Method for manufacturing a master die for a diffusion plate and diffusion manufactured by said method

#1. Field of the Invention

#The present invention relates to a diffusion plate which is used, for example, as a focusing screen in a single lens reflex camera, and a method for manufacturing a master die for such a diffusion plate.

#2. Description of Related Art

#The invention will be described below in detail with reference to the accompanying drawings, in which;

#FIG. 1 is a schematic view of a structure of a known diffusion plate having the highest possible density arrangement of micro lenses;

#FIGS. 2, 3, and 4 are diagrams which show defocused images of a point light source by the diffusion plate, as shown in FIG. 1, at wavelengths of 450 nm, 550 nm, and 650 nm, respectively;

#The illustrated embodiments, which will be discussed below, are applied to a diffusion plate which is used as a focusing screen provided in, for example, a view finder of a single lens reflex camera. In FIG. 113, a bundle of rays, reflected from an object to be photographed, are transmitted through a taking lens 101 and reflected by a quick return mirror 102, before being converged onto a focusing screen 100, so that a photographer can observe an image of the object through an eyepiece 103 and a pentagonal prism 104 of a view finder.

#FIG. 24 shows a basic pattern of a diffusion plate, according to a first embodiment, in which microlenses f (micro structures) of 1.2 .mu.m height and 10 .mu.m diameter are arranged with the highest possible density at a pitch of 16 .mu.m. FIG. 25 shows another basic pattern of a diffusion plate, according to a first embodiment, in which microlenses f (microstructures) of 1.2 .mu.m height are arranged in a manner having the highest density possible. The microlenses are arranged having a pitch of 16 .mu.m, similar to FIG. 24, but there is a difference of 30.degree. in the orientation between FIG. 24 and FIG. 25.

#FIG. 26 shows a resultant pattern of a diffusion plate which is a combination of the basic patterns shown in FIGS. 24 and 25. Note that there is no periodicity in the resultant pattern of the superimposed basic patterns. Although the resultant pattern may appear periodic, it is not.