Picking the right telescope can be an extremely daunting task at first, but after reading this article in full, I can guarantee you that you'll have the necessary "know-how" to understand which telescopes suit your needs, and which ones don't.
So without wasting any time, let's jump into it.
For those under some time pressure, here's a summary of the main takeaways, although it goes without saying that I'd recommending giving the whole article a read.
Short answer
There are 4 main properties of a telescope that you need to consider when choosing the right one for you:
Aperture - the diameter of the mirror if it's a reflector and the lens if it's a refractor
Focal length - the distance from the lens/mirror to the focal point (where the light converges to produce an in-focus image)
Focal ratio, or f/ratio - the focal length divided by the aperture
Weight
The aperture determines how clear an image will be, and the higher the aperture the better. The focal length determines how high of a magnification you can achieve, and the higher the focal length, the higher the magnification.
A high focal length (>1200mm) is optimal for planetary observation, while a low focal length (<800mm) is ideal for wide-field, deep space observation.
The focal ratio will determine how "fast" the telescope is, which essentially describes how quickly the telescope can collect light. A low f/ratio (<f/5) is considered a fast telescope, and will produce bright images much quicker than a telescope with a higher f/ratio (>f/8).
Often overlooked, the weight of the telescope should also be a factor in your decision making, as the ability to pack a telescope in the back of a car and drive to a less light-polluted area is an absolute game-changer.
Even if you're not interested in going to those lengths, being able to easily move a telescope around a garden to open up different field of views can also not be undervalued.
Additionally, even beginner/intermediate level reflecting telescopes can weigh over 10kg, which when paired with an equatorial tracking mount, which can typically weigh over 10kg themselves, can result in a hefty load that someone with poor flexibility/strength probably shouldn't mess around with!
Table of contents
The Basics
Whenever you see an advert for a telescope, there are 4 main properties of that telescope that you should be keeping an eye out for:
Aperture
Focal Length
f/ratio or focal ratio
Weight
The aperture of a telescope (or camera lens) is simply the diameter of the mirror/lens (depending on which type of telescope it is) that's essentially collecting the light that will eventually be directed to either your eyes, if you're visually observing, or a camera sensor, if you're performing some form of imagery observation.
And why is it important to know the diameter of the mirror/lens?
Well, the larger the mirror/lens, the more light it's able to collect and hence the clearer the image that will be produced.
It's also important to remember that the surface area of the mirror/lens is proportional to the square of the diameter, meaning that if you double the diameter, you'll quadruple what is essentially the area that the mirror/lens is covering.
Unlike focal length and f/ratio, which we'll talk more about in a minute, the aperture of a telescope isn't really dependant on a person's preference, unless you consider that the larger the aperture, the larger and heavier the scope, hence the more awkward it is to use....
Generally speaking, you'll want to go for as high of an aperture as your pockets can afford, because a clearer image is always a good thing!
As I just hinted at though, the higher the aperture, the more it's going to cost you, and hence it's often a situation of trying to get as much aperture as possible, while not compromising on any of the other important properties such as focal length, f/ratio and weight (and without breaking the bank of course)
Typically, you'll see ranges for aperture of say 2 inches at the very lowest, and probably as high as 14 inches, if you're considering a budget of anywhere between £100 to £2000.
As a beginner, I'd advise that you stick between 4 and 10, depending on how much you value portability, which we'll talk about later when we come onto the different types of telescopes that you can buy.
So to summarise aperture, it's essentially how wide the mirror/lens is, which is what determines how clear of an image your eyes/camera lens is able to produce.
The higher the aperture, the clearer the image, and even a subtle increase in aperture will produce substantially clearer images, as they have an exponential relationship.
So next up we have focal length.
Without getting too lost in the specifics, the focal length of a telescope/camera is essentially the distance between the mirror/lens and the focus point.
When photons of light pass through a mirror/lens, they get redirected at a certain angle, and will eventually converge together at some point in space, which will allow you to see as clear of an image as possible (as your eyes/camera sensor is absorbing many photons at the same time, all of which came from different angles).
I'm sure you've all seen photos that are "out of focus", which means that the light wasn't converging at the camera sensor as it should do, and the lens was at the incorrect distance away from the sensor.
The same reasoning applies to when objects appear blurry - our eyes can slightly adjust the distance (focal length) from the focus point (the Retina) to the lens, which allows us to put objects that are at different distances in focus, but most people have eyes that aren't perfect in shape, which causes the focal length to deviate from what it should be, producing blurry images of objects that should otherwise be clear.
Getting this distance is crucial for producing in-focus images, and telescopes will be manufactured in such a way that you simply need to turn a wheel to bring the eyepiece closer, or further away from the telescope mirror/lens to bring an image into focus, which will depend on how far away the object is.
A higher focal length is by no means "better" than a lower focal length, and which one suits you best will completely depend on what you intend to be able to see.
Higher focal lengths will produce higher magnifications, making them ideal for getting close up shots of the ice-caps on Mars, or the rings of Saturn.
On the other hand, lower focal lengths will produce smaller magnifications, and are ideal for wide-field observations such as galaxies, nebulae, full shots of the Moon etc...
It really is up to you, but you just need to remember this one thing...
An Important Concept To Understand
There is no "catch-all" kind of telescope. I know that it's annoying to hear, as you just want to be able to see everything, but, unfortunately, you have to make a choice of which type of observing you'd prefer to do:
Planetary or;
Deep space
What you can do, however, if either you're completely unsure or you'd rather dabble in both types of observing, is go straight down the middle in terms of focal length, in order to get decent views of both of them.
Focal length ranges typically look like this:
200mm for very wide-field images (more like a camera lens than a telescope), perfect for landscape astrophotography, such as picturing the Milky Way
500mm for full shots of your average sized nebula, and a large galaxy such as Andromeda (M31)
700mm for small nebulae and galaxy clusters
1000mm for close up shots of galaxies and nebulae, and fairly wide-field shots of the planets.
1200mm for close up shots of the Moon's craters and for decent shots of the planets, while still being able to capture some small (or very distant) galaxies and nebulae
2000mm for viewing the Great Red Spot on Jupiter, the polar ice-caps on Mars, the craters on the Moon, the rings of Saturn, and decent images of Uranus and Neptune
3000mmm for absolute planet killers!
As you can see from this breakdown, you'll want to be looking at focal lengths of around 800-1400mm if you want a bit of both, but just bear in mind that it won't be a "best of both worlds" situation...
In my honest opinion, you're better off buying a telescope at the end of the spectrum that you prefer, and then investing a much smaller amount of money into a scope on the other end....
Obviously that's the ideal situation though, and it's sometimes not viable, in which case going down the middle with say a 1000mm Skywatcher Newtonian reflector would, in my opinion, be a good choice.
Telescopes with 3000mm of focal length will definitely set you back a comparatively large sum of money, more than likely in the £3000+ range, not to mention the mount that you'd have to buy to handle that beast, but that definitely doesn't mean to say that it's not possible.
In fact, you'll quite often hear of people owning something like a Celestron Edge 11HD, which has a focal length of 2800mm and aperture of 11 inches!
Unfortunately, I can't speak from experience with that one, seeing as it comes in at over £4000 just for the OTA (Optical Tube Assembly)....
But it's meant to be the ultimate planet killer for amateur astronomers, so if it's within your remit, I'd definitely advise heading over to Cloudy Nights for some reviews.
Fun Fact: I'm saying that 3000mm of focal length is a planet killer of a telescope, but remember that I'm talking about amateur astronomy.... The JWST (James Webb Space Telescope) has a focal length of 131 meters! That's 131,000mm... And an aperture of 6.5 meters.
Moving on to f/ratio.....
The focal ratio, or f/ratio for short, is just the relationship between the focal length and aperture of a telescope, and you can easily work it out by diving the focal length by the aperture.
The number that you end up with essentially describes how "fast" your telescope is. I know that might seem strange to describe a telescope as being fast or slow, but it's a really important factor to consider, especially if you plan on taking images through your telescope.
The f/ratio is a measurement of how quickly your telescope can collect light, and faster telescopes will produce brighter images than slower telescopes over the same exposure time, since they're able to collect more light in a given time period.
Unlike cameras, our eyes generally have a fixed exposure time, meaning that we can't wait and collect as much light as possible before producing an image.
The reason why this an important concept to understand is because it will greatly affect your ability to view certain objects in the night sky, as, naturally, there's a massive variation in terms of there being bright objects and dim objects.
Here's a list of the common f/ratios that you'll probably come across, and what they mean in terms of how fast or slow they are:
f/2 is extremely quick, and these telescopes, such as the Celestron RASA series, will set you back a hefty sum of money. They're not that great for viewing the planets, as they collect way too much light in a short period of time and everything just gets over-exposed, hence they're the ultimate telescopes for distant, dim objects like nebulae and galaxies.
f/5 is extremely common, especially for your classic Newtonian reflectors. It's not that slow nor that quick - a sweet spot if you like
f/10 is very slow when considering amateur equipment, and telescopes like these will perform at their best when viewing extremely bright objects like the planets in our solar system
Considering the f/ratio of a telescope is especially important if you plan on taking images with your telescope, as it will essentially determine how long you have to wait to produce images!
In short, tracking inaccuracies can ruin photos over time, and combined with the fact that, in the UK at least, you're lucky to even have a couple of hours of clear skies, the faster the telescope is the better.
Practically speaking, in spite of the fact that you could technically increase the exposure time of a camera sensor to several minutes before suffering from inaccuracies, slow telescopes (high f/ratio) will need much longer than the few minutes that you have to produce bright enough images of DSO (Deep Sky Objects), and unless you don't mind spending hours on end, probably over multiple days to produce a single image of a DSO, I'd advise considering a faster telescope (<f/6)
Another reason to consider a faster telescope is if you don't really want to get involved in practices like guiding, plate solving, stacking etc....
They're not really that relevant to this article, but suffice to say that they're essentially methods of achieving brighter, more detailed images.
If going through the hassle of these isn't very pleasing to you, then that's more of a reason to invest in a fast telescope as you'll produce better images over shorter periods of time, and you might not need to worry about guiding etc... (depending on what your goal is - ie just how good of an image you're aiming for)
The next fundamental is weight, which is obviously pretty straight-forward...
But definitely one that should not be overlooked! (In my opinion at least)
Trust me, the portability of a telescope is something that you should definitely be assessing, unless you're thinking of using the telescope on a fixed mount in an observatory... Otherwise, the ability to pack a telescope into the back of a car, and drive 45 minutes or so to a less light polluted area is honestly a game-changer.
Even if you just want to move it around the garden, it's still exceptionally convenient to have a telescope on the smaller and lighter side, especially if your flexibility/strength isn't what it used to be.
I know many people who choose to use refractors over reflectors, purely because they're often much smaller and lighter, despite them (generally speaking) being less "powerful" per pound or dollar, assuming a budget of a few hundred pounds/dollars.
I've just mentioned a key difference between a reflector and a refractor, but let's just clear that up a bit more for anyone who isn't totally sure what the differences are.
Reflector vs Refractor
To get straight to the point, reflector telescopes use mirrors to reflect light towards an eyepiece, where as refractor telescopes use lenses to refract light towards an eyepiece.
In and of itself, that doesn't really mean a lot, but it's the design that caters for the two different mechanisms that differentiates the telescopes from each other.
Lenses are far more expensive to manufacture than mirrors, which means that you often get way more bang for your buck in terms of aperture with a reflector than with a refractor.
However, because reflectors work by reflecting light off a mirror at the back of a telescope, they often have obtrusive and clunky designs, not to mention that they weigh considerably more than refractors.
One is neither better nor worse than the other in reality, and it ultimately just depends on your preferences.
They both come with their own faults, for example reflectors need collimating, and usually require coma-correctors if you plan on taking wide-field images of stars, and basic refractors suffer from chromatic aberration, but it's not really worth getting into here, since they're definitely not fundamentals, and unless you plan on taking the hobby very seriously, you don't need to worry about them at all.
Generally speaking, if you want to be able to get nice, colourful and closeup pictures of the planets, then you'll want to go for a reflector (refractors of the required aperture would be way too expensive for the average person), and if you want to take wide-field shots of nebulae and galaxies, then you should go for a refractor.
Simply put, refractors are more powerful per inch of aperture, but also far more expensive than reflectors.
It's worth saying here that you'll want to invest in a good equatorial tracking mount if you plan on taking images, so that your telescope can track objects as they move across the sky due to the Earth's rotation, but that's a bit off topic for this article.
The last thing that's worth covering is the plethora of accessories that you can buy to improve both visual observations and images.
There really are tons of different gadgets out there, but the most important ones to know about for a beginner or intermediate would be the following:
Barlow lenses - they slot between the eyepiece/camera to increase the magnification. They're extremely handy for getting closeup shots of planets or the Moon, and come in a few different levels of magnification - 2x, 3x and 5x. It's also worth noting that you can stack a 2x and 3x together to produce a 5x, if you don't want to get all 3, although barlow lenses do slightly affect the clarity of the image. In most cases though, it's neither here nor there.
Filters - broadly speaking, filters help to produce clearer images, but there's tons of different ones that each filter incident light in various different ways. Most notably though, I'd recommend lookout into the following:
light pollution filters if you don't have access to clear(ish) skies
H-alpha emission filters if you plan on taking images of nebulae that essentially release a lot of red light, and;
solar/lunar filters to look and take pictures of the Sun and the Moon.
Just to provide some context on that, everyday cameras have sensors that aren't very sensitive to red light (because there's not much of it around on Earth), but red is an extremely prominent colour elsewhere in the universe, as it comes from the emission of light from Hydrogen atoms (which account for roughly 75% of all the normal matter in the universe), hence being able to detect that is very beneficial. Instead, or as well as using filters though, you can also get dedicated astrophotography cameras that are sensitive to red light, and you're even able to modify everyday cameras to become sensitive to this H-alpha emission.
Focal reducers - these are lenses that go in front of eyepieces to essentially reduce the focal length of the telescope. They can be very handy if you have your eyes set on a telescope with a high focal length, but also want to dabble in some deep space imaging. However, they can be extremely expensive depending on the type of telescope and how much you need to reduce the focal length by. Ultimately, it might not be worth it for most people, but I do feel like it's worth mentioning.
That's pretty much everything that you need to know.... I know I've covered a fair amount in this article, and it's all very important information for people who are looking at buying their first ever telescope, or fancy upgrading, so I'll wrap up with a summary of what we've talked about. (I'll also include this at the beginning of this article for people under time pressure)
Summary
There are 4 main properties of a telescope that you need to consider when choosing the right one for you:
Aperture - the diameter of the mirror if it's a reflector and the lens if it's a refractor
Focal length - the distance from the lens/mirror to the focal point (where the light converges to produce an in-focus image)
Focal ratio, or f/ratio - the focal length divided by the aperture
Weight
The aperture determines how clear an image will be, and the higher the aperture the better.
The focal length determines how high of a magnification you can achieve, and the higher the focal length, the higher the magnification. A high focal length (>1200mm) is optimal for planetary observation, while a low focal length (<800mm) is ideal for wide-field, deep space observation.
The focal ratio will determine how "fast" the telescope is, which essentially describes how quickly the telescope can collect light. A low f/ratio (<f/5) is considered a fast telescope, and will produce bright images much quicker than a telescope with a higher f/ratio (>f/8).
Often overlooked, the weight of the telescope should also be a factor in your decision making, as the ability to pack a telescope into the back of a car and drive to a less light-polluted area is an absolute game-changer.
Even if you're not interested in going to those lengths, being able to easily move a telescope around a garden to open up different field of views can also not be undervalued.
Additionally, even beginner/intermediate level reflecting telescopes can weigh over 10kg, which when paired with an equatorial tracking mount, which can typically weigh over 10kg themselves, can result in a hefty load that someone with poor flexibility/strength probably shouldn't mess around with!
The Next Steps
Now that you've got an understanding of what you need, and feel like you're ready to start narrowing down what's probably a long list of telescopes, perhaps consider checking out my telescope reviews - I'll leave a link to them below.
What we've covered in this article though is more than enough for you to venture on your own, so with that mind, here's a few links to some telescopes that I'd recommend checking out, for all levels and price ranges.
The ones from Amazon are affiliate links, meaning that we'll receive a small percentage of the sale at no extra cost to you - It really does help Expansive to grow and provide as many people as possible with the opportunity to learn about our universe!
Although I'd definitely recommend checking out my products page for a more inclusive overview.
Thanks for reading!
Celestron AstroMaster 130EQ reflector
Celestron AstroMaster 102AZ refractor