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All About Binoculars

Don’t be fooled by binocular hype. Getting a good price on a good, bright, sharp, durable binocular isn’t hard. You just have to resist the silly ads and know a few basics, which you can read right here.

When bino shopping, forget all about “seeing 10 miles” and “the vision of an eagle.” Don’t pay attention to words like “bright, clear, precise or sharp.” Those are vague buzz words and glittering generalities. You need hard facts.

The fact is binoculars are confusing and complicated because they’re a black box. You can’t see in there to determine what parts are good or bad or even what they’re doing. So I’ll tell you:

There are two basic binocular types, roof prism and Porro prism. Roofs have straight barrels; Porros have dog-legged barrels. You’ll pay more to get a roof that’s as sharp as a Porro, but roofs are more durable, harder to knock out of alignment. Pay about $250 and up for a good roof prism; $150 and up for good Porro. Most folks go with roof because they’re more compact and “in fashion.”

Here are 8X and 10X binoculars, both with 42mm objectives, and both the same physical size. Changing power does not mean changing overall size.

The critical stuff you want in a roof prism are: Phase-coated BaK-4 prisms with silver mirror, or more expensive dielectric mirror,and fully multi-coated lenses. This means every air-to-glass surface is coated with several layers of anti-reflection coating. This maximizes light transmission and minimizes flair and glare. Coatings cost more, but don’t add weight or bulk. An 8X is more versatile than a 10X and easier to hold steadily. A 6X is even better for use in woods.

Now, here are some details to help you understand why the above features are important.

A binocular consists of an objective lens. That’s the big one out front that captures the light and forms the image. This image is then sent, upside down and backward, to additional lenses inside that correct for various aberrations, such as color shift and distortion. Next come the prisms, hefty chunks of glass that reorient the image properly and bounce the light back and forth in order to lengthen its travel. This is what creates magnification. The farther the light travels, the higher the magnification, which is why old telescopes were so long. Prisms shorten the barrel by bouncing the light from surface to surface. Then they pass it to the eyepiece lenses that act like a magnifying glass to further increase magnification. This is why many 8X and 10X binoculars are the same length. There’s just additional magnification in the eyepiece of the 10X. 

How Glass Is Ground Determines Sharpness
Several things contribute to sharpness and brightness. First, the lenses have to be precisely ground. Don’t buy the sales line about “better glass.” All manufacturers buy glass from a handful of glass makers, and they don’t specify Grade C or B instead of Grade A. It’s all the same basic quality. Its how that glass is ground that determines sharpness. Computers control the grind, so most lenses are excellent. (Those really cheap binos selling for less than $100 probably use plastic lenses — not so good — but check to be sure)

Next, the prisms have to be precisely ground and mounted. Cheap internal parts that hold things together can contribute to poor image quality, particularly after a bino has been used, worn and bumped around a bit. This is hidden quality you can’t see, but need. A brand’s reputation for durability counts here.

Phase coating improves sharpness of light coming out of roof prisms. Porro prisms don’t need it. A silver mirror is much brighter than a cheaper aluminum mirror, and dielectric mirrors are the brightest of all, but you pay more for them.

Binoculars come in a confusing variety of shapes and sizes.

Anti-reflection lens coatings are your biggest bang for buck. Uncoated glass reflects (wastes) about 4 percent of the light at each surface, coming and going. So one lens will cost you 8 percent of light. With an average of five lenses in a binocular, uncoated glass costs significant brightness. Worse, the reflected light bounces around inside like a billion ping pong balls, creating haze, flare and glare. Anti-reflection coatings, the more the better, can knock reflection loss down to less than .5 percent per lens surface. To make sure you get it, insist the binocular is FULLY multi-coated. If they advertise it as coated, it needs just one layer on one lens. Multi-coated means multiple layers on at least one lens. Fully multi-coated means all lenses get it. That’s what you want.

The objective lens lets in light. Magnification reduces light. An 8×40 fully multi-coated is bright enough to see game clearly 45 minutes after sunset. Going to a 50mm objective might give you one to three more minutes more viewing time. A 10×40 is slightly darker than an 8X and a 6X is slightly brighter.

Shop The Sportsman’s Guide great selection of Binoculars!

Ron Spomer has been photographing and writing about the outdoors for nearly four decades. He’s written seven books, hunted on six continents and been published in more than 120 magazines. He’s currently rifles’ editor at “Sporting Classics,” Travel columnist at “Sports Afield,” Field Editor at “American Hunter” and “Guns & Ammo” — Optics Columnist at “North American Hunter,” Contributing Editor at “Successful Hunter,” Senior Writer at “Gun Hunter,” and TV host of “Winchester World of Whitetail.” He will write on Shooting Tips weekly for sportsmansguide.com. You can read his blogs and catch some of his YouTube videos at www.Ronspomeroutdoors.com.

 

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