For discussion of projection screens.

10 responses total.

I am interested in a *reverse* (from the rear) projection screen that has very
high resolution. In effect, it should, scatter incident light accoreding to
the cosine law, but without spreading it. This would produce an image that
would be very sharp, and of uniform brightness from any viewing angle. I
imagine this would have to be a very thin - a mil perhaps - translucent sheet:
perhaps deposited on glass, or a thin polymer film. Is there anything like
this?

How big does it have to be and does it have to meet an exacting specification
for scatter?  It seems like the mylar films used for engineering drawings
would be a possible candidate.  (Polyester sheet)

They are usually more semi-transparent. You can see the location of a
light behind it. A true scattering screen would be uniformly lit by
a bulb behind it, and you would not be able to tell there was one bulb or
many. 

The purpose. A slide scanner is an expensive computer accessory. A
transperancy scanner is much less expensive. If one could project a slide upon
such a scattering film, one could scan it and get much better resolution
than scanning the slide itself.

Pretty neat idea.  I have been thinking about buying a negative scanner, but
so far have not taken the $$$ step.  Please keep us posted if you decide to
make one.  

To make one requires I find a true scattering screen....which takes us back
to #1 8^}.

Ah ha! Edmund Scientific lsits a "Glass Rear Projection Screen" in the
1989 (whoops!) catalog. [I have requested a new catalog - ES has a web site
at http://www.edsci.com/ and it says their catalog will be on-line -
tomorrow.]

I'll report back when and iff I carry this off - in the meantime,
what do you use/like in the way of projection screens?

I am a non-user of projection screens, but interested in your findings.

I've given a lot of public lectures illustrated with slides and bring along
my own projector, screen (and extension cord!) since I found that even some
institutions can't find one or another (or they are broken). 

I used a beaded screen for a long time, but the beads wear off, creating
dark streaks. I don't like aluminized screens, as they do not scatter
light well, so are not bright when viewed obliquely. I now have a screen
with an embossed white plastic surface, which works quite well. 

Translucent white like a diffuser lens?  They make commercial polypro compound
with calcium sulfate (I believe) filler.  Gives a nice white even light.  I
have never seen it in sheet material, but it may be available for commercial
lighting panels.  

Also if you are backlighting, the diffusing layer must need to be extremely
thin???

The screen is the "DA-LITE Flyer". The surface is dimpled with pits that
are very small and vaguely rectangular. The polymer is very white. It is
on a usual cloth backing, which is in the usual housing. 

Reverse (rear) projection does indeed require a very thin diffusing layer.
Ideally, each arriving photo weill be scattered once, according to the cosine
law. That's not possible and lots of light gets scattered twice and more,
which means it spreads horizontally in the scattering layer, and blurring the
image. However if the layer is very thin, it can't scatter the light very far
horizontally. The probloem is, that it must be both very thin *and* nearly
100% efficient in scattering. The glass rear-projection screens have
a very thin white layer "flashed" upon the clear glass. I haven't bought
one yet, until I determine what size I need to work with a scanner's
tranparency adapter.

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