# advice wanted: computers and [diy] rear projection screen



## tomwed (Jan 2, 2007)

My high school is doing bye bye birdie. I have computers and 2 projectors that are fairly new. My stage ceiling is 12 foot high. I want to build 2 frames covered with fabric [about 9'x12'wide]. My stage is 20' deep. I want to project different images from the back of the stage through the screen. The actors will perform some of the scenes in front of these screens on the apron. Other scenes will start out by being projected on the screen and then the screens will be pulled back to reveal an interior setting.

Has anyone done this?
What kind of material do i need to project through?
Where can I buy it?
Does anyone have a better idea?
Would they require special lighting?
Would it also function as a scrim?


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## Footer (Jan 2, 2007)

Rosco makes a very good rear projection screen that you can buy in rolls and cut to fit any size. I am using 3 12x9 screens on a show I am doing right now, and if they are built correctly, they give a great image. 

http://www.rosco.com/us/screens/roscoscreen.asp

As far as the projectors goes, the brighter the better. You want to keep as much light off of the screen, so no flat front light otherwise you will get blown out. Also, check the throw distance of your projectors to make sure that you can hit the screen size you need. If you need more flood, go get a mirror and do a mirror bounce to get some extra room.


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## tomwed (Jan 2, 2007)

I am stunned about how quickly and professionally I am being helped. thank-you for taking the time

What did you mean about needing more flood? Does that mean a bigger [broader] image?


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## Footer (Jan 2, 2007)

tomwed said:


> I am stunned about how quickly and professionally I am being helped. thank-you for taking the time
> What did you mean about needing more flood? Does that mean a bigger [broader] image?



Yes, usually most projectors you will find around a H.S. environment are made for projection a 6' image from around 10', when you amp that up to a 14' or 16' image you need a farther throw, so the projector has to be farther away from the screen. In a perfect world you could get different lenses for the projector, but usually the budget is not there for that (I'm spending 2k to rent 3 projectors with .8mm lenses for 3 days so I can get the short throw). Using a mirror to "bounce" the image will give you more throw distance.


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## Van (Jan 2, 2007)

I posted a reply in the New memebers section where you posted the same question so I'll refer you to there. As far as a larger area of projection goes you are usually much better off getting a better lens or upgrading your projector. I respect Footers suggestion, but have in the past expirienced several large difficulties with getting a quality image from a "bounced" projection.


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## Footer (Jan 2, 2007)

Van said:


> I posted a reply in the New memebers section where you posted the same question so I'll refer you to there. As far as a larger area of projection goes you are usually much better off getting a better lens or upgrading your projector. I respect Footers suggestion, but have in the past expirienced several large difficulties with getting a quality image from a "bounced" projection.



Very true, keystoning is a HUGE problem with it, as well as you do lose some transmission.


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## soundlight (Jan 2, 2007)

Wow. That's just what my school did this past semester, in terms of video technique. We started a scene on the projector, filmed beforehand, and then switched to the stage acting. We also used the screen to project backdrop pictures.

I'd second the comments about keystoneing and needing a really short throw projector, because most projectors have to be very far away to project the image size that you need.

Good luck!


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## tomwed (Jan 2, 2007)

soundlight

What material did you make your screens out of?

Where did you buy it?

thanks
tom


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## soundlight (Jan 3, 2007)

Actually, we went all out and bought a full, ultrasonic-seams Rosco RP screen that actually filled the whole back of the stage...but you don't need something that big. I'm pretty sure that we got a "light translucent" screen, mainly because of the need for something that could handle a lot of light on stage. If you were to use the Rosco material, a bolt of 110" cut material would cover almost 9', but if you made your screen 8.5x12 or so you'd have a much easier time making a 110" cut fit your needs.


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## avkid (Jan 3, 2007)

Tom, what kind of projectors do you have?


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## PhantomD (Jan 3, 2007)

We have this kind of arrangement and use it all the time, it's great and very versatile.

We have a permanently installed proper rear-projection screen in the middle of our stage which comes down on a winch (can be motorised) and we have a projector that comes out of a high-up-mounted motorised dropbox, suspended off the roof with the box at about cyc level. This drops the projector down out of nowhere when we need to use it, eliminates ALL keystone issues and is a very versatile.

We use a 2500 lumen projector and it is great competition for the lights, easily viewable from the back of the theatre...although I suggest you dim out any lights pointing straight on the screen.

I suggest 2100 lumens as a definite minimum light output - brand does not really matter - we have some cheap imported "PLUS" DLP projector and it's really great (recently had a colour issue fixed under warranty) - although I want to upgrade to a Sony LCD projector with higher lumens and a wired remote.

Hope this helps tomwed.


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## SHARYNF (Jan 3, 2007)

Just be aware that many times the spec's don't reflect the actual output. 
DLP's also have a delay in processing that can cause some issues if you are using it to project an image where lip sync can be a problem
Sharyn


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## PhantomD (Jan 4, 2007)

The delay in processing due to the spinning colour wheels isn't really that big...I don't think...nothing noticeable?


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## tomwed (Jan 4, 2007)

epson powerlite 755c
resolution 1024x768
2500 lumens 
contrast 400:1
keystone correction +- 30 degrees

i'm thinking i'll mount them on the back wall, 22' away
each one throwing about a 12x9 image
i know i'll need to experiment

i'm picking up some tricot, i tend to [need to realy?] do everything as cheaply as possible

what do you think?


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## SHARYNF (Jan 4, 2007)

PhantomD said:


> The delay in processing due to the spinning colour wheels isn't really that big...I don't think...nothing noticeable?



If you add any sort of video mixing device with sync that adds a delay (most of the ones that allow for the use of non gen locked cameras) it does become visible if you watch carefully, the additive delay is just enough to cause an issue . It is one of the downsides of the dlp tech
Sharyn


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## SHARYNF (Jan 4, 2007)

PhantomD said:


> We have this kind of arrangement and use it all the time, it's great and very versatile.
> We have a permanently installed proper rear-projection screen in the middle of our stage which comes down on a winch (can be motorised) and we have a projector that comes out of a high-up-mounted motorised dropbox, suspended off the roof with the box at about cyc level. This drops the projector down out of nowhere when we need to use it, eliminates ALL keystone issues and is a very versatile.
> We use a 2500 lumen projector and it is great competition for the lights, easily viewable from the back of the theatre...although I suggest you dim out any lights pointing straight on the screen.
> I suggest 2100 lumens as a definite minimum light output - brand does not really matter - we have some cheap imported "PLUS" DLP projector and it's really great (recently had a colour issue fixed under warranty) - although I want to upgrade to a Sony LCD projector with higher lumens and a wired remote.
> Hope this helps tomwed.



This is one of the problems with rear projection with the projector straight aim to the screen with no correction. On paper is looks ideal, but in practice you get the hot spot of the projector, this is why projecting from an off angle and key stone correcting really is helpful as you are not looking directly into the projector lens/lamp

Sharyn


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## PhantomD (Jan 4, 2007)

SHARYNF said:


> This is one of the problems with rear projection with the projector straight aim to the screen with no correction. On paper is looks ideal, but in practice you get the hot spot of the projector, this is why projecting from an off angle and key stone correcting really is helpful as you are not looking directly into the projector lens/lamp
> Sharyn



Why quote me when you say that? Our projector/screen are absolutely fine, no problems.

"The hot spot of the projector"?

Keystoning has its disadvantages too Sharon!

In our situation, where the brightness of the projector is perfectly matched to the installation and the venue, there is no issue!


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