Re: silver screens

[bercov@xxxxxxxxxxx (John Bercovitz)]

I wrote:

> What all are the options in silver screens? 

No answer.  I'm kind of surprised.  We have so many projectionists 
on this list.  Someone must know what's available these days.  Are 
straight silver screens still available or must one buy silver-
lenticular?  Who are the manufacturers?  

Dr. T wrote:

> I can just picture a meeting of the Oakland stereo club: "Who's this guy 
> sitting past the front row?", "But, that's John B., the ortho-man..." ;)

Hey, you laugh, but the other folks at the meeting didn't laugh!  They 
asked me to get out of the way.  8-)

> Do lenticular screens have a brightness advantage over
> non-lenticular silver screens?

Sure.  So let's talk about screens.  I have little first-hand 
experience so again I'll tell a pack of lies, or what I've read in 
books, and see if we can get a projectionist interested in talking.  
First off, a plane mirror would make a nice screen material because 
it reflects light to where you direct it and not all over 
tarnation.  Unfortunately, it's also obsessive about obeying the 
law that the angle of reflection is equal to the angle of incidence 
and so you'd never get the whole image to the observers.  Fine 
white paper or a painted wall is great for the highest resolution 
but there are two problems: Light is depolarized and the reflected 
light distribution is Lambertian (approximately) giving lots of 
light to the sides where no one sits, and to the floor and ceiling, 
for that matter, where also no one sits.  Screens with beads of 
glass on them have about the right light distribution but they also 
depolarize and they also send light to the floor and ceiling.  The 
glass lenticular screen has the right distribution of light to 
cover a wide audience and not the floor and ceiling but it also 
depolarizes light.  The old, plain, silver screen, with tiny bits 
of aluminum flake distributed in random orientations on its 
surface, sends light back in the right direction, so it's not 
wasting light, but it's not spread out enough to cover a wide 
audience.  So enter the silver lenticular which is basically a 
vertically-ribbed silver screen, the ribs or lenticules serving to 
spread the light out across the width of the audience.  This may be 
the best of both worlds if you have to cover a wide audience and 
you need to maintain polarization.

Since stereo viewing is poor if you sit very far from a line 
between projector and screen, I would question the need for a 
silver lenticular screen.  You should get better resolution and 
brightness from a plain silver screen.  Do we have some 
projectionists on the list who would like to set me straight on 
this?

Thanks,
John B


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