Front or rear projection, perhaps both, on ultra short throw system? - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 15 Old 08-08-11, 01:56 AM Thread Starter
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Re: If we want retroreflectivity as well??

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There is no such thing as a free lunch.
there isn't ?

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Mech is totally right! Discussions like this are why we have this Developer's forum! Since it's clear that retroreflection won't suite your needs we should probably break this off into it's own thread. Tell me what thread title to use and I'll be glad to do that.
That would be great..Thread title could be 'Projection onto transparent surfaces' or something you feel is apt..you know my needs

I'll post about the perforated film in the new thread

Cheers
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post #12 of 15 Old 08-08-11, 06:04 AM
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Re: Front or rear projection, perhaps both, on ultra short throw system?

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wapeye wrote: View Post
there isn't ?
Perhaps the figure-of-speech didn't carry. What I mean is that just as there is no such thing as a free lunch (someone has to buy or gather the food items and then do the work of preparing them), there is no way to fool Mother Nature. While it's possible to design a lens system that will correct for a number of optical problems (spherical aberration and other light distortion caused by bending light rays) there is always a price to be paid for it (weight and cost of additional corrective lenses in the light path).

In the case of optically active screens (High Power, Black Diamond, SuperNova, etc.) they don't have the ability to make much correction anyway so they just put up with the negative optical aspects of the screen and only talk about the positive aspects (brighter image on-axis).


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That would be great..Thread title could be 'Projection onto transparent surfaces' or something you feel is apt..you know my needs.
Done!

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I'll post about the perforated film in the new thread.

Cheers
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post #13 of 15 Old 08-08-11, 06:52 AM Thread Starter
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Re: Front or rear projection, perhaps both, on ultra short throw system?

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Perhaps the figure-of-speech didn't carry
oh..it did carry pretty well..i was just kidding with the rubeyes smiley

Here is an image of a raw (unprinted) perforated film:

If you're facing the dark side, you'll be able to see through the film to the other side. Of course, the vision would not be as clear as glass permits. In commercial application, the white side is printed with a graphic for advertising (on glass surfaces such as building facades or retail windows or rear windows of cars), for example:


My idea is to have no prints on the white side. Have the white side face the PJ and images are projected onto this. Now for low trasnmittance, I plan to have a switchable lcd film behind the perforated film.
Cross section:

This Liquid crystal film will be in the off state (which makes it frosted) while our PJ is painting images on the screen. When we want to see through the window, i.e. when the PJ is not operational, the LCD film switches on to become transparent.

Perforated films are a dollar to the square meter while LCD films can be as steep as a few hundred dollars per square meter. But i'm ready to look at costs subjectively

All thoughts welcome

Great help starting the thread Harp, thanks again
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post #14 of 15 Old 08-10-11, 06:24 AM Thread Starter
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Re: Front or rear projection, perhaps both, on ultra short throw system?

I got a demo of the Hitachi CP-250N PJ today. At 2500 lumens, 2000:1 contrast ratio, and a good crisp image onto their dull white matte finished textured interactive white board (a far cry from the DIY screen threads i've glimpsed upon HTS) with three full sized windows opened to let some decent ambient light in (albeit on a cloudy day)...and a 45" diagonal in 4:3 aspect ratio from just 12 inches away from the wall (basically how much the PJ protruded from the wall)...must admit I'm impressed

Am trying to get a demo of the Sanyo DWL-2500 PJ and will buy the better of the two to kick off the experiment. I'm also ordering samples of some frosted glass films and some perforated sheets (as mentioned). Still looking for a reliable and cheap vendor for the switchable (LCD) glass film.

Please bring in your thoughts/suggestions
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post #15 of 15 Old 08-10-11, 09:10 AM
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Re: Front or rear projection, perhaps both, on ultra short throw system?

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wapeye wrote: View Post
oh..it did carry pretty well..i was just kidding with the rubeyes smiley
No worries. Sometimes I forget that we are truly an international forum and certain figures-of-speech may not make it across the language barrier. Although the world does seem to be getting smaller every day.

That perforated film looks like interesting stuff! At first glance, I would be a little concerned that the hole pattern in it might generate a visible interference pattern when combined with the pixel grid of the projected image (Moire pattern), but only trying it would really determine this.

Quote:
My idea is to have no prints on the white side. Have the white side face the PJ and images are projected onto this. Now for low trasnmittance, I plan to have a switchable lcd film behind the perforated film.

This Liquid crystal film will be in the off state (which makes it frosted) while our PJ is painting images on the screen. When we want to see through the window, i.e. when the PJ is not operational, the LCD film switches on to become transparent.

Perforated films are a dollar to the square meter while LCD films can be as steep as a few hundred dollars per square meter. But i'm ready to look at costs subjectively
While I like this in theory, I think there might be a problem with the reflectance difference between the plastic film and the LCD film beneath it and that this would negatively impact the projected image. Here again only testing the theory would really tell you.

Quote:
Great help starting the thread Harp, thanks again
I hope we can help provide you with info to achieve your goal.

Quote:
I got a demo of the Hitachi CP-250N PJ today. At 2500 lumens, 2000:1 contrast ratio, and a good crisp image onto their dull white matte finished textured interactive white board (a far cry from the DIY screen threads i've glimpsed upon HTS) with three full sized windows opened to let some decent ambient light in (albeit on a cloudy day)...and a 45" diagonal in 4:3 aspect ratio from just 12 inches away from the wall (basically how much the PJ protruded from the wall)...must admit I'm impressed.

Am trying to get a demo of the Sanyo DWL-2500 PJ and will buy the better of the two to kick off the experiment. I'm also ordering samples of some frosted glass films and some perforated sheets (as mentioned). Still looking for a reliable and cheap vendor for the switchable (LCD) glass film.
Assuming that Hitachi was kicking out a real 2500 lumens, that 45" 4:3 screen would have been getting hit with around 370 fL! Wow that's a lot of light.

BTW, to calculate the amount of light hitting your screen simply divide the lumens of the PJ by the surface area of the screen in square feet (which can be found by multiplying the width in inches by the height in inches and dividing by 144).
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