JP2004132858A - System and method of measuring optical performance of optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method of measuring MTF(modulation transfer function) of an optical system (that is, lens to be measured) realizing space saving, quick measurement and cost reduction. <P>SOLUTION: The system is to measure optical performance including MTF of an objective optical system. The system comprises a mechanism means capable of controlling an optical system for measurement capable of using for measuring the optical performance of the objective optical system and building in the objective optical system based on the set measurement conditions, a measurement means for measuring a control quantity by the mechanism means, an operation output means for calculating the optical performance of the objective optical system and outputting, and a control means for setting the optical performance to be measured and the measurement conditions, and automatically controlling the mechanism means, the measurement means and the operational output means. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical performance of an optical system that forms an image on an object, and in particular, as an evaluation of a resolution performance of the optical system, an OTF (Optical Transfer Function) indicating a degree of deterioration of a spatial frequency component on an object or an image plane by the optical system. Alternatively, the present invention relates to measurement of optical performance including MTF (Modulation Transfer Function) excluding the phase component of the OTF.
[0002]
[Prior art]
Conventionally, various methods and apparatuses for measuring the OTF and MTF of an imaging lens have been proposed. For example, in U.S. Pat. No. 4,110,046, as shown in FIG. 5, a test lens (or a test lens) 12 is mounted on a mount attached to the analyzer 10, and light from a light source 14 provided at an object position is emitted. The light transmitted through the test lens 12 is detected by the analyzer 10, and the MTF of the test lens 10 is measured by the signal processor 16.
[0003]
For example, Japanese Patent Application Laid-Open No. 7-5073 by the present applicant discloses a light-emitting unit that projects a chart from the image plane of an imaging lens (or a lens to be inspected) through the imaging lens, and a light-receiving unit on the object side. It has been proposed to automate the measurement of MTF by adding a mechanism capable of moving the light receiving section within a predetermined plane.
[0004]
[Problems to be solved by the invention]
These devices and methods provide various optical performances such as astigmatism and chromatic aberration at each angle of view (also called image height) for detailed comparison with optical design data and analysis of manufacturing errors. There is a drawback that field curvature, distortion, and the like over the entire surface cannot be measured. Conventionally, there are devices for individual measurement, each time requiring time to change and adjust the lens to be inspected, and the space for those devices and the purchase cost of each device are required.
[0005]
Further, these apparatuses and methods have a drawback that errors in optical systems, charts, and light-receiving sensors other than the lens to be detected are included, so that MTF cannot be measured with high accuracy. Further, these apparatuses and methods arrange a light source or a reference chart on the object plane of the lens to be examined and arrange an analyzer on the image plane of the lens to be examined, or place a chart on the image plane of the lens to be examined. The light receiving unit is arranged on the object plane. As described above, these apparatuses and methods require a longer distance and a larger angle of view of the lens to be tested, since the light projecting unit or the light receiving unit is disposed at the actual object distance of the lens to be tested. Since the height of the measuring device is required, the size of the measuring device is increased. In addition, the measurement time is long in order to accurately move the light projecting unit or the light receiving unit, which is a main part of the measurement, over a long distance according to the angle of view of the lens to be measured, which requires a mechanism and a dark room having a large space. As a result, the cost of the apparatus and its accompanying equipment are required, which results in an increase in the cost of the measuring apparatus.
[0006]
MTF measurement is indispensable for producing high-quality lenses, and as the number of measurement items such as high-magnification zoom and anti-shake function increases with the multi-functionalization of lenses, space saving and quick measurement in factories and low prices are realized. There is a demand for a simple measuring device.
[0007]
Therefore, an object of the present invention is to provide an apparatus and a method for measuring the MTF of an optical system (that is, a lens to be measured) that realizes space saving, quick measurement, and cost reduction.
[0008]
[Means for Solving the Problems]
An apparatus for measuring an MTF of an optical system according to one aspect of the present invention is an apparatus for measuring an optical performance including an MTF of a target optical system, and is used for measuring the optical performance of the target optical system. A measurement optical system that can be incorporated with the target optical system and a mechanism that can adjust the target optical system based on a set measurement condition; a measurement unit that measures an adjustment amount by the mechanism; Calculation and output means for calculating and outputting the optical performance of the optical system, the optical performance to be measured, and the measurement conditions are set, and the mechanism means, the measurement means and the calculation output means are automatically set. And control means for controlling.
[0009]
The target optical system and the measurement optical system having a plurality of optical elements may include a plurality of mechanism units for adjusting the target optical system and the optical elements, respectively.
[0010]
The measurement device includes a first optical member that forms a secondary light source of the light source, and a chart that is provided near the secondary light source and that transmits part of light from the secondary light source and shields part of the light. A second optical member that causes the chart to emit light virtually from a predetermined distance, a support device that positions the target optical system in a predetermined arrangement, and a reflecting mirror that reflects light passing through the target optical system. A third optical member for forming an image of the chart together with the target optical system, a detection unit for detecting the image formed by the third optical member, and a detection unit for the image obtained from the detection unit. An arithmetic output device for calculating and outputting the MTF of the target optical system from the information may be provided.
[0011]
The reflecting mirror may have a substantially center of curvature at an object position or an image point of the target optical system. A means may be provided for enabling a calibration reflecting mirror to be inserted between the second optical member and the target optical system. The second member may also serve as at least a part of the third optical member.
[0012]
The first optical member, the chart, the second optical member, the third optical member, the measuring device main body including the detecting means, the support device, and the reflecting mirror are It may be configured to be capable of parallel translation and rotation. The detecting means may also detect a light amount and measure a transmittance of the target optical system. The chart includes, for example, rectangular or cross-shaped slits. The detection means may include a two-dimensional image sensor. The detection unit may include a two-dimensional image sensor, and pixels of the two-dimensional image sensor may be arranged non-parallel to a direction in which the slit extends.
[0013]
The light beam emitted from the second optical member is a first linearly polarized light, the light beam returned from the reflecting mirror is a second linearly polarized light orthogonal to the linearly polarized light, and the third optical member is the second linearly polarized light. Only polarized light may be imaged. The second or third optical member may include a zoom lens as an imaging lens. The object optical system may further include a unit that can be incorporated into and removed from the measurement optical system. The optical performance includes aberration.
[0014]
The target optical system whose MTF has been measured by any one of the above-described measuring devices also constitutes one aspect of the present invention.
[0015]
According to another aspect of the present invention, there is provided a method of measuring the optical performance of a target optical system, wherein the measurement optical system is used to measure the optical performance of the target optical system and the target optical system can be incorporated. A first step of setting measurement conditions of the target optical system, a second step of adjusting the measurement optical system and the target optical system that can be incorporated in the target optical system based on the measurement conditions, A third step of measuring a first optical performance of the target optical system using the measurement optical system incorporating the target optical system, and a second step of measuring the first optical performance of the target optical system from the first optical performance And a fourth step of calculating the optical performance of the above.
[0016]
The first step sets a plurality of measurement conditions, the second step adjusts the measurement optical system and the target optical system based on each measurement condition, and the third step sets the measurement conditions The first optical performance may be measured each time, and the fourth step may calculate the second optical performance using the first optical performance measured for each measurement condition. The first optical performance includes, for example, MTF.
[0017]
The first step sets the measurement conditions for each of a case where the target optical system is incorporated into the measurement optical system and a case where the target optical system is not incorporated, and the second step includes the step of: For each of the case where the target optical system is incorporated and the case where the target optical system is not incorporated, the arrangement is adjusted based on the measurement conditions described above, and the third step is performed in the measurement where the target optical system is not incorporated. Measuring a first MTF of the measuring optical system, and measuring a second MTF of the measuring optical system in which the target optical system is incorporated, wherein the fourth step is a step of measuring the measured MTF. The method may include calculating a difference between the first and second MTFs.
[0018]
The step of measuring the first MTF includes the step of measuring and storing before measuring the second MTF, and the calculating step of the fourth step includes the step of measuring the stored first MTF. May be used. Similarly, the step of measuring the second MTF includes the step of measuring and storing before measuring the first MTF, and the calculating step of the fourth step includes the step of measuring the stored 2 MTF may be used.
[0019]
A method for measuring the optical performance of a target optical system according to still another aspect of the present invention is used for a first step of setting measurement conditions for calibration and for measuring the optical performance of the target optical system. A second step of adjusting the measurement optical system based on the calibration measurement conditions, and a third step of measuring a first MTF of the measurement optical system that does not incorporate the target optical system; A fourth step of creating calibration data from the measurement conditions for calibration and the first MTF; a fifth step of setting measurement conditions of the target optical system; and a step of setting the measurement conditions of the target optical system. A sixth step of adjusting the target optical system, a seventh step of measuring a second MTF of the measurement optical system in which the target optical system is incorporated, and the measurement conditions of the target optical system. 2nd M An eighth step of creating pre-calibration data from F; a ninth step of subtracting the calibration data from the pre-calibration data to calculate a calibrated third MTF of the target optical system; A tenth step of determining the optical performance of the target optical system from MTF.
[0020]
The first step sets a plurality of calibration measurement conditions, the second step adjusts the measurement optical system based on each calibration measurement condition, and the third step includes a calibration measurement condition. 21. The method according to claim 20, wherein the first MTF is measured for each condition, and the fourth step creates the calibration data from a plurality of the measurement conditions for calibration and a plurality of the first MTFs. the method of.
[0021]
The steps of performing the first to fourth steps in advance and storing the calibration data and the ninth step may use the stored calibration data. The fifth step sets a plurality of measurement conditions, the sixth step adjusts the target optical system based on each measurement condition, and the seventh step sets the second measurement condition for each measurement condition. MTF may be measured, and in the eighth step, the pre-calibration data may be created from a plurality of the measurement conditions and a plurality of the second MTFs.
[0022]
The target optical system whose MTF has been measured by the above method also constitutes one aspect of the present invention.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an MTF measuring apparatus 100 according to an embodiment of the present invention for measuring the optical performance including the MTF of the lens TL to be measured will be described with reference to the accompanying drawings. Here, FIG. 1 is a schematic optical path diagram of the MTF measuring apparatus 100. The MTF measuring apparatus 100 includes a first optical member 102, a second optical member 104, a third optical member 106, a chart 124, a calibration reflecting mirror 136, and a test lens TL as an optical system. Supporting device 140 for supporting, reflecting mirror 150, detecting means 160, MTF calculation output device 170, MTF measuring device main body control / measuring device 180, calibration reflecting mirror control / measuring device 182, reflecting mirror control / measuring It has a device 184 and an overall system control device / optical performance calculation output device 188.
[0024]
The first optical member 102 includes a light source 112, an elliptical mirror 114, a diffusion plate 116, a light shielding plate 118, a condenser lens 120, and a color filter 122, and has a function of forming a secondary light source of the light source 112.
[0025]
The light source 112, for example, a halogen lamp or a mercury lamp is disposed at one focal point of the elliptical mirror 114, and forms an image of the light source 112 at another focal point of the elliptical mirror 114. A light shielding plate 118 is arranged so that unnecessary light does not leak to the image forming point. Between the light source 112 and the light-shielding plate 118, a diffusion plate 116 that can adjust the light distribution characteristics of light is arranged to make light from an actual object as close as possible. The condenser lens 120 and the color filter 122 illuminate the chart 124 provided with the slit with light having a predetermined spectral characteristic. As described above, the first optical member 102 illuminates the pseudo imaging point.
[0026]
The chart 124 is a pseudo imaging point for MTF measurement. Specifically, it transmits a minute line width, and absorbs or reflects the others. The chart 124 has a slit 125a or the like having a cross or rectangular shape as shown in FIG. The chart 124 is provided near the secondary light source formed by the first optical member 102 and has a function of transmitting a part of light from the secondary light source and blocking part of the light.
[0027]
The second optical member 104 includes a half mirror 126, an imaging lens 128, and an aperture 130, and has a function of causing the chart 124 to emit light virtually from a predetermined distance. A light beam having passed through the chart 124 with a predetermined light beam diameter at a predetermined distance is imaged on the chart 124 by a half mirror 126, an image forming lens 128, and an aperture 130. In the example of FIG. 1, the chart 124 is formed on the image forming plane 132 of the lens TL to be measured. In this case, the chart imaging magnification β is approximately β = s2 / s1. Here, s1 is the distance from the chart 124 to the imaging lens 128, and s2 is the distance from the imaging lens 128 to the imaging surface 132. The diaphragm 130 is set so as to be a light beam effective for the lens TL to be measured. The test lens TL is arranged so that the light beam emitted from the second optical member 104 is at a desired image forming position on the test lens TL.
[0028]
The test lens TL is mounted on the support device 140, and the support device 140 arranges the test lens TL in a predetermined posture. The light beam emitted from the test lens TL forms an image of the slit of the chart 124 at the object position of the test lens TL.
[0029]
At an object position of the test lens TL, a reflecting mirror 150 having a center of curvature substantially at the object position is arranged. In the example shown in FIG. 1, the reflecting mirror 150 is constituted by a convex mirror having a center of curvature at the object position. When the object position of the test lens TL is an infinite edge, a plane mirror is provided instead of the convex mirror, and when the object position is on the left side of the reflecting mirror, a concave mirror is provided. In another embodiment, the reflecting mirror 150 is a flat mirror. A film is formed on the surface of the reflecting mirror 150 so as to reflect light at a used wavelength.
[0030]
The third optical member 106 includes a stop 130, an imaging lens 128, and a half mirror 126, and has a function of forming an image of the chart 124 together with the lens TL to be measured. In the present embodiment, the second optical member 104 also serves as the third optical member, so that it is possible to reduce the number of components and thereby reduce the cost of the measuring device. The light beam reflected by the reflecting mirror 150 is reflected, passes through the lens to be measured TL, passes through the stop 130 and the imaging lens 128, and is reflected by the half mirror 126.
[0031]
In another embodiment, another half mirror is disposed between the second optical member 104 and the test lens TL, and the second optical member 104 and the third optical member 106 are provided with an imaging lens together. Is also good. Since the overall magnification of the chart 124 is determined from the performance and position of the imaging lens 128, the test lens TL, and the imaging lens (not shown) arranged on the third optical member 106, the overall magnification can be changed more freely. Become.
[0032]
At a position conjugate with the chart 124, a two-dimensional image sensor 160 as a detecting unit for detecting an image formed by the third optical member 106 is arranged, and detects an image forming state of a slit of the chart 124.
[0033]
The two-dimensional imaging device 160 is connected to the MTF calculation output device 170. The MTF calculation output device 170 includes a calculation unit that converts the imaging state detected by the two-dimensional imaging device 160 into an MTF value, and an output unit that records and displays the MTF value and prints out the image on paper.
[0034]
Here, the first optical member 102, the chart 124, the second optical member 104, the third optical member 106, and the two-dimensional image sensor 160 are integrated to constitute the MTF measuring apparatus main body 101. As shown in FIG. 1, the apparatus main body 101 can be driven in x, y, and z axes (perpendicular to the plane of the paper), θz (rotation about the z axis), and θy (rotation about the y axis). The control / measurement device 180 can control and measure the driving amount of the device main body 101. The control / measurement device 182 controls a unit 137 described later to control the attachment / detachment of the calibration reflecting mirror 136. The reflecting mirror 150 can be driven in the x-axis, the y-axis, and the z-axis (perpendicular to the paper). The control and measurement device 184 can control and measure the driving amount of the reflecting mirror 150.
[0035]
The whole system control device / optical performance calculation output device 188 can input and set desired optical performance and desired measurement conditions. Further, the whole system controller / optical performance calculation output device 188 commands the drive of these controllers 180 to 184 to predetermined positions based on the input values. Further, the overall system control device / optical performance calculation output device 188 collects each measurement amount, calculates the desired optical performance under desired measurement conditions from each MTF, and records, displays, or prints out the result on paper. An output unit for performing such operations is provided, so that desired optical performance can be automatically measured.
[0036]
The MTF of the test lens TL measured by the measuring device 100 includes the error of the chart 124, the MTF of the second optical member 104, the error of the reflecting mirror 150, the MTF of the third optical member 106, And an error of the two-dimensional image sensor 160. If these errors are known in advance, the values can correct the measured MTF of the test lens TL. However, since the accumulation of individual errors is inaccurate and these errors change, It is beneficial to simply measure these errors using the measurement device 100.
[0037]
Therefore, as shown in FIG. 1, a means 137 capable of inserting the calibration reflecting mirror 136 is provided in front of the lens TL to be inspected, and the reflecting mirror 136 for calibration is inserted into the optical path and exits from the second optical member 104. Optical adjustment is performed so that the light flux returns to the original position, and the MTF is measured. The means 137 is controlled by the control / measurement device 182 as described above.
[0038]
The measurement result in this state is obtained by adding the calibration reflecting mirror 136 instead of the lens TL and the reflecting mirror 150, the MTF of the chart 124, the second optical member 104, and the third optical member 106, and the two-dimensional An MTF containing the image sensor 160 is obtained. Since the reflecting mirror 150 and the calibrating reflecting mirror 136 are unitary, measurement and processing can be performed with high accuracy, and it is sufficiently possible to prevent the measurement accuracy from being affected. Even if there is an effect, it is possible to measure with high accuracy and correct from it because it is a single substance.
[0039]
By subtracting this MTF measurement result from the above-mentioned MTF measurement result, the MTF of the true test lens TL is measured. These two MTF measurements are independent measurements, and the measurement order may of course be reversed. If the change is small, it is also possible to use the value of the MTF at the calibration reflecting mirror 136 measured previously.
[0040]
When a certain finite object distance is created as the calibration reflecting mirror 136, the luminous flux emitted from the second optical member 104 is divergent light so that the shape is concave, and if it is parallel (when the object distance is infinite). If it is a flat surface, and if it is convergent light (when the object position is on the right side of the calibration reflecting mirror 136 in FIG. 1), it is made convex so that the light beam emitted from the second optical member 104 can be restored. .
[0041]
As described above, since the MTF measuring device 100 of the present embodiment includes the calibration reflecting mirror 136 and the calibration means 137, it is possible to measure the MTF with high accuracy. Further, instead of the same two complicated light projecting and receiving optical units as in the prior art, the first optical member 102, the chart 124, the second optical member 104, the third optical member 106, and the detection Since the MTF measuring device main body 101 composed of the means 160 is integrated and the rest is composed of the reflecting mirror 150 having a simple configuration, a cable for supplying electricity to the light source 112, the detecting means 160, and the like is provided only to the MTF measuring device main body 101. The unit to be connected or to be precisely optically adjusted is also very easy to handle with only the main body 101 thereof.
[0042]
Further, in order to change the object distance and the angle of view of the test lens TL, which are important parameters of the MTF measurement, the MTF measurement device main body 101 and the test lens TL or the support device 140 and the reflecting mirror 150 are relatively parallel. It becomes possible by moving and rotating. To this end, a mechanism (not shown) capable of moving or rotating the MTF measuring apparatus main body 101 and the lens to be inspected TL or the supporting apparatus 140 and the reflecting mirror is provided, and each optical axis is predetermined using the detecting means 160 of the MTF measuring apparatus main body 101. Make optical adjustments. Further, the present embodiment has a feature that the measurement can be performed with twice as high sensitivity as the present invention transmits twice, as compared with the conventional measurement of the lens under test once.
[0043]
FIG. 2 shows two types of charts 124 when detection is performed by the two-dimensional image sensor 160. FIG. 2A shows a case where the chart 124 has a cross-shaped slit 125a and the MTF in the yz direction orthogonal to the MTF can be simultaneously measured by the cross-shaped slit 125a having a small line width. ing. As a result, astigmatism can be measured from the defocus characteristic of the MTF. FIG. 2A schematically shows the cross slit 125a on the two-dimensional image sensor. In practice, the image of the cross slit 125a is degraded by the lens TL to be inspected, so that the end of the cross slit is not Be clear.
[0044]
Small black rectangles P arranged in yz indicate pixels of the two-dimensional image sensor. By configuring the pixel P array and the end of the cross slit 125a to be non-parallel, it is possible to reduce a measurement error due to a relative difference between the pixel P and the end. The image in the y direction of the cross slit 125a is detected at the upper and lower oblique lines Py, and the relative difference of z from the end of the cross slit is corrected according to the height of each y, integrated, and the MTF in the z direction is measured. I do. As for the MTF in the y direction, the image in the z direction of the cross slit 125a is detected by the left and right hatched portions Pz, and the MTF in the y direction is measured similarly to the z direction.
[0045]
FIG. 2B shows a state in which the orthogonal rectangular charts 125b and 125c are separated from each other as long as the images do not interfere with each other, and the MTF in the yz direction can be measured similarly to FIG. 2A. . As in FIG. 2A, hatched portions Py ′ and Pz ′ are detection portions of the two-dimensional image sensor 160. If the rectangular slits 125b and 125c have only one direction, one MTF in the direction perpendicular to the slit can be measured. If a large number of MTFs are arranged, MTFs in many directions can be measured simultaneously. However, the chart is enlarged accordingly so that the images do not interfere with each other.
[0046]
In the present invention, instead of the above-described two-dimensional image sensor 160, MTF measurement by a light amount detection method by scanning a single slit and a single slit on an image forming surface thereof, which is commonly used, can be used. For this purpose, a thin rectangular slit is provided as the chart 124, and a narrow rectangular slit that can be scanned is disposed in place of the two-dimensional image sensor 160, and a photomaru or silicon sensor that can detect the amount of transmitted light is disposed behind the narrow rectangular slit.
[0047]
In the actual MTF measurement, it is difficult to set the best focus position by other means. Specifically, the reflecting mirror is slightly moved in the optical axis direction to relatively defocus the chart image on the two-dimensional image pickup device, and the MTF is set. Is measured, and the defocus position showing the best MTF is determined as the best focus position. In this embodiment, defocus can be easily achieved by moving only one reflecting mirror 150. In another embodiment, defocusing is performed by moving the MTF measuring apparatus main body 101 and the lens to be tested TL instead of the reflecting mirror 150.
[0048]
Hereinafter, an MTF measuring apparatus 100A according to another embodiment of the present invention will be described with reference to FIG. Here, FIG. 4 is a schematic optical path diagram of the MTF measuring apparatus 100A, and the same members as those in FIG. 1 are denoted by the same reference numerals.
[0049]
In the MTF measuring apparatus 100, the first optical member 102 illuminates a pseudo image forming point, and the chart 124 is a pseudo image forming point for MTF measurement. The test lens TL is arranged so that the light beam emitted from the second optical member 104 is at a desired image forming position on the test lens TL. The second optical member 104 forms an image of the chart 124 at infinity, but forms an image in accordance with the object distance of the lens to be measured. The light beam emitted from the test lens TL forms an image of the slit of the chart 124 at the object position of the test lens TL. The reflecting mirror 150 is arranged as a convex mirror having a center of curvature substantially at the object position of the lens TL to be measured.
[0050]
On the other hand, in the MTF measurement device 100A, the first optical member 102 illuminates the pseudo object, and the chart 124 is a pseudo object for MTF measurement. The test lens TL is arranged such that the light beam emitted from the second optical member 104 is at a desired object position of the test lens TL. The second optical member 104 forms an image of the chart 124 at infinity, but forms an image in accordance with the object distance of the lens TL to be measured. The light beam emitted from the test lens TL forms an image of the slit of the chart 124 at the image forming point of the test lens TL. The reflecting mirror 150A is arranged as a concave mirror having a substantially center of curvature at an image forming point on the image forming surface 134 of the lens TL to be measured.
[0051]
The shapes of the slits 125a to 125c and the pixel arrangement of the two-dimensional image sensor 160 shown in FIGS. 2A and 2B can be applied to the MTF measuring apparatus 100A shown in FIG.
[0052]
Further embodiments of the measuring devices 100 and 100A are listed below.
(1) In order to optically adjust the relative positions of the MTF measuring apparatus main body 101, the test lens TL, and the reflecting mirrors 150 and 150A, the test lens TL is fixed and the other MTF measuring apparatus main bodies and the reflecting mirror are driven. I let it. This method does not drive the test lens TL, and is effective for a large test lens TL and a test lens TL having various shapes and weights. However, even when the test lens TL is small and lightweight, the same optical adjustment can be performed by fixing the MTF measuring apparatus main body 101 and driving the test lens TL and the reflecting mirror 150.
(2) The calibration reflecting mirror 136 can use a convex surface, a flat surface, and a concave shape depending on the image forming position in the example shown in FIG. 1 and the object position in the example shown in FIG.
(3) As the first optical member 102, the chart 124 can also be illuminated directly using only a refractive system as a light source. Although the divergence of the light source 112 is not effectively used, there is an advantage that a natural light distribution can be provided.
(4) The reflection mirrors 150 and 150A can be reflected by a collimator lens and a plane mirror. In addition, when the test lens TL is a part of the imaging lens 128 and the wavefront near the imaging position does not ideally become a spherical wave, an aspheric surface is used as the reflecting mirror 150 to return to the original optical path. By doing so, the MTF measurement of the test lens TL can be performed.
(5) In the embodiment shown in FIGS. 1 and 4, since the light beam transmits through the test lens TL twice, when the light beam transmits once, the surface reflection of the test lens TL is transmitted to the two-dimensional image sensor 160. There is a possibility of entering. In order to prevent this, the half mirror 126 shown in FIG. 1 is used as a polarization beam splitter, and the light entering the lens TL is linearly polarized. The plate is arranged in a predetermined direction, turned into circularly polarized light, reflected by the reflecting mirror 150, and, when transmitted again through the quarter-wave plate, becomes linearly polarized light orthogonal to the first transmitted light. As a result, the surface reflection generated during the first transmission of the test lens TL has the same azimuth as that of the incident polarized light, so that it does not enter the two-dimensional image sensor 160 by the polarization beam splitter, but returns to the light source, and The reflection can be eliminated.
(6) If the light amounts of all the pixels of the two-dimensional image sensor 160 are detected, the transmittance of the lens TL to be measured can be measured at the same time. Furthermore, the reflectances of the calibration mirror and the reflecting mirror are measured independently, and the transmittance of the lens to be measured is more accurately measured from the light intensity at the time of measuring the calibration MTF, the light intensity at the time of measuring the lens to be measured, and their reflectance. it can.
(7) By using an optical fiber instead of the diffusion plate 116, the diffusion characteristics of the optical fiber can be used.
(8) In order to inspect various types of lenses TL having different focal lengths and F-numbers and lenses TL to be inspected of a zoom lens, the optimum light flux incident on the lens TL to be inspected, the line width of the chart, the measurement sensitivity, etc. Is performed. For this purpose, the imaging lens, the chart, the imaging lens and the aperture can be exchanged. Also, if the imaging lens is a zoom lens, the focal length, F-number, and object distance of the zoom lens are changed without changing the lens. The inspection lens can be easily measured.
[0053]
Hereinafter, the method for measuring the MTF of the lens to be measured according to the present invention will be described with reference to FIG. Here, FIG. 3 is a flowchart showing an example of the measuring method of the present invention. Such a measuring method can use any of the measuring devices 100 and 100A.
[0054]
First, the power supply and the like of the MTF measuring devices 100 and 100A are turned on (step 1002). In particular, it is preferable to turn on the light in advance if it is unstable immediately after lighting, such as a light source.
[0055]
Next, the measurer sets conditions for automatic measurement with the whole system control device 188 (step 1004). For example, in addition to the MTF, astigmatism, chromatic aberration, distortion (distortion), and field curvature at a plurality of image plane positions of the test lens TL are set as optical performance, and the reference position and the reference position are set as conditions of the test lens TL. When a zoom ratio, an F-number, and an object distance are input, a diffusion plate 116, a color filter 122, a chart 124, an imaging lens 128, and an aperture 130, which are measurement conditions of the MTF measurement apparatus main body 101, are selected.
[0056]
Next, the selected diffusion plate 116, color filter 122, chart 124, image forming lens 128, aperture 130, and the image forming position of the chart 124 (the image forming position in FIG. Are set (step 1006). A slide mechanism, a rotation mechanism, and the like, which enable automation of setting, and a control system are provided respectively. However, if the setting conditions are fixed, the setting may be manual instead of automatic.
[0057]
Next, the calibration reflecting mirror 136 is inserted, and optical adjustment is performed (step 1008). One example of this optical adjustment is to tilt and translate the calibration reflecting mirror 136 so that the light beam emitted from the second optical member 104 is restored. The adjustment can be performed automatically by monitoring the center position or blur of the image of the chart 124 of the two-dimensional image sensor 160.
[0058]
Next, the MTF is measured (Step 1010). Specifically, the image signal from the two-dimensional image sensor 160 is processed and calculated to calculate an MTF value, which is recorded (memory).
[0059]
Next, when the calibration values such as the various diffusion plates 116, the color filters 122, the chart 124, the imaging lens 128, the aperture 130, and the imaging position of the chart 124, which are the MTF conditions, are obtained, the MTF measurement is performed again. Set the conditions and repeat the above procedure. Next, the calibration mirror is removed from the optical path (Step 1012).
[0060]
Next, various diffusion plates 116, color filters 122, a chart 124, an imaging lens 128, an aperture 130, an imaging position of the chart, and the like, which are the MTF measurement conditions of the lens to be inspected, are set (step 1014).
[0061]
Next, the test lens is attached to the support device 140. Next, the overall system control device 188 sets various conditions of the MTF measuring device main body 101 corresponding to the zoom ratio, the object distance, the F-number, the image plane position, and the angle of view, which are the measurement conditions of the test lens TL, and sets the MTF. Various measurement conditions are set in the apparatus main body 101 via the measuring apparatus main body control / measurement apparatus 180, and the movement amount is sent to the entire system control apparatus 188 (step 1016).
[0062]
Next, the reflecting mirror 150 is set at a position instructed by the overall system controller 188 via the reflecting mirror control / measuring device 184, and the amount of movement is sent to the overall system controller 188 (step 1018). Note that the MTF measurement conditions, the MTF measurement device movement, the measurement conditions of the lens to be inspected TL, and the setting of the position of the reflecting mirror 150 can be independently set, and the order is arbitrary.
[0063]
Next, the MTF measuring device main body 101 (that is, the first optical member 102, the chart 124, the second optical member 104, the second optical member 104, and the second optical member 104) is formed so that the image of the chart 124 is correctly formed on a predetermined position of the two-dimensional image sensor 160. The relative positions of the unit constituted by the three optical members 106 and the two-dimensional imaging device 160), the lens to be measured TL, and the reflecting mirror 150 are adjusted, and the movement amount at that time is sent to the overall system control device 188 (step 1020). ). At this time, the optical adjustment can be automatically performed by monitoring the center position and blur of the image of the chart 124 of the two-dimensional image sensor 160.
[0064]
Next, the MTF is measured (step 1022). Specifically, the image signal from the two-dimensional image sensor 160 is processed and calculated to calculate the MTF value. Next, the MTF value of the true test lens TL is calculated from the MTF value using the correction value of the calibration reflecting mirror 136.
[0065]
Further, the various conditions are changed, the MTF value of the true test lens is obtained, and the various conditions and the MTF value at that time are output as numerical values, tables, or diagrams (step 1024).
[0066]
Next, the process returns to the above-described predetermined step and repeats the process according to the automatic measurement condition set in step 1004. For example, when only the position of the image plane is changed, the position of the MTF measuring apparatus main body 101 is moved to a position corresponding to the image plane, and the reflecting mirror 150 is also moved to the predetermined position. Send to controller 188.
[0067]
When the MTF measurement instructed by the whole-system control device 188 is completed, the optical performance calculation output device 188 outputs each image from the MTF value at each image plane position and the movement amount of the MTF measurement device main body 188 and the reflecting mirror 150. The astigmatism and chromatic aberration at the surface position, the distortion (distortion) over the entire image plane, and the curvature of field are calculated, and are output for recording, display, printout on paper, etc. (step 1026).
[0068]
Finally, the lens TL to be inspected is removed, each power is turned off, and the like, and the process is completed.
[0069]
As described above, according to the embodiment of the present invention, optical performance such as astigmatism and chromatic aberration of the test lens TL, distortion over the entire image plane, and curvature of field can be measured. In addition, by simply adding that the MTF is measured with the calibration reflecting mirror 136 inserted, it is possible to easily measure the MTF with high accuracy.
[0070]
Further, the position of the object and the angle of view are set at an arbitrary object distance by the reflecting mirrors 150 and 150A or the second optical member 104, and by the relative positions and angles of the MTF measuring device main body 101, the reflecting mirror 150, and the lens TL to be measured. Since it can be set arbitrarily, a large space is not required. Further, the MTF measuring devices 100 and 100A have a small amount of movement, are easy to operate, and can quickly measure the MTF of the lens TL to be measured. Further, since the light projection and the light reception of the chart 124 can be integrated as the MTF measurement device main body 101, the size and cost of the device can be reduced. Further, since the light passes through the test lens TL twice, the MTF of the test lens TL can be measured with high sensitivity and high reliability.
[0071]
【The invention's effect】
According to the present invention, it is possible to provide an apparatus and a method for measuring the MTF of an optical system (that is, a lens to be inspected) that realizes space saving, quick measurement, and cost reduction.
[Brief description of the drawings]
FIG. 1 is a simplified optical path diagram of an MTF measurement device according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining a position of an image of a chart on a two-dimensional image sensor used in the MTF measuring device shown in FIG. 1 and a pixel array used in the two-dimensional image sensor.
FIG. 3 is a flowchart for explaining a measuring method according to the present invention.
FIG. 4 is a simplified optical path diagram of an MTF measurement device according to another embodiment of the present invention.
FIG. 5 is an external perspective view for explaining a conventional MTF measuring device.
[Explanation of symbols]
100, 100A MTF measuring device 101 MTF measuring device main body 102 First optical member 104 Second optical member 106 Third optical member 124 Chart 136 Calibration reflecting mirror 140 Supporting device 150, 150A Reflecting mirror 160 Two-dimensional image sensor 170 MTF calculation output device 180 MTF measurement device main body control / measurement device 182 Calibration reflector control / measurement device 184 Reflector mirror control / measurement device 188 Overall system control device / optical performance calculation output device

Claims (30)

An apparatus for measuring optical performance including MTF of an object optical system,
A measuring optical system used to measure the optical performance of the target optical system and the measuring optical system and the target optical system that can be incorporated into the target optical system, and a mechanism capable of adjusting the target optical system based on a set measurement condition; ,
Measuring means for measuring the amount of adjustment by the mechanism means,
Calculation output means for calculating and outputting the optical performance of the target optical system,
A measuring apparatus comprising: a control unit that sets the optical performance to be measured, the measurement conditions, and automatically controls the mechanism unit, the measuring unit, and the calculation output unit. The measurement apparatus according to claim 1, further comprising a plurality of the mechanism units for adjusting the target optical system and the optical elements of the target optical system and the measurement optical system having a plurality of optical elements. The measuring device comprises:
A first optical member for forming a secondary light source of the light source;
A chart provided in the vicinity of the secondary light source and transmitting part of the light from the secondary light source and blocking part of the light;
A second optical member for causing the chart to emit light virtually from a predetermined distance,
A support device for setting the target optical system in a predetermined arrangement,
A reflecting mirror for reflecting light having passed through the target optical system,
A third optical member that forms an image of the chart with the target optical system;
Detecting means for detecting the image formed by the third optical member;
The measurement device according to claim 1, further comprising: a calculation output device that calculates and outputs an MTF of the target optical system from information of the image obtained from the detection unit. The measuring apparatus according to claim 3, wherein the reflecting mirror has a center of curvature substantially at an object position of the target optical system. The measuring apparatus according to claim 3, wherein the reflecting mirror has a substantially center of curvature at an image forming point of the target optical system. The measuring apparatus according to any one of claims 3 to 5, further comprising a unit that enables a calibration reflecting mirror to be inserted between the second optical member and the target optical system. The measuring device according to any one of claims 3 to 6, wherein the second member also serves as at least a part of the third optical member. The first optical member, the chart, the second optical member, the third optical member, the measuring device main body including the detection means, the support device, and the reflecting mirror are The measuring device according to any one of claims 3 to 7, wherein the measuring device is configured to be capable of parallel movement and rotation. 9. The measuring apparatus according to claim 3, wherein the detecting unit detects a light amount and also measures a transmittance of the target optical system. The measuring device according to claim 3, wherein the chart includes a rectangular slit. The measuring device according to claim 3, wherein the chart includes a cross-shaped slit. The measuring device according to claim 3, wherein the detecting unit includes a two-dimensional image sensor. The said detection means has a two-dimensional image sensor, The pixel of the said two-dimensional image sensor is arranged non-parallel with respect to the direction in which the said slit extends, The Claims 10 or 11 characterized by the above-mentioned. measuring device. The light beam emitted from the second optical member is a first linearly polarized light, the light beam returned from the reflecting mirror is a second linearly polarized light orthogonal to the linearly polarized light, and the third optical member is the second linearly polarized light. 14. The measuring device according to claim 3, wherein only the polarized light is imaged. The measuring device according to claim 3, wherein the second optical member includes a zoom lens serving as an imaging lens. 16. The measuring device according to claim 3, wherein the third optical member has a zoom lens as an imaging lens. 17. The measuring apparatus according to claim 3, further comprising a unit capable of incorporating and removing the target optical system from the measuring optical system. 18. The measuring device according to claim 1, wherein the optical performance includes an aberration. 19. The target optical system for which an MTF has been measured by the measurement device according to any one of claims 1 to 18. A method for measuring the optical performance of a target optical system,
A first step of setting a measurement optical system used to measure the optical performance of the target optical system and the measurement optical system that can be incorporated into the target optical system, and a measurement condition of the target optical system;
A second step of adjusting the measurement optical system and the target optical system that can be incorporated into the target optical system based on the measurement conditions;
A third step of measuring a first optical performance of the target optical system using the measurement optical system incorporating the target optical system;
Calculating a second optical performance of the target optical system from the first optical performance. The first step sets a plurality of measurement conditions,
The second step adjusts the measurement optical system and the target optical system based on each measurement condition,
The third step measures the first optical performance for each measurement condition,
The method according to claim 20, wherein the fourth step calculates the second optical performance using the first optical performance measured for each of the measurement conditions. 22. The method according to claim 20, wherein the first optical performance comprises an MTF. The first step sets the measurement conditions for each of a case where the target optical system is incorporated in the measurement optical system and a case where the target optical system is not incorporated,
In the second step, for each of the case where the target optical system is incorporated into the measurement optical system and the case where the target optical system is not incorporated, the arrangement is adjusted based on the above measurement conditions,
The third step is a step of measuring a first MTF of the measurement optical system in which the target optical system is not incorporated, and a second MTF of the measurement optical system in which the target optical system is incorporated. Measuring the
23. The method according to any one of claims 20 to 22, wherein the fourth step comprises calculating a difference between the measured first and second MTFs. Measuring the first MTF includes measuring and storing before measuring the second MTF;
24. The method of claim 23, wherein the calculating of the fourth step utilizes the stored first MTF. Measuring the second MTF includes measuring and storing in advance before measuring the first MTF;
24. The method of claim 23, wherein the calculating of the fourth step utilizes the stored second MTF. A method for measuring the optical performance of a target optical system,
A first step of setting calibration measurement conditions;
A second step of adjusting a measurement optical system used to measure the optical performance of the target optical system based on the calibration measurement conditions;
A third step of measuring a first MTF of the measurement optical system that does not incorporate the target optical system;
A fourth step of creating calibration data from the calibration measurement conditions and the first MTF;
A fifth step of setting measurement conditions of the target optical system;
A sixth step of adjusting the target optical system based on the measurement conditions of the target optical system;
A seventh step of measuring a second MTF of the measurement optical system incorporating the target optical system;
An eighth step of creating pre-calibration data from the second MTF together with the measurement conditions of the target optical system;
A ninth step of subtracting the calibration data from the pre-calibration data to calculate a calibrated third MTF of the target optical system;
A tenth step of determining the optical performance of the target optical system from the third MTF. The first step sets a plurality of calibration measurement conditions,
The second step adjusts the measurement optical system based on each calibration measurement condition,
The third step measures the first MTF for each measurement condition for calibration,
21. The method according to claim 20, wherein the fourth step generates the calibration data from a plurality of the measurement conditions for calibration and a plurality of the first MTFs. Performing the first to fourth steps in advance and storing the calibration data;
28. The method of claim 26 or claim 27, wherein the ninth step utilizes the stored calibration data. The fifth step sets a plurality of measurement conditions,
The sixth step adjusts the target optical system based on each measurement condition,
The seventh step measures the second MTF for each measurement condition,
21. The method according to claim 20, wherein the eighth step generates the pre-calibration data from a plurality of the measurement conditions and a plurality of the second MTFs. A target optical system measured by the method according to any one of claims 19 to 29.

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