Magnifying binocular - courtesy - www.fotosearch.com
Binoculars have a lot of uses, even for ordinary mortals. We often associate binoculars with hunting and fishing, bird watching, boating, and studying stars, planets, and comets. The truth is, to opera fans, sports aficionados, and travelers, binoculars are extremely useful. Another truth is, those who do use them do not know how they work.
If you want to know how binoculars work, read on. However, before going inside the inner workings of this piece of equipment, it would be helpful to define a few terms:
1) Objective lens. This is the lens at the front of the binocular. Its function is to gather light, which it directs to another lens.
2) Eyepiece lens. This refers to the lens at the back of the binocular through which a user looks when examining an object.
3) Magnifying power. The magnifying power of a binocular refers to the number of times an object is magnified and is often expressed as a number with the letter “x” signifying “times”. This power commonly ranges from 6x to 10x. A 6x binocular will make an object viewed through it appear six times closer that it actually is.
4)Optical tube. This is the tubular structure that holds the lenses and the prisms of your binoculars. It is also called the lens barrel.
There are different designs of binoculars, and these work differently from each other.
The Galilean design binoculars use convex objective lenses and concave eyepiece lenses. The objective lens admits light and sends it to another lens, which magnifies the image. In this design, the objective and eyepiece lenses are aligned within the optical tube. Additional lenses may be placed between them for greater magnification. While Galilean binoculars do not provide a wide field of view, nor a high magnifying power, they are inexpensive and are sufficient as opera or concert binoculars.
Prism binoculars provide higher magnifying power than those of Galilean design. This is because of their concave eyepiece lenses. Such lenses, however, turn the image upside down. To flip it back up, prisms are installed in between the objective and eyepiece lenses. The two types of commonly used prisms are the Porro prism and the roof prism.
You can identify Porro prism binoculars by their offset optical tubes, that is, the objective and eyepiece lenses are not in line in a single tube. Some designs have the front lenses closer to each other than the eyepieces, while others feature the reverse. The light coming through the objective lens travels towards a triangular prism, and is deflected at right angles twice within it. It moves to another prism, positioned slightly ahead and to the side of the first, where it is again deflected twice. Upon leaving the second prism, the light goes on to the eyepiece.
Binoculars using roof prisms have their objective and eyepiece lenses in line within an optical tube. This is possible because roof prisms are small and shallow enough to be attached to the roof of the optical tube. This prism is configured in such a way that the light from the objective lens is deflected at a downwards angle and bounces back upwards. It is again bent towards the same direction it travelled when it first passed through the objective lens, thus, exiting though the eyepiece lens.
As prism binoculars offer better and clearer images, wider field of view, and higher magnification, these are often the choice of users who appreciate quality in their equipment.
