How to Choose Binocular Magnification

Vaughn Clark

You can understand the optical magic of binoculars just by looking through them. Magnification, or power, is the term used to express that bigger image. But when it comes to choosing binocular magnification, things can get out of focus because it also concerns when and what you intend to view, how far that object is away, whether you or the object is in motion, and the clarity of the image you expect to see.

Instructions

Difficulty: Moderately Easy

Step 1

Determine what you will use the binoculars for. For day hiking, size and weight are not a dominant factor, but you may have other uses such as birding, mountaineering, watching sports, boating or astronomy. Once you decide your overall use, you can better determine the suitable magnification as it relates to the actual physical size of the instrument, cost and other technical factors.

Step 2

Understand the three basic parts of binoculars to better understand magnification. The large objective lens gather the light and focus it down to a small inverted image on the prisms located inside the binocular housing. The prisms re-invert the image, reorienting it for proper viewing. Finally, the eye lenses or eye piece magnifies the image presented on the viewing side of the prisms, which then present it to the eye.

Step 3

Understand the two numbers that express the properties of a pair of binoculars. As an example, consider a pair of 7x50. The seven is the magnification number, which expresses how many times larger the image will appear compared to normal. The 50 is the diameter, in millimeters, of the large objective lens. Variable magnification, or zoom, binoculars have two numbers before the "x" such as 7-15x25. These binoculars use movable lens configurations that can focus through a range of magnifications.

Step 4

Consider the trade-offs of high and low magnification. Greater magnification means magnified shakes and tremors of your hands. It also means a less bright image, a smaller field of view and a shallower depth of field (the range in which the image is in focus). Also keep in mind the near focus, or the minimum distance at which an object will still be in focus. A higher magnification will have a more distant near focus.

Step 5

Take into account the versatility of zoom binoculars. If you anticipate using your binoculars for general use but would like occasional high magnification, think about zoom binoculars. But be advised that a zoom binocular has an inferior optical quality at any given magnification compared with that of a fixed binocular of that same magnification.

Tips & Warnings

Compare magnification by looking through the eye piece with one eye while viewing through the unaided eye with the other.

Resources

Binoculars at Trails.com

Article Written By Vaughn Clark

Living in Boise, Idaho, Vaughn Clark has been a freelance writer for 18 years. His articles have appeared in "Backpacker" magazine, "The New Times," the "Ventura County Star," and "Santa Barbara News-Press." He has also published poetry and written three full-length adventure screenplays.

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