How to focus the beam from a UV laser as much as possible?

Question

Electronics

What optics should be selected? What is the formula for all of this? Need thickness less than 0.2mm for laser printer to produce PCB with photoresist.

Answer 1

At home, you will not be able to provide such an accurate focusing of the beam.
For the production of PCB with photoresist, a pattern printed on a transparent film and UV lamps are used to provide illumination through a pattern pressed against the applied photoresist.
Transparencies for laser printers are commercially available. The accuracy of applying the toner to the film is 600 dpi typically. There are services for making photomasks, if you need to get even finer lines.
In any case, this method will provide more predictable results than laser beam illumination.