CN101460295B

CN101460295B - Optical system manufacturing method

Info

Publication number: CN101460295B
Application number: CN2007800208192A
Authority: CN
Inventors: 增渊友一; 今冈雅之; 泷谷俊哉; 林宏太郎; 石原淳; 松本安弘; 奥村佳弘
Original assignee: Konica Minolta Opto Inc
Current assignee: Konica Minolta Opto Inc
Priority date: 2006-06-05
Filing date: 2007-05-30
Publication date: 2012-12-05
Anticipated expiration: 2027-05-30
Also published as: KR20080113298A; CN101460295A; WO2007142100A1; JP4111251B2; KR101034431B1; JPWO2007142100A1

Abstract

A projection optical system (PS) manufacturing method evaluates an optical performance of an entire system from approximate planes of all the optical planes in the projection optical system (PS) and changes at least one of the approximate planes of all the optical planes (such as a reduction side lens plane (S(L2s)) of a second lens L2 of an initial article referred to as 'a change approximate plane') so as to obtain a change amount of tbe change approximate plane when optimal optical performance is obtained as the entire system. According to the change amount, a correction treatment amount for the cavity plane of a metal mold corresponding to the change approximate plane is obtained to perform correction treatment, thereby manufacturing a new cavity plane.

Description

Method for manufacturing optical system

Technical Field

The present invention relates to a method for manufacturing an optical system mounted on an image projection apparatus (projector) or the like.

Background

In recent years, optical elements molded from a resin such as plastic have been used in optical systems such as projection optical systems and laser scanning optical systems. This is because such a resin optical element is inexpensive and lightweight as compared with an optical element made of a glass material, and has excellent mass productivity.

The resin optical element is manufactured by a molding method such as injection molding or injection compression molding using a mold (mold member). Therefore, the resin optical element has an advantage that a curved surface (optical surface) having an aspherical shape or a free-form surface shape can be easily formed, as compared with a glass optical element.

However, when an optical element having an optical surface with a complicated shape such as an aspherical shape or a free-form surface shape is molded by a mold, surface defects are likely to occur due to uneven cooling and shrinkage of the optical surface. Therefore, generally, the surface shape of the defect is measured, and the mold is corrected based on the measurement result (patent document 1).

Patent document 2 exemplifies a surface shape measurement. The method of patent document 2 uses data of 3-dimensional measurement of an optical surface to approximate the optical surface to a polynomial of an aspherical surface, and introduces the polynomial approximation surface into an optical system to evaluate the optical performance (aberration change) of an optical element. Then, by evaluating the optical performance, an optical surface (optical surface having the most suitable shape) required to exhibit the desired optical performance can be found, and the optical surface shape can be optimized by performing the correction processing on the mold.

Patent document 1: japanese patent laid-open No. Hei 7-60857

Patent document 2: japanese patent laid-open publication No. 2004-361274

Disclosure of Invention

However, the evaluation method of patent document 2 approximates the error between the measurement data (3-dimensional measurement data) of the optical surface and the predetermined design value data to a polynomial expression (error polynomial expression) as the entire surface. Therefore, when a moire (a moire portion) is present locally on the measured optical surface, if a high-order approximation formula is used to properly express the moire portion, a high-order moire is generated at a position other than the moire (a non-moire portion). On the other hand, if a lower order approximation formula is used in order to appropriately express the non-corrugated portion, the corrugated portion cannot be appropriately expressed.

In the method of molding an optical element of patent document 1, in order to appropriately correct the waviness, the cavity surface of the mold corresponding to the optical surface is subjected to correction processing, and the optical element is reshaped by offsetting an error between the measurement data of the optical surface and the predetermined design value data.

However, in this molding method, when the optical system includes a plurality of optical elements, it is necessary to correct the shape of the mold of each optical element based on the design value. Therefore, the number of times of mold correction is at least as large as the number of optical surfaces of the optical element, which makes it extremely time-consuming to manufacture the optical system.

The present invention has been made in view of the above circumstances. It is another object of the present invention to provide a method for efficiently and inexpensively manufacturing an optical system (more specifically, an optical system including a plurality of optical elements) in a short time.

The present invention is a method for manufacturing an optical system having a plurality of optical surfaces by molding using a mold member. The manufacturing method of the optical system comprises the following steps: setting approximate surfaces of all optical surfaces of the optical system including an optical surface formed by initial molding; a first optical performance evaluation step of evaluating the optical performance of the entire system from the approximate surfaces of all the optical surfaces in the optical system; a change amount calculation step of calculating a change amount of the change approximation surface when the entire system exhibits the optimum optical performance, wherein at least 1 of the approximation surfaces of all the optical surfaces, which is formed by the mold member, is used as a change approximation surface, and at least 1 of the approximation surfaces of all the optical surfaces, which is formed by the mold member, is not used as the change approximation surface, but is used as a non-change approximation surface; a first correction processing step of obtaining a correction processing amount of a cavity surface of the mold member corresponding to the variation approximation surface based on the variation amount, and performing correction processing to produce a new cavity surface; a first molding step of molding an optical element using the correction die member processed in the first correction processing step; and a second molding step of molding the optical element by using a mold member other than the correction mold member.

With this manufacturing method, it is not necessary to perform the correction processing for all cavity surfaces of all the mold members. That is, in this manufacturing method, for example, a desired optical surface can be used as a variation approximation surface, and the correction processing can be performed preferentially on the corresponding cavity surface. Therefore, the number of times of correction of the mold member is small, and the optical system can be manufactured efficiently and inexpensively in a short time.

In addition, the first forming step includes: setting an approximate surface based on a measurement result of a surface shape of an optical surface corresponding to the new cavity surface in an optical element molded by a mold member having the new cavity surface; a second correction processing step of performing correction processing on the new cavity surface so as to cancel out a shape error between an approximate surface of the optical surface corresponding to the new cavity surface and the new cavity surface; and a step of molding the optical element by using the correction die member processed in the second correction processing step.

The second correction processing is performed only on the facet (new facet) on which the correction processing has been performed. Therefore, the second correction processing reduces the burden as compared with the case where correction processing is performed on all facets. Further, by performing correction processing for canceling out the shape error with high accuracy, the optical performance of the optical system can be made within an allowable range. Therefore, by the method for manufacturing an optical system including the second correction process with a small load, an optical system exhibiting high optical performance can be easily manufactured.

However, in the step of setting the approximate surface, it is preferable that the approximate surface be set based on the shape of the measurement surface of the optical surface formed by the initial forming, for the optical surface formed by the forming using the mold member.

In the step of setting the approximate surface, when the optical surface is a polished surface, it is preferable to set design data of the optical surface as the approximate surface in the polished surface.

In addition, it is preferable that the approximate surface of each optical surface in the optical system and the approximate surface having the largest difference in design data of the optical surface corresponding to each approximate surface be a change approximate surface.

In addition, it is preferable that the approximate surface of each optical surface in the optical system and the approximate surface of the optical surface closest to the optical surface having the largest difference in design data between the optical surfaces corresponding to the approximate surfaces are changed as the approximate surface.

Further, it is preferable that the variation approximation plane is at most 2 planes.

The step of setting the approximate plane preferably includes a space division setting step of dividing a plane perpendicular to the predetermined reference axis of the optical surface of the optical element into a plurality of parts and setting a plurality of spaces based on the divided planes, and the approximate expression in which the boundaries between the spaces are continuous is used.

In this manufacturing method, it is preferable that the approximate expression is a function of at least 3 times or more. In addition, continuity means that the 2 nd derivative of the approximation formula is continuous at the boundary between the divided spaces. Moreover, a spline function may be cited as an example of the approximate expression.

Further, the optical system preferably includes at least 1 lens and at least 1 mirror as the elements molded by the mold member, and at least the lens surface is preferably used as the surface of the variation approximation surface.

Further, it is preferable that at least 1 of the lens and the mirror included in the optical system is formed by glass molding.

In addition, the optical system preferably includes a non-rotationally symmetrical surface, and the approximate surface corresponding to the non-rotationally symmetrical surface in the variation amount calculating step is preferably a variation approximate surface.

The optical system preferably includes at least 1 lens and at least 1 mirror as elements molded by the mold member, and at least 1 lens surface is a non-rotationally symmetrical surface, and the non-rotationally symmetrical surface is preferably a change approximation surface in the change amount calculating step.

In addition, when at least 1 lens and at least 1 mirror are included in the optical system as the optical element (particularly, when at least 1 of the lens and the mirror included in the optical system is formed by glass molding), it is preferable to use a lens surface of at least 1 surface as the change approximation surface.

According to the method for manufacturing an optical system of the present invention, the cavity surface corresponding to the optical surface which is likely to affect the optical performance can be preferentially corrected. Therefore, the number of times of correction of the mold member is small, and the optical system can be manufactured efficiently and inexpensively in a short time.

Drawings

Fig. 1 is a flowchart showing steps of a method for manufacturing a projection optical system.

Fig. 2 is a plan view showing a measurement state of a lens surface of the second lens.

Fig. 3 is a plan view showing a lens surface division space.

Fig. 4 is a dot diagram of a projection optical system containing only an original.

FIG. 5 is a dot diagram of a projection optical system including a reshaped product.

Fig. 6 is a dot array diagram of a projection optical system including glass optical elements and resin optical elements, which are composed of only the original product (but only half of the negative axis side in the Z-axis direction on the screen surface).

Fig. 7 is a dot array diagram showing half of the positive axis side in the Z-axis direction on the screen surface, unlike fig. 6.

FIG. 8 is a dot arrangement diagram of a projection optical system including a glass optical element and a resin optical element and including a reshaped product (except for a negative half in the Z-axis direction on the screen surface).

Fig. 9 is a dot array diagram showing half of the positive axis side in the Z-axis direction on the screen surface, unlike fig. 8.

Fig. 10 is a structural diagram of the image projection apparatus.

Description of the reference symbols

PS projection optical system (optical system)

M1 first mirror (optical element)

L1 first lens (optical element)

M2 second mirror (optical element)

L2 second lens (optical element)

M3 third mirror (optical element)

M4 fourth mirror (optical element)

FM plane mirror (optical element)

SCN screen

PDS image projection device

Design value data of F optical element

f initial cavity surface data of metal mold

G original surface data of original product

D new facet data

Detailed Description

Embodiment mode 1

An embodiment of the present invention will be described below with reference to the drawings.

1. Image projection device

The image projection apparatus PDS shown in fig. 10 includes: a screen SCN, an illumination optical system (not shown), a light modulation element MD for modulating light from the illumination optical system, and a projection optical system PS for guiding light (image light) modulated by the light modulation element MD to the screen SCN. The image projection apparatus PDS is a rear projection type apparatus that obliquely projects light emitted from the light modulation element MD (reduction side) to the rear surface of the screen SCN (enlargement side).

The projection optical system PS includes a first mirror (spherical mirror) M1, a first lens (rotationally asymmetric free-form surface lens) L1, a second mirror (rotationally symmetric aspherical mirror) M2, a second lens (rotationally asymmetric free-form surface lens) L2, a third mirror (rotationally asymmetric free-form surface mirror) M3, a fourth mirror (rotationally asymmetric free-form surface mirror) M4, and a plane mirror FM, which are arranged in this order in the order in which light travels from the light modulator MD to the screen SCN.

A protective glass cover CG is disposed in front of the light modulator MD (on the light emitting surface of the modulated light), and an optical stop ST for blocking part of the light is disposed between the first mirror M1 and the first lens L1. The plane mirror FM is a reflecting mirror that reflects light reflected from the fourth mirror M4 back and guides the reflected light to the screen SCN.

2. Manufacturing process for projection optical system

Here, a method for manufacturing the projection optical system (optical system) PS will be described with reference to the flowchart of fig. 1 (operation steps 1 to 22). Further, since the reflection surface of the plane mirror FM is not a curved surface, a resin molding method advantageous for the subsequent curved surface production is not used, and another production method is used. Further, since the plane mirror FM hardly largely affects the optical performance, the projection optical system PS does not include the plane mirror FM in the subsequent evaluation of the optical performance and the like.

Step 1: optical design procedure for all optical elements

First, 6 (8-sided) optical designs were made from the first mirror M1, the first lens L1, the second mirror M2, the second lens L2, the third mirror M3, and the fourth mirror M4 as optical elements.

Specifically, the reflection surface S (M1) of the first mirror M1, the reduction-side lens surface S (L1S) and the enlargement-side lens surface S (L1e) of the first lens L1, the reflection surface S (M2) of the second mirror M2, the reduction-side lens surface S (L2S) and the enlargement-side lens surface S (L2e) of the second lens L2, the reflection surface S (M3) of the third mirror M3, and the reflection surface S (M4) of the fourth mirror M4 (the surfaces expressed in this way may also be referred to as design optical surfaces) as optical surfaces (S).

However, the designed optical surface is set so that the entire projection optical system PS (the entire system) can exhibit a desired optical performance. In addition, when the polynomial expressing the designed optical surface is "F", the polynomial F corresponding to each optical surface can be listed later. The designed optical surface expressed by the polynomial F may be referred to as "design data".

Design optical surface corresponding to the reflection surface S (M1) of the first mirror M1: f [ S (M1) ]

Design optical surfaces corresponding to the reduction-side lens surface S (L1S) of the first lens L1: f [ S (L1S) ]

Design optical surfaces corresponding to the magnification-side lens surface S (L1e) of the first lens L1: f [ S (L1e) ]

Design optical surface corresponding to the reflection surface S (M2) of the second mirror M2: f [ S (M2) ]

Design optical surfaces corresponding to the reduction-side lens surface S (L2S) of the second lens L2: f [ S (L2S) ]

Design optical surfaces corresponding to the magnification-side lens surface S (L2e) of the second lens L2: f [ S (L2e) ]

Design optical surface corresponding to the reflection surface S (M3) of the third mirror M3: f [ S (M3) ]

Design optical surface corresponding to the reflection surface S (M4) of the fourth mirror M4: f [ S (M4) ]

In addition, the following expression (expression 1) using the local orthogonal coordinate (X, Y, Z) with the surface vertex of each designed optical surface as the origin is given as an example of the polynomial expression expressing the designed optical surface.

Formula 1

Wherein,

x: the amount of displacement from the reference plane in the X direction at the position of the height H (based on the plane vertex)

H: height in the direction perpendicular to the X-axis, i.e.

Co: curvature of surface apex

Epsilon: 2 degree of surface parameter

Ai: aspheric coefficient of order i

Gjk: and the surface coefficients of the free-form surface of the j times of Y and the k times of Z.

Step 2: metal mold design process for all optical elements

Next, a mold (first to eighth molds) is designed based on each optical element. For this purpose, machining Data (digital Control Data) is generated from design Data of all optical surfaces. Wherein the machining tool is a diamond cutter having a circular front end. Therefore, the contact point of the diamond cutter tip on the machined surface changes as the shape of the workpiece in the die changes. Therefore, machining data is generated by calculating machining point coordinates in consideration of the shape of the machining tool.

Further, a cavity surface of the mold (a surface of the mold for molding the optical surface) is plated with nickel containing phosphorus. The facet is then machined with a diamond cutter and the facet is finished by grinding the entire extent of the facet uniformly.

The cavity surface of each of the dies (the first die to the eighth die) may be expressed by a polynomial expression "f". Thus, the polynomial f corresponding to each cavity surface (T) in the following can be listed. The facets expressed by the polynomial f may also be referred to as "initial facet data".

Cavity surface T (M1) of the first metal mold corresponding to reflection surface S (M1) of first mirror M1: f [ S (M1) ]

Cavity surface T (L1S) of the second metal mold corresponding to the reduced-side lens surface S (L1S) of the first lens L1: f [ S (L1S) ]

Cavity surface T (L1e) of the third metal mold corresponding to the magnification-side lens surface S (L1e) of the first lens L1: f [ S (L1e) ]

Cavity surface T (M2) of the fourth metal mold corresponding to the reflection surface S (M2) of the second mirror M2: f [ S (M2) ]

Cavity surface T (L2S) of the fifth metal mold corresponding to reduction-side lens surface S (L2S) of second lens L2: f [ S (L2S) ]

Cavity surface T (L2e) of the sixth metal mold corresponding to the magnification-side lens surface S (L2e) of the second lens L2: f [ S (L2e) ]

Cavity surface T (M3) of the seventh metal mold corresponding to reflection surface S (M3) of third mirror M3: f [ S (M3) ]

Cavity surface T (M4) of the eighth metal mold corresponding to reflection surface S (M4) of fourth mirror M4: f [ S (M4) ]

And step 3: initial shaping process for all optical elements

Then, a resin as an optical element material is injection-molded using the first to eighth molds to produce all the optical elements (the initial optical element may be referred to as an "original product", and the molding may be referred to as "original molding").

However, it is necessary to perform repetitive molding under molding conditions in which the surface accuracy of the optical surface to be molded is not so different. For this purpose, various tests were conducted on molding conditions (parameters) such as a melting temperature (resin temperature) of a material of the optical element, a mold temperature of a mold, an injection speed and an injection pressure at the time of injecting a material of the optical element, and molding conditions having optimum reproducibility were set.

For example, the molding conditions of the second lens L2 are as follows. The second lens L2 produced under the following molding conditions had a thickness (core thickness) of 3.5mm and a maximum effective range EA of 52mm in diameter (see fig. 2 and 3 described later).

Resin temperature: 285 deg.C

Temperature of the die: 135 deg.C

Injection speed: 15mm/s

Injection pressure: 1050kg/cm²

And 4, step 4: surface shape measuring step of all the original products

Next, the shape of the optical surface of all the original products was measured. Further, the apparatus for measuring the surface shape is not limited, and examples thereof include an ultra-high precision three-dimensional measuring machine UA3P manufactured by panasonic electric industry, a surface profiler (Form Talysurf) manufactured by Taylor Hopkinson, and the like.

The measurement state is as shown in fig. 2 (however, fig. 2 measures the reduction-side lens surface S (L2S) of the second lens L2). Fig. 2 is a diagram based on a local right-hand orthogonal coordinate system (X, Y, Z) in which the plane vertex of the lens surface S (L2S) is used as an origin and the normal direction of the optical surface is used as an X axis (reference axis). Specifically, YZ plane (plane formed in Y-axis direction and Z-axis direction) is illustrated.

Then, the measurement method performs line measurement along one direction (Z-axis direction) of the YZ plane. In this measurement method, line measurement was performed at a pitch interval of 0.15mm (measurement interval in the Z-axis direction). The measurement interval in the Y-axis direction is 1.0mm, and the measurement point may be referred to as "measurement point MP".

Further, if the measurement point MP is not present in the periphery of the light transmission range (effective range EA) of the lens surface S (L2S), the accuracy of the approximate surface of the original product described later is lowered. Therefore, the line measurement is performed in a wider range than the effective range EA (for example, a range wider by 0.5mm than the effective ranges EA in the Y-axis direction and the Z-axis direction).

The raw data for measuring the optical surface includes, in addition to the molding variation, the movement amounts in the respective axial directions of the X, Y, and Z axes and the setting errors in the measurement of the axial rotation about the X, Y, and Z axes. Then, the measurement data of the composition of the measurement point MP is calculated in consideration of these setting errors.

And 5: approximate surface setting process for all original products

Next, the approximate surface of the optical surface of all the original products was set using the measurement data. As shown in fig. 3, in order to set the approximate plane, the space division setting step is performed by dividing the YZ plane (a plane perpendicular to the X axis) covering the effective range EA into 25 parts (5 parts in the Y axis direction × 5 parts in the Z axis direction) on average, and setting a plurality of spaces (divided spaces, which are spaces in which the thicknesses of the divided YZ planes (divided planes DA) extend in the X axis direction) based on the divided YZ plane.

Then, the optical surface (original surface) of the original is approximated by a polynomial in consideration of a plurality of divided spaces. As an example of a function suitable for such approximation, a spline function (B-spline function, etc.) may be mentioned. Then, the spline function will be described below. The spline function is defined as follows (in the case of a 5-th-order spline function).

When the node vector in the X direction when the interval is divided into n parts in any X direction is (X0, X0, X0, X0, X0, X0, X1, X2, X3, X4, …, X (n-1), xn, xn, xn, xn, xn, xn), where X is, the basis function of the B-spline is defined as the following formula (formula 2).

Formula 2

{b_{i} (x)}_{i = 0}^{n}

Similarly, when the node vector in the Y direction when the Y direction is divided into m parts is (Y0, Y0, Y0, Y0, Y0, Y0, Y1, Y2, Y3, Y4, …, Y (m-1), ym, ym, ym, ym) the basis function of the B-spline is defined as the following formula (formula 3).

Formula 3

{b_{i} (y)}_{j = 0}^{m}

The surface function f (x, y) of the 5-th-order B-spline function at this time is defined by the linear sum (expression 4) of the spline bases of (n +5) × (m +5) bases of the surface.

Formula 4

However, the basis functions bi, k (x) of the B-spline of degree k are functions expressed by the following formulas (formula 5, formula 6),

formula 5

b_i，0(x)＝1(x_i≤x<_i+1)

Not equal to 0 (the rest)

Formula 6

b_{i, k} (x) = \frac{x - x_{i}}{x_{i + k} - x_{i}} b_{i, k - 1} (x) + \frac{x_{i + k + 1} - x}{x_{i + k + 1} - x_{i + 1}} b_{i + 1, k - 1} (x)

bi, k (x) has a value only under the condition of the following formula (formula 7) except that it is "0".

Formula 7

x_i≤x<x_i+k+1

Further, a spline function G corresponding to the optical surface of each optical element of the original product can be listed later. The approximation plane represented by the spline function G is also referred to as "original plane data".

Approximate surface corresponding to the reflection surface S (M1) of the first mirror M1 of the original product: g [ S (M1) ]

Approximate surface corresponding to the reduction-side lens surface S (L1S) of the original first lens L1: g [ S (L1S) ]

Approximate surface corresponding to the magnification-side lens surface S (L1e) of the original first lens L1: g [ S (L1e) ]

Approximate surface corresponding to the reflection surface S (M2) of the second mirror M2 of the original: g [ S (M2) ]

Approximate surface corresponding to the reduction-side lens surface S (L2S) of the original second lens L2: g [ S (L2S) ]

Approximate surface corresponding to the magnification-side lens surface S (L2e) of the original second lens L2: g [ S (L2e) ]

Approximate surface corresponding to the reflection surface S (M3) of the third mirror M3 of the original product: g [ S (M3) ]

Approximate surface corresponding to the reflection surface S (M4) of the fourth mirror M4 of the original: g [ S (M4) ]

As an example, the approximate surface coefficients of the spline function G [ S (L2e) ] representing the approximate surface corresponding to the magnification-side lens surface S (L2e) of the second lens L2 are shown in tables 1 and 2.

Coefficients of node vectors

TABLE 1

Coefficients of function bases of faces

TABLE 2

Step 6: step of evaluating optical properties of entire system composed of original product

Then, the optical simulation apparatus performs an optical performance evaluation of the projection optical system PS, that is, an optical performance evaluation process of the original-type optical system (first optical performance evaluation process) by referring to the original surface data (G [ S (M1) ], G [ S (L1S) ], G [ S (L1e) ], G [ S (M2) ], G [ S (L2S) ], G [ S (L2e) ], G [ S (M3) ], and G [ S (M4) ]). Therefore, it is necessary to input original surface data corresponding to all the optical surfaces to optical simulation software in the optical simulation apparatus.

The optical simulation device may be any of various optical simulation devices that have been used in the past, and is not particularly limited. Further, the item for evaluating the optical performance is not particularly limited. For example, various aberration evaluations, magnification evaluation, Modulation Transfer Function (MTF) evaluation, or histogram evaluation may be performed.

Thus, the dot diagram shown in fig. 4 is an example of evaluation of optical performance. The dot diagram of fig. 4 is a dot diagram calculated from the original plane data to represent the imaging characteristics (marked with a scale of ± 1 mm) by overlapping dots of 3 wavelengths (460nm, 546nm, 620nm) at 25 evaluation points of the screen plane SCN. The coordinates (Y, Z) in the figure are local coordinates (Y, Z; mm) of the screen surface SCN indicating the projection position of the point barycenter of each evaluation point. In addition, since the projection optical system PS is a plane-symmetric optical system with respect to the screen plane XY plane, the dot diagram shows only a half of the negative axis side in the Z-axis direction on the screen plane SCN, and the remaining half is omitted.

And 7: judging step of optical performance evaluation result of projection optical system composed of original product

Here, it is judged whether or not the optical performance of the projection optical system PS constituted by the original product is within the allowable range as a result of the evaluation of the optical performance. Then, the subsequent steps are determined based on the determination result.

For example, when the optical performance of the projection optical system PS constituted by the original is within the allowable range, the projection optical system PS has a sufficiently satisfactory optical performance. Therefore, the correction processing of the mold is not required. Therefore, the manufacturing of the projection optical system PS can be completed (step 7 → step 20).

On the other hand, if the optical performance of the projection optical system PS constituted by the original product is out of the allowable range, the optical performance of the projection optical system PS is not sufficiently satisfactory. Therefore, the mold must be modified. Then, a process of obtaining new cavity surface data (referred to as "new cavity surface data") of the mold and then performing the re-molding using the mold after the correction processing based on the new cavity surface data will be described.

And 8: calculating correction amount of specific optical surface

In general, the original surface data of each optical element is often different from the design data. However, the projection optical system PS having sufficient optical performance can be manufactured by resetting the mold shape of the optical surface (specific optical surface) of a specific optical element without correcting the molds of all the optical elements.

Specifically, the original surface data other than the specific optical surface is fixed, and the projection optical system PS is redesigned by changing the specific optical surface. Although the specific optical surface may be any surface, a surface having the largest difference between the original surface data and the design data (the surface having the largest shape error) is preferable as the specific optical surface. This is because, since the original surface data of the remaining optical surfaces other than the specific optical surface is less different from the design data, the re-design of the specific optical surface results in less deviation of the projection optical system PS from the design performance.

The specific optical surface may be a surface closest to the surface having the largest shape error. For example, when the maximum shape error surface is a flat surface, the correction of the die shape may not be desired. In this case, the specific optical surface may be the surface closest to the surface having the largest shape error. This is because the state of the light beam incident on the surface closest to the maximum shape error surface is close to the state of the light beam incident on the maximum shape error surface, and the change from the design performance is small as a result of redesigning the specific optical surface.

Next, a case will be described as an example in which the specific optical surface is used as the reduction-side lens surface S (L2S) of the second lens L2, and the cavity surface T (L2S) of the fifth metal mold corresponding to the reduction-side lens surface S (L2S) of the second lens L2 is corrected. The correction processing on the facet T (L2s) corresponding to the specific optical surface is also referred to as "first correction processing".

First, new facet data of the first modified facet T (L2s) is defined as "D" as follows.

D＝f[S(L2s)]+H

Wherein,

f [ S (L2S) ]: initial facet data for facet T (L2s)

H: a function (for example, a spline function) indicating a correction amount for the existing facet T (L2 s).

Then, when the coefficients included in the function H (spline function H will be described as an example later) are determined, the new facet data D can be determined. Then, optical performance evaluation was performed using the original plane data of the reduction-side lens surface S (L2S) of the second lens L2, i.e., "G [ S (L2S) ] + H", in which the spline function H was taken into consideration.

Specifically, the optical simulation apparatus performs an optical performance evaluation of the projection optical system PS with reference to the original surface data (G [ S (M1) ], G [ S (L1S) ], G [ S (L1e) ], G [ S (M2) ], G [ S (L2S) ] + H, G [ S (L2e) ], G [ S (M3) ], and G [ S (M4) ] (the optical performance evaluation is also referred to as a "search optical performance evaluation", and a result of the search optical performance evaluation is also referred to as a "search result").

The search for optical property evaluation is described in detail here. The shape change of the specific optical surface is optimized to be close to the optical performance (design value) of the design data (F [ S (M1) ], F [ S (L1S) ], F [ S (L1e) ], F [ S (M2) ], F [ S (L2S) ], F [ S (L2e) ], F [ S (M3) ], F [ S (M4) ]) of the projection optical system PS. The term "optimization" as used herein means finding a so-called local minimum value, and does not necessarily require an optimum value. Then, the result of optimization (search result) may have desired performance. When the optimum result is achieved by the search optical performance evaluation, the spline function H is determined.

Therefore, the variation amount calculation step is to obtain the variation amount (i.e., the spline function H) of the original surface data G [ S (L2S) ] of the reduction-side lens surface S (L2S) of the second lens L2 when the projection optical system PS is brought into the optimum performance by varying the original surface data G [ S (L2S) ] of the reduction-side lens surface S (L2S) of the second lens L2 (i.e., G [ S (L2S) ] + H. The original plane data G [ S (L2S) ] may be optimized by using the correction amount as a variable without directly changing the original plane data G and obtaining the change amount as a difference.

Table 3 and table 4 show coefficients of the spline function H determined later. When the coefficient is determined, the correction processing amount to be performed on the cavity surface T (L2s) of the fifth metal mold is determined based on the coefficient.

Coefficients of node vectors

TABLE 3

Coefficients of function bases of faces

TABLE 4

And step 9: metal mould correcting process corresponding to specific optical surface

Then, the cavity surface T (L2s) of the fifth metal mold is subjected to a first correction process, i.e., a first correction process step, based on the determined correction process amount. Therefore, the first correction processing is correction processing for realizing the facet T (L2s) corresponding to the new facet data D.

Step 10: forming with the corrected metal mold

Next, a new second lens L2 is formed using the fifth metal mold subjected to the first correction processing (reshaping). The second lens L2 thus reshaped may be referred to as a "reshaped article".

Step 11: surface shape measuring step of remolded article

Next, the reduction-side lens surface S of the new second lens L2 is measured using an apparatus for measuring the surface shape (L2S) as in step 4. The measurement data may also be referred to as "measurement data of a remolded product".

Step 12: approximate surface setting step of remolded product

Then, as in step 5, the approximate surface (approximate surface of the specific optical surface) of the reduction-side lens surface S (L2S) of the second lens L2 of the reshaped product is set using the reshaped product measurement data. The approximate surface of the lens surface S (L2S) thus set may be referred to as "reshaped surface data" (G' [ S (L2S) ]).

Step 13: optical performance evaluation step for projection optical system including reshaped product

Then, as in step 6, the optical simulation apparatus performs the optical performance evaluation of the projection optical system PS, that is, the optical performance evaluation process of the optical system containing the type of the reshaped product, by referring to the original surface data (G [ S (M1) ], G [ S (L1S) ], G [ S (L1e) ], G [ S (M2) ], G [ S (L2e) ], G [ S (M3) ], G [ S (M4) ]), and the reshaped product surface data (G' [ S (L2S) ]).

That is, the optical performance of the projection optical system PS including the first mirror M1, the first lens L1, the second mirror M2, the third mirror M3, and the fourth mirror M4 as the original products, and the second lens L2 as the reshaped product was evaluated. The results of the optical performance evaluation are shown in fig. 5 as a dot-sequence chart (fig. 5 shows the same expression as fig. 4).

Step 14: judging step of optical performance evaluation result of projection optical system

Then, it is determined whether or not the result of evaluation of the optical performance of the projection optical system PS including the reshaped product (e.g., the dot diagram in fig. 5) is within the allowable range. Then, when the optical performance of the projection optical system PS including the reshaped product is within the allowable range, the projection optical system PS has a sufficiently satisfactory optical performance. Thus, the manufacturing can be completed (step 14 → step 20).

Step 15: additional processing procedure for new cavity surface data

However, when the optical performance of the projection optical system PS including the reshaped product is out of the allowable range, the optical performance of the projection optical system PS is not sufficiently satisfactory. The situation where the optical performance cannot be sufficiently exhibited is caused by the fact that the cavity surface T (L2s) of the fifth metal mold subjected to the first correction processing is not processed in accordance with the new cavity surface data D, or the fact that the optical surface is not uniformly cooled, shrinkage during cooling of the optical element, molding conditions are not optimized, or the like.

Then, correction processing (additional processing) is performed to cancel out the shape error between the new cavity surface data D and the re-formed product surface data G' [ S (L2S) ] defined in step 12, that is, a second correction processing step is performed.

Step 16: forming using additional metal mold

Then, the second lens L2 is formed again (additional forming) using a fifth metal mold having an additionally processed cavity surface T (L2 s). The second lens L2 additionally molded in this way may be referred to as an "additional product".

And step 17: surface shape measuring step of the additional product

Next, the reduction-side lens surface S of the second lens L2 as an additional product is measured using an apparatus for surface shape measurement (L2S) as in step 4. The related measurement data may also be referred to as "additional measurement data".

Step 18: approximate surface setting step of additional product

Then, as in step 5, the approximate surface of the reduction-side lens surface S (L2S) of the second lens L2 of the additional product is set using the additional product measurement data. The approximate surface of the set lens surface S (L2S) may also be referred to as "additional product surface data" (G "[ S (L2S) ]).

Step 19: optical performance evaluation step for projection optical system including additional component

Then, as in step 6, the optical simulation apparatus performs the optical performance evaluation of the projection optical system PS, that is, the optical performance evaluation step including the add-type optical system, by referring to the original surface data (G [ S (M1) ], G [ S (L1S) ], G [ S (L1e) ], G [ S (M2) ], G [ S (L2e) ], G [ S (M3) ], G [ S (M4) ]), and the add-on surface data (G "[ S (L2S) ]). That is, the optical performance of the projection optical system PS including the first mirror M1, the first lens L1, the second mirror M2, the third mirror M3, and the fourth mirror M4 as original products and the second lens L2 as additional products was evaluated.

Then, it is determined whether or not the optical performance is within the allowable range based on the result of the evaluation of the optical performance of the projection optical system including the additional component (step 19 → step 14). When the optical performance of the projection optical system PS including the supplement is within the allowable range, the projection optical system PS has a satisfactory optical performance. Thus, the manufacturing can be completed (step 19 → step 14 → step 20).

However, when the optical performance of the projection optical system PS including the additional product is out of the allowable range, the optical performance of the projection optical system PS is not sufficiently satisfactory. Therefore, additional processing (additional processing; step 14 → step 15 a plurality of times) is performed again.

Then, the surface shape of the second lens L2 (re-added article) molded using the fifth metal mold after the re-addition processing was measured, and the approximate surface was set based on the measurement data to evaluate the optical performance (steps 16 to 19). Then, based on the result of the optical performance evaluation (based on the result of the optical performance evaluation of the optical system including the re-addition type), if the optical performance of the projection optical system PS including the re-addition is within the allowable range, the manufacturing can be completed (step 19 → step 14).

However, if the optical performance of the projection optical system PS including the re-added product is out of the allowable range, the cavity surface T (L2s) of the fifth metal mold must be additionally processed again. That is, additional processing or the like is continued (steps 15 to 19 are repeated) until the optical performance of the projection optical system PS is within the allowable range in step 14 (step 19 → yes in step 14).

In addition, in step 14, a mold that can mold the optical element in which the optical performance of the projection optical system PS is within the allowable range is also referred to as a correction mold (correction mold member).

Step 20-22: completion of optical System

Finally, the optical element produced by molding using the correction die (first molding step; step 20) and the optical element produced by molding using the non-correction die (die other than the correction die) (second molding step; step 21) are assembled to complete the optical system (step 22).

3. Summary of the invention

In the manufacturing method described above, the optical element material is molded by a mold (mold member) to manufacture each optical element (original product) in the projection optical system PS having a plurality of optical elements, and the approximate surface (original surface data) of each optical surface is set by defining the approximate expression based on the measurement result of the surface shape of the optical surface of each manufactured optical element.

The manufacturing method evaluates the optical performance of the entire projection optical system PS from the approximate surfaces of all the optical surfaces in the entire system, and changes at least 1 surface (for example, the reduction-side lens surface S (L2S) of the original second lens L2, which is referred to as "change approximate surface") of the approximate surfaces of all the optical surfaces, thereby obtaining the amount of change in the change approximate surface when the optimal optical performance is exhibited in the entire system (in addition, the approximate surface that is not changed is referred to as a non-change approximate surface). Then, a correction processing amount of the cavity surface of the metal mold corresponding to the variation approximation surface is obtained based on the variation amount, and correction processing is performed to create a new cavity surface.

This manufacturing method does not perform the correction processing on all cavity surfaces of the entire metal mold. For example, in this manufacturing method, the facet corresponding to the largest shape error facet can be corrected with priority. Therefore, the number of times of the mold correction is small, and the projection optical system PS can be manufactured efficiently and inexpensively in a short time.

In this manufacturing method, the correction processing of the mold is performed based on the optical performance evaluation of the projection optical system PS. That is, the cavity surface corresponding to a specific optical surface (for example, the cavity surface T (L2s) of the fifth metal mold) is corrected so that the projection optical system PS can exhibit the optimum optical performance, not so that the cavity surface is corrected so as to form the optical surface having the same data as the design data F of the optical surface.

Therefore, even if there is a shape error (error from the design data F) in the optical surface other than the specific optical surface (for example, the reduction-side lens surface S (L2S) of the original second lens L2), there is no problem as long as the specific optical surface is a surface shape that allows the projection optical system PS to exhibit the optimum optical performance. Therefore, this manufacturing method is less susceptible to shape errors of the respective optical surfaces in the projection optical system PS. This is because, in order to form an optical surface having the same data as the design data F of the optical surface, it is necessary to perform high-precision correction processing on all the facets when performing correction processing on the facets, and the optical performance of the projection optical system PS is optimized.

However, the 1 st correction processing (first correction processing; fabrication of a new facet) for the facet corresponding to the specific optical surface may not be performed with high accuracy. At this time, the optical performance of the projection optical system PS including the optical element (for example, the second lens L2 of the reshaped product) formed by the metal mold having the new cavity surface and the optical element (original product) formed by the existing metal mold is out of the allowable range.

In this manufacturing method, the approximation surface is set by defining an approximation formula based on the measurement result of the surface shape of the optical surface corresponding to the new cavity surface in the optical element (for example, the second remolded lens L2) molded by the mold having the new cavity surface. In this manufacturing method, the new facet is corrected so that a shape error between the approximate surface of the optical surface corresponding to the new facet and the new facet (for example, an error between the re-molded surface data G' [ S (L2S) ] and the new facet data D) is cancelled.

This correction processing, i.e., the second correction processing, is performed to solve the shape error, but the correction processing may be performed only on the facet that has been corrected (new facet). Therefore, the burden of the second correction processing is smaller than that in the case of performing the correction processing on all the facets.

However, when the 2 nd correction processing (second correction processing) of the cavity surface corresponding to the specific optical surface is performed with high accuracy, the optical performance of the projection optical system PS including the optical element (e.g., the second lens L2 of the add-on product) molded by the mold having the cavity surfaces subjected to the plural correction processing and the optical element (original product) molded by the existing mold is within the allowable range. Thus, the manufacturing method can manufacture the projection optical system PS that easily exhibits high optical performance due to the presence of the second correction processing with a light load.

The above-described manufacturing method is particularly effective for manufacturing a reflection optical system including a plurality of eccentric surfaces, particularly an optical system including a free-form surface. In general, the error in forming is often an error (for example, a dust component) asymmetrical to a design value. Therefore, if the surface (particularly, free-form surface) change approximation surface is not a rotationally symmetric surface but a non-rotationally symmetric surface, the molding error is easily corrected. In addition, the eccentric plane refers to a plane having no rotational symmetry axis; or even if there is a rotational symmetry axis, the symmetry axis is offset from the center of the effective plane by a large plane.

In addition, the approximate surfaces (original surface data, reshaped surface data, additional surface data, and the like) of the optical surfaces of the optical elements of the projection optical system PS are used for the optical performance evaluation. Specifically, optical performance was evaluated by ray tracing simulation using powers obtained from the surface shape of the approximate surface. Therefore, the setting method of the approximation plane is very important.

For example, when a local moire (a moire portion) is present on the measured optical surface, if a high-order approximation formula is used to appropriately express the moire portion, high-order moire occurs at a position other than the moire (a non-moire portion). On the other hand, if a low-order approximation formula is used to properly represent the non-corrugated portion, the corrugated portion cannot be properly represented.

Therefore, it is preferable to express the approximate surface (original surface data, reshaped surface data, additional surface data, and the like) of the optical surface by using a function capable of efficiently expressing the moire part of the optical surface, for example, a spline function. Further, a spline function is given as an example, in which a plane (YZ plane; see fig. 3) perpendicular to a predetermined reference axis (for example, X axis) of the optical surface of the optical element is divided into a plurality of parts, and a plurality of spaces (divided spaces) based on the divided planes are set, and the boundaries between the divided spaces are continuous.

However, the number of times of the spline function or the like is preferably at least 3 or more (the above description is made by exemplifying 5-degree spline function). In the case of a spline function of 3 or more degrees, an approximation plane corresponding to each divided space can be set using the measurement point MP in the divided space. In particular, when a function of at least 3 or more orders (for example, a spline function) is used, the 2-order derivatives of the approximation formula are continuous at the boundary between the divided spaces, and the powers of the approximation planes are continuous without causing a step difference or the like in the approximation plane at the boundary of the divided spaces, so that ray tracing simulation can be performed.

The number of times of the spline function or the like is preferably 4 to 8. This is because the local moire part, which has a large influence on the optical performance in the projector range, can be expressed by a 4-8 th order function. Further, the approximate surface is generated by a 4-to 8-th-order function, so that a local ripple shape which greatly affects optical performance can be expressed, and a higher-order ripple portion which hardly affects optical performance can be removed to function as a filter function.

Embodiment mode 2

The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present invention.

For example, the influence of the reduction-side lens surface S (L2S) and the enlargement-side lens surface S (L2e) of the second lens L2 on the optical performance is corrected by changing the shape of the reduction-side lens surface S (L2S) of the second lens L2, but the present invention is not limited thereto. For example, the influence of the enlargement-side lens surface S (L2e) of the second lens L2 on the optical performance may be corrected by a change in the shape of the reduction-side lens surface S (L2S) of the second lens L2 or the reflection surface S (M3) of the third mirror.

It is important to correct the mold so that at least 1 surface shape of the optical surface included in the projection optical system PS changes in order to optimize the optical performance of the projection optical system PS. However, the shape of the optical surface through which light passes is changed, and the optical performance can be effectively improved, and the image height of the light is substantially the same as the image height of the light transmitted through the optical surface that affects the optical performance. Therefore, for example, it is preferable to correct the influence of the enlargement-side lens surface S (L2e) of the second lens L2 on the optical performance by the shape change of the reduction-side lens surface S (L2S) of the second lens L2.

In addition, when setting a divided space (in the space dividing step), the relationship between the number of divided spaces and the number of measurement points in the divided space is important. For example, when the number of measurement data MP is large although the number of divided spaces is small, the shape error is substantially the same as when the shape error is expressed by the error polynomial of the entire surface. Therefore, local ripples are not exhibited on the approximate plane.

On the other hand, for example, when the number of measurement data MP is small despite the large number of divided spaces, the number of measurement data MP in the direction perpendicular to the measurement direction (measurement data MP in the Y-axis direction perpendicular to the Z-axis direction in fig. 3) is reduced in the divided spaces although local ripples on the optical surface are approximated. As a result, the approximation accuracy in the reduced measurement data MP direction (Y-axis direction in fig. 3) is degraded.

In view of the above, it is considered preferable that the number of divided spaces is large and the number of measurement data MP is large. However, in this case, it takes a long time to measure the surface shape, and the accuracy of the measurement data MP is lowered by the influence of temperature drift of the measuring instrument due to changes in the environmental temperature and humidity and the deterioration of the original optical surface. In addition, the measurement efficiency is also decreased due to the large number of measurement data MP.

Therefore, the number of divided spaces and the number of measurement points in the divided spaces are preferable because the approximation accuracy of the local waviness of the optical surface and the approximation accuracy of the optical surface due to the decrease in the number of measurement points MP in the divided spaces can be ensured, and the measurement efficiency can be improved. As an example, a measurement method shown in fig. 3 may be mentioned in which a space is divided into 25 spaces and 5 lines are measured for each divided space.

When the approximation plane is generated, the approximation accuracy increases as the number of measurement lines per divided space increases. However, for example, when the approximation plane is generated by a 5-degree function that affects the optical performance of the projector range, it is preferable to generate the approximation plane with high accuracy by 5 lines per divided space, but the approximation plane can be generated with high accuracy by at least 3 lines.

In fig. 3, the line measurement is performed along the Z-axis direction, but may be performed along the Y-axis direction. Further, the line measurement (matrix measurement) may be performed along two axes of the Y axis direction and the Z axis direction. Here, the measurement efficiency of the matrix measurement is reduced. The line measurement in one direction (Y-axis direction or Z-axis direction) is more efficient than the matrix measurement.

The polynomial expressing the design data F or the initial cavity surface data F is not particularly limited, and may be a spline function.

In addition, all the optical elements may not be molded articles. The first mirror M1, which is a spherical surface, may be an abrasive article, for example. Further, glass molding may be used instead of resin molding. In addition, the optical performance evaluation may be performed using the approximate surfaces of all the optical elements without obtaining the approximate surfaces for all the optical elements. For example, when the first mirror M1 is a glass polished product, since a shape substantially matching the design value can be obtained, the design data can be used as the approximate surface of the first mirror M1.

Embodiment 3

Embodiment 3 will be explained. Note that members having the same functions as those used in embodiments 1 and 2 are given the same reference numerals, and description thereof is omitted.

Various materials (glass, resin, etc.) may be used as the material of the optical element such as a mirror or a lens. However, the temperature required for molding a glass optical element is higher than the temperature required for molding a resin optical element, and the molding accuracy of a glass optical element (particularly, a glass optical element having a large outer dimension) is more likely to be lower than the molding accuracy of a resin optical element due to the high temperature. Therefore, it is difficult to form the glass optical element in accordance with the designed surface shape.

In general, when the effective beam widths of light reaching the surfaces of the optical elements (e.g., the mirror surface and the lens surface) are substantially the same, if the amount of surface shape error of each surface is the same, the surface shape error of the mirror surface causes a larger deterioration in optical performance than the surface shape error of the lens surface causes a larger deterioration in optical performance (i.e., the sensitivity of the optical performance of the mirror surface is higher than that of the lens surface). Therefore, in the projection optical system PS in which the glass optical element and the resin optical element are combined, when the glass optical element is a mirror, an error is likely to occur in the surface shape of the mirror, and the optical performance of the projection optical system PS is greatly affected.

The dot diagrams of fig. 6 and 7 are examples of the optical performance.

These dot charts are calculated from the original plane data of the projection optical system PS including the glass first mirror M1 and the glass second mirror M2, the resin first lens L1, the resin second lens L2, the resin third mirror M3, and the resin fourth mirror M4. Here, the deterioration of the optical performance shown in these dot charts is caused by the fact that the reflecting surface S (M2) of the second reflecting mirror M2 is not formed into a desired surface shape.

The dot arrangement diagrams of these figures show imaging characteristics (marked with a scale of ± 1 mm) by superimposing dots of 3 wavelengths (460nm, 546nm, 620nm) at 45 evaluation points on the screen surface SCN. Fig. 6 shows only the positive half of the screen surface SCN in the Z-axis direction, and fig. 7 showsThe other half is on the negative axis side in the Z-axis direction. The coordinates (Y, Z) in the figure represent the same as those in fig. 4 and 5 (in the other figures, "e^-nIs "" 10 ""^-n」)。

In order to prevent deterioration of optical performance shown in fig. 6 and 7, the manufacturing method described above may be used. That is, each optical element (original product) in the projection optical system PS having a plurality of optical elements is manufactured by molding an optical element material (glass or resin) with a mold, and the approximate surface (original surface data) of each optical surface is set by defining an approximate expression based on the measurement result of the surface shape of the optical surface of each manufactured optical element.

Then, the optical performance of the entire system is evaluated from the approximate surfaces of all the optical surfaces, and at least 1 surface (change approximate surface) of the approximate surfaces of all the optical surfaces is changed to obtain the amount of change of the change approximate surface when the entire system exhibits the optimum optical performance, and the correction processing amount of the cavity surface corresponding to the change approximate surface is obtained based on the amount of change, and the first correction processing is performed to create a new cavity surface.

However, in the projection optical system PS including the mirror and the lens, it is preferable to use a lens surface of at least 1 surface as the variation approximation surface. When reshaping is performed using the new facet data D as a target value after performing the first correction process based on the variation H of the original facet data, if a shape error occurs between the new facet data D and the reshaped facet data G', the optical performance is deteriorated. However, since the sensitivity of the lens surface is lower than that of the mirror surface (reflection surface of the mirror), the influence on the optical performance is smaller when the variation approximation surface is the lens surface.

Then, the amount of change in the original surface data (G [ S (L1S) ], G [ S (L2S) ]) is determined using the reduction-side lens surface S (L1S) of the first lens L1 and the reduction-side lens surface S (L2S) of the second lens L2 of the projection optical system PS as change approximation surfaces. Then, the correction processing amount of the cavity surface of the mold corresponding to the variation approximation surface (the cavity surface T (L1s) of the second mold and the cavity surface T (L2s) of the fifth mold) is obtained based on the variation amount, and the first correction processing is performed to create a new cavity surface.

Then, after the new first lens L1 and the second lens L2 are reshaped by the second metal mold and the fifth metal mold which have been subjected to the first correction processing, the surface shapes of the reduction-side lens surface S (L1S) of the new first lens L1 and the reduction-side lens surface S (L2S) of the second lens L2 are measured, and data of approximate surfaces of these surface shapes (reshaped surface data, G '[ S (L1S) ], G' [ S (L2S) ]) are obtained.

Fig. 8 and 9 are dot charts obtained from the surface data of the reshaped product (G '[ S (L1S) ], G' [ S (L2S) ]) and the original surface data (G [ S (M1) ], G [ S (L1e) ], G [ S (M2) ], G [ S (L2e) ], G [ S (M3) ], G [ S (M4) ]) (the same expressions are given to fig. 8 and 9 as fig. 6 and 7).

That is, these dot charts show the evaluation of the optical performance of the projection optical system PS including the first mirror M1, the second mirror M2, the third mirror M3, and the fourth mirror M4 as the original products, and the first lens L1 and the second lens L2 as the reshaped products. And the results of these optical property evaluations can be judged to be within the allowable range.

In particular, the second mirror M2 of the projection optical system PS is a rotationally symmetric aspherical mirror made of glass. Generally, when a rotationally symmetric aspherical mirror is molded by glass molding, it is difficult to form a rotationally symmetric mirror surface due to low molding accuracy. That is, an error in the asymmetrical surface shape is likely to occur in the mirror surface (fig. 6 to 9 show the positive axis side and the negative axis side in the Z axis direction on the screen surface SCN from the viewpoint of the asymmetrical surface shape error).

However, it is difficult to correct the free-form surface of the cavity surface of the mold corresponding to the mirror surface. This is because the trimming process on the cavity surface of the high-temperature-resistant glass molding die is more difficult than the trimming process on the cavity surface of the resin molding die.

Therefore, instead of correcting the cavity surface T (M2) of the fourth mold (glass molding mold) corresponding to the second reflector M2, the cavity surfaces (T (L1S), T (L2S)) of the second mold and the fifth mold (resin molding mold) corresponding to the first lens L1 and the second lens L2 made of resin are corrected, and thus the deterioration of optical performance due to the surface shape error of the reflecting surface S (M2) of the second reflector M2 is more easily solved.

In addition, since the free-form surface shape of the cavity surfaces T (L1S) and T (L2S)) of the second mold and the fifth mold can be easily corrected, an error in the asymmetrical surface shape generated on the reflection surface S (M2) of the second reflector M2 can be easily corrected (canceled).

As described above, in the projection optical system PS including at least 1 mirror and at least 1 lens, it can be said that the lens surface of at least 1 surface is the most preferable surface when the change is approximate from the viewpoint of sensitivity to optical performance. In particular, when the lens surface is a surface similar to a change, the deterioration of optical performance due to a surface shape error of a mirror formed of glass, specifically, a surface shape error generated on a reflecting surface (mirror surface) which is a rotationally symmetric aspherical surface is easily corrected.

However, it is not limited thereto. In the case where the lens surface (preferably, the lens surface of a resin lens) is a surface similar to the change, the deterioration of the optical performance due to the surface shape error of the lens surface of the glass-molded lens, specifically, the surface shape error generated in the lens surface which is a rotationally symmetric aspherical surface is also easily corrected. This is because the sensitivity of the lens surface is lower than that of the mirror surface, and therefore, the influence on the optical performance is small even when a shape error occurs in the reshaped product.

Finally, it is needless to say that the embodiments obtained by appropriately combining the techniques disclosed above are also included in the technical scope of the present invention.

Claims

1. A method for manufacturing an optical system is provided,

an optical system having a plurality of optical surfaces is manufactured by molding using a mold member, the method comprising:

setting approximate surfaces of all optical surfaces of the optical system including an optical surface formed by initial molding;

a first optical performance evaluation step of evaluating the optical performance of the entire optical system from the approximate surfaces of all the optical surfaces in the optical system;

a change amount calculation step of calculating a change amount of the change approximation surface when the entire system exhibits the optimum optical performance, wherein at least 1 of the approximation surfaces of all the optical surfaces, which is formed by the mold member, is used as a change approximation surface, and at least 1 of the approximation surfaces of all the optical surfaces, which is formed by the mold member, is not used as the change approximation surface, but is used as a non-change approximation surface;

a first correction processing step of obtaining a correction processing amount of a cavity surface of the mold member corresponding to the variation approximation surface based on the variation amount, and performing correction processing to produce a new cavity surface;

a first molding step of molding an optical element using the correction die member processed in the first correction processing step;

and a second molding step of molding the optical element by using a mold member other than the correction mold member.

2. The method of manufacturing an optical system according to claim 1,

the first forming step includes:

a step of setting an approximate surface in the optical element molded by the mold member having the new cavity surface, based on a measurement result of a surface shape of the optical surface corresponding to the new cavity surface;

a second correction processing step of performing correction processing on the new cavity surface so as to cancel out a shape error between an approximate surface of the optical surface corresponding to the new cavity surface and the new cavity surface;

and a step of molding the optical element by using the correction die member processed in the second correction processing step.

3. The method of manufacturing an optical system according to claim 1,

in the step of setting the approximate surface,

an approximate surface is set based on a measured surface shape of the optical surface formed by the initial forming on the optical surface formed by the molding using the mold member.

4. The method of manufacturing an optical system according to claim 1,

in the step of setting the approximate surface,

when the optical surface is a polished surface, the design data of the optical surface is set as an approximate surface on the polished surface.

5. The method of manufacturing an optical system according to claim 1,

the approximate surface having the largest difference between the design data of the approximate surface of each optical surface in the optical system and the optical surface corresponding to each approximate surface is used as the variation approximate surface.

6. The method of manufacturing an optical system according to claim 1,

the variation approximation surface is an approximation surface of an optical surface disposed closest to the approximation surface of each optical surface in the optical system, the optical surface having the largest difference between the design data and the approximation surface.

7. The method of manufacturing an optical system according to claim 1, wherein the variation approximation plane is at most 2 planes.

8. The method of manufacturing an optical system according to claim 1,

the step of setting the approximate surface includes:

and a space division setting step of dividing a plane perpendicular to a predetermined reference axis of the optical surface of the optical element into a plurality of parts and setting a plurality of spaces based on the divided planes, wherein an approximation formula in which the boundaries between the spaces have continuity is used.

9. The method of manufacturing an optical system according to claim 8, wherein the approximation formula is a function of at least 3 times or more.

10. The method of claim 9, wherein the continuity is that the 2 nd derivative of the approximate expression is continuous at the boundary between the spaces.

11. The method of manufacturing an optical system according to any one of claims 8 to 10, wherein the approximate expression is a spline function.

12. The method of manufacturing an optical system according to claim 1,

the optical system contains at least 1 lens and at least 1 mirror as elements shaped with a mold member,

at least a lens surface is used as the variation approximation surface.

13. The method of manufacturing an optical system according to claim 12, wherein at least 1 of the lens and the mirror included in the optical system is formed by glass molding.

14. The method of manufacturing an optical system according to claim 1,

the optical system contains a non-rotationally symmetric surface,

in the variation amount calculating step, an approximation plane corresponding to the non-rotationally symmetric plane is set as a variation approximation plane.

15. The method of manufacturing an optical system according to claim 14,

at least a lens surface is used as the variation approximation surface.

16. The method of manufacturing an optical system according to claim 15,

at least 1 of the lens and the mirror included in the optical system is formed by glass shaping.