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USE OF A THIN FILM OPTICAL FILTER TO ACHIEVE UNIFORM IMAGE IRRADIANCE

IP.com Disclosure Number: IPCOM000024065D
Original Publication Date: 1979-Aug-31
Included in the Prior Art Database: 2004-Apr-02
Document File: 2 page(s) / 179K

Publishing Venue

Xerox Disclosure Journal

Abstract

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.

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XEROX DISCLOSURE JOURNAL

USE OF A THIN FILM OPTICAL FILTER Proposed Classification TO ACHIEVE UNIFORM IMAGE IRRADIANCE U.S. CL 350/311

Kenneth W. Aitfather mt. CL G02b 5/20 James R. Law

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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 follows

4

                                       a 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.

To correct for this irradiance falloff, an optical filter S is placed at the entrance (or exit) of lens 5. Filter 84s a thin film filter having a narrow band transmission profile which varies in a sec 9 relation with the angle of incidence. The filter will therefore transmit approximately 100% of the light incident at the wide angles and transmit only a portion of the energy incident at narrow angles.

Volume 4 Number 4 July/August 1979 485

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                  XEROX DISCLOSURE JOURNAL 486 Volume 4 Number 4 July/August 1979

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