Cameras and Photography Explained

Plenty of acronyms crop up in the technical aspects of talking about cameras. Here are some of them that are used on this site, and what they mean (disclosure: I used an AI agent to scan through all my writing on this site to see which acronyms I’ve used and then synopsize their meaning; I then edited that work):

• AA — Anti-Aliasing. Usually refers to the filter in front of the sensor (also called an OLPF, Optical Low-Pass Filter) that slightly blurs detail so that fine patterns don't produce moiré and false color. Many recent cameras omit it to gain perceived acuity.
• ACR — Adobe Camera Raw. Adobe's raw converter, used inside Photoshop and Bridge. It shares its conversion engine with Lightroom.
• ADC — Analog-to-Digital Conversion. In digital cameras, we take an analog charge compiled by the sensor photosite's reaction to the amount of light it is exposed to, and convert it to a digital value (typically referenced as a DN, see below) for recording.
• ADL — Active D-Lighting. Nikon's in-camera tone adjustment. The camera underexposes to protect highlights, then lifts the shadows in the resulting JPEG. Note that any raw file is still affected by the underexposure, but not the shadow boost.
• AF — Autofocus. The camera focuses the lens itself, using either phase detection or contrast detection (or both).
• AF-C — Autofocus–Continuous. Continuous-servo focus: the camera keeps adjusting focus for as long as you hold focus activation via the shutter release or AF-ON button, so it will follow a moving subject.
• AF-ON — Autofocus On. The button on the back of many cameras that activates focus, which lets you separate focusing from the shutter release (a technique called back-button focus).
• AF-S — Autofocus–Single. Single-servo focus: the camera focuses once and locks. Confusingly, Nikon also uses AF-S to designate lenses with a Silent Wave Motor (AF-S NIKKOR).
• AI — Artificial Intelligence. Used loosely by marketing departments. In cameras it usually means subject detection and recognition built with ML (see below), and in software it usually means noise reduction, masking, or upscaling done via a pre-trained model.
• AI — Automatic Indexing. Nikon's 1977 change to the F-mount, where a ridge on the aperture ring tells the camera the lens's maximum aperture and current setting for metering. Pre-AI lenses can damage most Post-AI bodies if mounted.
• AI-S — Automatic Indexing–Shutter. Nikon's 1981 update to AI lenses, which made the aperture travel linear so that the camera could control it in Program and Shutter-priority modes.
• APS-C — Advanced Photo System type-C. The name comes from the 1996 APS film format's "Classic” frame size. Used today for sensors of about 23.5 x 15.6mm (Canon's are slightly smaller), which produce a 1.5x (1.6x for Canon) crop compared to full frame. Nikon calls this format DX, Fujifilm and Sony just call it APS-C.
• ASIC — Application-Specific Integrated Circuit. A custom chip designed to do particular jobs. Camera image processors (BIONZ, DIGIC, EXPEED) are ASICs.
• BCN — BCN (Business Computer News). A Japanese company that tracks retail sales at Japanese stores, and whose weekly and annual rankings are often quoted (and over-interpreted) as an indication of market share.
• BIF — Birds in Flight. One of the most demanding tests of a camera's autofocus system.
• BIONZ — Sony image processor. Not actually an acronym, but the name Sony gives its camera image processing chips (see ASIC).
• BSI — Back-Side Illuminated. Early image sensors were made with the electronics on top, and gaps where light passed down into the chip. BSI flipped the chip over so that light went directly into the light sensing area, putting the electronics on the bottom. This allows for more light to get to the light sensing area.
• CA — Chromatic Aberration. Color fringing caused by a lens not bringing all wavelengths of light to the same point. Lateral CA (color edges toward the frame corners) is easily corrected in software; longitudinal CA (color fringes in front of and behind the focus point) is much harder to remove.
• CCD — Charge-Coupled Device. The original type of image sensor is essentially an array of linked capacitors, and data is passed from one to another until it reaches processing areas outside the light sensing area of the chip. They have high color fidelity and low noise levels, but are prone to blooming and other issues.
• CDS — Correlation Double Sampling. Reduces noise propogation and increases data acuracy on an image sensor by taking two samples, one just after the charge capture area is reset, another after the image data has been collected.
• CES — Consumer Electronics Show. A large electronics trade show held in Las Vegas every January.
• CF — CompactFlash. CompactFlash was the dominant card format in professional DSLRs for many years. 
• CFe — CFexpress. CFexpress is a PCIe-based storage card, in Type A, B, and C sizes. Type B has the same physical size as XQD and is used by Canon, Nikon, and Panasonic. Type A is about the same size as an SD card and is used by Sony.
• CIPA — Camera & Imaging Products Association. The Japanese camera industry trade group. CIPA publishes monthly shipment numbers for the industry, and sets standards such as the battery life (photos per charge) and stabilization (how much motion can be removed) tests.
• CLS — Creative Lighting System. Nikon's flash system, which currently includes i-TTL metering and wireless control of remote flashes.
• CMOS — Complementary Metal-Oxide-Semiconductor. In image sensors, this differs from CCD in that every photosite (pixel) is individually addressable and can have its own electronics. This allows for more sophisticated control of individual photosite data.
• CP+ — Camera & Photo Imaging Show. Japan's main camera trade show, held in Yokohama, typically either in February or March.
• CPS — Canon Professional Services. Canon's support program for working professionals.
• CPU — Central Processing Unit. The general-purpose processor in a computer (or camera). Nikon also uses "CPU lens" to mean a lens with electronic contacts.
• DCIM — Digital Camera Images. The folder name that the camera file system standard (DCF) requires on a memory card. Your images are stored in numbered folders inside it.
• DFD — Depth From Defocus. Panasonic's contrast-detect autofocus method, which uses known blur profiles of the lens to estimate how far, and in which direction, to drive focus.
• DG — Sigma lens designation. Sigma's marking for lenses designed to cover full frame (DC lenses cover only APS-C, DN lenses are designed for mirrorless).
• DIGIC — Digital Imaging Core. Canon's name for its camera image processors (see ASIC).
• DN — Digital Number. The actual value for a photosite reported to the camera's image processing (or raw saving) by the sensor and its related electronics.
• DNG — Digital Negative. Adobe's openly documented raw file format. A few cameras record it directly, and other raw files can be converted to it.
• DOF — Depth of Field. The range of distances in front of and behind the focus point that appears acceptably sharp. Determined by aperture, focal length, focus distance, and the size at which you view the image.
• DR — Dynamic Range. Refers to the range of light that can be recorded from darkest (black) to brightest (white) values. Be careful in comparing DR numbers, as there are multiple types of DR. For example, Engineering DR is typically measured from a Signal to Noise ratio of 1:1 up to the saturation point of the photosite (FWC, see below). Usable, or Photographic, DR generally uses a Signal to Noise ratio of 20:1 or thereabouts, as when signal and noise are equal, there’s not recognizable information.
• DSLR — Digital Single Lens Reflex. A digital camera that uses a mirror to show the image through the lens in an optical viewfinder (see SLR).
• DSNU — Dark Signal Non-Uniformity. Refers to noise that is created within the light detecting mechanism (Photo Diode) when the sensor is not exposed to light. 
• DX — Nikon’s APS-C format. Nikon's name for its APS-C sensor size (about 23.5 x 15.6mm), and also for lenses designed to cover only that size. Produces a 1.5x crop compared to FX.
• ED — Extra-low Dispersion. Glass that bends different wavelengths of light more equally than regular optical glass, used to reduce chromatic aberration (CA). Other makers use their own names (UD, LD, SLD, etc.).
• EF — Electro-Focus. Canon's fully electronic lens mount for its EOS SLRs, introduced in 1987.
• EF-S — Electro-Focus–Short back focus. Canon's lenses for its APS-C DSLRs (introduced in 2003). They only mount on APS-C bodies.
• EFCS — Electronic Front-Curtain Shutter. The sensor begins the exposure electronically and the camera’s mechanical shutter rear curtain ends it. This reduces vibration (shutter shock), though it can alter out-of-focus highlights at very fast shutter speeds.
• ETTR — Expose To The Right. The practice of setting exposure so that the histogram is pushed as far to the right as possible without clipping highlights, to maximize the data recorded and minimize noise.
• EV — Exposure Value. A single number that represents a combination of aperture and shutter speed. A change of 1 EV is one stop: either a halfing or doubling of the light.
• EVF — Electronic Viewfinder. A small display viewed through an eyepiece that shows the image coming from the sensor.
• EVIL — Electronic Viewfinder Interchangeable Lens. An early name for what we now usually call mirrorless cameras.
• EXIF — Exchangeable Image File Format. The standard for the capture data (camera, lens, exposure, date, etc.) that the camera embeds in an image file.
• EXPEED — Nikon image processor. Not actually an acronym, but the name Nikon gives its camera image processing chips (see ASIC).
• FE — Sony full-frame E-mount lens. Sony's designation for E-mount lenses that cover full frame (plain E lenses cover only APS-C).
• FF — Full Frame. A sensor of approximately 36 x 24mm, the same size as a 35mm film frame.
• FPN — Fixed Pattern Noise. Refers to noise due to random variations in the underlying silicon. Such noise happens at very low levels in current image sensors, but is definitely present. See also PRNU.
• FSI — Front-Side Illuminated. Refers to the original image sensor design, where electronics lived on the top of the chip and light was allowed through to the light catching portion via “holes” (apertures) in the top level.
• FTZ — F-to-Z. Nikon's adapter that lets F-mount lenses be used on Z-mount cameras.
• FWC — Full Well Capacity. The maximum charge that can be stored in response to light by a photosite, typically stated in electrons. 
• FX — Nikon full-frame format. Nikon's name for its full frame (36 x 24mm) sensor size, and for lenses that cover it.
• GAS — Gear Acquisition Syndrome. The urge to buy new equipment in the belief that newer is better and it will improve your photos.
• GFX — Fujifilm medium format. Not an acronym, but the name of Fujifilm's mirrorless system using a 44 x 33mm sensor.
• GN — Guide Number. A measure of flash power. Distance to subject multiplied by aperture equals the GN, at a stated ISO (typically 100). Check whether the GN is using feet or meters, as the distance units in the GN = distance * aperture calculation needs to have matching units to give correct answers.
• GPS — Global Positioning System. Satellite positioning, used to record the location where a photo was taken. This term is now more generic, as it is sometimes used to also refer to other navigation systems, such as NavIC (India), GLONASS (Russia), BeiDou (China), Galileo (Europe), and QZSS (Japan). Not all these systems work globally, but the device providing “GPS information” may be getting that via cellular towers or other systems than the US-created GPS. The proper term for generic positioning should be GNSS (Global Navigation Satellite System).
• GPU — Graphics Processing Unit. The graphics processor in a computer. Raw converters and AI-based tools rely heavily on it for speed.
• HDMI — High-Definition Multimedia Interface. The video and audio connector used to send a camera's output to an external monitor or recorder.
• HDR — High Dynamic Range. This term has multiple variations. Originally, it typically meant multiple images taken and later merged to form a new one with more dynamic range (originated with the NRO [National Reconnaissance Organization], I believe). More recently, television standards have a specific definition for HDR that also involves display requirements. 
• HEIF — High Efficiency Image File Format. A newer alternative to JPEG that uses HEVC (H.265) compression. It can store 10-bit data in a file smaller than an 8-bit JPEG.
• HLG — Hybrid Log-Gamma. An HDR standard developed by the BBC and NHK. HLG video and stills display reasonably on standard displays and fully on HDR ones.
• HSM — Hyper Sonic Motor. Sigma's ultrasonic focus motor.
• IBC — International Broadcasting Convention. The broadcast and video trade show held in Amsterdam each September; the European counterpart to NAB.
• IBIS — In-Body Image Stabilization. Stabilization done by moving the sensor, so it works with any lens.
• ICC — International Color Consortium. The group that defines color profiles. An ICC profile describes how a particular device (monitor, printer, paper) reproduces color, so that color can be managed between devices.
• ILC — Interchangeable Lens Camera. Any camera (DSLR or mirrorless) that accepts different lenses.
• IPTC — International Press Telecommunications Council. The standard for caption, credit, copyright, and keyword information embedded in an image file.
• IR — Infrared. Light beyond red that we can't see. Sensors are sensitive to it, so cameras have an IR-blocking filter; IR photography requires removing or bypassing that filter. On this site, IR is also sometimes short for the Imaging Resource web site.
• IS — Image Stabilization. Canon's name for stabilization (in lenses, and as IBIS in bodies).
• ISO — International Organization for Standardization. The standards body whose ISO 12232 standard defines camera sensitivity ratings. On a digital camera, the ISO setting determines how much the sensor's output is amplified and brightened; the sensor itself doesn't become more sensitive.
• JPEG (also JPG) — Joint Photographic Experts Group. The group that created the standard, and the common 8-bit compressed image format. JPEG compression is lossy: data is discarded to make the file smaller.
• LCD — Liquid Crystal Display. The type of display used for most camera rear screens.
• LR — Lightroom. Adobe's photo cataloging and raw conversion program (see ACR).
• LUT — Look-Up Table. A table that maps input color and tone values to output values. Commonly used in video to convert Log footage to a normal look.
• ML — Machine Learning. Training software on large numbers of examples so that it can recognize things (subjects, noise, edges) on its own. The basis for most of what is called AI in cameras.
• MSRP — Manufacturer's Suggested Retail Price. The list price set by the maker. Actual selling prices can be lower, particularly during promotions.
• MTF — Modulation Transfer Function. A measurement of how well an optical system preserves contrast across different spatial frequencies. Be careful about comparing MTF claims. Some are theoretical, some are measured, some use 10/30 for the tangential/saggital evaluation, some use 10/40 or other numbers. Finally, there are at least three methods by which MTF is measured in practice, with slanted-edge and line-spread being common among those reporting MTF numbers on photography Web sites.
• NAB — National Association of Broadcasters. The trade organization's annual show in Las Vegas (NAB Show) each April is the primary video and broadcast trade show in the US.
• NAND — Not AND. A type of logic gate, and the name for the flash memory used in memory cards and SSDs.
• ND — Neutral Density. A filter that reduces the amount of light reaching the sensor without changing its color, allowing longer shutter speeds or wider apertures.
• NEF — Nikon Electronic Format. Nikon's raw file format.
• NPS — Nikon Professional Services. Nikon's support program for working professionals.
• NPU — Neural Processing Unit. A processor (or part of one) designed for the calculations ML and AI requires. Increasingly found in camera processors, phones, and computers.
• NR — Noise Reduction. Processing to reduce noise in an image. Cameras typically offer High ISO NR, and Long Exposure NR (which takes a second, dark exposure and subtracts it).
• NRW — Nikon raw (Coolpix). The raw file format used by Nikon's Coolpix compact cameras. Similar to NEF, but with some different structure.
• OIS — Optical Image Stabilization. Stabilization done by moving a lens element. Panasonic's (and phone makers') term.
• OLED — Organic Light-Emitting Diode. A display technology where each pixel produces its own light. Most current EVFs use small OLED panels.
• OS — Optical Stabilizer. Sigma's lens stabilization marketing monicker. Of course, OS also means Operating System.
• OSS — Optical SteadyShot. The marketing name for Sony's lens stabilization.
• PC-E — Perspective Control–Electronic. Nikon's tilt/shift lenses, with an electronically controlled aperture (yes, there were older PC lenses). 
• PD — Power Delivery. The USB standard (USB PD) for supplying higher power over a USB-C cable, used to charge or run cameras. In autofocus discussions, PD can also mean Phase Detection when used to talk about autofocus, or Photo Diode when used to talk about image sensors.
• PF — Phase Fresnel. Nikon's diffractive lens element, which makes telephoto lenses much shorter and lighter.
• PJ — Photojournalism. Also photojournalist.
• PMA — Photo Marketing Association. The photo retail trade group, whose annual show was for many years the US's main camera trade show. It was eventually folded into CES.
• PRNU — Photo Response Non-Uniformity. The formal name for random fixed pattern noise. 
• QE — Quantum Efficiency. A value expressed in percentage that reflects how many of the photons actually present were converted into charge within a sensor.
• RAID — Redundant Array of Independent Disks. Multiple drives combined to act as one, for speed, protection against a drive failing, or both. Note that RAID isn't a backup.
• RF — Canon mirrorless mount. Canon's full-frame mirrorless lens mount, introduced in 2018 (Canon has never formally said what RF stands for). RF also means Radio Frequency, as in radio-controlled flash.
• RF-S — Canon APS-C mirrorless lens. Canon's RF-mount lenses designed to cover only APS-C.
• RGB — Red, Green, Blue. The three primary colors that digital images are built from. Most sensors put a red, green, or blue filter over each photosite (the Bayer pattern), with the missing values for each pixel filled in by demosaicing.
• SD — Secure Digital. The most common memory card format (SDHC and SDXC are its higher capacity versions). For high-speed SD, see UHS.
• SLR — Single Lens Reflex. A camera that uses a mirror and prism to show the image through the taking lens in an optical viewfinder.
• SNR — Signal to Noise Ratio. How strong a signal (information) is to noise, often expressed in dB (decibels). I generally say the SNR has to be at least 20:1 in order to get meaningful data that can fully distinguished from noise, but others have different standards.
• SPAD — Single-Photon Avalanche Diode. A sensor design where each photosite can detect a single photon, by triggering an avalanche of charge. So far it's used in niche markets (such as Canon's low-light security cameras).
• SSD — Solid-State Drive. Storage using flash memory (see NAND) instead of spinning disks.
• TC — Teleconverter. An optic placed between lens and camera that increases focal length (typically 1.4x or 2x) at the cost of light (one or two stops) and some image quality.
• TIFF — Tagged Image File Format. A flexible image format that can store 8- or 16-bit data, uncompressed or with lossless compression. Common for edited masters and for printing. But also note that TIFF forms the basis for virtually every raw file format, where the raw file follows the tagged structure, it just has different definitions for some of the data in the structure (and may add to the structure).
• TTL — Through The Lens. Metering (of ambient light or flash) done with light that has passed through the taking lens.
• UHS (I and II) — Ultra High Speed. The bus speed classes of SD cards. UHS-I tops out at 104MB/s, UHS-II at 312MB/s and uses a second row of contacts, which the camera must also support.
• USB (A, B, C) — Universal Serial Bus. The connection standard for computers and devices. A, B (including Mini-B and Micro-B), and C are connector shapes. The connector doesn't tell you the speed, which is set by the USB version.
• UV — Ultraviolet. Light beyond violet that we can't see. UV filters were needed with film; on digital cameras they're mostly used as lens protection.
• VC — Vibration Compensation. Tamron's marketing name for lens stabilization.
• VR — Vibration Reduction. Nikon's name for image stabilization (in lenses, and as IBIS in bodies; the two combined are called SynchroVR).
• WB — White Balance. Adjusting the image so that neutral colors appear neutral under the light that was present.
• WPPI — Wedding and Portrait Photographers International. The name for an event photographer trade group, as well as its annual convention and trade show in Las Vegas.
• XF — Fujifilm X-mount lens. Fujifilm's main line of X-mount lenses (the XC lenses are the budget line).
• XMP — Extensible Metadata Platform. Adobe's standard for storing metadata, either inside a file or in a "sidecar" .xmp file next to a raw file.
• XQD — XQD card. Not officially an acronym. A PCIe-based card format defined by Nikon and Sony, which was eventually succeeded by CFexpress Type B (the same size and shape).