Glossary
Abbe number The reciprocal of dispersion.
aberrations Optical errors in a lens which limit its capabilities – causing the images it forms to differ from subject appearance, usually in small details.
accelerator Chemical ingredient of developer to speed up the otherwise low activity of developing agents. Normally an alkali such as sodium carbonate, borax or (high-contrast developers) sodium hydroxide. Also known as ‘activator’ or ‘alkali component’.
achromatic lens Corrected for chromatic aberration exactly in two separate wavelengths, usually red and blue, which are brought into the same focus plane.
acid Chemical giving solutions in water with pH below 7. Because acid neutralizes an alkali, acidic solutions are often used to halt development – as in stop bath or fixer.
active pixel sensor See CMOS.
acutance Physical measure of how the transition from high density to low density reproduces in a developed film which has been exposed to a high contrast (test chart) subject.
A/D converter A device used to convert analogue (continuously variable) signals to digital (discrete steps) data.
adaptation Ability of the eye to change its sensitivity to light (generally, or in different colour receptors). Adaptation occurs naturally when there is a change in the colour or intensity of the subject light.
adaptor ring Narrow threaded ring which fits the front rim of a lens to allow use of accessories of a different (‘step-up’ or ‘step-down’) diameter.
additive colour processes Processes which represent subject colours by adding together different quantities of primary coloured light – red, green and blue, characterized by the use of narrow cutting red, green and blue filters or the equivalent phosphors.
additive printing Printing onto colour paper by giving separate red, green and blue light exposures.
addressability Refers to how many points on the display screen can be addressed by the graphics card adapter.
AE Automatic exposure metering.
AE lock (AE-L) Control for holding a particular automatic exposure reading in the camera’s memory.
aerial perspective Sense of depth conveyed by changes of tone with distance. Typically seen in a rolling landscape when atmospheric haze is present lowering the contrast of distant areas.
AF Autofocus.
AF illuminator Infrared source, in camera flashgun or built into body, used to illuminate subject and assist the image-measuring autofocus lens mechanism.
AF lock (AF-L) Locks an autofocus lens in its present focus setting.
alkali Chemicals giving solutions in water with pH above 7. Solution feels slippery to the touch, can neutralize acid. See also accelerator.
aliasing Also known as ‘jaggies’. A rough-edge effect seen most clearly on diagonal lines in an electronic image. Created by undersampling. Forms a noticeable ‘staircase’ appearance due to the large square pixels present. Becomes invisible in high-resolution (small pixel) images.
ambient light General term covering existing subject lighting, i.e. not specially provided by the photographer.
anaglyph Method of viewing stereo pairs by which left- and right-hand positive stereo images are presented overlapped and in contrasting colours (typically deep red and deep green). You view these results through spectacles with green and red eyepieces, so that each eye sees only its respective image and you experience one 3D picture.
anastigmat lens Lens corrected to be largely free of astigmatism (totally so at one subject distance), and having minimal curved field.
angle of view Angle, formed at the lens, between lines from the extreme limits of a (distant) scene just imaged within the diagonal of the picture format. Varies with focal length and format size.
anhydrous (anhyd) Dehydrated form of a chemical. More concentrated than the same substance in crystalline form.
ANSI speed number American National Standards Institute number designating the light sensitivity of a printing paper.
anti-aliasing filter A filter in front of the digital sensor and behind the camera lens, minimizing aliasing and moire patterns.
anti-halation Light absorber present in film to prevent refection or spread of light giving ‘haloes’ around bright highlights. Disappears during processing.
aperture preview SLR camera control to close the lens diaphragm to the actual setting used when exposing. For previewing depth of field.
aperture priority mode You set the lens aperture you require and the camera sets the appropriate shutter speed, to give correct exposure according to the camera’s built-in metering system.
apochromatic (apo) lens Lens highly corrected for chromatic aberration at three wavelengths (usually blue, green and red) instead of the customary two. Also dispenses with the need to correct your focus setting when taking infrared pictures.
APS Advanced photographic system. System of amateur easy-load cameras and film 24 mm wide, introduced in 1996.
area array A CCD sensor in the form of a flat grid of photosites. Therefore allows the full image in the camera to be captured instantaneously, i.e. moving subject matter, or use of flash.
archival processing Procedures during processing aiming for the most stable image possible.
artificial light General term for any man-made light source. Artifcial-light film, however, normally refers to tungsten illumination of 3200 K.
ASA American Standards Association, responsible for ASA system of speed rating. Doubling the ASA number denotes twice the light sensitivity. Now replaced by ISO.
aspheric contour A shape not forming part of a sphere. In lens manufacture this is physically difficult because most grinding/polishing equipment functions with spherical action.
auto-bracketing A rapid series of pictures taken by the camera automatically, each giving a slightly different exposure.
autochrome Early colour transparency (plate) system, using a mosaic of additive colour filters.
autofocus System by which the lens automatically focuses the image (for a chosen area of subject).
Av Aperture value. Auto-exposure camera metering mode. You choose the aperture, the meter sets the shutter speed. (Also known as aperture priority mode.)
average gradient A measure of contrast using the characteristic curve of a film. It is obtained by finding two points on the characteristic curve, the first at 0.1 above Dmin and the second at 1.5 units log relative exposure from the first point and taking the slope of the line joining the two points.
B setting See bulb.
bag bellows Short, baggy form of bellows used on view cameras for a wide-angle lens. Allows camera movements otherwise restricted by standard lens bellows.
barn doors Set of folding metal flaps fitted around front of spotlight. Controls light spill or limits beam.
barrel distortion Aberration by which the image of a square is more magnified at the centre than at its edges – forming a shape like the cross-section of a barrel.
barrier filters Deep red filters which stop blue and green wavelengths or visually opaque filters. Used for infrared photography.
baryta paper See fibre-based paper.
baseboard camera Camera with fold-open baseboard, which supports lens and bellows.
between-lens shutter Bladed (or ‘leaf’) shutter positioned between elements of a lens, close to aperture.
bicubic interpolation Interpolation method where the new pixel is calculated involving 16 of the pixel’s neighbouring values.
bilinear interpolation Interpolation method where the new pixel is calculated by taking an average of its four closest neighbours.
biological decay Type of deterioration in photographic media. It occurs due to living organisms, such as mould and bacteria that damage films and prints.
bit Short for binary digit. The smallest unit of digital information in a computer, a 1 or a 0.
bit depth The number of bits used to represent each pixel in a digital image. (Determines its colour or tone range.)
bitmapped An image formed by a grid of pixels. The computer assigns a value to each pixel – ranging from 1 ‘bit’ of information (simply black or white) to as much as 24 bits per pixel (assigning x, y coordinates and value) for full colour images.
black body (Planckian radiator) A solid metal dark body that does not refect incident light. When heated it becomes incandescent and radiates continuously throughout the spectrum. It first emits red light and as the temperature increases, its colour changes towards blue or ‘white hot’.
bleacher Chemical able to erase or reduce image density.
blocking Artefact due to compression (JPEG). The edges of the pixel blocks created by the compression algorithm may not match exactly as a result of information being discarded from the block.
blooming The electronic equivalent of fare. Leakage of charge between CCD elements caused by gross overexposure forms streaks or haloes around bright image highlights.
blooming, of lenses See lens coating.
blue-sensitive Emulsion sensitive to the blue region only of the visible spectrum. Also known as ‘ordinary’.
bounced light Light which is reflected off an intermediate surface before reaching the subject. If the surface is relatively large and matt surfaced the resulting illumination will be soft in quality.
bracket In exposure, to take several versions of a shot giving different exposure levels. See also autobracketing.
brightness range The difference in luminance between darkest and lightest areas of the subject or image. Combined effect of lighting ratio and subject reflectance range.
bromide paper Printing paper with predominantly silver bromide emulsion.
bubble-jet Inkjet printer technology where each ink is forced into a tiny nozzle by heat.
bulb Also ‘brief’. The B setting on a shutter – keeps the shutter open for as long as the release remains pressed.
bulk film Film sold in long lengths, usually in cans.
burning-in See printing-in.
burst mode Mode in digital cameras to capture a rapid sequence of images (similar to the motor drive in film cameras).
byte Standard measurement of digital file size. One byte represents 8 binary digits, allowing 255 possible numerical combinations (different sequences of 1 s and 0 s). One kilobyte is 1024 bytes and so on. See also grey level.
C-41 Processing chemicals and procedure used for the vast majority of colour (and monochrome chromogenic) negative films.
cable release Flexible cable which screws into the camera shutter release. Allows shutter to be fired (or held open on ‘B’) with minimal shake.
capacitor Unit for storing and subsequently releasing a pulse of electricity.
cast Overall bias towards one colour.
CC value (colour compensating value) It is the nominal value of the required CC filter.
CCD element A single light-sensitive area within a CCD (charge-coupled device) able to record a unique image detail. Known also as a photosite. The distance between the centres of two adjacent CCD elements is known as their element pitch.
CD-ROM Compact disc, read-only memory. Similar in appearance to 5.25 in audio CD, able to carry large quantities of computer compatible digital data, including images and application software programs.
CdS Cadmium disulphide. Battery-powered light sensor cell, widely used in exposure hand meters.
characteristic curve Graph relating image density to log10 exposure, under given development conditions. Also known as H and D curve.
chemical decay Type of deterioration in photographic media. It is related to changes of the chemistry of the photographic image.
chlorobromide paper Warm-tone printing paper. Emulsion contains silver chloride and silver bromide.
chromogenic process Colour process which uses dyes chemically formed during processing to create the hues of your final image. Results contain no silver.
CI See contrast index.
cibachrome Outdated product name for dye-bleach colour print material now known as Ilfochrome.
CIE Commission Internationale de l’ éclairage. Originator of a standard system for precise description of colours.
circle of acceptable definition Defnes the physical extent of an image through the lens that will be sharp and conform to some measure of acceptable objective image quality.
circles of confusion Discs of light making up the image formed by a lens, from each point of light in the subject. The smaller these discs the sharper the image.
CIS (contact image sensor) Scanner technology based on red, green and blue LEDs and a row of sensors which has width equal to the width of the scanning area, i.e. the glass plate.
click stops Aperture settings which you can set by physical ‘feel’ as well as by observing a printed scale.
clipping Occurs when one or more of the red, green or blue values of the output image reaches the maximum or minimum value of which the system is capable.
close-up lens Additional element added to the main lens, to focus close objects.
closed loop imaging system Hardware chain which consists of a few high-end devices, usually with a single input and output method.
CMM (colour management module) Software ‘engine’ which performs all the calculations for colour conversions.
cold-light enlarger Enlarger using a fluorescent tube grid. Gives extremely diffused illumination. Also known as a cold-cathode enlarger.
CMOS (complementary metal-oxide semiconductor) More recent, and potential successor to CCD as an electronic imaging light-sensor. Advantages include higher pixel count, less battery power consumption and lower cost.
CMYK Cyan, magenta, yellow (and black). The first three are the basic subtractive colour dyes formed in most colour emulsions, and for printers’ inks. (As pure black is unobtainable by combining CMY inks, it is added as a ‘4th colour’ in printing, to improve image body and contrast, and to economize in the use of the much more expensive colour inks, if all three would be present in any area.)
colloidal silver A suspension of finely divided silver particles – e.g. coating the bottom of trays and deep tanks containing used developer, or covering the emulsion itself as ‘dichroic fog’.
colour development A step in processing (or toning) in which coupler compounds form dyes where development is taking place.
colour filter array An arrangement where each pixel of the sensor is covered by a red, green or blue filter.
colour gamut The range of colours that can be output by an imaging system under particular conditions.
colour head An enlarger lamphead with a CMY colour printing filtering system built in.
colour interpolation See demosaicing.
colour separation exposures A series of three separate exposures, taken through deep red, green and blue filters onto panchromatic black and white film. By recombining these images in appropriate final dyes, inks or pigments, all the hues of the original scene can be recreated.
colour management system (CMS) Electronic calibration program to ensure uniformity of colour appearance of digital images across input/monitor/output devices. Should ensure that what you see on the monitor matches what you finally receive printed out.
colour space Three-dimensional system where each colour is described by three coordinates.
colour temperature Way of defning the colour of a (continuous spectrum) light source, in Kelvin. Equals the temperature, absolute scale, at which a blackbody radiator would match the source in colour.
complementary colours Resulting colour (cyan, magenta or yellow) when one of the three primary colours (red, green or blue) is subtracted from white light. Also called ‘subtractive primaries’, ‘secondary colours’.
compression Compression of digital image data, to reduce storage requirements or
transmission speed across networks. Can be ‘lossless’ or ‘lossy’ (allowing greater compression at the expense of resolution). See also JPEG.
condenser Simple lens system to concentrate and direct light from a source, e.g. in a spotlight or enlarger.
contact print Print exposed in direct contact with negative, therefore matching it in size.
contrast index (CI) A measure of contrast used by Kodak. Determined, in simple terms, by drawing an arc 2.0 (baseline) units long cutting the material’s characteristic curve and centred on a point which is 0.1 units above minimum density. The slope of the straight line joining these two points is the contrast index. You give it a numerical form by continuing the straight line until it cuts the baseline, then quote the tangent of the angle made. Typically a film developed to a CI of 0.56 should print well on grade 2 paper, using a diffuser enlarger.
control strips Pre-exposed strips of film or paper used to test the accuracy and consistency of processing.
coupled dyes Compounds which have reacted to the (by)products of colour development to form visible colours.
covering power The area of image considered of useful quality that a lens will produce. Must exceed your camera picture format, generously so if movements are to be used.
CPU Central processing unit. The main box-like part of a computer, containing its processor chip and motherboard.
crop factor The ratio of the sensor format relative to a 35 mm frame.
cropping To trim one or more edges of an image, usually to improve composition.
cross front Camera movement. Sideways shift of lens, parallel to film plane.
CWA Centre-weighted average. Exposure measured by averaging out picture contents, paying more attention to central areas than corners.
CRT Cathode ray tube. Display technology based on a vacuum tube with an anode, a cathode and three electron guns. A layer of phosphors is inside the front face of the tube, grouped in triads for red, green and blue colours.
D log H curve See characteristic curve.
Dmax Maximum density.
Dmin Minimum density.
dark current Spurious electrical charge which progressively builds up in CCD elements without exposure to light. Creates ‘noise’.
darkslide Removable plastic or metal sheet fronting a sheet-film holder or film magazine.
data migration Periodical transfer of digital data from old storage to new media.
daylight film Colour film balanced for subject lighting of 5500 K.
DCS Digital camera system. The designation used by Kodak/Nikon for their range of SLR digital cameras.
dedicated flash Flash unit which fully integrates with camera electronics. Sets shutter speed; detects film speed, aperture, light reading, subject distance, etc.
demosaicing The process of calculating missing colour values from adjacent colour filtered pixels.
dense Dark or ‘thick’, e.g. a negative or slide which transmits little light. Opposite to ‘thin’.
densitometer Electro-optical instrument for reading the densities of a film or paper image.
density Numerical value for the darkness of a tone. The log (to base 10) of opacity (qv).
depth mode Automatic-exposure camera program which aims to preserve as much depth of field as possible in selecting aperture and shutter speed settings.
depth of field Distance between nearest and furthest parts of a subject which can be imaged in acceptably sharp focus at one setting of the lens.
depth of focus Distance of the film (or printing paper) can be positioned either side of true focus while maintaining an acceptably sharp image, without refocusing the lens.
developing agent Chemical ingredient(s) of a developer with the primary function of reducing lightstruck silver halides to black metallic silver.
device-dependent colour space Colour space native to input and output devices.
device-independent colour space Colour space that specifes colour in absolute terms.
diaphragm Aperture formed by an overlapping series of blades. Allows continuous adjustment of diameter.
diffraction Change in the path of light rays when they pass close to an opaque edge.
diffusion transfer process Any process by which a positive photographic print is made by physically transferring silver, or dyes, from the exposed material onto a receiving surface.
digital Something represented by, or using, numbers. A string of pulses of either 0 or 1 values only. Images in digital form are relatively easy to manipulate electronically, edit and re-record without quality losses. Also used in photography as a general term to differentiate forms of image sensing, processing, etc. which function by electronic rather than chemical means.
digital lenses Lenses, normally for medium- or large-format cameras, designed to give
appropriately high optical image resolution and flat field to match the performance of highend matrix or linear array digital (CCD) sensors.
DIN Deutsche Industrie Normen. German-based system of film speed rating, much used in Europe. An increase of 3 DIN denotes twice the light sensitivity. Now replaced by ISO.
dioptre Reciprocal of a metre. The dioptric power of a lens is its focal length divided into 1 m.
dispersive power Related to the change in the refractive index of the optical material with respect to the wavelength of the light. The greater the difference between the refractive indexes for red and blue light, the greater the dispersion in the glass.
dithering Method used by non-continuous tone printers to create all the colours of the digital image using a limited number of inks and more than one dots per pixel.
dodging See shading.
dome ports Used in the housings for underwater photography. Dome ports are used for wide-angle lenses. The curvature of the dome is ideally matched with the focal length of the lens.
DPI Dots per inch. A measure of the image resolution of an electronic printer.
drum scanner Highest quality scanner for transparencies, negatives and prints. Originals are mounted on the curved surface of a rotating transparent drum, read by a fine beam of transmitted or reflected light line by line and gradually advancing in very fine increments.
drying mark Uneven patch(es) of density on film emulsion, due to uneven drying. Cannot be rubbed off.
DSLR Digital single lens reflex camera.
dummy pixels See optically black pixels.
DX coding Direct electronic detection of film characteristics (speed, number of exposures, etc.) via sensors in the camera’s film-loading compartment.
dye-bleach processes Colour processes by which three even layers of ready-formed dyes are destroyed (bleached) in certain areas. The dyes remaining form the final coloured image.
dye-image film Film in which the final processed image comprises dyes, not black silver.
dye-sublimation A desktop digital printing process which uses tiny heating elements to evaporate CMY pigments from a plastic carrier band, depositing these smoothly onto a receiving surface such as paper.
dynamic range Electronic terminology for the maximum tone range that a recording medium can capture.
E-6 Processing chemicals and procedure used for the vast majority of colour slide/ transparency films.
easel See masking frame.
edge numbers Frame number, film-type information, etc. printed by light along film edges.
effective diameter (of lens aperture) Diameter of light beam entering lens which fills the diaphragm opening.
electronic flash General term for common flash units which create light by electronic discharge through a gas-filled tube. Tubes give many flashes, unlike expendable flashbulb systems.
emulsion Mix of light-sensitive silver halides, plus additives and gelatin.
emulsion lift Term referring to the process by which the image-carrying top surface of a Polaroid print is removed from its paper base, physically manipulated and resited on a new (paper or film) support.
encoding The process of turning the pixel values into binary code.
EV Exposure value.
exposure-compensation dial Camera controls effectively overriding film-speed setting (by + or - exposure units). Used when reading difficult subjects, or if film is to be ‘pushed’ or ‘held back’ to modify contrast.
exposure latitude Variation in exposure level (over or under) which still produces acceptable results.
exposure zone One of the 0-X one-stop intervals in which the exposure range of a negative is divided in the zone system.
extension tube Tube, fitted between lens and camera body, to extend lens-to-film distance and so allow focusing on very close subjects.
f-numbers International sequence of numbers, expressing relative aperture, i.e. lens focal length divided by effective aperture diameter. Each change of f-setting halves or doubles image brightness.
false colour film Film designed to form image dyes which give a positive picture in colours substantially different to those in the subject.
fast Relative term – comparatively very light-sensitive.
ferrotype sheet Polished metal plate used for glazing glossy fibre-based prints.
fibre-based paper Printing paper with an all-paper base.
field angle of view See angle of view.
field camera Traditional-type view camera, often made of wood. Folds for carrying on location.
file format Defnes the way in which image data is stored.
file size Volume of digital data. Determined by (a) chosen image resolution and (b) the dimensions of your final image.
fill factor The ratio of the photosensitive area inside a pixel to the pixel area.
fill-in Illumination that lightens shadows, so reducing contrast.
film holder Double-sided holder for two sheet films, used with view cameras.
film pack Stack of sheet films in a special holder. A tab or lever moves each in turn into the focal plane.
film plane The plane, in the back of the camera, in which the film lies during exposure.
film speed Figure expressing relative light sensitivity. See speed point.
filter (optical) Device to remove (absorb) selected wavelengths or a proportion of all wavelengths.
filter (digital) An image transform function built into a software program, or added as a ‘plug in’, to alter a digital image in some specific way. Examples – blur, sharpen, and distort shape.
filter factor Factor by which exposure should be increased when an optical filter is used. (Does not apply if exposure was read through lens plus filter.)
fisheye Extreme wide-angle lens, uncorrected for curvilinear (barrel) distortion.
fixer Chemical solution which converts silver halides into soluble salts. Used after development and before washing, it removes remaining light-sensitive halides, so ‘fixing’ the developed black silver image.
fare Unwanted light, scattered or reflected within lens or camera/enlarger body. Causes fare patches, degrades shadow detail.
fare factor Subject luminance range divided by the illuminance range of its image.
flashbulb Older type of flash source. Usable only once and ignited by simple battery/capacitor system.
flashing Giving a small extra exposure (to an even source of illumination) before or after image exposure. Lowers the contrast of the photographic material.
flash memory Secure Digital or Compact Flash. Card system able to remember image data, even when power is turned off. Used to store images in many compact digital cameras, and removable plug-in card reader, laptop computer, etc.
flat A subject or image lacking contrast, having minimal tonal range. Also the name for a temporary structure used in the studio to simulate a wall.
flat-bed scanner Lightbox-type device able to convert photographic prints, artwork or transparencies up to about 8 _ 10 (including mounted originals) into digitized data for inputting to computer.
flat ports Used in the housing for underwater photography. Flat ports are used with long focal length lenses for close-ups or shots that start or end above the water; they do not require a dioptric correction lens.
fluorescence The visible light radiated by some substances when stimulated by (invisible) ultraviolet radiation.
focal length Distance between a sharp image and the lens, when the lens is focused for an infinity subject. More precisely, between this image and the lens’s rear nodal point.
focal plane Plane on which a sharp-focus image is formed. Usually at right angles to lens axis.
focus hold See AF lock.
focus priority See trap focus.
fog Unwanted veil of density (or bleached appearance, in reversal materials). Caused by accidental exposure to light or chemical reaction.
format or ‘frame’ General term for the picture area given by a camera.
FP sync Camera shutter flash synchronization circuit designed to suit FP (‘focal plane’) flashbulbs, now discontinued.
frame transfer array A CCD architecture. It comprises an imaging area, a charge storage area and a serial readout register array.
FTP File transfer protocol.
gamma Tangent of the angle made between the base- and straight-line portion of a film’s characteristic curve. In digital imaging devices it is calculated using their transfer function.
gamut See colour gamut.
gamut mismatch Occurs when the gamuts of two imaging devices do not coincide.
gelatin Natural protein used to suspend silver halides evenly in an emulsion form. Permits entry and removal of chemical solutions.
glossy Smooth, shiny print-surface finish.
gradation Variation in tone.
grain Clumps of developed silver halide crystals forming the silver image. Coarse grain destroys detail, gives a mealy appearance to even areas of tone.
graininess A subjective measure of film grain, taking into account the overall visual impression of the enlarged result under practical viewing conditions. It has to be based on ‘average’ observers reporting on just acceptable levels of grain pattern.
granularity An objective measure of film grain. It is measured under laboratory conditions using a microdensitometer which tracks across the processed image of an even mid-grey tone.
grey level Each discrete tonal step in an electronic image, encoded in its digital data. Most electronic images contain 256 grey levels (_8 bits) per colour.
grey scale Set of tones, usually in steps from minimum to maximum density. Grey scales are available on paper or film base. They can be used to lay alongside subjects to act as a guide in final printing. Grey scales exposed onto photographic material act as process control strips.
GN guide number Number for simple flash exposure calculations, being flashgun distance from subject times f-number required (ISO 100/21° film). Normally relates to distances in metres.
hard Contrasty – harsh tone values.
hard disk Digital memory device, often permanently housed inside the computer but also in removable form.
hardener Chemical which toughens the emulsion gelatin.
hardware Equipment. In digital photography the computer, film scanner, digital back, etc. rather than the software programs are needed to run them. Similarly in silver halide photography items such as the camera, enlarger, processor, rather than film or paper.
high key Scene or picture consisting predominantly of pale, delicate tones and colours.
highlights The brightest, lightest parts of the subject.
histogram The tonal range of an image shown graphically as a chart containing a series of vertical bars, the relative frequency of occurrence plotted against image density or pixel value.
HMI Hydrargyrum (mercury) medium arc iodide. Specialist continuous-type light source, flicker-free and with a daylight matching colour temperature.
holding back Reducing development (often to lower contrast). Usually proceeded by increased exposure. Also called ‘pulling’. Term is sometimes used to mean shading when printing.
hot shoe Flashgun accessory shoe on camera; it incorporates electrical contacts.
hue The colour – blue, green, yellow, etc. – of a material or substance.
hyperfocal distance Distance of the nearest part of the subject rendered sharp with the lens focused for infinity.
hypo Abbreviation for sodium hyposulphite, the fixing agent since renamed sodium thiosulphate. Also common term for all fixing baths.
ICC Profile See profile.
image adjustments A generic set of operations that are usually performed by the user to enhance and optimize the image. They involve resizing, rotating and cropping of the image, correction of distortion, tone or colour, sharpening and removal of noise.
image noise (in digital images) A random variation in pixel values throughout the image. Often described as the equivalent to grain in silver halide film.
image setter Digital output device. A high-resolution laser exposes image data, typically in screened form, onto photographic film which is then used to make ink printing plates.
incandescent light Illumination produced from electrically heated source, e.g. the tungsten wire filament of a lamp.
incident light Light reaching a subject, surface, etc.
incident-light reading Using an exposure meter at the subject position, pointed towards the camera, with a diffuser over the light sensor.
indexed image Image that contains a reduced range of colours to save on storage space. The palette is a look-up table (LUT) with a limited number of entries (usually 256).
infinity A subject so distant that light from it effectively reaches the lens as parallel rays (in practical terms the horizon).
inkjet printer Digital printer forming images by using a very fine jet of one or more inks.
instant-picture material Photographic material with integral processing, e.g. Polaroid.
integral tripack Three-layered emulsion. Term still often applied to modern colour emulsions which may utilize many more layers but are still essentially responsive to red, green and blue.
interline transfer array A CCD architecture. Each pixel has both a photodiode and an associated charge storage area.
internegative Intermediate negative – usually a colour negative printed from a colour transparency to make a negative/positive colour print.
Internet Global connection system between computer networks, for two-way fow of information.
interocular distance The distance between a pair of human eyes.
interpolated resolution See interpolation.
interpolation Increasing the number of pixels in an electronic image file by ‘filling in’ the missing colour information from the averaged values of surrounding pixels. Image definition is reduced. May be necessary if an image was scanned in at insufficient resolution for your final print size.
inverse square law With a point source of light, intensity at a surface is inversely proportional to the square of its distance from the source, i.e. half the distance, four times the intensity.
inverted telephoto lens A lens with rear nodal point well behind its rear element. It therefore has a short focal length but relatively long lens-to-image distance, allowing space for an SLR mirror system.
IR Infrared. Wavelengths longer than about 760 nm.
IR focus setting Red line to one side of the lens focus-setting mark, used when taking pictures on IR film.
ISO International Organization for Standardization. Responsible for ISO film speed system. Combines previous ASA and DIN figures, e.g. ISO 400/27.
joule See watt-second.
JPEG Joint Photographic Experts Group. Standard image data ‘lossy’ compression scheme used to reduce the file size of digital images.
Kelvin (K) Measurement unit of colour temperature. After scientist Lord Kelvin.
key light Main light source, usually casting the predominant shadows.
kilowatt One thousand watts.
kilobyte 1024 bytes of data.
large format General term for cameras taking pictures larger than about 6 × 9 cm.
laser printer Normally refers to digital printers using the xerographic (dry toner) process, although several other devices such as light-jet employ laser technique.
latent image Exposed but still invisible image.
latitude Permissible variation. Can apply to focusing, exposure, development, temperature, etc.
LB value (light-balancing value) Refers to the red or blue LB filter. It is the difference between the selected film’s colour temperature and that of the measured light source.
LCD screen Liquid crystal display screen. Commonly used for laptop computer monitors and desktop computer displays; small playback or viewfinder screens attached to compact digital cameras or used as a transparent frame on an overhead projector to form a ‘data projector’ for presenting large images direct from computer memory. Also the source of electronically energized black lettering, symbols, etc. used in a camera’s viewfinder or top-plate readout.
leafshutter See between-lens shutter.
LED Light-emitting diode. Gives illuminated signal (or alphanumeric information) alongside camera viewfinder image, and in other equipment displays.
lens coating Transparent material deposited on lens glass to suppress surface refections, reduce fare and improve image contrast.
lens hood, or shade Shield surrounding lens (just outside image field of view) to intercept sidelight, prevent fare.
light meter Device for measuring light and converting this into exposure settings.
light trap Usually some form of baffe to stop entry of light yet allow the passage of air, solution, objects, according to application.
lighting ratio The ratio of the level of illumination in the most strongly lit part of the subject to that in the most shadowed area (given the same subject reflectance throughout).
line image High-contrast image, as required for copies of line diagrams or drawings.
linear array CCD sensor comprising a narrow row of RGB bar-filtered photosites. This scans across the image (within a camera or flat-bed scanner, for instance) driven by a stepper motor.
linear perspective Impression of depth given by apparent convergence of parallel lines, and changes of scale, between foreground and background elements.
line pair (lp) One black line plus the adjoining white space on an optical test chart pattern.
lith film Highest contrast film. Similar to line but able to yield negatives with far more intense blacks.
log H scale Range of exposures expressed on a logarithmic scale (base 10). Here each doubling of exposure is expressed by an increase of 0.3.
long-peaking flash Electronic flash utilizing a fast stroboscopic principle to give an effectively long and even peak of light. This ‘long burn’ allows an FP shutter slit to cross and evenly expose the full picture format, at fastest speeds.
lossless compression Compression algorithm that retains all the information, allowing perfect reconstruction of the image.
lossy compression Compression algorithm that discards information which is, visually, less important.
low key Scene or picture consisting predominantly of dark tones, sombre colours.
luminance The amount of light energy emitted or reflected.
LUT Look-up table.
M Medium-delay flashbulb. Flash sync connections marked M close the circuit before the shutter is fully open. Sometimes found on vintage cameras. Do not use for electronic flash.
macro lens Lens specially corrected to give optimum definition at close subject distances.
macrophotography Term often used incorrectly, see photomacrography.
magnification In photography, linear magnification (height of object divided into height of its image).
manual override The capability to operate an automatic camera in a manual, i.e. non-automatic mode.
masking General term for a wide range of methods of selectively modifying tone, contrast and colour rendering of existing negatives or transparencies before printing or reproduction. Achieved through sandwiching a parent image with film bearing positive or negative versions made from it and having controlled tonal characteristics. Also achieved electronically, e.g. during scanning for photomechanical reproduction.
masking frame Adjustable frame which holds printing paper during exposure under enlarger. Also covers edges to form white borders.
mat, or overmat Cardboard rectangle with cut-out opening, placed over print to isolate finished picture.
matt Non-shiny, untextured surface finish.
maximum aperture The widest opening (lowest f-number) a lens offers.
ME Multiple exposure control. Allows superimposition of pictures in the camera.
mechanical decay Type of deterioration in photographic media. It is related to changes in the structure of the photographic image, such as its size and shape.
megabyte (MB) 1024 kilobytes of data.
megapixel One million pixels.
microlenses Small lenses fitted to the surface of each pixel of a sensor.
microphotography Production of extremely small photographic images, e.g. in microfilming of documents.
micropiezo Inkjet printer technology where a piezo crystal becomes distorted when electric current is applied and the difference in pressure causes ink to be forced out of the nozzle.
midtone A tone midway between highlight and shadow values in a scene.
mired Micro-reciprocal degree. Unit of measurement of colour temperature; equal to one million divided by colour temperature in Kelvin.
mirror lens Also ‘catadioptric’ lens. Lens using mirrors as well as glass elements. The design makes long focal length lenses more compact, less weighty, but more squat.
mirror lock (ML) Enables the viewing mirror of an SLR camera to be locked in the ‘up’ position while the shutter, etc. is used normally. Used to avoid vibration, or to operate motor drives at fastest framing rates, or to accommodate an extremely short focal length lens.
mode The way in which a procedure (such as measuring or setting exposure) is to be carried out.
modelling light Continuous light source, positioned close to electronic flash tube, used to preview lighting effect before shooting with the flash itself.
modem MOdulator/DEModulator. Converts digital data to analogue signals and as such is the unit which connects your computer to a non-digital telephone system for transmission of information by audio means.
moiré pattern Coarse pattern formed when two or more patterns of regular lines or textures are superimposed nearly but not exactly in register. Term derived from pattern effects when layers of moiré silk are overlapped.
monoblock Generates power for separate flash heads. It contains capacitors which store power at very high voltage to be switched to a number of flash heads.
monochrome Single colour. Also general term for all forms of black and white photography.
monolight Combines the powerpack and the flash head. Typically rated at 250–500 W sec.
monorail camera Metal-framed camera, built on rail.
motor drive Motor which winds on film after each exposure.
MTF Modulation transfer function. A measure of the ability of an imaging system (lens, or recording medium, or both) to resolve fine detail.
Multimedia Presentation method (often interactive) integrating still images, video, text and audio components. Ranges from theatrical scale shows to CD-ROMs produced for use by individuals on personal computers.
ND Neutral density. Colourless grey tone.
natural vignetting See vignetting.
nearest neighbour interpolation Interpolation method where the new pixel value is allocated based on the value of the pixel closest to it.
neutral density filter Colourless grey filter which dims the image by a known amount.
nodal points Two imaginary points on the lens axis where it is crossed by the principal planes of the lens (given that the same medium, e.g. air, is on both sides of the lens). Rotating a lens about a vertical axis passing through its rear nodal point leaves the image of a distant subject stationary – a principle exploited in panoramic cameras.
noise See image noise.
normal lens Lens most regularly supplied for a particular camera; typically has a focal length equal to the diagonal of the picture format.
notching code Notches in sheet film, shape-coded to show film type.
offset lithography High volume, ink-based mechanical printing process, by which ink adhering to image areas of a lithographic plate is transferred (offset) to a ‘blanket’ cylinder before being applied to paper or other suitable receiving surface.
OHP Overhead projector. Lightbox with lens and 45° mirror unit supported above it. Projects large transparencies etc. onto a screen for group viewing.
one-shot processing Processing in firesh solution, which is then discarded rather than used again.
opacity Incident light divided by light transmitted (or reflected, if tone is on a non-transparent base).
open flash Firing flash manually while the camera shutter is held open.
optical resolution Defned by the number of individual elements and their spacing.
optically black pixels Groups of photosites that are covered by a metallic light shield that prevents light from reaching the photosites during exposure.
OLED displays Organic light-emitting diode displays.
ortho Orthochromatic sensitivity to colours. Monochrome response to blue and green, insensitive to red.
out-of-gamut colours The colours, visible to the human observer, which lie outside the gamut of an imaging system.
outputting Creating an actual print or transparency of some kind from a digital image. (Image quality and size mainly determined by file size.)
paletted image See indexed image.
pan and tilt head Tripod head allowing smooth horizontal and vertical pivoting of the camera.
pan film Panchromatic sensitivity. Monochrome response to all colours of the visual spectrum.
panning Pivoting the camera about a vertical axis, e.g. following horizontal movement of the subject.
parallax Difference in viewpoint which occurs when a camera’s viewfinding system is separate from the taking lens, as in compact and TLR cameras.
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PC lens Perspective control lens. A lens of wide covering power on a shift (and sometimes also pivoting) mount. See shift lens.
PCS (profile connection space) A device-independent colour space into which all colours are transformed into and subsequently out of it.
PE Continental code for resin-coated paper. See RC paper.
PEC Photoelectric cell. Responds to light by generating minute current fow. Used in older, non-battery hand meters, and some cameras.
pentaprism Multi-sided silvered prism. Refects and converts laterally reversed image on the focusing screen of an SLR camera to a right-reading form.
PF Power focus control. Manual focusing performed electronically by pressing buttons or a lever on the camera body. (Like controlling electrically driven windows in a car.)
pH Acid/alkalinity scale 0–14, based on hydrogen ion concentration in a solution. 7 is neutral, e.g. distilled water. Chemical solutions with higher pH ratings are increasingly alkaline, lower ones acid.
photoCD A Kodak designed CD format for storing photographs as digital files. Typically one disc may contain up to 100 images, each one stored in five levels of resolution.
photofood Bright tungsten studio-lamp bulb. Often either 3400 or 3200 K.
photogram Image recorded by placing an object directly between sensitive film (or paper) and a light source.
photomacrography Preferred term for extreme close-up photography giving magnification of ×1 or larger, without use of a microscope.
photomicrography Photography through a microscope.
photosite The area on a sensor that contains a photodiode.
pincushion distortion Aberrations by which the image of a square is less magnified at the centre than at its edges – forming a shape like a nineteenth century pincushion.
pixel Abbreviation of ‘picture element’. The smallest element capable of resolving detail in a light-sensitive (i.e. CCD) device, or displaying detail on a monitor screen. Digital images are composed of thousands or millions of pixels – the eye merges these differently coloured spots into areas of continuous tones and additively formed colours.
pixel pitch The centre-to-centre distance between pixels. It relates to the overall pixel size. Important in determining the maximum level of detail that the system is able to reproduce.
Planckian radiator See black body.
PMT Photomultiplier tube. Light-sensing devices long established in use in drum scanners.
polarized light Light waves restricted to vibrate in one plane at right angles to their path of direction.
polarizing filter Grey-looking filter, able to block polarized light when rotated to cross the plane of polarization, used to block surface refections, and for haze penetration in landscapes.
Polaroid back Camera magazine or film holder accepting instant-picture material.
positive Image with tone values similar to those of the original subject.
posterized image (digital) An image artefact resulting in large jumps between pixel values. Result of insufficient sampling.
powerpack See monoblock.
PPI Pixels per inch. A measure of the image resolution of an electronic scanner or display.
PQ Developer using phenidone and hydroquinone as developing agents.
preservative Chemical ingredient of processing solution. Preserves its activity by reducing oxidation effects.
press focus Lever on most large-format camera shutters. Locks open the shutter blades (to allow image focusing) irrespective of any speed set.
primary colours Of light: red, green and blue.
printing-in Giving additional exposure time to some chosen area, during printing.
profile A data file containing information about the colour reproduction capabilities of a device.
program, programme or P Setting mode for fully automatic exposure control. The camera’s choice of aperture and shutter settings under any one set of conditions will then depend on its built-in program(s).
program back Data imprinting camera back with additional camera control features such as autobracketing, time-lapse and exposure program display.
program shift ‘Program’ mode allows the camera to select both shutter and aperture settings, but the shift control allows user to bias it towards faster shutter speeds, or smaller apertures (‘speed’ or ‘depth’). May also be biased automatically, when you ft either a wide-angle or a telephoto lens.
pulling See holding back.
push-processing Increasing development, usually to improve speed or increase contrast.
quantization The process of allocating a continuous input range of tone and colour to a discrete output range which changes in steps.
RAM Random access memory. Integrated circuits providing a temporary data store in a computer, etc., to allow rapid data access and processing. Data held on RAM is lost when the computer is switched off. See also ROM.
rangefinder Optical device for assessing subject distance, by comparison from two separate viewpoints.
rapid fixer Fast-acting fixing bath using ammonium thiosulphate or thiocyanate as fixing agent.
RC paper Resin (plastic)-coated base printing paper.
rebate Unexposed parts outside a film’s picture areas.
reciprocity failure Breakdown of the usual reciprocal exposure relationship between time and intensity (twice the exposure time compensates for an image half as bright, and vice versa).
reciprocity law Exposure = intensity × time.
reducer Chemical able to reduce the density of a processed image. (Paradoxically the chemical term ‘reducing agent’ is also applied to developing agents.)
reflected-light reading Measuring exposure (usually from the camera position) with the light sensor pointing towards the subject.
refraction Change in the direction of light as it passes obliquely from one transparent medium into another of different refractive index.
refractive index Relates to the light-bending power of a glass. The refractive index of an optical material varies with frequency and hence wavelength.
relative aperture See f-number.
replenisher Solution of chemicals (mostly developing agents) designed to be added in controlled amounts to a particular developer, to maintain its activity and compensate for repeated use.
resampling See Interpolation.
resolution The capability of an imaging system to distinguish between two adjacent points in an image and is a measure of the detail recording ability of a system.
restrainer Chemical component of developer which restrains it from acting on unexposed halides.
retrofocus lens See inverted telephoto lens.
reversal system Combination of emulsion and processing which produces a direct image of similar tonal values to the picture exposed onto the material.
RGB Red, green, blue. The primary colours of light. The tri-colour (additive) filter colours used in digital cameras, scanners, etc. to record the full spectrum of image colours. Images are also reformed on computer monitors, TV screens and additive photographic colour materials by means of primary coloured phosphors or filter mosaics.
RH Relative humidity.
ring flash Circular electronic flash tube, fitted around the camera lens.
ringing Compression artefact (JPEG), visible around high-contrast edges as a slight ‘ripple’.
rising front Camera front which allows the lens panel to be raised, parallel to the film plane.
rollfilm back Adaptor back for rollfilm.
ROM Read only memory. Form of digital memory which can only be read from – cannot be overwritten. The basic instructions that make a computer work, permanently installed at the factory, are stored in ROM. See also RAM.
safelight Working light of the correct colour and intensity not to affect the light-sensitive material in use.
saturated colour A strong, pure hue – undiluted by white, grey or other colours.
scanners A variety of computer input devices, able to convert an existing image into a stream of digital data. See Flat-bed, Drum, etc.
screen ruling (also screen frequency) The number of rows of dots in a halftone image within a given distance – normally quoted in lines per inch (lpi).
SCSI Small computer systems interface. Cabled hardware used between a computer and peripheral devices. Allows data to be transferred at high speed. (Cable length is, however, restricted.)
second curtain sync Camera synchronization for electronic flash whereby contacts are closed just before the second blind of the FP shutter starts to close. With long-duration exposures this means that flash records sharp detail at the end of exposure, and blur trails due to any movement record during the earlier part – e.g. moving objects in pictures ‘head up’ their blur, and do not record as if moving backwards.
secondary colours See complementary colours.
selective focusing Precise focus setting and shallow depth of field, used to isolate a chosen part of a scene.
self-timer Delayed-action shutter release.
shading Blocking off light from part of the picture during some or all of the exposure.
shadows In exposure or sensitometric terms, the darkest important tone in the subject.
sheet film Light-sensitive film in the form of single sheets.
shift camera General term for a bellowless, wide-angle architectural camera with movements limited to up/down/sideways shift of the lens panel. No pivots or swings.
shift lens Wide-covering power lens in a mount permitting it to be shifted off-centre relative to film format.
shutter lag The delay between the moment that you press the shutter release button and the moment that the image is captured.
shutter priority mode You set the shutter speed and the camera sets the appropriate aperture to give correct exposure according to the built-in metering system. Also known as Tv mode.
signal-to-noise ratio In digital data the ratio of valid information to unwanted electrical interference. The S/N ratio should always be as high as possible.
silver halides Light-sensitive compounds of silver plus alkali salts of a halogen chemical – e.g. bromine, chlorine, iodine. Now also used as a general term for photography using chemical-coated film and paper, to differentiate it from newer electronic methods of photography, i.e. utilizing CCD light sensors.
slave unit Flash unit which reacts to light from another flash and fires simultaneously.
SLR Single-lens reflex.
snoot Conical black tube fitted over spotlight or small food. Restricts lighting to a small circular patch.
soft (1) Low contrast. (2) Slightly unsharp or blurred.
spectrum Radiant energy arranged by wavelength. The visible spectrum, experienced as light, spans approximately 400–700 nm.
speed mode Automatic exposure camera program aiming to preserve as much fireezing of action as possible in selecting shutter speed and aperture.
speed point Point on a photographic characteristic curve used to determine the speed rating of a film (or paper). For example, in current ISO and DIN systems two points (M and N) are shown on the material’s characteristic curve. M lies where processed density is 0.1 above fog. N lies 1.3 log exposure units from point M in the direction of increasing exposure, and development time is picked which makes N correspond to a processed density of 0.8 greater than M. When these conditions are satisfed the exposure at M is the numeral value from which the speed rating is calculated.
spot meter Hand meter, with aiming viewfinder, to make spot exposure readings.
spot mode Narrow-angle exposure reading of the subject with a TTL meter. The small area measured is outlined on camera’s focusing screen.
spotting Retouching in small white specks or hairs, generally on prints – using water colour, dye or pencil.
standard lens See normal lens.
still life General term for an inanimate object, set up and arranged in or out of the studio.
still video A now largely outdated electronic camera system producing an analogue signal recorded onto an internal foppy disk. Overtaken by modern digital camera devices.
stock shots Photographs taken for long-term picture library use (and often sold time and again over the years). Stock shots are catalogued under thousands of cross-referred subject types. They are increasingly marketed as CD-ROMs containing 100 or so images per disk.
stock solution Chemical stored in concentrated liquid form, diluted for use.
stop bath Acidic solution which halts development, reduces fixer contamination by alkaline developer.
strobe Inaccurate general term for electronic flash. Strictly means fast-repeating stroboscopic lamp or flash.
subject The thing being photographed. Term used interchangeably, and inaccurately, with object, although more relevant to a person, scene or situation.
subtractive colour processes Processes which represent subject colours by superimposed cyan, magenta and yellow images. Each of these layers subtract unwanted quantities of red, green or blue respectively from white light.
super-sampling Chopping an analogue signal range into more digital steps than are required in the final data. (In digital cameras this helps to improve image shadow detail.) Results in an enlarged file.
supplementary lens See close-up lens.
sync lead Cable connecting flashgun to shutter, for synchronized flash firing.
synchro-sun Flash from the camera used to ‘fill-in’ shadows cast by sunlight.
T setting ‘Time’ setting available on some large format camera shutters. Release is pressed once to lock shutter open, then pressed again to close it.
tele-extender Supplementary lens system fitted between camera lens and body, to increase focal length. Also reduces the relative aperture of the lens.
telephoto Long focal length lens with shorter back focus, allowing it to be relatively compact.
tempering bath Large tank or deep tray, containing temperature-controlled air or water.
Accepts drums, tanks, bottles or trays to maintain their solution temperature during processing.
TFT (thin-film transistor) TFTs control each colour pixel of the LCD screen.
tinting Applying colour (oils, dye, water colours) to a print by hand.
TLR Twin-lens reflex.
tone curve In digital photography a graph, displayable on the computer monitor, representing the ratio of input to output image tone ranges. (A ‘no change’ situation is represented by a straight line at 45°.) Acts as a control guide when modifying contrast, or density, or the individual tone ranges of each colour channel, e.g. to alter colour balance.
toning Converting a black silver image into a coloured compound or dye. The base remains unaffected.
transfer curve A mapping function of input and output tone values of an imaging device, allowing precise control over specific parts of the tonal range.
transparency Positive image on film. Term includes both 35 mm and 120 slides and larger formats.
trap focus Autofocusing mode by which the camera shutter remains locked until an object moves into the lens’s zone of sharp focus.
TTL Through-the-lens camera reading, e.g. of exposure.
tungsten-light film Colour film balanced to suit tungsten light sources of 3200 K.
Tv mode Time value exposure mode. Used on some cameras to designate shutter priority mode.
uprating Increasing your film’s speed setting (or selecting a minus setting on the exposure compensation dial) to suit difficult shooting conditions. Usually followed up with extended development.
UV Ultraviolet. Wide band of wavelengths less than about 390 nm.
UV filter Filter absorbing UV only. Appears colourless.
value Term used in the Munsell colour system. It refers to a colour’s luminance factor or brightness.
variable-contrast paper Monochrome printing paper which changes contrast grade with the colour of the exposing light. Controlled by filters.
View camera Camera (usually large format) in which the image is viewed and focused on a screen in the film plane, later replaced by a film holder. View cameras are primarily used on a stand. See also field camera.
viewpoint The position from which the camera views the subject.
vignetting Fading off the sides of a picture into plain black or white, instead of having abrupt edges.
warm tone A brownish black and white silver image. Often adds to tonal richness.
watt-second Light output given by one watt burning for one second. Used to quantify and compare the power output of electronic flash (but ignores influence of flash-head reflector or diffuser on exposure).
wetting agent Detergent-type additive, used in minute quantity to lower the surface tension of water. Assists even action of most non-acid solutions, and of drying.
white light Illumination containing a mixture of all wavelengths of the visible spectrum.
wide-angle lens Short focal length lens of extreme covering power, used mostly on cameras to give a wide angle of view.
working solution Solution at the strength actually needed for use.
X Electronic flash. Any flash sync socket and/or shutter setting marked X is for electronic flash. (Also suits flashbulbs at exposures of 1.8 sec or slower.)
zone system System embracing subject brightness range, negative exposure, development and printing, to give you control over final print tone values. Ideally allows you to previsualize and decide the tonal range of your result at the time of shooting.
zoom lens Lens continuously variable between two given focal lengths, while maintaining the same focus setting.
zooming Altering the focal length of a zoom lens.