PAN (WITH A CAMERA) During the course of photographing a scene, to swing the camera around in such a way as to follow the action. Derived from: Panorama. Camera pans are commonly described as slow-pan, fast-pan, swish-pan, and jerky-pan.

PAPER, VARIABLE CONTRAST Photographic paper coated with emulsions having contrast characteristics grading from soft to hard, depending on the color of the exposing light as modified by a series of filters supplied for that purpose.

PARALLAX The apparent displacement of an object seen from different points. Commonly encountered in photography in the difference between the image seen in the viewfinder and that actually taken by the lens.

PERSISTENCE OF VISION A property of the eye that consists of an inability to detect the flickering of a light that exceeds a certain critical frequency.

PERSPECTIVE The relative size and alignment of objects as recorded on a plane surface; the illusion of three dimensions created on a flat surface.

PHOTOELECTRIC CELL A cell that converts light energy proportionally into electrical energy. It is used in exposure meters and sound recorders and reproducers.

PHOTOMETER An instrument for measuring the visual intensity of light, specifically for comparing the relative intensities of light emitted from different sources of illumination. (PIA)

PICKUP TUBE The imaging device of a video camera that converts light into electrical energy-the video signal.

PINHOLE (l) Term applied to tiny spots in a photographic negative; usually produced as the shadow of a dust particle during exposure, more rarely the result of chemical dust contamination or gas bubble formation in the gelatin layer due to improper processing. (2) Tiny or white or clear areas in a print or drawing material.

PINT, LIQUID A unit of capacity equal to 16 fluid ounces, or 473.17 milliliters.

PIXEL The smallest single picture element with which an image is constructed. The light-sensitive elements in a CCD (chip) camera.

PLANE A surface which has no curvature; a perfectly flat surface.

POLARIZER An optical device for converting unpolarized, or natural light, into polarized light.

POSITIVE, BLACK AND WHITE A photographic image on film, plate, or paper in which light tones appear light and dark tones are rendered dark

POSITIVE FILM Photographic film, designed for the printing of positive transparencies from negatives.

POSITIVE PRINT A print in which the light and dark areas as they exist in the original.

POTASSIUM BROMIDE (BROMIDE OR POTASH), KBr White crystals, very soluble in water. Used as a restrainer in developing solutions. Also used in bleaches and clearing solutions.

POTASSIUM HYDROXIDE KOH Caustic alkali used as an accelerator in photographic developers. Concentrated solutions are quite caustic and will attack the skin, causing painful burns. Similar to sodium hydroxide.

POWER, RESOLVING The measure of the ability of a lens, a photographic material, or a combination of both, to distinguish detail under certain specific conditions, among which are the shape and contrast of the target, the quantity of illumination, the exposure and the method of processing. The measure of this ability is expressed in lines per millimeter or in angular resolution of a lens.

PREROLL To start a videotape and let it roll for a few seconds before it is put in the playback or record mode, so the electronic system has time to stabilize.

PRESERVATIVE The ingredient of a photographic developer that protects it from rapid oxidation.

PRINTER, CONTACT A photographic printer in which the negative is held in contact with print material during the exposure. The image of a print made with a contact printer is the same size as the image in the negative.

PRINTER, PROJECTION A photographic printer in which the negative is positioned some distance from the print material; the image being projected onto the print material. The image of a print made with a projection printer is usually larger than the image in the negative.

RADIANT ENERGY Energy in the form of an electromagnetic wave; for example, gamma rays, X rays, ultraviolet energy, light, infrared energy, radiant heat, and radio waves.

RADIATION The process of emitting electromagnetic energy.

RECIPROCITY LAW Exposure is equal to the intensity of the exposing light multiplied by the time during which it acts. The same density should be produced in a photosensitive material by an equal exposure obtained by doubling the intensity of the light and cutting the time of the exposure in half. This law is only approximately followed by photographic materials, and deviations from it are known as reciprocity law failures.

RECTILINEAR In a straight line. When applied to a lens, it indicates that images of straight lines produced by the lens are not distorted.

REDUCING AGENT A chemical constituent of a photographic developer that changes the exposed silver halide to metallic silver. Reducing agents must be combined with other chemicals to confine their activity to the silver grains that have been exposed, to control the rate of reaction, and to preserve the agent from combining with oxygen in the air before it can do the work of development. Reducing agents are also called photographic developers.

REFLECTED LIGHT Light that has been deflected from an opaque surface; not having been absorbed.

RELATIVE APERTURE The relative aperture is the ratio of equivalent focal length to the diameter of the effective aperture. The symbol for relative aperture written as a fraction is f/ followed by a numerical value. To illustrate, the expression f/2 signifies that the diameter of the effective aperture is one half of the focal length.

RELATIVE HUMIDITY Ration of aqueous vapor present in a space at a given temperature, as compared with the greatest amount it could possibly contain at that temperature.

REPLENISHER An additional agent used to maintain the chemical strength of a processing solution at a constant level. (NMA)

RESOLUTION In optics, the ability of a lens system to reproduce an image in its finest details. See RESOLVING POWER.

RESOLVING POWER The degree to which a lens, optical system, or film emulsion is able to define the details of an image, expressed as the maximum number of black lines, with equal white interspaces per millimeter discernible in the image. Results obtainable for a given lens or emulsion vary with contrast of the original image and with development.

RESTRAINER The ingredient of a photographic developer that prevents too rapid development and that minimizes chemical fog.

RETICULATION A processing defect affecting gelatin layers on a photographic film which, upon drying, shows an irregular surface due to the formation of small, irregular scaly patterns. Sharp differences in the temperatures of successive processing solutions and insufficient hardening of the gelatin are the usual causes of reticulation.

RGB The separate red, green, and blue color (chrominance), or C , video signals.

SCALE, FOCUSING A calibrated scale that permits focusing a camera without the use of a range finder or ground glass.

SCRIM Diffusing medium placed in front of lamps.

SEMIMATTE A surface having a moderate, interrupted sheen midway between glossy and dull, or full matte.

SENSITIVITY The degree to which an emulsion reacts by the formation of a latent image under given exposure conditions, especially as this relates to exposure by different wavelengths (colors) of light. (NMA)