EP0033185A2
Expired / Lapsed
EP
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Method and apparatus for compensating for illumination defects in an optical system
Assignee: Xerox Corp
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Filing: 1981-01-05
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Granted: —
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Expires: 2001-01-05
Abstract
Abstract A graded-density filter (36) for a copier has a radially- increasing transmission and is mounted in a fixed position relative to a projection lens (34) in the copier optical system. The filter has a transmission profile which provides compensation, at all magnifications, for photoconductor irradiance falloff due to cos', as well as other circularly-symmetrical non-uniformities in the optical system, such as lens exit pupil distortion.
Inventors
- 👤 James D. Rees
- 👤 Donna U. Ozern
- 👤 Kenneth W. Altfather, Jr.
- 👤 James A. Critchlow
- 👤 William L. Lama
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 10:36
CPC Classifications
G; G03; G03G; G03G15/00; G03G15/04; G03G15/041; G03B; G03B27/00; G03B27/32; G03B27/52; G03B27/54; G03B27/542
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
121 words
A full-frarne, flash-exposure system for a copier including: an object plane (24) on which a document to be reproduced is to be supported; a flash illumination source (39) for illuminating said object plane, and a lens (34) for projecting an image of said document onto an imaging plane (38), characterised by means for compensating for circularly-symmetric exposure variation at said image plane comprising a non-uniform transmission filter (36) mounted in a fixed relation to said lens and having its center on the lens's optical axis, said filter having a central circular area (42) of graded density which provides, for light passing therethrough, a radially-symmetrical light transmission profile which is minimum at the center and which increases with distance from the center.
Claim 2
Dependent Claim
121 words
A full-frarne, flash-exposure system for a copier including: an object plane (24) on which a document to be reproduced is to be supported; a flash illumination source (39) for illuminating said object plane, and a lens (34) for projecting an image of said document onto an imaging plane (38), characterised by means for compensating for circularly-symmetric exposure variation at said image plane comprising a non-uniform transmission filter (36) mounted in a fixed relation to said lens and having its center on the lens's optical axis, said filter having a central circular area (42) of graded density which provides, for light passing therethrough, a radially-symmetrical light transmission profile which is minimum at the center and which increases with distance from the center.
Claim 3
Dependent Claim
67 words
The full-frame, flash-exposure system of claim 1, characterised in that the filter hasstransparent annular area (43) defined by the outer edge of said central area and the outer edge of said filter, said transparent area providing maximum transmission of light therethrough, whereby said filter provides exposure compensation at said imaging plane for the effect of cos 4 variation, transmission variations and exit pupil distortion of said lens.
Claim 4
Dependent Claim
44 words
The full-frame, flash-exposure system of claim 1 or 2, characterised in that the density profile of said circular area flattens out at its outer edges causing it to have a transition point in its profile whereby transmission increases smoothly with radial distance to 100%.
Claim 5
Dependent Claim
22 words
The full-frame, flash-exposure system of any preceding claim, characterised in that the position of the filter is adjustable along its optical axis.
Claim 6
Dependent Claim
21 words
The full-frame, flash-exposure system of any preceding claim, characterised by said filter being mounted on the object side of said lens.
Claim 7
Dependent Claim
22 words
The full-frame, flash-exposure system of any of claims 1-4, characterised by said filter being mounted on the image side of said lens.
Claim 8
Dependent Claim
59 words
The full-frame, flash-exposure system of any preceding claim characterised by means for changing the magnification of said optical system, said means at least effecting a translation of said lens and filter to maintain document registration; wherein said filter maintains its position on the lens's optical axis at any magnification position to compensate for exposure variations throughout the magnification range.
Claim 9
Dependent Claim
116 words
In a full-frame, flash-exposure copier wherein a platen (24) is substantially uniformly flash illuminated and a lens (14) projects an image of a document placed on said platen onto an imaging plane (38), a method for correcting said system for cos4 falloff and circularly-symmetrical lens non-uniformities introduced at extreme angles, characterised by comprising the steps of a) determining relative illumination level of an image projected onto an image plane at a plurality of field angles; b) defining a filter transmission profile (41) which compensates for both Cos4 and lens non-uniformity effects, and c) grading the density of the central circular portion (45) of a transparent filter so that said filter will have the required transmission profile.
Claim 10
Dependent Claim
116 words
In a full-frame, flash-exposure copier wherein a platen (24) is substantially uniformly flash illuminated and a lens (14) projects an image of a document placed on said platen onto an imaging plane (38), a method for correcting said system for cos4 falloff and circularly-symmetrical lens non-uniformities introduced at extreme angles, characterised by comprising the steps of a) determining relative illumination level of an image projected onto an image plane at a plurality of field angles; b) defining a filter transmission profile (41) which compensates for both Cos4 and lens non-uniformity effects, and c) grading the density of the central circular portion (45) of a transparent filter so that said filter will have the required transmission profile.
References Cited (Backward Citations)
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