THINGS YOU SHOULD KNOW BEFORE YOU PURCHASE YOUR NEXT BINOCULARS

Basically, binoculars do two main things for you. They increase the size of the image you are viewing, and they let in more light than your eyes can, making images appear brighter in low light conditions.  Binoculars consist of two optical systems that are connected by a hinge sharing a common focus system.  Using a Binocular An image can be projected simultaneously for both eyes providing a realistic perception of depth.

A.  BINOCULAR TYPES
The following types of binoculars can be found in the market place for the consumer:

Full size (Standard)
Compact (Foldable)
Wide Angle
Zoom
Waterproof
Focus Free
Binocam

FULL SIZE
They are the typically BIG comes with a 35 mm in diameter or larger objective lens.

COMPACT
These are the more modern compact and foldable binoculars with an objective lens of less than 32 mm, usually fits in the palm of your hands.

WIDE ANGLE
These are just like full size binoculars but the WA binoculars allow users to observe wide angle view.  Wide angle binoculars usually bares anywhere from 400ft F.O.V at 1000yards all the way up to 900ft. 

ZOOM
Zoom Binoculars are convenient to use when more power is needed for a particular subject matter.  The zoom mechanism on these types of binoculars allows viewers to enjoy not just one magnification but a choice of many.  They have variable magnification allowing to view up-close of the distance without changing binoculars.
Some consumers believe it is convenient to have a variable magnification, whilst more professional users reject this idea due to the weight and less sharper image and the ability to stabilize the image at high magnification.

WATERRPOOF
Waterproof binoculars are 100% Waterproof and are usually Fogproof.  If the binocular is Fogproof they are sealed with an O ring and purged with nitrogen which is a technique allowing to keep them dry inside after a complete immersion.

FOCUS FREE
They are designed to focus in automatically at certain distance and power.  Focus free binoculars are usually used for fast moving object viewing, for example Horse Racing, Car Racing, Air Show and so on.

BINOCAM
They are built with DIGIAL CAMERA sensor and a traditional Binoculars, these types of Binoculars provides the best of both worlds…BINOCULARS and a High Quality DIGITAL Camera in One.   

B.  BINOCULAR PERFORMANCE
The Brightness and sharpness you see through a binocular is determined by a number of factors:
Magnification aka Power
Optical coating
Lens diameter
Prism Type / Grade

MAGNIIFCATION – POWER
Magnification is the degree to which the object being viewed is enlarged.
Binoculars are often referred to as number followed by an x i.e. 7x50
The first number indicates the power an object can be brought closer compared to a normal eye. The lower the magnification, the brighter the image, higher power will reduce the field of view.
                                         
The ideal magnifications are:
In daylight observation  6x - 8x
From dusk to dawn   7x - 10x
For observation in mountains  10x - 12x
Hunting     8x - 12x
Water sports   7x
Astronomy   15x - 70x

C.  TYPES OF COATING
The type and quality of coating will determine the following:
Up to 30% of light gathering can be lost if optics aren’t coated.
The quality of the coating increases the light gathering and results in a brighter image
In the centre of the image the sharpness is the highest
The lower the difference in sharpness of the image in the centre compared to the outer side, the higher the quality

TYPES OF COATING
Various coating processes on the lenses, prisms and objectives will determine the brightness and the light gathering of a binocular.
The following coating references are being used in the industry.
Coated = A single layer on at least one lens surface the objective is coated with a colored layer applied in a chamber

Fully Coated = Single layer on all air to glass surfaces the objective is coated with several colored layers, the prisms and eyepieces have between 2 and 6 magnesium fluoride coating applied on .

Multi-Coated = One or more lenses/prisms are coated with multiple, the prisms and eyepieces have between 4 and 8 magnesium fluoride coating applied on .

Fully Multi-Coated = Multiple layers on all air to glass surfaces the are coated with several colored layers, the prisms and eyepieces have between 4 and 16 magnesium fluoride coating applied on .

COLORED COATING REFERENCES
Ruby (Orange) coated optics are covered by an additional multi layer surface reducing any light reflections. In practice the difference is hardly perceivable for the average human eye. Consumers in countries with bright light and sunny weather (Mediterranean) tend to perceive this is a distinct advantage.

Blue Coated optics have been developed in order to filter out light reflections as much as possible at the same time keeping light gathering ability as high as possible. This technique was possible by using the progressive color pigmentation technique (intensifying the degree of color pigments) obtaining a more discrete appearance on the optics.

Green Colored optics are usually being used in the Night Vision Industry were they are useful at night and in conjunction with a light amplifier device. But now days most higher end Binoculars are equipped with such color and are usually fully multi coated.  The coating technique is the same than on the Blue coated treatment but in practical use the results can hardly be perceived as an advantage.

D.  LENS DIAMETER
The second number in the formula (i.e. 7X50) indicates the front lens diameter in mm
The larger the objective lens the more light enters the binocular and the brighter the image.

On a 6 – 8 magnification 20-32 mm is normal
On a 7 – 9 magnification 35 – 50mm is normal
On a 10 – 36 magnification 50 – 70mm is normal

Doubling the size of objective diameters quadruples the light gathering ability
But in reality the size of the lens must be considered along with the exit pupil and intended usage.

E.  LIGHT TRANSMISSION
This refers to the quality of the optics or its ability to deliver a maximum of light
The greater the objective diameter the more light enters, but the heavier and bigger the binocular are.

F.  BRIGHTNESS
The brightness of an image depends upon several factors:
Magnification applied to the image at the eyepiece;
Intensity of the light coming from the object being viewed
Diameter size of the objective as a light gathering lens.
The type and quality of glass used for the objective lens.
Transmission and reflection loss of light in passing through the instrument.

RELATIVE BRIGHTNESS INDEX (RBI)
Relative brightness index or RBI is used as a comparison of image brightness but it does have severe limitations as discussed below. It is determined by square root of  the exit pupil. An RBI of 25 or more is considered useful in low light conditions. In bright light conditions an RBI of 9 would have no brightness advantage over one of 50.

RBI = Diameter / Power = exit pupil x square root.
Example : 7x50 binocular 50/7 = 7.14  x 7.14 = 50.98 = relative brightness.

TWILIGHT FACTOR
Twilight factor is a measurement of viewing sharpness and image detail in low light conditions. The larger the twilight factor, the more efficient the low light performance. This indication has some limitations. To calculate the twilight factor, take the square root of the power multiplied by the objective lens diameter.
Example on a 7X42 binocular.
TWILIGHT FACTOR 7x42 = 294 (square root) = 17.14 = twilight factor
This formula takes magnifications more into account than the relative brightness index and is a better indication for the quality of brightness. When observing in greater detail a distant object you will seek to obtain a higher contrast and therefore will have to compromise between the magnification and the objective lens diameter.

G.  FIELD OF VIEW
This is the side to side measurement of the circular viewing field.
It is defined by the width in feet or meters of the area visible at 1000 yards or 1000 meters. The higher the magnification, the narrower the field of view.
A wide field of view is recommended to follow action ( i.e. sport)
Binoculars with a wide field of view usually have a magnification between 2 and 6. Some binoculars offer wide angle eyepieces which increase the field of view compared to the normal eyepieces.

H.  EXIT PUPIL
This refers to the size of the circle of light visible at the eyepiece of a binocular in form of a disc. The larger the exit pupil the brighter and sharper the image.

To determine the size divide the objective diameter by the power:

Example 7X50 Binocular = 50/7 = 7.14mm

Since the average human eye’s pupil opens about 2-3mm in daylight and up to 7mm at night the ideal exit pupil on binoculars shouldn’t be less than 2 mm but not more than 7mm as the human eye can’t take any advantage of it.

I.  EYE RELIEF
This is the distance a binocular can be held away from the human eye and still present the full field of view.
Long eye relief (LER) is ideal for those wearing glasses as they offer more comfort on observation A larger ocular lens (eyepiece) offers long eye relief and more comfort on observation
Binoculars with larger ocular lenses are more expensive, but offer higher quality and more viewing comfort.

J.  EYECUPS
This allows you to view through the binocular with or without glasses
There are three most common types of eyecups :
Twist up
Pop-up
Rubber fold down

K.  INTER PUPILLARY DISTANCE IPD
The distance between the eyes varies form one person to the other and most binoculars allow to make an adjustment by bringing the tubes of the binocular closer together or apart.

L.  DIOPTER ADJUSTMENT
Most binoculars have this option on one eyepiece, mostly on the right side. It allows to compensate for vision difference between both eyes and is used when focusing.

M.  FOCUSING
There are three major types of focusing systems are being used on a binoculars today.
CENTER FOCUS
INDIVIDUAL FOCUS
AUTO FOCUS aka FOCUS FREE

CENTER FOCUSING
First close your right eye and by using the centre focus adjust until you see a sharp image. Then close your left eye and open the right eye and adjust the right eyepiece diopter until the  perfect focus is obtained.

INDIVIDUAL FOCUSING
Individual focusing allows a very precise focusing adjustment but it requires to adjust the right and left eyepieces individually.

AUTO FOCUS – FOCUS FREE
These are focus free binoculars offering an instant image and will only be of interest during sport activities or certain outdoor activities.

N.  PRISM TYPES
The prism system of a binocular reduces the size needed to provide focal length.
It turns the image that is upside down to the right side up

There are three most common types of prism construction:

ROOF PRISMS
PORRO PRIMS
REVERSE PORRO
ROOF:  The prisms overlap and are aligned allowing to have a slim construction
PORRO: The objective is offset from the eyepiece offering greater depth perception and field of view
REVERSE:  The objectives are offset from the eyepiece in a horizontal way reducing the total size of the construction by about 30%compared to the rational Porro Prism.

O.  PRISM QUALITY
The most common quality standards of prisms are expressed as follows

BAK-4 prisms are made of barium crown glass (Higher Density)
BAK-7 prism are made of boro-silicate

The difference is that the BAK 4 prisms have a higher glass density eliminating more light scattering and offering sharper images.
By following the steps below you would be able determine weather or not  your binocular carries an BAK-4 or BK-7 Prism:

Hold the binocular in a 10 to 15° angle about 30 – 50cm away from the eye
If you see a poor quality square sized lens shape / shadows appears on the exit pupil it mean you have BK-7
If you see a full 360° circle appears on the exit pupil you can be sure you have BAK-4

Q.  TRIPOD ADAPTABLE
Generally all BARSKA binoculars above 10 power are tripod adaptable.
The most common criteria upon choosing binoculars can be summarized under the following

R.  BIRD WATCHING
For bird watching an 8x21 model may be fine on a bright day for observing a bird approximately 10 to 20 feet away. But, if you’re observing an eagle’s nest ½ mile away, a 15x70, 12x50, 20x50 model on a tripod may be sufficient. In practice you would expect to encounter different light conditions and expect to move from distant focusing to very close  focusing. Under those conditions it is recommendable to take the following binoculars into consideration:
8X32  8X42  10X42  8X56  7X50

S.  SPORTS ACTIVITY
For sports, if you are in a stadium, depending upon where your seats are located if you are between the middle and the first few rows you would prefer 8X21 8x32 7X35, whilst if you are sitting between the middle and the upper end you would prefer to have a 10X42 10X50.
Depending on the time of the event, late afternoon or early evening, you would need to take a binocular with a larger objective lens for better viewing.

T.  ASTRONOMY
For astronomy, a 7x50 model may be fine for observing the moon. To see more details on planets, you’ll need a larger and more powerful objective such as an 8x56, 9x63, 12x50, 15x70, or 25-45x100. Of course, a tripod will be needed for the larger binoculars due to the size, weight, and magnification.  Choose a binocular that has 5mm of Exit pupil or more for best viewing pleasure.

U.  FOR BACKPACKING
For backpacking, you may want to keep your weight to a minimum and prefer to carry a pair of compact binoculars such as an 8x21, 8x25, 10x25 or 12x25 or even a monocular. However, if you are serious about observing distance scenery or wildlife, you may not mind the extra weight of 7x50, 8x40, 8X32, 8x42 in order to obtain more magnification and/or better resolution or light gathering ability.

V.  FOR BOATING AND YACHTING
For most boat owners or those observing close to the water the ideal binoculars will be a 7x50 Waterproof. It offers good performance under low light conditions whilst at the same time it offers a very good field of view and a very good stabilization. For some people a 10X42 and 10X50 is a good alternative.  Keep in mind that the higher the power the lower the stabilization capacity.

W.  WHAT COULD GO WRONG WITH A BINOCULAR
Usually there isn’t a lot that can go wrong with a binocular even over the years as long as you keep it stored in a safe and dry place.
However you might expect to encounter the following problems:

Double Image: It is caused by the binocular being out of collimation after it had a shock and needing an adjustment. The collimation is the alignment of the optical elements of binocular to the mechanical axis. The readjustment can be done in an optical repair centre and the costs of adjustment will not be covered by the warranty. 
Broken lens: This can only be caused by a shock and the only way to get it repaired is to find an optical repair centre. However in most cases the costs of repairing it will exceed the cost of buying a new one.
Darker image on zoom binoculars: as power increases, the exit pupil decreases; the larger the exit pupil, the brighter the image; the exit pupil decreases in sizes and the image brightness decreases at the same time;

X.  CONCLUSION
The ideal binocular doesn’t exist, the consumer needs to decide on weight and usage.  Ideally YOU the consumer should have 3 different types of binoculars: compacts, outdoor, general observation.  Most people don’t know much about binoculars, neither the average shop assistant.  So before you make your next Binocular pruchase consider this What will I be using this Binocular For?  Then select the binoculars that offers exactly that!

By Ronnie Hossain
Huntinggear (Trusted Ebay PowerSeller)