| How much power do you need?
binocular made have a set of numbers assigned to them such as
6x15, 7x35, 7x50, 8x30, etc. The first number (6x, 7x, 8x) refers
to a level of magnification usually called the "power"
of a binocular, namely the extent the binocular magnifies objects
being viewed. So a binocular of 8x makes an object look 8 times
larger than it does to the naked eye and consequently makes
it appear eight times nearer. The last number (15, 35, 50) refers
to the diameter of the objective lens in millimeters. The objective
lens is usually the largest lens farthest from the eye. The
lens closest to the eye is called the ocular lens.
It is unwise to select binoculars solely on the basis of power.
Some people think that the higher the power number, the better
the binocular. This is not always true. The power of the binocular
must be carefully chosen to provide exactly the right magnification
for your particular use.
The clarity and definition of the subject being viewed decreases
as the power increases. In addition, a binocular magnifies
BOTH the object being viewed AND any motion caused by shaky
hands, moving vehicles, water motion on a boat, etc.
It is generally recognized, therefore, that above 8x, a binocular
should be used with a tripod to obtain best results.
| How does power affect field of view or brightness?
high power number usually means a smaller field of view and
lower brilliance of the image that reaches the eye. Binocular
brightness is critical for indoor sports, outdoor birding in
shaded areas and hunting.
All binoculars can be used at night or during the daytime. But
certain binoculars are better adapted to night viewing than
others; some even have "night vision" modes. Binoculars
with the largest objective lenses are desired because more light
can be admitted. The average diameter of a person's eye during
the daytime under average conditions is about 4 millimeters
but at night expands to about 7 millimeters.
Therefore, a binocular that utilizes the full diameter of the
expanded pupil is better for night use. Thus, a 7x5O which has
a large exit pupil (7 mm) and utilizes the full diameter of
the expanded pupil of the eye is considered to be an especially
fine night binocular.
| What is relative brightness & exit pupil all about?
| Relative Brightness and Exit Pupil are determined mathematically.
The exit pupil of a binocular is the disc of light you see in
the eyepiece when holding a binocular at arms length towards
a bright light. To compute Exit Pupil: divide the diameter of
the objective lens in millimeters by the power of the binocular.
To compute Relative Brightness: square the Exit Pupil. Example
7x35, means the prism binocular described magnifies seven times
and has an objective lens of 35 millimeters. Exit pupil equals
5 and 5 squared equals a relative brightness of 25.
| What is field of view?
|Field of view refers to the diameter
of the area seen through a binocular. It should be noted again
that in line with the laws of physics, the higher the power
the smaller must be the field of view and vice versa. Field
of view is often expressed as an angle. Retractable eyecups
allow eyeglass wearers a full field of view.
| What are the different focusing methods?
Focusing" binoculars are focused by turning a single wheel
that move the lens elements together. The right eyepiece can
be adjusted to compensate for any difference in vision between
the right and left eye. Because they are convenient to use,
Central Focusing binoculars are the most popular.
"Individual Focusing" binoculars are adjusted for
each eye at the eyepiece. Because they are adjusted individually,
this type on binocular can be nearly moisture proof and sturdy
in construction. Boaters, hikers and sportsmen tend to choose
this type of design.
| What about alignment?
|It is important that both barrels
of a binocular be optically parallel so that the image from
both barrels will merge into one perfect circle; otherwise,
undue strain is caused and, in extreme cases, it is impossible
to resolve the two images. High quality binoculars are very
carefully checked for alignment.
| Does Binocular construction matter?
with strength requirements, most good binoculars are manufactured
of the lightest materials available and are as lightweight and
compact as the optical formula and built-in ruggedness will
permit. Finest quality ground and polished prisms are clamped
and screwed to carefully machined recesses in bubble-free castings.
Exterior surfaces are protected with multiple coats of a synthetic
enamel or with high quality textured plastics. Each binocular
is generally dehumidified and sealed in air-conditioned, dustless,
| What are coated lenses and prisms?
All air-to-glass surfaces on most binoculars are coated with
specially formulated optical coatings that eliminate internal
glare and reflections while increasing light transmission significantly.
Most objective lenses are coated with an ultra-violet coating
which minimizes the effect of the sun's rays. Most prisms are
chamfered to absorb diffused rays, giving brighter, clearer
| What is the difference between weather-resistant and waterproof binoculars?
rate their products by the "Japanese Industrial Standard"
(JIS). Ratings are established through tests to prove protection
against the ingress of water. It is important to understand
that there are degrees to which an instrument is "waterproof."
The classifications range from one to eight. Eight is the highest
level of water protection. Here is a breakdown of the classification
system and where Pentax binoculars fall:
Class 4:Splash-proof from any direction
Class 5: Jet-proof from any direction
Class 6: Watertight submersible to 1 meter
Class 7: Submersible to 1/2 atmosphere (16.5 feet)
Class 8: Products designed specifically for underwater use such
as an underwater camera.
To make a binocular weather-resistant, special "O"
rings are used in constructing the binocular to keep water from
entering the instrument. To make a binocular waterproof, "O"
rings are used in a special internal design that allows the
binocular to be totally sealed. The binocular is then filled
with nitrogen which makes it waterproof and submergible. Weather-resistant
and waterproof binoculars are also "fogproof."
| What should I look for if Astronomy is my purpose?
||buy as much magnification
as you can afford
typically 10x, 12x, 15x power
||in astronomy you will frequently
be viewing the same object for some time -- lightweight
binoculars are an advantage
||some binoculars come with
a screw thread hole for attaching a tripod attachment
(others can use a small adapter which clamps on to the
middle part of the binoculars)
||check that stars appear
as point sources, with no sign of chromatic aberration
· anti-reflection coatings -- these result in more
of the light actually getting through the many lens surfaces
to reach your eye
|| look for a smooth, fine
control. For astronomical use avoid autofocus types
||some binoculars have an
optical stabilizer built-in to minimize shake motion
| What should I look for if I'm into birding?
people ask "I want to buy a pair of binoculars
as a gift for a friend who's into birdwatching, which
ones would you recommend.?". In Jack Connor's book
entitled "The Complete Birder: A Guide to Better
Birding. (Houghton Mifflin, 1987)", he offers the
Keep these things in mind when you go looking for binoculars:
||An important point of
magnification mathematics is the principle of diminishing
returns. Each step up in power gains you less. The way
the eye and mind process visual information makes a magnified
image seem closer rather than larger, and for this reason
the 10x's seem just 10 % more powerful than the 5x's.
||Most birding is conducted
well inside the range of lower-powered binoculars, so
other factors must be considered.
principle of diminishing returns in magnification mathematics
is the higher the magnification, the lower the light transmission.
When all other things are equal, lower-power lenses allow
more light to reach the eye than lenses of higher power.
||An under-publicized fact
is that in ordinary daylight any binocular of equal optical
quality will be equally as bright, no matter what the
differences are in their objective size and power.
||For an evening
search for owls or rails, you may want to borrow a pair
of 7x50s, the binocular size that amateur astronomers
||Field of view is crucially
important at close range. When you consider field of view
(the size of the area you can see in the binoculars),
you should convert the measurement by moving the decimal
point two places to the left. Binoculars that give you
250 ft. at 1,000 yards are giving you 2.5 feet at 10 yards.
||Another example of the
principle of diminishing returns: the higher the power,
the narrower the field of view.
||If you wear eyeglasses
and want to see as well as you can, fold-down the rubber
eyecups are a must. Those who do not wear glasses should
also look carefully at any binoculars they are planning
to buy to see how deeply the ocular lenses are recessed.
Some poorly designed models have such deeply recessed
oculars that full field of view is not possible even for
people with 20/20 vision.
||Binoculars that focus
near at hand are essential for successful woodland birding.
A close-focus range of 15 ft. to 18 ft. is the least you
||Porro-prism design: Advantage:
quick focus, larger exit pupils, focus more closely, wider
field of view. Disadvantage: weight.
||Roof prism design: Advantage:
better power-to-weight ratio, focuses more finely (though
not as closely); good for hawk watching and shorebirding;
water resistant and durable. Disadvantage: Cost.
||Pocket design: Advantage:
weight; portability. Disadvantage: image darker; very
narrow field of view.
If there's a simple rule to follow
spend as much
as you can afford. If you're an active birder, you'll
be looking through your binoculars for hundreds of hours
each year. Why not treat yourself? A trip to Alaska will
cost you more than even the most expensive binoculars.
The trip will last a week or two. A really good pair of
binoculars can last your
| What are the types of binoculars available?
A standard or full-size binocular can be used for everything
from nature observation to spectator sports.
Compact binoculars are smaller and lighter in weight and
are a good choice to take along to the theater or concerts
or on hikes and hunting trips.
Wide angle binoculars are ideal for tracking fast-moving
action across wide areas such as football fields, racetracks
and wilderness terrain.
A zoom binocular allows the user to increase the magnification
in order to focus in on the details. From distant to near
view, it's the best of both worlds.
Waterproof binoculars deliver clarity despite foul weather
conditions including fog, rain and ice. O-ring sealed
and nitrogen purged for reliable fogproof, waterproof
| What are PORRO and ROOF prisms anyway?
|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, stream-lined shape in which the
lenses and prisms are in a straight line.
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