ZP_Salon

Atelier Bonryu(E)

zone plate photography

Pattern of zone plate: As described previously a pattern of a zone plate is designed so that light waves diffracted at transparent zones arrive at a focal point in phase, where the intensity of light is enhanced. Usually the “number of zones” means the sum of the numbers of both the transparent and the opaque zones but sometimes the number of the transparent zones is called the number of zones. In this site we employ the former standard definition in principle. We count the transparent zones as m=1,2,....M where M is the total number of the transparent zones, and count both the transparent and the opaque zones as n=1,2,...N where N is the total number of zones. When we designate a boundary circle between a transparent zone and an opaque zone, we call it as “the n-th boundary circle counted from inside”. Sometimes, it is conveniently called as “the outer boundary of the m-th transparent zone” or “the inner boundary of the m-th transparent zone”.

The radius of the n-th boundary circle counted from inside

is given as (*1)

where

and

denote the wavelength and the focal length, respectively. This formula is valid both for a positive zone plate (with a transparent central zone) and for a negative zone plate (with an opaque central zone). However, to design a zone plate, it may be convenient to assign the radius of the outer boundary of the m-th transparent zone counted from inside as