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Choosing Binoculars

No matter which model you choose all Binoculars follow the same principal.

Lenses at the front collect the image ( Objective Lenses) and Eyepieces (Ocular lens) at the back magnify the image.

There are prisms in-between to turn the image the right way up.

Step One

Choose the design

There are two major types of Binoculars. They are the Porro Prism Binoculars and the Roof Prism Binoculars. They are classed by the types of prisms that they use

Porro Prism

Porro prism binoculars are the most common type of binoculars and follow the traditional design with the eyepieces and objective lenses offset from each other.

(the objective lens is not in line with the ocular lens)

Their lower price and excellent image clarity make them the most popular choice.

This type of binocular performs better for astronomy.

Porro prism binoculars have a single pivot between the two halves of the binocular so are easy to adjust for the distance between your eyes

Giant binoculars

Giant binoculars are dedicated to astronomy and offer larger apertures and objectives for increased brightness and magnification of night-sky objects and reveal spectacular views of large objects like open star clusters. A common specification for giant binoculars is 20x80 or 25x100 and represent the best compromise between magnification, brightness, and field of view for general astronomical observing.

Due to their increased size and weight, a heavy-duty tripod or other solid mount is required for these instruments.

Opera glasses

Opera glasses, (or theater binoculars) are compact, low-power binoculars.
Magnification of 5x or below is usually desired in order to minimize image shake and maintain a large enough field of view. Opera glasses use Galilean optics, having a convex objective but a concave eyepiece. This allows the glasses to produce an upright with a compact size.
Some Opera glasses have an in-built light to read programs etc.

Roof prism

Roof prism binoculars offer a more compact design. With the objective lenses and eyepieces in line with each other. They have straight tubes and look like two telescope mounted next to each other. (the front-objective lens is in line with the rear-ocular lens),

Roof prism types are not necessarily better than porro prism types but they are an ideal choice when size and weight is a factor.

Roof-prisms cost more to manufacture and tend to be more expensive and are more difficult to adjust to the spacing of your eyes.

Do not attempt to economize on roof prism binoculars.

Compact

By using smaller objective lenses and modern manufacturing processes both porro prism and roof prism binoculars are available in compact versions. These are great for portability, light in weight, and easily tucked into pocket, purse, or glove compartment but there is a trade off in image quality. While they remain great for daylight use at a moment's notice, they aren't your choice for viewing in low light situations

Monoculars

Monoculars are usually pocket sized, and are great for grabbing a quick look at objects. They are inexpensive, and can be pulled out of your pocket at a moment's notice.
They may have Roof or Porro prisms.

Step Two

Choose the Specification

Magnification

When selecting a pair of binoculars, you'll need to understand what the numbers mean. Be they 8x21, 10x25 12x50 or any other number combination.

There are always two numbers separated with an "x".

The first number refers to the power or magnification provided by the eyepiece.. So 10x means the binoculars will magnify the subject ten times bigger than the size seen by the human eye.

Generally, the higher the magnification, the narrower the field of view field of view .

The second number is the size of the objective lens measured in millimetres

So 10x25 binoculars have an objective lens diameter of 25mm. The larger the objective lens allows more light to pass through, and the brighter and clearer the final image.

Field of view (field of vision)
Binoculars are advertised with their field of view specified in one of two ways - angular field of view, and linear field of view
Angular field of view is normally specified in degrees
Linear field of view is a ratio of lengths
binoculars with a 5.8 degree (angular) field of view might also be advertised as having a (linear) field of view of 305 ft per 1000 yd or 102 mm per meter.
angular field can be converted to linear field using this formula
A = 0.0191 x L
Where
A = the angular field of view in degrees.
L = the linear field of view in feet per 1000 yd.

Field of view is the area seen when you look through the binoculars. Imagine a train is 1000 yards away. If the binoculars have a field of view of 360 feet at 1000 yards, then you will see 360 feet of the train.

Minimum focus (or close focus)

The minimum focus is the nearest distance at which the binoculars will focus on an object. A binocular will not focus on an object closer than this minimum distance. This feature is important for some applications such as watching birds in the garden.

potential brightness

The potential brightness of the view can be found by dividing the objective size by the magnification in order to obtain the size of the exit pupil,

for example an 10x50 pair has an exit pupil of 50/10 = 5mm.
A result of at least 5 is desirable, and higher if the binoculars are to be regularly used in poor light.
The complicating factor is that the size of the human eye pupil varies depending on the amount of light. In bright daylight, it is only about 3.5mm wide, but it opens out to about 7mm in darkness.
So At night 7x50 (with an exit pupil of 50/7 = 7.14mm) gives the brightest view possible and 7x60 (with an exit pupil of 60/7 = 7.57mm) would be no brighter.
As people get older their pupils can't open as wide, so senior citizens may find 7x40 or even 7x35 just as bright as 7x50.

Step Three

Choose the Additional Features

Many binoculars include additional features that you may find useful, including :-

Waterproof

Ideal for marine use or water sports. They can be fully immersed without damage

Weatherproof

Great for all weather use. Not suitable for immersion

Rubber armoured and Shockproof

A synthetic rubber coating, which helps protect the body from physical damage due to knocks, bumps and corrosive elements. The rubber armour also provides a firm, comfortable grip

Image stabilisers

Help to reduce image tremor

Prisms

BAK-4 prisms are the best; they are made of superior optical glass(barium crown glass) that produces clearer images.
BK-7 prisms are also used (borosilicate glass), usually in lower priced binoculars. These are satisfactory, but they are inferior to the BAK-4 prisms. Some manufacturers will not tell you what kind of prisms they use, usually because they are of inferior quality.

Coatings

In the 1930's it was discovered that when glass was coated with magnesium fluoride more light would be transmitted. A single layer coating reduces light loss by about 1.5% per optical surface.

Ruby Coated

Ruby coatings are intended to reduce glare in bright light. When using expensive good quality (RC) ruby coated binoculars the coating does what it was designed for and reduces glare.
Unfortunately the market is completely flooded with cheap ruby coated binoculars which filter red to compensate for poor quality optics that do not properly converge the color spectrum. By eliminating red from the spectrum, the optics appear to do a better job of minimizing color abberations. They really do nothing more than turn the view a greenish, "night vision like" colour
They are very bad for astronomy because they actually reduce the amount of light that is transmitted to your eyes. This coating has nothing to do with the mineral ruby and has no redeeming qualities.

Coated.

This is the lowest level of coating available. It consists of usually one layer of magnesium fluoride coating on the front lens element and the eyepiece. When viewed from an angle the lens will have a very faint bluish tint. This type of lens coating is found only on inexpensive binoculars and will not produce images as bright as multi-coated binoculars.

Fully Coated

With Fully Coated (FC), Every glass to air surface has one layer of coatings. These are usually the standard in lower priced binoculars.
Don't even consider binoculars that aren't fully coated. for serious use.

Multi coated lenses

Multi Coated (MC) are the most common coating system for affordable binoculars. Quality wise they are quite a step up from simple coatings and usually means that most glass to air surface is at least coated with a layer of special chemicals, and some of them are coated with multiple layers (usually the front lens and eyepiece lens). When viewed at an angle these lenses show a significant blue or green tint.

Increased light transmission and reduced reflections and flare and will be brighter than "fully coated" binoculars.

Fully Multi Coated

Fully Multi Coated - FMC - SMC - The highest level of coating generally available. Basically every glass to air surface has multiple layers of coatings. When viewed at an angle these lenses show many different coloured reflections.

All things being equal, the coating in your binoculars will make quite a difference. If you are serious user you may want to consider only Fully Multi Coated binoculars.

Remember

Binoculars you use constantly are better than ones that stay in the car or in the cupboard because they're too heavy or cumbersome to carry or because they were so expensive that you're afraid to take them anywhere.

We offer a large range of binoculars. With a pair to suit just about every need.

Binocular Suitability Chart
	7x50	8x21	8x30	8x40	10x25	10x50
General	Good	Good	Excellent	Excellent	Good	Good
Bird Watching	Excellent	Good	Good	Excellent	Good	Excellent
Hiking	Fair	Excellent	Good	Good	Excellent	Fair
Horse Racing	Excellent	Good	Good	Excellent	Excellent	Excellent
Motor Racing	Excellent	Good	Good	Excellent	Good	Good
Indoor Sports	Excellent	Good	Good	Excellent	Good	Good
Long Observation	Fair	Fair	Good	Good	Good	Excellent
Astronomy	Excellent	Unsuitable	Fair	Good	Unsuitable	Excellent

Having purchased a pair of binoculars, it's necessary to adjust them for your personal use.
First set the eyepiece spacing using the hinge in the middle to set the distance between the eyepieces to match the distance between your eyes so that you see a full, round image through each individual eyepiece, and a single round image when both are used together, with no dark shadowing around the edge of either eyepiece.

How to Focus: Binoculars

There is often a difference between the left and right eye, a dioptre adjustment is necessary to accommodate for differences in the strength of each eye. Once the dioptre adjustment has been set, the main central wheel will focus both eyes equally

It is a very common misconception that the right eye dioptre adjustment should be made before the centre-focus whereas it should in fact be the other way round. Once the dioptre adjustment has been set, the main central wheel will focus both eyes equally. The left eye is focussed first using the central wheel, after which the right eye can be balanced using the dioptre adjustment on the right.

These instructions assume that the dioptre adjustment is on the right hand eyepiece.

To focus your binoculars properly, follow these easy steps:

1. Cover the front of the right tube lens (right objective) with your lens cap (or hand, or close your right eye)

2. Look through the binoculars at an object with lots of contrast, such as a tree branch or TV aerial against a light sky in the middle distance (30 feet). Use the centre focus wheel and adjust the focus until a clear and sharp image appears.

3. Remove the lens cap from the right objective and cover the front of the left tube lens (left objective) with your lens cap (or hand, or close your left eye)

4. Look through the binoculars again at the same object as in step 2. Turn the dioptre focus ring so that the image is clear and sharp for your right eye.

DO NOT touch the centre focus control while you are focusing the right eyepiece to your right eye

Now you are finished. What you have just done is adjusted the binoculars for your individual eyes. (Practically everybody's left and right eyes are different.) From now on, you only need to use the centre focus wheel when you focus on at things at different distances

Look at the settings for your dioptre adjustment (most binoculars have symbols or numbers to indicate the setting).

Remember where your optimal setting is on the eyepiece's scale, so you can re-adjust your binoculars to that point should the setting be changed by another user.

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