Binoculars Power, Magnification and Aperture


When you’re in the market for binoculars, you’ll soon find that each model is described with two numbers, the first being the magnification, or “power,” and the second referring to the diameter in millimeters of the objective lens (the aperture). For example, 10×50, 7×35 or 8×42. Simply put, for example, a 7x pair of binoculars will enlarge an object by seven times. Most binoculars on the market today feature an objective lens of 35 mm to 50 mm. Since power is often one of the most important factors for buyers and users of binoculars, you may hear people refer to simply an 8x or a 10x or a 12x.

The aperture controls how much light is collected by the binoculars, and thus how bright your view will be. A wide aperture (a higher number) is most important in low-light settings such as viewing night birds or the night sky. Be aware that binoculars with wider apertures (say, 50mm or more) do let in more light but they also weigh more.

It’s likely the purpose for which you’ll use the binoculars will dictate the magnification you will seek. For example, binoculars marketed to birdwatchers are generally in the 7x to 10x range, although some birders prefer 12x or even 15x. If your interest is in observing a large scene, be advised that smaller magnification numbers means a wider field of view and thus more birds, stars or other objects that can be seen at one time.

Also, with greater magnification usually comes a higher price. But if you really want or need the added power, such as if age or other factors are compromising your eyesight, there’s really no question that greater magnification will be worth the added cost.

Bigger is not always better, and this holds true when it comes to binoculars. There are even some applications for which the magnification can actually be too high. When binoculars get to 12x and beyond, the field of view is noticeably smaller, and, because they’re heavier, they’re harder to hold steady without your hands shaking. Ironically, you could end up seeing less, not more. Also, high magnification binoculars can less effective in low-light situations.

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