Photography Terms: A Working Glossary
A reference glossary of core photography terms covering exposure, optics, composition, sensor technology, and file formats.
Exposure
Aperture — The opening inside a lens through which light passes, expressed as an f-number (f/1.8, f/8, f/16). A lower f-number means a wider opening and more light; a higher f-number means a narrower opening and less light. Aperture also controls depth of field: wide apertures produce shallow focus, narrow apertures produce deeper focus across the frame.
Shutter Speed — The length of time the camera’s sensor is exposed to light, expressed in fractions of a second (1/500s, 1/60s) or whole seconds for long exposures. Fast shutter speeds freeze motion; slow shutter speeds blur it. Shutter speed and aperture together determine total exposure.
ISO — The sensor’s sensitivity to light. A low ISO (100, 200) produces a clean image in bright conditions; a high ISO (3200, 12800) allows shooting in low light but introduces digital noise. Native ISO refers to the sensitivity range where the sensor performs without amplification artifacts.
Exposure Triangle — The relationship between aperture, shutter speed, and ISO. Changing one requires adjusting at least one other to maintain the same overall exposure. Understanding the triangle means understanding the trade-offs: more light through the aperture means shallower depth of field; more sensitivity via ISO means more noise.
Exposure Value (EV) — A single number representing a combination of aperture and shutter speed at a given ISO. A one-stop change in EV doubles or halves the total light reaching the sensor.
Histogram — A graph showing the distribution of tones in an image from pure black (left) to pure white (right). A histogram spiking at the right edge indicates overexposure (blown highlights); one bunched at the left indicates underexposure (crushed shadows). Exposing to the right – placing tones as far right as possible without clipping – preserves the most shadow detail in RAW files.
Dynamic Range — The range of tones a sensor can capture simultaneously, from the darkest shadow to the brightest highlight, before either end clips to pure black or pure white. Measured in stops. A wider dynamic range allows recovery of detail in both highlights and shadows during post-processing.
Metering — The camera’s method of measuring scene brightness to determine exposure. Evaluative or matrix metering averages the entire frame; center-weighted metering prioritizes the middle of the frame; spot metering reads a small area, typically the focus point.
Optics and Lenses
Focal Length — The distance, in millimeters, between the lens’s optical center and the sensor when focused at infinity. Shorter focal lengths (24mm, 35mm) produce a wider field of view; longer focal lengths (85mm, 200mm, 400mm) produce a narrower field of view and bring distant subjects closer.
Crop Factor — A multiplier applied to a lens’s focal length when used on a sensor smaller than full-frame (36 x 24mm). An APS-C sensor with a 1.5x crop factor makes a 50mm lens behave like a 75mm in terms of field of view. The lens itself does not change; the smaller sensor captures a portion of the image circle the lens projects.
Depth of Field (DoF) — The range of distance within a scene that appears acceptably sharp. Controlled by aperture, focal length, and subject distance. Wide apertures, longer focal lengths, and closer focusing distances all reduce depth of field.
Bokeh — The visual quality of the out-of-focus areas in an image, particularly background blur. The word comes from Japanese. Bokeh quality is determined by lens design, aperture blade count and shape, and spherical aberration characteristics.
Compression — The apparent collapsing of depth between foreground and background elements when shooting from a distance. Caused by shooting distance rather than focal length: the greater the distance from the scene, the smaller the ratio between near and far elements, and the more the scene appears to stack. The telephoto lens makes the necessary distance practical but does not itself create the effect.
Perspective Distortion — Apparent distortion of subject geometry caused by proximity, not by the lens. Wide angle lenses used close to a subject exaggerate depth cues, making near elements appear disproportionately large relative to far elements.
Maximum Aperture — The widest opening a lens can achieve, indicated by its f-number rating. Zoom lenses with a single maximum aperture figure (f/2.8) maintain that aperture throughout the zoom range; those with two figures (f/3.5-5.6) have a variable maximum aperture that narrows as focal length increases.
Image Stabilization (IS / OSS / VR / OIS) — A system that compensates for camera shake, either inside the lens or in the camera body (IBIS – In-Body Image Stabilization). Measured in stops of stabilization.
T-Stop — A measurement of actual light transmission through a lens, as opposed to the f-stop, which describes the geometric aperture opening. T-stops account for light lost to internal reflections and glass elements. Used primarily in cinema lenses.
Minimum Focus Distance — The closest distance at which a lens can achieve focus. A lens with a shorter minimum focus distance can render small subjects larger in the frame.
Magnification Ratio — The ratio of a subject’s size on the sensor to its actual size. A 1:1 ratio (true macro) means the subject is reproduced at life size on the sensor.
Autofocus
Phase Detection AF — An autofocus system that splits incoming light to measure how out-of-focus the image is and in which direction, allowing the lens to move directly to the correct focus position. Fast and accurate, especially for moving subjects.
Contrast Detection AF — An autofocus system that moves the lens until maximum contrast is detected at the focus point. More accurate than phase detection in static situations but slower, as it must hunt for the contrast peak.
Eye AF / Subject Recognition AF — Autofocus systems that identify and track specific subjects – human eyes, animal eyes, vehicles, aircraft – using on-sensor image processing. Modern implementations maintain lock through significant movement and scene changes.
Continuous AF (AF-C / AI Servo) — An autofocus mode that continuously adjusts focus as a subject moves. Used for sports, wildlife, and any scene with subject motion.
Single AF (AF-S / One-Shot) — An autofocus mode that locks focus on a stationary subject and holds it until the shutter is released. Used for still subjects where precise focus placement matters more than tracking speed.
Sensor and Image Technology
Full Frame — A sensor size equivalent to a 35mm film frame: 36 x 24mm. The reference standard against which other sensor sizes are measured.
APS-C — A sensor format smaller than full frame, approximately 23.5 x 15.6mm (Sony, Nikon) or 22.3 x 14.9mm (Canon). Requires a crop factor of approximately 1.5x (1.6x for Canon).
Micro Four Thirds (MFT) — A sensor format used by OM System and Panasonic, measuring approximately 17.3 x 13mm. Crop factor of 2x.
BSI (Back-Side Illuminated) — A sensor architecture in which the wiring layer is moved behind the photosite, allowing more light to reach each photosite. BSI sensors offer better low-light performance compared to front-illuminated designs of the same size.
Stacked Sensor — A sensor design in which the imaging layer and processing circuitry are manufactured as separate bonded layers. The dedicated processing layer allows dramatically faster readout speeds, reducing rolling shutter and enabling high frame rates.
Rolling Shutter — A distortion artifact caused by the sequential readout of sensor rows rather than simultaneous capture of the entire frame. Fast lateral motion can cause vertical lines to appear skewed. Stacked sensors with fast readout significantly reduce rolling shutter.
RAW — An unprocessed image file containing the raw sensor data before in-camera processing is applied. RAW files preserve maximum dynamic range and color information and allow extensive post-processing with minimal quality loss.
JPEG — A compressed image format that applies in-camera processing and discards much of the original sensor data. Smaller file size than RAW; limited post-processing latitude.
Bit Depth — The number of tonal values available per color channel. An 8-bit file offers 256 values per channel; a 14-bit RAW file offers 16,384 values per channel. Higher bit depth allows more aggressive post-processing without visible banding.
Composition and Light
Rule of Thirds — A compositional guideline dividing the frame into a 3x3 grid and suggesting that subjects and horizon lines be placed along the grid lines or at their intersections rather than centered.
Leading Lines — Compositional elements – roads, fences, rivers, architectural lines – that draw the viewer’s eye through the frame toward the subject or into the depth of the scene.
Negative Space — Empty or uncluttered areas of a frame that provide visual breathing room and isolate or emphasize the subject.
Contre-Jour — Shooting into or against the light source. Produces silhouettes, rim lighting, lens flare, and halo effects depending on exposure and lens characteristics.
Golden Hour — The period shortly after sunrise and before sunset when sunlight is warm in color temperature, low in angle, and soft in quality. Preferred for landscape and portrait photography.
Color Temperature — A measurement in Kelvin (K) describing the warmth or coolness of a light source. Lower values (2700-3200K) are warm and orange; higher values (5500-6500K) are neutral to cool and blue. Daylight is approximately 5500K.
White Balance — A camera setting that compensates for the color temperature of the ambient light to render whites as neutral.
Fill Light / Fill Flash — A secondary light source used to reduce contrast by lifting shadow areas closer to the brightness of the highlights.
File and Output
Megapixel (MP) — One million pixels. Higher megapixel counts allow larger prints and tighter crops but produce larger files and require better lenses to resolve the available detail.
Lossless Compression — File compression that reduces file size without discarding any image data. The original data can be perfectly reconstructed from the compressed file.
Lossy Compression — File compression that discards image data to achieve smaller file sizes. JPEG uses lossy compression; repeated saving of a JPEG progressively degrades quality.
Color Space — A defined range of colors a file can represent. sRGB is the standard for web and consumer use. Adobe RGB covers a wider range, preferred for print workflows.
Dynamic Range (post-processing) — In editing contexts, the latitude available to recover detail in highlights and shadows from a RAW file. Sensors with high dynamic range allow significant exposure corrections without visible degradation.