Hi Uli,
It’s actually quite simple:
Step 1: Google is your friend. Find a website that offers a zone plate calculator, e.g.
http://www.whizkidtech.redprince.net/zoneplate/
Step 2: Think about what specifications you need (focal length, aperture, etc.), have them calculated, and print them out (preferably as a negative, i.e. transparent black, opaque white. (Naturally, at an enlargement of 5–10 times if possible). White paper will do.
Step 3: Photograph the whole thing onto reproduction film, which you should develop as hard as possible. When photographing, the scale is of course important so that the whole thing matches the dimensions calculated in advance.
Now stick the film into a pinhole holder with the appropriate aperture diameter.
Done.
Regards
Martin
