Causes completely blurred images. There are six types of aberrations: spherical, coma, astigmatism, curvature of field, distortion and chromatic.

AF (Autofocus) Lock

Used to prevent autofocus operation once the subject is in focus.

AF Sensor

The sensor used to detect focus in cameras equipped with autofocus operation.


Advanced Photo System. A photographic system that uses 24mm film with a magnetic layer to record exposure and other information. It can be printed in three formats, printing includes an “index print”, and the film stays in the cassette after processing. Most APS cameras are point-and-shoots.


The adjustable opening in a camera lens used to control the amount of light reaching the film. The size of this hole is called the f-stop.


Refers to lenses designed to correct for color aberrations. Usually used in telephoto lenses that have large maximum apertures. (See Chromatic Aberration.)


Abbreviation for American Standards Association. In conjunction with a number, e.g., ASA 400, refers to film “speed” or sensitivity. The higher the number, the more sensitive the film.


Not a continuous curve. Refers to elements in lenses which have been designed to compensate for distortion by having different curves on individual elements. Allows for a more compact lens.


An optical defect that causes light rays from an off-axis point to form images at different positions.



Light coming from behind the photo subject. Can cause underexposure of the main subject with autoexposure systems.


Accordion-like device on cameras that allows the lens to move toward or away from the film-plane. Usually used for close-up or macro work.

Black and White Film

Light-sensitive film that, when processed, produces a black and white, negative image. The resulting “negative” is projected onto light-sensitive paper to make black and white photographic prints.


Unsharp. Caused by inaccurate focus or excessive movement of the camera or subject.


A word, of Japanese origin, used to describe the out-of-focus elements in an image (e.g., “That image has nice bokeh.”).


Practice of varying exposure to insure accurate exposure of a given subject; e.g., exposing “one stop under” and “one stop over”.


Shutter speed setting where the shutter stays open as long as the shutter release is depressed. Usually indicated by a B on the shutter speed selector.


Cable Release

A cable device for releasing the shutter. Usually used for slow shutter speeds when the camera must remain absolutely still.

Chromatic Aberration

A type of image distortion that usually appears as a rainbow on the edge of objects towards the outside of an image. Occurs when light rays passing through a lens focus at different points, depending on the light wavelength. An “apochromatic” lens corrects for this problem.

Chromogenic Film

Black and white film made for processing in C-41 color chemicals.

Color-negative Film

Light-sensitive film that, when processed, produces a colored, negative image. The resulting “negative” is projected onto light-sensitive paper to make photographic prints.


Where light rays pass through an off-axis point causing the lens to focus at different points causing blur.

Continuous Service AF

Used to allow the camera to continue focusing as long as the shutter release is slightly pressed. This allows an AF camera to take a picture even if the picture is not in focus. Used for taking pictures of fast moving subjects. Also know as “Continuous Predictive Autofocus” or “Predictive Autofocus”.


The difference between light and dark values. Usually refers to the gradation between black and white. Fewer gray values are described as “high contrast.” Many shades of gray are low contrast.

Convertible Lens

A multi-piece lens. The pieces assemble or disassemble to form different focal lengths.


A form of protection provided by the laws of the United States (title 17, U.S. Code), and other countries, to the authors of “original works of authorship,” including literary, dramatic, musical, artistic, and certain other intellectual works. This protection is available to both published and unpublished works. Section 106 of the 1976 US Copyright Act generally gives the owner of copyright the exclusive right to do and to authorize others to reproduce, distribute, perform the work, and/or display. These laws are similar in all countries. Laws regarding ownership of images or written material.


To enlarge an image so that parts are cut or left off the print.

Curvature of Field

When light rays passing through a lens tend to focus on a curved plane rather than a flat plane resulting in images that are not sharp.


D-Type Lens

Nikon lens designation for lenses that communicate distance to subject information with Nikon camera bodies.


Dark material used to cover the photographer’s head and the ground-glass viewing screen on large format cameras.


“Dark”, light-tight space for processing and printing photographic materials.


Thin, flat piece of metal or plastic, which protects unprocessed film from light exposure.

Dedicated Flash

Electronic flash designed to work with the meter and exposure system of a specific camera.


The amount or “density” of silver on an exposed and processed piece of film.

Depth of Field (DOF)

The distance between the farthest and nearest points which are in focus. “Depth-of-field” can also be used to describe the zone of acceptable sharpness before and behind a given focused subject. DOF varies according to numerous factors such as lens focal length, aperture, shooting distance, etc.


Chemical that converts silver halide on film to a visible, black image.


Another word for aperture. Can also be a type of shutter. See: Leaf Shutter.


Bounced light. Light “refracts” off opaque materials softening and blurring an image.


Material that softens and “diffuses” light in order to soften the edges in an image.


Light rays of different wavelengths deviate different amounts through a lens causing a rainbow effect around points and edges.


Optically, where straight lines are not rendered perfectly straight in a focused image. The two types of “distortion” are barrel and pincushion.

DX Coding

Type of bar coding used to electronically communicate film speed to the camera.


ED (Extra Low Dispersion) Glass

A glass developed and trademarked by Nikon Corporation, used in telephoto lenses to obtain optimum correction to help prevent chromatic aberration. These lenses are resistant to temperature changes, preventing focus shift problems in lenses that use calcium fluorite crystal elements.

EF Lens

Designation for Canon EOS system autofocus lenses.


The light sensitive, chemically active surface on photographic film and paper.


A photographic print made by “enlarging” an image from a piece of film.


The amount of light that reaches film or the combination of f-stop and shutter speed that controls the amount of light. Also used to describe an exposed piece of film.

Extension Tubes

Hollow metal tubes used to extend the length of a lens. Used for “macro” or close-up photography.


F Numbers

Numbers on the outside of the lens corresponding to the aperture opening. The larger the number (e.g., F/22), the smaller the opening of the lens; the smaller the number (e.g., F/2.8) the larger the opening of the lens. The f-number is equal to the focal length divided by the aperture diameter.


Photosensitive material used in a camera to record an image. Made from a thin, transparent base coated with light sensitive chemicals.


Transparent lens attachments used to change the color, or other characteristics, of an image. They are used both on the camera and in the darkroom.

Fisheye Lens

Super wide-angle lens. Angle of view can approach 180 degrees. Nearly infinite depth- of-field.

Fixed Focal Length

A camera with a non-removable, non-zoom lens. The lens focal length can’t, therefore, be changed.


Reflected light from lens elements, metal, etc. Appears as a non-uniform haze or bright spots on the film. Usually occurs when bright light (sun) enters the lens.


Artificial light source. Usually camera mounted but also larger studio models called strobes.

Flash Sync (Synchronization)

The shutter speed that corresponds to the timing of the flash. Any faster and the shutter won’t be open for the duration of the flash. Any shorter and subject movement might cause blur.


A special glass used by Canon in selected pro lenses to correct for chromatic aberration.

Focal Length

The distance between the back lens element and the focal plane. In 35mm format, lenses with a focal length of approximately 50mm are called normal (standard), lenses 35mm and shorter are called wide-angle, and lenses with a focal length of more than approximately 70mm are called telephoto lenses.

Focal Plane

The area of the camera where the lens focuses on the film.

Focal Plane Shutter

A shutter placed just off the surface the focal plane.

Focal Point

The point on the optical axis where light rays form a sharp image of a subject. An ideal lens would allow light rays to reflect from a subject, travel through the optical axis and converge to a point after they pass through the lens.


To move the lens, or film, in relation to the focal plane in order to record a sharp image on the film.

Focus Mode

Three basic types of focus modes exist for AF cameras: Single servo AF, Continuous AF and Manual AF. Different cameras may use different nomenclature to identify these modes.

Focus Priority

A camera mode where the shutter cannot be released until the subject is in focus.

Focus Tracking

Where the camera’s microprocessor (computer) analyzes a moving subject’s speed, anticipates the position of the subject at the exact moment of exposure, and focuses the lens based on this information.

Focusing Screen

Refer to Ground Glass. Usually on large format cameras- a piece of frosted glass at the focal plane where the lens projects an image for focusing and composition.


Can mean either the size of the camera or the size of the film. For camera sizes there are APS, 35mm, medium and large formats. For film formats there are APS, 35mm, 645, 6×6, 6×7, 6×9, 4×5, 5×7, 8×10, etc.



Refers to contrast rating of black and white enlargement papers. Zero is the lowest contrast and 5 is the maximum contrast.


Exposed and processed silver halide crystals and colored dyes. After processing they turn black or appear colored and form the miniature “grain” that makes up an image on a piece of film.

Ground Glass

Frosted glass used as a viewing mechanism in cameras without prisms. The glass is positioned so that the lens projects an image on it for focusing and composition purposes.

Guide Number

A number used to describe the output power of a flash. Usually expressed using an ISO film speed of 100 and a foot or meter distance.


High Key

A high contrast image consisting mostly of highlights with little shadow detail.


The bright to white range of tones in an image.

Hyperfocal Distance

The closest point at which a camera can be focused where the depth of field includes infinity.


Image Plane

The area at which a lens forms a sharp image, i.e., the film plane if, and when focused correctly.

Incidental Light

Light measured as it falls on a surface, rather than light reflected from a surface. Measured from the subject, not the camera.


In relation to camera focus: the horizon.


Light not visible with the human eye. Measured at the red end of the spectrum, it can be photographed with special film.

Infrared Compensation Index (IR Setting)

An index mark on a camera lens used to correctly focus infrared film. With most lenses, the focal plane for infrared film is slightly removed from that of visible-light photography.

Internal Focusing (IF) System

A system used where the internal elements in the lens are the only parts that move during focusing. This prevents the physical length of the lens from changing, allows for faster focus, reduces aberrations, and allows for ease of use for filters that require specific alignment such as polarizers, graduated, etc.


Stands for “Image Stabilizer”. This is available in some Canon EF lenses and compensates for camera shake allowing slower shutter speeds.


The International Organization for Standardization (ISO) is a worldwide federation of national Standards bodies from some 130 countries, one from each country. ISO is a non- governmental organization established in 1947. The mission of ISO is to promote the development of standardization and related activities in the world with a view to facilitating the international exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological and economic activity. ISO’s work results in international agreements, which are published as International Standards. “ISO” is not an acronym, it is a word, derived from the Greek isos, meaning “equal”, which is the root of the prefix “iso-” that occurs in a host of terms, such as “isometric” (of equal measure or dimensions) and “isonomy” (equality of laws, or of people before the law).



Key Light

When lighting a photographic subject, the main light source.


Latent Image

The exposed but undeveloped image on a photosensitive surface.


How much variation an emulsion allows while still delivering acceptable exposures, i.e., how “forgiving” a film is.


Liquid Crystal Display. An information display method. Usually used for external displays on cameras or other electronic devices.

Leaf Shutter

Camera shutter located in the lens. Utilizes a spring with the aperture control device to control the exposure time. Useful because it can be synched with a flash at any speed.


Light Emitting Diode. An information display method. Usually used for viewfinder displays since it can be seen in the dark.


An optical device used to control and focus light.

Lens Coatings

Thin anti-reflective materials applied to the surface of a lens in single or multiple layers to help reduce light reflection and increase amount of transmitted light.

Lens Drive Systems

There are two different types of AF lens drive systems offered: One system utilizes a motor located inside the camera, which autofocuses the lens via a drive shaft. The other system utilizes a motor inside the lens.

Lens Hood/Shade

A lens addition used to minimize lens “flare” or unwanted light from reaching the lens.


Radiated energy which forms that portion of the spectrum visible to the human eye.

Light Box

A device for viewing film. Constructed of a light source (usually sunlight balanced fluorescent) behind a glass or plastic surface on which the film is placed for viewing.

Light Meter

A light sensitive device used for evaluating the amount of light in a scene for exposure. There are four types: Incidental meter, reflective meter, flash meter and spot meter



Commonly, close up photography. Specifically, any photography where the level of magnification is 1:1 or larger.


The size of an image relative to the subject as expressed in a ratio.

Matte Field

A textured surface that disperses light to form a clear image, and is used in viewfinder optical systems. See Ground Glass.


Any measuring device. In photography it usually refers to a light meter, although it could refer to a color meter.


A small number of prisms located on a focusing screen. The microprisms break up out-of-focus images into small segments that appear fuzzy, allowing focusing on subjects without distinct lines.

Mirror Lens

A lens, which uses mirrors as well as glass elements to control and focus an image. Usually a telephoto lens.


Type of exposure method used by a camera, e.g., manual mode, aperture priority mode, picture mode, flash mode, etc.


Tending towards one color.

Motor Drive

A device for automatically winding the film in a camera. Most contemporary cameras have them built-in.



A processed piece of film where the image is reversed so that the shadows are light and the highlights are dark.

Neutral Density Filter

A dark, color-neutral filter used to control the amount of light reaching the film.

Newton Rings

Colored, ring-shaped patterns that appear between two transparent tightly pressed surfaces like glass or film. Caused by moisture between the surfaces refracting the light.

Normal Lens

A lens where the focal length is approximately equal to the diagonal of the film size it’s being used for. This is also representative of the field of view of human sight. In APS, approximately 28mm, in 35mm approximately 50mm, in medium format approximately 90mm, in 4×5 approximately 200mm.



When light sensitive material is exposed to too much light resulting in film that is too dense to print or view well.



Photo material that is sensitive to all colors that the human eye can perceive.


The act of following a moving subject with the camera while releasing the shutter.


In photography, an image proportionally more rectangular than a 35mm film frame. Also, a type of camera for exposing film in a panoramic format.


In rangefinder cameras, the difference between the image seen by the lens and the viewfinder. The discrepancy increases as the subject moves closer to the camera. This does not occur in SLR cameras


A prism in an SLR camera that allows the photographer to view the image while it is being focused.


The visual representation of three-dimensional space in a two dimensional medium. Three dimensions are implied by converging lines and a focal point.


Tungsten light source with a metal reflector.

Pinhole Camera

A camera with a fixed aperture made by poking a hole in a piece of metal. Usually made from a small enclosed container such as an oatmeal box or small tin.


An imaginary line or field which lies perpendicular to the optical axis.


Use of polarizing filters to control the direction light travels. The effects are minimizing glare and reflections, and saturation of colors, especially in landscapes.

Polarizing Filter

Two pieces of polarizing material which rotate on an axis so that the polarizing effect can be increased or decreased.

Portrait Lens

Usually a lens with a moderately long focal length (80-100mm in 35mm cameras). Some portrait lenses use glass with a subtle diffusing or “soft focus” effect.


A photographic image in which the light areas correspond to light areas in the subject, and the dark areas correspond to the shadow areas in the subject. Also called a slide or transparency.


Banding or lack of continuous tones in an image. Can be a deliberate effect or, more commonly, a result of over-manipulation or compression in a digital image.

Primary Colors

Red, yellow, and blue, the three colors which combined make white light.

Principal Point

A point from where the focal length of the lens is measured. Normally located at the center of the lens. However, compound lenses have two principal points, and the location of these principal points cannot be determined by appearance.


A piece of transparent material (i.e., glass or plastic) that is capable of bending light.


In photography, the chemical process by which a latent photographic image is converted to a stable, visible image.


A device used to enlarge film images by focusing light through them onto a flat surface.


Products made for advanced amateurs. Prosumer items usually have high-end features at more consumer-friendly prices. For example, a prosumer film may have higher color saturation and smaller grain than consumer film, but won’t be kept refrigerated like a professional film.




A camera with a viewfinder separate from the lens. Not an SLR.

Rear Focus

The focused area behind the subject.

Rear Focusing System

When focusing, only the rear lens group moves. This eliminates the physical length of the lens during focusing and allows for faster focusing. (Refer to Internal Focusing.)

Reciprocity Failure

Photosensitive materials require a linear sensitivity within a certain range. Beyond that, their sensitivity requires that exposure times be increased in larger amounts than normal.

Recycling Time

The time it takes for a strobe or battery-pack to recharge enough that it can power a flash burst.

Reflected Light Reading

Light meter reading made by pointing the meter towards the subject. It will vary depending on the subject as different materials reflect different amounts of light.


A tool for redirecting light- usually a white or metallic card or umbrella.

Reflex Camera

A camera that uses a mirror to reflect light onto ground glass for viewing and focusing.

Relative Aperture

Diameter of the aperture divided by the focal length of the lens. Expressed numerically as an f-stop.

Release-Priority AF

In release-priority autofocus operation, the shutter can be released at any time whether the subject is in focus or not. Used in fast-moving situations where the photographer doesn’t want to lose any of the action.


(Also known as Resolving Power) The ability to reproduce small details in a photograph. Resolving power is used to quantify lens performance and is measured in lines per millimeter (1/mm). The measurement indicates how many black lines placed at equal intervals within 1mm can be resolved by a particular lens.


To alter a finished print or piece of film in order to cover up undesirable marks or elements.

Reversal Materials

Photo-sensitive materials that when processed become positive images, i.e., slides, transparencies and certain print materials.

Rising Front

The ability on a camera to raise the lens in relation to the film to control focus and distortion. Usually only on large format cameras.


Non-sheet film. Film that comes in a roll and can be exposed in multiple “frames.”

Roll-Film Adapter

An attachment for sheet film cameras that allows the use of roll film.



A red or orange darkroom light that black and white photo papers aren’t sensitive to.

Selenium Cell

A light sensitive electronic device that emits electricity in proportion to the amount of light falling on it. Used for light meters.


Black and white negatives that separate the continuous colors of an image into two to four colors for offset printing. The most common separations are for CMYK printing (cyan, magenta, yellow and black).

Sheet Film

Film that is cut into individual sheets usually 4×5 (insert space after 5) in. (insert space after .) or larger.


The mechanical device in a camera that controls the amount of time light is allowed to expose the film.

Shutter Priority

A camera exposure mode where the photographer chooses a shutter speed and the microprocessor in the camera sets a corresponding aperture for best exposure.

Silver Halide

The light sensitive component in chemically treated, photosensitive surfaces.

Silver Nitrate

Chemical used in photo developers and treated photosensitive surfaces.

Single-Servo AF

An autofocus mode that locks when the subject comes into focus and stays locked as long as the shutter release button is lightly pressed. Used when shooting stationary objects.

Single Lens Reflex (SLR) Camera

A camera that uses a mirror and prism to allow the photographer to see through the main lens.


A light sensitive trigger device used to synch strobes and flashes without an electronic synch cord.


A transparency (usually 35mm) mounted in a square paper or plastic frame.

Slide Film

Light-sensitive film that, when processed, produces a transparent film image. 35mm “transparencies” are usually mounted as slides. Transparencies can be printed or projected with a slide projector.


An effect achieved by diffusing an image either in the camera or printing stage. Can be done with special lenses or by placing diffusion devices or materials between the light source and the light-sensitive material.


Also known as the Sabbatier effect. Usually achieved by exposing a developing image to white light during the development process. The effect is a partial reversal of the image.


The visible separation of light into colored bands by directing white light through a prism.


In photography, the sensitivity of a photosensitive material. This is expressed as either an ASA or ISO number.

Spherical Aberration

A lens fault which results in degraded image quality at the film plane. It is caused by light rays passing through the lens from a single point on the optical axis focused at different points according to incident height. Spherical aberration can be reduced by stopping down the lens.

Split Image Rangefinder

Two prisms with faces angled in opposite directions and used to aid in focusing. A subject will appear split while out-of-focus, allowing a photographer to adjust for accurate focus.

Spot Meter

A light meter, which takes its reading at an angle of 1 to 8 degrees. Used for the Zone System or to determine the reflective values of specific elements in a scene.


Retouching dust spots or other fine blemishes in a photographic image with a small brush. Usually done on prints.

Standard Lens

Refer to “Normal Lens.”


Photography that uses two images taken from slightly different angles to produce the illusion of three dimensions when seen through a special viewing device.

Stopping Down

To decrease the size of aperture in a lens, e.g., to stop down from f3.5 to f16. Increases depth-of-field.


A view camera movement used to control depth-of-field and perspective. Allows the angle relation of the film plane and lens to be changed from side-to-side.



An optical device used to increase the effective focal length of a lens. It is mounted between the camera and the lens and usually comes in two different sizes: 1.4X and 2.0X. A 1.4X teleconverter increases focal length by 1.4 times, while a 2.0X increases focal length by 2.0 times. The aperture of the lens is also increased by the same amount as the focal length is increased. For example, a 2.0X teleconverter increases focal length of a 200mm lens to 400mm; however, the aperture of F/2.8 is decreased to F/5.6.

Telephoto Lens

A lens with a long focal length- longer than the diagonal of the film format used.


In photography, usually refers to the gray values in an image.


A processed and stabilized positive film image, i.e., a slide is a transparency.


A collapsible camera support with three legs.


Refers to flash or exposure metering which is read “through the lens” at the film plane.


A metal filament used in most light bulbs. Makes a reddish/yellow colored light. There are special films and filters for correcting the color cast of tungsten light.


UD Glass

A Canon designation for lenses designed to correct for chromatic aberration. See: Ultra Low Dispersion.

Ultra Low Dispersion

A type of glass used by Canon to make lens elements. “UD” glass corrects for chromatic aberration.


Allowing too little light to reach a photosensitive material. Results in a “thin” or light image with negative material and a “dense” or dark image with reversal material.


Canon designation for “Ultrasonic Motor”. Canon’s fastest autofocus lens technology.

UV Filter

Filter used to reduce the amount of ultraviolet light reaching film. Ultraviolet light can cause an image to appear hazy.


View Camera

A camera, usually large format that has a ground glass back for viewing the subject.


An optical viewing device for framing and focusing an image in a camera.


The effect from blocking the light at the edge of an image. Can be caused accidentally by a combination of wide-angle lens and filters, or on purpose as a deliberate effect.


Wide-Angle Lens

A lens with a focal length less than the diagonal of the film format it’s being used for. For 35mm, usually wider than 50mm. For medium format, wider than 90mm.




Zone System

A system developed by Ansel Adams, Fred Archer, and Minor White to pre-visualize, optimize and control black and white film exposure as well as the print process.

Zoom Lens

A lens which has a variable focal length, e.g., 70-200mm.



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