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.

Basics: Lens Aperture

Exposure is controlled by the aperture and the shutter speed settings. The aperture setting also influences depth of field, thus plays a major part in creative focusing decisions. Aperture settings are called f-numbers, and are expressed by "f/" followed by the number of the aperture set.

Aperture settings are indicated on a lens by a series of numbers; with some cameras and lenses there is no aperture scale on the lens barrel and the settings appear in the camera's viewfinder and/or LCD panel. A typical aperture scale might read: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16. Each number indicates the ratio of the actual diaphragm opening to the focal length of the lens in use, thus any same aperture on any lens always allows in the same amount of light. As these are actually fractional numbers the smaller numbers signify larger openings. Thus, f/2 (or 1/2) represents a wider opening (or greater value) than f/16 (or 1/16).

As mentioned, f-numbers represent the same light value regardless of the lens or format in use. Thus, f/2 on a 50mm lens for a 35mm camera delivers the same amount of light through the lens as f/2 on a 200mm lens for a medium-format camera, even though the diameter of the openings themselves are different. If this wasn't the case the entire light control system in photography simply wouldn't work.

Each subsequent number in an aperture scale represents a halving or doubling of the amount of light that the aperture allows through the lens. (You can calculate the next higher number in any one-stop-step scale by multiplying the previous number by 1.4). Each step in the scale (say, from f/2 to f/2.8) is called a stop. Thus, every time you open up or close down the lens by one stop (opening means going to the next lower number, or wider opening; closing down means going to the next higher number, or narrower opening) you are changing the amount of light entering by the power of 2. A one stop change (say, f/8 to f/5.6) is a 2X difference; a two-stop change (sat f/8 to f/4) is a 4X difference; and so forth.

The best way to see how aperture settings effect light transmission is to take the lens off the camera, hold it up to the light and click through the aperture settings. (Note: Some lenses do not allow for aperture changes on the lens itself, but rely on the camera to change apertures,) You'll see that the maximum aperture, say f/2, is the widest opening. As you click through the scale, you'll see the diaphragm in the lens getting smaller. Think of water as it flows through a pipe. Given that the water will always fill the pipe, a larger diameter pipe will allow more water through. This can be applied to light flow and the aperture diameter.

Most lenses and cameras today allow for partial stops, like older lenses with click stops, or detents, between the aperture settings. On older lenses these are half-stops, and though not marked indicate a halfway point between the two aperture numbers on the ring. On newer lenses you can have 1/3, 1/4 or other fractional spreads. These step-less aperture settings means any value can be set, such as f/9.7 or f/11.3. These values are indicated in the camera viewfinder and/or the LCD panel on the camera.

Aperture rings are usually inscribed with all the available full stop settings on the lens, from the maximum, or widest, to minimum, or narrowest lens opening. The range of the aperture scale may differ depending upon the construction of the lens and its focal length. One scale may read f/2, 2.8, 4, 5.6, 8, 11, 16, while another may read f/4, 5.6,8, 11, 16, 22, 32 (the latter is more typical of zoom or telephoto lenses.) The lowest number in the scale (thus the widest opening) is called the maximum aperture; the highest number on the scale (thus the narrowest opening) is called the minimum aperture.

Photo and text copyright George Schaub 2010. Aperture settings allow you to control the depth of field, what appears sharp and unsharp in your photo. To get focus from foreground to background here an f/16 setting was used.