Zoom lens
A zoom lens gives you the ability to
set the projector at a convenient location, and adjust
the projected image size. This
allows the same adjustment that you get by moving a
projector closer and further away from a screen, without
actually moving it
Zoom Lens Specification
Zoom Lens capability is detailed as a ratio between
its standard size and its maximum size. E.g. 1.2:1
details a maximum of 20% zoom from the original size.
Zoom lenses range from 1.1:1 up to 2.0:1
or more. |
Contrast Ratio
Contrast is the ratio
between the brightest and darkest areas of the image.
The two types of technology LCD and DLP have very
different maximum contrast ratio's.
Contrast ratios should be high (1500:1 or higher) to get
the best video or photo image. For computer graphics and
data presentation, 400:1 is usually ample.
LCD
tend to be around 400:1 whilst a dlp can achieve 2000:1.
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Screen Size Matters
The larger the screen the more power your projector will
need. A small screen of say 50cm may require a 2000 lumen
projector whereas a 100cm may require 3000 or 4000 lumens.
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Standard Types of Projector
The
standard two types of technology used in projectors are LCD
and DLP.
LCD - Liquid Crystal Display is a thin, flat
display device made up of any number of colour or monochrome
pixels arrayed in front of a light source or reflector
DLP - Digital Light Processing is a technology
used in projectors and video projectors.
LCOS - Liquid Crystal On Silicon
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Projector Resolution
The resolution of a projector is the amount of detail
that a projector may show. The larger the numbers
the greater the potential definition of the image.
Different dimensions of resolution are given abbreviated
names
Standard Screen Projector Dimensions (4:3 ratio)
- SVGA 800 x 600
- XGA 1024 x 768
Home Cinema Projector Dimensions (16:9 raitio)
- WVGA 854 x 480
- WSVGA 1024 x 576
- WXGA 1280 x 720
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Wireless projectors are catching on fast. No more
messy cables, quicker set-up and the ability to switch
between presentations on different laptops on the fly are
all appealing prospects.
Due to bandwidth restrictions, wireless projectors are
not yet capable of displaying full motion video without
reducing the frame rate, and hence the wireless
functionality is not suitable for home cinema.
Most wireless projectors use the WiFi standard. You
will require a compatible wireless card in your PC to take
advantage of this technology.
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Progressive Scan
A Progressive Scan converter takes an Interlaced Scan
formatted signal, and converts it to a superior signal
where the complete picture is drawn from top to bottom
in one pass. This results in less flicker and smoother
motion.
Most TV signals are sent in an "Interlaced Scan"
format. First the display device (TV or projector)
displays the image's odd lines, one at a time from top
to bottom. This takes about one sixtieth of a second. It
then fills in the even lines, taking another one
sixtieth of a second. So the full picture is first drawn
with half its information missing, which is then filled
in. In all the process takes 1/30 of a second per
complete frame.
Some DVD players have progressive scan converters
built in, and may have the option to output in either
progressive or interlaced scan modes. Some projectors
(in particular the specialist home cinema projectors)
also have progressive scan converters built in.
Alternatively, it is possible to purchase an inexpensive
progressive scan converter as a separate unit which can
convert your TV and DVD signals. |
 Multiple Computer Ports
If you want to connect multiple
computers or video sources to the projector
simultaneously, you will need multiple input jacks to
accommodate this. For example, you may want to connect a
notebook computer and a desktop computer to support two
consecutive presentations, or two different presenters.
If your projector only has one computer source, you'll
have to unplug the notebook and plug in the desktop
between presentations. Check to make sure the projector
has enough connections to support your typical use.
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Video Signal Standards:
Most business projectors accept
composite video, S-video, and computer/RGB signals as
three types of signal transmission.
Most projectors also recognize YPbPr/YCbCr
component video as well. However, there are two
all-digital standards known as DVI and HDMI. Many new
computer video cards feature DVI or HDMI output, which
allow the user to keep the signal in the digital domain
and eliminate analog to digital conversions.
If you are interested in optimizing
video performance and you have a video source that
offers DVI or HDMI output, check to see which of the
projectors on your list possess a digital input. The
spec sheet may say HDMI, DVI-I, or DVI-D.
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