JP2007147952A - Method for adjusting position of imaging optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an appropriate method for adjusting the position of an imaging optical system by which the range of depth of field is not varied and a stable image is obtained by restraining variation in setting the position of an imaging optical system used for a wavefront coding imaging system relative to an imaging device. <P>SOLUTION: In the method for adjusting the position of the imaging optical system, the position of the imaging optical system in an optical axis direction is set based on a position where the image sharpness of a chart is lowered by arranging the chart at a predetermined distance, and obtaining the position where the image sharpness of the chart is lowered by moving the imaging optical system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wavefront coding image forming apparatus that is used in a wavefront coding imaging system and has an optical system for obtaining a wavefront coded image.

  2. Description of the Related Art Conventionally, a lens group for guiding subject light, and an imaging device that records the subject image as digital image data by photoelectrically converting subject light transmitted through the lens group by an image sensor and performing predetermined processing. ing.

  There are two types of imaging devices, one that moves the lens group mounted in accordance with the subject distance and performs focus adjustment, and the other that has a fixed focus type in which the lens group is fixed at a position corresponding to a predetermined subject distance.

  The fixed focus type is low-cost, but the shooting distance range is limited to the range that can be covered by the depth of field, and is not suitable for close-up shooting etc. Although it is possible to shoot with good image quality from infinity to a close distance, it also requires a moving mechanism and the like, resulting in an increase in size and cost.

In recent years, as a solution to such a problem, a subject image obtained by using a lens group for image formation and a wavefront coding optical system is photoelectrically converted by an imaging device or the like, and a predetermined A / D conversion or the like is performed. By performing further image processing on the image data obtained by performing the above processing, a wavefront coding image that can obtain an image having good sharpness from infinity to a close range while being a fixed focus type A system has been proposed (see, for example, Patent Document 1).
JP 2005-502084 Gazette

  The wavefront coding imaging system of the above-mentioned patent document 1 arranges a wavefront coding optical system composed of a rotationally asymmetric surface with respect to the optical axis at a position where a diaphragm of a lens group for image formation is arranged. The image data is obtained from the image of the subject thus formed, and further subjected to predetermined image processing on the image data, thereby obtaining image data having good sharpness from infinity to a close range. As a result, it is possible to obtain an image having a good sharpness from infinity to a close distance while being a fixed focus type. That is, in a wavefront coding imaging system, the final image obtained has a very deep depth of field and depth of focus.

  For this reason, in the conventional method of obtaining the imaging optical system position where the sharpest image can be obtained with respect to the chart arranged at a predetermined distance, such as focus adjustment, the setting variation of the imaging optical system position becomes large and accurate. There is a problem that position cannot be set.

  In view of the above problems, the present invention suppresses variation in position setting of the imaging optical system used in the wavefront coding imaging system with respect to the imaging element, and appropriate imaging optics that can obtain a stable image without variation in the depth of field range. The object is to obtain a system position adjustment method.

  The above object is achieved by the invention described below.

  1. In an imaging optical system position adjustment method for an imaging optical system composed of a lens group for guiding subject light and a wavefront coding optical system with respect to an imaging element disposed behind the imaging optical system, a chart is provided at a predetermined distance. Arranging and moving the imaging optical system to obtain a position where the image sharpness of the chart is lowered, and setting the position of the imaging optical system in the optical axis direction based on the position where the image sharpness is lowered An imaging optical system position adjustment method characterized by the above.

  2. 2. The imaging optical system position adjusting method according to 1, wherein the distance at which the chart is arranged is a near-field depth limit distance.

  3. An imaging optical system position adjustment method for an imaging optical system configured of a lens group for guiding subject light and a wavefront coding optical system with respect to an imaging element disposed behind the imaging optical system, and a chart at a predetermined distance A first position where the imaging optical system is moved in the feeding direction to reduce the image sharpness of the chart, and the imaging optical system is moved in the feeding direction to reduce the image sharpness of the chart. An image pickup optical system position adjustment method comprising: setting a position of the image pickup optical system in the optical axis direction based on the second position.

  4). 4. The imaging optical system position adjustment method according to 3, wherein the distance at which the chart is arranged is a distance corresponding to ½ of the depth of focus.

  ADVANTAGE OF THE INVENTION According to this invention, the suitable imaging optical system position adjustment which suppresses the dispersion | variation in the position setting with respect to the image pick-up element of the image pick-up optical system used for a wavefront coding imaging system, and a stable image is obtained without the variation in depth of field range. It becomes possible to obtain a method.

  Hereinafter, the present invention will be described in detail with reference to embodiments, but the present invention is not limited thereto.

  First, the wavefront coding imaging system will be briefly described.

  FIG. 1 is a block diagram of a wavefront coding imaging system 200 including a wavefront coding image forming apparatus 50 including an imaging optical system according to the present embodiment.

  As shown in the figure, the wavefront coding image forming apparatus 50 photoelectrically captures an imaging optical system composed of a lens group 51 for image formation and a wavefront coding optical system 52 and subject light transmitted through the imaging optical system. The imaging element 53 to be converted and a lens barrel that holds these imaging optical systems are configured. The subject light is incident on the wavefront coding image forming apparatus 50, and an image after passing through an imaging optical system composed of the lens group 51 and the wavefront coding optical system 52 (hereinafter, this image is referred to as a primary image) is captured. It is formed on the element 53.

  The lens group 51 of the wavefront coding image forming apparatus 50 is an optical system having imaging performance. The wavefront coding optical system 52 is disposed at the position of the stop surface, which is the entrance pupil position of the lens group 51, and has a function of changing the phase of incident subject light. The image pickup element 53 changes the state of the image on the image plane by the wavefront coding optical system 52 and obtains a slightly unclear primary image.

  The imaging device 53 is a solid-state imaging device such as a CCD (Charge Coupled Device) type image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor.

  The output from the image pickup device 53 of the wavefront coding image forming apparatus 50 is subjected to processing such as predetermined A / D conversion and becomes primary image data 54.

  The primary image data 54 is subjected to image processing by the image processing means 55, and final image data 56 is obtained. The image processing means 55 restores an image from the unclear primary image data 54 given the wavefront coding by the wavefront coding optical system 52, thereby obtaining a final image 56 having a deep depth of field and a focal depth. The outline of the wavefront coding imaging system 200 has been described above.

  Hereinafter, an example of a specific configuration of the wavefront coding image forming apparatus 50 will be described.

  FIG. 2 is a cross-sectional view showing a schematic configuration of the wavefront coding image forming apparatus 50 according to the present embodiment.

  In the figure, reference numeral 41 denotes a printed circuit board, and the image sensor 53 is mounted on the printed circuit board 41 by COB (Chip On Board). Signal output from the image sensor 53 and signal input to the image sensor 53 are performed by a circuit (not shown) electrically connected to the printed circuit board 41.

  Reference numeral 42 denotes an outer frame member, which is positioned and fixedly bonded to a light receiving surface of the image pickup device 53 of the printed circuit board 41 at a predetermined position. An infrared light cut filter 43 is bonded and fixed to the outer frame member 42.

  A lens barrel 44 is disposed inside the outer frame member 42. The lens barrel 44 holds an imaging optical system including a lens group 51 and a disk-shaped wavefront coding optical system 52, and the wavefront coding optical system 52 is disposed at the stop position of the lens group 51. In this example, the object-side surface 52a of the wavefront coding optical system 52 corresponds.

  A key-shaped protrusion 44t is formed at least at one location on the circumferential surface of the lens barrel 44 where the wavefront coding optical system 52 is attached. On the other hand, the disk-like wavefront coding optical system 52 has a key groove-like recess 52m formed at a position corresponding to the protrusion 44t, and the recess 52m and the protrusion 44t are engaged to assemble. . Thereby, the wavefront coding optical system 52 is positioned in the rotational direction with respect to the lens barrel 44.

  Similarly, a key-shaped protrusion 42 t is formed on the cylindrical inner peripheral surface of the outer frame member 42. On the other hand, the cylindrical lens barrel 44 is formed with a key groove-shaped recess 44m at a position corresponding to the protrusion 42t, and the recess 44m and the protrusion 42t are engaged to assemble. Thereby, the lens barrel 44 is rotationally locked by the outer frame member 42.

  A compression coil spring 45, which is an urging member, is incorporated between the outer frame member 42 and the lens barrel 44, and the lens barrel 44 is urged toward the subject by the compression coil spring 45. On the other hand, a female screw portion 42n is formed at the distal end portion of the outer frame member 42, and a pressing member 46 having a male screw portion 46n that is screwed into the female screw portion 42n is assembled.

  By rotating the holding member 46 and moving it with respect to the outer frame member 42, the lens barrel 44 that contacts the pressing member 46 and the lens group 51 in the lens barrel 44 and the wavefront coding optical system 52 are in contact with the holding member 46. The image pickup optical system configured by can be moved straight in the direction of the optical axis O, and the position of the image pickup optical system in the direction of the optical axis O with respect to the image pickup element 53 can be adjusted.

  As described above, the wavefront coding image forming apparatus 50 according to the present embodiment is positioned in the rotational direction around the optical axis O of the wavefront coding optical system 52 with respect to the imaging element 53. Thereby, the image processing software for obtaining the final image from the primary image used in the wavefront coding imaging system 200 can be simplified, and the required storage medium capacity can be reduced and the processing time can be shortened. A wavefront coding image forming apparatus can be obtained.

  A method of adjusting the position of the imaging optical system of the wavefront coding image forming apparatus 50 in the optical axis O direction with respect to the imaging element 53 (hereinafter also referred to as focus adjustment) will be described.

  Since the wavefront coding imaging system is a system that can obtain a final image having a very deep depth of field as described above, in the conventional method, it is not possible to appropriately set the position of the imaging optical system. Have difficulty. The imaging optical system position adjustment method described below uses the wavefront coding imaging system 200 shown in FIG. 1 and the optical axis O direction of the imaging optical system of the wavefront coding image forming apparatus 50 shown in FIG. This is a conceptual description of the position adjustment method.

  FIG. 3 is a diagram for explaining an example of a method for adjusting the position of the imaging optical system of the wavefront coding image forming apparatus in the optical axis O direction with respect to the imaging element.

  FIG. 5A is a diagram showing the depth of field of the final image obtained by the wavefront coding imaging system. As shown in the figure, for example, assuming that a region where a final image having a contrast of 75% or more with respect to the maximum value of sharpness (contrast) is obtained is the depth of field, the wavefront coding imaging system shown in FIG. The final image has a depth of field from 1 / R of 0 or infinity to 1 / R of 5 or 0.2 m.

  FIG. 5B shows a method for adjusting the position of the imaging optical system in the direction of the optical axis O with respect to the imaging device.

  In the figure, for example, a chart is arranged at a position where 1 / R is 5 or 0.2 m, and the position where the chart image is 75% or more of the maximum sharpness (contrast) of the final image (for example, the figure). The state as shown by the broken line A in FIG. Thereafter, the imaging optical system is retracted, and the retraction is stopped at a position where the sharpness of the final image of the chart image is approximately 75% (a state indicated by a solid line B in the figure). As a result, the imaging optical system can be set at a position where the final image is within the depth of field from 0.2 m to infinity as shown in FIG.

  In the above description, the example in which the chart is arranged at the position of the depth of field limit has been described. However, the chart is arranged at a closer distance, and similarly, the position where the sharpness of the final image is 75% is obtained, and a predetermined amount Alternatively, the imaging optical system may be retracted only, or the imaging optical system may be disposed at a longer distance, and similarly, a position where the sharpness of the final image is 75% is obtained, and the imaging optical system is advanced by a predetermined amount.

  In this way, by arranging the chart at a predetermined distance and moving the imaging optical system to set the position in the optical axis direction of the imaging optical system based on the position where the sharpness of the final image of the chart changes. Therefore, it is possible to perform appropriate position setting of the photographing optical system of the wavefront coding imaging system that has a very wide depth of field and that can obtain a final image with a smooth sharpness peak.

  In addition, by setting the distance at which the chart is placed as the distance of the depth of field limit on the near side, it is easy to set the appropriate position of the imaging optical system of the wavefront coding imaging system without complicated calculations. Can be performed.

  FIG. 4 is a diagram for explaining another example of the position adjustment method in the direction of the optical axis O with respect to the imaging element of the imaging optical system of the wavefront coding image forming apparatus.

  FIG. 6A is a diagram showing the depth of field of the final image obtained by the wavefront coding imaging system, which is the same as FIG.

  FIG. 5B shows a method for adjusting the position of the imaging optical system in the direction of the optical axis O with respect to the imaging device.

  In the figure, for example, a chart is arranged at a position where 1 / R is 2.5, that is, 0.4 m. This distance is the center of the depth of focus from infinity to 0.2 m, that is, a distance corresponding to ½.

  First, the imaging optical system is extended to a position where the sharpness (contrast) of the final image of the chart image is approximately 75% of the maximum value (for example, the state shown by the broken line C in the figure), and the pressing at this time The position of the member 46 (see FIG. 2) is stored.

  Next, the imaging optical system is turned on, and after the sharpness (contrast) of the final image of the chart image reaches 75% or more with respect to the maximum value, the drawing optical system is further turned on to obtain the highest sharpness (contrast) of the final image of the chart image. Renormalization is stopped at a position where the value is approximately 75% (for example, a state shown by a broken line D in the figure).

  The amount of rotation of the pressing member 46 is determined from the position of the pressing member 46 at this time and the position of the pressing member 46 that has already been stored. The imaging optical system can be set at a position within the depth of field from 2 m to infinity.

  As described above, the chart is arranged at a predetermined distance, the imaging optical system is moved in the feeding direction, the first position where the image sharpness of the chart is lowered, and the imaging optical system is moved in the feeding direction and the chart. By obtaining the second position where the image sharpness of the image is reduced, a region where the final image maintains high contrast is obtained, and the position of the imaging optical system in the optical axis direction is set based on the position of this region. As a result, it is possible to set an appropriate position of the photographing optical system of the wavefront coding imaging system that has a very wide depth of field and that can obtain a final image with a smooth sharpness peak.

  That is, according to the position adjustment method of the imaging optical system described in FIG. 3 or FIG. 4, focus position adjustment with respect to the imaging element of the imaging optical system of the wavefront coding imaging system having a very wide depth of field is performed at one place. The adjustment can be performed simply by using the chart arranged in (1), the time required for the adjustment can be shortened, and appropriate position setting can be performed at low cost.

  In addition, by arranging the chart at a position at half the depth of focus, it is possible to easily set an appropriate position of the photographing optical system of the wavefront coding imaging system without requiring complicated calculation. .

  In addition, although the region where a final image having a contrast of 75% or more with respect to the maximum value of sharpness (contrast) is obtained is described as the depth of field, this numerical value is an example for explanation, and Of course, it is not limited.

1 is a block diagram of a wavefront coding imaging system including a wavefront coding image forming apparatus including an imaging optical system according to the present embodiment. It is sectional drawing which shows schematic structure of the wavefront coding image forming apparatus which concerns on this Embodiment. It is a figure for demonstrating an example of the position adjustment method of the optical axis O direction with respect to an image pick-up element of the imaging optical system of a wavefront coding image forming apparatus. It is a figure for demonstrating the other example of the position adjustment method of the optical axis O direction with respect to an image pick-up element of the imaging optical system of a wavefront coding image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 41 Printed circuit board 42 Outer frame member 43 Infrared light cut filter 44 Lens barrel 45 Compression coil spring 46 Holding member 50 Wavefront coding image forming apparatus 51 Lens group 52 Wavefront coding optical system 53 Imaging element 200 Wavefront coding imaging system

Claims (4)

In an imaging optical system position adjustment method for an imaging element disposed behind the imaging optical system of an imaging optical system composed of a lens group for guiding subject light and a wavefront coding optical system,
Place the chart at a predetermined distance,
A position where the image sharpness of the chart decreases by moving the imaging optical system is determined, and a position in the optical axis direction of the imaging optical system is set based on the position where the image sharpness decreases. An imaging optical system position adjustment method. The imaging optical system position adjusting method according to claim 1, wherein the distance at which the chart is arranged is a short-distance depth limit of depth of field. In an imaging optical system position adjustment method for an imaging element disposed behind the imaging optical system of an imaging optical system composed of a lens group for guiding subject light and a wavefront coding optical system,
Place the chart at a predetermined distance,
A first position at which the image sharpness of the chart is lowered by moving the imaging optical system in the feeding direction; and a second position at which the image sharpness of the chart is lowered by moving the imaging optical system in the feeding direction. An image pickup optical system position adjusting method, wherein the position of the image pickup optical system in the optical axis direction is set based on the position of the image pickup optical system. The imaging optical system position adjusting method according to claim 3, wherein the distance at which the chart is arranged is a distance corresponding to ½ of the depth of focus.

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