projecting through window ?

[oxygen]

Is there anyone who can advise me about projecting through glass ?
i am presenting an installation for permanent use..this building doesnt exist yet.
(a "mickey mouse solution" wont really do it, though
big financial adjustments won't be good either..).
There is a big window glass i'm projecting through, the distance from the glass inside is 2 meters, the distance outside to the wall is also 2 meters. (sum:4meters distance)
This window needs to be 2 meters high, so special glass might be too expensive.
Now i would like to know do you really need special glass, like kristal?
is that what they use in cinema's? are there other options? tips?
types of glass? information?..?
i'm using a 3200 ansilumen videoprojecector with wideangle.
Would using a better projector solve a bit of the problem??
The projection will only be used at night and is 4 meters high x
1-1,5 meter broad.
thanks for any advise!! and much appreciated!!
olga
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i read this in the archives
quote:
A small piece of advice : do not project trough glass/plexi/whatever especially with a 2000 lumen outdoor.
Firstly : as your glass/... isn't perfectly transparant your projection-beam will scatter (read : your image-quality will go down, bad) You would need cristal or something to do that.
Secondly : 2000 lumen isn't too much for the outdoor, putting something in between of your beamer and the screen doesn't sound like a good idea (you will lose some light at the glass/...)

[ristuuk]

I've never had a problem projecting through glass, last time we hired a regular portacabin with regular glass windows to house the projectors. only problem was ventilation...had to keep opening the door to stop the windows from steaming up.
it was cold outside

[rickmaersk]

I just did a test with a 2500 lumen Sanyo through 5.5mm glass with the glass half way between the screen and the projector. It didn't make much difference if the glass was there or not. Certainly no effect on focus, maybe very very slightly dimmer.
I think you would have to avoid double glazing, smoked glass and dirt on the window.
Rick

[neeko]

10% loss on lumin count per surface on std glass. thats ten on entry and ten on exit = 20% note: the inverse square law will make the effects more noticable the further the glass is from the lens

[rickmaersk]

Is this a special law that only applies to projector light or is this light in general?
Your inverse square law point makes no sense. It wouldn't matter where you took your 20% out. Think of the practical implications.
Shall I set the projector up again and get the light meter out?

Rick

[oxygen]

"10% loss on lumin count per surface on std glass. thats ten on entry and ten on exit = 20% note: the inverse square law will make the effects more noticable the further the glass is from the lens"

i hope you are wrong on this one...
specially on the last part. as we need the 2 or 3 meters distance from the window glass... (is std used as regular glass?)
anyway. i'll have to do some seeerious research on this
if the concept will be excepted.

[neeko]

Originally posted by rickmaersk
Is this a special law that only applies to projector light or is this light in general?
Your inverse square law point makes no sense. It wouldn't matter where you took your 20% out. Think of the practical implications.
Shall I set the projector up again and get the light meter out?

Rick

It may not make any sense over there in the art collage rick. But
The inverse square law is still fundimental in projection.
percieved luminosity = inversesquare of screensize and distance.
Did you forget everything we ever taught ya?

[charlielangridge]

Dont forget that cheap glass has a tendency to warp and this will create a second "lens" from the glass, something you dont want!

[rickmaersk]

[QUOTE][B]It may not make any sense over there in the art collage rick. But
The inverse square law is still fundimental in projection.
percieved luminosity = inversesquare of screensize and distance.

the inverse square law will make the effects more noticable the further the glass is from the lens

Neeko
I did many gigs in an art college but i actually have an engineering degree.
The inverse square law applies to the luminosity NOT the light absorbing quality of the glass.
Of course for a given lens setting the image brightness( and size) will depend on the projection distance. But it won't matter where the glass is.
Here's an example
Oxygen's set up is as follows:
Screen width: 4m
Projection distance:4m
Let's assume an arbitrary screen brightness at 4m without the glass of: 100 units

Set up no. 1: no glass
Brightness of projected image 100 units

Set up no. 2: glass at 1m from projector
at one quarter of the projection distance the image would be 16 times brighter.
i.e. 1600 units
Reduction in



The implications of the glass having transmissve characteristics relating to the inverse square law are too weird to make sense. Imagine 2 identical projectors set up opposite eachother. There is a rear screen above each projector. There is a sheet of glass inbetween them. As we move the glass closer to one projector the image above it would get darker as the inverse square law will make the effects more noticable the further the glass is from the lens. And the other image would get brighter! You don't even need a projector to know this is wrong. Try it with a lightbulb and a CD jewel case.

[rickmaersk]

Sorry, I hit the send key before I'd finished the maths:

Oxygen's set up is as follows:
Screen width: 4m
Projection distance:4m
Standard glass ( whatever that is)
Let's assume an arbitrary screen brightness at 4m without the glass of: 100 units

Set up no. 1: no glass
Brightness of projected image 100 units

Set up no. 2: glass at 1m from projector
at one quarter of the projection distance the image would be 16 times brighter.
i.e. 1600 units
Reduction in brightness by 20% leaves 1280 units
Brightness of screen at 4m would be the 1280 units spread over 16 times the area i.e. 1280/16 = 80 units

Set up no. 2: Glass at 3.75m from projector
Brightness just before glass= 100/(3.75/4)x(3.75/4)=114 units
Reduction in brightness due to glass = 20%
Brightness just after glass = 91 units
Remaining 91 units spread over 1.138 times the area= 91/1.138=79.9units

CONCLUSION
Only the transmissivity of the glass matters, not its location.

I also wondered where the "20% loss with standard glass" came from?
I can still get the lightmeter, projector and glass out if you like.
Cheers,
Rick