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Accessory Shoes - also often called "Hot Shoe"
While early flash type shoes were simple metal brackets, today's hot shoe is located centered at the top of the camera. Prior to becoming a hot shoe the bracket had no electrical connection to the camera. Today, we would call it a "cold shoe." It was just a convenient way to hold the camera and flash together. To install a flash unit, you 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. Some accessory shoes like early Nikon professional film cameras had a special dedicated design which set the flash off center around the rewind knob. Today's hot shoes are built as part of the SLR or DSLR camera and are general located above the camera's viewfinder. They electrically connect the camera and flash and can provide sophisticated communication between them.
Aberration
Aberrations are failings of the ability of the lens to produce a true image. There are many forms of aberration. Lens designers can generally correct most aberrations in prime lenses and in the midrange areas of zoom lenses, but some aberrations remain, even in top quality professional SLR and DSLR lenses. Generally, the more expensive the lens, the fewer its aberrations. While no single lens is perfect, an ideal lens reproduces a subject faithfully, as a clearly defined image. Aberrations, which can be divided into six basic faults, based on how they affect the image in the lens.
- Spherical aberration is when there is an increased refraction of light when they strike a lens near its edge, in comparison with those that strike the lens nearer the center. It signifies a deviation of the device from the norm, resulting in an imperfection of the produced image.
- Curvature of field is an optical defect which causes points on an object plane perpendicular to the lens axis to appear curved rather than flat.
- Astigmatism is when 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 to be drawn out along two sharp lines, one radial to the optical axis and the other perpendicular to the line, in two different planes near the curvature of field.
- Coma is an optical defect which 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 edge of the image.
- Distortion are different effects due to the design and construction of the lens which result in a distorted appearance. For an example, an rectangle may appear as a barrel or pin cushion-shaped object. This is often seen in the two focal length ends of zoom lenses, which in the middle focal lengths these effects are absent.
- Chromatic 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 colors, each aberration will give a different value corresponding to each color thus producing blurred images.
Automatic Exposure
AE-L (Automatic Exposure Lock)
Auto exposure Lock is a metering system button which can be used to hold the exposure setting while a camera is using its built-in exposure meter in automatic or semi-automatic modes. It is most commonly used in situations where there exposure is better set by aiming the camera away from the center of the eventual final composition of the image. Using the AE-L permits the photographer to obtain the correct exposure settings and recompose the photograph for the desired image while retaining the correct exposure.
Ambient Light
This is the naturally occuring available light surrounding a subject. It is the light existing in an indoor or outdoor setting not created by any illumination supplied by the photographer.
Angle Of View
This is the area of a scene that a lens covers or sees. The angle of view is determined by the focal length of the lens. A wide-angle lens (short-focal-length) includes more of the scene than a normal (normal-focal-length) or telephoto (long-focal-length) lens. Basically, there are three types of angles which can be measured, based on horizontal, vertical and diagonals of the film frame or image sensor. The lens is normally designed to cover the widest angle in the diagonal direction, however, with today's DSLR cameras having a variety of sensor sizes, some lenses are built to cover smaller smaller sensors only, while others can cover the smaller sensors, all the way to what are considered "full size" sensors. The angle of view is the angle between imaginary lines drawn from the opposite ends of the film or sensor plane to the second nodal point of the lens. All objects within this angle will be recorded by the lens on the film or sensor.
Anti-Alias
This is a process which smootes the appearance of rough edges in computer images, sometimes called "jaggies" or "staircasing" by adding partially transparent pixels along the boundaries of diagonal lines which are merged into a smoother line by our eyes.
Aperture
The aperture is the opening in the lens which allows a specific amount of light to pass through at any moment of time. 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 sizes are 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 depth of field where the image will be sharply focused. The bigger the aperture, the shorter depth of field. 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 indicated by its f/number, is the ratio of the diameter of the opening to the focal length of the lens.
Aperture Priority
This is an exposure mode which permits you set the aperture while the camera sets the shutter speed for proper exposure, at a specific ISO or film speed/sensor sensitivity. If you change the aperture, or the light level changes, the shutter speed changes automatically. Apart when using a camera for sport or action photography where the subject is in motion, aperture priority today is the most common preference in photography.
Aperture ring
This is 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.
APS - Advanced Photo System
A film format used for still photography, marketed by Eastman Kodak under the brand name Advantix. The film is 24 mm wide, and has three image formats: H for "High Definition" (30.2 × 16.7 mm; aspect ratio 16:9; 4x7" print), C for "Classic" (25.1 × 16.7 mm; aspect ratio 3:2; 4x6" print) and P for "Panoramic" (30.2 × 9.5 mm; aspect ratio 3:1; 4x12" print)
Aspect Ratio
This is 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.
ATA
ATA means the camera supports the electrical interface standard, defined by the PC Card Association (formerly PCMCIA), known as ATA (AT Attachment). Today, most computers have ATA support built-in. ATA is supported by most operating systems such Microsoft Windows and Apple's operating systems, and generally all major manufacturers of personal computing systems.
Auto Exposure Bracketing
Auto Exposure Bracketing performs automatic exposure bracketing with varied shutter speed and/or aperture settings according to the desire of the photographer.
Auto-focus (AF)
Auto-focus is a system by which the camera lens or the camera body automatically focuses the image based on a selected part of the picture subject. Currently, most current SLRs DSLRs and Point & Shoot cameras are auto-focus based.
AF-I & AF-S lenses
This is Nikon's series of AF lenses, which integrate motors into their lenses. This gives these lenses quick, ultra quiet autofocus operations. While the AF-S lenses housing a silent wave motor for quicker and quiet operations than the AF-I lenses both perform autofocus rapidly.
Automatic iris
This is the 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.
AV
The Aperture value, usually refers to aperture settings.
Averaging Meter
This is a light measuring device which calculates exposure based on the overall brightness of the entire image area. Averaging tends to produce good exposures of bright and dark areas which contain detail. This method of exposure determination has been supplanted by newer more accurate metering.
If you have any suggested additions or corrections to the Glossary, please contact us.
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