How to Buy Binoculars

According to experts, “binoculars are the world’s most used optical instrument other than eyeglasses.” Those who wear glasses out of necessity know the complicated difficulty in selecting a pair. Binoculars have a similar multitude of specifications and numbering systems. Here are some tips and tricks for picking out a binocular.

Most binoculars are labeled with two or at most three numbers if they have a zoom feature. The first of these numbers explains the magnification the instrument is capable of. A simple way to remember is the first number means the object you are viewing is X times larger than life. If the first number on two different binoculars is the same, it means they magnify the same amount. When there are three numbers, the first two indicate the range of magnification. For example, an instrument that has the number 2-5×6 will magnify between two and five times life size. However, the downside to magnification, especially in higher numbers, is the image clarity and stability decreases as the magnification increases. Typically, any set of binoculars with a magnification higher than 10x will need a tripod to be useful.

The second number listed is the “diameter or width of each front lens, measured in millimeters.” While magnification for two pairs of binoculars may be the same, the quality is markedly different depending on the diameter. Larger width equals a clearer, sharper view. On the other hand, larger also means heavier, so if you are looking for a field or hiking binocular, a smaller, lighter model may be better for you. When conversing with a salesman or binocular enthusiast, they will probably mention the “field of view” for any given model. This term simply refers to “the amount of territory you see when you look through the binocular.” As magnification goes up, the field of view goes down, so if a large area is what you are hoping to see, a lower magnification will work better for you. Another term you might hear mentioned is the “twilight factor.” Far from being a book or movie series starring sexy vampires, the twilight factor is a mathematical formula that can estimate how much detail you can see in poor light such as twilight. “Twilight factor is the square root of magnification [multiplied by] objective. A 10×40 will have a twilight factor of 20 [since that is the] square root of 10×40.”
Courtney Shipe

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