JP2010164908A - Imaging optical system and figure measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging optical system which has a variable amount of axial chromatic aberration. <P>SOLUTION: The imaging optical system has an imaging lens 3, and a first lens 1 and a second lens 2 which can move in an optical axis direction of the imaging lens 3, and by moving at least one of the first lens 1 and the second lens 2 in the optical axis direction, the amount of axial chromatic aberration of the imaging optical system is variably adjusted, and by changing a positional relationship in the optical axis direction of the first lens 1 and the second lens 2, fluctuation of chromatic aberration of magnification of the imaging optical system accompanying fluctuation of the axial chromatic aberration is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface shape measuring device using axial chromatic aberration of an imaging optical system, and an imaging optical system that can be applied to the surface shape measuring device.

  One of the methods for optically measuring the surface shape of industrial product parts and the like is to use the axial chromatic aberration of the optical system (see Patent Documents 1 and 2, etc.). The principle is that a measurement surface is illuminated with a plurality of lights having different wavelengths (continuous spectrum light or wavelength tunable light source), an image of the measurement surface is formed by an imaging optical system, and a focusing wavelength at each position of the image is formed. From this, the height of each position on the measurement surface is calculated.

  The measurement range (dynamic range) in the height direction of such surface shape measurement is substantially determined by the amount of axial chromatic aberration inherent in the imaging optical system (objective lens). Therefore, when measuring various measurement surfaces having different amounts of unevenness, it is necessary to prepare a plurality of objective lenses having different amounts of axial chromatic aberration and replace them.

  Therefore, an object of the present invention is to provide an imaging optical system in which the amount of axial chromatic aberration is variable, and a surface shape measuring device in which the dynamic range in the height direction is variable.

  One aspect illustrating the imaging optical system of the present invention is an imaging optical system that includes an imaging lens, and a first lens and a second lens that are movable in the optical axis direction of the imaging lens. By moving at least one of the second lenses in the optical axis direction, the amount of axial chromatic aberration of the imaging optical system is variably adjusted, and the positional relationship between the first lens and the second lens in the optical axis direction is changed. By doing so, the variation of the chromatic aberration of magnification of the imaging optical system accompanying the variation of the amount of longitudinal chromatic aberration is suppressed.

  Another embodiment illustrating the imaging optical system of the present invention is arranged in an optical path between an imaging lens that forms an image of the observation surface and the observation surface or its conjugate image and the imaging lens, And a first cemented lens and a second cemented lens that share the optical axes of each other, and the first cemented lens has a first plano-convex lens and a concave surface that is formed by reversing the convex surface of the first plano-convex lens. The first plano-convex lens and the first plano-concave lens have the same refractive index with respect to a predetermined wavelength, and with respect to other wavelengths. The second cemented lens has a refractive index different from each other, and the second cemented lens has a second plano-convex lens having a convex surface whose curve is gentler than that of the cemented surface of the first cemented lens, and a concave surface formed by reversing the convex surface of the second plano-convex lens. The second plano-concave lens, the convex and concave surfaces of both The wavelength characteristics of the refractive index of the second plano-convex lens are the same as those of the first plano-concave lens, and the wavelength characteristics of the refractive index of the second plano-concave lens are the same. The distance between the observation surface or its conjugate image and the first cemented lens is variable, the distance between the first cemented lens and the second cemented lens is variable, and the second cemented lens. The distance between the focusing lens and the imaging lens is variable.

Further, in one aspect illustrating the surface shape measuring apparatus of the present invention, a light source that emits light having a plurality of different wavelengths, a measurement surface is illuminated with light emitted from the light source, and an image of the measurement surface is formed in that state. Any one of the above-described imaging optical systems and detection means for detecting a focusing wavelength at each position of an image formed by the imaging optical system.

  According to the present invention, an imaging optical system with a variable amount of axial chromatic aberration and a surface shape measuring device with a variable dynamic range in the height direction are realized.

1 is a configuration diagram of an imaging optical system according to a first embodiment. FIG. The 1st figure which expressed the junction lens 1 and the junction lens 2 with the thin lens. The 2nd figure which expressed the junction lens 1 and the junction lens 2 with the thin lens. The graph which shows the wavelength characteristic of the refractive index of S-TIH10 and S-LAL18. The graph which shows the wavelength characteristic of the power of the junction lens 1 and the junction lens 2. FIG. The graph which shows the axial chromatic aberration of 1st Example (before correction | amendment). The graph which shows the paraxial magnification of 1st Example (before correction | amendment). The graph which shows the substantial magnification chromatic aberration of 1st Example (before correction | amendment). The graph which shows the axial chromatic aberration of 1st Example (after correction | amendment). The graph which shows the substantial magnification chromatic aberration of 1st Example (after correction | amendment). The spherical aberration curve figure of 1st Example (after correction | amendment). The spot diagram of 1st Example (after correction | amendment). 6 is a graph showing the telecentricity of the first embodiment. The optical system sectional drawing of 2nd Example. FIG. 6 is a longitudinal aberration diagram of the second example. The coma aberration figure of 2nd Example. The spot diagram of 2nd Example. The graph which shows the substantial magnification chromatic aberration of 2nd Example (before correction | amendment). The graph which shows the substantial magnification chromatic aberration of 2nd Example (after correction | amendment). The graph which shows the telecentricity of 2nd Example (before correction | amendment). The graph which shows the axial chromatic aberration of 2nd Example (after correction | amendment). The spherical aberration figure of 2nd Example (after correction | amendment). The block diagram of the surface shape measuring apparatus of 2nd Embodiment. The figure explaining the relationship between three types of wavelength bands and the wavelength of three types of illumination light. The figure which shows the pattern of the chart 15. The figure which shows the relationship between the wavelength of illumination light, and the intensity distribution of a slit image. The figure which shows the difference in the focus position of three types of illumination light.

[First Embodiment]
Hereinafter, an embodiment of an imaging optical system in which the amount of axial chromatic aberration is variable will be described.

  First, the configuration of the imaging optical system will be described.

  FIG. 1 is a configuration diagram of the imaging optical system, and the upper, middle, and lower stages in FIG. 1 show states with different lens positions.

  As shown in FIG. 1, in the imaging optical system, a cemented lens 1, a cemented lens 2, and an imaging lens 3 are arranged in order from the object O side, with their optical axes being in common. Yes. Here, the imaging lens 3 is, for example, a first objective lens of a microscope. Among these, the cemented lens 1 and the cemented lens 2 are elements inserted to adjust the amount of longitudinal chromatic aberration of the imaging optical system.

In the first cemented lens 1, a plano-convex lens 11 and a plano-concave lens 12 having a concave surface formed by reversing the convex surface of the plano-convex lens 11 are joined to each other by their convex and concave surfaces in order from the object O side. And its appearance is a plane parallel plate. The material of the plano-convex lens 11 and the material of the plano-concave lens 12 are mutually with respect to a reference wavelength λ ₀ (here, 573 nm) within the use wavelength range of the imaging optical system (here, 400 to 700 nm). The same refractive index is shown, and different refractive indexes are shown for other wavelengths within the used wavelength range. A combination of the material of the plano-convex lens 11 and the material of the plano-concave lens 12 is selected as a combination having an Abbe number as far as possible. This is because, if selected in this way, a wide adjustment range of the axial chromatic aberration amount can be secured.

Hereinafter, the refractive index of the plano-convex lens 11 is represented by n ₁ (λ) as a function of the wavelength λ, and the refractive index of the plano-concave lens 12 is represented by n ₂ (λ) as a function of the wavelength λ.

The cemented lens 2 includes, in order from the object O side, a plano-convex lens 21 having a convex surface whose curve is gentler than that of the cemented surface of the cemented lens 1, and a plano-concave lens 22 having a concave surface formed by inverting the convex surface of the plano-convex lens 21. Are joined to each other by their convex and concave surfaces, and the appearance thereof is a plane parallel plate. The material of the plano-convex lens 21 is the same as that of the plano-concave lens 12, and the material of the plano-concave lens 22 is the same as that of the plano-convex lens 11. Therefore, the refractive index of the plano-convex lens 21 is n ₂ (λ), and the refractive index of the plano-concave lens 22 is n ₁ (λ).

The cemented lens 1, the cemented lens 2, and the imaging lens 3 are held in a common lens barrel via a holding mechanism, and by the holding mechanism, the distance d ₀ of the cemented lens 1 with respect to the object O and the cemented lens 1 are The distance d ₃ of the cemented lens 2 and the distance d ₆ of the imaging lens 3 with respect to the cemented lens 2 can be adjusted. Hereinafter, these intervals d ₀ , d ₃ , d ₆ are referred to as “lens surface intervals d ₀ , d ₃ , d ₆ ”.

Here, by adjusting at least one of the lens surface distance d ₀ and the lens surface distance d ₃ , the amount of axial chromatic aberration of the imaging optical system can be adjusted. However, it is not desirable that the chromatic aberration of magnification of the imaging optical system fluctuates at that time. Therefore, the holding mechanism, by which the lens surface spacing d ₀ interlocking lens spacing d _3, suppress the fluctuation of the magnification chromatic aberration of the imaging optical system.

In other words, if the position of one of the cemented lens 1 and the cemented lens 2 in the optical axis direction is unchanged, the image magnification changes at a wavelength other than the reference wavelength λ ₀ , so that the holding mechanism has a lens surface distance d ₀ . by interlocking the lens spacing d ₃ to the movement, keep the image magnification constant.

  As the holding mechanism, an electric stage that individually controls the positions of the cemented lens 1, the cemented lens 2, and the imaging lens 3, or the junction lens 1, the cemented lens 2, and the imaging lens 3 are connected to control each position. A cam mechanism or the like can be applied. Incidentally, when the electric stage is applied, the adjustment of the axial chromatic aberration amount is electrically performed, and when the cam mechanism is applied, the adjustment of the axial chromatic aberration amount is manually performed. However, even if a cam mechanism is applied, the axial chromatic aberration amount can be adjusted electrically by connecting an electric motor to the cam mechanism.

Hereinafter, conditions that the lens surface distances d ₀ and d ₃ should satisfy in order to suppress the occurrence of lateral chromatic aberration as much as possible will be described using mathematical expressions. The code conventions in each equation are as follows.

  Surface number: The order from the object O side to the real image side is set to be positive.

  -Surface spacing: The direction from the object O side to the real image side is positive.

  -Light beam height: When the optical axis is taken horizontally, the direction away from the optical axis is taken positively.

  Ray angle: The ray angle in the direction where the absolute value is π / 2 or less starting from the optical axis, and the clockwise rotation on the paper surface of FIG.

  -Radius of curvature of the surface: Take an absolute value and take it positive regardless of the irregularities of the surface.

First, if the radius of curvature of the cemented surface of the cemented lens 1 is R ₁ and the radius of curvature of the cemented surface of the cemented lens 2 is R ₂ , the power φ ₁ (λ) of the cemented lens 1 and the power φ _{2 of the} cemented lens ₂ ( λ) is given by:

Further, since the refractive indexes n ₁ (λ) and n ₂ (λ) are equal to each other at the reference wavelength λ _{0 as} described above, the following equation is established.

Therefore, the following equation is established between the powers φ ₁ (λ) and φ ₂ (λ).

Next, as shown in FIG. 2, the cemented lens 1 and the cemented lens 2 are respectively represented by a thin lens S ₁ and a thin lens S ₂ , and a virtual image I (λ) (viewed from the object O and the imaging lens 3 side). The paraxial magnification M between (see FIG. 3) is calculated. In the calculation, each quantity is defined as follows.

· Α _k (λ): a thin lens _{S k} thin the lens _{S k +} rays _{r k} angle and makes with the optical axis AX _{h k} towards ₁ (lambda): light _{r k} and the thin lens intersection of the height of the _{S k + 1.}

E _k (λ): an interval between the thin lens S _k and the thin lens S _{k + 1} (hereinafter referred to as “thin lens interval”).

· Φ _k (λ): the power of the thin lens _{S k.}

First, when the paraxial ray tracing equations before and after the first surface (thin lens S ₁ ) are expressed in a matrix, the following is obtained.

Further, since the angle α ₀ is sufficiently small in the paraxial ray tracing, the following equation is established.

Similarly, when the paraxial ray tracing equations before and after the second surface (thin lens S ₂ ) are expressed in a matrix, the following is obtained.

According to the above equations (5), (6), and (7), the relationship between the angles α ₀ and α ₂ (λ) is expressed as equation (8).

Further, the paraxial magnification M (λ) between the object O and the virtual image I (λ) is expressed by the angles α ₀ and α ₂ (λ) as shown in the following formulas by the invariant of Helmholtz-Lagrange.

  According to this equation (9), if the following equation holds regardless of the value of the wavelength λ, the paraxial magnification M (λ) between the object O and the virtual image I (λ) does not depend on the wavelength λ. It can be seen that the paraxial optical magnification chromatic aberration of the imaging optical system does not occur.

However, according to the equation (8), the thin lens intervals e ₀ (λ) and e ₀ (λ) that satisfy the equation (10) regardless of the value of the wavelength λ are e ₀ (λ) = e ₁ ( It can be seen that only λ) = 0.

Therefore, in the following, the relationship between the thin lens intervals e ₀ and e ₁ that satisfies the expression (10) or a condition close to it in at least the used wavelength range (here, 400 to 700 nm) of the imaging optical system is searched.

First, since the expression (4) is satisfied at the reference wavelength λ ₀ in the use wavelength region as described above, the expression (10) is satisfied regardless of the thin lens intervals e ₀ and e ₁ . Therefore, the relationship between the thin lens intervals e ₀ and e ₀ that establishes the expression (10) at a certain appropriate wavelength λ ₁ that is separated from the reference wavelength λ ₀ within the used wavelength range is as follows. It is considered that the condition close to the equation (10) can be established in the entire region of ˜700 nm.

Hereinafter, it referred to the wavelength lambda ₁ as "magnification wavelength lambda _1", magnification wavelength lambda ₁ in the formula (10) thin lens distance _{e 0} as to establish (lambda _1), the relationship between _{e 1} (lambda ₁₎ Ask.

The relationship between the thin-lens intervals e ₀ (λ ₁ ) and e ₁ (λ ₁ ) that satisfy the equation (10) at the equal wavelength λ ₁ is λ = λ ₁ and the equation for the equation (8) It is obtained by substituting (10), formula (1), and formula (2).

When the equation (11) is solved for the thin lens interval e ₀ (λ ₁ ), the following equation is obtained.

Similarly, when the equation (11) is solved for the thin lens interval e ₁ (λ ₁ ), the following equation is obtained.

That is, the expressions (11), (12), and (13) are the relationships of the thin lens intervals e ₀ and e ₁ that establish the expression (10) at the equal wavelength λ ₁ . It is a relationship that should be established.

In addition, these Formula (11), Formula (12), and Formula (13) are properly used properly. For example, to derive a thin lens distance _{e 0} (lambda ₁₎ suitable therefor a thin lens distance _{e 1} (lambda ₁₎ may be using equation (12), the thin-lens distance _{e 0} (lambda ₁₎ In order to derive an appropriate thin lens interval e ₁ (λ ₁ ), equation (13) may be used.

However, in an actual imaging optical system, due to the distortion aberration (distortion aberration having wavelength dependency) of the cemented lens 1 and the cemented lens 2, the real image height at the equal wavelength λ ₁ is close to 1 × magnification. Slightly deviates from the axial image height.

For this reason, a slight correction is applied to at least one of the thin lens intervals e ₀ (λ ₁ ) and e ₁ (λ ₁ ) satisfying each of the expressions (11), (12), and (13), thereby distortion aberration. It is desirable to compensate for the image shift due to. Incidentally, it is known from experiments by numerical calculation that the amount of compensation is appropriately ± 10% or less of the value of the thin lens interval e ₀ (λ ₁ ) or e ₁ (λ ₁ ).

Next, a method for calculating axial chromatic aberration of the imaging optical system will be described with reference to FIG. In the calculation, it is necessary to convert the thin lenses S ₁ and S ₂ into the cemented lenses S ₁ and S ₂ which are thick lenses.

First, as shown in FIG. 3, when the position of the virtual image I (λ) of the wavelength λ as viewed from the imaging lens 3 side is expressed by a distance e _I (λ) from the thin lens S ₂ , the following equation is obtained. is there.

The height h ₁ (λ) included in the formula (14) is represented by the following formula according to the formula (5) described above.

  Therefore, when the formula (15) and the formula (8) described above are substituted into the formula (14), the following formula is obtained.

In consideration of the air-converted value of the center thickness of the plano-concave lens 22, the distance d _I (λ) from the final surface of the cemented lens 2 to the virtual image I (λ) can be expressed by the following equation.

However, t ₂₂ is the center thickness of the plano-concave lens 22. Incidentally, since the imaging lens 3 is fixed, the value of the lens surface interval d ₆ should be set in the present embodiment, the above equations (16), uniquely determined from (17).

Then, the axial chromatic aberration [Delta] d _I (lambda) is expressed as follows as a reference distance _{d I} a (lambda ₀₎ of the virtual image I (λ _0).

Therefore, the axial chromatic aberration Δd _I (λ) that the combination of the thin lens intervals e ₀ and e ₁ brings to the imaging optical system can be calculated by the above equations (16), (17), and (18). it can. The axial chromatic aberration data in Examples described later are all derived from these equations.

Incidentally, in FIG. 3, when the virtual image I (λ) is located on the right side of the object O, the value of the axial chromatic aberration Δd _I (λ) is a negative number, and the virtual image I (λ) is located on the left side of the object O. In this case, the value of axial chromatic aberration Δd _I (λ) is a positive number.
[Supplement to the first embodiment]
In the first embodiment, at least one of the cemented lens 1 and the cemented lens 2 may be arranged in a state opposite to the front and back.

  The imaging lens 3 in the first embodiment is an objective lens of a microscope, that is, an imaging lens whose image formation position is at infinity, but other imaging lens whose image formation position is a finite position. It may be. In that case, the insertion destination of the cemented lens 1 and the cemented lens 2 may be either the object side or the image side of the imaging lens 3 (may be in any other convergent light beam or any divergent light beam). .)

  The imaging lens 3 in the first embodiment is an imaging lens that forms an image of an object, but may be a relay lens that relays an intermediate image formed by another imaging lens.

In any case, the distance between the object O or its conjugate image and the cemented lens 1 may be regarded as the lens surface distance d ₀ described above.

In addition, when the imaging optical system according to the above-described embodiment is applied to a surface shape measuring device (for example, a surface shape measuring device according to a third embodiment described later), in order to ensure the absolute accuracy of the measurement value, the shape is It is desirable to calibrate the instrument using a known sample prior to measurement.
[First embodiment]
The first embodiment of the imaging optical system in which the amount of axial chromatic aberration is variable will be described below.

  The imaging optical system of the present embodiment is formed by arranging a cemented lens 1, a cemented lens 2, and an imaging lens 3 in order from the object side. Among these, the imaging lens 3 is a first objective lens of a general-purpose microscope. Here, the cemented lens 1 and the cemented lens 2 will be described in detail.

  Table 1 shows lens data of the cemented lens 1 and the cemented lens 2. The order of incidence of light rays is the order of the object O, the cemented lens 1, and the cemented lens 2. However, as described above, the sign of the curvature radius of the surface was positive regardless of the unevenness of the surface.

  In Table 1, the glass materials S-TIH10 and S-LAL18 are listed in the optical glass catalog of OHARA, Inc. As shown in The lower part of Table 1 shows coefficients indicating the wavelength characteristics of the refractive indexes of S-TIH10 and S-LAL18. Each coefficient when the relationship between refractive index n and wavelength λ is expressed by the following equation. It is.

  The wavelength unit of the above formula is μm.

FIG. 4 is a graph showing the wavelength characteristics of the refractive indexes of S-TIH10 and S-LAL18. As shown in FIG. 4, the refractive indexes of both glass materials are 1.7302 near the wavelength of 573 nm. This wavelength 573 nm is the reference wavelength λ ₀ of this embodiment.

FIG. 5 is a graph showing the wavelength characteristics of the power of the cemented lens 1 and the cemented lens 2. As shown in FIG. 5, in the wavelength region of 400 to 700 nm, the absolute value of the power of the cemented lens 1 and the absolute value of the power of the cemented lens 2 are each less than 0.01. This wavelength range of 400 to 700 nm is the used wavelength range of this example. Further, the powers of both become 0 in the vicinity of the reference wavelength λ ₀ = 573 nm. Further, referring to FIG. 5 and Table 1 described above, it can be seen that the focal lengths (reciprocal of power) of the cemented lens 1 and the cemented lens 2 are sufficiently larger than the lens surface spacing.

Here, in this example, 425 nm was selected as the equal wavelength λ ₁ other than the reference wavelength λ ₀ = 573 nm. In this embodiment, the value of the thin lens interval e ₀ (λ ₁ ) is selected first, and the value of the thin lens interval e ₁ (λ ₁ ) suitable for the thin lens interval e ₀ (λ ₁ ) (13) Selected based on

Further, in this embodiment, the lens surface interval from the object O to the first surface (interval corresponding to the surface number 0) from the selected thin lens interval e ₀ (λ ₁ ), e ₁ (λ ₁ ). d ₀ and the lens surface interval (interval corresponding to surface number 3) d ₃ from the third surface to the fourth surface were derived by the following equations.

  However, the symbols in the formula are as follows.

T ₁₁ : Center thickness of the plano-convex lens 11 (interval between rows of surface number 1).

T ₁₂ : center thickness of the plano-concave lens 12 (interval between rows of surface number 2)

T ₂₁ : Center thickness of the plano-convex lens 21 (interval between rows of surface number 4).

N ₁ (λ ₁ ): the refractive index of the plano-convex lens 11 and the plano-concave lens 22 at the same wavelength λ ₁ .

N ₂ (λ ₁ ): refractive index of the plano-concave lens 12 and the plano-convex lens 21 at the same wavelength λ ₁

Table 2 is a table showing a combination example (combination example of the lens surface intervals d ₀ and d ₃ ) of the thin lens intervals e ₀ and e ₁ in the present embodiment.

In Table 2, the column indicated by “No. ₀ ” indicates the lens surface interval d ₀ , and the column indicated by “No. 3” indicates the lens surface interval d ₃ . The column indicated by “No. 6” indicates the distance d _I (λ ₀ ) from the second surface (surface number 6 in Table 1) of the plano-concave lens 22 to the virtual image I (λ ₀ ).

FIG. 6 is a graph showing the axial chromatic aberration according to the combination example shown in Table 2. As is apparent from FIG. 6, the amount of axial chromatic aberration changes according to the thin lens interval e ₀ (λ ₁ ).

FIG. 7 is a graph of paraxial magnification according to the combination examples shown in Table 2. The data in FIG. 7 is obtained by calculation based on Expression (9). As is apparent from FIG. 7, the paraxial magnification is completely 1 at the equal wavelength λ ₁ (= 425 nm) and the reference wavelength λ ₀ (= 573 nm).

  FIG. 8 is a graph showing substantial lateral chromatic aberration according to the combination examples shown in Table 2. The data in FIG. 8 indicates the height of the virtual image I (λ) obtained by ray tracing (ray tracing by a thick lens) of a principal ray having an object height of 1 mm under the object-side telecentric condition.

As is clear from FIG. 8, according to the combination example shown in Table 2, it can be seen that the magnification deviates from _{1 at the} equal wavelength λ ₁ (= 425 nm). This is considered to be due to wavelength-dependent distortion. Incidentally, the amount of deviation from the magnification 1 becomes more conspicuous as the thin lens interval e ₀ (λ ₁ ) is larger.

Therefore, in this example, each thin lens interval e ₁ (and lens surface interval d ₃ ) shown in Table 2 was corrected little by little as shown in Table 3.

In Table 3, “Correction amount No. 3” indicates the correction amount Δd ₃ , and “Correction amount / e ₁ ” is the ratio (%) of the correction amount Δd ₃ with respect to the thin lens interval e _1. surface interval No.3 "is a lens spacing _{d 3} after correction. The individual correction amount Δd ₃ was selected within a range in which the ratio of the correction amount Δd ₃ can be suppressed to 10% or less.

Here, when the correction amount Δd ₃ selected in this embodiment is expressed by a function (here, a quadratic expression) of the thin lens interval e ₀ (λ ₁ ), the following expression is obtained.

If expressed in this way the correction amount [Delta] d ₃ as a function of the thin lens distance e _{0 (λ 1),} can easily obtain the optimum correction amount [Delta] d ₃ for any thin lens distance e _{0 (λ 1)} .

FIG. 9 is a graph of axial chromatic aberration according to the combination example (combination example after correction) shown in Table 3. As is clear from FIG. 9, even when the above-described correction was performed, the relationship between the thin lens interval e ₀ (λ ₁ ) and the amount of longitudinal chromatic aberration remained good.

  FIG. 10 is a graph showing substantial lateral chromatic aberration according to the combination examples shown in Table 3. The data in FIG. 10 shows the height of the virtual image I (λ) obtained by ray tracing (ray tracing with a thick lens) of a principal ray having an object height of 1 mm under the object-side telecentric condition. As apparent from FIG. 10, according to the correction described above, the chromatic aberration of magnification was improved, and a state close to magnification 1 was obtained at each wavelength.

  The imaging optical system of the present embodiment is one in which the above-described cemented lens 1 and cemented lens 2 are inserted into the object space of the imaging lens 3. By the insertion, the axes of the entire system of the imaging optical system are obtained. On-axis chromatic aberration due to the cemented lenses 1 and 2 is added to the upper chromatic aberration. Further, since the insertion of the cemented lens 1 and the cemented lens 2 is almost equivalent to the insertion of a plane-parallel plate, a new spherical aberration is generated in the entire imaging optical system.

FIG. 11 is an aberration diagram showing spherical aberration in the combination examples shown in Table 3 (corrected combination examples). The data shown in FIG. 11 is obtained by simulation (ray tracing). The left part of FIG. 11 is a spherical aberration diagram when the thin lens interval e ₀ (λ ₁ ) is 3 mm, and the central part of FIG. 11 is when the thin lens interval e ₀ (λ ₁ ) is 4 mm. FIG. 11 is a spherical aberration diagram, and the right part of FIG. 11 is a spherical aberration diagram when the thin lens interval e ₀ (λ ₁ ) is 5 mm. The four curves in each aberration diagram are, in order from the left, spherical aberration when the wavelength λ is 700 nm, spherical aberration when the wavelength λ is 600 nm, spherical aberration when the wavelength λ is 500 nm, and wavelength. The spherical aberration when λ is 400 nm is shown. As is clear from FIG. 11, the spherical aberration generation pattern is maintained regardless of the thin lens interval e ₀ (λ ₁ ).

FIG. 12 is a spot diagram of the best focus position according to the combination example (combination example after correction) shown in Table 3. The data in FIG. 12 is data at the reference wavelength λ ₀ (= 573 nm), but the spot diagrams at other wavelengths are also substantially the same as those at the reference wavelength λ ₀ (= 573 nm), and are not shown.

  Here, usually, when the imaging lens 3 is used as the first objective lens of the surface shape measuring apparatus, the object O side of the imaging lens 3 is often telecentric. However, since the cemented lens 1 and the cemented lens 2 are inserted into the object space of the imaging lens 3 of the present embodiment, strictly speaking, the telecentricity may be lost depending on the wavelength.

  FIG. 13 is a graph showing telecentricity according to the combination example (combination example before correction) shown in Table 2. The data in FIG. 13 was obtained by ray tracing a chief ray having an object height of 1 mm, and shows the tangent of the angle formed by the ray after passing through the cemented lens 1 and the cemented lens 2 with the optical axis. Yes. The telecentric data of the combination example shown in Table 3 (corrected combination example) is almost the same as that shown in FIG.

FIG. 13 shows a case where the value of the thin lens interval e ₀ (λ ₁ ) is 3 mm, a case of 3.5 mm, a case of 4 mm, a case of 4.5 mm, and a case of 5 mm. These five curves are displayed, but they almost overlap. That is, the telecentricity of the imaging optical system is maintained regardless of the thin lens interval e ₀ (λ ₁ ).
[Second Embodiment]
The second embodiment of the imaging optical system in which the amount of axial chromatic aberration is variable will be described below. Here, differences from the first embodiment will be mainly described.

  The imaging optical system of the present embodiment is formed by arranging a cemented lens 1, a cemented lens 2, and an imaging lens 3 in order from the object side. The imaging lens 3 is a first objective lens of a microscope, and a second objective lens of the microscope is disposed on the image side. Incidentally, between the first objective lens and the second objective lens is a parallel system, and a beam splitter or the like can be inserted.

  FIG. 14 is an optical path diagram (optical system cross-sectional view) of the imaging optical system (imaging lens 3, cemented lens 2, and cemented lens 1). In FIG. 14, the object O is located on the right side, and the polygonal line shown in FIG. 14 indicates a parallel light beam incident from the imaging lens 3 side.

  Table 4 shows lens data of the imaging lens 3, the cemented lens 2, and the cemented lens 1.

In Table 4, the data description order is opposite to that of the first embodiment, and the imaging lens 3, the cemented lens 2, the cemented lens 1, and the object O are in this order. Although it is a calculation image plane and actually refers to the object plane, the reference wavelength λ ₀ and the equal wavelength λ ₁ of this embodiment are the same as those of the first embodiment (λ ₀ = 573 nm). , Λ ₁ = 425 nm).

  Table 5 shows data of the glass material used for the imaging lens 3.

Table 6 is a table showing a combination example (combination example of the lens surface intervals d ₀ and d ₃ ) of the thin lens intervals e ₀ and e ₁ of the present embodiment.

In Table 6, the column indicated by “No. 23” indicates the lens surface interval d ₀ , and the column indicated by “No. 20” indicates the lens surface interval d ₃ . The column indicated by “No. 17” indicates the distance from the second surface (surface number 18 in Table 4) of the plano-concave lens 22 to the virtual image I.

The chromatic aberration correction of the imaging optical system (imaging lens 3, cemented lens 2, and cemented lens 1) of the present embodiment is performed so that the chromatic aberration at the thin lens interval e ₀ (λ ₁ ) = 3 mm is minimized. It was.

FIG. 15 is a longitudinal aberration diagram of the imaging optical system (imaging lens 3, cemented lens 2, and cemented lens 1) when the thin lens interval e ₀ (λ ₁ ) is 3 mm (in order from the left, spherical aberration, non-spherical aberration). Point aberration, distortion aberration). The spherical aberration data is data for wavelengths of 400 nm, 500 nm, 600 nm, and 700 nm.

FIG. 16 is a coma aberration diagram of the imaging optical system (imaging lens 3, cemented lens 2, and cemented lens 1) when the thin lens interval e ₀ (λ ₁ ) is 3 mm.

FIG. 17 is a spot diagram of the best focus position of the imaging optical system (imaging lens 3, cemented lens 2, cemented lens 1) when the thin lens interval e ₀ (λ ₁ ) is 3 mm.

  FIG. 18 is a graph showing substantial lateral chromatic aberration according to the combination examples shown in Table 6. The data in FIG. 18 indicates the height of a virtual image I (λ) obtained by ray tracing (ray tracing by a thick lens) of a chief ray having an object height of 1 mm under the object-side telecentric condition.

Also in this example, the individual thin lens intervals e ₁ (and lens surface intervals d ₃ ) shown in Table 6 were corrected little by little as shown in Table 7.

In Table 7, “Correction amount No. 20” indicates the correction amount Δd ₃ , and “Correction amount / e ₁ ” is the ratio (%) of the correction amount Δd ₃ with respect to the thin lens interval e _1. surface interval No.20 "is a lens spacing _{d 3} after correction. The individual correction amount Δd ₃ was selected within a range in which the ratio of the correction amount Δd ₃ can be suppressed to 10% or less.

Here, when the correction amount Δd ₃ selected in this embodiment is expressed by a function (here, a quadratic expression) of the thin lens interval e ₀ (λ ₁ ), the following expression is obtained.

If expressed in this way the correction amount [Delta] d ₃ as a function of the thin lens distance e _{0 (λ 1),} can easily obtain the optimum correction amount [Delta] d ₃ for any thin lens distance e _{0 (λ 1)} .

  FIG. 19 is a graph showing substantial lateral chromatic aberration according to the combination examples shown in Table 7. The data in FIG. 19 shows the height of a virtual image I (λ) obtained by ray tracing (ray tracing by a thick lens) of a chief ray having an object height of 1 mm under the object-side telecentric condition.

  As is apparent from FIG. 19, the lateral chromatic aberration was improved by the above-described correction, and a state close to magnification 1 was obtained at each wavelength.

FIG. 20 is a graph showing telecentricity according to the combination example (combination example before correction) shown in Table 6. The data of FIG. 20 is obtained by simulation (ray tracing), and the notation method is the same as that of FIG. Data according to the combination example shown in Table 7 (combination example after correction) is almost the same as that in FIG. As is apparent from FIG. 20, the telecentricity is maintained regardless of the thin lens interval e ₀ (λ ₁ ).

FIG. 21 is a graph of axial chromatic aberration according to the combination example (combination example after correction) shown in Table 7. As apparent from FIG. 21, axial chromatic aberration is excellently changes according to thin lens distance e _0.

FIG. 22 is a diagram showing spherical aberrations according to the combination examples (corrected combination examples) shown in Table 7. The data shown in FIG. 22 is obtained by simulation (ray tracing). As is clear from FIG. 22, there is almost no variation due to the wavelength of the spherical aberration pattern. [Second Embodiment]
In the following, an embodiment of a surface shape measuring apparatus using on-axis chromatic aberration of the imaging optical system will be described.

  FIG. 23 is a configuration diagram of a surface shape measuring apparatus.

  In FIG. 23, reference numeral 300 denotes the imaging optical system described in the first embodiment. In the imaging optical system 300, an imaging lens 3, which is a first objective lens of a microscope, a cemented lens 2, and a cemented lens 1 are arranged. The image lens 3 is held by a holding mechanism 4. The second objective lens 7 is disposed on the image side of the imaging optical system 300. Hereinafter, the imaging lens 3 in the imaging optical system 300 is referred to as a “first objective lens 3”.

  In FIG. 23, the light beam emitted from the light source device 141 is collimated by the light source collimator 142 and is subjected to a diffusing action by the diffusing element 143. The diffusing element 143 may be a normal diffusing plate or a so-called fly-eye lens.

The illumination optical system 144 having positive power is arranged so that its focal position coincides with the diffusion element 143. A chart 15 is installed at the other focal point of the illumination optical system 144. When the light source device 141 is driven in this state, the chart 15 is illuminated. The optical system from the light source device 141 to the illumination optical system 144 is the illumination device 14.

  The light source device 141 is a light source capable of emitting illumination light having a spectrum based on an external command, and the wavelength band of the illumination light can be arbitrarily adjusted (for example, disclosed in JP-A-2008-170850). ).

  The illumination optical system 144 illuminates the chart 15 from an oblique direction so that the light intensity distribution on the chart 15 is a non-rotationally symmetric distribution with respect to the optical axis of the illumination optical system 144.

  The light beam that has passed through the chart 15 (the light beam for projecting the pattern of the chart 15 onto the object O) passes through the lens 16, is bent in the optical path by the plane mirror 12, and then passes through the partial aperture stop 5 for projection light. pass. The partial aperture stop 5 for projection light is a stop provided in a region on one half of the aperture stop surface of the first objective lens 3, and the illumination light emitted from the chart 15 is efficiently directed to the first objective lens 3 side. Let it pass. The illumination light that has passed through the first objective lens 3, the cemented lens 2, and the cemented lens 1 illuminates the object O from an oblique direction, and projects the pattern of the chart 15 on the surface of the object O.

  The reflected light (or scattered light) generated by the object O returns to the first objective lens 3 via the cemented lens 1 and the cemented lens 2, and only the light beam that has passed through the partial aperture stop 6 for imaging light is the second objective. The light enters the lens 7. The partial aperture stop 6 for imaging light is provided in a non-formation region of the partial aperture stop 5 for projection light on the aperture stop surface of the first objective lens 3.

  Note that the installation destination of the partial aperture stop 5 for projection light and the partial aperture stop 6 for imaging light (that is, the aperture stop surface of the first objective lens 3) is not necessarily at the illustrated position. When the imaging lens described in the second embodiment is used as the objective lens 3, it is between the lenses arranged inside the first objective lens 3.

  Here, the pattern of the chart 15 is a striped pattern as shown in FIG. 25, for example. The portion shown in white in FIG. 25 is a slit through which light passes. The orientation of the chart 15 is set so that the longitudinal direction of the slit is perpendicular to the paper surface of FIG. Therefore, the direction of the boundary line between the two types of aperture stops 5 and 6 described above is parallel to the longitudinal direction of the slit projected onto the object O.

  The light source device 141 simultaneously emits three types of illumination light having different wavelengths. In order to cope with this, a branching prism 8 is installed immediately after the second objective lens 7. The branching prism 8 branches incident light into light of three different wavelength bands, and is of the same type as, for example, an RGB three-color separation prism used in a three-plate camera.

  In the optical path of three types of wavelength bands (hereinafter referred to as “first wavelength band”, “second wavelength band”, and “third wavelength band”) where the branching prism 8 branches, imaging for the first wavelength band is performed. A camera 9, an imaging camera 10 for the second wavelength band, and an imaging camera 11 for the third wavelength band are individually arranged.

  The branching prism 8 preferably branches while crossing over adjacent bands among the first wavelength band, the second wavelength band, and the third wavelength band. Further, it is desirable that the second objective lens 7 and the branching prism 8 have chromatic aberration corrected in the entire system of both.

  FIG. 24 is a diagram for explaining the relationship between the three types of wavelength bands where the branching prism 8 branches and the wavelengths of the three types of illumination light emitted by the light source device 141. The horizontal axis of FIG. 24 indicates the wavelength, and the vertical axis indicates the transmittance of the three types of optical paths branched. In FIG. 24, “BAND1”, “BAND2”, and “BAND3” represent the first wavelength band, the second wavelength band, and the third wavelength band, respectively.

  As shown in the upper part of FIG. 24, among the three types of illumination light simultaneously emitted by the light source device 141, the wavelength of the first illumination light belongs to the first wavelength band, and the wavelength of the second illumination light is the second wavelength band. The wavelength of the third illumination light belongs to the third wavelength band.

  24, the light source device 141 scans the wavelength of the first illumination light within the first wavelength band, scans the wavelength of the second illumination light within the second wavelength band, The wavelength of illumination light is scanned within the third wavelength band. These scans are performed in parallel.

  Further, during such wavelength scanning, the imaging camera 9 for the first wavelength band, the imaging camera 10 for the second wavelength band, and the imaging camera 11 for the third wavelength band are formed on the respective imaging surfaces. Fifteen images (slit images) are taken repeatedly. Imaging by each camera is performed in parallel.

  According to such operations of the light source device 141 and the imaging cameras 9, 10, and 11, data of each wavelength belonging to a wide wavelength band can be acquired in a short time.

  Note that, as shown in the middle or lower part of FIG. 24, when the emission wavelength overlaps the crossover region between the adjacent wavelength bands, separation by wavelength becomes impossible, so the light source device 141 has the number of illumination lights simultaneously emitted. Is appropriately reduced so that two types of emission wavelengths do not exist within one type of wavelength band.

  FIG. 27 is a diagram illustrating differences in the focal positions of three types of illumination light having different wavelengths. In FIG. 27, circles F1, F2, and F3 are the focal positions of the three types of illumination light. The difference in line type in FIG. 27 represents the difference in wavelength. As is clear from FIG. 27, the wavelength for focusing varies depending on the height of the surface of the object O.

  FIG. 26 is a diagram illustrating the relationship between the wavelength of the illumination light and the intensity distribution of the slit image. The left column in FIG. 26 shows illumination light of various wavelengths directed to a certain part on the object O, and the column on the right side of FIG. 26 shows the intensity distribution of the slit image generated by various wavelengths in the part. Show.

As shown in FIG. 26, the peak position of the intensity distribution of the slit image varies depending on the wavelength. As shown in the center of the left column, when illumination light of a certain wavelength is in focus, the peak position (coordinate value in the X-axis direction) of the slit image of that wavelength is a predetermined value X Matches _zero .

  Therefore, the control / calculation unit 13 shown in FIG. 23 calculates the wavelength of the illumination light in the focused state from the peak position (the coordinate value in the X-axis direction) of the slit image of each wavelength, The height of the above-described part is calculated by comparing with the axial chromatic aberration (known) of the first objective lens 3.

  Further, the control / calculation means 13 performs such height calculation for each part on the object O, and the distribution of the calculated height on the object O is used as a surface shape data of the object O, a monitor (not shown). Output to.

  As described above, the imaging optical system 300 (the first objective lens 3, the cemented lens 2, the cemented lens 1, and the holding mechanism 4) described in the first embodiment is applied to the surface shape measuring apparatus of the present embodiment as described above. Has been.

Therefore, if the user drives the lens surface distance d ₀ via the holding mechanism 4, each of the lens surface distances d ₃ and d ₆ (see FIG. 1) is automatically and appropriately driven accordingly.

Therefore, the surface shape measuring apparatus according to the present embodiment can freely adjust the dynamic range in the height direction, and there is no possibility that the measurement accuracy is lowered by the adjustment.
[Supplement to the aspect described above]
In one aspect illustrating the imaging optical system of the present invention, the first lens is a first cemented lens in which a first plano-convex lens and a first plano-concave lens are cemented with each other by their convex and concave surfaces, and the second lens is A second cemented lens in which the second plano-convex lens and the second plano-concave lens are cemented with each other by their convex and concave surfaces may be used.

  Further, it is desirable that the first plano-convex lens and the first plano-concave lens show the same refractive index with respect to a predetermined wavelength and show different refractive indexes with respect to other wavelengths.

  The wavelength characteristic of the refractive index of the second plano-convex lens is the same as the wavelength characteristic of the refractive index of the first plano-concave lens, and the wavelength characteristic of the refractive index of the second plano-concave lens is the wavelength of the refractive index of the first plano-convex lens. It may be the same as the characteristic.

Another embodiment illustrating the imaging optical system of the present invention is different from a predetermined wavelength when the first cemented lens is represented by a first thin lens and the second cemented lens is represented by a second thin lens. for a given wavelength lambda _1, the viewing surface or spacing e ₀ and its conjugate image and the first thin lens _{(lambda 1),} the spacing e ₁ between the first thin lens and the second thin lens _{(lambda 1)} is , The relationship of equation (12), the relationship of equation (13), the relationship obtained by correcting equation (12) with a correction width of 10% or less, and the equation (13) obtained by correcting with a correction width of 10% or less. It is desirable to satisfy any of the relationships

Where R ₁ is the absolute value of the radius of curvature of the cemented surface of the first cemented lens, R ₂ is the absolute value of the radius of curvature of the cemented surface of the second cemented lens, and n ₁ (λ ₁ ) is the predetermined wavelength λ ₁ is the refractive index of the first plano-convex lens with respect to 1, and n ₂ (λ ₁ ) is the refractive index of the first plano-concave lens with respect to the predetermined wavelength λ _1. Also, the first cemented lens, the second cemented lens, and the imaging lens are It is desirable that aberration correction of the entire imaging optical system, specifically, chromatic aberration and Seidel 5 aberration correction is performed when the lens is disposed in a predetermined positional relationship.

  DESCRIPTION OF SYMBOLS 1 ... Joint lens 1, 2 ... Joint lens 2, 3 ... Imaging lens (1st objective lens), 4 ... Holding mechanism, 141 ... Light source device, 142 ... Light source collimator 143, diffusing element, 144, illumination optical system, 15 ... chart, 12 ... flat mirror, 5 ... partial aperture stop for projection light, 6 ... part for imaging light Aperture stop, 7 ... second objective lens, 8 ... branch prism, 9 ... imaging camera for first wavelength band, 10 ... imaging camera for second wavelength band, 11 ... first Imaging camera for 3 wavelength bands

Japanese Patent No. 2812371 JP 7-229720 A

Claims (8)

An imaging lens;
In an imaging optical system comprising a first lens and a second lens that are movable in the optical axis direction of the imaging lens,
By moving at least one of the first lens and the second lens in the optical axis direction, the amount of axial chromatic aberration of the imaging optical system is variably adjusted, and the first lens and the second lens By changing the positional relationship in the optical axis direction, fluctuations in lateral chromatic aberration of the imaging optical system due to fluctuations in the amount of longitudinal chromatic aberration are suppressed. The imaging optical system according to claim 1,
The first lens is a first cemented lens in which a first plano-convex lens and a first plano-concave lens are cemented with each other by their convex and concave surfaces.
The imaging optical system, wherein the second lens is a second cemented lens in which a second plano-convex lens and a second plano-concave lens are cemented with each other by their convex and concave surfaces. The imaging optical system according to claim 2,
The imaging optical system, wherein the first plano-convex lens and the first plano-concave lens exhibit the same refractive index with respect to a predetermined wavelength and different refractive indexes with respect to other wavelengths. In the imaging optical system according to claim 2 or 3,
The wavelength characteristic of the refractive index of the second plano-convex lens is the same as the wavelength characteristic of the refractive index of the first plano-concave lens, and the wavelength characteristic of the refractive index of the second plano-concave lens is the refractive index of the first plano-convex lens. An imaging optical system characterized by having the same wavelength characteristics as An imaging lens for forming an image of the observation surface;
A first cemented lens and a second cemented lens which are arranged in an optical path between the observation surface or a conjugate image thereof and the imaging lens and share the optical axes of each other;
The first cemented lens is
A first plano-convex lens and a first plano-concave lens having a concave surface made of an inverted shape of the convex surface of the first plano-convex lens are joined to each other by both the convex surface and the concave surface. 1 plano-concave lens shows the same refractive index with respect to a predetermined wavelength, and shows different refractive indexes with respect to other wavelengths,
The second cemented lens is
A second plano-convex lens having a convex surface with a gentler curve than the cemented surface of the first cemented lens, and a second plano-concave lens having a concave surface formed by reversing the convex surface of the second plano-convex lens; The wavelength characteristics of the refractive index of the second plano-convex lens are the same as the wavelength characteristics of the refractive index of the first plano-concave lens, and the wavelength characteristics of the refractive index of the second plano-concave lens are , The same as the wavelength characteristic of the refractive index of the first plano-convex lens,
The distance between the observation surface or its conjugate image and the first cemented lens is variable, the distance between the first cemented lens and the second cemented lens is variable, and the second cemented lens and the imaging lens The imaging optical system is characterized in that the interval of is variable. The imaging optical system according to claim 5,
When the first cemented lens is represented by a first thin lens and the second cemented lens is represented by a second thin lens,
For a predetermined wavelength λ ₁ different from the predetermined wavelength, an interval e ₀ (λ ₁ ) between the observation surface or its conjugate image and the first thin lens, the first thin lens and the second thin lens, The interval e ₁ (λ ₁ ) of
The following relationship or the relationship obtained by correcting the following relationship with a correction width of 10% or less is satisfied.

Where R ₁ is the absolute value of the radius of curvature of the cemented surface of the first cemented lens, R ₂ is the absolute value of the radius of curvature of the cemented surface of the second cemented lens, and n ₁ (λ ₁ ) is the above-mentioned value. An imaging optical system, wherein a refractive index of the first plano-convex lens with respect to a predetermined wavelength λ ₁ and n ₂ (λ ₁ ) is a refractive index of the first plano-concave lens with respect to the predetermined wavelength λ ₁ . In the imaging optical system according to claim 5 or 6,
The aberration correction of the entire system of the imaging optical system is performed when the first cemented lens, the second cemented lens, and the imaging lens are arranged in a predetermined positional relationship. Image optics. A light source that emits light of a plurality of different wavelengths;
The imaging optical system according to any one of claims 1 to 7, wherein the measurement surface is illuminated with light emitted from the light source, and an image of the measurement surface is formed in that state.
Detecting means for detecting a focusing wavelength at each position of an image formed by the imaging optical system;
A surface shape measuring device comprising:

Images