Glossary | DSLRU - Knowledge Has Never Been This Affordable

# | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

- # -

35mm: 35mm film is the basic film gauge most commonly used for both still photography and motion pictures. It was introduced by George Eastman in 1892. 35mm film is generally 24mm wide (between the perforations) and 36mm along the long side of the image. This closely mirrors the 4:3 ratio seen on earlier televisions and the NTSC standard (720 x 480).

- A -

Aberration

In general terms this is the failure of a lens to produce exact point-to-point correspondence between an object and its image. In reality, there are many kinds of aberrations - some shift colors in one direction or another while others distort the image as if the image is warped. Some aberrations are desired: a fisheye lens technically creates an aberration.

Accessory Shoe

See "Hot Shoe."

AE Lock

A camera feature which locks the settings affecting exposure (aperture, ISO, and shutter speed). This feature is not often used, but occasionally a photographer will lock exposure and then recompose the image.

AI Servo Focus

An auto focus mode found on Canon cameras (on Nikons it's called "continuous focus"). This is a mode or feature that attempts to keep a moving subject in focus by continually adjusting the focus of the camera lens as the subject moves toward and away from the camera. When in use, the lens will constantly maintain its focus on the subject. This mode is commonly used for sports and action photography. "AI" refers to artificial intelligence, as the camera attempts to constantly predict where the subject is about to be. Before servo focus the photographer would generally pre-focus on an area where he/she thought the best action would take place; today he/she can follow the entire sequence of events, and select the best later.

Ambient Light

Light that exists in a scene without an on- or off-camera strobe or flash.

Angle of View

Typically used when referring to a lens, this is a measurement of the angle the lens can see. The angle is measured from the focal point inside the lens, and is smaller for longer focal lengths. The angle of view can be "effectively" modified by different sensor sizes. On a full-frame camera, a 300mm lens has an angle of view measuring 8 degrees while a 50mm lens's angle of view is 46 degrees.

Aperture

A measure of the size of the "hole" in the lens through which light travels. A "large aperture" allows more light to come through the lens and to hit the image sensor than a "small aperture." Aperture is denoted by the "f-number," a reciprocal of the focal length and the aperture size, typically measured in millimeters. An f-number of 2.8 (written f/2.8) on a 300mm lens indicates that the "hole" is about 107mm wide. An f-number of 5.6 (f/5.6) indicates an opening of about 54mm on the same lens. Thus, larger f-numbers indicate smaller apertures.

Aperture Priority (Av)

A camera mode that allows the photographer to set the aperture they wish to use. The camera will then attempt, via its auto-exposure feature, to set a proper shutter speed and, occasionally, a proper ISO to result in a well-exposed image.

APS

An acronym for Advanced Photo System, this was a system that defined a film size smaller than 35mm. "APS-C" was the most common format, and it defines an image sensor approximately equivalent in size to the Advanced Photo System "classic" size negatives. These negatives were 25.1 × 16.7mm and had an aspect ratio 3:2. Cameras with sensors approximately this size are found in many DSLRs with sensor sizes ranging from 20.7×13.8mm to 28.7×19.1mm.

ASA

A measurement used to state the "speed" of film. ASA stands for "American Standards Association" and is the digital equivalent of ISO. Film with a higher ASA rating was more sensitive to light, but resulted in more grain. See also "ISO."

Aspect Ratio

The proportion of height to width of something, typically an image but also an image sensor, your television, your computer monitor, a print, etc. For example, a television which can display an image 1920 x 1080 has an aspect ratio of 16:9. Older non-HD televisions - and many DSLRs - have an aspect ratio of 4:3.

Auto Exposure (AE)

A camera feature that automatically chooses certain settings in an attempt to produce an image that is properly exposed. The settings which affect exposure are aperture, ISO, and shutter speed. For example, in aperture priority (Av) mode, the camera will typically adjust the shutter speed and potentially the ISO.

Autofocus (AF)

A camera and lens feature that attempts to focus automatically and without manual twisting of a focus ring.

Autofocus (AF) Assist Lamp

A light which illuminates in darker conditions to aid the camera's autofocus system. Often these lights are red and many times they project a grid of red lines.

Autofocus (AF) Lock

A camera feature that signifies, often with a light in the viewfinder and/or an audible beep, that the camera and lens have achieved focus on the subject. Some cameras may have settings that prevent the photographer from taking an image until AF lock is achieved. Photographers will often use AF lock when they "focus and recompose."

Autofocus (AF) Sensor

A component of a DSLR that is responsible for determining not only when a camera is in focus but which direction the focus needs to shift to achieve focus.

The location of these sensors is often indicated through the viewfinder by red squares or circles. Many cameras allow you to define an active AF sensor, group of sensors, or the whole. Many will flash the AF sensor in the viewfinder when it achieves focus manually.

AF Sensors detect contrast sharpness and can be arranged vertically, horizontally, or diagonally. Some AF sensors contain multiple angles and are often called "cross-type" AF sensors.

Available Light

Light that exists naturally in the scene. Outside, this often means the sun, moon, headlights, or streetlights. Indoors, this includes existing ceiling lights, lamps, etc. Essentially, so long as the photographer isn't supplying the light, it's called "available light." On- and off-camera strobes and hot lights are not "available light."

- B -

Backdrop: A background placed behind the subject of a photograph and usually a cloth. Backdrops come in solid colors as well as with designs, patterns, or printed scenes.
Background: The region behind the subject of a photograph. Sometimes this refers to an artificial background like a cloth draped behind a subject.
Backlighting: Light which places the subject between the camera and the light source. Backlighting results in shadowing or silhouetting of the subject.
Ballhead (or Ball Head): A piece of equipment that allows a camera's position and aim to be manipulated. Typically found on tripods, a ball head gets its name from the large ball that is rotated and clamped in place.
Bellows: A pleated, expandable portion of a camera, typically seen on large- or medium-format cameras, to allow the lens to be moved with respect to the focal plane for focusing. Bellows provides a flexible dark enclosure between the sensor and the lens. In some bellows systems, the photographer can change the angle of the lens with respect sensor, providing alterations of perspective distortion and of the object plane of focus. In standard DSLRs, extension tubes fulfill the role of bellows (except the tilting) and are an inexpensive way reduce the minimum focus distance of any given lens.
Bitmap: An image format or a means of storing an image wherein each pixel is defined. The .bmp image format is a bitmap, but so too are most other formats: JPEG, TIFF, PNG, and GIF, among others, though the latter are typically referred to as rasterized or raster images. In contrast to a bitmap is a vector image, which defines mathematical shapes to draw an image.
Blur: A smearing of a color or image. Blur occurs for a number of reasons, but two reasons account for the majority of instances of blur: camera shake and action/motion blur. Other forms of blur include zoom blur (zooming in or out while taking an image), pan blur (panning on one item, such as a race car, will blur the non-moving parts of the image).
Body: The main portion of a DSLR, excluding external flashes, interchangeable lenses, and the like. The body houses the viewinder, mirror, lens mount, etc. Many DSLRs are made available as a "body only" or bundled in a "kit" with a lens.
Body Cap: A piece of equipment that covers the lens mount on a camera body when a lens is not attached to the camera. Typically plastic, these also usually come with every camera with removable lenses.
Bokeh: The quality of out-of-focus blurred portions of a photograph. The quality of bokeh can be manipulated by mechanical aspects of the lens, including the number and shape of the aperture blades.
Bounce Flash: Light which is not directed at the subject but which is first "bounced" off a neighboring object - such as a ceiling, wall, umbrella, or the like - before falling upon the subject. The act of bouncing makes the flash softer by making the effective light source larger, which reduces the harshness of shadows.
Bounce Light: See bounce flash, though sometimes "bounce light" is used to differentiate between light bounced from a flash or strobe and light bounced from another source, such as a hot light or the sun.
Bracketing: A technique of taking several shots of the same subject using different camera settings. Bracketing is useful in situations that make it difficult to obtain a satisfactory image with a single shot, especially when a small variation in exposure parameters has a comparatively large effect on the resulting image. Bracketing is typically done with exposure, focus, white balance, or flash, though other types (ISO bracketing) are possible as well.
Brolly: A colloquial term for umbrella. A "brolly box" is a softbox created by using a shoot-through umbrella.
Buffer: Memory storage that sits, sequentially, between the camera's sensor and the memory card within the camera. Images are written to the buffer, the data is processed, and the final result is written to the memory card. Buffer size, memory card write speed, and image processing speed can affect how many photos your camera can take at a rapid rate before the buffer is full.
Bulb: A camera mode which keeps the shutter open so long as a button is depressed. In the film era, the photographer would squeeze a rubber bulb to keep the lens open.
Burning: A technique used to manipulate the exposure of selected area(s) in an image. Burning darkens the area(s) of the image. The term stems from the days of print, negatives, and positives.
Burst (and Burst Rate): A series of photos taken with a single press of the shutter button. The burst rate is the number of images a camera can take per time period (typically per second). DSLRs may have a different burst rate or maximum count depending on whether they're recording RAW or JPEG images.

- C -

Cable Release

A wired remote control for a camera. Using a wired remote control to release the shutter can reduce vibrations, particularly if used with mirror lockup.

Camera Shake

The act of moving the camera while taking a picture, introducing unintentional and unwanted blur. Camera shake can be overcome with good technique, image stabilization/vibration reduction, and/or faster shutter speeds.

Catchlight

Light reflected as a highlight in the eye of the subject, typically an animal. Catchlights in portraits often add depth and vibrancy to the subject.

CCD

One of two main types of sensors used in digital cameras. CCD stands for "charge coupled device." Light waves are converted into electrical impulses, which are then converted to data through a series of conversions.

CD-R

An acronym for "compact disc - recordable." This is a CD on which you can "burn" data. CD-R is often a good way to share large files relatively easily and without using a network (including the Internet) as a means of transfer.

Center Weighted

A metering mode which places more importance on the central 40 to 60% of the image while considering the remaining image to a lesser degree. In average lighting conditions this system can work but excessively dark or light areas, particularly towards the edges of the frame, can fool this type of metering

Chromatic Aberration

The failure of a lens to focus all colors at the same point. This can occur because the refractive index of a lens varies by wavelength. Chromatic aberration manifests as "fringing" of color along boundaries that separate dark and light parts of an image. Lens manufacturers combat chromatic aberration primarily via lens coatings.

Circle of Confusion

An optical spot caused by a cone of light rays from a lens which do not come into perfect focus. In photography, the circle of confusion ("CoC") is used to determine the depth of field. A standard value of CoC is often associated with each image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement. CoC is also known as disk of confusion, circle of indistinctness, blur circle, or blur spot.

Circular Polarizer

A special polarizer often required by DSLRs. The simpler version, a linear polarizer, can often throw off a DSLR's built-in metering system. Circular polarizers filter out light polarized perpendicularly to the axis of the filter. This both reduces reflections from some surfaces (water, windows, etc.) and can darken the sky.

CMOS

One of two main types of sensors used in digital cameras. CMOS stands for "complementary metal-oxide semiconductor." Light waves are converted into electrical impulses, which are then converted to data through a series of conversions.

CMOS sensors are easier and cheaper to produce than CCD sensors due to a more conventional manufacturing process. CMOS sensors also consume less power than equivalent CCD sensors.

Color Temperature

A measurement of the "tinge" of the light based on black body radiation. Measured in degrees kelvin, light that's more orange is cooler (and about 2500K) while light that's warmer contains more blue (5500K).

CompactFlash

A mass storage device format used in DSLRs and other portable electronics equipment. CompactFlash (CF) cards use flash memory in a standardized enclosure. First created by SanDisk in 1994, CompactFlash competes primarily the SD memory card format for popularity in DSLRs.

Continuous Focus

See "AI Servo Focus."

Contrast

The amount of difference between the lightest and darkest parts of an image. High-contrast images have a large difference; low-contrast images images have little difference.

Copyright

A form of intellectual property that gives the author of an original work exclusive right for a certain period of time, including the right of publication, distribution, and adaptation. A work for which the copyright has expired is said to have entered the "public domain." Copyright is automatically granted to the author for any expressible form of an idea or information that is substantive, discrete, or fixed in a medium. A digital image, regardless of its residence on your camera's memory card or your computer's hard drive, is effectively copyrighted to the photographer the instant they press the shutter button.

Crop

The process of removing the edges of an image. Cropping is often used to effectively "zoom in" on a subject or to remove distracting elements at the edges of an image.

Crop Factor

The ratio of the dimensions of a camera's image area or sensor size compared to the 35mm format. The most commonly used definition of crop factor is the ratio of a 35mm frame's diagonal (43.3mm) to the diagonal of the image sensor in question.

This ratio is also commonly referred to as a "focal length multiplier" since multiplying a lens focal length by the crop factor gives the focal length of a lens that would yield the same field of view if used on a 35mm or "full-frame" camera.

Cross Processing

Stemming from a print film method of deliberately processing one type of film in solutions intended for another type of film to create certain types of effects, the process was often seen in fashion and band photography. In the digital age it refers to any process which results in unusual color shifts that result in a "cross processed look."

- D -

Darkroom: A light-sealed room that allows for the processing of light-sensitive photographic materials. Darkrooms have largely gone by the wayside, though digital photographers will sometimes jokingly refer to their computer as their "virtual" or "digital" darkroom. The name of Adobe's "Lightroom" application is a play on this term.
Daylight: A pre-set white balance setting meant to account for an average daylight color temperature. In truth, daylight can range from 5000K to 6500K, though most cameras pre-set this mode to about 5500K.
Depth of Field (DoF): How much of your image in front of and behind your focus point is sharp. For example, if you focus on a fence and objects four feet in front of and eight feet behind the fence are in focus, the depth of field is twelve feet. Most often, DoF is used generally, such as "narrow depth of field" or "thin" depth of field.
Depth of Field Preview Button: This button will stop-down the lens, closing the aperture blades, to the currently specified aperture value (f-Stop). By pressing this button and looking through the viewfinder, you can preview the depth of field of the final image. When the lens is wide open (e.g. f/2.8), there will be no visible change when pressing this button because the lens defaults to a completely open position. With a small aperture (e.g. f/22), the viewfinder will appear very dark because there is significantly less light coming in through the lens.
Diffraction: Diffraction is the general term when light (or another type of wave) hits an obstacle of some sort. Diffraction causes things you encounter every day. For example, you can hear sound around a corner because when waves encounter an obstacle, they appear to bend around it. Similarly, when a wave encounters a small hole (relative to the frequency of the wave), it will diverge (imaging parallel light rays suddenly going every which way, interfering with one another). This is particularly relevant to photography when considering optimum sharpness for a given lens and sensor. The aperture in your lens is a small opening, and light will bend as it goes through the aperture. As you pick larger aperture values (giving smaller openings in the lens), the light is bent more. The smaller the pixels in your sensor, the sooner you see these diffraction artifacts. Although logically shooting at a larger aperture value would give a sharper image due to more depth of field, you might be at the diffraction limit of your camera, and fine details (such as texture detail) will blur out because of the diffraction of light through the small lens aperture.
Diffuser: A diffuser is a device that causes incoming light to be scattered over the surface of the device. Instead of having a harsh, point light, such as the sun, the entire surface of the device becomes a light source, and the larger surface gives a softer light. To see this effect, hold up a tissue towards a light source. Using a diffuser when shooting will help remove extreme contrast (bright highlights and harsh shadows) from an image, which is often useful in portrait and macro photography.
Diopter: A diopter is a measurement of the light bending (refractive) power of a lens. For example, a 4 diopter lens has a magnification power of 2X, meaning an object viewed through a 4 diopter lens would appear twice as large. It is strictly defined as 1/focal length where focal length is in meters.
Dispersion: Put simply, dispersion is the phenomenon which causes white light to split into a rainbow. It can also cause chromatic aberration in a lens if the components of incoming light are split (e.g. if blue light is dispersed slightly less than red light, you'll see an artifact in the image).
Distortion: Distortion occurs when the straight lines in a scene do not appear completely straight in an image. Sometimes distortion is intentional, such as with a fisheye lens, where the image is distorted so that it appears to be placed on a sphere. Other times, it's a natural result of the camera lens, such as the perspective distortion when standing at the base of the tall building and taking a photo, pointing the camera towards the top of the building. Sometimes, distortion is unintentional and results from lower-quality lenses. Chromatic aberration is an example of unintentional distortion more common in low-end lenses. Many software packages have tools to correct (or add for creative effect) distortion.
Dodging: A technique used to manipulate the exposure of selected area(s) in an image. Dodging lightens the area(s) of the image. The term stems from the days of print, negatives, and positives.
Double Exposure: See Multiple Exposure
DPI: A synonym for "dots per inch." Typically used to describe printing resolution.
DSLR: Strictly, a digital single lens reflex camera (DSLR) is a camera with a mirror that directs light from a lens to an optical viewfinder so that you see through the lens when looking through the viewfinder. They allow for a more accurate framing and depth of field preview than non-SLR cameras. Unlike a traditional film SLR, a DSLR records to a digital sensor instead of film. DSLRS often have other features, such as interchangeable lenses. Some newer cameras either replace the mirror entirely or supplement it with a live-view electronic viewfinder where the camera electronically transmits the light falling onto the digital sensor to a digital display screen.
Dynamic Range: Exposure difference between the brightest and darkest parts of a scene. This number is typically measured in stops, and the more "dynamic range" a sensor or film can record, the "better" that camera is often judged to be as more dynamic range will preserve more details in the shadows and highlights.

- E -

E-TTL

E-TTL stands for Evaluative Through the Lens, which is a Canon EOS flash metering system and has been standard on Canon cameras since 2004. With E-TTL, the camera uses the same evaluative meter that it uses to determine image exposure to determine the proper flash exposure, rather than having a separate flash metering system such as with normal TTL metering. E-TTL does use a brief, almost imperceptible pre-flash to help with exposure, which can cause unintentional reactions, such as people blinking before the primary flash fires.

Effective

The "effective" focal length of a club is the focal length multiplied by the "crop factor." A 50mm lens on a camera with a crop factor of 1.6 is said to have an "effective" focal length of 80mm because it exhibits the same field of view as an 80mm lens on a full-frame camera.

Electronic Viewfinder (EVF)

A small, digital display showing a live view of the light captured by a digital sensor through the current lens. Unlike optical viewfinders, which use a mirror and pentaprism to redirect light from a lens into a viewfinder, EVFs can approximate the selected exposure and give a live preview of the final image. However, some EVFs are difficult to see in low-light. Furthermore, they require extra battery power to operate and sometimes have an update lag.

Element

The individual pieces of glass used in the construction of lenses. Each one is individually ground and polished to perform a specific task, such as focusing the light or correcting for aberrations. Elements are often collected into "groups."

Emulsion

A mixture of two or more unblending liquids used in developing film.

Enlargement

Increasing the size of an image. Technically even printing a 4x6 photo from a 35mm piece of film is an "enlargement" but this commonly refers to sizes above an 8x10 or so.

EXIF

An acronym for "Exchangeable Image File Format," this is a specification that provides for specific metadata tags (copyright, image capture date, etc.) within the contents of the image file itself. EXIF data is supported in JPEG and TIFF formats, but not PNG or GIF, among others.

Exposure

The first definition refers to the total amount of light allowed to fall on the sensor or film during the process of taking a photograph. An image which contains bright images is said to be "over-exposed" and one that is too dark "under-exposed."

An "exposure" can also mean one image, or a single shutter cycle. For example, a "long exposure" is one which keeps the shutter open for several seconds.

Exposure Compensation

A technique for adjusting the exposure to something other than that which the built-in meter considers accurate. When shooting a bright subject you may add (positive) exposure compensation, and vice versa for a dark subject.

Exposure Value (EV)

A relative combination of shutter speed, aperture, and ISO that produce the same exposure. EV is also used to indicate an interval, with 1 EV corresponding to a standard power-of-2 exposure step, commonly referred to as a “stop." Note that images with the same EV will not necessarily yield the same image. Exposure time determines the amount of motion blur, aperture determines depth of field, ISO determines noise, etc.

Extension Tube

An accessory used primarily for macro photography. Extension tubes contain no optical elements - their sole purpose is to move the lens farther from the sensor because, the farther away the lens, the closer the lens can focus, and the closer you can get to the subject the larger the subject will appear on the sensor.

- F -

f-Number

The ratio of the lens' focal length to the diameter of the aperture. For example, at f/4, a 100mm lens has an aperture measuring roughly 25mm. At 300mm, an f/2.8 lens will have an aperture measuring roughly 107mm. A wide angle lens (16mm) at f/22 would have an aperture measuring only 0.7mm.

f-Stop

A single f-stop or stop represents a doubling (or halving) of light. This can be done by controlling any combination of the three points in the triangle of exposure: ISO, aperture, or shutter speed. A "stop" of light can also refer to the power of a flash, the ambient light (i.e. "when the sun moves behind that cloud we lose two stops of light."), or anything else that affects the amount of light that reaches the film or sensor.

Fast Lens/Film

A lens is considered "fast" when it has a fairly wide aperture (f/4 or larger for super telephoto lenses, f/2.8 or larger for shorter telephoto lenses, and f/2 or larger for more normal and wide angle lenses.

Film is considered "fast" when the ISO or ASA rating is high.

Field of View

Area that's visible through an optical instrument.

File Format

The way or manner in which a document or file is encoded. A JPEG is an image file format, a text file can be a TEXT file format, and a TIFF file is another file format. Every different kind of file on your computer is a different file format.

Fill Flash

Flash used to brighten shadowy or darker areas of an image. For example, if you're taking a picture of a person with the sun in the background, you may need fill flash so the person's face is not a silhouette or in shadow.

Film

A general word to describe the often celluloid material used to capture images prior to a few years ago. Now considered "ancient." :-)

Film/Sensor Plane

The plane that is aligned exactly along the surface of the film or sensor. A DSLR's tripod mount is usually centered beneath the sensor and on the sensor plane.

An object is in focus when light coming from the object comes to a precise point on the film or sensor plane.

Filter

A piece of glass (or sometimes plastic) that you put in the optical path to achieve an effect ranging from polarization to reduction in light (a neutral density filter) or even to reduce or add a color cast to an image. Filters tend to either screw into the front of a lens, drop into the lens, or rest in a filter holder.

Fisheye Lens

A wide-angle lens that takes in an extremely wide, hemispherical image. Originally developed for use in meteorology to study cloud formation and called "whole-sky lenses", fisheye lenses quickly became popular in general photography for their unique, distorted appearance.

Fixed Focal Length

A lens which is incapable of "zooming" or changing its focal length. These lenses are indicated with a single "mm" number, such as "50mm" or "300mm" and not two numbers, as in "24-70mm." See also prime lens.

Flare

A typically undesired effect caused by light diffraction and scattering within the elements of a lens. If you point your lens towards the sun, lens flare is more likely. Lens hoods help to reduce lens flare by reducing the likelihood that the sun can hit the front element of your lenses.

Flash

A general word to describe any strobed lighting, though typically it refers to the small, portable "speed lights" and not the studio strobe.

Flash Duration

The length of time a flash puts out light. Often, a flash will output the majority of its light very quickly, but some tail off faster or slower than others. A flash with a long duration can produce ghost trails.

Flash Sync

The firing of a photographic flash coinciding with the shutter. This can be used in darker situations or to provide specific lighting, or to stop action by allowing the photographer to use a faster shutter speed.

Flood Lamp

A continuous light source, also sometimes called a "hot light" (as they get quite hot to the touch), which can be used to light a scene rather than strobes. Flood lamps allow for longer shutter speeds and do not change intensity or "fire" like a flash, so they typically require less experimentation than a flash or strobe at the expense of not being as powerful.

Focal Length

A measure of how strongly a lens focuses light. A system with a shorter focal length has greater optical power than one with a long focal length as it bends the rays more strongly, bringing them to a focus in a shorter distance. Longer focal length is associated with larger magnification of distant objects, and a narrower angle of view. Conversely, shorter focal length or higher optical power is associated with a wider angle of view.

Focal Plane

The plane that is both perpendicular to the axis of a lens or mirror and which passes through the focal point. The focal plane is rarely important, but can be very important when shooting a multi-image panorama.

Focal Point

The place on which you focus in an image, for example someone's left eye in a portrait, or a sensor in the camera which can assist the lens or the photographer in achieving focus.

Focus

To concentrate really hard and block out distractions. Just kidding. Focus refers to the act of making the rays of light from an object focus on the sensor or film plane. That object is then said to be "in focus."

Focus and Recompose

A technique which essentially asks that you focus on something (manually or automatically using one of your camera's focus sensors) and then recompose the image without refocusing. This technique can work with deep depth of field, but fails with narrow depth of field as the distance to the subject can change slightly when you recompose.

Focus Mode

The method by which focus is achieved. Essentially, man (manual focus) or machine (autofocus). Autofocus modes can be made to focus on a steady object ("one-shot" AF), to track a moving object ("servo" AF), or to intelligently switch between one-shot and servo ("AI servo" AF).

Focus Priority

A camera mode which, when enabled, will not allow a photographer to take an image until the chosen focus sensor(s) indicate that they've achieved focus on an object.

Focus Screen

A flat translucent material, usually ground glass, found in a system camera that allows the user of the camera to preview the framed image in a viewfinder. Often, a focusing screen has etched markings that differ from model to model. Some DSLRs allow the user to change the focus screen.

Focus Tracking

Also called "servo" mode, this is an autofocus mode that attempts to keep a moving object in focus by continually adjusting the focal distance of a lens. Ideally, a photographer can take an image at any point and achieve a subject that's in focus.

Focusing

The act of achieving focus, whether done manually or automatically.

Fogging

Deterioration of image quality due to condensation build-up on the lens, light flooding, the effects of a chemical processor, or other things. Fogging tends to reduce saturation and contrast.

Foreground

The area in front of the subject of a photograph, or the objects or landscape or items nearer to the camera than those in the background.

Format

When dealing with memory cards, to "format" a card is to prepare the card for the storage of images by erasing existing files and creating a file system.

Format can also refer to the size of the film or the sensor, as in "medium format" and "large format" cameras.

- G -

Gamma: A nonlinear operation used to code and decode luminance values in still image systems. The typical gamma value for a computer display is 2.2, though for many years Macs used a gamma of 1.8, which appears "brighter" than the Windows standard "2.2" (which, for a few years, has been the standard in Mac OS X as well).
Gamut: A certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a printer or on a computer display.
Gradation: Changes or transitions in a characteristic or quality of a part of an image e.g. its lightness, texture, density either wihin an area of the image or between one area and another. Generally a "smooth" gradation is better than one with "posterization" or a sharp break from one area to another.
Graduated Filter: A filter whose properties change over a distance. The most common is a graduated neutral density filter: a darker area will give way to a lighter or clear area.
Grain: The random optical texture of processed photographic film due to the presence of small grains of a metallic silver developed from silver halide that have received enough photons. In digital photography, "noise" is essentially the equivalent of "grain."
Grey Card: A flat object of a neutral gray color that derives from a flat reflectance spectrum. Many grey cards are also close to 18% grey in order to help a photographer set the exposure, but a grey card does not need to be 18% grey to serve as a reference for determining the color temperature. Grey cards, with the proper color temperature, display equal intensity in the Red, Green, and Blue channels.
Greyscale: An entirely desaturated image, rendered only in shades of black/grey.
Guide Number: An electronic flash measurement that quantifies a flash's ability to illuminate a subject at a specific film or sensor sensitivity and angle of view. A higher guide number indicates a more powerful flash. Doubling the guide number means the flash can illuminate an object at twice the distance, or for an object at the same distance can be used at one quarter the sensitivity. Doubling the guide number requires a quadrupling of the flash's power, as the area to be illuminated increases as the square of the distance due to the inverse-square law.

- H -

Haze: Reduction in visible contrast of a scene due to scattering of light by particles suspended in air. Haze can be brought about by poor quality glass in a lens or by atmospheric conditions that scatter light.
High Key: A style or method of lighting that reduces the contrast ratio in an image and primarily limits it to the brighter tones.
Highlights: The brighter tones in an image. The opposite of shadows.
Histogram: A graph which acts as a representation of the tonal distribution in a digital image. It plots the number of pixels for each tonal value, from black to white, left to right. By looking at the histogram for a specific image a viewer will be able to judge the entire tonal distribution at a glance. Photographers can use histograms as an aid to show the distribution of tones captured, and whether image detail has been lost to blown-out highlights or blacked-out shadows.
Hot Light: The opposite of a strobe or flash, a hot light is one that continually puts out light - like an incandescent bulb - to light a scene or an object. Hot lights are often literally hot to the touch and can be easier to use, but are not as powerful as a strobe.
Hot Shoe: A mounting point on the top of a camera to attach a flash unit. The hot shoe is shaped somewhat like an inverted, squared-off "U" of metal. The matching adapter on the bottom of the flash unit slides in from the back of the camera and is sometimes secured by a clamping screw on the flash. In the center of the "U" is a metal contact point. This is used for standard, brand-independent flash synchronization. Normally the metal of the shoe and the metal of the contact are electrically isolated from each other. To fire the flash, these two pieces are shorted together. The flash unit sets up a circuit between shoe and contact—when it is completed by the camera, the flash fires.
Hyperfocal Distance: The closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp; that is, the focus distance with the maximum depth of field. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.

- I -

Image Editor: A piece of software capable of editing an image. Common image editors include Photoshop and Lightroom from Adobe, Aperture from Apple, and various other applications.
Image Plane: The plane that contains the object's projected image, and lies beyond the back focal plane.
Image Stabilization: A series of gyroscopes in a lens or camera body designed to counteract shake while holding the camera. Image stabilization often has several modes and can sometimes intelligently determine whether the camera is panning in one direction to minimize shake in the other direction or to auto-disable itself when the camera is on a tripod.
Incident Light: The light which falls on the subject. In a light meter, those that measure incident light are held up near the subject and often measure the incident light through a soft white hemispherical attachment. See also reflected light.
Infinity: Objects whose focal plane and image plane one and the same, or close enough to essentially be the same. A lens focused at infinity achieves focus from the hyperfocal distance to "infinity."
Infinity Focusing: The method of focusing to infinity because the subject(s) intended to be in focus are so far away that the angle between the rays of light reflected from them is very small.
Infrared: A method of photography which uses special film or a modified sensor that is sensitive to the infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about 900 nm. Usually an "infrared filter" is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum (the filter thus looks black or deep red).
Inkjet: A type of printer (or a method of printing) that reproduces a digital image by propelling variably-sized droplets of ink onto a page. Inkjet printers are the most common type of printer and range from small inexpensive consumer models to very large and expensive professional machines.
Inverse Square Law: Any physical law stating that some physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity. In photography, flash power and aperture exhibit the effects of the inverse square law.
ISO: A measurement of the amount of amplification an image sensor applies to the photons that fall on it. A higher ISO is a more amplified image and is more subject to noise. ISO is similar to a film's "speed" or ASA rating.

- J -

Jaggies: The informal name for artifacts in raster images, most frequently from aliasing, which in turn is often caused by non-linear mixing effects producing high-frequency components and/or missing or poor anti-aliasing filtering prior to sampling.

- K -

Kelvin

In photography, kelvin is often used in the measure of the color temperature of light sources. Color temperature is based upon the principle that a black body radiator emits light whose color depends on the temperature of the radiator. Black bodies with temperatures below about 4000 K appear reddish whereas those above about 7500 K appear bluish. Color temperature is important in the fields of image projection and photography where a color temperature of approximately 5600 K is required to match "daylight" film emulsions.

Key Light

The first and usually most important light used in a lighting setup. The purpose of the key light is to highlight the form and dimension of the subject. The key light is not a rigid requirement; omitting the key light can result in a silhouette effect.

Keystoning

Also called keystone distortion, this occurs when you point a camera upwards at a vertical surface with the top of the film plane tilted away from the building. It's named after the trapezoidal look of an arch keystone. This type of distortion is corrected by making the film plane parallel to the surface.

- L -

Large Format

Large photographic films, large cameras, view cameras (including pinhole cameras) and processes that use a film or digital sensor generally 4 x 5 inches or larger.

LCD

An acronym for liquid crystal display. In photography, the LCD typically refers to either a screen or display on the back of the camera for displaying images, menus, settings, etc. or can refer to a type of display attached to a computer.

Leaf Shutter

A type of camera shutter consisting of a mechanism with one or more pivoting metal leaves which normally does not allow light through the lens onto the film, but which when triggered opens the shutter by moving the leaves to uncover the lens for the required time to make an exposure, then shuts.

LED

An acronym for light-emitting diode. An LED is a semiconductor light source and are often used as indicator lamps in cameras. Their use in computer displays is increasing and many laptop screens are now LED instead of LCD.

Lens

An optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.

In laymen's terms, it's the thing you stick on your camera body, and the class of objects of which most photographers can never have enough.

Lens Barrel

The (often metal) tube that contains all of the lens elements.

Lens Cap

Also called a lens cover, this easily lost piece of plastic provides protection from scratches and minor collisions for your lenses. These typically come standard with your lens and can cover both ends of a detachable lens.

Lens Coating

Also called an optical coating, this is one or more thin layers of material deposited on a lens which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating, which reduces unwanted reflections from surfaces, and is commonly used on photographic lenses.

Lens Hood/Shade

A device used on the end of a lens to block the sun or other light source in order to prevent glare and lens flare.

Lens Mount

An interface - mechanical and often also electrical - between a photographic camera body and a lens. It is confined to cameras where the body allows interchangeable lenses (such as a DSLR).

Lens Speed

This refers to the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens may be referred to as "fast" or "slow" depending on its maximum aperture compared to other lenses of similar focal length designed for a similar film format. Lens speed is a useful quantitative way to compare similar lenses.

A lens with a larger maximum aperture (a smaller minimum f-number) is called a fast lens because it delivers more light to the focal plane, allowing a faster shutter speed. A smaller maximum aperture (larger minimum f-number) is "slow" because it delivers less light intensity and requires a slower shutter speed.

Light Box

Fabric reflectors that attach to studio lighting to create soft lighting by diffusing a strobe flash.

Also, a container with several lightbulbs and a pane of frosted glass on the top. It is used by photography professionals viewing translucent films, such as slides. This device was originally used to sort photographic plates with ease. It is also used by visual artists for photo-referencing.

Light Meter

A device used to measure the amount of light. A light meter is often used to determine the proper exposure for a photograph. Typically a light meter will include a computer, either digital or analogue, which allows the photographer to determine which shutter speed and f-number should be selected for an optimum exposure, given a certain lighting situation and film speed.

Low Key

A style or method of lighting that reduces the contrast ratio in an image and primarily limits it to the darker tones.

Luminance

A photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. In simpler terms, the luminance is the brightness of something.

- M -

Macro

A word meaning close-up photography in which objects are often represented at close to a 1:1 ratio on the sensor or film. For example, if a honeybee is 12mm in length and your camera's sensor is 24mm, a macro shot of the honeybee would fill half the frame or more. A macro lens is a special type of lens that provides close-up focus and provides near-life-size reproduction of a subject.

Magnification

The process of enlarging something only in appearance, not in physical size. This enlargement is quantified by a calculated number also called magnification. When this number is less than one it refers to a reduction in size, sometimes called minification or de-magnification.

Magnification is often used in discussions regarding macro photography.

Manual Camera

A camera which doesn't have any of those newfangled "automatic" modes - focus, exposure, metering, etc.

Manual Mode (M)

A mode on a DSLR which allows the photographer to determine the aperture, shutter speed, and ISO level to determine the exposure. Manual mode doesn't necessarily mean that the photographer can't use autofocus mode, as that's a lens setting and not a camera body setting.

Matrix Metering

Also called multi-zone metering, this mode is also called matrix, evaluative, honeycomb, segment metering, or esp (electro selective pattern) metering on some cameras. The camera measures the light intensity in several points in the scene, and then combines the results to find the settings for the best exposure. How they are combined/calculated deviates from camera to camera. The actual number of zones used varies wildly, from several to over a thousand. However performance should not be concluded on the number of zones alone, or the layout. In general, the most advanced metering is found on SLRs.

Medium Format

Cameras making use of sensors larger than that of a 35 mm film frame but smaller than those used in large format cameras. Often, medium format film cameras can be fitted with digital camera backs, converting them to digital cameras.

Megapixel

One million pixels.

Meter

The act of measuring the light, often to determine the exposure, in a digital camera.

Metering

The act of measuring light levels in order to properly expose an image, to determine a flash level, or to otherwise adjust levels of light.

Microprism

A small lens which sits above a sensor to gather light and focus it within an image well (a pixel on the sensor).

Midtone

The tonal range that occupies the middle of a histogram and isn't highlights or shadows.

Mirror Box

A series of mirrors that reflect light from the main mirror through the viewfinder to the photographer.

Mirror Lens

A lens that includes not only lenses but curved mirrors for focusing light and the formation of an image on a sensor or film plane.

Mirror Lockup

Often abbreviated MLU, this is a feature employed in many Single Lens Reflex (SLR) cameras. It allows the operator to reduce vibration-induced motion blur during exposure. It also allows the mounting of lenses which extend into the SLR's mirror box when mounted.

Mirror Slap

The noise (and vibrations) that result from the mirror flipping up in order to expose the sensor or film to the light path.

Mode

The operational setting of a camera which defines how the camera will operate. Common modes include aperture priority (Av), shutter priority (Tv), full auto or Programmed mode (P), and "night time portrait" or "sports."

Monochrome

A term generally used to describe a photograph in one color or shades of one color. A monochromatic object or image is one whose range of colors consists of shades of a single color or hue; monochrome images in neutral colors are also known as grayscale or black-and-white.

Monopod

Also called a unipod, this is a single staff or pole used to help support a camera in the field. It provides more support than hand-holding a camera but less support than a tripod.

Motor Drive

A powered film transport mechanism. Historically, film loading, advancing, and rewinding were all manually driven functions. The desires of professional photographers for more efficient shooting, particularly in sports and wildlife photography, and the desires of amateur and novice photographers for easier to use cameras both drove the development of automatic film transport. Some early developments were made with clockwork drives, but most development in the field has been in the direction of electrically driven transport.

MTF

A method of measuring sensor or lens resolution. Spatial resolution is typically expressed in line pairs per millimeter (lppmm), lines of resolution, contrast vs. cycles/mm, or MTF (the modulus of OTF). The MTF may be found by taking the two-dimensional Fourier transform of the spatial sampling function. Smaller pixels result in wider MTF curves and thus better detection of higher frequency energy.

Multicoated

A lens which has several coatings, often because each coating will serve a different purpose such as reducing glare or haze, managing aberrations or fringing, etc.

Multiple Exposure

A multiple exposure is an image created from multiple images composited together. With film cameras, photographers would create multiple exposures by exposing the same piece of film multiple times or by sandwiching slides together. Some digital cameras, notably Nikon DSLRs, let you take digital in-camera multiple exposure images, where it automatically combines successive images in the camera for you. It's also possible to create a multiple exposure image by compositing images together in a photo editing tool. Multiple exposure images are useful for creating creative effects. For example, taking an out of focus shot and then an in focus shot of a subject as a multiple exposure image creates a dreamy feel to the image due to the blurred exposure while preserving detail due to the sharp exposure.

Multiplier

See crop factor. The multiplier is amount by which the focal length of a lens is multiplied on a crop sensor camera.

- N -

Neutral Density (ND) Filter

A colorless (clear) or grey filter. An ideal neutral density filter reduces and/or modifies intensity of all wavelengths or colors of light equally, giving no changes in hue of color rendition.

The purpose of standard photographic neutral density filters is to allow the photographer greater flexibility to change the aperture, exposure time and/or blur of subject in different situations and conditions of Atmosphere of Earth.

Noise

Noise is a result of amplification of the photons striking the sensor in a digital camera. Two kinds of noise exist - chromatic and luminescent - and both increase as the ISO value (the amplification) increases. Modern DSLRs have relatively low noise at fairly high ISO values.

Normal Lens

A lens that reproduces perspective that generally looks "natural" to a human observer under normal viewing conditions, as compared with lenses with longer or shorter focal lengths which produce an expanded or contracted field-of-view. Lenses of shorter focal length are called wide-angle lenses, while longer focal length lenses are often referred to as telephoto lenses.

On a full-frame camera, a 50mm lens is considered a "normal lens."

- O -

Off-Camera Flash: A flash - often a hot shoe flash - that's been removed from a camera's hot shoe but which is still being used to illuminate the subject. Though a studio strobe is technically an "off-camera flash," this term typically refers to small hot shoe flashes used in a somewhat non-standard fashion.
Optical Axis: A line along which there is some degree of rotational symmetry in an optical system. The optical axis is an imaginary line that defines the path along which light propagates through the lens and camera. For a system composed of simple lenses and mirrors, the axis passes through the center of curvature of each surface, and coincides with the axis of rotational symmetry.
Over-Exposure: An image which is rendered too bright or brighter than it appears to the naked eye, or one which exhibits a lot of clipped highlights.

- P -

Panning

The horizontal movement or rotation of a camera. Panning a camera results in a motion similar to that of someone shaking their head "no" and can be done intentionally to create blur or to follow a moving subject, such as a runner or a race car.

Panorama

Any wide-angle view or representation of a physical space, a panorama in photography usually consists of several shots which are digitally "stitched" together to create a final photograph that is quite wide relative to the height. Not all panoramas are horizontal, but horizontal panoramas are more common.

Parallax

An apparent displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. View cameras, or any camera with a viewfinder that does not use light coming through the lens, suffers from "parallax error."

Parallax Error

The change in perspective that results from two different optical paths or lines of sight. DSLRs do not have parallax error because the photographer sees light that follows the same optical path as the camera sensor, but many point-and-shoot cameras with viewfinders can suffer parallax error.

Pentaprism

A five-sided reflecting prism commonly used in the camera's prism box to reflect light twice, which deviates the light bouncing off the camera body mirror and directs it towards the photographer's eye via the viewfinder without inverting the image.

Perspective

The location from which a photographer captures an image. A photographer can have a low perspective by lying on the ground, or climb a tree or take images from a plane to gain a high perspective. The perspective is simply the location of the "eye" or camera relative to the subject of the image.

Photoflood

A reusable electric lamp that produces a bright continuous light for illumination of a subject or scene.

Pinhole Camera

A very simple camera with no lens and a single very small aperture. Simply explained, it is a light-proof box with a small hole in one side. Light from a scene passes through this single point and projects an inverted image on the opposite side of the box. Cameras using small apertures and the human eye in bright light both act like a pinhole camera.

Pixel

A shortened version of "picture element," a pixel is a single point in animage. The pixel is the smallest addressable screen element, it is the smallest unit of picture which can be controlled. Each Pixel has its own address. The address of a pixel corresponds to its coordinate. Pixels are normally arranged in a 2-dimensional grid, and are often represented using dots or squares. Each pixel is a sample of an original image, where more samples typically provide more-accurate representations of the original. The intensity of each pixel is variable.

Point and Shoot (P&S)

Also called a compact camera, a point-and-shoot camera is a still camera designed primarily for simple operation. Most use focus-free lenses or autofocus for focusing, automatic systems for setting the exposure options, and have flash units built in.

Point-and-shoots are by far the best selling type of camera. They are popular with people who don’t consider themselves photographers but want an easy to use camera for vacations, parties, reunions, and other events.

Polarization

The arrangement of waves (of light) in a single, unified direction. A polarizing filter achieves this effect, which can reduce glare, reflections, and increase the intensity of the blueness of the sky.

Polarizer

A device that converts light of undefined or mixed polarization into a beam with well-defined polarization. Polarizers can reduce glare or reflections and enhance the blueness of the sky.

Polarizing Filter

A filter which polarizes light.

Portrait Lens

A lens which has been deemed to be suitable for portrait photography. Typically such a lens has a focal length of 75 to 105mm.

Positive

The opposite of negative, which is to say that a film negative presents the opposite values, while a positive shows colors in their intended form rather than their opposite.

Posterization

Conversion of a continuous gradation of tone to several regions of fewer tones, with abrupt changes from one tone to another. This was originally done with photographic processes to create posters. It can now be done photographically or with digital image processing, and may be deliberate or may be an unintended artifact of color quantization.

Preset Focus

Often a feature of a lens, this includes the ability to save and recall a focal distance in order to jump quickly to it. This is useful if the photographer needs to focus on something at a predetermined distance and focus the lens to that distance quickly.

Prime Lens

A lens with non-moving internal optics that provide only one focal length and cannot be "zoomed." These lenses are marked with a single focal length, for example the Canon EF 50mm f/1.8 lens has a focal length of 50mm. A prime lens is the opposite of a zoom lens, which has a variable focal length.

Prismatic Finder

A viewfinder which uses a pentaprism to send the image through to the photographer.

Projector

A device that shines light onto a surface, often mounted on a wall or hanging from a ceiling, for the purpose of displaying an image.

Prosumer

A category of consumer who falls above the needs of the casual photographer but below a professional or semi-professional photographer.

Pulling

A process involving over-exposure and under-development, effectively decreasing the sensitivity of the processed film. It is achieved by developing the film for a shorter time, and possibly at a lower temperature. Film that has been pull processed will display the opposite change in visual characteristics. This may be deliberately exploited for artistic effect.

Pushing

Push processing in photography, sometimes called uprating, refers to a film developing technique that increases the effective sensitivity of the film being processed. Push processing involves developing the film for more time, possibly in combination with a higher temperature, than the manufacturer's recommendations. This technique results in effective over-development of the film, compensating for under-exposure in the camera. Push processing allows relatively insensitive films to be used under lighting conditions that would ordinarily be too low for adequate exposure at the required shutter speed and aperture combination. This technique alters the visual characteristics of the film, such as higher contrast, increased grain and lower resolution. Saturated and distorted colours are often visible on film that has been push processed.

- Q -

- R -

Rangefinder

A camera fitted with a range-finding focusing mechanism allowing the photographer to measure the subject distance and take photographs that are in sharp focus. Most varieties of rangefinder show two images of the same subject, one of which moves when a calibrated wheel is turned; when the two images coincide and fuse into one, the distance can be read off the wheel. Older, non-coupled rangefinder cameras display the focusing distance and require the photographer to transfer the value to the lens focus ring; cameras without built-in rangefinders could have an external rangefinder fitted into the accessory shoe. Earlier cameras of this type had separate viewfinder and rangefinder windows; later the rangefinder was incorporated into the viewfinder. More modern designs have rangefinders coupled to the focusing mechanism, so that the lens is focused correctly when the rangefinder images fuse.

RAW

A camera raw image file contains minimally processed data from the image sensor of either a digital camera. Raw files are so named because they are not yet processed and therefore are not ready to be printed or edited with a bitmap graphics editor. Normally, the image is processed by a raw converter in a wide-gamut internal colorspace where precise adjustments can be made before conversion to a "positive" file format such as TIFF or JPEG for storage, printing, or further manipulation, which often encodes the image in a device-dependent colorspace. These images are often described as "RAW image files" based on the erroneous belief that they represent a single file format. In fact there are dozens if not hundreds of raw image formats in use by different models of digital equipment (like cameras or film scanners).

Raw image files are sometimes called digital negatives, as they fulfill the same role as negatives in film photography: that is, the negative is not directly usable as an image, but has all of the information needed to create an image. Likewise, the process of converting a raw image file into a viewable format is sometimes called developing a raw image, by analogy with the film development process used to convert photographic film into viewable prints. The selection of the final choice of image rendering is part of the process of white balancing and color grading.

Like a photographic negative, a raw digital image may have a wider dynamic range or color gamut than the eventual final image format, and it preserves most of the information of the captured image. Raw image formats' purpose is to save with minimum loss of information the data that are obtained from the sensor, and the conditions surrounding the capturing of the image (the metadata).

Rear Curtain Sync

A flash mode which fires the flash at the end of the exposure. An object moving left to right will be frozen to the right with a (possible) ghost trail to the left. This mode is often used in sports photography to show speed or movement.

Rear Focus

An error in which a camera/lens combination focuses behind or farther away from the camera than the object on which it believes it has achieved focus. Some DSLRs can adjust for a rear focusing lens. A severely rear focusing lens may need to be recalibrated by a technician.

Reciprocity Failure

For most photographic materials, reciprocity is valid with good accuracy over a range of values of exposure duration, but becomes increasingly inaccurate as we depart from this range: reciprocity failure, reciprocity law failure, or Schwarzschild effect. As the light level decreases out of the reciprocity range, the increase in duration, and hence of total exposure, required to produce an equivalent response becomes higher than the formula states; for instance, at half of the light required for a normal exposure, the duration must be more than doubled for the same result. Multipliers used to correct for this effect are called reciprocity factors.

Recompose

To move a camera in such a way that the image rectangle is different than it was previously. You can recompose by switching from portrait to landscape mode, by zooming, or by tilting or panning the camera.

Recycling Time

The time you need to wait before your flash is available to fire another burst of light. This is never low enough for the demanding photographer.

Red Eye

A photographic effect which causes the eyes of human subjects to appear red due to light bouncing off the blood vessels of the retina. A common fix is to make the red eyes black or dark grey.

Reflected Light

The light which bounces off of a subject. In a light meter, those that measure incident light are aimed at the subject to measure the light being reflected from the subject, which can vary depending on the color of the subject itself. See also incident light.

Reflector

An improvised or specialised reflective surface used to redirect light towards a given subject or scene. These can be white, silver, gold, or another color and can take on various shapes, from spherical, parabolic, flat, etc.

Release Priority AF

An autofocus mode which gives priority to the shutter release, which is to say that the camera will allow a photo to be captured even if the camera does not sense that it has achieved focus lock.

Resolution

An indication of the amount of detail that is captured. Like the other metrics, resolution is just another factor out of many in determining the quality of an image. Furthermore, different methods of creating an image make it impossible to compare the resolutions of cameras simply based on the number of pixels produced by the image sensor. For example, the Sigma SD14 camera uses Foveon technology, which is quite different from most other digital cameras. It claims to be a 14 megapixel camera, but is generally considered to have detail-capturing capabilities roughly equivalent to 9 megapixels in terms of Bayer sensors.

Retouch

The application of image editing techniques to photographs in order to enhance or correct. For example, senior photos are commonly retouched to remove acne and smooth skin tones.

Ring Flash

A circular photographic flash that fits around the lens, especially for use in macro (or close-up) photography. Its most important characteristic is providing even illumination with few shadows visible in the photograph, as the origin of the light is very close to (and surrounds) the optical axis of the lens. When the subject is very close to the camera, as is the case in macro photography, the distance of the flash from the optical axis becomes significant. For objects close to the camera, the size of the ring flash is significant and so the light encounters the subject from many angles in the same way that it does with a conventional flash with soft box. This has the effect of further softening any shadows.

Ring flashes are also very popular in portrait and fashion photography. In addition to softening shadows, the unique way that a ring flash renders light gives the model a shadowy halo which is a common feature of fashion photography.

- S -

Saturation

The intensity of a color, from full intensity or the brightest and most complete expression of that color to very low intensity, which appears as a tinted grey variant (including white and black). A greyscale image is said to be completely desaturated.

Scheimpflug Principle

A geometric rule that describes the orientation of the plane of focus of an optical system (such as a camera) when the lens plane is not parallel to the image plane. It is commonly applied to the use of camera movements on a view camera.

Scrim

A translucent gauze type material that may be fastened onto a frame, and used outdoors to reduce the intensity of, and soften harsh light on subjects/people being photographed.

Seamless Background

A background which is laid on the ground and which curves upwards onto a wall. A subject will stand or rest on the background and will appear in photographs without a seam.

Selective Focus

The process of using a small depth of field to choose only a small or limited portion of an image to be in focus.

Self Timer

A device on a camera that, when enabled, gives a delay between the pressing of the shutter release and the shutter firing. It is most commonly used to allow photographers to take a photo of themselves, hence the name, though it can also be used to reduce camera shake by letting the camera settle down after the photographer presses the shutter button.

Sensor Resolution

The number of pixels a digital sensor can record, typically measured in megapixels (millions of pixels).

Servo AF

A method of autofocus which attempts to keep moving subjects in focus, theoretically allowing the photographer to capture a relatively sharp, in-focus image at any point in time.

Shadows

The darker - but not completely black - areas of an image.

Sharpness

The crispness of lines in an image, and the opposite of "blur" or "out of focus." Sharpness is a relative quality, as a bunch of images can be "acceptably sharp" while differing in their relative sharpness compared against each other.

Many image editors allow the adjustment of sharpness via an "unsharp mask" or other methods.

Shutter

The element within a camera that opens and closes very quickly, allowing light from the lens to pass through to the sensor or film.

Shutter Curtain

A portion of a shutter mechanism which opens and closes to expose or block a camera's sensor or film to the light coming from the lens.

Shutter Lag/Latency

The time delay between when the photographer presses the shutter release and the camera starts recording the exposure.

Shutter Priority (Tv)

A shooting mode where the photographer selects the desired shutter speed and ISO, and the camera automatically picks the right aperture value for the proper exposure.

Shutter Release

Typically refers to a wired remote control (also called a "bulb") that essentially behaves like a camera's shutter release button. The use of a shutter or cable release can reduce camera vibration over using the shutter button itself.

Shutter Speed

The duration of time for which a camera's film or sensor is exposed. Faster shutter speeds often require the use of two or more curtains, so not every region of the film or sensor is exposed at the same exact moment.

Single Lens Reflex

A type of camera that uses a semi-automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital sensor, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film.

Skylight Filter

A complete waste of money that salesmen in photography stores push onto unsuspecting customers.

Slave

See Slave Flash.

Slave Flash

A flash which is triggered via an optical sensor. When the optical sensor sees a dramatic and sudden increase in light (from the master flash), it triggers the flash to fire.

Slow Sync

A function that tells your camera to shoot with both a longer shutter speed as well as firing the flash. This can allow the photographer to get a relatively sharp shot of your main subject as well as get some ambient light from the background and foreground. Wedding photographers love their slow sync, boys and girls.

Snapshot

Often used as a put-down, as in "that's just a snapshot," this term typically refers to an image which does not appear to have been carefully constructed or into which little thought or concern for framing or artistic value appears to have gone.

Snoot

A tubular or conical attachment placed over a flash to produce a narrow beam of light, often used to highlight part of an object or subject without lighting neighboring parts.

Soft Box

A type of photographic lighting device, one of a number of photographic soft light devices. All the various soft light types create soft diffused light by directing light through some diffusing material, or by "bouncing" light off a second surface to diffuse the light. The best known form of bouncing source is the umbrella light where the light from the bulb is bounced off the inside of a metalized umbrella to create a soft indirect light.

Soft Focus

A lens flaw or an intentional technique in which the image is gently blurred despite having the proper focal length. A soft focus lens deliberately introduces spherical aberration in order to give the appearance of blurring the image while retaining sharp edges; it is not the same as an out-of-focus image, and the effect cannot be achieved simply by defocusing a sharp lens. Soft focus is also the name of the style of photograph produced by such a lens.

Soft Lighting

Light that tends to "wrap" around objects, casting shadows with soft edges. The softness of the light depends mostly on the distance from the light (closer lights are softer than distant lights) and the size of the light source (larger is softer).

The softness of a light source can also be determined by the angle between the illuminated object and the 'length' of the light source (the longest dimension that is perpendicular to the object being lit). The larger this angle is, the softer the light source.

Solarization

A phenomenon in photography in which the image recorded on a negative or on a photographic print is wholly or partially reversed in tone. Dark areas appear light or light areas appear dark. The term is synonymous with the Sabattier Effect when referring to negatives, but is technically incorrect when used to refer to prints.

Spectrum

Generally, a band of colors, as seen in a rainbow, produced by separation of the components of light by their different degrees of refraction according to wavelength.

In photography, a spectrum can refer to the entire range of visible light or the range of colors present in one particular image.

Speed

A general term that refers to the amount of light. More light results in a higher "speed" because a faster shutter speed is required to yield a properly exposed image.

Spherical Aberration

An optical effect observed in a lens that occurs due to the increased refraction of light rays when they strike the lens near its edge in comparison with those that strike nearer the centre. It results in an imperfection of the produced image. Spherical aberration should not be confused with barrel distortion; whereas barrel distortion affects the shape of the image, spherical aberration affects its sharpness.

Split Prism

A kind of focus screen that some photographers prefer.

Spot Meter

A metering mode in which the camera measures a very small portion of the scene (typically 1-5%). This is also typically the very center of the scene, but some cameras allow the user to choose an off-center spot. Alternatively, a photographer can recompose after metering.

Stop Down

The act of reducing the size of the iris (aperture) of a lens. This increases the depth of field of the image, but results in dimmer images at the film plane. Photographers can compensate for this by increasing the exposure time, using a photographic film with a higher ISO rating, or, in digital cameras, increasing the light sensitivity of the sensor.

Strobe

A device used to produce regular flashes of light. Any "flash" is a strobe light, though the term "strobe" typically refers to studio lighting while the term "flash" typically refers to the smaller variants that sit in a camera's hot shoe.

Sunny 16 Rule

A rule of thumb that helps a photographer estimate the proper exposure. In general, at f/16 on a sunny day, using the reciprocal of the ISO (e.g. 1/ISO) as the shutter speed will give a fairly correct exposure. The rule can be extended to other shutter speeds, ISO ratings, and apertures (for example, f/5.6, ISO 100, 1/800). Corollaries extend the rule to other conditions as well: f/11 for slightly overcast conditions, f/8 for overcast, and f/5.6 for heavy overcast.

- T -

Teleconverter

Sometimes called tele extender, this is a secondary lens which is mounted between the camera and lens. Its job is to enlarge the central part of an image obtained by the lens. The use of a 2× teleconverter gives the effect of using lens with twice the focal length. It also decreases the intensity of the light reaching the film by a factor of 4 (an equivalent of doubling the focal ratio) as well as the resolution (by a factor of 2).

Telephoto Lens

A lens with a focal length longer than about 70 or 80mm. Telephoto lenses are often used to shoot subjects which are farther away, with super-telephoto lenses starting at about 200 to 300mm.

TIFF

An acronym for Tagged Image File Format, this is a lossless file format that's widely supported by image-manipulation applications, by publishing and page layout applications, by scanning, faxing, word processing, optical character recognition and other applications.

Tilt and Shift Lens

A lens which can both tilt and shift. Often used in architectural photography so that tall buildings appear without converging lines, tilt-shift photography took off as a means of "faking miniatures" in 2009 or so.

"Tilt-shift" actually encompasses two different types of movements: rotation of the lens plane relative to the image plane, called tilt, and movement of the lens parallel to the image plane, called shift. Tilt is used to control the orientation of the plane of focus (PoF), and hence the part of an image that appears sharp; it makes use of the Scheimpflug principle. Shift is used to change the line of sight while avoiding the convergence of parallel lines, as when photographing tall buildings.

Tonal Range

A photographic term used to describe the quality of color and tone ranging from an image's darkest shadow through to the brightest highlight details, including all of the transitions in between these extreme levels.

Toy Camera

Simple, inexpensive film box cameras made almost entirely out of plastic, often including the lens. The term is misleading, since they are not merely 'toys' but are in fact capable of taking photographs. Many were made to be given away as novelties or prizes. Many professional photographers have utilized toy cameras and the often strange optical effects of their inexpensive lenses to take award-winning photographs.

Tripod

A three-legged object used as a platform to prevent camera movement and to increase stability. They are necessary when slow-speed exposures are being made, or when telephoto lenses are used, as any camera movement while the shutter is open will produce a blurred image. In the same vein, they reduce camera shake, and thus are instrumental in achieving maximum sharpness. A tripod is also helpful in achieving precise framing of the image, or when more than one image is being made of the same scene, for example when bracketing the exposure. Use of a tripod may also allow for a more thoughtful approach to photography.

TTL

A photographic term describing a feature of cameras capable of measuring light levels in a scene through their lens. This information can then be used to select a proper exposure (average luminance), and/or control the amount of light emitted by a flash connected to the camera.

TTV

A photographic term describing a feature of cameras capable of measuring light levels in a scene through their viewfinder. This information can then be used to select a proper exposure (average luminance), and/or control the amount of light emitted by a flash connected to the camera.

Tungsten

Conventional filament bulb domestic lighting is technically tungsten lighting, but in photography the term is usually applied to photoflood bulbs, which are brighter and more consistent.

- U -

Umbrella

A valuable tool for photographers, both as a prop when photographing subjects in inclement weather or, with a reflective inside, as a diffusion device when employing artificial lighting, and as a glare shield and shade, most often in portrait situations.

Under-Exposure

An image which is rendered too dark or darker than it appears to the naked eye, or one which exhibits a lot of clipped shadows.

USM

Ultrasonic motor. Canon's term for their ultra-quiet autofocus drives on their lenses. Nikon calls this technology the Silent Wave Motor, and other manufacturers have their own name for it as well.

UV Filter

Individual compounds or mixtures that prevent ultraviolet (UV) light from coming through. UV filters are used in photography to reduce haziness or fogginess created by ultraviolet light.

The UV filter absorbs ultraviolet rays without changing the exposure. With most images, people will not see a difference when a UV filter is used. However, UV filters (in particular filters lacking coating) may introduce flaring and have negative impact on contrast and sharpness, especially when a strong light source is present.

- V -

Variable Focus Lens: See Zoom Lens.
View Camera: A type of camera first developed in the era of the Daguerreotype and still in use today, that comprises a flexible bellows which forms a light-tight seal between two adjustable standards, one of which holds a lens, and the other a viewfinder or a photographic film holder.
Viewfinder: The component of a camera that you look through to see an image. On an SLR, this image comes directly from the lens, as opposed to a rangefinder camera which has a separate viewing optic. While the viewfinder on an SLR provides a more accurate representation of the final image, a rangefinder camera does not suffer from viewfinder blackout.
Viewfinder Blackout: The period of a time when an SLR's mirror is lifted up so that the lens' image falls on the sensor (or piece of film), exposing the image but causing the viewfinder to be black.
Vignette: The effect when an image is darker and/or less-saturated around the edges than at the center. Vignetting can be unintentional and undesired, such as from stacked filters, or intentional to help bring focus to the subject.

- W -

White Balance: An adjustable setting to neutralize a color cast created by certain types of lighting. Tungsten lights, for example, create a yellowish cast in an image. When shooting with JPEG, this value is burned into the image and can't be adjusted without losing data. With a RAW file, this value can be changed after shooting without losing data.
White Card: A white object placed in a scene that a photographer can measure to set the camera's white balance.
Wide-Angle Lens: A lens that provides a very wide field of view, capturing far more in a single image than you see with the your eye. Wide-angle lenses are often useful for landscapes or shots where you want to capture a strong feeling of place.

- X -

- Y -

- Z -

Zone System: A system developed by Ansel Adams and Fred Archer for determining the proper exposure for an image. A zone refers to a range of tones, with pure black being Zone 0 and pure white being Zone 10. In brief, to determine the proper exposer with the zone system, you determine the key item in a scene and place its exposure on the desired zone, allowing the other items in the scene to fall in the appropriate zones.
Zoom Flash: A setting on some flashes that allows the photographer to adjust the coverage of the flash's beam so that it matches the current lens' focal length. For example, a 28mm lens needs a wider flash beam than a 105mm lens.
Zoom Lens: A lens with moving internal optics that allow for a shift in the focal length. These lenses are marked with a range of focal lengths, for example the Canon EF 24-70 f/2.8L lens has a focal length ranging from 24mm to 70mm. A zoom lens is the opposite of a prime lens, which has a fixed focal length.