How To Buy A Telescope

By Neil Francis

So you’ve visited Perth Observatory, and experienced a small taste of what there is to see in our marvellous southern skies, and you’ve decided to buy a telescope. We’re excited for you, because you’re going to discover a whole new world! But there seem to be many options, so where do you start? You may already have looked on the internet, and found the many technical details to get lost in. We hope that this guide will help you decide what’s best for you and how you may want to use your telescope, without too much technical nitty-gritty.

The first question is, what’s important to you? Are you a small person who needs a telescope that can safely be carried up and down stairs? Do you have children too impatient to give you ten minutes to locate a nebula? Or is a slower astronomy experience more your style, where half the fun is the thrill of the chase, skilfully hunting down galaxies and other faint fuzzies? Do you have a dedicated observing location that is fortunate to see dark skies? Or do you need to transport it in a car? Where will you store it? What is your budget? How interested are you in astronomy? Have a think about these things because they’re as important as any of the technical matters. We’ll come back to them later in the article. A good telescope is one that you’ll use, and not necessarily the biggest or best.

We hope that your experience at the observatory has given you realistic expectations about what can be seen with a telescope. You’ve seen the bright colourful photos from the Hubble Space Telescope countless times in magazines, on TV and on the internet. Amazing images like these are approachable through a modern backyard astrophotography set up, but this is a bad place to start for a beginner as a lot of time, money and experience goes into creating photos like that. We’ll focus on what’s seen through an eyepiece for this article, as photography is an advanced topic, and the best telescopes for eyepiece viewing are not best for photography. Most objects that can be seen by eye are very faint, and our eyes aren’t good at perceiving colour in faint objects. This means that much of the universe you see through the telescope will lack the intense colours you see in the photos.

Don’t let this discourage you from buying a telescope. We think there’s magic in seeing a galaxy 50 million light years away with your very own eyes. M87 is this far away, home of the first black hole that professional astronomers have directly imaged, and currently in our early winter sky, in Virgo. The light that left that galaxy not long after dinosaurs roamed the earth has travelled for 50 million years just to touch and be absorbed by your eyeball so that you can experience it! In a sense, you’ve actually touched the billions of stars in that galaxy! And this is something that you can experience with a modest telescope. We think that much of the wonder that comes from a telescope comes from knowing what it is that you’re looking at, and not just the view in the eyepiece.

That said, there are some sights best experienced through a telescope. You can see details with a backyard telescope that you may never have seen in the photos. How can this be? Well to create a photo that exposes nebulae well, in all of their glorious colour, it’s common to overexpose their bright details and so these are often lost in the photos. The Trapezium in The Great Nebula in Orion (M42) is an example of this. At the heart of M42 can be seen these four bright stars, even in the smallest of telescopes, and yet you rarely see these in the glossy photos. These

Another matter of expectations is how your viewing will be handicapped by light pollution and the atmosphere. Here in Perth we often have very light polluted skies and this means that many of the fainter objects in the sky that would be obvious from the wheat belt are difficult for us to see, both by naked eye and even in the telescope. Planets, double stars, open clusters, and the brightest nebula and galaxies are easy to find from our backyard skies, but fainter objects need dark skies. If you’re able to transport your telescope away from Perth you’ll have a much better viewing experience (and the Astrotourism WA website will be able to help you find places to view the sky from our country towns).

The atmosphere also degrades the heavens through what astronomers call “seeing”. Our atmosphere is often turbulent and this makes views fuzzy in larger telescopes, or causes stars and planets to jump around or break up into strange shapes in small telescopes. This can change from day-to-day, and even by the hour, and is often worse on hot summer’s nights. Seeing means that there’s a practical upper limit to how much a telescope can magnify because trying to magnify more than seeing allows just brings us big fuzzy views instead of small fuzzy views.

Okay, so now that we’ve managed our expectations, we’ve considered our answers to the questions above, how can this help us choose a telescope?

Is it right for me to buy a telescope now?

Astronomy with a telescope can be a rewarding experience with a good first telescope and a bit of knowledge. There are many cheap options available with claims of high magnifications, but a good entry level astronomical telescope with modest magnification will set you back at least $400 and either provide a capable instrument for casual use for many years, or provide a stepping stone to further acquisitions if your interest expands. Lesser equipment is likely

to show a very limited set of objects, have flimsy mounting that is frustrating to use and is more likely to be unsatisfying and deter your budding interest. Cheap telescopes are available, but as with much in life you really do get what you pay for. It’s best to stay away from small refractor telescopes for $100 at discount shops. These telescopes are likely to be poor quality, have shaky mounts and the shops are unlikely to offer good advice or after sales support.

How interested in astronomy are you? Without spending much money, you could spend some time learning from others by joining a club or organisation of like-minded people. You can spend time researching topics through internet web searches, visit your mobile device app store for astronomy software, or pop by your local public library and borrow a book or two. You may like to get outside under the night sky with a “star wheel”, or “planisphere” ($10-$25), planetarium software for your mobile device ($0-$5 for entry level tools), or borrow a pair of binoculars or buy second hand (<$100).

Binoculars can provide views of many of the brightest objects and many objects that can be seen during a night sky tour at Perth Observatory can at least be spotted in binoculars. Moderately sized binoculars like 10x50 and 8x40 are very portable, easy to use, and can easily be grabbed to look at objects and appreciate that the sky contains more than just stars. The first number refers to the magnification and the second to aperture in millimetres. They can be used for other activities like bird watching, in addition to looking at the sky. Learning to find your way around the sky with these inexpensive tools will make using a telescope more enjoyable.

A telescope is a physical experience, quite unlike looking at images on the internet or watching a documentary. When you’re outside looking at the sky it may be quiet and cold, will hopefully be dark, and it can involve a surprising amount of movement, and sometimes awkward body positioning, as you seek objects out by eye, and direct a telescope to those objects. It’s often best enjoyed with a thermos and warm clothes, and maybe even a tea break with cake! Do you enjoy being outside? Do you have the mobility to use the telescope you’re considering? Do you enjoy cake? Then a telescope could be the way to go.

Don’t I just want a telescope that magnifies a lot?

Surprisingly, no! Ignore telescopes advertised with a strong emphasis on magnification. Most objects that we look at in the sky don’t require magnifications above 200x. Unlike a microscope, the greatest value that a telescope brings is not magnification, but in light gathering. Telescopes make dim objects brighter, and this is often more important than magnification, also optics that collect lots of light provide more resolution. This is the difference between magnifying an object a lot and seeing a fuzzy image, vs seeing a sharp image. Any telescope can provide high magnification with the right eyepiece, but the more light that’s collected the better the image. Those adverts that scream high magnifications are being misleading by not emphasising what’s important, and are often associated with poor quality instruments.

Four key aspects to a first telescope are:

Diameter (also called aperture) of the main lens or mirror – this determines how much light is gathered

Steadiness of the mounting – determines how steady images will be, and how frustrating it will be to get the telescope pointing at the object you want to see.

Sales and service support – you will need advice and service over time

Cost constraints – getting good ‘bang for your buck’

It’s generally accepted that the best value for money telescopes for beginners, are medium aperture (6-8”, 150-200mm) ‘Dobsonian’ style telescopes.

Their value attributes are:

They provide enough light gathering aperture to give good object views at modest magnifications for most object types.

They have a solid manually manipulated mounting that is easy to use

Their manual operation provides a great basis for learning the night sky and how to find and follow objects in it

$400-$600 price point (excluding shipping)

The compromises made for these values are:

The size of the telescope and mount makes them larger than some will find ideal, especially if there is a frequent need to transport the telescopes

The manual nature of the mount means object location and tracking at higher magnifications are more difficult than electronic automated ‘GoTo’ telescope mountings. Many telescopes now sold do include attachments for a mobile phone that, along with an appropriate app, can help with locating objects even with a fully manually operated mount.

If these compromises are strong considerations, then your first telescope is likely to be more expensive. ‘Collapsible Dobsonian’ telescopes that are slightly more compact for transport and with ‘GoTo’ capabilities are available but will increase cost to approximately $1500 and above.

Entry level telescopes will come with adequate 1.25” diameter eyepieces, however significant improvement can be achieved with higher quality 1.25” or 2” eyepieces as a future upgrade, independent of the telescope and mount. Good eyepieces will be in the $100-$250 price range. Eyepieces together with the main lens or mirror of the telescope set the magnifications available to you on the telescope. The main lens or mirror is not changed, but a range of eyepieces can be used. As eyepieces are standard sizes they can be used not just with your first telescope, but with future telescopes you may buy.

Apart from ‘webcam’ planetary photography, Dobsonians have very limited astrophotography use. Narrow field ‘deep-sky’ astrophotography requires a solid, automated, tracking mount and will require a considerably higher budget to do this well. This is a topic in its own right and not considered a ‘first telescope’ consideration. The expensive ‘widefield’ refractors that are also sometimes used for astrophotography make poor telescopes for visual use, at their price point.

Buying local for advice and support is recommended for a first astronomical telescope, however Perth is not well serviced by retail shops that stock and service a wide range of astronomical equipment. Advice from astronomical groups and observatories should be sought on current suppliers and experiences.

Do I need a computerised telescope that can find and track objects?

All telescope designs can be purchased in versions that find and track objects for you, but a telescope that offers automated tracking can be twice the cost as one with the same diameter of main mirror. So there is a substantial premium in tracking vs a non-tracking telescope with the same light gathering ability and quality of images. An inexpensive option that is found on many telescopes sold today is a mobile phone holder. With this you can use your phone with appropriate software to help you push

your telescope to point to the object that you’ve chosen to see. Your phone has orientation sensors so it can identify the direction and angle of your telescope to figure out what it is looking at, and help you find what you’re looking for.

Small telescopes are sometimes offered on equatorial mounts. These mounts aim to follow the apparent motion of the stars through the sky. Less expensive equatorial mounts are often not solidly built and may be frustrating. They will also require alignment with a point in the sky called the south celestial pole, that all stars appear to rotate around. Instructions will be provided, but the process may be annoying when you regularly move the telescope. We prefer the larger diameter Dobsonians that have simple, yet stable, mounts, but require manual tracking.

If your day job sees you sitting in front of a computer all day, then perhaps you might enjoy escaping from this to an instrument that’s free of motors and computers? There can be excitement in planning a night of viewing and then meticulously hunting down each of the objects, through the use of paper charts. Others may find this frustrating.

Two situations that may favour computerised tracking telescopes are (a) when you want to show objects to an audience, and (b) if you have limited time for the hobby and want to get the most out of the limited time that you have for viewing, rather than searching for objects. Objects like planets may quickly move out of view, and this requires more enthusiasm for learning to track with your telescope than some may have. This may be especially the case with an audience and especially if they are young children.

Manual handling and transport considerations

Many of us don’t have backyards or dark skies at home to observe from and this means you’ll need to take your telescope on road trips to get the best from it. As an apartment dweller without a backyard, up a flight of stairs, and who lives alone, I appreciate how important the physicality of a telescope is. Pay attention to the mass of the telescope and mount that you’re considering, and the fact that telescopes are awkward loads that often have their centre of gravity well away from your body. If you are small then it can even be difficult to see where you are going while carrying one. Tall, strong people, without injury or disability can come to grief through distraction, and when handling a telescope that is too big for them. If you choose a big telescope that you can only just handle then the effort will discourage you from using it. A better choice may be a smaller aperture scope that is more manageable.

Can you transport it in your car? A Dobsonian with a 10” aperture is about the limit that tall strong people can handle from the perspective of carrying on level ground, and that can also fit in the luggage and back seat sections of a small hatchback, leaving space for a passenger beside the driver. Smaller 6”-8” instruments are more manageable. Larger telescopes can be purchased that disassemble into smaller pieces and can be re-assembled at the viewing site, but these are much more expensive and the work required in transporting and setting them up may be frustrating for a beginner.

Do you have space for a telescope? Consider how much space you will need, and whether or not you have it. A type of telescope called a catadioptric, or compound, telescope can offer larger magnifications in more compact sizes than Dobsonians. This may be desirable if you’re most interested in observing planets, which can benefit from higher magnifications when the seeing permits this, and space is an issue for you. There is a cost premium in choosing these designs, however. Binoculars can be a good first choice, if handling and space considerations are important to you.

Dobsonians require a process called collimation to be do when they’re moved. It sounds much scarier than it is, and is a skill that can be quickly learnt, and only requires a few minutes to apply. Regular collimation will get the best views out of such a telescope. Compound telescopes, and refractor telescopes can be more grab-and-go in that they don’t require regular adjustments.

Above all, we recommend you set yourself up for success by going slowly and learning as much as you can before buying. Your first telescope acquisition should be one that gives many years of enjoyment, or be the start to a fascinating hobby that can take many paths as your interest grows.

While we can’t go past the value for money in manually tracked Dobsonians, they may not be the best for everyone. If you need to make compromises for ergonomics, manual handling, storage or patience reasons, know that any good quality instrument can provide a wealth of objects to see, and will provide better images than anything early astronomers like Galileo could have dreamed of owning. Often there are details to be seen, but we’re not observant enough to notice. Revisit objects regularly and you will notice more and more, and you will also become more aware of how views change with atmospheric seeing. Learning to see is an important skill that will be acquired with time and can be gained even on smaller aperture telescopes.

Good luck for your new adventure!