1. Magnification
The magnification of a binocular is the number that is written with the x. So if the binocular says 7x, it means it magnifies the subject seven times. For instance, a bird 1,000 metres away will appear as if it was at a distanc e100 metres away as see with the naked eyes. The best magnifications for regular use are between 7x and 12x, anything beyond and it will be tough to manage without a tripo
2. Objective Lens Diameter
The objective lens is the one opposite the eye piece. The size of this lens is crucial because it determines the amount of light that enters the binoculars. So for low light conditions, you get better images if you have a bigger diameter objective lens. The lens size in mm comes after the x. A ratio of 5 in relation to the magnification is ideal. Between an 8x25 and 8x40 lenses, the latter creates a brighter and better image with its bigger diameter.
3. Lens Quality, Coating The lens coating is important because it reduces the amount of light reflected and allows the maximum amount of light to enter. The quality of the lens, meanwhile, ensures the image is aberration free and has better contrast. The best lenses work better in low light conditions as they transmit more light. They also ensure that the colours are not washed out or distorted. Users with spectacles should look for a high eyepoint.
4. Field of View/Exit Pupil
FoW refers to the diameter of the area seen through the glasses and is expressed in degrees. The larger the field of view the larger the area you can see. Exit pupil, meanwhile, is the image formed on the eyepiece for your pupil to see. Lens diameter divided by magnification gives you the exit pupil. An exit pupil of 7mm gives maximum light to the dilated eye and is ideal for use in twilight and dark conditions.
5. Weight & Eye Strain
One should consider the weight of a binocular before buying it. Consider if using the binoculars for a prolonged time tires you. Similarly, use a binocular and see if it is taxing on your eye. While it is difficult to use regular binoculars for more than a few minutes at a time, the high-end ones hardly cause any eye strain and can be used for long hours at a stretch if needed.
6. Waterproofing
Since binoculars are an essentially outdoor products, it is important that they have some degree of waterproofing-this is usually denoted as "WP". While regular models can stay under limited amounts of water for a few minutes, the high-end models are left undamaged even after a couple of hours submerged in water.
A BINOCULAR FOR THE OCCASION
TRAVEL Look for compact, lightweight models with mid-range magnification and field of view.
BIRD & NATURE WATCHING Needs wide field of view and magnification of between 7x and 12x.
OUTDOORS Look for rugged models with waterproofing, portability and durability. Ideal magnification is between 8x and 10x. Also look for large objective diameter and good lens coating so that it works well in rising and setting sun conditions.
MARINE Look for waterproofing with a wide field of view and vibration reduction if possible.
ASTRONOMY Aberration corrected binoculars with large objective diameter and exit pupil are best.
THEATRE/MUSEUM Compact models with magnification of 4x to 10x can be effective while watching stage performances. In museums, lightweight models with low magnification and focusing distance of less than two metres are recommended.
SPORTS Look for wide field of view and 7x to 10x magnification. Zoom functionality can be an added advantage.
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