So you want to buy a telescope...?
The short version:
Don't. Buy binoculars instead.
The long version:
Sooner or later, anyone interested in looking at the night sky will think about buying a telescope. Looking at the stars with the naked eye is nice enough, but nothing beats a telescope that can magnify the Moon, planets and galaxies by 300x ... or does it?
The sad truth is that many first-time buyers of small (or not-so-small) cheap telescopes end up bitterly disappointed. Why is this?
First: they might buy the telescope from the local camera shop, post office or discount store. The instrument usually looks good - nice colour, bristling with shiny bits & pieces, and lots of little lenses that must mean it's a really powerful telescope (look at the size of that extension tube!). The trouble is - and with all due respect to the sales assistants in those outlets - they are almost certainly not being advised by someone who really understands telescopes. Granted, the staff in a good camera shop ought to know a bit more, and be able to take the time to give the best advice for you, but it's not necessarily the case.
Second: they have been wooed by glossy advertising on the display and especially by the allure of high magnification coupled with pictures of galaxies and nebulae that will have been taken by very much larger telescopes. [For more about telescope magnification, see What does THAT mean?]
All of this means that the unsuspecting buyer has dreams of seeing the Moon and planets in great detail, but when they get the telescope home and take it out on the first clear night, discover that it is harder than they thought:
If this sounds like I'm trying to put you off by deliberately making it sound hard, I'm not. I'm trying to put you off making a mistake by making it sound realistic; that way, you are therefore more likely to continue enjoying the pursuit of astronomy instead of being put off for life.
If, after reading this, you still want to view the night sky (and who doesn't?), then the best advice you can have is to go and buy some binoculars. There are several reasons for this:
But what about seeing the planets up close? It's true that you won't be able to see Saturn's rings or the Moon's craters so clearly as you would with a good telescope, but there is more to be seen than those sights (good though they are). For example, on a moonless night, you will be able to look at the thousands of stars in the Milky way - many more than you can see with the naked eye; you will be better able to see the colours of the stars; you will probably be able to see Jupiter's brightest moons; you will be able to find many star clusters and nebulae, and the nearest galaxies outside our own - the 2 Magellanic Clouds. These in particular are best seen with the very low powers that binoculars provide, being larger than the field of view of most telescopes.
And of course, when the Moon is in view, you will be able to see some detail on its surface - craters, mountains and the dark 'seas'. You will be able to follow its phases as it progresses from New Moon through crescent, to half, then gibbous and full. As the phase increases to full, you will notice the changing appearance from night to night, until at full it is a brilliant, almost dazzling, disk, covered with dark patches and bright streaks (these streaks are the remnants of meteorites that have hit the Moon then exploded, casting material almost halfway around the Moon in some cases.
Don't. Buy binoculars instead.
The long version:
Sooner or later, anyone interested in looking at the night sky will think about buying a telescope. Looking at the stars with the naked eye is nice enough, but nothing beats a telescope that can magnify the Moon, planets and galaxies by 300x ... or does it?
The sad truth is that many first-time buyers of small (or not-so-small) cheap telescopes end up bitterly disappointed. Why is this?
First: they might buy the telescope from the local camera shop, post office or discount store. The instrument usually looks good - nice colour, bristling with shiny bits & pieces, and lots of little lenses that must mean it's a really powerful telescope (look at the size of that extension tube!). The trouble is - and with all due respect to the sales assistants in those outlets - they are almost certainly not being advised by someone who really understands telescopes. Granted, the staff in a good camera shop ought to know a bit more, and be able to take the time to give the best advice for you, but it's not necessarily the case.
Second: they have been wooed by glossy advertising on the display and especially by the allure of high magnification coupled with pictures of galaxies and nebulae that will have been taken by very much larger telescopes. [For more about telescope magnification, see What does THAT mean?]
All of this means that the unsuspecting buyer has dreams of seeing the Moon and planets in great detail, but when they get the telescope home and take it out on the first clear night, discover that it is harder than they thought:
- if they didn't spend time learning how to use the telescope in daylight, it will be almost impossible in near-darkness
- when they try to find something (anything!) to look at, they will learn that the small finder 'scope is not aligned properly, and is therefore useless
- if they are lucky enough to be able to find something through the main telescope, they will soon find that it drifts out of view pretty quickly, and when they try to move the tube to follow it - assuming they can sort out the various knobs etc - they will probably find that it moves the wrong way!
- after all that, if they manage to keep the object in view, it will probably be wobbling all over the place every time the telescope is touched even slightly, and to top it all, they are crouched down at an impossible angle, with a sore neck developing.
If this sounds like I'm trying to put you off by deliberately making it sound hard, I'm not. I'm trying to put you off making a mistake by making it sound realistic; that way, you are therefore more likely to continue enjoying the pursuit of astronomy instead of being put off for life.
If, after reading this, you still want to view the night sky (and who doesn't?), then the best advice you can have is to go and buy some binoculars. There are several reasons for this:
- binoculars are easy to hand-hold, without the need for a tripod or complicated mount
- binoculars are relatively cheap
- binoculars allow you to use both eyes for viewing comfort
- binoculars can be fetched from the cupboard and put back there afterwards with no difficulty
- binoculars can easily be used for other pastimes as well
But what about seeing the planets up close? It's true that you won't be able to see Saturn's rings or the Moon's craters so clearly as you would with a good telescope, but there is more to be seen than those sights (good though they are). For example, on a moonless night, you will be able to look at the thousands of stars in the Milky way - many more than you can see with the naked eye; you will be better able to see the colours of the stars; you will probably be able to see Jupiter's brightest moons; you will be able to find many star clusters and nebulae, and the nearest galaxies outside our own - the 2 Magellanic Clouds. These in particular are best seen with the very low powers that binoculars provide, being larger than the field of view of most telescopes.
And of course, when the Moon is in view, you will be able to see some detail on its surface - craters, mountains and the dark 'seas'. You will be able to follow its phases as it progresses from New Moon through crescent, to half, then gibbous and full. As the phase increases to full, you will notice the changing appearance from night to night, until at full it is a brilliant, almost dazzling, disk, covered with dark patches and bright streaks (these streaks are the remnants of meteorites that have hit the Moon then exploded, casting material almost halfway around the Moon in some cases.
All right, that's what you can see with binoculars, but which ones should you buy? As with anything, you will generally get what you pay for, and cheap ones may be disappointing. Having said that, cheap binoculars will probably disappoint less than a cheap telescope.
The first comment to be made is about the numbers marked on binoculars. These are used to denote (1) how much magnification they provide, and (2) how large the front (objective) lenses are. So, a common size used in astronomy is 7x50. This means they magnify 7 times, and have lenses 50mm in diameter. Now, if you divide the second number by the first, you have the size of the exit pupil - a relative indication of how bright the image will be. Thus, 50 divided by 7 is approximately 7. The important thing here is that the pupil of your eye is around 7mm across when wide open, so if the binoculars have a 7mm exit pupil, they will use the full width of your pupil, and so will give the brightest image your eye can use.
Repeating this with 2 other common sizes useful for astronomy - 10x50 and 8x40 - you have exit pupils of 5mm for each (50/10 & 40/8). While therefore not as good as 7x50 for looking at fainter objects such as galaxies and nebulae, they will be quite satisfactory. When comparing binocular image brightnesses by this method, you actually need to use the square of the exit pupil diameter. So, although 5 is just lower than 7, by using the square of each number (i.e. the number multiplied by itself), you have a true indication of the relative brightness: 7x7=49 ... 5x5=25. So the image in a 10x50 or 8x40 binocular will actually be half as bright as a 7x50. This will be fine for a beginner's use. [Note: these comments apply only to low-light viewing, such as astronomy or around dusk; in daylight your eye's own pupil will generally be smaller than the exit pupil of the binoculars mentioned.]
The other thing to note is that the larger the binoculars, the heavier they will be, and more difficult to hold steady for long periods. 8x40 is a reasonable compromise of size, weight, brightness and magnification, but it's a matter of personal choice. The best thing is to find some way of holding them steady by supporting your elbows or shoulders, or if you wish, you may be able to buy a small clamp that will allow you to mount them on a photographic tripod (this is especially important for anything larger than 10x50).
If you do decide to buy binoculars, take your time, try several models in a good shop, and see what feels best in your hands, or against your eyes - this is especially important if you wear glasses; spend some time looking through them to make sure you can see through them easily. 2 different models with the same specification, made by different manufacturers, might feel quite different, and you might have a definite preference for one over the other, so it's worth looking around a bit before you commit. Don't let yourself be rushed into a choice by an eager and persuasive shop assistant. The sky will wait! If you're not certain whether you are making the right choice, hold back until you are.
Finally, modern optical instruments have coated lenses, to reduce flare and internal reflections, which help provide a brighter, clearer view. Buy ones with the best coating you can afford, preferably multi-coated. You may see a "fully coated" description, but this isn't as good as "multi-coated" or "fully multi-coated"
The first comment to be made is about the numbers marked on binoculars. These are used to denote (1) how much magnification they provide, and (2) how large the front (objective) lenses are. So, a common size used in astronomy is 7x50. This means they magnify 7 times, and have lenses 50mm in diameter. Now, if you divide the second number by the first, you have the size of the exit pupil - a relative indication of how bright the image will be. Thus, 50 divided by 7 is approximately 7. The important thing here is that the pupil of your eye is around 7mm across when wide open, so if the binoculars have a 7mm exit pupil, they will use the full width of your pupil, and so will give the brightest image your eye can use.
Repeating this with 2 other common sizes useful for astronomy - 10x50 and 8x40 - you have exit pupils of 5mm for each (50/10 & 40/8). While therefore not as good as 7x50 for looking at fainter objects such as galaxies and nebulae, they will be quite satisfactory. When comparing binocular image brightnesses by this method, you actually need to use the square of the exit pupil diameter. So, although 5 is just lower than 7, by using the square of each number (i.e. the number multiplied by itself), you have a true indication of the relative brightness: 7x7=49 ... 5x5=25. So the image in a 10x50 or 8x40 binocular will actually be half as bright as a 7x50. This will be fine for a beginner's use. [Note: these comments apply only to low-light viewing, such as astronomy or around dusk; in daylight your eye's own pupil will generally be smaller than the exit pupil of the binoculars mentioned.]
The other thing to note is that the larger the binoculars, the heavier they will be, and more difficult to hold steady for long periods. 8x40 is a reasonable compromise of size, weight, brightness and magnification, but it's a matter of personal choice. The best thing is to find some way of holding them steady by supporting your elbows or shoulders, or if you wish, you may be able to buy a small clamp that will allow you to mount them on a photographic tripod (this is especially important for anything larger than 10x50).
If you do decide to buy binoculars, take your time, try several models in a good shop, and see what feels best in your hands, or against your eyes - this is especially important if you wear glasses; spend some time looking through them to make sure you can see through them easily. 2 different models with the same specification, made by different manufacturers, might feel quite different, and you might have a definite preference for one over the other, so it's worth looking around a bit before you commit. Don't let yourself be rushed into a choice by an eager and persuasive shop assistant. The sky will wait! If you're not certain whether you are making the right choice, hold back until you are.
Finally, modern optical instruments have coated lenses, to reduce flare and internal reflections, which help provide a brighter, clearer view. Buy ones with the best coating you can afford, preferably multi-coated. You may see a "fully coated" description, but this isn't as good as "multi-coated" or "fully multi-coated"
After you have spent a few months looking at the sky with binoculars, you should have a better idea of whether or not you really want to advance to a telescope. If you have enjoyed the experience and still want to see more, then it's likely you will be sufficiently motivated to get the best out of a telescope. You will probably also have read some books and magazines and browsed a few websites, and will be better placed to understand some of the issues around buying telescopes. You might also have a better idea of what you want to look at in particular, which can be relevant to the choice of instrument.
If you wish to discuss anything about buying a telescope or binoculars, feel free to come along to one of our regular meetings - we will be only too happy to assist :)
If you wish to discuss anything about buying a telescope or binoculars, feel free to come along to one of our regular meetings - we will be only too happy to assist :)