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What to Look For When Buying a Telescope

Choosing the right telescope, particularly for your first instrument, is a difficult task and you may be tempted to turn to forums and facebook groups for help.

“Hi, I am new to this. What telescope should I get?”

An apparently innocent and straightforward question that will blow wide open the proverbial Pandora’s box:

Get a Dobson. No, get a Newton. A Frac will be better. What is it that you want to do? Get a binocular. Neither, consider the mount first! Yes, but what is your budget? Enough with these questions already, use google! (yes, some people get really annoyed about such posts). 

And don’t even try to add to your question a link to that amazing and shiny $50 telescope found on amazon 🙂

The question, as such, is very poorly formulated. You would not go on the internet asking “hi guys, I am hungry. What should I eat?”, wouldn’t you?

But what is that you should know and say to ask that question in the proper way?

With this article, I will help you make the best informed decision for your needs. Or, at least, to ask a better question.

what to look for in a telescope

Do You Really Need A Telescope?

First thing first: I know you want a telescope but… do you really need one?

The observable universe, at 93 billion light-years across, is rather large and everything is so far away from us that of course you need a telescope. Or is it?

Funny enough, the things for which you really need a telescope are those closer to you

How so? Well, size and distance defines the apparent size for an object, in this case, how large celestial objects appear to be in the sky.

Take the Andromeda galaxy. Sure enough is far, sitting about 2.5 million light-years from us, but is also 220 000 light-years in diameter. 

On the other hand, the Moon is in our backyard, a mere 350 000 km from us. But the Moon diameter is 10 000 000 000 000 000 times smaller than that of Andromeda.

If Andromeda were bright enough for us to see it in all its glory, it would appear in the sky about 6 times larger than the full Moon. Unfortunately, we can only spot its bright core as an unimpressive small, greyish cloud.

A common 200mm telephoto lens, though, is long enough to show you the Andromeda core, the spiral arms, and the many dust lanes within the disc of the galaxy.

Andromeda galaxy photographed with a 200mm lens
The Andromeda galaxy, photographed with a 200mm lens.

But take a photo of the Moon with the very same 200 mm lens, and you will not see much more than what is already visible at the naked eye.

Moon photographed with a 200mm lens
The Moon photographed with a 200mm lens.

For the planet it is even worse. Point your 200mm lens at Jupiter, the largest planet in our Solar System, and you will get a featureless bright dot with, if you are lucky, four even smaller dots around it: Jupiter’s largest moons. 

For the planets you need a telescope, there is no other way. 

So, if you are interested in photography and in deep-sky, you may be better off starting with a star tracker and your classic photographic equipment.

deep sky images taken with a regular camera
No telescope was used for these images, just regular photographic lenses and a SkyWatcher Star Adventurer Pro star tracker.

Get a telephoto lens around 3-400mm (or longer) and a photographic tripod, and you can start getting images of the entire lunar disc that show a good deal of details.

closeup image of the moon shows lots of details
The Moon photographed at 400mm shows quite a lot of details.

Finally, since the Sun has the same apparent size as the Moon, a simple solar filter on your longest telephoto lens and a tripod will be enough to photograph with ease the sunspots.

But to observe the Moon and to have a true immersive experience with the night sky, a simple 8×40 binocular is hard to beat, without all the complications and constraints of a telescope. 

What Telescope Is Best For You? Test Case Scenarios

Ok, so you really want a telescope, but how to decide?

three different types of telescopes
These are only three of the many more types of telescopes available on the market.

A few classic scenarios will help you to get familiar with the many options available on the market.

Telescopes For Kids And Beginners On A Budget

Kids are naturally curious and, sooner or later, they will start asking about those shiny things they see up there.

child looking through a telescope
My 3 years old is discovering the Celestron FirstScope 76/300 tabletop telescope. She is crazy for the Moon 🙂

If you are looking for a telescope to initiate a young kid to the wonders of the universe, here is what you should look for:

  • a budget-safe telescope
  • a small and lightweight telescope
  • a telescope that is easy to use and fast to set up

A small tabletop dobsonian like the Celestron FirstScope 76/300 telescope fits the bill perfectly and is by far the best option. 

Celestron FirstScope 76:300
My Celestron FirstScope 76/300: a good and affordable choice for kids, with a useful accessory pack, you can buy as an extra to extend the scope capabilities.

It is so easy, simple, and cheap that you can let your kid do the setup and everything, rather than just raise him/her to look through the eyepiece.

We grown-ups can also benefit from fast setup time and ease of use typical of tabletop dobson telescopes.

choice-telescope-setup

If you don’t have much space for storing your telescope, a tabletop telescope with a collapsible trousse design is a very compact instrument, for the dobson standard.

holding a SkyWatcher Heritage 130p flextube 130:650
Me holding my SkyWatcher Heritage 130p flextube 130/650. Once in use, the tube length doubles but the whole assembly weighs only about 6kg: still a compact and portable setup.

Among these compact dobsons, the SkyWatcher Heritage 130p Flextube 130/650, Skywatcher Flextube Heritage 150p, are a very good choice. The Orion StarBlast 4.5, while not collapsible, is still worth considering

Orion StarBlast 4.5

The Orion StarBlast is a rather compact tabletop dobson, with a classic manual alt/az mount, very simple to use.

These telescopes are a no brainer to use and so fast to set up, that will not be a problem to prepare everything for letting you comfortably observe the Moon and the planets even for quick sessions.

teenager looking through telescope to see Jupiter
My older son is observing Jupiter for a few minutes before dinner. No long setup here to hold you from having a quick glance at the sky whenever you can.

While portable, a dobson, particularly a tabletop one can be difficult to use in the field, far from the comfort of your garden.

If you often travel to a different location, the Celestron Starsense Explorer 127/1000 is a more suitable choice. This telescope comes with a computerized mount controlled by your mobile to easily frame your target.

While all these telescopes are meant for visual astronomy, you can take photos and videos with your mobile phone or compact camera using an adapter to hold it at the eyepiece.

moon photographed with iphone and skywatcher 130p flextube
The Moon with my iPhone on the SkyWatcher 130p Flextube and 25mm eyepiece.

Finally, if you want something easy particularly suited for planetary and lunar observation and photography, the Skywatcher Virtuoso can be a better choice.

This setup combines a very compact 90/1250 Maksutov telescope to a motorized tabletop alt/az mount, and you can attach a DSLR or planetary camera directly to the telescope. 

Skywatcher Virtuoso

The Skywatcher Virtuoso is a great beginner telescope for exploring and photographing the wonders of the Solar System.

Telescopes For General Observation

If you want to be serious about observing the cosmos, you may want to look at something more performant than the previous telescopes, with better optics and larger aperture. 

A classic dobson is the best choice and great value for the money, as they offer the largest aperture you could buy with your budget.

It is not for nothing that dobsonian telescopes are called “light buckets”.

The Orion SkyQuest XT8 Classic dobson is a classic 200/1200 dobson. Similar telescopes can be found in the catalog of all the most common brands, from SkyWatcher to Celestron.

Orion SkyQuest XT8

The Orion SkyQuest XT 8 Classic is a nice 200/1200 f/6 dobson.

Dobsonian telescopes are reflecting telescopes mounted on an alt/az rocker box, which allows for a smooth and easy manual tracking.

choice-telescope-manual-tracking-dobson

But they are big and heavy, not easy to transport in location.

A more portable classic is the Celestron Astromaster 130/650 EQ, which is intended mostly for visual observations.

Celestron AstroMaster 130EQ

The Celestron Astromaster EQ comes with a manual equatorial mount.

Same as for the classic dobson telescopes before, all major brands have similar Newton telescopes like the astromaster in their catalog.

Telescopes To Observe And Photograph The Moon And The Planets

Planets look very small in the sky. Even Jupiter requires long focal lengths if you want to see some details on its surface.

Once again, dobsonian telescopes pack both a long focal length and a large aperture, making it a good choice.

But if you limit yourself to the exploration of the Solar System, another kind of telescope can outperform a dobson in a more portable and compact package: a Maksutov telescope.

holding a SkyWatcher Skymax 90:1250 Maksutov telescope
Posing with my tiny SkyWatcher Skymax 90/1250 Maksutov telescope.

Maksutov are catadioptric telescopes characterized by a short tube, a low weight and sharp optics. Together with Cassegrain telescopes, they are often considered to be the perfect grab & go solution.

They offer superb views of the Moon and the Planets and can nicely resolve bright star clusters. But because of the long focal length, they have a high f-ratio, which makes them not ideal for faint deep sky objects.

Easy to use, a Maksutov can reach focus with almost anything you can attach to it, and the compactness and lightness of the tube means you can use them on relatively light mount too, both for visual and photography.

using a SkyWatcher Skymax 90:1250 for lunar and planetary astrophotography
I use my SkyWatcher Skymax 90/1250 on both my lightweight Skywatcher Star Adventurer and my Skywatcher Az-GTi mounts for lunar and planetary astrophotography.

Skywatcher has a full line of Maksutov: 90/1250, 102/1300, 127/1500, 150/1800, and 180/2700 but, due to their weight, only the first two can be comfortably used on a SkyWatcher Star Adventurer (or similar trackers) and small computerized mount as the Skywatcher Az-GTi alt/az mount.

Skywatcher Skymax 102/1300

The Skywatcher Skymax 102/1300.

The Schmidt-Cassegrain Celestron Nexstar family offers a range of telescopes with computerized alt/az mount and are great alternatives to Maksutov. 

Celestron NexStar 5SE

The Celestron Nexstar 5se.

Thanks to dedicated reducers, they can also be used for deep sky astrophotography if mounted on an equatorial mount.

All Rounder Telescopes

While it is not easy to find a telescope that performs great with every target, there are scopes that are reasonably good.

A good all-rounder telescope should offer a bright image thanks to a large aperture and a decent focal length

Accessories such as dedicated focal reducers and wide-field eyepieces can improve the telescope performances on deep sky observation and astrophotography.

The Celestron C6 and C8 are compact and light Schmidt-Cassegrain telescopes that are great grab & go all-rounder telescopes, particularly the C6, also available in a bundle with a computerized equatorial mount.

Celestron C6
The Celestron C6, a versatile Schmidt-Cassegrain telescope.

The SkyWatcher 130 PDS and 150 PDS (also available in a bundle with a computerized equatorial mount) are two cost-effective reflector telescopes that are particularly suited for both observation and photography, thanks to a generous backfocus and a solid dual-speed focuser.

Skywatcher Explorer 150:750 PDS with EQ5 Pro Synscan Mount
The Skywatcher Explorer 150/750 PDS with EQ5 Pro Synscan Mount.

Refractor telescopes are great and more portable than classic reflectors, are easy to clean and do not need to be collimated. Also, refractors are often more contrasted than reflectors and may offer sharper images.

SkyWatcher has the EvoStar and Esprit line of refractors that are very good, with the Evostar 72ED being a favorite among enthusiast astrophotographers. 

SkyWatcher EvoStar 72 ED

The SkyWatcher EvoStar 72 ED, a good performer that is also lightweight. Great for astrophotography too.

All major brands offer a complete selection of refractor telescopes. But they cost and weigh more than equivalent reflecting telescopes.

What Should You Look For In A Telescope?

So, with so many choices around, what should you look for in a telescope, to be sure you will buy the right one for you?

Common Features To Look For

Telescopes come in different designs and variations, but they all share some important features you should carefully consider before you pull the plug on a particular setup.

Aperture

Aperture is king! 

telescope aperture and resolution
The effect of increasing the aperture on the image resolution. (Image credit: Christopher Go).

In the world of telescopes, with aperture, we define the diameter of the front lens or opening, depending on the telescope design. 

The aperture is fixed, and the larger the telescope, the more details you can see and the brighter the image is. 

Also, a large aperture telescope allows for a greater magnification limit.

Focal length

As for photographic lenses, the longer the focal length, the larger the target appears to be in the field of view of the telescope.

Long focal length telescopes are ideal for lunar and planetary observation and photography.

But are they good for getting close to deep sky objects? For this, the f-ratio is crucial

F-ratio

The ratio between the focal length and the aperture of a telescope defines its f-ratio and, same as with photographic lenses, the lower the f-ratio, the brighter the image.

Moon and planets are fairly bright, and it is not uncommon to use setups with an f-ratio of 20 or more.

But deep sky objects are very dim and to visually observe them you need a fast telescope, something in the order of f/5.

With a camera you are not limited to the light gathering capability of your eye. However, even so, you still want to collect a fair amount of light in a reasonably short time and a fast (low) f-ratio definitely helps.

That said, you can see why it is difficult to do deep sky observation and photography with a long focal telescope. My Skymax 1250/90 is a f/14: a fast f/5 telescope with the same focal length would have an aperture (diameter) of 1250/5 = 250 mm.

Not a small, light and/or cheap scope.

Optical Aberrations

All telescopes have some sort of optical aberrations: coma, field curvature, or chromatic aberration

example of what Is Chromatic Aberration
Example of chromatic aberration.

They are not a deal breaker for visual observation, but for photography, you need to take care of them.

Fast reflectors suffer from coma, and if you want to use them for photography, you have to have a coma corrector.

Achromatic refractorssuffer from both field curvature and chromatic aberrations. A field flattener (sometimes combined to a focal reducer) is necessary to improve deep sky performances.

uncorrected field curvature from my SkyWatcher EvoGuide 50 ED
The circle in the image shows “runaway” stars along the edge of the image, a sign of an uncorrected field curvature from my SkyWatcher EvoGuide 50 ED.

Apochromatic refractors make use of low dispersion ED lenses to reduce or eliminate chromatic aberration.

All these “fixes” come at a cost, and you should consider them when deciding your budget, particularly if you intend to do astrophotography with your telescope.

Focuser

The focuser allows you to focus the image when you photograph or look through the eyepiece.

There are different designs available, from the simple helical focuser to double-speed crayford focusers for precise focusing.

Cheap focusers will not support the weight of a camera and are not really useful for astrophotography.

The focuser of the Celestron FirstScope 76:300
The focuser of the Celestron FirstScope 76/300 can’t hold much more weight than that of an eyepiece.

Another thing to consider when shopping for your telescope.

Backfocus

How far back a telescope can focus the image will decide if it can be used for astrophotography.

If the back focus is very long, you can use extension tubes to place the camera sensor at the right distance from the scope, but if the back focus is too close to the back of the telescope, you will not be able to achieve focus.

Budget newtonian telescopes are meant for observation only and their back focus is too short for reaching focus with a camera. 

The only option for using a camera in prime focus is to use a barlow lens, which extends the back focus of the telescope, but this comes at the cost of working with a narrow and darker image.

In this case, it is better to work in eyepiece projection mode, with a small compact camera or your camera phone held at the eyepiece with a proper mounting adapter.

connect iPhone to the eyepiece of SkyWatcher Heritage 130p
It is simple to connect my iPhone to the eyepiece of my SkyWatcher Heritage 130p Flextube with a cheap universal phone adapter.

The Celestron NexYZ is my favorite adapter for a camera phone, but is heavy so your focuser must be good enough. Not a problem with Maksutov telescopes, though, as the eyepiece is not on the focuser.

Celestron NexYZ

The Celestron NexYZ is a universal adapter with independent fine adjustment on three axes, to allow precise alignment between the phone and the eyepiece.

Mount

The mount you will put the telescope on is as important as the telescope itself, if not more.

The mount must be able to comfortably support the weight of the telescope plus accessories and to allow you to reliably track the motion of the celestial bodies.

This can be done either manually (mostly for observation with budget equipment) or using precise motors (a must for astrophotography). Computerized mounts with GoTo capability are for high-end setups.

As a rule of thumb, the larger the scope, the sturdier the mount must be and this comes, once again, at a cost.

For astrophotography, it is commonly accepted that the total weight of the equipment should not exceed the 50% (or 75%) of the declared maximum payload for the mount. 

The type of mount is crucial.

Alt/Az mounts are perfect for visual observations, but they are not the right kind of mount for astrophotography.

Alt:Az mount and how it tracks the stars
The working principles for an alt/az mount.

If you want to photograph, you need to take long exposures and for this you need an equatorial mount.

As opposed to alt/az mounts, the equatorial ones not only track the movement of a target across the sky, but it also compensates for the field rotation.

equatorial mount and how it tracks the stars
The working principle for an equatorial mount.

Size And Portability

Finally, there is the question of size and portability. A complete setup can weigh anywhere from 2kg to 100kg.

And the telescope size can range anywhere from 30cm to over a 1 meter or more.

When you shop for a new telescope, ask yourself these questions:

  • Do I have the space to store the whole setup?
  • Do I need to move the gear to a darker location, or can I observe/image from my place?
  • Do I need to hike with my equipment?

What Are You Most Interested In?

We have left for last what perhaps is the most important question you should answer. 

What do you want to do with your telescope: observation or photography?

While telescopes come in many flavors (designs), roughly speaking, they all let you see up close things that are far and look small in the sky. 

If before starting reading this article you could think you would be able to see and photograph with any of them, it should be clear by now that this is not true.

The reason for this is that for a given application, you have to consider the whole package: the telescope and the mount it sits on.

To observe, you could do with a setup as simple as a small telescope sitting on a ball head: it will be frustrating to keep the target in the frame, but with the planet is still doable. 

Most of the dobsonian telescopes commonly recommended for beginners wanting to observe the night sky are mounted on large and smooth alt/az mounts for manual tracking.

If you want to photograph with a telescope, particularly deep sky, you need much better equipment. 

A motorized equatorial mount large enough to comfortably support the weight of the telescope and accessories is a bare minimum

But a computerized mount with GoTo capability and a guiding system is highly recommended.

Observation Vs Astrophotography: Which Is Better?

Observation and astrophotography are very different. Observing is probably cheaper, less demanding on the equipment and on your time and skills than photographing. 

But before discarding the possibility of using the equipment for photography, realize that even the largest telescope will not let you see things as in photography

You are against the limit of the human eye, which is not very good to pick up faint light, particularly if its source is small. And forget about all those nice colors too: most of the time you will see greyish puffy clouds with some details.

Also, to observe deep-sky objects, you must be under a decently dark sky (Bortle 3 or lower).

Still, observing can be a great experience for viewing the Moon, the planets, double stars, and globular clusters.

What Is Your Budget?

I am more of an astrophotography enthusiast than a visual astronomer, but I can say that of the two, chances are astrophotography requires the bigger budget.

You can, of course, do astrophotography on a budget, with a star tracker such as the Skywatcher Star Adventurer Pro, your DSLR, and photographic lenses, but in general, in the long run, photography will cost you more than observation.

recommended setup of the skywatcher
The SkyWatcher Star Adventurer PRO is a great tracker that you will not easily outgrow.

A decent dobsonian telescope for observation, with a couple of eyepieces and a red dot star finder, can cost you around 200 euros, new. To that, add a barlow lens and an adapter to snap some videos with your phone and you are good to go.

Sure, you can then improve the quality of the eyepieces (and some are not cheap), but let’s say that at 3-400e, you can have a good amateur setup for visual observations.

If you want a motorized mount, maybe with a GoTo capability, then you have to double or triple that budget.

For astrophotography, a tracker that will allow you good flexibility will set you back of about 400e. 

But if you are mainly interested in starry landscapes and milky way shots, you can start with the Omegon Minitrack LX2 for as little as 200e with the required ball head and wedge.

Omegon Minitrack LX2
The Omegon Minitrack LX2: the perfect grab & go tracking device for starry landscapes and wide star fields.

A budget of 500e will let you photograph with lightweight photographic equipment, as no telescope will fit on a tracker. 

Some notable exceptions to the previous statement are very light refractors like the William Optics Red Cat Z51 and Maksutov telescopes like the Skywatcher Skymax 90/1250

Full-grown astrophotography mount will set you back by at least 700e, particularly if they have GoTo.

Finally, a word about the many bundles (mount + telescope) you can find on the classic webshops: while the price tag can be interesting, understand that many combinations are really suitable for observation only. The mount is not usually good enough for deep sky astrophotography.

Astrophotography is very demanding compared to visual observation.

Types Of Telescope

The first astronomical use of a telescope dates back to Galileo Galilei. With as little as 30x magnification, Galileo and its telescope paved the road for modern astronomy.

But the term “telescope” is a very general one, and it is used to indicate any optical instrument able to magnify distant objects. In practice, there are three main designs of telescopes and many more variants of those designs.

Each has its own set of pros and cons.

Reflecting Telescopes (Reflectors)

In a reflecting telescope, the image is collected from the front opening, reflected by the primary mirror at the back of the telescope to a secondary mirror on the front, which reflects the image towards the eyepiece or the camera.

working scheme of a Newtonian reflector telescope
The working scheme of a Newtonian reflector telescope. (Image credit: Krishnavedala).

As large mirrors are relatively cheap, this kind of telescope has a great value for money, but for maximum performances, mirror collimation must often be checked and, eventually, recovered.

Newtonians (and Dobsons), Cassegrains, and Ritchey-Chretien telescopes are all reflectors.

Pros

  • Good value for money
  • Affordable large aperture telescopes
  • Fast f-ratio
  • Versatiles
  • Great for visual observations

Cons

  • Portability
  • Need for periodic collimation
  • May suffer from coma
  • Not always suitable for astrophotography
  • Diffraction spikes on bright stars

Refracting Telescopes

Refractors work the same as photographic lenses, with the light being collected and focused by passing through a series of lenses.

Working principles of a refracting telescope
Working principles of a refracting telescope. (Image credit: Ohio University).

Because of the use of lenses, the design is more complex than that of reflectors and refractors are more expensive, particularly when low dispersion glass is used to correct chromatic aberration.

But because of the use of lenses, the size of a refractor is much more compact than that of an equivalent reflector, so they are highly portable.

Also, being the tube smaller than that of equivalent reflectors, the cooling time is minimum and the instrument is ready to use with no delay.

Not having mirrors, collimation is not an issue and maintenance is reduced to just keep the optics clean.

Pros

  • Great performances
  • Suitable for astrophotography
  • Compacts
  • Versatiles
  • Short cooldown time
  • Very low maintenance

Cons

  • Expensive
  • Weight
  • May suffer from field curvature as well as chromatic aberration

Catadioptrics Telescopes (Compounds)

In a catadioptric telescope, light is both refracted and reflected as in this design, a lens is combined with a curved mirror.

Working principle for a Maksutov catadioptric telescope
Working principle for a Maksutov catadioptric telescope. (Image credit: Wikipedia).

The most common catadioptrics are Maksutov-Cassegrain and Schmidt-Cassegrain telescopes.

Pros

  • Good value for money
  • Relative large aperture
  • Contrasted and crisp image
  • Portability
  • Little maintenance
  • Best for lunar and planetary observation and astrophotography

Cons

  • Often they have a high f-ratio
  • Some are not very suitable for deep sky observation and astrophotography due to the high f-ratio
  • Long cooldown time

A Short Video To Guide You In The Choice Of Your First Telescope

This great video by J. Kelly Beatty from Sky and Telescope Magazine, nicely summarises what you need to know and to consider for making the right choice.

Conclusion

As you see, the choice of a telescope is not for the faint of heart: many concepts play together when looking for the right instrument and the right setups for your intended use, and this article has just scratched the surface of what there is to know.

But at least now you know how to pose your question properly: always state your expectations, budget, and intended use when asking for help in choosing a telescope.

About Andrea Minoia

Andrea Minoia works as a researcher in a Belgian university by day and is a keen amateur astrophotographer by night.

He is most interested in deep sky photography with low budget equipment and in helping beginners along their journey under the stars.