Re: [ATM] Telescope could focus light without a mirror or lens

["Mel Bartels" <mbartels@bbastrodesigns.com>]

> Bob May wrote:
> >
> > All in all, something that is neat for doing crude optics with
> > but not going to be used for astronomical purposes as it is not
> > going to do the job.
> The fine print I read had me thinking that the results were
> strongly dependent on wavelength, perhaps as much as a singlet.



This came up in an article reporting a proposal for an exoplanet resolving
space telescope.  

In reviewing a couple of articles behind the zone plate, it looks like one
needs millimeter control of the holes and rings.  The plate needs to be held
flat to the same magnitude as the critical focus zone: millimeter resolution
for longer focal ratios.  And for planets, solar and lunar imaging, dumping
90% of the light is a blessing.  

There are examples of zonal plate photography on the web.

Mel Bartels


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