting up and using a telescope weighing much more than 20 lbs. For telescopes beyond about 117mm in aperture, the telescope is usually in two parts - a tube (the "optical telescope assembly" or OTA) and the mount for the telescope. At 250mm the OTA is at least 20lbs, and the mount at least another 20lbs. Putting the two together is not something I would want to see anyone under 16 try without a lot of experience. Beyond 150mm things get heavier in a hurry. My 254mm Newtonian reflector is in three 30lb parts. My 254mm Cassegrain (which I've complained about in plenty of classes) has a 25lb tripod, and a 67lb OTA/mount assembly.
Refractors and Reflectors
This choice, for the first-time telescope buyer, is really quite simple. If your budget has you considering only apertures 75mm and smaller (about $300 in 2024), you will be buying a refractor - a telescope creating its images using lenses only. If you are able to afford a 117mm aperture or larger, you'll be buying a reflector of one form or another. There are refractors for those aperture sizes, but the price shoots over $1300 for just the OTA without a mount, and these are generally used for photography, not visual observing. One disadvantage of most reflector designs is that attention needs to be paid to aligning their mirrors, or "collimation". Generally most first-time telescope owners don't understand collimation, and therefore my guess is it is ignored, but among other issues this means reflectors are not as likely to travel well as refractors, as they will tend to go out of alignment during travel.
Mounts
What I have learned most firmly is that a telescope is only as good as its mount. All of the frustrations I've had with telescopes have been with mounts, and that includes not only for visual observing, but most definitely for photography. There are two decisions to be made about mounts, and these vary with budget again, but also with what you are trying to get out of the experience of owning a telescope.
Mounts can be manually controlled, or computer-controlled. There is a very large cost difference, not surprisingly. A computer-controlled mount moves the telescope continuously to counteract the rotation of the Earth, keeping the object you are observing in view. All modern computer-controlled mounts will also allow you to select the object you want to observe and move the telescope to the right position to see it. This is very, very convenient, however, it comes with two significant drawbacks for a student, not considering the price problem. First, setting up a computerized mount is not particularly easy - most systems require you to point the mount at true north, and then go through a star alignment process each time you use the telescope. The most recent computerized mounts have a way of automatically doing the whole alignment automatically, but that involves a camera, which adds even more to the cost. The other drawback is that using a computerized mount will mean you never "learn the sky" - you will have no need to know the constellations, nor where any of the objects you observe are located in the constellations. Beyond those drawbacks, you need power in the form of batteries or a power cord.
Manual mounts require constant adjustment to keep an object in view. The better manual mounts have slow motion controls that should make this easier. For reflectors 150mm or larger in aperture there is the "Dobsonian" mount that requires you to push on the tube of the telescope to move it - sounds awful, but really this is one of the better options as this motion is usually very smooth and becomes intuitive quickly. It is also a very inexpensive mounting option.
The other choice to make in mounts is how motion is distributed between two axes of rotation. In an altitude-azimuth mount, the motions are up and down (altitude) and rotation around the horizon (azimuth). The advantage is that these are natural, intuitive directions to move in. The disadvantage is that these are not aligned to how objects move through the sky because of Earth's rotation, and so both altitude and azimuth must be continually changed to keep an object in view. The German Equitorial Mount has one axis aligned to the axis of Earth's rotation, which means only one motion is needed (if the mount is properly aligned to point true north) to keep an object in view. This makes tracking an object very easy in a manual mount; however, the motions of an equitorial mount are very unnatural, which can make finding objects with a manual mount very frustrating. Generally, I would say only get an equitorial mount if you are getting a computerized mount, otherwise stick with the altitude-azimuth mount.
Types of Reflectors
At the price range we are interested in for a first telescope, a refractor is a refractor. There are differences at higher price ranges, which is something I personally am starting to think more about. But when it comes to reflectors, there are three options, maybe only two in this price range.
A Newtonian reflector has two mirrors - a primary mirror at the bottom of the tube reflects light back up to a secondary mirror, which then sends the light out a hole in the side of the tube near the upper end, and into the eyepiece. The advantage is price of this simple assembly. The disadvantage is that you need to view near the upper end of the tube. That leads to a ladder, in my case in the front yard. Newtonians can be mounted on either an equitorial mount or an altitude-azimuth mount, usually in the form of a Dobsonian mount, which is a very inexpensive but quite steady and easy to use option.
A Cassegrain reflector has two mirrors and an almost-flat lens. The primary and secondary mirrors are similar to those in a Newtonian, though the secondary mirror is much larger than in a Newtonian, and sends the light through a central hole in the primary and into the eyepiece. There is also a "window" over the open end of the telescope, which is actually a slight but necessary lens for this design. The advantage here is that you view from the lower end of the telescope - no ladder, and a slight advantage in that the window protects the internal optics from dust and slows the aging of the coatings. The disadvantage is price, driven by that window-lens. All but the smallest apertures are going to be out of a first telescope price range.
Lastly, there are Matsukov reflectors. They look similar to Cassegrains, but the secondary mirror is actually part of the outer window-lens and not a separate piece of glass. This works adequately for moderate aperture sizes (up to about 125mm), and significantly lowers the price compared to a Cassegrain telescope. Depending on your budget, these can be a very good option.
Used Equipment
Going back to the problem of budget, and the fact that your budget will quickly narrow the options you will be wanting to trade, there is a vibrant second-hand market for telescopes. It is a sad truth that modern telescopes usually outlast the interest that prompted the purchase, and that most people do not buy the right telescope for their needs. There is usually an understanding that a telescope in good condition is worth something, and so we end up with a lot of used equipment being offered for sale. To see what may be available, you can look at major telescope sellers, who often offer used equipment as well, but at a very large mark up. You can also look at forums, such as the used equipment section of www.cloudynights.com (a personal favorite site for other reasons). At least there they will know what they are talking about. Even local astronomy clubs may have used equipment they are willing to sell or lend out.
Now a much riskier proposition is to look at something like CraigsList, or the Facebook equivalent. The potential for finding a great deal is much higher there, but so is the potential for ending up with damaged or broken equipment. I am always disturbed to see photos of telescopes on CraigsList where the open end of the telescope is pointed at the ground because the seller has no idea what a telescope is. I have seen great deals, and I know people who have bought very nice instruments for 1/5th of the value of the telescope. But you really want someone looking at what is being offered who knows what they are looking at.
Summary
The decisions to make when purchasing a telescope for the first time can be daunting, and as you see above there are a lot of considerations to be made if you are making a significant investment. There are no simple answers, and different families will have different needs leading to different best solutions. My purpose here was not to provide a simple set of answers, but to explain the various options and give some ideas on how to evaluate them. Assuming you can't reach a decision, or are more confused after reading this than you were beforehand, just contact me and we'll work through this together.