Diffusion for Homemade film projector

[TroyG]

Hey there, gang!

I'm in the midst of building an attachment for the back of my Graphic View that will make it function as a film projector. Its simply a housing that will velcro on the back of it and carries a light source and a slot for film. My light source of choice is is strips of LED tape, mostly for weight and heat reasons. However, since it's many tiny LEDs, I need to diffuse the light substantially so as to avoid many hot spots.

My question is this: where should I put the diffusion? My initial thought was to install it partway between the lights and the film, but I think the further from the lights it is, the better job it will do of evening out the light, is that correct? If so, the film holder I've made for this system two glass pieces hinged together. That way I can sandwich slides of any format (up to 4x5) in the holder and drop it in. If more distance is better, would it behove me to attach the diffusion gel directly to one side of the film holder? That way the greatest possible distance between the light and the film is achieved and as long as I slide the holder in the right way, I don't see why that wouldn't be fine. But thats why I am asking you all! Do you foresee a problem with affixing the diffusion to the backside of the glass slide holder? Should I perhaps do both and install one sheet of diffusion partway between the film and the holder and some on the holder as well?

As always, thank you for your time and wisdom!

[plaubel]

I really believe that you need more power than some LED strips for a bright slideshow, especially with sandwiches.
For braking the light rays (diffusion) I would bring the diffusor next to the light source, between bulbs and film.

If your DIY project doesn't work successful, you could buy something like this:

166954
Right light source, right diffusion, right optical system, and of course right size for using 4x5" slides :-)

Ritchie

[Jac@stafford.net]

Your post persuaded me to my storage place where I found a lot of large diffusion filters intended for cine work. Some are black dot types, others are simply diffuse. Look into the same.

@plaubel - do we need that exact breed of dog to make it work?

[TroyG]

I wish I could buy a projector but so many have propriety lamp/lamp housings. Plus, I can't seem to find many ones that still work online. That and I shoot 4x5, 6x7, and 6x6 slides and don't want to have three projectors. Not to mention I don't really want to mount them in cardboard. That's where the glass sandwich came from: a want for multi-format and no need for mounting.

As per light output I know it'll be quite low. According to spec I should have 810 lumens. The two things I have going for me there is it'll be indoors in a dark room and I don't need to get it very large. Even blowing up a 4x5 up 6ft (assuming my wall has a 0.8 gain structure) at 810 lumens yields approximately 242 Lux. Of course thats not accounting for light loss in the glass sandwich, diffusion gel, and optics, but I think I'd have some wiggle room.

I'll install it between lamp and film, then! Thank you. Hopefully it ends up being adequate, if not, I'd be on the hunt for one of those! My dog would look good next to a projector also!

[plaubel]

@plaubel - do we need that exact breed of dog to make it work?

Not for the projection itself.
But for pulling the beamer around, a strong dog is a good partner :-)


""That and I shoot 4x5, 6x7, and 6x6 slides and don't want to have three projectors""

This type works with 24x36 mm, up to 9x12cm, but he will never reach the quality of MF projectors.

""Even blowing up a 4x5 up 6ft (assuming my wall has a 0.8 gain structure) at 810 lumens yields approximately 242 Lux. Of course thats not accounting for light loss in the glass sandwich, diffusion gel, and optics, but I think I'd have some wiggle room.""

I have no idea what 242 Lux in reality means, but I wish you all the best for your Project.

It may be a good idea to have a look at optical systems like projectors and enlargers.
You surely want to collect the LED light ( remember the condenser lenses) and to bring the rays in a required direction, if you need bright light.
For diffusing the LED points, a longer distance to the film may help.

It is possible to build a really good DIY projector.
But it will take time and a lot of try and error in spite of some optical knowledge.

Years ago I followed a selfmade project and shared some ideas.
This guy planned to realise a 6x9xm and another 4x5" projector.
After a while and concerning the quality/costs-factor, he gave up the 4x5" project for some reasons, but today he sells his 6x9 projectors.

The Epidiascope shown before hasn't perfect quality, but for me it is good (and bright) enough to throw 150cm images to the wall.
Having a look onto this system may give some ideas concerning dimensions (lightsource/film/lens) within the whole system, too.

[jim10219]

You could build your own diffuser. I made one out of the side of a plastic jug from work. It’s made out of the perfect milky white translucent material for such things, and just required cutting to size. Another option would be to make a ground glass. You could even try sanding some acrylic. I’d say look for something from 400 to 800 grit. Or even try a light coat of white spray paint.

Something else that might help is lining the box with the LED’s in aluminum foil ( attached with super 77 spray glue). That will help to reflect more light and decrease hot spots. Just be sure to isolate your electrical contacts so they don’t short out on the aluminum. Liquid electrical tape works well for this.

You might be able to get enough light that way. Though I imagine you’ll still need to figure out some solution to deal with the heat, because while LED’s don’t generate a lot of heat on their own, getting enough to make a decent projection probably will.