P3D Re: Viewers and white LEDs

[Tom Hubin <thubin@xxxxxxxxx>]

Hello Greg,

>   If you go with condensor lenses then
> I guess they need to be equal in diameter
> to the size of the film. This isn't too
> bad for 5 perf Realist images but would
> make for a big light box for a medium
> format viewer (70-some mm diagonal).

A 70mm diameter condenser lens is heavy if you use spherical or aspheric
lenses. But light weight Fresnel lenses are available that should be
adequate. Keep in mind that all distances and focal lengths have also
scaled up. The LED is twice as far away if you want to illuminate a
slide that is twice as large. The eyepiece lens is twice as far away.
The condenser lens still needs to image the light source onto the
eyepiece so that focal length has also doubled. Seems like it is no more
difficult than a 35mm viewer. Just larger.
 
>   BTW Edmund Scientific sells holgraphic
> diffusers in 25 and 50mm diameter. They
> have 10, 15, 20, 25, 30, 40, 60 and 80
> degree diffusing angles available.
> Unfortunately they are $90 and $130 a
> piece (25, 50mm). Part Number J54-492
> to -507.

I saw that in the catalog. Very expensive for a home viewer. You are
paying for exact control of the diffusion angle. Seems like there ought
to be a cheap material that we can adapt as a small angle diffuser. I
wonder if we can buy small chunks of rear projection lenticular screens
to use as small angle horizontal diffusers. 

Tom Hubin
thubin@xxxxxxxxx