Photography Glossary - H
•Halation - diffused ring of light typically formed around small brilliant highlight areas in the subject. It is caused by light passing straight through the emulsion and being reflected back by the film base on the light sensitive layer. This records slightly out of register with the original image.
•Halogens -a group of chemical elements. In photography, three of these, bromine, chlorine and iodine are used with silver to produce light sensitive material.
•Half-frame - negative format of 18 x 24mm. Images are recorded on a vertical axis on standard 35mm film, thus giving 72 half-frame images on film designed for 36 exposures.
•Half-frame camera - camera designed to use 35mm film in a half-frame format.
•Half-plate - picture format measuring 4 ¾ x 6 ½ inches. Some early cameras produced negatives of this size.
•Half-silvered mirror is a glass sheet evenly coated with a substance which transmits part of the light incident on it and reflects the remainder. Used for beam splitting devices in holography, and for front projection.
•Halftone - mechanical process for printing continuous tone images in ink.
•Halogens - collective term for the elements chlorine, bromine and iodine, which are combined with silver to produce the light sensitive crystals used as the basis for photographic emulsions.
•Hand coloring - process of applying color tints, in the form of paint, to a photographic image to create or enhance the color effect.
•Hanger - frame for holding sheet film for processing.
•Hard - defines a scene, negative or print with high contrast.
•Hardeners - chemicals often used with a fixing bath to strengthen the physical characteristics of an emulsion. The most common hardeners are potassium or chrome alum.
•Hard gradation - term denoting the quality of harsh contrast in a photograph.
•Heat filter - optical attachment made of thick infrared absorbing glass, used to absorb heat radiation from alight source without diminishing output.
•Heliography - early photographic process invented by Niepce, employing a polished pewter plate coated with bitumen of Judea.
•Herschel effect - the destruction of an exposed image by infrared radiation.
•Hide - camouflaged barrier used by natural history and wildlife photographers.
•High art photography - general term for an early form of artistic photography (1851-1870), in which photographers set out to match the style and subject matter of paintings of the period.
•High contrast developer - solutions used to produce high contrast images.
•High key - photograph which contains large areas of light tones, with few middle tomes or shadows.
•Highlights - the brightest ares of the subject, represented on a negative by dense deposits of black metallic silver, but reproducing as bright areas on the positive print.
•Hill cloud lens - lens with a 180° angle of view, used for photographing cloud formations and other meteorological work.
•Holding back - 1. Shortening the development time given to film to help reduce image contrast. 2. Method of decreasing exposure given to selective areas of the print. Also referred to as dodging.
•Holography - system of photography, using neither a camera not lens, in which laser beams create an interference patter recorded directly on appropriate light sensitive sheet film or plates. After processing, viewing the image by the light of a laser gives a three dimensional image.
•Horizon - line at which earth and sky appear to meet. Its position, which can be altered by titling the camera or by cropping the image determines whether the sky or the landscape concentrates interest in the picture. A low horizon (tilting the camera up) concentrates interest in the sky while a high horizon (tilting the camera down) concentrates interest in the landscape.
•Hot shoe - fitting on the top of many cameras designed to hold accessories, such as a flash gun.
•Hot spot - often undesirable concentration of the central beam of a flood or spotlight on the subject.
•Hue - name of the color (e.g. red, blue, yellow).
•Hydrobromic acid - acid liberated during the developing process by the reduction of bromide.
•Hydrochloric acid - chemical used in some bleaching solutions.
•Hydrogen peroxide - chemical used in hypo clearing agents.
•Hydroquinone - reducing agent. It is used in developers to provide high contrast results in the presence of a strong alkali.
•Hyperfocal distance - distance between the camera and the hyperfocal point.
•Hyperfocal point - nearest point to the camera which is considered acceptably sharp when the lens is focused on infinity. When a lens is focused on the hyperfocal point, depth of field extends from a distance halfway between this point and the camera to infinity.
•Hypersensitizing - method of increasing the light sensitivity of a photographic emulsion prior to exposure.
•Hypo - common name for a fixing agent, derived from an abbreviation of hyposulfite of soda, the misnomer applied to sodium thiosulfate during the 19th century.
•Hypo eliminator - chemical bath which removes traces of fixing agent from an emulsion.
•"Ideal" format - film format in the proportion of 4 to 3, e.g. 6 x 4.5cm. This ratio is considered the ideal shape by some manufacturers and many photographers for both vertical and horizontal composition.
•IF (Internal Focusing) - system in which only the internal lens group shifts during focusing. IF benefits include focusing without changing the physical length of a lens body, faster focusing, reduced diameter of the focusing ring, closer minimum focusing distance, and aberrations corrected throughout the entire focusing distance range.
•Illuminance - term quantifying the illumination of, or incident light falling on a surface.
•Image - two dimensional representation of a real object, produced by focusing rays of light.
•Image plane - plane commonly at right angles to the optical axis at which a sharp image of the subject is formed. The nearer the subject is to the camera, the greater the lens image plane distance.
•Impressionism - art movement in which painters broke away from the techniques of continuous brushstrokes and clearly expressed detail. They were largely concerned with the effects of light and color.
•Incident light attachment - accessory for a hand held exposure meter which allows it to give incident light readings. Many models come with this accessory permanently attached.
•Incident light reading - measurement, by light meter, of the amount of incident light falling upon a subject. The light meter is placed close to the subject, pointing towards the main light source.
•Indicator chemical - neutral chemical which can be added to a sample of a solution to indicate its pH level or the presence of hypo.
•Infectious development - development action which occurs in processing "lith" materials. The oxidation of hydroquinone produces new and highly active reducing agents, semiquinones, in the presence of a low quantity of sodium sulfite. This results in a very high contrast image.
•Infinity - in photographic terms is a distance great enough to be unaffected by finite variations. In practice this relates to most subjects beyond 1000 meters or, in landscape terms, the horizon.
•Infrared - rays that occur beyond the red end of the electro-magnetic spectrum and are invisible to the human eye. They can be recorded on specially sensitized films, producing images in black & white or color.
•Infrared compensation index - used to compensate the focus for black and white infrared film. Color IR film generally does not require compensation.
•Infrared focus - see IR setting.
•Instamatic camera - compact camera popular in the 1960s and 70s with very simple controls, taking 126 film and yielding a 28 x28 mm negative.
•Instant picture camera - camera, usually with simple controls, producing a finished photographic print within minutes of the film being exposed, (e.g. Polaroid cameras and materials).
•Integral tri-pack - three emulsions, usually of different character, coated on the same film base. The system is used mainly on color materials and also on some special purpose black & white materials.
•Integrating - term used to describe a method of arriving at an exposure setting by taking an average of the light readings from the bright areas and the and the shadow areas of the subject.
•Intensification - chemical method of increasing the density of the photographic image. It is only suitable for treating negative materials and works better on negatives that have been underdeveloped rather than underexposed.
•Intensity scale - exposure scale in which the time of exposure remains constant but the intensity of light increases in regular stops.
•Interchangeable lens system - system of lenses of different focal lengths made to fit the same camera body.
•Interference - interaction of light waves when they meet and either reinforce or cancel each other (e.g. holograms).
•Interleaving - method of agitating more than one sheet of photographic paper in the same tray of chemicals.
•Intermittency effect - states that, a number of short, separate exposures will not produce the same photographic result when combined as a single exposure of equivalent total duration.
•Internegative - negative made on special color film designed for making copy prints from color slides.
•Intersection of thirds - compositional technique whereby the image area is divided horizontally and vertically into equal thirds by means of four imaginary lines. The main subject is considered strongly placed it it is positioned at the intersection of any two of these lines.
•Interspersed aspect ratio - basic requirement of certified photofinishers and certified photo finishing equipment. It specifies the three APS system print formats - C, H and P.
•Inverse square law - states that, when the light source is a point, illumination on a surface is inversely proportional to the square of the distance of the light source.
•Inverted telephoto lens - lens construction which gives a short focal length with a long back focus or lens-film distance. It enable wide-angle lenses to be produced for small format cameras, where space is required for mirrors, shutters, etc.
•Iodine - chemical used in reducers and bleachers.
•Iris diaphragm - continuously adjustable lens aperture consisting of interposed metal leaves.
•Irradiation - by the physical structure of the emulsion and the distribution of the silver halide grains cause rays of light to be scattered as they travel through the emulsion.
•IR setting - mark usually in red, found on many camera lens mounts. It indicates the focus change required for infrared photography.
•IS (Image Stabilizer) - feature that minimizes the effects of camera shake. Originally designed for video cameras. Canon has transferee the technology to its EF lenses.
•I setting - mark found on some cheap box cameras which indicates an instantaneous shutter speed of approximately 1/50 second.
•ISO - International Standards Organization. Used instead of ASA as prefix to film speeds. The scale is identical to the ASA scale.
•Ivorytype - obsolete printing process designed to give the impression of a painting on ivory. A hand colored print was impregnated with wax and squeegeed face down on hot glass. The paper base was then back by ivory tinted paper.
•IX (Information Exchange) - ability of APS film to communicate with devices, and devices to communicate with film.
•JCII - Japan Camera Inspection and Testing Institute. It is an organization in Japan to monitor export quality of Japanese made cameras.
•JPEG - format for compressed graphics files. JPEG graphics are commonly used as part of World Wide Web.
•Joule - unit used to quantify the light output of electronic flash. A joule is equal to one watt second of 40 lumen-seconds. The measure is used to compare flash units in terms of power output.
•K14 - Kodak's chemical process for developing Kodachrome slides.
•Kallitype - obsolete printing process, resembling the platinum process. The image is formed in metallic silver rather than expensive platinum.
•Kelvin (K) - unit of measurement on the absolute temperature scale, used to describe the color content of continuous spectrum light sources.
•Kerr cell - high speed shutter without moving parts, using two crossed polarizing filters at either end of a cylinder filled with nitrobenzine.
•Keyed emulsion sensitivity - term used to describe the color response of color printing papers which have peak sensitivities to the three dye colors present in the same manufacturers color negatives.
•Kilowatt - unit of 1000 watts. Used to measure the power of an electrical light source.
•Kinetic - concerned with movement and motion.
•Knifing - method of removing marks and other blemishes from the surface of a print by gentle scraping with the tip of a sharp knife.
•Kostinsky effect - development effect in which dense image points are inclined to move apart, relative to each other, and light image points to move together, relative to each other. This occurs because developer is not being equally distributed over the image point and is rapidly exhausted when to heavily exposed image points are close together.
•Kromskop - early viewing instrument invented by F.E. Ives, embodying a system of mirrors and color filters to synthesize a full color image. This enabled monochrome transparencies made from separation negatives to be rear-illuminated through blue, green and red filters, and then been seen combined in register as a single image.
•Lamp - general term used to describe the various kinds of artificial light sources used in photography.
•Lamp black - pure carbon pigment, made from soot deposited from burning oils.
•Lamp house - light tight housing of an enlarger or projector, which contains the light source.
•Lantern slides - old term used to describe transparencies.
•Large format camera - general term for any camera having a picture format of 4 x 5 inches or larger.
•Laser - abbreviation for Light Amplification by Stimulated Emission of Radiation.
•Latensification - method of increasing relative film speed by fogging after exposure and before development. It can be achieved by chemical or light means.
•Latent image - invisible image produced by exposure which can be made visible by development.
•Lateral reversal - mirror image reversal of the subject from left to right, as found in the viewfinders of some reflex cameras.
•Latitude - degree by which exposure can be varied and still produce an acceptable image. The degree of latitude varies by film type. Faster films tend to have greater latitude than slower films.
•LCD - liquid crystal diode. LCD is an electronic solid state display system commonly used for the face of wrist watches, and also used to display exposure information in the viewfinder of most modern day cameras. A surface can be temporarily changed from transparent to dense black by application of a charge. The LCD can be programmed to display any required black shape.
•Lead acetate - crystalline, highly poisonous powder used in some toning and intensifying solutions.
•Leader - beginning of a roll of film, which is attached to the camera's take up spool.
•Leaf shutter - see Between the lens shutter.
•LED - light emitting diode. LED is an indicator light used to convey exposure information.
•Lens - optical element made of glass or plastic and capable of bending light. A lens may be constructed of single or multiple elements.
•Lens barrel - metal or plastic tube with a blackened inner surface, in which the lens elements and mechanical components of the lens are mounted.
•Lens cap - plastic, rubber or metal cover which fits over the front or back of the lens to protect it.
•Lens coating - layer or multiple layers of thin anti-reflective materials applied to the surface of lens elements to reduce light reflection and increase the amount of transmitted light.
•Lens drive system - used in autofocus SLR cameras. One type has a motor located inside the lens; in another, a motor inside the camera body turns the lens via a drive shaft.
•Lens hood - opaque tube, either cylindrical, square of funnel shaped, use to shield a lens from stray light outside the field of view.
•Lens shade - see Lens hood.
•Lens shutter camera - camera with the shutter built into the lens.
•Lens speed - largest lens opening (smallest f-number) at which a lens can be set. A fast lens transmits more light and has a larger opening than a slow lens. Determined by the maximum aperture of the lens in relation to its focal length. The speed of a lens is relative to it's focal length. A 400 mm lens with a maximum aperture of f/3.5 is considered extremely fast, while a 28mm f/3.5 lens is thought to be relatively slow.
•Lens system - describes the type and quantity of lenses available for use with a particular camera.
•Lenticular screen - lens system consisting of a screen containing a number of small lenses.There are two applications of lenticular systems. They are used in some exposure meters to gather light and to determine the angle of acceptance of light by the meter. A lenticular screen consisting of a number of lenses et into rows can be used at the camera stage to produce stereoscopic images by synthesizing binocular vision.
•Light - visible radiated energy which forms part of the electro-magnetic spectrum in the wavelength range of 4000-7000 Å (400-720 nm).
•Lightbox - box of fluorescent tubes balanced for white light and covered with translucent glass or plastic. Used for viewing, registering or correcting film negatives and positives.
•Lighting ratio - ratio of the brightness of light falling on the subject from the main (key) light and other (fill) lights. A ratio of about 3:1 is normal for color photography.
•Light meter - alternate term for exposure meter.
•Light sources - general term applied to any source of light used in photography.
•Light tent - tent like structure made of translucent material hung around a frame. The fabric diffuses the light coming from outside the tent so that highly reflective subjects placed inside the tent can be photographed without reflections.
•Light-tight - term denoting a material or piece of equipment that is impervious to light.
•Light trail - image track recorded on photographic material when a point of light is shifted during exposure.
•Light trap - system of entry to a darkroom which allows easy access, but prevents unwanted light from entering.
•Light value - alternative term for exposure value (EV).
•Limiting aperture - actual size of the aperture formed by the iris diaphragm at any setting.
•Linear perspective - apparent convergence of parallel lines with increasing distance in a two dimensional image.
•Line film - high contrast film which, after correct development, gives negatives of black and white only (with no grays).
•Line image - photographic image consisting of black areas and clear film i.e. white.
•Linked Ring Brotherhood - group of pictorialist photographers who broke away from the Photographic Society of Great Britain. Existed between 1892-1910.
•Lippman process - early color process invented by Professor Gabriel Lippmann (1845-1921). Light first passed through an almost transparent emulsion layer and was then reflected back by a layer of mercury. The interference between reflected and incident light produced a latent image in the emulsion which could be given b&w processing, but when backed with a mirror appeared in color.
•Lith film - extreme form of line film, which produces very high contrast images when used in conjunction with a special lith developer.
•Local control - method of controlling the final quality of a print by increasing or decreasing the exposure given to localized areas of the print by selective masking.
•Log e - logarithmic value (to the base 10) of the relative brightness exposed on the film when undergoing sensitometric testing.
•Long focus - a lens in which the focal length is much greater than the diagonal of the film format with which it is used.
•Low key - photograph in which tones are predominantly dark and there are few highlights.
•Lumen second - unit to measure the total light output of a photographic source.
•Luminance - measurable amount of light which is emitted by or reflected from a source.
•Luminance meter - alternate term for exposure meter.
•Luminescence - visible light produced from a surface submitted to invisible radiation such as UV, X rays and son on. Unlike fluorescent light it continues to be emitted after the existing source is removed, gradually fading away.
•Luminous flux - intensity of a light source, measured in lumens.
•Mackie line is an effect sometime found on a negative or print, in which a light line forms along the boundaries of the darkest image areas. It may also be caused during processing by the diffusion of exhausted developer, lack of agitation, or by solarization.
•Macro attachment are supplementary elements attached to the front of a normal lens to give an extreme close-up facility.
•Macro lens is a lens specially designed to give accurate resolution of a very near subject without the need for supplementary attachments. Sometimes, incorrectly, referred to as a micro lens.
•Macrophotography is photography which produces an image larger than the original subject size without the use of a microscope.
•Magazine is a light-tight container holding roll film.
•Magenta is the complimentary color to green. It is composed of blue and red light.
•Magnification is the size of the image relative to the size of the subject used to produce it. It is an expression of the ratio of the subject-lens distance to the image-lens distance. When object distance = image distance, magnification = 1.
•Magnification ratio see Magnification.
•Main light see Key light.
•Mask is an opaque material used to cover the edges of the printing paper, and thus produce borders when the paper is exposed to light.
•Masking is a system of controlling negative density ranges or color saturation through the use of unsharp masks.
•Masking frame is an adjustable frame used to hold printing paper in position under the enlarger, also referred to as an enlarging easel.
•Mat is an alternative term used for matte. Also describes the cardboard surround in a picture frame.
•Matte field is a granular textured surface that disperses light in order to form a clear image. Used in the viewfinder optical system.
•Matrix is a relief image, usually made from gelatin and used for processes such as dye transfer printing.
•Matte box is a mask used to make images suitable for wide-screen projection.
•Meniscus lens is a simple lens consisting of a single piece off glass, thicker at the center than at the edges. It has one concave and one convex face.
•Mercuric chloride is a chemical used in certain types of intensifiers.
•Mercury vapor lamp is an artificial light source produced by passing current through mercury vapor in a tube.
•Metal print is a photographic print made on a sensitized metal surface
•Methyl alcohol is a volatile, poisonous spirit commonly known as wood alcohol. Used as a substitute for pure alcohol in some photographic processes.
•Metolquinone is a combination of metol and hydroquinone, used as a developing agent (MQ developer).
•Microfiche is a sheet of microfilm usually forming part of a filing system.
•Microfilm is a film used to produce a microscopic record of a document and intended for projection.
•Microflash is an electronic flash of very short duration used to illuminate subjects traveling at a very high rate of speed.
•Micro lens is a lens for microscopic photography. Not to be confused with a Macro lens.
•Microphotograph is a photograph produced to a very small size which can be viewed with a microfilm reader.
•Microprism collar is a grid type ring found in the center of a camera focusing screen, usually surrounding a split image screen.
•Midtone is an area in a print or scene that contains average values.
•Millimicron (mµ) is one thousandth part of a micron.
•Miniature camera is a term commonly applied to cameras with a format size of less than 35mm.
•Mired is an abbreviation for the term micro reciprocal degrees, a scale of measurement of color temperature. The mired value of a light source is calculated by dividing 1,000,000 by its color temperature in Kelvins.
•Mirror box is a box containing one or more mirrors, usually angled to the light beam, as in the main body of an SLR camera.
•Mirror lens is a lens system which uses mirrors within its internal construction. Most lenses of this type have a mixture of reflecting and refracting optics and are known as catadioptric lenses.
•Microfiche is a sheet of microfilm usually forming part of a filing system.
•Mode is the prime operating function of SLR cameras, e.g. manual mode, aperture priority mode, shutter priority mode, etc.
•Modeling light is a light used to create a three dimensional effect achieved through the perception of form and depth.
•Modelscope is a device employing a short rigid endoscope fitted with a right angle mirror at its tip, used to photograph scale models from a seemingly eye-level viewpoint
•Modular enlarger is an enlarger with interchangeable filtration heads and illuminations systems.
•Monobath is a single solution which combines developer and fixer for processing b&w negatives. It is a quick simple system but does not allow for development control.
•Monochromatic are light rays of a single wavelength.
•Monochrome is single colored. It is most frequently applied to black and white photographs, but can also describe sepia and other toned images.
•Monopack is an outdated term describing a film carrying system.
•Monorail camera is a sheet film camera, of modular construction, mounted on a rail system to give maximum camera movements.
•Montage is a composite picture made from a number of photographs.
•Mordant is a colorless dye absorbing substance used in some forms of toning. The silver image is converted into a mordant then soaked in dye.
•Mosaic is a composite made up from a patchwork of partly overlapping photographs.
•Motor drive is an automatic film wind-on mechanism which can be attached to some cameras. While the shutter remains depressed the film will keep winding on after exposure.
•Mottle is a processing fault characterized by random print density differences.
•Mount is a frame and/or backing used to support and protect prints and transparencies.
•MQ/PQ developers are developing solutions containing the reducing agents metol and hydroquinone or phenidone and hydroquinone.
•M-synch is a flash setting or socket which synchronizes the firing of the shutter with the peak light output of a flash bulb.
•MTF (Modulation transfer function) A comparison of contrast between a test chart and the reproduced image. One of the measurements of lens performance used in the manufacturing process.
•Multi-band photography is a method of aerial photography using cameras and scanners which are sensitive to different wavelengths in the spectrum to record different subject characteristics.
•Multimode camera is a 35mm camera that will operate in several modes.
•Multiple exposure is the technique of making more than one exposure on the same film frame, normally so that the images are superimposed.
•Multiple flash is the use of more than one flash unit, usually operating simultaneously to light a subject.
•Munsell system is a method of precise color description, based on comparison with comprehensive hue and saturation charts. Has closest application to pigments, whereas the CIE system relates directly to light.
•Nadar is the name adopted by the first aerial photographer, G. F. Tournachon, who took photographs from an air balloon.
•Nanometer is a unit of measurement of light wavelength. A nanometer is one millionth of a millimeter.
•Naphtha is a volatile petroleum based solvent such as benzine or gasoline (but not kerosene).
•ND is an abbreviation for neutral density.
•Near ultraviolet are wavelengths from about 400nm down to 250nm. Most photographic emulsions are sensitive to this range of bands.
•Negative is the image produced on a photographic emulsion by the product of exposure and development, in which tones are reversed so that highlights appear dark and shadows appear light.
•Negative carrier supports the negative between the light source and the enlarging lens of an enlarger.
•Negative lens is a simple concave lens that causes rays of light to diverge away from the optical axis.
•Negative/positive paper is paper used to print a positive color image from a negative.
•Neo-coccine is a red dye used in retouching to stain the gelatin.
•Neutral density is a technique which makes possible shorter printing times in color printing.
•Neutral density filter describes a gray camera filter which has an equal opacity to all the colors of the spectrum and so does not affect the colors in the final image. It is used to reduce the amount of light entering the camera when aperture or shutter settings must remain constant.
•Neutral filtration in color printing is the filtration at which color balance is achieved, rendering a neutral gray ion the film image as a neutral gray on the photographic paper.
•Neutralizer is a chemical designed to counteract and make inactive another chemical solution.
•New Objectivity is an approach to the subject matter of photography originating in Germany in the 1920s. The photographer remains an impartial observer, intensifying the appreciation of forms and structures in ordinary things but de-personalizing his/her approach.
•New Realism is an alternative name for New Objectivity.
•Newton's rings are rings of colored light produced when two glass or transparent surfaces are in partial contact.
•Nitraphot is a tungsten filament lamp similar to the photoflood but with a longer working life.
•Nitrate base was an early flexible film support which was highly inflammable.
•Nitric acid is used in emulsion manufacture, in toners, and in bleaches, it is highly corrosive.
•Nodal plane is an imaginary line passing through the nodal point, perpendicular to the optical axis.
•Nodal points are located in two areas in a compound lens system. The front nodal point is where rays of light entering the lens appear to aim. The rear nodal point is where the rays of light appear to have come from, after passing through the lens. Nodal points are used to calculate optical measurements.
•Non-silver processes are image making processes that do not require the use of metallic silver, such as Gum bichromate.
•Non-substantive is a name given to color film in which the color couplers are not contained within the emulsion, but are introduced during processing.
•Normal lens describes a lens with a focal length approximately equal to the diagonal of the film format for which it is being used.
•Notch is a V or U shaped cut into one edge of sheet film. It denotes the location of the sensitive side of the film as well as identifying the type of film.
•Objective is the lens used closest to the specimen in microscopes or telescopes.
•Off the film metering is a meter which determines exposure by reading light reflected from the film during exposure. Pioneered by Olympus on its OM2n. Most flash modes have OTF.
•Oil reinforcement is a method of altering the tonal range of prints on matte or textured fiber papers. The dried print is rubbed with a medium consisting of two parts of turpentine to one of mastic varnish and one of linseed oil. Artists oil color is then applied locally to the print.
•One shot color camera is an obsolete plate camera making three color separation negatives from a single exposure.
•One shot developer is a developer that is used on a single occasion and then discarded.
•Opacity is the light stopping power of a a material. The greater the opacity of a substance, the more light its stops. In photography, opacity is expressed as a ration of the amount of light falling on the surface of the material to the amount of light transmitted by it.
•Opalescent is like opal, a material with a cloudy-white translucent appearance.
•Opal lamp is a filament lamp with an opal glass bulb for optimum diffusion.
•Opalotype is an obsolete printing process in which a carbon-process image is transferred on to translucent opal glass.
•Opaque liquid is a dense red or black pigment, dissolved in water to form a liquid paint used to fill in film areas that are required to pint as pure white.
•Open flash is a method of flash operation using the following sequence: shutter opened, flash fired, shutter closed. Usually shutter duration is unimportant since the available light is much dimmer than the flash.
•Opening up is increasing the size of the lens aperture or decreasing the shutter speed to admit more light to the film.
•Optical axis is an imaginary line passing horizontally through the center of a compound lens system.
•Optical bench is a device for measuring the optical performance of lenses.
•Optical glass is used for manufacturing lenses and prisms. It is specially manufactured to be free of defects and distortion, and to withstand heat and humidity. Each type f optical glass is classified according to its refractive index and light dispersive quality. Two or more types of optical glass are typically used in the component elements of photographic lenses.
•Optical sensitizing is a method of increasing a films sensitivity by the use of dyes.
•Optical wedge is a strip of material, clear at one end and gradually increasing in opacity, which is used to determine the effect of light intensities on sensitized materials.
•Optics is the science dealing with the behavior of light.
•Ordinary emulsion is a term applied to a photographic emulsion which is only sensitive to ultra-violet and blue light.
•Orthochromatic is used to describe an emulsion which is sensitive to blue and green light, but insensitive to red.
•Orth-phenylene diamene is a fine-grain developing agent.
•Over-development is a term indicating that the amount of development recommended by the manufacturer has been exceeded. It can be caused by prolonged development time or an increase in development temperature, and usually results in an increase in density and contrast.
•Over-exposure is an expression used to indicate that the light sensitive material has been excessively exposed.
•Over-run lamp is a tungsten light source specifically used at a higher voltage than normal to increase light output and achieve constant color temperature.
•Oxalic acid are soluble white crystals used in some toners.
•Oxidation product is the chemical produced by a color developer during the conversion of exposed silver halides to black metallic silver.
Photograpy Glossary - P
•Painting with light - technique of lighting large, dark interior. The camera, mounted on a tripod, is given a long time exposure. The photographers moves continuously around the interior, giving flash or battery powered photoflood illumination to the shadow areas.
•Pan and tilt head - tripod head allowing the camera to be tilted up and down or turned through a 360° arc.
•Panchromatic - photographic emulsion sensitive to all the colors of the visible spectrum and to a certain amount of ultra-violet light. The sensitivity is not uniform throughout the spectrum.
•Panchromatic vision filter - filter through which the subject can be viewed approximately as it would appear in monochrome as recorded by a panchromatic emulsion.
•Panning - technique of photographing moving subjects. While the shutter is open, the camera is swung in the same direction as the subject is moving. This creates a blurred background, but a sharp subject.
•Panorama - picture presenting a continuous view of the landscape, produced either by using a panoramic camera or from a composite of several images.
•Panoramic camera - camera with a special type of scanning lens which rotates on its rear nodal point and produces an image of the scanned area on a curved plate or film.
•Paper base - support for the emulsion used in printing papers.
•Paper characteristic curve - describes a graphical relationship between exposure values and image density of a printing paper. Each brand of paper may have a different initial characteristic curve. The shape of the curve can be altered by different developers, development times, temperatures, and toning.
•Paper grade - numerical and terminological description of paper contrast: numbers 0 - 1 soft; number 2 normal; number 3 hard; number 4 - 5 very hard; number 6 ultra hard. Similar grade number from different manufacturers do not have the same characteristics.
•Paper safe - light-tight container for unexposed photographic papers, with an easy open positive closing lid.
•Parabolic mirror - silvered glass or metal reflector with a parabolic axial cross-section, used to produce near parallel rays from a light source positioned at its geometrical focus.
•Parallax - difference between the image seen by a viewing system and that recorded on film. Only TTL viewing systems avoid parallax error.
•Paraphenylenediamine - reducing agent used in some fine grain and color developers.
•Paraphotography - general term for non-silver-halide image forming processes.
•Paraxial - rays nearest the optical axis of a lens.
•Patch chart - squared pattern test strip often made when color printing by the additive method.
•PCT - see Photo color transfer.
•PEC - see Photo-electric cell.
•Pellicle (pellicule) - thin film used in one-shot color cameras as a semi-reflecting surface.
•Pentaprism - optical device, usually fitted on 35mm cameras, which makes it possible to view the image while focusing. A mirror device laterally reverses the image so that the scene is viewed through the camera upright and the right way round.
•Percentage solution - solution containing a given quantity of a dissolved substance in a stated volume of solvent.
•Perforations - accurately spaced holes punched throughout the length of film for still cameras. Basically the perforation function as a guide for precision registration of film and also provide mechanical movement from frame to frame.
•Periphery photography - technique used to photograph the entire inner or outer surface of a cylinder or tube.
•Permanence tests - methods of establishing whether long term permanence of an image has been achieved.
•Perspective - relationship of size and shape of three-dimensional objects represented in two-dimensional space.
•Petzval lens - early lens system developed by Joseph Petzval. It had a very wide aperture and was relatively free from aberration. Many modern lenses have developed from this simple three-element design.
•Phenol varnish - resin used to produce a hard durable top coating.
•Phosphorescence - property held by some materials of absorbing light of one wavelength and emitting it as light of a different wavelength.
•Phosphotophotography - technique of projecting an infrared image on a phosphorescent surface.
•Photo color transfer - method of making color enlargements by exposing on full size sheet film which is then soaked in a activator solution and rolled in face contact with receiving paper. The sandwich is then left in normal light for 6-8 minutes and peeled apart to give a finished print.
•Photo elasticity - method of determining stress patterns in structures with the aid of polarized light.
•Photo-electric cell - light sensitive cell. Two types are used in exposure meters. A selenium cell generates electricity in proportion to the amount of light falling upon its surface. A cadmium sulfide cell offers a resistance to a small electric charge when light falls upon it. Cadmium sulfide cells are more sensitive then selenium, especially at low light levels.
•Photo-engraving - production of a relief printing surface by chemical or mechanical means, with the aid of photography.
•Photo-etching - technique of contact printing an image on lith film on a presensitized zinc plate which is then processed and chemically etched to give a relief image.
•Photo file index print - makes ordering reprints and enlargements easy. A small print shows a positive, "thumbnail" version of every picture on an APS roll. Each thumbnail picture is numbered on the index print to match the frames inside the cassette.
•Photoflood - artificial light source using a tungsten filament lamp and a dish reflector.
•Photogenic drawing - original name given by William Fox Talbot to his earliest method of recording camera images.
•Photogram - pattern or design produced by placing opaque or transparent objects on top of a sensitive emulsion, exposing it to light and then developing it.
•Photogrammetry - method of making precise measurements from photographs.
•Photography - literally writing or drawing with light (from the Greek words photos meaning light and graphos, writing). First suggested by Sir John Herschel to William Fox Talbot in 1839.
•Photogravure - method of printing photographs from an etched copper plate.
•Photolamp - tungsten filament photographic lamp with a large diffused bulb, giving light of 3200 K (kelvin).
•Photolinen - laminate of linen and paper coated with black and white photographic emulsion. It is used for photographic wall coverings.
•Photolithography - lithographic printing process using an image formed by photographic means.
•Photometer - instrument for measuring light being reflected from a surface. It works by comparing the reflected light with a standard source produced within the photometer.
•Photomicrography - system of producing larger than life photographs by attaching a camera to a microscope.
•Photon - particle of light energy. It is the smallest quantity of radiant energy that can be transmitted between two systems.
•Photo-reportage - use of photographs in newspapers and magazines, to supplement or replace written journalistic accounts.
•Photo-resistor - photoelectric cell which varies in its electrical resistance according to the light received.
•Photo-silkscreening - method of silkscreening images, using a stencil produced photographically.
•Photo telegraphy - transmission of pictures between two points by means of radio or telegraph. A print is wrapped around a cylinder and scanned by a small spot of light. Reflected light values are transmitted as a stream of signals. They control an exposing light source at the receiving station, which exposes light sensitive material on a similar drum.
•Photo-transistor - light sensitive electronic component which functions as a switch. Used for slave firing of electronic flash heads.
•pH scale - numerical system running from 0-14 and used to express the alkalinity or acidity of a chemical solution. 7 is neutral. Solutions with a lower pH value are increasingly acidic, and those with a higher pH value are increasingly alkaline
•Physical development - system of development in which silver is contained in suspension within the developer and is attracted to the emulsion by silver halides which have received exposure.
•Physiogram - photographic patter produced by moving a regulated point of light over a sensitive emulsion.
•Pictorialist - photographs which are a picturesque, decorative art in their own right and appeal to the viewers sense of beauty.
•Piezo-electric flash - tiny flash bulbs (normally housed in flash cubes) which can be fired by a very low current produced by striking a piezo-electric crystal. Such bulbs can therefore be used without a battery.
•Pigment - coloring material that is insoluble in the liquid carrier with which it is mixed. Examples include paint or poster color.
•Pigment processes - making a positive print by using the property of bichromated colloids by changing their physical characteristics with exposed light. Gum bichromate is a pigmented process.
•Pinacryptol - yellow and green dye powders which are used in desensitizing solutions.
•Pincushion distortion - lens aberration causing parallel, straight lines at the edge of the image to curve toward the lens axis.
•Pinhole camera - camera without a lens which uses a very small hole pierced in one end to allow light to pass through and form an image on the back of the camera which can be covered by film.
•Pixels - abbreviation for picture elements. The tiny squares of light making up the picture are transmitted in digital form and reconstituted as a visual image.
•Plane - imaginary straight line on which image points may lie or which passes at right angles through a set of points perpendicular to the optical axis.
•Plates - early photographic glass plates coated with emulsion.
•Plate camera - camera designed to take glass plates but often adapted to take cut film.
•Platinotype - obsolete contact printing process popular among pictorialists.
•Point source lamp - arc type lamp producing light from a small gap between two carbon rods.
•Polarization - light said to travel in a a wave motion along a straight path, vibrating in all directions. Polarization can be brought about with a polarizing filter which causes light to vibrate in a single plane only. Polarizing filters are used over camera lenses and light sources to reduce or remove specular reflection from the surface of objects.
•Polarizing filter - colorless gray filter made from stressed glass. Polarizing filters are used over light sources or camera lenses to reduce or remove specular reflection from certain types of surfaces.
•Polaroid camera - an instant picture camera designed for Polaroid materials.
•Pola-screen - another term for a polarizing filter.
•Portrait lens - lenses produced specifically for portraiture. They usually have a long focal length and produce a slightly diffused image.
•Positive - in photography, the production of prints or transparencies in which light and dark correspond to the tonal range of the original subject.
•Positive lens - simple lens that causes light rays from a subject to converge to a point.
•Positive/positive printing - process for printing a color transparency directly on paper to produce a positive print.
•Posterization - photographic technique using a number of tone separated negatives which are printed on high contrast material. A master negative is made by printing these in register. The final print from this contains selected areas of flat tone in place of continuous tone. Sometimes incorrectly referred to as solarization.
•Potassium bromide - chemical used as a restrainer in most developing solutions and as a rehalogenizing agent in bleaches.
•Potassium carbonate - highly soluble alkaline accelerator used in most general purpose and print developing solutions.
•Potassium chloride - chemical used in some bleaches and sensitizers.
•Potassium citrate - chemical used in blue and green toners.
•Potassium dichromate - See Potassium bichromate.
•Potassium ferricyanide - chemical used in Farmer's reducer as a bleach.
•Potassium hydroxide - caustic potash. Highly active alkali, used as the basis for high contrast developing solutions.
•Potassium iodide - chemical used in bleaches, toners and intensifiers.
•Potassium metabisulfite - acidifier used in fixers and stop baths.
•Potassium permanganate - chemical used extensively in reducers, bleaches and toners.
•Potassium persulfate - chemical sometimes used in super-proportional reducers.
•Potassium sulfide - chemical used in sulfide toning.
•Potassium thiocyanate - chemical used in some fine grain developers as a silver solvent.
•Prehardener - chemical solution used to harden the gelatin of an emulsion prior to processing.
•Preservative - chemical, commonly sodium sulfite, used in developing solutions to prevent rapid oxidation of the reducing agents in use.
•Preset focus shooting - technique in which focus is set at a predetermined setting and the shutter is released when the subject moves into the focus point.
•Pre-soak - preparatory water bath for film or paper prior to processing that prevents uneven development. It is essential in some color processes.
•Press focus lever - lever found on the between-lens shutter of many large format cameras. It allows the shutter blades to be held open for lens focusing no matter what shutter speed has been set.
•Primary colors - three primary additive colors of the spectrum in terms of transmitted light. These colors are blue, green and red.
•Principal axis - imaginary line which passes through the center of curvature of all the lens elements.
•Principal planes - imaginary lines which pass through the nodal planes of a lens system.
•Principal point - point from which the focal length is measured. The principal point of a simple lens is located at the center of the lens. Compound lenses have two principal points, the location of which cannot be determined by appearance.
•Print - in photography is an image, normally positive, which has been produced by the action of light on paper or similar material coated with a light sensitive emulsion.
•Printing - process employed to make one or a number of images on paper or similar material.
•Printing-in - system of local shading control used in printing in which additional exposure is given to selected areas of a print.
•Printing-out papers - light sensitive printing papers which visibly darken during exposure to sunlight. Also referred to as contact printing papers.
•Prism - transparent medium capable of bending light to varying degrees, depending on wavelength.
•Processing - sequence of steps whereby a latent photographic image is converted into a visible, permanent image.
•Process lens - lens system designed specifically for high quality copying.
•Projection cutting - any method of printing in which the image is optically projected on the sensitized material.
•Projector - apparatus used to display enlarged still or moving images on to a screen.
•Proportional reducer - chemical method of reducing excess density and contrast from a photographic negative.
•Protective toning - toning process used to protect black and white prints from fading and give archival permanence. Usually used selenium or gold toners.
•Pulling - method of underrating the normal ISO speed of a film to produce an overexposed latent image.
•Pushing - method of overrating the normal ISO speed of a film to produce an underexposed latent image. Used to increase the working speed of a film.
•Push processing - increasing the development time of a film to increase its effective speed. See Pushing.
•Pyro - reducing agent sometimes used in developing solutions.
