JP3213642B2 - Lens performance evaluation method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for evaluating the performance of a lens used for an objective lens of a microscope.

[0002]

2. Description of the Related Art As an apparatus for evaluating lens performance, M
Although a TF measuring device and an apparatus using an interferometer are generally used, these methods have a drawback that they cannot be applied to assembly adjustment because of long measuring time. Japanese Patent Application Laid-Open No. 63-147117 discloses a conventional technique which solves this drawback and enables evaluation in a short time. FIG.
3 to 15 show a configuration used for this evaluation method. 13, reference numeral 104 denotes a pinhole disposed on a reference object plane; 109, a test lens; 110, a reference image plane of the test lens; 100, an optical system for measurement; And a screen 127.

FIG. 14 shows a pupil quadrant prism 126. The prism 126 is formed by laterally joining four wedge prisms 189 having the same wedge angle. In such a configuration, when the image of the pinhole 104 is formed at a point 110 ′ different from the reference image plane 110 by the test lens 109, the projection lens 125 and the pupil-divided prism 1
Due to 26, the quadrilateral connecting the centers of gravity or centers of the four point images 190 formed on the screen 127 is not a square but a distorted shape as shown in FIG. That is, since the angle α ₀ shown in the figure is larger than 90 °, by measuring this angle α ₀ , the image point 1
The distance Δx from 10 ′ to the reference image point 110 can be measured. In addition, astigmatism can be measured by measuring the maximum rotation angle of the four point images when the test lens 109 or the measurement optical system 100 is rotated. In this case, a reference image point 11 serving as a measurement reference for the distance Δx
The adjustment of the position of 0 is performed by using a preparation adjustment , and is removed and used at the time of measurement. Maintenance of the reference image point is performed as needed using this adjustment jig.

[0004]

However, when the lens performance is measured by the above-described method, the reference image point 110 is measured.
Is difficult to adjust and maintain, resulting in a distance Δx
There is a problem that the measurement accuracy of the measurement becomes poor. In addition, it is difficult to measure off-axis performance with high accuracy. An object of the present invention is to provide a lens performance evaluation method and apparatus capable of evaluating lens performance including off-axis performance with high accuracy by solving such problems.

[0005]

FIG. 1 shows the basic structure of the present invention, in which a first pinhole plate 1, a test lens 2, a second pinhole plate 3, an imaging lens 4, and a pupil 4 are provided. A split prism 5, a light receiving element 6, an image measuring unit 7, and a display unit 8 are sequentially arranged on an optical path. The first pinhole plate 1 has a plurality of pinholes 1a as shown in FIG. The second pinhole plate 3 is the lens 2 to be inspected.
At the point image position of the first pinhole plate 1. As shown in FIG. 3, the second pinhole plate 3 has
The pinhole 3a is formed, and the pinhole 3a is set to be larger than the point image of the pinhole 1a of the first pinhole plate 1.

The pupil-four-split prism 5 is disposed near the exit pupil of the imaging lens 4, and is formed by laterally joining two types of wedge prisms 5a and 5b having the same wedge angle as shown in FIG. Have been. The pupil four-segment prism 5 and the imaging lens 4 form a four-segment imaging lens A, and a light receiving element 6 is arranged at a point image position of the four-segment imaging lens A. The image measuring unit 7 measures the position of the center of gravity or the center (see FIG. 5) of each of the four point images formed on the light receiving element 6, and calculates the amount of defocus or the amount proportional thereto from the measured value. Is calculated. Display 8
Displays the output from the image measuring unit 7 in a visible manner. In addition,
The second pinhole plate 3, the four-part imaging lens A and the light receiving element 6 can be relatively moved with respect to the first pinhole plate 1 and the lens to be inspected in a direction orthogonal to the optical axis.

In the above configuration, four point images of the pinhole 3a are formed on the light receiving element 6 as shown in FIG.
The image measuring unit 7 calculates the position of the center of gravity or the center of each of these point images.
The amount of focus shift or an amount proportional thereto is calculated by measuring the position, and adjustment is made so that this amount becomes zero. this
After the adjustment , an image of an arbitrary pinhole 1a on or off the axis of the first pinhole plate 1 is created near the pinhole 3a of the second pinhole plate 3, and this image is located at the position of the pinhole 1a. Is formed at a position corresponding to.

Here, since the size of the pinhole 3a is larger than the size of this image, the second pinhole plate 3, the four-part imaging lens A and the light receiving element 6 are integrated into a direction orthogonal to the optical axis in the plane of the drawing. passed through the pinhole 3a without only light flux is eliminated to form the point image P ₁ or P ₂ of pinholes 1a at any position by moving the, without receiving the noise light from the other pinhole The same amount as before is detected. This detected value is a shift amount of the point image in the optical axis direction from the reference position, or a focus shift amount or an amount proportional thereto. By detecting the reference image point by directly illuminating the pinhole 3a, the amount of defocus at this time or an amount proportional thereto can be measured, so that adjustment and maintenance that does not require a preparation jig can be performed.

[0009]

Embodiment 1 FIGS. 6 to 10 show Embodiment 1 of the present invention, and the same elements as those in FIG. 1 are assigned the same reference numerals.
In FIG. 6, reference numeral 9 denotes a halogen lamp as a light source;
Denotes a lens, 11 denotes a mirror, and 12 denotes a lens. The halogen lamp 9 is fixedly arranged in the lamp house 13,
The illumination optical system is configured by fixing the lens 10, the mirror 11, and the lens 12 to a mount 14 communicating with the lamp house 13. The gantry 14 and the lamp house 13 are detachable from each other. A first mounting mount 15 having a mounting screw inside is mounted on an upper portion of the gantry 14, and a second mounting mount 16 is detachably mounted on the upper portion of the first mounting mount 15. ing. On the upper part of the second mounting mount 16, a first rotation mechanism 17 and a uniaxial linear movement mechanism 1 are sequentially arranged.
8, second rotation mechanism 19 and third mounting mount 2
0 are sequentially attached, and these are hereinafter collectively referred to as a moving mechanism unit.

A fourth mounting mount 21 is removably mounted on the upper part of the third mounting mount 20. The fourth mounting mount 21 has a second pinhole plate 3,
A four-division imaging lens A composed of an imaging lens 4 and a pupil four-segment prism 5 is arranged in order from the bottom, and a CCD camera 22 having a light receiving element 6 is mounted on the upper part thereof.

Meanwhile, five, along with the test lens frame 23 holding the sample lens 2 in the interior of the first mounting mount 15 is mounted by the mounting screws, the outer side of the first attachment mount 15 first with pinholes 1a of the pinhole plate 1 pinhole frame 24 which holds a (see FIG. 7) is attached. 25 is a storage unit for storing the reference measurement value, and 26 is a calculation unit for outputting the difference between the measurement value and the reference measurement value.

Next, the operation and the measuring means will be described. First, prior to the measurement, as shown in FIG.
Remove the test lens frame 23 and the pinhole frame 24, and
The pre-measurement is performed by directly attaching the fourth mounting mount 21 to the mounting mount 15. That is, by directly illuminating the second pinhole plate 3 with the halogen lamp 9 and the illumination optical system, as shown in FIG.
The four-divided image a is formed on the light receiving element 6. Image measurement unit 7
Measures the position of the center of gravity of each of these four point images. These coordinates are represented as (X ₁ , Y ₁ ), (X ₂ , Y ₂ ),
(X ₃ , Y ₃ ), (X ₄ , Y ₄ ), and the amount of defocus F from the reference position is calculated using Equation 1, and this result is displayed on the display unit 8 and simultaneously stored in the storage unit 25. Remember. Here, k is a coefficient determined by the image-side numerical aperture of the test lens.

[0013]

(Equation 1)

The value calculated in this way is used to remove a measurement error caused by an error in the arrangement of the four-division imaging lens A. Note that this pre-measurement can be simply performed by removing only the first pinhole plate 1 from the state of FIG. After this preliminary measurement, the measurement is started with the arrangement shown in FIG. That is, the first pinhole plate 1 is illuminated by the halogen lamp 10 and the illumination optical system. As shown in FIG. 7, five pinholes are formed in the first pinhole plate, and the images of these pinholes are brought into the vicinity of the second pinhole plate 3 by the lens 2 to be measured. It is formed.

For convenience of explanation, only three of the point images P ₁ , P ₂ and P ₃ will be described. Where P ₁ is the image of the first image of the pinhole 1a located at the center (on the axis) of the pinhole plate, P ₂ pinholes 1a in the center to the right, P ₃ is the side opposite the center of the P ₂ It is an image of the pinhole 1a on the further left side. Second pinhole plate 3
Point image P ₁ in the center (on the axis) of, P _2, since a large pinholes 3a than P ₃ are formed, passes through all the pinhole 3a, the light beam to form the point image P ₁ as shown And
This light beam forms a four-divided image on the light receiving element 6.
On the other hand, other light beams, that is, light beams forming the point images P ₂ and P ₃ are cut off by the second pinhole plate 3 and do not reach the light receiving element 6, so that noise does not occur. . Therefore, since a four-divided image of the pinhole at the center of the first pinhole plate 1 is formed on the light receiving element 6, the center of gravity of each of the four point images is measured by the image measuring unit 7 as described above. And the coordinates (X ₁ , Y ₁ ), (X ₂ , Y ₂ ),
Using (X ₃ , Y ₃ ) and (X ₄ , Y ₄ ),
The amount of defocus F from the reference position is calculated, the difference between the value of F and the value of F measured in advance stored in the storage unit 25 is calculated by the calculation unit 26, and this is displayed on the display unit 8. I do. This display value is based on the reference image point position (second pin) of the image point formed by the test lens when the object point is arranged at the center (on the axis) of the reference object point position (the position of the first pinhole plate 1). The shift amount from the position of the hole plate 3), that is, the focus shift is accurately represented.

Next, the second rotation mechanism 19 causes the second
While rotating the pinhole plate 3, the four-division imaging lens A, and the CCD camera 22 as a single body, the astigmatism B at that time is calculated by Expression 2, and this value B is displayed on the display unit 8.

[0017]

(Equation 2)

Since this value changes with rotation, the maximum value during one rotation becomes the amount of astigmatism. In addition, the rotating 4
The eccentricity of the point image can be measured by measuring and displaying the radius of gyration of the average coordinates of the individual images. Thereafter, the uniaxial linear motion mechanism 18 is operated to move the second pinhole plate 3, the four-division imaging lens A, and the CCD camera 22 as a single body as shown in FIG. And point image P
Only the luminous flux forming ₂ passes through the pinhole 3a. Then, the amount of defocus, the amount of astigmatism, and the amount of eccentricity at this time are measured.

Further, the portion arranged above the first rotation mechanism 17 is rotated 180 ° by the rotation mechanism 17 .
Is rolling, pinholes 3a only light flux that forms a point image P ₃
Let through. Then, the amount of defocus, the amount of non-aberration, and the amount of eccentricity at this time are measured. The point image of the other point images i.e. the point image P _1, P _2, other than the pinhole 1a corresponding to P ₃ 2 one pin holes 1a 90 ° and 270 °
The rotation can be measured in the same manner.

In the above description, five pinholes 1a are used. By increasing the number of the pinholes, accurate evaluation of the lens to be inspected is possible. That is, the distortion can be obtained by analyzing the measurement group of the amount of eccentricity, and the image distortion can be known by analyzing the measurement group of the amount of defocus.

In the present embodiment, in addition to the above-described configuration, a chromatic aberration can be measured by inserting a removable interference filter (not shown) at an appropriate position between the first pinhole plate 1 and the halogen lamp 9. It becomes possible. The light source 9 and the illumination optical system need only be capable of uniformly illuminating the first pinhole plate 1 and are not limited to the illustrated configuration.

In this embodiment, since the change of the measuring device is always compensated for a change with time or an environmental change, there is an effect that maintenance is unnecessary.

[0023]

Second Embodiment FIG. 11 shows a second embodiment of the present invention. In FIG. 11, reference numeral 27 denotes an adjustment frame for adjusting the distance between the four-division imaging lens A and the light receiving element 6, and 28 is fixed after the adjustment. For the clamp screw. The moving mechanism unit in the present embodiment includes a first mounting mount 15 and a first rotating mechanism 1.
7. Uniaxial linear motion mechanism 18 and third mounting mount 20
The other configuration is the same as that of the first embodiment. In this embodiment, the moving mechanism unit, the lens frame 23 to be inspected, and the pinhole frame 24 are removed as in the first embodiment.
The pre-measurement is performed by directly attaching the fourth mounting mount 21 to the mounting mount 15, but unlike the first embodiment, the adjustment frame 27 is attached to the fourth mounting mount 21 so that the focus shift amount F becomes zero. To adjust the distance between the four-division imaging lens A and the light receiving element 6, and then fix it with the clamp screw 28. After that, by disposing as shown in FIG. 11 and measuring the point image P ₁ by the test lens 2 in the same manner, the focus shift amount is directly obtained without performing the difference calculation. The astigmatism amount and the eccentric amount on the axis are rotated by the first rotation mechanism 17 to obtain the first embodiment.
Can be obtained in the same way as

Next, the one-axis linear motion mechanism 18 is operated, and the second pinhole plate 3, the four-division imaging lens A, the CCD camera 2
2 are moved to the right by a predetermined distance so that only the luminous flux forming the point image P ₂ is pinhole 3.
The light can be passed through a, and the amount of defocus and the amount of eccentricity at this time can be known. Also, the astigmatic difference between the sagittal direction and the metrical direction can be obtained.

Further, by rotating the portion disposed above the first rotary mechanism 17 by the rotation of the rotary mechanism 17, respectively focusing displacement amount for other point images including point image P ₃ , The amount of eccentricity, and the astigmatic difference can be sequentially obtained. The distortion and the field curvature can be obtained in the same manner as in the first embodiment.

In this embodiment, since the prior measurement as in the first embodiment is not required, the measurement can be performed in a short time.

[0027]

Third Embodiment FIG. 12 shows a third embodiment of the present invention. The moving mechanism unit in the present embodiment includes a first mounting mount 1.
5, Double-axis linear motion groove 29 and third mounting mount 20
Only the configuration is the same as that of the second embodiment. In the present embodiment, when performing off-axis measurement, since it does not rotate,
The astigmatic difference between the two coordinate axes of the light receiving element 6 can be obtained, which is different from the second embodiment. In the second and third embodiments, the amount of astigmatism can be obtained by rotating the lens frame 23 in the same manner as in the first embodiment.

[0028]

As described above, according to the present invention, the lens performance including the off-axis performance can be evaluated with high accuracy.

[Brief description of the drawings]

FIG. 1 is an optical path diagram showing a basic configuration of the present invention.

FIG. 2 is a front view of a first pinhole plate.

FIG. 3 is a front view of a second pinhole plate.

FIG. 4 is a front view of an image formed on a light receiving element.

FIG. 5 is a perspective view of a pupil quadrant prism.

FIG. 6 is a sectional view of Embodiment 1 of the present invention.

FIG. 7 is a front view of a first pinhole plate according to the first embodiment.

FIG. 8 is a cross-sectional view showing a preliminary measurement of Example 1.

FIG. 9 is a front view of an image forming example according to the first embodiment.

FIG. 10 is a cross-sectional view of Example 1 during measurement.

FIG. 11 is a sectional view of a second embodiment of the present invention.

FIG. 12 is a sectional view of a third embodiment of the present invention.

FIG. 13 is an optical path diagram showing a conventional evaluation method.

FIG. 14 is a perspective view of a conventional pupil quadrant prism.

FIG. 15 is a front view of a conventional image forming example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first pinhole plate 2 lens to be inspected 3 second pinhole plate 4 imaging lens 5 pupil quadrant prism 6 light receiving element 7 image measurement unit A quadrant imaging lens

Claims (5)

(57) [Claims] 1. A point image formed by a lens to be inspected at a light spot is converted by a four-division imaging lens comprising an imaging lens and a pupil four-division element.
A plurality of secondary point images, and calculating the amount of defocus or a proportional amount thereof from the measured value of the position of the center of gravity or the center of each of these point images. A pinhole is disposed at a reference image point, and the pinhole and the four-division imaging lens are integrally moved in at least one direction, so that a plurality of light points disposed on the reference object surface are measured by the lens to be inspected. A lens performance evaluation method characterized by passing only a light beam forming an arbitrary one of the point images through a pinhole. 2. The method according to claim 1, wherein an amount of defocus of the pinhole is detected.
2. The lens performance evaluation method according to claim 1, wherein the detected value is subtracted from the defocus amount of the image by the test lens, and the subtracted value is used as a true defocus amount of the test lens. 3. The lens performance evaluation method according to claim 1, wherein a distortion is measured from a group of measurement of eccentricity of a point image formed by the test lens. 4. The lens performance evaluation method according to claim 1, wherein a curvature of field is measured from a measurement group of a focus shift amount of a point image formed by the test lens. 5. A wedge prism having the same wedge angle disposed in the vicinity of an exit pupil, which is side-joined to re-form a point image of a light spot by a lens to be detected as four point images. Four-division imaging lens having a divided pupil four-division prism, a light receiving element arranged at a reference image plane position of the four-division imaging lens, and four point images formed on the light receiving element An image measuring unit that measures the position of the center of gravity or the center of each to calculate the amount of defocus or a proportional amount thereof, wherein the light spot is disposed on a reference object surface of the lens to be inspected. Consists of a pinhole and a pinhole arranged on the optical axis of the reference image plane of the lens to be inspected, and forms an arbitrary point image from a plurality of point images by the lens of the pinhole to be inspected. The pinhole, the four-division imaging lens, and the A lens performance evaluation device, wherein a light receiving element is integrally movable with respect to a test lens provided with a plurality of pinholes in a direction orthogonal to an optical axis.