Never look at the sun through Binoculars, Telescopes or any other optical equipment.
Magnification and Brightness.
All Binoculars are described with a number, for example, 8x21. The first number tells you the Magnification, so 8x makes a subject appear eight times closer.
If you are viewing small subjects at long distances, you will probably need a larger Magnification and for subjects at close distance, you will probably find a smaller magnification is better. You should be aware that more powerful Binoculars will magnify any unsteadiness when you are holding the instrument (shake), so choosing a smaller Magnification may give an apparently sharper image than a larger Magnification.
The second number tells you the diameter of the objective lens (that’s the large lens at the other end of the Binoculars from the eyepiece). Dividing the diameter of the objective lens by the magnification of the Binoculars gives a measure of how bright the Binoculars will be (Brightness Index). For example, an 8x21 binocular has a BI of 21/8=2.6. In daylight, a BI of 2 to 3 is normally satisfactory, but in low light, a BI of around 5 or more (e.g. 8x40, 7x50) will be much better.
Angle of View
If you can see a wide area of the subject, it’s much easier to find the part of the subject you want to look at. Generally, the more powerful Binoculars have a narrower angle of view, but there are variations between models. A good 8x Binocular should have an angle of view of 6 to 7 degrees, or more, while a 12x model may offer as little as 4 or 5 degrees.
Lens Coatings
All good binocular lenses are coated in order to reduce internal reflections and improve the image quality. It’s possible to give even better viewing, for example, by the use of Ruby Anti-UV Coated Lenses, which help to cut through haze, as well as protecting your eyes against the harmful effects of ultra violet light.
BaK-4 Prisms
Some binoculars are constructed with BaK-4 Prisms, which utilise a superior glass to provide brighter, clearer, sharper images than would be achieved with ‘ordinary’ prisms.
Long Eye Relief
If you wear spectacles, you may find long eye relief helpful, as it will allow you to view a subject in greater comfort, without pressing your glasses against the eyepieces. It’s also helpful for short sighted users.
