Browse Prior Art Database

DOUBLE APERTURE STOP FOR RELATIVE ILLUMINATION CONTROL

IP.com Disclosure Number: IPCOM000024141D
Original Publication Date: 1979-Oct-31
Included in the Prior Art Database: 2004-Apr-02
Document File: 2 page(s) / 364K

Publishing Venue

Xerox Disclosure Journal

Abstract

In a normal lens, illuninatio-in the image plane increases as the field angle 9 increases according to cos- . Exposure compensation with field angle can be achieved by use of a double aperture stop. By separating two aperture stop surfaces along the lens axis and appropriately shaping the open areas in each, the amount of open area for the combination can be made to increase with field angle.

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XEROX DISCLOSURE JOURNAL

DOUBLE APERTURE STOP FOR

RELATIVE ILLUMINATION CONTROL William Lama
Edgar E. Price

Proposed Classification

U~S~CL 350/205 IntO Cl. G02b 9/00

FIG. IA FIG. /8

Volume 4 Number 5 September/October 1979 645

FIG. 2

[This page contains 1 picture or other non-text object]

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DOUBLE APERTURE STOP FOR RELATIVE ILLUMINATION CONTROL (Cont'd)

In a normal lens, illuninatio~in the image plane increases as the field angle 9 increases according to cos~ . Exposure compensation with field angle can be achieved by use of a double aperture stop. By separating two aperture stop surfaces along the lens axis and appropriately shaping the open areas in each, the amount of open area for the combination can be made to increase with field angle.

Figure Ia shows a first surface 10 which would be located at the normal aperture stop position within the lens. Surface 10 has a central clear area of radius RI, an opaque band of inner radius Ri and outer radius R2, a second clear band of inner radius R2, outer radius R3 and a second opaque band of inner radius R3, outer radius R4. The second surface 12 in Figure lb is clear except for an opaque ring

having an inner radius R2 and outer radius R3. While these surfaces are shown side by side in Figure 1, in an optical system both surfaces would be centered on the

optical axis with the second surface closer to the image by a prescribed distance but still within the lens, When viewed from a field point on the optical ax...