We often get asked “which telescope should I get”, maybe for yourself or as a present. Well as you might expect there’s no right answer for everyone, but here are a few ideas and things to consider.
There is one answer to the question: “what’s the best telescope to get” and that is: “the one you’ll actually use”! There’s no point buying a telescope that gathers dust because it’s too heavy to carry outside, or too cheap to actually see anything, or doesn’t do what you wanted it to do, or… You get the idea.
I’m really aiming this article at beginner telescopes, perhaps as presents, rather than trying to cover all of the issues for a more experienced astronomer. However, a lot of the same principles do apply.
Hopefully this gets you started. Here are a few things to consider before buying that telescope.
Telescope Help Shop
If you do buy a telescope for Christmas, why not come along to our “Telescope Help Shop“. We’ll show you how to use it and what to look at. Keep an eye on our website for more details and the next event.
ASE Observing List for Beginners
Our ASE-24: Observing List for Beginners is now available, so that you know what objects to look at and how to find them with that new telescope.
How much do you want/have to spend?
Of course it would be nice to have an unlimited budget but few of us do. (However, if you do you might want to consider buying Hubble! Shipping costs could be high though…) So decide how much you have to spend and then do your research based on that.
I would suggest you don’t spend less than about £130 though or it might come under the “too useless to see anything worthwhile” category (just my opinion on what I’ve seen) which might just put you off before you’ve even started. Perhaps instead you should consider a good pair of binoculars – there’s nothing more satisfying than lying back in a deckchair on a dark night and sweeping along the Milky Way with binoculars.
There are decent cheaper telescopes such as this one (£99), described as a table-top telescope, but you will need something solid to put it on. Tables aren’t generally regarded as being solid telescope mounts so you may need to buy a solid tripod to put it on anyway. The mount is as important as the telescope itself and for beginner telescopes they are sold together as a whole setup. That’s one reason why you shouldn’t go too low.
Disclaimer
Of course we’ve got to have one. This article is just one of many opinions – you’ll get as many as there are telescopes, and there are a lot available. We don’t – and won’t – actually recommend any specific telescope or supplier. This article is based on what we have seen, purchased, used and suppliers that we’ve bought from in the past. The telescopes shown are just examples but it would be impossible for us to review all of the ones shown here.
Having said that, astronomical instrument suppliers are in general a pretty good and helpful bunch. They live or die by their reviews so if they offer bad service they usually don’t last long.
Most suppliers will offer all of the telescopes shown here, even local ones who may not have them in store but can order them up for you if that’s what you prefer.
You can see a list of suppliers on the links page.
What do you want to see and do?
If you’re new to astronomy or buying it for somebody else then the chances are that you don’t really know exactly what you want to do but you want to see some good stuff. That’s fair enough, so you want a telescope that can show you a good range of things such as the Moon, planets, star clusters, nebulae and galaxies. All of the telescopes listed below will allow you to view these things to some level.
Or maybe you do know and you want to see or photograph those fantastic colour images that you see in astronomy magazines or on the NASA website?
Time to be realistic: those were often (not always) taken using expensive equipment or by astronomers with many years of experience behind them. Putting your eye to the end of a telescope will rarely show that.
I don’t mean to put you off – quite the opposite. In fact when you look through a telescope for the first time at the Moon, satellites of Jupiter or the rings of Saturn, I promise you you’ll never be the same again! The connection between your little eye and the rest of the universe is just mind-blowing! When you look directly at a galaxy, it’s so far away that you are in fact looking millions of years back in time. You’re seeing that galaxy as it was millions of years ago, when it’s light started out on the journey towards your eye. TELESCOPE = TIME MACHINE!
If you do want to take photos through your telescope you can do simple imaging with most telescopes – even using your smartphone camera (you can get attachments to hold the phone at the eyepiece end of the telescope – many different types and prices). A motor drive certainly helps but is not essential for the Moon for example. Here’s a photo I took by attaching my DSLR on the end of a simple 80mm refactor on an altazimuth mount (see below for what this means) with no motor drive.
And with a bit of practice and experience you really can take amazing images of the night sky. See our Flickr Group for examples of what some of our members have done with a wide range of equipment.
But start out with realistic expectations and you won’t be disappointed.
Get a good book such as Turn Left at Orion, which will show you what to expect, what objects will look like in different telescope sizes, and many ideas of what to look at. Keep an eye on our website for ideas of what to observe at various times in the year. We have published articles on Globular clusters, Open clusters, comets, the Moon, Lunar eclipse, …
WARNING: Never look at the Sun directly!
If you want to observe the Sun, get advice first. It’s important that you use the right equipment or you will blind yourself, permanently! If you get a telescope with a solar filter for use at the eyepiece, DO NOT USE IT! It is dangerous. Solar filters should only be used over the main objective. Don’t take the risk – get advice! There are safe ways to do it and we can help you do it properly.
Types of telescope
There are essentially 3 types of telescope:
Refractor
As used by Galileo, this is what most people think of when they think of a telescope, with a lens at the front and you look through an eyepiece at the end of a long tube. Refractors tend to be cheap at the lower end of the market but very expensive at the top end. The size in mm is the diameter of the main lens which determines how much light you gather.
Refractors are generally maintenance free but cheaper ones can show some false colour fringes around brighter stars. But if Galileo could discover the moons of Jupiter, rings of Saturn and craters on the Moon with something a fraction as good as one of these, then you can too – for yourself.
Here are some examples with links to different supplier websites. There are many more on offer that may be more suitable but these are some examples to help you decide.
Basic 102mm refractor on an app controlled altazimuth mount (see below). About £340
102mm refractor on an altazimuth mount (see below) with slow motion controls for fine movement. About £340
90mm refractor on an altazimuth mount (see below) with slow motion controls for fine movement. About £160
Reflectors
The Newtonian reflector was invented by Isaac Newton in the 17th century and is one of the most common types of telescope in use. In a Newtonian reflector there is a main mirror at the bottom end of the telescope which focuses and reflects the light up to a smaller secondary mirror near the top of the tube which then directs the the light off to the side where you can view the object through an eyepiece.
It’s easier to built large reflectors than refractors, so they tend to be bigger instruments. The larger the lens or mirror, the more light gathering power it has and so you can view fainter objects. Reflectors do require some maintenance though, such as adjusting mirror alignment (collimation), and after many years of use the mirrors may also need to be re-aluminised. They don’t show false colour like refractors because they don’t use lenses.
Here are some examples with links to supplier websites:
130mm reflector on an equatorial mount with slow motions for fine movements. About £200
130mm reflector on a GOTO altazimuth mount. For use with a smartphone app. About £360
200mm reflector on a dobsonian mount (see below). The most light gathering power here and a good all-rounder – very popular. About £290 (There is 150mm version of this for £220)
Compound
A compound telescope can be of several types: a Cassegrain, Schmidt-Cassegrain or Maksutov among others. The two most common types are Maksutovs and Schmidt-Cassegrains with Maksutovs being the most common for smaller scopes. They are similar in that light passes through a glass corrector plate at the front of the tube, hits the main mirror at the bottom, reflects up to the secondary attached to the corrector plate and is then focused down through a hole in the centre of the main mirror. You then view the image through an eyepiece at the bottom of the tube in a similar position to a refractor.
Compound telescopes tend to be more expensive and of longer focal lengths, making them best suited for observing the Moon and planets, although they are useful for observing other objects too. They don’t generally show false colour. One of the downsides can be cool-down time. Because they have a thick corrector lens at the front, it can take longer to cool down to the outside temperature when you take the telescope outside. If you get thermal tube currents it can affect the image quality. So take the telescope outside for a while to cool down before you use it. (This applies to all telescopes actually but more so with compounds.)
Here are some examples with links to supplier websites:
Diagrams clipartxtras.com
90mm Maksutov on a GOTO altazimuth mount. About £300
102mm Maksutov on an equatorial mount with manual slow motion controls. About £280
127mm Maksutov on an app controlled GOTO altzimuth mount. About £480
Telescope mounts
There are 2 basic types of telescope mount: altazimuth and equatorial. It is important that whichever mount you choose it should be sturdy enough to hold the telescope without shaking. If the mount is wobbly then it doesn’t matter how good the telescope is.
Altazimuth mount
An altazimuth mount is very simple and rotates in two axes: up and down vertically and in a circle horizontally. Altazimuth mounts are the simplest to use.
There is a type of altazimuth mount called a Dobsonian (named after John Dobson, the man who invented them) and they are particularly easy to use. They are usually floor standing (smaller ones can be used on a table) and you simply push the telescope around and point it at the object you want to observe. The telescope glides easily on simple, smooth bearings.
Equatorial mount
An equatorial mount is more complicated. It sits at an angle so that one axis points at the celestial pole (the part of the sky above the Earth’s pole). This is so that the mount can track objects in the sky by rotating in just one axis.
GOTO mounts
Both altazimuth and equatorial mounts can be GOTO. A GOTO mount is driven in both axes by small motors that point the telescope at objects in the sky for you, controlled by a hand controller. The motors will then track the object and keep it centred in the eyepiece for long periods of time. The controller generally contains a database of thousands of objects. You go through an alignment routine at the start of every observing session to tell the mount where it is pointing, which requires you to be able to identify a small number of bright stars. It’s a gadget, it’s fun, but also useful if you find it hard to locate fainter objects because of light pollution.
App controlled mounts
The latest altazimuth GOTO mounts can be controlled by a smartphone app. Take the Skywatcher AZ-GTi mount as an example. After downloading and installing the app, it will take you through an alignment sequence and then allow you to find and track many objects in the sky. Very simple to use but also very powerful.
A word about aperture, magnification, focal length and f-ratios
Sound complicated? Not really but adverts can make it confusing.
If you see a telescope advertised something like: “See stars and galaxies at magnifications of over 300x” – then it’s missing the point and probably not one you should buy. And if you buy it in a toy shop then it’s probably a toy!
Aperture is the size (diameter) of the objective – the main lens or mirror used to catch the light. The larger the better, as long as it’s good quality.
Focal length is the distance behind (in front for a reflector) the objective that the image is brought to a focus. At this point you place an eyepiece to magnify it. A refractor or reflector will be approximately as long as the focal length. A compound telescope has a folded light path and so is shorter and more compact.
F-ratio is a measure of the focal length divided by the aperture. A telescope is said to be fast if it has a small f-ratio (say f4 – f8) and slow if it has a larger one (f9 – f15). Fast telescopes generally work better for star clusters, galaxies and nebulae. Slow telescopes generally work better for the Moon, planets and Sun. Both work fine for all objects though but if you want to specialise, choose appropriately.
Magnification isn’t everything – in fact it’s less important than aperture. The eyepiece you use with a telescope determines the magnification.
To work out the magnification: take the focal length of the telescope (in mm) and divide it by the focal length of the eyepiece. So for example a refractor with a focal length of 600mm with an eyepiece of focal length 20mm will give a magnification of 30x, a good choice for smaller telescopes. I know it seems low and not very exciting but it really is true.
I generally use my telescopes at magnifications of about 30 – 60x as that gives the most pleasing views. If you’re looking at the Moon, planets and some smaller objects, then sometimes you might want to increase the magnification to see more details, but only if the conditions allow. There’s something called “seeing” which is a measure of how stable the atmosphere is. If seeing is poor, and it often is in Scotland, then objects may be fuzzy and dance around in the eyepiece. A higher magnification will just increase the fuzzy dancing.
Summary
- Choose a telescope that will actually get used.
- Consider joining a local astronomical society. The Astronomical Society of Edinburgh has telescopes to lend to members so you can decide what to buy yourself. You can also get help and guidance from experienced astronomers.
- If you have a small amount to spend maybe choose some good binoculars instead.
- Decide what you want to see and do with the telescope and choose a telescope type and size to match.
- Make sure you know how big and heavy the telescope will be – you want to be able to move it outside!
- Refractors and Maksutovs are best suited to Moon and planets, large reflectors to nebulae, star clusters and galaxies, but all telescopes will work for all objects.
- Choose an altazimuth, Dobsonian or equatorial mount.
- Decide if you want/need GOTO – it’s a fun gadget, is very helpful but not totally necessary and adds to the cost.
- Don’t add too many, if any, accessories to start with. As you get more experienced you can buy more or better eyepieces when you know what you need.
- Use it to explore the wonders of the universe. You’ll love it!
- Come along to our special “Telescope Help Shop” to get help on how to use it.
- Use our ASE24: Observing List for Beginners to get you started.
Article by Mark Phillips
I’ve been an astronomer since I was 9 and over the past 40-odd years I’ve bought and used many different telescopes – far too many according to my wife. Not all of them were the right purchases at the time, so I hope this helps you avoid some of the pitfalls. There is no right answer for everyone.