JP2010071747A - Method and device of measuring optical characteristics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve in a simple manner the resolution with respect to a point image in a method and a device of measuring an optical characteristics for obtaining a point image intensity distribution in an optical system to be detected. <P>SOLUTION: The method of measuring an optical characteristics is adapted to obtain a point image intensity distribution of an optical system to be detected, in such a manner that light from a point light source is incident on the optical system to be detected and an point image by the optical system to be detected is captured by means of an image capturing device. The lights from a plurality of point light sources are incident on the optical system to be detected; the interval between the plurality of light sources is made, in such a manner that a plurality of point images by the optical system to be detected are positioned on different positions of pixels of the image capturing device; and at least portions at inner side rather than the external peripheral parts do not overlap one another. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical characteristic measuring method and apparatus for obtaining a point image intensity distribution of a test optical system.

As a method for obtaining the point image intensity distribution of the test optical system, light from a point light source is incident on the test optical system, and the point image by the test optical system is received by an image sensor to obtain the point image intensity distribution. Are known.
JP 2006-271503 A

  However, when the test optical system is, for example, a camera lens or the like, the diffraction limit is on the order of microns, so the size of the point image is on the order of the size of the pixel of the image sensor. Therefore, it becomes difficult to detect the shape of the point image finely by the image sensor, and it becomes impossible to obtain a sufficient resolution for the point image.

  Therefore, it is conceivable to enlarge the point image beyond the diffraction limit and receive the light on the image sensor and measure the shape. In this case, high precision is required for the magnifying optical system for enlarging the point image, and the cost increases. There is a problem.

  In addition, by moving the image sensor little by little with respect to the point image, it may be possible to obtain the effect of improving the resolution as if moving the slit sensor. In this case, however, a moving mechanism for moving the image sensor is necessary. This leads to a problem that the space efficiency decreases and the cost increases.

  The present invention has been made to solve such a conventional problem, and an object thereof is to provide an optical characteristic measuring method and apparatus capable of easily improving the resolution with respect to a point image.

  According to a first aspect illustrating the present invention, light from a point light source is incident on a test optical system, a point image by the test optical system is received by an image sensor, and the point image intensity of the test optical system An optical characteristic measurement method for obtaining a distribution, wherein light from a plurality of point light sources is incident on the test optical system, and intervals between the plurality of point light sources are determined by a plurality of point images by the test optical system. An optical property measuring method is provided, which is located at different positions of the pixels of the image sensor and does not overlap at least the inside of the outer periphery.

  According to a second aspect illustrating the present invention, a mask member in which a plurality of openings each serving as a point light source are formed, an image sensor that receives a point image formed by a test optical system by light from the openings, and The plurality of apertures in the mask member so that the plurality of point images by the optical system to be tested are located at different positions of the pixels of the imaging element and at least the inside of the outer peripheral portion does not overlap. There is provided an optical property measuring apparatus characterized by being formed at an appropriate interval.

  In the present invention, the resolution for a point image can be easily improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 shows a first embodiment of the optical property measuring apparatus of the present invention.

  The optical characteristic measuring apparatus includes a light source 11, a diffusion plate 13, a mask member 15, an image sensor 17, and an image processing unit 19. A test lens L is disposed between the mask member 15 and the image sensor 17. The test lens L is an imaging optical system in which optical characteristics such as a point image intensity distribution are measured by an optical characteristic measuring device. A test lens L in FIG. 1 is a photographing lens of a camera, and includes a plurality of lenses, for example, 5 lenses in 2 groups, but is shown as a single lens.

  As the light source 11, a light source 11 that generates monochromatic light having a predetermined wavelength is used. The diffusion plate 13 diffuses light from the light source 11. The mask member 15 has a plurality of pinholes (described later) for forming point light sources. Note that the point light source includes a surface light source having a fine size. In this embodiment, a circular surface light source is used.

  The image sensor 17 captures a plurality of point images (described later) formed by the lens L to be examined. The image sensor 17 is a monochrome image sensor 17. A large number of pixels (described later) are two-dimensionally arranged on the light receiving surface of the image sensor 17. An image sensor such as a CCD or CMOS can be used for the image sensor 17.

  The image processing unit 19 includes an A / D conversion unit 21, a buffer memory 23, a CPU 25, a storage unit 27, and an input / output interface (input / output I / F) 29. The buffer memory 23, the CPU 25, the storage unit 27, and the input / output I / F 29 are connected via a bus 31 so that information can be transmitted. Connected to the input / output I / F 29 are an output device 33 for displaying the progress of image processing and processing results, and an input device 35 for receiving input from the user.

  The image signal from the image sensor 17 is converted into a digital signal by the A / D converter 21 and output. The output result is temporarily held in a frame memory (not shown) and then held in the buffer memory 23.

  The CPU 25 controls the optical characteristic measuring device in accordance with an input from a user received via the input / output I / F 29. When the CPU 25 receives an instruction from the user via the input device 35, the CPU 25 reads the control arithmetic program from the storage unit 27 and starts it. Then, control is performed such as capturing a plurality of point images formed on the image sensor 17, storing the captured images in the storage unit 27, and displaying them on the output device 33. As the output device 33, a monitor, a printer, or the like is used. As the input device 35, a keyboard, a mouse, or the like is used.

  The storage unit 27 holds a control calculation program of the optical characteristic measurement device controlled by the CPU 25, a captured image, optical characteristic data of the lens L to be tested, and the like. Programs and data held in the storage unit 27 can be referred to as appropriate from the CPU 25 via the bus 31.

  FIG. 2 schematically shows a configuration of a main part of the above-described optical property measuring apparatus. In FIG. 2, the light from the pinhole 15 a formed in the mask member 15 is incident on the test lens L, and the point image T by the test lens L is received by the pixel 17 a of the image sensor 17.

  FIG. 2 is a diagram ignoring the scale for easy understanding, and is drawn like measurement of a completely different image height. However, actually, it is as shown in FIG. 3, and the difference in image height is very slight. Even if it is drawn as shown in FIG. 3, it is clear that the width of the actual pixel 17a is still enlarged in the image height direction in consideration of the order of microns.

  FIG. 4 shows a state in which the positional relationship between the point image T and the pixel 17a in FIG. The pinhole 15a of the mask member 15 is formed such that the positional relationship between the point image T and the pixel 17a is as shown in FIG. The pinholes 15a of the mask member 15 have the same size, and the point images T have the same size. By using the same size, the calculation in the image processing unit 19 can be facilitated.

  In FIG. 4, the plurality of point images T are located at different positions of the pixel 17a. In this embodiment, the interval L between the plurality of point images T is set at a different position from the multiple of the pitch P of the pixels 17a of the image sensor 17 so as to be positioned at different positions of the pixels 17a. The interval L between the plurality of point images T can be easily set by using, for example, the Vernier principle. In this embodiment, the plurality of point images T are formed at intervals L so as not to overlap each other. The plurality of point images T may be formed at intervals such that the inner side does not overlap at least the outer peripheral portion. Further, when the first dark ring is clearly present, it may be formed at an interval so that at least the inside of the first dark ring does not overlap. In short, it is good if a plurality of point images T interfere with each other and it becomes difficult to detect the point images T. Each pixel 17a has a square shape and the same size. The auxiliary line H indicated by a dotted line in FIG. 4 is a line segment passing through the center of each pixel 17a in the X direction and the Y direction, and the intersection of the auxiliary lines H is the center position of the pixel 17a.

  In FIG. 4, a total of nine point images T of three rows in the X direction and three rows in the Y direction are formed. The centers of the three point images T located at the center in the Y direction are located at the center in the Y direction of the pixel 17a. The centers of the three point images T located on the upper side in the Y direction are located on the lower side of the center of the pixel 17a in the Y direction. The centers of the three point images T located below the Y direction are located above the center of the pixel 17a in the Y direction. The centers of the three point images T located at the center in the X direction are located at the center in the X direction of the pixel 17a. The centers of the three point images T located on the right side in the X direction are located on the left side of the center of the pixel 17a in the X direction. The centers of the three point images T located on the left side in the X direction are located on the right side of the center of the pixel 17a in the X direction. In this way, the nine point images T are located at different positions of the pixel 17a.

  In the optical characteristic measuring apparatus described above, when the test lens L is accurately placed on the optical axis between the mask member 15 and the image sensor 17 and the light source 11 is turned on, the test lens L is exposed to the plurality of pinholes 15a. Light is incident, and a plurality of point images T are received by the image sensor 17. Then, the point image T received by the image sensor 17 is subjected to image processing in the image processing unit 19 and a predetermined calculation is performed to obtain a point image intensity distribution.

  In the optical characteristic measuring apparatus described above, a plurality of pinholes 15 a are formed in the mask member 15, the distance L between the plurality of pinholes 15 a, and the plurality of point images T formed by the lens L to be tested are Since they are located at different positions, the resolution for the point image T can be easily improved.

That is, as shown in FIG. 5, by moving the pixel 17a of the image pickup element 17 with respect to one point image T little by little from position 1, position 2, position 3, and position 4, the slit sensor is moved. Such a resolution improvement effect can be obtained. On the other hand, in FIG. 2, the right point image T among the three point images T corresponds to the position 1 in FIG. Further, the center point image T corresponds to the state at position 2 in FIG. 5, and the left point image T corresponds to the state at position 3 in FIG. Therefore, in the present invention, the amount of information with respect to the point image T is increased, and an effect of improving the resolution as if moving the slit sensor can be obtained. However, in the present invention, since a moving mechanism for moving the image sensor 17 is not necessary, the apparatus can be configured simply. Note that the formation of the pinhole 15a in the mask member 15 can be easily performed with high accuracy by a lithography technique. Further, in the present invention, since no magnifying optical system for enlarging the point image T is necessary, the apparatus can be configured simply.
(Second Embodiment)
Hereinafter, a second embodiment of the optical property measuring apparatus of the present invention will be described. In this embodiment, the same elements as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, the light source 11 is a white light source having a wide spectrum width. As the white light source, a super continuum light source, a metal halide light source, or the like is used.

  Further, the image sensor 17 is a color image sensor having pixels 17a in a Bayer array. As shown in FIG. 6, the imaging element 17 is provided with R (red), G (green), and B (blue) primary color transmission filters in a Bayer array type. Each pixel 17a has a square shape and the same size. An auxiliary line H indicated by a dotted line in FIG. 6 is a line segment passing through the center of each pixel 17a in the X direction and the Y direction, and the intersection of the auxiliary lines H is the center position of the pixel 17a.

  In FIG. 6, a total of four point images T of two rows in the X direction and two rows in the Y direction are formed. The four point images T are located at the intersections of R (red), G (green), and B (blue) pixels 17a at the centers, and R (red), G (green), and B (blue) pixels. It is located across 17a. In a color imaging device having a Bayer array pixel 17a, if the point image T is formed across the pixel 17a, the entire point image T cannot be recognized. In each point image T in FIG. 6, a quarter portion of the B (blue) point image T, a quarter portion of the R (red) point image T, and a 1 / portion of the R (red) point image T. Only the point image T of the portion 2 can be detected.

  In this embodiment, four point images T are used as a set in order to obtain the entire point image T of each color. By combining the B (blue) portions of the four point images T in FIG. 6, the entire B (blue) point image T can be obtained. By combining the R (red) portions of the four point images T in FIG. 6, the entire R (red) point image T can be obtained. By synthesizing the G (green) portions of the four point images T shown in FIG. 6, twice the entire G (green) point image T can be obtained. Therefore, the information of the point image T of G (green) is used in half.

  A set S of four point images T in FIG. 6 is for obtaining the entire point image T of each color, and corresponds to each point image T in FIG. FIG. 7 shows a state in which each point image T in FIG. 4 is replaced with a set S of four point images T in FIG. In FIG. 7, the boundaries of the set S of four point images T are indicated by bold lines. The pinhole 15a of the mask member 15 is formed such that the positional relationship between the point image T and the pixel 17a is as shown in FIG.

  In FIG. 7, a total of 9 sets S of point images T of 3 rows in the X direction and 3 rows in the Y direction are formed. The center of the point image T of the three sets S located at the center in the Y direction is located at the center in the Y direction of the pixel 17a. The center of the point image T of the 3 sets S located on the upper side in the Y direction is located below the center of the pixel 17a in the Y direction. The center of the point image T of the three sets S located on the lower side in the Y direction is located above the center in the Y direction of the pixel 17a. Further, the center of the point image T of the three sets S located at the center in the X direction is located at the center in the X direction of the pixel 17a. The center of the point image T of the 3 sets S located on the right side in the X direction is located on the left side of the center of the pixel 17a in the X direction. The center of the point image T of the three sets S located on the left side in the X direction is located on the right side of the center of the pixel 17a in the X direction. In this way, the nine sets S of point images T are located at different positions of the pixels 17a.

In this embodiment, a plurality of point images T are formed across the pixels 17a of the color image sensor 17, and the plurality of point images T are synthesized to obtain the entire point image T for each color. The entire point image T of each color can be detected easily and reliably. Since a plurality of point images T for obtaining the entire point image T of each color are set as one set S, and each set S is positioned at a different position of the pixel 17a of the image sensor 17, the color image sensor 17 The resolution for the point image T can be easily improved.
(Supplementary items of the embodiment)
As mentioned above, although this invention was demonstrated by embodiment mentioned above, the technical scope of this invention is not limited to embodiment mentioned above, For example, the following forms may be sufficient.

  (1) In the above-described embodiment, the example in which the lens L to be examined is a photographing lens of a camera has been described. However, for example, an optical system of an optical device such as a telescope or a microscope may be used.

  (2) In the above-described embodiment, the example in which the interval L between the plurality of point images T is set to the interval L different from the pitch P of the pixels 17a of the image sensor 17 or a multiple thereof has been described. The gap L may be formed, and the mask member 15 may be rotated to have a different pitch P. Also, taking advantage of the fact that the point image interval on the imaging surface can be finely adjusted by changing the position of the point image pattern on the imaging surface and the object surface while maintaining the focus position, that is, by slightly changing the magnification. It is also effective to adjust the point image interval with respect to the element pitch. This is because a change in optical characteristics accompanying a slight change in magnification is usually negligible.

  (3) In the above-described embodiment, the example in which the size of the pinhole 15a of the mask member 15 is the same size has been described, but it may be different.

It is explanatory drawing which shows 1st Embodiment of the optical characteristic measuring apparatus of this invention. It is explanatory drawing which expands and shows typically the principal part of FIG. It is explanatory drawing which shows the state of FIG. 2 by a more realistic dimension. It is explanatory drawing which shows the position of the point image of FIG. 2 planarly. It is explanatory drawing which shows the measuring method which moves an image pick-up element with respect to a point image. It is explanatory drawing which shows the set of the point image for obtaining the whole point image of each color from a color image sensor. It is explanatory drawing which shows the state which replaced each point image of FIG. 4 with the set of point images.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Light source, 15 ... Mask member, 15a ... Pinhole, 17 ... Image sensor, 17a ... Pixel, 19 ... Image processing part, L ... Test lens, T ... Point image.

Claims (8)

An optical characteristic measurement method in which light from a point light source is incident on a test optical system, a point image by the test optical system is received by an image sensor, and a point image intensity distribution of the test optical system is obtained,
Light from a plurality of point light sources is incident on the test optical system, and intervals between the plurality of point light sources are set such that a plurality of point images by the test optical system are located at different positions of the pixels of the image sensor. And an optical property measuring method characterized in that at least the inner side of the outer peripheral portion does not overlap. The optical property measuring method according to claim 1,
The optical characteristic measuring method, wherein an interval between the plurality of point images is different from a pitch of a pixel of the image sensor or a multiple thereof. In the optical characteristic measuring method according to claim 1 or 2,
The optical characteristic measuring method, wherein the plurality of point images do not overlap at least inside the first dark ring. In the optical characteristic measuring method according to any one of claims 1 to 3,
The image sensor is a color image sensor having pixels in a Bayer array, and a plurality of point images are formed across the pixels, and a plurality of point images are synthesized to obtain an entire point image for each color. A method for measuring optical characteristics. A mask member formed with a plurality of openings each serving as a point light source;
An image sensor that receives a point image formed by the test optical system by light from the aperture, and the mask member includes the plurality of apertures, and a plurality of point images by the test optical system capture the image. An optical characteristic measuring apparatus, wherein the optical characteristic measuring apparatus is formed at a position where pixels of the element are different from each other and at least an inner side does not overlap with an outer peripheral portion. In the optical characteristic measuring device according to claim 5,
The optical characteristic measuring apparatus, wherein an interval between the plurality of point images is different from a pitch of a pixel of the image sensor or a multiple thereof. In the optical characteristic measuring device according to claim 5 or 6,
The optical characteristic measuring device, wherein the plurality of point images do not overlap at least the inside of the first dark ring. In the optical characteristic measuring device according to any one of claims 5 to 7,
The image pickup device is a color image pickup device having pixels with a Bayer array, and a plurality of point images are formed across the pixels, and a plurality of point images are synthesized to obtain an entire point image for each color. A characteristic optical characteristic measuring apparatus.

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