- Data projectors – page overview
- Principle of data projectors
- Technologies
- Resolution
- Features, functions and applications
- Important maintenance instructions for data projectors
- Important notes regarding the warranty for data/video projectors
Data projectors have established themselves as the
indispensible tools for professional presentations. Great progress has
been made to make the installation and operation of portable projectors
as easy as possible so that there is no need for any time-consuming
preparation of the equipment.
The information on these pages has been devised to
assist you in obtaining the best possible projection image of your
information. This is not difficult when you understand the design and
functional principles that are shared between virtually all data
projectors. Simply take a few minutes to read this chapter – and any
problems you might have encountered will be a thing of the past. As data
projectors are widely available and offer a wide range of functions,
they are sometimes not used to their full potential so that the quality
of the image is rather poor. Please note that not all data projector
functions are useful in all projection situations.
Principle of data projectors
Nearly all portable data projectors work in the same
way. The image to be projected is transmitted in the form of electrical
signal data from a PC or a video source through a number of interfaces
to the projector. These signals are then converted into an image on the
microdisplay in the projector. A strong light – normally consisting of a
long-life gas discharge lamp – emits its light onto the microdisplay.
The resulting image is then projected through a vario (zoom) lens onto a
screen, which should be located above the lens level.
Technologies
At the moment, there are two predominant technologies available in the market of portable projectors, namely the DLPTM
technology by Texas Instruments and the 3LCD technology promoted by
Epson and others. Both technologies have their advantages and
disadvantages. To understand these, we must first examine their
technical principles.
DLP™
DLP stands for Digital Light Processing. The key
components are a tiny chip and micromirrors. Each micromirror represents
one pixel of the image. These mirrors can be repositioned rapidly to
reflect light either through the lens or on to a heatsink where it is
absorbed. Depending on the mirror position, a bright or dark pixel is
projected. Multi-coloured images are produced by placing a spinning
colour wheel between the lamp and the micromirrors, which deflects the
light into the primary colours of red, green and blue (RGB), which are
projected in sequence. As these rapid changes are invisible to the human
eye, the impression of a continuous colour image is created.
3LCD
3LCD technology uses three microdisplays made of
polycrystalline silicone. LCD stands for Liquid Crystal Display. The
liquid crystals act like valves, each representing one pixel of the
image. The white light from the lamp is split into the basic colours and
then beamed separately through the three displays. The three colour
images are combined using a prism to form a full-colour image, which is
then projected onto the screen through a lens (source of figure:
AV-Views).
LCOS
LCOS (Liquid Crystal on Silicon) technology is a
relatively new development. Similar to DLPTM technology, it is based on
reflection of the light. With LCOS, the light is not, however,
controlled by mechanical mirrors but by liquid crystals. As the silicon
chip surface coated with liquid crystals is completely smooth, the
projected image does not show any raster structure. With LCOS
technology, it is possible to produce high-resolution images using
low-cost chips. As with DLPTM, three chips are used for the three
primary colours. The design of the optical engine is, however, much more
complex than in 3LCD or DLPTM. With the launch of the XEED series,
Canon was the first company to offer compact and powerful LCOS
projectors with high resolution.
Advantages and disadvantages
What is the effect of the data projector technology
on the projector and the image? DLPTM data projectors are simpler in
design and therefore tend to be more compact, sturdy and lighter in
weight than 3LCD data projectors. A perfect example of this technology
is the Geha compact 215. As the light is reflected on the surface, DLPTM
technology produces images without interfering stray light, allowing
for better contrast. This is, however, not of great significant in
everyday business use, as the contrast is limited by the ambient light.
As the pixels of the image are very close to each other, the image is
homogenous. With 3LCD projectors, the design of the image-generating
unit leads to shadows that are visible as a faint "fly screen" in the
image.
On the other hand, 3LCD data projectors produce vibrant saturated colours, while DLPTM
projectors for business applications compromise in this area to improve
brightness, which is achieved by adding a white sector to the RGB
colour wheel. The "rainbow effect" associated with older DLPTM models,
which is created by sequential colour projection has virtually been
fully eliminated in new data projectors.
As
the chips used in 3LCD technology are not transparent, they must be
cooled with air, which makes the projectors highly susceptible to dust.
The organic filter materials used in 3LCD data projectors decompose
under the influence of light, so that they are not suitable for
continuous use and must be replaced regularly. For more information on
the above technologies, see www.dlp.com und www.3lcd.com.
Resolution
The resolution of the image is determined by the
number of pixels it contains. It is normally indicated in numbers of
columns and rows. Resolution of currently available models:
Designation
|
Pixels
|
Image format
|
|---|---|---|
Business
| ||
SVGA
|
800 x 600
|
4 : 3
|
XGA
|
1024 x 768
|
4 : 3
|
SXGA
|
1280 x 1024
|
5 : 4
|
SXGA+
|
1400 x 1050
|
4 : 3
|
UXGA
|
1600 x 1200
|
4 : 3
|
WXGA
|
1280 x 800
|
16 : 10
|
WXGA
|
1440 x 900
|
16 : 10
|
Video
| ||
NTSC
|
640 x 480
|
4 : 3
|
PAL / SECAM
|
768 x 576
|
4 : 3
|
Wide NTSC
|
852 x 480
|
16 : 9
|
PALplus
|
1024 x 576
|
16 : 9
|
HD720
|
1280 x 720
|
16 : 9
|
HD1080
|
1920 x 1080
|
16 : 9
|
The
following general rule applies: the greater the resolution, the more
details are visible in the projected image. The resolution of data
projectors is fixed and cannot be adjusted. In a series of projectors,
the image quality is therefore determined by the weakest link. To
achieve best results, all elements from the signal to the projection
screen must be compatible and carefully chosen. The resolution of all
components must match that of the displays built into the projector. All
other resolutions must be calculated, which can lead to blurry images.
For business applications, an image format of 4 : 3 is the standard.
Home cinema systems use image formats of 16 : 9. The new business format
of 16 : 10 is still rarely used and only a limited number of data
projector models are actually able to detect it!
Features, functions and applications
Many of the data projector features are very useful
in particular situations. There are, however, some pitfalls with certain
functions!
Automatic source detection:
This user-friendly function ensures that the image source is detected automatically by the data projector.
Blank, mask, shutter:
The projected image is dimmed down. These functions
are very useful if you wish to shift the audience's attention away from
the projection to the speaker. They might also be activated during short
breaks to avoid switching off and restarting the data projector. While
this prolongs the service life of the lamp, it can damage the 3LCD
chips, so that this function is normally limited to a maximum of 15
minutes. When this period has lapsed, the lamp is automatically switched
off.
Ceiling installation:
Portable projectors generate an image above the
projection level. If you wish to install the data projector on the
ceiling, the image must be produced below the projection level. To
achieve this, you can simply mount the projector upside down and
activate the ceiling installation function. The projected image is then
put on its head to appear correctly on the screen. Data projectors
feature threaded bores for easy installation on ceilings.
Digital zoom:
Use the zoom function to ensure that even the people
sitting in the last row can read the fine print in your tables. The
size of the image is not changed in the process. See also •Zoom
function.
Freeze:
With the freeze function, the projected image can be
frozen during the presentation. You might use this function to page
forward through your slides or to work on the PC without your audience
noticing it.
OSD:
The OnScreenDisplay function projects the data
projector function buttons onto the image. A variable OSD is most
useful, as it ensures that certain sections of the image are not
constantly covered. In some data projectors, the dialogue can also be
completely switched off, so that no parts of the image are hidden.
Projection ratio, PR (see fig. 1):
The projection ratio varies from model to model and
is used to calculate the size of the image and its distance from the
projector. This ratio is denoted as the distance (between the lens and
the projection screen) over the image width. If the image width is
given, simply multiply it by the PR to calculate the distance. If the
distance is fixed, divide it by the PR to determine the image width. For
zoom lenses, the calculations are based on the extreme values.
Reset, default settings:
This feature is known to most people from their PC.
If everything freezes, try to reset the data projector. All settings are
reset to the default, or average, settings. You might need to change
the menu language from English to German.
Trapezoid correction, keystone correction:
With parallel projection, all portable data
projectors produce a rectangular image above the projection level. If
the image is to be projected to a higher position, data projectors can
normally be tilted slightly by adjusting its front foot. The resulting
image is however trapezoid in size, so that its upper edge is wider than
the bottom one. Using the automatic (or manual) trapezoid correction,
the image can be corrected. This, however, affects the image quality, as
the pixels must be recalculated. While this function is very useful for
portable data projectors that are in frequent use at various locations,
it should never be used for fixed installation. A much better image can
be achieved by placing the data projector on a projector table that can
be adjusted in height, or by adjusting the projection screen with the
keystone bracket.
Wide angle lens:
To create large images in rooms where space is
restricted, many portables are equipped with lenses with a short focal
length and thus a smaller projection ratio. Such projectors are,
however, more prone to produce trapezoid images. It is therefore very
important to project the image parallel to the data projector!
Zoom function:
The size of the projected image can be easily
adjusted to the size of the projection screen by turning the zoom ring
at the lens. The zoom range of data projector lenses is, however, only
1.3 to 1 (largest image to smallest image at a constant distance) and
thus much smaller than that of cameras.
Important maintenance instructions for data projectors
Please note that projectors must cool down after
use. Therefore do not disconnect the projector immediately from the
power supply, unless, of course, you have an "unplug & go" data
projector. Regularly clean the air filters, following the instructions
in the data projector manual. This is normally required every 200 to 300
operating hours. It must, of course, also be done in projectors that
are mounted on ceilings and might not easily be accessible! 3LCD data
projectors are not suitable for continued operation from six hours per
day upwards! The organic filter materials must be allowed to cool down
for a prolonged period every day, as they are otherwise destroyed. If
the image shows cloudy discolouration, immediately switch off the
projector.
Important notes regarding the warranty for data/video projectors
Data/video projectors are subject to special warranty terms.
Normally, the warranty period is 36 months, unless
specified otherwise in the documentation. It does not cover consumables
and wear parts, such as lamps, air filters, LCD panels, polarisation
filters and colour wheels. Lamps are covered by a separate lamp
warranty.
It is only valid if the device is used according to
the instructions and if the use restrictions (< 6 hours per day) are
adhered to. In addition, all maintenance instructions must be adhered
to.
Damage caused by improper use or installation,
external impact, transportation, repairs or modification carried out by
unauthorised parties are not covered by warranty. Neither is damage due
to artificial fog, high air humidity, cigarette smoke or other
aggressive media and solvent vapours. The warranty further excludes
damage caused by the use of consumables such as lamps and air filters
that do not meet the required technical specifications. Projectors
operated in continuous mode are not covered by warranty (with the
exception of the Panasonic PT-D-4000, PT-D5700 und PT-DW5100 models).
Geha lamp warranty for data projectors
The first lamp installed in Geha data projectors is covered by warranty for a period of 180 days or 500 hours (whichever is reached first). The warranty does not cover replacement lamps.
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