JP2011053048A - Lens evaluation method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inspect eccentricity and inspect the resolution of a lens with high accuracy without performing complicated operation. <P>SOLUTION: A test chart 14 is provided with a chart pattern for evaluating the resolution. The central part of the chart pattern is positioned on a measuring optical axis Ls. A test lens 12 is positioned on the measuring optical axis Ls. An image of the chart pattern is formed on a reticle plate 16 through the test lens 12. A reticle indicating a position through which the measuring optical axis Ls passes is attached to the reticle plate 16. The image of the chart pattern and an image of the reticle on the reticle plate 16 are magnified by a projection lens 17 to be imaged on a screen 18. Through the image of the chart pattern and the image of the reticle projected on the screen 18 in a magnified manner, the resolution and eccentricity of the test lens 12 are evaluated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lens evaluation method and apparatus for evaluating the resolution of various lenses mounted on optical / electronic devices such as digital cameras and projectors.

  Optical and electronic devices such as digital cameras and projectors are equipped with various lenses for collecting and expanding light. For example, a digital camera is equipped with an imaging lens that forms an image of light from a subject on a CCD. In the case of a 3D projector whose market has been expanding in recent years, a relay lens is individually used for each of the left and right channels of the 3D projector. Since this relay lens individually relays the left and right images displayed on the display surface of the original image to the projection optical system, high accuracy is required for imaging performance.

  These various lenses are inspected in the optical / electronic device manufacturing process to determine whether the performance such as resolution has a desired value. In the inspection of lens resolution, a test chart for resolution evaluation is used, and a lens to be inspected is positioned at a certain distance from the test chart. A focus glass is arranged on the imaging surface of the test lens, and a chart image is formed on the focus glass. The chart image is partially enlarged with a magnifying glass and observed, and the resolution of the test lens is evaluated by visually determining whether the edge of the chart image is clear.

  In addition to visual inspection, an image of a chart pattern projected through the lens to be inspected is captured by a CCD or the like, and the resolution of the lens is evaluated by analyzing the image obtained by the imaging with a computer. (Patent Document 1).

JP-A-10-90119

  In the case of the visual inspection described above, a flat rubbed glass is used as the focus glass, and the chart image formed on the rubbed surface is partially enlarged with a magnifying glass, but the rubbed surface is too rough. Therefore, it is difficult to evaluate the resolution because the edges of the image are disturbed, and conversely, if the roughness of the rubbing surface is too fine, the diffusivity is reduced and it is difficult to identify the edges of the image. Moreover, in the case of resolution evaluation by a computer, the equipment cost becomes enormous.

  An object of this invention is to provide the lens evaluation method and apparatus which can test | inspect the resolution of a lens accurately.

  In order to achieve the above object, the lens evaluation method of the present invention includes a chart image displayed on a test chart for resolution evaluation passing through a test lens positioned on a measurement optical axis passing through a central portion of the chart image. An intermediate image is formed on a transparent plate with a reticle at a position where the measurement optical axis passes, and the intermediate image and the reticle image are enlarged by a projection lens and formed on a screen. The resolution and decentering state of the test lens are evaluated from the chart image and the reticle image.

  Since the center of the chart image and the reticle image are overlapped on the screen to determine the decentered state of the lens to be tested, the decentered state can be obtained without performing complicated operations. Can be inspected.

  The test chart used in the present invention is a negative type test chart illuminated from the back side. Further, in the present invention, by using a zoom lens as the projection lens, the sharpness of the edge of the chart image can be expanded to such an extent that it can be visually observed.

  The lens evaluation apparatus according to the present invention includes a resolution evaluation test chart on which a chart image is displayed, a lens holder that positions and holds a test lens on a measurement optical axis passing through a central portion of the chart image, and the test object. A transparent plate positioned on the focal plane of the test lens and having a reticle attached at a position through which the measurement optical axis passes, and the chart image and the reticle image intermediately formed on the transparent plate by the test lens And a projection lens for enlarging and forming an image on a screen.

  Since the lens holder is moved in parallel with the measurement optical axis and an adjustment mechanism capable of measuring the amount of movement is provided, the lens can be obtained even when a desired result cannot be obtained by one resolution evaluation. The resolution can be evaluated again by moving the holder in the measurement optical axis direction within a certain range of movement.

  According to the present invention, a chart image is formed on a transparent plate, and the chart image on the transparent plate is enlarged by a projection lens and formed on a screen so that the sharpness of the edge of the chart image is visually observed. Therefore, the resolution of the lens to be inspected can be inspected with high accuracy.

It is a front view of the lens evaluation apparatus of this invention. It is a side view of a test chart. (A) is a front view of the inspection table, and (B) is a left side view of the inspection table. (A) is a front view of a lens holder, (B) is a side view of a lens holder. It is a side view of a reticle plate. It is a side view of a screen. It is explanatory drawing used in order to demonstrate aligning the reticle of a reticle plate on the optical axis of a projection lens. It is explanatory drawing used in order to demonstrate aligning the center part of a chart pattern on the optical axis of a calibration lens, and the optical axis of a projection lens. It is explanatory drawing used in order to demonstrate the evaluation method of the resolution and eccentric state of a to-be-tested lens.

  As shown in FIG. 1, the lens evaluation device 10 evaluates the resolution of the test lens 12 in the lens holder 11. The lens evaluation apparatus 10 includes a light source 13, a test chart 14, an inspection table 15, a reticle plate 16, a projection lens 17, and a screen 18. In the lens evaluation device 10, when the test lens 12 having no eccentricity is set on the inspection table 15, the optical axis L 1 of the test lens 12 and the optical axis L 2 of the projection lens 17 are positioned on the measurement optical axis Ls. As described above, the light source 13, the test chart 14, the inspection table 15, the reticle plate 16, the projection lens 17, and the screen 18 are placed on the surface plate 20. An example of the lens to be examined is a relay lens mounted on a projector.

  As shown in FIG. 2, the test chart 14 includes a light-transmitting chart pattern 23 for evaluating the resolution of the test lens 12 on a substantially black light-shielding portion 22 that substantially blocks light from the light source 13. ing. The test chart 14 is a negative test chart in which the chart pattern 23 is displayed brightly against the background of the substantially black light-shielding portion 22 when illuminated by the light source 13 from behind. The test chart 14 is installed so that the central portion 23a of the chart pattern 23 is positioned on the measurement optical axis Ls.

  The chart pattern 23 is located on the right side of the three horizontal slits 32 to 36 arranged in the central area 26 and the four corner areas 27 to 30 in the vertical direction at regular intervals, and is fixed. Three vertical slits 37 to 41 arranged in the horizontal direction at intervals are provided. The number of slits may be other than three, and the slits provided in the central area and the four corner areas may be other various patterns.

  As shown in FIGS. 3A and 3B, the inspection table 15 includes a mount table 45 for holding the lens holder 11 and a position fixing unit for fixing the position of the lens holder 11 set on the mount table 45. 46 and an adjustment mechanism 47 that moves the mount base 45 in the direction of the optical axis L1. As shown in FIGS. 4A and 4B, the lens holder 11 set on the mount base 45 includes a test lens 12, a cylindrical part 50 that holds the test lens 12, and an outer peripheral part of the cylindrical part 50. And a flange portion 51 attached to the central portion in the direction of the optical axis L1. A positioning hole 51 a for determining the positional relationship with the mount base 45 is formed in the flange portion 51.

  As shown in FIGS. 3A and 3B, the mount base 45 has a substantially rectangular parallelepiped shape and includes a holding portion 53 that holds the lens holder 11. The holding portion 53 is cut slightly larger than the diameter D of the cylindrical portion 50 of the lens holder from the upper surface of the mount base 45 to a certain depth. In addition, the outer peripheral shape of the cylindrical portion 50 is further below the certain depth. The cut surface is cut into a semicircular shape. The mount base 45 is provided with positioning pins 45a to be inserted into the positioning holes 51a of the flange portion.

  The position fixing unit 46 includes a clamp plate 55, a slide mechanism 56, and an operation lever 57. The clamp plate 55 is formed in a substantially C shape, and pressing members 55a for pressing the flange portion 51 of the lens holder are provided at both ends. The slide mechanism 56 slides the clamp plate 55 between a pressing position where the pressing member 55a presses the flange portion 51 and a retracting position where the lens holder 11 can be attached and detached by retracting from the pressing position. . The operation lever 57 is attached to the slide mechanism 56 so as to be rotatable. The slide mechanism 56 is operated by the rotation of the operation lever 57.

  The adjustment mechanism 47 directs the movable stage 60 according to the rotation of the movable stage 60 on which the mount 45 is mounted, the fixed stage 61 on which the movable stage 60 is movably attached in the direction of the measurement optical axis Ls, and the micro screw 62a. And a micrometer 62 to be moved. When the movable stage 60 is moved by the operation of the micrometer 62, the lens holder 11 set on the mount base 45 is moved in the measurement optical axis Ls direction. The movement amount of the lens holder 11 is displayed on a movement amount display unit 61 a attached to the fixed stage 61.

  As shown in FIG. 5, the reticle plate 16 is positioned on the focal plane of the test lens 12, and the light from the test lens 12 forms an image on the reticle plate 16. Therefore, a chart pattern image (not shown) is formed on the reticle plate 16 as an intermediate image.

  The reticle plate 16 includes a substantially black cross-shaped reticle 66 that shields light on the light transmitting portion 65. The reticle plate 16 shields light that strikes the reticle 66 out of the light from the lens 12 to be tested, and transmits light through the other portion, that is, the light transmitting portion 65, so that the light transmitting portion 65 displayed brightly by the transmitted light. Is a positive type test chart in which the reticle 66 is displayed in substantially black. Therefore, on the reticle plate 16, the image of the reticle 66 is formed as an intermediate image together with the image of the chart pattern. Moreover, the reticle plate 16 is installed so that the intersection 66a of the reticle is located on the optical axis L2 (see FIG. 1) of the projection lens 17.

  The projection lens 17 is composed of a zoom lens, and expands the light emitted from the reticle plate 16 at a constant magnification and projects the expanded light toward the screen 18. Since the projection lens 17 has a high resolution much higher than the resolution of the test lens 12, the use of the projection lens 17 does not affect the evaluation of the resolution of the test lens 12.

  As shown in FIG. 6, a chart pattern image 70 and a reticle image 71 are projected on the screen 18 by the light emitted from the projection lens 17. These images 70 and 71 inspect the resolution and eccentricity of the lens 12 to be examined. When evaluating the resolution of the lens 12 to be examined, first, the slit image 72a in the central area 72 having a high edge sharpness is visually counted. Similarly, slit images 73a to 76a having high edge sharpness are visually counted in the four corner areas 73 to 76. In any of the central area 72 and the four corner areas 73 to 76, when a predetermined number or more of slit images 72 a to 76 a having high edge definition are confirmed, the lens 12 to be tested has a desired resolution. It is determined that

  Here, the image 70 of the chart pattern on the screen 18 is enlarged by the projection lens 17 to such an extent that the sharpness of the edge can be reliably confirmed visually. Therefore, the slit images 72a to 76a having high edge sharpness can be reliably counted visually. Further, in the conventional resolution inspection, the sharpness of the edge of the image may be lowered depending on the surface roughness of the flat-rubbed glass. However, by using the screen 18, the chart pattern image 70 having a sharp edge can be obtained. Can be copied. Further, since the zoom lens is used for the projection lens 17, the projection distance and the screen size can be arbitrarily set according to the contents of the resolution inspection or can be changed for each inspection.

  Further, the decentered state of the lens 12 to be examined is determined based on whether or not the reticle image 71 overlaps the slit image 72 a in the central area of the chart pattern image 70. When the reticle image 71 overlaps the slit image 72a and also overlaps the central portion 70a of the chart pattern image 70, the optical axis L1 of the test lens is positioned on the measurement optical axis Ls, and It is determined that the analyzing lens 12 is not decentered. On the other hand, when the image 71 does not overlap the slit image 72a, it is determined that the optical axis L1 of the test lens is not located on the measurement optical axis Ls and the test lens 12 is decentered. . In this embodiment, the decentered state of the test lens is determined based on the overlap of the chart pattern image and the slit image. In addition, the test lens decentering is performed by various methods using the chart pattern image and the slit image. The lead state can be determined.

  Next, the operation of the lens evaluation device 10 will be described. First, as shown in FIG. 7, the screen 18, the projection lens 17, and the reticle plate 16 are placed on the surface plate 20. A light source 80 is provided behind the reticle plate 16, and light is applied from the light source 80 to the reticle plate 16. As a result, light from the light source 80 is projected onto the screen 18 via the reticle plate 16 and the projection lens 17, and an image 71 of the reticle is projected onto the screen 18. Then, the reticle plate 16 is set so that the intersecting portion 71a of the reticle image is positioned on the optical axis L2 of the projection lens.

  Then, as shown in FIG. 8, after removing the light source 80, the inspection table 15, the test chart 14, and the light source 13 are arranged behind the reticle plate 16. Then, the lens holder 11 on which the calibration lens 82 that is not eccentric is mounted is placed on the holding portion 53 of the mount base 45, and the positioning pins 45a of the mount base are inserted into the positioning holes 51a of the flange portion. This prevents the lens holder 11 from rotating on the holding portion 53. Then, the slide mechanism 56 is operated with the operation lever 57 to slide the clamp plate 55 from the retracted position to the pressed position. As a result, the flange portion 51 is pressed by the pressing member 55a of the clamp plate 55, so that the position of the lens holder 11 on the mount base 45 is fixed. The calibration lens and the test lens have the same lens configuration.

  Then, light is applied from the light source 13 to the test chart 14. Thus, the light from the light source 13 is projected onto the screen 18 via the test chart 14, the calibration lens 82, the reticle plate 16, and the projection lens 17, and the chart pattern image 70 and the reticle image 71 are converted into the screen 18. It is projected on. Then, the test chart 14 is set so that the central portion 23a of the chart pattern 23 is positioned on the same measurement optical axis Ls on the optical axis L3 of the calibration lens 82 and the optical axis L2 of the projection lens. Further, the inspection table 15 is set so that the reticle plate 16 is positioned on the focal plane of the calibration lens 82. When the installation of the test chart 14 and the inspection table 15 is completed, the lens holder 11 on which the calibration lens 82 is mounted is removed.

  Then, as shown in FIG. 9, the lens holder 11 on which the lens 12 to be inspected is mounted is set on the mount base 45, and the mount base is the same as in the case of the lens holder 11 on which the calibration lens 82 is mounted. The position of the lens holder 11 at 45 is fixed. Then, light is applied from the light source 13 to the test chart 14. Thereby, the light from the light source 13 is projected onto the screen 18 via the test chart 14, the test lens 12, the reticle plate 16, and the projection lens 17, and the chart pattern image 70 and the reticle image 71 are converted into the screen 18. It is projected on.

  Then, among the slit images 72a to 76a projected on the screen 18, those having a high edge sharpness are counted. In any of the central area 72 and the four corner areas 73 to 76, when the slit images 72 a to 76 a having high edge sharpness are confirmed by a certain number or more, the lens 12 to be examined has a desired resolution. It is determined that

  If a certain number or more of slit images with high edge sharpness cannot be confirmed, the micro screw 62a is operated to move the lens 12 to be measured in the direction of the optical axis L1 by a certain amount of movement. At this time, by moving the test lens 12 within a range of a certain amount of movement, slit images 72a to 76a having high edge sharpness are obtained in both the central area 72 and the four corner areas 73 to 76. When a certain number or more is confirmed, it is determined that the lens 12 to be examined has a desired resolution. On the other hand, even if the test lens 12 is moved beyond the range of a certain amount of movement, if the slit images 72a to 76a having high edge sharpness cannot be confirmed by a certain number or more, the test is performed. It is determined that the lens 12 does not have the desired resolution.

  Further, on the screen 18, when the reticle image 71 overlaps the slit image 72a and also overlaps the central portion 70a of the chart pattern image 70, the optical axis L1 of the test lens is the measurement optical axis. It is determined that the lens 12 to be examined is not decentered and located on Ls. On the other hand, when the image 71 does not overlap the slit image 72a, the optical axis L1 of the test lens is not located on the measurement optical axis Ls, and the test lens 12 is decentered. To be judged.

  In the present embodiment, a negative type test chart with a chart pattern that transmits light is used, and illumination from behind the test chart displays a bright image of the chart pattern with the black light-shielding portion in the background. However, instead of this, by using a light reflection type test chart having a chart pattern in which white and black are alternately arranged at regular intervals, and illuminating from the left and right front of the test chart, an image of the chart pattern is obtained. It may be displayed.

DESCRIPTION OF SYMBOLS 10 Lens evaluation apparatus 11 Lens holder 12 Test lens 13 Light source 14 Test chart 16 Reticle plate 17 Projection lens 18 Screen 23 Chart pattern 47 Adjustment mechanism 66 Reticle 70 (Chart pattern) image 71 (Reticle) image

Claims (6)

  The chart image displayed on the test chart for resolution evaluation is passed through a test lens positioned on the measurement optical axis passing through the center of the chart image, and on a transparent plate with a reticle attached at the position where the measurement optical axis passes. Forming an intermediate image, enlarging the intermediate image and the image of the reticle with a projection lens to form an image on a screen, and resolving the resolution of the test lens with the chart image and the image of the reticle enlarged on the screen; A lens evaluation method characterized by evaluating an eccentric state.   The lens evaluation method according to claim 1, wherein an eccentric state of the lens to be measured is determined based on whether or not a center portion of the chart image and the image of the reticle overlap on the screen.   The lens evaluation method according to claim 1, wherein the test chart is a negative type test chart illuminated from the back side.   4. The lens evaluation method according to claim 1, wherein the projection lens is a zoom lens. Test chart for resolution evaluation with chart image displayed,
A lens holder for positioning and holding the test lens on the measurement optical axis passing through the center of the chart image;
A transparent plate that is positioned on the focal plane of the lens to be examined and has a reticle attached at a position through which the measurement optical axis passes;
A lens evaluation apparatus comprising: a projection lens that enlarges the chart image intermediately formed on the transparent plate by the test lens and the image of the reticle to form an image on a screen.   The lens evaluation apparatus according to claim 5, further comprising an adjustment mechanism that moves the lens holder in parallel with the measurement optical axis and that can measure the amount of movement.

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