I think it's safe to say that I don't understand half-tone processes very well, but I'm pretty sure that they are designed to give something that looks like continuous tone results when working with essentially infinite contrast media like lithographic plates.
Suppose the only film in the world was litho film or similar "all-or-nothing" media. Is there any way to use a halftone screen in the camera itself so that you could achieve pictorial results?
If you have a process camera with a vacuum back, it could be used for pictorial results. I did a self portrait once.
The halftone process does exactly what you explain. It breaks a picture into a grid. You'll print tiny dots for highlights, checkerboards for middle gray and almost solid with tiny white dots for shadows. To make a halftone negative you would use a screen to project a fuzzy grid on the high-contrast film. The very earliest screens were two sheets of thin glass with parallel lines etched and inked. Then the two sheets of glass were crossed at 90 degrees back to back to make a checkerboard pattern. Held at a specific distance from the film, each checkerboard square projected a fuzzy image. Where the subject was bright, the whole square would go black but where it was dark the square would only get a threshold pinpoint of dark on the negative. I never actually saw one of the glass screens except in old books.
Later there were contact screens which were basically continuous tone copies of the shadow that the glass screens would project on the film. This is what you probably could get your hands on. You would lay it on top of your film and use a vacuum easel to get the air out.
My God. This thread brings back some interesting memories. I spent almost 8 years as an offset camera operator. Not only did I shoot thousands of B&W halftone negatives from B&W prints, and drawings, but I also did 4 color seperations on a process camera. The camera took up two rooms (one was a dark room) had a copy board that was 40x50 inches, and a film back that was 30x40 inches. It also had four dual tube pulsed xeon lights to illuminate the art work. A single color seperation could take up to 3 to 4 hours.
Polaroid used to sell a halftone kit for their pack film cameras and backs. I used to have one for my MP-4 back in the 80s; sadly, I don't recall ever using the beast.
So If I wanted to do something like this with a 4x5 camera, how would I go about getting a halftone screen and how far would I put it from the film?
A print shop may have half-tone screens leftover from the pre scanner/digital days.
Screens are exposed in contact with the film - there is also the issue of using flash and bump exposures to obtain a full tonal scale, but that is an entire world of alchemy on its own :)
You could only shoot halftones in a camera with a vacuum back. Any air space between the film and the halftone screen film will give you a fuzzy image in that spot. When I made halftone exposures in a process camera; in addition to vacuum, I used a roller to remove air pockets before exposures.
If you are serious going with this , I advise you to use rotogravure elliptical screening like National Geographic Magazine uses. I think you can go from more ordinary way and get your scan file and send to prepress shop via email and if you want a black and white , order the cyan rotogravure screened film.
If they have automatic printer with a developer , it takes their 5 minutes.
At 1994 , AGFA presented crystal screening and it was made using smallest screening dots and density of them. I am far from the sector for 10 years but I think Heidelberg , AGFA , Kodak , Fuji have screen printers. Visit them , learn their technology , select one , find a prepress office who does it and voila.
I originally asked this because I wanted to try photography using glass plates coated with photoresist. I work in the semiconductor industry and regardless of what happens to film, we will always have semiconductor photoresist as long as electronics are being manufactured. The problems with using photoresist are that it's an infinite-contrast medium like litho film, and it's only sensitive to UV light.
Originally Posted by BetterSense
Now you're talking. The "contact halftone screen" needs a vacuum as already pointed out. But older technology glass screen will solve that problem because you have to shim it a certain distance away from the lith film to get a penumbra.
Get the photoresist guys to make you a linescreen grid on glass. A checkerboard pattern. They have the tools to draw lines an atom thick. They could make a checkerboard right off the bat (the old timers had to draw straight lines and cross them for a sandwich. For your purpose look for maybe 65-85 lines per inch. You can experiment with available lith film. There may be unevenness due to your film not lying flat.
I always appreciate your ideas to apply technology in unexpected ways