Continuous slanted edge focus measurements system

Abstract

A continuous slanted edge focus measurement system characterizes focus of a camera lens. The measurement system may be used to measure effects on focus on caused by factors such as thermal focal shift, humidity focal shift, focal shift caused by changing parts in the camera, and focal shift by changing the camera design. An accurate measurement system enables camera designers to optimize focus under a variety of different conditions and ensure consistency in the products.

What is claimed is: 
     
         1 . A measurement system, comprising:
 a holder configured to secure a camera;   a first sub-system having a slanted edge target surface with a target pattern configured to capture an image by the camera, the target pattern comprising a slanted edge positioned to intersect a center of the image; and   a second sub-system beneath the first sub-system, the second sub-system having an illuminating surface configured to illuminate the target pattern.   
     
     
         2 . The measurement system of  claim 1 , wherein the slanted edge is at an acute angle relative to an optical axis of the camera. 
     
     
         3 . The measurement system of  claim 1 , wherein the target pattern further comprises fiducials comprising horizontally-oriented lines in the image when captured by the camera. 
     
     
         4 . The measurement system of  claim 3 , wherein the horizontally-oriented lines have equal width and different lengths. 
     
     
         5 . The measurement system of  claim 4 , wherein the fiducials are at varying distances from the camera. 
     
     
         6 . The measurement system of  claim 4 , wherein the fiducials have varying lengths that decrease with distance from the camera. 
     
     
         7 . The measurement system of  claim 4 , wherein the fiducials have approximately equal width. 
     
     
         8 . The measurement system of  claim 1 , wherein the second sub-system extends past the first sub-system at an edge of the measurement system opposite the holder. 
     
     
         9 . The measurement system of  claim 8 , wherein the edge is a far edge. 
     
     
         10 . The measurement system of  claim 1 , further comprising:
 a fixture to support the holder, the first sub-system, and the second sub-system; and   an enclosure to enclose the holder, the first sub-system, the second sub-system, and the fixture.   
     
     
         11 . The measurement system of  claim 1 , wherein the slanted edge target surface slopes upward at a first angle with respect to a horizontal ground plane with increasing distance from the camera. 
     
     
         12 . The measurement system of  claim 11 , wherein the illuminating surface slopes upward at a second angle with respect to the horizontal ground plane with increasing distance from the camera. 
     
     
         13 . The measurement system of  claim 1 , wherein the first sub-system comprises:
 a slanted edge target panel including the slanted edge target surface;   a diffuser layer configured to diffuse light emitted from the second sub-system; and   a support layer configured to provide structural support for the diffuser layer and the slanted edge target panel.   
     
     
         14 . The measurement system of  claim 1 , wherein the holder comprises:
 a unit holder configured to hold the camera at a fixed position and orientation; and   a relay lens positioned along an optical axis of the camera between the camera and the first sub-system.   
     
     
         15 . A system, comprising:
 a holder configured to secure a camera;   a target surface with a pattern configured to capture an image by the camera, the pattern including a slanted edge positioned to intersect a center of the image; and   an illuminating surface configured to illuminate the target pattern.   
     
     
         16 . The system of  claim 15 , wherein the target surface comprises:
 a slanted edge target panel;   a first layer configured to diffuse light emitted from the illuminating surface; and   a second layer configured to support for the first layer and the slanted edge target panel.   
     
     
         17 . The system of  claim 15 , wherein the holder secures the camera at a fixed position and orientation and includes a relay lens. 
     
     
         18 . The system of  claim 15 , wherein the pattern includes fiducials comprising lines in the image when captured by the camera. 
     
     
         19 . A slanted edge target system, comprising:
 a panel having a slanted edge target surface; and   a target pattern in the slanted edge target surface, the target pattern comprising a slanted edge positioned to intersect a center of an image when captured by a camera.   
     
     
         20 . The slanted edge target system of  claim 19 , wherein the target pattern further comprises fiducials comprising lines in the image when captured by the camera.