Binoculars are a type of telescope that allows a user to view far away objects using both eyes. This requires the use of two separate telescopes, one for each eye, thus allowing binocular vision. Unlike a monocular, which uses only one telescope device to view objects, binoculars allow for three-dimensional viewing and promotes visual acuity, or clarity. They are generally small enough to be handheld, and many varieties are lightweight so they can be carried and stored easily. Binoculars are easier to hold and steady for viewing than a monocular because both hands are working to steady the instrument in a more comfortable and stable position.
Binoculars have countless practical applications for both hobbyists and professionals. They are a must for bird watchers and hunters, and they are handy to have at professional sporting events in which a spectator may be very far away from the action. In a professional setting, binoculars are essential for seafaring vessels and can be useful for a variety of scientists such as geologists, meteorologists, and other environmental professions. Different types of binoculars are often used for military applications as well. At many tourist attractions such as the Grand Canyon, large, swivel-mounted binoculars have been placed near the attraction so tourists can view objects far away. They are often coin-operated and give the tourist only a limited amount of time in which to use the viewer.
Binoculars use a series of prisms to magnify an image for the user. A large ocular lens on the far end of the binocular takes in all the light it can capture. The image, however, is inverted, and the naked human eye would see an upside down image, which is not very useful. Therefore, a prism is placed in between the human eye and the first lens in order to flip the image over. The image then must be focused, which can be done by using the center focus adjustment knob, or by moving the individual eyepieces to line up with your eye.
The most commonly used types of binoculars are porro prism binoculars, which use a positive eye piece, or ocular, to view images. This system inverts the image, and a system of mirrors or prisms must be used in order to make the image appear upright. The porro prism system allows for greater magnification and image quality, hence their popularity.