Re: compensating zone plate

----- Original Message -----
From: "Colin Talcroft" <ctalcroft@yahoo.com>

> Perhaps a silly,
> just-woke-up-and-checked-my-mail-while-still-sleepy
> kind of thought, but.....

I think we are invading the domains of the sci.xrays.focusing.devices
newsgroup with this thread! :-)

> What would happen if you projected a zone plate
> pattern of rings onto the surface of a largish half
> sphere? Wouldn't that bring the outer rings closer to
> the film plane? Would that help to compensate for fall
> off? I imagine you'd need a lot of rings.

would that be a convex or concave half sphere (as seen from the film)?
Either way, the more rings you have the faster the ZP but the less signal to
noise ratio you'll have. In a zoneplate, the only imaging forming light is
that which has been diffracted by the very edges of the dark rings.

> Also, I've long wondered why no one makes zone plates
> by etching and staining glass. Every zone plate I've
> seen has dirty, scratched, cloudy clear zones because
> it's been made on film base.

It shouldn't necesarily be so, otherwise, all very dark objects+shadows in
our regular photos should have white spots, scratches and white clouds. I
admit that processing lith film in a developer like dektol, tend to produce
those imperfection you mention, but by experimenting with dektol dilution
and film exposure, a combination of those 2 factors can be reached that
produce clean enough clear rings.

> Wouldn't glass be better?
> Could probably be done using photoetching. Maybe too
> complicated, probably too expensive.

Probably, besides, there is no money in selling this stuff, ZPs are so
esotheric for many people. I sell Zoneplates and if I really charged my
time spent doing them, they should easily cost at least 4 times what I sell
them for. I make then on lith film, BTW.

Guillermo
Received on Tue Aug 21 13:21:04 2001