Mastering Digital SLR Photography Terms

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David D. Busch Glossery

additive primary colors

The red, blue, green and blue hues which can be used by themselves or in combinations to create all other colors that you capture with a digital camera.

Adobe RGB

One of two color space choices offered by the typical dSLR. Adobe RGB is an expanded color space useful for commercial and professional printing, and it can reproduce a larger number of colors. Most vendors recommend against using this color space if your images will be displayed primarily on your computer screen or output by your personal printer.

ambient lighting

Diffused, nondirectional lighting that doesn't appear to come from a specific source but, rather, bounces off walls, ceilings, and other objects in the scene when a picture is taken.

analog/digital converter

The module in a camera that electronically converts the analog information captured by the camera's sensor into digital bits that can be stored as an image.

angle of view

The area of a scene that a lens can capture, determined by the focal length of the lens. Lenses with a shorter focal length have a wider angle of view than lenses with a longer focal length.

anti-alias

A process that smoothes the look of rough edges in images (called jaggies or staircasing) by adding partially transparent pixels along the boundaries of diagonal lines that are merged into a smoother line by our eyes.

aperture

The size of the opening in the iris or diaphragm of a lens, relative to the lens's focal length. Also called an f/stop. For example, with a lens having a focal length of 100mm, an f/stop with a diameter of 12.5mm would produce an aperture value of f/8

Aperture-priority

A camera setting that allows you to specify the lens opening or f/stop that you want to use, with the camera selecting the required shutter speed automatically based on it's light-meter reading and your ISO sensitivity setting.

artifact

A type of noise in an image, or an unintentional image component produced in error by a digital camera during processing, usually caused by the JPEG compression process in digital cameras.

aspect ratio

The proportions of an image as printed, displayed on a monitor, or captured by a digital camera.

autofocus

A camera setting that allows the camera to choose the correct focus distance for you, based on the contrast of an image (the image will be at maximum contrast when in sharp focus). The camera can be set for single-servo autofocus (AF-S), in which the lens is not focused until the shutter release is partially depressed, continuous-servo autofocus (AF-C), in which the lens refocuses constantly as you frame and reframe the image, or manual focus.

back lighting

A lighting effect produced when the main light source is located behind the subject. Back lighting can be used to create a silhouette effect, or to illuminate translucent objects.

barrel lighting

A lens defect that causes straight lines at the top or side edges of an image to bow outward into a barrel shape.

blooming

An image distortion caused when a photosite in an image sensor has absorbed all the photons it can handle so that additional photons reaching that pixel overflow to effect surrounding pixels, producing unwanted brightness and overexposure around the edges of objects.

blur

To soften an image or part of an image by throwing it out of focus, or by allowing it to become soft due to subject or camera motion. Blur can also be applied in an image editing program.

bokeh

A term derived from the Japanese word for blur, which describes the aesthetic qualities of the out-of-focus parts of an image. Some lenses produce "good" bokeh and others offer "bad" bokeh. Some lenses produce uniformly illuminated out-of-focus discs. Others produce a disc that has a bright edge and a dark center, producing a "doughnut" effect, which is the worst from a bokeh standpoint. Lenses that generate a bright center that fades to a darker edge are favored, because their bokeh allows the circle of confusion to blend more smoothly with the surroundings. The bokeh characteristics of a lens are most important when you're using selective focus (say, when shooting a portrait) to deemphasize the background, or when shallow depth of field is given because you're working with a macro lens, with a long telephoto, or with a wide-open aperture.

bounce lighting

Light bounced from a continuous light source or flash off a reflector, including ceilings and walls, to provide a soft, natural-looking light.

bracketing

Taking a series of photographs of the same subject at different settings, including exposure and white balance, to help ensure that one setting will be the correct one. The camera allows you to choose the order in which bracketed settings are applied, or bracket sequence.

buffer

The digital camera's internal memory where an image is stored immediately after it is taken until it can be written to the camera's non-volatile (semi-permanent) memory card.

burst mode

The digital camera's equivalent of the film camera's motor drive, used to take multiple shots within a short period of time, each stored in a memory buffer temporarily before writing them to the media.

calibration

A process used to correct for the differences in the output of a printer or monitor when compared to the original image. Once you've calibrated your scanner, monitor, and/or your image editor, the images you see on the screen more closely represent what you'll get from your printer, even though calibration is never perfect.

Camera Raw

A plug-in included with Photoshop that can manipulate the unprocessed images captured by digital cameras, such as the camera's RAW files. The latest versions of this module can also work with JPEG and TIFF images.

camera shake

Movement of the camera, aggravated by slower shutter speeds, which produces a blurred image.

center-weighted metering

A light-measuring device that emphasizes the area in the middle of the frame when calculating the correct exposure for an image.

channel

In an electronic flash, a channel is a protocol used to communicate between a master flash unit and the remote units slaved to that main flash. The ability to change channels allows several master flash units to operate in the same environment without interfering with each other.

chromatic aberration

An image defect, often seen as green or purple fringing around the edges of an object, caused by a lens failing to focus all colors of a light source at the same point.

circle of confusion

A term applied to the fuzzy discs produced when a point of light is out of focus. The circle of confusion is not a fixed size. The viewing distance and amount of enlargement of the image determine whether we see a particular spot on the image as a point or as a disc.

close-up lens

A lens add-on that allows you to take pictures at a distance that is less than the closest-focusing distance of the lens alone.

CMYK color model

A way of defining all possible colors in percentages of cyan, magenta, yellow and black. Black is included to improve the rendition of shadow detail. CMYK is commonly used for printing.

Why does the K represent black in CMYK?

To differentiate it from blue in the RGB color model

color correction

Changing the relative amounts of color in an image to produce a desired effect, typically a more accurate representation of those colors. Color correction can fix faulty color balance in the original image, or compensate for the deficiencies of the inks used to reproduce the image.

compression

Reducing the size of a file by encoding using fewer bits of information to represent the original. Some compression schemes, such as JPEG, operate by discarding some image information, while others, such as compressed RAW, preserve all the detail in the original.

continuous-servo autofocus

An automatic focusing setting (AF-C) in which the camera constantly refocuses the image as you frame the picture. The setting is often the best choice for moving subjects.

contrast

The range between the lightest and darkest tones in an image. A high-contrast image is one in which the shades fall at the extremes of the range between white and black. In a low-contrast image, the tones are closer together.

dedicated flash

An electronic flash unit designed to work with the automatic exposure features of a specific camera.

depth-of-field

A distance range in a photograph in which all included portions of an image are at least acceptably sharp. You can see the available depth-of-field at the taking aperture by pressing the depth-of-field preview button, or estimate the range by viewing the depth-of-field scale found on some lenses.

diaphragm

An adjustable component, similar to the iris in the human eye, that can open and close to provide specific-sized lens opening, or f/stops and thus control the amount of light reaching the sensor or film.

diffuse lighting

Soft, low-contrast lighting

digital processing chip

A solid-state device found in digital cameras that's in charge of applying the image algorithms to the raw picture data prior to storage on the memory card.

diopter

A value used to represent the magnification power of a lens, calculated as the reciprocal of a lens's focal length (in meters). Diopters are most often used to represent the optical correction used in a viewfinder to adjust for limitations of the photographer's eyesight, and to describe the magnification of a close-up lens attachment.

equivalent focal length

A digital camera's focal length translated into the corresponding values for a 35mm film camera. The value can be calculated for lenses used on APS-C cameras by multiplying by 1.5

exchangeable image file format (Exif)

Developed to standardize the exchange of image data between hardware devices and software. A variation on JPEG, Exif is used by most digital cameras, and includes information such as the date and time a photo was taken, the camera settings, resolution, amount of compression, and other data.

exposure

The amount of light allowed to reach the film or sensor, determined by the intensity of the light, the amount admitted by the iris of the lens, the ISO sensitivity set in the camera and the length of time determined by the shutter speed.

exposure compression

Exposure compression, which uses exposure value (EV) settings, is a way of adding or decreasing exposure without the need to reference f/stops or shutter speeds. For example, either by using a larger f/stop or slower shutter speed, or both. The camera offers both conventional exposure compensation and flash exposure compensation.

fill lighting

In photography, lighting used to illuminate shadows. Reflectors or additional incandescent lighting or electronic flash can be used to brighten shadows. One common technique outdoors is to use the camera's flash as a fill.

filter (in photography)

A device that fits over the lens, changing the light in some way.

filter (in image editing)

A feature that changes the pixels in an image to produce blurring, sharpening and other special effects. Photoshop includes several interesting filter effects, including Lens Blur and Photo Filters.

flash sync

The timing mechanism that ensures that an internal or external electronic flash fires at the correct time during the exposure cycle. A digital SLR's flash sync speed it the highest shutter speed that can be used with flash.

focal length

The distance between the film and the optical center of the lens when the lens is focused on infinity, usually measured in millimeters.

focal plane

A line, perpendicular to the optical axis, which passes through the focal point forming a plane of sharp focus when the lens is set at infinity. A focal plane indicator is etched into the camera on the top panel.

focus tracking

The ability of the automatic focus feature of a camera to change focus as the distance between the subject and the camera changes. One type of focus tracking is predictive, in which the mechanism anticipates the motion of the object being focused on, and adjusts the focus to suit.

format

To erase a memory card and prepare it to accept files.

fringing

A chromatic aberration that produces fringes of color around the edges of subjects, caused by a lens's inability to focus the various wavelengths of light onto the same spot. Purple fringing is especially troublesome with backlit images.

front-curtain sync (first-curtain sync)

The default kind of electronic flash synchronization technique, originally associated with focal plane shutters, which consists of a traveling set of curtains, including a front curtain, which opens to reveal the film or sensor, and a rear curtain, which follows at a distance determined by shutter speed to conceal the film or sensor at the conclusion of the exposure. For a flash picture to be taken, the entire sensor must be exposed at one time to the brief flash exposure, so the image is exposed after the front curtain has reached the other side of the focal plane, but before the rear curtain begins to move. Front-curtain sync causes the flash to fire at the beginning of this period when the shutter is completely open, in the instant that the first curtain of the focal plane shutter finishes its movement across the film or sensor plane. With slow shutter speeds, this feature can create a blur effect from the ambient light, showing as patterns that follow a moving subject with the subject shown sharply frozen at the beginning of the blur trail.

front lighting

Illumination that comes from the direction of the camera.

f/stop

The relative size of the lens aperture, which helps determine both exposure and depth-of-field. The larger the f/stop number, the smaller the f/stop itself.

geotagging

Adding location information, such as latitude, longitude, and elevation to an image file.

graduated filter

A lens attachment with variable density or color from one edge to another. A graduated neutral-density filter, for example, can be oriented so the neutral-density portion is concentrated at the top of the lens's view with the less dense or clear portion at the bottom, thus reducing the amount of light from a very bright sky while not interfering with the exposure of the landscape in the foreground. Graduated filters can also be split into several color sections to provide a color gradient between portions of the image.

gray card

A piece of cardboard or other material with a standardized 18% reflectance. Gray cards can be used as a reference for determining correct exposure or for setting white balance.

group

A way of bundling more than one wireless flash unit into a single cluster that all share the same flash output setting, as controlled by the master flash unit.

high contrast

A wide range of density in a print, negative, or other image

highlights

The brightest parts of an image containing detail.

high-speed sync

A method for syncing external flashes at shutter speeds higher than their maximum sync speed by increasing the flash duration through multiple bursts to match the speed of the focal plane shutter.

histogram

A kind of chart showing the relationship of tones in an image using a series of 256 vertical bars, one for each brightness level. A histogram chart, such as the ones the camera can display during picture review, typically looks like a curve with one or more slopes and peaks, depending on how many highlight, midtone, and shadow tones are present in the image. The camera can also display separate histograms for the red, green and blue channels of an image.

hot shoe

A mount on top of a camera used to hold an electronic flash, while providing an electrical connection between the flash and the camera. Also called an accessory shoe.

hyperfocal distance

A point of focus where everything from half that distance to infinity appears to be acceptably sharp. For example, if your lens has a hyperfocal distance of four feet, everything from two feet to infinity would be sharp. The hyperfocal distance varies by the lens and the aperture in use. If you know you'll be making a grab shot without warning, sometimes it is useful to turn off your camera's automatic focus, and set the lens to infinity, or, better yet, the hyperfocal distance. Then, you can snap off a quick picture without having to wait for the lag that occurs with most digital cameras as their autofocus locks in.

image rotation

A feature that senses whether a picture was taken in horizontal or vertical orientation. That information is embedded in the picture file so that the camera and compatible software applications can automatically display the image in the correct orientation.

image stabilization

A technology that compensates for camera shake, usually by adjusting the position of the camera sensor or lens elements in the response to movement of the camera.

incident light

Light falling on a surface.

International Organization for Standardization (ISO)

A governing body that provides standards used to represent film speed, or the equivalent sensitivity of a digital camera's sensor. Digital camera sensitivity is expressed in ISO settings.

interpolation

A technique digital cameras, scanners, and image editors use to create new pixels required whenever you resize or change the resolution of an image based on the values of surrounding pixels. Devices such as scanners and digital cameras can also use interpolation to create pixels in addition to those actually captured, thereby increasing the apparent resolution or color information in an image.

jaggies

Staircasing effect of lines that are not perfectly horizontal or vertical, caused by pixels that are too large to represent the line accurately.

JPEG

A file "lossy" format (short for Joint PHotographic Experts Group) that supports 24-bit color and reduces file sizes by selectively discarding image data. Digital cameras generally use JPEG compression to pack more images onto memory cards. You can select how much compression is used (and, therefore, how much information is thrown away) by selecting from among the other quality settings offered by your camera. (In the camera's case, those are Fine, Standard and Basic.)

Kelvin (K)

A unit of measure based on the absolute temperature scale in which absolute zero is zero; it's used to describe the color of continuous-spectrum light sources and applied when setting white balance. For example, daylight has a color temperature of about 5500K, and a tungsten lamp has a temperature of about 3400K.

lag time

The interval between when the shutter is pressed and when the picture is actually taken. During that span, the camera may be automatically focusing and calculating exposure. With digital SLRs, lag time is generally very short: with non-dSLRs, the elapsed time easily can be one second or more under certain conditions.

latitude

The range of camera exposures that produces acceptable images with a particular digital sensor or film.

lens flare

A feature of conventional photography that is both a bane and creative outlet. It is an effect produced by the reflection of light internally among elements of an optical lens. Bright light sources within or just outside the field of view cause lens flare. Flare can be reduced by the use of coatings on the lens elements or with the use of lens hoods. Photographers sometimes use the effect as a creative technique, and Photoshop includes a filter that lets you add lens flare at your whim.

lighting ratio

The proportional relationship between the amount of light falling on the subject from the main light and other lights, expressed in a ratio, such as 3:1.

live view

The ability of recent cameras to provide a real-time preview image, as seen by the sensor, on the rear-panel color LCD, achieved by flipping up the mirror and opening the shutter.

lossless compression

An image-compression scheme, such as TIFF, that preserves all image detail. When the image is decompressed, it is identical to the original version.

lossy compression

An image-compression scheme, such as JPEG, that creates smaller files by discarding image information, which can affect image quality.

macro lens

A lens that provides continuous focusing from infinity to extreme close-ups, often to a reproduction ratio of 1:2 (half life-size) or 1:1 (life-size).

matrix metering

A system of exposure calculation that looks at many different segments of an image to determine the brightest and darkest portions, the base f/stop, and shutter speed on settings derived from a database of images stored in the camera's firmware.

maximum burst

The number of frames that can be exposed at the current settings until the buffer fills.

midtones

Parts of an image with tones of an intermediate value, usually in the 25% to 75% brightness range. Many image-editing features allow you to manipulate midtones independently from the highlights and shadows.

mirror lock-up

The ability of the camera to retract its mirror to reduce vibration prior to taking the photo and to allow access to the sensor for cleaning.

modeling light

A secondary light used to provide a preview of the lighting effect of an electronic flash unit. A modeling light can be an incandescent or fluorescent bulb, or may be simulated by a series of low-power bursts lasting a few seconds.

neutral color

A color in which red, green, and blue are present in equal amounts, producing a gray.

neutral-density filter

A gray camera filter that reduces the amount of light entering the camera without affecting the colors

noise

In an image, pixels with randomly distributed color values. Noise in digital photographs tends to be the product of low-light conditions and long exposures, particularly when you've set your camera to a higher ISO rating than normal.

noise reduction

A technology used to cut down on the amount of random information in a digital picture, usually caused by long exposures at increased sensitivity ratings. Noise reduction is automatically applied for long exposures, and it involves the camera automatically taking a second blank/dark exposure at the same settings that contain only noise, and then using the blank photo's information to cancel out the noise in the original picture. Although the process is very quick, it does double the amount of time required to take the photo.

normal lens

A lens that makes the image in a photograph appear in a perspective that is like that of the original scene, typically with a field of view of roughly 45 degrees.

overexposure

A condition in which too much light reaches the film or sensor, producing a dense negative or a very bright/light print, slide, or digital image.

pincushion distortion

A type of lens distortion in which lines at the top and side edges of an image are bent inward, producing an effect that looks like a pincushion.

polarizing filter

A filter that forces light, which normally vibrates in all directions, to vibrate only in a single plane, reducing or removing the specular reflections from the surface of objects and effectively darkening the sky when shooting with the sun at an incident angle of 90 degrees from the axis of the lens.

RAW

An image file format, such as Nikon's NEF or Canon's CR2 format, that includes all the unprocessed information captured by the camera after conversion to digital form. RAW files are very large compared to JPEG files and must be processed by a special program such as Adobe's Camera Raw filter after being downloaded from the camera.

rear-curtain sync (second-curtain sync)

An optional kind of electronic flash synchronization technique, originally associated with focal plane shutters, which consists of a traveling set of curtains, including a front (first) curtain (which opens to reveal the film or sensor) and rear (second) curtain (which follows at a distance determines by shutter speed to conceal the film or sensor at the conclusion of the exposure). For a flash picture to be taken, the entire sensor must be exposed at one time to the brief flash exposure, so the image is exposed after the front curtain has reached the other side of the focal plane, but before the rear curtain begins to move. Rear-curtain sync causes the flash to fire at the end of the exposure, an instant before the second or rear curtain of the focal plane shutter begins to move. With slow shutter speeds, this feature can create a blur effect from the ambient light, showing as patterns that follow a moving subject with the subject shown sharply frozen at the end of the blur trail. If you were shooting a photo of The Flash, the superhero would appear sharp, with a ghostly trail behind him.

red-eye

An effect from flash photography that appears to make a person's eyes glow red, or an animal's yellow or green. It's caused by light bouncing from the retina of the eye and is most pronounced in dim illumination (when the irises are wide open) and when the electronic flash is close to the lens and, therefore, prone to reflect directly back. Image editors can fix red-eye through cloning other pixels over the offending red or orange ones.

RGB color

A color model that represents the three colors-red, green, and blue-used by devices such as scanners or monitors to reproduce color. Photoshop works in RGB mode by default and even displays CMYK images by converting them to RGB.

saturation

The purity of color; the amount by which a pure color is diluted with white or gray.

selective focus

Choosing a lens opening that produces a shallow depth-of-field. Usually this is used to isolate a subject in portraits, close-ups, and other types of images, by causing most other elements in the scene to be blurred.

self-timer

A mechanism that delays the opening of the shutter for some seconds after the release has been operated.

sensitivity

A measure of the degree of response of a film or sensor to light, measured using the ISO setting.

shadow

The darkest part of an image, represented on a digital image by pixels with low numeric values.

sharpening

Increasing the apparent sharpness of an image by boosting the contrast between adjacent pixels that form an edge.

shutter

In a conventional film camera, the shutter is a mechanism consisting of blades, a curtain, a plate, or some other movable cover that controls the time during which light reaches the film. Digital cameras use actual mechanical shutters for the slower shutter speeds (less than 1/250th second) and an electronic shutter for higher speeds.

shutter-priority

An exposure mode in which you set the shutter speed and the camera determines the appropriate f/stop.

side lighting

Applying illumination from the left or right sides of the camera.

slave unit

An accessory flash unit that supplements the main flash, usually triggered electronically when the slave senses the light output by the main unit, or through radio waves.

slow sync

An electronic flash synchronizing method that uses a slow shutter speed so that ambient light is recorded by the camera in addition to the electronic flash illumination/ That allows the background to receive more exposure for a more realistic effect.

specular highlight

Bright spots in an image, exhibiting no detail, caused by reflection of light sources.

spot metering

An exposure system that concentrates its measurement on a small area in the image.

sRGB

One of two color space choices available with your camera. The sRGB setting is recommended for images that will be output locally on the user's own printer, as this color space matches that of the typical inkjet printer and a properly calibrated monitor fairly closely.

subtractive primary colors

Cyan, magenta, and yellow, which are the printing inks that theoretically absorb all color and produce black. In practice, however, they generate a muddy brown, so black is added to preserve detail (especially in shadows). The combination of the three colors and black is referred to as CMYK.

through the lens (TTL)

A system of providing viewing and exposure calculation through the actual lens taking the picture.

time exposure

A picture taken by leaving the shutter open for a long period, usually more than one second. The camera is generally locked down with a tripod to prevent blur during the long exposure.

tungsten light

Light from ordinary room lamps and ceiling fixtures, as opposed to fluorescent illumination.

underexposure

A condition in which too little light reaches the film or sensor, producing a thin negative, a dark slide, a muddy-looking print, or dark digital image.

unsharp masking

The process for increasing the contrast between adjacent pixels in an image, increasing sharpness, especially around edges.

vignetting

Dark corners of an image, often produced by using a lens hood that is too small for the field of view, a lens that does not completely fill the image frame, or generated artificially using image-editing techniques (usually to enhance the appearance of certain kings of images, such as portraits)

white balance

The adjustment of a digital camera to the color temperature of the light source. Interior illumination is relatively red; outdoor light is relatively blue. Digital cameras set correct white balance automatically or let you do it through menus. Image editors can often do some color correction of images that were exposed using the wrong white balance setting, especially when working with RAW files that contain the information originally captured by the camera before white balance was applied.

WiFi

WiFi (short for "wireless fidelity") is applied to wireless local area networks (WLAN) that uses specifications in the 802.11 family.

zoom head

The capability of an electronic flash to change the area of its coverage to more closely match the focal length setting of a prime or zoom lens.

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