Porro Prism System
The objective is offset
from the eyepiece offering greater depth perception and a wider
field of view.
Reverse Porro System
The objectives are
offset from the eyepiece in a horizontal way reducing the total size
of the construction by about 30% compared to the traditional porro
The common standards of optical
prisms are barium-crown (BAK-4) glass or borosilicate (BK-7)
glass. The BAK- 4 is a higher quality glass that reduces
light scattering, resulting in sharper and brighter images.
Magnification is the
number of times the object being viewed is enlarged. Binoculars are
often identified by two numbers, for example: 10×50. The first
number indicates the magnification or the power of the binocular,
expressed by the letter “x”, for times. This means that the object
being viewed appears to be 10 times closer than would be seen with
the naked eye.
OBJECTIVE LENS DIAMETER
The second number in
the reference (i.e. 10X50) indicates the diameter of the objective
lens or the front lens. The larger the objective lens, the better
the light transmission, thus the brighter the image.
Binoculars with a wider field of
view. This wide-angle feature is better for capturing action or fast
Zoom binoculars have variable powers of
magnification allowing you to view closer in the distance without
Waterproof binoculars are
O-ring sealed for complete waterproof protection to keep dry inside
after immersion in water. Some binoculars are also fogproof which
means that they are nitrogen-purged to prevent anti-fogging inside
the optical surfaces.
Various coating processes on
the lenses and prisms will determine the brightness and the light
gathering of a binocular, providing higher contrast and brighter
images. The different types of coating are:
Coated – A single layer on at least one lens surface
Coated – A single layer on all air-to-glass lens
Multi-Coated – Multiple layers on at least one lens
Fully Multi-Coated – Multiple layers on all air-to- glass
FIELD OF VIEW ( F.O.V)
This is the
side-to-side linear measurement of the of the circular field seen
through a binocular. It is defined by the width in feet of the area
visible at 1000 yards, or in meters at 1000m. The higher the
magnification, the narrower the field of view.
CLOSE FOCUS DISTANCE
The closest distance to
the observed object that the binoculars can be used while retaining
a sharp focus.
The measurement of the binocular’s
ability to distinguish fine detail and sharpness.
This refers to the size of the
small disc of light visible at the eyepiece of a binocular. To
determine the size of the exit pupil, divide the objective diameter
by the power: For example, a 10×50 binocular will have an exit
pupil of 5mm
This is the distance a binocular
can be held away from the human eye and can still observe the entire
field of view. Long Eye Relief (LER) reduces eyestrain and is more
comfortable for eyeglass wearers.
The mechanism that is used to
focus both barrels of a binocular on the object being viewed. They
are normally three types of focus systems.
Center Focus – Where the focusing knob is located in the center
of the binocular
Individual Focus – Where the focusing knob is
located individually in each eyepiece
Fixed focus – No focusing
A ring adjustment for
fine-focusing which is usually provided around one eyepiece. This
allows to compensate for vision difference between the right and
The most common eyecups are twist-up,
pop-up, or rubber fold-down