JP2011141145A - Measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring apparatus which measures the transmission wavefront of an optical system of which the exit pupil position is finite with high precision. <P>SOLUTION: The measuring apparatus (100) for measuring the transmission wavefront of an optical system of which the exit pupil position is finite is a measuring apparatus for measuring the characteristics of an optical system under measurement by a wavefront sensor (10) for detecting light under measurement directed to the optical system under measurement through the optical system under measurement (40) and includes a light collecting optical system (30) for collecting the light under measurement to the image point of the optical system under measurement and an XY-axis moving unit (16A) for moving the wavefront sensor (10) with respect to the light collecting optical system in a direction crossing the optical axis of the light collecting optical system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a measuring apparatus that measures a transmitted wavefront of an optical system with high accuracy. In particular, the present invention relates to a measurement apparatus that measures a transmitted wavefront of an optical system having a finite exit pupil position.

  An interferometer is generally used to measure the transmitted wavefront of a lens to be measured such as a telephoto lens. In the interferometer disclosed in Patent Document 1, light emitted from a laser light source is divided into reference light and test light by a beam splitter. This reference light is reflected by the reference surface and returns to the beam beam splitter again. The test light enters from a direction that coincides with the optical axis of the test lens, and passes through the test lens. Then, the test light is reflected by the reflecting surface, passes through the test lens again, and returns to the beam splitter. Then, after the reference light and the test light are combined, they are collected by the imaging lens to form interference fringes on the observation surface. In such an interferometer, since laser light having high coherence is used, interference fringes with a clear contrast can be observed, and the uneven shape of the test lens can be evaluated with high accuracy. . That is, the interferometer disclosed in Patent Document 1 can observe the transmitted wavefront of the test lens that matches the optical axis of the test lens.

JP-A-10-160582

  However, in general optical systems, there are many cases where the exit pupil is at a finite position from the image plane, and light having an angle of view, that is, the principal ray of the convergent light beam directed toward the image point is inclined with respect to the optical axis. There is a demand for a test lens that is such an optical system to observe the off-axis transmitted wavefront by inclining the principal ray from the interferometer side with respect to the optical axis of the test lens and making the beam incident. It is conceivable to place the interferometer tilted, but tilting the interferometer within a plane including the vertical axis is not preferable for measurement because the optical system inside the interferometer may be distorted due to the influence of gravity.

  Therefore, the present invention provides a measuring apparatus that measures the transmitted wavefront of an optical system with a finite exit pupil position with high accuracy.

  The measuring apparatus according to the first aspect is a wavefront sensor that detects test light directed to the test optical system via the test optical system, and is a measurement apparatus that measures the characteristics of the test optical system. The measuring apparatus includes: a condensing optical system that condenses the test light on the image point of the test optical system; and a first that moves the wavefront sensor relative to the condensing optical system in a direction intersecting the optical axis of the condensing optical system. 1 moving part.

  The measuring apparatus of the present invention allows light whose tilted principal ray of the convergent light beam is incident on the test optical system to observe the transmitted wavefront, and the measuring apparatus can finely sample the transmitted wavefront and the wavefront It is possible to evaluate up to high frequency components.

1 is a diagram illustrating an outline of a configuration of a first measuring device 100. FIG. (A) is the schematic plan view which showed the relationship between the condensing lens 31 and the light beam L31A of test light. (B) is a schematic side view in which the light beam L31A of the test light is incident on the test lens 41. (c) is a schematic plan view showing the relationship between the condenser lens 31 and the light beam L31B of the test light. is there. (D) is a schematic side view of the light beam L31B of the test light entering the test lens 41. FIG. FIG. 6 is a diagram for explaining conditions of the condenser lens 31. It is the figure which showed the outline of the structure of the 2nd measuring apparatus 200. FIG. FIG. 5A is a plan view of the focus reference plate 32. FIG. 5B is a cross-sectional view of the side surface of the focus reference plate 32. It is a figure which is measuring the focus position of the reference | standard focusing screen 32 in the 2nd measuring apparatus 200. FIG. FIG. 6 is a diagram showing an outline of the configuration of a third measuring apparatus 300. FIG. 6 is a diagram illustrating an outline of a configuration of a fourth measuring apparatus 400. It is the figure which showed the outline of the structure of the 5th measuring apparatus 500. FIG.

(First embodiment)
<Configuration of first measuring apparatus 100>
A case will be described as the first embodiment in which the measuring apparatus is a Twiman-Green interferometer.

  FIG. 1 is a diagram showing an outline of the configuration of the first measuring apparatus 100. The first measuring apparatus 100 includes a wavefront sensor 10, an electronic calculator 21, a test optical system 40, and a condenser lens 31.

  The wavefront sensor 10 includes a light source 11, a beam splitter 12, a reference mirror 13, an imaging lens 14, an image sensor 15, and an XY axis moving device 16A. Since it is necessary to use light having good coherence in the interferometer, laser light is used as the light source 11. The beam splitter 12 is, for example, a half mirror, and splits one light beam emitted from the light source 11 into two light beams of reference light and test light. The reference mirror 13 is a plane mirror that reflects the reference light guided from the beam splitter 12 and returns it to the beam splitter 12. The imaging lens 14 is composed of two convex lenses, and images the light guided from the beam splitter 12 on the image sensor 15.

  The image sensor 15 converts interference fringes formed on the image sensor 15 into an electrical signal. Specifically, the imaging device 15 is a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like. The XY axis moving device 16A moves the wavefront sensor 10 in the X axis and Y axis directions. Here, the direction in which the laser light is irradiated from the light source 11 is the −X axis direction, the direction of the light irradiated from the wavefront sensor 10 to the condenser lens 31 is the −Z axis direction, and the axis is perpendicular to the X axis and the Z axis. Is the Y axis.

The condenser lens 31 is a unit of a condensing optical system that converts a plane wave irradiated from the wavefront sensor 10 into a spherical wave and guides it to the optical system 40 to be tested. In the first measuring apparatus 100, a convex lens is used as the condenser lens 31, and the plane wave irradiated from the wavefront sensor 10 is converted into a spherical wave.
The electronic computer 21 receives an electrical signal related to interference fringes sent from the image sensor 15 and analyzes the transmitted wavefront of the lens 41 to be examined.

  The test optical system 40 is an optical system including an optical component to be inspected, a test lens 41 that is an optical component to be inspected, and a reflecting mirror 42 that reflects the test light transmitted through the test lens 41. It is comprised by. The reflecting mirror 42 is a plane mirror.

<Operation of First Measuring Apparatus 100>
Next, an operation when measuring the test lens 41 by the first measuring device 100 will be described.
The light beam irradiated from the light source 11 in the −X-axis direction enters the beam splitter 12 (arrow L1). The beam splitter 12 has a half mirror, and divides light into reference light and test light. The test light (arrow LY 1) from the beam splitter 12 toward the test optical system 40 in the −Z axis direction is converted from a plane wave to a spherical wave by the condenser lens 31. The test light (arrow LY2) converted into the spherical wave is incident on the test lens 41 with an inclination with respect to the optical axis AX41 of the test lens 41. The test light transmitted through the test lens 41 is reflected by the reflecting mirror 42 and travels again through the test lens 41 toward the condenser lens 31 (arrow LY3). Then, the test light passes through the condenser lens 31 and returns to the beam splitter 12.

  On the other hand, reference light, which is light traveling in the −X-axis direction from the beam splitter 12, travels toward the reference surface 13 (arrow LX1). The reference light is reflected by the reference surface 13 and returns to the beam splitter 12 (arrow LX2). In the beam splitter 12, the test light returned from the test optical system 40 and the reference light reflected and returned from the reference surface 13 are overlapped to become combined light and travel in the + Z-axis direction (arrow LC1). The combined light becomes interference fringes and forms an image on the image sensor 15 through the imaging lens 14. The interference fringes are analyzed by the electronic computer 21, whereby the transmitted wavefront of the lens 41 to be measured can be measured.

  The wavefront sensor 10 has an XY axis moving device 16A. The XY axis moving device 16A can freely move the wavefront sensor 10 in the XY plane. The condenser lens 31 has a larger aperture than the beam diameter of the wavefront sensor 10. For this reason, the wavefront sensor 10 can make the laser light incident on all positions on the condenser lens 31. Therefore, when the transmitted wavefront of the test lens 41 is to be measured in a state where the chief ray is tilted with respect to the optical axis of the test lens 41, the test light 41 is tilted with an arbitrary tilt. It can be made to enter. Further, the incident position of the test light on the focus lens 31 can be changed depending on the diameter of the test lens 41 or the like.

  The test lens 41 is supported by a stage (not shown). The test lens 41 to be inspected in the present embodiment has a finite exit pupil position from a predetermined focal length and image plane, and the test lens 41 is arranged at an appropriate position according to the focal length and angle of view. Is done.

<Relationship of Test Light Irradiated to Condensing Lens 31 and Test Lens 41>
FIG. 2A is a schematic plan view showing the relationship between the condenser lens 31 and the light beam L31A of the test light. The incident position of the light beam L31A of the test light from the wavefront sensor 10 to the condenser lens 31 is shown. The light beam L31A of the test light is incident on a position far from the optical axis AX31 of the condenser lens 31. FIG. 2B is a schematic side view of the test light beam L31A entering the test lens 41. FIG.

  FIG. 2C is a schematic plan view showing the relationship between the condenser lens 31 and the light beam L31B of the test light. The incident position of the light beam L31B of the test light from the wavefront sensor 10 to the condenser lens 31 is shown. The light beam L31B of the test light is incident at a position near the optical axis AX31 of the condenser lens 31. FIG. 2D is a schematic side view in which the light beam L <b> 31 </ b> B of the test light enters the test lens 41. As shown in FIG. 2B or FIG. 2D, the optical axis AX31 of the condenser lens 31 and the optical axis AX41 of the test lens 41 are not coaxially arranged on the XY plane.

  The XY-axis drive device 16A (FIG. 1) moves the position of the wavefront sensor 10 when measuring the transmitted wavefront of the lens 41, and thereby the position of the test light irradiated on the condenser lens 31 Can be adjusted. 2A to 2D show examples when the wavefront sensor 10 moves in the −X-axis direction with respect to the condenser lens 31. FIG. Although not shown, the XY axis drive device 16A can also move the position of the wavefront sensor 10 in the Y axis direction.

  In the first measurement apparatus 100, the test light emitted by the wavefront sensor 10 can be incident on the test lens 41 by adjusting the position of the wavefront sensor 10 using the XY axis moving device 16 </ b> A. Further, the test light can be returned into the wavefront sensor 10 via the condenser lens 31. At this time, if the NA of the condensing lens 31 is slightly larger than or coincides with the NA of the lens 41 to be measured, the first measuring apparatus 100 can efficiently use the light to be used, and the wavefront is made fine. It is possible to measure, and it is possible to evaluate even a high frequency component as a wavefront.

  As shown in FIG. 2A, when the light beam L31A of the test light enters a position far from the optical axis AX31 of the condenser lens 31, as shown in FIG. The principal ray AXL of the light beam L31A is incident on the test lens 41 at an angle θA with respect to the optical axis AX41 of the test lens 41. On the other hand, as shown in FIG. 2C, when the light beam L31B of the test light enters the position near the optical axis AX31 of the condensing lens 31, as shown in FIG. The principal ray AXL of the light beam L31B is incident on the test lens 41 at an angle θB with respect to the optical axis AX41 of the test lens 41. As shown in FIG. 2B, the inclination θA of the principal ray AXL with respect to the optical axis AX41 is larger than the inclination θB.

  As shown in FIGS. 2A and 2C, the angle of the principal ray of the test light on the test lens 41 can be adjusted by the incident position of the test light on the condenser lens 31. In the measurement of the transmitted wavefront, if the wavefront sensor 10 and the condenser lens 31 are tilted, the angle of the principal ray of the test light to the test lens 41 can be adjusted, but this is caused by the distortion of the optical system inside the wavefront sensor 10. Distortion of the light that occurs.

  In the measurement of the transmitted wavefront of the present embodiment, the wavefront sensor 10 is arranged so that the interferometer beam faces the −Z axis direction when measuring any image point away from the optical axis AX41 of the test lens 41. Since the wavefront sensor 10 is not tilted, the light distortion caused by the distortion of the optical system inside the wavefront sensor 10 can be suppressed.

  In the first embodiment, the position of the wavefront sensor 10 is moved and the transmitted wavefront on the test lens 41 is measured. However, the position of the wavefront sensor 10 is fixed, and the test lens 41 and the condenser lens 31 are measured. It is also possible to adopt a configuration in which the transmitted wavefront measurement is performed by adjusting the position of.

<Conditions for the condensing lens 31>
In order for the first measuring apparatus 100 to measure the off-axis performance of the test lens 41, the light transmitted through the condenser lens 31 is guided to the test lens 41, and the test light from the test lens 41 is again transmitted to the wavefront sensor. It must be returned to within 10. Since the principal ray of the test lens 41 is inclined, the condenser lens 31 must have a larger numerical aperture NA than that of the test lens 41. Otherwise, only a part of the test light returns into the wavefront sensor 10, and the wavefront of the test lens 41 cannot be measured without vignetting. Therefore, the condensing lens 31 needs a lens having a large numerical aperture NA (small F value).
FIG. 3 is a diagram for explaining the condition of the numerical aperture NA of the condenser lens 31.

  In FIG. 3, the plane wave (test light) emitted from the wavefront sensor 10 is converted into a spherical wave (test light) by the condenser lens 31. This spherical wave is focused on the image plane 33 of the condenser lens 31. Thereafter, the spherical wave (test light) spreads and enters the exit pupil 45 of the test lens 41.

The numerical aperture NA ₀ of the condenser lens 31 is expressed by the following equation in air.
NA ₀ = sin θ ₁ (1)
Here, the angle a is the aperture angle light emitted from an object on the optical axis expect the exit pupil of the condenser lens 31 is 2 [Theta] _1.

The incident angle θ ₀ of the test light to the test optical system 40 (see FIG. 1) is expressed by the following equation.
θ ₀ = tan ⁻¹ (Yu / Lu) (2)
Here, Yu is the maximum image height of the test optical system, and Lu is the distance from the test optical system exit pupil 45 to the image plane 33.

Further, the numerical aperture NA ₁ of the test optical system 40 is expressed as follows.
NA ₁ = 1 / (2Fu) (3)
Here, Fu is the F value of the test optical system 40.

NA ₁ satisfies the following expression.
NA ₁ = sin α ₀ (4)
Here, it is the aperture angle of the exit pupil 45 of the optical system to be measured 41 and 2.alpha _0.

The following equations are derived from Equations 3 and 4.
α ₀ = sin ⁻¹ (NA ₁ ) = sin ⁻¹ (1 / 2Fu) (5)

Since θ ₁ is the sum of θ ₀ and α ₀ , θ ₁ is expressed by the following equation.
θ ₁ = θ ₀ + α ₀ (6)

In the test lens 41 having a finite exit pupil position, the off-axis luminous flux is vignetted when the NA of the condensing lens 31 is matched with the NA of the test lens 41. Therefore, it is necessary to use the condensing lens 31 having a small F value and a bright condensing optical system so as to surely return the test light into the wavefront sensor 10. For that purpose, the NA of the condensing optical system actually used must be made larger than NA ₀ calculated from the incident light. Therefore, the following inequality must hold.
NA> sinθ ₁ (7)

From Equation 2, Equation 5, Equation 6, and Equation 7, the following inequality 8 is derived.
... (8)

Further, in order to surely return the returned light into the wavefront sensor 10, it is necessary to select a bright lens having a small F value as the lens of the condensing optical system. Therefore, if the F value of the condensing optical system is F1, at least F1 must be smaller than Fu. Therefore, the relationship between F1 and Fu must satisfy the following equation.
F1 <Fu (9)

Furthermore, if the focal length of the condensing optical system is fd and the diameter of the light beam of the test light from the wavefront sensor 10 is φi, then F1 = fd / φi, so Equation 9 can be converted as follows.
fd <Fuφi (10)

  The optical system of the first measuring device 100 can measure the entire visual field of the lens 41 to be measured finely by satisfying the mathematical expressions 8 and 10.

(Second Embodiment)
<Configuration of Second Measuring Device 200>
FIG. 4 is a diagram showing an outline of the configuration of the second measuring apparatus 200. The second measuring device 200 includes a wavefront measuring device 20, a reference focusing plate 32, a test optical system 40, and an electronic computer 21. The wavefront measuring apparatus 20 includes the wavefront sensor 10, the condenser lens 31, and the reflecting member 18. The wavefront sensor 10 has the configuration described in the first embodiment.

  The wavefront measuring device 20 includes an XY-axis moving device 16B that can move the wavefront measuring device 20 in the X-axis and Y-axis directions, and a Z-axis moving device 17 that can move the wavefront measuring device 20 in the Z-axis direction. It has. The XY-axis moving device 16B or the Z-axis moving device 17 attached to the wavefront measuring device 20 can simultaneously move the wavefront measuring device 20 without changing the relative position between the wavefront sensor 10 and the condenser lens 31. it can. The reference focusing screen 32 has a reflecting surface 321 having a high reflectivity and a high flatness on a surface on the condensing optical system side, and a small opening 322 that is a hole through which a light beam passes. The reference focusing plate 32 is disposed between the wavefront measuring apparatus 20 and the test optical system 40 and is disposed substantially on the image plane 33 of the test optical system 41.

  FIG. 5A is a plan view of the focus reference plate 32. The focus reference plate 32 has at least one Z-axis side surface as a reflection surface 321 and has a substantially square plane. In addition, a total of 25 round small openings 322 of 5 rows and 5 columns are formed in the X-axis and Y-axis directions. The adjacent small openings 323 in the X-axis direction and the Y-axis direction are arranged at equal intervals, and the position of each small opening 323 corresponds to the position where the transmitted wavefront on the test lens 41 is desired to be measured. In FIG. 5A, the focus reference plate 32 is square but may be rectangular. When the focus reference plate 32 is rectangular, for example, a total of 25 rows of 5 rows and 5 columns in the X-axis and Y-axis directions are used. A round small opening 322 is formed.

  FIG. 5B is a cross-sectional view of the focus reference plate 32 taken along the dotted line AA in FIG. When it is desired to measure the transmitted wavefront of the test lens 41 (see FIG. 4), the XY axis moving device 16B is set so that the optical axis AXL (indicated by E1) of the test light enters the small aperture 322. The wavefront measuring apparatus 20 is moved. That is, the XY axis moving device 16B focuses the focus lens 31 on the small aperture 322.

  When the focal position of the focus lens 31 is to be adjusted, the XY axis moving device 16B is used by the wavefront measuring device 20 so that the optical axis AXL (indicated by E1) of the test light is reflected by the reflecting surface 321. Move. That is, the XY axis moving device 16B moves the focal position of the focal lens 31 onto the reflecting plate 321.

<Measurement of focal position of lens 41>
The test lens 41 is incorporated into a product such as a camera after measuring the transmitted wavefront using the wavefront measuring apparatus 200. For example, the test lens 41 is an interchangeable lens, and the CCD of the camera is disposed on the focal plane of the test lens 41. The focal plane of the test lens 41 is the position of the image plane 33 in FIG. However, in practice, the focal plane of the lens 41 to be tested may be slightly shifted from the position of the design image plane 33. Image quality deterioration occurs due to the shift of the focal plane of the test lens 41. For this reason, it is important to accurately measure the focal position of the lens 41 to be examined.

  FIG. 6 is a diagram illustrating a state in which the position of the reference focusing screen 32 is being measured in the second measuring apparatus 200. A method for measuring the focal position of the lens 41 will be described with reference to FIG.

  A reference focusing plate 32 is disposed in the vicinity of the image plane 33. The wavefront measuring apparatus 20 moves relative to the reference focusing plate 32 so that the test light is irradiated onto the reflection surface 321 of the reference focusing plate 32. The test light emitted from the wavefront sensor 10 enters the condenser lens 31 in the −Z-axis direction as indicated by an arrow LA1. The test light passes through the condenser lens 31 as indicated by the arrow LA2, is reflected by the reflecting surface 321 of the reference focusing plate 32, and enters the condenser lens 31 again as indicated by the arrow LA3. The position at which the test light indicated by the arrow LA3 is incident on the condenser lens 31 is symmetrical with respect to the position where the test light indicated by the arrow LA2 is irradiated from the condenser lens 31 with the optical axis AX31 as the center. Thereafter, the light passes through the condenser lens 31 and is reflected by the reflecting member 18. The test light reflected by the reflecting member 18 proceeds as indicated by an arrow LA4, is reflected by the reflecting surface 321 of the reference focusing plate 32, and enters the condenser lens 31 again as indicated by an arrow LA5. The test light that has passed through the condenser lens 31 returns to the wavefront sensor 10 as indicated by the arrow LA6.

  The electronic computer 21 can measure the position of the standard focusing screen 32 by analyzing the combined light of the test light and the reference light that has returned to the wavefront sensor 10.

  Here, the reflecting member 18 is disposed so as not to block the optical axis of the condenser lens 31 so as not to block the test light indicated by the arrow LA1. Further, the size of the reflecting member 18 is close to the radius of the condensing lens 31 so that the test light reflected by the reflecting surface 321 (arrow LA3) can correspond to any position on the condensing lens 31. On the other hand, it is desirable to have a larger size.

  As a result of measuring the position of the reference focusing screen 32 by the electronic computer 21, if the focal position of the condenser lens 31 does not coincide with the position (Z-axis direction) of the reflecting surface 321 of the reference focusing plate 32, the Z-axis movement is performed. The device 17 moves the wavefront measuring device 20 in the Z-axis direction. Then, the focal position of the condenser lens 31 and the reflecting surface 321 of the reference focusing plate 32 are made to coincide. Thus, the focal position of the condenser lens 31 is calibrated. If reconfirmation is necessary, the test light indicated by LA1 is again emitted from the wavefront sensor 10. The test light indicated by the arrow LA6 is analyzed by the electronic computer 21.

  Thereafter, the wavefront measuring apparatus 20 is moved slightly in the X direction or the Y direction so that the test light can pass through the small opening 323 of the reference focus plate 32, and measures the focal position of the test lens 41. The focal position of the test lens 41 is measured by moving the wavefront measuring device 20 in the Z-axis direction by the Z-axis moving device 17 and focusing on the image sensor 15. Then, the electronic calculator 21 calculates the deviation of the lens 41 to be examined from the image plane 33. When the focal position at each small aperture 322 is sequentially measured, the electronic calculator 21 can also analyze the curved state and the inclined state of the image plane of the lens 41 to be examined. With the method as described above, the accurate focal position of the lens 41 to be measured can be measured.

  Further, the test light (arrows LA1 to LA6) in FIG. 6 reciprocates between the condenser lens 31 and the reference focusing screen 32 twice. For this reason, the measurement sensitivity of the focal position is doubled. Further, if the incident angle of light when entering the reference focusing plate 32 obliquely is θ, the length of the optical path is between the condenser lens 31 and the reference focusing plate 32 as compared to the length of the optical path when not inclined. Is 1 / cos θ times. Therefore, the measurement accuracy can be improved by 1 / cos θ.

  In the second embodiment, it is also possible to use a focus reference plate 32B (not shown) in which the small opening 322 is not opened. When the focus of the condenser lens 31 is obtained, a focus reference plate 32B is inserted into the image surface 33. When measuring the transmitted wavefront of the test optical system 40, the focus reference plate 32B is moved to a position where the focus reference plate 32B does not block the test light. In this case, it is not always necessary to attach the XY axis moving device to the wavefront measuring apparatus 20, but it is necessary to attach the XY axis moving device to the focus reference plate 32B.

(Third embodiment)
<Configuration of Third Measuring Apparatus 300>
FIG. 7 is a diagram showing an outline of the configuration of the third measuring apparatus 300. The third measuring apparatus 300 includes a test concave mirror 43 and a reflective concave mirror 44 in the test optical system 40, and can measure the reflected wavefront of the test concave mirror 43.

  The configuration of the wavefront sensor 10 is the same as that of the second measuring device 200. Since the incident position of the light beam on the condenser lens 31 can be adjusted by moving the wavefront sensor 10 by the XY axis moving device 16A, the incident position of the test light on the test concave mirror 43 is the XY of the wavefront sensor 10. It is adjusted by the shaft moving device 16A. The configurations of the wavefront measuring device 20 and the reference focusing screen 32 are also the same as those of the second measuring device 200. The reference focusing screen 32 is disposed on the image plane 34 of the concave mirror 43 to be examined. The focal length of the condenser lens 31 is adjusted to the image plane 34 by the Z-axis moving device 17 of the wavefront measuring device 20. When measuring the reflected wavefront of the concave mirror 43 to be detected, the wavefront measuring device 20 is moved by the XY axis moving device 16B of the wavefront measuring device 20, and the position of the small aperture 321 (see FIG. 6A) of the reference focusing screen 32 The focus position of the condensing lens 31 is adjusted.

  The plane wave irradiated from the wavefront sensor 10 is converted into a spherical wave by the condenser lens 31 and is incident on the concave mirror 43 to be detected. Thereafter, the light reflected by the concave concave mirror 43 is reflected by the reflective concave mirror 44 and returns to the wavefront measuring device 20 through the concave concave mirror 43 and the condenser lens 31 as return light. The beam splitter 12 overlaps with the light reflected by the reference mirror 13 to create a combined light, and forms an image on the image sensor 15 through the imaging lens 14. The light reaching the image sensor 15 creates interference fringes, which are analyzed by the electronic computer 21.

(Fourth embodiment)
<Configuration of Fourth Measuring Device 400>
FIG. 8 is a diagram showing an outline of the configuration of the fourth measuring apparatus 400. 4 is a measurement apparatus that uses a polarization beam splitter 121 instead of the beam splitter 12 such as a half mirror as a unit for dividing the light beam into two in the fourth wavefront sensor 30. The light source 11B is provided with a unit capable of emitting a light beam including P-polarized light and S-polarized light.

  In order to use the polarization beam splitter 121, a quarter-wave plate WP 1 is disposed between the polarization beam splitter 121 and the condenser lens 31. A quarter-wave plate WP1 is disposed between the polarization beam splitter 121 and the reference mirror 13. A polarizing plate WP2 is disposed between the polarizing beam splitter 121 and the imaging lens 14. Other configurations of the apparatus are the same as those of the first measuring apparatus 100.

<Operation of Fourth Measuring Apparatus 400>
Next, an operation when measuring the test lens 41 with the fourth measuring device 400 will be described.
A light beam including P-polarized light and S-polarized light is irradiated from the light source 11B as indicated by an arrow L11. The beam speed is divided into S-polarized light and P-polarized light in the polarization beam splitter 121.

  As indicated by the arrow LY11, the test light of P-polarized light (or S-polarized light) reflected in the −Z-axis direction passes through the quarter-wave plate WP1 and becomes circularly polarized light and travels toward the condenser lens 31. As indicated by an arrow LY12, the test light passes through the condenser lens 31 and travels toward the test lens 41, passes through the test lens 41, and is reflected by the reflecting mirror. The light reflected by the reflecting mirror 42 returns to the reverse optical path to the reflecting mirror 42 as indicated by an arrow LY13. The returned circularly polarized test light becomes S-polarized light (P-polarized light) in the quarter-wave plate WP1 as shown by an arrow LY14, returns to the polarizing beam splitter 121, and passes through the polarizing beam splitter 121.

  On the other hand, the S-polarized light (or P-polarized light) transmitted through the polarizing beam splitter 121 and traveling in the −X-axis direction becomes circularly polarized light by the quarter-wave plate WP1 and travels toward the reference mirror 13 as indicated by an arrow LX11. As indicated by an arrow LX12, the light reflected by the reference mirror 13 becomes P-polarized light (S-polarized light) by the quarter-wave plate WP1, returns to the polarizing beam splitter 121, and is reflected by the polarizing beam splitter 121.

  The light returned from the test optical system 40 and the reference mirror 13 overlaps in the polarization beam splitter 121, and is adjusted to polarized light in the same direction by the polarizing plate WP2 as indicated by an arrow LC11 to form interference fringes. The light beam of the interference fringe passes through the imaging lens 14, and the light imaged on the image sensor 15 is analyzed by the electronic computer 21. In this way, the fourth measuring apparatus 400 measures the transmitted wavefront of the test lens 41.

(Fifth embodiment)
FIG. 9 is a diagram showing an outline of the configuration of the fifth measuring apparatus 500. The fifth measuring apparatus 500 uses the Shack-Hartmann sensor 51 for the interference fringe detection unit of the fifth wavefront sensor 35 instead of the imaging lens 14 and the image sensor 15 of the first measuring apparatus 100 of the first embodiment. . The Shack-Hartmann sensor 51 includes a plurality of lens arrays 52 and the image sensor 15.

  The light beam that passes through the Shack-Hartmann sensor 51 is converted into a small light beam for each lens array 52 and condensed on the image sensor 15. Since the lens array 52 has a role as a condensing unit, an imaging lens is not necessary. Further, unlike the interferometer, the Shack-Hartmann sensor 51 can use light with poor coherence as a light source. Therefore, a light source such as a white light source may be used as the light source 11A of the measurement apparatus 500 in FIG. Other configurations are the same as those of the first measurement apparatus 100.

  When the transmitted wavefront of the test lens 41 is measured using the fifth measuring device 500, the wavefront sensor 50 is moved by the XY axis moving device 16A to adjust the position of the light beam incident on the condenser lens 31, and the test is performed. The transmitted wavefront measurement position on the lens 41 is determined. The optical path through which the light beam passes is the same as that of the first measuring device 100. The test light returned from the test optical system 41 and the reference light reflected by the reference mirror 13 pass through the beam splitter 12 and go to the Shack-Hartmann sensor 51. The plurality of lens arrays 52 convert the light beam guided from the beam splitter 12 into a small light beam and collect it on the image sensor 15. Since the reference light is reflected by the reference mirror 13 that forms the ideal wavefront, it is condensed on the optical axis of each microlens array 52. However, since the test light includes the aberration of the test lens 41, the test light is not necessarily condensed on the optical axis of the lens array 52. The wavefront aberration of the test lens 41 can be obtained from the amount of positional deviation between the converging points of the reference light and the test light. Since the measurement with the reference light and the test light is performed independently, a shutter (not shown) is disposed between the beam splitter 12 and the reference mirror 13 and between the beam splitter 12 and the condenser lens 31. .

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to these. It will be apparent to those skilled in the art that various modifications, substitutions, improvements, combinations, and the like can be made.

10, 30, 35, 37 Wavefront sensor 11, 11A, 11B Light source 12 Beam splitter 13 Reference mirror 14 Imaging lens 15 Imaging element 16A, 16B XY axis moving device 17 Z axis moving device 18 Reflecting member 20 Wavefront measuring device 21 Computer 31 Condensing lens 32, 32B Reference focusing plate 40 Optical system to be tested 41 Test lens 42 Reflective mirror 43 Test concave mirror 44 Reflective concave mirror 45 Exit pupil 51 Shack-Hartmann sensor 52 Lens array 100, 200, 300, 400, 500 Measurement Device 121 Polarizing beam splitter 321 Reflecting surface 322 Small aperture AXL Main ray of test light AX31 Optical axis of condenser lens 31 AX41 Optical axis of test lens 41 WP1 1/4 wavelength plate WP2 Polarizing plate

Claims (9)

A wavefront sensor for detecting test light directed to the test optical system through the test optical system, a measuring device for measuring the characteristics of the test optical system,
A condensing optical system for condensing the test light on the image point of the test optical system;
A first moving unit that moves the wavefront sensor relative to the condensing optical system in a direction intersecting the optical axis of the condensing optical system;
A measuring apparatus comprising:   The measurement apparatus according to claim 1, wherein a numerical aperture (NA) of the condensing optical system is larger than a numerical aperture of the optical system to be measured. When the maximum image height of the test optical system is Yu, the distance from the exit pupil of the test optical system to the image plane is Lu, and the F value of the test optical system is Fu, the aperture of the condensing optical system The measuring apparatus according to claim 2, wherein the number (NA) satisfies the following expression.
When the diameter of the condensing optical system is larger than the diameter of the test light, the focal length fd of the condensing optical system, and the beam diameter φi of the test light,
fd <Fu × φi
The measurement apparatus according to claim 3, wherein: A focus reference plate disposed between the condensing optical system and the test optical system, and the surface on the condensing optical system side has a reflective surface with a high reflectance;
A reflection member that is disposed on the wavefront sensor side of the condensing optical system, does not include the optical axis of the test light, and does not block the test light, and has a reflecting surface on the condensing optical system side; ,
A second moving unit that moves the wavefront sensor and the condensing optical system with respect to the focus reference plate in an optical axis direction of the condensing optical system and a direction intersecting the optical axis;
The measuring apparatus according to any one of claims 1 to 4, further comprising:   The measuring apparatus according to claim 5, wherein the focus reference plate has a small opening through which the test light can pass.   The measuring apparatus according to claim 1, wherein the test optical system includes a transmission lens and a reflecting mirror, and the characteristic includes wavefront aberration.   The measuring apparatus according to claim 1, wherein the test optical system includes a concave mirror and a reflecting mirror, and the characteristic includes wavefront aberration.   The measurement apparatus according to claim 1, wherein the wavefront sensor includes a Twyman-Green interferometer or a Shack-Hartmann sensor.