Single-lens reflex camera
A single-lens reflex camera is a camera that uses a mirror and prism system that permits the photographer to view through the lens and see what will be captured. With twin lens reflex and rangefinder cameras, the viewed image could be different from the final image; when the shutter button is pressed on most SLRs, the mirror flips out of the light path, allowing light to pass through to the light receptor and the image to be captured. Prior to the development of SLR, all cameras with viewfinders had two optical light paths: one path through the lens to the film, another path positioned above or to the side; because the viewfinder and the film lens cannot share the same optical path, the viewing lens is aimed to intersect with the film lens at a fixed point somewhere in front of the camera. This is not problematic for pictures taken at a middle or longer distance, but parallax causes framing errors in close-up shots. Moreover, focusing the lens of a fast reflex camera when it is opened to wider apertures is not easy.
Most SLR cameras permit upright and laterally correct viewing through use of a roof pentaprism situated in the optical path between the reflex mirror and viewfinder. Light, which comes both horizontally and vertically inverted after passing through the lens, is reflected upwards by the reflex mirror, into the pentaprism where it is reflected several times to correct the inversions caused by the lens, align the image with the viewfinder; when the shutter is released, the mirror moves out of the light path, the light shines directly onto the film. The Canon Pellix, along with several special purpose high speed cameras, were an exception to the moving mirror system, wherein the mirror was a fixed beamsplitting pellicle. Focus can be adjusted manually automatically by an autofocus system; the viewfinder can include a matte focusing screen located just above the mirror system to diffuse the light. This permits accurate viewing and focusing useful with interchangeable lenses. Up until the 1990s, SLR was the most advanced photographic preview system available, but the recent development and refinement of digital imaging technology with an on-camera live LCD preview screen has overshadowed SLR's popularity.
Nearly all inexpensive compact digital cameras now include an LCD preview screen allowing the photographer to see what the CCD is capturing. However, SLR is still popular in high-end and professional cameras because they are system cameras with interchangeable parts, allowing customization, they have far less shutter lag, allowing photographs to be timed more precisely. The pixel resolution, contrast ratio, refresh rate, color gamut of an LCD preview screen cannot compete with the clarity and shadow detail of a direct-viewed optical SLR viewfinder. Large format SLR cameras were first marketed with the introduction of C. R. Smith's Monocular Duplex. SLRs for smaller exposure formats were launched in the 1920s by several camera makers; the first 35mm SLR available to the mass market, Leica's PLOOT reflex housing along with a 200mm f4.5 lens paired to a 35mm rangefinder camera body, debuted in 1935. The Soviet Спорт a 24mm by 36mm image size, was prototyped in 1934 and went to market in 1937. K. Nüchterlein's Kine Exakta was the first integrated 35mm SLR to enter the market.
Additional Exakta models, all with waist-level finders, were produced up to and during World War II. Another ancestor of the modern SLR camera was the Swiss-made Alpa, innovative, influenced the Japanese cameras; the first eye-level SLR viewfinder was patented in Hungary on August 23, 1943 by Jenő Dulovits, who designed the first 35 mm camera with one, the Duflex, which used a system of mirrors to provide a laterally correct, upright image in the eye-level viewfinder. The Duflex, which went into serial production in 1948, was the world's first SLR with an instant-return mirror; the first commercially produced SLR that employed a roof pentaprism was the Italian Rectaflex A.1000, shown in full working condition on Milan fair April 1948 and produced from September the same year, thus being on the market one year before the east German Zeiss Ikon VEB Contax S, announced on May 20, 1949, produced from September. The Japanese adopted and further developed the SLR. In 1952, Asahi developed the Asahiflex and in 1954, the Asahiflex IIB.
In 1957, the Asahi Pentax combined the right-hand thumb wind lever. Nikon and Yashica introduced their first SLRs in 1959; as a small matter of history, the first 35 mm camera to feature through the lens light metering may have been Nikon, with a prototype rangefinder camera, the SPX. According to the website below, the camera used Nikon'S' type rangefinder lenses. Through-the-lens light metering is known as "behind-the-lens metering". In the SLR design scheme, there were various placements made for the metering cells, all of which used CdS photocells; the cells were either located in the pentaprism housing, where they metered light transmitted through the focusing screen. Pentax was the first manufacturer to show an early prototype 35 mm behind-the-lens metering SLR camera, named the Pentax Spotmatic; the camera was shown at the 1960 photokina show. However, the first
In optics, a Porro prism, named for its inventor Ignazio Porro, is a type of reflection prism used in optical instruments to alter the orientation of an image. It consists of a block of glass shaped as a right geometric prism with right-angled triangular end faces. In operation, light enters the large rectangular face of the prism, undergoes total internal reflection twice from the sloped faces, exits again through the large rectangular face; because the light exits and enters the glass only at normal incidence, the prism is not dispersive. An image travelling through a Porro prism is rotated by 180° and exits in the opposite direction offset from its entrance point. Porro prisms are most used in pairs, forming a double Porro prism. A second prism, rotated 90° with respect to the first, is placed such that light will traverse both prisms; the net effect of the prism system is a beam parallel to but displaced from its original direction, with the image rotated 180°. Double Porro prism systems are used in small optical telescopes to re-orient an inverted image, in many binoculars where they both erect the image and provide a longer, folded distance between the objective lenses and the eyepieces.
The two components of the double Porro system are cemented together, the prisms may be truncated to save weight and size. While a single porro prism can be constructed to work as well as a roof prism, it is used as such. Therefore, to reduce the cost of production for a porro prism, the edge of the roof is left out. Sometimes only one small window as entrance surface and one window as exit surface are polished; the distinction between a roof prism and a porro prism is that for the roof prism the roof edge lies in the same plane as entrance and exit beam, while for a porro prism the roof edge is orthogonal to the plane formed by the beams. Furthermore, the roof prism has no displacement and a deviation between 45° and 90°, while in a single porro prism the beam is deviated by 180° and displaced by a distance of at least one beam diameter. A variation on the double Porro prism is the Porro-Abbe prism
Diffraction spikes are lines radiating from bright light sources, causing what is known as the starburst effect in photographs and in vision. They are artifacts caused by light diffracting around the support vanes of the secondary mirror in reflecting telescopes, or edges of non-circular camera apertures, around eyelashes and eyelids in the eye. In the vast majority of reflecting telescope designs, the secondary mirror has to be positioned at the central axis of the telescope and so has to be held by struts within the telescopes tube. No matter how fine these support rods are they diffract the incoming light from a subject star and this appears as diffraction spikes which are the Fourier transform of the support struts; the spikes represent a loss of light. Although diffraction spikes can obscure parts of a photograph and are undesired in professional contexts, some amateur astronomers like the visual effect they give to bright stars – the "Star of Bethlehem" appearance – and modify their refractors to exhibit the same effect, or to assist with focusing when using a CCD.
A small number of reflecting telescopes designs avoid diffraction spikes by placing the secondary mirror off-axis. Early off-axis designs such as the Herschelian and the Schiefspiegler telescopes have serious limitations such as astigmatism and long focal ratios, which make them useless for research; the brachymedial design by Ludwig Schupmann, which uses a combination of mirrors and lenses, is able to correct chromatic aberration over a small area and designs based on the Schupmann brachymedial are used for research of double stars. There are a small number of off-axis unobstructed all-reflecting anastigmats which give optically perfect images. Refracting telescopes and their photographic images do not have the same problem as their lenses are not supported with spider vanes. Iris diaphragms with moving blades are used in most modern camera lenses to restrict the light received by the film or sensor. While manufacturers attempt to make the aperture circular for a pleasing bokeh, its shape tends towards a polygon with the same number of sides as blades when stopped down to high f-numbers.
Diffraction spreads out light waves passing through the aperture perpendicular to the roughly-straight edge, each edge yielding two spikes 180° apart. As the blades are uniformly distributed around the circle, on a diaphragm with an number of blades, the diffraction spikes from blades on opposite sides overlap. A diaphragm with n blades yields n spikes if n is and 2n spikes if n is odd. In normal vision, diffraction through eyelashes – and due to the edges of the eyelids if one is squinting – produce many diffractions spikes. If it is windy the motion of the eyelashes cause spikes that move around and scintillate. After a blink, the eyelashes may come back in a different position and cause the diffraction spikes to jump around; this is classified as an Entoptic phenomenon. A cross screen filter known as a star filter, creates a star pattern using a fine diffraction grating embedded in the filter, or sometimes by the use of prisms in the filter; the number of stars varies by the construction of the filter, as does the number of points each star has.
A similar effect is achieved by photographing bright lights through a window screen with vertical and horizontal wires. The angles of the bars of the cross depend on the orientation of the screen relative to the camera. In amateur astrophotography, a Bahtinov mask can be used to focus small astronomical telescopes accurately. Light from a bright point such as an isolated bright star reaching different quadrants of the primary mirror or lens is first passed through grilles at three different orientations. Half of the mask generates a narrow "X" shape from four diffraction spikes. Changing the focus causes the shapes to move with respect to each other, as shown in the illustration; when the line passes through the middle of the "X", the telescope is in focus and the mask can be removed. Diffraction spikes explained by Astronomy Picture of the Day. Merrifield, Michael. "Diffraction Spikes". Deep Sky Videos. Brady Haran
Chemical vapor deposition
Chemical vapor deposition is a deposition method used to produce high quality, high-performance, solid materials under vacuum. The process is used in the semiconductor industry to produce thin films. In typical CVD, the wafer is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Volatile by-products are produced, which are removed by gas flow through the reaction chamber. Microfabrication processes use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline and epitaxial; these materials include: silicon, fluorocarbons, tungsten, titanium nitride and various high-k dielectrics. CVD is practiced in a variety of formats; these processes differ in the means by which chemical reactions are initiated. Classified by operating conditions: Atmospheric pressure CVD – CVD at atmospheric pressure. Low-pressure CVD – CVD at sub-atmospheric pressures. Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer.
Ultrahigh vacuum CVD – CVD at low pressure below 10−6 Pa. Note that in other fields, a lower division between high and ultra-high vacuum is common 10−7 Pa. Most modern CVD is either LPCVD or UHVCVD. Classified by physical characteristics of vapor: Aerosol assisted CVD – CVD in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically; this technique is suitable for use with non-volatile precursors. Direct liquid injection CVD – CVD in which the precursors are in liquid form. Liquid solutions are injected in a vaporization chamber towards injectors; the precursor vapors are transported to the substrate as in classical CVD. This technique is suitable for use on solid precursors. High growth rates can be reached using this technique. Classified by type of substrate heating: Hot wall CVD – CVD in which the chamber is heated by an external power source and the substrate is heated by radiation from the heated chamber walls. Cold wall CVD – CVD in which only the substrate is directly heated either by induction or by passing current through the substrate itself or a heater in contact with the substrate.
The chamber walls are at room temperature. Plasma methods: Microwave plasma-assisted CVD Plasma-Enhanced CVD – CVD that utilizes plasma to enhance chemical reaction rates of the precursors. PECVD processing allows deposition at lower temperatures, critical in the manufacture of semiconductors; the lower temperatures allow for the deposition of organic coatings, such as plasma polymers, that have been used for nanoparticle surface functionalization. Remote plasma-enhanced CVD – Similar to PECVD except that the wafer substrate is not directly in the plasma discharge region. Removing the wafer from the plasma region allows processing temperatures down to room temperature. Atomic-layer CVD – Deposits successive layers of different substances to produce layered, crystalline films. See Atomic layer epitaxy. Combustion Chemical Vapor Deposition – Combustion Chemical Vapor Deposition or flame pyrolysis is an open-atmosphere, flame-based technique for depositing high-quality thin films and nanomaterials.
Hot filament CVD – known as catalytic CVD or more initiated CVD, this process uses a hot filament to chemically decompose the source gases. The filament temperature and substrate temperature thus are independently controlled, allowing colder temperatures for better absorption rates at the substrate and higher temperatures necessary for decomposition of precursors to free radicals at the filament. Hybrid Physical-Chemical Vapor Deposition – This process involves both chemical decomposition of precursor gas and vaporization of a solid source. Metalorganic chemical vapor deposition – This CVD process is based on metalorganic precursors. Rapid thermal CVD – This CVD process uses heating lamps or other methods to heat the wafer substrate. Heating only the substrate rather than the gas or chamber walls helps reduce unwanted gas-phase reactions that can lead to particle formation. Vapor-phase epitaxy Photo-initiated CVD – This process uses UV light to stimulate chemical reactions, it is similar to plasma processing, given.
Under certain conditions, PICVD can be operated near atmospheric pressure. Laser Chemical vapor deposition - This CVD process uses lasers to heat spots or lines on a substrate in semiconductor applications. In MEMS and in fiber production the lasers are used to break down the precursor gas-process temperature can exceed 2000 °C-to build up a solid structure in much the same way as laser sintering based 3-D printers build up solids from powders. CVD is used to deposit conformal films and augment substrate surfaces in ways that more traditional surface modification techniques are not capable of. CVD is useful in the process of atomic layer deposition at depositing thin layers of material. A variety of applications for such films exist. Gallium arsenide is used in photovoltaic devices. Amorphous polysilicon is used in photovoltaic devices. Certain carbides and nitrides confer wear-resistance. Polymerization by CVD the most versatile of all applications, allows for super-thin coatings which possess some de
A pentaprism is a five-sided reflecting prism used to deviate a beam of light by a constant 90° if the entry beam is not at 90° to the prism. The beam reflects inside the prism twice, allowing the transmission of an image through a right angle without inverting it as an ordinary right-angle prism or mirror would; the reflections inside the prism are not caused by total internal reflection, since the beams are incident at an angle less than the critical angle. Instead, the two faces are coated to provide mirror surfaces; the two opposite transmitting faces are coated with an antireflection coating to reduce spurious reflections. The fifth face of the prism is not used optically but truncates what would otherwise be an awkward angle joining the two mirrored faces. A variant of this prism is the roof pentaprism, used in the viewfinder of single-lens reflex cameras; the camera lens renders an image, both vertically and laterally reversed, the reflex mirror re-inverts it leaving an image laterally reversed.
In this case, the image needs to be reflected left-to-right as the prism transmits the image formed on the camera's focusing screen. This lateral inversion is done by replacing one of the reflective faces of a normal pentaprism with a "roof" section, with two additional surfaces angled towards each other and meeting at 90°, which laterally reverses the image back to normal. Reflex cameras with waist-level finders, including many medium format cameras, display a laterally reversed image directly from the focusing screen, viewed from above. In surveying a double pentaprism and a plumb-bob are used to stake out right angles, e.g. on a construction site. Pentamirror Single-lens reflex camera Digital single-lens reflex camera Retroreflector
Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of waves around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle. In classical physics, the diffraction phenomenon is described as the interference of waves according to the Huygens–Fresnel principle that treats each point in the wave-front as a collection of individual spherical wavelets; these characteristic behaviors are exhibited when a wave encounters an obstacle or a slit, comparable in size to its wavelength. Similar effects occur when a light wave travels through a medium with a varying refractive index, or when a sound wave travels through a medium with varying acoustic impedance. Diffraction has an impact on the acoustic space. Diffraction occurs with all waves, including sound waves, water waves, electromagnetic waves such as visible light, X-rays and radio waves. Since physical objects have wave-like properties, diffraction occurs with matter and can be studied according to the principles of quantum mechanics.
Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1660. While diffraction occurs whenever propagating waves encounter such changes, its effects are most pronounced for waves whose wavelength is comparable to the dimensions of the diffracting object or slit. If the obstructing object provides multiple spaced openings, a complex pattern of varying intensity can result; this is due to the addition, or interference, of different parts of a wave that travel to the observer by different paths, where different path lengths result in different phases. The formalism of diffraction can describe the way in which waves of finite extent propagate in free space. For example, the expanding profile of a laser beam, the beam shape of a radar antenna and the field of view of an ultrasonic transducer can all be analyzed using diffraction equations; the effects of diffraction are seen in everyday life. The most striking examples of diffraction are those.
This principle can be extended to engineer a grating with a structure such that it will produce any diffraction pattern desired. Diffraction in the atmosphere by small particles can cause a bright ring to be visible around a bright light source like the sun or the moon. A shadow of a solid object, using light from a compact source, shows small fringes near its edges; the speckle pattern, observed when laser light falls on an optically rough surface is a diffraction phenomenon. When deli meat appears to be iridescent, diffraction off the meat fibers. All these effects are a consequence of the fact. Diffraction can occur with any kind of wave. Ocean waves diffract around other obstacles. Sound waves can diffract around objects, why one can still hear someone calling when hiding behind a tree. Diffraction can be a concern in some technical applications; the effects of diffraction of light were first observed and characterized by Francesco Maria Grimaldi, who coined the term diffraction, from the Latin diffringere,'to break into pieces', referring to light breaking up into different directions.
The results of Grimaldi's observations were published posthumously in 1665. Isaac Newton attributed them to inflexion of light rays. James Gregory observed the diffraction patterns caused by a bird feather, the first diffraction grating to be discovered. Thomas Young performed a celebrated experiment in 1803 demonstrating interference from two spaced slits. Explaining his results by interference of the waves emanating from the two different slits, he deduced that light must propagate as waves. Augustin-Jean Fresnel did more definitive studies and calculations of diffraction, made public in 1815 and 1818, thereby gave great support to the wave theory of light, advanced by Christiaan Huygens and reinvigorated by Young, against Newton's particle theory. In traditional classical physics diffraction arises because of the way; the propagation of a wave can be visualized by considering every particle of the transmitted medium on a wavefront as a point source for a secondary spherical wave. The wave displacement at any subsequent point is the sum of these secondary waves.
When waves are added together, their sum is determined by the relative phases as well as the amplitudes of the individual waves so that the summed amplitude of the waves can have any value between zero and the sum of the individual amplitudes. Hence, diffraction patterns have a series of maxima and minima. In the modern quantum mechanical understanding of light propagation through a slit every photon has what is known as a wavefunction which describes its path from the emitter through the slit to the screen; the wavefunction is determined by the physical surroundings such as slit geometry, screen distance and initial conditions when the photon is created. In important experiments the existence of the photon's wavef
In optics, the Airy disk and Airy pattern are descriptions of the best-focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light. The Airy disk is of importance in physics and astronomy; the diffraction pattern resulting from a uniformly illuminated, circular aperture has a bright central region, known as the Airy disk, which together with the series of concentric rings around is called the Airy pattern. Both are named after George Biddell Airy; the disk and rings phenomenon had been known prior to Airy. They succeed each other nearly at equal intervals round the central disc.... However, Airy wrote the first full theoretical treatment explaining the phenomenon. Mathematically, the diffraction pattern is characterized by the wavelength of light illuminating the circular aperture, the aperture's size; the appearance of the diffraction pattern is additionally characterized by the sensitivity of the eye or other detector used to observe the pattern.
The most important application of this concept is in telescopes. Due to diffraction, the smallest point to which a lens or mirror can focus a beam of light is the size of the Airy disk. If one were able to make a perfect lens, there is still a limit to the resolution of an image created by such a lens. An optical system in which the resolution is no longer limited by imperfections in the lenses but only by diffraction is said to be diffraction limited. Far from the aperture, the angle at which the first minimum occurs, measured from the direction of incoming light, is given by the approximate formula: sin θ ≈ 1.22 λ d or, for small angles θ ≈ 1.22 λ d, where θ is in radians, λ is the wavelength of the light in meters, d is the diameter of the aperture in meters. Airy wrote this as s = 2.76 a, where s was the angle of first minimum in seconds of arc, a was the radius of the aperture in inches, the wavelength of light was assumed to be 0.000022 inches. The Rayleigh criterion for resolving two objects that are point sources of light, such as stars seen through a telescope, is that the center of the Airy disk for the first object occurs at the first minimum of the Airy disk of the second.
This means that the angular resolution of a diffraction-limited system is given by the same formulae. However, while the angle at which the first minimum occurs depends only on wavelength and aperture size, the appearance of the diffraction pattern will vary with the intensity of the light source; because any detector used to observe the diffraction pattern can have an intensity threshold for detection, the full diffraction pattern may not be apparent. In astronomy, the outer rings are not apparent in a magnified image of a star, it may be that none of the rings are apparent, in which case the star image appears as a disk rather than as a full diffraction pattern. Furthermore, fainter stars will appear as smaller disks than brighter stars, because less of their central maximum reaches the threshold of detection. While in theory all stars or other "point sources" of a given wavelength and seen through a given aperture have the same Airy disk radius characterized by the above equation, differing only in intensity, the appearance is that fainter sources appear as smaller disks, brighter sources appear as larger disks.
This was described by Airy in his original work: The rapid decrease of light in the successive rings will sufficiently explain the visibility of two or three rings with a bright star and the non-visibility of rings with a faint star. The difference of the diameters of the central spots of different stars... is fully explained. Thus the radius of the spurious disk of a faint star, where light of less than half the intensity of the central light makes no impression on the eye, is determined by, whereas the radius of the spurious disk of a bright star, where light of 1/10 the intensity of the central light is sensible, is determined by. Despite this feature of Airy's work, the radius of the Airy disk is given as being the angle of first minimum in standard textbooks. In reality, the angle of first minimum is a limiting value for the size of the Airy disk, not a definite radius. If two objects imaged by a camera are separated by an angle small enough that their Airy disks on the camera detector start overlapping, the objects cannot be separated any more in the image, they start blurring together.
Two objects are said to be just resolved when the maximum of the first Airy pattern falls on top of the first minimum of the second Airy pattern. Therefore, the sma