JP2006329791A - Shape evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shape evaluation method capable of evaluation corresponding to optical performance of a measuring object. <P>SOLUTION: This method has a shape data acquisition process for acquiring shape data by measuring the shape of an optical element; a coordinate transformation process for performing coordinate transformation of a measuring coordinate system CRDm used for measurement in the shape data acquisition process to a prescribed reference coordinate system CRDs by using a coordinate transformation parameter; an evaluation value calculation process for determining an evaluation value which is a variation of the optical performance MTF, relative to a prescribed evaluation parameter from the shape data in the reference coordinate system CRDs; a coordinate transformation parameter determination process for changing the value of the coordinate transformation parameter, repeating the coordinate transformation process and the evaluation value calculation process, and determining the value of the coordinate transformation parameter with which the evaluation value (MTF) becomes the maximum or the minimum; and a coordinate transformation process for performing coordinate transformation by using the determined value of the coordinate transformation parameter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for measuring the shape of an optical element such as a lens or a prism.

  Conventionally, a three-dimensional shape of an object to be measured is measured using a measuring device such as a three-dimensional measuring machine. Then, based on the measurement result, it is evaluated whether or not the shape measurement value satisfies the component standard value. At this time, if there is an installation error of the object to be measured with respect to the coordinate system of the measuring apparatus, the coordinate system of the measured value does not match the coordinate system to be evaluated. For this reason, there is an inconvenience that the measured value and the component standard value cannot be collated accurately.

  Therefore, for example, Patent Document 1 discloses a method of correcting an installation error of an object to be measured and evaluating an error between a design shape and a measurement shape. This will be described below. First, the three-dimensional shape of the optical element is measured with a three-dimensional measuring machine or the like to obtain a shape measurement data string. Next, the shape measurement data string is coordinate-transformed with respect to the design shape. And an evaluation value is calculated | required from the shape measurement data sequence after coordinate transformation.

  Further, a coordinate conversion parameter that minimizes the evaluation value is determined by convergence calculation. The parameters for coordinate conversion are parallel movement of X, Y, and Z and rotational movement along the respective axes, and indicate installation errors of the object to be measured. The evaluation value is the root mean square (hereinafter referred to as RMS) of the deviation between the shape measurement data string and the design shape. As a convergence calculation method, a known method such as a least square method is used.

  Then, the coordinates of the shape measurement data string with respect to the design shape are obtained. From this result, a measured value such as PV (Peak to Valley) or RMS is calculated. In this way, the measured object is evaluated by collating the measured value with the component standard value.

Japanese Patent No. 2520202

  However, the result of collating the measured value obtained using the RMS of deviation between the shape measurement data string and the design shape as the evaluation value (that is, the evaluation index) and the component standard value corresponds to the optical performance of the optical element. There may not be. For example, when there are local protrusions on the surface shape of the optical element, even if the RMS of the deviation between the shape measurement data string and the design shape is minimized, the optical performance is not always in the best state. Absent. For this reason, in the conventional shape evaluation method, the optical element that is the object to be measured may not be appropriately evaluated based on the collation result.

  The present invention has been made in view of the above, and an object thereof is to provide a shape evaluation method capable of performing an evaluation corresponding to the optical performance of an object to be measured.

  In order to solve the above-described problems and achieve the object, according to the present invention, a shape data acquisition step for measuring the shape of an optical element to acquire shape data, and shape data with respect to a predetermined reference coordinate system An evaluation value for obtaining an evaluation value for a predetermined evaluation parameter from a first coordinate conversion step for converting the measurement coordinate system used for measurement in the acquisition step using a coordinate conversion parameter and shape data in the reference coordinate system A calculation step, the evaluation value is a change amount of the optical performance, a coordinate conversion parameter determination step for determining a coordinate conversion parameter value at which the evaluation value is maximum or minimum, and the determined coordinate conversion It is possible to provide a shape evaluation method characterized by including a second coordinate conversion step of performing coordinate conversion using a parameter value.

  Further, according to a preferred aspect of the present invention, in the shape data acquisition step, each shape data is acquired for two or more surfaces of the optical element, and in the coordinate conversion parameter determination step, the coordinate conversion parameter is determined for each shape data. Final shape data acquisition step for determining the value, performing coordinate conversion using the determined coordinate conversion parameter value, and acquiring the final shape data, and the reference for determining the reference axis of each shape data from the final shape measurement data An axis determining step.

  According to a preferred aspect of the present invention, in the shape data acquisition step, the shape is measured for two or more surfaces in the optical element, each shape data in the same measurement coordinate system is acquired, and each shape data and For each of all the shape data, a coordinate conversion step, an evaluation value calculation step, a coordinate conversion parameter determination step, a coordinate conversion step, a final shape data acquisition step, and a reference axis determination step are performed, and the reference axis of all the shape data It is desirable to calculate

  Further, according to a preferred aspect of the present invention, each of the coefficient calculation step for calculating a coefficient indicating the degree of influence on the change amount of the optical performance according to the coordinate position of the target shape on the reference coordinate system, and each after the coordinate conversion It is preferable to further include a deviation calculating step for calculating a deviation from the target shape of the shape measurement data string, and in the evaluation value calculating step, the deviation and a coefficient corresponding to the coordinate position of the target shape are used.

  According to a preferred aspect of the present invention, a coefficient calculating step for calculating a coefficient indicating the degree of influence on the amount of change in optical performance according to the distance from the reference axis of the target shape on the reference coordinate system, and coordinate conversion A deviation calculating step of calculating a deviation from the target shape of each subsequent shape measurement data string, and using a coefficient corresponding to the deviation and the distance from the reference axis of the target shape in the evaluation value calculating step Is desirable.

  Further, according to a preferred aspect of the present invention, the determination step for calculating the optical element based on the final shape obtained in the final shape data acquisition step and determining the optical element is performed. It is desirable to have

  In the shape evaluation method according to the present invention, in the evaluation value calculation step, an evaluation value is obtained for a predetermined evaluation parameter from shape data in the reference coordinate system. The evaluation value is the amount of change in optical performance. For this reason, the shape evaluation corresponding to the optical performance of the optical element can be performed. As a result, it is possible to provide a shape evaluation method capable of performing an evaluation corresponding to the optical performance of the object to be measured.

  Embodiments of a shape evaluation method according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this Example.

  A shape evaluation method according to Embodiment 1 of the present invention will be described. FIG. 1 is a flowchart showing the measurement procedure of this embodiment. The object to be measured is a double-sided aspheric lens having two surfaces. The measured surface is one of the two surfaces of the double-sided aspheric lens.

In step S101, the surface to be measured is measured with a three-dimensional measuring machine, and a shape measurement data string (Xai, Yai, Zai) is acquired.
However,
Xai is the X coordinate of the i-th acquired measurement point,
Yai is the Y coordinate of the i-th acquired measurement point,
Zai is the Z coordinate of the i-th acquired measurement point. Step S101 corresponds to a shape data acquisition step.

In step S102, the measurement coordinate system including the shape measurement data string (Xai, Yai, Zai) is subjected to coordinate conversion using the coordinate conversion parameter P with respect to the reference coordinate system including the target shape. Thereby, the shape measurement data string (Xbi, Ybi, Zbi) in the reference coordinate system is obtained. Step S102 corresponds to the first coordinate conversion step. The target shape is, for example, a design aspheric shape. As the target shape, for example, the following (1) and (2) can be used (see Japanese Patent No. 2885422 or Japanese Patent No. 3322210).
(1) Aspherical surface shape whose aspherical coefficient is determined by convergence calculation so that the deviation from the shape measurement data string is minimized (2) Designed aspherical surface by convergence calculation so that the deviation from the shape measurement data string is minimized A shape with only the paraxial curvature of the shape changed

  The optical axis in designing the target shape is made to coincide with the Z axis of the reference coordinate system (hereinafter referred to as “reference axis” as appropriate). In this embodiment, the target shape is an aspherical surface. For this reason, the design optical axis of the target shape is equal to the rotational symmetry axis of the shape. Also, the Z coordinate (hereinafter referred to as “shape apex” as appropriate) on the optical axis of the target shape is made to coincide with the origin (0, 0, 0) of the reference coordinate system.

  The coordinate conversion parameter P includes parallel movement of X, Y, and Z, rotation with the X axis as a rotation axis (hereinafter referred to as “A rotation” as appropriate), and rotation with the Y axis as a rotation axis (hereinafter referred to as “ B rotation ”) and rotation with the Z axis as the rotation axis (hereinafter referred to as“ C rotation ”as appropriate). The surface to be measured is a rotationally symmetric aspherical surface. For this reason, the coordinate transformation parameter P is a variable of X, Y, Z translation and A, B rotation, and C rotation is zero.

  In step S103, an evaluation value (MTF) is obtained using the shape measurement data string (Xbi, Ybi, Zbi) in the reference coordinate system. FIG. 2 shows a flowchart for obtaining the evaluation value. Step S103 corresponds to an evaluation value calculation step. This will be described below.

  In step S201 of FIG. 2, an optical performance simulation of the entire optical system including the surface to be measured is performed using known optical simulation (abbreviated as “SIM” in the drawing) software. Thus, an MTF (Modulation Transfer Function, hereinafter referred to as “design MTF”) in an ideal state, that is, a state in which the manufacturing error of the entire imaging optical system is zero is obtained.

  In step S202, the shape measurement data string (Xbi, Ybi, Zbi) in the reference coordinate system is approximated by a Zernike polynomial to obtain an approximate surface shape in the reference coordinate system.

  In step S203, the approximated surface shape is input to the optical simulation software by making the reference axis coincide with the designed optical axis. In step S204, an optical simulation of the entire optical system is performed to obtain an MTF using a surface shape measurement value (hereinafter, referred to as “measurement MTF” as appropriate).

In step S205,
Evaluation value = design MTF−measurement MTF
The evaluation value is obtained from the formula of In this case, the evaluation value substantially indicates the amount of decrease in MTF due to surface shape manufacturing errors. Next, returning to FIG.

  In step S104, a coordinate conversion parameter P1 that minimizes the evaluation value is obtained by convergence calculation. As a convergence calculation method, a known method such as Newton's method is used. In step S105, it is determined whether or not the evaluation value is minimum. When the determination result is false (No), the process returns to step S102. When the determination result is true (Yes), the process proceeds to step S106. Steps S104 and S105 correspond to a coordinate conversion parameter determination step.

  In step S106, the shape measurement data string (Xai, Yai, Zai) is coordinate-transformed using the coordinate transformation parameter P1 that minimizes the evaluation value. Then, a shape measurement data string (Xci, Yci, Zci) that minimizes the evaluation value is obtained. Step S106 corresponds to a second coordinate conversion step and a final shape data acquisition step.

  In step S107, a measurement value is calculated using the shape measurement data string (Xci, Yci, Zci). The measured values are, for example, the RMS of the deviation between the target shape and the design shape, the PV of the deviation between the target shape and the design shape, the MTF reduction amount, that is, the evaluation value described above. In addition, it is possible to divide the conditions such as obtaining the RMS of the deviation between the target shape and the design shape according to the distance from the reference axis.

  Based on the measurement value calculated in step S108, it is determined whether or not the optical element satisfies the component standard value. When the optical element does not satisfy the component standard value, sorting such as reworking or discarding the optical element can be performed.

  FIG. 3 shows coordinate conversion in the evaluation of the above-described embodiment. In FIG. 3A, the target shape is determined by the reference coordinate system CRDs. On the other hand, as shown in FIG. 3B, the shape measurement data string is defined by the measurement coordinate system CRDm. Then, as shown in FIG. 3C, a shape measurement data string (Xbi, Ybi, Zbi) indicated by a dotted line in the drawing is obtained in step S102. Then, through steps S103, S104, S105, and S106, the shape measurement data string (Xci, Yci, Zci) indicated by the solid line in (c) can be obtained.

  According to the present embodiment, the measured value of the surface of the optical element can be calculated using the optical performance called MTF as an evaluation index. As described above, in the related art, the measurement value is calculated using the RMS of the deviation between the shape measurement data string and the design shape as an evaluation index. For this reason, the optical element may not be appropriately evaluated according to the optical performance. On the other hand, in this embodiment, the object to be measured can always be appropriately evaluated according to the optical performance.

  Each configuration of the present embodiment can be variously modified and changed. For example, in this embodiment, the object to be measured is an aspherical surface. However, the shape is not limited to this, and the shape can be evaluated in the same manner for a flat surface, a spherical surface, and a free-form surface. However, when the object to be measured is a plane, the coordinate conversion parameter P is a variable of Z translation and A rotation and B rotation, and X and Y translation and C rotation are zero. Further, when the surface to be measured is a spherical surface, the coordinate transformation parameter P is a variable of parallel movement of X, Y, and Z, and A rotation, B rotation, and C rotation are 0 respectively. Further, when the surface to be measured is a free-form surface, the coordinate transformation parameter P is a variable of X, Y, Z translation, A rotation, B rotation, and C rotation.

  The evaluation value is MTF, but the evaluation value may be another example as long as it is a parameter indicating optical performance. Examples of parameters indicating optical performance include radial MTF, tangential MTF, spherical aberration, coma, astigmatism, Petzval aberration, distortion aberration, axial chromatic aberration, and off-axis chromatic aberration.

  Further, the evaluation value may be a combination of parameters indicating the optical performance with weight. Furthermore, a weight may be attached according to the distance from the designed optical axis. For example, (MTF × 1 on the designed optical axis) + (MTF × 0.5 at the position of the image height of 50% of the maximum image height) + (MTF × at the position of the image height of 80% of the maximum image height) You may give a weight like 0.2). In addition, instead of the optical performance of the optical system including the surface to be measured, the optical performance of only the surface to be measured may be used as the evaluation value.

  A shape evaluation method according to Embodiment 2 of the present invention will be described. In the present embodiment, the evaluation value calculation method in step S103 described above is different from that in the first embodiment. Other procedures are the same as those in the first embodiment, and redundant description is omitted. FIG. 4 is a flowchart for obtaining the evaluation value of this embodiment.

  In step S301, a coefficient K used for calculating the evaluation value is determined in advance. The coefficient K is a function whose value changes according to the designed distance from the optical axis. Hereinafter, for the sake of simplicity, description will be made simply as “coefficient K”. Hereinafter, a procedure for determining the coefficient K by optical simulation will be described. An optical performance simulation of the imaging optical system including the surface to be measured is performed using known optical simulation (SIM) software. Thus, the MTF in the ideal state, that is, the state where the manufacturing error of the entire imaging optical system is zero (hereinafter, referred to as “design MTF” as appropriate) is obtained.

  Shape data having a shape error on the surface to be measured is created by other known software. As the shape data having a shape error, a plurality of shape data having different shape error amounts according to the distance from the designed optical axis are created. The shape data having a shape error is represented by, for example, a Zernike polynomial.

  Shape data having each shape error is input to optical simulation software. Next, the obtained MTF is compared with the design MTF. Then, the amount of decrease in MTF is obtained.

  Thereby, the relationship between the shape error amount corresponding to the distance from the designed optical axis and the MTF reduction amount is experimentally obtained. From this result, a coefficient K corresponding to the distance from the designed optical axis, which shows the influence of the shape error on the MTF reduction amount, is determined.

In steps S302 and S303, for the shape measurement data string in the reference coordinate system for obtaining the evaluation value using the coefficient K, the distance L (= (X ² + Y ² ) ^1/2 ) of each data from the reference axis, A Z-direction deviation Zd between the shape measurement data string and the target shape in the reference coordinate system is obtained. As described above, the reference axis and the design optical axis coincide. For this reason, the Z-direction deviation Zd is multiplied by the coefficient K in accordance with the distance L from the reference axis of each data to obtain the weighted Z-direction deviation KZd. In step S304, the RMS of the weighted Z-direction deviation KZd of each data is obtained. The calculated RMS is used as an evaluation value.

  In this embodiment, complicated software processing such as optical simulation is not performed when calculating the evaluation value. This facilitates convergence calculation. As a result, in addition to the effect of the first embodiment, there is an effect that the processing time can be shortened.

(Modification)
In the case of this embodiment, the object to be measured is a rotationally symmetric aspherical surface. For this reason, the evaluation value is obtained using a coefficient corresponding to the distance from the designed optical axis. Here, when the object to be measured is a free-form surface, the evaluation value can be obtained using a coefficient K indicating the degree of influence on the change amount of the optical performance according to the reference coordinate position (X, Y).

  Next, a shape evaluation method according to Example 3 of the present invention will be described. In this embodiment, the object to be measured is a double-sided aspheric lens. The measured surfaces are the front and back surfaces of a double-sided aspheric lens. As shown in FIG. 5A, in the first reference coordinate system CRD1, a first target shape that is a design value of the surface is defined. Further, as shown in FIG. 5B, in the second reference coordinate system CRD2, a second target shape that is a design value of the back surface is defined.

  As shown in FIG. 5C, the shape measurement data string (Xa1i, Ya1i, Za1i) and the shape measurement data string (Xa2i, Ya2i, Za2i) of the back surface of the aspherical lens in the same measurement coordinate system are acquired. To do. Hereinafter, this same measurement coordinate system is simply referred to as a measurement coordinate system CRDm. For obtaining the shape measurement data string, for example, a measurement method disclosed in Japanese Patent Application Laid-Open No. 2002-71344 and Japanese Patent No. 3486546 can be used.

  The same as step S102, step S103, step S104, and step S105 of the first embodiment for the front surface shape measurement data string (Xa1i, Ya1i, Za1i) and the back surface shape measurement data string (Xa2i, Ya2i, Za2i), respectively. Process.

  Then, the shape measurement data string (Xa1i, Ya1i, Za1i) is coordinate-transformed using the coordinate transformation parameter P1 that minimizes the surface evaluation value. Thereby, the shape measurement data string (Xc1i, Yc1i, Zc1i) in the first reference coordinate system CRD1 that minimizes the evaluation value can be obtained ((a) in FIG. 6). Similarly, the shape measurement data string (Xc2i, Yc2i, Zc2i) in the second reference coordinate system CRD2 can be obtained for the back surface using the coordinate conversion parameter P2 ((b) of FIG. 6).

  Next, as the measurement values, the inclination of the reference axis on the back surface with respect to the front surface and the position of the apex of the shape are obtained. In the first reference coordinate system CRD1, the optical axis in designing the target shape of the surface is the Z axis, and the vertex of the shape is the origin (0, 0, 0) of the reference coordinate system CRDm. Here, coordinate transformation is performed to restore the coordinate transformation by the coordinate transformation parameter P1 again. For this purpose, a coordinate conversion parameter P1a to be restored is obtained. Then, the coordinate transformation is performed on the reference axis and the apex of the shape using the coordinate transformation parameter P1a. Thereby, the inclination (A1, B1) of the reference axis AX1 of the surface and the coordinates (Xd1, Yd1, Zd1) of the shape vertex in the measurement coordinate system CRDm are obtained ((a) of FIG. 7). However, A1 is the amount of A rotation and B1 is the amount of B rotation. Similarly, with respect to the back surface, the inclination (A2, B2) of the reference axis AX2 of the back surface and the coordinates (Xd2, Yd2, Zd2) of the shape vertex (Xd2, Yd2, Zd2) of the back surface in the measurement coordinate system CRDm are obtained using the coordinate conversion parameter P2a ( b)). Note that the coordinate transformations shown in FIGS. 7A and 7B correspond to the final shape data acquisition step and the reference axis determination step.

  Next, a coordinate conversion parameter Pm1 is obtained in which the slope (A1, B1) of the surface reference axis AX1 is (0, 0) and the coordinates of the shape vertex (Xd1, Yd1, Zd1) are (0, 0, 0). . Using the coordinate conversion parameter Pm1, the inclination (A2, B2) of the reference axis AX2 on the back surface and the coordinates (Xd2, Yd2, Zd2) of the apex of the shape are converted. Then, the inclination (Am2, Bm2) of the reference axis AX2 on the back surface of the front surface reference and the coordinates (Xm2, Ym2, Zm2) of the apex of the shape are obtained ((c) in FIG. 7).

In the above calculation,
{Vertex of target shape} ≈ {Intersection of Z-axis and shape measurement data string (Xc1i, Yc1i, Zc1i) in the first reference coordinate system}
And approximate. However, as another approximation, instead of the vertex of the shape of the target shape, {intersection of Z axis and shape measurement data string (Xc1i, Yc1i, Zc1i) in the first reference coordinate system} may be used or calculated. good.

  According to the present embodiment, in addition to the effects of the first embodiment, it is possible to evaluate the position of each surface on the basis of one surface of an optical element composed of two or more surfaces using the optical performance called MTF as an evaluation index. it can.

(Modification)
In this embodiment, the object to be measured is an aspheric lens, and the surface to be measured is the front and back surfaces of the aspheric lens. However, the present invention is not limited to this, and the present invention can also be applied to an optical element such as a prism having three or more surfaces. Needless to say, the evaluation value may not be the MTF, but may be the evaluation value shown in the modification of the first embodiment or the second embodiment.

  A shape evaluation method according to Example 4 of the present invention will be described. The object to be measured is a double-sided aspheric lens. The measured surfaces are the front and back surfaces of a double-sided aspheric lens. This embodiment is different from the third embodiment in that a predetermined calculation is performed for the shape of the entire lens including the front and back surfaces in addition to the calculation regarding the front and back surfaces of the double-sided aspheric lens. The same parts as those in the first embodiment, the second embodiment, and the third embodiment are denoted by the same reference numerals, and redundant description is omitted.

  First, according to the same procedure as in the third embodiment, as shown in FIGS. 8A and 8B and FIG. 9A and FIG. 9B, respectively, the reference axis is set using the coordinate conversion parameters P1a and P2a. Transform the vertex of the shape. Thereby, the inclination (A1, B1) of the reference axis AX1 of the surface and the coordinates (Xd1, Yd1, Zd1) of the shape vertex in the measurement coordinate system CRDm are obtained ((a) of FIG. 10). Similarly, for the back surface, the inclination (A2, B2) of the reference axis AX2 of the back surface and the coordinates (Xd2, Yd2, Zd2) of the shape vertex in the measurement coordinate system CRDm are obtained ((b) of FIG. 10).

  In this embodiment, the target shape is the design shape of the aspheric lens, that is, the shape of the entire lens including the front surface and the back surface. The optical axis in the design of the target shape is made to coincide with the Z axis of the reference axis coordinate system (hereinafter referred to as “lens reference axis AX3” as appropriate). Further, the Z coordinate (hereinafter, the top of the lens shape) of the surface on the optical axis in the design of the target shape is made to coincide with the origin (0, 0, 0) of the reference coordinate system.

  With respect to the third reference coordinate system CRD3 (FIG. 8C) including the target shape, the front surface shape measurement data string (Xa1i, Ya1i, Za1i) and the back surface shape measurement data string (Xa2i, Ya2i, Za2i) Transform the measurement coordinate system including Thus, the surface shape measurement data string (Xe1i, Ye1i, Ze1i) and the back surface shape measurement data string (e2i, Ye2i, Ze2i) in the third reference coordinate system CRD3 are obtained ((c) in FIG. 9).

  Next, an evaluation value is obtained using the surface shape measurement data string (Xe1i, Ye1i, Ze1i) and the back surface shape measurement data string (Xe2i, Ye2i, Ze2i) in the third reference coordinate system CRD3. The evaluation value is obtained according to the following procedure.

  An optical performance simulation of the optical system including the object to be measured is performed by using known optical simulation software, and an MTF in an ideal state, that is, a manufacturing error of the entire imaging optical system is zero (hereinafter referred to as “design MTF” as appropriate). .)

  The surface shape measurement data string (Xe1i, Ye1i, Ze1i) in the third reference coordinate system CRD3 is approximated by a Zernike polynomial. Thereby, the approximate surface shape of the surface in the third reference coordinate system CRD3 is acquired. Similarly, the approximate surface shape of the back surface in the third reference coordinate system CRD3 is acquired.

  The lens reference axis AX3 is made to coincide with the designed optical axis (in the case of a rotationally symmetric aspherical surface, it coincides with the rotationally symmetric axis). In this state, the approximate surface shape of the front surface and the approximate surface shape of the back surface are input to the optical simulation software. Next, an optical simulation of the optical system is performed, and an MTF using the actual measured value of the lens shape (hereinafter referred to as “measured MTF” as appropriate) is obtained.

And
Evaluation value = design MTF−measurement MTF
The evaluation value is obtained from the formula of Up to this point, the process corresponds to step 103 in the first embodiment.

  Next, a coordinate conversion parameter P3 that minimizes the evaluation value is obtained by convergence calculation. Next, using the coordinate conversion parameter P3, the surface shape measurement data string (Xa1i, Ya1i, Za1i) and the back surface shape measurement data string (Xa2i, Ya2i, Za2i) are coordinate-converted ((c) in FIG. 9). . Then, the front surface shape measurement data string (Xf1i, Yf1i, Zf1i) and the back surface shape measurement data string (Xf2i, Yf2i, Zf2i) that minimize the evaluation value are obtained.

  Next, as the measurement values, the inclination of the surface reference axis AX1 and the inclination of the reference axis AX2 of the front surface with respect to the lens reference axis AX3, the vertex of the surface shape with respect to the top of the lens shape, and the shape of the back surface Find the vertex position. In the first reference coordinate system CRD1, the reference axis of the surface shape measurement data string (Xc1i, Yc1i, Zc1i) is the Z axis, and the vertex of the shape is the origin of the reference coordinate system. Here, the coordinate transformation is performed again to restore the coordinate transformation based on the coordinate transformation parameter P1. For this reason, the coordinate conversion parameter P1a is obtained. Then, the coordinate transformation is performed on the reference axis and the apex of the shape using the coordinate transformation parameter P1a. Thereby, the inclination (A1, B1) of the reference axis AX1 of the surface and the coordinates (Xd1, Yd1, Zd1) of the shape vertex in the measurement coordinate system CRDm are obtained ((a) of FIG. 10). Similarly, with respect to the back surface, the inclination (A2, B2) of the reference axis AX2 of the back surface and the coordinates (Xd2, Yd2, Zd2) of the shape vertex (Xd2, Yd2, Zd2) of the back surface in the measurement coordinate system CRDm are obtained by the coordinate conversion parameter P2a ((b) of FIG. )).

  In the third reference coordinate system CRD3, the lens reference axis is the Z axis, and the vertex of the lens shape is the origin of the reference coordinate system. Here, the coordinate transformation by the coordinate transformation parameter P3 is restored again. For this reason, the coordinate conversion parameter P3a is obtained. Then, coordinate conversion is performed between the lens reference axis and the vertex of the lens shape using the coordinate conversion parameter P3a. Thereby, the inclination (A3, B3) of the lens reference axis AX3 and the coordinates (Xd3, Yd3, Zd3) of the apex of the lens shape in the measurement coordinate system CRDm are obtained ((c) in FIG. 10).

  Next, a coordinate conversion parameter Pm3 is obtained in which the inclination (A3, B3) of the lens reference axis AX3 is (0, 0) and the coordinates (Xd3, Yd3, Zd3) of the lens shape vertex are (0, 0, 0). . Using the coordinate transformation parameter Pm3, the inclination (A1, B1) of the surface reference axis AX1 and the coordinates of the shape vertex (Xd1, Yd1, Zd1), the inclination (A2, B2) of the reference axis AX2 of the back surface, and the shape vertex The coordinates (Xd2, Yd2, Zd2) are converted. Accordingly, the inclination (Am1, Bm1) of the surface reference axis AX1 and the coordinates of the shape vertex (Xm1, Ym1, Zm1), the inclination (Am2, Bm2) of the reference axis AX2 of the back surface, and the shape vertex of the lens reference. The coordinates (Xm2, Ym2, Zm2) can be obtained ((d) in FIG. 10).

  According to the present embodiment, in addition to the effects of the third embodiment, the position of each surface is evaluated based on the reference axis AX3 of the entire optical element composed of two or more surfaces, using MTF optical performance as an evaluation index. Can do.

(Modification)
In this embodiment, the object to be measured is an aspheric lens, and the surface to be measured is the front and back surfaces of the aspheric lens. The present invention is not limited to this, and the present invention can also be applied to an optical element such as a prism having three or more surfaces. Further, the evaluation value is not limited to the MTF, and may be the modified example of the first embodiment or the one described in the second embodiment. In the simulation, shape measurement data is used, but the present invention is not limited to this. For example, if the thickness (center thickness) of the optical element and the refractive index of the material used for the optical element can be measured, a simulation may be performed using these measurement data.

  As described above, the shape evaluation method according to the present invention is particularly useful for evaluation based on the optical performance of the surface shape of the optical element.

It is a flowchart which shows the evaluation procedure of Example 1 of this invention. 10 is another flowchart showing the evaluation procedure of Example 1. FIG. 6 is a diagram illustrating coordinate conversion in the evaluation of Example 1. 10 is a flowchart showing an evaluation procedure of Example 2. 10 is a diagram illustrating coordinate conversion in evaluation of Example 3. FIG. It is another figure which shows the coordinate transformation in evaluation of Example 3. FIG. It is another figure which shows the coordinate transformation in evaluation of Example 3. FIG. It is a figure which shows the coordinate transformation in evaluation of Example 4. FIG. It is another figure which shows the coordinate transformation in evaluation of Example 4. FIG. It is another figure which shows the coordinate transformation in evaluation of Example 4. FIG.

Explanation of symbols

CDRs reference coordinate system CDRm measurement coordinate system CDR1 first reference coordinate system CDR2 second reference coordinate system CDR3 third reference coordinate system P1, P2, P3 coordinate transformation parameters AX1, AX2, AX3 reference axes P1a, P2a, P3a coordinates Conversion parameter

Claims (6)

A shape data acquisition step of measuring the shape of the optical element to acquire shape data;
A first coordinate conversion step of converting the measurement coordinate system used in the measurement in the shape data acquisition step with respect to a predetermined reference coordinate system using a coordinate conversion parameter;
An evaluation value calculation step for obtaining an evaluation value for a predetermined evaluation parameter from the shape data in the reference coordinate system,
The evaluation value is a change amount of the optical performance,
Furthermore, a coordinate conversion parameter determination step for determining a value of the coordinate conversion parameter that maximizes or minimizes the evaluation value;
And a second coordinate conversion step for performing coordinate conversion using the determined value of the coordinate conversion parameter. In the shape data acquisition step, each shape data is acquired for two or more surfaces of the optical element,
In the coordinate transformation parameter determination step, determine the value of the coordinate transformation parameter for each shape data,
A final shape data acquisition step of performing coordinate conversion using the determined value of the coordinate conversion parameter and acquiring final shape data;
The shape evaluation method according to claim 1, further comprising a reference axis determination step of determining a reference axis of each shape data from the final shape measurement data. In the shape data acquisition step, the shape is measured for two or more surfaces of the optical element, and each shape data in the same measurement coordinate system is acquired,
For each of the shape data and all of the shape data, the coordinate conversion step, the evaluation value calculation step, the coordinate conversion parameter determination step, the coordinate conversion step, the final shape data acquisition step, and the reference axis determination step And
The shape evaluation method according to claim 2, wherein a reference axis of all the shape data is calculated. A coefficient calculating step for calculating a coefficient indicating the degree of influence on the amount of change in optical performance according to the coordinate position of the target shape on the reference coordinate system;
A deviation calculating step of calculating a deviation from the target shape of each shape measurement data string after coordinate conversion,
The shape evaluation method according to any one of claims 1 to 3, wherein in the evaluation value calculation step, the deviation and a coefficient corresponding to a coordinate position of the target shape are used. A coefficient calculating step of calculating a coefficient indicating the degree of influence on the amount of change in optical performance according to the distance from the reference axis of the target shape on the reference coordinate system;
A deviation calculating step of calculating a deviation from the target shape of each shape measurement data string after coordinate conversion,
The shape evaluation method according to claim 1, wherein in the evaluation value calculation step, a coefficient corresponding to the deviation and a distance from a reference axis of the target shape is used.   Further, the method includes a determination step of calculating a measurement value that is an index of evaluation of the optical element based on the final shape obtained in the final shape data acquisition step and performing a determination regarding the optical element. The shape evaluation method as described in any one of Claims 1-5.

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