halftones and dpi for screen printing

Getting back to your original question.  If the printer says they can print a 65 LPi halftone dot, then your file only has to be 130 PPi ( 2x the LPi ).  The DPi is determined by whatever output device you are using.  In order to process and print a 65 LPi halftone, you would need around a 1200 DPi output device.  Photoshop doesn't care what DPi you use.

There's no need to go to Illustrator with the photo.  You can print from Photoshop using the 1-bit halftone.  The thing that you have to keep in mind is not so much DPI ( which is an output resolution ), but the actual screen mesh used for the actual screen printing.  You also have to figure "screen angles" into the matrix because the screen angles are affected by not only the grament material, but the screen mesh, too.  So, I would recommend contacting the printer and finding out what screen frequency ( LPi / lines per inch ) will work best on the type of garment you are planning to print-on and ask the printer what mesh they plan to use for your job.  I've seen 35 LPi halftones; I've also seen 65 LPi halftones.  The finer the screen mesh, the higher the LPi.  Tell the printer you have a 2-color job printing halftones and you need to know what LPi and what angles to use for color #1, and color #2.  Then, you can input that information into the separation halftone files in Photoshop.  Remember to discuss the garment type ( thread count ) and the mesh of the screen.  If the printer is good and knows what they are doing, they will give you everything you need to know.  If they do not, they'll refuse the job.

dyad,

I believe this is one for the Photshop or Illustrator forum.

http://forums.adobe.com/community/photoshop/general

http://forums.adobe.com/community/illustrator/illustrator_general?view=discussions#/?per_page=100