What are optical devices. Optical devices

The knowledge gained by researchers about light phenomena made it possible to create many optical instruments that greatly expand the boundaries of human capabilities. You already know about a simple and common device - glasses. Today we will discuss the principle of operation of other optical devices.

The angle of view is the angle formed by the rays emanating from extreme points object and pass through the optical center of the eye.

The limiting angle of view is the smallest angle of view at which a person still distinguishes two points separately, approximately equal to 1/60 of a degree.

Optical instruments are used to increase the angle of view. According to their purpose, optical devices can be divided into two large groups:

devices for viewing very small objects (loupe, microscope), providing the opportunity to "enlarge" the objects of observation.

devices for viewing distant objects (spotting scope, binoculars, telescope). These objects "bring closer" the objects of observation.

Dandruff is a short focus cleaning lens for viewing small objects. Its focal length is from 1 cm to 15 cm. The magnification that can be obtained with a magnifier depends on its optical power. Calculations show that this increase is equal to the ratio of the distance of the best view to the focal length of dandruff. Glasses (short-focus cleaning lenses taken in a frame) of a microscope, telescope, binoculars and other optical instruments also act like dandruff. The eyepiece of any optical instrument is always placed near the eye.

A microscope is used when very small objects need to be examined. The main optical parts of the microscope are an objective and an eyepiece - two cleaning lenses, each of which operates independently. An enlarged and real image is created with the help of a lens, which is examined with the help of an eyepiece. The microscope gives an imaginary, reverse, enlarged image of small objects. The image of an object obtained with the help of an objective and an eyepiece is reversed, therefore, an additional lens or a reverse prism is placed in the telescopes between the objective and the eyepiece, which “flips” the image and makes it straight. Microscopes are used in science, technology, forensics, and medicine. A powerful lens can magnify up to 100 times, while the eyepiece gives a magnification of no more than 20 times. So the best optical microscope can give an increase up to 100.20 = 2000.

A telescope is an instrument (spotting scope) designed to observe celestial bodies. It allows you to distinguish close luminous points and observe very distant luminous objects. It, like a microscope, can be made from two lenses. The lens closest to the eye is the eyepiece, and the second is the lens. The purpose of the eyepiece in a telescope and a microscope is almost the same. The "role" of a lens in a telescope is the "opposite" of that of a lens in a microscope. If the magnification of a microscope increases with an increase in the optical power of the lens (with a decrease in the focal length), then the telescope, on the contrary, "brings" the object the stronger, the greater the focal length of the lens.

Calculations show that the "zoom" given by the telescope is equal to the ratio of the focal length of the objective to the focal length of the eyepiece. Focal length telescope lens can reach tens of meters. These telescopes "zoom in" thousands of times.

Cameras are optical devices in which real images of objects are reduced and fixed on a special element. The structure of the camera is similar to the structure of the eye. AT digital cameras the process of obtaining an image is much more complicated, but the principles and fundamentals of photography remain unchanged. The principle of operation of the camera is applied both to the film camera and to video cameras.

With the help of cameras and projectors, an image is obtained on the screen - real, enlarged, inverted. And so that the characters do not go upside down on the screen, the film in the movie camera is installed upside down.

Optical devices help us explore the world. The telescope allows you to detect and examine the outlines and details of distant cosmic bodies, and the microscope reveals the secrets of our planet, such as the structure of living cells.

Our eyes are essentially optical instruments. When we look at an object, the lens system located in front of each eye forms its image on the retina - the fundus layer containing approximately 125 million light-sensitive cells. Light falling on the retina causes the cells to send an electrical nerve signal to the brain, allowing us to visually perceive the object.

In addition, the eyes have a brightness adjustment system. In bright light, the pupil instinctively constricts, reducing the brightness of the image to an acceptable level. In low light, the pupil expands, increasing the brightness of the image.

How the lens works

The lens system of the eye consists of a convex lens of the lens and a curved membrane in front of it filled with liquid, which is called the cornea. The cornea provides four-fifths of the entire focusing process. Fine adjustment is carried out by the lens, whose surface curvature is changed by the muscular ring (capsule) located around it. When the eye is unable to take the desired shape, usually due to disorders in these muscles, images of visible objects become blurry.

The most common visual impairment is the inability to focus on the retina of the image. individual items. If the lens system of the eye is too strong, in other words, if it is very convex, then distant objects will blur, and close ones will give clear images. People with this disorder are called nearsighted. If the convexity of the lens is insufficient, then close objects will blur, and images of distant objects will remain clear. Those with this vision are called farsighted. Both disorders can be corrected by using glasses or contact lenses. Nearsighted people wear glasses with concave lenses (thinner in the middle) that allow their eyes to focus on distant objects. Farsighted people wear glasses with convex lenses (thick in the center).

Increase

Strong convex lenses are often used as magnifying glasses. The first magnifying devices were used about 2000 years ago. Ancient Greek and Roman documents describe how a round glass vessel filled with water can be used to magnify objects. Lenses made entirely of glass appeared much later and were probably first used in the 11th century by monks working on manuscripts. At the end of the 13th century, magnifying glasses with low magnification were already used in glasses to correct farsightedness. But the technique of making concave lenses to correct myopia was not invented until the early 15th century.

telescopes

When magnifying glasses appeared, people naturally tried to use two such glasses instead of one in order to get even greater magnification. Experimentally, it was found that at a certain distance between the lenses, a distant object can be seen with a significant increase. This arrangement of lenses served as the basis for the creation of the first telescope, which at that time was called a spotting scope. The invention of this device is sometimes attributed to the English philosopher and naturalist Roger Bacon who lived in the 13th century. But perhaps the palm belongs to Arab scientists.

Galilean refractor

The spotting scope, created in 1608 by the Dutch optician Hans Lippershey, attracted the attention of the Italian scientist Galileo. Within a short time, the scientist improved Lippershey's design and created several pipes with improved characteristics. With their help, he made a number of discoveries, including mountains and valleys on the Moon, as well as four satellites of Jupiter.

Galileo's discoveries showed the importance of the telescope, and the type of instrument he used became known as the Galilean telescope. The convex lens of his objective collected light from the observed object. And the concave lens of the eyepiece deflected the light rays in such a way that they created an enlarged direct image. The lenses were mounted in tubes, one of which (smaller diameter) slid inside the other. This made it possible to adjust the distance between the lenses, while obtaining a clear image.

Galileo's telescope works using the principle of refraction (deflection) of light and is therefore also known as a refractor telescope. Another type of refractor telescope is characterized by the convexity of both lenses. This design creates an enlarged but inverted image and is known as an astronomical telescope.

Newton reflector

One major problem with early refracting telescopes was a lens defect called chromatic aberration that caused unwanted color halos around images. To remedy this shortcoming, English scientist Isaac Newton designed the reflecting telescope in the 1660s. To concentrate light rays and create an image, a concave mirror is used instead of an objective lens, which does not form color halos. A flat mirror reflects light into a convex eyepiece lens mounted on the side of the main tube. An instrument of this type is known as a Newtonian telescope.

microscopes

Magnifying glass sometimes called simple microscope, since it is used when observing small objects.

A compound microscope consists of two convex lenses. The objective lens creates a magnified image, which is then magnified again by the eyepiece lens. As with an astronomical telescope, this image is reversed. Many compound microscopes have a set of objective lenses with varying degrees of magnification.

Optical instruments have opened to man two polar worlds in terms of scale - the cosmic world with its vast expanses and the microcosmic one, inhabited by the smallest organisms. TV Broadcast, demonstration of a movie, fast shooting of the terrain, accurate measurement of distances and speeds are possible only through the use of optical instruments.

The most common devices that form images. These are a telescope and binoculars, a microscope and a magnifying glass, a camera and a slide projector ... A projection apparatus is one of the most characteristic devices that form an image (Fig. 1). If the projector is adapted to display a movie, it is called a movie camera. If it is used to demonstrate transparencies, then this is a slide projector. In a slide projector, a transparent photograph - a slide D, illuminated by the light of a condenser K, is placed near the focal plane of the lens so that a clear image is obtained on the screen. The image size depends on the projector's distance from the screen. When changing this distance, it is necessary to change the position of the lens relative to the transparencies. If you put an illuminated object instead of a screen, then it will be displayed at the location of the transparencies. Now, if you put a film instead of a transparencies and remove the condenser, you get a camera circuit.

The optical scheme of the human eye also resembles that of a camera. The eye forms an image on its retina. The size of the image of an object on the retina depends on the angle at which we see the object. Thus, the angular diameter of the Sun is 32. This angle determines the size of the image of the Sun on the retina. When two extreme points of an object are seen at an angle less than 1, they merge on the retina and the object appears to the observer as a point. In this case, we say that the resolution of the eye does not exceed one minute of arc.

The telescope makes it possible to increase the angle at which a distant object is visible. The first telescope was created at the beginning of the 17th century. G. Galileo. Let us describe the path of rays from a distant object in a modern spotting scope. From the extreme points of the object, parallel rays fall on the lens and outline the contour of the object in the focal plane. Through the eyepiece, the image is viewed at an angle greater than , at which the object is visible to the naked eye. Angular magnification of the telescope. The optical scheme shown in fig. 2 is a diagram of a refractor - a telescope with a lens objective. A telescope with a mirror lens is called a reflector or reflective telescope. The first reflector was built by I. Newton in 1668 (Fig. 3).

A telescope with a lens diameter D allows you to observe objects or points of an object located at an angular distance , if we assume that the length of the light wave emitted by the object is µm. It turns out that the larger the diameter of the telescope, the more small parts object are distinguishable with its help. For the largest refractors, the objective diameter does not exceed . It is technically easier to make a large-diameter mirror and build a reflector.

The world's largest telescope with a -meter mirror was built in the Soviet Union. It is designed to observe variable galaxies, pulsars, quasars and other space objects.

To view a small object at a large angle, it is brought as close to the eye as possible. However, the eye lens clearly depicts an object on the retina if it is placed no closer than 10 cm from the eye. At smaller distances, the maximum curvature of the lens is insufficient to obtain a clear image on the retina. Therefore, very small objects are examined through a magnifying glass or microscope - devices that increase the angle at which the object is visible.

Magnifiers invented in the 17th century the Dutch naturalist A. Leeuwenhoek, the discoverer of the world of microorganisms, gave an increase of 300 times. The microscope design was improved in the 1650s. English scientist R. Hooke. But until the 20s. 19th century microscopes could not compete with very good loupes. Progress has been made through the development of complex multi-lens lenses. Minimum dimensions object, distinguishable in a microscope, are determined by the dependence: A. Here A is a constant equal to approximately 1. For green light, μm. For an object to be seen at an angle G, a magnification of 1000 times is sufficient.

Spectral optical instruments are designed to study the spectral composition of light. They play an important role in the development of science and are used both to study the processes occurring in the microcosm and for applied purposes. For example, with the help of modern spectral equipment, one can judge the shape of an atomic nucleus and perform an accurate elemental analysis of a substance. An example of a spectral instrument is a spectroscope (Fig. 4), in which the emission spectrum can be observed visually. The main part of the spectroscope is a prism or diffraction grating. The lens collects the studied radiation on the slit of a collimator - a device that forms a light beam of low divergence - a "parallel" beam. After passing through a prism, such a beam is converted into n beams traveling at different angles if the radiation consists of electromagnetic waves with lengths. The lens on the screen will give images of the slit A, which form the spectrum. When it is required to study "almost" monochromatic radiation, for example, the spectral composition of one line, a high-resolution instrument is installed in series with a spectroscopic prism instrument. Without preliminary decomposition of light devices high definition cannot be used, because they can only work in a very narrow range of wavelengths.

The creation of lasers opened up new paths in optical instrumentation.

Modern laser gyroscopes are capable of operating under high mechanical overloads, they can be installed on rockets, spaceships. Laser magnetometers for measuring weak magnetic fields and devices for measuring particle velocity and size distributions have been built. Laser optical radars are successfully used for various purposes (Fig. 5). high brightness laser radiation makes it possible to transfer it to long distances, and the short duration of the laser pulse provides exceptional distance measurement accuracy. The laser velocity meter is interesting (Fig. 6). Reflected from a moving particle, the laser light will change its frequency of oscillation. At normal speeds, this change due to the Doppler effect is negligible. And yet, due to the high phase stability and monochromaticity of laser light, it can be measured, and the measured value can be used to determine the velocity of a particle, for example, a liquid moving in a turbulent flow (see Turbulence).

Physicists and engineers are developing an optical computer. Its design capacity is more than 1 billion operations per second, i.e., ten times more than that of the fastest computers that currently exist. The basis of such a machine will be laser devices. And her memory will be optical, based on holographic data recording (see Holo-raffia). On a 10 X 10 hologram, more than 100 million units of information can be recorded: for such a volume of information, about 1 million pages of printed text would be required. With the help of holographic optics, complex mathematical calculations, differentiation of functions, integral operations are performed today, the most complex equations are solved. Optical elements - component designs of many devices. Thus, controlled optical transparencies enable an image obtained with the help of an image that is not perceived by the eye. electromagnetic radiation, convert to visible radiation.

Optical devices based on fiber optics make it possible to examine the internal organs of a person and prevent serious diseases.

So, modern optical instruments are absolutely necessary and are widely used in many branches of the national economy, in scientific research.