[MF3D.FORUM:937] Re: MF Projectors

[Tom Hubin <thubin@xxxxxxxxx>]

Rod Sage wrote:
> 
> The recent discusion by Tom Hubin and other regarding MF projection got
> me to wondering. It seems that one major problem is the closeness of the
> film chips, condensers etc.. I am wondering about a reverse ViewMaster
> Stereomatic 500 type set-up. The Stereomatic 500 uses a single bulb in
> the center and 90 degree mirrors to aim the light forward through the
> film chips. Anyway, how would it work to have a MF projector with bulbs
> condensors etc. outbound with light aimed towards each other and then
> turn the light forward using mirrors?
> (B) ()()\ /()() (B)
>           _ _
>          L L
> 
> With B as bulbs and mirrors in center and L as lenses. Just a thought.
> Rod S.

No problem. This is what I suggested. 

However, if the filament radiates in all directions then putting the
lamp in the center is more efficient because you use half as many lamps
to do the job. This might require more mirrors for MF. The cost of
mirrors is reasonable when you think about replacing the pair of 500
watt lamps with a single 500 watt lamp and saving on cooling or heat
damage or cost of lamps. Or using a single 1000 watt lamp and doubling
your light to the screen.

Efficient use of light is paramount in stereo projection because of the
37.5% (3/8) transmission of typical projection polarizers and 75% (3/4)
transmission of the viewing glasses. That means that 9/32 of the light
gets to the eye compared to non stereo projection. So you need to start
with 32/9 times as much light per channel or 64/9 as much total light
power. That is just over 7 times as much light as common projectors.

So the image brightness of a stereo projector using a pair of 500 watt
lamps (1000 watts total) compares to a non stereo projector using a 143
watt lamp. (1000/7 = 143) 

Feel free to challenge these numbers. I'm making them up as I go. The
issue will not change even if I am off a factor of 2 someplace. Stereo
projection using dichroic polarizers is very lossy. Don't give up any
light without a fight. 

Tom Hubin
thubin@xxxxxxxxx
AO Systems Design