I used to use the Kodak lith film with the built in dot pattern - they used an elliptical dot shape so that as you got to the mid grays all four corners of the dots didn't touch at once which could cause a bump in the curve - ie a sudden transition that could be visible. Instead, pairs of dots would touch in the long direction at about 40% and all dots would touch at about 60% so you got a musc smoother scale - but could have issues when printing multiple colors at standard angles to each other. The links show some examples of the effect of dot shape.
https://workflowhelp.kodak.com/displ...out+dot+shapes
I'll look around and see if litho film like that is still produced. If not, I'd imagine that's something you can't reproduce with a contact screen over a negative, no?
http://the-print-guide.blogspot.com/...ot-shapes.html
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