Does anyone have experience with making background transparencies? What brand of "papaer" should I look for or does it matter. Do I need a piece of ground glass behind the transparency?
Background Transparencies
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Bob
Background Transparencies
I've used photostats directly (index-matched to glass), but there are polarization problems to deal with. My best results have been when I made a contact copy of the photostat image on a glass photoplate. This is pretty standard for photoresist shooters, I believe. I used to make registered glass contact copies from pin-registered photostats for use as backgrounds in multi-color rainbow holograms for Steve Provence ("King of the Embossed Achromat"), whose studio was next door to mine in Boulder Creek a dozen years ago. Kodak HRP and a green filtered halogen lamp were used. I believe you can still get Kodak HRP plates (green sensitive with AH coating) from Imtec in Sunnyvale.
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Dinesh
Background Transparencies
For quick and dirty, we use a black and white laser printer. Joy makes the image in bitmap mode in photoshop, loads an ordinary transparency film (available at Staples eg) and sends it to the laser printer. An important consideration is to buy the same brand of film as the printer you use. She then has to fill it in with a black marker. We then tape it onto a diffusion glass and back-light the diffusion glass. Remember that in this technique, the diffusion glass is the object and the transparency doesn't have to be applied with any great stability requirement.
For a "real job" we make a mask as above, only much more carefully. We then image this onto a glass plate via an ancient enlarger ( a ginormous beast with a slide for negative film and a projection lens system that projected the negative onto a platform where you placed the positive paper). Develop the bejeesus out of it, really, really dark. This also is placed in front of a diffusion glass, ie the mask is between diffusion glass and H2, and back-lit from the diffusion glass side.
This is a standard method used in photoresist, as Bob says. We did this all the time in the company I worked at.
For a "real job" we make a mask as above, only much more carefully. We then image this onto a glass plate via an ancient enlarger ( a ginormous beast with a slide for negative film and a projection lens system that projected the negative onto a platform where you placed the positive paper). Develop the bejeesus out of it, really, really dark. This also is placed in front of a diffusion glass, ie the mask is between diffusion glass and H2, and back-lit from the diffusion glass side.
This is a standard method used in photoresist, as Bob says. We did this all the time in the company I worked at.
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JohnFP
Background Transparencies
Transparencies are easily made with a laser printer. When we did transparencies as a background we mounted the transparency on to a piece of ground glass with the ground glass toward the film and the transparency away from the film and on the smooth side of the glass. The ground glass was not too "ground". We never had a problem with polarization with this method. It may not project the desired effect but it did in our case and that was just as a background scenery.