AE Automatic Exposure; Three kinds are available: programmed auto exposure, aperture-priority auto exposure and shutter-priority auto exposure.
AF-I (Nikon) Lens with built-in autofocus drive motor. CPU is also built in. AF-I Nikkor lenses send information on distance to the camera body and are classified as D-type AF Nikkor lenses.
AI (Nikon) Automatic index; Nikon’s system for telling the camera’s exposure meter what the lens’ maximum aperture is.
AI/S (Nikon) Automatic index/Shutter; Nikon’s lens mount permitting automatic operation in shutter-priority and program auto-exposure systems.
Aperture The variable opening produced by the iris-diaphragm through which light passes to the film plane. Measured in f/stops.
Aperture Priority Autoexposure systems wherein the photographer selects the aperture and the camera selects the appropriate shutter speed.
APO Apochromatic; a type of lens which focuses different wavelengths of light on the filmplane for improved image sharpness. Especially useful in telephoto lenses. (Chromatic aberration is corrected).
ASA American Standards Association; (see ISO).
B (Bulb) At the B setting, the shutter remains open as long as the shutter release button remains fully depressed.
Bracketing Take a series of pictures at different exposures.
Close-Up The general term for pictures taken at relatively close distances, from 1/10 life-size (1:10) to life-size (1:1).
Coating A layer or multiple layers of thin anti-reflective materials applied to the surface of lens elements to reduce light reflection (flare) and increase the amount of transmitted light.
Depth of Field The range of acceptably sharp focus in front of and behind the distance the lens is focused on.
Diaphragm A series of metal “blades” that can be manipulated to form a larger or smaller opening through which the light is admitted.
Digital Imaging The new evolution of the art of photography where images are scanned into an electronic format and then “processed” with software such as Adobe Photoshop.
DIN International Standard (see ISO).
DX-Coding Code printed on film cartridges providing most new cameras with film speed information.
Element One piece of glass comprising the internal optics of a lens. (See Group).
EOS (Canon) Electronic Optical System; Canon’s current line of autofocus cameras and accessories.
E-TTL (Canon) Evaluative, through-the-lens flash metering.
EV Exposure Value; A number that represents available combinations of shutter speed and aperture offering the same exposure effect when scene brightness remains the same. Each EV number can be applied to various shutter speed and aperture combinations.
Exposure Light striking a sensitized material (film or paper emulsion).
Exposure Compensation Modifying the shutter speed and/or lens aperture recommended by the camera’s light meter in order to produce special creative effects or to meet special requirements.
Fill-Flash Exposure consisting of a combination of flash and “available light” balanced to produce a pleasing mix of the two.
Fisheye An ultra-wide angle lens which purposely introduces barrel distortion so straight lines near the edges of the frame appear to curve out.
Flare Image degradation caused by stray light which passes through the lens but is not focused to form the primary image. Often caused by light bouncing off internal air-to-glass surfaces.
Focal Length The distance from the optical center of a lens to the image plane when the lens is focused to infinity.
Golden Rectangle An image ratio (width vs the height) that makes the most pleasing, balanced impression on the viewer. Panoramics are long and skinny; square negatives often make it hard for the viewer to recognize the central focus of a composition. A 35mm format is pretty close to a golden retangle.
Group Two or more elements cemented together within a lens. Lenses are described as having a certain number of elements in a certain smaller number of groups.
Hot Shoe A mounting device, usually built onto the top of a camera, that enables a flash unit, or speedlight, to be mounted on and triggered by the camera.
ISO International Standards Organization; the number represents the film’s sensitivity to light. A higher ISO number indicates the film is more sensitive and requires less light for a proper exposure.
Macro Focusing Macro focusing, applied to zoom lenses, moves the lens group(s), enabling the lens to focus closer than the normal focusing distance from close-up shooting.
Matrix Autoexposure metering where the camera sets both aperture and shutter speed according to data stored in the camera’s built-in memory, comparing the scene to be photographed to reference scenes.
Photography From the Greek the means “painting or writing with light.”
Resolution A word with many meanings. In digital imaging, it most often refers to the number of pixels per inch in an image file. It can also refer to printer resolution, digital camera CCD resolution, etc. In traditional photography, if refers to the ability of a lens or photographic material to reproduce small details and is measured in lines per millimeter.
Rule of Thirds The rule states that an image should be imagined as divided into nine equal parts by two equally-spaced horizontal lines and two equally-spaced vertical lines, and that important compositional elements should be placed along these lines or their intersections.   Further Information and some more.
Shutter Priority When the photographer selects the shutter speed and the camera automatically sets the corresponding aperture.
Shutter Speed How fast the camera’s shutters open. Determines how long the film is exposed for.
SLR Single Lens Reflex; a camera with one lens (as opposed to Twin Lens Reflex like the Rolleiflex) that involves a mirror and prism that the viewer looks through (as opposed to a point and shoot or rangefinder where the viewer looks through a separate viewfinder.
Sunny-16 Rule A guideline that states that you can expose a normal scene, lit by bright sunlight, at an aperture of f16 and a shutter speed equivalent to the film speed (ISO or ASA) being used.
TTL Through-the-lens; commonly used when referring to metering through the lens as opposed to via a separate meter. Effective for fill-flash and other tricky lighting situations.
USM (Canon) UltraSonic Motor; Canon’s fastest, quietest autofocus lens mechanism.
Prime lens A lens that has just one focal length only (in contrast to a zoom lens that covers a wider range of lengths), known for their advanced optics and quality. They generally have less moving parts and so manufacturers are able to concentrate their efforts on adding quality glass and menanisms.