Optical system for forming a windowed web in a color cathode ray tubescreen structure

Claim 1

An improvement in an optical system for photo-forming the multiple window pattern of the opaque interstitial web of a composite color cathode ray tube screen structure on a screen bearing surface having a foraminous mask spacedly related thereto and a central axis therethrough to provide a variable gradient of screen window sizes from center to edge of said screen and effect substantially constant window sizes in annular orientation progressively about said central axis, said optical system having an axis and incorporating therealong a primary elongated source of exposure illumination having a longitudinal axis oriented substantially normal to said system axis in a manner to emit substantially nonsymmetrical illumination relative to the axis of said system, an associated light source collector rod, and a lens having transverse X and Y axes with a center plane therethrough, said optical system being positioned in a manner to direct light emanating from said collector rod through said foraminous mask to photo-dispose the multiple window pattern of said interstitial web on said screen-bearing surface, said improvement comprising: a composite light attenuation coating of differential nonsymmetrical density discretely vapor disposed in first and second related and predetermined patterns relative to a surface of said lens in a manner to affect the light transmitted by the lens portion utilized for the passage of exposure illumination therethrough, said lens being oriented in said optical system with its X axis substantially parallel with the longitudinal axis of said elongated light source, said first vapor-disposed attenuation coating pattern having a differential density affecting primarily the Y axis region of said lens in a gradually decreasing manner, from the central region of said lens to the periphery thereof, said second vapor-disposed attenuation coating pattern being in general of hEavier differential density than said first pattern and being in the substantially generic form of a modified lemniscate having a major dimension oriented in the lens transverse region related primarily to the X axis thereof and a minor dimension substantially coincident with the related Y axis of said lens, said lemniscate formation having a waist section with substantially equi-sized lobe portions on either side of said center plane including the related Y axis of said lens, said related attenuation patterns of differentially vapor-disposed coating providing control of the exposure illumination to effect a predetermined variable gradient of window diameters from center to edge in said interstitial screen pattern and provide windows of substantially constant size in annular orientation progressively about the central axis of the composite screen structure.