1.
Optics
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Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light, because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. Most optical phenomena can be accounted for using the classical description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice, practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines, physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics. Historically, the model of light was developed first, followed by the wave model of light. Progress in electromagnetic theory in the 19th century led to the discovery that waves were in fact electromagnetic radiation. Some phenomena depend on the fact that light has both wave-like and particle-like properties, explanation of these effects requires quantum mechanics. When considering lights particle-like properties, the light is modelled as a collection of particles called photons, quantum optics deals with the application of quantum mechanics to optical systems. Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields, photography, practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fibre optics. Optics began with the development of lenses by the ancient Egyptians and Mesopotamians, the earliest known lenses, made from polished crystal, often quartz, date from as early as 700 BC for Assyrian lenses such as the Layard/Nimrud lens. The ancient Romans and Greeks filled glass spheres with water to make lenses, the word optics comes from the ancient Greek word ὀπτική, meaning appearance, look. Greek philosophy on optics broke down into two opposing theories on how vision worked, the theory and the emission theory. The intro-mission approach saw vision as coming from objects casting off copies of themselves that were captured by the eye, plato first articulated the emission theory, the idea that visual perception is accomplished by rays emitted by the eyes. He also commented on the parity reversal of mirrors in Timaeus, some hundred years later, Euclid wrote a treatise entitled Optics where he linked vision to geometry, creating geometrical optics. Ptolemy, in his treatise Optics, held a theory of vision, the rays from the eye formed a cone, the vertex being within the eye. The rays were sensitive, and conveyed back to the observer’s intellect about the distance. He summarised much of Euclid and went on to describe a way to measure the angle of refraction, during the Middle Ages, Greek ideas about optics were resurrected and extended by writers in the Muslim world
2.
Light
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Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to light, which is visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m. This wavelength means a range of roughly 430–750 terahertz. The main source of light on Earth is the Sun, sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the used by living things. Historically, another important source of light for humans has been fire, with the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence, for example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey. Visible light, as all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term sometimes refers to electromagnetic radiation of any wavelength. In this sense, gamma rays, X-rays, microwaves and radio waves are also light, like all types of light, visible light is emitted and absorbed in tiny packets called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality, the study of light, known as optics, is an important research area in modern physics. Generally, EM radiation, or EMR, is classified by wavelength into radio, microwave, infrared, the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths, when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. There exist animals that are sensitive to various types of infrared, infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, which is how these animals detect it, above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nanometers and the internal lens below 400. Furthermore, the rods and cones located in the retina of the eye cannot detect the very short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, various sources define visible light as narrowly as 420 to 680 to as broadly as 380 to 800 nm
3.
Focal length
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The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a focal length has greater optical power than one with a long focal length. For a thin lens in air, the length is the distance from the center of the lens to the principal foci of the lens. For a converging lens, the length is positive, and is the distance at which a beam of collimated light will be focused to a single spot. For a diverging lens, the length is negative, and is the distance to the point from which a collimated beam appears to be diverging after passing through the lens. The focal length of a lens can be easily measured by using it to form an image of a distant light source on a screen. The lens is moved until an image is formed on the screen. In this case 1/u is negligible, and the length is then given by f ≈ v. Back focal length or back focal distance is the distance from the vertex of the last optical surface of the system to the focal point. For an optical system in air, the focal length gives the distance from the front. If the surrounding medium is not air, then the distance is multiplied by the index of the medium. Some authors call these distances the front/rear focal lengths, distinguishing them from the front/rear focal distances, defined above. In general, the length or EFL is the value that describes the ability of the optical system to focus light. The other parameters are used in determining where an image will be formed for an object position. The quantity 1/f is also known as the power of the lens. The corresponding front focal distance is, FFD = f, in the sign convention used here, the value of R1 will be positive if the first lens surface is convex, and negative if it is concave. The value of R2 is negative if the surface is convex
4.
Ray (optics)
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In optics a ray is an idealized model of light, obtained by choosing a line that is perpendicular to the wavefronts of the actual light, and that points in the direction of energy flow. This allows even very complex systems to be analyzed mathematically or simulated by computer. Ray theory does not describe phenomena such as interference and diffraction, a light ray is a line that is perpendicular to the lights wavefronts, its tangent is collinear with the wave vector. Light rays in homogeneous media are straight and they bend at the interface between two dissimilar media and may be curved in a medium in which the refractive index changes. Geometric optics describes how rays propagate through an optical system, objects to be imaged are treated as collections of independent point sources, each producing spherical wavefronts and corresponding outward rays. Rays from each point can be mathematically propagated to locate the corresponding point on the image. There are many special rays that are used in modelling to analyze an optical system. These are defined and described below, grouped by the type of system they are used to model, an incident ray is a ray of light that strikes a surface. The angle between this ray and the perpendicular or normal to the surface is the angle of incidence, the reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface. The angle between the normal and the reflected ray is known as the angle of reflection. The Law of Reflection says that for a surface, the angle of reflection always equals the angle of incidence. The refracted ray or transmitted ray corresponding to an incident ray represents the light that is transmitted through the surface. The angle between this ray and the normal is known as the angle of refraction, and it is given by Snells Law. Conservation of energy requires that the power in the incident ray must equal the sum of the power in the ray, the power in the reflected ray. If the material is birefringent, the ray may split into ordinary and extraordinary rays. A meridional ray or tangential ray is a ray that is confined to the containing the systems optical axis. A skew ray is a ray that does not propagate in a plane that contains both the point and the optical axis. Such rays do not cross the optical axis anywhere, and are not parallel to it
5.
Focus (optics)
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In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent and this non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, aberrations tend to get worse as the aperture diameter increases, while the Airy circle is smallest for large apertures. An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, the border between these is sometimes defined using a circle of confusion criterion. A principal focus or focal point is a focus, For a lens, or a spherical or parabolic mirror. Since light can pass through a lens in either direction, a lens has two focal points—one on each side, the distance in air from the lens or mirrors principal plane to the focus is called the focal length. Elliptical mirrors have two points, light that passes through one of these before striking the mirror is reflected such that it passes through the other. The focus of a mirror is either of two points which have the property that light from one is reflected as if it came from the other. Diverging lenses and convex mirrors do not focus a beam to a point. Instead, the focus is the point from which the light appears to be emanating, a convex elliptical mirror will reflect light directed towards one focus as if it were radiating from the other focus, both of which are behind the mirror. A convex hyperbolic mirror will reflect rays emanating from the point in front of the mirror as if they were emanating from the focal point behind the mirror. Conversely, it can focus rays directed at the point that is behind the mirror towards the focal point that is in front of the mirror as in a Cassegrain telescope. Autofocus Cardinal point Defocus aberration Depth of field Depth of focus Far point Focus Fixed focus Bokeh Focus stacking Focal Plane
6.
Collimated light
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Collimated light is light whose rays are parallel, and therefore will spread minimally as it propagates. A perfectly collimated beam, with no divergence, would not disperse with distance, such a beam cannot be created, due to diffraction. Light can be collimated by a number of processes, for instance by means of a collimator. Perfectly collimated light is said to be focused at infinity. Thus, as the distance from a point source increases, the spherical wavefronts become flatter and closer to plane waves, the word collimate comes from the Latin verb collimare, which originated in a misreading of collineare, to direct in a straight line. In practice, gas lasers can use concave mirrors, flat mirrors, the divergence of high-quality laser beams is commonly less than 1 milliradian, and can be much less for large-diameter beams. Laser diodes emit less-collimated light due to their short cavity, synchrotron light is very well collimated. It is produced by bending relativistic electrons around a circular track, when the electrons are at relativistic speeds, the resulting radiation is highly collimated, a result which does not occur at slower speeds. The light from stars can be considered collimated for almost any purpose, because they are so far away they have almost no angular size, light from the Sun is nearly collimated by the time it reaches Earth because of its distance from the Earth. A perfect parabolic mirror will bring parallel rays to a focus at a single point, conversely, a point source at the focus of a parabolic mirror will produce a beam of collimated light creating a Collimator. Since the source needs to be small, such a system cannot produce much optical power. Spherical mirrors are easier to make than parabolic mirrors and they are used to produce approximately collimated light. Many types of lenses can also produce collimated light from point-like sources and this principle is used in full flight simulators, that have specially designed systems for displaying imagery of the Out-The-Window scene to the pilots in the replica aircraft cabin. Collimation refers to all the elements in an instrument being on their designed optical axis. It also refers to the process of adjusting an optical instrument so that all its elements are on that designed axis. With regards to a telescope, the term refers to the fact that the axis of each optical component should be centered and parallel. Most amateur reflector telescopes need to be re-collimated every few years to maintain optimum performance, collimation can also be tested using a shearing interferometer, which is often used to test laser collimation. Decollimation is any mechanism or process which causes a beam with the minimum possible ray divergence to diverge or converge from parallelism, decollimation must be accounted for to fully treat many systems such as radio, radar, sonar, and optical communications
7.
Pupil
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The pupil is a hole located in the centre of the iris of the eye that allows light to strike the retina. In humans the pupil is round, but other species, such as cats, have vertical slit pupils, goats have horizontally oriented pupils. In optical terms, the pupil is the eyes aperture. The image of the pupil as seen from outside the eye is the entrance pupil, on the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil. The pupil is a located in the centre of the iris of the eye that allows light to strike the retina. The iris is a structure, consisting mainly of smooth muscle. Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil, the iris contains two groups of smooth muscles, a circular group called the sphincter pupillae, and a radial group called the dilator pupillae. When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil, the dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, cause the pupil to dilate when they contract. These muscles are referred to as intrinsic eye muscles. The sensory pathway is linked with its counterpart in the eye by a partial crossover of each eyes fibers. This causes the effect in one eye to carry over to the other, the pupil gets wider in the dark but narrower in light. When narrow, the diameter is 2 to 4 millimeters, in the dark it will be the same at first, but will approach the maximum distance for a wide pupil 3 to 8 mm. In any human age group there is considerable variation in maximal pupil size. For example, at the age of 15, the dark-adapted pupil can vary from 4 mm to 9 mm with different individuals. After 25 years of age the pupil size decreases, though not at a steady rate. At this stage the pupils do not remain completely still, therefore may lead to oscillation, the constriction of the pupil and near vision are closely tied. When this muscle contracts, it reduces the size of the pupil and this is the pupillary light reflex, which is an important test of brainstem function. Furthermore, the pupil will dilate if a person sees an object of interest, certain drugs cause constriction of the pupils, such as opioids
8.
Lens (optics)
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A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a piece of transparent material, while a compound lens consists of several simple lenses. Lenses are made from such as glass or plastic, and are ground. A lens can focus light to form an image, unlike a prism, devices that similarly focus or disperse waves and radiation other than visible light are also called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. The word lens comes from the Latin name of the lentil, the genus of the lentil plant is Lens, and the most commonly eaten species is Lens culinaris. The lentil plant also gives its name to a geometric figure, the variant spelling lense is sometimes seen. While it is listed as a spelling in some dictionaries. The oldest lens artifact is the Nimrud lens, dating back 2700 years to ancient Assyria, david Brewster proposed that it may have been used as a magnifying glass, or as a burning-glass to start fires by concentrating sunlight. Another early reference to magnification dates back to ancient Egyptian hieroglyphs in the 8th century BC, the earliest written records of lenses date to Ancient Greece, with Aristophanes play The Clouds mentioning a burning-glass. Some scholars argue that the evidence indicates that there was widespread use of lenses in antiquity. Such lenses were used by artisans for fine work, and for authenticating seal impressions, both Pliny and Seneca the Younger described the magnifying effect of a glass globe filled with water. The Viking lenses were capable of concentrating enough sunlight to ignite fires, between the 11th and 13th century reading stones were invented. Often used by monks to assist in illuminating manuscripts, these were primitive plano-convex lenses initially made by cutting a sphere in half. As the stones were experimented with, it was understood that shallower lenses magnified more effectively. Lenses came into use in Europe with the invention of spectacles. Spectacle makers created improved types of lenses for the correction of vision based more on knowledge gained from observing the effects of the lenses. With the invention of the telescope and microscope there was a deal of experimentation with lens shapes in the 17th. Opticians tried to construct lenses of varying forms of curvature, wrongly assuming errors arose from defects in the figure of their surfaces
9.
Mirror
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This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light. The most familiar type of mirror is the mirror, which has a flat screen surface. Curved mirrors are used, to produce magnified or diminished images or focus light or simply distort the reflected image. Mirrors are commonly used for personal grooming or admiring oneself, decoration, Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for light, however, mirrors designed for other wavelengths of electromagnetic radiation are also used. The first mirrors used by people were most likely pools of dark, still water, the requirements for making a good mirror are a surface with a very high degree of flatness, and a surface roughness smaller than the wavelength of the light. The earliest manufactured mirrors were pieces of polished stone such as obsidian, examples of obsidian mirrors found in Anatolia have been dated to around 6000 BC. Mirrors of polished copper were crafted in Mesopotamia from 4000 BC, polished stone mirrors from Central and South America date from around 2000 BC onwards. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze, Mirrors made of other metal mixtures such as copper and tin speculum metal may have also been produced in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were owned by the wealthy. Stone mirrors often had poor reflectivity compared to metals, yet metals scratch or tarnish easily, depending upon the color, both often yielded reflections with poor color rendering. The poor image quality of ancient mirrors explains 1 Corinthians 13s reference to seeing as in a mirror, glass was a desirable material for mirrors. Because the surface of glass is smooth, it produces reflections with very little blur. In addition, glass is very hard and scratch resistant, however, glass by itself has little reflectivity, so people began coating it with metals to increase the reflectivity. According to Pliny, the people of Sidon developed a technique for creating crude mirrors by coating glass with molten lead. Glass mirrors backed with gold leaf are mentioned by Pliny in his Natural History and these circular mirrors were typically small, from only a fraction of an inch to as much as eight inches in diameter. These small mirrors produced distorted images, yet were prized objects of high value and these ancient glass mirrors were very thin, thus very fragile, because the glass needed to be extremely thin to prevent cracking when coated with a hot, molten metal. Due to the quality, high cost, and small size of these ancient glass mirrors
10.
Diaphragm (optics)
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In optics, a diaphragm is a thin opaque structure with an opening at its center. The role of the diaphragm is to stop the passage of light, thus it is also called a stop. The diaphragm is placed in the path of a lens or objective. The centre of the diaphragms aperture coincides with the axis of the lens system. Most modern cameras use a type of adjustable diaphragm known as an iris diaphragm, see the articles on aperture and f-number for the photographic effect and system of quantification of varying the opening in the diaphragm. A natural optical system that has a diaphragm and an aperture is the human eye, the iris is the diaphragm, and the opening in the iris of the eye is the aperture. An analogous dev in a lens is called an iris diaphragm. In the early years of photography, a lens could be fitted with one of a set of interchangeable diaphragms, the iris diaphragm in most modern still and video cameras is adjusted by movable blades, simulating the iris of the eye. The diaphragm has two to twenty blades, depending on price and quality of the device in which it is used, straight blades result in polygon shape of the diaphragm opening, while curved blades improve the roundness of the iris opening. In a photograph, the number of blades that the diaphragm has can be guessed by counting the number of diffraction spikes converging from a light source or bright reflection. For an odd number of blades, there are twice as many spikes as there are blades. In case of a number of blades, the two spikes per blade will overlap each other, so the number of spikes visible will be the number of blades in the diaphragm used. This is most apparent in pictures taken in the dark with small bright spots, some cameras, such as the Olympus XA or lenses such as the MC Zenitar-ME1, however, use a two-bladed diaphragm with right-angle blades creating a square aperture. Similarly, out-of-focus points of light appear as polygons with the number of sides as the aperture has blades. If the blurred light is circular, then it can be inferred that the aperture is round or the image was shot wide-open. The shape of the opening has a direct relation with the appearance of the blurred out-of-focus areas in an image called bokeh. A rounder opening produces softer and more natural out-of-focus areas, some lenses utilize specially shaped diaphragms in order to create certain effects. Some modern automatic point-and-shoot cameras do not have a diaphragm at all, unlike a real diaphragm, this has no effect on depth of field
11.
Exit pupil
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In optics, the exit pupil is a virtual aperture in an optical system. Only rays which pass through this virtual aperture can exit the system, the exit pupil is the image of the aperture stop in the optics that follow it. In a telescope or compound microscope, this image is the image of the element as produced by the eyepiece. The size and shape of disc is crucial to the instruments performance. The term exit pupil is sometimes used to refer to the diameter of the virtual aperture. Older literature on optics sometimes refers to the pupil as the Ramsden disc. To use an instrument, the entrance pupil of the viewers eye must be aligned with. This properly couples the optical system to the eye and avoids vignetting, the location of the exit pupil thus determines the eye relief of an eyepiece. Good eyepiece designs produce an exit pupil of diameter approximating the eyes apparent pupil diameter, if the disc is larger than the eyes pupil, light will be lost instead of entering the eye, if smaller, the view will be vignetted. Since the eyes pupil varies in diameter with viewing conditions, the exit pupil diameter depends on the application. A set of 7×50 binoculars has a pupil just over 7.1 mm. The emergent light at the eyepiece then fills the eyes pupil, in daylight, when the eyes pupil is only 4 mm in diameter, over half the light will be blocked by the iris and will not reach the retina. However, the loss of light in the daytime is not significant since there is so much light to start with. By contrast, 8×32 binoculars, often sold with emphasis on their compactness, have a pupil of only 4 mm. That is sufficient to fill a typical daytime eye pupil, making these binoculars better suited to daytime than night-time use. The maximum pupil size of an eye is typically 5–9 mm for individuals below 25 years old. The optimum eye relief distance also varies with application, for example a rifle scope needs a very long eye relief to prevent recoil from causing it to strike the observer. The exit pupil can be visualized by focusing the instrument on a bright, nondescript field and this projects a disc of light onto the card
12.
Cardinal point (optics)
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In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of a rotationally symmetric, focal, optical system. These are the points, the principal points, and the nodal points. The only ideal system that has achieved in practice is the plane mirror. Cardinal points provide a way to simplify a system with many components. The cardinal points lie on the axis of the optical system. Each point is defined by the effect the optical system has on rays that pass through that point, the paraxial approximation assumes that rays travel at shallow angles with respect to the optical axis, so that sin θ ≈ θ and cos θ ≈1. Aperture effects are ignored, rays that do not pass through the stop of the system are not considered in the discussion below. The front focal point of a system, by definition, has the property that any ray that passes through it will emerge from the system parallel to the optical axis. The rear focal point of the system has the reverse property, the front and rear focal planes are defined as the planes, perpendicular to the optic axis, which pass through the front and rear focal points. An object infinitely far from the optical system forms an image at the focal plane. For objects a finite distance away, the image is formed at a different location, but rays that leave the object parallel to one another cross at the rear focal plane. A diaphragm or stop at the focal plane can be used to filter rays by angle, since. No matter where on the object the ray comes from, the ray will pass through the aperture as long as the angle at which it is emitted from the object is small enough. Note that the aperture must be centered on the axis for this to work as indicated. Using a sufficiently small aperture in the plane will make the lens telecentric. Similarly, the range of angles on the output side of the lens can be filtered by putting an aperture at the front focal plane of the lens. This is important for DSLR cameras having CCD sensors, the pixels in these sensors are more sensitive to rays that hit them straight on than to those that strike at an angle. A lens that does not control the angle of incidence at the detector will produce pixel vignetting in the images and this means that the lens can be treated as if all of the refraction happened at the principal planes
13.
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
14.
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
15.
Telescope
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A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation. The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s and they found use in both terrestrial applications and astronomy. Within a few decades, the telescope was invented, which used mirrors to collect. In the 20th century many new types of telescopes were invented, including radio telescopes in the 1930s, the word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galileis instruments presented at a banquet at the Accademia dei Lincei, in the Starry Messenger, Galileo had used the term perspicillum. The earliest recorded working telescopes were the telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals, Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, Galileo heard about the Dutch telescope in June 1609, built his own within a month, and improved upon the design in the following year. Also in 1609, Thomas Harriot became the first person known to point a telescope skyward in order to make observations of a celestial object. The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs, in 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector. The invention of the lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter. The largest reflecting telescopes currently have objectives larger than 10 m, the 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937, since then, a tremendous variety of complex astronomical instruments have been developed. The name telescope covers a range of instruments. Most detect electromagnetic radiation, but there are differences in how astronomers must go about collecting light in different frequency bands. The near-infrared can be collected much like light, however in the far-infrared and submillimetre range. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm to 2000 μm, on the other hand, the Spitzer Space Telescope, observing from about 3 μm to 180 μm uses a mirror. Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the range from about 0.2 μm to 1.7 μm
16.
Objective (optics)
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In optical engineering, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be a lens or mirror, or combinations of several optical elements. They are used in microscopes, telescopes, cameras, slide projectors, CD players, objectives are also called object lenses, object glasses, or objective glasses. The objective lens of a microscope is the one at the bottom near the sample, at its simplest, it is a very high-powered magnifying glass, with very short focal length. This is brought close to the specimen being examined so that the light from the specimen comes to a focus inside the microscope tube. The objective itself is usually a cylinder containing one or more lenses that are made of glass. Microscope objectives are characterized by two parameters, magnification and numerical aperture, the magnification typically ranges from 4× to 100×. Numerical aperture for microscope lenses typically ranges from 0.10 to 1.25, corresponding to focal lengths of about 40 mm to 2 mm, respectively. A typical microscope has three or four lenses with different magnifications, screwed into a circular nosepiece which may be rotated to select the required lens. These lenses are often color coded for easier use, the least powerful lens is called the scanning objective lens, and is typically a 4× objective. The second lens is referred to as the objective lens and is typically a 10× lens. The most powerful out of the three is referred to as the large objective lens and is typically 40–100×. Some microscopes use an oil-immersion or water-immersion lens, which can have greater than 100. These objectives are designed for use with refractive index matching oil or water. These lenses give greater resolution at high magnification, numerical apertures as high as 1.6 can be achieved with oil immersion. Camera lenses need to cover a large plane so are made up of a number of optical lens elements to correct optical aberrations. Image projectors use objective lenses that simply reverse the function of a lens, with lenses designed to cover a large image plane. In a telescope the objective is the lens at the front end of a refractor or the primary mirror of a reflecting or catadioptric telescope
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Astrophotography
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Astrophotography is a specialized type of photography for recording photos of astronomical objects and large areas of the night sky. The first photograph of an object was taken in 1840. This is done by long time exposure since both film and digital cameras can accumulate and sum light photons over long periods of time. Astrophotography is a subdiscipline in amateur astronomy usually seeking aesthetically pleasing images rather than scientific data. Amateurs use a range of special equipment and techniques. With a few exceptions, astronomical photography employs long exposures since both film and digital imaging devices can accumulate and light photons over long periods of time, the amount of light hitting the film or detector is also increased by increasing the diameter of the primary optics being used. Since the Earth is constantly rotating, telescopes and equipment are rotated in the direction to follow the apparent motion of the stars overhead. This is accomplished by using either equatorial or computer-controlled altazimuth telescope mounts to keep celestial objects centered while the earth rotates, all telescope mount systems suffer from induced tracking error due to imperfect motor drives and mechanical sag of the telescope. Tracking errors are corrected by keeping a selected aiming point, usually a bright guide star, sometimes the object to be imaged is moving, so the telescope has to be kept constantly centered on that object. Guiding was formerly done manually throughout the exposure with an observer standing at the telescope making corrections to keep a cross hair on the guide star, since the advent of computer-controlled systems this is accomplished by an automated systems in professional and even amateur equipment. These all require specialized equipment such as telescopes designed for imaging, for wide field of view. Astronomical CCD cameras may use cryogenic cooling to reduce thermal noise, specialized filters are also used to record images in specific wavelengths. The development of astrophotography as a tool was pioneered in the mid-19th century for the most part by experimenters and amateur astronomers. Because of the long exposures needed to capture relatively faint astronomical objects. Early photographic processes also had limitations, the daguerreotype process was far too slow to record anything but the brightest objects, and the wet plate collodion process limited exposures to the time the plate could stay wet. The first-known attempt at astronomical photography was by Louis Jacques Mandé Daguerre, inventor of the process which bears his name. Tracking errors in guiding the telescope during the long exposure meant the photograph came out as an indistinct fuzzy spot, the Sun may have been first photographed in an 1845 daguerreotype by the French physicists Léon Foucault and Hippolyte Fizeau. No photographic alteration was caused by the light of the corona condensed by a lens for two minutes, during totality, on a sheet of paper prepared with bromide of silver, the Suns solar corona was first successfully imaged during the Solar eclipse of July 28,1851
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Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world
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Depth of field
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In some cases, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, a small DOF may be more effective, in cinematography, a large DOF is often called deep focus, and a small DOF is often called shallow focus. Precise focus is possible at one distance, at that distance. At any other distance, a point object is defocused, and will produce a blur spot shaped like the aperture, when this circular spot is sufficiently small, it is indistinguishable from a point, and appears to be in focus, it is rendered as acceptably sharp. The acceptable circle of confusion is influenced by visual acuity, viewing conditions, the increase of the circle diameter with defocus is gradual, so the limits of depth of field are not hard boundaries between sharp and unsharp. For 35 mm motion pictures, the area on the film is roughly 22 mm by 16 mm. The limit of tolerable error was traditionally set at 0.05 mm diameter, while for 16 mm film, where the size is half as large. More modern practice for 35 mm productions set the circle of confusion limit at 0.025 mm, for full-frame 35mm still photography, the circle of confusion is usually chosen to be about 1/30 mm. Many sources propose CoC limits as a fraction of the film format diagonal, the three formats above at fraction 1/1500 would use 0.029,0.056, and 0.017 mm. Traditional depth-of-field formulas and tables assume equal circles of confusion for near and far objects, the loss of detail in distant objects may be particularly noticeable with extreme enlargements. Achieving this additional sharpness in distant objects usually requires focusing beyond the hyperfocal distance, with this approach, foreground objects cannot always be made perfectly sharp, but the loss of sharpness in near objects may be acceptable if recognizability of distant objects is paramount. Other authors have taken the position, maintaining that slight unsharpness in foreground objects is usually more disturbing than slight unsharpness in distant parts of a scene. The combination of length, subject distance, and format size defines magnification at the film / sensor plane. DOF is determined by subject magnification at the film / sensor plane, for a given f-number, increasing the magnification, either by moving closer to the subject or using a lens of greater focal length, decreases the DOF, decreasing magnification increases DOF. For a given magnification, increasing the f-number increases the DOF. If the original image is enlarged to make the final image, when focus is set to the hyperfocal distance, the DOF extends from half the hyperfocal distance to infinity, and the DOF is the largest possible for a given f-number. The comparative DOFs of two different format sizes depend on the conditions of the comparison, the DOF for the smaller format can be either more than or less than that for the larger format. In the discussion that follows, it is assumed that the images from both formats are the same size, are viewed from the same distance, and are judged with the same circle of confusion criterion
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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
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Optical aberration
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An optical aberration is a departure of the performance of an optical system from the predictions of paraxial optics. In an imaging system, it occurs when light from one point of an object does not converge into a point after transmission through the system. Aberrations occur because the simple theory is not a completely accurate model of the effect of an optical system on light. Aberration leads to blurring of the produced by an image-forming optical system. Makers of optical instruments need to correct optical systems to compensate for aberration, the articles on reflection, refraction and caustics discuss the general features of reflected and refracted rays. Aberrations fall into two classes, monochromatic and chromatic, monochromatic aberrations are caused by the geometry of the lens or mirror and occur both when light is reflected and when it is refracted. They appear even when using light, hence the name. Chromatic aberrations are caused by dispersion, the variation of a refractive index with wavelength. They do not appear when monochromatic light is used, if an otherwise perfect wavefront is aberrated by piston and tilt, it will still form a perfect, aberration-free image, only shifted to a different position. Defocus is the true optical aberration. The introduction of simple auxiliary terms, due to C. F. Gauss, named the focal lengths and focal planes, permits the determination of the image of any object for any system. The Gaussian theory, however, is true so long as the angles made by all rays with the optical axis are infinitely small. The investigations of James Clerk Maxwell and Ernst Abbe showed that the properties of these reproductions and these authors proved, however, that no optical system can justify these suppositions, since they are contradictory to the fundamental laws of reflection and refraction. Consequently, the Gaussian theory only supplies a convenient method of approximating to reality and this, and related general questions, have been treated — besides the above-mentioned authors — by M. Thiesen and H. Bruns by means of Sir W. R. Hamiltons characteristic function. Reference may also be made to the treatise of Czapski-Eppenstein, pp. 155–161, a review of the simplest cases of aberration will now be given. Let S be any system, rays proceeding from an axis point O under an angle u1 will unite in the axis point O1. The caustic, in the first case, resembles the sign >, if the angle u1 is very small, O1 is the Gaussian image, and O1 O2 is termed the longitudinal aberration, and O1R the lateral aberration of the pencils with aperture u2. This hole is termed the stop or diaphragm, Abbe used the term stop for both the hole and the limiting margin of the lens
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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
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Angle of view
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In photography, angle of view describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the general term field of view. It is important to distinguish the angle of view from the angle of coverage, typically the image circle produced by a lens is large enough to cover the film or sensor completely, possibly including some vignetting toward the edge. A cameras angle of view not only on the lens. Digital sensors are usually smaller than 35mm film, and this causes the lens to have an angle of view than with 35mm film. In everyday digital cameras, the factor can range from around 1, to 1.6. For lenses projecting rectilinear images of distant objects, the focal length. Calculations for lenses producing non-rectilinear images are more complex and in the end not very useful in most practical applications. Angle of view may be measured horizontally, vertically, or diagonally, for example, for 35mm film which is 36 mm wide and 24mm high, d =36 mm would be used to obtain the horizontal angle of view and d =24 mm for the vertical angle. Because this is a function, the angle of view does not vary quite linearly with the reciprocal of the focal length. However, except for wide-angle lenses, it is reasonable to approximate α ≈ d f radians or 180 d π f degrees. The effective focal length is equal to the stated focal length of the lens. Angle of view can also be determined using FOV tables or paper or software lens calculators, consider a 35 mm camera with a lens having a focal length of F =50 mm. The dimensions of the 35 mm image format are 24 mm ×36 mm, here α is defined to be the angle-of-view, since it is the angle enclosing the largest object whose image can fit on the film. We want to find the relationship between, the angle α the opposite side of the triangle, d /2 the adjacent side, S2 Using basic trigonometry, we find. For macro photography, we neglect the difference between S2 and F. From the thin lens formula,1 F =1 S1 +1 S2, a second effect which comes into play in macro photography is lens asymmetry. The lens asymmetry causes an offset between the plane and pupil positions
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Entrance pupil
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In an optical system, the entrance pupil is the optical image of the physical aperture stop, as seen through the front of the lens system. The corresponding image of the aperture as seen through the back of the system is called the exit pupil. If there is no lens in front of the aperture, the entrance pupils location, optical elements in front of the aperture will produce a magnified or diminished image that is displaced from the location of the physical aperture. The entrance pupil is usually an image, it lies behind the first optical surface of the system. This point is important in panoramic photography, because the camera must be rotated around it in order to avoid errors in the final. Panoramic photographers often incorrectly refer to the pupil as a nodal point. In photography, the size of the pupil is used to calibrate the opening and closing of the diaphragm aperture. The f-number, N, is defined by N = f/EN, increasing the focal length of a lens will usually cause the f-number to increase, and the entrance pupil location to move further back along the optical axis. The entrance pupil of the eye, which is not quite the same as the physical pupil, is typically about 4 mm in diameter. It can range from 2 mm in a brightly lit place to 8 mm in the dark. Exit pupil Transmittance Pupil magnification Stops and Pupils in Field Guide to Geometrical Optics Greivenkamp, John E,2004
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Z-scan technique
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In nonlinear optics z-scan technique is used to measure the non-linear index n2 and the non-linear absorption coefficient Δα via the closed and open methods, respectively. As nonlinear absorption can affect the measurement of the index the open method is typically used in conjunction with the closed method to correct the calculated value. For measuring the real part of the refractive index, the z-scan setup is used in its closed-aperture form. In this form, since the nonlinear material reacts like a weak z-dependent lens, to measure the imaginary part of the nonlinear refractive index, or the nonlinear absorption coefficient, the z-scan setup is used in its open-aperture form. In open-aperture measurements, the aperture is removed and the whole signal is measured by the detector. By measuring the whole signal, the small distortions become insignificant. Despite its simplicity, in cases, the original z-scan theory is not completely accurate. Generally, a variety of mechanisms may contribute to the nonlinearity, the nonlocal z-scan theory, can be used for systematically analyzing the role of various mechanisms in producing the nonlocal nonlinear response of different materials. In this setup an aperture is placed to prevent some of the light reaching the detector. The equipment is arranged as can be seen in the diagram, a lens focuses a laser to a certain point, and after this point the beam naturally defocuses. After a further distance an aperture is placed with a detector behind it, the aperture causes only the central region of the cone of light to reach the detector. Typically values of the normalized transmittance are between 0.1 < S <0.5, the detector is now sensitive to any focusing or defocusing that a sample may induce. This in effect sets the normalized transmittance to S =1 and this is used in order to measure the non-linear absorption coefficient Δα. The main cause of non-linear absorption is due to two-photon absorption and this method is similar to the closed z-scan method, however the sensitivity of the system is increased by only looking at the outer edges of the beam by blocking out the central region. This is achieved by replacing the aperture with disks that block the central part of the beam, the method got its name from the way in which the light passes around the disk to the detector in a similar way to an eclipse. A further improvement to the eclipsing z-scan method is to add a lens behind the aperture so that the light is focused onto the detector, Z-scan measurements of Optical Non linearities Z-scan measurement summary by Rüdiger Paschotta
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Condenser (optics)
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A condenser is an optical lens which renders a divergent beam from a point source into a parallel or converging beam to illuminate an object. In the context of microscopy, the parallel illumination scheme is known as Köhler illumination whereas the converging illumination scheme is known as critical illumination, condensers are an essential part of any imaging device, such as microscopes, enlargers, slide projectors, and telescopes. The concept is applicable to all kinds of radiation undergoing optical transformation, such as electrons in electron microscopy, condensers are located above the light source and under the sample in an upright microscope, and above the stage and below the light source in an inverted microscope. They act to gather light from the light source and concentrate it into a cone of light that illuminates the specimen. The aperture and angle of the cone must be adjusted for each different objective lens with different numerical apertures. Condensers typically consist of a diaphragm and one or more lenses. Light from the source of the microscope passes through the diaphragm and is focused by the lens onto the specimen. After passing through the specimen the light diverges into a cone to fill the front lens of the objective. The first simple condensers were introduced on pre-achromatic microscopes in the 17th century, robert Hooke used a combination of a salt water filled globe and a plano-convex lens, and shows in the Micrographia that he understands the reasons for its efficiency. Makers in the 18th century such as Benjamin Martin, Adams and this was a simple plano-convex or bi-convex lens, or sometimes a combination of lenses. With the development of the modern achromatic objective in 1829, by Joseph Jackson Lister, by 1837, the use of the achromatic condenser was introduced in France, by Felix Dujardin, and Chevalier. English makers early took up this improvement, due to the obsession with resolving test objects such as diatoms, by the late 1840s, English makers such as Ross, Powell and Smith, all could supply highly corrected condensers on their best stands, with proper centring and focus. It is erroneously stated that these developments were purely empirical - no-one can design a good achromatic, on the Continent, in Germany, the corrected condenser was not considered either useful or essential, mainly due to a misunderstanding of the basic optical principles involved. Thus the leading German company, Carl Zeiss in Jena, offered nothing more than a very poor chromatic condenser into the late 1870s. There are three types of condenser, The chromatic condenser, such as the Abbe where no attempt is made to correct for spherical or chromatic aberration. It contains two lenses that produce an image of the source that is surrounded by a blue. The aplanatic condenser is corrected for spherical aberration, the compound achromatic condenser is corrected for both spherical and chromatic aberrations. The Abbe condenser is named for its inventor Ernst Abbe, who developed it in 1870, the Abbe condenser, which was originally designed for Zeiss, is mounted below the stage of the microscope
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Optical microscope
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The optical microscope, often referred to as light microscope, is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were invented in their present compound form in the 17th century. Basic optical microscopes can be simple, although there are many complex designs which aim to improve resolution. The image from a microscope can be captured by normal light-sensitive cameras to generate a micrograph. Originally images were captured by photographic film but modern developments in CMOS, purely digital microscopes are now available which use a CCD camera to examine a sample, showing the resulting image directly on a computer screen without the need for eyepieces. Alternatives to optical microscopy which do not use visible light include scanning electron microscopy, there are two basic types of optical microscopes, simple microscopes and compound microscopes. A simple microscope is one which uses a lens for magnification. A compound microscope uses several lenses to enhance the magnification of an object, the vast majority of modern research microscopes are compound microscopes while some cheaper commercial digital microscopes are simple single lens microscopes. Compound microscopes can be divided into a variety of other types of microscopes which differ in their optical configurations, cost. A simple microscope uses a lens or set of lenses to enlarge an object through angular magnification alone, the use of a single convex lens or groups of lenses are still found in simple magnification devices such as the magnifying glass, loupes, and eyepieces for telescopes and microscopes. A compound microscope uses a close to the object being viewed to collect light which focuses a real image of the object inside the microscope. That image is magnified by a second lens or group of lenses that gives the viewer an enlarged inverted virtual image of the object. The use of a compound objective/eyepiece combination allows for higher magnification. Common compound microscopes often feature exchangeable objective lenses, allowing the user to quickly adjust the magnification, a compound microscope also enables more advanced illumination setups, such as phase contrast. There are many variants of the optical microscope design for specialized purposes. Comparison microscope, which has two light paths allowing direct comparison of two samples via one image in each eye. Inverted microscope, for studying samples from below, useful for cell cultures in liquid, student microscope, designed for low cost, durability, and ease of use. Polarizing microscope, similar to the petrographic microscope, phase contrast microscope, which applies the phase contrast illumination method
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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
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Photographic film
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This article is mainly concerned with still photography film. For motion picture film, please see film stock, photographic film is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, the emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of any practical use. Instead, a short exposure to the image formed by a camera lens is used to produce only a very slight chemical change. This creates an invisible latent image in the emulsion, which can be developed into a visible photograph. In addition to light, all films are sensitive to ultraviolet, X-rays. Unmodified silver halide crystals are only to the blue part of the visible spectrum. This problem was overcome with the discovery that certain dyes, called sensitizing dyes, first orthochromatic and finally panchromatic films were developed. Panchromatic film renders all colors in shades of gray approximately matching their subjective brightness, by similar techniques special-purpose films can be made sensitive to the infrared region of the spectrum. In black-and-white photographic film there is one layer of silver halide crystals. When the exposed silver halide grains are developed, the silver halide crystals are converted to metallic silver, color film has at least three sensitive layers, incorporating different combinations of sensitizing dyes. Typically the blue-sensitive layer is on top, followed by a filter layer to stop any remaining blue light from affecting the layers below. Next come a green-and-blue sensitive layer, and a sensitive layer. During development, the silver halide crystals are converted to metallic silver. Because the by-products are created in direct proportion to the amount of exposure and development, following development, the silver is converted back to silver halide crystals in the bleach step. It is removed from the film during the process of fixing the image on the film with a solution of ammonium thiosulfate or sodium thiosulfate, fixing leaves behind only the formed color dyes, which combine to make up the colored visible image. Later color films, like Kodacolor II, have as many as 12 emulsion layers, the earliest practical photographic process, the daguerreotype, introduced in 1839, did not use film. The light-sensitive chemicals were formed on the surface of a copper sheet
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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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Shutter speed
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The amount of light that reaches the film or image sensor is proportional to the exposure time. 1/500th of a second will let half as much light in as 1/250th, the cameras shutter speed, the lenss aperture, and the scenes luminance together determine the amount of light that reaches the film or sensor. Exposure value is a quantity that accounts for the shutter speed and this will achieve a good exposure when all the details of the scene are legible on the photograph. Too much light let into the results in an overly pale image while too little light will result in an overly dark image. Multiple combinations of speed and f-number can give the same exposure value. According to exposure value formula, doubling the exposure time doubles the amount of light, for example, f/8 lets 4 times more light into the camera as f/16 does. In addition to its effect on exposure, the speed changes the way movement appears in photographs. Very short shutter speeds can be used to freeze fast-moving subjects, very long shutter speeds are used to intentionally blur a moving subject for effect. Short exposure times are called fast, and long exposure times slow. Adjustments to the aperture need to be compensated by changes of the speed to keep the same exposure. The agreed standards for shutter speeds are, With this scale, camera shutters often include one or two other settings for making very long exposures, B keeps the shutter open as long as the shutter release is held. T keeps the open until the shutter release is pressed again. The ability of the photographer to take images without noticeable blurring by camera movement is an important parameter in the choice of the slowest possible speed for a handheld camera. Through practice and special techniques such as bracing the camera, arms, or body to minimize movement, using a monopod or a tripod. If a shutter speed is too slow for hand holding, a support, usually a tripod. Image stabilization on digital cameras or lenses can often permit the use of shutter speeds 3–4 stops slower, Shutter priority refers to a shooting mode used in cameras. It allows the photographer to choose a shutter speed setting and allow the camera to decide the correct aperture and this is sometimes referred to as Shutter Speed Priority Auto Exposure, or TV mode, S mode on Nikons and most other brands. Shutter speed is one of methods used to control the amount of light recorded by the cameras digital sensor or film
32.
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
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Diameter
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In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle, both definitions are also valid for the diameter of a sphere. In more modern usage, the length of a diameter is called the diameter. In this sense one speaks of the rather than a diameter, because all diameters of a circle or sphere have the same length. Both quantities can be calculated efficiently using rotating calipers, for a curve of constant width such as the Reuleaux triangle, the width and diameter are the same because all such pairs of parallel tangent lines have the same distance. For an ellipse, the terminology is different. A diameter of an ellipse is any chord passing through the midpoint of the ellipse, for example, conjugate diameters have the property that a tangent line to the ellipse at the endpoint of one of them is parallel to the other one. The longest diameter is called the major axis, the word diameter is derived from Greek διάμετρος, diameter of a circle, from διά, across, through and μέτρον, measure. It is often abbreviated DIA, dia, d, or ⌀, the definitions given above are only valid for circles, spheres and convex shapes. However, they are cases of a more general definition that is valid for any kind of n-dimensional convex or non-convex object. The diameter of a subset of a space is the least upper bound of the set of all distances between pairs of points in the subset. So, if A is the subset, the diameter is sup, if the distance function d is viewed here as having codomain R, this implies that the diameter of the empty set equals −∞. Some authors prefer to treat the empty set as a case, assigning it a diameter equal to 0. For any solid object or set of scattered points in n-dimensional Euclidean space, in medical parlance concerning a lesion or in geology concerning a rock, the diameter of an object is the supremum of the set of all distances between pairs of points in the object. In differential geometry, the diameter is an important global Riemannian invariant, the symbol or variable for diameter, ⌀, is similar in size and design to ø, the Latin small letter o with stroke. In Unicode it is defined as U+2300 ⌀ Diameter sign, on an Apple Macintosh, the diameter symbol can be entered via the character palette, where it can be found in the Technical Symbols category. The character will not display correctly, however, since many fonts do not include it. In many situations the letter ø is a substitute, which in Unicode is U+00F8 ø
34.
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
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Lens speed
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Lens speed refers to the maximum aperture diameter, or minimum f-number, of a photographic lens. Lenses may also be referred to as being faster or slower than one another, with 35mm cameras, the fastest lenses are typically in the normal lens range near 50mm and there are several high-quality fast lenses available that are relatively inexpensive. For example, the Canon EF 50mm f/1.8 II or Nikon AF Nikkor 50mm f/1. 8D are very inexpensive, but quite fast and optically well-regarded. Old fast manual focus lenses, just as the Nikkor-S or Nikkor AI-S 50mm f/1.4, were historically produced abundantly, especially outside of the normal lenses, lens speed also tends to correlate with the price and/or quality of the lens. This is because lenses with maximum apertures require greater care with regard to design, precision of manufacture, special coatings. At wide apertures, spherical aberration becomes significant and must be corrected. Faster telephoto and wide-angle retrofocus designs tend to be more expensive. The fastest lenses in production now are f/1.2 or f/1.4, with more at f/1.8 and f/2.0. For example, the 1911 Encyclopædia Britannica states that. For scale, note that f/0.5, f/0.7, f/1.0, f/1.4, and f/2.0 are each 1 f-stop apart, as an f-stop corresponds to a factor of square root of 2, about 1.4. Thus around f/1.0, a change of 0.1 corresponds to about 1/4 of an f-stop, f/1.0 is about 50% faster than f/1.2, which is about 50% faster than f/1.4. As of 2012, Canon, Nikon, Pentax and Sony all make an autofocus 50mm f/1.4 lens and these are not unusual lenses and are relatively inexpensive. Canon also makes autofocus 50mm and 85mm f/1.2 lenses, while Nikon makes a manual focus 50mm f/1.2 lens, Pentax makes a 50mm f/1.4 lens and 55mm f/1.4 lens for APS-C cameras, see Pentax lenses. Sony makes a 50mm f/1.4 lens which is a continuation of the Minolta AF 50mm f/1.4 lens, the maximum exposure time in free-hand photography can be enhanced even more also for fast lenses, if the camera is equipped with an image stabilisation system. In the mid 60s there was something of a fad for fast lenses among the major manufacturers, in 1966 in response to the trend Carl Zeiss displayed a prop lens christened the Super-Q-Gigantar 40mm f/0.33 at photokina. Made from various parts found around the factory the claimed speed and focal lengths were purely nominal, ultimately, the speed of a lens is limited by mechanical constraints of the camera system. This sets a limit close to f/1.0 to f/1.2 for most SLR mounts, whereas lenses for rangefinder and mirrorless cameras can be faster, as they can be brought closer to the image plane. Reproduction lenses incapable of infinity focus can have nominal f-numbers smaller than this limit, as the limit applies to the working f-number and it should be noted that only the working f-number correctly assesses the light gathering power of the lens
36.
135 film
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135 is photographic film in a film format used for still photography. It is a film with a film gauge of 35 mm. Its engineering standard for the film is controlled by ISO1007, the term 135 was introduced by Kodak in 1934 as a designation for the cassette for 35 mm film, specifically for still photography. It quickly grew in popularity, surpassing 120 film by the late 1960s to become the most popular photographic film size, despite competition from formats such as 828,126,110, and APS, it remains so today. 135 camera film always comes perforated with Kodak Standard perforations, the size of the 135 film frame has been adopted by many high-end digital single-lens reflex and digital mirrorless cameras, commonly referred to as full frame. Even though the format is smaller than historical medium format and large format film, it is much larger than image sensors in most compact cameras. Individual rolls of 135 film are enclosed in single-spool, light-tight, the film is clipped or taped to a spool and exits via a slot lined with flocking. The end of the film is cut on one side to form a leader and it has the same dimensions and perforation pitch as 35 mm movie print film. Most cameras require the film to be rewound before the camera is opened, disposable cameras use the same technique so that the user does not have to rewind. Since the 1980s film cassettes have been marked with a DX encoding pattern, conforming cameras detect this, different films are sensitive to light at different degrees, this film speed is standardised by ISO.135 film has been made in several emulsion types and sensitivities. Since the introduction of digital cameras the most usual films have colour emulsions of ISO 100/21° to ISO 800/30°, films of lower sensitivity and higher sensitivity are for more specialist purposes. There are colour and monochrome films, negative and positive, monochrome film is usually panchromatic, orthochromatic has fallen out of use. Film designed to be sensitive to infrared radiation can be obtained, more exotic emulsions have been available in 135 than other roll-film sizes. The term 135 format usually refers to a 36×24 mm film format, the 36×24 mm format is common to digital image sensors, where it is typically referred to as full frame format. On 135 film, the dimension of the 36×24 mm frame runs parallel to the length of the film. The perforation size and pitch are according to the standard specification KS-1870, for each frame, the film advances 8 perforations. This is specified as 38.00 mm and this allows for 2 mm gaps between frames. Each camera model has a different location for the sprocket which advances the film, therefore, each camera model’s frame will vary in position relative to the perforations
37.
Half-frame camera
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A half-frame camera is a camera using a film format at half the intended exposure format. A common variety is the 18×24 mm format on regular 135 film and it is the normal exposure format on 35mm movie cameras. For still cameras using the 35mm film, the format is 24×36 mm. There was a vogue of half-frame cameras in the 1960s, mainly from Japan and it allowed for a very compact camera, using commonly available film, unlike other subminiatures that used exotic films. This vogue ended when cameras like the Rollei 35 or the Olympus XA showed that it was possible to make cameras as small as the half-frame ones, with a half-frame camera, one can fit twice as many pictures onto a standard roll of film. For example,72 exposures on a 36-exposure roll,48 on a 24-exposure one, the exposures have a vertical orientation as opposed to the horizontal orientation of a 35mm SLR or rangefinder, with the exception of the Konica Recorder, whose film mechanism runs vertically. The most advanced half-frame camera that was designed as such from the start is the Yashica Samurai single lens reflex and these are mainly of interest as collectibles. A list of half-frame cameras, by Massimo Bertacchi
38.
APS-C
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Advanced Photo System type-C is an image sensor format approximately equivalent in size to the Advanced Photo System classic negatives of 25. 1×16.7 mm, an aspect ratio of 3,2. Sensors approximating these dimensions are used in many digital single-lens reflex cameras, Mirrorless interchangeable-lens cameras, APS-C size sensors are also used in a few digital rangefinders. Such sensors exist in different variants depending on the manufacturer. All APS-C variants are considerably smaller than 35 mm standard film which measures 36×24 mm, sensor sizes range from 20. 7×13.8 mm to 28. 7×19.1 mm, but are typically about 22. 5×15 mm for Canon and 24×16 mm for other manufacturers. Each variant results in a different angle of view from lenses at the same focal length. This is why each manufacturer offers a range of lenses designed for its format, the quality of the image from an APS-C sensor is higher when compared to a smaller sensor due to its larger size which allows it to collect more light. However, compared to a camera, image quality is lower. Most DSLR and third party lens manufacturers now make lenses designed for APS-C cameras. Actual multiplier factor is 1. 255× for the 1D Digital,1. 28× for the Canon EOS-1D Mark III and 1. 29× for the Canon EOS-1D Mark IV. Leica M8 is 1. 33× Canon, Nikon, Pentax, whilst Canon uses a factor of 1. 6×, the other three brands all use 1. 5×. APS-C cameras use an area to form the image than traditional 35 mm cameras. For example, a 28 mm lens is a wide angle lens on a traditional 35 mm camera. But the same lens on an APS-C camera, with a factor of 1. 6×, has the same angle of view as a 45 mm lens on a 35 mm camera—i. e. Several third-party lens manufacturers, such as Tamron, Tokina, and Sigma, Canon introduced the Canon EF-S line of lenses in 2003 alongside the 300D. These lenses place the rear of the closer to the cameras sensor. This has several benefits, including lighter lenses and a field of view. EF-S lenses are compatible with Canons APS-C digital SLRs, with the exception of the early Canon EOS D30, Canon EOS D60, and Canon EOS 10D, EF-S lenses will not physically mount on Canons full-frame digital or 35mm film SLRs. More recently, the introduced the EF-M line for its EOS M series of mirrorless interchangeable-lens cameras
39.
Image circle
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The image circle is the cross section of the cone of light transmitted by a lens or series of lenses. When this light strikes a target such as film or a digital camera sensor, it forms a circle of light. Various sensor aspect ratios may be used which all fit inside the image circle,3,2,4,3,16,9. A lens to be used on a camera that provides movements must have an image circle larger than the size of the image format, the New Ansel Adams Basic Photography Series/Book 1. ISBN 0-8212-1092-0 Ray, Sidney F.2000, in The Manual of Photography, Photographic and Digital Imaging, 9th ed. Ed. Ralph E. Jacobson, Sidney F. Ray, Geoffrey G. Atteridge, ISBN 0-240-51574-9 Ray, Sidney F.2002. Applied Photographic Optics, 3rd ed. Oxford, Focal Press ISBN 0-240-51540-4 Langford, view Camera Technique, 3rd ed, 62–67
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Large format
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Large format refers to any imaging format of 4×5 inches or larger. Large format is larger than medium format, the 6×6 cm or 6×9 cm size of Hasselblad, Rollei, Kowa, and Pentax cameras, and much larger than the 24×36 mm frame of 35 mm format. The main advantage of large format, film or digital, is higher resolution at the pixel pitch. A 4×5 inch image has about 16 times the area, and thus 16× the total resolution, of a 35 mm frame. Large format cameras were some of the earliest photographic devices, and before enlargers were common, it was normal to just make 1,1 contact prints from a 4×5, 5×7, or 8×10-inch negative. The most common format is 4×5 inches, which was the size common cameras used in the 1930s-1950s, like the Graflex Speed Graphic and Crown Graphic. Above 8×10 inches, the formats are referred to as Ultra Large Format and may be 11×14, 16×20, or 20×24 inches or as large as film, plates. Many large formats are horizontal cameras designed to make big negatives for contact printing onto press-printing plates, the Polaroid 20×24 camera is one of the largest format instant cameras in common usage and can be hired from Polaroid agents in various countries. Many well-known photographers have used the 235 pounds, wheeled-chassis Polaroid, architectural and close-up photographers in particular benefit greatly from this ability. These allow the front and back of the camera to be shifted up/down and left/right, a number of actions need to be taken to use a typical large format camera, resulting in a slower, often more contemplative, photographic style. A tripod is used for view camera work, but some models are designed for hand-held use. These technical cameras have separate viewfinders and rangefinders for faster handling, in general large format camera use, the scene is composed on the cameras ground glass, and then a film holder is fitted to the camera back prior to exposure. Failure to Polaroid an exposure risks discovery later, at the time of film development, the 4×5 inch sheet film format was very convenient for press photography since it allowed for direct contact printing on the printing plate, hence it was widely used in press cameras. This was done well into the 1940s and 1950s, even with the advent of more convenient, the 35 mm and medium format SLR which appeared in the mid-1950s were soon adopted by press photographers. Large format photography is not limited to film, large digital camera backs are available to fit large format cameras and these are either medium-format digital backs adapted to fit large format cameras, step and repeat Multishot systems, or scanning backs. Scanning backs can take seconds or even minutes to capture an image. When using a Sinar Macroscan unit and 54H data files, over 1 gigabyte of data is produced, high quality fine art prints can be made at sizes in the range of 40x50 from a 4×5 original, and well beyond that for larger negatives. The Library of Congress uses various large format digital scans for American Memories in the current JPEG2000 format, and the older MrSID, JPEG, and TIFF formats
