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The Project
Having completed TARDIS
(Project 8) which called for a
dedicated computer to provide the dual VGA stream to the monitors,
it seemed like a logical step to use this computer to feed two
projectors.
I was already familiar with stereo
projection use film slides and therefore had a projection screen.
The exercise now was to find two projectors of the right standard
and to make an appropriate staging for them that would include
alignment features for each and a polarising filter carrier for
each. Another consideration was the sound system needed to
suit the size of auditorium expected for presentations.
A further consideration was the production
of slideshows to satisfy both TARDIS and the proposed projection
rig. With these factors in mind I chose to search eBay for
suitable projectors, pay due consideration to the specification
and cost.
The Projectors
The choice that I made was two Acer PD523
Figure 1.
which I bought for less than £600 each.
The specification for these included the following key features
1. DLP Technology to avoid inherent
polarisation difficulties. LCD projectors cause polarisation
problems.
2. XGA native resolution (1024 x 768 pixels)
with a capability to process SXGA (1280 x 1024) the standard used
for most monitor sizes and hence TARDIS.
3. VGA connectivity to the computer.
Perhaps this can be taken for granted in the case of most
projectors, with or without an adaptor.
4. Settings to allow my TARDIS slideshows to
be shown. Taken care of by the SXGA (1280 x 1024) processing and settings
to allow flipping of the projected image. This reverses the
inverted image orientation used with TARDIS.
Other factors were considered less critical
as most projectors nowadays are bright enough with an adequate
contrast level. In actual fact, I am able to run the
projectors in 'economy mode' and with the brightness set to around
50%, giving me an extended lamp life over the 2,000 hours claimed
for the regular settings. With a good 5ft (160cm) screen,
these settings are fine.
Mounting the Projectors
Most of the projector mounting rigs that I
have seen involved a framework designed to mount both projectors.
I decided that is not really necessary for other than a fairly
permanent rig. I decided that a simple 'cradle' that sits on
top of the first projector and supports the second is all that I
required. The cradle was made of timber and MDF. I was
lucky to find that our old friends B&Q had some wood beading that
matched the profile if the projector.
Figure 3.
I made provision for locating the front and
back projector feet and added an adjustment feature for both back
feet.
Figure 3.
The Computer
The system that I have built is small,
light and looks OK too. I shall not bore you with all the detail, but
I did decide to install a dual head graphic card and settled for one with
two VGA outputs. It is a PNY Quadro 4 280 NVS Low Profile PCI
Express and cost £130.
An alternative to using a dual head graphic card is to
upgrade your current one with an adapter such as the Matrox DUALHEAD2GO
Figure 14 / 15.
for Notebook and Desktop PC's. This takes the existing single monitor
display output (i.e. external VGA output) from your system and expands it
into dual display outputs, allowing you to run your Windows desktop at up to
2560 x 1024 resolution stretched across two displays, ideal for stereo our
purpose. Using DualHead2Go in conjunction with the built-in display of
your computer, you actually benefit from 3 displays at a time. The
included Matrox PowerDesk software seamlessly manages window positioning and
message pop-up. The more powerful your existing graphics, the more powerful
the DualHead2Go multi-display environment. The Matrox DualHead2Go costs
around £100 and is compatible with a wide range of laptop and desktop
computer systems. Check first at -
www.matrox.com/graphics/en/corpo/products/home.php#rgu
Barry Aldous, Updated
November 2006.
Any questions? Please contact
barry@aldous.net
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