USE OF A THIN FILM OPTICAL FILTER TO ACHIEVE UNIFORM IMAGE IRRADIANCE
Original Publication Date: 1979-Aug-31
Included in the Prior Art Database: 2004-Apr-02
Xerox Disclosure Journal
In the figure, lamps 2 provide full frame uniform illumination for document 3 on platen 4. Lens 5 projects an image of document 3 onto image plane 6. As is well known, the irradiance in the image plane falls off with a distance -rom the axis. This falloff, in the case of a non-vignettinglens, often follows4a cos 9 relationship where 9 is the semi-fieldangle. Near the optical axis the cos 9 factor varies only slightly from unity but with full frame exposure systems, the incidence falls off towards the edges to a value that may be on the order of half that of the axial value.