focusing zoneplates

I'm going to try making some zoneplates. I've read about that zoneplates
require focussing. None of my cameras pinhole cameras can focus. Is
zoneplate focusing necessary in all cases? Is focusing needed only for
subjects that are close to the camera?

Does it matter whether a positive or negative image of the zone plate is
used? Does the center circle have to be opauque?

Thanks

Gord

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Gordon J. Holtslander Dept. of Biology
holtsg@duke.usask.ca 112 Science Place
http://duke.usask.ca/~holtsg University of Saskatchewan
Tel (306) 966-4433 Saskatoon, Saskatchewan
Fax (306) 966-4461 Canada S7N 5E2
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Received on Thu Jan 3 12:38:29 2002