Glossary of Photography Terms
Digital photography is developing rapidly and providing imaging professionals, enthusiasts and amateurs continuously with new features and capabilities in their equipment. Yet, this innovation in cameras, lenses and accessories often coincides with the creation of new terminology. The resulting plethora of phrases, acronyms or number-letter combinations can be daunting, and the listing of definitions below is intended to cut through the jargon and try to explain the various photography terms.
There are, of course, many imaging terms needing explanation and many photography concepts meriting discussion. The following list is just a modest selection of hopefully useful definitions. Over time, the listing will be continuously expanded, though. So please bookmark the page and check back regularly.
- 1080i is a video format that records at 1920x1080 pixels and has an aspect ratio of 16:9. The "i" in the term stands for interlaced, which means that odd and even vertical lines of a video are only updated with every second frame. A first pass refreshes 1920x540 pixels for the even scan line fields, and the second pass 1920x540 for the odd scan line fields. Interlacing reduces the data transfer needs compared with 1080p, and diminishes perceived flickering.
- 1080p is a video format that records at 1920 lines of horizontal resolution and 1080 lines of vertical resolution, and thus has an aspect ratio of 16:9. It is alternatively called Full HD. The "p" in the term stands for progressive, which means that videos are displayed line after line. The output looks sharper and more defined than 1080i, particularly during scenes with a lot of fast motion.
4K is a video technology that offers a horizontal resolution of about 4,000 pixels. Several 4K formats exist, notably 4K-CDI and 4K-UHD. The individual image frame contains about 8 million pixels and is about four times as detailed as a Full HD frame. The additional detail translates into sharper images and gives the videographer more control in post-production to resize, crop and stabilize the footage. On the downside, 4K videos are heavier in terms of file size and require a high performance data-processing flow.
Video resolutions Designation Alternative name Resolution 8K 7680 x 4320 4K DCI Cinema 4K 4096 x 2160 4K UHD Ultra HD 3840 x 2160 2K 2048 x 1080 1080p Full HD 1920 x 1080 720p High Definition 1280 x 720
- 4K DCI:
- 4K DCI is a high resolution video image format as defined by the Digital Cinema Initiatives (DCI). It is alternatively called Cinema 4K. 4K DCI features 4096 pixels on the horizontal side and has often a 17:9 aspect ratio, thus 2160 vertical pixels. 4K DCI is frequently used as the image recording format on professional video cameras that shoot footage for cinema projection.
- 4K UHD:
- 4K UHD ("Ultra High Definition") is a video recording format found on many digital still and video cameras. It features a 16:9 aspect ratio with 3820 x 2160 pixels that corresponds to the resolution of Ultra-HD TV sets. 4K UHD has exactly twice the resolution of Full HD in both the vertical and the horizontal dimension.
- 720p is a video format that has a resolution of 1280x720 pixels and a 16:9 aspect ratio. It is often also called High Definition video. The "p" stands for progressive, which means that videos are displayed line after line. 720p footage contains less than half the number of pixels of Full HD.
- Aberration refers the inability of a lens to reproduce a subject in an accurate and sharp image. There are several different forms of lens aberrations, notably spherical aberration, chromatic aberration, astigmatism, field curvature, coma, and distortion. The detrimental impact of these faults can be reduced by compound lens constructions, or by stopping down the aperture.
- Accessory shoe:
- An accessory shoe is a metal or plastic fitting on the top of the camera. It is designed to support external devices such as flash guns, viewfinders, or microphones. Early "cold shoes" were merely physical attachment points, while "hot shoes" provide electronic contacts to operate the mounted flash gun or other accessory.
- Anti-aliasing filter:
- see Low Pass Filter.
- An APO-lens is an optic that has been apochromatically corrected and, thus, delivers superior performance in terms of sharpness and color accuracy. By using special optical designs and low-dispersion glass (often fluorite glass), manufacturers try to ensure that blue, green, and red light rays fall into a single plane of focus. In non-APO lens designs, the different wavelengths of light cause the color rays to focus at slightly different distances from the lens, which can create an impression of blurredness when examined closely. The Leica APO-Telyt-R 3.4/180mm of 1975 was the first APO-lens that was widely commercialized, forming the starting point for Leica's APO-Telyt line of (super-)teles.
- Aspect Ratio:
- The Aspect Ratio is the proportional relationship of image width to image height. It is generally written as two numbers separated by a colon. In still camera photography, the most common aspect ratios are 3:2 and 4:3. In videography, an aspect ratio of 16:9 is used for high definition recording. Many digital cameras provide the option of switching between alternative aspect ratios.
- Astigmatism is a form of lens aberration that causes blur towards the edges and corners of an image. It results from sagittal (radial) lines being focused differently from tangential lines. For example, the spokes of a wheel (sagittal lines) might be well focused, while the rims of the wheel (tangential lines) are blurred, or vice versa. The extent of astigmatism of a lens can be deduced from the degree of divergence between its sagittal and tangential MTF curves. Stopping down the aperture reduces the detrimental impact of astigmatism to some extent.
- Bokeh is an important imaging characteristic of a photographic lens. The term is an English transliteration of the Japanese word for "blur." It refers to out-of-focus areas around the highlights within an image, where it appears as little circles. Bokeh that is smooth, round-shaped, and blends seemlessly into darker shadow areas is generally assessed as being desirable. Lens abberations and the shape of the aperture blades influence the quality of the bokeh, with blades that form a perfect circle delivering a superior rendering. The nature of the bokeh is particularly central to the photographic expression whenever the depth of field is narrow, such as in macro, portrait and tele-photography.
- Chromatic aberration:
- Chromatic aberration is a form of lens aberration that manifests itself as Color Fringing along boundaries that separate dark and bright parts of the image. It occurs because individual lens elements have different refractive indices for different wavelengths of light, so that a lens fails to focus all colors to the same convergence point. Chromatic aberration can be reduced by using a compound lens, in which the individual lens elements are based on materials with differing dispersion characteristics. By combining two lens elements in an achromatic lens, two wavelength can be corrected, and by using an assembly or three lens elements in an apochromatic or apo-lens, all three wavelength (red, blue, and green) get focused on the same point.
- Cinema 4K:
- see 4K DCI.
- Cine lens
- Cine lenses are optimized for use on professional motion picture cameras. Cine lenses differ in several important characteristics from still-centered camera lenses, even though they might share the same lens mount. On the outside, they are solid, all metal constructions. They feature external gears for use with a follow focus or a motorized zoom control, and have an aperture control ring that makes it possible to steplessly adjust the aperture while recording. Cine lenses also have a detailed, calibrated distance scale and a large focus throw that facilitates finetuning of the focus. On the inside, cine lenses are designed to control for "breathing", so that focus adjustment do not yield (small) changes in the angle of view (as often seen in still lenses). Moreover, cine zooms will be para-focal optics, which means that they maintain focus throughout the zoom range (while still zooms will generally not). Because of the need to avoid image shift during focusing or zooming, cine lenses require complex mechanical designs and tight manufacturing tolerances. The demands in terms of optical quality and consistency are generally also greater for cine lenses. This need for consistency motivates the measurement of the speed of cine lenses in terms of t-stops, which not only takes the aperture opening (the f-stop) into account, but reflects the amount of light that is actually transmitted to the sensor.
- Coma is a form of lens aberration that results in off-axis light points appearing as having a tail, like a comet. Coma is particularly detrimental for astro- or night photography. Comatic aberration can be minimized through compound lens design, but few regular photographic lenses are well corrected for this type of optical flaw. In order to reduce the adverse impacts of coma, it is often necessary to choose small apertures, even in low light situations.
- DNG – Digital NeGative:
- DNG is an open, lossless raw image format, introduced in 2004 by Adobe. The DNG specification was conceived and developed with the intent of providing a lossless file format for long-term storage and archiving of digital photographs. Most camera manufacturers have their own proprietary raw image file formats, even though some (Leica, Pentax, Ricoh, Samsung) have embraced DNG. Yet, Adobe provides the free Adobe DNG Converter that can translate raw files from most digital cameras into DNG format. Also, Adobe's photo manipulation software, notably Photoshop and Lightroom, can similarly generate DNG files. Working in DNG rather than camera-specific raw has the advantage of interoperability among different camera systems, broad software support, and reduced risk of obsoleteness.
- Distortion is a form of lens aberration that results in straight lines being projected as being bowed outwards (barrel distortion) or inwards (pincushion distortion). Distortion is particularly noticeable in many zoom lenses, with barrel distortion appearing at wide-angle focal lengths and pincushion distortion at the telephoto end. The detrimental effects of distortion can often be corrected through image processing software.
- EXIF (EXchangeable Image File):
- EXIF refers to the standard that specifies the storage of metadata within digital image files. Such metadata comprises information on the camera, date, focal length, aperture, shutter speed and other shooting characteristics. These recordings can be very helpful for organizing photographs, performing searches and retrieving vital information about the way a particular photograph was captured. Many image gallery programs recognize EXIF data and optionally display them alongside the images. Alternatively, if EXIF data is not needed and small image file size is a priority, such as for web use, the metadata can be stripped from the image.
- Field Curvature:
- Field Curvature is a form of lens aberration that results in uneven focus across the image. It is caused by curved optical elements projecting an image on a flat sensor surface. The detrimental impacts of field curvature on image quality can be reduced by stopping the lens down.
- Focus Breathing:
- Focus breathing refers to changes in the focal length and angle of view of a lens when the focus distance is altered. This phenomenon is caused by some elements within a lens moving during focus action, while others are not, thereby possibly changing the optical characteristics of the lens. Cine lenses are corrected for focus breathing, while most still lenses are not. For example, the Nikon 70-200mm f/2.8 VR II is reported to have a maximum effective focal length of only 135mm at mimimum distance (1.4m). – For a more detailed explanation of focus breathing, see the nice discussion of the issue by Bob Atkins.
- Focus Peaking:
- Focus peaking is a digital imaging tool that indicates areas of sharp focus while the photographer or videographer uses manual focusing. The tool highlights image areas that are in focus through a colored outline on the display. Camera users can select the color and the intensity with which the contours are displayed through corresponding menu settings. Focus peaking makes it possible to quickly focus manual lenses (or when working in manual focus mode). The tool is particularly appreciated by videographers in situation when they are trying to capture moving subjects and do not want to rely on the autofocus system of the camera to track the targets consistently.
- FTM – Full-time manual:
- Full-time manual (or manual focus override) is a feature that makes it possible to focus an autofocus lens manually without switching from AF to MF mode. FTM thus enables the photographer to adjust and finetune focus instantly by simply turning the focus ring. This is particularly useful when AF is slow or hunting because of low light or lack of contrast in the subject, when there is not have enough time to change the focus point, or when shooting macro photos with very shallow depth of field.
- Full HD (High Definition):
- see 1080p.
- GIF (Graphic Interface Format):
- GIF is a lossless format for image files. It supports up to 8 bits per pixel, and can reference up to 256 colors. The limited color palette means that GIF files are well suited for simpler images, like graphics or logos, but less appropriate for reproducing color photographs. The GIF format is widely used for internet display, even though the PNG format has gradually been replacing it, due to better compression and more flexible handling of transparency. One of the remaining advantages of GIF over PNG, however, is that GIF supports not only still, but also animated images. Animated GIF files consist of a number of frames that are displayed in succession and can resemble short, looping videos.
- High Definition (HD):
- see 720p.
- A hotshoe is a metal bracket on top of a camera that makes it possible to attach accessories, such as an external flash. In contrast to a coldshoe (or "accessory shoe"), a hotshoe has electrical contacts that make it possible to exchange information between the camera and the accessory. For example, the camera might pass data to the flash gun on when and for how long the flash light should be fired. The dimensions of the hotshoe are standardized, but the electrical contacts are generally manufacturer-specific, so that there are incompatibilities across brands.
- Hyperfocal Point:
- The hyperfocal point is the point beyond which all objects are considered acceptably sharp, when a lens is focused at infinity. Knowing the hyperfocal distance is notably useful in landscape photography. In particular, focusing a camera at the hyperfocal point ensures the greatest possible depth of field from half this distance all the way to infinity. To achieve this level of depth of field, a photographer will first focus on the most distant object within the scene, then manually adjust the focusing distance as close as possible while still retaining an acceptably sharp background. Alternatively, specialized calculators, such as the one at cambridgeincolour, can be used to determine the optimal focusing point.
- IBIS – In-Body Image Stabilization:
- IBIS refers to a system to reduce the adverse impacts of camera shake that is build into the camera body. It works by moving the sensor in such a way as to counteract the motion of the camera. This sensor shift is achieved by actuators that respond to information from movement-detecting gyroscopes. IBIS functions with all lenses that are attached to the camera. Also, it can correct motion across all five axis of movement, while lens-based optical image stabilization systems can not counteract movement around the lens axis ("roll"). However, IBIS is not as effective as optical image stabilization for long tele-photo lenses, because the distance the sensor needs to shift to offset the camera movement becomes too large at long focal lengths.
- JCII (Japan Camera Industry Institute) sticker:
- A gold-coloured, oval JCII sticker accompanied all photographic equipment exported by Japan from the 1950s to the mid-1980s. It generally carried a second acronym – JMDC, which stands for Japan Machinery Design Center. The JCII sticker certified that the exported equipment was functional and not simply a copy of a foreign (German) product. The sticker reflected an effort by the Japanese authorities to combat the poor reputation that some of its manufacturers had earned abroad after infringing patents and copying items made in other countries. It did not mean that the individual item had undergone any testing and did not guarantee any superior quality. Thus, there is little intrinsic value in these stickers apart from the re-assurance that the product is not simply a cheap knock-off. However, the removal of the "Passed" sticker from the camera or lens can sometimes leave permanent marks or discoloration on the surface to which it was attached.
- JPEG (Joint Photographic Experts Group):
- JPEG is a commonly used file format for image compression in digital imaging devices. The acronym stands for Joint Photographic Experts Group, the institution that created the standard. JPEG is a "lossy" compression format, with the amount of image quality loss increasing with the degree of compression. The compression algorithm works well on photographs of realistic scenes with smooth transitions of tone and color, and file size reductions of 50 percent can be realized without significant perceptible loss in image quality. At higher compression rates, JPEG files start to show compression artifacts, such as blockiness and pixelation.
- Keystone correction:
- Keystone correction or keystoning is a feature that makes it possible to eliminate converging lines in images that are the result of capturing (or projecting) an object from an angle. Trapezoidal distortion is particularly common in architectural photography, such as when taking a shot from the bottom of a tall building. Keystone correction can be achieved by using a tilt-shift lens, by activating respective in-camera functions (for example, in selected Olympus models), or by making adjustments through software. The corrections done in-camera and through image processing software will lead to a cropped image and result in some loss of resolution.
- Low-Pass Filter:
- Optical low-pass filters (also called anti-aliasing filters) are integral parts of most digital sensor assemblies, where they help to suppress the adverse effects of moiré and false colour. They do this by blocking infrared light and slightly blurring fine detail at the photosite level before it reaches the sensor. As a side-effect, however, the sharpness of the image capture is reduced. Since maximum sharpness is desirable for some shooting situations, notably in landscape photography, some high resolution cameras (the Nikon D800E was the first DSLR) have become available that do not contain a low pass filter. These cameras can provide more detailed images, but might occasionally show some moiré.
- Macro rail:
- A macro rail or focusing rail is a type of tripod head that makes it possible for the photographer to move the camera forwards and backwards in very precise steps. It is used in macro-photography where depth-of-field is very shallow. In these circumstances, it is convenient to focus the camera lens such that the desired level of magnification is achieved, while using the macro-rail to move the entire camera-lens-system until the subject is in sharp focus. Good macro-rails, such as the pictured Benro MP-80, are solidly build, have knobs for fine adjustment along the x and y-axis and are able to lock the rail positions, so that the setting does not slip under the weight of the camera system. Also, a quick release mechanism, such as Arca-Swiss, provides additional handling convenience.
- Manual focus override:
- see Full-time manual.
- Minox is a Germany-based manufacturer of cameras, best known for its miniature models. The company has been producing a series of very compact cameras since the 1930s that utilize 8x11mm film. The small size of the camera in combination with the macro-focusing ability of its lens made the Minox popular with intelligence agencies – in real life, as well as in movie depictions. For example, James Bond was shown using a Minox A III in "On Her Majesty's Secret Service" of 1969 to photograph maps that showed the target areas for biological contamination by the "Angels of Death". The company subsequently also produced 35mm compact cameras and more recently digital cameras, but remains best known for its spy camera vintage.
- Mirrorless interchangeable lens camera (MILC):
- As their name suggests, mirrorless cameras do not have a flip-up mirror that diverts the light that enters through the lens to a prism and then the optical viewfinder of a DSLR. Instead, the light goes straight to the sensor, and the latter then generates an image on the rear LCD or in the electronic viewfinder. Because a MILC does not have a mirror and prism assembly, it can be smaller and lighter, and have a shorter flange to focal plane distance. The latter is advantageous for lens design and, in particular, makes it possible to produce more compact optical systems. On the downside, the imaging sensor and associated processing engine in mirrorless cameras have multiple tasks to complete, including focus acquisition, while DSLR have a separate, dedicated autofocus module. This heavy burden on information processing and display can mean that the live view feed in MILC might be slightly delayed and lag behind the action during burst shooting. Another challenge for mirrorless cameras is battery life, as the display on the LCD or electronic viewfinder requires additional electrical power that a DSLR with an optical viewfinder does not have to dispense.
- Moiré patterns are artifacts that are caused when a fine structure in the subject matches the photosite pattern of the imaging chip. The term is derived from the French name of a silk fabric that shows a rippled appearance. Moiré occurs whenever the detail of the subject doesn't fall precisely over one sensor photosite or another, so that the imaging engine has to estimate the correct value. This can result in errors that create a secondary, artificial pattern in luminance or color. Moiré is specific to digital imaging. In analog photography, the photo sensitive grains in film are arranged in a random, organic way and there is no interpolation across non-sensitive spaces. Scenes with repetitive high-frequency detail (such as fabric, straight hair, or architecture) that exceeds the sensor resolution are particularly prone to moiré. The artifacts take the form of waves or rings of color and tone, or turn parallel lines into maze-like squiggles. Camera producers try to prevent the artifacts from occuring by placing low-pass filters in front of the sensor. Also, cameras with very high resolution sensors are generally less likely to be affected by moiré, as the individual pixels are relatively close to each other and there is less nxeleed to interpolate across empty spaces. If the artifacts nevertheless show up in images, post-processing software, such as Adobe Lightroom or Capture One, can be used to reduce the adverse effects.
- Noise reduction (NR):
- Noise reduction is the process of removing random variations in brightness or color from an image. Noise gives photos a grainy appearance and can have a major impact on image quality. It is the result of background electrical currents interfering with the main light signal that the sensor receives. The smaller the photosites on a sensor are and the weaker the light is that hits the sensor, the noisier an image will tend to be. In this context, noise reduction is the process of determining whether the observed pixel values constitute noise or real photographic detail, and average out the former while attempting to preserve the latter. Noise reduction can be done in the camera or during post-processing.
- OIS (Optical Image Stabilization):
- Optical image stabilization is a mechanism that is implemented inside a camera lens to reduce jitter from handshake and, thus, to obtain sharp images even for slow shutter speeds. OIS works by having gyroscopic sensors detect lens movement, and then to use electromagnets to move a floating lens element orthogonally to the optical axis. OIS is frequently incorporated in tele-photo lenses, where it is most effective in reducing handshake-induced image deterioration. Some manufacturers (e.g. Olympus, Panasonic) are combining OIS with in-body image stabilization to further enhance the extent of shake reduction.
- OVF (Optical Viewfinder):
- Optical viewfinders are systems of mirrors and prisms that represent a view of a scene and thus make it possible for the photographer to accurately frame a picture. On DSLRs, the OVF shows what the lens will project on the sensor in combination with a number of exposure parameters. Optical viewfinders provide better dynamic range than electronic viewfinders, offer an instantaneous view of the action, and do not require any battery power. Conversely, they can not display as much information as EVFs, cover often less than 100% of the field of view, and can be hard to use in dim light. OVFs on DSLRs also require a flip-up mirror mechanism, which adds to the bulk and weight of the camera.
- Pixel pitch:
- Pixel pitch is an indicator of pixel size on an imaging sensor. It refers to the physical distance from one pixel to the next, and is measured in microns (µm). While pixel pitch corresponds to pixel size, the actual area that captures light may be slightly smaller, due to wiring and structural elements taking up some space. Everything else equal, a larger pixel pitch suggest a better light gathering capacity of the sensor and higher image quality, in particular under difficult lighting conditions.
- Program Mode:
- Program mode is one of the exposure modes on photographic cameras. It is indicated by a "P" on the mode dial. In Program mode, the camera will select values for the aperture and shutter speed that generate a correctly exposed picture. The camera does this by taking a meter reading from the scene and then uses internal algorithms to select a suitable shutter speed and aperture. The choice of exposure parameters will thereby take the focal length and speed of the attached lens into account. Other camera settings, such as ISO, white balance, or exposure compensation remain under the control of the photographer. Program mode is a convenient way to take quick shots without having to worry about exposure settings. On the other hand, program mode delivers appropriate exposure values only for "average" photographic situations. The algorithm does not know whether the particular scene would benefit, for example, from a large aperture value to achieve shallow depth of field or a short shutter speed to freeze subject motion. Many cameras therefore feature a possibility for the photographer to shift the aperture and shutter speed combination in order to control depth of field or avoid motion blur.
- QTVR (QuickTime Virtual Reality):
- QTVR is an image file format that allows the creation and viewing of photo-panoramas. It is based on Apple's QuickTime Player. QTVR panoramas are images that surround the viewer. They are generated by software-assembling several photos taken with a wide-angle lens and a spherical tripod head that makes it possible to rotate the camera around the nodal point of the lens. Two types of QTVR scenes exist: cylindrical panoramas that consist of a horizontal row of photographs wrapped around the viewer, and spherical panoramas that also include shots of the top and the bottom. The viewer uses his computer mouse or keyboard for navigation within the scenes, so as to change the perspective within the surround-panorama.
- RAW Files:
- A raw image file contains unprocessed data from the image sensor. It is not directly usable as an image, but has to undergo a process of conversion and transformation to be turned into a viewable output. Most camera manufacturers maintain their idiosyncratic raw image formats, but these can be converted into the standard DNG format for archiving or editing purposes. Working with raw files makes it possible for the photographer to precisely control the image generation process, and to finetune the conversion of the raw sensor information into a viewable image, whereas the image processor that is build into the camera is optimized for the average or typical shooting situation. Parameters that can be adjusted with raw image data include white balance, colour saturation, contrast, sharpness, and noise reduction. All changes to raw image files are non-destructive, as only the metadata that controls the rendering is changed, while the original sensor-derived information remains untouched. Disadvantages of working with raw image files include the larger file size of uncompressed RAW compared with compressed JPEG-files and the additional step(s) needed to develop a viewable image.
- Shutter Shock:
- Shutter shock refers to image blur caused by shutter vibration in mirrorless cameras. At certain shutter speeds – typically 1/20s to 1/200s – the movement of the shutter causes the camera body to vibrate, which leads to image degradation. The problem can be avoided by using the electronic shutter (if available).
- Soligor was a USA and Germany-based photographic equipment supplier that was best known for its third party lens offerings at competitive prices. Soligor was originally a brand name of Allied Impex Corporation, a trading company that had been based on the US East Coast since 1938. AIC sold cameras, lenses, and accessories under the Soligor name that it did not manufacture itself, but rather commissioned from Japan-based producers, such as Komine, Sun Optical, and Tokina. In 1968, Soligor was transformed into a subsidiary company of AIC in Germany that became a major photographic equipment supplier until it filed for bankruptcy in 2011. Soligor leaves a legacy of some remarkable innovations, including the creation of the T4 interchangeable mount that made it possible to use the same lens on different camera brands, and several well regarded lenses, such as the Soligor 5.6/400mm or Soligor 6.3/400mm telephoto primes.
- Spherical aberration:
- Spherical aberration is a form of lens aberration that causes image blur, particularly when using large apertures. It is the result of light rays towards the edge of a lens element being focused onto a different point than those going through the center of the lens. Spherical aberration can be reduced by using compound lens construction and, in particular, by including aspherical lens elements in the optical formula.
- Stop-down metering:
- Stop-down metering is a light metering method in which the photographers selects the working aperture before determining the exposure parameters. Stop-down metering is mainly used with legacy manual lenses that do not have any aperture coupling with the camera body. In this case, the photographer focuses with the lens wide open, as more light makes it easier to acquire proper focus. Once the focus has been set, the lens is stopped down to the desired aperture in order to take the meter reading and adjust the shutter speed and ISO for correct exposure. Stop-down metering is different from Aperture Priority, because with the latter metering takes place at open aperture and the lens is stopped down via electronic or mechanical coupling between the lens and the camera only at the very moment when the shutter button is being pressed and opens up again immediately afterwards.
- Telecentric Lens:
- A telecentric lens is an optic that produces an image from light rays that run parallel to the optical axis and hit the sensor orthogonally. Telecentric lenses offer high contrast and sharpness from corner to corner, but require relatively large rear lens elements. With traditional film lens designs, the peripheral light rays hit the sensor at an angle and not all light might be received by the light-sensitive pixels (unless micro-lenses to gather the light are placed on top of each photosite), leading to light and image quality fall-off towards the borders and corners of the image. Many of the optics specifically produced for digital system cameras make use of tele-centric design principles.
- Ultra High Definition (UHD):
- see 4K UHD.
- USM – Ultra-Sonic Motor:
- USM refers to a fast and quiet autofocus motor used in DSLR lenses. The USM motor is driven by ultrasonic oscillation. It provides faster and quieter autofocus than a conventional micro-motor.
- UV Filter:
- An UV or ultraviolet filter is mounted in front of the lens to reduce the amount of ultraviolet light that strikes the film or sensor. UV filters are transparent to visible light, but block out shorter ultraviolet wavelengths. In film photography, they were used to increase contrast and avoid a blueish color cast from appearing in scenes with strong exposure to UV light (such as mountain landscapes). Since digital sensors contrary to film are insensitive to UV light, the filters do not provide any image quality benefit. Indeed, by adding another layer of glass, they increase the risk of flare occurring. Nevertheless, many digital photographers continue to use UV filters as a means of protection of the front element.
- Vignetting (sometimes called light fall-off) refers to the progressive darkening of image corners in comparison to the center. Vignetting is a characteristic of many lenses. Because of shading from the lens barrel and intrinsic lens characteristics, peripheral light rays are partially blocked so that the light that reaches the image plane towards the borders and extreme corners is less intense and the colors appear less saturated. Vignetting is most pronounced at large apertures. Once stopped down, the lens barrel is less of a hindrance for peripheral light to enter through the (small) aperture, and the image plane becomes more uniformly exposed. While modern photographic lenses are designed to avoid light fall-off, vignetting can be used for artistic purposes, so as to enhance the visual impact of the center of the image or to create a vintage look. Such artificial vignetting can be achieved with special filters mounted in front of the lens, or via post-processing in image editing software.
- White Balance:
- White balance is an electronic process that adjusts for different temperatures of lighting in order to make white objects appear white in images. Different light sources emit light of different relative warmth or coolness. Candlelight or a tungsten bulb produce a warm light that contains a lot of long, orange wavelength, while shade or a heavily overcast sky gives a cold light with plenty of short, blue wavelength. While the human eye is very good at judging what is white under different light sources, digital cameras can struggle to do the same. In addition to an Automatic White Balance setting, digital cameras therefore have a number of presets from which a photographer can choose, such as Tungsten, Fluorescent, Daylight, Flash, Cloudy, and Shade. Moreover, the Customs White Balance setting in many cameras makes it possible for the photographer to take a picture of a white object (such as a sheet of paper) under a certain lighting and thus tell the camera what should be rendered as white in subsequent images under that lighting environment.
- xD-Picture Card:
- xD-Picture cards are a type of flash memory cards. The format was promoted by Olympus and Fujifilm and used in some of their digital cameras. The acronym xD stands for eXtreme Digital. Four different categories of xD-cards have been made available with different capacity and speed specifications: standard, M, M+, and H. The latter provide the best performance. xD cards are physically smaller than Secure Digital and Memory Stick cards, but fell behind competing formats in terms of transfer speed and maximum storage capacity. Even though the format was never officially discontinued, Olympus ceased to support xD cards in new cameras since the release of its PEN E-P1 in 2009.
- Yashica was a Japan-based manufacturer of film cameras and lenses. The company was established in 1949, acquired by Kyocera in 1983, and ceased production in 2005. In the early 1970s, Yashica engaged in a cooperation with Carl Zeiss to produce the professional-level Contax RTS SLR-camera with lenses based on the common Contax-Yashica mount. Yashica-branded SLR cameras offered many features derived from the premium Contax models at a lower price point. However, Yashica never made the technological transition to autofocus-SLRs and, as a result, lost market share and commercial viability.
- Zoom lens:
- A zoom lens is an optic for which the focal length and, thus, the angle of view can be varied. Zoom lenses offer the convenience of switching to a different focal length without having to change lenses. Parafocal zooms maintain focus when the focal length is changed, while varifocal zooms do not. Most zooms used for still photography are varifocal. Moreover, many zoom lenses have a telescopic design and extend in physical length when the photographer changes to a longer focal length, although internally zooming designs are also available and are often preferred by enthusiast and professional photographers. Zoom lenses are more complex in their optical structure than prime lenses and tend to be bigger, heavier, and more expensive. Also, they generally do not provide the same fast aperture openings as primes and tend to be less sharp, although the image quality differences have become small with the latest optical advancements.
A glossary is hardly ever complete, and there are always terms, abbreviations and expressions that could usefully be added with their definitions and explanations. Some vendor-specific terms are described on separate pages on this site. You can browse a Micro Four Thirds glossary that mainly covers terms coined by Olympus and Panasonic for their camera systems, as well as a set of explanations for Leica terminology. Hopefully these resources are helpful in cutting through the jargon.