Glossary of Photo Terms

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C-D

CA  – Chromatic Aberration
Refers to the inability of a lens to focus all wavelengths of light (colors) equally. Light of higher frequency (blue) is focused at a slightly different angle than low frequency light (red) which causes the different colors to focus either in front or behind the focal plane. This causes a color fringing to appear in an image and an associated loss of sharpness, especially at the corners where the light is bent at the greatest angle. Lenses can be made using coatings (expensive) and exotic glass that focuses all wavelengths more equally (more expensive) to correct for this. This is one of the reasons that those $1400 pro lenses cost the way they do and why they perform so well.

CDAF – Contrast Detect Autofocus
Contrast detection autofocus reads information directly off of a portion of the sensor and evaluates the level of contrast. Unlike Phase Detection autofocus, this method can’t determine whether the area is focused too near or too far. This requires the focusing system to focus the lens in steps with readings taken at each step until high contrast is detected. Since it has no way of predicting what the highest contrast reading will be, the lens must focus past the point of maximum contrast until the contrast drops off and then reverse back to the maximum. Because contrast detection requires the lenses to be focused in decreasingly smaller steps, older lenses designed for the precise directional instructions sent by Phase Detect AF don’t work very well.

Center-Weighted Metering – Central Area Metering
A metering mode that measures the entire frame but gives more importance to the central area of the frame. This is a useful mode when the subject fill most of the frame. While it may cause some under- or over-exposure of the background, the subject will be properly exposed.

CF  – Compact Flash
A memory card format that is widely used in DSLR cameras because of the large capacities and high transfer speeds available. They come in two sizes (actually, one size with two thicknesses): 43×36×3.3 mm for Type I and 43×36×5 mm for Type II. Most CF-compatible cameras made in the last five years will take either size.

CoC  – Circle of Confusion
A sharp image has all in-focus areas of the image rendered on the focal plane as tiny points of light. If the focus of the image or part of the image occurs before or after the focal plane, it is rendered as a circle instead of a point with the circle getting larger as the focus moves farther away from the focal plane. That is a Circle of Confusion. Depth of field in an image is determined by how far the focus can occur before or after the focal plane without the Circle of Confusion becoming too large, causing that part of of the image to appear out of focus.

CPL – Circular Polarizer
This is a special type of polarizer that will filter the glare from a scene but still allows the metering and autofocus sensors to work in a DSLR (or film SLR). 

CR – Camera RAW
Common forum abbreviation for Adobe’s Camera RAW RAW image editor

Crop Factor – Focal Length Multiplier
DSLRs aren’t all created equal. The 35mm film format that they are descended from used a rectangle of film that measured 24mm x 36mm. There are a few cameras that use digital sensors that use the same dimensions as 35mm film. These are referred to as “full-frame” and tend to be high-end units and rather expensive. Most of the DSLR models use a sensor that is about the same size as the frame of an APS-C film camera, about 24mm x 16mm. Because the diagonal measure of an APS-C sensor is only about 66% of a full 35mm frame, it only captures the central area of the image circle projected by the lens. The end result is that the “apparent” focal length of a lens on an APS-C camera it 1.5x what it would be on a full-frame camera (1/.66 = 1.5). This is called the “crop factor” since the effect is the same as cropping the center out of a full-frame image and enlarging it. Another player is the Four Thirds standard. It uses a sensor that has one half the area of full-frame and, therefore, a crop factor of 2.0x. A 50mm lens on a 1.5x crop factor sensor would give the same apparent magnification as a 75mm short telephoto on a full-frame sensor or 35mm film. The same lens on a Four Thirds sensor would perform like a 100mm telephoto. There are a few variations, but this illustrates the point. When looking for a lens, you need to be aware of the crop factor of your camera to have an idea of what to expect from a given focal length.

CZ – Carl Ziess
Designation on top-tier Sony SLR lenses indicating that they were developed in collaboration with Carl Zeiss, Inc.

DC – APS-C only
Sigma term for a lens designed for the smaller image circle required by an APS-C sized sensor. Cannot be used on a film or full-frame camera without vignetting.

DG – Digital
Sigma term designating that a full-frame (FF) lens has been optimized for digital photography by re-shaping the rear element, additional coatings, etc..

Di  – Digitally Integrated
Tamron designation for lenses capable of providing focal-length & distance information to the camera they attach to. Additional coatings and rear-element designs reduce ghosting (reflections from the shiny sensor bouncing off the lens back to the sensor.)

Di-II – Digitally Integrated -APS-C only
Tamron designation for their Di lenses designed for the smaller image circle required by an APS-C sized sensor. Cannot be used on a film or full-frame camera without vignetting.

D-Lighting – Active D-Lighting
Nikon term for image dynamic range enhancement technology implemented in their cameras that uses software to balance the highlight and shadow exposure to more closely represent how the human eye sees. Active D-Lighting applies the changes automatically as the image is recorded.

DMF  – Direct Manual Focus
An camera/lens feature that allow fine manual focus after autofocus is achieved without having to switch from autofocus to manual focus.

DOF – Depth Of Field
Nearest and farthest distance from the point the camera is focused on where objects will be in acceptably sharp focus.

DPI – Dots Per Inch
DPI is a printing standard used for mechanical printers that lay down discreet points of pigment or dye and not for printing presses that use inked plates. DPI is a fixed measurement based on the number of dots in an inch with a larger print requiring more dots rather spreading a fixed number of dots over a larger area as described in the PPI (Pixels Per Inch) display measurement.

DR – Dynamic Range
The Dynamic Range is the ratio between the highest and lowest measurable values as in recording sound or light. In photography it describes the film or sensor’s ability to capture a range of details in a scene from both bright and shadowed areas. Neither film nor digital has the dynamic range that the human eye is capable of, which is why images often look a lot different than you remember seeing them, with bright areas washed out and scenery hidden in shadows. Bracketing and HDR imaging can overcome this and some cameras can improve the dynamic range internally through special processing chips or software.

DRO – Dynamic Range Optimization (or Optimizer)
Sony term for image dynamic range enhancement technology implemented in their Alpha series camera that uses a dedicated hardware processor to measure as many as 4000 segments of an image during capture and increases or decreases the sensitivity of the analyzed segments at the time of exposure to balance the highlight and shadow exposure to more closely represent how the human eye perceives a scene. 

DSLR – Digital Single-Lens Reflex
An SLR with a digital sensor instead of film.

DT – APS-C only
Sony/Minolta designation for a lens designed for the smaller image circle required by an APS-C sized sensor. Cannot be used on a film or full-frame camera without vignetting.

DX – APS-C only
Nikon or Tokina designation for a lens designed for the smaller image circle required by an APS-C sized sensor. Cannot be used on a film or full-frame camera without vignetting

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