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Glossary of Photographic Terms and Abbreviations... by Charlie Davis o Aliasing…Low frequency artifacts that appear when signal energy above the Nyquist frequency reaches a digital sensor. This is normally prevented by use of an Anti-Aliasing filter in front of the sensor. o Ambient Light…The light currently illuminating an object or space. See "Available Light". o Anti-Aliasing Filter…An optical filter constructed of a thin birefringent material. The thicker the material, the greater the blurring. See: http://en.wikipedia.org/wiki/Birefringent o AOV…"Angle of View"...see "FOV". o Aperture…The opening through which a lens accepts light. Also called "iris". o APS-C…Generally the size of an APS-C film frame, ie, 25.1 x 16.7 mm, but APS-C sensors vary widely in actual size. o Available Light…The light currently illuminating an object or space. See "Ambient Light". o Bayer Sensor…A sensor that has 4 sets of colored photosites arranged in a 2 x 2 array. Normally the 4 photosites have 1 red, 1 blue, and 2 green filters, but other combinations are also used in a few sensors. Note that these 4 photosites be- come four full-color pixels, even though each is only a single color photosite, by performing Bayer demosaicing (which involves sampling other surrounding photosites). o Bottom-feeder dSLR…Same as "Entry-level dSLR". A term of derision, implying that the owner can't afford a "real" dSLR or is not smart enough to use a "real" dSLR. o Bridge Camera…A camera that has characteristics of cameras with mirrors and cameras w/o mirrors. A hybrid camera. A bridge camera "bridges" the gap between the two primary types of cameras. o CA…See "Chromatic Aberration". o CCD…"Charge Coupled Device"…one of two primary types of sensors, the other being CMOS. o Chimping…on cameras which have no electronic preview of the image through the viewfinder (such as most dSLRs), this refers to looking at the image on the LCD afterward, which requires pulling the camera down from the face and looking down at the back of the camera. This looks similar to one primate grooming another and looking to see if the little black speck being held (after biting it) is dead. It's a VERY degrading description when used by users of cheap P&S cameras to de- scribe the behavior of users of expensive dSLRs! o Chromatic Aberration…(CA) Failure to focus all wavelengths (colors) of light at the same spot. This causes colored borders in high contrast subjects. It's also called "PF", which stands for "Purple Fringe", as CA is often exhibited as a purple border. "Green Fringe", Blue Fringe", and "Yellow Fringe" are also common, but nobody uses "GF", "BF", or "YF". o CMOS…"Complimentary Metal-Oxide Semiconductor"….one of two types of sensors, the other being CCD. o Compact Camera…A camera that is about the size and shape of a deck of cards. o Curvature-of-Field…Some lenses, especially WA ones, focus at similar distances off-axis vs on axis. This causes the image to be slightly OOF at the edges when the subject and image planes are flat. o DC…"Digicam"...any digital camera, but normally a small one. o Depth-of-Field…(DOF)…The range of object distances at which the image appears sharply focused. Highly subjective! Although there are "formulas" to calculate DOF, they are based on empirical statistics. o Diffraction Limited…Reduced resolution of a lens, due to a small aperture. o Diffraction…An effect that produces fringes/rings when light passes through a small hole . o Digicam…A Digital Camera of any sort, but it generally means, a cheap one (ie, dSLRs are not normally referred to as "digicams"). o DR…"Dynamic Range"...the difference between the brightest and dimmest light levels that can be captured. o dSLR…"digital Single Lens Reflex". Also DSLR, D-SLR, and d-SLR. o Entry-level dSLR…The cheapest dSLR that a manufacturer makes, targeted at new users. o ETTR…"Expose to the Right"...the concept that if you watch the right side of the histogram and adjust the exposure until the brightest parts of the image just touch (or come just shy of touching) the right edge, the exposure is "right". o EV…"Exposure Value" describes all combinations of exposure time and f/number that give a specific exposure. 1 EV is defined as a 1 second exposure at f/1. See also "LV". o Exposure…The combination of illumination, exposure time, aperture, and sensor sensitivity used to create a photographic image. Some people prefer to ignore the illumination (but there are instances when the photographer HAS to control the illumination). o FF…See "Full Frame". o FL…See "Focal Length". o Flash…A device to illuminate the scene to be photographed. Most commonly the light is produced from a small quartz (glass) tube filled with a mixture of gasses (mostly Xenon) that, when ionized by an electrical discharge, glow brightly at a color temperature of about 5600 degrees Kelvin, which is the color temperature of noon sunlight. People call these many names; Flash, FlashGun, FlashHead, SpeedLight, SpeedLite, etc...but not FlashLight...it's reserved for something else. o Flat Field…When a lens renders a flat subject as a flat image (on the sensor), it's said to have a "flat field". Many WA lenses don't have a flat field. See also "Curvature-of-field". o F/number…A number that represents the facility of a lens to capture light. Normally described as f/n or f:n (the "n" is the "F/number"). The "F/#"or "F:#" form implies focal length divided by the aperture diameter. See "Aperture" and "F-stop". o Focal Length…(FL)…The distance from the image (on the sensor) to the lens when the lens is focused on an object at infin- ity. Technically, the point on the lens used for this measurement is the "exit pupil". o FOV…"Field of View". The angle subtended by the scene. It can be expressed as the horizontal angle, the vertical angle, or the diagonal angle, but normally the horizontal FOV is the default. Some pedants try to confuse everyone with "Angle of View". AOV and FOV are synonyms. The problem arises because FOV is sometimes stated as "abc ft at xyz yards", like for binoculars. But it is stated as an anglular measure by educated people. o F-stop…A full "F-stop" is defined as a standard aperture value that allows half as much light through as the previous stop and twice as much light as the next stop. The "standard" full "F-stops" are: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc. Many cameras also allow half "F-stops" to be set. They are: 1.2, 1.8, 2.4 , 3.5, 4.8, 6.8, etc. A few cameras even use 1/3-stops. The "definition" of F:1 is that the diameter of the glass opening in the lens is equal to the focal length. o Full-frame…Same size as a 35mm frame, ie, 36mm x 24mm. Yes, there are other "full-frame" sizes, but when this term is used it's referring to the "standard" 35mm still picture frame. o Geometric Distortion…A characteristic of lenses that make straight lines curved. If they bow out, it's called "barrel distortion". If they bow in, it's called "pin-cushion distortion". A WA lens with terrible geometric distortion is labeled a "fish-eye" lens in order to appeal to customers. ;-) o HDR…"High Dynamic Range"...a technique wherein several images w/ different EVs are combined to increase the DR. o ISO…International Standards Organization…they write the rules for measuring all types of things. For cameras, the relevant term is "ISO Sensitivity", a measure of the ability of the sensor to capture photons and the subsequent gain of associated electronics. Be aware that the ISO Standard that governs measuring and specifying digital sensor sensitivity is broad…it allows 5 different ways of performing these sensitivity measurements. These 5 procedures are roughly equivalent, but they can be used by a manufacturer to gain a marketing advantage (with customers who think that bigger parameters mean better products). Independent labs that test camera sensitivity using a single method, find a wide variability! o LCD…"Liquid Crystal Display" The little screen on the back of most digital cameras. It is NOT normally called a "Viewfinder"…it's called an "LCD Screen". o LAS…"Lens Acquisition Syndrome" is a fatal disease that renders the victim broke financially. o LV…"Light Value" refers to a "light level" for either incident or reflected light…a synonym for "EV at ISO 100 sensitivity". o MLU…"Mirror Lock-Up" is a feature of mirror-type dSLRs that eliminates one source of vibration. o MOS…"Metal Oxide Semiconductor". There are two types of MOS…"NMOS" and "PMOS"…both are used in a "CMOS" process. Olympus uses an NMOS sensor, but call it "Live MOS" for marketing reasons. o MTF…"Modulation Transfer Function". Indicates the contrast of a B/W pattern at a given spatial frequency relative to the contrast at low spatial frequencies. It's used to measure and quantify the resolution of a lens. o Normal Lens…A lens that "sees" a view similar to what the human eye sees. In technical terms, it has a horizontal field of view about 40 degrees. With a 35mm film camera, this meant a 50mm lens, but modern, smaller sensor cameras require a shorter focal length. For example, a 35mm lens is often described as a "normal" lens for APS-C sized cameras. For com- pact cameras, the "normal" FL is much smaller yet. o NR…"Noise Reduction". Specifically, it's a computer algorithm that examines an area of an image, decides if there is a specific noise pattern present, and tries to remove that pattern w/o affecting the sharpness of detailed elements in that area. o Nyquist Frequency…Half the sampling frequency of a discrete signal. See http://en.wikipedia.org/wiki/Nyquist_frequency. o OOF…"Out Of Focus". o Perspective Distortion…Making parallel lines appear to merge. Perspective distortion is a characteristic of all lenses. It's NOT a defect! It's caused by a photographer pointing the camera up or down at an object. Sometimes this is unavoidable, as when photographing a tall building. Other times it's controllable by the photographer, as when photographing a room (the camera needs to be ½ way between the floor and the ceiling). o PF…"Purple Fringing" is a form of Chromatic Aberration (CA). I can be caused or exacerbated by the micro-lenses on the face of the sensor. o Photosite…The actual photodiode that generates current proportional to the photon density impinging on it. o Pixel…The smallest complete element in a digital picture. "Pixel" stands for "picture element". o Exposure…The combination of illumination, exposure time, aperture, and sensor sensitivity used to create a photographic pixels can be seen), occasionally to the exclusion of other important image elements (which can be seen by viewing the entire picture). Pixel-peepers are annoying to holistic photographers, artists, and others of the right-brain persuasion. o Pixel Density…A measure of how tightly packed photosites are. Sorta the inverse of photosite area. Some people believe that sensors with large photosites (and thus low pixel densities) have better IQ. Some misguided souls don't. o Point & Shoot…An automatic camera. Also "P&S" and "PnS". A term of derision, implying that the owner is not smart enough to use a "real" camera with manual controls. Point & Shoot is also a life-style decision and a perfectly valid way of taking pictures…with any camera (even a dSLR)! o PP…"Post Processing" with a photo editor. o Prosumer Camera…A small camera with manual controls. Also used to refer to a dSLR that is targeted at beginners. o PS…Photoshop, the granddaddy of photo editors. o Resolution…There are 3 types important to digital imaging. 1. Spatial resolution (ie, line pairs per unit length), 2. Spectral resolution (ie, the ability to distinguish different colors), and 3. Radiometric resolution (ie, the bit depth of intensity represen- tation). Normally, people mean the first one, ie, the ability of a lens/sensor/processor to resolve small spatial details. o Sensor…The piece of processed Silicon, pronounced SIL-i-con, not SIL-e-cone (silicone…not capitalized, is used in breast implants) in a camera that senses images. o SLR…"Single Lens Reflex". A camera with a mirror that reflects the image from the main lens to a viewing screen. That image is then viewed by an optical viewfinder. o SLR-like…Looks like an SLR, but isn't (ie, it doesn't have a mirror). It can sound like an SLR if the designers added the electronic sound of a mirror going flip-flop. o Stitching…The technique of combining several overlapping images to make one larger image. o Super-zoom Camera…A small camera with an 8X (or greater) zoom lens. Also can refer to a zoom lens that has a wide FL range. o Telecentric Lens…A lens that has parallel light rays that hit perpendicular to the sensor. See: http://en.wikipedia.org/wiki/Telecentric_lens. Olympus claims to have "near" telecentric lenses...they are lenses that approximate a "real" telecentric lens...these lenses require large elements, to minimize the angle-of-incidence issues caused by the color mask and/or micro-lens array. A "real" telecentric lens would have its exit pupil infinitely far in front of the lens and would NOT change the size of the image when the lens was focused. These lenses are big and expensive! o TTL…"Through the Lens". Applies both to measuring exposure and computing flash power by looking through the primary lens. o USM…"Un-Sharp Mask". A legacy term from the film photography days. In spite of the strange name, it's an algorithm used (among other things) to sharpen digital photographs. o WA…"Wide Angle"…a lens that captures a big scene. |