In the old days, approaching shore was the most dangerous part of sailors' journey. Due to adverse climatic conditions, shallows or coastal rocks could cause a shipwreck. Sailors were saved by lighthouses, the best navigational structures of that time. For a long time, fires were simply kindled on their peaks, later kerosene lamps served as light sources, until electricity was used. In the 19th century, the Fresnel lens became the life-saving light, making the light of the lighthouse the brightest and most visible from afar.
The composite compound lens was created by Augustin Fresnel, a French physicist, creator of the wave theory of light. The Fresnel lens is made up of individual small thickness concentric rings adjacent to each other and forming a cylinder with a light source inside. In cross section, the rings have the shape of prisms. Each of the rings collects light into a parallel narrow beam of rays that radiates from the center. When the cylinder rotates around the light source, the rays of light extend to the very horizon. The color of the rays, their number, the time interval between them make up a special unique handwriting of the lighthouse. A summary with the characteristics of various lighthouses was available on board the ships, and it was from it that the sailors found out which lighthouse was in front of them.
The Fresnel lenses installed on the lighthouses were a major step in equipping them with powerful light sources. These complex compound lenses made it possible to increase the concentration of light intensity up to 80,000 candles. Before Fresnel's invention, it was possible to focus the light of a burning wick or lantern only by placing the lantern in the focus of a converging lens of a sufficiently large diameter or a concave mirror. For these purposes, a one-piece optical element of a large size was needed, which, under the influence of its own gravity, could burst. Therefore, dozens of concave mirrors were used, each with a separate lantern at its focus. This decision was inconvenient.
The composite Fresnel lens helped to achieve an increase in light intensity, its concentration in a given direction. The assembly of individual optical elements did not reflect light, but worked in transmission, rotating around a light source that emitted constant intensity in all directions.
Since then, Fresnel designs have remained an unsurpassed technical device, used not only for river buoys and lighthouses. In the form of Fresnel lenses, glasses of various signal lights, traffic lights, car headlights, parts of lecture projectors were first made. Then loupes were created in the form of rulers, made of transparent plastic, with subtle circular grooves, each of which was a miniature ring prism, but in general theywere a converging lens. The resulting lens is used as a magnifying glass to magnify an object, like a camera lens that creates an inverted image.
Over time, the scope of Fresnel lenses has expanded significantly. It includes the development of photographic equipment, various lighting devices, tracking sensors for security systems, an energy concentrator for solar collectors, and mirrors used in telescopes. The optical properties of lenses are also used in the field of multimedia. For example, DNP, the largest manufacturer of high-tech projection screens, creates Supernova screens based on the lens. And rear projection screens use not only the Fresnel lens, but also other optical technologies, which allows you to get the most unique display facilities.
Depending on the field of application, lenses may have different diameters, vary in type. There are two types of lenses: annular and waist. The first are designed to direct the flow of light rays in one direction. Ring lenses have found use in manual work with small details, replacing conventional magnifiers. Waist lenses capable of transmitting beams of light in any given direction are used in the industrial sector.
Fresnel lens can be positive (collecting) and negative (diffusing). The negative polyvinyl lens with a short focus increases the field of view noticeably. It is known as the Fresnel parking lens. The widening of the viewing angle it gives allows you to see obstacles below the car withoutincluded in the field of view of the side mirrors or the rear-view mirror. This lens greatly facilitates maneuvering when parking, towing a trailer and reversing, avoiding running into playing children, animals or other objects.
The Fresnel lens has become a multifunctional tool, its invention has played an important role in the development of the technological field.
