I have found out some interesting things about the economical mask making process which was discussed here a while back. First I found a paper on this process which goes into some detail on what works and why. It is: Suleski, Thomas and Donald O'Shea. "Fidelity of PostScript-generated masks for diffractive optics fabrication". Applied Optics. February, 1995. p.627-34. I just ran an experiment using this process of laser printing to film and then photoreducing by a factor of 10 only to discover exactly what O'Shea has published. There are indeed limits to this process. Thermal fluctuations, small dust particles, and lens aberrations are the biggest causes of problems based upon what I've read and heard from people. The best O'Shea has been able to do is 8um with his lens system, although he mentions using a better system for a 2um resolution. The people I've talked to have only been able to do 5um stuff with their ruby-lith process. The best I personally was able to do was about 20um. Justin Mansell | "The voyage will be a success only 1626 E. 115th St. #102| if the ships do not collide AND each Cleveland, OH 44106 | ship is seaworthy." (216) 754-1691 | -C.S. Lewis on Morality