Binoculars are categorized using a numbering system that can be a bit confusing for someone being introduced to binoculars for the first time. It is important to understand this numbering system though, because a small change in numbers can mean a massive difference in binocular experience. For instance, individuals looking for binoculars suited for hunting would not wish to purchase a pair designed for stargazing, and vice versa. Fortunately, figuring out the numbering system is not all that difficult, and a little knowledge can go a long way.
Magnification
The first number in the designation indicates the intensity of magnification, or how many times closer an object will appear through the binoculars as opposed to the naked eye. The magnification process of the binoculars is conducted through the ocular lenses, which are the lenses closest to the eyes when the binoculars are in use. The size of the lenses do not necessarily have any bearing on the intensity of the magnification, as difference lens qualities will sometimes allow smaller lenses to have a higher capacity for magnification.
Higher magnification isn’t always necessarily an advantage, however, because intensity of magnification is inversely proportional to field of view. Meaning, the higher the magnification gets the narrower the field of view becomes. Users might be able to see something incredibly close, but they will lose what is going on around the object. If surroundings are important, like with activities such as birdwatching or spectator sports, then a higher magnification may not be the right choice. Being able to see the pores on a soccer goalie’s face is impressive, but the experience will be rendered moot if the ball being kicked at those pores is not visible in the scene.
Increasing the magnification of a pair of binoculars will also make them less stable. If shakiness is an issue to consider, again, opting for the highest magnification available might not be the best choice. With extremely high magnification, even binoculars taking advantage of monopods or tripods become shaky. With that being said, it is also important to consider the user’s ability to hold the binoculars steady over prolonged periods of time if the binoculars will be handheld. Even the lightest pair of binoculars can become strenuous to hold given a long enough period of time.
Aperture
The second number is the designation refers to the aperture of a pair of binoculars. The aperture is controlled by the objective lenses, or the lenses furthest from the eyes when the binoculars are in use. Unlike the magnification number, the aperture number does in fact refer to the size of the objective lenses. The number represents the size of the diameter of the objectives lenses in millimeters. The larger this number becomes, the wider the lenses and the more light they gather when in use. Although written about camera lenses, this is a great article explaining aperture. The size of the objective lenses also affects the physical size of a pair of binoculars. The larger the size of the objective lenses, the larger the casing of the binoculars will have to become. Although different materials are used as casings, this also usually means that the weight of a pair of binoculars will increase with the aperture number. This is something to think about when the binoculars will be used in a handheld fashion especially.
A good pair of binoculars with a small objective lens diameter will most likely be best used for light trail duty or as a backup set that can be stored in a glove compartment. Binoculars with higher aperture characteristics can be used for more intense activities where the amount of light is very important to the end result. For instance, a set of binoculars with an extremely large diameter objective lens would be perfect for hobby astronomy. While binoculars probably won’t be able to achieve the same results as a telescope, they are a portable and flexible way of staying in tune with the stars without being too encumbered.
While the numbering system of binoculars can be a bit intimidating at first, breaking the set down into individual components can make determining the best combination for a specific task a lot easier. And, the best way to really understand the system is to get out there and try a pair on for size. Many retailers will be more than happy to allow the testing of a pair of binoculars in order for the customer to be happy and confident with their purchase.