1.
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
2.
Rotary disc shutter
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A rotary disc shutter is a type of shutter. It is notably used in motion picture cameras, rotary shutters are semicircular discs that spin in front of the film gate, alternately allowing light from the lens to strike the film, or blocking it. When blocking the light, the portion of the film is advanced. The spinning disc then exposes the new frame of film, the nature of light-sensitive film requires a shutter to block the light and prevent smearing of the image as the film is advanced through the camera. Digital sensors do not require a rotary shutter, although some digital cinema cameras do have them. On more advanced cameras the open portion of the shutter can be adjusted and this shutter setting is referred to as the shutter angle. Adjusting the shutter angle controls the proportion of time that the film is exposed to light during each frame interval, the angle of the shutter forms a proportion to the time that each frame of film is exposed, Shutter Angle 360 ∘ = Exposure Time Frame Interval. The primary reason that cinematographers adjust the angle is to control the amount of motion blur that is recorded on each successive frame of film. A tight shutter angle will constrict motion blur, a wide shutter angle will allow it. A 180° shutter angle is considered normal, so for instance, at 24 fps the frame Interval value is 0.04167 second. Using an exposure time of 1/50 second gives a shutter angle value of 173° and this is the reason for the rule-of-thumb Use an exposure time twice the value of the frames-per-second to get normal motion blur. Tight shutters create a stuttering stop-motion animation look that has become popular in action, in particular, tight shutters are used to capture particles flying through the air, such as dirt from an exploding mortar. On most film cameras the shutter angle is changed by removing the lens and this cannot be done while the camera is operating. Some cameras such as the Arriflex 435ES can modify their shutter angle during the shot and this is sometimes referred to as an electronic shutter. An electronic shutter can compensate for the change caused by a speed ramp without changing the aperture. Other types of shutter adjustments, such as an out-of-phase shutter, normally the film is held steady in the gate whenever it is exposed to light. Special shutter adjustments allow the film to be exposed while the mechanism is actually moving the film to the next frame. In the film Saving Private Ryan, cinematographer Janusz Kamiński used such an adjustment to give his film the look of World War II newsreel photography
3.
Film speed
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Film speed is the measure of a photographic films sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system. A closely related ISO system is used to measure the sensitivity of digital imaging systems, highly sensitive films are correspondingly termed fast films. In both digital and film photography, the reduction of exposure corresponding to use of higher sensitivities generally leads to reduced image quality, in short, the higher the sensitivity, the grainier the image will be. Ultimately sensitivity is limited by the efficiency of the film or sensor. The speed of the emulsion was then expressed in degrees Warnerke corresponding with the last number visible on the plate after development. Each number represented an increase of 1/3 in speed, typical speeds were between 10° and 25° Warnerke at the time. The concept, however, was built upon in 1900 by Henry Chapman Jones in the development of his plate tester. In their system, speed numbers were inversely proportional to the exposure required, for example, an emulsion rated at 250 H&D would require ten times the exposure of an emulsion rated at 2500 H&D. The methods to determine the sensitivity were later modified in 1925, the H&D system was officially accepted as a standard in the former Soviet Union from 1928 until September 1951, when it was superseded by GOST 2817-50. The Scheinergrade system was devised by the German astronomer Julius Scheiner in 1894 originally as a method of comparing the speeds of plates used for astronomical photography, Scheiners system rated the speed of a plate by the least exposure to produce a visible darkening upon development. ≈2 The system was extended to cover larger ranges and some of its practical shortcomings were addressed by the Austrian scientist Josef Maria Eder. Scheiners system was abandoned in Germany, when the standardized DIN system was introduced in 1934. In various forms, it continued to be in use in other countries for some time. The DIN system, officially DIN standard 4512 by Deutsches Institut für Normung, was published in January 1934, International Congress of Photography held in Dresden from August 3 to 8,1931. The DIN system was inspired by Scheiners system, but the sensitivities were represented as the base 10 logarithm of the sensitivity multiplied by 10, similar to decibels. Thus an increase of 20° represented an increase in sensitivity. ≈3 /10 As in the Scheiner system, speeds were expressed in degrees, originally the sensitivity was written as a fraction with tenths, where the resultant value 1.8 represented the relative base 10 logarithm of the speed. Tenths were later abandoned with DIN4512, 1957-11, and the example above would be written as 18° DIN, the degree symbol was finally dropped with DIN4512, 1961-10
4.
F-number
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The f-number of an optical system such as a camera lens is the ratio of the systems focal length to the diameter of the entrance pupil. It is a number that is a quantitative measure of lens speed. It is also known as the ratio, f-ratio, f-stop. The f-number is commonly indicated using a hooked f with the format f/N, the f-number N or f# is given by, N = f D where f is the focal length, and D is the diameter of the entrance pupil. It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the pupil diameter in terms of f and N. Ignoring differences in light transmission efficiency, a lens with a greater f-number projects darker images, the brightness of the projected image relative to the brightness of the scene in the lenss field of view decreases with the square of the f-number. Doubling the f-number decreases the brightness by a factor of four. To maintain the same photographic exposure when doubling the f-number, the time would need to be four times as long. Most lenses have a diaphragm, which changes the size of the aperture stop. The entrance pupil diameter is not necessarily equal to the aperture stop diameter, a 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A200 mm focal length f/4 lens has a pupil diameter of 50 mm. The 200 mm lenss entrance pupil has four times the area of the 100 mm lenss entrance pupil, a T-stop is an f-number adjusted to account for light transmission efficiency. The word stop is sometimes confusing due to its multiple meanings, a stop can be a physical object, an opaque part of an optical system that blocks certain rays. In photography, stops are also a used to quantify ratios of light or exposure. The one-stop unit is known as the EV unit. On a camera, the setting is traditionally adjusted in discrete steps. Each stop is marked with its corresponding f-number, and represents a halving of the light intensity from the previous stop. This corresponds to a decrease of the pupil and aperture diameters by a factor of 1/2 or about 0.7071, each element in the sequence is one stop lower than the element to its left, and one stop higher than the element to its right
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.
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
7.
Exposure value
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In photography, exposure value is a number that represents a combination of a cameras shutter speed and f-number, such that all combinations that yield the same exposure have the same EV. Exposure value is used to indicate an interval on the photographic exposure scale, with a difference of 1 EV corresponding to a standard power-of-2 exposure step. The EV concept was developed by the German shutter manufacturer Friedrich Deckel in the 1950s and its intent was to simplify choosing among equivalent camera exposure settings by replacing combinations of shutter speed and f-number with a single number. This was especially helpful to beginners with limited understanding of the shutter speed and aperture. The concept became known as the Light Value System in Europe, the proper EV was determined by the scene luminance and film speed, it was intended that the system also include adjustment for filters, exposure compensation, and other variables. With all of elements included, the camera would be set by transferring the single number thus determined. Exposure value has been indicated in various ways, although all camera settings with the same EV nominally give the same exposure, they do not necessarily give the same picture. The f-number determines the depth of field, and the shutter speed determines the amount of motion blur, if the EV is known, it can be used to select combinations of exposure time and f-number, as shown in Table 1. Greater exposure values are appropriate for photography in more brightly lit situations, to avoid confusion, some authors have used camera exposure to refer to combinations of camera settings. The 1964 ASA standard for automatic exposure controls for cameras, ASA PH2. 15-1964, took the same approach, common practice among photographers is nonetheless to use “exposure” to refer to camera settings as well as to photometric exposure. If, for example, the f-number is changed, an equivalent exposure time can be determined from t 2 t 1 = N22 N12. Performing this calculation mentally is tedious for most photographers, but the equation is solved with a calculator dial on an exposure meter or a similar dial on a standalone calculator. If the camera controls have detents, constant exposure can be maintained by counting the steps as one control is adjusted, the ratio t/N2 could be used to represent equivalent combinations of exposure time and f-number in a single value. But for many such combinations used in photography, the ratio gives a fractional value with a large denominator. For example, beginning with 1 s and f/1, decreasing exposure gives the simple sequence 0,1,2,3, the last two values shown frequently apply when using ISO100 speed imaging media in outdoor photography. Current cameras do not allow direct setting of EV, and cameras with automatic exposure control generally obviate the need for it, EV can nonetheless be helpful when used to transfer recommended exposure settings from an exposure meter to an exposure calculator. Used as an indicator of camera settings, EV corresponds to actual combinations of shutter speed, when the actual EV matches that recommended by the light level and the ISO speed, these settings should result in the “correct” exposure. If the common value of K =12.5 is used, at EV =15 the luminance is 380 cd/ft2 or 4096 cd/m2
8.
Mode dial
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A mode dial or camera dial is a dial used on digital cameras to change the cameras mode. Most digital cameras, including dSLR and SLR-like cameras, support modes, on point-and-shoot cameras which support modes a range of scene types is offered. On dSLR cameras and SLR-like cameras, mode dials usually offer access to manual settings, the more compact point-and-shoot cameras, and cameras offering a great many modes, do not have mode dials, using menus instead. Some SLR lenses themselves offer control over such as aperture. On most dSLRs and SLR-like bridge cameras, the dial is located at the top of the camera. On point-and-shoot cameras, however, the mode dials location is less standard, on many models, it is found on top like dSLRs. On other point-and-shoots, particularly those with a body, the dial is found on the back of the camera. Some thin cameras use a slide rather than a dial. Various camera types and specific cameras have different modes, the simpler dial in the top illustration has, Manual modes, Manual, Program, Shutter priority, Aperture priority. Automatic modes, Auto, Action, Portrait, Night portrait, Landscape, most dSLRs have a few manual settings and a small sample of automatic modes. Most SLR-like cameras have manual modes and several automatic scene modes, on point-and-shoot cameras, all manual control may be condensed into one mode or may be completely absent. Many compact cameras show a large array of scene modes, point-and-shoot and SLR-like digital cameras usually have a movie mode to capture videos, and many modern dSLRs also support movie modes. Detailed information found by users on the supported by digital cameras are to be found in the ongoing list of digital camera modes. Manual modes include, P, Program mode offers the photographer control over shutter speed. A or Av, Aperture priority AKA Aperture value allows the photographer to control the aperture, while the shutter speed, S or Tv, Shutter priority AKA Time value allows the photographer to control the shutter speed, while the aperture and ISO sensitivity are calculated by the camera. For example in portrait mode the camera would use an aperture to render the background out of focus. In the same conditions a smaller aperture would be used for a landscape. Some cameras have tens of modes, showing the majority only in the rather than on the dial
