For the curious here is some information that will hopefully dispel the mystery surrounding choosing the right pair of binoculars.
Magnifictaion (Power)
Binoculars
are often referred to by two numbers separated by an "x". For example,
8x32. The first number is the power of magnification of the binocular.
With an 8x32 binocular, the object being viewed appears to be eight
times closer than you would see it with the unaided eye.
Objective Lens Size
The
second number in the formula (8x32) is the diameter of the objective
front lens. The larger the objective lens, the more light that enters
the binocular and the brighter the image.
Prism Systems
The
prism system of a binocular reduces the size needed to contain a long
optical path and turns what would be an upside-down image
right-side-up. There are two types of prism systems, roof and porro.
Roof Prism System
In
roof prism binoculars, the prisms overlap closely, allowing the
objective lenses to line up directly with the eyepiece. The result is a
slim, streamlined shape in which the lenses and prisms are in a
straight line. Roof prism binoculars are less bulky and more rugged
than an equivalent porror model.
Porro Prism System
In
porro prism binoculars, the objective or front lens is offset from the
eyepiece. Porro prism binoculars provide a greater depth perception and
generally offer a wider field-of-view. Because of the simplicity of
this system, some of the best values can be with a porro design.
Waterproof/Fogproof
Some
binoculars are O-ring sealed and nitrogen-purged for total waterproof
and fogproof protection. These modesl can withstand complete immersion
in water and stay dry inside. The interior optical surfaces won't fog
due to rapid temperature change or humidity.
Prism Glass
Most
optical prisms are made from boroscillicate (BK-7) glass or barium
crown (BaK-4) glass. BaK-4 is the higher quality glass yielding
brighter images and high edge-to-edge sharpness.
Coated Optics
Lens surface coatings reduce light loss and glare due to reflection for a brighter, higher-contrast image with less eyestrain.
Types of Coatings:
Coated - A single layer on at least one lens surface.
Fully Coated - A single layer on all air-to-glass surfaces.
Multi-Coated - Multiple layers on at least one lens surface.
Fully Multi-Coated - Multiple layers on all air-to-glass surfaces.
Field-of-View (F.O.V.)
The
side-to-side measurement of the circular viewing field or subject area.
It is defined by the width in feet or meters of the area visible at
1000 yards or meters. A wide-angle binocular features a wide
field-of-view and is better for following action. Generally, the higher
the magnification, the narrower the field-of-view.
Resolution
Resolution, or definition, is the ability of a binocular to distinguish fine detail and retain clarity.
Exit Pupil
Refers
to the size of the circle of light visible at the eyepiece of a
binocular. The larger the exit pupil, the brighter the image. To
determine the size, divide the objective lens diameter by the power (an
8x32 model has an exit pupil of 4mm).
Eye Relief
The
distance a binocular 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.
Eyeglass Wearers - Eyecups
The
distance a binocular 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.
Diopter Adjustment
A
"fine focus" adjustment ring usually provided around one eyepiece to
accommodate for vision differences between the right and left eyes.
Rubber Armor
Rubber
armor provides multiple benefits. It helps protect the binocular from
the bumps and scratches that come with day-to-day use. It provides a
comfortable gripping surface for making them easier to hold on to. It's
easy to wipe clean after a tough day in the field. And it suppresses
noise if the binocular bumps aluminum or other non-rubber surfaces,
which might otherwise spook wildlife.
