P3D Re: white LEDs

[Tom Hubin <thubin@xxxxxxxxx>]

Hello Greg,

>   Tom H. is talking about using a single LED
> per side and condensor optics to project all
> of the emitted light through the film chip.
> This is much more efficient than bouncing the
> light off a white reflector or diffusing it
> with white or frosted plastic or glass.

I may have found an ok diffuser. Edmunds has lenticular cylindrical
arrays in large sheets. The 53 per inch and 64 per inch arrays should
diffuse over about 10 to 11 degrees. The 142 per inch array should
diffuse over about 30 degrees. These are sold in 11 inch to 15 inch
square sheets. I do not know if they are rigid or filmy. 

The nominal diffusion angle is determined by dividing half the cylinder
width by the cylinder focal length. Then the inverse tangent will give
you a half angle. Double this to get the full divergence angle. I do not
know how the light is distributed within this angle. Does anybody have
some of this material or any other material that they would be willing
to part with? I can experiment with a small piece and a laser pointer to
determine the suitability of the material.

To be suitable, the material must diffuse the light the way I want it to
and also the user should not be able to see the lines of the diffuser.
That means placing it far enough away from the slide that the lines are
way out of focus.

Since the user is viewing through the eyepiece I would like to know what
the expected depth of field is. The focal length of the eyepiece might
be 45mm. The usable aperture is limited by the users eye pupil to about
7mm in low light. Maybe 3mm pupil if there is lots of light. I'm
thinking that placing the lenticular diffuser about 7mm to 20mm behind
the slide should blur the lenticular lines and any details of a Fresnel
lens. Any thoughts or experimental data on this?

Tom Hubin
thubin@xxxxxxxxx