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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Lens and glasses. History of invention and production
Directory / The history of technology, technology, objects around us Before talking about the invention of glasses, let us briefly recall what a lens is and why it can be used to correct visual defects. A lens is usually called a transparent body bounded by spherical surfaces. (There are lenses in which only one surface is spherical and the other is flat. However, a flat surface can also be considered as spherical if we assume that it has an infinitely large radius of curvature.)
A well-known property of a lens is its ability to change the direction of light rays falling on it in a certain way. Why is this happening? Even in ancient times, people noticed that light, passing from one transparent medium to another (for example, from air to water or glass), changes its direction or, as they say, is refracted. Everyone can easily observe examples of light refraction. For example, if we dip a pencil into a glass of water so that half of it is in water and half in air, and then we look at the glass from the side, it will seem to us that the pencil is broken in the part that falls on the border of air and water. In lenses, the beam is refracted twice, once entering it, and the second time leaving it. By changing the curvature of the lens in different ways, different refraction effects can be achieved. So, some lenses can collect light into a point, while others, on the contrary, scatter it. Moreover, lenses in which the middle is thicker than the edges are converging, and those in which the middle is thinner than the edges are divergent.
The point at which the rays of light converge after refraction in a converging lens is called the focus, and the distance from the center of the lens to the focus is its focal length. The greater the curvature of the lens, that is, the smaller the radius of the spherical surfaces that form the lens, the shorter its focal length. A diverging lens also has its focus - they call it the point at which the continuations of the rays scattered by the lens converge. The most important feature of a lens, on which all its optical properties are based, is the ability to focus light, that is, to collect light rays emanating from any point back to one point. And since any object can be imagined as a collection of an infinite number of points, the lens creates an image not only of any point of the object, but of the entire object as a whole. However, the image in the lens will not be an exact repetition of the object - it will, firstly, be inverted and, secondly, will differ in size. The reason is that the distance from the lens to the object and the distance from the image to the lens are not equal to each other. If, for example, the distance from the lens to the image is five times greater than the distance from the lens to the object, then the image will be five times larger than the object itself. This explains the well-known ability of a lens to enlarge the image of an object, to make it more convenient for viewing. Moreover, the greater the curvature of the lens (the smaller its focal length), the stronger it increases. If, on the contrary, the distance to the object is greater than the distance to the image, then the image is reduced. Clear images of objects are obtained only when they are projected onto a plane passing through the focus of the lens and perpendicular to its main optical axis (the main optical axis of the lens is called a straight line passing through the centers of spherical surfaces limiting the lens). It is known that the human eye is an optical system. Rays of light entering the eye are refracted at the surface of the cornea and lens. The lens is a transparent layered body, similar to a lens. A special muscle can change the shape of the lens, making it either less or more convex. Due to this, the lens either increases or decreases its curvature and with it the focal length. In general, the optical system of the eye can be considered as a converging lens with a variable focal length that projects an image onto the retina. If the object is very far away, the image is obtained on the retina of a normal eye without any tension of the lens muscle. When the object approaches, the lens is compressed and the focal length is reduced so that the image plane is again aligned with the retina. Thus, the eye is in a normal (relaxed) state when it looks into the distance. However, in many people, the eyes in a relaxed state create an image of a distant object not on the retina, but in front of it. As a result, the image of each point of the object is projected onto the retina not as a dot, but as a circle. The subject is blurred. Such people cannot see clearly distant objects, but they see well those that are near. This visual defect is called myopia. A similar situation arises when the image of distant objects is obtained behind the retina. This defect is called farsightedness. A far-sighted person sees distant objects well, but cannot distinguish those that are near. Both of these shortcomings are corrected with the help of glasses. If you are nearsighted, you need glasses with divergent lenses. After passing through such a lens, the rays of light are focused by the lens exactly on the retina. Therefore, a myopic person armed with glasses can see distant objects, just like a person with normal vision. Farsightedness is also corrected with glasses, but only with converging lenses.
Glasses, being a very simple optical device, bring people with visual impairments a huge relief in everyday life. Without glasses, these people would constantly feel their inferiority, and with highly developed myopia or hyperopia, they could find themselves in the position of invalids. In recent decades, when visual defects (especially myopia) have become extremely common, almost every person begins to use glasses at one age or another. Therefore, it is obvious that glasses should be ranked among the greatest technical inventions. Although their design is very simple, glasses appeared relatively late - only during the Middle Ages, when they learned how to produce high-quality, transparent and uniform glass. Meanwhile, people got acquainted with the properties of lenses much earlier - at the dawn of civilization. In ancient times, lenses were made from transparent stones - primarily from rock crystal and beryl. Many such lenses were found during excavations in Egypt, Greece, Mesopotamia, and Italy. Several lenses were found during excavations of the legendary Troy (the age of these latter is estimated at about 2500 BC). A small crystal lens, made around 1600 BC, was found in the ruins of the Palace of Knossos in Crete. The very first glass lenses, dated approximately to the XNUMXth-XNUMXth centuries BC, were found in Sargon (Mesopotamia). In more recent times, glass lenses have been made more frequently. However, there is not a single mention that the lens was already used as an optical instrument then. Although several ancient works on optics have come down to us, none of them reports that lenses were used to correct visual defects. There is not even any evidence that the lenses were used as a magnifying glass (loupe) when performing some small work (for example, making gems), despite the fact that the ability of lenses to magnify the images of objects was, of course, well known. But why then were those ancient lenses made, which were discussed above? Apparently, they served only as decoration. The first glasses appeared in the XNUMXth century in Italy. At this time, Italian glass craftsmen were considered the most skilled glass makers, grinders and polishers in the world. Venetian glass was especially famous, products from which often had a very complex, intricate shape. Constantly processing spherical, curved and convex surfaces, now and then bringing them to the eyes, the craftsmen eventually noticed the optical possibilities of glass. The ingenious idea to connect two lenses with the help of a frame came, according to legend, in 1285 to the glass master Salvino Armati from Florence. He also established the first production of glasses. Nothing more is known about this man. However, the device he invented, which made it possible to easily and quickly smooth out visual defects, immediately became widespread. Long-focus convex, converging lenses were inserted into the very first glasses, and they served to correct farsightedness. Much later, it was discovered that with the help of the same glasses, by inserting concave diverging lenses into them, it is possible to correct myopia. The first descriptions of such glasses belong only to the XNUMXth century. Author: Ryzhov K.V.
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