Photographic paper is a paper coated with a light-sensitive chemical formula, used for making photographic prints. The light-sensitive layer of the paper is called the emulsion, the most common chemistry was based on silver salts but other alternatives have been used. The initial light exposure is carefully controlled to produce a gray scale image on the paper with appropriate contrast and gradation. Photographic paper may be exposed to light using digital printers such as the LightJet, with a camera, by scanning a modulated light source over the paper, despite the introduction of digital photography, photographic papers are still sold commercially. Photographic papers are manufactured in standard sizes, paper weights. A range of emulsions are available that differ in their sensitivity, colour response. Colour papers are available for making colour images. The effect of light in darkening a prepared paper was discovered by Thomas Wedgwood in 1802, photographic papers have been used since the beginning of all negative–positive photographic processes as developed and popularized by William Fox Talbot.
After the early days of photography, papers have been manufactured on a scale with improved consistency. Photographic papers fall into one of three sub-categories, Papers used for negative-positive processes and this includes all current black-and-white papers and chromogenic colour papers. Papers used for positive-positive processes in which the film is the same as the final image, Papers used for positive-positive film-to-paper processes where a positive image is enlarged and copied onto a photographic paper, for example the Ilfochrome process. In Chromogenic colour papers, the layers are sensitive to red and blue light, respectively producing cyan, magenta. Modern black-and-white papers are coated on a range of bases, baryta-coated paper. In the past, linen has been used as a base material, fiber-based photographic papers consist of a paper base coated with baryta. Tints are sometimes added to the baryta to add colour to the final print. Most fiber-based papers include a clear hardened gelatin layer above the emulsion which protects it from physical damage, Papers without a supercoating are suitable for use with the bromoil process.
Fiber-based papers are chosen as a medium for high-quality prints for exhibition, display. These papers require careful processing and handling, especially when wet, they are easier to tone, hand-colour and retouch than resin-coated equivalents
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of a system determine the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of importance for the appearance at the image plane. If an aperture is narrow, highly collimated rays are admitted, a wide aperture admits uncollimated rays, resulting in a sharp focus only for rays coming from a certain distance. This means that a wide aperture results in an image that is sharp for things at the correct distance, the aperture determines how many of the incoming rays are actually admitted and thus how much light reaches the image plane. In the human eye, the pupil is the aperture, an optical system typically has many openings or structures that limit the ray bundles. In general, these structures are called stops, and the stop is the stop that primarily determines the ray cone angle. In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the stop or the opening itself.
For example, in a telescope, the stop is typically the edges of the objective lens or mirror. One speaks of a telescope as having, for example, note that the aperture stop is not necessarily the smallest stop in the system. Magnification and demagnification by lenses and other elements can cause a large stop to be the aperture stop for the system. In astrophotography, the aperture may be given as a measure or as the dimensionless ratio between that measure and the focal length. In other photography, it is given as a ratio. Sometimes stops and diaphragms are called apertures, even when they are not the stop of the system. The word aperture is used in other contexts to indicate a system which blocks off light outside a certain region. In astronomy, for example, a photometric aperture around a star usually corresponds to a window around the image of a star within which the light intensity is assumed. The aperture stop is an important element in most optical designs and its most obvious feature is that it limits the amount of light that can reach the image/film plane.
This can be unavoidable, as in a telescope where one wants to collect as much light as possible, or deliberate
A darkroom is a workshop used by photographers working with photographic film to make prints and carry out other associated tasks. It is a room that can be completely dark to allow the processing of the light sensitive photographic materials, including film. Various equipment is used in the darkroom, including an enlarger, baths containing chemicals, darkrooms have been created and used since the inception of photography in the early 19th century. Darkrooms have many various manifestations, from the space used by Ansel Adams to a retooled ambulance wagon used by Timothy H. OSullivan. From the initial development to the creation of prints, the process allows complete control over the medium. Other applications of darkrooms include the use in testing, such as magnetic particle inspection. A sheet of paper is exposed to the enlarged image from the negative. When making black-and-white prints, a safelight is commonly used to illuminate the work area, since the majority of black-and-white papers are sensitive to only blue, or to blue and green light, a red- or amber-colored light can be safely used without exposing the paper.
Color print paper, being sensitive to all parts of the visible spectrum, another use for a darkroom is to load film in and out of cameras, development spools, or film holders, which requires complete darkness. During exposure, values in the image can be adjusted, most often by dodging and/or burning, usually thin pieces of colored plastic, can be used to increase or decrease an images contrast. One method of printing, called split filter printing, is where the photographer determines two separate exposure times using two separate filters to create a single print. This method allows the photographer to achieve a broad range, with detailed highlights. After exposure, the printing paper is ready to be processed. Photographers generally begin printing a roll of film by making a print of their negatives to use as a quick reference to decide which images to enlarge. Some large format photographers, such as Edward Weston, make only contact prints of their large negatives, the paper that has been exposed is processed, first by immersion in a photographic developer, halting development with a stop bath, and fixing in a photographic fixer.
The print is washed to remove the processing chemicals and dried. There are a variety of other, additional steps a photographer may take, such as toning
Eastman Kodak Company, commonly referred to as Kodak, is an American technology company that produces imaging products with its historic basis on photography. The company is headquartered in Rochester, New York and is incorporated in New Jersey, Kodak provides packaging, functional printing, graphic communications and professional services for businesses around the world. Its main business segments are Print Systems, Enterprise Inkjet Systems, Micro 3D Printing and Packaging and Solutions and it is best known for photographic film products. Kodak was founded by George Eastman and Henry A, during most of the 20th century, Kodak held a dominant position in photographic film. The companys ubiquity was such that its Kodak moment tagline entered the lexicon to describe a personal event that was demanded to be recorded for posterity. Kodak began to struggle financially in the late 1990s, as a result of the decline in sales of photographic film, as a part of a turnaround strategy, Kodak began to focus on digital photography and digital printing, and attempted to generate revenues through aggressive patent litigation.
In January 2012, Kodak filed for Chapter 11 bankruptcy protection in the United States District Court for the Southern District of New York. In February 2012, Kodak announced that it would stop making digital cameras, pocket video cameras and digital picture frames, in January 2013, the Court approved financing for Kodak to emerge from bankruptcy by mid 2013. Kodak sold many of its patents for approximately $525,000,000 to a group of companies under the names Intellectual Ventures, on September 3,2013, the company emerged from bankruptcy having shed its large legacy liabilities and exited several businesses. Personalized Imaging and Document Imaging are now part of Kodak Alaris, on March 12,2014, it announced that the board of directors elected Jeffrey J. Clarke as chief executive officer and a member of its board of directors. As late as 1976, Kodak commanded 90% of film sales, Japanese competitor Fujifilm entered the U. S. market with lower-priced film and supplies, but Kodak did not believe that American consumers would ever desert its brand.
Kodak passed on the opportunity to become the film of the 1984 Los Angeles Olympics, Fuji won these sponsorship rights. Fuji opened a plant in the U. S. and its aggressive marketing. Fuji went from a 10% share in the early 1990s to 17% in 1997, fujis films soon found a competitive edge in higher-speed negative films, with a tighter grain structure. The complaint was lodged by the United States with the World Trade Organization, on January 30,1998, the WTO announced a sweeping rejection of Kodaks complaints about the film market in Japan. Although Kodak developed a camera in 1975, the first of its kind. In the 1990s, Kodak planned a journey to move to digital technology. CEO George M. C. Fisher reached out to Microsoft, Apples pioneering QuickTake consumer digital cameras, introduced in 1994, had the Apple label but were produced by Kodak
Factors considered may include unusual lighting distribution, variations within a camera system, non-standard processing, or intended underexposure or overexposure. Cinematographers may apply exposure compensation for changes in angle or film speed. Most DSLR cameras have a display whereby the photographer can set the camera to either over or under expose the subject by up to three f-stops in 1/3rd stop intervals. Each number on the scale represents one f-stop, decreasing the exposure by one f-stop will halve the amount of light reaching the sensor, the dots in between the numbers represent 1/3rd of an f-stop. In photography, some cameras include exposure compensation as a feature to allow the user to adjust the automatically calculated exposure, camera exposure compensation is commonly stated in terms of EV units,1 EV is equal to one exposure step, corresponding to a doubling of exposure. Exposure can be adjusted by changing either the lens f-number or the exposure time, if the mode is aperture priority, exposure compensation changes the exposure time, if the mode is shutter priority, the f-number is changed.
If a flash is being used, some cameras will adjust it as well, the earliest reflected-light exposure meters were wide-angle, averaging types, measuring the average scene luminance. When measuring a scene with atypical distribution of light and dark elements, or an element that is lighter or darker than a middle tone. For example, a scene with predominantly light tones often will be underexposed and that both scenes require the same exposure, regardless of the meter indication, becomes obvious from a scene that includes both a white horse and a black horse. A photographer usually can recognize the difference between a horse and a black horse, a meter usually cannot. When metering a white horse, a photographer can apply exposure compensation so that the horse is rendered as white. Many modern cameras incorporate metering systems that measure scene contrast as well as average luminance, in scenes with very unusual lighting, these metering systems sometimes cannot match the judgment of a skilled photographer, so exposure compensation still may be needed.
An early application of compensation was the Zone System developed by Ansel Adams. Developed for black-and-white film, the Zone System divided luminance into 11 zones, with Zone 0 representing pure black, the meter indication would place whatever was metered on Zone V, a medium gray. The meter indication, remains Zone V, the Zone System is a very specialized form of exposure compensation, and is used most effectively when metering individual scene elements, such as a sunlit rock or the bark of a tree in shade. Many cameras incorporate narrow-angle spot meters to facilitate such measurements, because of the limited tonal range, an exposure compensation range of ±2 EV is often sufficient for using the Zone System with color film and digital sensors. Exposure value Exposure index Light meter Zone System Exposure bracketing Auto Exposure Bracketing
It is evoked by light with a predominant wavelength of between 490–520 nm, between the wavelengths of blue and green. In the subtractive color system, or CMYK, which can be overlaid to produce all colors in paint and color printing, cyan is one of the colors, along with magenta, yellow. In the additive color system, or RGB color model, used to all the colors on a computer or television display, cyan is made by mixing equal amounts of green. Cyan is the complement of red, it can be made by the removal of red from white light, mixing red light and cyan light at the right intensity will make white light. The web color cyan is synonymous with aqua, other colors in the cyan color range are teal, electric blue and others described as blue-green. Its name is derived from the Ancient Greek κύανος, transliterated kyanos, meaning blue, dark blue enamel. It was formerly known as blue or cyan-blue, and its first recorded use as a color name in English was in 1879. Further origins of the name can be traced back to a dye produced from the cornflower.
In most languages, cyan is not a color term. Reasons for why cyan is not linguistically acknowledged as a color term can be found in the frequent lack of distinction between blue and green in many languages. The web color cyan shown at right is a color in the RGB color model. In X11 colors, this color is called both cyan and aqua, in the HTML color list, this same color is called aqua. The web colors are more vivid than the used in the CMYK color system. To reproduce the web color cyan in inks, it is necessary to add some white ink to the printers cyan below, so when it is reproduced in printing, it is not a primary subtractive color. It is called aqua because it is a commonly associated with water. Cyan is one of the inks used in four-color printing, along with magenta and black. While both the secondary and the subtractive primary are called cyan, they can be substantially different from one another. Cyan printing ink can be saturated or less saturated than the RGB secondary cyan, depending on what RGB color space
Depth of field
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
A silver halide is one of the chemical compounds that can form between the element silver and one of the halogens. In particular, chlorine and fluorine may each combine with silver to silver bromide, silver chloride, silver iodide. As a group, they are referred to as the silver halides. Silver halides are light-sensitive chemicals, and are used in photographic film. The gelatin is a part of the emulsion as the protective colloid of appropriate physical and chemical properties. Gelatin may contain elements which increase the light sensitivity of the emulsion. When a silver halide crystal is exposed to light, a sensitivity speck on the surface of the crystal is turned into a speck of metallic silver. If the speck of silver contains approximately four or more atoms, areas of the emulsion receiving larger amounts of light undergo the greatest development and therefore results in the highest optical density. Silver bromide and silver chloride may be used separately or combined, depending on the sensitivity, silver fluoride is not used in photography.
Silver halides are used to make corrective lenses darken when exposed to ultraviolet light. Silver halides, except for silver fluoride, are insoluble in water. Silver nitrate can be used to precipitate halides, this application is useful in analysis of halides. The three main silver halide compounds have distinctive colours that can be used to quickly identify halide ions in a solution, the silver chloride compound forms a white precipitate, silver bromide a creamy coloured precipitate and silver iodide a yellow coloured precipitate. However, close attention is necessary for other compounds in the test solution, some compounds can considerably increase or decrease the solubility of AgX. Examples of compounds that increase the solubility include, thiocyanate, thiourea, ammonia, thioether, scientists from Tel Aviv University are experimenting with silver halide optical fibers for transmitting mid-infrared light from carbon dioxide lasers. The fibers allow laser welding of human tissue, as an alternative to traditional sutures
Photographic processing or development is the chemical means by which photographic film or paper is treated after photographic exposure to produce a negative or positive image. Photographic processing transforms the latent image into an image, makes this permanent. All processes based upon the process are similar, regardless of the film or papers manufacturer. Exceptional variations include instant films such as made by Polaroid. Kodachrome required Kodaks proprietary K-14 process, Kodachrome film production ceased in 2009, and K-14 processing is no longer available as of December 30,2010. Ilfochrome materials use the dye destruction process, all photographic processing use a series of chemical baths. Processing, especially the development stages, requires very close control of temperature, the film may be soaked in water to swell the gelatin layer, facilitating the action of the subsequent chemical treatments. The developer converts the latent image to macroscopic particles of metallic silver, a stop bath, † typically a dilute solution of acetic acid or citric acid, halts the action of the developer. A rinse with water may be substituted.
The fixer makes the image permanent and light-resistant by dissolving remaining silver halide, a common fixer is hypo, specifically ammonium thiosulfate. Washing in clean water removes any remaining fixer, residual fixer can corrode the silver image, leading to discolouration and fading. The washing time can be reduced and the more completely removed if a hypo clearing agent is used after the fixer. Film may be rinsed in a solution of a non-ionic wetting agent to assist uniform drying. Film is dried in an environment and placed into protective sleeves. Once the film is processed, it is referred to as a negative. The negative may now be printed, the negative is placed in an enlarger, many different techniques can be used during the enlargement process. Two examples of enlargement techniques are dodging and burning, the negative may be scanned for digital printing or web viewing after adjustment, and/or manipulation. † In modern automatic processing machines, the bath is replaced by mechanical squeegee or pinching rollers
In optics, chromatic aberration is an effect resulting from dispersion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have different refractive indices for different wavelengths of light, the refractive index of transparent materials decreases with increasing wavelength in degrees unique to each. Since the focal length f of a lens is dependent on the index n. There are two types of aberration and transverse. Axial aberration occurs when different wavelengths of light are focused at different distances from the lens, transverse aberration occurs when different wavelengths are focused at different positions in the focal plane. The acronym LCA is used, but ambiguous, and may refer to either longitudinal or lateral CA, for clarity and these two types have different characteristics, and may occur together. Axial CA occurs throughout the image and is specified by optical engineers and vision scientists in the unit of focus known widely as diopters, transverse CA does not occur in the center, and increases towards the edge, but is not affected by stopping down.
In the earliest uses of lenses, chromatic aberration was reduced by increasing the length of the lens where possible. For example, this could result in extremely long telescopes such as the very long aerial telescopes of the 17th century, isaac Newtons theories about white light being composed of a spectrum of colors led him to the conclusion that uneven refraction of light caused chromatic aberration. There exists a point called the circle of least confusion, where chromatic aberration can be minimized and it can be further minimized by using an achromatic lens or achromat, in which materials with differing dispersion are assembled together to form a compound lens. The most common type is a doublet, with elements made of crown. This reduces the amount of chromatic aberration over a range of wavelengths. By combining more than two lenses of different composition, the degree of correction can be increased, as seen in an apochromatic lens or apochromat. Similarly, the benefit of apochromats is not simply that they focus 3 wavelengths sharply, many types of glass have been developed to reduce chromatic aberration.
These are low dispersion glass, most notably, glasses containing fluorite and these hybridized glasses have a very low level of optical dispersion, only two compiled lenses made of these substances can yield a high level of correction. The use of achromats was an important step in the development of the optical microscope, an alternative to achromatic doublets is the use of diffractive optical elements. Diffractive optical elements are able to generate arbitrary complex wave fronts from a sample of material which is essentially flat. Diffractive optical elements have negative characteristics, complementary to the positive Abbe numbers of optical glasses