Atelier Bonryu(E)

zone plate photography

 
 

Laboratory: Zone Plate Photography

Principle of Zone Plate Photography

- Remark -

Remark#1: Radius of a Zone

A pattern of a Fresnel zone plate consists of alternatively placed transparent and opaque zones.  Both patterns with a transparent central zone (a positive zone plate) and with an opaque central zone (a negative zone plate) are permissible.  The radius of the outer circular boundary  of the m-th transparent zone is given by the following equations where
are the wavelength of light and a designed focal length.
         
: a positive zone plate
         
         : a negative zone plate
In the case of a positive zone plate the first zone (m=1) is the central circle and the radius is given as
.  The radius is equal to that of a pinhole with a focal length
  derived by a simplified method (Pinhole Salon Remark#4).  As described previously if the pinhole radius is optimized with respect to the divergence due to diffraction the pinhole radius is given as
.  But for the calculation of the zone plate radius we don’t consider a similar condition and, therefore, an equation with different coefficient was obtained.  The difference of the coefficients has little effect on taking a pinhole photograph.
 
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