Half tone screens and half tone negative reproduction

[blindpig]

I suspect you'd be way ahead printing your photos on some iron on material as the halftone screens aren't black and white as Jim Jones said.The soft edges the dots have won't reproduce well on a silk screen because of the nature of the gray dot pattern and conflicting silk screen lines and the halftone line arrangement of the halftone screen itself,
IMHO.

[Gary Beasley]

The resulting halftone you would produce should have hard edges to the dots. The soft edges of the screen dot used on lithographic film creates dots of different sizes to cause the visual effect of grey tone. The spacing of the dots will cause moire patterns with the silkscreen mesh if oriented wrong and/or the line ratio is not good. Experimentally I found that a 300 mesh screen works well with a 75 line screen printing on non textile flatwork.

[senderoaburrido]

I managed to find a guy who has an old industrial printing camera who has some in Ontario. He has a bunch of these screens, and he's willing to chop them down to size for 5$ a piece. I'll update once I receive them.

Just to be clear: I enlarge onto the copy negative with a slate of glass keeping the contact screen flush over it, right?

[Gary Beasley]

Right. The screen is actually photo emulsion so you will want to determine the emulsion side of it and place it emulsion to emulsion. The halftones generally require a bump exposure to bring up the shadow dot. Experimentation will find the right bump exposure, a weak diffuse light giving just enough to create a small dot without any other exposure. Then you find the required exposure to the image to get a highlight dot that is still open enough to print right.

[senderoaburrido]

What do you mean by a "bump exposure"?

[Gary Beasley]

It's a non image exposure for bringing the shadow dots up. Without it the image would be blank in the black zones and shadow detail would be lost. In practical use the smallest shadow dot that will remain open using the printing method chosen is determined and the required bump exposure to get that size dot in the shadow is used before or after the image exposure. For silkscreen that will be a bit large due to the ink flooding into the small dot detail so the positive will look a lot more gray than you want the finished print to look.

[bob carnie]

Gary or others -

I have a question slightly off topic but I think relevant
Some of the best Carbon Colour Printers and Gum Printers for that matter are using a stocastic screen pattern to create their prints.
The screen is applied at a screen printing shop that is traditionally what you all are talking about here.

I am working with continuous tone silver film or I am using pictorico overhead transparancy film and separating the the image into four negatives and making prints with some success. Using
tri colour gum over pd.

I have some knowledge of the graphic arts - film to plate - film less plates but not at a level that I would like( for example I remember the bump but could not explain.}

Here is the question.

I have a Image setter that can produce a con ton negative or print... have you ever heard of applying a screen to each file that is then sent to an image setter like mine or
an inkjet printer.. I think the end result would be a negative with the required hard dot that may hold the pigments much easier.

I am thinking that this would work as if I scan and 35mm colour negative or black and white negative- put it to my image setter and make prints- the resulting print if you take a loupe
to the print or film you will see the film grain, and not pixels as one would imagine... therefore I am taking the leap that the pixels are smaller than the input original.

If so applying a fine screen pattern would then of course be visible in somewhat the same manner. which the would work much like the Ganglers, Taylors of this world.

This application could have great benefit to rotogravure workers or colour alternative workers wanting to lay down tone without a lot of image bleed from trying to do it with contone film.
BTW the contone film works but the resulting print is somewhere between a Fresson or a dye transfer- I think by applying a hard dot at the file stage may work.

your or any thoughts on this would be appreciated.

I actually have more questions but I will see how this one plays out.

Bob

It's a non image exposure for bringing the shadow dots up. Without it the image would be blank in the black zones and shadow detail would be lost. In practical use the smallest shadow dot that will remain open using the printing method chosen is determined and the required bump exposure to get that size dot in the shadow is used before or after the image exposure. For silkscreen that will be a bit large due to the ink flooding into the small dot detail so the positive will look a lot more gray than you want the finished print to look.

[bob carnie]

Also I do apologize to the OP if this takes the topic off track.

[Gary Beasley]

I've got no experience with imagesetters but a platemaking machine is doing much the sameexcept it burns a hardedge screen pattern withe required printing angles or some will also do stochastic dot as well. Its all in the software driving it so you might want to pose that question to you imagesetter tech or manufacturer and see if the software for that particular machine will support what you want to do. I know imagesetters came a little before the laser platemakers and were making litho style negs for plateburning the old fashioned way, so it may be a case of using different film and chemistry to get what you want.

[senderoaburrido]

When you say non-image exposure, you mean that I do an initial exposure of the negative I want to copy the image to without the original transparency in the enlarger, so that there is already a lightly exposed, uniform halftone pattern across the entire negative? I feel like my reading comprehension is poor, here. Should I maybe consult a manual for this process? There must be one online.