# US 7,609,441 B2 · Distorted pupil relay for spectral filtering > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,609,441 B2 - Document ID: US7609441B2 - Status: Granted - Kind: B2 - Application number: 11/138,782 - Filed: 2005-05-26 - Published: 2006-11-30 - Granted: 2009-10-27 - Earliest claimed: 2005-05-26 - Assignees: The Boeing Company - Inventors: Mark A. Lundgren - Web page: https://patentgrep.com/patent/US7609441B2 ## CPC - G02B 27/0025: {for optical correction, e.g. distorsion, aberration} - G02B 13/0095: {Relay lenses or rod lenses (in instruments for viewing the inside of hollow bodies G02B23/2446)} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract A system and method for spectral filtering of images are provided. The system and method utilize a first biconic lens surface to astigmatize a substantially 2-D system pupil into a substantially 1-D pupil (e.g., slit-shaped), and a second biconic lens surface to restore the astigmatic pupil to good quality. Advantageously, the light stream may be filtered with a variable filter. ## Claims ### Claim 1 An optical system, comprising: a first biconic surface that receives a plurality of light ray bundles originating from a two-dimensional image of an object, the first biconic surface distorting a pupil from a circular shape to a slit shape thereby compressing the plurality of light ray bundles into a compressed beam of light with a slit-shaped cross-section; a variable filter for filtering the compressed beam of light; and a secondary group of biconic surfaces that corrects aberrations from the filtered beam of light and provides a filtered two-dimensional image at an image focal plane, the secondary group of biconic surfaces including a weak biconic surface and a strong biconic surface. ### Claim 2 (depends on 1) The system of claim 1, wherein the first biconic surface has a radius of 150 mm in one direction and is flat in another direction, and wherein the second biconic surface has a radius of 6.9 mm in one direction and is flat in another direction. ### Claim 3 (depends on 1) The system of claim 1, wherein the pupil has a width compressed by a ratio of about 10:1. ### Claim 4 (depends on 1) The system of claim 1, wherein the pupil is distorted from a circular shape with a diameter of about 10 mm to a slit shape with a maximum width of about 1 mm. ### Claim 5 (depends on 1) The system of claim 1, wherein the variable filter is selected from the group consisting of a circular variable filter, a linear variable filter, an electronically variable filter, and a prism. ### Claim 6 (depends on 1) The system of claim 1, further comprising a first relay lens for providing an intermediate image of the object. ### Claim 7 (depends on 1) The system of claim 1, further comprising a system stop including a circular aperture with a diameter of about 15 mm providing a field of view of about 0.5 degree. ### Claim 8 (depends on 1) The system of claim 1, further comprising a relay lens optically coupled to the first biconic surface for relaying the compressed beam of light to the variable filter. ### Claim 9 An optical system, comprising: a first relay lens for providing an intermediate two-dimensional image of an object through a circular system stop; a first biconic lens group optically coupled to the first relay lens, the first biconic lens group receiving a plurality of light ray bundles originating from the intermediate two-dimensional image and distorting a pupil from a circular shape to a slit shape thereby compressing the plurality of light ray bundles into a compressed beam of light with a slit-shaped cross-section; a second relay lens optically coupled to the first biconic lens group for relaying the compressed beam of light; a variable filter optically coupled to the second relay lens for filtering the compressed beam of light; and a second biconic lens group optically coupled to the variable filter for correcting aberrations from the filtered beam of light to restore a filtered two-dimensional image at an image focal plane, the second biconic lens group including a weak biconic surface and a strong biconic surface. ### Claim 10 (depends on 9) The system of claim 9, wherein the pupil has a width compressed by a ratio of about 10:1. ### Claim 11 (depends on 9) The system of claim 9, wherein the variable filter is selected from the group consisting of a circular variable filter, a linear variable filter, an electronically variable filter, and a prism. ### Claim 12 A method of spectral filtering, comprising: receiving a plurality of light ray bundles originating from a two-dimensional image of an object at a first biconic surface; distorting a pupil from a circular shape to a slit shape with the first biconic surface thereby compressing the plurality of light ray bundles into a compressed beam of light with a slit-shaped cross-section; filtering the compressed beam of light; and correcting aberrations from the filtered beam of light with a secondary group of biconic surfaces to provide a filtered two-dimensional image at an image focal plane, the secondary group of biconic surfaces including a weak biconic surface and a strong biconic surface. ### Claim 13 (depends on 12) The method of claim 12, wherein the image of the object is provided to the first biconic surface with a first relay lens. ### Claim 14 (depends on 12) The method of claim 12, wherein the pupil is distorted to have a width compressed by a ratio of 10:1. ### Claim 15 (depends on 12) The method of claim 12, wherein the compressed beam of light is relayed from the first biconic surface to a variable filter with a relay lens. ### Claim 16 (depends on 15) The method of claim 15, wherein the variable filter is selected from the group consisting of a circular variable filter, a linear variable filter, an electronically variable filter, and a prism. ### Claim 17 A pupil relay system, comprising: a first lens group for receiving a plurality of light ray bundles originating from a two-dimensional image of an object, the plurality of light ray bundles produced by an optical system having an aperture stop, the first lens group including a first biconic surface capable of inducing an astigmatic pupil of the stop; and a second lens group that reduces the astigmatism induced by the first biconic surface and provides a filtered two-dimensional image at an image focal plane, the second lens group including a weak biconic surface and a strong biconic surface. ### Claim 18 (depends on 17) The system of claim 17, wherein the first and second lens groups each form achromatic doublets having positive optical power. ### Claim 19 (depends on 17) The system of claim 17, further comprising a variable filter at the astigmatic pupil of the stop, the variable filter selected from the group consisting of a circular variable filter, a linear variable filter, an electronically variable filter, and a prism.