If you check out the May/June 2002 issue of "View Camera" magazine, you will find an article written by Bob Herbst which shows step-by-step instructions for making optically enlarged negatives in the darkroom with the idea of printing for alternative processes. If you are unable to locate that particular issue, you can go directly to his web site at www.bobherbst.com. and click on "Writings". He recommends using APHS film which is no longer available, but you can probably use litho film from Ultrafine.