JP2011075516A - Inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection apparatus capable of inspecting the optical performance of a lens to be inspected although the inspection apparatus is of a small type. <P>SOLUTION: The inspection apparatus 20 includes a projection optical system 21 for projecting an image of a light source (opening 3a of a light shielding plate 3) which is a point light source or a line light source on a focal plane of a lens 30 to be inspected, a rotating mirror 7 which reflects the light from an image of a light source penetrating through the lens 30 to be inspected and forming an image again at substantially the same position as the image of the light source on the focal plane by the lens 30 to be inspected, and a relay optical system 22 for relaying the image of the light source whose image is formed again by the lens 30 to be inspected on an image sensor 9. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inspection apparatus.

  Interchangeable lenses for single-lens reflex cameras are becoming popular, and higher performance is required compared to the silver salt film era. Many users view image data (digital photographs) at the same size on a personal computer screen, so that the performance and sweetness of the photographic lens has become clearer than before. On the other hand, autofocus photographic lenses equipped with DC motors and ultrasonic motors have become the mainstream, and angular velocities are monitored for camera shake correction, and some lenses or lens groups of the optical system are perpendicular to the optical axis. An anti-vibration lens that detects the position in the surface and brakes the generated angular velocity to cancel is increasing. Conventionally, this function, which has been frequently requested for lenses with long focal lengths, is increasingly demanded for standard lenses and wide-angle lenses. Furthermore, in the amateur layer, lenses with a zoom ratio of more than 10 times covering from wide to tele are gaining popularity, and the difficulty of optical design and mechanism design is increasing.

  In order to mount an actuator such as a motor unit or an anti-vibration lens unit, the optical design is required to reduce the size and weight of the focus group, reduce the amount of movement, and reduce the size and weight of the anti-vibration lens group. For this reason, the mechanism design must maintain rigidity with a more complicated structure, making the use of resin parts more severe. Despite various restrictions, it is possible to achieve reasonable design performance by increasing the number of aspheric surfaces, expanding the degree of freedom of shape, and using a lot of anomalous dispersion glass, and an effective optical adjustment routine and adjustment mechanism with good operability The detailed optical performance evaluation means enables mass production of high quality lenses. Thus, in order to achieve stable optical performance in mass production, a mass production inspection apparatus capable of measuring the optical performance of the lens to be examined in a short time with high accuracy is essential. This type of measuring device is required not only for final optical performance determination but also for alignment of the lens group during assembly adjustment.

  In this way, mass production performance of commonly used focal-range photographic lenses has improved considerably compared to the silver salt era. However, for photographic lenses with a long focal length, the evaluation device becomes large, so the conventional resolution chart is used. The current situation is to judge, but since it is an artificial judgment, there were many variations in the results of the physical condition and fatigue level of the reader, and the reader. As the number of pixels in digital cameras is rapidly increasing, it must be said that the visual resolving power judgment is low in product inspection capability. For this reason, such a variation is reduced by introducing a measuring instrument that finally measures optical performance by measuring MTF or the like (see, for example, Patent Document 1). The back projection type inspection apparatus disclosed in Patent Document 1 is frequently used in mass production.

JP 2007-093243 A

  However, when an enlarged projection with a lateral magnification β = −1 / 30 to −1/50 is performed with a photographing lens (for example, 600 mm) in a long focal region, the inspection distance becomes 18 m to 30 m, which is unrealistic. If the evaluation is performed at an inspection distance of about 15 m, the evaluation is close to the closest distance because the focal length is long. Since the super telephoto lens is required to have infinite optical performance for its intended purpose, evaluation at an inspection distance close to a close distance is not desirable. On the other hand, if a decolimator is used for back projection to realize infinite evaluation, a focal length at least five times that of the lens to be measured is required to make the residual aberration of the decollimator negligible. For example, if the focal length of the lens to be tested is 600 mm, the focal length of the decorremeter will be 3000 mm or more. The maximum diameter φ of such a super telephoto lens is 140 mm or more, and the diameter of the decorremeter lens must be larger than this. Furthermore, in order to measure on-axis and at least four off-axis simultaneously, five decorometers must be arranged. However, it is not practical to arrange five 3000 mm decorrimators. If it is to be realized, the decorremeter has a large diameter, and the five decorimators will interfere unless they are separated from the lens to be measured. Even if convergent light is emitted from the test lens as a finite system, the light flux is hardly reduced at about β = −1 / 30, and it is inevitable that the five decollimators are separated from the test lens. Therefore, a huge space is essential to simultaneously measure the on-axis and off-axis optical performance of a telephoto lens having a small angle of view and a large front lens diameter. In addition, alignment of the off-axis decorremeter is extremely difficult. If it is finite, it will affect the lateral magnification if it shifts in the optical axis direction, and adjusts the angle of the decorometer by reading the direction and amount deviated from the origin of the coordinates of the sensor placed on the focal plane of the decorometer. The accuracy of the measured image height changes depending on how far the sensor reference can be taken. Further, even with orthographic projection, the problem of enlarging the apparatus and the difficulty in aligning the off-axis collimator cannot be solved.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an inspection apparatus capable of inspecting the optical performance of a lens to be measured with high accuracy while being small in size.

  In order to solve the above problems, an inspection apparatus according to the present invention includes a projection optical system that projects an image of a light source that is a point light source or a line light source onto a focal plane of a test lens, and a light source that has passed through the test lens. A rotating mirror that reflects light from the image and re-images the image of the light source on the focal plane by the test lens, and an image of the light source re-imaged by the test lens. A relay optical system for relaying upward.

  Such an inspection apparatus is a unit in which the projection optical system and the relay optical system are integrated, and the unit is shifted in a plane orthogonal to the optical axis of the lens to be tested so that the image of the light source is focused on the lens to be tested. It is preferably configured to move in a plane.

  In such an inspection apparatus, the rotating mirror is centered on a rotating shaft extending from the optical axis of the lens to be tested on the rotating mirror so as to be orthogonal to a plane including the optical axis and the shift direction of the unit. It is preferable to be configured to reflect light from the image of the light source by being rotated and to form an image again at a position substantially the same as the image of the light source on the focal plane by the test lens.

  In such an inspection apparatus, the unit is configured to be movable in a direction orthogonal to the optical axis of the test lens, and the unit and the test lens are connected to the optical axis of the test lens. It is preferable to be configured to be rotatable relative to the center.

  At this time, it is preferable that the rotating mirror is configured to rotate relative to the test lens integrally with the unit.

  In such an inspection apparatus, each of the projection optical system and the relay optical system includes at least two groups of a collimating lens and a decorimating lens, and a test object is disposed between the collimating lens and the decorating lens. It is preferable to have an optical path splitting element that splits the optical path of the projection optical system and the relay optical system with respect to the lens.

  At this time, it is preferable that the decorating lens of the projection optical system and the collimating lens of the relay optical system are constituted by one decorating / collimating lens.

  Further, at this time, it is preferable that the image of the light source can be defocused by moving the decorimating / collimating lens along the optical axes of the imaging optical system and the relay optical system.

Further, such an inspection apparatus has the following formula (−βt) ≦ 2.0, where βt is the projection magnification of the projection optical system.
It is preferable to satisfy the following conditions.

Also, such an inspection apparatus has the following formula 1 ≦ βr <20, where βr is the lateral magnification of the relay optical system.
It is preferable to satisfy the following conditions.

  When the inspection apparatus according to the present invention is configured as described above, it is possible to provide an inspection apparatus that can inspect the optical performance of the lens to be measured with high accuracy while being small.

It is explanatory drawing which shows the structure of an inspection apparatus. It is description which shows operation | movement in the case of defocusing in order to measure the optical performance of the optical axis direction of a to-be-tested lens in the said inspection apparatus. It is explanatory drawing which shows operation | movement in the case of measuring the optical performance with respect to the off-axis light of a to-be-tested lens in the said inspection apparatus.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the configuration of the inspection apparatus 20 according to the present embodiment will be described with reference to FIGS. The inspection apparatus 20 includes a projection optical system 21 that irradiates the test lens 30 with light from a point light source or a line light source, a relay optical system 22 that condenses the light transmitted through the test lens 30 on the image sensor 9, have. Here, the projection optical system 21 is disposed between the light source 1 and the lens 30 to be tested, and is a light shielding device in which the condenser lens 2 and an opening 3a made of a pinhole or a slit are formed in order from the light source 1 side. A plate 3, a projection optical system collimating lens 4, an optical path splitting element 5 comprising a beam splitter or a half mirror, and a decorimating / collimating lens (projecting optical system decorating lens) 6 are included. The relay optical system 22 is disposed between the test lens 30 and the image sensor 9 and shares the projection optical system 21, the optical path splitting element 5, and the decorimating / collimating lens 6. , In order, a decorating / collimating lens (relay optical system collimating lens) 6, an optical path splitting element 5, and a relay optical system decorating lens 8. A rotating mirror 7 is disposed on the opposite side of the decorimating / collimating lens 6 with the test lens 30 interposed therebetween. The decorimating / collimating lens 6 functions as a decorating lens in the projection optical system 21 and functions as a collimating lens in the relay optical system 22.

  Here, the condenser lens 2 is disposed so as to collect the light from the light source 1 in the opening 3a of the light shielding plate 3, and the projection optical system so that the focal point thereof substantially coincides with the opening 3a. A collimating lens 4 is arranged. Further, the image pickup surface of the image pickup device 9 is arranged on the focal point of the relay optical system decorimating lens 8 so as to substantially coincide. In addition, the projection optical system 21 according to the present embodiment is arranged so that the light emitted from the light source 1 is reflected by the transmission / reflection surface 5a of the optical path splitting element 5 and guided to the lens 30 to be tested. The system 22 is arranged so that the light from the lens 30 to be tested is transmitted to the imaging element 9 through the transmission / reflection surface 5a. Further, when the opening 3a of the light-shielding plate 3 is a pinhole, an area sensor is arranged as the image sensor 9 to detect the image of this pinhole. When the opening 3a is a slit, the image of this slit is displayed. In order to detect, it is desirable to arrange a line sensor as the image sensor 9 (in the case of a line sensor, it is desirable to arrange the direction in which the line sensor extends so as to be substantially orthogonal to the slit-shaped image).

  The optical elements constituting the projection optical system 21 and the relay optical system 22 are arranged so that their optical axes coincide with each other within a predetermined accuracy. As shown in FIG. Then, it is called “mechanism axis A”. Here, in the inspection apparatus 20, the light source 1, the condenser lens 2, the light shielding plate 3, the projection optical system collimating lens 4, the optical path dividing element 5, the decorating / collimating lens 6, the relay optical system decorating lens 8, and the imaging element 9 are The unit 10 is configured to be movable (shiftable) in a direction orthogonal to the mechanism axis A. That is, as shown in FIG. 3, when the direction in which the mechanism axis A extends is the X axis, and the direction orthogonal to the X axis (for example, the direction in which the light source 1 is located with respect to the optical path dividing element 5) is the Y axis, The unit 10 is configured to be shiftable in the Y-axis direction. Further, the optical axis of the lens 30 to be examined is arranged in the same direction as the mechanism axis A (coincides with or extends substantially in parallel), and this optical axis is referred to as “reference axis B” in the following description. " Further, the rotation mirror 7 is configured to be rotatable about a rotation axis passing through the reference axis B and extending in the Z′-axis direction on the rotation mirror 7 when the direction orthogonal to the XY plane is Z ′. ing.

  In the inspection apparatus 20 having such a configuration, the light emitted from the light source 1 is condensed on the opening 3 a of the light shielding plate 3 by the condenser lens 2. That is, when the opening 3a of the light shielding plate 3 is a pinhole, the opening 3a functions as a point light source, and when it is a slit, it functions as a line light source. The light transmitted through the opening 3a is condensed by the projection optical system collimating lens 4 and converted into substantially parallel light, then reflected by the transmission / reflection surface 5a of the optical path dividing element 5, and further, the decorimating / collimating lens 6 And is formed as a primary image IM of the opening 3 a of the light shielding plate 3. The test lens 30 is arranged so that the image side focal point (focal plane) substantially coincides with the primary image IM (when the mechanism axis A and the reference axis B substantially coincide as shown in FIG. 1). Is incident on and reflected by the rotating mirror 7 (in this case, the reflecting surface of the rotating mirror 7 is arranged substantially perpendicular to the mechanism axis A). ing). Then, the light reflected by the rotating mirror 7 is condensed by the lens 30 to be tested, and after the image of the opening 3a is formed again at the position of the primary image IM, it is converted into substantially parallel light by the decorimating / collimating lens 6. Is done. Further, the substantially parallel light passes through the transmission / reflection surface 5 a of the optical path splitting element 5 and is condensed on the imaging surface of the imaging element 9 by the relay optical system decorating lens 8. As described above, the optical performance (OTF, MTP, and PTF) of the test lens 30 can be calculated from the point spread function (PSF) or the line spread function (LSF) acquired by the image sensor 9.

  As described above, the inspection apparatus 20 according to the present embodiment uses the autocollimation method, which is a method for simply observing a diffraction image from the old days. Since this method does not require a collimator, it leads to downsizing of the apparatus. Further, since the light passes through the lens 30 twice (double pass), the amount of aberration appears twice, which can be said to be an inspection method suitable for evaluation of a super telephoto lens with little aberration. Further, since an expensive collimator is not used, it is advantageous in terms of cost. Further, as shown in FIG. 1, in the case of the test lens 30 having a long focal length, a pinhole or slit image (primary image IM) is projected at a position conjugate with the focal plane and passed through the test lens 30. Further, by guiding the light reflected by the rotating mirror 7 and returning to the focal plane (position of the primary image IM) to the image sensor 9 by the relay optical system 22, the optical performance of the lens 30 to be measured can be measured. , Leading to high measurement sensitivity and space saving.

  By the way, in order to measure the optical performance of the test lens 30 in the optical axis direction using this inspection apparatus 20, as shown in FIG. 2, the decorimating / collimating lens 6 is moved in the optical axis direction (along the mechanism axis A). ) It is desirable to have a moving structure. As shown in FIG. 2, the image displacement in the optical axis direction due to defocusing can be canceled one-to-one by the defocusing displacement of the decorimating / collimating lens 6 immediately after that.

  Further, in order to measure the optical performance on the axis of the lens 30 to be tested using the inspection apparatus 20, the measurement is performed with the mechanism axis A and the reference axis B substantially coincided with each other. On the other hand, the off-axis optical performance of the lens 30 to be measured is measured by shifting the above-described unit 10 in a plane perpendicular to the mechanism axis A (in the XY plane). Here, assuming that the focal length of the lens 30 to be examined is f, the angle of view is θ, and the image height is y, the relationship y = ftanθ holds. That is, the mechanism axis A moves in parallel with the reference axis B by shifting the unit 10. At this time, if the distance from the reference axis B of the primary image IM moved in the focal plane of the lens 30 to be tested is an image height y, the rotating mirror 7 is moved from the mechanism axis A by θ / 2 about the rotation axis Z ′. By rotating in the plane including the measurement image height (in the XY plane), as shown in FIG. 3, the light reflected by the rotating mirror 7 is collected by the test lens 30, and the above-described image height y is obtained. It is condensed again at the position. Furthermore, since it is condensed on the image sensor 9 by the relay optical system 22, it is possible to acquire PSF or LSF and measure the optical performance of the off-axis image height. For example, when measuring the optical performance when the focal length of the test lens 30 is 300 mm and the image height is 15.1 mm, the half angle of view of the test lens 30 is θ = 2.9 °. By tilting by 2 × θ = 1.45 °, the entire unit 10 in FIG. 3 is shifted by y = 15.1 mm. Thus, by configuring the entire unit 10 so as to be shiftable in a plane (XY plane) perpendicular to the mechanism axis A, it is possible to measure the on-axis and off-axis optical performance of the lens 30 to be tested.

  Note that the lens 30 and the set of the unit 10 and the rotating mirror 7 are relatively rotated with the reference axis B as the center axis (for example, the lens 30 to be tested is rotated around the reference axis B, or The unit 10 and the rotating mirror 7 are integrally rotated about the reference axis B with respect to the test lens 30), whereby the optical power of the test lens 30 by off-axis light from an arbitrary image height around the reference axis B is obtained. Performance can be measured. Here, the position on the focal plane where the image of the opening 3a of the light shielding plate 3 is incident on the lens 30 to be examined from the off-axis direction is preferably at least four directions with the reference axis B as the center. Furthermore, it is desirable that these four directions are arranged symmetrically with respect to the reference axis B in this focal plane.

  In such an inspection apparatus 20, the projection magnification of the projection optical system 21 is defined such that the focal length of the projection optical system collimating lens 4 is defined as Ftd and the focal length of the projection optical system decorating lens (decorimating / collimating lens 6) is defined as Ftc. It is desirable that βt be near the same magnification or a reduction ratio, that is, satisfy the following expression (1).

(−βt) = Ftd / Ftc ≦ 2.0 (1)

  By configuring the projection magnification βt of the projection optical system 21 so as to satisfy the conditional expression (1), the manufacturing accuracy of the opening (pinhole or slit) 3a of the light shielding plate 3 is reduced. It is difficult to obtain the roundness of a small-diameter hole or the continuity of an edge with a small slit. However, a high spatial frequency cannot be obtained with a large pinhole and slit width. In order to obtain a spatial frequency of 100 lp / mm, a pinhole or slit image corresponding to 0.005 mm must be projected onto the focal plane of the lens 30 to be examined. If this is projected with βt <−2.0, it is very difficult to manufacture the light shielding plate 3 (chart or mechanical slit). In addition, it is more preferable when the upper limit of conditional expression (1) is 1.0, and it is more preferable when the upper limit is 0.5.

  Further, the lateral magnification βr of the relay optical system 22 defined as Frc as the focal length of the relay optical system decorimating lens 8 and Frd as the focal length of the relay optical system collimating lens (decorimating / collimating lens 6) is equal to or equal to It is desirable to satisfy the magnification ratio, that is, the following expression (2).

1 ≦ βr = Frc / Frd <20 (2)

By configuring the lateral magnification βr of the relay optical system 22 to satisfy the conditional expression (2), the desired high frequency is enlarged and relayed by the optical system, so the spatial frequency on the image sensor 9 is set low. A sensor having a wide dynamic range can be selected as the image sensor 9. It should be noted that the illuminance at the image sensor 9 is inversely proportional to the square of the lateral magnification βr. Therefore, if the upper limit of condition (2), illuminance on the image pickup device 9, image plane illuminance is lowered so becomes 1/20 ^second when .beta.r = -1, the imaging accordingly The light storage time in the element 9 becomes too long and becomes impractical.

  Further, it is desirable that the transmission / reflection ratio of the transmission / reflection surface 5a in the optical path splitting element (beam splitter or half mirror) 5 of the projection optical system 21 is approximately half. However, since the luminance of the light source 1 and the illuminance on the image sensor 9 contribute the most, the optimum ratio varies depending on the setting of the projection magnification of the light source 1 and the relay magnification to the image sensor 9.

  When the test lens 30 is a super telephoto system, its half angle of view is about 6 degrees or less, and the setting angle of the rotating mirror 7 arranged in front of the test lens 30 is required to be at least half or less as described above. It becomes. Therefore, since the half angle of view is small, it is difficult to simultaneously arrange the on-axis mirror and the off-axis mirror as the rotating mirror 7. It is therefore desirable to perform on-axis and off-axis measurements individually rather than simultaneously. In addition, it has a means to read the position in the optical axis direction when defocusing, scans on-axis and several off-axis locations separately, and interpolates the best position on the axis with a spline function etc. It is desirable to determine the optical performance (such as MTF) of the off-axis image height based on the position in the optical axis direction.

  In the above embodiment, the light emitted from the light source 1 is reflected by the optical path splitting element 5 and guided to the test lens 30, and the light transmitted through the test lens 30 is transmitted through the optical path splitting element 5 to obtain an image sensor. The projection optical system is described so that the light emitted from the light source 1 is transmitted through the optical path dividing element 5 and the light transmitted through the test lens 30 is reflected by the optical path dividing element 5. 21 and the relay optical system 22 may be disposed.

DESCRIPTION OF SYMBOLS 1 Light source 3 Light-shielding plate 3a Opening part (point light source or line light source)
DESCRIPTION OF SYMBOLS 4 Projection optical system collimating lens 5 Optical path division | segmentation element 6 Decolimate collimating lens 7 Rotating mirror 8 Relay optical system decorimating lens 9 Image sensor 10 Unit 20 Inspection apparatus 21 Projection optical system 22 Relay optical system 30 Test lens

Claims (10)

A projection optical system that projects an image of a light source that is a point light source or a line light source onto a focal plane of a lens to be examined;
A rotating mirror that reflects light from the image of the light source that has passed through the test lens and re-forms the light at the same position as the image of the light source on the focal plane by the test lens;
An inspection apparatus comprising: a relay optical system that relays an image of the light source formed again by the lens to be examined onto an image sensor.   The projection optical system and the relay optical system are integrated into a unit, and the unit is shifted in a plane orthogonal to the optical axis of the lens to be tested, whereby the image of the light source is converted to the focal plane of the lens to be tested. The inspection apparatus according to claim 1, wherein the inspection apparatus is configured to be moved within the apparatus.   The rotating mirror is rotated about an axis of rotation extending from the optical axis of the lens to be tested on the rotating mirror so as to be orthogonal to a plane including the optical axis and the shift direction of the unit. The inspection apparatus according to claim 2, configured to reflect light from an image of a light source and form the image again at a position substantially the same as the image of the light source on the focal plane by the lens to be examined.   The unit is configured to be movable in a direction perpendicular to the optical axis of the test lens, and is capable of relative rotation between the unit and the test lens around the optical axis of the test lens. The inspection apparatus according to claim 2 or 3, wherein the inspection apparatus is configured.   The inspection apparatus according to claim 4, wherein the rotating mirror is configured to rotate relative to the lens to be measured integrally with the unit.   Each of the projection optical system and the relay optical system includes at least two groups of a collimating lens and a decorimating lens, and the projection with respect to the test lens is between the collimating lens and the decorimating lens. The inspection apparatus according to claim 1, further comprising an optical path splitting element that splits an optical path of the optical system and the relay optical system.   The inspection apparatus according to claim 6, wherein the decorating lens of the projection optical system and the collimating lens of the relay optical system are configured by a single decorating / collimating lens.   The inspection apparatus according to claim 7, wherein the image of the light source is configured to be defocused by moving the decorimating / collimating lens along the optical axes of the imaging optical system and the relay optical system. When the projection magnification of the projection optical system is βt, the following formula (−βt) ≦ 2.0
The inspection apparatus according to any one of claims 1 to 8, which satisfies the following condition. When the lateral magnification of the relay optical system is βr, the following formula 1 ≦ βr <20
The inspection apparatus according to any one of claims 1 to 9, which satisfies the following condition.

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