JP2005331345A - Lens inspection device and lens inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens inspection device and a lens inspection method for evaluating not only the performance of a lens single body but also the performance of the assembled state as an imaging device which is the final product. <P>SOLUTION: An imaging part 7 is equipped with an imaging element 6 to which the scaling of the light receiving quantity similar to an imaging element provided in an imaging device using a lens is applied, and a chart 4 wherein white domains and black domains spreading radially at equal angles from the center point are arranged alternately adjacently is imaged, and an evaluation part 10 determines the ratio of gray domains included in the image, to thereby determine the quality of an inspection object lens. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lens inspection device and a lens inspection method used for a camera or the like.

  Conventionally, when performing a performance evaluation or inspection of a taking lens of a camera, a chart board on which a chart for resolution evaluation is captured using a lens to be inspected, and the resolution of the image of the chart is visually determined. For example, a method of evaluating performance using an MTF (Modulation Transfer Function) method disclosed in Patent Document 1 is used. For example, Patent Document 2 discloses an MTF inspection apparatus using an optical fiber bundle such as a fiber optic plate (hereinafter referred to as FOP) or a solid-state image sensor such as a CCD.

  For example, as a conventional lens inspection device, an imaging lens to be inspected is positioned by a holder, attached in that state to a movable part of a transport device, and an evaluation chart plate is moved at a predetermined distance in front of the imaging lens There is something that can be arranged. The evaluation chart plate is composed of a chart plate for evaluating drawing performance in the telephoto state and a chart plate for evaluating drawing performance in the wide-angle state, and the optical axis direction (Z direction) and light of the photographing lens by the driving means. It arrange | positions so that a movement in the direction (X direction) orthogonal to an axial direction is possible. On this evaluation chart plate, a chart for resolving power evaluation is drawn.

  On the other hand, an optical fiber bundle called a flat fiber optic plate (F-FOP) is disposed behind the taking lens. One end of the optical fiber bundle is an incident surface of the chart image that has passed through the photographing lens. On the other hand, the other end of the optical fiber bundle is an emission surface of the chart image. An optical system (enlarging optical system) for enlarging the chart image emitted from the optical fiber bundle is disposed behind the optical fiber bundle. An imaging means such as a CCD camera is attached behind the optical system so as to receive an image from the optical system, and a cover glass is disposed on the imaging element constituting the CCD camera, that is, the front surface of the CCD element. The optical fiber bundle, the optical system, and the CCD camera constitute a photographing block.

  This imaging block is configured to be movable in three dimensions in XYZ directions, and is held by an XYZθ stage which is a moving and rotating means that can also rotate in the θ direction about the Z axis. This XYZθ stage is held on a transfer device. Further, the CCD camera is connected to an arithmetic processing unit that functions as a control unit and a determination unit by appropriate means (for example, cable connection). The arithmetic processing unit calculates the three-dimensional position of the incident surface of the optical fiber bundle based on the information of the chart image captured by the CCD camera, and adjusts the position and angle of a certain CCD element and the pattern of the chart, The position of the XYZθ stage is controlled. The arithmetic processing unit is connected to a display device. Furthermore, the arithmetic processing unit outputs a calculation value of the drawing performance of the photographing lens as a digital value based on the image information of the chart imaged by the CCD camera. The display device includes a CRT display or a liquid crystal display that displays an output result of the arithmetic processing unit.

  The apparatus configured in this manner first holds the photographic lens on the holder, sets the lens focal length to the focal length in the telephoto state or the wide-angle state, and according to this, a chart for evaluating the drawing performance in the telephoto state The evaluation chart plate is moved so that either the plate or the chart plate for evaluating the drawing performance in the wide-angle state faces the photographing lens and is located on the focal plane. Next, the incident surface of the optical fiber bundle is initially operated by an XYZθ stage and moved to a position corresponding to the chart to be analyzed. At this time, a real image of the chart is formed on the incident surface of the optical fiber bundle, and the real image light flux is incident on the CCD camera through the exit surface and is imaged.

  The arithmetic processing unit calculates the three-dimensional position of the incident surface of the optical fiber bundle from the image information of the evaluation chart imaged by the CCD camera so as to match a certain CCD element with the position and angle of the chart pattern. In addition, the position of the XYZθ stage is controlled. After determining the position of the entrance surface of the optical fiber bundle and the position of the CCD camera in this way, each value for evaluating the imaging performance of the imaging lens by further calculating the information of the image captured by the CCD camera with an arithmetic processing unit. And this value is output as a digital value and displayed on a display device (see, for example, Patent Document 3).

JP-A-9-243515 JP-A-10-206993 Japanese Patent Application Laid-Open No. 2002-31585 (pages 4 to 5, FIGS. 1 and 2)

  Since the conventional lens inspection device is configured as described above, performance evaluation is performed on a single lens, so that when a lens such as a CCD camera module lens is evaluated, for example, it is assembled in an imaging device as a final product. It is difficult to compare with the numerical value of performance, and when evaluating after incorporating a lens into the imaging device, even if the lens alone is defective, the imaging device is regarded as defective, and the productivity of the imaging device deteriorates. there were.

  The present invention has been made to solve the above-described problems, and includes a lens inspection device and a lens inspection method for evaluating not only the performance of a single lens but also the performance of an assembled state as an imaging device as a final product. The purpose is to obtain.

  The lens inspection apparatus according to the present invention includes an imaging element in which the received light amount is scaled in the same manner as an imaging element provided in an imaging apparatus in which a lens is used as an imaging unit.

  According to the present invention, since the image pickup device having the same amount of received light as that of the image pickup device provided in the image pickup apparatus in which the lens is used as the image pickup means is provided, the problem that cannot be determined by the optical inspection of the lens alone is finally obtained. It is possible to determine before assembling the imaging device as a product, and there is an effect that the productivity of the imaging device can be improved.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
FIG. 1 is an explanatory diagram showing the configuration of a lens inspection apparatus according to Embodiment 1 of the present invention. The illustrated lens inspection device 11 includes a lens holding mechanism unit 1, an illumination 3 such as a light, a chart 4 such as a panel on which a chart image to be imaged is drawn, a chart holding mechanism unit 5 that holds the chart 4, An imaging unit (imaging unit) 7 that captures the chart 4 using the lens to be inspected, and the imaging unit 7 are moved to adjust the distance between the lens to be inspected and the imaging device 6 provided in the imaging unit 7. A focus adjustment unit 8 is provided. The imaging unit 7 is connected to the image processing unit 9 by connection means such as a cable 7a so that the output signal of the imaging element 6 is output to the image processing unit 9. The image processing unit 9 is connected to, for example, a personal computer or an evaluation unit (evaluation unit) 10 having a function equivalent to that of a personal computer having display means for displaying a captured image and the like and having a calculation / determination function in data processing. The lens to be inspected refers to a single lens or a lens unit in which a plurality of lenses are combined. Hereinafter, various lenses to be inspected will be referred to as a lens to be inspected. .

  The inside of the lens inspection apparatus 11 is configured as follows. The lens holding mechanism unit 1 and the chart holding mechanism unit 5 are installed to face each other. Specifically, the test lens held by the lens insertion portion 2 of the lens holding mechanism portion 1 and the chart 4 held by the chart holding mechanism portion 5 are installed so as to face each other. The chart holding mechanism unit 5 is fixed to, for example, the inner wall surface 11a of the lens inspection device 11, and the lens holding mechanism unit 1, the imaging unit 7, and the focus adjusting unit 8 are provided on the inner wall surface 11b side facing the inner wall surface 11a. On the inner wall surface 11b side, for example, the focus adjustment unit 8 is fixed to the inner wall surface 11b. The focus adjustment unit 8 moves the imaging unit 7 in the direction of moving away from or approaching the test lens as indicated by the arrow a in FIG. 1, that is, the distance between the test lens and the image sensor 6. It has a mechanism to adjust.

  Inside the lens inspection device 11, the lens holding mechanism 1 fixed to the inner wall surface 11b using a columnar member is installed in front of the imaging unit 7, that is, between the imaging unit 7 and the chart 4, for example. The lens holding mechanism section 1 is provided with a lens insertion section 2 for fixing the lens to be tested while detachably mounting the lens to be tested on a portion facing the chart 4. In the portion of the lens holding mechanism portion 1 where the lens insertion portion 2 is provided, the imaging light transmitted through the test lens while the lens insertion portion 2 holds the test lens reaches the imaging device 6. A transmission hole (not shown) is provided. That is, the imaging unit 7 is mounted on the focus adjustment unit 8 so that the imaging element 6 can receive the transmitted light of the test lens fixed to the lens insertion unit 2. As described above, the imaging unit 7 that images the chart 4 is arranged on the exit surface side of the lens to be examined. In this arrangement, the positional relationship between the test lens and the image sensor 6 is the same as that of the final product such as a camera module. For example, the illumination 3 is arranged near both sides of the lens holding mechanism unit 5 as shown in the figure, and is provided by adjusting the light irradiation direction, the number of installed units, and the like so that the brightness that illuminates the chart 4 does not vary.

  The image pickup unit 7 includes, for example, a CCD element that converts light received as the image pickup element 6 into electric charges, a V driver that drives the light reception / output operation of the image pickup element 6 in the vertical direction, and the light reception / output of the image pickup element 6. A timing generator for driving the output operation in the horizontal direction and an analog front end for converting the output signal of the CCD element into a digital signal are provided. Such an imaging element such as a CCD element is provided with a microlens so that a uniform amount of light is received from the center of the light source, and the received light amount is scaled by the microlens. The imaging device has been optimized for scaling by micro lens for each model, and since the scaling is different for imaging devices of different models, if compatibility with the lens of the imaging device is not preferable, An effect such as darkening of the peripheral portion of the image occurs. For this reason, the lens inspection apparatus according to the present invention is configured such that the optical system including the image sensor 6 is equivalent to the final product so that the performance of the test lens can be accurately evaluated.

  As described above, the image processing unit 9 is connected to the imaging unit 7 by connection means such as the cable 7a, and has an image processing function and processing characteristics equivalent to those of the final product imaging apparatus. The image processing unit 9 includes a control unit such as a digital signal processor (DSP), for example, and inputs an image signal captured by the imaging unit 7, and performs automatic exposure adjustment, automatic white balance adjustment, output image size adjustment, color interpolation / Data processing such as gradation correction and color difference matrix conversion is performed to generate and output image data.

  The evaluation unit 10 is connected to the image processing unit 9 by a connecting means such as a cable, and performs arithmetic processing, determination processing, and the like of the image data input from the image processing unit 9, and also includes a focus adjustment unit 8 as described later. It performs operation control. In FIG. 1, illustration of the connection between the evaluation unit 10 and the focus adjustment unit 8 is omitted.

Next, the operation will be described.
FIG. 2 is a flowchart showing the operation of the lens inspection apparatus according to the first embodiment. First, the test lens is inserted into the insertion unit 2 and is held by the lens holding mechanism unit 1 and fixed inside the lens inspection device 11 (step ST101). The image processing unit 9 captures an image of the chart 4 illuminated by the illumination 3 using the imaging unit 7. Based on the image data output from the image processing unit 9 at this time, the evaluation unit 10 controls the focus adjustment unit 8 to perform focus adjustment so that the image of the chart 4 is clearly captured (step ST102). The focus adjustment includes, for example, a driving unit that slides the imaging unit 7 on the focus adjustment unit 8, and the evaluation unit 10 performs arithmetic processing on data related to the focus of the image data acquired from the image processing unit 9, and the calculation result The focus control unit 8 performs feedback control based on the above to slide the position of the imaging unit 7. Further, the focus adjustment unit 8 includes an operation unit such as a crown and a mechanism in which the imaging unit 7 mounted according to the operation of the operation unit slides, and the user manually operates the operation unit to perform imaging. The distance between the unit 7 and the test lens may be adjusted. At this time, the image data captured by the imaging unit 7 may be reproduced and displayed on the display unit of the evaluation unit 10 and adjusted by the user. By adjusting the focus by moving the position of the imaging unit 7, the distance between the lens to be tested and the imaging unit 7 arranged in the lens inspection apparatus is the same as the distance when the final product is assembled.

  The image processing unit 9 images the chart 4 using the imaging unit 7 with the focus adjusted as described above, and performs automatic exposure adjustment, automatic white balance adjustment, output image size adjustment, color interpolation, Image data is generated by performing processing such as gradation correction and color difference matrix conversion, and is output to the evaluation unit 10. The evaluation unit 10 acquires the image data processed in this way (step ST103). The image data acquired at this time is obtained by performing imaging and data processing using the imaging device 6 and the image processing unit 9 equivalent to the imaging device as the final product, and is acquired by the imaging device as the final product. Is equivalent to. The evaluation unit 10 performs predetermined calculation and determination processing on the acquired image data, reproduces the image data as an image, displays the image data on a display unit provided therein, and allows the user to confirm (step ST104). The evaluation unit 10 that has input the image data from the image processing unit 9 performs predetermined processing and determination processing as described above. At this time, calculation is performed using the input image data, for example, data related to the focus included in the image data, and a numerical value indicating the performance related to the focus is obtained. After the performance related to the focus is digitized in this way, a standard value set in advance and a numerical value indicating the performance related to the focus are compared to determine whether the test lens is good or not, and the determination result is displayed on the display unit of the evaluation unit 10. To display. Here, the focus-related performance has been described as an example. However, the other performances of the lens to be tested are similarly quantified and determined to determine whether the lens to be tested can be used for the final product.

  The lens inspection device 11 according to the first embodiment acquires an inspection result under the same conditions as those in the case of assembling the imaging device as the final product in this way, and performs a determination using the inspection result to thereby determine the lens. For example, it is possible to evaluate the lens performance related to the compatibility with the scaling of the image sensor, which was difficult to judge by only evaluating the optical performance of a single unit. At the inspection stage, it is possible to determine the quality of the lens to be tested and select it.

  As described above, according to the first embodiment, since the test lens is inspected with the optical system equivalent to the imaging device of the final product, the test lens that has not been known unless the imaging device is assembled. Defects can be determined before assembling, and the occurrence of defective products in the image pickup apparatus can be suppressed, and productivity can be improved.

Embodiment 2. FIG.
The lens inspection apparatus according to the second embodiment is configured similarly to the lens inspection apparatus 11 described with reference to FIG. 1 in the first embodiment. Here, the description of the parts configured in the same manner as the lens inspection apparatus 11 according to the first embodiment will be omitted, and the parts that are characteristic of the lens inspection apparatus according to the second embodiment will be described.

  FIG. 3A is a conceptual diagram showing a chart image used in the lens inspection apparatus according to Embodiment 2 of the present invention. The illustrated chart image 12 is a white area and a black area that are radially spread at an equal angle from the center point 20 of the chart image 12 and are adjacent to each other. For example, twelve pairs of black areas are included, and white areas and black areas are alternately arranged. This chart image 12 is drawn on the chart 4 shown in FIG. 1 and is provided in the lens inspection apparatus according to the second embodiment. Note that the number of pairs of white areas and black areas is not limited to twelve.

  3-2 is an explanatory diagram in which a part of the chart image captured by the lens inspection apparatus according to the second embodiment is enlarged. This figure is an enlarged view of a portion corresponding to the portion 13 of the chart image 12 shown in FIG. 3A in the image obtained by taking the chart image 12 of FIG. 3A. It is shown that the white region 14, the gray region 16, the black region 15, and the gray region 17 are included in the white region and black region pair 22. In other words, the image area of the captured pair 22 includes gray areas 16 and 17 on both sides of the black area 15 in addition to the adjacent white area 14 and black area 15. Further, even in another pair of white area and black area of the pair 22, the captured image includes a gray area as illustrated in the boundary portion between the white area and the black area.

Next, the operation will be described.
FIG. 4 is an explanatory diagram in which a chart image captured by the lens inspection apparatus according to the second embodiment is digitized. This figure shows a pair of adjacent white areas and black areas existing on the circumference 21 drawn by a dashed line with a distance r from the center point 20 of the chart image 12 shown in FIG. The brightness of the image area is digitized and represented in a graph. The vertical axis of the graph in FIG. 4 indicates a numerical value representing the brightness of the pixel in the image data output from the image processing unit 9 shown in FIG. The image data exemplified here has 256 gradations, and the output numerical value shown on the vertical axis in FIG. Also, the horizontal axis of the graph of FIG. 4 indicates the pixel numbers sequentially assigned to 2πr pixels existing on the circumference 21 starting from an arbitrary place on the circumference 21 shown in FIG. It is. In FIG. 4, the horizontal axis represents pixel numbers 227 to 257 assigned to pixels related to a part of the circumference 21 provided on the pair 22 of the white region and the black region, and the vertical axis represents a numerical value determined as described later. Represents the brightness of the pixels with pixel numbers 227 to 257.

  FIG. 4 shows an image having the following brightness, for example. Pixels from pixel number 227 to pixel number 239 on the left end side in the figure have gradations indicating brightness white, and range from an upper limit numerical value indicating gray to an upper limit numerical value indicating white (white level). It has the numerical value of. The pixel range indicated by this pixel number range is a white area, and the area width is A. Pixels from pixel number 240 to pixel number 243 have gradations indicating brightness of gray, and have numerical values ranging from an upper limit numerical value indicating gray to a lower limit numerical value indicating gray. The pixel range indicated by this pixel number range is a gray region, and the region width is B1. Pixels from pixel number 244 to pixel number 253 have gradations indicating brightness of black, and have numerical values ranging from a lower limit numerical value indicating gray to a lower limit numerical value indicating black (black level). The pixel range indicated by the pixel number range is a black region, and the region width is C. Pixels of pixel number 254 and pixel number 255 have gradations indicating brightness of gray, and have numerical values in a range from a lower limit numerical value indicating gray to an upper limit numerical value indicating gray. The pixel range indicated by this pixel number range is a gray region, and the region width is B2.

FIG. 5 is a flowchart showing the operation of the lens inspection apparatus according to the second embodiment. This flowchart shows a lens inspection method according to the second embodiment. First, the test lens is inserted into the insertion unit 2, held by the lens holding mechanism unit 1, and fixed inside the lens inspection device 11 (step ST101). The activated image processing unit 9 processes the process of step ST102 in the same manner as described in the first embodiment, and the evaluation unit 10 acquires image data obtained by the imaging unit 7 capturing the chart image 12 (step ST103). ). The evaluation unit 10 that has input the image data from the image processing unit 9 is the data indicating the brightness of the pair 22 part on the circumference 21 at an arbitrary distance r from the center point 20 with respect to the chart image 12 of the obtained image data. Is digitized for each pixel as described with reference to FIG. 4 (step ST201). From the digitized data, the width A of the white area, the width C of the black area, and the widths B1 and B2 of the gray area are obtained for each pair (step ST202). Using the obtained widths A, B1, B2, and C of each region, an evaluation value is calculated using the following equation (1) (step ST203). This evaluation value is the ratio of all gray areas in the pair 22.
Evaluation value = (| B1-B2 | × 2 / (A + B1 + B2 + C)) (1)

  For each pair of white areas and black areas on the circumference 21, evaluation values are calculated for 12 pairs of white areas and black areas in the image of the chart increase 12 illustrated in FIG. In this way, the pixels on the circumference 21 are divided into predetermined ranges, for example, the white areas and the black areas are paired as described above, and the evaluation value of each pair is calculated, so that the lens body is arranged in the circumferential direction. It is possible to detect a test lens whose resolution deteriorates at a specific portion when divided into two. Evaluation values are obtained for all circumferential directions of the test lens, that is, for all pairs on the circumference 21, and the maximum value among them is set as a determination value for the test lens (step ST204), and this determination value is set in advance. The quality of the test lens is determined by comparing with the specified value. The larger the evaluation value or determination value, the greater the resolution degradation. In this way, for example, the unequal resolution of the test lens can be quantified by obtaining the evaluation value for each of the regions divided in the circumferential direction of the test lens, such as the pair 22. become. Further, by setting the distance r from the center point 20 appropriately, a desired portion of the lens to be inspected can be inspected. The prescribed value described above is a value set according to the performance required for the lens to be examined.

  As described above, according to the second embodiment, the chart image 12 having the white area and the black area extending radially from the center point 20 is captured using the test lens, and the image data is input to the evaluation unit 10. The width of the white area, black area, and gray area of the image indicated by the image data is obtained for each area that is a pair of the adjacent white area and black area, and the evaluation value is obtained by determining the ratio of the gray area included in the pair. Since the quality of the test lens is judged using the largest value among the evaluation values of each pair as the judgment value, the test lens is formed when the optical axis of the test lens is deviated. There is an effect that it is possible to evaluate the non-directional resolution degradation that occurs when there is an influence of residual stress generated during the process.

It is explanatory drawing which shows the structure of the lens inspection apparatus by Embodiment 1 of this invention. 5 is a flowchart showing the operation of the lens inspection apparatus according to Embodiment 1. It is a conceptual diagram which shows the chart image used for the lens inspection apparatus by Embodiment 2 of this invention. FIG. 10 is an explanatory diagram in which a part of an image of a chart imaged by the lens inspection device according to the second embodiment is enlarged. It is explanatory drawing which digitized the image of the chart imaged with the lens test | inspection apparatus by Embodiment 2. FIG. 6 is a flowchart illustrating an operation of the lens inspection device according to the second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Lens holding mechanism part, 2 Lens insertion part, 3 Illumination, 4 chart, 5 chart holding | maintenance mechanism part, 6 Imaging element, 7 Imaging part (imaging means), 8 Focus adjustment part, 9 Image processing part, 10 Evaluation part (Evaluation) Means), 11 Lens inspection device, 12 Chart image, 13 Enlarged portion, 14 White region, 15 Black region, 16, 17 Gray region, 20 Center point, 21 Circumference, 22 pairs.

Claims (5)

A chart used for evaluation of the lens to be inspected, an imaging means for imaging the chart using the lens to be inspected, and the performance of the lens to be inspected based on image data output from the imaging means In a lens inspection apparatus provided with an evaluation means for evaluating,
A lens inspection apparatus, wherein the image pickup unit includes an image pickup element in which the received light amount is scaled in the same manner as an image pickup element included in an image pickup apparatus using the lens. A chart used for evaluation of the lens to be inspected, an imaging means for imaging the chart using the lens to be inspected, and the performance of the lens to be inspected based on image data output from the imaging means In a lens inspection apparatus provided with an evaluation means for evaluating,
The chart includes a chart image in which white areas and black areas that spread radially at an equal angle from the center point are alternately adjacent to each other,
The evaluation unit obtains a ratio of a gray area included in an image when the imaging unit images the chart, and determines whether the lens to be inspected is good or bad based on the ratio of the gray area. Lens inspection device.   The evaluation means sets neighboring white areas and black areas as a set in the captured image, and determines the ratio of the gray areas included in the set from each area width to evaluate the resolution of the lens to be inspected. The lens inspection device according to claim 2.   The evaluation means sets a plurality of sets in the captured image, obtains the ratio of the gray area of each set, and evaluates the largest value as the resolution of the lens to be inspected. 3. The lens inspection device according to 3. A process in which the imaging means uses the lens to be inspected to image a chart image in which white areas and black areas extending radially at equal angles from the center point are alternately adjacent; and
The evaluation means inputs the image data output from the imaging means, sets a circle having a certain distance from the center point of the chart image to the image indicated by the image data, and sets the brightness of the pixels on the circle Quantifying and setting the white area, black area and gray area of the image;
The evaluation means sets a neighboring white area and black area in the image as a set, and calculates a ratio of gray areas included in each set to obtain an evaluation value;
A lens inspection method comprising: a step in which the evaluation means determines a pass / fail of a lens to be inspected by using the largest value among the evaluation values of each set as a determination value of the lens to be inspected.

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