An Occassional Glossary: C, D, E

Here's a bit more on the ongoing glossary project, C through E

Center-weighted Metering Pattern: In a metering scheme, an exposure system that takes most of its information from the center portion of the frame. Most center-weighted systems also take additional readings from the surrounding areas, but weight the reading towards the center.

Color Balance (digital camera): The setting in a digital camera that matches the available or artificial light to faithfully renders color.

Color Temperature: Described by the Kelvin scale, which is defined in degrees. It is used as a standard for judging the effect or color cast a certain light source will have on color rendition.


Continuous: The shooting mode that allows for continuous firing without lifting the finger from the shutter release button In tonality, a smooth range of tones from black to white. In autofocus, allowing shutter release regardless of whether subject focus has been attained.

Contrast: The relationship between the lightest and darkest areas in a scene and/or photograph. A small difference means low contrast; a great difference, high contrast. High contrast scenes may cause exposure metering problems; however, their “difficulty” can mean they hold the potential for more expression. In addition, combining bracketed exposures, HDR and tone curve compensation techniques can overcome high contrast challenges, Though contrast is often linked with scene brightness, there can be low contrast in a bright scene and high contrast in dim light. Contrast can also describe attributes of color, composition, and inherent qualities of film and sensors.

Correct Exposure: The combination of aperture and shutter speed that yields a full-toned image and the best possible representation of the scene. The constants in an exposure calculation are the ISO or sensitivity of the sensor and the brightness of the scene; the variables are the aperture and shutter speed.


Dedicated Flash: A flash that coordinates with the camera's exposure, and sometimes focusing, systems. Dedicated flashes may, among other things, automatically pick up the camera’s ISO setting, set the camera sync speed, and "tell" the camera when it’s ready to fire. Flashes dedicated to autofocusing cameras may also vary their angle of flash throw (coverage) according to the lens in use (even with zoom lenses), and emit autofocus beams that aid focusing in very dim light or even total darkness. For outdoor work, dedicated flashes may provide totally automatic fill flash exposure. In short, a dedicated flash can make flash photography as simple as automated natural light photography.

Depth of Field: The zone, or range of distances, within a scene that will record as sharp. Depth of field is influenced by the focal length of the lens in use, the f-stop setting on the lens, and the distance from the camera to the subject. It can be shallow or deep, and can be totally controlled by the photographer. It is one of the most creative and profound image effects available to photographers.

Depth-of-field Preview Button: A switch, button, or electronic push button on SLRs that allows the photographer to preview the depth of field of a selected aperture in the viewfinder. During composition the lens is wide open, thus the depth of field in the viewfinder is always that of the maximum aperture of the lens. DOF Preview is very useful for critical selective focus shots.

Dynamic Range: The ability of a sensor to record a certain range of light.

Electronic Flash: Known as a flashgun, strobe, or speedlight, a device consisting of a gas-filled tube that is fired by an electrical charge. It can be mounted directly on the camera hot shoe (which links the shutter release to the flash firing), or on a bracket or stand, and be connected to the camera via a sync cord or wirelessly through IR beams or radio signals.

Equivalent Exposure: Recording the same amount of light, even though aperture and shutter speeds have shifted. For example, an exposure of f/11 at 1/125 second is equivalent to an exposure of f/8 at 1/250 second.

Exposure: The amount of light that enters the lens and strikes the sensor. Exposures are broken down into aperture, which is the diameter of the opening of the lens, and shutter speed, which is the amount of time the light strikes the film. Thus, exposure is a combination of the intensity and duration of light.

Exposure Compensation Control: A camera function that allows for overriding the automatic exposure reading. The bias, or shift, can be set in full or partial stops. Used in difficult lighting conditions, when the reflective meter might fail (that is, dark or bright value dominance), or for deliberate under- or overexposure of a scene. Can also be used to bracket exposures.

Exposure Meter: Light-reading instrument that yields signals that are translated to f-stops and shutter speeds.

EV Numbers: A system of expressing exposure that combines apertures and shutter speed. Scene brightness translated to aperture and shutter speed values. For example, EV 15 at ISO 100 might mean 1/1000 second at f/5.6, or 1/500 second at f/8. EV numbers are often used as shorthand for the combined aperture and shutter speed value combinations and are used for making exposure compensation, when doing autoexposure bracketing or for readouts of exposure.

Very Selective Focus

There are a number of lenses that allow you to break the rules of depth of field. Because you can shift and tilt these lenses on an unusual axis not parallel to the image sensor, you can correspondingly tilt (up and down) and shift (side to side) the planes of focus in the photo. This technique is often used by large format, view camera photographers to attain unusually deep depth of field, where the shifts and tilts can be coordinated between both the front (lens stage) and back of the camera itself. Because the back of a DSLR is rigid there is less freedom of movement, and while specialty lenses can be used to create very deep depth of field, I use them for creating an almost angular plane of focus, thus a very shallow depth of field and “odd” focusing effects. What is most unusual is that these lenses allow you to turn the rules of depth of field on their head, if you will, by allowing you to have sharpness in, for example, one subject six feet away on the right side of the frame while another subject six feet away on the left side is quite unsharp.

While you can attain this effect via software, shooting with lenses that mount on your camera in the field is a much more visceral and engaging activity. I have used two types of lenses for this work-- “Lensbabys”, with various options for effects and operation, and a PC (perspective control) lens. Both are available for most every make of DSLR. They require manual focusing but usually can be used with automatic exposure, albeit with some occasional exposure compensation required.

PC lenses have a tilt and shift mechanism with various knobs and locks on the barrel. This allows you to tilt the lens to and fro and shift plus and minus. If you look at the back of the lens you will notice the rear element is recessed into the barrel. This so-called retrofocus-type construction allows the lens to be swung to and fro because the coverage of the lens circle exceeds the diameter of the sensor or film. Most of these pricey lenses are constructed so the tilts and shifts do not cause excessive vignetting, although you should watch for that with some more extreme movements.

You can play with the planes of focus in odd ways with one of the Lensbabys (www.lensbaby.com). This replaces the normal lens directly on your camera and allows you to shift the focusing planes so they are not parallel to the camera, something that is at odds with how we think about photographic sharpness. You do this by literally twisting or pressing down on one side of the lens; the bellows in the mount give way to make the lens surfaces sit at odd angles to the sensor. The lens can be shot wide open (usually about f/2.8) as supplied, or you can insert small diaphragms that create various aperture settings. I usually don’t use those stops as I want as shallow a plane of focus as possible.

Tools: PC (perspective control) lens or one of the Lensbaby models. Live View if available. Aperture priority or manual exposure mode. Manual focusing.