NSL Photography's™ Glossary of Photographic Terms - D

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D-type AF Nikkor lenses (Nikkor is a registered brand of Nikon lenses)
AF Nikkor lenses that send distance information to compatible Nikon SLR and DSLR cameras. The information is used for 3D Color Matrix Metering or 3D Multi Sensor Balanced Fill Flash with Nikon Speedlight electronic flash units. Some third party lens manufacturers lenses which provide these same functions in their compatible lenses.

DC (Defocus Image control)
A lens family introduced by Nikon, designated as DC lens, mainly for portrait photography. The lens enables the photographer to control background and foreground blur precisely, resulting in strikingly attractive portraits.

A light tight area used for processing films and for printing and processing prints. Darkrooms are also used to load and unload film holders and some cameras.

Data Disk
A circular, rotating disk at the end of Advanced Photo System (APS) film cassettes that functions as a circular bar code. It tells the camera, via an optical sensor, the film speed, type and exposure length through a reflective bar code.

Dedicated Flash
An automatic flash which works only with specific cameras. Dedicated flash units automatically set the proper flash sync speed and lens aperture, and electronic sensors within the camera. They automatically control exposure by regulating the amount of light from the flash.

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.

The blackness of an area in a negative or print that determines the amount of light that will pass through it or reflect from it. Sometimes referred to as contrast.

Depth of Field
The zone of acceptable sharpness in front of and behind the subject on which the lens is focused. It is dependent on three major 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.

Depth of Focus
The distance range over which film could be shifted at the film plane inside the camera and still have the subject appear in sharp focus. This is often misused to mean depth of field.

An adjustable device inside the lens which is similar to the iris in the human eye and generally comprised of six or seven overlapping metal blades, continuously adjustable from "wide open" to "stopped down." It controls the amount of light allowed to pass through the lens and expose the film or sensor when a photo is taken. It also in part controls the amount of depth of field the photograph will have. The openings are calibrated in f-numbers. The more blades used the more natural and rounded the opening will be.

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

Softening detail or light with a material which scatters light.

Even if the other possible aberrations were totally eliminated, images could still have a distorted appearance. For an example, an 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 is due to the inability of a lens to render straight lines perfectly straight will not improve by stopping down the lens. There are two general types of distortion.

  • Barrel: Straight lines are bowed in at the edges of the picture frame resembling the sides of a barrel, and present in small amounts in some wide angle or wide angle-zoom lenses.
  • Pincushion: The opposite of barrel distortion where straight lines are bowed in toward the middle to resemble the sides of a pincushion. It's present in small amounts in some telephoto and telephoto-zoom lenses.
Holding back the image-forming light from a part of the image projected on an enlarger easel during part of the basic exposure time to make that area of the print lighter. Software for digital images can simulate the same effect.

Double Exposure
Two pictures taken on one frame of film, or two images printed on one piece of photographic paper or digital print paper.

A digital single-lens reflex camera (digital SLR) is a digital camera which uses a mechanical mirror system and pentaprism to direct light from the lens to an optical viewfinder on the back of the camera.

In a DSLR, for viewing purposes, its mirror reflects the light coming through the attached lens upwards at a 90 degree angle, then reflects it twice by the pentaprism, rectifying it for the photographer's eye. While the photo is taken, the mirror swings upward, the aperture narrows (if set smaller than wide open), and the shutter opens, allowing the lens to project light onto the image sensor. A second shutter covers the sensor, marking the end of the exposure, and the mirror lowers while the shutter resets. All of this happens automatically over a period of milliseconds.

DSLRs are often preferred by professional still photographers because they allow an accurate preview of framing close to the moment of exposure, and because DSLRs allow the user to choose from a variety of interchangeable lenses. Most DSLRs also have a function that allows accurate preview of depth of field.

Dynamic Range
Dynamic range in photography describes the ratio between the maximum and minimum measurable light intensities (white and black, respectively), however, in the real world, scenes rarely are true white or black, but instead are made up of varying degrees of intensity and subject reflectivity. The concept of dynamic range is therefore more complicated,

The dynamic range of a digital camera can be described as the ratio of maximum light intensity measurable, at a specific pixel saturation, to minimum light intensity measurable. The most commonly used unit for measuring dynamic range in digital cameras is the f-stop, which describes total light range by powers of 2. Sometimes the f-stop is described as a "zone" or "ev."

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