Fread Vinton, age 17, of Winston Salem, N.C., for his question:

HOW DO BINOCULARS WORK?

Historians believe the first telescope was made in 1608 by a Dutch optician named Hans Lippershey. But back in the 1200s scientists were experimenting with magnifying lenses. The famous Italian astronomer, Galileo, built his first telescope in 1609. A rather crude instrument, Galileo's telescope was able to magnify objects 33 times.
Binoculars, which are also called field glasses, are actually two small telescopes with a separate viewing tube and a set of lenses for each eye.
The simplest type of field glass has two tubes joined together side by side. It can be adjusted by means of a knob which moves the lenses in each tube closer together or farther apart.
Replacing the simplest field glass in almost all areas where magnification is needed is the prism binocular. In such binoculars, two prisms reflect the light in each tube before it reaches the eye. The light enters the binocular through the magnifying lens at the front, strikes one prism and then is reflected forward. The light then strikes another prism and is reflected to the lens or lenses in the eyepiece where the viewer sees it.
Prisms inside binoculars are useful in three ways: they turn right side up the reverse image that the magnifying lens brings in; they help to make the binoculars smaller because the light is reflected from one prism to another, not in a straight line; in most binoculars, the magnifying lenses can be set farther apart than the eyepieces are which makes for better stereoscopic vision at distances.
Good binoculars also have achromatic lenses which compensate for the bending of the different light rays.
In addition, many high quality binoculars also have specially coated lenses to reduce glare.
Binoculars are made in different magnifying powers and with lenses of different diameters. The magnifying power and lens diameter are usually given together, such as 6 x 30 or.7 x 50. First figure given is that of the magnifying power. With a 6 x 30 binocular, therefore, an object would become six times larger than when seen with the naked eye, and the diameter of the lens would be 30 millimeters.
An opera glass is a smaller double telescope. Most have a double convex lens for its object glass and a double concave lens for its eyepiece. The convex lens throws an image which the concave lens turns upright and magnifies. The image then appears upright instead of upside down as with an astronomical telescope.