EP0338200A2
Expired / Lapsed
EP
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Method and apparatus for characterization of optical systems
Assignee: International Business Machines Corp
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Filing: 1989-02-09
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Granted: —
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Expires: 2009-02-09
Abstract
Abstract A method and apparatus is provided to quantitatively characterize a lense or optical system as to best focus position at various locations of the lense as well as to determine the curvature or focal surface, and the relative depth of focus of the various locations. A test vehicle is provided having an array of object groups, each object group being comprised of a small object (12) having a size about equal to the resolution limit of the lense or optical system and a large object (10) having a size substantially larger than the resolution limit of the lense or optical system, the groups being separated by opaque areas. The test vehicle is interposed in the lense path and the focal length set at a position which will resolve the large object but not the small object on an image sensor. The sensor is moved orthogonally with respect to the lense and the focal length changed and the object group projected again on the sensor. These steps are repeated successively until both large and small object images are resolved, and further continued thereafter until only the large object is resolved. A series of large and small images is produced for each object group, and the median point of the small image series for each object group represents the best focal distance for the location of the lense corresponding to that object group.
Inventors
- 👤 Roger Lawrence Barr
- 👤 Marc Cote
- 👤 Timothy Richard Farrell
- 👤 Sharon Breed Sisler
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 11:45
CPC Classifications
G; G03; G03F; G03F7/00; G03F7/70; G03F7/70483; G03F7/70591; G03F7/706; G03F7/70216; G03F7/70241; G03F7/70605; G03F7/70616; G03F7/70641; G03F9/00; G03F9/70; G03F9/7003; G03F9/7023; G03F9/7026
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
292 words
A method of quantitatively characterizing an optical system, comprising the steps of providing a test vehicle (Fig. 1) having at least one object group (Fig. 1a) thereon, each object group having a large object (10) and a small object (12) said small object having a size of approximately the resolution limit of the optical system, said large object being of a size significantly larger than the resolution limit of the optical system, projecting an image of said object group (Fig. 2) through the optical system onto an image sensor (Fig. 5) with the optical system located at a preselected distance from the image sensor such as to allow the larger image to be sensed as an image but the smaller image not to be sensed, thereafter orthogonally displacing said image sensor with respect to said optical system and changing the focus length of the optical system and then projecting the object group onto said sensor at the changed location, repeating the orthogonal displacement and change of focus and projection steps until both the small object and the large object in the group are sensed as images by the image sensor, continuing to repeat the orthogonal moves and changes of focus length and projection steps successively until the larger object is sensed as an image, and the small object is not sensed by the image sensor to thus provide a series of images (Fig. 2) from each group starting with the image of a large object only progressing through images of large and small object to an image of a large object only, whereby the focal distance at the median point of the image series of each group containing the small objects represents the best focus of that portion of the optical system.
Claim 2
Independent Claim
292 words
A method of quantitatively characterizing an optical system, comprising the steps of providing a test vehicle (Fig. 1) having at least one object group (Fig. 1a) thereon, each object group having a large object (10) and a small object (12) said small object having a size of approximately the resolution limit of the optical system, said large object being of a size significantly larger than the resolution limit of the optical system, projecting an image of said object group (Fig. 2) through the optical system onto an image sensor (Fig. 5) with the optical system located at a preselected distance from the image sensor such as to allow the larger image to be sensed as an image but the smaller image not to be sensed, thereafter orthogonally displacing said image sensor with respect to said optical system and changing the focus length of the optical system and then projecting the object group onto said sensor at the changed location, repeating the orthogonal displacement and change of focus and projection steps until both the small object and the large object in the group are sensed as images by the image sensor, continuing to repeat the orthogonal moves and changes of focus length and projection steps successively until the larger object is sensed as an image, and the small object is not sensed by the image sensor to thus provide a series of images (Fig. 2) from each group starting with the image of a large object only progressing through images of large and small object to an image of a large object only, whereby the focal distance at the median point of the image series of each group containing the small objects represents the best focus of that portion of the optical system.
Claim 3
Dependent Claim
74 words
The invention as defined in claim 1, wherein an array of object groups is provided at spaced locations corresponding to various locations of the focus surface (Fig. 3) of the optical system, said object groups being separated by substantial opaque regions, whereby the number of small images sensed in a given series with respect to the number of small images sensed in any other series represents the relative depth of focus (Fig. 4) therebetween.
Claim 4
Dependent Claim
17 words
The invention as defined in claim 1 or 2 wherein the small object (12) is a symmetrical.
Claim 5
Dependent Claim
34 words
The invention as defined in one or more of the preceding claims, wherein the orthogonal movement is directed to produce a side-by-side juxtaposed series of large object images and small object images (Fig. 2a).
Claim 6
Dependent Claim
200 words
The invention as defined in one or more of the preceding claims wherein the test vehicle has at least one small object thereon, said small object having a size approximating the resolution limit of the optical system, projecting said object on an image sensor (Fig. 5) with the image sensor located at a focal distance which will not resolve the object as an image, thereafter orthogonally displacing said sensor with respect to the optical system and changing the focal distance, and then projecting the object as an image on the image sensor at the changed location, repeating the orthogonal displacement, and change of focus, and projection steps until the small object is sensed as an image on the image sensor to thus provide a series of images, continuing to repeat the orthogonal moves and changes of focal length and projecting steps successively until the small object is not sensed by the image sensor, said method further characterized by providing means to determine the focal distance at which each small object image is resolved, whereby the focal distance at the median point of each series of small object images represents the best focus position of that portion of the optical system.
Claim 7
Dependent Claim
61 words
The invention as defined in claim 5, wherein the means to determine the focal distance of each small object image includes a large object (10) associated with each small object (12) on the test vehicle (Fig. 1) to define an object group, and wherein the large object is of a size substantially larger than the resolution limit of the optical system.
Claim 8
Dependent Claim
22 words
The invention as defined in one or more of the preceding claims, wherein the image sensor (Fig. 5) includes photo sensitive material.
Claim 9
Dependent Claim
20 words
The invention as defined in claim 7, wherein the photo sensitive material is developed to produce a permanent image pattern.
Claim 10
Dependent Claim
136 words
A test vehicle (Fig. 1) for use in determining the best focal distance of an optical system, the focus surface or curvature of the optical system (Fig. 3) and the relative depth of focus throughout the field of said optical system (Fig. 4) comprising, an array of object groups for spacing projection onto an image sensor (Fig. 5) arranged at spaced locations on said test vehicle corresponding to various positions of the focus surface of the exposure field at the optical system to be measured, each object group comprising a large object and a small object, said small object having a size of approximating the resolution limit of the optical system to be measured and said large object having a size significantly larger than said resolution limit, said object groups being separated by substantial opaque regions.
Claim 11
Dependent Claim
136 words
A test vehicle (Fig. 1) for use in determining the best focal distance of an optical system, the focus surface or curvature of the optical system (Fig. 3) and the relative depth of focus throughout the field of said optical system (Fig. 4) comprising, an array of object groups for spacing projection onto an image sensor (Fig. 5) arranged at spaced locations on said test vehicle corresponding to various positions of the focus surface of the exposure field at the optical system to be measured, each object group comprising a large object and a small object, said small object having a size of approximating the resolution limit of the optical system to be measured and said large object having a size significantly larger than said resolution limit, said object groups being separated by substantial opaque regions.
References Cited (Backward Citations)
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