An Occassional Glossary: A, B

AMBIENT LIGHT: The light in the scene, as opposed to the light provided by the photographer with flash, photofloods, etc.

ANGLE OF VIEW: The maximum angle a lens covers in the field. Measured in degrees, and qualified by terms such as wide-angle, normal, and telephoto. A wide angle lens has a wider angle of view than a telephoto lens.

APERTURE: The opening of a lens, the size of which is controlled by a diaphragm. The term aperture is also used to designate f-stops, such as f/4, f/5.6 etc. Actual aperture size may be different on different lenses but always allow in the same amount of light. Thus, f/11 on a 110mm focal length lens allows in the same amount of light as f/11 on a 28mm lens. The wider the opening, the lower the f-number, the more light is let through the lens.

APERTURE PRIORITY: An autoexposure mode in which you select the aperture and the exposure system selects the appropriate shutter speed for a correct exposure. Sometimes referred to as Av or simply A on exposure mode control panels.

ARTIFICIAL LIGHT: Any light not directly produced by the sun. Can be tungsten, flash, household bulbs, sodium vapor street lamps, etc.

AUTOEXPOSURE: A method of exposure where aperture and shutter speed settings are first read, then set, by the camera itself. Various autoexposure modes allow you to customize, or bias the automation.

AUTOEXPOSURE LOCK: A pushbutton, switch, or lever that locks in exposure after you have made a reading, regardless of a change in camera position or light conditions. Useful for making highlight or shadow readings of select portions of the frame, and an essential feature for critical exposure control with automated cameras.

AUTOFOCUS: A method of focusing where focusing distances are set automatically. In SLRs, a passive phase detection system that compares contrast and edge of subjects within the confines of the autofocus brackets in the viewfinder and automatically sets focusing distance on the lens. Autofocusing motors may be in the camera body or the lens itself. Active IR (infrared) autofocusing systems may also be in some cameras in the form of beams that are emitted from the camera or flash, bounce off the subject, then return and set focusing range, and are used when light or contrast is too low for the passive system to work.

AUXILIARY LENS: An add-on optical device that alters the focal length of the prime lens for closeup, telephoto, or other special effects photography. Closeup lenses, for example, usually comes in +1, +2, and +3 powers; the higher the number the greater the magnification. As differentiated from Lensbaby optics, auxiliary lenses are usually added onto the camera lens via the threads on the lens collar.

AUXILIARY LIGHT: A flash, strobe, or tungsten lamp or bulbs used to change the character of light in a scene. Any light under the control of the photographer.

AVAILABLE LIGHT: The light that's normal in a scene, although the term is generally used when the light level is low. Available light shooting usually involves high ISO settings, low shutter speeds and apertures, and/or the use of a tripod.

AVERAGING: In light metering, a metering setup where the light is read from most of the viewfinder frame (70%) then averaged to yield an overall, standard exposure for the scene that averages all the values read to middle gray.

B or BULB: A shutter setting that indicates that the shutter will remain open for as long as the shutter release is pressed. The term originated with the rubber air shutter bulbs used to operate shutters in the old days. B settings are generally used in nighttime and time/motion study photography.

BACKGROUND: The portion of a scene that sits behind the main, foreground subject. We can make the background sharp or de-focused through the use of selective focus techniques.

BACKLIGHTING: From camera position, light that comes from behind the subject. Usually, a backlit main subject will be underexposed unless the metering system is set to read selectively off the subject. Extreme backlighting can be exploited to create silhouettes.

BATTERY: The power supply of the camera and flash. In many of today's cameras (and certainly in flashes), no power means no pictures.

BLACK-AND-WHITE: Monochrome images. Though we think of black and white mainly in terms of a grayscale, monochrome images can have a wide variety of subtle tones, from blue- to brown-black.

BLUR: Unsharpness because of the movement of the camera or subject during exposure. Though we usually want images sharp, blur can be used for many creative effects.

BOUNCE LIGHT: In flash photography, directing the burst of light from the flash so it literally bounces off a ceiling, wall, or other surface to illuminate the subject. This method of flash is often preferred because it softens the overall light and eliminates the harsh, frontal look of an on-camera, straightforward flash.

BRACKET: Making exposures above and below the normal exposure, or that which is suggested by the camera's autoexposure system. Useful as a failsafe method for getting "correct" exposure in difficult lighting conditions. Bracketing can also be used to make subtle changes in the nuance of tone and light in any scene and is an essential ingredient in HDR processing.

BRIGHTNESS: The luminance of objects. The brightness of any area of the subject is dependent on how much light falls on it and how reflective it is. Brightness range is the relationship we perceive between the light and dark subjects in a scene. Brightness contrast is a judgement of the relative measure of that range, such as high, low, or normal.

BURNING-IN: In processing, giving additional density (dark tones) to a portion of a print or image.

BURNT-OUT: Jargon that refers to loss of details in the highlight portion of a scene due to overexposure. It might mean that no image detail has been recorded, or that highlights show no texture or tonal information.

Photo and text: copyright George Schaub 2010. Backlighting is when the main light in the scene sits behind the subject facing camera position. It can be used for creating silhouettes or here as a combination of silhouette and translucent light quality.