In-camera half-toning

[BetterSense]

The whole point of the exercise, though, was to be able to make continuous-tone pictures using semiconductor photoresist, because it's safe to say that photoresist is going to be around longer than litho film. I guess I need to find a photoresist that is sensitive to near-visible light or the deal's off anyway due to the UV thing.

 

[holmburgers]

I think you should still try it. It's just a matter of how long the exposure takes, not if it will take. It will, it just might take a day or two.. haha, hopefully not.

 

[holmburgers]

Picked up a Polaroid half-tone line screen (85 lines per inch) on eBay recently. It's made for some Polaroid camera, but it's 4x5" and should work well for that format as well.

The trick will be mounting it and adjusting the spacing.

However, what does anyone know about making analog half-tones? Like approximately how far from the film should the screen go? My limited understanding is that distance from the film and the f-stop allows for control over the half-toning.

Does anyone know of old trade publications, or instructional pamphlets for making half-tones? Surely there's a lot, this just isn't a field of research I've really looked into.

 

[holmburgers]

eBay #160722629230

This is a Kodak Gray Negative Contact Screen. It is an 85 line eliptical dot screen. It is 8x10 inches. The Kodak stock number is 148 6399.

Can anyone tell me what exactly this is for? Is it for creating half-tones by contact printing, or something else?

 

[Bill Burk]

It is for creating halftones from continuous tone subject. It is placed in contact with the film (or photosensitive material) as a sandwich using a weak vacuum to maintain contact. You could use it for contacting a negative, or expose in a process camera. It would be "hard" to use in a regular camera because it would be hard to make a sandwich with the screen in close contact with the film.

85 lines is relatively coarse, newspaper grade, suitable for a hand-coated high-contrast light sensitive material. Great for experimenting because it will give successful (at least interesting) results even if your material is crude or the contact is imperfect.

 

[holmburgers]

Awesome Bill, thanks much.

I have the abovementioned polaroid halftone screen (also relatively course), but I have yet to figure out a way to actually utilize it in my camera. With this thing, I can just do it on my baseboard. Great!

Ok, now just to be sure.... you place this in contact with a senstive film and then project a negative onto that sandwich(?) At first I was thinking that maybe you could stack all 3 elements; sensitive film / half-tone screen / negative <--- light source and contact print it.

Or would both ways be effective?

This press stuff is still a bit of a mystery to me... I thought that a certain degree of separation (1/16th" for instance) was necessary in half-toning.

 

[Bill Burk]

Both ways will work. Space was only needed if the contact screen was itself high-contrast black crosshatch lines etched on glass. These contact screens are basically continuous tone fuzzy dots.

 

[holmburgers]

Thanks again Bill, that makes sense.

What I really need is a good book outlining photomechanical techniques. Any recommendations?

 

[Bill Burk]

Hoo boy, I used to read these things like Zone System manuals. I gave my entire library of print books away to photo teacher Alex Robb about 23 years ago. Can't remember a single title.

The most interesting ones talk about glass halftone screens and letterpress.

 

[holmburgers]

Shoot... well I'll have to do some digging. I'm sure there's no shortage!

 

[Joe VanCleave]

I'm assuming the OP wants to use semiconductor-grade photoresist because he expects it to be available for many years to come. Of course, this implies he will have to use TMAH (TetraMethylAmmoniumHydroxide)-based developer for his plates. Not so sure how easy this will be to acquire in small quantities.

An alternative process is photogravure, which uses a similar light-sensitive coated plate, but one which becomes water-soluble after exposure to UV light, making development much easier. I would assume the print-making industry will be around for a long time, and that there are enough artisans working in this medium (photogravure) to make the materials readily available for years to come. The process, you may be aware, produces a plate suitable for impression-printing in a press, using ink onto paper.

Properly printed to the right paper, photogravure images are wonderful to view and are very archival, and were in fact the first high-volume publication method for printing photographic images.

~Joe