[simpits-tech] Rear projection material+mylar mirrors+projectorratios

[Brian Sikkema]

Heya Rob,

Thanks for the tips! Sounds interesting. But on the
third question, I wasn't really going for the amount
of lumens, but the actual size of the projected image
- i.e. a projector 6' away will make an image roughly
2'x3' in size, etc (just using random numbers for
that example - no idea what it would actually be).

Brian



>------- Original Message -------
>From    : Rob Hommel[mailto:rhommel at mad.scientist.com]
>Sent    : 1/22/2008 9:01:28 PM
>To      : simpits-tech at simpits.org
>Cc      : 
>Subject : RE: Re: [simpits-tech] Rear projection
material+mylar mirrors+projectorratios
>
 >Question #1
Brian, there are several materials that may be used, 
Gene and I have used a high thread count sheet
manufactured by "Martha Stewart" successfully. 
On the pricey side look at diffusion glass for rear
projection this is what the pros use. You can make
your own if 
you are willing. Various sizes are available from
most glass manufactures, they are typically quite
heavy as well as
expensive. 

To make our own use a sheet of plate glass and create
a diffuse surface to project your image upon. Your
diffuse surface may be created using a 6X6 piece of glass
and brake fluid. Apply the brake fluid on the surface
of the plate glass and using your 6X6 glass tool move
the glass in a circular motion moving the brake fluid
as needed 
until the entire surface of your diffuse glass
appears uniformly opaque.

Question #2
I have not tried any of the methods for stretching
mylar at this time, some look pretty good. I worry
about my ability to do it right the first time. 
Just so as you know I think it is worthy of a try
sometime in the future.

Question #3
The light projected is reduced according to what is
referred to as the Chi square law. The light is
reduced according to the square of the distance.
Imagine if you will
that the projected image at 2 foot is a 2 foot by 2
foot square at 1700 lumins. At 8 feet the image
projected is a square 8 foot by 8 foot the lumins
would by reduced by 
the square of the distance in this care 8 square is
64 square feet the total lumins at any point equals
1/64th of the total lumins. Hope this helps.

Keep 'em Flying
Rob Hommel

----- Original Message -----