re: Cooling Stereo Projectors

[P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

Interesting post by Peter Penhallow regarding Colin Clay's article.

>This article will mainly, therefore, be of interest to those building
>a stereo projector from scratch or modifying older stereo projectors
>to take quartz-halogen lamps.

Yes it sure was of interest to me since I am in the ON and OFF process
of building one also. It's good to know that others have gone before
me in that regard. 3D projectors that is. Over the holidays, I tried
out different types of lamps that were readily available in my local
mega hardware store. So far prelimenary results look promising. The 
projector in question will be a stereo viewmaster projector.
The info on the fan was interesting, and will come in useful in future
projects but for the above one will not need any fan. It will use 
convection cooling only. As for the heat filters, this also is useful
info. This aspect can't be avoided.
 
The location of the polarizing filter, makes sense if the slide doesn't
depolarize the light. From what I have read here in P3D it seems in
most cases it doesn't. So putting the polarizer before the slide, to
protect irreplaceable slides is worthwhile. Polarizers can always be 
replaced. Incidently, I had thought about putting the polarizers before
the slide regarding UV radiation but didn't mention that in one of my
earlier posts. Instead I suggested some kind of plastic be placed to
reduce not only the IR but more specifically the UV. I didn't mention
using the polarizer because of the depolarization concerns. 
See digest 1738.

It would be interesting to know, what type of lamps he was referring
to in his original article. As for my project, as I mentioned, it won't
(hopefully) need any fan. Preliminary tests seem to confirm this. The
design in mind is something that can be made with of the shelf components.
This is for several reasons. First is availability, second is ease of
construction and third is cost. The housing hasn't been made and it will
be manual focus.

The lamp consists of a 12V 50W halogen lamp with dichroic reflector built
as one piece. These are rather inexpensive. Going price is very roughly 5
dollars. The dichroic properties of the reflector mean that it collects
the lamp radiation and produces a high intensity focussed beam. The dichroic
coating transmits much of the infrared radiation while reflecting the UV
and visible. The 12V lamps of course need a power supply. 
I decided to go with a Starlite, made by Westron. This basically is made up
of a 50W transformer, fixture that screws in to most standard 120V lamp
sockets, 12V lamp socket, and the heat absorbing glass. This goes for about
$40. There are 12V lamps with the HAG built in, but they were much more
expensive, $20 each at my local hardware store. There are several types of
halogens on the market readily available, that are meant for house lighting.
The 120V ones I have seen so far didn't have the above features and radiated 
intense heat and a wider beam. 

As for the optics, I used a surplus 50mm lense that came from an old SLR 
camera. I mounted everything into place, to see how well it would perform
with a VM reel. So far everything is only in 2D and if it works well, I
will progress to 3D. I projected it to about 15 feet away and the image
compared very favorably to a 300W VM 2D projector. The projected image
is just as sharp and will take some measurments with a photometer in the
near future to compare brightness.
If all works out well, will be in the market for another surplus lens.
If not, at least I will have another nice 2D VM projector, which will
run on 50W instead of 300W and won't need a fan to boot! If nothing works
out, at least I will have learned something. BTW I don't know if it's good
practice, to use a surplus SLR lense for projection, but it seems to work.
Reminds me a bit of Bugs Bunny where he is floating in the air and someone
tells him your breaking the Law of Gravity. Bugs replies, he never studied
the Law of Gravity. Thats all for now.

Gabriel
   
  


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