CAN I USE ANY OLD BINOCULARS?
if you want steady views over prolonged periods. Common sizes are:
8x40, which almost anyone over the age of 10 can hold steadily
10x50, which most adults can hold steadily (this size is a popular compromise between size and weight)
15x70, which really needs to be mounted, although it can be briefly handheld
You should also check that the distance between the eyepieces, or ‘interpupillary distance’ will adjust to your eyes. If you observe while wearing glasses, ensure that the binoculars have enough distance (‘eye relief ’) from the eyepiece to your ideal eye position; 18mm or more should be fine.
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 size and type, get the best quality you can for your budget and start exploring the night sky. In principle, yes: even plastic-lensed 4x20 toy binoculars can show you astronomical objects that you otherwise couldn’t see, such as the moons of Jupiter. So, if you already have a pair of small binoculars, for example a 6x30 or 8x32 pair, try them out under the stars: you’ll be amazed at how much more you can see. The optical quality will also make a difference and you may find that there are things you can see with good-quality small binoculars like 8x42s that are beyond the capability of an entry-level 15x70. But avoid zoom binoculars: good ones don’t exist.