Defocused unicell photometer with diffusion zone

Claim 1

A defocused unicell photometer for use in photographic apparatus comprising: a photosensitive transducer having a photosensitive surface thereon of predetermined dimension, said transducer operating to provide an output response which varies in correspondence to the intensity of actinic radiation incident to said photosensitive surface; a positive lens element of predetermined focal length concentrically disposed about an optical axis which axis ultimately intersects said photosensitive surface, said lens element being spaced apart from said photosensitive surface by a distance different from said lens focal length and cooperating with said photosensitive surface to define a field of view for said photometer such that said lens element operates to direct actinic radiation incident thereon from said field of view towards said photosensitive surface, said lens element additionally having at least one light diffusing zone disposed on only a portion of the surface of said lens element for scattering that portion of actinic radiation, which directly impinges on said zone from said field of view at angles which would otherwise be refracted into a path directed toward the center of said photosensitive surface, to reduce the intensity of said portion of actinic radiation which ultimately impinges on said photosensitive surface from said zone thereby effecting a corresponding suppression in that portion of said output response from said transducer which is directly attributable to said portion of actinic radiation, and means for stationing said transducer and lens element in substantially lighttight, spaced apart relation with respect to each other.