Wednesday, February 25, 2009

Terms beginning with "A" in Photography

(1) Something that prevents light from being brought into sharp focus, disenabling the formation of a clear image.
(2) Lens flaw - the inability of a lens to reproduce an accurate, focused, sharp image. Aberration in simple lenses is sub-categorized into seven types:
  • Astigmatism - lines in some directions are focused less sharply than lines in other directions,
  • Chromatic aberration or Axial chromatic aberration - different wavelengths of light coming into focus in front of and behind the film plane, resulting in points of light exhibiting a rainbow-like halo and reduction in sharpness,
  • Coma - the image of a point source of light cannot be brought into focus, but has instead a comet shape,
  • Curvilinear distortion - distortion consisting of curved lines,
  • Field curvature - the image is incorrectly curved,
  • Lateral chromatic aberration also known as Transverse chromatic aberration - variation in the magnification at the sides of a lens (this aberration type used to be termed “lateral color”),
  • Spherical aberration : - variation in focal length of a lens from center to edge due to its spherical shape - generally all parts of the image, including its center.
The effects of lens aberration usually increase with increases in aperture or in angle of field.

ABSORPTION - Occurs when light is partially or completely absorbed by a surface, converting its energy to heat.

ABSTRACT - In the photographic sense, an image that is conceived apart from concrete reality, generally emphasizing lines, colors and geometrical forms, and their relationship to one another.

ACCESSORY SHOE - A fitting generally located on top of a camera to which accessories (such as a flash unit) are attached.

ACHROMATIC - Free from chromatic aberration. An achromatic lens is able to transmit light without separating it into colors.

ACUTANCE - A measure of the sharpness with which the film can produce the edge of an object.

ADAPTER RING - Also called a “Stepping ring” - enables a filter of one size to be attached to a lens of another size.

ADDITIVE COLOR - Mixing colored lights to result in another light color.

ADVANCED PHOTO SYSTEM (APS) - A camera system brought forth in 1996 as a new foolproof photography system for weekend snapshooters and people who had not yet ventured into photography. It introduced a new film size (requiring new camera designs to use it) and a new means of photofinishing.

AE LOCK - Auto Exposure Lock or "AE-L" - permits you to take an exposure meter reading from part of a scene and to keep the reading to apply it to the entire composition. The photographer first aims the camera at a specific area, takes a meter reading, locks in that reading using the camera's AE Lock, then recomposes the image and takes the picture.

AERIAL - Above ground; in the air. Also casually refers to a picture taken from the air, as in an “aerial” or an “aerial photograph.”

AERIAL PERSPECTIVE - The perception of depth or distance caused by atmospheric haze and its effect on tonal change in an image.

AERIAL PHOTOGRAPHY - Photography conducted above ground, commonly understood to be picture-taking from an aircraft.

AF - Abbreviation for “Autofocus”

AF LOCK - Autofocus Lock - Causes the camera to stop automatically focusing. AF lock is typically used when the subject is outside of the viewfinder’s autofocus sensor(s). The photographer first aims the camera so that subject comes automatically into focus, “locks” in that focus setting using AF lock so that autofocus is temporarily disabled, then recomposes the image and takes the picture.

AGITATION - Gentle movement of liquid photo-processing chemicals (developer, stop-bath, fixer) during processing of film or paper in order to achieve uniform results.

AIR - A relatively large area of white space in a layout.

AMBIENT LIGHT - Existing light surrounding a subject; the light that is illuminating a scene without any additional light supplied by the photographer. “Available light” and “existing light” are two other terms that mean the same thing.

ANAMORPHIC LENS - a lens that compresses a wide-angle of view into a standard frame.

ANGLE OF INCIDENCE - Light striking a surface is called “incident light.” It becomes “reflected light” when it reflects from the surface. The “angle of incidence” is the angle at which the incident light strikes the surface, and is measured from a line that is perpendicular to the surface (called the “normal”).

ANGLE OF VIEW - Also known as the “Field of view,” “FOV” and the “Angle of the field of view”, it is the extent of the view taken in by a lens. The focal length of a lens, in conjunction with film size, determines the angle of view. Wide-angle lenses have a wider angle of view than do telephoto lenses. A “standard” lens has an angle of view equal to the diagonal of the film, which is generally around 52 or 53.

ANTI-ALIASING - Smoothing the edges of objects in a digital image to reduce the appearance of "stair steps".

ANTI-SHAKE - Technology that combats a lens's movement caused by camera shake to reduce blur in an image.

APERTURE - A circle-shaped opening in a lens (a hole, really) through which light passes to strike the film. The aperture is usually created by an iris diaphragm that is adjustable, enabling the aperture to be made wider or narrower, thereby letting in more or less light. The size of the aperture is expressed as an f-number, like f/8 or f/11.

APERTURE PREVIEW - Controlled by a button or switch on some cameras, this feature permits you to look at the scene in the viewfinder with the aperture stopped down to the opening you intend to use when taking the picture. It is a handy aid in checking the effect of depth of field - i.e. what will be in focus.

APERTURE PRIORITY - A function or shooting mode of a semi-automatic camera that permits the photographer to preset the aperture and leaves the camera to automatically determine the correct shutter speed. What does that mean? You select the aperture setting you want and the camera then automatically calculates the appropriate corresponding shutter speed for proper exposure. It's like a fully-automatic camera except you totally control the aperture.

APO - See Apochromatic

APOCHROMATIC - often shortened to APO, means corrected for spherical and chromatic aberration. Lenses that are apochromatic cause all visible light wavelengths to focus on the film plane. Lenses that are not corrected for chromatic aberration tend to focus red, green and blue wavelengths on different planes.

APS - Acronym for "Advanced Photo System".

ARCHIVAL TECHNIQUES - The handling, treating and storage of photographic materials in a manner that lessens their deterioration from aging or from reaction to other materials.

ARTEFACTS - See "Artifacts" below. "Artefacts" is the usual British spelling of "Artifacts."

ARTIFACTS - Sometimes spelled "artefacts" - Picture degradations that occur as a result of image-processing tasks, such as compressing an image which can result in an increase in digital "noise".

ARTIFICIAL LIGHT - Illumination that comes from a man-made source, such as electronic flash.

ASA - The now defunct film speed rating system of the USA Standards Institute, which was formerly called the American Standards Association - hence the acronym “ASA”. The ASA system has been replaced by the more universal ISO system.

ASPECT RATIO - The ratio of a picture's length to its width. For example, 35mm film has an aspect ratio of 3:2. Also applies to computer and television screens, image sensors and photographic prints. Computer monitors typically have an aspect ratio of 4:3, as do most digital cameras.

ASPHERIC (ASPHERICAL) LENS - A lens element that changes shape across its surface as opposed to one having a smooth continuous arc. Generally, an aspherical lens deviates slightly from an exactly spherical shape, and is relatively free from aberrations. Light rays are bent more at the edges of a conventional spherical lens than they are at the center, causing them to come into focus before the film plane. A lens made with aspherical elements focuses all the light rays passing through it on the film plane.

AUTO-BRACKETING - Occurs when your camera is set to automatically bracket exposures for a series of images when you press the shutter release one time.

AUTO EXPOSURE or AUTOEXPOSURE - Shutter speed and aperture are set automatically by the camera based on its interpretation of the camera's exposure meter readings. Some high-end cameras employ highly-sophisticated, computerized autoexposure systems that seem to be almost foolproof, whereas most consumer cameras' autoexposure systems work best in average lighting situations.

AUTOFOCUS - Ability of a lens and camera to focus automatically on an object within its focusing sensors.

AUTOMATIC APERTURE - An automatic aperture remains fully open until the shutter is released, at which time it closes down to the pre-set aperture size in order for the picture to be properly-exposed. An automatic lens has an automatic aperture.

AUTOMATIC CAMERA - Camera that adjusts the aperture and shutter speed automatically using its built-in exposure meter.

AUTOMATIC EXPOSURE - Also known as “Autoexposure,” (see above) this is a system in an autoexposure camera that meters the light and automatically adjusts the aperture and shutter speed settings for proper exposure of the film.

AUTOMATIC FLASH - Electronic flash unit that automatically adjusts flash duration and intensity based on flash-to-subject distance, providing correct exposure.

AUTOMATIC LENS - A lens that remains open at its widest aperture until the shutter is released, regardless of the aperture setting. Such a lens facilitates focusing with through-the-lens cameras since the maximum amount of light reaches the viewfinder. When the shutter is released, the aperture automatically stops down to its pre-set opening so that proper exposure is made, then returns to a wide-open position until the next time.

AUTOWINDER - Also known as Automatic Film Winder - A camera mechanism that automatically advances the film to the first frame, then advances to the next frame when the shutter is released to take a picture, and usually also automatically rewinds the film into its cartridge when the last frame has been exposed.

AVAILABLE LIGHT - Existing light surrounding a subject; the light that is illuminating a scene without any additional light supplied by the photographer. “Ambient light” and “existing light” are two other terms that mean the same thing.


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