Photographic Glossary-A

16 Base
Image resolution of 3072 x 2048 pixels, which is suitable for desktop publishing applications.

1-Bit colour
The least number of colours per pixel for a graphics file. Each pixel is either black or white.

24- Bit colours/16.7 million colours
Each pixel has 24 bits assigned to it, which produces 16.7 million colours. This setting is best for displaying photographic images.

2-stage Shutter Release
A 2-stage shutter release is the industry standard among current electronic cameras. In order to activate the Autofocus mechanism and the light meter, slightly press the shutter release. Holding the release halfway maintains the focusing point and the exposure parameters (AE Lock), and allows for re-composition of the picture, if so desired by you. To take the picture, simply push down on shutter release all the way.

32-Bit colour
A digital image format that incorporates 256 shades in 8-bits for each of the three-colour channels (RGB) and includes a mask (alpha) channel with a possible 256 levels of opacity.

3D Color Matrix Meter
Basically, a Nikon pioneered technology first started featured on its flagship model, the F5, will expect more models to include this to fully utilise this. 3D Color Matrix Meter * evaluates not only each scene's brightness and contrast but, using a special Red Green Blue (RGB) sensor, it also evaluates the scene's colors. Then its powerful micro-computer and database together guide it to unequalled exposure control.Currently, 3D Color Matrix Meter will work only with F5 & with D-type Nikkor lenses, other new Nikon models should roll out to fully utilised this exclusive features.

4 Base
Image resolution of 1536 x 1024 pixels. This image is ready to be used by High Definition Television Systems.

4-Bit colour/16 colours
Each pixel has four colours assigned to it, which produces 16 colours.

64 Base
Image resolution of 6144 x 4096 pixels that is the maximum size image file that is available on a Pro Photo CD.

8- Bit colour/256 colours
Each pixel has eight colours assigned to it, which produces 256 colours.

8MM
A common high end tape format. Current capacities range up to 25 Gigabytes.

A.S.A.
An absolute term indicating a film's sensitivity to light. The letters stands for American Standards Association . The term as been replaced by ISO standing for International Standards Organization.

A/D converter
A device used to convert analog data to digital data. Analog data is continuously variable, while digital data contains discrete steps.

A3
Paper size for documents measuring up to 11.7" x 17".

A4
Paper size for documents measuring up to 8.27" x 11.69".

A5
Paper size for documents measuring up to 5.83" x 8.28".

ABC
Auto Backlighting Control, metering feature that automatically recognises a subject in back lighting condition and increase the exposure to compensate. Also sometimes refer as AEB (Auto Exposure Control). Auto Bracketing control: Metering feature that automatically produces three or four different exposures with one press of the shuttle release. Usually one with the recommended exposure by the camera reading, others at user specified intervals above or below the recommended setting.

Aberration
(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 colour”)
Spherical aberration - variation in focal length of a lens from centre to edge due to its spherical shape - generally all parts of the image, including its centre. The effects of lens aberration usually increase with increases in aperture or in angle of field. Failing in the ability of a lens to produce a true image. There are many forms of aberration and the lens designer can often correct some only by allowing others to remain. Generally, the more expensive the lens, the less its aberrations (More attention to optical quality). While no single lens is called a 'perfect lens'. The "ideal" lens would reproduce a subject in a faithful, clearly defined image on film. Aberrations, which can be divided into six basic faults, affect the Ideal performance in an optical system.
a) Spherical aberration. Basically, a beam of light passing through a lens parallel to the optical axis converges to form 3 focused image on the film. Spherical aberration is the term for an optical fault caused by the spherical form of a lens that produces different focus points along the axis for central and marginal rays.
b) Curvature of field. This optical defect causes points on an object plane perpendicular to the lens axis to focus on a curved surface rather than a plane.
c) Astigmatism. Rays of light from a single point of an object which is not on the axis of a lens fail to meet in a single focus thus causing the image of a point to be drawn out into two sharp lines, one radial to the optical axis and another perpendicular to this line, in two different planes near the curvature of field.
d) Coma. This optical defect causes the image of an off-axis point of light to appear as a comet-shaped blur of light. Coma, as well as curvature of field and astigmatism, degenerate the image forming ability of the lens at the rims of the picture.
e) Distortion. Even if the first four aberrations were totally eliminated, images could result that still have a distorted appearance. For an example, an rectangle may appear as a barrel or pin cushion-shaped object.
f) Chromatic aberration. This aberration is caused by light rays of different wavelengths coming to focus at different distances from the lens. Blue will focus at the shortest distance and red at the greatest distance. Since the natural rays of light are a mixture of colours, each aberration will give a different value corresponding to each colour thus producing blurred images.

Abort
To stop a program while its running. Aborting can be initiated by the user or by the program itself.

Abrasion marks
on the emulsion surface of the film are caused by scratching. It can be due to traces of dirt trapped between layers of film as it is wound on the spool, dirt in the film holder or grit on the pressure plate

Absolute colorimetric
A rendering intent that aims to maintain colour accuracy at the expense of preserving relationships between colours, used to predict how images will appear when printed on paper or other substrate with a distinct colour cast, such as newsprint. With absolute colorimetric rendering intent, colours that falls inside the destination gamut remain unchanged, while out-of gamut colours are clipped. Colours are not scaled to the destination white point.

Absolute white
In theory, a material that perfectly reflects all light energy at every visible wavelength. In practice, a solid white known spectral data used as the “reference white " for all measurements of absolute reflectance.

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, colours and geometrical forms, and their relationship to one another.

Accelerator
Is a chemical added to a developer solution to speed up the slow working action of the reducing agents in the solution.

Access time
The time required for a data storage device to locate and retrieve data.

Access
To acquire data into a computer system, typically from a storage device or from an input device.

Accessory shoe
Is a metal or plastic fitting on the top of the camera which support accessories such as viewfinder, rangefinder, or flash gun. The term " hot shoe " is sometimes uses as an alternative to accessory shoe.

Accessory Shoes
- also often called "Hot Shoe". The early flash types were simple metal brackets. To install a flash unit, you just slide the mounting foot of the flash into the accessory shoe. No electrical connection is made between camera and flash - it's just a simple and convenient way to attach the flash unit to the camera. Subsequent accessory shoes have been built as part of the camera and usually right on top of the camera's pentaprism; others are separate items that you mount on the camera body when you need them. Some like the Nikon early professional camera has special dedicated which was designed around the rewind knob.

Accessory
An add-on to a computer; a peripheral like a mouse or a printer. Something not central to the computer's operation.

Accuracy
The extent to which a machine vision system can correctly measure or obtain a true value of a feature. The closeness of the average value of the measurements to the actual dimension.

Acetate base
Non-inflammable base support for film emulsions which replaces the highly inflammable cellulose nitrate base.

Acetate filters
A coloured piece of acetate sheeting used over light sources as opposed to optical quality filters used over camera lenses.

Acetic acid
Is a chemical used for stop bath which stops the action of the alkaline developer.

Acetone
A solvent chemical used in certain processing solutions that contain materials not normally soluble in water.

Achromatic
Is a lens system that has been corrected for chromatic aberration.

Acid free
Specially prepared mounting boards, album pages, tissues, and storage boxes designed to house prints for maximum archival permanence.

Acid hardener
Is a substance used in acid fixer to help harden the gelatin of the emulsion.

Acquire module
A Graphics Program plug-ins, which provide direct access to scanners, digital cameras, video sources and other file formats.

Acquire
The opening up and importing of files into a given software application. The term is applied differently with in different types of software. With imaging software it is most often done through a twain interface or plug-in mini-application.

Acrobat reader
Adobe's electronic document format. Documents can be created from within a word processor, from postscript, or from scanned pages. The documents are highly portable, yet maintain the look of the original. Acrobat is especially useful in this area because Adobe makes the reader available for free.

Action
A Photoshop command sequence you can record and replay to automate recurrent imaging tasks.

Activator
A solution used in rapid access processors to activate developing agents present in certain emulsions of photographic products.

Active-Matrix Display
A type of flat panel LCD display used in laptop and portable computers. Active matrix displays produce a superior image to passive matrix displays.

Actual size
The size of an image when it was scanned ( not enlarged or reduced in area or viewing perspective ).

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

AD conversion
Analog-Digital Conversion. In order to process a continuous analog signal in a computer (e.g. a photo), it must first be digitized, which means, converted into a specific mathematical format of binary code. Pictures are usually digitized with the help of a digital camera or a scanner.

Adapter ring
Is a circular mount, available in several sizes enabling accessories such as filters to be used with lenses of different diameters.

Adaptive compression
A type of compression software commonly used to back up files. The method of compression changes with the type of file, and is not recommended for photographic images because it may destroy original data.

Additive colour model
The color model in which colours are produced by combining various percentages of red, green, and blue light. In the additive colour model, white is produced by mixing 100% of each primary, whereas black is produced the absence (i.e., 0%) of each primary. The additive colour model is used by computer monitors to produce their display.

Additive palette
This is a set of colours selected to represent, as closely as possible, the colours in the original source image.

Additive primary colours
Red, Green, Blue; The 3 colours used to create all other colours when direct, or transmitted light is used .They are called additive primaries, because when those are superimposed they produce white.

Addressable resolution
The maximum number of pixels an imaging device is capable of manipulating, and not necessarily the same amount the monitor is capable of displaying..

Adjustable Camera
Commonly called the manual camera. A camera with manually adjustable settings for distance, lens openings, and shutter speeds. e.g. Nikon FM series, Carl Zeiss S2, Pentax K1000, Yashica FX-3 super etc.

Adjustable-Focus Lens
A lens that has adjustable distance settings.

Adobe colour engine (ACE)
The colour management model created by Adobe Systems, Incorporated that is the default conversion engine used for ICC colour-managed colour conversions with Adobe applications.

Adobe gamma
A utility for calibrating and characterizing a monitor to produce an ICC profile for use in Adobe Photoshop and other ICC-aware applications. Although still bundled with Windows versions of photoshop, it has been replaced on the Macintosh by the calibration routine built into Apple ColorSync.

Adobe RGB (1998)
The RGB working space created by Adobe Systems, incorporated that provides a fairly large gamut of colours and is well-suited for documents that will be converted to CMYK

Advanced Photo System (APS):
Kodak's attempt to make photography easier for the casual user. The film is referred to as IX240 and is only 24 mm wide compared with the 36mm width of 35mm film. This will cause grain to be more noticeable in the APS due to a higher magnification to achieve the same size prints although Kodak claims that grain has been reduced due to improvements in the emulation used for the new APS films. Most APS cameras are of the Point and Shoot category with very few SLR models available. A new standard in consumer photography developed by Kodak and four other System Developing Companies - Canon, Fuji, Minolta and Nikon - based on a new film format and innovative film, camera and photofinishing technologies. Generally, APS cameras are more compact in size, weight and embodied most of the latest and most advance technologies available. There are options in various sizes of print out and it will even provide a thumbnail prints (Contact sheet) for you to select or preview prior to actual printing. There have a different series of lenses and some of the 35mm format AF lenses can even be shared (With limitation or effective focal length will increased). You can say, it is a different system camera all together. So much for the brighter side, but there are drawbacks as well and it is not that economical as I originally thought it supposed to be.

AE (Automatic Exposure)

AE-L (Automatic Exposure Lock)
Auto exposure Lock. Metering feature that used to hold the exposure setting when used in the automatic mode. Used most commonly in situation where off centering of the subject in composition and wish to retain the exposure setting of the subject OR where the level of exposure reading both the subject of interest and the background exposure reading is different e.g.. back lighting. Used to hold an automatically controlled shutter speed and/or aperture. Recommended when the photographer wants to control an exposure based on a scene's particular brightness area with Center Weighted or Spot Metering.

AF illumination lamp
An infrared beam that the camera fires to assist in auto focusing.

AF sensor
The sensor used to detect focus in cameras equipped with an autofocus function. Algorithm - a rule or process (often mathematical) used by a computer to make a decision or series of decisions.

AF
Abbreviation for " Autofocus ".

AF-I & AF-S lenses
Nikon's new series of AF lenses, involves the integration of coreless motors into their super telephoto lenses. This gives these lenses quick, ultra quiet autofocus operations. While the AF-S lenses housing a silent wave motor for even quicker and quiet operations than the AF-I lenses, which was being in the stage of being replaced by the newer series.

Agitation
Keeping the developer, stop bath, or fixer in a gentle, uniform motion while processing film or paper. Agitation helps to speed and achieve even development and prevent spotting or staining.

AGP ( accelerated graphics port )
A new bus specification that enables personal computers to quickly display 3-D graphics.

Air bubbles
Clear areas---usually round---on film, produced by bubbles of air trapped on the film during development. They are caused by insufficient agitation while developing the film.

Airbrush
A digital tool which gives the effect of spraying a paint / air mixture over an image. Most graphic packages incorporate an assortment of brushes that are user definable.

Albumen print
A photographic printing process using egg whites in the emulsion.

Algorithm
The specific process in a computer program used to solve a particular program.

Aliasing
When a line or any shape (curve, circle or font text character) is painted, and its edges are not perfectly horizontal or vertical, some pixels are only partially covered. The resulting jagged-edged lines are said to be aliased. Aliasing gives lines a "stair-step" or "jaggy" appearance. The greater the number of dots or pixels on your display, the higher the display resolution, and the less noticeable aliasing is to the human eye.

Alkalinity
Denotes the degree of alkali in a solution, measured in pH values. All values above pH 7 are alkaline.

Alpha channel
An extra 8-bit, grayscale channel in an image - often used for creating masks to isolate part of an image. he degree of opacity of an image in computer graphics. Not the same as luminance.

Alpha Chip Analog
An electronic signal, tone or other measure that is continuously variable in its level. A Digital Equipment Corporation produced RISC chip that is known for its processing speed.

Alphabetical Coding
Some early lenses such as Nikon and Olympus uses some alphabetical coding to illustrate the composition of their lenses. For an example, each ZUIKO Lens is described with an alphabetical prefix and suffix such as F . ZUlK0 AUTO-S, AUTO-T, etc. The prefix represents the number of elements in a lens in alphabetical order. For an instance, "A"=1 element, "B"=2 elements, "D"=4 elements, and so forth. "AUTO" signifies automatic diaphragm. The suffix represents the type of lens: "S": Standard, "W"=Wide Angle and "T"=Telephoto. While another example:
U (Uns) for 1 lens element
B (Bini) for 2 elements
T (Tres) for 3 elements
Q (Quatour) for 4 elements
P (Pente) for 5 elements
H (Hex) for 6 elements
S (Septem)for 7 elements
0 (Octo) for 8 elements
N (Novem) for 9 elements
D (Decem) for 10 elements

Alphanumeric
A combination of letters and numbers.

Alternative Processes
This term covers at least 35 distinct processes, some historic and some not; most having to do with processing the final print for unconventional effect.

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. Ambient Light
The available natural light completely surrounding a subject. Light already existing in an indoor or outdoor setting that is not caused by any illumination supplied by the photographer i.e. not by artificial light source.

Ambient temperature
Crudely, room temperature. Some photographic chemicals can be used "at ambient" (with appropriate correction of processing times) while other types need to be heated or cooled to a specific temperature required by a particular process.

Amidol
Soluble reducing agent which works at low pH values

Analog to digital (A/D) converters
A device which converts an analog signal into a digital signal. Complex waveforms are converted into simple strings of numbers.

Analogous colours
Colours that are next to each other on the colour wheel.

Analogue
Continuous signals; data presented or collected in continuous form. This data is shown on an instrument that can change constantly. For example, speedometers or thermometers are analog devices. Analog signals can represent many different real-world things, like video, audio, (voice, music) and physiological waveforms (ECG, heartsounds, respiration).

Anamorphic sizing
Unequal scale change in the horizontal and vertical direction of a scanner. This enables the scanner to adjust the ratio in the horizontal and vertical direction.

Anastigmat
Is a compound lens which has been corrected for the lens aberration " astigmatism ".

Angle of flash coverage
The measurement in degrees of the angle formed by lines projecting from the center of the flash to the extremities of the field of coverage.

Angle of incidence
When light strikes a surface it forms an angle with an imaginary line known as the : normal, which is perpendicular to the surface. The angle created between the incident ray and the normal is referred to as the angle of incidence.

Angle Of View
The area of a scene that a lens covers or sees. Angle of view is determined by the focal length of the lens. A wide-angle lens (short-focal-length) includes more of the scene-a wider angle of view-than a normal (normal-focal-length) or telephoto (long-focal-length) lens. Currently, the widest view available is 220 degree (achieved by Nikon's Nikkor 6mm F2.8 fisheye lens - 220 degree; while the narrowest is Nikon, 2000mm F11 Reflex Nikkor, only slightly over 1 degree of view. It can also be explained as the extent of the view taken in by a lens. For any particular film size, it varies with the focal length of the lens. Usually expressed on the diagonal of the image area. Basically, there are three types of angles which can be measured (based on horizontal, vertical and diagonals of the film frame), the lens must be designed to cover the widest angle in the diagonal direction. Thus, the angle of view is the angle between imaginary lines drawn from the opposite ends of the film plane to the second nodal point of the lens. All objects within this angle will be recorded by the lens on the film.

Angular field
The angle subtended at the lens by the diameter of the largest circle within which the lens gives an image of acceptable sharpness and even illumination.

ANSI
Is a rating for photographic materials devised by the American National Standards Institute.

Anti-aliasing
The process of reducing Stair-Stepping by smoothing edges where individual pixels are visible.

Anti-fogging agent
Constituent of a developer that inhibits or reduces fogging during development.

Antihalation backing
Is a dye used on backs of most films capable of absorbing light which passes through the emulsion. This way it reduces the amount extraneous light can be reflected from the camera back through the emulsion.

Antireflection coating
One or more thin layers of refractive material ( often magnesium fluoride ) coated upon the surface of a lens to minimize surface reflection. It is deposited on the lens by vaporization of the metal in vacuum.

A-PEN
Annealed polyethylene naphthalate-a polyester material used as the base on Advanced Photo System film; thinner, stronger and flatter than the acetate base traditionally used in consumer photographic roll films.

Aperture control
The ring on the camera lens (a pushbutton on some models) that, when turned, adjusts the size of the opening in the iris diaphragm and changes the amount of light that reaches the film.

Aperture lens opening
The opening in a camera lens through which light passes to expose the film. The size of aperture is either fixed or adjustable. Aperture size is usually calibrated in f-numbers. The larger the number, the smaller the lens opening.

Aperture priority
An exposure mode on an automatic or autofocus camera that lets you set the aperture while the camera sets the shutter speed for proper exposure. If you change the aperture, or the light level changes, the shutter speed changes automatically. Apart from the sport or action arena, aperture priority is the most common & effective automatic preference in photography. It can also be explained as automatic exposure system in which the lens aperture is set by the photographer, and the camera sets the shutter speed. Can be used in the stop-down mode with any lens that does not interfere with the metering system. Under many shooting circumstances the use of a specific aperture may be required. By using the aperture priority setting on a camera, the aperture remains fixed, and the camera picks the corresponding shutter speed based on internal light meter readings. Allows you to choose the aperture (e.g. large at F1.8 for portrait, of small at F16 for landscapes).

Aperture ring
A ring, located on the outside of the lens usually behind the focusing ring, which is linked mechanically to the diaphragm to control the size of the aperture; it is engraved with a set of numbers called f-numbers or f- stops.

Aperture
Lens opening. The hole or opening formed by the metal leaf diaphragm inside the lens or the opening in a camera lens through which light passes to expose the film. The size of aperture is either fixed or adjustable. Aperture size is usually calibrated in f- numbers-the larger the number, the smaller the lens opening. Aperture affects depth of field, the smaller the aperture, the greater is the zone of sharpness, the bigger the aperture, the zone of sharpness is reduced. The hole or opening formed by the metal leaf diaphragm inside the lens; controls amount of light and depth of field, prevents vignetting and reduces lens aberrations; the size of the aperture is indicated by its f-number, i.e., the ratio of the diameter of the opening to the focal length of the lens; a large aperture is indicated by a small numerical f-number. Opening through which light passes through the lens en route to the film. The use of overlapping blades controls the diameter of the opening, similar to the iris of the eye. Depth of Field is controlled by the aperture. The wider the opening (lower number), the less depth of Field that is observed. The smaller the opening (higher number), the greater the depth of field. A pinhole camera has an enormous DOF because of the extremely small aperture, on the order of 150 or greater. Changing the aperture by one value on the following scale, is considered a 1 stop change: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64, 90, 128.... Any value between these values is considered a partial stop change. A change from any value to the value immediately next to it changes the amount of light reaching the film by a factor of two. The numbers on the aperture ring correspond to a ratio between the focal length of a lens and the diameter of the aperture opening. A setting of f:8 means that the opening in the blades is 1/8th the focal length, f:5.6 is 1.5.6tt the focal length and so on. The iris in the lens through which light passes to exposed the film. The higher the number, the smaller the amount of light that hits the film.

Aplanat
Is a lens which has been corrected for spherical aberration.

APO
Apochromatic. Having the ability to bring all colours of the visible spectrum to a common plane of focus, within close tolerances, usually refer to a lens with such superior colour correction. Also refer to "ED", "LD", "SD", "UD".

Apochromatic
The inability to bring light of all colours to the same plane of focus is known as chromatic aberration. Light refraction is a function of wavelength, and as such each colour is normally brought to as lightly different plane of focus. By using complex lens designs, special glass materials and coating, designer can bring the colours within a much narrower focus. When such a lens is designed it is said to be Apochromatic.

Application
A computer software program designed to meet a specific need.

APS
An abbreviation for Advanced Photo System. It is a film cartridge system that magnetically records all picture data for each frame of film. This data is then used by the photo finisher to provide you with better pictures and new services that can't be found with traditional film cameras.

Archival Image
An image meant to have lasting utility. Archival images are of a higher resolution and quality than the digital image to the user on-screen. The file format most often associated with archival images is TIFF, or Tagged Image File Format, as compared to on-screen viewing file format, which are usually JPEGs and GIFs.

Archival Processing
Processing designed to protect a print or negative as much as possible from premature deterioration caused by chemical reactions.

Archival scans
Digital images serve as surrogates of the original. At this point in time, there is no such thing as an Archival or Preservation scan that acts as an exact replica or replacement of the original, as it is not yet possible to record every piece of information found in the original with today's scanner technology.

Area CCD
A square or rectangular CCD that can capture an entire image at once, which is essential for dynamic subjects and flash photography.

Array camera
A digital camera that uses a large CCD chip to sense the entire image at one time rather than scanning the image one row of pixels at a time.

Array processor
A specific portion of a large computer system that assists processing data quickly. An array processor is sometimes capable of performing several operations simultaneously.

Artifact
Colour faults or line faults that visibly impact the image negatively. Any visible degradation of an image caused by scanning, editing or compressing the image. Often artifacts are regular or repeating, rather than random.

Artificial Intelligence
The use of computers to solve problems and process information in ways that approximate human thought.

Artificial light
Light produced by electricity instead of by nature. Generally the term refers to light specially set up by the photographer, such as flash or photo lamps. Photographic emulsions have different sensitivity to daylight and artificial light, and film may be rated for either type. Light from a man-made source, usually restricted to studio photo lamp and domestic lighting. When used to describe film (also known as Type A or Type B) invariably means these types of lighting.

ASA
American Standards Association. Group that determining numerical ratings of speed for US made photosensitive products. e.g. films. In 1982, its role and its influence was narrow down by the establishment of the ISO (International Standards Organisation).

ASCII
An acronym for the American Standard Code for Information Interchange is an ANSI binary-coding scheme consisting of 128 seven bit pattern for printable characters and control of equipment function. ASCII is the basis for information exchange between many computer systems.

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. The ratio of width to height. Used in the imaging industry to define applicability of an image to fit a page, screen, monitor, or frame. For example, a 35mm frame is 3:2, a TV is 4:3, and HDTV is 16:9.

Aspherical lens
A lens whose curved surface does not conform to the shape of a sphere; lenses are usually ground or molded with spherical surfaces; because a spherical surface lens has difficulty in correcting distortion in ultra-wideangle lenses or coma in large-aperture lenses brought about by spherical aberration, an aspherical lens is used.

Aspherical surface
A lens surface that possesses more than one radius of curvature. The aspherical elements compensate for the multitude of lens aberrations common in simpler lens designs.

Astigmatism
A lens aberration or defect that is caused by the inability of a single lens to focus oblique rays uniformly. Astigmatism causes an object point to appear as a linear or oval-shaped image.

ATA
ATA- This means the camera supports the electrical interface standard, defined by the PC Card Association (formerly PCMCIA), known as ATA (AT Attachment). This is the mobile computing equivalent of the IDE standard for desktop computers. Most computers have ATA support built-in. ATA is supported by most operating systems like Microsoft Windows 3.1, Windows '95, Windows CE, IBM OS/2, Apple System 7, etc. ATA is supported by most computer manufacturers including IBM, Compaq, Packard Bell, Dell, Gateway 2000, etc.

Attachment
A file, such as a photograph, sent along with an e-mail message so it can be viewed or saved at the recipient's end.

Auto balance
A system for detecting errors in colour balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.

Auto bracketing
A system that automatically makes a series of exposures at different exposure settings when the shutter is released, to increase the chances of obtaining a correctly exposed image.

Auto Exposure Bracketing
Auto Exposure Bracketing performs automatic exposure bracketing with varied shutter speed and/or aperture.

Auto exposure lock
A push-button, switch, or lever that locks in exposure after the initial reading has been made, regardless of a change in camera position or light conditions after the lock is activated. Release of the lock button returns the exposure system to normal. Useful for making highlight or shadow readings of select portions of the frame, and an essential feature for critical exposure control with automated cameras.

Auto levels
This is a very basic automatic correction technique employed by scanning and image processing software. Usually, the process takes an Integrated reading of the image and attempts to adjust the image by targeting a neutral scale for all values. This only works in a perfectly neutral image and often Auto Levels alone is insufficient to perform quality image optimization.

Autochrome
Early commercial colour photography process in which the principals of additive colour synthesis were applied.

Auto-exposure
The camera has a built-in light meter and computer that measures available light and sets exposure for you. A feature on moderately-priced to expensive cameras. Most serious amateurs and professionals want to be able to occasionally turn off (or "override") the auto-exposure feature for those situations where they want to manually set a special exposure. Similarly, many auto-exposure cameras allow you to select "aperture-priority" or "shutter-priority" for exposure (see "exposure" to learn why). In fact many older auto-exposure cameras (from the 1970's) only featured either "aperture-priority" of "shutter-priority.

Autofocus (AF)
System by which the camera lens (most popular) or the camera body (only available in Contax AX) automatically focuses the image of a selected part of the picture subject. The autofocus camera revolution first popularised with the launch of Minolta's Maxxium. Currently, most current SLRs are autofocus based. Device used in certain cameras, projectors and enlargers that focuses the image automatically.

Auto-load
A camera that has an (alleged) simple way to load film. There are many different approaches depending on the camera. Generally, you drop the film canister into the camera, pull out an extra inch of film to a certain mark, and close the camera. Gears and a motor in the camera then grab the film and advance it to the spool. Avoids the old hassles of getting the end of the film attached to the take-up spool. Found on nearly all auto-wind cameras. A handy feature that speeds up changing film.

Automatic Camera
A camera with a built-in exposure meter that automatically adjusts the lens opening, shutter speed, or both (program) for proper exposure.

Automatic exposure setting
A system that automatically sets correct exposure by linking a camera’s exposure meter with the shutter or aperture or both. There are three main types: aperture priority, when the photographer sets the aperture and the camera selects the appropriate speed; shutter priority, when the photographer chooses the speed and the camera sets the correct aperture; and programmed, when the camera sets both aperture and shutter speed. Aperture priority is advantageous when you want to control depth of field; shutter priority comes into its own particularly in action photography; and programmed exposure can be useful when the photographer has to react quickly. Abbreviated AE.

Automatic flash
An electronic flash unit with a light-sensitive cell that determines the length of the flash for proper exposure by measuring the light reflected back from the subject.

Automatic focus
A camera system that automatically brings the lens into sharp focus on the subject. Auto focus systems operate very quickly and reliably, and can usually focus more rapidly than the photographer can unaided. However, there are instances when manual focusing is preferable to automatic: for example, few auto focus systems can cope adequately when the subject is behind bars, such as animals in a zoo. Abbreviated AF.

Automatic gain control
A process by which gain is automatically adjusted as a function of input or other specified parameter.

Automatic iris
Lens diaphragm which is controlled by a mechanism in the camera body coupled to the shutter release. The diaphragm closes to any preset value before the shutter opens and returns to the fully open position when the shutter closes.

Autowinder
Film wind-on mechanism which moves the film on one frame each time the shutter is released.

AV
The Aperture value, usually refer to aperture settings.

Available light
The light that is present in a scene, either indoors or out, that is not added by the photographer. Also called ambient light or existing light.

Axis lighting
Light pointed at the subject from a position close to the camera's lens.