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Straight Shooters Cast Bullets
Rifle Magazine
September - October 2003
Volume 35, Number 5
ISSN: 0162-3583
Number 209
On the cover...
The Model 1873 Springfield was the mainstay of the U.S. Army until it was replaced by the .30 U.S. (aka .30-40 Krag) in 1892. Rifle photo by Gerald Hudson. Whitetail Deer photo by Ron Spomer.
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High-Magnification Binoculars

The downside to a big binocular is both weight and size, but in many situations there's no substitute for sheer magnification, which also requires an adequate objective lens. The Missouri Breaks is the sort of country where a binocular of at least 10x can really help the hunter.

Americans like big vehicles, big houses and big cartridges. Many even like big hair. This often carries over into hunting binoculars.

Most hunters believe that more magnification helps find more game. There's some truth to this, but there are some practical limits to extra magnification.

The first is the size of the objective lenses. Many hunters know the objective lenses control the amount of light entering any telescope (and a binocular is a pair of telescopes). But few realize that small objectives also limit optical sharpness so tend to buy binoculars a little too small for the sharpest view.

The most extreme case I've encountered was Hill Griffin, a Florida bow hunter who ended up in the same moose camp with me in British Columbia. Hill wanted a small binocular but also wanted magnification. Before our hunt I didn't even know that Nikon made a 6-24x zoom compact!

Curious, I asked to try them one evening when we were glassing a couple of bulls across a valley. The little glass was light and handy, and you could "zoom" up to 24x to look at the moose. Trouble was, at any magnification over about 8x, the moose could just as well have been elk, or even woolly mammoths.

The problem with high magnification and small objectives is that most stray (diffracted) light entering a telescope comes in around the edges of the objective lens. This light gets scattered both by the lens mount and the fact light entering farthest from the center of a lens has to bend more. The smaller the lens, the higher the percentage of light entering around the edges, and high magnification makes matters worse.

For good definition (the optical quality most hunters call sharpness), the diameter of the objective lens should measure, in millimeters, at least four times the magnification. This means that for serious glassing, an 8x binocular should have about a 32mm objective at a minimum. This formula assumes quality optics, as I've looked through 8x32 binoculars that couldn't separate a moose from a woolly mammoth at any distance over 500 yards.

For the finest definition, an objective at least five to six times the magnification helps enormously, one reason making decent optics is easier if everything's bigger. I've seen $100 10x50 glasses that beat the heck out of $400 10x20s.

But big glass doesn't do us any good if we don't know how to use it. Back when I was guiding in central Montana, many hunters showed up with various high-power binoculars. Some of these were $34.87 Cheap-Mart compacts, so didn't count, but others were full-sized glass from some of the best names in the business. At the time my main binocular was a 7x35 Nikon porro-prism that, when acquired in 1986, retailed for a little over $100. Some guides became very discouraged with their $800 10x50s when I kept finding mule deer before they did. One offered to sell me his, on the spot, for half of what he paid.

There really wasn't any problem with their glass - and none with mine either. I still have that "primitive" 7x35, and despite not being rubbed-armored or waterproof, it's still one of the sharpest 7x binoculars I've ever seen. I wasn't terribly disadvantaged optically - but mostly I knew how to glass.

When we'd ease up to the rim of a coulee, I'd sit down with my back against a tree and hold my binocular steadily on one spot, looking around inside the field of view until satisfied no deer lurked there. Then I'd shift to another area and work it over. Meanwhile my guide might also be sitting down (especially if I insisted), but most often he'd be holding his binocular in one hand. The only time he actually raised his glass was after he'd eyeballed a stand of ponderosa pine and found something suspicious.

There's zero advantage to high magnification if you don't hold the glass steady. Skimming the scenery or glassing offhand is like trying to watch TV while jitterbugging. Sit or lie down, rest your elbows and look at one place until you're certain there's nothing there. To get really steady, grab the bill of your NRA baseball cap along with the binocular.

I had a couple other minor advantages as well. First, I'd been hunting mule deer for over 20 years and knew what a buck looked like when bedded down behind a juniper.

A second advantage lay in lower magnification. The area of our eye where we perceive the sharpest detail is actually quite small - and the more magnification we use, the smaller it gets. In the Bull Mountains we hardly ever glassed deer more than 1,000 yards away, and often half that. Here the larger "sweet spot" in my 7x35s (about twice the size of a 10x's, since the area of a circle increases by the square of its radius) actually gave me an advantage in finding game.

Out on the pronghorn prairies, this advantage disappeared, one reason that before the next season I also acquired a 10x40 Bausch & Lomb. Not only are tan-and-white pronghorns in olive-drab sagebrush far easier to find than gray-brown mule deer in gray-brown timber, but glassing at a mile or more allows the sweet spot of a 10x to go to work.

Most of us can't hand-hold binoculars of more than about 12x steadily enough to gain much benefit, even if we sit down and grab our baseball cap. This is why many high-power glasses also come adapted for tripod use. In some parts of the country, notably the desert Southwest, hunters commonly use tripod-mounted binoculars of 15x or more. Not only do such huge glasses provide a sharper view than the equivalent spotting scope, but they're more comfortable. Most of us squint the off-eye when using spotting scopes, creating muscular strain that can become almost painful after an hour of glassing

Tripod glassing works great, but you've got to carry lots of stuff. I like to pack along a smaller binocular for stalking, and even a big binocular doesn't match a spotting scope for evaluating a buck two miles away. So you've now got two binoculars - one a honker, plus a spotting scope and tripod. For anything except glassing from a vehicle, it's just too much, so in big country these days I generally foot-hunt carrying a 10x or 12x binocular, plus a compact spotter and tripod. For extended glassing with the spotting scope, I carry some tape to cover the left lens of my eyeglasses, allowing me to glass with both eyes open.

Once you get used to a 10x or 12x binocular, it's handy even down in the thick stuff. If I'm going to be moving very little and sitting a lot, I often carry a big glass into the whitetail thickets, especially when grunting and rattling. Many hunters don't think you need a binocular under 100 yards, but with your naked eye, you probably aren't seeing half the deer that come to the horns. How do I know this? By glassing carefully with a 10x or 12x. Big glass has such a shallow depth of field that you can "fuzz out" most brush and trees, often bringing a particle of deer into sharp focus. High magnification can help us find more game, but only if we know how to use it.

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