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"D" terms

"Daguerre" to "Dynamic range"

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DAGUERRE, Louis Jacques Mand, 1789-1851 - French painter who, in 1839, with Nicphone Nipce, invented the daguerrotype.

DAGUERROTYPE - (1) An obsolete photographic process in which a picture made on a silver surface sensitized with iodine was developed by exposure to mercury vapor. (2) A picture made by this process.

DARKCLOTH - Material used to cover the photographer’s head and camera to block surrounding light in order to better view the image on the camera’s ground glass viewing screen.

DARKROOM - A room in which total darkness is achievable, permitting light-sensitive materials such as film to be handled without fear of their exposure to light.

DARKSLIDE - An opaque sheet that is slid in place over the front of a sheet film holder to protect the film from exposure to light.

DAYLIGHT FILM - Color film designed to render correct color balance when exposed in normal daylight.

A camera equipped with a DEDICATED FLASH performs fully-automatic flash functions with simplicity.
A camera equipped with a DEDICATED FLASH performs fully-automatic flash functions with simplicity.

DEDICATED FLASH - An electronic flash unit that integrates automatically with a specific camera’s exposure meter and exposure controls, permitting simplified, fully-automatic use of the flash. A dedicated flash is designed to work with a particular model, brand or type of camera.

DEFINITION - Sharpness of an image (as seen by the clarity of detail) formed by an optical system.

DENSITOMETER - Instrument that measures optical density of part of a negative or print.

DENSITY - The relative opacity (blackness) of an area of a negative, a transparency or a print. The greater the density, the less light can be transmitted through it. (Sometimes density is also referred to as "Contrast.")

DEPTH OF FIELD - The range of distance in a scene that appears to be in focus and will be reproduced as being acceptably sharp in an image. Depth of field is controlled by the lens aperture, and extends for a distance in front of and behind the point on which the lens is focused.

DEPTH OF FIELD PREVIEW BUTTON - Many cameras are equipped with a preview button that, when pressed and held in, stops the lens down to the preselected aperture, allowing you to see how much foreground or background are in focus.

DEPTH OF FIELD SCALE - Markings on the barrel of a lens that show the depth of field for a particular aperture and a particular focus setting.

DEPTH OF FOCUS - A zone of focus in the camera. If an image is focused on a ground glass screen in a camera, depth of focus makes it possible to move the screen slightly backward or forward and still have the image in acceptable focus.

DEVELOPER - A solution for developing a film or photographic paper - i.e. for turning an exposed film's or paper's latent image into an image that can be seen.

DEVELOPING TANK - A light-proof container used for processing exposed film.

An adjustable DIAPHRAGM in a lens controls the size of the aperture.
An adjustable DIAPHRAGM in a lens controls the size of the aperture.

DIAPHRAGM - A ring or plate with a hole in the center, the size of which controls the amount of light entering the camera. An adjustable diaphragm in a lens enlarges or reduces the size of the hole, or aperture, thereby permitting more or less light to pass through the lens to the film or digital sensor.

DIASCOPE - A viewer designed to enhance the viewing of autochromes.

DIFFRACTION - A phenomenon exhibited by a light’s wave front when passing the edge of an opaque object (one that does not allow light to pass through it). The light becomes modulated, causing a redistribution of the light’s energy within the wave front. You will see it at the edges of the object’s shadow, in the form of minute dark and light bands. The edges of the shadow have a fuzzy appearance. Think of ripples meeting a rock in a pond. They go around the rock in a new series of ripples that can be seen on the sides of the rock. Light waves behaving in a similar manner are said to be diffracted.

DIFFUSED LIGHT or DIFFUSE LIGHTING - Light that is scattered and spread out as opposed to specular light. Diffused light is softer than direct light, with shadows that are less sharply-defined (lower contrast).

DIFFUSER - Material that diffuses light. A diffuser may be a translucent material or a rough-surfaced reflective material, both of which scatter light’s rays, thereby softening the light.

DIFFUSING - (1) Moderating light so it is softened (diffused), generally either by reflecting it off a material that scatters the light or by placing a diffusing panel of translucent material between the light source and the subject. (2) Softening of detail in a print with a diffusion disk or other light-scattering material.

DIFFUSION-CONDENSER ENLARGER - An enlarger that has both a condenser system (for greater contrast) and a diffused light, producing less contrast than a condenser enlarger but more contrast and sharper detail than a diffusion enlarger (see below).

DIFFUSION ENLARGER - An enlarger in which the light is diffused, and therefore spread more evenly as it strikes and passes through the negative, resulting in less sharpness of detail. Negative flaws (scratches, etc.) are de-emphasized with a diffusion enlarger.

DIGICAM (also DIGI-CAM) - A digital camera.

DIGITAL CAMERA - A camera that takes pictures without film, but instead records the image on an image sensor chip in a format that is readable by a computer.

DIGITAL MANIPULATION - Altering a digital image using image-editing software, such as Adobe Photoshop.

DIGITAL ZOOM - Zoom effect in some digital cameras that is not true (optical) zoom, but is instead an enlargement of the information from the center of the CCD or CMOS (image sensor).

DIGITIZATION - The process by which analog images are converted to a digital form.

DIN - German standards system that expressed a film speed rating by a number followed by a degree symbol ( ° ). DIN derives its name from the initials of the Deutsche Industrie Normen or Deutsche Industries Norm. The DIN system has been replaced by the more universal ISO system.

DIOPTER - A unit of measure of the refractive power (strength or magnifying power) of a lens. A prescription for eyeglasses is normally written with numbers that represent diopters. Greater vision correction is needed as the diopter measurement increases. In photography, the term is used (1) with close-up lenses to indicate their magnification and focal length, and (2) with corrections to the camera viewfinder's lens when adjusting it to suit the user's eyesight, enabling the photographer to focus an image on the ground glass without wearing his or her eyeglasses. Note that not all camera's viewfinders can be adjusted to compensate for the photographer's eyesight. When they can, the cameras are sometimes said to have a "diopter."

DISPLAY - (1) A viewing screen, like that of a computer's monitor or a camera's LCD screen. (2) To show or exhibit, as in a display of one or more images.

DISTORTION - Misrepresentation of proportions of objects or of their arrangement in a scene. The two main types of lens distortion are: (1) Barrel distortion, in which the straight lines near the edges of the viewframe appear bowed outward from the center, like a barrel-shape; and (2) Pincushion distortion in which the same lines bend in towards the center.

DIVERGING LIGHT RAYS - Light rays that diverge, that is, continue to recede from each other, spreading or drawing apart. The opposite is "converge".

DODGING - Blocking a portion of the light when printing a photograph or manipulating a digital image so that an area of the image will be made lighter.

DOMINANT OBJECT - The object in a photograph that is predominant, usually one that is given the most visual weight and often appearing in the foreground.

DOUBLE-EXPOSURE - Exposing the same image frame twice. A typical double-exposure shows the same subject twice in the same image.

DOWNLOAD - Transfer files from a storage device to a computer. When you transfer your digital camera's or memory card's image files to your computer, you are "downloading" them. (Note: Upload refers to transferring a file from a computer to another storage device.)

DPI - Dots Per Inch - A measure of print resolution, that is, the number of dots of ink per linear inch of an image. The greater the number of dots, the higher the image's resolution.

DRAGGING THE SHUTTER - A technique that involves using flash with a long exposure (from a slow shutter speed) to also capture background objects that are in ambient light.

DROP-IN LOADING - Camera system that automatically advances film to the first frame when the camera's back is closed.

This enlargement is DRY-MOUNTED to foam-core.
This enlargement is DRY-MOUNTED to foam-core.

DRY MOUNTING - A means of attaching a print to a backing using a thin paper stock coated on each side with a dry cement that melts under heat.

DSLR or dSLR - Digital single lens reflex.

DUOTONE - A black and white (grayscale) image that has a single color added to it. "Duo" refers to the two "colors" - black and the other color - that are combined in the image. In printing, two color plates (one black; one a color) are used to print a duotone image.

DX - A coding system using a pattern of squares printed on a film cassette that can be read by a DX-enabled camera to automatically set film speed for the camera’s exposure meter, to set the number of frames and other data. Also called "DX coding" or "DX encoding."

DYNAMIC RANGE also known as Tonal Range - (1) The range between the lightest and darkest areas of an image. A picture containing very bright areas and very dark areas has a "wide" dynamic range. In a black and white image, dynamic range refers to the various shades of gray between solid black and absolute white. (2) The measure of the range of brightness levels that can be recorded by a camera's sensor. (See "Clipping" for further info on overexposed areas of an image.)

The highlight area (the sky) is
The highlight area (the sky) is "blown out" or too bright. No camera could capture the full dynamic range in such an image, where the very bright and very dark areas are too extreme.

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