Binocular Buying Guide
This guide has been compiled to aid
you to better understand the jargon surrounding binoculars and
so help you choose the right pair of binoculars for you.
What the numbers mean
Numbers are used to indicate binocular specifications, for
example 8x40. The first number is the magnification. This number
tells you how many times larger or nearer an object will appear
when viewed through the binocular. Eight times larger than with
the naked eye in our example. The second number indicates the
diameter of the objective lenses in millimeters (40mm in our
example). The objective lenses are the large lenses at the front
of the binocular. The larger the objective lens diameter the
more light it can transmit back to the eye. Higher numbers don't
necessarily mean better binoculars. Magnification and light gathering
power should be determined by your application.
Zoom binoculars are also available, for example 7-15x24, where
the magnification can be varied from 7x to 15x.
Field of View
The width of the area (in meters) seen through the binoculars
at a specified distance (usually 1,000 meters) is the field of
view. Generally the lower the magnification the wider the field
of view. Binoculars with a wide field of view make it easier
to scan large areas or follow a moving object.
The exit pupil is the bright circle of light that appears
in the rear (ocular) lens when the binocular is held away from
the eye. The diameter of the exit pupil in millimeters is equal
to the front (objective) lens diameter divided by the magnification.
5mm in our example above. All other things being equal, the higher
the number the brighter the binocular. An exit pupil of at least
6-8mm is recommended for low light applications.
- The distance between the binocular's exit pupils, which are
adjustable to suit the indervidual.
The eye relief determines how far your eye can be from the
eyepiece while still allowing a full field of view through the
binocular. This is important to eyeglass wearers who should look
for a High Eye Relief design. In most binoculars the eyecups
can be folded back to aid spectical wearers.
- There are two basic design types of binoculars: Porro Prism
and Roof Prism (also called Dach Centre Focus or DCF).
- Porro prism binoculars are the conventional type with large
lenses in the front and small lenses in the back. The front and
rear lenses are offset.
- These come in two types:
- Mini Centre Focus (MCF) - Compact design havig the ojbective
lenses closer together than the eyepieces.
- Zeiss Design Centre Focus (ZDCF) - A design havig the ojbective
lenses further apart than the eyepieces.
- Roof prism binoculars are designed with both sets of lenses
aligned in the same tube, like two telescopes side by side.Porro
prism binoculars are generally brighter and less expensive. Roof
prism designs are more expensive but usually more robust.
- Center and Individual are the two focusing systems commonly
found in binoculars.
- Center focus binoculars are equipped with a center mounted
wheel that simuntaneously focuses both tubes.
- Individual focus binoculars have individual adjustment rings
on each eyepiece. This allows separate focusing of each tube.
This system is popular in Military and Marine binoculars.
- Quality center focus binoculars provide some type of diopter
adjustment to compensate for the small difference between the
viewers right and left eyes. Minimum Focus Distance is also a
consideration in binocular selection. A close focusing binocular
allows you to view objects closer in in sharp detail.
- Because the left and right eyes are rarely exactly the same,
a balancing focus adjustment is provided.
- This is an ultra-fine chemical deposit on the lens surface
that cuts down reflections reducing light loss and flare.
- "Coated Binoculars" usually means only the outer
surfaces are coated.
- "Ruby Coated Binoculars" Red/Orange coating to
reduce UV haze over long distances.
- "Multi-coated Binoculars" One or more lens is coated
with several layers.
- "Fully Multi-coated Binoculars" Every lens in the
binocular is coated with several layers.
Armored binoculars are covered with a rubber or polyurethane
material that makes them more resistant to impact damage and
scratches. The armoring helps eliminate disturbing noise caused
by contact with metal objects. Most armored models are easier
to grip and provide better resistance to the elements. Check
the specifications if water proofing/resistance is important.
Water resistant models are not damaged by humidity or light rain.
Water proof binoculars can actually be submerged without damage.
Compact models are smaller and lighter than conventional binoculars.
A lightweight roof prism design allows some 8x and 10x models
to be easily carried in a pocket. This is a considerable advantage
for hikers, sports enthusiasts, or anyone desiring good performance
in a small package.
Image Stabilization (IS)
- Designed by Canon to allow the use of higher magnification
binoculars whilst cutting down on image movment.
Selecting the Right Binocular
- Choosing the right binoculars for you is not a difficult
task. Some factors to consider are magnification, brightness,
size/weight, exposure to the elements, and price.
- First decide what your primary use will be. If you are viewing
at long distances or want to see greater detail you may want
to select a binocular with a 10x or greater magnification. For
moderate distances a 7x or 8x may be more useful. A higher magnification
binocular is usually larger and heavier and sometimes less bright.
Lower magnification models tend to have a wider field of view
and make it easier to keep an object in view while in motion,
on a rocking boat for example. Look for a large objective lens
if you work in low light, as in viewing at dawn or dusk.
- Larger binoculars are generally easier to hold steady and
offer a brighter image than compact binoculars. They are however,
less convenient and heavier.
- Your primary use will determine the best balance of these
factors. You may find that your needs are so diverse you need
more than one pair. Remember when considering price, you are
investing in a quality optical instrument that will give you
many years of viewing pleasure.