Glassing is the use of optics (such as binoculars) to more easily locate animals.
How To Buy Binoculars
are essentially 2 small telescopes placed side-by-side, each consisting
of a pair of lenses to bring distant objects closer and a pair of
prisms in each chamber to orient the image right-side-up. Binoculars can
be used for hunting, bird-watching, astronomy or watching the action at
sporting events or concerts. Here's how to choose binoculars to meet
Understand the numbers. Binoculars are referred to with 2
numbers, such as 7 x 35 or 10 x 50. The number before the "x" is the
magnification factor, or power; the 7 x 35 lenses will make objects
appear 7 times closer, while the 10 x 50 lenses will make objects appear
10 times closer. The second number is the diameter of the main
(objective) lenses in millimeters; 7 x 35 lenses are 35 millimeters
(1.38 inches) in diameter, while 10 x 50 lenses are 50 millimeters (1.97
inches) in diameter. Dividing the second number by the first yields the
exit pupil value, or the diameter of the light beam that reaches your
eye in millimeters. (For both example lenses, 35 divided by 7 or 50
divided by 10, is 5 millimeters.)
The higher the magnification, the dimmer the image, and while
the image you see will be larger, your field of view will narrow, and
consequently, you'll find it harder to keep the image focused. If you
choose binoculars with 10 x magnification or greater, get a pair with a
tripod socket so you can mount and steady your binoculars when needed.
If you need a wide field of view, choose a lower magnification.
The larger the objective lens, the more light it can gather,
which is important in low-light activities such as astronomy or hunting
at dawn or dusk. However, the larger the lenses are, the more the
binoculars will weigh. Generally, most binoculars have objective lenses
with a diameter of 30 to 50 millimeters (1.18 to 1.97 inches), with
compact binoculars having lenses 25 millimeters (1 inch) and under and
astronomical binoculars having lenses larger than 50 millimeters.
The larger the exit pupil, the more light that reaches your
eyes. The human eye dilates from 2 to 7 millimeters, depending on how
little light is available. Ideally, you should shoot for an exit pupil
value that matches the width your eyes dilate to.
Consider the lenses. Most binoculars have glass lenses, which
generally provide better image quality, but often cost more than plastic
lenses. (However, a set of plastic lenses that provide the same image
quality as a set of glass lenses will cost more.) Glass also partially
reflects the light hitting it, but this can be compensated for with the
Lens coatings are described with the following codes: C means
that only some surfaces have been coated with a single coating layer; FC
means that all glass lens surfaces other have been coated; MC means
that some surfaces have been coated with multiple layers; and FMC means
that all glass lens surfaces have been coated with multiple layers.
Multiple-layer coatings are generally superior to single coatings but
add to the cost of the binoculars.
Plastic lenses, while generally of poorer image quality, are
more rugged than glass lenses and should be considered for situations
where durability is important, such as mountain climbing.
Evaluate the eyepieces. The eyepiece lenses should rest a
comfortable distance from your eyes, and even further if you wear
glasses. This is called "eye relief" and normally ranges from 5 to 20
millimeters (0.2 to 0.98 inches). If you wear glasses, you'll need an
eye relief of 14 to 15 millimeters (0.55 to 0.59 inches) or greater, as
most eyeglasses rest from 9 to 13 millimeters (0.35 to 0.5 inches) from
Many binoculars include rubber eye cups around the eyepieces to
help you seat the eyepieces over your eyes when using the binoculars.
If you wear glasses, look for binoculars with eye cups that retract or
flip out of the way.
Test the focusing ability. Look at how closely you can focus
the binoculars in the store and measure the distance between them and
the object you're looking at.
Binoculars focus in one of 2 ways: Most binoculars have a
center-post mechanism, along with a diopter corrector to allow for one
of your eyes being stronger or weaker than the other. Waterproof
binoculars, however, usually have individual focusing for each lenses,
with controls on each eyepiece.
Some binoculars are "focus-free," with no ability to adjust
the focus whatsoever. These binoculars can cause eyestrain if you
attempt to focus on something closer than the pre-set distance.
Look at the prism design. Most binoculars have their main
lenses spaced wider than the eyepieces, thanks to the Porro prisms they
use. This makes the binoculars larger but makes nearby objects appear
more 3-dimensional. Binoculars that use roof prisms let the main lenses
rest in line with the eyepieces, making the binoculars more compact but
usually at the cost of image quality. However, roof prism binoculars can
be made to deliver images of quality equal to Porro prism binoculars
but at greater cost.
Less expensive binoculars use BK-7 prisms, which tend to square
off one side of the image, while more expensive binoculars use BAK-4
prisms, which deliver more light and sharper, rounder images.
Decide how heavy a pair of binoculars you can handle. As
noted, high-magnification and large-lens binoculars weigh more than
standard binoculars. You can compensate for the weight and stabilize the
binoculars by mounting them on a tripod or with a strap that lets you
carry them around your neck, but if you plan to travel long distances,
you may want to settle for less powerful but lighter binoculars.
Consider waterproof versus water-resistant. If you don't plan
on using your binoculars in bad weather or in conditions where they'll
get wet very often, you can get by with water-resistant binoculars. If
you plan to take them along whitewater rafting or skiing, get waterproof
Look at the manufacturer's reputation and guarantees. Consider
how long the manufacturer has been in business and what other optical
products they make, if any, as well as how they'll handle matters if the
binoculars get damaged.
Some binoculars have the capability to view images in a range
of magnifications, letting you take in an entire scene or zoom in to
your favorite part of it. Note that as you increase the magnification,
your field of view will narrow and you'll find it harder to stay focused
on the image.
Some more expensive, high-magnification binoculars include
built-in stabilizers to help you stay focused on an image. Generally,
these binoculars cost $1,000 or more.