Kicking off your interest in astronomy needn't be expensive. It can be if you want to set up your own observatory to study variable stars or hunt for new asteroids but, to start with, it should always be free - or at the very most the token entrance fee to a museum or astronomical society.
Astronomical equipment, while far cheaper than it was 10 years ago, is quite expensive and its best to get to know what you want for yourself before you take the plunge. A retailer can advise you - and most will advice you honestly - but they can't predict your rate of development, such as wanting bigger scopes or an imaging set up to photograph what you're seeing.
For this reason, it's always better to learn about astronomical equipment as you learn your way around the skies before taking the plunge (unless, of course, you have money to burn and can buy the best equipment to start with). For many, it won't become apparent what equipment is right for them until they've looked through a range of scopes and discussed their needs and concerns with other, more knowledgeable, people.
This excellent article by London-based amateur astronomer Paul Hill, however, will give you a very helpful introduction to your first telescope purchase if you decide you just can't wait to get a view from your own eyepiece.
The resources on this site will help you get acquainted with astronomy and maybe spark an interest in other areas you perhaps hadn't considered, but chatting through your interests and requirements will pay dividends... and prevent you from making an expensive purchase that you soon outgrow or leaves you disappointed from the outset.
- Firstly, go to meetings of astronomical groups and societies. They'll help you form an opinion of whether this interest is a passing curiosity, a lifelong hobby or a new career path. Find your nearest astronomical society here.
- Secondly,museums and exhibitions on astronomy and associated sciences will also help you understand where your interest lies. It may be that you don't want to spend hours outside at night and what you're really after is a night-school or part-time BSc. course to take your curiosity to a new level.
- Finally, speak to anyone you know that owns binoculars or a scope and get them to show you what they can see through it. Then ask them about their equipment (cost, durability, what it reveals in the sky - and what it doesn't!). Again society meetings are ideal for this. Even the biggest amateur telescope won't reveal the detail that the Hubble space telescope does, so knowing what you can see through a range of scopes will prevent you from being disappointed when you use your new pride and joy for the first time.
When buying a telescope there's no substitute for talking to an experienced retailer to ensure your expectations are met with the right equipment. But a bit of etiquette - don't get advice from one retailer and then buy the recommended equipment from a cheaper one. They all know one another and news travels!
Simple Guide to Telescope Types
A refracting telescope, or 'frac' has the classic sleek look of a traditional telescope and is likely to be the image conjured up when you think about astronomy.
The light enters through a lens (or multiple lens elements), which bend the light onto an eyepiece to achieve focus. The objective lens and the eyepiece lenses combine to create the magnification.
'Achromatic' refers to the method of enhancing objective lenses to counteract the loss of colour due to different wavelengths of light bending at different angles. Achromats typically bring the reds and blues into focus at the same point.
'Apochromatic' or 'apo' refers to the use of lens elements designed to bring reds, greens and blues into focus at the same point with lens coatings or extra lens elements. This is an improvement on the more traditional achromat.
Because of the need for heavy glass, refractors will always require a trade off between size of the objective lens you want and the weight you are prepared to accept. Reflectors allow much more light gathering at a fraction of the weight but the image quality of a quality refractor will always be far superior to that of a reflector of a similar size or even of a smaller size.
- Portable and compact (especially the smaller apochromats)
- Exceptionally sharp and contrasty observations
- More suited to astrophotography - simpler
- Shorter focal lengths make for better wide-field views - though achromats have longer focal lengths for planetary and lunar
- Some degree of chromatic aberration (false colour), less so with apochromatic refractors
- Larger apertures are very expensive
- No need to regularly collimate (adjust mirror alignment)
Ranging from the humble Newtonian to the modern Catadioptrics, reflectors use mirrors (or mirrors & lenses) to focus the light they gather onto the eyepiece.
The light comes into the front of the scope, hits a large curved primary mirror, which focuses the light onto a smaller secondary mirror. This second mirror is held at a 45 degree angle to turn the light, and focus it, towards the eyepiece on the side of the telescope tube.
On modern versions, such as the Schmidt Cassegrain and the Maksutov, the light enters through a simple lens, bounces off the primary mirror, is sent towards a secondary mirror from when it is bounced back again towards a hole in the centre of the primary mirror - where the eyepiece sits. To grossly oversimplify, the further the light travels in the tube, the greater the magnification, so bouncing the light back and forth before it reaches the eyepiece is a common way of shortening the tube length of a reflector.
This means the body of the scope can trade length for diameter to gather more light and ensure high magnification without sacrificing it to a scope that is too unwieldy for amateurs to use.
- Cheaper for large apertures (especially Newtonians),
- therefore, more magnification permissible.
- No chromatic aberration (false colour)
- Longer focal lengths (light paths) means better for planetary and lunar observations than apochromats
- Less contrast and sharpness than refractors
- Less portable and often cumbersome
- The fixings for the secondary mirrors cause spikes around stars (this can look pretty at first, but may become frustrating)
Other start-up equipment:
I’ve separated this guide into two sections, ‘must have’ and ‘nice to have’, with a few words about each item and a rough price for the amateur astronomer.
Many of the items range widely in cost but it will at least give you a lower or upper end price. As this is intended for beginners, I’ll not dwell on the mega-expensive equipment as there’s plenty of equipment available for starters without having to dive too deeply into your pockets. But be aware that astronomy is an expensive hobby and you will always find new/improved/better equipment to open up your wallet on a continual basis!
Mount/Tripod (£100 - £1,000)
These come in two main types: alt-azimuth, which has a pan and tilt function, and equatorial, which requires a polar alignment but allows you to follow your chosen objects through the sky along one axis. An alt-azimuth tripod is the simplest and most intuitive option but an equatorial mount is better for gently following your object as it moves through the sky and preferable if you intend to pursue astrophotography. Another consideration is do you want a manual tripod for your scope or a GoTo? GoTo mounts need not be expensive (starting at around £220) but they will find sky objects for you and keep them in the field of view automatically. It is also worth pointing out here that a sturdier/heavier mount will reduce the amount of eyepiece shake in windy conditions and during focusing, but this is a trade off against the portability of lighter mounts.
Eyepieces (from £40 each)
Later on you’ll probably want to buy a range of eyepieces which have better quality lenses or provide a wider field of view, but initially a good range of plossl eyepieces is a must when starting off. Three or four plossls (or Super Plossls) from 40mm to 6.4mm will give you enough flexibility to view the best of the night sky that your telescope will allow.
Star Diagonal/Erecting Prism (£25 - £250)
This is essentially an angled mirror that allows you to view sky objects in a more comfortable position. They come in 45 and 90º varieties which mean that you don’t have to lie on the ground to view objects near the zenith. They have the added benefit of flipping the image to the ‘right-way-round’ position so that the moon and planets don’t look upside down. In many cases your telescope’s focuser will not wind-out far enough to achieve focus if you just pop your eyepiece into your scope, but a diagonal provides extra ‘back focus’, making this an essential piece of kit for most amateur astronomers.
Battery pack (£40+)
If you have a GoTo mount or are running a laptop away from a convenient mains electricity supply, you'll probably want a 'power tank', which is essentially a car battery with a few extra ports and sockets. They can contain cigarette lighter sockets for your mount, inverters for 3 pin plugs, bright white lights, red light filters, and USB sockets (for your iPod/iPhone). My advice would be to go for ones from camping/vehicle accessory suppliers as they often have greater functionality at a reduced cost.
Nice to have:
Red light torch (around £20)
It takes around half an hour for your eyes to adapt well enough to the dark to appreciate the full splendour of the skies you’re sat beneath and any white light will very quickly undo all that long awaited benefit. Red light, however, doesn't affect your ‘dark adaptation’ and a torch with red LEDs will allow you to swap eyepieces, read star charts or poor coffee without affecting your delicate sensitivity.
Finderscope (£20 -£100)
Often unnecessary in very small scopes, a finder scope is a must for bigger telescopes if you want to find your desired object in the night sky. These are mounted on top of your scope and calibrated to ensure they are centred on the same object – this can be done by using a bright star or planet, a feature on the moon or even a distant terrestrial object such as a house-light or tree. Finder scopes are usually small scopes with a wider field of view and smaller magnification than your main scope, with cross hairs to let you bring your desired object into the field of view of your main, higher magnification, viewing scope. Modern alternatives include Red Dot Finders which shine a laser dot (circle or cross-hairs) onto a small glass plate – these are attached to, and calibrated with, your main scope in the same way.
Finder scopes are more intuitive for most beginners but red dot finders have the advantage of allowing you to see all the sky when seeking objects.
Barlow lenses (£20 - £250)
These lenses allow you to decrease the focal length and thereby increase the magnification of your scope by placing them between your scope and the eyepiece. Barlows come in a range of sizes (most commonly 2x or 3x) which allow you to double or triple your magnification with any given eyepiece. However, increasing magnification amplifies atmospheric effects and decreases the light collected so using Barlows is a balancing act – but one that can produce very gratifying results for lunar or planetary observations.
Light pollution filter (£20 - £80)
If you’re observing from – or near - a city, then the chances are that you’ll have light pollution reflected back from the atmosphere to contend with. In order to minimise its effects, filters are available with coatings that block the specific wavelength of street lights but allow the wavelengths of light that you want to observe through. These are screwed into the end of your eyepiece or diagonal and they’re especially effective at enhancing nebulae.
Moon Filter (£15 - £80)
Think of these as sunglasses for astronomers! The moon reflects a surprising amount of light, especially in its gibbous phases, and moon filters will make observing the moon more comfortable and allow you to tease out more surface detail. Standard moon filters have a specific light transmission level whereas Variable Polarising Filters allow you to adjust the level of shade simply by twisting the filter.
Binoviewer (£140 - £1k+)
A binoviewer will just slot into where you eyepiece goes to give you stereo vision. This not only gives you more comfortable viewing but also enhances the image as you’re seeing it with both eyes; and the effect is really quite astounding. Higher power eyepieces or barlows can be used to increase the magnification.
Many astronomy equipment retailers will be able to set you up with a perfectly adequate starter kit that includes everything you'll need for well under £500/$700. But don't be tempted to buy a scope from a supermarket or non-astronomy specific retailer as they are likely to have grossly inferior optics and/or mirrors that will not only prevent you from getting the most from your scope, but stand a good chance of putting you off astronomy altogether.
Magnification isn't everything - the quality of the glass/mirrors and the tube assembly are far more important. A telescope that promises 600x magnification is your first clue that the scope isn't worth buying; it would need to have a 12" aperture to achieve that kind of magnification:
As a rule of thumb, the maximum effective magnification can be calculated as follows:
diameter of aperture (in mm) x 2 - ie, 150mm aperture x 2 = 300x magnification
diameter of aperture (in inches) x 50 - ie, 6" aperture x 50 =300x magnification
so you can see that 150mm and 6" are the same and anything more than 300x magnification will result in a severe diminution of image quality.
For more of the science/maths stuff to help you understand a telescope's capabilities see here.