HELP: What kind of film is used in making color separations (and who sells it?)??

Donald Miller said:

If you are wanting to take a camera negative to an enlarged positive, then I would suggest that you look into APHS film. This film is a halftone film that I have used for masking and also for making enlarged negatives (requires an intermediary step beyond what you want to do).

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I've got some on order with Freestyle, could you please elaborate on what exactly "halftone" is? (as opposed to..?)

Donald Miller said:

I have used dektol in dilutions that range from 1-30 for unsharp masks to 1-10 for continuous tone negatives of normal density.

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I keep hearing the term "unsharp mask". I'm only acquianted with it as pertains to <gasp!> photoshop. I know it must stem from some traditional process. Would you be willing to elaborate on this subject? Does it yield the same results as its digital counterpart? (namely.. sharpening images)