Super cheap DIY rear projection screen for my classroom - AVS Forum
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post #1 of 5 Old 07-31-2011, 02:32 PM - Thread Starter
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Hi. I'm a first grade teacher with an LCD projector and a document camera. I've asked if I could mount my projector on the ceiling, and the school said absolutely not.

So the projector must live on a cart or table in the classroom. The problem is that in order for the image to be the correct size, the projector has to be in the middle of the room.

When you teach first grade, you have the students on the floor a lot. Two things are important. First, where the kids look and what they need to listen to have to be in the same place. So my voice needs to be coming from someplace close to where they are looking. Also, during direct instruction they need to be in close proximity to the teacher - eye contact is important.

This is all very difficult with a projector sitting on a cart, in the middle of the room, blocking their view.

I use the projector connected to my computer for all sorts of things - displaying images, choral reading, sight words, an much more. I use the document camera to display writing templates, handwriting practice, and read-alouds. 99% of the time, the images are static. Occasionally I show a video from the computer, but not real often.

I've decided to try building a DIY rear projection setup on the cheap - and I mean really cheap.

Here's what I want to try: The projector will be directly under the screen, facing rearward, away from the viewing students. About 4 or 5 feet back will be a large mirror - the largest I can find at Home Depot or Ikea - mounted on a table that pivots (I have something perfect for this job if it works). I'm hoping the mirror will reflect the image back to the screen and be viewable.

I've already tried rear projection without the mirror, and the projector facing forward behind the screen. It worked just using a wrinkled sheet, but the image was too small for my liking and I could only move the projector so far back. I could move the screen forward, but that would take up floor space.

Will it work with the mirror? Do I really need a front surface mirror or can I get by with a regular mirror? The image will be bounced almost directly back at the screen from a distance of about 4 or 5 feet. What will happen to the hot spot? The bottom of the screen will be at least four feet from the floor, and my students are all around four feet tall or less.

And finally, what is the BEST material to use for the screen? I've heard spandex, cotton sheets, painters drop cloths, and shower curtains. I've also read that Tyvek works too, but doesn't that stuff have printing on it?
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post #2 of 5 Old 08-02-2011, 11:40 AM
 
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First, a front surface mirror is best, but a rear surface mirror will work--either will lose some light output, though. You might notice a slight double image, but that should be okay for your situation. Project on a wall and measure the screen size vs. the projection distance and trace a sideview of projector, light projecting out of lens, and screen onto a piece of 1/4 inch ruled grid paper--where 1/4" = 12" or something you relate to. Then fold to your hearts content until you get the proper distance setup and the mirror height will pop out of your diagram at the fold. Width of the mirror will be based on whatever screen ratio you are using: e.g. 4:3, or 16:9. If the you need to project off axis to lower the projector or to increase projection angle, you will have to deal with some keystoning adjustment and a more mirror height.



I've made many folded mirror projection units back in the day using sony 15" tvs, a projection lens and a mirror. The image will be reversed or upside down and you will have to compensate in the image settings for this. A translucent shower curtain will work for a screen. Search for other rear projection units on the DIY thread.
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post #3 of 5 Old 08-03-2011, 08:55 AM - Thread Starter
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Wow.

Thank you very much. Your information might very well have a positive impact on how I deliver instruction to my first grade students. Go ahead and buy yourself an "I made the world a better place" beer (or mocha or hot chocolate) today. I'm heading to Lowe's to look for a mirror and some screen material.
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post #4 of 5 Old 08-03-2011, 10:14 AM
 
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Any teacher willing to go through this much effort (granted it also will be a fun project) to excite first graders to learn deserves more applause than I can give...You'll be the favorite teacher in school (if the administrators don't get in the way--of course).
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post #5 of 5 Old 08-09-2011, 05:48 AM
 
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MrC--Any progress?
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