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
porro model.
 Porro Prism System
In porro prism binoculars the objective or front
lens is offset from the eyepiece. Porro prism
binoculars provide 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 models can withstand complete immersion in water
and stay dry inside. The interior optical surfaces
won’t fog due to rapid temperature change
or humidity.
Magnification (Power)
Binoculars are often referred to by two
numbers separated by an "x". For
example: 8x32. The first number is the power or 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 or front lens. The larger the objective
lens, the more light that enters the binocular and
the brighter the image. Prism Glass
Most optical prisms are made from borosilicate (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
Bushnell® binoculars come with twist-up, pop-up
or soft rubber fold down eyecups which go down for
eyeglass wearers. These options allow everyone to
see the entire field-of-view.  Diopter Adjustment
A "fine focus" adjustment ring usually
provided around one eyepiece to accommodate for vision
differences between the right and left eyes.
 Rainguard®
Our exclusive, patented, hydrophobic (water-repellent)
coating on which condensation from rain, fog or snow
forms in much smaller droplets than on standard coatings.
Smaller droplets scatter less light, which results
in increased light transmission and a clearer image.
Makes the binocular useful even when looking directly
into the driving rain.
PC-3® Phase
Coating
Found on the best roof prism binoculars, this chemical
coating is applied to the prisms to enhance resolution
and contrast. Would not provide an advantage on porro
prism models. 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 |
