Glossary of Photo Terms

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A-B

A Mode – Aperture Priority Mode
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 and ISO (if it is set to Auto-ISO) to set the proper exposure. This mode gives you excellent control over depth of field.

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

AE Lock – Auto Exposure Lock
A function of many cameras that allows you to compose, press the control associated with AE Lock (usually tagged “AEL”) and recompose without the camera re-evaluating exposure. Also see AEL below.

AEL – Auto Exposure Lock
Typically the tag on 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.

AF – Auto-focus
Introduced to mainstream SLRs in 1985 by Minolta, autofocus refers to the camera’s ability to focus on a subject without input from the photographer.

AF-I – Auto Focus Internal
Nikon term for their early in-lens motor technology (Replaced by AF-S)

AF Micro-Adjust – Micro-Adjust
DSLR Camera setting to compensate for small errors between the phase-detection sensor calibration and the actual focal point on a lens that causes a small amount of front or back focus. The camera maintains a database of lenses that it has been adjusted for and loads the setting when a particular lens is attached. MIrrorless cameras aren’t susceptible to this since their autofocus sensors are on the focal plane already and don’t require calibration. Some mirrorless camera do have a micro-adjust setting if lens adapters are available to them that use reflective phase-detection technology like the Sony LA-EA4.

AF-S – Auto Focus Silent-wave
Nikon term for their in-lens motor technology.

Ambient Light –  Also: Natural light
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.

Aperture – Also: f/-stop
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.

APO  – Apochromatic  
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.

APS-C – Advanced Photo System – Type “C”
Refers to imaging sensors that are approximately the same size and aspect ratio as the  APS-C film frame: 25.1mm × 16.7mm. In a DSLR or Mirrorless camera they record 66% of the frame area of a Full-frame sensor which make the effective focal length 1.5x longer than it would be on a Full-frame camera. A 200mm lens on an APS-C camera would capture an image equivalent to a 300mm lens on Full-frame. This is great for long lenses but is a handicap for wide angle where a 16mm ultra-wide lens appears as if it was a 24mm wide angle.

APS-H – Advanced Photo System – Type “H”
Canon developed imaging sensors that Measure 27.9mm × 18.6mm. Developed before Full-frame was economically available and retained for speed through the EOS 1D Mk IV. The smaller-than-full-frame size makes the effective focal length 1.3x longer than it would be on a Full-frame camera. A 200mm lens on an APS-C camera would capture an image equivalent to a 260mm lens on Full-frame. This was a benefit to sports and wildlife shooters who were the target demographic.

AS – Anti-Shake
Older Minolta/Sony term for their in-body image-stabilization technology. Now SSS for Super Steady Shot

Aspect Ratio – 3:2, 4:3, etc.
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.

Av Mode – Canon’s A Mode -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 and ISO (if it is set to Auto-ISO) to set the proper exposure. This mode gives you excellent control over depth of field.

Backlight – Backlighting
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.

Barrel Distortion – Spherical Distortion
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.

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

BIF  – Bird In Flight
Image of a bird in flight. Has its own term since a successful capture is often problematic and a good BIF shot is brag-worthy.

Bit Depth – 8-bit, 12-bit, 14-bit, etc.
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.

BMP – Bitmap
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.

Bokeh – Sometimes “Boke”
“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 therefore very subjective.

Bracketing  – Auto-bracketing
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.

Buffer  – Buffer Memory
The buffer memory is where the camera’s processor stores the image file until it can be written to 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 or Mirrorless dozens to hundreds. 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 my 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 an advanced DSLR or Mirrorless with a big buffer, fast controller and memory card may be able to take shots at ten or more frames per second for a half minute before slowing down.

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