How to select
the right
binoculars
Objective lens size. The second number in the formula, in this case 25,
is the diameter of the objective lens—the lens located on the end of the
binoculars farthest away from your eye when viewing. The larger the objective lens size, the more light will enter the binoculars and the brighter the
viewed image will appear.
Field of view (FOV). This is the side-to-side measurement of the circular
viewing field, defined by the width in feet or meters of the visible area viewed
from 1,000 yards or meters. Generally, the higher the magnification, the narrower the field of view. So if you are looking at a football field, an FOV of 400
feet means that at a distance of 1,000 yards you will see 400 feet of the field.
Prism system. There are two types of prism systems in binoculars—roof
and porro. With roof prisms, the objective, or front, lens lines up directly with
the eyepiece, which allows a streamlined shape for less bulk, lighter weight
and greater ruggedness. Porro prisms require the objective lens to align slightly
offset from the eyepiece, which provides greater depth perception and a wider
field of view.
1. Determine how you will use the
binoculars. There is a wide variety of sizes,
magnifying powers and features for all kinds
of applications or preferences.
• Small, compact binoculars that fit in your
pocket are perfect for hiking, camping and
sporting events.
• Digital binoculars, which combine a digital
camera with the binoculars, can capture
that special moment.
• Giant binoculars work for amateur
astronomers or avid stargazers.
• Binoculars with night vision appeal to
hunters, hikers and birders.
Type of glass. Most optical prisms are made from borosilicate (BK- 7) or
barium crown (BaK- 4) glass. BaK- 4 is higher-quality glass, which results in
brighter images and high edge-to-edge sharpness.
2. Buy the best. You get what you pay
for, so pay for the features you want. The
grade of glass, quality of the prisms and
barrel construction make all the difference
in the binoculars’ performance and durability.
BaK- 4 prisms are superior to BK- 7.
Coated optics. Lens surface coatings reduce light and glare. There are four
types: coated (single layer on at least one lens surface); fully coated (single
layer on all air-to-glass surfaces); multi-coated (multiple layers on at least one
lens surface); and fully multi-coated (multiple layers on all air-to-glass surfaces).
Exit pupil. This reflects the size of the circle of light visible at the eyepiece.
The larger the exit pupil, the brighter the image. To determine the size, divide
the objective lens diameter by the power (a 10 x 25 model has an exit pupil
of 2.5mm).
Eye relief. This is the distance the binoculars can be held away from the
eye and still present the full field of view. Extended or long eye relief reduces
eyestrain and is ideal for eyeglass wearers.
Waterproof/fogproof. Some binoculars are sealed with O-rings and nitrogen
purged to make them completely waterproof and fogproof. They can withstand
total immersion in water, staying dry inside, and their interior optical surfaces
won’t fog due to rapid temperature change or humidity. A
3. Try before you buy. Binoculars that
are perfect for your spouse may not be the
ones for you. If possible, test them at the
store; if that’s not an option, or if you’re buying them online, make sure you can return
them. Don’t struggle or strain when testing—
you should be able to see through the
binoculars quickly and easily. If you can’t,
try another pair.
With high-quality binoculars, you should
not even be aware of them when they’re in
use. Your attention should be on what you’re
viewing, not the binoculars. Good binoculars
make you feel as if you’re seeing through
your own eyes, only everything seems closer.
If the optics are inferior, your eyes will feel a
slight sense of relief when you stop looking
through the binoculars.
