I keep finding new uses for binoculars. Only yesterday the pair I always carry in the door pocket of my Chevy pickup helped me to identify a soaring turkey vulture. And just last week I used the same Bushnell Discoverer 7x24mm binocular to read a house number I couldn't make out with my aging eyes.
Binoculars sure have changed, though, in the 20 years since I bought my first pair. Many of today's models are made from rugged, long-lasting materials that are light in weight, shockproof, and even waterproof. The fog-hating, multi-coated optics are better, too. Options now available include super wide angle, power zoom, and permanent focus.
A Jason Perma Focus binocular perches next to the bird book in our living room. When feathered visitors gather at the outside feeder 10 yards away, anyone in the family can quickly identify them. Like a rifle scope, the binoculars are always in focus, regardless of who looks through the lenses.
Bird watching, fishing, boating, big-game hunting, and many other outdoor activities would be less fun and their enthusiasts less successful without the aid of modern field glasses, spotting scopes, and rifle scopes.
Thanks to these enhanced optics, my family is enjoying venison all year. Last fall in Montana, a power zoom Copitar binocular helped me identify a mule deer buck; the 2.5-8x36mm Simmons Whitetail Classic scope mounted atop my rifle made my aim true.
If you're in the market for sporting optics, however, how do you know what to look for? Then, how much should you pay? The answers lie in understanding how optics work and in learning a few key terms.
The ocular lens on a binocular is the one closest to your eye. It is smaller around than the objective lens, which is farthest from your eye. Terms like 7x35 mean the binocular magnifies objects seven times (or seven power) over what the naked eye sees and that the objective lenses have a diameter of 35 millimeters. The more diameter, the greater the relative brightness, or how much light the lenses gather.
As magnification increases, more light is needed to maintain brightness. Besides increasing the diameter of the objective lens, relative brightness can be improved by up to 50 percent by fully coating both ocular and objective lenses, along with the prism.
So how does a binocular work? Simply, really. All lenses bend light rays to a point where they form an image. The distance from the lens to where the rays meet is called focal length. The longer the focal length, the more an object can be magnified. Here, prisms do a handy job: They purposely bend light to create a longer focal length. So they increase the power of binoculars and scopes without increasing the size or weight of the optics themselves.
Now, a word about field of view, which is the width of an area--in degrees or feet--that you can see 1,000 yards away. One degree represents 52.5 feet of width at 1,000 yards. As magnification goes up, naturally the field of view goes down.
Depth of field refers to the distance in focus both in front of the subject and behind the subject. In the manner that an expensive camera lens produces good depth of field, a quality binocular does too.
The same holds true for resolution, or how finely a lens defines an image. The best (and most expensive) lenses do not fall off around the perimeter.
Before buying any binocular, test its sharpness on printed words such as street signs at a distance, and check out the product's ability to define objects in low light. Holding the binocular against the sky at arm's length (instead of next to your eyes) will produce what is known as the exit pupil--two small circles of light on the ocular lens. The larger those exit pupils are, the more light that will pass through the binocular, an important consideration if you're outdoors at dawn or dusk.
According to Nikon experts, a person's pupil in diameter ranges from 2mm in bright light to 7mm at dark. For normal daylight viewing the company recommends choosing a binocular with 2.5 to 3.5mm exit pupils. Low-light, overcast days call for 3.5 to 5.0mm, and extreme low-light conditions require 5.0 to 7.0 mm exit pupils.
How much magnification do you need? Most outdoor sport enthusiasts can hand hold a 10 power binocular. Those with zoom capability to 15 power require locking elbows or resting arms against something solid. Magnification beyond 15 power, such as the optics found in spotting scopes, must be stationed on a tripod.
Better binoculars feature diopter focus adjustments, which enable the user to fine tune the right ocular lens and to adjust for differences in vision between the right and left eye.
Other considerations: Soft rubber eyecups that fold down are comfortable for eyeglass wearers. Focusing bars make for more rapid focusing, and zoom controls change magnification with the flip of a lever. Accessories abound and include lens cap, case, and neck strap.
Binoculars small enough to fit in shirt pockets are among the handiest outdoors. Last summer my wilderness river trout guide tied our dry flies after using his little 6-ounce binoculars to study insects floating by.
In May I helped a wildlife biologist look for a woodcock chick that his setter insisted was under our noses. Without his little binoculars we would not have been able to pick out the fledgling for banding from a look-alike world of shadow and shine.
I now own three pairs of binoculars, two rifle scopes, and a spotting scope. I assure you that before you read this I will have found new uses for them.
Copyright (c) 1997 Tom Huggler. All rights reserved.