In his monograph entitled "Light",  Richard C. MacLaurin explains Fresnel diffraction by asking what happens when light propagates, and how that process is affected when a barrier with a slit or hole in it is interposed in the beam produced by a distant source of light. He uses the Principle of Huygens to investigate, in classical terms, what transpires. The wave front that proceeds from the slit and on to a detection screen some distance away very closely approximates a wave front originating across the area of the gap without regard to any minute interactions with the actual physical edge.
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Types[ edit ] There are two main types of Fresnel lens: imaging and non-imaging. Imaging Fresnel lenses use segments with curved cross-sections and produce sharp images, while non-imaging lenses have segments with flat cross-sections, and do not produce sharp images. In the abstract case of an infinite number of segments, the difference between curved and flat segments disappears. Imaging[ edit ] Spherical A spherical Fresnel lens is equivalent to a simple spherical lens , using ring-shaped segments that are each a portion of a sphere, that all focus light on a single point.
This type of lens produces a sharp image, although not quite as clear as the equivalent simple spherical lens due to diffraction at the edges of the ridges. Cylindrical A cylindrical Fresnel lens is equivalent to a simple cylindrical lens , using straight segments with circular cross-section, focusing light on a single line.
This type produces a sharp image, although not quite as clear as the equivalent simple cylindrical lens due to diffraction at the edges of the ridges. Non-imaging[ edit ] Spot A non-imaging spot Fresnel lens uses ring-shaped segments with cross sections that are straight lines rather than circular arcs.
Such a lens can focus light on a small spot, but does not produce a sharp image. These lenses have application in solar power, such as focusing sunlight on a solar panel. These lenses focus light into a narrow band. They do not produce a sharp image, but can be used in solar power, such as for focusing sunlight on a pipe, to heat the water within: . They are also used to correct several visual disorders, including ocular-motility disorders such as strabismus.
Fresnel lenses have been used to increase the visual size of CRT displays in pocket televisions , notably the Sinclair TV They are also used in traffic lights. Fresnel lenses are used in left-hand-drive European lorries entering the UK and Republic of Ireland and vice versa, right-hand-drive Irish and British trucks entering mainland Europe to overcome the blind spots caused by the driver operating the lorry while sitting on the wrong side of the cab relative to the side of the road the car is on.
They attach to the passenger-side window. Multi-focal Fresnel lenses are also used as a part of retina identification cameras, where they provide multiple in- and out-of-focus images of a fixation target inside the camera. For virtually all users, at least one of the images will be in focus, thus allowing correct eye alignment. Fresnel lenses have also been used in the field of popular entertainment.
The British rock artist Peter Gabriel made use of them in his early solo live performances to magnify the size of his head, in contrast to the rest of his body, for dramatic and comic effect. In the Terry Gilliam film Brazil , plastic Fresnel screens appear ostensibly as magnifiers for the small CRT monitors used throughout the offices of the Ministry of Information.
However, they occasionally appear between the actors and the camera, distorting the scale and composition of the scene to humorous effect. Photography[ edit ] Canon and Nikon have used Fresnel lenses to reduce the size of telephoto lenses. Photographic lenses that include Fresnel elements can be much shorter than corresponding conventional lens design.
Nikon calls their technology Phase Fresnel. View and large format cameras can utilize a Fresnel lens in conjunction with the ground glass , to increase the perceived brightness of the image projected by a lens onto the ground glass, thus aiding in adjusting focus and composition. Illumination[ edit ] Inchkeith lighthouse lens and drive mechanism High-quality glass Fresnel lenses were used in lighthouses, where they were considered state of the art in the late 19th and through the middle of the 20th centuries; most lighthouses have now retired them from service.
The light path through these elements can include an internal reflection , rather than the simple refraction in the planar Fresnel element. These lenses conferred many practical benefits upon the designers, builders, and users of lighthouses and their illumination. Among other things, smaller lenses could fit into more compact spaces. Greater light transmission over longer distances, and varied patterns, made it possible to triangulate a position.
For reasons of economy, weight, and impact resistance, newer cars have dispensed with glass Fresnel lenses, using multifaceted reflectors with plain polycarbonate lenses. However, Fresnel lenses continue in wide use in automobile tail, marker, and reversing lights. Glass Fresnel lenses also are used in lighting instruments for theatre and motion pictures see Fresnel lantern ; such instruments are often called simply Fresnels. The entire instrument consists of a metal housing, a reflector, a lamp assembly, and a Fresnel lens.
A holder in front of the lens can hold a colored plastic film gel to tint the light or wire screens or frosted plastic to diffuse it. The Fresnel lens is useful in the making of motion pictures not only because of its ability to focus the beam brighter than a typical lens, but also because the light is a relatively consistent intensity across the entire width of the beam of light. Eisenhower Aircraft carriers and naval air stations typically use Fresnel lenses in their optical landing systems.
The "meatball" light aids the pilot in maintaining proper glide slope for the landing. In the center are amber and red lights composed of Fresnel lenses. If the lights appear above the green horizontal bar, the pilot is too high. If it is below, the pilot is too low, and if the lights are red, the pilot is very low.
The Fresnel lens has seen applications for enhancing passenger reading lights on Airbus aircraft: in a dark cabin, the focused beam of light does not dazzle neighboring passengers. Projection[ edit ] The use of Fresnel lenses for image projection reduces image quality, so they tend to occur only where quality is not critical or where the bulk of a solid lens would be prohibitive.
Cheap Fresnel lenses can be stamped or molded of transparent plastic and are used in overhead projectors and projection televisions. Fresnel lenses of different focal lengths one collimator , and one collector are used in commercial and DIY projection. The collimator lens has the lower focal length and is placed closer to the light source, and the collector lens, which focuses the light into the triplet lens, is placed after the projection image an active matrix LCD panel in LCD projectors.
Fresnel lenses are also used as collimators in overhead projectors. Solar power[ edit ] Since plastic Fresnel lenses can be made larger than glass lenses, as well as being much cheaper and lighter, they are used to concentrate sunlight for heating in solar cookers , in solar forges, and in solar collectors used to heat water for domestic use. They can also be used to generate steam or to power a Stirling engine.
Fresnel lenses can concentrate sunlight onto solar cells with a ratio of almost Fresnel lenses can be used to sinter sand, allowing 3D printing in glass.
In the horror manga Uzumaki by Junji Ito , the concentric patterns of the Fresnel lens of a lighthouse are melted by heat and form a spiral. A Fresnel lens features as a prominent fixture in the film The Lighthouse.
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