Okay, introduction and my crazy projector project.

Hello All,
So I am involved in this crazy projection project and I have been all over the net looking at stuff and I am hoping that I can get some help from y'all.
The project that I am helping with is called a roto-tri-phantascope!! I love that name. It's sorta a crazy old fashioned slide projector with three different projection lenses and the slides are on a loop of 'film' that rotates thru each projection lense in turn. One of the lenses was angled down, the other straight ahead and another angled slightly up. They were used back in the day to project images of ghosts, angels, spirits, demons onto a translucent screen, or even better, onto a wall of smoke or fog. With the three angled lenses the projected images would start on the ground and appear to rise up high into the sky.
Another crazy thing about these projectors is that they used lime-light as a light source. Lime-light is the intense bright white light produced when an oxy-hydrogen flame is directed onto Calcium Carbonate.

So maybe this post should be in the madscience section or whatever but we are projecting an image and it seems like this is the best place to go to get real world info on how exactly to project an image.

Some of the things I am worried about are: the intense heat of the lime-light-how can I protect the optics from it, If I can even use the plastic Fresnel lenses in this case.

Luckily I am not building the machine or figuring out how to make the lime-light work. I am just supposed to help them figure which lenses to use (hence my earlier post).
So if someone wanted to shoot me back some ideas on how to deal with the heat and which lenses to use (see my earlier post) I would really really appreciate it.
forget lime-light

This will be MUCH easier, and MUCH safer if you forget about using a limelight. Just do the same thing using a metal halide lamp: No toxic fumes, no open flames, no film igniting!

If your film is large format (ie. say 4" diagonal frames), then you mgiht consider CRT projection lenses. They give you a really large bright image, by focussing on something within a few centimeters. If your film is smaller, then you might want to use standard 35 mm slide projector lenses or even 16 mm movie projector lenses.

All of these can be obtained at surplus prices (or even free), since a lot of these technologies are being replaced by digital stuff.
Hi Guy and thanks for the response I really appreciate it.

This will be MUCH easier, and MUCH safer if you forget about using a limelight. Just do the same thing using a metal halide lamp: No toxic fumes, no open flames, no film igniting!

Believe me I know this. This projector is for an art installation at the Burning Man Arts Festival. I am not the main artist I have just been tapped to help them figure out the optics. The artist has a page that explains her vision.
Here's a shot of the phantascope
To give you an idea of scale the ball feet are one foot diameter.
So the whole point is to make it using retro tech stuff and yes it should be a bit dangerous.

Thanks for the tip on the film size. I don't know if they have seriously decided on a format yet...you know artists sometimes its hard to nail them down on the details......which I am sure is going to have me pulling my hair out over this.

Thanks again for the reply
scale of device

Based on the size of the whole device, I think the big CRT projection lenses would be great. I have seen them for as little as $25 for a matched set of three on eBay. They could easily be dressed up for "authenticity" using some DIY brass cylinders, to get that 18th century look.

You might want to suggest the artist work with a $100 metal halide setup for initial design & testing. The trickiest part will be getting the limelight portion to work for more than a couple of minutes, without serious melting and fire issues. I suspect that will be so unsuccessful, that she will instead choose to go with the MH lamp for the actual shows.

Unless she had in mind a single show of a few minutes, that ends with the entire device self-destructing! (Which, of course, would be part of the performance art.)

One point though: Your description of the illusion does not match the design in the drawings. If the film rotates counter-clockwise past the bottom lens, the object will appear 1/3 of the way up the "screen" and then move down. As rotation continues past the middle lens, the object will jump suddenly to a height 2/3 up the "screen" and appear to move down. Then as rotation continues past the top lens, the image will jump to the top of the "screen" and appear to move down before dissappearing. If you rotate the film clockwise, then the image will still have the jumps but will move upward within each 1/3 of the "screen". (Just in the wrong order!) So in neither case will it appear to start at the bottom and move continuously up to the top.

If it must move continuously , then I think you will need to use a point-source lamp without any lenses. This projects the images much like the sun through a stained-glass window. (ie. not a focussed projection)


2005-03-14 12:47 am
How about angling the top lens down, and the bottom lens up, and running the film top to bottom? As drawn below there will be a gap between projections, but if the lenses have a bigger focal length I think the optics could be worked out.


Although...I almost didn't say anything. I thought the tradition at Burning Man was to have some massive elaborate contraption that doesn't work as planned, or breaks, and then everyone smokes some "cigarettes" and decides they like the effect anyway, or what it says about postmodern anachro-mysticism, man! Success!
Yeah, that would work

Much better. With the right focal length lenses and the film the right distance back from the lenses, I think this would give you pretty smooth bottom-to-top images. They might get dim or even dissappear briefly as the film object moves from one lens to another, but since the "screen" is just a smoke cloud, I don't think that would be very distracting!

But maybe it would also work with no lenses at all: Just a very bright point-source lamp doing direct unfocussed projection. This would give you lousy video images, but it might be fine for projecting "spirits" on smoke. This is "magic lantern" technology from about 1850! It's worth an experiment or two to see.

The key relationship would be the size of the film versus the size of the lamp. A MH lamp, a carbon-rod arc lamp or a small limelight would be good with film say about 12" wide and 3 or 4 feet from the lamp.