JP2012058085A - Lens inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens inspection apparatus capable of measuring not only image forming performance for an on-axis light beam of a lens to be inspected but also image forming performance for an off-axis light beam as accurate numerical data in a wide angle range.SOLUTION: A lens inspection apparatus 10 includes: a center collimator 21 for applying cross chart beams 43 to 45 to a lens 12 to be inspected rotatably held by a lens holding part 15; first and second side collimators 22, 23; and an imaging part 28 for imaging cross charts passed through the lens 12 to be inspected. The first and second side collimators 22, 23 for inspecting image forming performance for the off-axis light beam of the lens 12 to be inspected can be freely moved by first and second rotary stages 24, 25 and first and second guides 26, 27, and can make the cross chart beams 43 to 45 incident on an incident surface of the lens 12 to be inspected from a position 105° to the optical axis 13 of the lens 12 to be inspected.

Description

  The present invention relates to a lens inspection apparatus for measuring and inspecting the optical performance of a lens.

  In order to inspect the performance of a lens that is built in or used in a camera, a lens inspection device that can measure digitized data based on, for example, MTF (Modulation Transfer Function) is used. As such a lens inspection device, a test chart facing a certain distance from the test lens is imaged in the air through the test lens, and the aerial image of the test chart is magnified by the magnifying optical system, and then the CCD or For example, Japanese Patent Application Laid-Open No. 2004-151820 discloses a method of capturing an image with a CMOS type image sensor and analyzing the obtained image data to collect numerical data.

  This lens inspection apparatus is configured so that both the test chart and the image sensor can be shifted within a plane orthogonal to the optical axis of the lens to be tested. This makes it possible to measure the lens performance outside the optical axis of the lens to be examined. For example, a wide-angle lens can easily evaluate the field curvature.

  In addition, the lens inspection apparatus described in Patent Document 2 below is for evaluating the imaging performance of a fisheye lens in particular, and a test chart is arranged at a position that becomes an image plane behind the lens in a normal use state, and the image is displayed. The image is projected onto a semi-transparent screen arranged in front of the fisheye lens, so that the image formation state of the test chart can be observed from the back side of the semi-transparent screen.

JP 2004-163207 A JP 2006-125980 A

  The apparatus described in Patent Document 1 enables accurate measurement because the test chart image is directly formed only by the lens to be examined, but the test chart and the image sensor are in a plane perpendicular to the optical axis. Therefore, it is difficult to cause the light beam from the test chart to enter the lens to be examined from the off-axis direction inclined at about 45 ° or more from the optical axis. Even if it can be made incident, the test lens looks at the pattern of the test chart from an oblique direction, and the test pattern is formed as a reduced image in that direction, which affects the measurement accuracy. Given this, it is not possible to sufficiently inspect the imaging performance with respect to the off-axis light beam. Moreover, although the apparatus of patent document 2 can be basically used for inspection of wide-angle lenses other than fish-eye lenses, it is premised on evaluation by visual observation, and quantitative numerical data cannot be measured with high accuracy.

  The present invention has been made in consideration of the above-mentioned background. The purpose of the present invention is to provide accurate numerical data in a wide angle range for imaging performance for off-axis light flux as well as imaging performance for the on-axis light flux of the test lens. The object is to provide a lens inspection apparatus capable of measuring.

  In achieving the above object, the lens inspection apparatus of the present invention is supported on a base member, and is supported on the base member, a lens holding portion that holds the lens to be tested so as to be rotatable around the optical axis, A center collimator that incorporates a test chart and a collimating lens and makes the parallel light from the test chart enter the lens under test from the optical axis thereof, and moves away from the optical axis as it approaches the lens holding part side from the center collimator side. As described above, a linear first guide provided on the base member, and linearly movable by the first guide and swinging about an axis perpendicular to the base member at an arbitrary position on the first guide A test chart and a collimating lens are built in and supported by the lens holder. A first side collimator for allowing parallel light from a test chart to enter; and a first side collimator that is parallel to the optical axis of the lens to be tested and movably supported in two directions in a plane perpendicular to the optical axis; And an imaging unit that captures an image of the test chart from the center collimator or the first side collimator formed in the air.

  The first guide extends from the vicinity of the center collimator beyond the position where the lens to be tested is held in the optical axis direction, and the optical axis of the first side collimator is 120 from the optical axis of the center collimator. It is desirable to set the swing range of the first side collimator so that it tilts to °°, so that it is possible to inspect the imaging performance for off-axis light beams from near the maximum field angle of the super wide angle or fisheye lens. It becomes. Furthermore, it is also effective for efficient measurement to provide the second side collimator so as to be symmetrical with the first side collimator with respect to the optical axis of the center collimator. In addition, it is desirable to use a plurality of types of test charts built in each of the above collimators, and select and use the optimum one according to the measurement conditions.

  According to the present invention, in addition to the center collimator that causes the parallel light from the test chart to enter the test lens held by the lens holding portion as the on-axis light beam, the side on which the parallel light from the test chart is incident as the off-axis light beam. In addition to providing a collimator, the side collimator can be freely moved close to the lens to be examined and can be swung to an arbitrary angle, so that the angle of incidence is incident on the optical axis of the lens to be examined having a large angle of view. As for off-axis light flux, numerical data can be accurately measured under various inspection conditions.

It is a top view which shows the structure of the lens inspection apparatus by this invention. FIG. 2 is a central sectional view of FIG. 1. FIG. 2 is a schematic cross-sectional view showing the first side collimator of FIG. 1 in a central cross section. It is a figure which shows a chart board. It is a horizontal sectional view showing the angle of the chart light incident on the test lens set in the lens holding part. It is a block diagram which shows an electric structure. It is explanatory drawing of the shift | offset | difference of the aerial image of a to-be-tested lens, and the optical axis center of a microscope part. It is a figure which shows the measurement location on the entrance plane of a to-be-tested lens. It is a figure when the 1st, 2nd side collimator is moved from FIG. FIG. 10 is a diagram when the first and second side collimators are further moved from FIG. 9.

  The lens inspection apparatus 10 according to the present invention is devised so as to be able to inspect lens performance including a fisheye lens, and is fixed to a pedestal 41 provided on a base member 40 as shown in FIGS. A lens holding unit 15 in which a lens 12 to be tested for performance measurement is rotatably held around the optical axis 13, a cross chart (test chart) 16 to 19 (see FIG. 4), and a collimating lens 36 are incorporated. And a center collimator 21 for inspecting the lens 12 held by the lens holder 15 with parallel light with a cross chart from the optical axis 13 to inspect the performance of the lens 12 on the axial beam. . The center collimator 21 is fixed to the base member 40 by a fixed frame 42.

  The lens inspection apparatus 10 includes cross charts 16 to 19 and a collimator lens 36, and makes parallel light with a cross chart applied from the outside of the optical axis 13 to the lens 12 held by the lens holding unit 15. A first side collimator 22 and a second side collimator 23 for inspecting the performance of the lens 12 to be tested with respect to an off-axis light beam are provided. The first side collimator 22 and the second side collimator 23 are arranged at positions that are line-symmetric with respect to the outgoing optical axis 43 of the center collimator 21, and are attached to the first and second rotary stages 24 and 25. The lens holding unit 15 is rotated around the optical axis 13 in 45 ° increments by a lens holding unit motor 115 (see FIG. 6).

  The first and second rotary stages 24 and 25 are fixed to first and second slide stages 46 and 47 provided on the first and second guides 26 and 27, respectively, and are rotatable about an axis perpendicular to the base member 40. And rotated by first and second rotary stage motors 111 and 112 (see FIG. 6). The first and second guides 26 and 27 are linearly arranged on the base member 40 and include first and second slide stages 46 and 47 that are movably supported by a feed screw and a guide rail. The two slide stages 46 and 47 are driven by first and second slide stage motors 113 and 114 provided on the first and second guides 26 and 27, respectively.

  The first and second guides 26 and 27 are arranged in a U shape so as to be separated from the optical axis 13 as they approach the lens holding unit 15 side from the center collimator 21 side, and are covered in the optical axis direction from the vicinity of the center collimator 21. The first and second side collimators 22 and 23 are extended beyond the position where the analyzer lens 12 is held, and the first and second side collimators 22 and 23 are inclined in the opposite directions from the optical axis of the center collimator 21 to 120 °. The swing range of the second side collimators 22 and 23 is set.

  The center collimator 21 and the first and second side collimators 22 and 23 include a chart plate 30 having cross charts 16 to 19 and a light source unit 32 that projects light onto the chart plate 30. The light source unit 32 includes an LED 33, a heat sink 34, and a condenser lens 35, and irradiates the chart plate 30. Any one of the cross charts 16 to 19 is set on the optical path of the chart plate 30, and the chart light to which any one of the cross charts 16 to 19 is applied from the collimating lens 36 focused on the position of the chart plate 30. Parallel light is emitted toward the lens 12 to be examined.

  The lens inspection device 10 includes an imaging unit 28 that images the chart light that has passed through the lens 12 to be examined. The imaging unit 28 enlarges and observes the aerial image of the cross charts 16 to 19 formed by the test lens 12 and forms an image of the cross charts 16 to 19 observed by the enlargement optical system 50. A lens 51 and a camera unit 52 that captures an image formed by the imaging lens 51 are provided, and are placed on a three-dimensional stage 55 and fixed to the base member 40. The three-dimensional stage 55 includes a Y stage 56 that moves the imaging unit 28 in the vertical direction (vertical direction in FIG. 2), an X stage 57 that moves the Y stage 56 horizontally (vertical direction in FIG. 1), and an X stage 57. Is moved in parallel with the optical axis 13 (left and right direction in FIGS. 1 and 2).

  As shown in FIG. 4, the cross charts 16 to 19 of the chart plate 30 are symbols for MTF measurement, and the thickness of the lines increases in the order of 16, 17, 18, and 19. In the first and second side collimators 22 and 23, one of the cross charts 16 to 19 is selected depending on the incident position (incident angle) (see FIG. 5) of the light incident from the collimating lens 36 onto the incident surface 60 of the lens 12 to be examined. Is selected. The center collimator 21 uses a cross chart 16. Alternatively, a cross chart having a crosshair pattern slightly thinner than the cross chart 16 may be used. The chart plate 30 used for the center collimator 21 may use a pattern different from the cross charts 16 to 19 used for the first and second side collimators 22 and 23, and an appropriate one is used depending on the lens to be measured. You can do that.

  As shown in FIG. 5, the first and second side collimators 22 and 23 are arranged in the horizontal direction in which the outgoing optical axes 44 and 45 of the emitted chart light pass through the optical axis 13 on the incident surface 60 of the test lens 12. The light is incident obliquely horizontally on the optical axis 13 from the left-right direction of the lens 12 to be measured. The first and second side collimators 22 and 23 alternately make the chart light incident on the incident surface 60 of the test lens 12 rotated every 45 ° by the lens holding unit 15, and sequentially measure the MTF. Accordingly, it is possible to perform measurement in the range of 360 ° with respect to the lens 12 to be measured only by rotating the lens holding portion 15 by 180 °. Since the measurement can be performed twice with a single lens set, the measurement accuracy is improved by reducing the rotational positioning number of the lens 12 to be measured, which has a large influence on the measurement accuracy.

  As shown in FIG. 6, the control device 100 includes a CPU 102, a system memory 103, and a motor driver 105. The CPU 102 drives and controls the eight motors 111 to 118 via the eight drivers 105. The first and second side collimators 22 and 23 irradiate the periphery of the test lens 12 with the chart light, but the center position of the aerial image 64 of the cross charts 16 to 19 transmitted through the test lens 12 is the magnifying optical system. When the optical axis 53 is deviated from the 50 optical axis 53, the aerial image 64 does not appear in the imaging range 62 of the magnifying optical system 50 as shown in FIG. Therefore, the magnification of the magnifying optical system 50 is lowered to widen the shooting range, for example, to the range indicated by 63, and the cross pattern of the aerial image 64 is placed within the shooting range.

  The camera unit 52 finds the center position of the cross pattern from the luminance in the X-axis direction and the Y-axis direction, and obtains a deviation amount 65 from the optical axis 53 of the magnifying optical system 50. Information on the obtained shift amount 65 is transmitted to the CPU 102. Based on this information, the CPU 102 drives the first and second rotary stage motors 111 and 112 and the first and second slide stage motors 113 and 114 via the driver 105, and the first and second side collimators 22. , 23 is adjusted to adjust the incident position of the outgoing optical axes 44 and 45 of the chart light to the lens 12 to be examined, so that the center of the aerial image 64 of the chart light is the center of the photographing range 62 of the magnifying optical system 50 (light Axis 53). Thereafter, the magnification of the magnifying optical system 50 is restored, and the photographing range is restored.

  The image magnified by the magnifying optical system 50 is imaged by the imaging lens 51 and captured by the camera unit 52. The imaging unit 28 transmits focus information to the CPU 102 from the imaging result of the camera unit 52. The CPU 102 drives the X stage motor 116, the Y stage motor 117, and the Z stage motor 118 via the driver 105 to automatically adjust the focus of the cross charts 16 to 19 imaged on the camera unit 52 by the three-dimensional stage 55. To do. Focus adjustment is performed by movement of the Z stage 58 in the Z-axis direction. If the chart light incident on the incident surface 60 of the lens 12 to be tested is off-axis light, the X-axis and Y-axis directions depend on the position in the Z-axis direction. Since the position also changes, the X stage 57 and the Y stage 56 adjust the position in the X-axis and Y-axis directions.

  The CPU 102 moves the Z stage 58 in the Z-axis direction, and causes the imaging unit 28 to measure not only the image initially formed on the camera unit 52 but also the MTFs of the images at several points whose focus positions are changed. The imaging unit 28 obtains the MTF value at the best focus position from among them. Even when there is no best focus position among the measured several points, the best focus position and the MTF value at that time can be interpolated from the obtained data.

  Next, the effect of the present invention will be described through MTF measurement of the lens 12 to be examined by the lens inspection device 10. As shown in FIG. 8, the test lens 12 performs MTF measurement at 25 locations on the incident surface 60. All the 25 positions are input to the system memory 103. The test lens 12 is set on the lens holding unit 15. In the center collimator 21, the cross chart 16 is set on the chart plate 30, the power is turned on, and the chart light (emitted optical axis 43) to which the pattern of the cross chart 16 is applied is centered on the incident surface 60 (see FIG. 8 at 71).

  The chart light (43) transmitted through the central portion of the test lens 12 is observed by the magnifying optical system 50, and the design is imaged on the camera unit 52 by the imaging lens 51. After focus adjustment of the imaged cross chart 16 is performed, the image information of the cross chart 16 is transmitted to the CPU 102, and the MTF at the central portion 71 of the lens 12 to be measured is measured. Here, since the light incident on the test lens 12 is parallel light, both the center collimator 21 and the first and second side collimators 22 and 23 form an image on a plane perpendicular to the optical axis 13. Therefore, the optical axis 53 of the magnifying optical system 50 is used in a state parallel to the optical axis 13 of the lens 12 to be measured, and thus stable measurement can always be performed.

  Next, for example, the cross chart 17 is set on the chart plate 30 of the first side collimator 22, and the chart light (emitted optical axis 44) to which the pattern of the cross chart 17 is given is tilted by 20 ° in the horizontal direction ( 5) toward the pupil position of the lens 12 to be examined. The CPU 102 drives the first and second rotary stages 24 and 25 and the first and second slide stages 46 and 47 based on the data stored in the system memory 103, and from the first and second side collimators 22 and 23. The outgoing optical axes 44 and 45 of the emitted chart light are correctly incident on predetermined positions of the test lens 12. The incident position on the incident surface 60 is a position indicated by 72 in FIG.

  An aerial image 64 (see FIG. 7) of the chart light (43) transmitted through the test lens 12 is observed by the magnifying optical system 50, and the cross chart 17 is imaged on the camera unit 52 by the imaging lens 51. When the center of the pattern of the cross chart 17 imaged by the camera unit 52 and the optical axis 53 of the magnifying optical system 50 do not coincide with each other, the first and second rotary stages 24 and 25 and the first rotary stage 24 and 25 are arranged so as to coincide with each other. The positions of the first and second side collimators 22 and 23 are adjusted by the second slide stages 46 and 47. In addition, the position of the imaging unit 28 is adjusted by the three-dimensional stage 55, and the focus of the captured cross chart 17 is adjusted. The image information of the cross chart 17 is sent to the CPU 102, and the MTF at the position 72 on the incident surface 60 of the lens 12 to be measured is measured.

  Next, the MTF at the position indicated by 73 in FIG. 8 is measured by the second side collimator 23. The outgoing optical axis 45 of the chart light of the second side collimator 23 is incident on the incident surface 60 with an inclination of 20 ° (see FIG. 5) from the opposite side of the first side collimator 22 with respect to the optical axis 13 of the test lens 12. Is done. The measurement is the same as the first side collimator 22, and the cross chart 17 is set and the MTF is measured. When the center position is deviated, alignment is performed and adjustment is also performed.

  When the measurement of the positions 72 and 73 shown in FIG. 8 is completed, the CPU 102 drives the lens holding unit motor 115 via the driver 105 and moves the lens holding unit 15 to 45 based on the data stored in the system memory 103. Rotate. 8 moves to positions 72 and 73, and the chart light of the cross chart 17 enters the positions 74 and 75 from the first and second side collimators 22 and 23. And each MTF is measured. The lens holding unit 15 repeats the rotation of 45 °, and the MTFs at positions 72 to 79 on the incident surface 60 are measured. As the lens holding portion 15 is rotated about the optical axis 13, the axial symmetry of the lens 12 to be tested can also be inspected. Axisymmetric testing is useful for plastic lenses.

  As shown in FIG. 9, the lens holding part 15 is rotated and returned to the initial position. In a wide-angle lens such as a fisheye lens, the magnification changes depending on the position (view angle) with respect to the center, so the cross chart used is changed from 17 to 18. The CPU 102 drives the first and second rotary stage motors 111 and 112 and the first and second slide stage motors 113 and 114 via the driver 105, and based on the data stored in the system memory 103, the first The second side collimators 22 and 23 are moved and rotated in the directions of arrows 48 and 49, respectively, so that the emission direction of the chart light is 80 and 81 inclined by 62.5 ° with respect to the optical axis 13 of the lens 12 to be examined. In the direction shown (see FIG. 5), the chart light is incident on the positions indicated by 82 and 83 in FIG. While the lens holding part 15 is rotated every 45 °, the MTF is measured by the cross chart 18 at positions 82 to 89 shown in FIG.

  As shown in FIG. 10, the lens holding portion 15 is rotated to the initial position, and the cross chart is changed to 19. The first and second side collimators 22 and 23 are further moved and rotated in the directions of arrows 48 and 49, and directions indicated by 90 and 91 inclined by 105 ° with respect to the optical axis 13 of the lens 12 to be tested (see FIG. 5), the chart light is caused to enter the positions indicated by 92 and 93 in FIG. The collimating lenses 36 of the first and second side collimators 22 and 23 are set close to the lens 12 to be examined by the first and second guides 26 and 27 opened in a letter C, and are set to the optical axis 13. In this case, off-axis light that is greatly tilted can be incident from a close position. Subsequently, the MTF is measured by the cross chart 19 at positions 92 to 99 shown in FIG. 8 while rotating the lens holding portion 15 every 45 °.

  In addition, what is necessary is just to determine the incident angle (measurement point) of the incident angle of the chart light in the said embodiment, and the entrance plane 60 of the to-be-tested lens 12 according to the property of the lens to be measured. In addition, although two side collimators are provided, the lens holding unit 15 may be rotated 360 ° by selecting one, and may be selected in consideration of the properties of the lens to be measured. Further, it may be used for CTF inspection or projection resolution inspection. The above embodiment is an inspection apparatus in which the optical axis of the test lens is horizontally arranged. However, the entire apparatus such as the center collimator and the imaging unit is vertically arranged, and the optical axis of the test lens is arranged vertically. May be.

DESCRIPTION OF SYMBOLS 10 Lens inspection apparatus 12 Test lens 13 Optical axis (Optical axis of test lens)
15 Lens holder 16-19 Cross chart (test chart)
DESCRIPTION OF SYMBOLS 21 Center collimator 22 1st side collimator 23 2nd side collimator 24 1st rotation stage 25 2nd rotation stage 26 1st guide 27 2nd guide 28 Imaging part 30 Chart board 32 Light source part 33 LED
34 heat sink 35 condensing lens 36 collimating lens 40 base member 41 pedestal 42 fixed frame 43 outgoing optical axes 44, 80, 90 (for the first side collimator) outgoing optical axes 45, 81, 91 Output optical axis (of second side collimator) 46 First slide stage 47 Second slide stage 48, 49 Arrow 50 Magnifying optical system 51 Imaging lens 52 Camera unit 53 Optical axis (for magnifying optical system) 55 Three-dimensional stage 56 Y stage 57 X stage 58 Z stage 60 Incident surface (of the lens to be examined) 62 Imaging range of magnifying optical system 50 64 Aerial images of cross charts 16 to 19 71 to 79, 82 to 89, 92 to 99 On incident surface 60 Position 100 Control device 102 CPU
103 System memory 105 Driver (for motor) 111 Motor for first rotation stage 112 Motor for second rotation stage 113 Motor for first slide stage 114 Motor for second slide stage 115 Motor for lens holding portion 116 Motor for X stage 117 Y stage motor 118 Z stage motor

Claims (4)

A lens holding unit supported on the base member and rotatably held around the optical axis;
A center collimator that is supported on the base member, incorporates a test chart and a collimating lens, and makes the test lens enter parallel light from the test chart from the optical axis thereof;
A linear first guide provided on the base member so as to move away from the optical axis as approaching the lens holding part side from the center collimator side;
The lens is supported by the first guide so as to be linearly movable and swingable about an axis perpendicular to the base member at an arbitrary position on the first guide, and includes a test chart and a collimating lens. A first side collimator for allowing parallel light from the test chart to enter the lens to be tested held by the holding unit from outside the optical axis;
From the center collimator or the first side collimator, which is supported in parallel with the optical axis of the lens to be examined and movable in two directions in a plane perpendicular to the optical axis, and is imaged in the air by the lens to be examined. An imaging unit for capturing an image of the test chart;
A lens inspection apparatus comprising:   The first guide extends from the vicinity of the center collimator beyond the position where the lens to be tested is held in the optical axis direction, and the optical axis of the first side collimator is 120 from the optical axis of the center collimator. 2. The lens inspection apparatus according to claim 1, wherein a swing range of the first side collimator is set so as to be inclined to [deg.].   A second guide is provided at a position that is line-symmetric with the first guide with respect to the optical axis of the center collimator. The second guide is linearly movable by the second guide, and is attached to the base member at an arbitrary position on the second guide. A test chart and a collimator lens are built in such a manner that they can swing around a vertical axis, and parallel light from the test chart is incident on the test lens held by the lens holding unit from the optical axis. The lens inspection apparatus according to claim 2, further comprising a second side collimator.   4. The lens according to claim 3, wherein a plurality of types of test charts are built in each of the center collimator and the first and second side collimators, and any one test chart can be selected for each collimator. Inspection device.

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