| Active Matrix TFT: A common type of LCD used in laptops, cameras, and LCD projection panels that were produced in the late 1980s to early 1990s. A typical active matrix TFT display is a single panel of LCD glass that controls all three primary colours. TFT displays are noted for their quick response time and their ability to display full motion video and animations without image ghosting. |
| Active Matrix: Term used to describe LCD Displays, which have micro-transistors that "open" and "close" each pixel. |
| Amplifier A device which increases or boosts the level of an input signal by increasing its amplitude. |
| Analog: An analog video signal uses a variable voltage to equal the pixel value, as opposed to digital pulses. |
| Anamorphic: Process that horizontally condenses (squeezes) a 16:9 image into a 4:3 space, preserving 25 percent more vertical resolution than letterboxing into the 4:3 space. For the signal to appear with correct geometry, the display must either horizontally expand or vertically squish the image. |
| ANSI Contrast: Contrast is the ratio between black and white. The larger the contrast ratio, the greater the ability of a projector to show subtle colour details and tolerate extraneous room light. There are two methods used by the projection industry: 1) Full On/Off contrast measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. 2) ANSI contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio. When comparing the contrast ratio of projectors, make sure you are comparing the same type of contrast. Full On/Of contrast will always be a larger number than ANSI contrast for the same projector. |
| ANSI Lumens: A standard for measuring light output used for comparing projectors. Unfortunately, there are enough variables that the eye will often disagree radically with the ANSI rating. At best, ANSI lumens do fairly well comparing "apples" to "apples". If however one projector uses halogen lamps and another metal-halide, the halogen projector will seem noticeable dimmer even if the two units rate the same. Other variables, including type of LCD technology (active matrix TFT, Poly-Si, passive), type of overall technology (LCD vs DLP vs CRT), and contrast ratios all affect the end result. |
| Aperture: In television optics, it is the effective diameter of the lens that controls the amount of light reaching the photoconductive or photo emitting image pickup sensor. |
| Aspect Ratio: The ratio of image width to image height. Common motion-picture ratios are 1.85:1 and 2.35:1. Television screens are usually 1.33:1 (also known as 4:3), which is similar to the Academy standard for films in the '50s. HDTV is 1.78:1, or 16:9. When widescreen movies (films with aspect ratios wider than 1.33:1) are displayed on 1.33:1 televisions, the image must be letterboxed, anamorphically squeezed, or panned-and-scanned to fit the screen. |
| AVI Short for Audio Video Interleave, the file format for Microsoft's Video for Windows standard. |
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Back Room Projector: A projector with a "long-throw" lens designed to be used from the far back of the room, often in a projection booth, balcony, or back of an auditorium. Many typical projectors have third party lenses available for "long-throw" applications. |
| Backlit: Refers to a remote control, or on projector control panel, that has buttons and controls that are illuminated. This is a major asset when using the projector in a darkened or semi-darkened room. Many projectors have backlit remote controls, while the number of projectors with backlit control panels is much smaller. As projectors have gotten brighter, room lights tend to stay on, so while nice, having backlit controls is no longer important to many users. |
| Bandwidth: In audio, the range of frequencies a device operates within. In video, the range of frequencies passed from the input to the output. |
| Black Level: Light level of the darker portions of a video image. A black level control sets the light level of the darkest portion of the video signal to match that of the display's black level capability. Black is, of course, the absence of light. Many displays, however, have as much difficulty shutting off the light in the black portions of an image as they do creating light in the brighter portions. CRT-based displays usually have better black levels than DLP, plasma, and LCD, which rank, generally, in that order. |
| BRI (Basic Rate Interface): The most common kind of ISDN interface available in the US. BRI contains two B channels, each with 64 kbps capacity, and a single D channel (16 kbps) which is used for signaling and call progress messages. |
| Brightness: For video, the overall light level of the entire image. A brightness control makes an image brighter; however, when it is combined with a contrast, or white level control, the brightness control is best used to define the black level of the image (see Black Level). For audio, something referred to as bright has too much treble or high-frequency sound. |
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CANDLEPOWER: A term used for the luminous intensity of a light source. The intensity in any one direction from the standard candle is one candela. |
| Chromaticity: The colour quality of light that is defined by the wavelength (hue) and saturation. Chromaticity defines all the qualities of colour except its brightness. |
| Chrominance: The chrominance of a picture refers to its color saturation and hue. |
| Codec: Mathematical algorithms used to compress large data signals into small spaces with minimal perceived loss of information. |
| Color Temperature: A method of measuring the \"whiteness\" of a light source. Metal halide lamps have very high temperatures compared to halogen or incandescent lights. The chromaticity of an ideal \"black body\" when it is heated to a specific temperature in Kelvin (K). It is the measure of the color of light, not actual temperature. |
| Composite Video Signal: The combined picture signal, including vertical and horizontal blanking and synchronizing signals. |
| Composite Video: A signal that contains both chrominance and luminance on the same 75-ohm cable. Used in nearly all consumer video devices. Chrominance is carried in a 3.58-mHz sideband and filtered out by the TV's notch or comb filter. Poor filtering can result in dot crawl, hanging dots, or other image artifacts. |
| Contrast Ratio: The ratio between white and black. The larger the contrast ratio the greater the ability of a projector to show subtle color details and tolerate extraneous room light. There are two methods used by the projection industry: 1) Full On/Off contrast measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. 2) ANSI contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio. When comparing the contrast ratio of projectors make sure you are comparing the same type of contrast. Full On/Off contrast will always be a larger number than ANSI contrast for the same projector. |
| Contrast: Relative difference between the brightest and darkest parts of an image. A contrast control adjusts the peak white level of a display device. |
| CRT(Cathode Ray Tube) A CRT projector is a video projector that uses a small, high-brightness CRT (or picture tube) as the image generating element. The image is then focused and enlarged onto a screen using a lens kept in front of the CRT face. Most modern CRT projectors are colour and have three separate CRTs (instead of a single, colour CRT), and their own lenses to achieve colour images. The red, green and blue portions of the incoming video signal are processed and sent to the respective CRTs whose images are focused by their lenses to achieve the overall picture on the screen. |
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Decibel dB or decibel is a measure of the power ratio of two signals, provided they are measured across a common impedance. |
| DIRECT PROJECTORS Projectors, which project an image directly onto the work or drawing surface (i.e. drawing table or wall). The image can then be traced or re-drawn with a variety of mediums. |
DLP, Digital Light Processing: Digital Light Processing (DLP) is a technology used in projectors and video projectors. DLP ([1]) was originally developed at Texas Instruments, in 1987 by Dr. Larry Hornbeck.
Texas Instruments remains the primary manufacturer of DLP technology, which is used by many licensees who market products based on T.I.\'s chipsets. The Fraunhofer Institute of Dresden, Germany, also manufactures Digital Light Processors, termed Spatial Light Modulators, for use in specialized applications. For example, Micronic Laser Systems of Sweden utilizes Fraunhofer\'s SLMs to generate deep-ultraviolet imaging in its Sigma line of silicon mask lithography writers.
The single-chip DLP™ is the most portable of all our players. Currently you can find single-chip DLP™ projectors that weigh less than 2 pounds. Digital Light Processing is the product of the great minds at Texas Instruments. |
| DLP™ (three-chip) Digital Light Processing
The three-chip DLP™ has the best looking images of all the players. The three-chip system is much like the single-chip DLP™ only better. |
| Dolby Digital: An encoding system that digitally compresses up to 5.1 discrete channels of audio (left front, centre, right front, left surround, right surround, and LFE) into a single bitstream, which can be recorded onto a DVD, HDTV broadcast, or other form of digital media. When RF-modulated, it was included on some laser discs, which requires an RF-demodulator before the signal can be decoded. Five channels are full-range; the .1 channel is a band-limited LFE track. A Dolby Digital processor (found in most new receivers, preamps, and some DVD players) can decode this signal back into the 5.1 separate channels. Most films since 1992's Batman Returns have been recorded in a 5.1 digital format, though a number of films before that had 6-channel analogue tracks that have been remastered into 5.1. |
| DVI: Digital Visual Interface. Connection standard developed by Intel for connecting computers to digital monitors such as flat panels and DLP projectors. A consumer electronics version, not necessarily compatible with the PC version, is used as a connection standard for HDTV tuners and displays. Transmits an uncompressed digital signal to the display. The latter version uses HDCP copy protection to prevent unauthorized copying. See also HDMI. |
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Fader: The control on a projector that allows you to control the balance of sound between the projectors internal speakers and the external speakers (PA, powered speakers). Only a couple of projectors offer this convenient feature. |
| Focal Length: The distance from the surface of a lens to its focal point. |
| Focus: The focus on a projector defines the minimum and maximum projection distances. |
| Frame Rate: Number of images per second displayed in a video stream. Approximately 24 frames per second (fps) is considered full-motion video. |
| FXL: The most popular halogen lamp in use in lower cost projectors and overhead projectors. The lamps typically last about 40 hours, however for convenience, most projectors using halogen lamps carry a spare, and a quick method of going to the backup lamp. Metal halide lamps and UHP lamps are used in most of the medium and higher priced, more powerful portables. |
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Halogen Lamps: Used in most low- and medium-priced projectors, these lamps last about 40 hours, with consistent output throughout their lives. Although halogens look very white compared to a normal incandescent lamp, they are not as white as metal halide units. Most projectors using halogen lamps carry a spare lamp inside. |
| HDTV: High-Definition Television. There is no official definition, but usually refers to a 16:9 image with twice the horizontal and vertical resolution of existing system, accompanied by 5.1 channels of Dolby Digital audio. Other definitions include an image with 720 progressive or 1080 interlaced active (top to bottom) scan lines. 1280:720p and 1920:1080i are typically accepted as high-definition scan rates. |
High-Definition television (HDTV) : High-Definition television (HDTV) means broadcast of television signals with a higher resolution than traditional formats (NTSC, SECAM, PAL) allow. Except for early analog formats in Europe and Japan, HDTV is broadcasted digitally, and therefore its introduction sometimes coincides with the introduction of digital television (DTV).
HDTV is defined as 1080 active lines, 16 x 9 aspect ratio in ITU-R BT.709. However, in the ATSC broadcast standard used in the United States and other countries, any ATSC resolution with 720 or more active lines is considered HDTV. |
| Hz: Hertz or cycles per second. Something that repeats a cycle once each second moves at a rate of 1 Hz. |
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Infrared Remote: The traditional remote control, it transmits infrared like a television remote. Typical range is limited to 30-35-ft. Infrared requires line of site or a bounce off of a hard surface. The presenter must pay attention to where the remote is pointed. Some projectors have an IR sensor in both the front and rear of the projector, which can help a bit. When working at or near the maximum distance pointing right at the receiver is necessary. Remember 'line of sight'. A person's head directly between your remote and the projector may be enough to render it unusable. |
| Inverse Square Law The law that states that in the absence of reflective surfaces, sound pressure (or light) falls off at a rate inverse to the square of the distance from its source. In other words, every time you double your distance from the sound source, the sound pressure level is reduced by a factor of 4, or 12 dB. |
| ISDN (Integrated Services Digital Network): Completely digital telephone/telecommunications network which carries voice, data, and video over existing telephone network infrastructure. It is designed to provide a single interface for hooking up a phone, fax machine, PC, etc. See Also: How to Order ISDN |
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Keystone Correction: Keystone correction makes a projected image rectangular. This can be accomplished by positioning the projector to be perpendicular to the screen. Since it is not always possible, most projectors are equipped with keystone correction that allows the image to be keystone corrected (made rectangular) by adjusting optics, making mechanical adjustments, or applying digital correction to the image. Keystone correction can be one- or two-dimensional and manual or automatic, depending on the projector and the manufacturer. |
| Keystone: A form of video image distortion in which the top of the picture is wider than the bottom, or the left is taller than the right, or vice versa. The image is shaped like a trapezoid rather than a rectangle. The type of distortion created when the projector is not positioned perpendicular to the receiving plane (table or wall). Identified by having one side of the projected image larger than the opposite side (trapezoidal). Always measure all sides of your image to insure accuracy. |
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LCD: An LCD projector is a device utilized for displaying video images or data. They are the modern equivalent to the slide projector and overhead projector used in the past.
LCD (liquid crystal display) projectors usually contain three separate LCD glass panels, one each for the red, green, and blue components of the video signal. Light from a halogen lamp, which outputs an ideal color temperature and a broad spectrum of color is split by a prism into the three component colors. As light passes through the LCD panels, individual pixels can be opened to allow light to pass, or closed to block the light, as if each little pixel were fitted with a Venetian blind. This activity modulates the light and produces the image that is projected onto the screen.
With a lens that \"projects\" the image on any flat surface and does not require large \"furniture\" (like a big TV would), LCD projectors tend to be smaller and much more portable than older systems. The best image quality can be accomplished with a blank white or grey surface to project on, and for this reason dedicated projection screens are often used.
LCD projection technology is the current leader of the pack, having captured the majority of the market share of all projectors sold. Most LCD projectors have three panels. |
| Long Throw Lens: A lens designed for projection from the back of a room, or rather the back of a long room. Long throw lenses would be used a projection booth in the back of a theater, etc. A typical long throw lens might have to be 50 to 100 FT back to project a 10FT diagonal image. |
| LUCIGRAPH (LUCI): A popular name for an indirect-type of projector. Often used to identify all types of artist projectors. |
| Luminance: It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m2). |
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Maximum Resolution: Maximum Resolution refers to the highest resolution that a given display device can support. If the Maximum Resolution exceeds the Native Resolution, , the image is usually scaled to match or approximate the Native Resolution of the projector. Some display devices allow pan and scan where rather than scaling the image, the display devices allows you to use the native resolution of the display to view portions of the higher resolution image. Scaling reduces the image resolution and produces some artifacts in the image that are more apparent when viewing text than graphics or video. |
| Metal halide: Metal halide light bulbs give off a much brighter image and last longer than halogen. High-end, and some medium projectors now use metal halide bulbs. |
| Multiplex: Multiplex allows you to split an image into several panels on a single screen. |
| Multiplexing: The condensing of many signals into a few or one signal that still represents all of them. An LCD panel performs the de-multiplex function. It takes video signals that contain whole frames of video data and displays them as individual signals on each pixel. |
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Native Resolution: Native Resolution is the number of physical pixels in a display device. For example, an XGA display has a native resolution of 1024 physical pixels of resolution horizontally and 768 pixels vertically or 786,432 total pixels. |
| NTSC: National Television Standards Committee. Government-directed committee that established the U.S. color TV standard in 1953. Also known, sarcastically, as Never Twice the Same Color or Never The Same Color due to the inherent difficulty in achieving proper color calibration. |
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OEM: Original Equipment Manufacturer. A company that gathers components from other manufacturers and sells under their own name. An OEM version of a product is supported by the seller, not the actual manufacturer. |
| OHP: The common abbreviation for overhead projector. |
| Opaque projectors A general classification of projectors, which project images from any solid or opaque copy such as photos or drawings. Opaque projectors require a darkened or totally dark room for best results. |
| Overhead Projector: A device consisting of a light source, a transmissive or reflective platform, and a focusable lens assembly. An OHP is designed to project images from tranparencies or LCD projection panels onto a screen. |
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PA Public Address system. A sound reinforcement system enabling live performances to be heard by the audience. |
| PAL: A European and international broadcast standard for video and broadcasting; higher resolution than NTSC. |
| Passive Matrix LCD: The original LCDs, these are controlled by a single processing system, for the whole screen, unlike active and poly-si, which have discrete circuits for each "pixel." This results in a panel with terrible color dynamics and contrast (typically 15:1). They are also incredibly slow: On passive laptop computers, the cursor (or anything else) moving on the screen, goes invisible until you stop moving it (submarining) Only one or two projectors use any type of passive matrix display. |
| PBX (Private Branch Exchange): Small version of the phone company's larger central switching office. A PBX is a private telephone switch. It is connected to groups of lines from one or more central offices and to all of the telephones at the location served by the PBX. |
| Pixel: A pixel is a small dot that represents a single element of a display. |
| Plasma: Flat-panel display technology that ignites small pockets of gas to light phosphors. |
| Projector: A projector is a device that integrates a light source, optics system, electronics and display(s) for the purpose of projecting an image from a computer or video device onto a wall or screen for large image viewing. There are hundreds of products available in the market and they are differentiated by their resolution, performance and features. These devices attach to a computer or video device, as you would connect a monitor. |
| Pulse Code Modulation: (PCM) Pulse Code Modulation: (PCM) a way to convert sound or analog information to binary information (0s and 1s) by taking samples of the sound and record the resulting number as binary information. Used on all CDs, DVD-Audio, and just about every other digital audio format. It can sometimes be found on DVD-Video. |
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QXGA: QXGA is the resolution of 2048 x 1536 pixels. |
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Rainbow Effect The DLP "Rainbow Effect"
This visual artifact is best described as brief flashes of perceived red, blue, and green "shadows" observed most often when the projected content features bright/white objects on a mostly dark/black background (the scrolling end credits of many movies being a common example). Some people perceive these rainbow artifacts all of the time, while others say they only see them when they let their eyes pan across the image. Yet others do not notice the artifact at all. |
| RCA Jacks: Receptacles for coaxial cables carrying line-level audio signals. Also called phono-type connectors. |
| Rear Screen Projector: Using an opaque screen, the projector is placed behind the screen, invisible to the audience. It projects onto the screen and the audience sees it on the other side. Good rear projection screens actually produce brighter images than some standard screens. So as not to waste space behind the screen, ideally a projector with a short throw lens is used. Since the projector can be placed even with the middle of the screen, without blocking anyone's view, keystoning is not a problem. Some mid-room projectors have available third-party short throw lenses. Since the image is projected through the screen, the image must be reversed. |
| Refresh Rate: The speed at which a display updates its picture given in Hz. |
| RGB: Red, Green, Blue. Can refer to an unprocessed video signal or the colour points of a display device. Together these three colours make up every colour seen on a display device. |
| RJ11, RJ45, or RJ48 Different types of jacks,can be used for an ISDN line. The RJ11 is the most common in the world and is most often used for analog phones, modems, and fax machines. RJ48 and RJ45 are essentially the same, as they both have the same 8-pin configuration. An RJ11 jack can fit into an RJ45/RJ48 connector, however, an RJ45/RJ48 jack cannot fit into an RJ11 connector. |
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S-VHS: Super VHS. Enhancement to regular VHS that offers improved luminance resolution. (400 lines or so.) |
| S-Video: A video transmission standard that uses a 4-pin mini-DIN connector to send video information on two signal wires called luminance (brightness, Y) and chrominance (color, C). S-Video is also referred to as Y/C. A composite signal, typically found coming out of an RCA jack on the back of most VCRs has the Y and C information combined into one signal. The advantage of having luminance and chrominance separated is that a comb filter is not needed inside the video projector to separate the composite signal into the luminance and chrominance signals. A comb filter can reduce the sharpness of your video image. |
| Screen Door Effect : The Screen Door Effect or FPN (Fixed Pattern Noise) is a visual artifact of the projection technology use in digital projectors, where the fine lines separating the projector's pixels become visible in the projected image. This results in an image that appears as if viewed through a screen door. It can appear as a grid like structure or as a hexagonal structure. |
| SECAM: A French and international broadcast standard for video and broadcasting; higher resolution than NTSC. |
| Short throw lens: A short throw lens is designed to project the largest possible image from a short distance. |
| Single-chip projectors In a projector with a single DMD chip, colors are produced by placing a color wheel between the lamp and the DMD where it is reflected out through the optics. The color wheel is usually divided into four sectors: the primary colors: red, green, and blue, and an additional clear section to boost brightness. Since the clear sector reduces color saturation, in some models it may be effectively disabled, and in others it is omitted altogether. |
| Skew: A signal distortion where one part of a signal arrives at a different time than another and causes color fringes to the sides of an object. |
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sRGB: Standard Red, Green, and Blue, and is a standard for rendering color evenly across a variety of platforms. |
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Subwoofer: A speaker designed to reproduce very low bass frequencies, usually those below about 80 Hz. |
| Surround The surround refers to the flexible ring encircling the edge of the woofer cone — it connects the cone to the speaker basket. It must be pliable enough to let the woofer travel freely, yet strong enough to guide and control cone movement. (The further the cone can travel, the stronger the bass.) Surrounds are usually made of cloth, foam, or rubber. Rubber tends to last the longest. |
| SVGA: SVGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An SVGA display has 800 horizontal pixels and 600 vertical pixels giving a total display resolution of 480,000 individual pixels that are used to compose the image delivered by a projector. |
| SXGA: SXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An SXGA display has 1,280 horizontal pixels and 1,024 vertical pixels giving a total display resolution of 1,310,720 individual pixels that are used to compose the image delivered by a projector. |
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TFT: Thin Film Transistor. A type of LCD display where each pixel is controlled by one to four transistors. TFT screens are sometimes called active matrix LCDs. |
| Three-chip projectors: A three-chip DLP projector uses a prism to split light from the lamp, and each primary color of light is then routed to its own DMD chip, then recombined and routed out through the lens. Single-chip DLP systems are capable of displaying 16.7 million colors, whereas three-chip DLP systems can display up to 35 trillion colors. |
| Transparency projector: Includes all models of projectors, which project transparencies only. Generally will not project slides without accessory attachments. Excellent for use in normal room light and where large images are desired. |
| Tungsten halogen lamp A type of lamp, which contains the elements halogen gas and tungsten sealed in high-pressure envelope. Produces a high intensity light throughout its life. |
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UXGA: UXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A UXGA display has 1,600 horizontal pixels and 1,200 vertical pixels giving a total display resolution of 1,920,000 individual pixels that are used to compose the image delivered by a projector. |
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VCR: Video Cassette Recorder. |
| VGA: VGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A VGA display has 640 horizontal pixels and 480 vertical pixels giving a total display resolution of 307,200 individual pixels that are used to compose the image delivered by a projector. |
| VHS: Vertical Helical Scan (or as JCV calls it, "Video Home System"). Widely used method of recording audio and video electrical signals onto magnetic tape. |
| Video Capture: Process of converting analog video to digital video. |
Video projector: A video projector takes a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other inconsistencies through manual settings. Video projectors are widely used for conference room presentations, classroom training, and home theatre applications.
Video projectors may also be built into cabinets which use a rear projection screen to form a single unified display device, now popular for "home theater" applications. |
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Wi-Fi: Wi-Fi is Wireless Fidelity and is based on the IEEE 802.11 specifications for wireless local area networks (WLAN) developed by a working group of the Institute of Electrical and Electronics Engineers (IEEE). There are four specifications in the family: 802.11, 802.11a, 802.11b, and 802.11g. All four uses the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing. |
| WMA: Windows Media Audio. Similar to MP3 but considered a more efficient compressor allowing for smaller file sizes for a given quality. |
| Woofer The woofer, a speaker's largest cone, reproduces bass and lower midrange notes. To operate efficiently, a cone should be made of material that is stiff, yet lightweight. Cones made of aluminum, synthetic film (like polypropylene), poly mixed with other materials (like mica), or treated paper provide excellent sound, and stand up to the heat, cold, and moisture that car speakers face on a daily basis. |
| WXGA: WXGA defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A WXGA display has 1,280 to 1,366 horizontal pixels and 720 to 768 vertical pixels, respectively, that are used to compose the image delivered by the projector. |
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XGA: XGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An XGA display has 1,020 horizontal pixels and 768 vertical pixels giving a total display resolution of 783,360 individual pixels that are used to compose the image delivered by a projector. |
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Zoom Lens Ratio: The ratio between the smallest and largest image a lens can project from a fixed distance. |
| Zoom Lens: A lens with a variable focal length providing the ability to adjust the size of the image on a screen by adjusting the zoom lens, instead of having to move the projector closer or further. |
