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The Binocular Advisor

Optics Myth 2:

Bigger binoculars are more powerful
.Zeiss Big & Little

REALITY - The size of the binocular tells you absolutely nothing about the power. Some 10-power binoculars are smaller than some 7-power ones.

For example, the Zeiss 10x25 Victory Compact (shown above—the black one, on the right) is only three quarters as long and weighs one third as much as a Zeiss Victory FL 7x42 (the green one, on the left). But of course the smaller 10x25 is "more powerful" than the larger 7x42.

What determines a binocular's power, or magnification, is the design of its eyepiece. And eyepiece design has little or no effect on the size of the binocular.

Often a manufacturer makes the same binocular in more than one power. For one example among many, the Eagle Optics Ranger (pictured below) comes in 8x42 or 10x42. See if you can tell which one is the ten power.

Ranger size comparison

The look the same, don't they? By the way, you wouldn't be able to tell by their appearance even in you were holding them in your hands—not without reading the numbers printed on the outside. The two models have the same dimensions, shape, and weight, and the share the same sized objective lenses. The difference is in their eyepieces, one of which magnifies the image 8-fold and the other 10-fold.

Well, then, what does make a binocular bigger?

Mainly it's the size of the objective lenses. (The objective lenses are in the end of the binocular closer to the object you're looking at). In the formula printed on the binocular, the size of the objectives is the second number. Binoculars that are 7x42, 8x42, and 10x42 all have objective lenses that are 42mm in diameter. Binoculars in the same product line with the same sized objectives will usually be the same size.

Copyright 2006 Michael and Diane Porter



Sharp-shinned Hawk

Optics Myths and Misconceptions