| 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 noticeably 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), contrast ratios, etc. all effect the end result. |
|
Aspect
ratio:
The most popular aspect ratio is 4:3 (4 by 3). Early
television and computer video formats are in a 4:3 aspect
ratio, which means that the width of the image is 4/3
times the height.
Examples: A 15 inch monitor is 12 inches wide
by 9 inches high (9 x 4/3 = 12). A resolution of 640x480
is a 4:3 format (480 x 4/3 = 640). Other formats are
5:4 used by the 1280x1024 SXGA resolution, 16:9 is used
by HDTV, and 3:2 for 35mm slides. |
|
| Brightness:
The attribute of visual perception in accordance with
which an area appears to emit more or less light. (Luminance
is the recommended name for the photo-electric quantity
which has also been called brightness.) |
|
|
| Colour
Dynamics:
"The whitest whites, reddest reds, etc." High
colour dynamics are a result of dynamic range/contrast
ratio's. When we describe a unit as having excellent
colour dynamics, the practical description might be
"rich colours, excellent definition, high contrast". |
|
| Component
Video:
Component Video is a method of delivering quality video
(RGB) in a format that contains all the components of
the original image. These components are referred to
as luma and chroma and are defined as Y'Pb'Pr' for analogue
component and Y'Cb'Cr' for digital component. Component
video is available on some DVD players and projectors. |
|
| Composite
Video Signal: The combined picture signal,
including vertical and horizontal blanking and synchronizing
signals. |
|
Contrast
Ratio:
The ratio between white and black. 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/Off contrast will always be a larger number than
ANSI contrast for the same projector. |
|
|
| dB:
dB or decibel is a measure of the power ratio of two
signals. In system use, a measure of the voltage ratio
of two signals provided they are measured across a common
impedance. |
|
Diagonal
Screen: A method of measuring the size of
a screen or a projected image. It measures from one
corner to the opposite corner. A 9FT high, 12FT wide,
screen has a diagonal of 15FT. Throughout this document
we assume that the diagonal dimensions are for the traditional
4:3 ratio of a computer image as per the example above.
Some screens are square, others particularly wide for
35mm slides 3:2 ratio. As such even if the screen is
12x12, we would rate it 15FT diagonal since that would
be the diagonal of the usable area.
OK, how about this! Remember high school? Here's your
old geometry lesson. X-squared times Y-squared equals
Z-squared. 3ft by 4ft screen = 3 squared (9), + 4 squared
(16), equals 25 (5 squared) a 5 ft diagonal image. |
|
Digital
Light Processing (DLP):
The commercial name for this technology from Texas Instruments
(TI). The technology inside is often referred to as
either "micro-mirrors", or DMD.
It works this way: build a few hundred thousand tiny
mirrors, and line them up in 800 rows of 600 mirrors
each. Now attach a hinge to each of those 480,000 mirrors.
Attach each of those 480,000 hinges to its own very
tiny motor! Power each motor with electrostatic energy!
The motors tilt their mirrors up to 20 degrees at incredible
speeds. This allows the mirrors to modulate light from
a lamp, and send the "modulated signal" out
through a lens, on to a screen. The most amazing part
of DLP micro mirrors, is the scale of size. The 480,000
mirrors (actually 580,000 are used), hinges and motors
are packed onto a "wafer" a bit larger than
your thumbnail. |
|
|
| DVI:
DVI means Digital Visual Interface. DVI is a standard
that defines the digital interface between digital devices
such as projectors and personal computers. For devices
that support DVI, a digital to digital connection can
be made that eliminates the conversion to analogue and
thereby delivers an unblemished image. |
|
| Focal
Length:
The distance from the surface of a lens to its focal
point. |
|
| International
Power Supply: A unit that can operate under
a international selection of power requirements. The
specs of units vary widely, but the minimum is 105-230
volts, and 50-60 cycles AC (alternating current). If
you see a specification like 110v, 220v instead of a
range, those ratings are usually +/- a given percent
such as 10%. Some units are "self-switching"
they will automatically switch to whatever power source
you plug it into. Others will have to be switched (internally
or externally to accommodate a difference voltage or
cycle range. |
|
| Keystone
Correction: Using
optics design or other methods to apply a "negative"
keystone to the image, which will partially cancel the
effects of keystoning. If you aim a projector with keystone
correction at a screen with the lens level with the
middle of the screen, you will note that the image at
the bottom is wider than at the top. When the projector
is in normal position, pointing upward 10-25 degrees,
the resulting image is fairly rectangular. |
|
| Keystoning:
Keystoning is caused when the projected image is not
perpendicular to the screen, making the top and bottom
of the image different lengths. |
|
|
| LCD:
LCD stands for liquid crystal display and comes in many
forms, sizes, and resolutions. Its primary purpose is
to present a digital image for viewing. A common use
of LCDs is as a display on a notebook computer. |
|
| Lens
Shift:
The Lens Shift feature of a projector allows the optical
lens to be physically shifted up and down (Vertical)
or left and right (Horizontal). Most all lens shift
mechanisms are motorized with vertical lens shift being
the most popular. With a projector that has lens shift
you can optically correct for keystone distorted images.
It is also used to help geometrically align images when
stacking projectors. |
|
| 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 in a projection booth in the back of a
theatre, etc. A typical long throw lens might have to
be 50 to 100 FT back to project a 10FT diagonal image. |
|
| Maximum
Distance:
Sometimes, rarely, the distance from the screen that
a projector can focus the image. Most of the time, it
is the manufacturer's opinion of how far from a screen
the projector can be to cast an image that is useable
(bright enough) in a fully darkened room. Generally
this is very subjective. One projector might quote a
distance that allows them to produce a 25FT diagonal
image, while another, brighter projector might quote
a distance that only equates to a 20FT image. Beware! |
|
| Maximum
Image Size:
The largest image a projector can throw in a darkened
room. This is usually limited by focal range of the
optics. |
|
|
| Metal
Halide Lamp:
The type of lamp used in many medium and all high ends
portable projectors. These lamps typically have a "half-life"
of 1000-2000 hours. That is they slowly lose intensity
(brightness) as they are used, and at the "half-life"
point, they are half as bright as when new. These lamps
output a very "hot" temperature light, similar
to mercury vapour lamps used in street lights. Their
whites are "extremely" white (with slight
bluish cast.) and make Halogen lamp's whites look very
yellowish by comparison. |
|
| NTSC:
The United States broadcast standard for video and broadcasting.
An older standard and lower resolution than systems
used in most of the world. |
|
| PAL:
A European and international broadcast standard for
video and broadcasting. Higher resolution than NTSC. |
|
| Power
Zoom:
A zoom lens with the zoom in and out controlled by a
motor, usually adjusted from the projector's control
panel and also the remote control. |
|
| 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 attached to a computer or
video device as you would connect a monitor. |
|
| QXGA:
QXGA 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 QXGA display has 2048 horizontal pixels
and 1536 vertical pixels giving a total display resolution
of 3,145,728 individual pixels that are used to compose
the image delivered by a projector. A QXGA display has
4 times the resolution of an XGA display. |
|
|
| Rear
Screen Projection:
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 like the Epson have available 3rd party short
throw lenses. Since the image is projected through the
screen, the image must be reversed. |
|
| Reverse
Image:
Reverse image is a feature found on most projectors
which flips the image horizontally. When used in a normal
forward projection environment text, graphics, etc,
are backwards. Reverse image is used for rear projection. |
|
| RGB:
Red, Green, Blue; the normal type of monitor used with
computers. Example of usage: RGB input or output
often referred to as Computer input or output. |
|
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(colour,
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. |
|
|
| SECAM:
A French and international broadcast standard for video
and broadcasting. Higher resolution than NTSC. |
|
| Short
Throw Lens:
A lens designed to project the largest possible image
from short distance. Most front room projectors use
short throw lens. They are often required for rear projection,
where the depth behind the screen is limited. A typical
short throw lens might produce a diagonal image size
of 10 FT, from a distance of 7 to 10 FT. |
|
| 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 1280 horizontal pixels
and 1024 vertical pixels giving a total display resolution
of 1,310,720 individual pixels that are used to compose
the image delivered by a projector. |
|
| 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 1600 horizontal pixels
and 1200 vertical pixels giving a total display resolution
of 1,920,000 individual pixels that are used to compose
the image delivered by a projector |
|
|
| 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. |
| |
| WiFi:
Click
here
to view our guide on WiFi technology. You will need
Adobe
Acrobat Reader to view this file. |
|
| WSXGA:
WSXGA defines a class of SXGA 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 WSXGA display has 1920 to 1600 horizontal
pixels and 1080 to 900 vertical pixels respectively
that are used to compose the image delivered by the
projector. |
|
| 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 1366 to 1280 horizontal pixels and
768 to 720 vertical pixels respectively that are used
to compose the image delivered by the projector. |
|
| 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 1020 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. |
|
|
| 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. |
|
| Zoom
Lens Ratio:
Is the ratio between the smallest and largest image
a lens can project from a fixed distance. For example,
a 1.4:1 zoom lens ratio means that a 10 foot image without
zoom would be a 14 foot image with full zoom. Conversely,
a 10 foot diagonal image at 15 feet with no zoom would
still be a 10 foot image at 21 feet at maximum zoom
(15 x 1.4 = 21 feet). A zoom lens is "not as bright"
as a fixed lens, and the higher the ratio, the less
light output. |
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