How to choose your first telescope

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Interested in buying a telescope but not sure where to start? Read our guide to selecting your first scope. In part one of three, we look at the different types of telescope available.

Man looking at the stars with telescope beside him. Credit: iStock

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By Tim Jardine

May 24, 2019 at 9:49 am

“What kind of telescope should I buy?” “How much should I spend on my first telescope?” “What are the differences between Dobsonians and Newtonians; reflectors and refractors?”

These are just some of the questions we regularly hear from readers who want to take their first steps in the world of practical astronomy.

They are certainly worth consideration to ensure you spend as little of your heard-earned cash to get great views of the night sky.

Tucked away in the corners of many garages and spare rooms sit dormant telescopes: telescopes designed to gather views of moons, stars and planets, purchased with excitement, but now gathering dust.

Perhaps some were too cumbersome to take in and out at night, others too complicated to set up, or maybe underwhelming views led to disappointment.

Tim Jardine pictured with his 18-inch Dobsonian. Beginners can afford to start with a much smaller model! Credit: Tim Jardine

As we look at the question “What type of telescope should I buy?”, we can say from the outset that the best telescope is one that is practical and comfortable to use regularly, and that provides exciting views of the night sky.

Admittedly, there is a bewildering array of equipment available; however, we can divide all those variations into just three basic types.

Most people will recognise the first type of telescope invented, which are known as refractors.

These employ glass lenses at the end of a tube to bring a magnified view of the sky to focus.

The second type we will consider, invented by Isaac Newton, are known as reflectors because they utilise mirrors instead of lenses to achieve an enlarged sky view.

The final type of telescope design involves mirrors with a hole in the middle. We call telescopes of this type Cassegrains.

With this basic separation into groups established, we can review the benefits and compromises of each.

Refractors

The Altair Starwave ASCENT 102ED F7 refractor telescope: easy to use and with a lightweight frame. Credit: BBC Sky at Night Magazine.

The most popular type of telescope, refractors have many appealing qualities.

They tend to be lightweight, easy to set up and intuitive to use, give sharp views and require practically no maintenance.

Interchangeable eyepieces offer varying magnifications and increase the range of viewable objects.

Good portability allows for trips to enjoy darker skies away from light polluted areas.

However, there is a saying in the world of telescopes that ‘aperture is king’. Or in basic terms, bigger is better.

When it comes to visual astronomy, bigger telescopes yield more impressive views.

In this respect refractors have limits. Very large lenses are prohibitively expensive and quite unmanageable for amateurs.

The right telescope can be determined by deciding where and how you will use your telescope; maybe at home, or to take to dark-sky sites.

Refracting telescopes available to the amateur today therefore tend to be available in apertures between 60 – 150mm.

Within that range we find inexpensive models with a single front lens, up to telescopes with multiple lenses that provide a sharper more natural view, at a premium price point.

The quality of the optics in the telescope, determined predominantly by their cost, will have a significant bearing on the quality of the views, and the cheap refractors that tend to be popular at electrical goods and camera shops are often disappointing.

Generally speaking, smaller refractors less than 90mm diameter are best suited for wider views of the night sky, which might include star clusters like the famous Pleiades, M45.

Although some detail and moons may be seen when observing Jupiter and Saturn, in either case the planet itself will appear quite small and very bright in the view.

Some brighter galaxies and nebulae may be visible under good skies, and with experience it becomes easier to pick out the interesting objects.

However, larger refractors 100mm in diameter and upwards can really open up the skies, and under reasonably dark skies there will be hundreds of deep-sky objects that can be viewed including galaxies, globular clusters of stars and bright nebulae.

Surface colours and details may be seen on Saturn, Jupiter and even Mars on a good night.

Lunar views too should be sharp with good definition in craters and rille features, as the larger optics enable the telescope to reveal more detail.

There is no doubt that a decent refractor, on a sturdy mount or tripod, can provide a thrilling stargazing experience, and whet the appetite for further sessions for many years.

Reflectors

Newtonians are among the most common reflectors used by amateur astronomers. This is the Orion 6-inch f/4 Newtonian astrograph. Credit: BBC Sky at Night Magazine

Reflecting telescopes have an open tube at the front and a round mirror inside the bottom of the tube, called the primary mirror.

Light entering the tube is reflected back inside the tube onto a much smaller angled secondary mirror, and then out through the side of the telescope near the top end, which is where the interchangeable eyepiece goes.

This design allows for much larger apertures than are possible with refractors, and amateur reflectors are available right up to a whopping 500mm diameter.

There are two ways of using reflectors. Smaller models up to 12 inches or so can be used on tripod-style mounts similar to those used for refractors.

A popular alternative option, though, is to mount the telescope tube onto a rotating base that sits on the floor.

This can be turned freely around, while the telescope can pivot up and down and thus be pointed anywhere in the sky.

Telescopes mounted in this way are known as Dobsonians and, compared penny for penny, offer the most cost-effective and rewarding views of the deep sky.

The Explore Scientific 16-inch Dobsonian GENERATION II. Note the rotating based and half-circle pivots that allow the telescope to be pointed up or down.

In fact the views offered by a relatively modest reflector can compare favourably with those offered by expensive refractors.

Dobsonians may be elegantly simple affairs – no wires, no batteries, you just point it at what you want to see – or they may include a full ‘Go-To’ control, which can automatically point the telescope at hundreds of sky objects.

There are compromises, as reflectors need their mirrors adjusting from time to time, although this shouldn’t put you off.

However, they can be heavy, bulky items that are awkward to take outside and bring back in, or to transport to darker sites, and they can take up a lot of room when not in use.

The largest Dobsonian models, although collapsible into manageable components, may even require the use of a stepladder when viewing objects high overhead!

Cassegrains

The Celestron Astro Fi 5 Schmidt Cassegrain enables users to download an app and control the scope with their smartphone. Credit: BBC Sky at Night Magazine

In use, Cassegrain telescopes are quite similar to refractors, in that you point the front end at the sky and you look into an interchangeable eyepiece on the back.

Comparatively heavy, they tend to be shorter lengthwise, and this compactness makes them ideal where storage space is limited.

These telescopes may need a little tweaking from time to time, to make sure the mirrors are lined up properly.

Cassegrain designs give a comparatively more magnified view for a given size of eyepiece, and for those wishing to experience the best views of the planets and our Moon, a Maksutov-Cassegrain or a Schmidt-Cassegrain telescope may well be the best option.

When sky conditions allow, details can be seen within the coloured bands of Jupiter and various colour bands on Saturn, along with the Cassini and other divisions of Saturn’s glorious ring system, not to mention polar caps and features on Mars.

Of course, other deep-sky objects may be viewed, with larger aperture Schmidt-Cassegrains providing the most satisfying experience.

Although the views may not be quite as tack sharp as those from refractors, they are a popular choice as a happy compromise between large enough aperture and manageable size.

Because of the higher magnifications provided by these telescopes, the object being observed will more quickly move out of view, and so they are often purchased with electronic tracking mounts to follow the targets as they move.

Taking the next step

The right telescope for you can be determined by deciding where and how you will use your telescope; maybe at home, or perhaps to take to dark-sky sites.

All three designs are available as basic models or with fully computerised controls and even built-in wi-fi for operation via smartphone.

A grab and go’ simple setup may best suit your needs, or you may want more complicated equipment with fully automatic operation to reveal more wonders of the night sky.

Whatever your choice, refractor, reflector, Cassegrain, it is advisable to make your purchase from specialist astronomy dealers that know all about the telescopes they offer and can answer the inevitable questions.

Astronomical Telescope constellation Aquila in the night sky. Eagle constellation Beautiful night sky Real night sky. Milky Way and Eagle constellation.

A good telescope combined with excellent viewing conditions away from light pollution will give you incredible views of the night sky. Credit: iStock

Telescopes: a brief buyers’ guide

There is a wide variety of telescope available on the market, and it pays to do research before buying. Our guide below provides a look at three different types at either end of the price spectrum.