Aberration

Lens flaw that causes unsharp images. There are six types of aberrations: spherical, coma, astigmatism, curvature of field, distortion and chromatic.

Absorption

Occurs when light is absorbed by a surface it hits and gets converted into heat waves.

Accessory shoe

Fitting to install accessories to a camera body; typically on top of the viewfinder, to attach a speedlight, a bubble level or any other accessory like a SC-17 cable.

Achromatic

A lens system designed to reduce chromatic aberration, i.e. to render the same focal length for red and blue light wavelengths at the focal plane.

Action Finder (Action Viewfinder)

An eye-level viewfinder allowing for complete view of the view field from a 2 to 3 inches distance; most convenient for fast moving objects and sports photography, as well as for detail copy work, making it less tiring.

Acutance

A measure of the sharpness with which the edge of an object can be depicted by film.

AE (Auto Exposure)

A system through which either the shutter speed or the lens aperture (semi-auto) or both (fully auto) are set automatically from the light meter. In high-end Nikon systems it is highly sophisticated; aided by a large data bank of different scenes to which the actual scene data is compared for highly improved accuracy, AE is virtually foolproof. Three types are available: Programmed Auto Exposure (P mode), where the camera sets both aperture and shutter speed; Aperture Priority AE, (A mode) when the user sets the aperture and the camera finds the most appropriate shutter speed; Shutter Priority AE (S mode), when the speed of the shutter is set by the user and the aperture by the camera.

AE Lock

A device to lock an Auto Exposure determined by the camera while the user recomposes.

AF (Autofocus)

When applied to a lens, it is the ability of a lens to focus automatically on an object within its focusing sensors. AF Nikkor lenses were introduced in 1986. When on Auto bodies, there is no need to use the aperture ring in auto modes. They are AI-S lenses with a built-in CPU and motor for AF operation. When applied to a camera it means it is equipped with autofocus capability (a CAM module) to perform with an autofocus lens.

AF (Autofocus) Assist Illuminator

A device to provide additional illumination into a subject where there is total darkness or dim light or not enough contrast in it to perform Auto Focus. It can be set to automatically turn itself on when needed for fast operation.

Ambient Light

The natural light in a scene.

Angle of View

It is the extent of the view taken in by a lens. It is determined by the focal length of a lens and film format. A “standard” 50mm lens for 35mm film has an angle of view equal to the diagonal of the film, which is 70° horizontally and 58° vertically. A 135mm "short telephoto" lens has a reduced angle of view of 29° horizontally and 23° vertically.

Angle of Flash coverage

The angle of coverage for even, uniform, edge-to-edge illumination by a speedlight. Usually expressed in terms of focal length. To accomplish such evenness it should always be of a focal length smaller or equal to that of the lens mounted on the camera body while using the flash. When the necessary angle of flash coverage cannot be accomplished through zooming of the head of the speedlight, it is increased with a built-in wide angle adapter that pulls out and flips down in front of the flash head, or with a dome diffuser.

Aperture

The adjustable opening in a camera lens that -like an eye's iris- controls the amount of light that reaches the film or digital sensor. The size of such aperture is called the f-stop, like f/2.8

Aperture Priority

Aperture Priority Auto Exposure, (A mode) when the user sets the aperture and the auto camera sets the most appropriate shutter speed. Most used mode as it is the appropriate for accurate depth of field control. Since the exposure decision is not entirely left to the camera's onboard computer, this is referred to as a semi-auto mode.

Apochromatic

Refers to lenses designed to correct for chromatic (color) aberrations. Usually used in telephoto lenses that have large maximum apertures.

ASA

Abbreviation for American Standards Association (Now ANSI). In photography, Used in conjunction with a number, e.g., ASA 400, refers to film or sensor "speed" or sensitivity to light. The higher the number, the more sensitive the film/sensor, allowing for faster shutter speeds and/or smaller f/stops. The ASA scale has been replaced by the one from ISO (International Organization for Standardization), the scale numbers remain the same; e.g. ASA 100 = ISO 100 (See ISO for further explanation)

Aspect Ratio

The ratio of width to height in photographic prints - 2:3 in 35 mm pictures to produce photographs most commonly measuring 3.5 x 5 inches or 4 x 6 inches; Advanced Photo System cameras deliver three aspect ratios as selected by the user.

Aspherical

Not a continuous curve. Refers to non-spherical elements in lenses designed to compensate for distortion by having different curves on individual elements. Nikon introduced the first photographic lens with aspherical lens elements in 1968. Allows for more compact lenses, lighter and better than others with only spherical elements. When applied to Nikkor lenses, the term implies excellent performance with absence of coma and other aberrations, even at their widest aperture.

Astigmatism

Causes light rays from an off-axis point to form images at different positions.

Available Light

Existing light surrounding a subject; whether natural or artificial, but not added by the photographer, like with strobes or speedlights.