Minolta/Sony term for cameras able to factor distance information provided by ADI compatible lenses to control electronic flash exposure.

AEL/

AE Lock

Typically a button used to hold the automatic exposure set by the camera from a brighter or darker area as you recompose to a different part of the scene. Used as a quick method of exposure compensation. On some models, this doubles as a slow synch button for use with flash.

Introduced to commercial SLRs in 1985 by Minolta, autofocus refers to the camera's ability to focus on a subject without input from the photographer.

Nikon term for their early in-lens motor technology (Replaced by AF-S)

Nikon term for their in-lens motor technology.

Ambient light is the light available in a scene without adding additional illumination specifically for the photograph. This may be light from a window, room lights, street lights, full sunlight or anything that lights the scene normally.

The lens f-number (usually called an  f-stop) is a ratio determined by dividing the diameter of the hole (aperture) in the lens body that lets light in by the focal length of the lens. 

Setting the camera to aperture-priority makes the aperture (f/-stop) the primary setting and forces the camera's metering system to adjust the shutter speed to set the proper exposure. This mode gives you excellent control over depth of field.

Optical technology designed to focus visible light equally regardless of wavelength. Apochromatic lenses use multiple individual lens elements that bend different colors of light at different angles resulting in all wavelengths focusing in the same spot.

Refers to imaging sensors that are approximately the same size and aspect ratio as the  APS-C film frame: 25.1mm × 16.7mm.

Minolta term for their in-body image-stabilization technology.

The aspect ratio is the ratio between the long and short side of digital sensors, film negatives, computer monitors or TV screens. Most cameras capture an image that is longer than it is wide and usually conform to two popular aspects, 3:2 and 4:3. 35mm film negatives exposed an area 36mm wide and 24mm tall. the ratio works out to 3:2 (using the lowest common denominator of 12) and has survived as the aspect ratio most often used by DSLR cameras. Standard TVs and most early computer monitors used a 4:3 ratio and as a result, many compact and the Four-Thirds system cameras used that format to provide better direct viewing. New HDTVs and wide-screen monitors usually have an aspect of 16:9 (HDTV standard) or 16:10, so many newer cameras, both compact and DSLR, now offer 16:9 as a format option.

Backlighting is the condition that occurs when the subject of the scene has bright light behind it (i.e. people against a sunset) making it difficult for the camera to meter correctly. The camera, even with sophisticated metering, always tries to average the scene to some extent. This causes the back-lit subject to be underexposed or even appear as a silhouette against the background. If your camera has the ability to use a small center portion of the frame to meter (spot-metering) you can force the exposure for the subject instead of the whole scene. Unfortunately, this will cause the background to be very over-exposed. A common fix for this is to use fill-flash. Forcing the flash to fire even though the scene is fairly bright will brighten the closer back-lit subject while maintaining the exposure for the rest of the scene.

Lenses that aren't properly corrected will cause straight lines in a scene to bow inwards (pincushion distortion) or outwards (barrel distortion). Most common in wide to normal lenses, barrel distortion isn't usually an issue unless it is extreme. It is most noticeable in photos of a building or other object with straight edges and can be distracting is it is too pronounced. Most modern lenses are well-corrected to prevent this, but with very wide angle lenses, it is very difficult to eliminate and some distortion may be visible at the widest setting of your camera or zoom lens. Some very wide lenses (fisheye lenses) make no attempt to correct the distortion and make use of their extreme curvature to provide artistic impact.

An out-of-calibration condition where the camera's focusing system indicates focus, but the lens is actually focused slightly behind the target.

Image of a bird in flight.

Bit depth refers to the number of bits of data that are used to record information for each pixel in an image. Generally, the more information captured per pixel, the more shades of color and levels of brightness can be addressed when processing the image for viewing or printing. Most digital camera record 10 to 14 bits of data with some very high-end medium-format backs recording at 16-bit. When shooting in JPEG mode (most compacts don't offer RAW) images are processed and stored in 8-bit format. An 8-bit image will display 256 levels per color per pixel for a total of about 16 million distinct colors (about 160% of what the human eye can discern). Most DSLRs record in 12-bit mode when shooting RAW with some that use 14-bits. The extra data can be used to recover highlights and pull detail out of shadows while processing a RAW file. One misunderstanding is that shooting JPEG only uses 8-bit images. The JPEG image that the camera processes uses all the available bit data to optimize the image before compressing it to 8-bit JPEG (some cameras do this better than others), so it's actually not much different than converting RAW to JPEG without adjusting any settings.

An uncompressed image format that is an actual digital map of each pixel's position, color and brightness. Bitmap is one of the oldest digital image formats and can be displayed on virtually any computer, PC, Mac Unix/Linux.

"Boke" (pronounced bo-keh) is a Japanese word that roughly translates into "blur" or "fuzzy" and refers to the out of focus areas of a photograph. A fairly new photographic term (15-20 years in common use), it describes the quality, or how "pleasing" the out of focus effect  looks and is therfore very subjective.

The practice of taking several shots of the same subject while increasing or decreasing the exposure from what the metering suggests. Many cameras provide Auto-bracketing that fires off several exposures in rapid succession with some above and some below the metered setting. The value of this was greater with film, but even with intant review on digital cameras, under- or over-exposure can sometimes reveal details that are hard to see on an LCD.

The buffer memory is where the camera's processor stores the image file until it can be written to the the camera's on-board memory or memory card. The buffer will always be at least a bit larger than the largest file that the camera can produce, but most cameras will have room for two, three or in the case of a high-performance DSLR dozens. For a single exposure the size of the buffer has little impact but in continuous (burst) shooting, a larger buffer allows more shots to be taken in a sequence before the buffer fills up and the camera needs to pause before the next shot. The speed of the camera's memory card controller and the memory card itself can affect how many shots the camera can take in a rapid sequence before it pauses. When shooting in burst mode, the buffer receives new images from the camera's processor while the controller writes images to the card (oldest first) clearing the buffer for another image. A small compact with a so-so controller may only be able to take three or four shots at two per second before filling the buffer and having to wait for space to clear whereas a semi-pro DSLR with a big buffer, fast controller and memory card may be able to take several dozen shots (or more) at five (or more) per second before slowing down.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Sony term for image dynamic range enhancement technology implemented in their Alpha series camera that uses a dedicated hardware processor from Apical to measure as many as 4000 segments of an image during capture and balances the highlight and shadow exposure to more closely represent how the human eye perceives a scene. 

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

See SLR.

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

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

Canon lens designed for their EOS cameras, both film and digital.

Canon designation for a lens designed for the smaller image circle required by an APS-C sized sensor. Cannot be used on a film or full-frame camera.

Nikon lens designation for their lenses that use ELD glass that refracts all wavelengths of light more equally to reduce Chromatic Aberration. 

A type of glass that refracts all wavelengths of light even more equally than LD glass to reduce Chromatic Aberration. 

This is Canon's term for their advanced electronic flash technology. It allows the camera to evaluate the exposure for the flash by using a pre-flash and measuring the exposure before firing the main burst.

A scale denoting relative illumination as it relates to photographic exposure with EV 0 equaling 1s at f/1.0 (or 2s at f/1.4) at ISO100. A typical indoor scene would be around EV 5-7 and outdoors on a sunny day would be EV 15.

Camera viewfinder that uses video imaging linked to the camera's sensor. This refers more to a small video unit magnified by an eyepiece that outwardly resembles an Optical Viewfinder but would, technically, include using the rear LCD screen to compose.

(also ILDC)

A new class of camera that uses a larger (DSLR-sized) 4:3 or APS-C sensor in a compact camera body with an electronic viewfinder linked to the camera's sensor. This eliminates the mirror box and allows for a much smaller camera body with more compact lenses than with a DSLR. Essentially, this is a Digicam like the Sony R1, Olympus C-8080 or Minolta A2 with the ability to use an assortment of lenses. The new Micro Four-Thirds standard is based on this concept.

Exif file data is embedded in JPEG files by the camera to record information about exposure, focal length, time of day, camera model and many other specific bits of information. Most editing programs and image viewers can access this data and some can add additional information like copyrights geo-location coordinates and comments.

The lens f-number (usually called an  f/-stop) is a ratio determined by dividing the diameter of the hole (aperture) in the lens body that lets light in by the focal length of the lens.  Since the ratio value gets larger as the diameter decreases, a lower f-number allows more light in than a larger one. Explained more completely in my article on low-light photography.

An out-of-calibration condition where the camera's focusing system indicates focus, but the lens is actually focused slightly In front of the target.

Refers to imaging sensors that are approximately the same size and aspect ratio as the standard 35mm film frame. 36mm × 24mm 

This is a technique for adding a small amount of flash to a scene to balance the subject against the ambient light. Often used to compensate for back-lighting or to brighten up shadows on subjects that are lit from the side or in bright sun.

Fisheye lenses got their name from the simple fact that the front element of the lens bulges out to the point of being almost a half-sphere, making it look like a fish's eye.  These are specialized wide angle lenses that usually provide a full 180° field of view. Because no effort is made in the design to correct for spherical distortion, the images taken with these lenses are very distorted with straight lines curved heavily outward, especially toward the edges. Originally developed for taking pictures of the entire sky to record cloud formations for meteorological studies, they are now used to make images where the extreme distortion can provide an artistic effect.

Technically, the distance from the nodal point of a lens to the focal plane when the lens is focused to infinity. Practically, it denoted the relative magnification of a lens with approximately 50mm equaling what the human eye sees, or 1x. Longer lenses magnify (300mm = 6x) and make objects seem closer. Shorter lenses give a wider view (24mm = .5x).

This is a standard developed jointly between Kodak, Olympus, Panasonic and through Panasonic, Leica to provide a designed-for-digital format that would allow for compact, fully-functional DSLRs that use a defined sensor size and could interchange lenses between manufacturers via a standard mount. The name comes from the agreed-upon standard sensor's aspect ratio that is 4:3 which is similar to most P&S cameras rather than a typical DSLR which has a 3:2 aspect like 35mm film.

The fixed plane in a camera's design where the image transmitted through the lens is rendered in focus. The sensor or film is always mounted at the Focal Plane. On most advanced cameras it is identified on the top of the body with a ɸ symbol.

The number of images a camera can capture every second.

Camera/lens setting that turns off autofocus completely and requires the lens to be focused manually.

Designation given to the highest tier of Minolta lenses. Now used to designate the premium non-Zeiss Sony lenses.

G-type Nikon lenses are designed for use with Nikon SLRs aand DSLRs where aperture is controlled from the camera body. The lack of an aperture ring limits the backward compatibility with some older film SLRs.

Equal to 1,073,741,824 bytes (closest exponent of two to one billion). used to denote the capacity of computer-related media such as memory chips or discs.

A technique that uses two or more bracketed exposures of the same subject and blends them to create a single image that covers a wider Dynamic Range that the camera is capable of in a single shot. The result is an image that has detail in both the bright and shadowed areas and is thought to more closely represent what the human eye sees.

Minolta term for lenses from their film era that were redesigned to take advantage of later model's faster focusing capability.

Sigma term for their in-lens motor technology

Canon term for image dynamic range enhancement technology implemented in their cameras that uses software to balance the highlight and shadow exposure to more closely represent how the human eye sees. i-Contrast applies the changes automatically as the image is recorded or in the camera afterward if you forgot to turn it on while shooting.

A lens that focuses by moving smaller internal components rather than the larger, heavier front elements.

(also EVIL)

A new class of camera that uses a larger (DSLR-sized) 4:3 or APS-C sensor in a compact camera body with an electronic viewfinder linked to the camera's sensor. This eliminates the mirror box and allows for a much smaller camera body with more compact lenses than with a DSLR. Essentially, this is a Digicam like the Sony R1, Olympus C-8080 or Minolta A2 with the ability to use an assortment of lenses. The new Micro Four-Thirds standard is based on this concept.

Canon term for their lens-based image-stabilization technology

The American Standards Association (ASA) developed a scale that all film makers could use to standardize the sensitivity of film. The ASA standard was adopted by the International Organization of Standardization and the rating was changed to ISO. Digital sensors rate their sensitivity using the ISO film standard and use standard values like ISO50, 64, 80, 100, 160, 200, 400, 800, 1600 and higher with each increase doubling the sensitivity of the previous one.

This is Nikon's term for their advanced electronic flash technology. It allows the camera to evaluate the exposure for the flash by using a pre-flash and measuring the exposure before firing the main burst.

A JPEG image is a compressed bitmap image format that was developed in the early '90s and is available as a recording option in virtually all digital cameras. Files are appended with ".jpg".

Designation given to the highest tier of Canon lenses that use advanced lens materials and designs to optimize image quality.

A type of glass that refracts all wavelengths of light more equally than normal glass to reduce Chromatic Aberration. 

Macro lenses are specially-designed to focus down to extremely short distances and produce a flat field of focus for copying documents and such. True macro lenses will focus close enough that the image produced on 35mm film or a full-frame sensor is life-size. In other words, if you took a 35mm slide of a dime, the image on the slide would be the same size as the dime. This is called a 1:1 macro. You’ll see a lot of zoom lenses with “macro” tacked onto their names. These lenses focus close, but seldom give more than a 1:4 ratio (the image on the film would ¼ the size of the dime). Macro lenses are usually f/2.8 and come in 50mm - 200mm fixed focal lengths. Whether 50mm or 200mm, they seldom get closer than 1:1 but the longer the lens, the farther away you can be from the subject at 1:1. This is useful for photographing small living things that get nervous as things get closer.

A metering mode that measures many parts of the frame and based on a set of pre-programmed evaluations, balances the exposure to give the best overall exposure to the scene. This mode performs a "best guess" based on the pattern detected by the metering and will automatically fire the flash to fill an under-exposed area or over-expose the background if the program perceives the subject (it will try to guess the subject based on the pattern) to be under-exposed. Over the years the "best guess" has evolved into a remarkably accurate process.

Equal to 1,048,576 bytes (closest exponent of two to one million). used to denote the capacity of computer-related media such as memory chips or discs.

Equal to 1,000,000 bits. Most commonly used as a measure of transfer speed of binary data (Mb/s). Because capacity is measured in megabytes (8 bits x 1024 x 1024) and speed in bits, a one megabyte file would take 8.38 seconds to transfer from a camera to a computer at 1 Mb/s.

Kinda self-descriptive…not auto-focus.

A class of cameras that use much larger film or sensors than cameras based on 35mm film cameras. Their exceptional image quality comes at a price that mostly limits their use to businesses and working professionals. 

Not autofocus. (Yup, just that simple!)

A feature on some SLRs and DSLRs that allows the reflex mirror to be locked into it's shooting position. This feature is used in long telephoto and macro work to eliminate the vibration caused by the slap of the mirror as it flips up out of the way when the shutter is released. Many DSLRs with this feature will include MLU in the 2 second self-timer function so the mirror is flipped up and the camera waits 2 seconds before releasing the shutter to allow the vibration to die down.

Not in focus. A soft image may be soft for a number of reasons. OOF is a common reason. Also refers to areas in an image that are intentionally not in focus.

Sigma term for their lens-based image-stabilization technology

Camera viewfinder that used lenses, either a separate assembly synchronized with the camera's lens or directly through the main lens via a mirror. 

An aspect of Chromatic Aberration that appears as a purple fringe  most often on the edges of high contrast areas between blue sky and darker objects like tree branches of the edges of buildings.  

Not an acronym. It refers to the unprocessed image format available in higher-end digital cameras. Sort of a digital "negative". The RAW format contains the basic image data that the sensor records before it is processed by the camera into a JPEG. A RAW file can be manipulated after-the-fact for exposure compensation, white-balance, noise-reduction, sharpness, contrast, color settings and almost any other adjustment options that the camera offers. Because each camera maker uses it's own RAW format, applying the adjustments requires either the proprietary software from the camera manufacturer, a dedicated RAW processing package like Bibble or a higher-end editing program like the ones available from Adobe or Corel. RAW is used by professional photographers where critical adjustments may be needed in post-production and over-used by general photographers "because the pros use it". (Though factual, that last part was a bit of editorializing.)

A lens that moves the rear element group to focus. Usually found in a larger telephoto where moving the huge front element to focus would be impractical.

A camera that uses a dual image parallax rangefinder system to focus.

A camera setting in an autofocus camera that allows the shutter to be released even if the focusing system does not confirm that focus has been achieved.

A memory card format that is widely used in compact cameras and increasingly, in consumer camcorders.  cameras because of the large capacities and high transfer speeds available. T

A memory card format that can be used in newer compact cameras and increasingly, in consumer camcorders. They are available in capacities from 4 GB up to 32GB large capacities and high transfer speeds available.

The delay between pressing the shutter release and the actual recording of the image.

A camera where the viewfinder uses the primary lens that provides the image to the film or digital sensor (digital SLR has been shortened to DSLR in common usage). The image is reflected to the viewfinder by a mirror that swings out of the light path during the actual exposure and swings back afterwards (hence, "reflex"). Usually refers to a camera that offers interchangeable lenses but a few models exist that use an optical SLR design with a fixed zoom lens.

A metering mode that measures only a small central area of the frame (usually indicated by a circle in the viewfinder). This is a useful mode when the subject is illuminated very differently than the rest of the scene or when you need the subject to be exposed as correctly as possible, but the rest of the scene can be sacrificed. It is also used when you want to expose the subject as a silhouette by spot-metering on the bright background and recomposing before shooting.

Pentax term for their in-lens motor technology

Hoya designation for filters with advanced anti-reflection coatings

Tamron term for their high-performance series of lenses

Sony term for their in-lens motor technology

Sony term for their image-stabilization technology

Add-on lenses that mount to the front of a lens or between the camera body and the lens and magnify the image from the lens as it passes through to the image plane.

TIFF was originally a 2-bit black and white format developed for early scanners and fax machines. Over the years it has evolved into a full-color standard widely used by document management programs and fax servers since the format allows the storing of multiple document pages and images in a single file.

Refers to automated metering systems that sample the light passing through the lens to determine the correct exposure, even when a flash is used. Older cameras used a hand-held meter or one mounted on the front of the camera measure the correct exposure after which the camera was set manually. Early automatic flash units required the camera to be set manually and used a meter on the flash to control exposure. 

Canon term for their in-lens motor technology (high-performance)

Tamron term for their lens-based image-stabilization technology

Nikon term for their lens-based image-stabilization technology

Zeiss lenses made for the Minolta/Sony A-mount. Available as top-end lenses for Minolta and Sony DSLRs (and some film SLRs).

Zeiss lenses made for the Nikon F-mount. These manual-focus only lenses are ultra-high quality and are generally considered to be some of the best made.

Zeiss lenses made for the Pentax K-mount. These manual-focus only lenses are the same ultra-high quality as the other mounts.

Zeiss lenses made for the Zeiss Ikon rangefinder camera.

Zeiss lenses made for older M-42 screw-mount cameras. These manual-focus only lenses are not only used for older film cameras, but can be fitted with adapters to work on many newer cameras..

Zeiss lenses made for the Hasselblad medium-format cameras. These manual-focus only lenses are used where critical sharpness is needed for the larger film format and now, larger digital sensors.