Optical devices help us to investigate world around. The telescope allows to find out and consider outlines and details of far space bodies, and a microscope opens secrets of our planet, such as a structure of live cages.
Our eyes, as a matter of fact, represent optical devices. When we look at a subject, the lens system located in a forward part of each eye, forms its image on a retina - the layer of an eye bottom containing about 125 million of photosensitive cages. Light falling on a retina forces cages to send an electric nervous signal to a brain, allowing us to perceive a subject visually.
Besides, eyes possess brightness control system. At bright illumination the pupil is instinctively narrowed, lowering brightness of the image to comprehensible level. At weak illumination the pupil extends, increasing brightness of the image.
As the lens operates
The Lens system of an eye consists of a convex lens of a crystalline lens and the filled liquid of the bent cover located before it which is called as a cornea. The cornea provides four fifth all process of focusing. Thin adjustment is carried out by a crystalline lens, whose curvature of a surface changes the muscular ring (capsule) located round it. When the eye cannot accept the necessary form, usually because of infringements in the given muscles, images of visible subjects become indistinct.
The Most widespread lack of sight is the impossibility to focus on a retina of the image of separate subjects. If the lens system of an eye too strong, in other words, if it very convex remote subjects will blur, and relatives - to give accurate images. People with such infringement call the short-sighted. If camber of a crystalline lens is insufficient, close subjects will blur, and accurate there are images of remote subjects. Owners of such sight name far-sighted. Both infringements can be corrected, using points or contact lenses. Short-sighted people wear glasses with concave lenses (more thin in the middle) which allow their eyes to be focused on remote subjects. Far-sighted people wear glasses with convex lenses (utolshchennymi in the center).
Strong convex lenses are often used as magnifying glasses. The first increasing devices were used approximately 2000 years ago. In Ancient Greek and ancient Roman documents it is described, how for increase in subjects it is possible to use the round glass vessel filled with water. The lenses completely made of glass have appeared much later and, possibly, for the first time have been used in XI century by the monks working on manuscripts. In the end of XIII century magnifying glasses with small increase were already used in points for far-sightedness correction. But the technics of manufacturing of concave lenses for short-sightedness correction has been invented only in the beginning of XV century.
When there were magnifying glasses, people, naturally, have tried to use instead of such one two has flown down to receive still bolshee increase. It was experimentally revealed that at certain distance between lenses the remote object can be seen with substantial growth. Such arrangement of lenses has formed a basis for creation of the first telescope which at that time was called as a telescope. The invention of this device sometimes attribute to the English philosopher living in XIII century and scientist Roger Bacon. But, probably, the palm belongs to the Arabian scientists.
the Refractor Galilee
The Telescope created in 1608 Dutch optikom by Hans Lippershi, has drawn attention of the Italian scientist Galilee. During short time the scientist has improved a design of Lippershi and has created some pipes with the improved characteristics. With their help it has made a number of opening, including mountains and valleys on the Moon, and also four companions of Jupiter.
Opening Galilee have shown importance of a telescope, and the type of the device used by it has received popularity as a telescope Galilee. The convex lens of its objective collected light from observable object. And the concave lens of an eyepiece rejected light beams in such a manner that they created the increased direct image. Lenses were established in the pipes one of which (smaller diameter) slid in another. It allowed to regulate distance between lenses, receiving thus the accurate image.
The Telescope Galilee works with use of a principle of refraction (deviation) of light and consequently is known also as a telescope-refractor. Other kind of a telescope-refractor is characterised by camber of both lenses. Such design creates increased, but the turned image and is known as an astronomical telescope.
At use of early telescopes-refractors there was one vital issue which is caused by the defect of lenses named a chromatic aberration and leading to occurrence round images of undesirable colour auras. For elimination of this lack English scientist Isaak Newton in 1660th years has designed a telescope-reflector. For concentration of light beams and image creation in it instead of an objective lens the concave mirror which is not forming colour auras is used. The flat mirror reflects light in the convex lens of an eyepiece established on the main pipe sideways. The device of this kind is known as Newton's telescope.
Magnifying glass sometimes name a simple microscope, since. It use at supervision of small objects.
The Difficult microscope consists of two convex lenses. The objective lens creates the increased image which then again increases an eyepiece lens. As well as in an astronomical telescope, this image is turned. Many difficult microscopes have the complete set of objective lenses with various degree of increase.