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Starting with Binoculars
Telescopes aren't the only option for observing the night sky, a pair of binoculars is ideal for budding astronomers.
New to astronomy and trying to work out what to buy for your first telescope? There's a simple answer to that question: don't buy one, buy two. Two small scopes joined with a hinge so that the distance between them can be adjusted to exactly match your eyes — binoculars. Binoculars allow you to observe hundreds of astronomical objects. Not only can you see many more objects through binoculars than with the naked eye, but the detail and color you can see will become richer too.
Binoculars are still suitable even if you want to do 'serious' astronomy. There are variable star observing programs designed specifically for binoculars and being lightweight and easy to carry makes them ideal for getting out and about to view a lunar graze or asteroid occultation.
Closer to home, why not simply wrap up warm, lie back on your garden recliner and just enjoy the objects your binoculars let you find as you cast your gaze among the stars. You'll soon be able to find your way around the night sky and navigate better than with the entry-level GoTo telescope you nearly bought instead.
What Size Should You Buy?
You'll notice that binoculars are classified by two numbers, their magnification and aperture. A 10x50 pair of binoculars has a magnification of 10x and each of the front lenses has an aperture of 50mm. These numbers also allow you to work out the size of the circle of light, or 'exit pupil', that emerges from the eyepieces: to do this you divide the aperture by the magnification. This means a 10x50 pair of binoculars has an exit pupil of 5mm. The exit pupil should be no larger than the dark-dilated pupils of your eyes: so a pupil of anywhere between 4-6mm is fine for your first pair of binoculars. Larger apertures can show you more but being heavier you will probably need to use a mount to keep a steady view over a longer period. The most common sizes are:
- 8x40: almost anyone over the age of 10 can hold these steadily.
- 10x50: most adults can hold these steadily, so this size is a popular compromise between size and weight.
- 15x70: this size really needs to be mounted, although they can be held for short periods.
It's also important to check that the distance between the two eyepieces will adjust to your eyes. If you wear glasses, check that the binoculars have enough distance from the eyepiece to your ideal eye position; 18mm or more should be adequate. Finally, there are two basic types of binoculars: Porro-prism and roof-prism. In any price range, roof-prisms are lighter but Porro-prisms tend to have better optical quality. Once you've decided on the size and type that best suits you, go for the best quality you can buy for your budget.
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