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Buying a Telescope

Telescope

You can now download a PDF version of this beginners' guide by clicking here.

So you’re interested in astronomy, and are considering buying your first telescope. This is going to cost you at least £100 preferably £200+ as a minimum if it’s to be of any real worth. So here are a few points for your consideration and some hints regarding amateur astronomy.

Are you serious?

Firstly, how serious are you? Do you think that observational astronomy as a hobby is likely to last for a while, or once you’ve had a good look around the sky you’ll lose interest?

Because this determines how much you should consider spending on your first (yes indeed, first!) telescope. If you just want a look around, get in touch with your local astronomy society and ask if you can join in one of their observing sessions. Quite a few societies run public observing sessions for people such as you. People who actually use telescopes are the right people to talk to about their advantages and disadvantages (but many are very biased!).

But do be very careful about buying a used telescope from someone at such sessions! Once you have had a good look at the night sky, you’ll get a much better idea of what you’re going to actually see. Regrettably you won’t see anything like the nice images seen in astronomical magazines. But it is a compelling and rewarding hobby!

What's up there to see?

The Moon - bright easy to find, visible most evenings, weather permitting. Easy to photograph. This is a good object to show off with, especially views along the terminator (the Moon's day/night dividing line). Contrary to expectation, observing the Moon at or near full is unrewarding (no contrast!). After you've seen it once, there's not much more to say about it. The chance of catching any Transient Lunar Phenomena is very remote indeed, otherwise nothing happens on the surface, nothing! (Forget looking for landed spacecraft, Selinites, etc!) It is a bright object and can spoil your night adaption. Many observers use a neutral density filter, if they ever observe the Moon.

The Sun - Very dangerous! One glimpse at the Sun through a telescope and you're blind! You can see sunspots, prominences, flares, etc, but it needs special (and fairly expensive!) equipment and a lot of know how. Stick to projecting the Sun's image onto a piece of white card, through a pinhole in another piece of card. It’ll do quite nicely! You can see Sunspots that way. But the Sun’s surface is only really active for a few years around the 11-year Sunspot cycle, the present one is due to peak in about 2014.

Planets -Now it starts to get a bit tricky. Many of the planets just are not in your observable sky, and may not be visible for years. Finding the outer planets (further out than Saturn) can be hard work, you’ll seldom be sure you’ve got what you are looking at, the most you’ll see is a small fuzzy disc. Finding the nearer planets is much easier (they are much bigger!), any telescope should show the four Galilean moons of Jupiter and the rings of Saturn. A reasonable telescope should also show the cloud bands of Jupiter and the gaps in Saturn’s ring system.

Venus can be seen as a cloudy sphere, but Mercury is dangerously close to the Sun for safe viewing.You don’t need much light gathering power (telescope aperture) for planets, but you do need magnification (seldom needed for deep-sky observing). This tends to make the planetary telescope a bit different from most others. However, a fairly decent telescope will cover planetary observing quite well, but may need a higher-magnification ocular. Comets - There's usually a comet or two around the sky most nights of the year. Finding them can be quite tricky and there's not a lot to see except for a fuzzy blob with a hint of a tail. By the time any of them get close enough to be spectacular, the view through a telescope is too restricted. Binoculars are better.

Meteors – Never telescope objects! Not even binocular objects. Get a sun lounger and warm clothing and some patience. Knowing when and where to look is important! (See my Meteors guide). Stars - In a nice dark area, well away from street lights, etc, the naked eye can see some 2000+ stars, mostly in a band called the Milky Way. All these are in our galaxy. With binoculars under the same good conditions, the view becomes quite stunning! Through a telescope this effect is seriously diminished, because of the much reduced field of view, although you’ll see more (even fainter) stars. Some stars are noticeably coloured, mostly yellow or orange, some very bright ones are bluish. Quite a few stars are doubles, some with some quite pretty colourings. All you’ll ever see is a point of light though. Amateurs do study stars, mostly binaries and variable stars, but this is quite specialised.

Deep Sky - Now this is getting serious! Galaxies, Nebulae, etc. can be found that are really spectacular, many are seriously beautiful. For many amateurs just finding the object is enough satisfaction (and for many, no mean achievement either!).

There are thousands within reach of modest equipment, though you'll need a tube (and associated equipment) totalling nearer to £2000 than £200 if you are serious! Photography (CCD) is quite popular with these objects.

N.B. Just don't expect a view through your tube anything as good as the published pictures of objects!

There are many other types of object to see, but like aurorae and meteors, etc, they are simply not telescope objects.

When to look

Many serious amateur deep-sky astronomers become armchair astronomers during the summer months. The night sky really never gets dark enough for the serious stuff. However, there's still much to see in the Summer sky that's really good, just avoid looking for faint fuzzies in summer time.

UK weather is a real problem, apart from Lunar interference (around full Moon).

For good observing you need anticyclonic conditions (only a few day old or else transparency deteriorates) with a good transparency and negligible high-level wind. Although you'd reasonably expect around twenty or so really good nights in a year, only about five or six will be those magic nights when it's all near-perfect (perfect doesn't exist in the UK's skies!).

Don't forget that the Moon may well spoil many an otherwise really good night!

Where to Observe

Light pollution is a serious problem, particularly from streetlamps. Much back garden observing is spoiled by high-intensity security light on nearby houses. Light Pollution filters are available and will block much reflected skylight from low-pressure sodium and mercury streetlamps, but are really for very serious astronomers only!

However, don't expect really dark skies (and therefore the ability to see faint objects) in or near a town. In the country, well away (more than 10km) from streetlights is best. If you take astronomy seriously, expect to take your tube for a ride.

Few UK amateurs have the luxury of a really good observing site in their back garden! However, a lot of very good astronomy can be done from your own garden, just be aware of the limitations.

What do you want to use your first telescope for?
Looking at the Moon & Planets?

OK, they are bright objects, except for the outer planets. However, quite often the planets are not in your observable sky and the outer ones are always quite difficult to find. You'll expect to see detail on Mars, maybe Saturn and Jupiter too.

Mercury is dangerously near to the Sun much of the time (looking at the Sun through any magnifying device, even for an instant, will damage your sight permanently). You'll see craters on the Moon quite well You'll also see Saturn's ring system and the cloud bands on Jupiter as well as the four Galilean moons.

So a small aperture refracting telescope will do. It needs fairly good magnification but not much light gathering power. Not too expensive an acquisition either.

A 60mm refractor would do well for this application, you can also use it for star observations with a fair measure of success.

Looking at Stars?

This gets a bit tricky as there are two conflicting requirements. If you want to look at groups of stars, you'll need a wide-field telescope and matching ocular (Eyepiece). If you want to look at rather special stars, like binaries, you'll need much higher-magnification optics.

A good compromise is, say, a 150mm Newtonian scope. This will allow use of both a wide-field ocular and a higher magnification one. It also has respectable Light Gathering Power and will give a rewarding view of many deep-sky objects. Because this optical system gives a good contrast it can be used for planetary work etc. It is also a good starter scope for astrophotography.

There's a wide range of styles and prices, none very expensive. You always get what you pay for.

Looking at Deep-sky objects? The faint fuzzies need a light bucket, a scope with as much Light Gathering Power as possible and not a lot of magnification. Large Newtonians are often used for this, but the catadioptric (mirror and lens) types (Maksutov and Schmitt-Cassegrains - SCTs) are very frequently used for this application.

Expect to see wonderfully far into the universe and be able to do astrophotography well. Not as much contrast as Newtonians, but all right for Lunar and not bad for planetary observing. An optical diameter to 250-300+ mm would be about right here. Very frequently these are computer controlled.

These types are fairly expensive.

Telescopes

All astronomical telescopes give an inverted image (for some you can get an erecting adaptor for terrestrial use). Catadioptric telescopes add insult to injury by laterally reversing (mirror imaging) the field as well! This makes using star charts very interesting indeed! It's generally reckoned that if you're serious about giving astronomy a good try, you shouldn't start will less than a 60mm refractor, or a 150mm reflector (Newtonian optics) , else you'll get too frustrated too quickly.

The larger the aperture of a telescope (diameter of objective lens or main mirror) the more detail you’ll see in astronomical objects and the more light you’ll gather (so you see fainter objects). The Focal Ratio (f-number) determines the telescopic field, the lower the f-number the wider the field of view. But higher f-numbers give a higher overall magnification limit.

Note well - Even very reputable astro-dealers will try to sell you what they've already got in stock! It can be very difficult to compare like with like across the different manufacturers as very few outlets have all the various agency agreements.

Refractors from Tele Vue are generally accepted as tops here, with Takahashi also very well thought of, Williams too. There's quite a few makes around where you don't pay as much for the name, but will still give a very satisfactory performance.

Reflectors from Orion and Vixen are very well thought of in this category. Again there are very many to choose from most of which will give very good value for money.

Catadioptric telescopes are dominated by those Celestron and Meade. Both are good and both have their stronger and weaker points, both incorporate some form of computer control. There's another interesting choice here; conventional and compact. Both manufacturers produce small, computer-driven scopes (Nexstar & ETX ranges). These are very good value for money, have a surprising capability and versatility, and are super serious starter scopes (with a good future).

Binoculars are not to be easily dismissed. Great for learning the sky and seeing quite wonderful starfields telescopes can't cover. Get a pair with large objective lenses (more light gathering power) but a quite modest magnification. Consider a pair of image stabilising ones, if they are in your budget. A binocular mounting arm can be fitted to a photographic tripod, now you can lie back on your sunlounger and observe in much greater comfort than any telescope observer. Great for comet and satellite spotting too!

Mountings

Between the telescope tube and the tripod top is the telescope mounting.
Many, less-expensive mountings are a simple Altitude/Azimuth (AltAz), that is they swing left and right on one bearing and up and down on another. Some of the better ones have slow-motion controls too. AltAz is fine for a starter scope, you can see all the sky, but you can't use it for photography (the image rotates!). Note that objects move quite rapidly (due to the Earth's rotation) and have to be followed manually.

Better telescopes have a polar mount (often called a German mounting). If this is set up correctly (aligned to point at the pole star) you only need to track using the Right Ascension (RA) axis (rather than the Declination (Dec) axis as well). This allows the mounting to be motorised and guided and is very suitable for astro-photography.

Top range telescopes often revert to having an AltAz mounting, but this is now fully driven and computer controlled and will follow an object in the sky. You can use this for photography, but after a few minutes the field of view has rotated enough to smear the image.

If such mountings were to be mounted on a wedge (set to your Latitude angle) to convert them to polar mounted, then they become very suitable for long-exposure photography.

Computer-controlled GOTO Polar mounts are now very popular and are reasonably priced.

A very simple manual mounting (not needing a tripod) is the Dobsonian. This allows AltAz operation with a really large diameter tube. Super for serious light buckets on a restricted budget. But make sure you know the sky well and have a gentle touch!!

Computer control

Do you want to spend your observing time looking at, or looking for objects? If you want to spend time looking for, get a manual mounting and some good star charts. If you want to spend your valuable observing time looking at things, seriously consider a computer-controlled system. Some computer assisted systems are quite good. The serious catadioptric scopes all make use of computers, usually having a GOTO function. This allows an object to be selected from a large database and have the scope slew directly to it. The small catadioptric scopes from Celestron & Meade are quite good in this respect.

What else will you really need?

Tripod - You will always need some form of really stable tripod. This needs to be heavy and stable and even a professional photographic tripod may not be good enough. The higher the magnification, the more stable it needs to be. Even then, tiptoe around people who are seriously observing! Excessive vibration makes the field of view wobble. This is why you can't really observe when there's any significant ground-level wind.

Slow-Motion Drives - Finding objects in the night sky is difficult as telescopes have a limited field of view and directly moving them by hand is simply too imprecise (Most telescopes have a low-magnification Finder scope attached). Slow motion drives are really necessary, unless you are already using a motorised mount. Usually these are on quite long drive cables so as to try to prevent hand vibration from causing the field of view to wobble overmuch.

Dewcap or Dew heater - UK weather frequently produces dewing conditions. You'll need to keep dew from forming on any glass at the skyward end of your tube. Long hoods (dewcaps) will postpone dewing, sometime for the whole evening. You may need an electric dew heater especially if you get serious.

Astrochart - You'll need some sort of astro-chart, reference books (for star-hopping) etc, in order to find your way around the night sky. Something line the Night Sky Month by Month will do nicely to start with, it'll (hopefully) stop you trying to find objects that are below your horizon for that season of the year!

Stellarium (stellarium.org) is a stunningly good planetarium program and totally free! Ideal for planning an evening’s observing.

Robert Garfinkle’s much praised book “Star-Hopping” is also a good buy.

Just remember that looking for objects lower than 30° above your horizon is fraught with atmospheric disturbances.

Red Torch - LED torches are good. It takes about 20 minutes to get full night vision sensitivity, a flash of white light will destroy it very quickly. Astronomers use red lights to see around the telescope and read their charts as dim red light is least damaging to night vision.

Oculars - Telescopes change their overall magnification by changing the focal length of the ocular (eyepiece). All telescopes should have replaceable oculars. When you feel you need to, consider purchase of an alternative ocular or so. The most useful (for typical UK conditions) are those that give a basic overall magnification of around 60 - 90 times for deep sky work.

For those really good nights when observing conditions are near-perfect, consider going up to around 300 times, in one or two stages to look at the planets, double stars, etc. Most deep sky observers seldom get above a 150 times magnification. N.B. The more magnification, the dimmer the image!

Focusers are important too. To get a good, sharp focus really needs a good focuser, preferably with a slow-motion facility.

Where to buy? Firstly, where not to buy from and what not to buy! Never buy a telescope from a toyshop. Never buy a telescope from a camera shop, unless they are specialised telescope dealers (few and very far between). Never buy a telescope that just advertises its magnification, or pushes it (it's not a prime selling point for serious observers).

Get hold of a copy of "Astronomy Now" and use the advertisers in that. They are all good, but some are better than others. Most firms have a good showcase on the WWW, but nothing is better than talking to them. A firm should find out what you want to do with the scope and advise you accordingly. They can only compare models within their own stock range. Very few will push a particular and maybe unsuitable model as they really want you to be a satisfied customer.

Good websites to start with are:-
celestron.uk.com
meade.uk.com
opticalvision.co.uk/astronomical_telescopes-sky-watcher.html
But do be prepared to shop around!

Don’t buy cheap! – You get what you pay for!!!

Astrophotography

Astrophotography (actually imaging) is quite possible with modern interchangeable lens CCD cameras. They are very sensitive to light and you can see the results almost instantly. Further, experimenting with exposures effectively costs nothing. The better telescopes can be fitted with an adaptor to mount the camera at the Prime Focus, using a T-Ring. Specialist astronomical cameras are much better, but their costs tend towards the astronomical! Be prepared to manipulate your images in PhotoShop to get the best out of them.

Summary

Don’t buy inexpensive if you can possible avoid it! The more you spend on a first scope, within reason, the longer it will last you. Otherwise you risk running out of interesting objects too soon. For those with serious intent, buy a 60mm refractor or better still, a 150mm Newtonian reflector on a German mount (top choice!). If you can afford it, go for one of the small GOTO catadioptrics (e.g. NexStar). If you want to experience the wonders of rich starfields (and get to learn the sky) consider a pair of good binoculars instead.

Clear skies!

© Jon Laver FRAS October 2014 - Reproduction for personal use is permitted. Otherwise no commercial use or reference without prior written agreement from the author.

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