*** What is a binocular?
Small optical instrument consisting of two similar telescopes mounted
on a single frame so that separate images enter each of the viewer's
eyes. As with a single telescope (monocular), distant objects appear
magnified, but the binocular has the additional advantage that it
substantially increases the range of depth perception of the viewer
because the magnified images are seen with both eyes. The frame of
a binocular is usually hinged to permit adjustment of the distance
between the telescopes. Focusing can be done by means of a wheel on
the central axis between the telescopes; turning the wheel changes
the distance from the objective lenses of the telescopes to the eyepieces.
Separate focusing of each telescope from the eyepiece may be provided
in some types of binocular. The term binocular now usually refers
to the prism binocular, in which light entering each telescope through
its objective lens is bent first one way and then the other by a pair
of prisms before passing through one or more additional lenses in
the eyepiece. The prisms aid in reducing the length of the instrument
and in enhancing the viewer's depth perception by increasing the distance
between the objective lenses. Other types of binocular include the
opera glass and the field glass; both use Galilean telescopes, which
do not employ prisms and which usually have less magnifying power
than the telescopes in prism binoculars. A binocular is often specified
by an expression such as ¡°7¡Á40¡± or ¡°12¡Á42¡± the first number indicates
how many times the binocular magnifies an object and the second number
is the diameter of either objective lens in millimeters. The size
of an objective lens is a measure of how much light it can gather
for effective viewing.
Binoculars magnify distant objects so that they appear nearer and
larger to the viewer. A binoculars essentially consist of a pair of
parallel telescopes joined at the center by a hinge. The hinge allows
the eyepieces to be brought to a suitable interpupil distance for
Classification of Optical Systems
Binoculars have left and right side barrels linked to each other by
an axle. Light enters the objective lenses and travels via prisms
to the eyepieces. These two most commonly types of prism systems have
resulted in two basic design types.
1) Porro prism design ( named after Ignatio Porro,the Italian physicist
who invented them in 1823 and first used them in binoculars), i.e.
the classic design
Porro Prism binoculars are characterized by the eyepieces being offset
from the objective lenses.
A distinctive shape characterised internally by the use of a combination
of two right angle porro prisms and externally by the offset positioning
of the eyepieces from the objective lenses.
In optics jargon, this is called a compound lens which reduces distortion.
The light then passes through the Porro prism (or roof prism in a
more compact design). The prism serves two purposes: it produces erect
images and folds the light path to reduce the physical size of the
binoculars. Light then passes through eyepieces and enters your eye.
One of the two eyepieces is usually adjustable to adaptor to each
user. Both eyepieces are adjusted together by center focusing.
2) Roof prism design, i.e. the modern disign
Roof Prism binoculars feature lenses positioned in line for a more
With the prisms positioned one over the other, the objective lenses
and the eyepieces are in line. The result is a more compact design
which allows compact binoculars to have full size power capabilities.
*** The Optical "Tripod"
Like a three legged stand (tripod), binocular performance balances
on three legs - 1), 2), 3) as follows :.
1) Magnification (or Power, how close it makes things
appear) and Aperture (or Diameter of Objective Lenses)
As you will see these numbers imprinted on the binocular itself, Binoculars
are specified mainly by a combination of two numbers e.g. 7x40, 7x50
or even 12x42. For example, 7x45 binoculars provide 7-times magnification
and have 40mm aperture of objective lenses.
The first number is the size of the binoculars magnification or power
itself, which is the degree to which the object being viewed is enlarged.
With a 7x40 binocular the image is 7 times larger than what you see
with the naked eye. The level of power affects the Brightness
of an image, so the lower the power of a binocular, the brighter the
image it delivers will be. In general, increasing power will reduce
both field of view and eye relief, which are also discussed here.
For any practical application, magnification usually ranges from 4
to 12. Anything higher than a power of 12x is not desirable for several
(i) the amount of light reaches the eyes decreases with increasing
power so that the object appears darker at higher magnification, powerful
binoculars are useless if the image is dim or fuzzy.
(ii) the field of view decreases with increasing power; and, most
(iii) the higher the power, the more sensitive viewing is to any little
movement. As a matter of fact, viewing through a pair of 15x binoculars
is an exhausting experience because even your heart beat or breathing
with make the image dance around!
The second number refers to aperture or the diameter of objective
lens (the lens furthest from the eye and closest to the object you
are looking at) in millimetres. A larger objective lens will take
in more light to enhance Resolution and
Brightness although there are limits to
the amount of light that your eye can receive. It determines the light
gathering ability of the instrument, with the greater light gathering
ability of a larger lens translating into greater detail and image
clarity. This is especially useful in low light conditions and at
Doubling the size of the objective lenses quadruples the light gathering
ability of the binocular. For instance, a 7x50 binocular has almost
twice the light gathering ability of a 7x40 binocular and four times
the light gathering ability of a 7x25 binocular. This might lead you
to assume that bigger is better when it comes to the diameter size
of the objective lenses, but in reality the size of the lens must
be considered along with Exit Pupil and
intended usage to determine the best binocular for you.
2) Resolution (sharpness and clarity)
Resolution is a measurement of the binoculars ability to distinguish
fine detail (sharpness and clarity), also referred to definition,
is the ability of a binocular to distinguish fine detailand retain
clarity Better resolution also provides more intense colour. All else
being equal (and it rarely is) a larger Aperture
will always deliver more detail to the eye than a smaller Aperture
lens regardless of the magnification.
In fact, actual resolution hinges on variety of factors: the quality
of the optical components, light transmission through the binoculars,
existing atmospheric conditions (e.g. heat haze), optical and mechanical
alignment (called collimation - please don't drop binoculars) and
the visual acuity of the user (your eyesight).
3) Brightness (light transmission)
determines the amount of light that the binocular takes in to send
to your eye. This in turn largely determines the brightness of the
image that you see. The larger Aperture
of the objective lens, the greater the brightness and the Resolution
(sharpness and clarity, resolving power) of the binocular and of the
image seen through the binocular.
It follows then, that a binocular with a large Aperture
of objective lens is best for light conditions such as late afternoons,
overcast days and astronomy (star gazing). Though a larger aperture
of objective lens means more light enters your eyes, it also means
a larger and longer binocular body. If you want to carry around a
pair of binoculars, a suitable aperture objective lens is between
20 and 50 mm.
Brightness can also be improved through the use of optical coating
or use a variety and combination of coatings to produce binoculars
suited for all situations. All lenses are usually optically coated
to reduce scattered light and improve light transmission. One of the
most popular coatings on the objective lens is ruby coating, which
provides both performance and durability. Optical glass (selected
lens and prism) surfaces are coated by magnesium fluoride to reduce
light loss and glare due to reflection. Most binoculars are fully
multi-coated to further enhance viewing and reduce eye strain. Some
binoculars have a special image enhancing, amber, high contrast coatings.
Main methods of Coating :
Fully Coated: all air to glass surfaces are coated.
Multi-Coated: One or more surfaces of one or more lenses have been
coated with multiple films.
Fully Multi-Coated: all air-to-glass surfaces have been multi-coated.
Rubicon tm (Ruby) Coated: Unique to TASCO our Rubicon coating consists
of 14 layers of varying colours and composition on the objective lenses.
Because of their ability to filter out uncomfortable red light and
provide brilliant daylight viewing, this is especially suited to binoculars
being used to view objects over water, snow or other bright conditions.
UVC (ultraviolet) Coated: Removes the glare resulting from excess
ultra-violet rays in the atmosphere providing a clearer more vivid
image especially in brilliant sunlight.
Please consider the following other factors when choosing a kind of
1) Field of View (FOV)
The Field of View (FOV) is the width of the area that you can see
through the binoculars, which is usually given as degrees or as length
at 1000 yards. The FOV is usually printed on the binocular - sometimes
as 'x feet at 1000 yards' or sometimes as 'y degrees'. In the latter
case 1 degree approximately equals 52 feet at 1000 yards.
As a general rule the field of view will decrease as Magnification
increases. However FOV is dependent on many factors and higher quality
binoculars will have a larger FOV than their cheaper counterparts.
Usually ranges from about 2 to 10 deg, the FOV can also be increased
by changing the design and shape of the binoculars lenses and these
are known as Wide-Angle Binoculars.
The size of the area that can be seen while looking through a pair
of binoculars is referred to as the field of view. The angular field
of view is indicated on the outside of the binocular, in degrees.
The linear field of view refers to the area that can be observed at
1,000 yards, and is expressed in feet. A larger field of view translates
to a larger area seen through the binocular.You can use angular field
to calculate the linear field by multiplying the angular field by
52.5. For example, if the angular field of a particular binocular
is 8¡ã, then the linear field will be 420 feet, i.e. the product of
8 x 52.5.
in general. A large field of view is especially desirable in situations
where the object viewed is likely to move, or when the user is moving.
2) Exit Pupil
The exit pupil refers to the size of the shaft of light transmitted
to the eye. The more light, the better the contrast. You can actually
see the exit pupil by holding the eyepiece of the binocular approximately
12 inches from your eye. It is the bright circle of light in the center
of the eyepiece. Exit pupil is expressed in millimeters and is normally
derived by dividing the power into the objective lens diameter. A
7x50 binocular has an exit pupil of 5mm (50 ¡Â 7).
3) Focusing Range
All binoculars have the ability to be focused for infinity. So a primary
point of distinction between binocular models is the minimum focus
range. Birders tend to favor models with a short focus range of about
15 feet, but 20 to 25 feet is usually acceptable.
4) Stray Light
When light entering the binoculars reflects off of interior surfaces,
the reflected light eventually exits inside the binoculars in the
form of stray light. This unfocused light typically diminishes the
image quality of the sight picture.
5) Twilight Performance
Using the below formulas gives a basic evaluation of low light performance,
however, one must keep in mind that they are mathematical formulas
and do not take into effect some of the most critical features in
optics; glass quality, number of lenses, precision of manufacturing
In a word, the Resolution and Brightness
of the image you see through a particular binocular or spotting scope
is determined by a number of different factors, including the interaction
of these factors. Magnification, optical
coating and Aperture are just
a few of the factors influencing how a binocular performs.
However, the single most important criterion in performance will always
be the quality of the optics. We deliver optical excellence through
careful consideration of quality in the glass and lens coatings used,
precise manufacturing processes, and excellent Quality
1) Wide-Angle Binoculars (i.e. our 7x50)
By altering the design and shape of the binoculars lenses an increased
Field of View can be obtained without sacrificing power. Wide angle
binoculars are ideal for sports events such as Football to capture
quick movements or for races when the action is spread over a broad
area or for travel where a panoramic view is desired.
2) Zoom Binoculars
Zoom binoculars have two power numbers which represent a range of
powers. There are two kinds of Zoom Binoculars :
One is continuous and uninterrupted, the other is discontinuous and
interrupted. A 8-20x50 binocular for example, brings objects from
8 to 20 times closer! For continuous and uninterrupted Zoom,it's like
having 13 binoculars in one! But for discontinuous and interrupted
Zoom, it's perhaps 8, 10, 12, 15, 20, or other.
3) InFocus tm - Focus Free Binoculars
InFocus binoculars are designed without a focus mechanism. Simply
pick them up and look. They aree always in focus ready to catch all
the action and are proving to be very popular with people who need
to look quickly to catch something such as plane-spotters,
travellers and yachtsmen (who only catch glimpses of things between
Please note however that they are designed for people with normal
or corrected to normal vision. The distance from which they are in
focus varies from person to person.
4) Compact Binoculars
With the prisms positioned one over the other utilising the Roof
prism design, the objective lenses and the eyepiece
centres are lined up creating a compact design with full size power.
Some compact binoculars will even fit into jeans pockets or a cigarette
5) Long Eye Relief Binoculars for Spectacle Wearers
If you wear spectacles or sunglasses and look through a binocular,
you may have noticed that its like looking down a long tunnel. The
long eye relief binoculars such as the Future range, are especially
designed to solve this problem.
The optics within the long eye relief system direct the focal point
further back behind the eyepiece so that you can see the full field
of view whilst wearing your glasses (spectacles or sunglasses).
Though all standard binoculars have eyecups
that fold away to accommodate eyeglass wearers, the long eye relief
binoculars provide the advantage of complete ease of use for spectacle
and eyeglass wearers (and for those who don't as well in the meantime).
6) Waterproof and Fogproof Binoculars
This describes a binocular's ability to remain completely dry on the
inside when exposed to moisture or total submersion in water. Binoculars
are sealed with O-rings and are filled with 100% arid nitrogen, which
also resists all forms of moisture.They have been tested underwater
and proven to be completely waterproof.
Hermetically sealed and nitrogen charged, these binoculars are fogproof
in extreme temperatures and conditions as well as being completely
7) Rubber Armoured
The rubber armour covering on many of binoculars absorbs shocks, provides
a non-slip surface, offers some weather protection and insulates your
hands against extremes of temperature.
8) Tripod Adapter and Bracket
When a binocular reaches higher powers (generally over 15x) you will
need some assistance to hold it steady enough for comfortable viewing.
While leaning against a fence or tree etc will often suffice, a much
better solution is to use a tripod. Most of these models will include
a tripod adapter fitting at the base of the hinge (covered by a screw-in
*** Types of Binoculars
1) The Standard
Excellent all-around binocular for birding, shooting, hunting and
outdoors. Ideal for a wide range of viewing. Comfortable size and
weight. Great binoculars for a closer look at those unexpected sights.
Optimum balance of magnification, brightness and field of view.
2) Compact Binoculars
Small Size, High Power Small enough to slip into pocket or purse;
strong enough to carry you into the center of the action. Rugged outdoor
3) Marine Binoculars
Waterproof, Fogproof Protection binoculars deliver clarity despite
foul weather conditions including fog, rain, ice, and salt water.
Standard equipment for serious sailors, avid hunters, hiker and other
4) Zoom Binocular
Distant View, Near View Get the best of both worlds. Locate the action
at a distance, then zoom in for closer inspection at the touch of
a lever. Variable magnification lets you glide from the far turn to
the homestretch. Great for tracking fast moving action across wide
areas such as football, soccer, or racetracks.
5) Astronomical Binoculars
Power and Brightness Approach the power of a telescope with the comfort
only delivered by a binocular. These binoculars are excellent for
astronomy, surveillance, and nature study where close-up detail and
long distance viewing are needed even under poor light conditions.
*** Choosing the Right Binoculars
Selecting the right binoculars is a matter of picking the best combination
of features for your specific needs. You should consider magnification,
bulk and weight, brightness, field
of view, optical quality, and cost.
For any given magnification, larger objective lenses gather more light
and yield a brighter image in dim light, but result in a bulkier,
The higher the power, the "shaker" the image will be, because
small hand movements are exaggerated. Therefore, we recommend a binocular
of moderate magnification (7x) unless more power is specifically required.
Lower power binoculars usually offer a wider field of view, allowing
you to take in more of a scene at one time.
Binoculars also always come in handy, whether you're an avid hunter
or an occasional audience or spectator in theatre or stadium. They
are essential gear for camping and hiking, a day in the field or a
vacation trip to the most adventurous location. Choosing the best
binocular for your needs isn't always easy. Consider when, where and
how often you plan to use them in order to select a binocular with
a combination of features that are right for you. We have given you
some pointers that we feel will help you make your decision, and enjoy
your purchase to its fullest.
How To Choose Use Recommendations
1) Stadium Sports
4X21, 8X25, & 10X25 Xtra-Wide Angle, and Zoom Features are an
added plus. The wide angle will keep you zoomed in on the action
2) Boating Any Waterproof model with a large objective lens and rubberized
1X50, 7X42, 8X42 or 10X42
3) Conctert &Theatre
5X25 8X25 Wide Angle. 4X30, 7V18, 10X42; compacts. Any Zoom or Wide
Any 7X35, 7X50, 8X42, standards, 8X30 & 10X30 compacts. Waterproof
models are great-just in case.
5) General Use/ Vacation
7X35, 8X42, 10X42 Standards, 8X30 & 10X30 Compacts, Compact and
Wide angle model are best.
6) Hunting Rubber armored, waterproof, and fogproof modesl
are best at 7X or 10X. 12X or 16X for distant game/varmints. Compacts
in a pocket for a hunter on the move.
7) Bird Watching
8X42 is standard, 10X42, 10X50 & 12X50 for details in smaller
species. At a distance, compact with a 30mm or greater objective,
any binocular with a long eye relief and good close focusing ability.
For more professional birdwatching, you may choose spotting
What Will The Binoculars Be Used For?
For stargazing, light gathering is the most important factor. Choose
a pair of binoculars with at least a 50mm aperture. our 7x50 model
is easily hand-holdable and provides nice, wide-field views of starry
swaths. The higher power 12x42 is also popular, and in fact is preferable
to the 7x50 where skyglow is a problem. "Giant" binoculars
of 70mm, 80mm or 100mm aperture will reveal fainter deep-sky objects
and more subtle detail, but a tripod is recommended for a steady view.
If you can afford the higher price (and a good tripod) and don't mind
the extra bulk, you'll be rewarded with incredible views. (The item
of giant binoculars, spotting scopes and telescopes are collecting,
The human eye on average has a 7mm pupil at night, so can be said
that we look at the world through a pair of 1x7 binoculars! It follows
then that even a small pair of 7x40 binoculars will show you a lot
more detail than your unaided eyes can see. When Galileo first looked
up through his primitive little telescope he only saw about as much
as we can see through an average pair of binoculars today and he managed
to create history. Binoculars are well worth remembering when it comes
to looking at the night sky. With binoculars the moon is fascinating
through all the lunar phases and even Jupiter and the four moons that
Galileo saw is quite possible. We won't go into great depth about
which binoculars are better than others for night viewing because
there are too many variables to be able to say which is better. Suffice
to say, any binoculars will show you a lot more than you can see without
them and wherever possible try to steady them with either a tripod
(use tripod bracket to attach the binoculars to any standard tripod)
or just lean against a fence or post. For those keen to explore the
night sky we recommend that you check our large range of telescopes.
For more professional birdwatching, you may choose telescopes.
The most popular models for birdwatching are 7x40 and 7x50. They're
small and nimble, offer steady hand-held views, and have sufficient
light grasp to provide bright, well-resolved images. If you plan to
study birds at close range, look for binoculars with a near-focus
distance of a few feet. Of course, other factors should play into
your buying decision, such as eye relief for use with eyeglasses,
optical coatings, and mechanical construction.
For more professional birdwatching, you may choose spotting
Which binocuolar to choose?
1) What do you need
For most people, you use a binocular for general purposes: spectator
sports, sight seeing, etc. Except for some special activities, the
most important criteria you need in choosing a binocular is portability
and ease-of-use. If a salesperson tries to convince you otherwise,
The first specification we need to decide is magnification
as indicated above. For all around purposes, 5x to 10x pretty much
covers everything. It is a common mistake to assume that the higher
the power, the more "powerful" your binocular is. The fact
of the matter is you will be exhausted in a few seconds looking at
the "dancing" image through a 15x binocular, unless you
want to carry a tripod everywhere you go. Some opera glasses offer
2x and 3x power, but you definitely will not regret it if you take
a regular 7x one with you instead. Another advice: never buy a zoom
binocular! You may think it is useful to change the power of magnification,
but it's cumbersome, difficult to use, and easily broken.
The second number is the Aperture of the
objective lens. In a 7x50 binocular, the objective lens diameter is
50 mm. It is true that the larger the objective lens you have, the
more light you gather from the object you are viewing. However, a
larger objective lens also means a longer and heavy binocular body.
So, you need to balance portability and lens size. I have boxes of
binocular samples from manufacturers, but I find myself usually put
a 7x50 or a 12x42 compact binocular in my pocket before leaving home.
There is also a practical limit on the size of the objective lens.
This is determined by the exit pupil of
a binocular. For a 7x50 binocular, divide 50 mm (objective lens size)
by 7 (power of magnification) gives 5 mm, which is the size of the
exit pupil. If you want to take full advantage of a large objective
lens, i.e., to collect all the light funneled through the binocular,
the binocular's exit pupil cannot be larger
than your eye's entrance pupil (you know, the black hole at the center
of your eyeball). This is where the limit comes in. The entrance pupil
of a human eye changes with the light condition, but the maximum size
is limited by age. The entrance pupil can reach 8 mm for a teenage,
but is only ~4 mm for a 50 year old. For an entrance pupil of 5 mm,
a 7x40 is just as good as a 7x50, but the latter is much heavier.
Of course, there are special needs. For example, experienced bird
watchers prefer a 40 or 42, even 50mm objective lens to gather more
light and see more details in deep shadow. A mariner likes our 7x50
because it is more forgiving when the deck is constantly moving.
2) Where to buy
Most people buy their binoculars from camera stores, discount department
stores, and sports/hunting stores. The truth is that none of these
stores is specialized in binoculars and the salesperson usually knows
nothing about binoculars, except what is printed on the box. It is
ok to buy from these places but you should be prepared to do your
own Quality Check and know what you need.
Some mail order firms tend to be specialized in binoculars and they
usually carry most common brand names. But make sure they have a return
policy, because you cannot see what you are buying on the phone. A
good mail order business should allow a 30 day trial period.
Here is a common myth about brand names. Many people tend to believe
that German brands and now some Japanese brands offer the best quality.
But, is it worth 10 times the price just for the name? Here is some
news you may find shocking: recently I visited several other large
optics factories and found that these factories make most of the common
brand names we know. As a matter of fact, these different brand names
often come from the same production line. The only difference is the
label! Unless you want to pay $800 for a binocular with the ultimate
quality, the difference between common brands is negligible.
3) Quality Check
When you have a binocular in your hands, you can do a few simple tests
to determine the quality. Remember: do not be fooled by the external
appearance or the high price tag. A good binocular should pass several
collimation refers to the alignment of the optical axis. The best
performance is reached when the optical axis of the objective lens
passes through the optical center of all lenses and prisms. This should
hold true for both optical barrel assemblies. For most binoculars,
poor collimation is not immediately obvious when you first pick it
up and view through it. This is because your eyeball will adjust to
compensate for misalignment in the optical instrument. Of course,
if you let your eye muscle strain like this for a few minutes, you
will feel the pain soon. Here is a simple way to check for collimation.
First, look at a target ~100 yards away with the binocular. Be sure
to adjust the center focus as well as the right eye piece. Now, relax
your eye for a minute by taking the binocular down. Look at the target
again with the left objective lens blocked by your hand. After a minute,
quick;y remove your hand which covers the objective lens. If the target
appears to be out of focus immediately but becomes in focus after
a second or two, the binocular is not collimated. Your eye is doing
the hard work to adjust collimation and focus. Choose a different
resolution determines how sharp the image is and how much fine detail
you can see. You can usually check this by comparing a few different
binoculars and look at the same target ~100 yards away. The manufacturer
usually specifies resolution by a number, e.g., 5 seconds of arc.
This means that the binocular should be able to resolve two fine features
at an angle of 5" apart. Professionals use standard test charts
very much like the one used in an eye doctor's office. You usually
do not need to bother with this kind of tests, unless you are talking
about a $1000 instrument. These test charts are available in the references
I cited earlier. But, your common sense is sufficient for most purposes.
(c) Star test
the ultimate test of an optical instrument is the so called "star
test". This is done by looking at the image of a distant star
in the night sky. To do this, locate a bright star at the center of
the field-of-view. The perfect image should appear as a round disk,
with a few weak, concentric rings due to diffraction. Almost all binoculars
will show some deviation from this perfect image. Some asymmetry is
acceptable, but if your binocular's star test yields an image which
is something like a triangle or a stick, try to get ride of it.
*** more knowledge and review about spotting scope, please