1.
Polarizing filter (photography)
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A polarizing / polarising filter is often placed in front of the camera lens in photography in order to darken skies, manage reflections, or suppress glare from the surface of lakes or the sea. Since reflections tend to be at least partially linearly-polarized, a linear polarizer can be used to change the balance of the light in the photograph, the rotational orientation of the filter is adjusted for the preferred artistic effect. This additional step avoids problems with auto-focus and light-metering sensors within some cameras, light reflected from a non-metallic surface becomes polarized, this effect is maximum at Brewsters angle, about 56° from the vertical for common glass. A polarizer rotated to pass only light polarized in the perpendicular to the reflected light will absorb much of it. This absorption allows glare reflected from, for example, a body of water or a road to be reduced, reflections from shiny surfaces are also reduced. This allows the color and detail of what is beneath to come through. Reflections from a window into a dark interior can be much reduced, some of the light coming from the sky is polarized. The electrons in the air molecules cause a scattering of sunlight in all directions and this explains why the sky is not dark during the day. But when looked at from the sides, the light emitted from an electron is totally polarized. Hence, a picture taken in a direction at 90 degrees from the sun can take advantage of this polarization, actually, the effect is visible in a band of 15° to 30° measured from the optimal direction. Perpendicularly incident light waves tend to reduce clarity and saturation of certain colors, the polarizing lens effectively absorbs these light waves, rendering outdoor scenes crisper with deeper color tones in subject matter such as blue skies, bodies of water and foliage. Much light is differentiated by polarization, e. g. light passing through crystals like sunstones or water droplets producing rainbows, the polarization of the rainbow is caused by the internal reflection. The rays strike the surface of the drop close to the Brewster angle. Polarizing filters can be rotated to maximise or minimise admission of polarised light and they are mounted in a rotating collar for this purpose, one need not screw or unscrew the filter to adjust the effect. Rotating the polarizing filter will make rainbows, reflections, and other polarized light stand out or nearly disappear depending on how much of the light is polarized, the benefits of polarizing filters are the same in digital or film photography. There are two types of polarizing filters readily available, linear and circular, which have exactly the same effect photographically, linearly-polarized light may also defeat the action of the Anti-aliasing filter on the imaging sensor. Circular polarizing photographic filters consist of a linear polarizer on the front, the quarter-wave plate converts the selected polarization to circularly polarized light inside the camera. This works with all types of cameras, because mirrors and beam-splitters split circularly polarized light the way they split unpolarized light
2.
UV filter
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UV filters are individual compounds or mixtures that block or absorb ultraviolet light. UV filters are used in sunscreens to protect skin or in photography to reduce the level of light that strikes the recording medium. UV filters can undergo transformation into less protective or more toxic products. These transformation products can health, historically, photographic films were mostly sensitive to UV light, which caused haziness or fogginess, and in color films a bluish hue. Therefore, as a standard, a UV filter was used, however, newer photographic film and digital cameras are highly insensitive to UV wavelengths. UV filters span the spectrum and are used for a wide variety of applications. Ortho Red ahave negativend Deep Ortho Red lights are used in diffusion transfer, typesetting films/paper. Yellow Gold, Yellow, Lithostar Yellow, and Fuji Yellow filters or safelights provide safe workspaces for contact proofing applications like screen printing and platemaking. Pan Green, Infrared Green, and Dark Green filters or safelights are commonly used in scanning applications, work with panchromatic film, and papers and x-rays. Many photographers and cinematographers still use UV filters as a protection for their lenses glass and coating, due to their low cost, however, UV filters may introduce lens flare and have an adverse impact on contrast and sharpness, especially when a strong light source is present. The correct names for such filters though, are UV pass filter and this is a very specialized area in photography. Excessive UV radiation can expose humans to various risks, including diseases such as sunburns, photo-aging. UV radiation can be classified as UVA, UVB and UVC, ultraviolet absorbing compounds are the main ingredients of sunscreen products and other personal care products. Chemical filters are used in combination in order to get sufficient protection against UV. They protect humans from the effects of UV radiation by absorbing, reflecting or scattering it. The reflection and scattering effecst are done by physical UV filters which are inorganic UV filters such as titaniumdioxide, absorption is accomplished by organic UV filters which are known as chemical UV filters. UV filters are being used due to growing concern about UV radiation and skin cancer. The levels of certain UV-filters in sunscreens vary from 0.5 to 10% and they enter the environment directly through bathing activities in oceans, rivers and lakes or through industrial waste water discharge. Several UV filters have been detected at ppb or ppt levels in surfacewater and wastewater and they are lipophilic and tend to accumulate in the aquatic environment’s soils and sediments as well as in the food chain
3.
Polarizer
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A polarizer or polariser is an optical filter that lets light waves of a specific polarization pass and blocks light waves of other polarizations. It can convert a beam of light of undefined or mixed polarization into a beam of well-defined polarization, the common types of polarizers are linear polarizers and circular polarizers. Polarizers are used in many techniques and instruments, and polarizing filters find applications in photography. Polarizers can also be made for other types of electromagnetic waves besides light, such as waves, microwaves. The simplest linear polarizer is the wire-grid polarizer, which consists of many fine parallel wires that are placed in a plane perpendicular to the incident beam. Electromagnetic waves which have a component of their electric fields aligned parallel to the wires will induce the movement of electrons along the length of the wires, for waves with electric fields perpendicular to the wires, the electrons cannot move very far across the width of each wire. Therefore, little energy is reflected and the incident wave is able to pass through the grid, in this case the grid behaves like a dielectric material. Overall, this causes the wave to be linearly polarized with an electric field that is completely perpendicular to the wires. The hypothesis that the waves slip through the gaps between the wires is incorrect, for practical purposes, the separation between wires must be less than the wavelength of the incident radiation. In addition, the width of each wires should be compared to the spacing between wires. Therefore, it is easy to construct wire-grid polarizers for microwaves, far-infrared. In addition, advanced techniques can also build very tight pitch metallic grids. Since the degree of polarization depends little on wavelength and angle of incidence, certain crystals, due to the effects described by crystal optics, show dichroism, preferential absorption of light which is polarized in particular directions. They can therefore be used as linear polarizers, the best known crystal of this type is tourmaline. However, this crystal is used as a polarizer, since the dichroic effect is strongly wavelength dependent. Herapathite is also dichroic, and is not strongly coloured, but is difficult to grow in large crystals, a Polaroid polarizing filter functions similarly on an atomic scale to the wire-grid polarizer. It was originally made of microscopic herapathite crystals and its current H-sheet form is made from polyvinyl alcohol plastic with an iodine doping. Stretching of the sheet during manufacture causes the PVA chains to align in one particular direction, valence electrons from the iodine dopant are able to move linearly along the polymer chains, but not transverse to them
4.
Photographic filter
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In photography and videography, a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. Sometimes they are used to make subtle changes to images. In monochrome photography coloured filters affect the brightness of different colours. Others change the balance of images, so that photographs under incandescent lighting show colours as they are perceived. There are filters that distort the image in a way, diffusing an otherwise sharp image, adding a starry effect. Linear and circular polarising filters reduce oblique reflections from non-metallic surfaces, many filters absorb part of the light available, necessitating longer exposure. As the filter is in the path, any imperfections—non-flat or non-parallel surfaces, reflections, scratches. There is no universal naming system for filters. The Wratten numbers adopted in the twentieth century by Kodak. Colour correction filters are often identified by a code of the form CC50Y—CC for colour correction,50 for the strength of the filter, photographic filters sell in larger quantities at correspondingly lower prices than many laboratory filters. The article on optical filters has material relevant to photographic filters, in digital photography the majority of filters used with film cameras have been rendered redundant by digital filters applied either in-camera or during post processing. Exceptions include the ultraviolet filter typically used to protect the front surface of the lens, the neutral density filter, the polarising filter, the only use of a clear filter is to protect the front of a lens. UV filters are used to block ultraviolet light, to which most photographic sensors. Normally, the glass or plastic of a lens is practically opaque to short-wavelength UV. A UV filter passes all or nearly all of the visible spectrum and it can be left on the lens for nearly all shots, UV filters are often used mainly for lens protection in the same way as clear filters. Strong UV filters are sometimes used for warming color photos taken in shade with daylight-type film. While in certain cases, such as harsh environments, a filter may be necessary. Arguments for the use of protection include, If the lens is dropped
5.
Photography
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Typically, a lens is used to focus the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a timed exposure. With an electronic sensor, this produces an electrical charge at each pixel. A negative image on film is used to photographically create a positive image on a paper base, known as a print. The word photography was created from the Greek roots φωτός, genitive of φῶς, light and γραφή representation by means of lines or drawing, several people may have coined the same new term from these roots independently. Johann von Maedler, a Berlin astronomer, is credited in a 1932 German history of photography as having used it in an article published on 25 February 1839 in the German newspaper Vossische Zeitung. Both of these claims are now widely reported but apparently neither has ever been confirmed as beyond reasonable doubt. Credit has traditionally given to Sir John Herschel both for coining the word and for introducing it to the public. Photography is the result of combining several technical discoveries, later Greek mathematicians Aristotle and Euclid also independently described a pinhole camera in the 5th and 4th centuries BCE. Daniele Barbaro described a diaphragm in 1566, wilhelm Homberg described how light darkened some chemicals in 1694. The fiction book Giphantie, published in 1760, by French author Tiphaigne de la Roche, the discovery of the camera obscura that provides an image of a scene dates back to ancient China. Leonardo da Vinci mentions natural camera obscura that are formed by dark caves on the edge of a sunlit valley, a hole in the cave wall will act as a pinhole camera and project a laterally reversed, upside down image on a piece of paper. So the birth of photography was primarily concerned with inventing means to capture, renaissance painters used the camera obscura which, in fact, gives the optical rendering in color that dominates Western Art. The camera obscura literally means dark chamber in Latin and it is a box with a hole in it which allows light to go through and create an image onto the piece of paper. Around the year 1800, British inventor Thomas Wedgwood made the first known attempt to capture the image in a camera obscura by means of a light-sensitive substance and he used paper or white leather treated with silver nitrate. The shadow images eventually darkened all over, the first permanent photoetching was an image produced in 1822 by the French inventor Nicéphore Niépce, but it was destroyed in a later attempt to make prints from it. Niépce was successful again in 1825, in 1826 or 1827, he made the View from the Window at Le Gras, the earliest surviving photograph from nature. Because Niépces camera photographs required a long exposure, he sought to greatly improve his bitumen process or replace it with one that was more practical. With an eye to eventual commercial exploitation, the partners opted for total secrecy, Daguerres efforts culminated in what would later be named the daguerreotype process
6.
Videography
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Videography refers to the process of capturing moving images on electronic media and even streaming media. The term includes methods of production and post-production. It was initially equivalent of cinematography, the advent of digital video recording in the late 20th century blurred the distinction between videography and cinematography, as in both methods the intermittent mechanism became the same. Nowadays, any work outside commercial motion picture production could be called videography. The word combines video from Latin, meaning I see or I apprehend, with the Greek terminal ending graphy and its contemporary sense is video writing or video recording. As the field progresses, videographers may produce their assets entirely on a computer without ever involving an imaging device, a videographer may be the actual camera operator or they may be the person in charge of the visual design of a production. One of the best known application is in workplace studies, the Sage Handbook of Visual Methods
7.
Camera
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Thumb|A2016 Nikon D810 A camera is an optical instrument for recording or capturing images, which may be stored locally, transmitted to another location, or both. The images may be individual still photographs or sequences of images constituting videos or movies, the camera is a remote sensing device as it senses subjects without physical contact. The word camera comes from camera obscura, which means dark chamber and is the Latin name of the device for projecting an image of external reality onto a flat surface. The modern photographic camera evolved from the camera obscura, the functioning of the camera is very similar to the functioning of the human eye. A camera may work with the light of the spectrum or with other portions of the electromagnetic spectrum. A still camera is a device which creates a single image of an object or scene. All cameras use the basic design, light enters an enclosed box through a converging lens/convex lens. A shutter mechanism controls the length of time that light can enter the camera, a display, often a liquid crystal display, permits the user to view scene to be recorded and settings such as ISO speed, exposure, and shutter speed. A movie camera or a video camera operates similarly to a camera, except it records a series of static images in rapid succession. When the images are combined and displayed in order, the illusion of motion is achieved, the forerunner to the photographic camera was the camera obscura. The oldest known record of this principle is a description by Han Chinese philosopher Mozi, Mozi correctly asserted that the camera obscura image is inverted because light travels in straight lines from its source. In the 11th century Arab physicist Ibn al-Haytham s wrote very influential essays about experiments with light through an opening in a darkened room. The use of a lens in the opening of a wall or closed window shutter of a room to project images used as a drawing aid has been traced back to circa 1550. Since the late 17th century portable camera obscura devices in tents, before the development of the photographic camera, it had been known for hundreds of years that some substances, such as silver salts, darkened when exposed to sunlight. The first person to use this chemistry to create images was Thomas Wedgwood, to create images, Wedgwood placed items, such as leaves and insect wings, on ceramic pots coated with silver nitrate, and exposed the set-up to light. These images werent permanent, however, as Wedgwood didnt employ a fixing mechanism and he ultimately failed at his goal of using the process to create fixed images created by a camera obscura. The first permanent photograph of an image was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles. Niépce had been experimenting with ways to fix the images of a camera obscura since 1816, the photograph Niépce succeeded in creating shows the view from his window
8.
Optical filter
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Filters mostly belong to one of two categories. The simplest, physically, is the filter, then there are interference or dichroic filters. Optical filters selectively transmit light in a range of wavelengths. They can usually pass long wavelengths only, short wavelengths only, or a band of wavelengths, the passband may be narrower or wider, the transition or cutoff between maximal and minimal transmission can be sharp or gradual. Optical filters are used in photography, in many optical instruments. Optical filters are essential in fluorescence applications such as fluorescence microscopy. Photographic filters are a case of optical filters, and much of the material here applies. Some photographic effect filters, such as star effect filters, are not relevant to scientific work, absorptive filters are usually made from glass to which various inorganic or organic compounds have been added. These compounds absorb some wavelengths of light while transmitting others, the compounds can also be added to plastic to produce gel filters, which are lighter and cheaper than glass-based filters. Alternately, dichroic filters can be made by coating a substrate with a series of optical coatings. Dichroic filters usually reflect the unwanted portion of the light and transmit the remainder, Dichroic filters use the principle of interference. Their layers form a series of reflective cavities that resonate with the desired wavelengths. Other wavelengths destructively cancel or reflect as the peaks and troughs of the waves overlap, Dichroic filters are particularly suited for precise scientific work, since their exact colour range can be controlled by the thickness and sequence of the coatings. They are usually more expensive and delicate than absorption filters. They can be used in such as the dichroic prism of a camera to separate a beam of light into different coloured components. The basic scientific instrument of this type is a Fabry–Pérot interferometer and it uses two mirrors to establish a resonating cavity. It passes wavelengths that are a multiple of the resonance frequency. Etalons are another variation, transparent cubes or fibers whose polished ends form mirrors tuned to resonate with specific wavelengths and these are often used to separate channels in telecommunications networks that use wavelength division multiplexing on long-haul optic fibers
9.
Camera lens
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A lens might be permanently fixed to a camera, or it might be interchangeable with lenses of different focal lengths, apertures, and other properties. While in principle a simple convex lens will suffice, in practice a compound made up of a number of optical lens elements is required to correct the many optical aberrations that arise. Some aberrations will be present in any lens system and it is the job of the lens designer to balance these and produce a design that is suitable for photographic use and possibly mass production. Typical rectilinear lenses can be thought of as improved pinhole lenses, as shown, a pinhole lens is simply a small aperture that blocks most rays of light, ideally selecting one ray to the object for each point on the image sensor. Here a pixel is the area of the detector exposed to light from a point on the object, making the pinhole smaller improves resolution, but reduces the amount of light captured. At a certain point, shrinking the hole does not improve the resolution because of the diffraction limit, beyond this limit, making the hole smaller makes the image blurrier as well as darker. Practical lenses can be thought of as an answer to the question how can a pinhole lens be modified to more light. A first step is to put a simple convex lens at the pinhole with a length equal to the distance to the film plane. The geometry is almost the same as with a pinhole lens. From the front of the camera, the hole, would be seen. If one were inside the camera, one would see the acting as a projector. The virtual image of the aperture from inside the camera is the exit pupil. Practical photographic lenses include more lens elements, a camera lens may be made from a number of elements, from one, as in the Box Brownies meniscus lens, to over 20 in the more complex zooms. These elements may themselves comprise a group of lenses cemented together, the front element is critical to the performance of the whole assembly. In all modern lenses the surface is coated to reduce abrasion, flare, and surface reflectance, to minimize aberration, the curvature is usually set so that the angle of incidence and the angle of refraction are equal. In a prime lens this is easy, but in a zoom there is always a compromise, the lens usually is focused by adjusting the distance from the lens assembly to the image plane, or by moving elements of the lens assembly. To improve performance, some lenses have a cam system that adjusts the distance between the groups as the lens is focused, manufacturers call this different things, Nikon calls it CRC, Canon calls it a floating system, and Hasselblad and Mamiya call it FLE. Glass is the most common used to construct lens elements, due to its good optical properties
10.
Monochrome photography
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Monochrome photography is photography where the image produced has a single hue, rather than recording the colors of the object that was photographed. It includes all forms of photography, which produce images containing tones of grey ranging from black to white. Other hues besides grey, such as sepia, cyan or brown can also be used in monochrome photography, monochrome photography is mostly used for artistic reasons in the contemporary world. Most modern black-and-white films, called panchromatic films, record the visible spectrum. Black-and-white photography is considered by some to be subtle and interpretive. Monochrome images are not direct renditions of their subjects, but are abstractions from reality, in computer terms, this is often called greyscale. Black-and-white photography is considered by some to add a more emotional touch to the subject, selenium toner produces a blue-black or purple image, similarly by converting silver into more stable silver selenide. Cyanotypes used iron salts rather than silver salts to create blue, monochrome images may be produced using black-and-white film or paper, or by manipulating color images using computer software. After software conversion to an image, one or more hues can replace the grey tones to emulate duotones, sepia. Black and White Film Information and Comparisons Chart
11.
Colour balance
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In photography and image processing, color balance is the global adjustment of the intensities of the colors. An important goal of this adjustment is to specific colors – particularly neutral colors – correctly. Hence, the method is sometimes called gray balance, neutral balance. Color balance changes the mixture of colors in an image and is used for color correction. Generalized versions of color balance are used to correct colors other than neutrals or to change them for effect. Image data acquired by sensors – either film or electronic image sensors – must be transformed from the values to new values that are appropriate for color reproduction or display. In film photography, color balance is achieved by using color correction filters over the lights or on the camera lens. It is particularly important that neutral colors in a scene appear neutral in the reproduction, most digital cameras have means to select color correction based on the type of scene lighting, using either manual lighting selection, automatic white balance, or custom white balance. The algorithms for these processes perform generalized chromatic adaptation, many methods exist for color balancing. Setting a button on a camera is a way for the user to indicate to the processor the nature of the scene lighting, another option on some cameras is a button which one may press when the camera is pointed at a gray card or other neutral colored object. This captures an image of the ambient light, which enables a digital camera to set the color balance for that light. There is a literature on how one might estimate the ambient lighting from the camera data. A variety of algorithms have been proposed, and the quality of these has been debated, a few examples and examination of the references therein will lead the reader to many others. Examples are Retinex, a neural network or a Bayesian method. Color balancing an image not only the neutrals, but other colors as well. An image that is not color balanced is said to have a color cast, Color balancing may be thought in terms of removing this color cast. Color balance is related to color constancy. Algorithms and techniques used to color constancy are frequently used for color balancing
12.
Exposure (photography)
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In photography, exposure is the amount of light per unit area reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. Exposure is measured in lux seconds, and can be computed from exposure value, in photographic jargon, an exposure generally refers to a single shutter cycle. For the same speed, the accumulated photometric exposure should be similar in both cases. A photograph may be described as underexposed when it has a loss of detail, that is. As the adjacent image shows, these terms are technical ones, there are three types of settings, manual, automatic and exposure compensation. Radiant exposure of a surface, denoted He and measured in J/m2, is given by H e = E e t, where Ee is the irradiance of the surface, measured in W/m2, t is the exposure duration, measured in s. Luminous exposure of a surface, denoted Hv and measured in lx⋅s, is given by H v = E v t, many photographic materials are also sensitive to invisible light, which can be a nuisance, or a benefit. The use of units is appropriate to characterize such sensitivity to invisible light. In sensitometric data, such as curves, the log exposure is conventionally expressed as log10. Photographers more familiar with base-2 logarithmic scales can convert using log2 ≈3.32 log10, correct exposure may be defined as an exposure that achieves the effect the photographer intended. A more technical approach recognises that a film has a physically limited useful exposure range. If, for any part of the photograph, the exposure is outside this range. In a very simple model, for example, out-of-range values would be recorded as black or white rather than the precisely graduated shades of colour and this ensures that no significant information is lost during capture. However, it is much easier to discard recorded information during post processing than to try to re-create unrecorded information. In a scene with strong or harsh lighting, the ratio between highlight and shadow luminance values may well be larger than the ratio between the maximum and minimum useful exposure values. A photograph may be described as underexposed when it has a loss of detail, that is. In manual mode, the photographer adjusts the lens aperture and/or shutter speed to achieve the desired exposure, manual exposure calculations may be based on some method of light metering with a working knowledge of exposure values, the APEX system and/or the Zone System. A camera in automatic exposure mode automatically calculates and adjusts exposure settings to match the subjects mid-tone to the mid-tone of the photograph, for most cameras this means using an on-board TTL exposure meter
13.
Kodak
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Eastman Kodak Company, commonly referred to as Kodak, is an American technology company that produces imaging products with its historic basis on photography. The company is headquartered in Rochester, New York and is incorporated in New Jersey, Kodak provides packaging, functional printing, graphic communications and professional services for businesses around the world. Its main business segments are Print Systems, Enterprise Inkjet Systems, Micro 3D Printing and Packaging, Software and Solutions and it is best known for photographic film products. Kodak was founded by George Eastman and Henry A, during most of the 20th century, Kodak held a dominant position in photographic film. The companys ubiquity was such that its Kodak moment tagline entered the lexicon to describe a personal event that was demanded to be recorded for posterity. Kodak began to struggle financially in the late 1990s, as a result of the decline in sales of photographic film, as a part of a turnaround strategy, Kodak began to focus on digital photography and digital printing, and attempted to generate revenues through aggressive patent litigation. In January 2012, Kodak filed for Chapter 11 bankruptcy protection in the United States District Court for the Southern District of New York. In February 2012, Kodak announced that it would stop making digital cameras, pocket video cameras and digital picture frames, in January 2013, the Court approved financing for Kodak to emerge from bankruptcy by mid 2013. Kodak sold many of its patents for approximately $525,000,000 to a group of companies under the names Intellectual Ventures, on September 3,2013, the company emerged from bankruptcy having shed its large legacy liabilities and exited several businesses. Personalized Imaging and Document Imaging are now part of Kodak Alaris, on March 12,2014, it announced that the board of directors elected Jeffrey J. Clarke as chief executive officer and a member of its board of directors. As late as 1976, Kodak commanded 90% of film sales, Japanese competitor Fujifilm entered the U. S. market with lower-priced film and supplies, but Kodak did not believe that American consumers would ever desert its brand. Kodak passed on the opportunity to become the film of the 1984 Los Angeles Olympics, Fuji won these sponsorship rights. Fuji opened a plant in the U. S. and its aggressive marketing. Fuji went from a 10% share in the early 1990s to 17% in 1997, fujis films soon also found a competitive edge in higher-speed negative films, with a tighter grain structure. The complaint was lodged by the United States with the World Trade Organization, on January 30,1998, the WTO announced a sweeping rejection of Kodaks complaints about the film market in Japan. Although Kodak developed a camera in 1975, the first of its kind. In the 1990s, Kodak planned a journey to move to digital technology. CEO George M. C. Fisher reached out to Microsoft, Apples pioneering QuickTake consumer digital cameras, introduced in 1994, had the Apple label but were produced by Kodak
14.
Color correction
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Without color correction gels, a scene may have a mix of various colors. Applying color correction gels in front of light sources can alter the color of the light sources to match. Mixed lighting can produce an undesirable aesthetic when displayed on a television or in a theatre, conversely, gels may also be used to make a scene appear more natural by simulating the mix of color temperatures that occur naturally. This application is useful, especially where motivated lighting is the goal, color gels may also be used to tint lights for artistic effect. The particular color of a light source can be simplified into a correlated color temperature. The higher the CCT, the bluer the light appears, sunlight at 5600K, for example, appears much bluer than tungsten light at 3200K. Unlike a chromaticity diagram, the Kelvin scale reduces the light sources color into one dimension, thus, light sources of the same CCT may appear green or magenta in comparison with one another. Fluorescent lights, for example, are very green in comparison with other types of lighting. However, some fluorescents are designed to have a high faithfulness to an ideal light and this dimension, along lines of constant CCT, is sometimes measured in terms of green–magenta balance, this dimension is sometimes referred to as tint or CC. The main color correction gels are CTB and CTO, a CTB gel converts tungsten light to daylight color. A CTO gel performs the reverse, note that different manufacturers gels yield slightly different colors. As well, there is no definition of the color of daylight since it varies depending on the location. Gels that remove the green cast of fluorescent lights are called minus green, gels that add a green cast are called plus green. Fractions such as 3/4, 1/2, 1/4, and 1/8 indicate the strength of a gel, a 1/2 CTO gel is half the strength of a CTO gel. Color filters may be applied over a lens to adjust its white balance. In video systems, white balance can be achieved by digital or electronic manipulation of the signal, however, some digital cinema cameras can record an image without any digital filtering applied. Using physical color correction filters to white balance can maximize the range of the captured image. Some professional cameras designed for ENG use filter wheels containing color correction filters and are designed to optimize performance for different color temperatures, in film cameras, no electronic or digital manipulation of white balance is possible in the original camera negative
15.
Astronomy
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Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets, while the phenomena include supernovae explosions, gamma ray bursts, more generally, all astronomical phenomena that originate outside Earths atmosphere are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe as a whole, Astronomy is the oldest of the natural sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, during the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the results and observations being used to confirm theoretical results. Astronomy is one of the few sciences where amateurs can play an active role, especially in the discovery. Amateur astronomers have made and contributed to many important astronomical discoveries, Astronomy means law of the stars. Astronomy should not be confused with astrology, the system which claims that human affairs are correlated with the positions of celestial objects. Although the two share a common origin, they are now entirely distinct. Generally, either the term astronomy or astrophysics may be used to refer to this subject, however, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics. Few fields, such as astrometry, are purely astronomy rather than also astrophysics, some titles of the leading scientific journals in this field includeThe Astronomical Journal, The Astrophysical Journal and Astronomy and Astrophysics. In early times, astronomy only comprised the observation and predictions of the motions of objects visible to the naked eye, in some locations, early cultures assembled massive artifacts that possibly had some astronomical purpose. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye, most of early astronomy actually consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon, the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the model of the Universe, or the Ptolemaic system. The Babylonians discovered that lunar eclipses recurred in a cycle known as a saros
16.
Dynamic range
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Dynamic range, abbreviated DR, DNR, or DYR is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and it is measured either as a ratio or as a base-10 or base-2 logarithmic value of the difference between the smallest and largest signal values, in parallel to the common usage for audio signals. The human senses of sight and hearing have a high dynamic range. A human is capable of hearing anything from a quiet murmur in a room to the sound of the loudest heavy metal concert. Such a difference can exceed 100 dB which represents a factor of 100,000 in amplitude, a human cannot perform these feats of perception at both extremes of the scale at the same time. The eyes take time to adjust to different light levels, the instantaneous dynamic range of human audio perception is similarly subject to masking so that, for example, a whisper cannot be heard in loud surroundings. In practice, it is difficult to achieve the full dynamic range experienced by humans using electronic equipment. For example, a good quality LCD has a range of around 1000,1. Paper reflectance can achieve a range of about 100,1. A professional ENG camcorder such as the Sony Digital Betacam achieves a range of greater than 90 dB in audio recording. A nighttime scene will usually contain duller colours and will often be lit with blue lighting, the dynamic range of human hearing is roughly 140 dB, varying with frequency, from the threshold of hearing to the threshold of pain. The dynamic range of music as normally perceived in a concert hall doesnt exceed 80 dB, the dynamic range differs from the ratio of the maximum to minimum amplitude a given device can record, as a properly dithered recording device can record signals well below the noise RMS amplitude. Digital audio with undithered 20-bit digitization is theoretically capable of 120 dB dynamic range, 24-bit digital audio calculates to 144 dB dynamic range. Multiple noise processes determine the noise floor of a system, noise can be picked up from microphone self-noise, preamp noise, wiring and interconnection noise, media noise, etc. Early 78 rpm phonograph discs had a range of up to 40 dB, soon reduced to 30 dB. Ampex tape recorders in the 1950s achieved 60 dB in practical usage, the peak of professional analog magnetic recording tape technology reached 90 dB dynamic range in the midband frequencies at 3% distortion, or about 80 dB in practical broadband applications. The Dolby SR noise reduction gave a 20 dB further increased range resulting in 110 dB in the midband frequencies at 3% distortion. Specialized bias and record head improvements by Nakamichi and Tandberg combined with Dolby C noise reduction yielded 72 dB dynamic range for the cassette
17.
Vignetting
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In photography and optics, vignetting is a reduction of an images brightness or saturation at the periphery compared to the image center. The word vignette, from the root as vine, originally referred to a decorative border in a book. Later, the word came to be used for a portrait which is clear in the center. A similar effect occurs when photographing projected images or movies off a projection screen, vignetting is often an unintended and undesired effect caused by camera settings or lens limitations. However, it is deliberately introduced for creative effect, such as to draw attention to the center of the frame. A photographer may deliberately choose a lens which is known to produce vignetting to obtain the effect, when using superzoom lenses, vignetting may occur all along the zoom range, depending on the aperture and the focal length. However, it may not always be visible, except at the widest end, in these cases, vignetting may cause an exposure value difference of up to 0. 75EV. There are several causes of vignetting and this has the effect of changing the entrance pupil shape as a function of angle. Darkening can be gradual or abrupt – the smaller the aperture, when some points on an image receives no light at all due to mechanical vignetting, then this results in an restriction of the field of view – parts of the image are then completely black. This type of vignetting is caused by the dimensions of a multiple element lens. Rear elements are shaded by elements in front of them, which reduces the lens opening for off-axis incident light. The result is a decrease in light intensity towards the image periphery. Optical vignetting is sensitive to the aperture and can often be cured by a reduction in aperture of 2–3 stops. Unlike the previous types, natural vignetting is not due to the blocking of light rays, the falloff is approximated by the cos4 or cosine fourth law of illumination falloff. Here, the light falloff is proportional to the power of the cosine of the angle at which the light impinges on the film or sensor array. Wideangle rangefinder designs and the designs used in compact cameras are particularly prone to natural vignetting. Telephoto lenses, retrofocus wideangle lenses used on SLR cameras, a gradual grey filter or postprocessing techniques may be used to compensate for natural vignetting, as it cannot be cured by stopping down the lens. Some modern lenses are designed so that the light strikes the image parallel or nearly so
18.
Infrared cut-off filter
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Infrared cut-off filters, sometimes called IR filters or heat-absorbing filters, are designed to reflect or block mid-infrared wavelengths while passing visible light. They are often used in devices with bright incandescent light bulbs to prevent unwanted heating, there are also filters which are used in solid state video cameras to block IR due to the high sensitivity of many camera sensors to near-infrared light. These filters typically have a hue to them as they also sometimes block some of the light from the longer red wavelengths. Thus a blue filter makes the picture look blue, a black filter marginally allows more light in the blue wavelength to pass resulting in a slight shift of the color temperature of the photo to a cooler color. Because of this, the term IR filters is used to refer to filters that pass infrared light while completely blocking other wavelengths. However, in applications the term IR filter still can be used as a synonym of infrared cut-off filter. Unlike the eye, sensors based on silicon have sensitivities extending into the near-infrared, such sensors may extend to 1000 nm. Digital cameras are equipped with IR-blocking filters to prevent unnatural-looking images. IR-transmitting filters, or removal of factory IR-blocking filters, are used in infrared photography to pass infrared light and block visible. Such filters appear black to the eye, but are transparent when viewed with an IR sensitive device, such filters can be used both over color camera lenses, and to filter visible light from IR illumination sources. Such filter stock is most easily made available most simply by having any commercial color negative film developed after being exposed to light. The leaders of 35mm film are ideal for this, without wasting an entire roll of film, in the same way, visually opaque black color-positive film emulsions mounted in cardboard, as for routine slide projection, provide inexpensive cardboard-mounted infrared filters. Film sizes larger than 35 mm may be handled in the way for larger filter production. For astrophotography, many photogenic targets are bright in the far red, removal of factory filters increases sensitivity to such targets, and may also increase sharpness, as such filters may also include anti-aliasing filters. UV filter Cold mirror and Hot mirror Interference filter
19.
Neutral-density filter
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It can be a colorless or grey filter. The purpose of a standard photographic neutral-density filter is to reduce the amount of entering the lens. Doing so allows the photographer to select combinations of aperture, exposure time and this is done to achieve effects such as a shallower depth of field or motion blur of a subject in a wider range of situations and atmospheric conditions. For example, one wish to photograph a waterfall at a slow shutter speed to create a deliberate motion-blur effect. The photographer might determine that to obtain the effect, a shutter speed of ten seconds was needed. ND filters can also be used to reduce the depth of field of an image where otherwise not possible due to a shutter speed limit. The shutter speed would be selected by finding the desired blur from subject movement and that offset would then be the amount of stops needed in the ND filter to use for that scene. Examples of this use include, Blurring water motion, reducing depth of field in very bright light. When using a flash on a camera with a shutter, exposure time is limited to the maximal speed. Without an ND filter, this can result in the need to use f/8 or higher, using a wider aperture to stay below the diffraction limit. Reduce the visibility of moving objects, ND filters find applications in several high-precision laser experiments because the power of a laser cannot be adjusted without changing other properties of the laser light. Moreover, most lasers have a power setting at which they can be operated. To achieve the light attenuation, one or more neutral-density filters can be placed in the path of the beam. Large telescopes can cause the Moon and planets to become too bright, a neutral-density filter can increase the contrast and cut down the brightness, making the Moon easier to view. A graduated ND filter is similar, except that the intensity varies across the surface of the filter and this is useful when one region of the image is bright and the rest is not, as in a picture of a sunset. The transition area, or edge, is available in different variations, the most common is a soft edge and provides a smooth transition from the ND side and the clear side. Hard-edge filters have a transition from ND to clear. Another type of ND filter configuration is the ND-filter wheel and it consists of two perforated glass disks that have progressively denser coating applied around the perforation on the face of each disk
20.
Graduated neutral-density filter
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A graduated neutral-density filter, also known as a graduated ND filter, split neutral-density filter, or just a graduated filter, is an optical filter that has a variable light transmission. Typically half of the filter is of neutral density which transitions, either abruptly or gradually and it is used to bring an overly-bright part of a scene into the dynamic range of film or sensor. For example, it can be used to darken a bright sky so that both the sky and subject can be properly exposed. ND filters can come in a variety of shapes and sizes and densities and can be used in all types of applications from still photography, motion photography. Center-spot filters are ND graduated filters that are opaque in the center and are clear at edges. These are used for special effects or to compensate for light falloff that is natural with large optics, Graduated filters were used in the early twentieth century, for example for darkening skies in landscape photos. One advertised brand was called the Lifa graduated filters for sky, cloud and these sky filters were not necessarily neutral, since they were used for black-and-white photography, and sometimes used a yellow top half to darken blue skies more. In a discussion at the Royal Photographic Society in 1910, some held the use of such graduated color screens to be quite limited. In more modern times, the use of graduated ND filters was popularized by Galen Rowell, Singh-Ray sold them as The Singh-Ray set of 4 Galen Rowell Graduated Neutral-Density Filters. A soft edge is a wider, smoother change from light to dark and this is used when the light and dark portions are not distinctly separated, such as a mountain and sky. A soft edge filter is less noticeable than a hard edge and it also has the benefit of making the sky more intense, darkening the sky the closer on the top. Below is a picture of what a hard edge and soft edge filter would look like and this method has the advantage that the shape of the mask can be freely defined in editing. The disadvantage is that it works with static subjects using a tripod
21.
Special effect
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Special effects are illusions or visual tricks used in the film, television, theatre, video game, and simulator industries to simulate the imagined events in a story or virtual world. Special effects are divided into the categories of optical effects. Mechanical effects are usually accomplished during the live-action shooting and this includes the use of mechanized props, scenery, scale models, animatronics, pyrotechnics and atmospheric effects, creating physical wind, rain, fog, snow, clouds, etc. Making a car appear to drive by itself and blowing up a building are examples of mechanical effects, mechanical effects are often incorporated into set design and makeup. For example, a set may be built with doors or walls to enhance a fight scene. An optical effect might be used to place actors or sets against a different background, since the 1990s, computer generated imagery has come to the forefront of special effects technologies. It gives filmmakers greater control, and allows many effects to be accomplished safely and convincingly and—as technology improves—at lower costs. As a result, many optical and mechanical effects techniques have been superseded by CGI, in 1857, Oscar Rejlander created the worlds first special effects movie by combining different sections of 30 negatives into a single image. In 1895, Alfred Clark created what is accepted as the first-ever motion picture special effect. While filming a reenactment of the beheading of Mary, Queen of Scots, as the executioner brought the axe above his head, Clark stopped the camera, had all of the actors freeze, and had the person playing Mary step off the set. He placed a Mary dummy in the place, restarted filming. Techniques like these would dominate the production of special effects for a century and it wasnt only the first use of trickery in cinema, it was also the first type of photographic trickery only possible in a motion picture, i. e. the stop trick. Georges Méliès accidentally discovered the same stop trick, according to Méliès, his camera jammed while filming a street scene in Paris. When he screened the film, he found that the trick had caused a truck to turn into a hearse, pedestrians to change direction. Because of his ability to manipulate and transform reality with the cinematograph. From 1910 to 1920, the innovations in special effects were the improvements on the matte shot by Norman Dawn. With the original matte shot, pieces of cardboard were placed to block the exposure of the film, Dawn combined this technique with the glass shot. Rather than using cardboard to block certain areas of the film exposure, from the partially exposed film, a single frame is then projected onto an easel, where the matte is then drawn
22.
Close-up filter
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In photography, a close-up filter, close-up lens or macro filter is a simple secondary lens used to enable macro photography without requiring a specialised primary lens. They work identically to reading glasses, allowing any primary lens to focus more closely, some manufacturers refer to their close-up lenses as diopters, after the unit of measurement of their optical power. Close-up lenses are usually specified by their power, the reciprocal of the focal length in meters. This is the working distance at which you will be able to take a picture with the close-up lens. It suffices to divide 1 by D, the value of the close-up lens, to get this maximal working distance in meters. A +3 filter will have a working distance of 0.333 m or 333 mm. Given the small size of most sensors a 20 mm insect will almost fill the frame at this magnification, using a zoom lens makes it easy to frame the subject as desired. This is the working distance at which you will be able to take a picture with the close-up lens. For example, a lens that can focus at 1.5 m combined with a +3 diopter close up lens will give a closest working distance of 1. 5/ =0.273 m. The magnification reached in those conditions is given by following formula, in the example above, the gain of magnification at Xmin will be =5.5. It is at this Xmin distance that you will get the highest magnification, to use a close up filter it is important to know those maximal and minimal distances, because only if you are within that range it will be possible to take a shot. There is not much of a range between the minimum and maximum values and the difference in magnification is quite moderate also. To use the filters for animals the size of the animal will determine the working distance, the close up filters are most effective with long focal length objectives and using a zoom lens is very practical to have some flexibility in the magnification. A good technique for sharp focussing is to take a picture at a focal length first to have optimal sharpness at the essential details. Photographic filter#Close-up and split diopter lenses Deep focus Close focus Close-up lenses technique
23.
Ultraviolet
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Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation constitutes about 10% of the light output of the Sun. It is also produced by electric arcs and specialized lights, such as lamps, tanning lamps. Consequently, the effects of UV are greater than simple heating effects. Suntan, freckling and sunburn are familiar effects of over-exposure, along with risk of skin cancer. Living things on dry land would be damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earths atmosphere. More-energetic, shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has both beneficial and harmful to human health. Ultraviolet rays are invisible to most humans, the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, near-UV radiation is visible to some insects, mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays, this gives birds true UV vision, reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow. UV also allows mammals to see urine trails, which is helpful for animals to find food in the wild. The males and females of some species look identical to the human eye. Ultraviolet means beyond violet, violet being the color of the highest frequencies of visible light, Ultraviolet has a higher frequency than violet light. He called them oxidizing rays to emphasize chemical reactivity and to them from heat rays. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, in 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm, in 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is absorbed by air, was made in 1893 by the German physicist Victor Schumann
24.
Visible spectrum
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The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called light or simply light. A typical human eye will respond to wavelengths from about 390 to 700 nm, in terms of frequency, this corresponds to a band in the vicinity of 430–770 THz. The spectrum does not, however, contain all the colors that the human eyes, unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can be made only by a mix of multiple wavelengths. Colors containing only one wavelength are called pure colors or spectral colors. Visible wavelengths pass through the window, the region of the electromagnetic spectrum that allows wavelengths to pass largely unattenuated through the Earths atmosphere. An example of this phenomenon is that clean air scatters blue light more than red wavelengths, the optical window is also referred to as the visible window because it overlaps the human visible response spectrum. The near infrared window lies just out of the vision, as well as the Medium Wavelength IR window. In the 13th century, Roger Bacon theorized that rainbows were produced by a process to the passage of light through glass or crystal. In the 17th century, Isaac Newton discovered that prisms could disassemble and reassemble white light and he was the first to use the word spectrum in this sense in print in 1671 in describing his experiments in optics. The result is red light is bent less sharply than violet as it passes through the prism. Newton divided the spectrum into seven named colors, red, orange, yellow, green, blue, indigo, the human eye is relatively insensitive to indigos frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some commentators, including Isaac Asimov, have suggested that indigo should not be regarded as a color in its own right. However, the evidence indicates that what Newton meant by indigo, comparing Newtons observation of prismatic colors to a color image of the visible light spectrum shows that indigo corresponds to what is today called blue, whereas blue corresponds to cyan. In the 18th century, Goethe wrote about optical spectra in his Theory of Colours, Goethe used the word spectrum to designate a ghostly optical afterimage, as did Schopenhauer in On Vision and Colors. Goethe argued that the spectrum was a compound phenomenon. Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow, the spectrum appears only when these edges are close enough to overlap. Young was the first to measure the wavelengths of different colors of light, the connection between the visible spectrum and color vision was explored by Thomas Young and Hermann von Helmholtz in the early 19th century
25.
Purple fringing
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In photography, and particularly in digital photography, purple fringing is the term for an out-of-focus purple or magenta ghost image on a photograph. This defect is generally most visible as a coloring and lightening of dark edges adjacent to areas of broad-spectrum illumination. Lenses in general exhibit axial chromatic aberration in which different colors of light do not focus in the same plane, normally, lens designs are optimized so that two or more wavelengths of light in the visible range focus at the same plane. Lens performance may be poor for such wavelengths in other ways too, most film has relatively low sensitivity to colors outside the visible range, so light spread in the near ultraviolet or near infrared rarely has a significant impact on the image recorded. However, sensors used in digital cameras commonly are sensitive to a range of wavelengths. Bright cloudy or hazy skies are strong sources of scattered violet and UV light, the term purple fringe used to describe one aspect of chromatic aberration dates back to at least 1833. However, Brewsters description with a fringe on one edge. A general defocus of the shortest wavelengths resulting in a fringe on all sides of a bright object is the result of an axial or longitudinal chromatic aberration. Quite often these effects are mixed in an image, purple fringing is usually attributed to chromatic aberration as described above, although it is not clear that all purple fringing can be explained this way. Shoot with a Haze-2A or other strong UV-cut filter, post-processing to remove purple fringing usually involves scaling the fringed colour channel, or subtracting some of a scaled version of the blue channel, or other blue-channel tricks
26.
Digital camera
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A digital camera or digicam is a camera that produces digital images that can be stored in a computer, displayed on a screen and printed. Most cameras sold today are digital, and digital cameras are incorporated into many devices ranging from PDAs, Digital and movie cameras share an optical system, typically using a lens with a variable diaphragm to focus light onto an image pickup device. The diaphragm and shutter admit the correct amount of light to the imager, just as with film, however, unlike film cameras, digital cameras can display images on a screen immediately after being recorded, and store and delete images from memory. Many digital cameras can also record moving videos with sound, some digital cameras can crop and stitch pictures and perform other elementary image editing. The history of the camera began with Eugene F. Lally of the Jet Propulsion Laboratory. His 1961 idea was to take pictures of the planets and stars while travelling through space to give information about the astronauts position, unfortunately, as with Texas Instruments employee Willis Adcocks filmless camera in 1972, the technology had yet to catch up with the concept. Steven Sasson as an engineer at Eastman Kodak invented and built the first electronic camera using a charge-coupled device image sensor in 1975, earlier ones used a camera tube, later ones digitized the signal. Early uses were military and scientific, followed by medical. In the mid to late 1990s digital cameras became common among consumers, by the mid-2000s digital cameras had largely replaced film cameras, and higher-end cell phones had an integrated digital camera. By the beginning of the 2010s, almost all smartphones had a digital camera. The two major types of image sensor are CCD and CMOS. A CCD sensor has one amplifier for all the pixels, while each pixel in a CMOS active-pixel sensor has its own amplifier, compared to CCDs, CMOS sensors use less power. Cameras with a small sensor use a back-side-illuminated CMOS sensor, overall final image quality is more dependent on the image processing capability of the camera, than on sensor type. The resolution of a camera is often limited by the image sensor that turns light into that discrete signals. The brighter the image at a point on the sensor. Depending on the structure of the sensor, a color filter array may be used. The number of pixels in the sensor determines the cameras pixel count, in a typical sensor, the pixel count is the product of the number of rows and the number of columns. For example, a 1,000 by 1,000 pixel sensor would have 1,000,000 pixels, final quality of an image depends on all optical transformations in the chain of producing the image
27.
Lens flare
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Lens flare refers to a phenomenon wherein light is scattered or flared in a lens system, often in response to a bright light, producing a desirable effect on the image. This happens through unintentional image formation mechanisms, such as internal reflection, lenses with large numbers of elements such as zooms tend to exhibit greater lens flare, as they contain multiple surfaces at which unwanted internal scattering occurs. These mechanisms differ from the image formation mechanism, which depends on rays from the refraction of the image itself. Flare manifests itself in two ways, as visible artifacts, and as a haze across the image, the haze makes the image look washed out by reducing contrast and color saturation. Visible artifacts, usually in the shape of the iris, are formed when light follows a pathway through the lens that contains one or more reflections from the lens surfaces. Flare is particularly caused by bright light sources. Most commonly, this occurs when shooting into the sun, and is reduced by using a hood or other shade. For good-quality optical systems, and for most images, flare is an effect that is widely distributed across the image and thus not visible. The spatial distribution of the lens flare typically manifests as several starbursts, rings, the specific spatial distribution of the flare depends on the shape of the aperture of the image formation elements. For example, if the lens has a 6-bladed aperture, the flare may have a hexagonal pattern, such internal scattering is also present in the human eye, and manifests in an unwanted veiling glare most obvious when viewing very bright lights or highly reflective surfaces. In some situations, eyelashes can also create flare-like irregularities, although these are technically diffraction artifacts, when a bright light source is shining on the lens but not in its field of view, lens flare appears as a haze that washes out the image and reduces contrast. This can be avoided by shading the lens using a lens hoods, in a studio, a gobo or set of barn doors can be attached to the lighting to keep it from shining on the camera. Filters can be attached to the lens which will also minimise lens flare. When using a lens, as is common in analog cinematography. This is most commonly seen in car headlights in a dark scene, a lens flare is often deliberately used to invoke a sense of drama. For both of these reasons artificial lens flare is an effect in various graphics editing programs. Lens flare was one of the first special effects developed for computer graphics because it can be imitated using relatively simple means, more sophisticated rendering techniques have been developed based on ray tracing or photon mapping. S. Costume designer Rita Riggs purposefully would sometimes dress Bea Arthur in Maude in a red that would flare to make a statement, director J. J. Abrams added numerous lens flares to the 2009 film Star Trek by aiming powerful off-camera light sources at the lens
28.
Lens hood
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In photography, a lens hood or lens shade is a device used on the front end of a lens to block the Sun or other light source to prevent glare and lens flare. Lens hoods may also be used to protect the lens from scratches, the geometry of a lens hood is dependent on three things, the focal length of the lens, the size of the front lens element and the dimensions of the image sensor or film in the camera. Flare occurs when light strikes the front element of a lens. This stray light often comes from very bright light sources, such as the Sun, bright studio lights, if a light source is in the lens angle of view, a lens hood will hardly have any effect, but the light does not have to cause lens flare. It is sufficient that stray light from a light source enters the lens. Multi-layer coatings in newer lenses also help to reduce lens flare, the shape of a lens hood can vary from a plain cylindrical or conical section to a more complex shape, sometimes called a petal, tulip, or flower hood. These more complex shapes take into account the final images shape, the geometry of a lens hood is dependent on three things, focal length of the lens, size of the front lens element, dimensions of the image sensor or film in the camera. Ideally, lens hoods should increase in length, and therefore in efficiency, as the length of the lens increases. Lens hoods are more prominent in long focus lenses because they have a viewing angle than that of wide-angle lenses. For wide angle lenses, the length of the hood cannot be as long as those for telephoto lenses, maximum aperture also affects the shape of a lens hood. As the aperture gets larger the amount of light and consequentially the amount of the frame the sensor sees increases.8, correctly made rectangular or square lens hoods are generally more efficient than cylindrical or conical ones because those shapes closely resemble the shape of the photograph. The same also applies to petal lens hoods, for these types of lenses, only cylindrical or conical lens hoods will work effectively. In addition, lens hoods can offer some degree of protection for the lens due to the hood extending farther than the lens itself. Lens hoods with an extending bellows design can be adjusted for depth and this means that the depth can be increased when used on longer focal length lenses, and reduced as necessary for shorter focal length lenses. Rubber lens hoods are flexible and generally collapse for storage, however other lens hoods must be removed if these features are not available and length extension of the lens is not preferred during storage. Barn doors – similar device used for stage lights, lens cover Matte box – similar, adjustable device used in still photography and video
29.
Color temperature
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The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable color to that of the light source. Color temperature is a characteristic of light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, horticulture. Color temperature is conventionally expressed in kelvins, using the symbol K, Color temperatures over 5000 K are called cool colors, while lower color temperatures are called warm colors. The fact that warm lighting in this sense actually has a color temperature often leads to confusion. The color temperature of the radiation emitted from an ideal black body is defined as its surface temperature in kelvins. This permits the definition of a standard by which light sources are compared, to the extent that a hot surface emits thermal radiation but is not an ideal black-body radiator, the color temperature of the light is not the actual temperature of the surface. An incandescent lamps light is thermal radiation, and the bulb approximates an ideal black-body radiator and this means that the emitted radiation does not follow the form of a black-body spectrum. These sources are assigned what is known as a color temperature. CCT is the temperature of a black-body radiator which to human color perception most closely matches the light from the lamp. Because such an approximation is not required for incandescent light, the CCT for an incandescent light is simply its unadjusted temperature, the Sun closely approximates a black-body radiator. The effective temperature, defined by the radiative power per square unit, is about 5780 K. The color temperature of sunlight above the atmosphere is about 5900 K, as the Sun crosses the sky, it may appear to be red, orange, yellow or white depending on its position. The changing color of the Sun over the course of the day is mainly a result of scattering of light and is not due to changes in black-body radiation. The blue color of the sky is caused by Rayleigh scattering of the sunlight from the atmosphere, some early morning and evening light has a lower color temperature due to increased low-wavelength light scattering by the Tyndall effect. Daylight has a similar to that of a black body with a correlated color temperature of 6500 K or 5500 K. For colors based on theory, blue occurs at higher temperatures. This is the opposite of the cultural associations attributed to colors, in red is hot. For lighting building interiors, it is important to take into account the color temperature of illumination
30.
Tungsten
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Tungsten, also known as wolfram, is a chemical element with symbol W and atomic number 74. The word tungsten comes from the Swedish language tung sten, which translates to heavy stone. Its name in Swedish is volfram, however, in order to distinguish it from scheelite, a hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth almost exclusively in chemical compounds. It was identified as a new element in 1781, and first isolated as a metal in 1783 and its important ores include wolframite and scheelite. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the elements discovered, melting at 3,422 °C,6,192 °F. Its high density is 19.3 times that of water, comparable to that of uranium and gold, polycrystalline tungsten is an intrinsically brittle and hard material, making it difficult to work. However, pure single-crystalline tungsten is more ductile, and can be cut with a hard-steel hacksaw, tungstens many alloys have numerous applications, including incandescent light bulb filaments, X-ray tubes, electrodes in TIG welding, superalloys, and radiation shielding. Tungstens hardness and high density give it military applications in penetrating projectiles, tungsten compounds are also often used as industrial catalysts. Tungsten is the metal from the third transition series that is known to occur in biomolecules. It is the heaviest element known to be essential to any living organism, tungsten interferes with molybdenum and copper metabolism and is somewhat toxic to animal life. In its raw form, tungsten is a hard metal that is often brittle. If made very pure, tungsten retains its hardness, and becomes malleable enough that it can be worked easily and it is worked by forging, drawing, or extruding. Tungsten objects are commonly formed by sintering. Of all metals in pure form, tungsten has the highest melting point, lowest vapor pressure, although carbon remains solid at higher temperatures than tungsten, carbon sublimes, rather than melts, so tungsten is considered to have a higher melting point. Tungsten has the lowest coefficient of expansion of any pure metal. The low thermal expansion and high melting point and tensile strength of tungsten originate from strong covalent bonds formed between tungsten atoms by the 5d electrons, alloying small quantities of tungsten with steel greatly increases its toughness. Tungsten exists in two crystalline forms, α and β. The former has a cubic structure and is the more stable form
31.
Incandescent light bulb
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An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated to such a high temperature that it glows with visible light. The filament, heated by passing a current through it, is protected from oxidation with a glass or quartz bulb that is filled with inert gas or evacuated. In a halogen lamp, filament evaporation is prevented by a process that redeposits metal vapor onto the filament. The light bulb is supplied with current by feed-through terminals or wires embedded in the glass. Most bulbs are used in a socket which provides mechanical support, Incandescent bulbs are manufactured in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low manufacturing costs, the remaining energy is converted into heat. The luminous efficacy of an incandescent bulb is 16 lumens per watt. Some applications of the incandescent bulb deliberately use the heat generated by the filament, such applications include incubators, brooding boxes for poultry, heat lights for reptile tanks, infrared heating for industrial heating and drying processes, lava lamps, and the Easy-Bake Oven toy. In addressing the question of who invented the incandescent lamp, historians Robert Friedel and Paul Israel list 22 inventors of incandescent lamps prior to Joseph Swan, historian Thomas Hughes has attributed Edisons success to his development of an entire, integrated system of electric lighting. In 1761 Ebenezer Kinnersley demonstrated heating a wire to incandescence and it was not bright enough nor did it last long enough to be practical, but it was the precedent behind the efforts of scores of experimenters over the next 75 years. Over the first three-quarters of the 19th century many experimenters worked with various combinations of platinum or iridium wires, carbon rods, many of these devices were demonstrated and some were patented. In 1835, James Bowman Lindsay demonstrated a constant electric light at a meeting in Dundee. He stated that he could read a book at a distance of one, however, having perfected the device to his own satisfaction, he turned to the problem of wireless telegraphy and did not develop the electric light any further. His claims are not well documented, although he is credited in Challoner et al. with being the inventor of the Incandescent Light Bulb, in 1838, Belgian lithographer Marcellin Jobard invented an incandescent light bulb with a vacuum atmosphere using a carbon filament. In 1840, British scientist Warren de la Rue enclosed a coiled platinum filament in a vacuum tube, although a workable design, the cost of the platinum made it impractical for commercial use. In 1841, Frederick de Moleyns of England was granted the first patent for an incandescent lamp, in 1845, American John W. Starr acquired a patent for his incandescent light bulb involving the use of carbon filaments. He died shortly after obtaining the patent, and his invention was never produced commercially, little else is known about him. In 1851, Jean Eugène Robert-Houdin publicly demonstrated incandescent light bulbs on his estate in Blois and his light bulbs are on display in the museum of the Château de Blois
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Printing
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Printing is a process for reproducing text and images using a master form or template. The earliest examples include Cylinder seals and other such as the Cyrus Cylinder. The earliest known form of printing came from China dating to before 220 A. D. Later developments in printing include the type, first developed by Bi Sheng in China around 1040 AD. Johannes Gutenberg introduced mechanical movable type printing to Europe in the 15th century, modern large-scale printing is typically done using a printing press, while small-scale printing is done free-form with a digital printer. Though paper is the most common material, it is frequently done on metals, plastics, cloth. On paper it is carried out as a large-scale industrial process and is an essential part of publishing. Woodblock printing is a technique for printing text, images or patterns that was used widely throughout East Asia and it originated in China in antiquity as a method of printing on textiles and later on paper. As a method of printing on cloth, the earliest surviving examples from China date to before 220 A. D, the earliest surviving woodblock printed fragments are from China. They are of silk printed with flowers in three colours from the Han Dynasty and they are the earliest example of woodblock printing on paper appeared in the mid-seventh century in China. By the ninth century, printing on paper had taken off, by the tenth century,400,000 copies of some sutras and pictures were printed, and the Confucian classics were in print. A skilled printer could print up to 2,000 double-page sheets per day, Printing spread early to Korea and Japan, which also used Chinese logograms, but the technique was also used in Turpan and Vietnam using a number of other scripts. This technique then spread to Persia and Russia and this technique was transmitted to Europe via the Islamic world, and by around 1400 was being used on paper for old master prints and playing cards. However, Arabs never used this to print the Quran because of the limits imposed by Islamic doctrine, block printing, called tarsh in Arabic developed in Arabic Egypt during the ninth-tenth centuries, mostly for prayers and amulets. There is some evidence to suggest that these print blocks made from non-wood materials, possibly tin, lead, the techniques employed are uncertain, however, and they appear to have had very little influence outside of the Muslim world. Though Europe adopted woodblock printing from the Muslim world, initially for fabric, block printing later went out of use in Islamic Central Asia after movable type printing was introduced from China. Block printing first came to Europe as a method for printing on cloth, images printed on cloth for religious purposes could be quite large and elaborate. When paper became relatively easily available, around 1400, the medium transferred very quickly to small religious images
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Color printing
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Color printing or colour printing is the reproduction of an image or text in color. The additive combination of any two colors in roughly equal proportion gives rise to the perception of a secondary color. For example, red and green yields yellow, red and blue yields magenta, yellow, cyan and magenta are merely the basic secondary colors, unequal mixtures of the primaries give rise to perception of many other colors all of which may be considered tertiary. While there are techniques for reproducing images in color, specific graphic processes. In this type of industrial or commercial printing, the used to print full-color images. Four inks are used, three colors plus black. These ink colors are cyan, magenta, yellow and key, cyan can be thought of as minus-red, magenta as minus-green, and yellow as minus-blue. These inks are semi-transparent or translucent, where two such inks overlap on the paper due to sequential printing impressions, a primary color is perceived. For example, yellow overprinted by magenta yields red, the secondary or subtractive colors cyan, magenta and yellow may be considered primary by printers and watercolorists. Two graphic techniques are required to prepare images for four-color printing, in the pre-press stage, original images are translated into forms that can be used on a printing press, through color separation, and screening or halftoning. These steps make possible the creation of printing plates that can transfer color impressions to paper on printing presses based on the principles of lithography. An emerging method of printing is six-color process printing which adds orange and green to the traditional CMYK inks for a larger and more vibrant gamut. However, such alternate color systems still rely on color separation, halftoning, color printing can also involve as few as one color ink, or multiple color inks which are not the primary colors. Using a limited number of inks, or specific color inks in addition to the primary colors, is referred to as spot color printing. Generally, spot-color inks are specific formulations that are designed to print alone, the range of available spot color inks, much like paint, is nearly unlimited, and much more varied than the colors that can be produced by four-color-process printing. Spot-color inks range from pastels to intense fluorescents to reflective metallics. Color printing involves a series of steps, or transformations, to generate a quality color reproduction, the following sections focus on the steps used when reproducing a color image in CMYK printing, along with some historical perspective. Woodblock printing on textiles preceded printing on paper in both Asia and Europe, and the use of different blocks to produce patterns in color was common
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Black and white
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Black and white, often abbreviated B/W or B&W, and hyphenated black-and-white when used as an adjective, is any of several monochrome forms in visual arts. Black-and-white images are not usually starkly contrasted black and white and they combine black and white in a continuum producing a range of shades of gray. Even when most studios had the capability to make color films they were not heavily utilized as using the Technicolor process was expensive, for the years 1940–1966, a separate Academy Award for Best Art Direction was given for black-and-white movies along with one for color. Television, Television program was first transmitted in black-and-white, scottish inventor John Logie Baird demonstrated the worlds first color television transmission on July 3,1928 using a mechanical process. Some color broadcasts in the US began in the 1950s, with color becoming common in industrialized nations during the late 1960s. In the United States, the Federal Communications Commission settled on a color NTSC standard in 1953, color television became more widespread in the U. S. between 1963 and 1967, when the CBS and ABC networks joined NBC in broadcasting full color schedules. Canada began airing color television in 1966 while the United Kingdom began to use a different color system from July 1967 known as PAL. The Republic Of Ireland followed in 1970, in China, black and white television sets were the norm until as late as the 1990s, color TVs not outselling them until about 1989. While seldom used now, many consumer camcorders have the ability to record in black-and-white. Photography, Photographs were either black-and-white or shades of sepia, color photography was originally rare and expensive and again often containing inaccurate hues. Color photography became more common from the mid-20th century, Today, black-and-white is a niche market for photographers who use the medium for artistic purposes. This can take the form of film or digital conversion to grayscale. For amateur use certain companies such as Kodak manufactured black-and-white disposable cameras until 2009, also, certain films are produced today which give black-and-white images using the ubiquitous C41 color process. Printing press, Most American newspapers were black-and-white until the early 1980s, The New York Times, some claim that USA Today was the major impetus for the change to color. In the UK, color was only introduced from the mid-1980s. Even today, many newspapers restrict color photographs to the front, similarly, daily comic strips in newspapers were traditionally black-and-white with color reserved for Sunday strips. Sometimes color is reserved for the cover, magazines such as Jet magazine were either all or mostly black-and-white until the end of the 2000s when it became all-color. Manga are typically published in black-and-white although now it is part of its image, many school yearbooks are still entirely or mostly in black-and-white
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Contrast (vision)
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Contrast is the difference in luminance or colour that makes an object distinguishable. In visual perception of the world, contrast is determined by the difference in the color and brightness of the object. The human visual system is sensitive to contrast than absolute luminance. The maximum contrast of an image is the contrast ratio or dynamic range, the human contrast sensitivity function shows a typical band-pass filter shape peaking at around 4 cycles per degree with sensitivity dropping off either side of the peak. The high-frequency cut-off represents the optical limitations of the systems ability to resolve detail and is typically about 60 cycles per degree. The high-frequency cut-off is related to the density of the retinal photoreceptor cells. The low frequency drop-off is due to lateral inhibition within the ganglion cells. A typical retinal ganglion cell presents a centre region with either excitation or inhibition, one experimental phenomenon is the inhibition of blue in the periphery if blue light is displayed against white, leading to a yellow surrounding. The yellow is derived from the inhibition of blue on the surroundings by the center, since white minus blue is red and green, this mixes to become yellow. For example, in the case of computer displays, contrast depends on the properties of the picture source or file. For some screens the angle between the surface and the observers line of sight is also important. There are many definitions of contrast. Some include color, others do not, travnikova laments, Such a multiplicity of notions of contrast is extremely inconvenient. It complicates the solution of many applied problems and makes it difficult to compare the results published by different authors, various definitions of contrast are used in different situations. Here, luminance contrast is used as an example, but the formulas can also be applied to other physical quantities, in many cases, the definitions of contrast represent a ratio of the type Luminance difference Average luminance. The rationale behind this is that a difference is negligible if the average luminance is high. Below, some definitions are given. Weber contrast is defined as I − I b I b, with I and I b representing the luminance of the features, the measure is also referred to as Weber fraction, since it is the term that is constant in Webers Law
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Orthochromasia
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In chemistry, orthochromasia is the property of a dye or stain to not change color on binding to a target, as opposed to metachromatic stains which change color. The word is derived from the Greek orthos, and chromatic, toluidine blue is an example of a partially orthochromatic dye, as it stains nucleic acids by its orthochromatic color, but stains mast cell granules in its metachromatic color. In spectral terms, orthochromasia refers to maintaining the position of spectral peaks, while metachromasia refers to a shift in wavelength, in photography, an orthochromatic light spectrum is one devoid of red light. In biology, orthochromatic refers to the greyish staining because of acidophilic and basophilic mixture in the cell, orthochromatic photography refers to a photographic emulsion that is sensitive to only blue and green light, and thus can be processed with a red safelight. The increased blue sensitivity causes blue objects to appear lighter, a cyan lens filter can be used with standard panchromatic film to produce a similar effect. This work was extended by others including Josef Maria Eder, who introduced the use of the red dye erythrosine in 1884
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Color photography
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Color photography is photography that uses media capable of reproducing colors. By contrast, black-and-white photography records only a channel of luminance. In color photography, electronic sensors or light-sensitive chemicals record color information at the time of exposure, monochrome images which have been colorized by tinting selected areas by hand or mechanically or with the aid of a computer are colored photographs, not color photographs. Their colors are not dependent on the colors of the objects photographed. Color photography has been the dominant form of photography since the 1970s, Color photography was attempted beginning in the 1840s. Early experiments were directed at finding a substance which would assume the color of the light falling on it. Other experimenters, such as Edmond Becquerel, achieved better results, over the following several decades, renewed experiments along these lines periodically raised hopes and then dashed them, yielding nothing of practical value. Gabriel Lippmann is remembered as the inventor of a method for reproducing colors by photography, based on the interference phenomenon, in 1886 Lippmanns interest had turned to a method of fixing the colors of the solar spectrum on a photographic plate. By April 1892, he was able to report that he had succeeded in producing color images of a glass window, a group of flags, a bowl of oranges topped by a red poppy. He presented his theory of photography using the interference method in two papers to the Academy, one in 1894, the other in 1906. The named colors are somewhat arbitrary divisions imposed on the spectrum of visible light. The test subject was a bow made of ribbon with stripes of colors, apparently including red. Creating colors by mixing colored lights in various proportions is the method of color reproduction. LCD, LED, plasma and CRT color video displays all use this method and this is also known as the RGB color model. In photography, the dye colors are cyan, a greenish-blue which absorbs red, magenta, a purplish-pink which absorbs green, and yellow. The red-filtered image is used to create a dye image, the green-filtered image to create a magenta dye image. When the three dye images are superimposed they form a color image. This is also known as the CMYK color model, most commonly, three pigment images were first created separately by the so-called carbon process and then carefully combined in register
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Polarization (waves)
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Polarization is a parameter applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave the direction of the oscillation is transverse to the direction of motion of the wave, a simple example of a polarized transverse wave is vibrations traveling along a taut string for example in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a direction, horizontal direction. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, in some types of transverse waves the wave displacement is limited to a single direction, so these also dont exhibit polarization. For example, in waves in liquids the wave displacement of the particles is always in a vertical plane. In linear polarization the fields oscillate in a single direction, in circular or elliptical polarization the fields rotate at a constant rate in a plane as the wave travels. Polarized light can be produced by passing unpolarized light through a polarizing filter, some of these are used to make polarizing filters. Light is also partially polarized when it reflects from a surface, according to quantum mechanics, electromagnetic waves consist of particles called photons. When viewed in this way, the polarization of a wave is determined by a quantum mechanical property of photons called their spin. A photon has one of two spins, it can either spin in a right hand sense or a left hand sense about its direction of travel. Circularly polarized electromagnetic waves are composed of photons with one type of spin. Linearly polarized waves consist of numbers of right and left hand spinning photons. Polarization is an important parameter in areas of science dealing with transverse waves, such as optics, seismology, radio, especially impacted are technologies such as lasers, wireless and optical fiber telecommunications, and radar. And incoherent states can be modeled stochastically as a combination of such uncorrelated waves with some distribution of frequencies, phases. Considering a monochromatic wave of optical frequency f, let us take the direction of propagation as the z axis. Being a transverse wave the E and H fields must then contain components only in the x and y directions whereas Ez=Hz=0. Using complex notation, we understand the instantaneous electric and magnetic fields to be given by the real parts of the complex quantities occurring in the following equations. Here ex, ey, hx, and hy are complex numbers, in the second more compact form, as these equations are customarily expressed, these factors are described using the wavenumber k =2 π n / λ and angular frequency ω =2 π f
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Digital single-lens reflex camera
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A digital single-lens reflex camera is a digital camera that combines the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor, as opposed to photographic film. The reflex design scheme is the difference between a DSLR and other digital cameras. In the reflex design, light travels through the lens, then to a mirror that alternates to send the image to either the viewfinder or the image sensor, the alternative would be to have a viewfinder with its own lens, hence the term single lens for this design. By using only one lens, the viewfinder of a DSLR presents an image that will not perceptibly differ from what is captured by the cameras sensor, like SLRs DSLRs typically use interchangeable lenses with a proprietary lens mount. A movable mechanical mirror system is switched down to light from the lens over a matte focusing screen via a condenser lens. Most of the entry-level DSLRs use a instead of the traditional pentaprism. Focusing can be manual or automatic, activated by pressing half-way on the release or a dedicated AF button. DSLRs typically use autofocus based on phase detection and this method allows the optimal lens position to be calculated, rather than found, as would be the case with autofocus based on contrast maximisation. Phase-detection autofocus is typically faster than other passive techniques, as the phase sensor requires the same light going to the image sensor, it was previously only possible with an SLR design. Digital SLR cameras, along with most other cameras, generally have a mode dial to access standard camera settings or automatic scene-mode settings. Sometimes called a PASM dial, they typically provide such as program, aperture-priority, shutter-priority. Scene modes vary from camera to camera, and these modes are inherently less customizable and they often include landscape, portrait, action, macro, night, and silhouette, among others. However, these different settings and shooting styles that scene mode provides can be achieved by calibrating certain settings on the camera, professional DSLRs seldom contain automatic scene modes as professionals often do not require these and professionals know how to achieve the looks they want. A method to prevent dust entering the chamber, by using a dust cover filter right behind the mount, was used by Sigma in its first DSLR. Olympus used a built-in sensor cleaning mechanism in its first DSLR that had a sensor exposed to air, several Canon DSLR cameras rely on dust reduction systems based on vibrating the sensor at ultrasonic frequencies to remove dust from the sensor. Interchangeable lenses for SLRs and DSLRs are built to operate correctly with a lens mount that is generally unique to each brand. There are also lens adapters that allow a lens for one mount to be used on a camera body with a different lens mount. Many lenses are mountable, diaphragm-and-meter-compatible, on modern DSLRs and on older film SLRs that use the lens mount
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Diffraction
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Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of shadow of the obstacle. In classical physics, the phenomenon is described as the interference of waves according to the Huygens–Fresnel principle. These characteristic behaviors are exhibited when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. Similar effects occur when a wave travels through a medium with a varying refractive index. Diffraction occurs with all waves, including sound waves, water waves, since physical objects have wave-like properties, diffraction also occurs with matter and can be studied according to the principles of quantum mechanics. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record observations of the phenomenon in 1660. If the obstructing object provides multiple, closely spaced openings, a pattern of varying intensity can result. This is due to the addition, or interference, of different parts of a wave that travel to the observer by different paths, the formalism of diffraction can also describe the way in which waves of finite extent propagate in free space. For example, the profile of a laser beam, the beam shape of a radar antenna. The effects of diffraction are often seen in everyday life and this principle can be extended to engineer a grating with a structure such that it will produce any diffraction pattern desired, the hologram on a credit card is an example. Diffraction in the atmosphere by small particles can cause a ring to be visible around a bright light source like the sun or the moon. A shadow of an object, using light from a compact source. The speckle pattern which is observed when laser light falls on a rough surface is also a diffraction phenomenon. When deli meat appears to be iridescent, that is diffraction off the meat fibers, all these effects are a consequence of the fact that light propagates as a wave. Diffraction can occur with any kind of wave, ocean waves diffract around jetties and other obstacles. Sound waves can diffract around objects, which is why one can hear someone calling even when hiding behind a tree. Diffraction can also be a concern in some applications, it sets a fundamental limit to the resolution of a camera, telescope
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Prism
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In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. At least two of the surfaces must have an angle between them. The exact angles between the surfaces depend on the application, the traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use prism usually refers to this type. Some types of optical prism are not in fact in the shape of geometric prisms, prisms can be made from any material that is transparent to the wavelengths for which they are designed. Typical materials include glass, plastic and fluorite, a dispersive prism can be used to break light up into its constituent spectral colors. Furthermore, prisms can be used to light, or to split light into components with different polarizations. Light changes speed as it moves from one medium to another and this speed change causes the light to be refracted and to enter the new medium at a different angle. The degree of bending of the lights path depends on the angle that the incident beam of light makes with the surface, the refractive index of many materials varies with the wavelength or color of the light used, a phenomenon known as dispersion. This causes light of different colors to be refracted differently and to leave the prism at different angles and this can be used to separate a beam of white light into its constituent spectrum of colors. Prisms will generally disperse light over a larger frequency bandwidth than diffraction gratings. Furthermore, prisms do not suffer from complications arising from overlapping spectral orders, prisms are sometimes used for the internal reflection at the surfaces rather than for dispersion. If light inside the prism hits one of the surfaces at a steep angle, total internal reflection occurs. This makes a prism a useful substitute for a mirror in some situations, ray angle deviation and dispersion through a prism can be determined by tracing a sample ray through the element and using Snells law at each interface. For the prism shown at right, the angles are given by θ0 ′ = arcsin θ1 = α − θ0 ′ θ1 ′ = arcsin θ2 = θ1 ′ − α. All angles are positive in the shown in the image. For a prism in air n 0 = n 2 ≃1 and this allows the nonlinear equation in the deviation angle δ to be approximated by δ ≈ θ0 − α + = θ0 − α + n α − θ0 = α. The deviation angle depends on wavelength through n, so for a thin prism the deviation angle varies with wavelength according to δ ≈ α, before Isaac Newton, it was believed that white light was colorless, and that the prism itself produced the color. It was only later that Young and Fresnel combined Newtons particle theory with Huygens wave theory to show that color is the manifestation of lights wavelength
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Image sensor
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An image sensor or imaging sensor is a sensor that detects and conveys the information that constitutes an image. It does so by converting the variable attenuation of light waves into signals, the waves can be light or other electromagnetic radiation. As technology changes, digital imaging tends to replace analog imaging, early analog sensors for visible light were video camera tubes. Currently, used types are semiconductor charge-coupled devices or active pixel sensors in complementary metal–oxide–semiconductor or N-type metal-oxide-semiconductor technologies, analog sensors for invisible radiation tend to involve vacuum tubes of various kinds. Digital sensors include flat panel detectors, today, most digital cameras use a CMOS sensor, because CMOS sensors perform better than CCDs. An example is the fact that they incorporate an integrated circuit, CCD is still in use for cheap low entry cameras, but weak in burst mode. Both types of sensor accomplish the task of capturing light. Each cell of a CCD image sensor is an analog device, when light strikes the chip it is held as a small electrical charge in each photo sensor. This process is repeated until all the lines of pixels have had their charge amplified. A CMOS image sensor has an amplifier for each compared to the few amplifiers of a CCD. Some CMOS imaging sensors also use Back-side illumination to increase the number of photons that hit the photodiode, CMOS sensors can potentially be implemented with fewer components, use less power, and/or provide faster readout than CCD sensors. They are also vulnerable to static electricity discharges. Another approach is to utilize the very fine dimensions available in modern CMOS technology to implement a CCD like structure entirely in CMOS technology and this can be achieved by separating individual poly-silicon gates by a very small gap. These hybrid sensors are still in the phase and can potentially harness the benefits of both CCD and CMOS imagers. There are many parameters that can be used to evaluate the performance of a sensor, including dynamic range, signal-to-noise ratio. For sensors of comparable types, the ratio and dynamic range improve as the size increases. In order to avoid interpolated color information, techniques like color co-site sampling use a mechanism to shift the color sensor in pixel steps. 3CCD, using three discrete image sensors, with the color separation done by a dichroic prism, while in general digital cameras use a flat sensor, Sony prototyped a curved sensor in 2014 to reduce/eliminate Petzval field curvature that occurs with a flat sensor
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Accessory lens
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In photography, a secondary lens is a lens designed to be used in conjunction with another lens, called the primary lens. A secondary lens may be designed to be used either in front of the primary lens, secondary lenses are typically simpler in mechanical design than other photographic lenses. Normally but not always there is no provision for control of focus or aperture, the most common secondary lens used behind the primary lens is the teleconverter. A typical teleconverter has a male and a lens mount of the same type. The resulting combination has a focal length than the primary lens alone. Any device similar to a designed to use the primary lens for wider angles than those for which it is designed is therefore likely to cause vignetting. Specialised secondary lenses may be used behind the lens to adapt a lens of one camera system and/or film format to another. These are called active adaptors or converters
