Numbers and specifications can be overwhelming at
first. This rough guide to choosing binoculars is our
attempt to give you the knowledge you'll need to choose
the right binocular for your application.
What do the numbers in a
binoculars name mean?
|Binoculars are often referred to by two numbers
separated with 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
|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.
|Note: The diameter of the objective lens is directly
related to the size of the binocular -- the larger
the objective lens, the larger (and often brighter)
How much magnification do
You will want a binocular with appropriate magnification.
Think about the demands of your hobby before you select
a pair of binoculars. How much detail do you need,
will you use your binoculars to view things close up
or far away, do you want a small binocular that you
can take anywhere?
The most popular binoculars are those with lower
magnifications. These magnifications offer wider fields
of view and are easier to hold steady than the binoculars
with higher magnifications. A wider field of view is
important when trying to follow fast-moving objects
such as warblers or athletes in sporting event.
Higher magnifications may offer greater detail, but
can also be difficult to hold steady because they have
narrower fields of view. People might choose to use
high magnification binoculars when viewing in open
terrain, or if the desired targets are often stationary.
Note:The diameter of the objective lens is directly
related to the size of the binocular -- the larger
the objective lens, the larger (and often brighter)
What are the different prism
Porro Prism models are offset in design, deliver
great optics for the dollar, but lack the durability
and compact styling of roof prism models.
|reversed porro prism
Mostly used in compact binoculars, a reverse porro
prism allows for a binocular that easily fits in
a fanny pack or coat pocket.
The prism system in a binocular typified
by a straight barrel design. Roof prism binoculars
are generally lighter and more compact than porro
The BaK-4 prism transmits more light at the edges
to enhance illumination for easy viewing in dim
What size binocular do I
Binoculars can be classified as either full-size
or compact binoculars. The size of the objective lens
affect how large or small a binocular is.
Full-size binoculars have at least 30mm of aperture
or greater. They offer the light gathering ability
needed to identify objects in low light conditions,
however are not always as portable as one might desire.
Compact binoculars have less than 30mm of aperture,
and are more portable than full-size models. However,
due to their limited light gathering capability, they
are best when ample light is available to the viewer.
What is the field of view?
When you look through your binoculars, the widest
dimension you can see is known as the field of view.
Some binoculars will feature unique lenses to provide
a "wide field" that is greater than normally
seen through binoculars of the same magnification.
A wide-field binocular is desirable for observing
in close quarters, deep woods or picking up anything
that is moving quickly across your viewing area.
Note: The field of view decreases as magnification
increases, so select a binocular with lower magnification
if a wide field of view is important to you.
What about light transmission
and optical coatings?
Light transmission describes the percentage of available
light that passes through your binoculars. The amount
of light can be increased with the use of anti-reflective
coatings on binocular lenses. When an anti-reflective
coating is applied to the glass surface of a binocular
it increases the amount of light that reaches your
The more complete and complex the coating scheme
is, the brighter and sharper the binocular image will
be. Better coatings on a binocular allow more light
to reach your eye, improving brightness and overall
What is eye relief, and what
if I wear eyeglasses while using binoculars?
Many models of binoculars will allow you to view
in comfort while wearing eyeglasses or sunglasses.
These binoculars have been designed to provide you
with longer eye relief.
Eye relief refers to the distance images are projected
from the eyepiece out to its focal point, measured
in millimeters. If you want to use your binoculars
with eyeglasses or sunglasses, look for binoculars
that offer at least 15mm of eye relief, including the
Audubon 8x25 and 10x25 compact, and the Audubon 8x40
Note: Without proper eye relief, the eyeglass wearer
will not see the full field of view.
When using your binoculars be sure you understand
the correct use of the eyecups. All binoculars will
allow you to adjust the eyecups. There may be a rubber
eyecup that can be folded down or a newer type that
either twists or slides up and down on the eyepiece
of the binocular.
If you're an eyeglass wearer using binoculars, you
always want to be sure you have the binocular eyecup
rolled back (placed in the down position) while using
your binoculars. This will allow you to see the widest
possible field of view through your binoculars. Conversely,
if you don't wear glasses, you'll enjoy your binoculars
more if you leave these eyecups fully extended (placed
in the up position). Doing so will help block out lateral
Do my binculars need to be
Binoculars are used outside in all kinds of weather.
If you expect that you will be using your binoculars
in rainy, wet weather (or if you use them around water),
consider a pair of waterproof binoculars. You'll pay
a bit more for this feature, but you'll also be able
to use these binoculars without fear of repairing or
replacing them just because they got wet.
Waterproof binoculars are literally submersible and
any water damage would be handled under the manufacturer's
warranty for the binocular.
Note: If waterproofing isn't necessary for your hobby,
then you can find good quality binoculars at lower
What makes a binocular appear
Brightness in your binoculars can be affected by
several things. Contrary to what many binocular users
believe, big objective lenses are not the only factor
to consider. The quality of glass used in binocular
prism and lens construction along with the quality
of the lens coatings on the binocular contribute more
to brightness than do big objectives.
Lens coatings are thin layers of chemicals applied
to the glass surfaces of the binoculars. These coatings
improve light transmission through the binocular. Coating
quality is affected by the number of coatings and whether
all binocular lenses, inside and out, are coated with
several layers of coatings.
Ideally, you should purchase binoculars that are
fully multi-coated, which means both sides of every
binocular lens are coated with at least several layers
of the anti-reflective chemical. High quality lens
coatings will appear as fairly light, subtle shades
of blue, green or violet.
A word of caution, beware of a binocular using heavily
colored lenses. These lenses will only cut down on
light transmission through the binocular.
Note: If all other things are equal in two binoculars,
a binocular with a larger objective lens will yield
a brighter image, but at the cost of greater size and
weight. Higher quality binoculars with a smaller lens
may very well be brighter than less expensive binoculars
with larger objective lenses.
How do I clean my binoculars?
Use common sense in the care and maintenance of
your binoculars. Always attempt to blow off any visible
dust or dirt from the binocular lenses before brushing
or rubbing anything on the glass of your binocular.
Next, use a lens cleaning tool like a Lens Pen or lens
cleaning tissue to gently wipe off any remaining marks
or spots from the lens of the binocular.
Remove stubborn things like dried water spots from
the lens of a binocular by lightly fogging the binocular
lens with your breath. If your waterproof binoculars
are badly soiled, you can even clean them by placing
them under lightly running water (to minimize any possible
Note: Do not use your shirt tail or pocket tissue
to clean your binoculars. These fibers may contain
material which will scratch the coatings on the binocular
Keep binocular eyecups and focus mechanisms free
of dirt and oil. An occasional wipe with rubbing alcohol
will extend the life of rubber eyecups on the binocular.
Check your neckstrap and its attachments for wear or
slippage, too. You don't want your bino to come flying
off and hit the ground!
What about the light gathering
ability of my binocular?
Your eye is uniquely designed to gather more or
less light as conditions change, but your binoculars
are not. Since the light gathering ability of a binocular
is fixed, it is important to select a model that best
meets your eye's need for light as viewing conditions
The exit pupil is the magnified image in the eyepiece
as it leaves the binocular to enter your eye. It is
an indicator of how well you will see an image through
your binoculars on a bright day, at twilight or at
night. Almost all binoculars gather more light than
is needed by your eye for viewing in bright conditions.
For the best viewing at twilight, you'll want a binocular
with a minimum exit pupil of 4mm.
Determining the Exit Pupil:
To determine the exit pupil of a binocular, simply
divide the objective lens by the magnification of the
binocular. If we use an 8x42 binocular as an example,
the 42mm objective lens divided by the magnification
of 8x gives us an exit pupil of 5.25mm. This tells
us that an 8x42 binocular is a good configuration for
In contrast, if we look at an 8x25 binocular, we
find that 25mm divided by 8x leaves us an exit pupil
of only 3.12mm. This means that an 8x25 binocular will
give sufficient brightness for daytime viewing, but
the image will not be as bright as you would like at
dawn and dusk.
How do I properly adjust
the diopter on my binocular?
All quality binoculars will allow you to separately
adjust the focus on eyepiece (usually the right eye)
with a diopter. This is done to compensate for any
differences between your eyes, providing the clearest
image possible through your binoculars. When adjusting
the diopter, pick a stationary object to focus on that
is beyond the close focus distance of the binocular,
approximately 50 yards away. Initially, while covering
the right objective lens with your hand, use the center
focus of the binocular until the target appears clear.
When adjusting the diopter, pick a stationary object
to focus on that is beyond the close focus distance
of the binocular, approximately 50 yards away. Initially,
while covering the right objective lens with your hand,
use the center focus of the binocular until the target
Once you've got the left eye focused as sharply as
possible- carefully, without moving the center focus
of the binocular and covering the left objective lens,
see if image sharpness through the right eye improves
by slowly moving the diopter adjustment back and forth.
Once you've found the setting that gives you the sharpest
image, note where the setting is and leave it there
-- you're done. From this point on, you simply use
the center focus to adjust both eyes while viewing.
Note: You should properly set the diopter adjuster
when you first use your binocular (make a note of your
setting). Check the diopter setting on your binocular
every so often to be sure your eyes haven't changed.
Always check it whenever you share your binocular with