If you look through binoculars, you will find distant objects appear nearer and larger. Why does this happen?
Binoculars are a pair of small telescopes built into a frame or casting. The two telescopes in binoculars are exactly similar in structure and meant for each eye. Each telescope is built into a funnel-shaped tube or cylinder. It consists of one objective lens and one eyepiece. The objective lens is kept towards the object and the eyepiece near the eye. The lenses are anti-reflection coated. Two prisms are also mounted between the objective lens and the eye piece to make the image of the object erect.
The light from the object falls on the objective lens and an inverted image is produced by it. This image is further inverted by the two prisms, thus the image becomes erect. The eyepiece further magnifies this image. This is how we see the erect and magnified image of the object.
Most of the binoculars have a single adjustable wheel or thumb screw for controlling the focus of both telescopes simultaneously. Some binoculars have separate focus wheels for each telescope for varying characteristics of the two eyes
Binoculars usually have two numbers printed or engraved somewhere on the outer covering. The first number is the power of magnification and the second number shows the diameter of the objective lens in millimeters. If the binoculars are marked 6 x 35, then it will magnify an object six times through an objective lens which is 35 mm in diameter.
Binoculars provide stereoscopic vision, i.e. depth perception at great distances by using both eyes at the same time. People often use them to see matches in playgrounds. Many modern microscopes also use binoculars. This is to get a clearer and three dimensional image of the object.
