(Automatic depth of field) The camera mode that automatically calculates sufficient depth of field for near and far subjects within the coverage of the seven AF focusing points, such as when several people are sitting at various distances from the camera.

Automatic exposure

(Automatic Exposure Lock) A camera control that lets the photographer lock the exposure from a meter reading. After the exposure is locked, the photographer can then recompose the image.

The natural or artificial light within a scene. Also called available light.

The amount or area seen by a lens or viewfinder, measured in degrees. Shorter or wide-angle lenses and zoom settings have a greater angle of view. Longer or telephoto lenses and zoom settings have a narrower angle of view.

The lens opening through which light passes. Aperture size is adjusted by opening or closing the diaphragm. Aperture is expressed in f-numbers such as f/8, f/5.6, and so on. See also f-number.

(Av Aperture-priority AE) A semiautomatic camera mode in which the photographer sets the aperture (f-stop), and the camera automatically sets the shutter speed for correct exposure.

A function where the camera focuses on the subject when you press the Shutter button. In Basic Zone modes the camera automatically focuses on the subject using the autofocus point or points shown in the viewfinder, or tracks a subject in motion and creates a picture with the subject in sharp focus. In Creative zone modes, you can manually select the AF point.

(aperture value) Indicates the aperture (f-stop). Also refers to Aperture-priority shooting mode on the Mode dial.

(Automatic White Balance) A white balance setting where the camera determines the color temperature of the light source automatically.

A lens aberration resulting in a bowing of straight lines outward from the center.

The number of bits (the smallest unit of information used by computers) used to represent each pixel in an image that determines the image's color and tonal range.

Describes shadow areas of an image lacking detail due to excess contrast.

To make multiple exposures, some above and some below the ideal exposure, calculated by the camera for the scene. Some digital cameras can also bracket white balance to produce variations from the average white balance calculated by the camera.

The perception of the light reflected or emitted by a source. The lightness of an object or image. See also luminance.

Temporary storage for data in a camera or computer.

A shutter speed setting that keeps the shutter open as long as the Shutter button is fully depressed.

The color reproduction fidelity of a digital camera's image sensor and of the lens. In a digital camera, color balance is achieved by setting the white balance to match the scene's primary light source. You can adjust color balance in image-editing programs using the color Temperature and Tint controls.

A numerical description of the color of light measured on the Kelvin scale. Warm, late-day light has a lower color temperature. Cool, early-day light has a higher temperature. Midday light is often considered to be white light (5000K).

In the spectrum of colors, a subset of colors included in the chosen space. Different color spaces include more or fewer colors.

A means of reducing file size. Lossy compression permanently discards information from the original file. Lossless compression does not discard information from the original file and allows you to re-create an exact copy of the original file without any data loss. See also lossless and lossy.

The range of tones from light to dark in an image or scene.

The zone of acceptable sharpness in a photo extending in front of and behind the primary plane of focus.

Adjustable blades inside the lens that open to a larger or smaller size based on the aperture that is chosen.

The difference between the lightest and darkest values in an image as measured in f-stops.

The amount of light reaching the light-sensitive medium — the film or an image sensor. It is the result of the intensity of light multiplied by the length of time the light strikes the medium.

A camera control that allows the photographer to overexpose (plus setting) or underexpose (minus setting) images by a specified amount from the metered exposure.

A built-in light meter that measures the amount of light on the subject. EOS cameras use reflective meters. The exposure is shown in the viewfinder and on the LCD panel as a scale with a tick mark under the scale that indicates ideal exposure, overexposure, and underexposure.

An attachment that fits between the camera body and the lens to increase the focal length of the lens.

A hollow ring attached between the camera lens mount and the lens that increases the distance between the optical center of the lens and the sensor, and decreases the minimum focusing distance.

A piece of glass or plastic that is usually attached to the front of the lens to alter the color, intensity, or quality of the light. Filters also are used to alter the rendition of tones, reduce haze and glare, and create special effects such as soft focus and star effects.

A lens with a 180-degree angle of view.

Unwanted light reflecting and scattering inside the lens causing a loss of contrast and sharpness and/or artifacts in the image.

A lens material with an extremely low index of refraction and dispersion when compared to optical glass. Fluorite features special partial dispersion characteristics that allow almost ideal correction of chromatic aberrations when combined with optical glass.

A number representing the maximum light-gathering ability of a lens or the aperture setting at which a photo is taken. It is calculated by dividing the focal length of the lens by its diameter. Wide apertures are designated with small numbers, such as f/2.8. Narrow apertures are designated with large numbers, such as f/22. See also aperture.

The distance from the optical center of the lens to the focal plane when the lens is focused on infinity. The longer the focal length is, the greater the magnification.

The point on a focused image where rays of light intersect after reflecting from a single point on a subject.

The point at which light rays from the lens converge to form a sharp image. Also the sharpest point in an image achieved by adjusting the distance between the lens and image.

See f-number and aperture.

See noise.

A card that reflects a known percentage of the light that falls on it. Typical grayscale cards reflect 18 percent of the light. Gray cards are standard for taking accurate exposure-meter readings and for providing a consistent target for color balancing during the color-correction process using an image-editing program.

A term describing a light or bright area in a scene, or the lightest area in a scene.

A graph that shows the distribution of tones or colors in an image.

A camera mount that accommodates a separate external flash unit. Inside the mount are contacts that transmit information between the camera and the flash unit and that trigger the flash when the Shutter button is pressed.

The color of a pixel defined by the measure of degrees on the color wheel, starting at 0 for red depending on the color system and controls.

A technology that counteracts unintentional camera movement when the photographer handholds the camera at slow shutter speeds or uses long lenses.

The farthest position on the distance scale of a lens (approximately 50 feet and beyond).

(International Organization for Standardization) A rating that describes the sensitivity to light of film or an image sensor. ISO in digital cameras refers to the amplification of the signal at the photosites. Also commonly referred to as film speed. ISO is expressed in numbers such as ISO 125. The ISO rating doubles as the sensitivity to light doubles. ISO 200 is twice as sensitive to light as ISO 100.

(Joint Photographic Experts Group) A lossy file format that compresses data by discarding information from the original file to reduce file size.

A scale for measuring temperature based around absolute zero. The scale is used in photography to quantify the color temperature of light.

A measure of the amount of light reflected or emitted. See also brightness and luminance.

A relationship where doubling the intensity of light produces double the response, as in digital images. The human eye does not respond to light in a linear fashion. See also nonlinear.

A term that refers to image file compression that discards no image data. TIFF is a lossless file format.

A term that refers to compression algorithms that discard image data in the process of compressing image data to a smaller size. The higher the compression rate, the more data that's discarded and the lower the image quality. JPEG is a lossy file format.

The light reflected or produced by an area of the subject in a specific direction and measurable by a reflected light meter.

A camera mode in which you set both the aperture and the shutter speed (as well as the ISO). Commonly used in low-light and night scenes and when you want to vary the exposure over or under the camera's ideal exposure.

A measure of the capacity of a digital image sensor. One million pixels.

Data about data, or more specifically, information about a file. Data embedded in image files by the camera includes aperture, shutter speed, ISO, focal length, date of capture, and other technical information. Photographers can add additional metadata in image-editing programs, including name, address, copyright, and so on.

An area of medium brightness; a medium gray tone in a photographic print. A midtone is neither a dark shadow nor a bright highlight.

A filter attached to the lens where half of the filter is darker than the other half to reduce the brightness difference between the sky and ground.

Extraneous visible artifacts that degrade digital image quality. In digital images, noise appears as multicolored flecks and as grain that is similar to grain seen in film. Both types of noise are most visible in high-speed digital images captured at high ISO settings.

A relationship where a change in stimulus does not always produce a corresponding change in response. For example, if the light in a room is doubled, the room is not perceived as being twice as bright. See also linear.

The switch to a wider f-stop, which increases the size of the lens diaphragm opening.

A technique of moving the camera horizontally to follow a moving subject, which keeps the subject sharp but blurs background details.

The place on the image sensor that captures and stores the brightness value for one pixel in the image.

A lens aberration causing straight lines to bow inward toward the center of the image.

The smallest unit of information in a digital image. Pixels contain tone and color that can be modified. The human eye merges very small pixels so they appear as continuous tones.

The most sharply focused part of a scene. Also referred to as the point of sharpest focus.

A filter that reduces glare from reflective surfaces such as glass or water at certain angles.

(pixels per inch) The number of pixels per linear inch on a monitor or image file. Used to describe overall display quality or resolution.

(Random Access Memory) The memory in a computer that temporarily stores information for rapid access.

A proprietary file format that has little or no in-camera processing. Processing RAW files requires special image-conversion software such as Canon Digital Photo Professional or Adobe Camera Raw. Because image data has not been processed, you can change key camera settings, including exposure and white balance, in the conversion program after the picture is taken.

A built-in device that measures light emitted by a photographic subject back to the camera.

A surface, such as white cardboard, used to redirect light into shadow areas of a scene or subject.

The number of pixels in a linear inch. Resolution is the amount of data in a digital image that represents detail. Also, the resolution of a lens that indicates the capacity of reproduction of a subject point of the lens. Lens resolution is expressed as a numerical value such as 50 or 100 lines, which indicates the number of lines per millimeter of the smallest black and white line pattern that can be clearly recorded.

(Red, Green, Blue) A color model based on additive primary colors of red, green, and blue. This model is used to represent colors based on how much light of each color is required to produce a given color.

As it pertains to color, a strong, pure hue undiluted by the presence of white, black, or other colors. The higher the color purity is, the more vibrant the color.

A mechanism that regulates the amount of time during which light is let into the camera to make an exposure. Shutter time or shutter speed is expressed in seconds and fractions of seconds such as 1/30 second.

(Tv Shutter-priority AE) A semiautomatic camera mode allowing the photographer to set the shutter speed and the camera to automatically set the aperture (f-number) for correct exposure.

A flash unit that is synchronized to and controlled by another flash unit.

A relatively small color space or gamut that encompasses a typical computer monitor.

See aperture.

To switch to a narrower f-stop, thereby reducing the size of the diaphragm opening.

A lens or zoom setting with a focal length longer than 50 to 60mm in 35mm format.

(Tagged Image File Format) A universal file format that most operating systems and image-editing applications can read. Commonly used for images, TIFF supports 16.8 million colors and offers lossless compression to preserve all the original file information.

The range from the lightest to the darkest tones in an image.

(Through-the-Lens) A system that reads the light passing through a lens that will expose film or strike an image sensor.

(Ultralow Dispersion) A lens made of special optical glass with optical processing characteristics similar to fluorite. UD lenses are effective in correcting chromatic aberrations in super-telephoto lenses.

The relative intensity of red, green, and blue in a light source. On a digital camera, white balance compensates for light that is different from daylight to create correct color balance.

Describes a lens or zoom setting with a focal length shorter than 50 to 60mm in full-frame 35mm format.