Many people use binoculars as a visual aid for seeing far away objects. This can include both indoor activities such as watching ballet and opera and outdoor activities such as bird watching, hunting or watching sport.
They are made up of two telescopes, one for each eye, connected by a bridge. The main visual difference between a pair of binoculars and a telescope is that the telescope allows one dimensional viewing, whereas a pair of binoculars offers three dimensional viewing.
They can range in price from under £50 for a basic pair to well over £2000 depending on the type and quality chosen.
Most binoculars include their magnification and objective specification in their description. As an example they might be described as 10x50 or 7-15x25.
In these examples 10x50 would denote a magnification capability of 10x and an Objective of 50mm; and 7-15x25 would denote a magnification capability of 7-15x and an Objective of 25mm.
What do these mean?
The magnification specification is how much the pair of binoculars will magnify the image by. So if the magnification is 8x, the viewed image will look 8 times larger (or 8 times closer to the user).
This can range from 7x to 18x for those requiring a high level of magnification.
The diameter of the lens (objective) is also important in the quality of the image, as a larger diameter will allow more light through. This means that the resulting image will be brighter and sharper on a pair of binoculars which has a wider diameter.
The diameter of models currently on the market can range from 25mm for the more basic binoculars to around 50mm which are suitable for those requiring a very high quality, brighter image.
Of course, with both magnification and the objective specification, you will be paying more for those binoculars with a higher specification, so you need to balance your requirements with your budget.
All binoculars carry a width specification of how much of the landscape or object can be viewed at one time. This is usually specified in degrees and binoculars with a specification of more than 65° are considered to have a wide field of view. The field of view is also often specified in metres or yards from a distance of 1000m or 1000 yards. So for example, if the specification is 90m, you would be able to view to a maximum width of 90 metres if you were standing 1000m away.
This is the size of the circular beam seen through the lens and is calculated by dividing the objective diameter by the magnification specification and generally speaking a larger exit pupil signifies a brighter image. There is no point in having an exit pupil which is larger than the size of a human pupil which is about 3mm in daylight conditions – but a larger exit pupil specification will be useful for night viewing.
This is the distance (measured in millimetres) from the rear lens to the exit pupil and can be an important factor for users who wear glasses for whom a longer eye relief gives them a better image.
This may be an important factor to you depending on your intended use. If you are going to be holding and viewing for extended periods of time, you might want to opt for a lighter pair of binoculars to avoid fatigue. The weight can vary quite considerably from under 300g to well over 1kg, excluding the batteries.
Likewise if you are going to be using them on holiday such as a safari, where space and weight is at a premium, you will probably go for a more compact and lightweight pair. Some models can be folded for easier storage and carrying.
If you prefer to blend in to the background, maybe if you are using your binoculars for hunting or bird watching, there are some models available in a camouflage or green colour.
If you are using your binoculars for activities such as watching ballet or opera, where magnification is not so important, you may opt for a lower specification and less expensive model.
If you will be using your binoculars for an activity that needs greater degree of magnification and detail such as bird watching, you may wish to invest in a more expensive pair of binoculars.
If you will be using your binoculars in bad weather or adverse conditions, you might consider a waterproof pair of binoculars with a rubber coating. Some models also have a water repellent lens coating and others float if accidentally dropped into water. If it is to be used near the sea, some models are resistant to salt water corrosion.