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A list of photographic terms and their meanings.

Film format. It's name referring to the size of the negative produced
When light falls on an object some of it is absorbed by the object and is usually converted to heat. The remainder either passes through the object or is reflected from it. The overall proportion of the incident light which is absorbed determines whether the object appears light or dark in tone, and the absorption characteristics at the various wavelengths of the visible spectrum determine its colour.
Angle of incidence
A ray of light falling on a surface forms an angle with an imaginary line drawn at right angles to the surface. The imaginary line is known as the normal and the angle between it and the incident ray is known as the angle of incidence.
Angle of reflection
A ray of light reflected from a surface forms an angle with an imaginary line drawn at right angles to the surface. The imaginary line is known as the normal and the angle between it and the reflected ray is known as the angle of reflection. The angle of reflection is always equal to the angle of incidence.
Angle of view
The maximum angle between rays of light passing through the lens from those parts of the subject which will just be included within the picture format. Usually quoted as the angle given by the diagonal of the picture.
Hole positioned concentrically with the optical axis of a lens to restrict the area of the lens through which light can pass. Usually adjustable in size, formed by an iris diaphragm. Main purpose is to regulate the strength of the light reaching the film. Also plays apart in the defining the depth of field.
Different Aperture Settings Animation of Aperture
Initials standing for Advanced Photo System. Using a negative of 26mm but storing data along side the photo for developing proposes.
Artificial light
Illumination other than natural daylight. The main sources of artificial light for photographic use are tungsten lamps, flashbulbs and electronic flash.
The American Standards Association rating of film speed (sensitivity of the emulsion to light). The scale is a simple arithmetical progression, double the ASA number indicating twice the film speed. Thus a film of 100 ASA (a medium speed film) is twice as fast as one of 50 ASA and half as fast as one of 200 ASA
Barn doors
Hinged flaps fitted to photographic flood and spot lights to control the width and direction of their light beam.
The support of a photographic film upon which the light-sensitive emulsion is coated.
Unsharpness of image due to movement of camera or subject at the moment of exposure.
Bounce flash
Flash lighting technique whereby the illumination is reflected on to the subject from a conveniently positioned and suitably reflective surface, such as a ceiling, in order to obtain a soft and diffused illumination of the subject.
The technique of taking additional pictures of a subject at exposures greater and less than the estimated exposure, in order to be certain of obtaining one picture with precisely the correct exposure.
Brightness range
The difference in luminance between the lightest and darkest tones of a subject. If all the subject tones are to be satisfactorily recorded, the brightness range must not exceed that which the film can handle.
B setting
A setting of the speed ring of a shutter, at which the shutter remains open for as long as the shutter release is depressed.
Cable release
Cable system for operating the camera shutter. One end screws into a threaded socket on the camera body or shutter, the other end is fitted with a plunger which allows smooth release of the shutter. Used with camera mounted on a tripod or other steady support and eliminates need for direct contact between hand and camera, thus reducing likelihood of camera shake.
Camera Repairer
Individual or company which repairs photographic equipment to a very high standard. Also whilst maintaining a good relationship with their customers and offering quick turnaround at a reasonable price. A example of this could only be Clive Christian.
Pre-loaded film container, usually de of plastic, which simply drops into the back of cameras designed to accept them, and facilitates film loading.
Catch lights
Specular reflections of the illumination source appearing in the surface of the subject, e.g. the pinpoint reflections in a portrait model's eyes.
Centre weighted metering
A through-the-lens (TTL) metering system in which the exposure reading is taken from the entire subject area included within the viewfinder, but with the sensitivity biased such that the intensity within the central area most affects the reading.
Changing bag
A light-tight fabric bag with elasticated arm-holes which can be used as a portable darkroom, e.g. for loading dark slides, loading film into a developing tank or rescuing a film from a jammed camera.
Colour sensitivity
The relative response of a photographic emulsion to the different wavelengths of the visible spectrum.
Colour temperature
A measure of the colour quality of a light source. Indicates the temperature, in Kelvins, of a black body radiating light of the same colour.
Concave lens
A lens which is thinner in the middle than at the edges and which, therefore, causes rays of light which are parallel on entering the lens to diverge on leaving it.
Degree of tonal separation in an image. A picture with only a small tonal range is said to be flat.
Converging lens
A lens which causes rays of light which are parallel on entering the lens to converge on leaving it.
Delayed action
Mechanism which delays the operation of the camera shutter for several seconds after the release is operated. Allows photographer to include himself in the picture or can be used to minimise the likelihood of camera shake when camera is mounted on a tripod.
Depth of field
Distance between the nearest and furthest points of the subject between which everything appears acceptably sharp on the photograph. Actual value depends on focused distance, lens focal length and lens aperture.
Depth of focus
Very small distance over which the film plane of a camera can be moved without affecting the visual sharpness of the image.
Mechanical arrangement of thin, pivoted blades which overlap to leave a central, roughly circular aperture, the diameter of which can be adjusted by rotating the blades on their pivots. Fitted within a lens to regulate the strength of the light reaching the film. Also plays a part in controlling depth of field.
Bending of light rays as they pass very close to the edge of an obstacle. Causes noticeable loss of sharpness when lenses are used at small apertures.
(Deutsche Industrie Norm) European version of film speed rating (See ASA) 100ASA=21DIN
Diverging lens
A lens which causes rays of light which are parallel on entering the lens to diverge on leaving it.
Electronic flash
Artificial light source in which light is produced by the sudden discharge of electrical energy through a tube containing xenon gas. The colour of the light approximates to that of daylight.
The light-sensitive coating of a photographic film or paper. Usually a suspension in gelatine of a silver halide plus other additives.
The total amount of light allowed to fall on a film to form the latent image, i.e. the product of the intensity of the light and the time during which it falls on the film. Intensity is controlled by the camera's lens aperture, time by the setting of the shutter.
Exposure latitude
The amount the exposure of a film may be varied from the precisely correct value and still produce an acceptable result. Dependent on the characteristics of the actual film being used, colour reversal films allowing less exposure latitude than colour negative or black-and-white films.
Exposure meter
Instrument used to measure the illumination of the subject and subsequently indicate the various combinations of shutter speed and aperture which will give correct exposure of the film.
Extension tubes
Tubes used between camera lens and body to increase the lens to film distance for close-up photography.
Fill-in light
Additional light used to lighten the shadows caused by the main light source, thus reducing contrast to an acceptable level.
Film speed
Numerical indication of a film's sensitivity to light. The two film speed scales in common use are ASA and DIN
A piece of transparent glass, gelatine or other material used to modify the nature of the light passing through it. Filters selectively absorb certain wavelengths, allowing others to pass unimpeded, the effect of which is usually to alter the visual colour of the light. May be used over the light source or, more commonly, directly over the camera lens.
Filter factor
Amount by which exposure must be increased to compensate for light absorbed by a filter. Usually marked on filter mount, e.g. 2x, 3x, etc.
Fish-eye lens
Lens of very short focal length and, therefore, with a very wide angle of view - up to 180 degrees with some lenses. A characteristic is gross distortion of the image, sometimes used for special effect.
Non-image forming light which reduces the contrast of the image. Usually caused by reflections from insufficiently blackened surfaces within the camera or by reflections from the internal glass surfaces of the lens. In modem lenses flare is kept to a minimum by 'blooming' (q.v.) each glass-to-sir surface.
Numbers indicating the light-passing power of a lens. Derived by dividing lens focal length by the effective diameter of the aperture. In most lenses the aperture is calibrated in a standard series of f-numbers, e.g. f2, 2.8, 4, 5.6, 8, 11, 16, etc., each of which passes half as much light as the previous one.
Focal length
A measure of the refracting power of a lens, focal length is the distance between the optical centre of the lens and the image it produces of an infinitely distant object.
Focal plane
In a camera, the plane at right angles to the axis of the lens at which the image of the subject should be formed, and as which the film is located.
Focal plane shutter
A shutter, immediately in front of the film plane, consisting of two blinds of opaque fabric or thin metal which are positioned end to end but separated by a gap of variable width. Initially one blind covers the film, protecting it from light. When the shutter is released this blind moves rapidly to one side, and its position over the film is taken by the second blind, The exposure is made as the gap between the blinds passes across the film, the shutter speed being determined by the width of the gap.
Adjustment of the lens to film distance according to the lens to subject distance, in order to ensure a sharp image on the film,
Focusing screen
Ground-glass screen in a reflex or view camera to facilitate viewing and focusing.
Hot shoe
A special accessory shoe which provides a direct electrical connection between the synchronising contacts of the camera shutter and a flashgun fitted into the hot shoe, thus eliminating the need for a synchronising lead.
Hyperfocal distance
The nearest distance at which the subject matter is acceptably sharp when the lens is focused on infinity. If the focusing is set to the hyperfocal distance the depth of field extends from half the hyperfocal distance to infinity.
Incident light reading
Exposure meter reading taken by measuring the light falling on the subject, rather than that reflected from it, Usually requires a special diffuser - often built into the meter - to be placed over the photo-cell.
Radiation, invisible to the human eye, falling just beyond the red end of the visible spectrum. Some films, both black-and-white and colour, are specially sensitised for photography by infra-red radiation, and are used in medical, forensic and other scientific applications
(K) Formerly 'degrees Kelvin' (K). Units of temperature on the absolute scale (same temperature intervals as the centigrade scale, but starting with 0 at absolute zero, i.e.273 C), used to measure the colour temperature of a light source.
Latent image
The invisible image present in an emulsion between exposure and development.
Leaf shutter
Shutter, usually comprising thin spring-loaded metal blades or 'leaves', positioned between the lens elements, next to the iris diaphragm. The fastest speed is usually limited by the inertia of the blades and operating mechanism to 1/500 sec. Electronic flash can be used at all speeds. Also known as the between-lens shutter.
Workings of a Leaf Shutter Animation of Leaf Shutter
Lens hood
Accessory which fits in front of the lens to shade it from bright light coming from outside the field of view. Such light is a potential cause of flare within the lens.
Long focus lens
Lens of focal length longer than that of the standard lens, and therefore having a narrower angle of view.
Macro lens
Lens specially designed to focus and operate efficiently at the small lens to subject distances encountered in close-up photography. Most macro lenses focus unaided down to a distance which gives an image which is half life-size, but by the addition of extension tubes or bellows can be used to achieve images which are up to several times larger than life-size.
Number of times image is larger than subject. Thus a magnification of 2 indicates the image is twice life-size, while a magnification of 0.5 indicates the image is half life-size.
Magnification ratio
An alternative way of quoting magnification, by indicating the ratio of image size to subject size. A magnification ratio of a:t thus indicates the image is twice life-size, a magnification ratio of t.'a indicates the image is half life-size.
Mirror lens
A 'lens' in which the image is formed mainly by reflection by mirrors instead of by refraction as in a conventional lens. Very long focal lengths are achieved for a compact physical size, The aperture is fixed and not adjustable.
Motor drive
Camera attachment which automatically winds on the film after each picture is taken. Allows pictures to be taken at a maximum rate of about five per second, useful for sports photography.
Image in which the tonal values of the subject are reversed, black appearing as white and white as black. In a colour negative the colours of the subject are also reversed, each colour being represented by its complementary, e.g. red appears as cyan, green as magenta, etc.
Open flash
Method of flash photography, only possible in conditions of very low ambient light, whereby shutter is opened on 'B', flash is fired manually, and shutter is closed again. Its use is sometimes convenient when photographing large interiors of buildings.
Parallax error
Discrepancy between the framing of a picture as seen through the viewfinder and as recorded on the film, caused by the slightly different viewpoints of viewfinder and lens in some cameras. Most noticeable when such cameras are used for close-up photography. SLR cameras, in which both viewing and taking of the picture are achieved through the same lens, do not suffer from parallax error.
In a reflex camera, a specially shaped prism which allows the camera to be used at eye level while providing a right-way-up and right-way-round view of the subject.
Polarising filter
Filter which passes only light rays which are vibrating in the same plane as the plane of polarisation of the filter. Used to reduce the effect of reflections from certain shiny surfaces and to darken blue skies and enhance the green of foliage.
Optical device in a camera, usually coupled to the focusing mechanism, which allows precise measurement of the camera to subject distance by the visual alignment of two superimposed images.
Work carried out on equipment by a competent technician like Clive Christian
Ring Flash
Flashunit equipped with a circular flash tube which can be attached to the front of a camera's lens. This is mostly used in close-up photographic to give an almost shadowless photo.
Selenium Cell
A Photoelectric cell which produces a small electric current which is proportional to the intensity of light falling upon it. This is used for metering proposes and requires no additional power from a battery.
Silicon Photodiode
A Photoelectric cell which unlike the Selenium cell (see above) needs battery power connected in series to operate. This type of cell is far sensitive and more responsive than the selenium.
Shift Lens
Special wide-angle lens in which the lens axis can be shifted from the normal, avoiding the necessity to tilt the camera in relation to the subject, which would cause distortion such as that known as 'converging verticals'. Mainly available for certain makes of SLR camera, and frequently used in architectural photography.
Single Lenses Reflex. System where the image is re-directed via a mirror mechanism for viewing. A mirror is placed at 45 degrees to the film plane projecting the image from the subject into a prism. This prism inverts the image and can be seen through the viewfinder on the camera .This image is identical to the image which will fall onto the film plane. The mirror assembly will move out of the way of light as the picture is taken.
Inside a SLR

Spot Metering
An exposure metering system which takes an exposure reading from the centre of the frame only. The light intensity without this central area is ignored by the metering system.
Lens Aperture alternative name.
Twin Lenses Reflex. A camera which contains two identical lenses, one for viewing the image, the other fitted with a shutter and iris assembly for taking the picture. The viewing lens image is reflected up by a mirror to a viewing screen. The screen can be viewed directly from above through a hood (waist-level finder) or through a prism (eye-level viewfinder)
Inside of a TLR

TTL metering
"Through The Lens" metering. Found in SLR cameras taking an exposure reading from the focus screen.
viewing mechanism on a camera showing an image of the picture to be taken. Zoom contacts have moving elements that adjusts the image through the viewer as the focal length of the lens changes.