METHOD AND DEVICE FOR ALGINING A LENS WITH AN OPTICAL SYSTEM

• US 20120113413A1
• Filed: 08/11/2009
• Published: 05/10/2012
• Est. Priority Date: 08/11/2009
• Status: Active Grant

• Current Assignee: Ao Ether Corporation
• Original Assignee: Ether Precision, Inc.
• Inventors: Miahczylowicz-Wolski, Cyril, Lusinchi, Jean-Pierre
• Granted Patent: US 8,773,652 B2
• Time in Patent Office: Days
• US Class Current: 356/124.5
• CPC Class Codes: G01M 11/0221 by determining the optical axis or position of lenses
• CPC Class Codes: G02B 13/0015 characterised by the lens design
• CPC Class Codes: G02B 27/62 Optical apparatus specially adapted for adjusting optical elements during the assembly of optical systems
• CPC Class Codes: G02B 7/023 permitting adjustment

Abstract

The invention comprises a process for pre-aligning a lens with an optical system, the process comprising: providing a lens and an optical system having an optical axis, wherein the lens is apt to be aligned with the optical system to form on an image plane an image of a source object, the image having top, bottom, left and right edges; coarsely positioning the lens with respect to the optical system; and in a plane normal to the optical axis of the optical system, correcting the position of the lens until the values of four Combination Modulation Transfer Functions (C-MTF) are in predetermined ranges, the C-MTF being calculated at four coarse measurement locations situated close to the edges of the image along two coarse positioning axes crossing the center of the image, each for a combination pattern comprising a combination of a Sagittal pattern and a Tangential pattern.

Claims

1. A process for pre-aligning a lens with an optical system, the process comprising:

providing a lens and an optical system having an optical axis, wherein the lens is apt to be aligned with the optical system to form on an image plane an image of a source object, the image having top, bottom, left and right edges;

coarsely positioning the lens with respect to the optical system; and

in a plane normal to the optical axis of the optical system, correcting the position of the lens until the values of four Combination Modulation Transfer Functions (C-MTF) are in predetermined ranges, the C-MTF being calculated at four coarse measurement locations situated close to the edges of the image along two coarse positioning axes crossing the center of the image, each for a combination pattern comprising a combination of a Sagittal pattern and a Tangential pattern.

2. The method of claim 1, wherein correcting the position of the lens until the values of the four C-MTFs are in predetermined ranges comprises repeating the steps:

calculating the C-MTFs; and

in a plane normal to the optical axis of the optical system, along a line parallel to the coarse positioning axis of the image comprising the coarse measurement location having the C-MTF with the lowest value, moving the lens by a predetermined step toward said coarse measurement location;

until any of the C-MTF is above a predetermined C-MTF threshold and the difference between the largest C-MTF and the smallest C-MTF is below a predetermined C-MTF difference threshold, or until the lens is moved a predetermined number of times.

3. The method of claim 2, further comprising:

providing a source object having, in four coarse measurement locations, a combination of a Sagittal pattern and a Tangential pattern.

4. The method of claim 3, further comprising:

providing a source object having, in its four coarse measurement locations, a checkerboard pattern having rows and columns respectively parallel and perpendicular to the top-to-bottom axis of the object.

5. The method of claim 1, wherein the two axes of the image comprising the coarse measurement locations follow the diagonals of the image, and wherein the four coarse measurement locations are situated at the four corners of the image.

6. The method of claim 1, wherein coarsely positioning the lens comprises aligning the center of the source object with the optical axis of the optical system;

and positioning the lens with respect to the optical system such that the image of the center of the source object formed on the image plane coincides with the intersection of the image plane and the optical axis of the optical system.

7. A process for aligning a lens with an optical system, the process comprising:

pre-aligning the lens with the optical system according to the method of claim 1;

adjusting the position of the lens, in the plane normal to the optical axis of the optical system along a line parallel to a first precise positioning axis that crosses the center of the image and passes through first and second precise measurement locations situated close to opposite edges of the image, until first and second Sagittal and Tangential Modulation Transfer Functions of the combined lens and optical system, calculated at the first and second precise measurement locations, are such that difference between the Sagittal Modulation Transfer Functions of the first and second precise measurement locations and difference between the Tangential Modulation Transfer Functions of the first and second precise measurement locations are minimal, each of the Modulation Transfer Functions being above a first predetermined threshold; and

adjusting the position of the lens, in the plane normal to the optical axis of the optical system along a line parallel to a second precise positioning axis that crosses the center of the image and passes through third and fourth precise measurement locations situated close to opposite edges of the image, until third and fourth Sagittal and Tangential Modulation Transfer Functions of the combined lens and optical system, calculated at the third and fourth precise measurement locations, are such that difference between the Sagittal Modulation Transfer Functions of the third and fourth precise measurement locations and difference between the Tangential Modulation Transfer Functions of the third and fourth precise measurement locations are minimal, each of the Modulation Transfer Functions being above a second predetermined threshold.

8. The process of claim 7, wherein:

the first and second precise measurement locations are situated at the middle of the top and bottom of the image, the first precise positioning axis being the vertical axis of the image and the first and second Sagittal and Tangential Modulation Transfer Functions being Top and Bottom Sagittal and Tangential Modulation Transfer Functions; and

the third and fourth precise measurement locations are situated at the middle of the left and right of the image, the second precise positioning axis being the horizontal axis of the image and the third and fourth Sagittal and Tangential Modulation Transfer Functions being Left and Right Sagittal and Tangential Modulation Transfer Functions.

9. The method of any of claim 8, wherein:

adjusting the position of the lens along a line parallel to the vertical axis of the image comprises;

adjusting the position of the lens along said line until;

any of a Top Sagittal Modulation Transfer Function (TS-MTF) and a Top Tangential Modulation Transfer Function (TT-MTF) of the combined lens and optical system, calculated at the middle of the top of the image, and

any of a Bottom Sagittal Modulation Transfer Function (BS-MTF) and a Bottom Tangential Modulation Transfer Function (BT-MTF) of the combined lens and optical system, calculated at the middle of the bottom of the image,

are above the first predetermined threshold; and

a value GmV=α

1((TS-MTF)−

(BS-MTF))ⁿ¹+β

1((TT-MTF)−

(BT-MTF))ⁿ²,

reaches a minimum below a third predetermined threshold, where α

1, β

1, n1, n2 are predetermined weighting factors; and

said adjusting the position of the lens along a line parallel to the horizontal axis of the image comprises;

adjusting the position of the lens along said line until;

any of a Left Sagittal Modulation Transfer Function (LS-MTF) and a Left Tangential Modulation Transfer Function (LT-MTF) of the combined lens and optical system, calculated at the middle of the left of the image, and

any of a Right Sagittal Modulation Transfer Function (RS-MTF) and a Right Tangential Modulation Transfer Function (RT-MTF) of the combined lens and optical system, calculated at the middle of the right of the image,

are above the second predetermined threshold; and

a value GmH=α

2((TS-MTF)−

(BS-MTF)ⁿ³+β

2((TT-MTF)−

(BT-MTF))ⁿ⁴ reaches a minimum below a fourth predetermined threshold, where α

2, β

2, n3, n4 are predetermined weighting factors.

10. The method of claim 9, where:

GmV reaches a minimum when the variation of GmV changes from negative to positive; and

GmH reaches a minimum when the variation of GmH changes from negative to positive.

11. The method of claim 9, wherein said adjusting the position of the lens along a line parallel to the vertical axis of the image comprises:

repeating the steps of;

calculating the Top and Bottom, Sagittal and Tangential Modulation Transfer Function values and the GmV value; and

moving the lens by a predetermined step in a first direction along a vertical line;

until the calculated values have the desired levels with respect to the first and third predetermined thresholds and GmV reaches a minimum or until the lens reaches a predetermined outward position; and

if the lens reaches said predetermined outward position in said first direction,

moving back the lens to its original position on said vertical line and

repeating the steps of;

calculating the Top and Bottom, Sagittal and Tangential Modulation Transfer Function values and the GmV value; and

moving the lens by a predetermined step in a direction opposite the first direction along said vertical line;

until the calculated values have the desired levels with respect to the first and third predetermined thresholds and GmV reaches a minimum or until the lens reaches a predetermined outward position in said opposite direction, in which case the lens is discarded.

12. The method of claim 9, wherein said adjusting the position of the lens along a line parallel to the horizontal axis of the image comprises:

repeating the steps of;

calculating the Left and Right, Sagittal and Tangential Modulation Transfer Function values and the GmH value; and

moving the lens by a predetermined step in a first direction along a horizontal line;

until the calculated values have the desired levels with respect to the second and fourth predetermined thresholds and GmH reaches a minimum or until the lens reaches a predetermined outward position; and

if the lens reaches said predetermined outward position in said first direction,

moving back the lens to its original position on said horizontal line and

repeating the steps of;

calculating the Left and Right, Sagittal and Tangential Modulation Transfer Function values and the GmH value; and

moving the lens by a predetermined step in a direction opposite the first direction along said horizontal line;

until the calculated values have the desired levels with respect to the second and fourth predetermined thresholds and GmH reaches a minimum or until the lens reaches a predetermined outward position in said opposite direction, in which case the lens is discarded.

13. The method of claim 1, further comprising providing an image sensor capable of sensing the image of the source object on the image plane.

14. An apparatus provided for implementing a method according to claim 1.

15. A source object to be used in an process for pre-aligning a lens with an optical system, the source object having, in each of four coarse measurement locations situated close to the edges of the object along two axes crossing the center of the object, a pattern comprising a combination of a Sagittal pattern and a Tangential pattern.

16. The source object of claim 15, further comprising, in each of four precise measurement locations situated close to the edges of the object along first and second precise positioning axes crossing the center of the object, a pattern comprising a juxtaposition of a Sagittal pattern and a Tangential pattern.

17. The source object of claim 16, having a top, a bottom, a left and a right;

wherein;

the middle of the top of the object comprises a juxtaposition of a Sagittal pattern and a Tangential pattern;

the middle of the bottom of the object comprises a juxtaposition of a Sagittal pattern and a Tangential pattern;

the middle of the left of the object comprises a juxtaposition of a Sagittal pattern and a Tangential pattern;

the middle of the right of the object comprises a juxtaposition of a Sagittal pattern and a Tangential pattern; and

wherein

the top-left, top-right, bottom left and bottom right corners of the object comprise each a combination of a Sagittal pattern and a Tangential pattern.

18. The source object of claim 15, wherein the juxtaposition of a Sagittal pattern and a Tangential pattern comprises a set of lines parallel to the first precise positioning axis of the object juxtaposed with a set of lines parallel to the second precise positioning axis of the object, each set of lines being on one side of the corresponding precise positioning axis of the object.

19. The source object of claim 15, wherein the combination of a Sagittal pattern and a Tangential pattern comprises a checkerboard pattern having rows and columns respectively parallel and perpendicular to a top-to-bottom axis of the object.

20. The source object of claim 15, wherein the juxtaposition of a Sagittal pattern and a Tangential pattern comprises a set of lines slanted by a few degrees with respect to the parallel to the first precise positioning axis of the object juxtaposed with a set of lines slanted by a few degrees with respect to the parallel to the second precise positioning axis of the object, each set of lines being on one side of the corresponding precise positioning axis of the object.

21. The source object of claim 15, wherein the combination of a Sagittal pattern and a Tangential pattern comprises a checkerboard pattern having rows and columns respectively slanted by a few degrees with respect to the parallel and perpendicular to a top-to-bottom axis of the object.