JP2009031076A - Inspection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection system capable of measuring the optical characteristics of lens and measuring the best image surface, in an opened state and narrowed state of an aperture, at the same time. <P>SOLUTION: An inspection device comprises a chart plate 3; sensors 13, 14 for detecting the light beam that is emitted from a light source 2 and has passed through the chart plate 3 as images, formed by a lens 4 to be inspected; a control device 16 for computing the optical characteristics from the intensity distribution of the images detected by the sensor 13, 14 while controlling the operation of the apertures of the lens 4 to be inspected. The control device 16 is constituted with a first step for acquiring the intensity distribution of the images by the lens 4 to be inspected, when the aperture is opened; a second step for acquiring the intensity distribution, in a state when the apertures is narrowed; a third step for acquiring MTF values from these intensity distributions and a fourth step for acquiring the difference between the position of the best image surface when the aperture is opened, and the position of that in the reduced state of the aperture from these MTF values. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inspection system for measuring MTF and OTF of a photographing lens.

  Shooting lenses (photographic lenses) have been developed for a long time, but recently, digital cameras have changed for silver halide cameras, so autofocus shooting lenses equipped with DC motors and ultrasonic motors have become mainstream. Many users watch at the same size on a personal computer screen, so the performance of lenses and the sweetness of focus have become clearer for photographic lenses. When mounting an actuator on such a photographic lens, it is essential to reduce the weight of the lens, reduce the amount of movement, and ensure the space for the mechanism. A lens with an anti-vibration function in a small high-power zoom is a crystal of technology and is required by many general users. In addition, due to the progress of manufacturing technology, the lens design can increase the number of aspheric surfaces, improve the degree of freedom of its shape, and use anomalous dispersion glass. Yes. On the other hand, it goes without saying that the improvement in design performance and the improvement in parts accuracy and assembly are more severe due to more optical adjustments than in the past.

In general, the autofocus detection uses a phase difference method on a part of an axial light beam which is narrowed by two or three steps from the open F number of the lens. However, if there is a problem that the spherical aberration is greatly different between the measurement light beam and the aperture area at the time of photographing due to the fact that there is no group spacing, etc., or if the manufacturing shape of the aspherical surface has errors in the region where the measurement light beam passes, An image obtained even when the camera is determined to be in focus is an image out of focus, and the image quality deteriorates due to the influence of the broken spherical aberration. Therefore, the difference between the best image plane when the aperture is reduced and the best image plane at the open is important. In the era of silver halide cameras, there are some users who greatly stretch, and even heavy users feel that aberration is a characteristic of the lens. On the other hand, the spherical flare allowed by a silver salt camera is often described as a mere blurred image in digital. For this reason, it is currently necessary for a general user to evaluate an image by enlarging the image with a personal computer, and it is necessary to evaluate an allowable aberration after lens assembly adjustment and a change in the best image plane between when the lens is opened and when it is reduced. In general, in the final inspection of a product, resolution evaluation or MTF measurement using an open projector is often performed (see, for example, Patent Document 1). In this case, it is preferable to perform an inspection by MTF measurement which has no room for artificial judgment. Measurement of the best image plane when the aperture is open and the best image plane when the aperture is reduced are performed separately for shortening the MTF measurement time, and the variation amount and direction are stored in the lens.
Japanese Patent Laid-Open No. 5-256441

  In order to supply a lens that satisfies the user in this way, it is necessary to inspect not only the optical characteristics when the lens is opened, but also the optical characteristics when the lens is closed and the change in the best image plane since the lens is opened. When evaluating the optical characteristics with the projection resolving power, the lens is moved in the optical axis direction with a motor to focus on the evaluation surface. However, at the same time, even if the lens aperture is electrically controlled to check the fluctuation of the best image plane position, the best image plane position will be judged visually even if the focus position is known from the number of pulses of the stepping motor. There was a problem that it was difficult to deal with. That is, mass production inspection is required to perform an operation for evaluating the optical characteristics and simultaneously measuring the fluctuation of the best image plane position and writing to the lens to be examined.

  The present invention has been made in view of such problems, and is an inspection system that is effective for mass-production inspection and capable of simultaneously measuring the optical characteristics of a lens and opening the aperture and the best image plane in a squeezed state. The purpose is to provide.

  In order to solve the above-described problems, an inspection system according to the present invention (for example, the inspection apparatus 1 in the embodiment) includes a chart plate on which a chart is formed, and a light beam emitted from a light source and passed through the chart by a lens to be tested. The image sensor (for example, on-axis and off-axis light receiving sensors 13 and 14) to detect as an image formed and the aperture of the lens to be tested are controlled, and from the intensity distribution of the image detected by the image sensor. And a control device for calculating optical characteristics of the lens to be examined. Then, the control device controls the aperture of the test lens to the open state, and obtains the intensity distribution of the image by the test lens, and controls the aperture of the test lens to the narrowed state. A second step of obtaining an intensity distribution of the image by the lens to be examined, a third step of obtaining an MTF value from each of the intensity distribution when the aperture is opened and when the aperture is reduced, and The fourth step is to obtain the difference in the position of the best image plane when the aperture is released from these MTF values and when the aperture is reduced.

  In such an inspection system according to the present invention, before the control device acquires the intensity distribution of the image by the test lens in the first and second steps, the intensity distribution of the image with the aperture opened. It is preferable to have a step of calculating the accumulation time when the aperture in the image sensor for obtaining a predetermined intensity or more from the image sensor is opened. Further, in the step of calculating the accumulation time, it is preferable that the accumulation time when the aperture is narrowed is calculated from the accumulation time when the aperture is opened.

  In the inspection system according to the present invention, the imaging element includes an on-axis light receiving sensor that detects an on-axis image based on a chart on the chart plate, and an off-axis light receiving sensor that detects an off-axis image based on the chart on the chart plate. It is preferred that

  When the inspection system according to the present invention is configured as described above, it is possible to simultaneously measure the evaluation of the optical characteristics of the lens, the aperture opening, and the best image plane in the squeezed state, which are effective for mass production inspection. From the characteristics, it is possible to accurately measure the difference in position on the optical axis of the best image plane.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In this embodiment, an MTF / OTF inspection apparatus that can measure a plurality of angles of view at the same time in an enlarged projection type, and the light receiving sensor is a surface perpendicular to the mechanical axis without the shift structure between the chart and the lens to be tested. A case will be described in which an inspection apparatus characterized by a structure that shifts within (moves within this vertical plane) is used. First, the configuration of the inspection apparatus 1 according to the present embodiment will be described. As shown in FIG. 1, the inspection apparatus 1 includes a light source 2 and a chart plate 3 inside, and an illumination unit 5 that holds a test lens (photographing lens) 4 and a relative movement with respect to the illumination unit 5. And a possible measuring unit 6.

  The light source 2, the chart plate 3, and the test lens 4 are arranged side by side on the optical axis (hereinafter referred to as “mechanical axis 7” of the inspection apparatus 1) in the illumination unit 5. . In this embodiment, the light beam emitted from the light source 2 is radiated onto the mechanical shaft 7 by the optical fiber 2a, a condenser lens (not shown), and the like, and is irradiated onto the chart plate 3. Further, the illumination unit 5 includes an illumination-side control unit 17 that moves the chart plate 3 back and forth along the mechanical axis 7 and further communicates with the attached lens 4 to control opening and closing of the aperture. Is provided.

  On the other hand, the measuring unit 6 is disposed on the light receiving side (on the opposite side of the light source 2 with the lens 4 to be tested) and is provided with a flat plate-like receiving unit 8 having a plane perpendicular to the mechanical axis 7. On the light source 2 side surface (light receiving side surface) of the receiving portion 8, a large biaxial plate (hereinafter referred to as “large stage 9”) that can move relative to the receiving portion 8 on the light receiving side surface. And a large stage drive unit 10 that operates on the receiving unit 8 is provided. Further, a small single-axis plate (hereinafter referred to as “small stage 11”) that can be relatively moved on the light receiving side surface of the large stage 9 and a small stage drive unit that operates the small stage 11 on the large stage 9 12 are provided. A plurality of small stages 11 are provided on the large stage 9 (for example, FIG. 2 shows a case where four small stages 11 are provided in the diagonal direction of the rectangular large stage 9). In this case, as shown in FIG. 2, the small stage 11 is configured to be movable relative to the large stage 9 in a diagonal direction (radially from the center of the large stage 9). In the following description, the center of the large stage 9 is referred to as “measurement-side origin”.

  As shown in FIG. 2, an on-axis light receiving sensor 13 is provided at the measurement side origin of the large stage 9, and an off-axis light receiving sensor 14 is provided on each small stage 11. Yes. The on-axis light receiving sensor 13 includes a vertical line sensor 13a extending in the vertical direction with respect to the installation surface (ground) of the inspection apparatus 1, and a horizontal line sensor 13b extending in the horizontal direction. On the other hand, the off-axis light-receiving sensor 14 has a vertical line sensor 14a extending in a diagonal direction (radially extending) from the measurement-side origin of the large stage 9 and a horizontal line extending in a direction perpendicular to the line extending in the diagonal direction. And line sensor 14b. In the inspection apparatus 1, the light receiving surfaces of all the sensors 13 and 14 are arranged so as to be located in substantially the same plane (hereinafter, this plane is referred to as “measurement plane”).

    The longitudinal line sensors 13a, 14a constituting the on-axis and off-axis light receiving sensors 13, 14 are used to detect an M (meridional) image of the chart formed on the chart plate 3, as will be described later. The horizontal line sensors 13b and 14b are used to detect an S (sagittal) image of the chart.

  The chart plate 3 is disposed at the position of the image plane of the lens 4 to be tested (that is, the position corresponding to the film plane or the imaging plane). The chart plate 3 is formed with a point image chart or a slit. In the following description, a case where the chart plate 3 is configured with a slit will be described. The chart plate 3 includes an on-axis inspection chart disposed so as to include the mechanical shaft 7 at the center of the chart plate (hereinafter referred to as “the origin of the chart plate”), and the mechanical plate 7 does not include the mechanical shaft 7. An off-axis inspection chart arranged at a position away from the shaft 7 (in a diagonal direction from the origin of the chart plate) is formed (not shown). The on-axis inspection and off-axis inspection charts correspond to the configurations of the on-axis and off-axis light receiving sensors 13 and 14, and the on-axis and off-axis inspection charts are for M images, respectively. The chart is composed of a chart and an S image chart, both of which are formed as slits. Light rays emitted from the light source 2 and transmitted through the chart (slit) of the chart plate 3 are imaged on the on-axis and off-axis light receiving sensors 13 and 14 by the test lens 4. At this time, the sensors 13a13b, 14a, and 14b constituting the on-axis and off-axis light receiving sensors 13 and 14 and the on-axis and off-axis inspection chart images of the chart plate 3 are configured to be orthogonal to each other. Yes. When the chart plate 3 is configured as a point image chart (pinhole), each of the on-axis light receiving sensor 13 and the off-axis light receiving sensor 14 can be configured by one area sensor.

  In the inspection apparatus 1 as described above, an image of the on-axis inspection chart (center slit) formed on the chart plate 3 (referred to as “on-axis image”) is formed on the on-axis light receiving sensor 13. In an ideal imaging state, an image of the off-axis inspection chart (referred to as an “off-axis image”) is formed on the corresponding off-axis light receiving sensor 14. However, when the test lens 4 is a lens with a large distortion, for example, even if the on-axis image can be captured by the on-axis light receiving sensor 13 on the axis, the off-axis image is received off-axis. The sensor 14 may come off. In such a case, the small stage drive unit 12 moves the small stage 11 relative to the large stage 9, thereby moving the off-axis light receiving sensor 14 in the radial direction and capturing an off-axis image.

  On the other hand, if the test lens 4 has transmission eccentricity, the chart image is deviated from the on-axis and off-axis light receiving sensors 13 and 14. Therefore, the large stage drive unit 10 operates the large stage 9 in the measurement plane to scan the on-axis image (center slit position) with the on-axis light receiving sensor 13 (in this case, the on-axis light receiving sensor 13 and the off-axis light receiving sensor 13). The light receiving sensor 14 is simultaneously aligned in the same amount and direction). Then, as described above, the off-axis light receiving sensor 14 (actually, the small stage 11) is actuated in the radial direction by the small stage driving unit 12 to scan the off-axis image and to align with the off-axis light beam. . In this way, by aligning the on-axis and off-axis light receiving sensors 13 and 14 in two stages, the objects that can be measured at high speed are expanded.

  In such an inspection apparatus 1, the off-axis light-receiving sensor 14 senses the imaging position of the off-axis light beam, and the deviation from the ideal image height and the actual angle of view can be known, so that asymmetry in all directions can be determined. Further, when the M image and S image line sensors (vertical line sensors 13a and 14a and horizontal line sensors 13b and 14b) are used as in this embodiment, the actual image height can be known from the M image sensor. In this embodiment, as shown in FIG. 2, by providing a small stage 11 that can be operated radially, the angle of view due to manufacturing errors, such as a lens having a large eccentricity such as a photographic lens or a lens having a large distortion, can be obtained. Measurement of a lens with a large change is also possible. In this embodiment, the vertical line sensor 14a and the horizontal line sensor 14b for detecting the M image and the S image of the off-axis light receiving sensor 14 are arranged on the small stage 11 so as to move integrally. It is also possible to arrange the sensor 14a and the horizontal line sensor 14b on independent plates so that they operate independently.

  The receiving unit 8 is provided with a measurement driving unit 15 that moves the measuring unit 6 along the mechanical axis 7 (moves in the left-right direction in FIG. 1). The large stage driving unit 10, small stage driving unit 12, measurement driving unit 15, on-axis light receiving sensor 13, off-axis light receiving sensor 14, and illumination side control unit 17 are electrically connected to the control device 16. The operations of the large stage drive unit 10, the small stage drive unit 12, and the measurement drive unit 15 are controlled, and the operations of the measurement unit 6, the large and small stages 9, 11 are controlled, and the illumination side The operations of the chart plate 3 and the test lens 4 are controlled via the control unit 17, and the detection signals from the on-axis and off-axis light receiving sensors 13, 14 are processed.

  FIG. 3 shows a control mechanism of the test lens 4. The control means 41 for controlling the operation of the test lens 4, the distance measurement means 42 and the photometry means 43, and the lenses constituting the test lens 4. The motor mechanism 45 moves the group in the optical axis direction, the lens position driving means 44 drives the motor mechanism 45, the diaphragm mechanism 47, and the exposure adjustment means 46 drives the diaphragm mechanism 47. The control means 41 controls the lens position driving means 44 based on the distance information from the distance measuring means 42 and operates the motor mechanism 45 to perform autofocus, and also performs exposure based on the illuminance information from the photometry means 43. The adjusting means 46 is controlled to adjust the opening of the throttle mechanism 47. In the present embodiment, the illumination side control unit 17 of the illumination unit 5 and the control unit 41 are electrically connected via an interface with the outside, and a control signal (lens position control information) transmitted from the control device 16 is connected. And the throttle opening control information), the operation of the motor mechanism 45 and the throttle mechanism 47 is controlled, and measurement is performed.

  In the measurement of the test lens 4 in the inspection apparatus 1, the ideal lens data of the test lens 4 is used in advance to ray trace from the image plane to the object plane to obtain the shooting distance and the actual object height. Keep it. The control device 16 controls the operation of the measurement drive unit 15 to move the measurement unit 6 along the mechanical axis 7 with respect to the distance between the chart plate 3 of the inspection device 1 and the on-axis and off-axis light receiving sensors 13 and 14. Thus, the calculated shooting distance is matched.

  Here, when the test lens 4 as described above is set on the illumination unit 5, if the test lens 4 has transmission eccentricity, a slit image is formed at a position shifted from the origin on the measurement side of the large stage 9. Is done. In such a case, the large stage 9 is operated in the vertical and horizontal directions within the measurement plane to scan the center slit image, and the vertical line sensor 13a and the horizontal line sensor 13b (or area sensor) of the on-axis light receiving sensor 13 are scanned. ) Is processed by the control device 16 to detect the image position of the on-axis image of the chart plate 3. As an image position detection method, for example, the center of gravity of a point image or line image or the coordinates of the pixel with the highest output is detected as the image position. At this time, if the transmission eccentricity error of the lens to be tested 4 is large, the chart image may be completely deviated from the pair of line sensors 13a and 13b (on-axis light receiving sensor 13). Therefore, it is necessary to set in advance in the control device 16 the procedure for scanning by operating the large stage 9. For example, if the large stage 9 is configured to scan efficiently by moving a rectangular area spirally from the outside to the inside, the scanning time can be saved. After scanning, the control device 16 moves the large stage 9 so that the image of the on-axis inspection chart is positioned at the center (or the center of the area sensor) of the on-axis light receiving sensor 13 (each of the line sensors 13a and 13b). The position is stored as the origin, and the centering is finished (this origin coincides with the above-mentioned origin on the measurement side).

  The control device 16 also operates the small stage 11 in the diagonal direction of the large stage 9, and the off-axis image is converted from the detected value of the off-axis light receiving sensor 14 in the same manner as the on-axis light receiving sensor 13. The small stage 11 is operated so as to be positioned at the center of the external light receiving sensor 14. As shown in FIG. 2, the small stage 11 is not only configured to operate in the diagonal direction (45 ° oblique) of the rectangular large stage 9 but also configured to operate with two axes in the vertical direction and the horizontal direction. It is also possible to do.

  In the inspection of the lens 4 to be inspected by the inspection device 1, a control signal is transmitted from the control device 16 to the illumination side control unit 17, and the chart plate 3 is moved back and forth by a predetermined movement amount with respect to the optical axis (mechanical shaft 7). (For example, about ± 1.0 mm with respect to the position of the best image plane in increments of 0.1 mm), and the best image plane and the areas before and after the defocus are detected by the on-axis and off-axis light receiving sensors 13 and 14. By measuring and calculating changes in contrast and phase of the chart image of the chart plate 3 as a function of spatial frequency, OTF and MTF are calculated from the measured values. At this time, in this inspection apparatus 1, since the on-axis image and the off-axis image can be detected at the same time, the optical characteristics (OTM, MTF) of the lens 4 to be measured can be inspected in a short time.

  By the way, in order to ensure an almost accurate OTF value of the test lens 4 using the inspection apparatus 1 as described above, a sensor (on-axis or off-axis is used when taking a line image intensity distribution or a point image intensity distribution. It is desirable to adjust the accumulation time of the light receiving sensors 13 and 14) so that the output is not less than a predetermined value. For example, when a sensor with a 12-bit output is used, it is desirable that the output be 8 bits or more. However, as shown in FIG. 4, the intensity distribution obtained by defocusing is lower in the output of the suncer as it gets farther away on the optical axis than the intensity distribution obtained near the best image plane. For the accuracy of the OTF and MTF values, an optimal accumulation time may be determined for each intensity distribution that is defocused and captured so that an output of a predetermined intensity or more can be secured. However, the intensity distribution is captured and stored from this output. This process takes time and is not suitable for mass production inspection. In addition, there is a method for obtaining the accumulation time in advance using information on the brightness of the optical system of the lens 4 to be examined, for example, an F number. However, when the brightness of the optical system is considered as illuminance, the spread of the intensity distribution changes and naturally the illuminance changes depending on the aberration of each lens or the adjustment of assembly. Therefore, in terms of design values, even if the F number is the same, the spread of the intensity distribution differs depending on the focal length, and furthermore, the intensity distribution differs for each lens of the same type due to manufacturing errors, and the optimum accumulation time cannot be uniquely determined.

  From the above, the optimum accumulation time of the sensor cannot be determined unless it is judged from the result of taking the intensity distribution once in a certain accumulation time. Therefore, in this embodiment, in the region including the best image plane, the intensity distribution of each defocus point is captured in a short accumulation time, and the accumulation time at the time of measurement is calculated from the output of the defocus point having a high output. It is configured.

  Hereinafter, a method for calculating the accumulation time for measurement will be described with reference to FIG. Assuming that the output of a pixel having an intensity distribution acquired at the accumulation time ts is Ws, the accumulation time tu for securing an output Wt of a predetermined intensity or higher is obtained by the following equation (1). Since this process determines the accumulation time of the on-axis and off-axis light receiving sensors 13, 14, it is necessary to defocus all the areas for measuring the optical performance of the lens 4 to be measured. However, it may be carried out within a limited range including the best image plane (for example, when measuring by moving ± 1.0 mm as described above, the range may be ± 0.5 mm). In addition, the intensity distribution measurement for calculating the accumulation time uses the detection result of the on-axis light receiving sensor 13.

  Next, when the aperture is narrowed, the accumulation time tu ′ when the aperture is narrowed by n stages is obtained by the following equation (2).

  In this case, the accumulation time is not actually obtained by performing a full scan, but the equation (1) is calculated from the optimum accumulation time tu for calculating the OTF and MTF of the best image plane at the time of opening obtained by the above equation (1). It is desirable to set tu ′ using 2). Further, in order to shorten the measurement time, it is desirable to measure with the accumulation time tu 'when narrowed down being the same as the accumulation time tu when open. Although the OTF and MTF values at low spatial frequencies increase due to the influence of dark current and disturbance, it is generally rare to make a pass / fail judgment based on the optical characteristics when the aperture is stopped, and the best image plane position when the aperture is reduced is dark current or disturbance This is because the influence from is not great.

  6 and 7 show a method for measuring the optical characteristics (OTF, MTF) of the lens 4 to be examined and the position of the best image plane when the aperture is opened and reduced using such an inspection apparatus 1. I will explain. First, in order to determine the accumulation times of the on-axis and off-axis light receiving sensors 13 and 14, the on-axis light receiving sensor is scanned by scanning the intensity distribution of each defocus point in a short accumulation time in an area including the best image plane. 13 (step S100). Then, from the measurement result of the defocus point having a high output, the accumulation time is calculated using the above-described equations (1) and (2) (step S110). Next, a control signal is transmitted from the control device 16 to the illumination side control unit 17, the aperture of the lens 4 to be tested is opened (step S120), and the chart plate 3 is moved to the optical axis (machine) via the illumination side control unit 17. The axis 7) is defocused back and forth by a predetermined amount of movement, and the intensity distribution of the best image plane and the chart image of the area before and after the accumulation time tu is acquired (step S130). Further, a control signal is transmitted from the control device 16 to the illumination side control unit 17, and the aperture of the lens 4 to be tested is reduced to, for example, about F number 5.6 or F number 8 (step S140). Then, the chart plate 3 is defocused with respect to the mechanical axis 7 by a predetermined amount of movement, and the intensity distribution of the chart image in the best image plane and the areas before and after it is obtained by the accumulation time tu ′ (step). S150). In the case of a lens that controls the aperture with a mechanical mechanism, it is only necessary to provide a lens equivalent to the mechanical mechanism of the camera on the apparatus side.

  As described above, the intensity distributions of two types of chart images, when the aperture of the lens 4 is opened and when the aperture is narrowed down, are acquired, and these intensity distributions are Fourier-transformed to obtain a specific low spatial frequency, for example, 10 OTF and MTF of [lp / mm] are calculated (step S160). In this case, in steps S130 and S150 described above, it is preferable to defocus at the same pitch and capture the intensity distribution of the chart image. Note that the difference in the position of the best image plane at the time of release and when the aperture is reduced is obtained from the MTF value. That is, the best image plane position is calculated from the peak value of the MTF value of 10 [lp / mm]. The MTF peak value may be obtained by interpolating several defocus points in the vicinity from the highest defocus point with a spline. Or you may obtain | require by fitting by the least squares method. As shown in FIG. 7, if the position on the optical axis of the best image plane at the time of opening is d0, and the position on the optical axis of the best image plane when the aperture is reduced is d ', the fluctuation of the best image plane is d0−. d ', and the controller 16 communicates this value with the lens 4 to be tested and writes it into the lens memory. The design value of the driving amount for moving the focus group for a plurality of shooting distances in the optical axis direction is written in the memory, and d0-d 'is added thereto, thereby achieving accurate focusing.

  As described above, according to the inspection apparatus 1 shown in the present embodiment, not only the optical characteristics (OTF and MTF values) when the aperture of the lens 4 to be tested is opened, but also the optical when the aperture is reduced. Characteristics can be detected. Furthermore, using these optical characteristics (particularly the MTF value), it is possible to accurately measure the difference in position on the optical axis of the best image plane when the aperture is opened and when the aperture is stopped.

  Further, according to the inspection apparatus 1, since the on-axis image and the off-axis image of the chart plate 3 can be detected at the same time, the optical characteristics (OTF, MTF) of a plurality of angles of view can be simultaneously measured with high accuracy in a short measurement time. And can be used for mass production inspection. Further, it is possible to evaluate the optical characteristics of a photographic lens having a relatively large transmission eccentricity by the optical performance of the image height defined with the mechanical axis 7 as a reference. Furthermore, by making the off-axis light receiving sensor 14 operable independently of the on-axis light receiving sensor 13, the inspection apparatus 1 can be highly versatile.

  Furthermore, in the conventional magnifying projection type inspection apparatuses, disturbances such as vibrations on the chart plate 3 and the lens 4 to be examined are also enlarged, and thus there is a drawback that they are vulnerable to disturbances. 1, the shift mechanism of the device 1 between the chart plate 3 and the lens 4 to be examined can be omitted, so that it is possible to adopt a device structure that is resistant to disturbances.

  In the above embodiment, the inspection apparatus 1 provided with the on-axis light receiving sensor 13 and the off-axis light receiving sensor 14 and configured to be able to simultaneously measure the on-axis image and the off-axis image of the chart plate 3 is used. Although the case has been described, the present invention is not limited to this configuration. For example, even if it is configured to detect only the on-axis image, the same effect can be obtained.

It is explanatory drawing which shows the structure of the inspection apparatus which concerns on this invention. It is explanatory drawing which shows arrangement | positioning and operation | movement of a sensor. It is a block diagram which shows the control mechanism of a to-be-tested lens. It is explanatory drawing for demonstrating the intensity distribution by a sensor, Comprising: (a) shows distribution near the best image plane, (b) shows distribution in the image plane distant from the best image plane. It is explanatory drawing for demonstrating the accumulation time of a sensor. It is a flowchart which shows the process sequence in the said inspection apparatus. It is explanatory drawing which shows the position of the best image surface when an aperture is open | released and when it restrict | squeezes.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inspection apparatus (inspection system) 2 Light source 3 Chart board 4 Test lens 13 On-axis light receiving sensor (imaging element) 14 Off-axis light receiving sensor (imaging element)
16 Control device

Claims (4)

A chart board on which a chart is formed;
An image sensor that detects a light beam emitted from a light source and passed through the chart as an image formed by a test lens;
A control device that controls the operation of the aperture of the test lens and calculates the optical characteristics of the test lens from the intensity distribution of the image detected by the imaging device;
The control device is
A first step of controlling the aperture of the lens to be opened to obtain an intensity distribution of the image by the lens;
A second step of obtaining an intensity distribution of the image by the test lens by controlling the aperture of the test lens to be in a narrowed state;
A third step of determining an MTF value from each of the intensity distributions when the aperture is opened and when the aperture is throttled; and
An inspection system comprising a fourth step of obtaining a difference in position of the best image plane when the aperture is released from the MTF value and when the aperture is reduced. The control device is
In the first and second steps, before acquiring the intensity distribution of the image by the lens to be examined, the intensity distribution of the image is measured in a state where the aperture is opened, The inspection system according to claim 1, further comprising a step of calculating an accumulation time when the aperture in the image sensor for obtaining the above intensity is opened.   The inspection system according to claim 3, wherein in the step of calculating the accumulation time, the accumulation time when the aperture is narrowed is calculated from the accumulation time when the aperture is opened.   2. The on-axis light receiving sensor for detecting an on-axis image of the chart plate by the chart and an off-axis light receiving sensor for detecting an off-axis image of the chart plate by the chart. -Inspection system given in any 1 paragraph.

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