Phase-type focusing screen

摘要

A focusing screen has a base plate with a planar surface. A plurality of unit regions are arrayed with a periodicity on the base plate planar surface. Each of the unit regions comprises (1) a first plurality of convex portions or concave portions having planar surfaces substantially parallel to the base plate planar surface and having a first height different from the base plate planar surface and having at least two different diameters, and (2) a second plurality of convex portions or concave portions having planar surfaces substantially parallel to the base plate planar surface and having a second height different from the base plate planar surface and having at least two different diameters.