[Steve]

D


D-type AF Nikkor lenses (Only apply to Nikon):
AF Nikkor lenses that send Distance Information to some of Nikon's cameras, Used for 3D Colour Matrix Metering or 3D Multi Sensor Balanced Fill Flash. Some third party lens manufacturers also supply compatible functions lenses too.

Darkroom:
A light tight area used for processing films and for printing and processing papers; also for loading and unloading film holders and some cameras. For image purist, the cycle of photograph is not complete if the darkroom process is not handled personally. Modern day equivalent is the image editor, (Photoshop, Paint Shop Pro, C1) many of which are available

Dedicated Flash:
A fully automatic flash that works only with specific cameras. Dedicated flash units automatically set the proper flash sync speed and lens aperture, and electronic sensors within the camera automatically control exposure by regulating the amount of light from the flash. A simple glance can differentiate by identifying the multiple contacts on the hot shoe (the place where the flash is mounted).

Definition:
The clarity of detail in a photograph.

Delayed action:
Mechanism delaying the opening of the shutter for some seconds after the release has been operated. Also known as self-timer.

Depth of Field:
The zone of acceptable sharpness in front of and behind the subject on which the lens is focused; extends approx. one-third in front of and two thirds behind the in-focus subject; dependent on three factors: aperture, focal length, and focused distance; the wider the aperture, the longer the focal length, and the closer the focused distance, the less the depth of field, and vice versa; in comparison to a normal lens, wide-angle lenses have inherently more depth of field at each f-number and telephoto lenses have less.
Since this element is very important, another simpler way to explain is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph. Depth of field depends on the lens opening, the focal length of the lens, and the distance from the lens to the subject or can explain as in simpler term as the zone of sharpest focus in front of, behind, and around the subject on which the lens is focused; Many newer DSLR’s allow DOF to be previewed in the camera - very handy for critical work.

Diaphragm:
An adjustable device inside the lens which is similar to the iris in the human eye; comprised of six or seven overlapping metal blades; continuously adjustable from "wide open" to "stopped down"; controls the amount of light allowed to pass through the lens to reach the sensor or film; also controls the amount of depth of field the photograph will have. Openings are usually calibrated in f-numbers. The more blades used will have a more natural and rounded spots. During viewing and focusing, the diaphragm remains wide open, allowing the maximum amount of light to go to the viewfinder for a bright and easy-to-focus image; at the instant of exposure, it stops down automatically to a particular aperture and then reopens to full aperture immediately afterward.

Diffuse Lighting:
Lighting that is low or moderate in contrast, such as on an overcast day.

Diffusing:
Softening of light of the image by means of reflectors or filters.

Dispersion:
The property of materials which have a refractive index that varies according to the wavelength of light, i.e., bend the rays of some colours more than others; a prism placed in the path of a ray of white light bends the blue and violet rays more than the orange and red, so that it spreads out or "disperses" the colours as a continuous spectrum.

Distortion:
Even if the other possible aberrations were totally eliminated, images could result that still have a distorted appearance. For an example, a rectangle may appear as a barrel or pin cushion-shaped object. A lens aberration which does not affect the sharpness of the image, but alters the shape of objects; the inability of a lens to render straight lines perfectly straight; does not improve by stopping down the lens; there are two types of distortion:

Barrel: Straight lines are bowed in at the edges of the picture frame resembling the sides of a barrel; present in small amounts in some wide-angle or wide-angle-zoom lenses, but uncorrected in fisheye lenses.

Pincushion: The opposite of barrel distortion; straight lines are bowed in toward the middle to resemble the sides of a pincushion; present in small amounts in some telephoto and telephoto-zoom lenses.

Double Exposure:
Two pictures taken on one frame of film, or two images merged in during post processing. Some cameras can have double exposure level depressed with multiple exposures and even with a motor drive.