A bit more on projectors...

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

A few more thoughts on stereo projection...

Gabriel wonders what happened to my sharp eyes when I concluded that
the 750W bulbs were brighter... Well, when my 500W bulbs died, the
change to 750W bulbs resulted in brighter images which leads me now 
to conclude that bulbs lose brightness towards the end of their life.
Also, the 500W bulb projectors that I have acquired were not as
bright as my 750W equipped projector but that must have to do with
projector maintenance.

At the end, what matters for me is that the 750W and 500W bulbs
register the same 6.2 EV value in my lightmeter.  Ken Luker points
out to a few differences between the two models.  I noticed another
one, the spacing of the first pair of condenser lenses in shorter 
in the 716.  If these difference reflect in light output remains
to be seen.  I do not have a 716 to experiment right now but would
do it when I get a chance.

Making light meter EV measurements if a fun and learning activity.
One EV difference means twice (or half) the amount of light.  With one
bulb shinning light the meter reads 5.2.  With two bulbs we have 6.2
100% increase (twice the amount of light, as expected).  I removed
the polarizing filters and registered 7.5 EV, a large difference
from the 6.2.  Simple calculations show that this 1.3 EV difference
corresponds to about 40% transmission.

I will do routine light measurements every time I set the projector
to make sure everything is OK.  Such measurements might be able
to detect when a bulbs is about to fail.

Mike K. mentions that the Tech Spec full sheet is expensive.  No one
says that research is cheap ;) ;) I ordered the full sheet and will
have to sell filters to make up my money!

Michael Kaplan mentions that he uses *glass* Hoya polarizers 
in front of his projector.  I wonder what the transmission in these
filters is... What is the f-stop adjustment when using them on the
camera?  The Tech Spec material also comes in unmounted glass form.
Price for one 50 mm filter is $25 and the claimed transmission is
45%, which is very good.  The question of course is, as Mike mentioned,
how well do these filters hold on heat.

Finally, my comment on optimizing all the steps involved, was mentioned
with the audience glasses in mind.  Especially dirty and depolarized
glasses.  Giving such glasses to an audience should be considered
a punishable crime!  The bottom line, what counts, is what the audience
sees...

George Themelis



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