JPH06117966A - Lens performance evaluation method and device - Google Patents

Abstract

PURPOSE:To evaluate the lens performance including that outside axis accurately. CONSTITUTION:A first pin hole plate 1, a lens 2 to be inspected, a second pin hole plate 3, a 4-division image-forming lens A consisting of an image-forming lens 4 and a pupil 4-division prism 5, and a light reception element 6 are laid out in order. Second pin hole plates 3 and the 4-division imageforming lens A are moved in one piece at right angel to a light path so that only the flux of light from one pin hole out of a plurality of pin holes 1a of the first pin hole plate passes. The operation is performed to all pin holes 1a and then the amount of focusing deviation or the proportional amount is calculated from the measured value the gravity of a point image formed at the light reception element 6 or a center position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens performance evaluation method for use in a microscope objective lens and the like, and a device therefor.

[0002]

2. Description of the Related Art As a device for evaluating lens performance, there is M
Although a TF measuring device and a device using an interferometer are generally used, they all have a drawback that they cannot be applied to assembly and preparation because of the long measuring time. Japanese Patent Laid-Open No. 63-147117 discloses a conventional technique that solves this drawback and enables evaluation in a short time. Figure 1
3 to 15 show the configuration used in this evaluation method. In FIG. 13, 104 is a pinhole arranged on the reference object surface, 109 is a lens to be inspected, 110 is a reference image plane of the lens to be inspected, 100 is an optical system for measurement, and a projection lens 125 and a pupil four-division prism 126. And a screen 127.

FIG. 14 shows a pupil four-division prism 126, which is formed by side-joining four wedge prisms 189 having the same wedge angle. In such a configuration, when the image of the pinhole 104 is formed at the point 110 'different from the reference image plane 110 by the lens 109 to be inspected, the projection lens 125 and the pupil quadrant prism 1
Due to 26, the quadrangle connecting the centers of gravity or centers of the four point images 190 formed on the screen 127 does not become a square but becomes a distorted shape as shown in FIG. That is, since the angle α ₀ shown in the figure becomes larger than 90 °, the image point 1 of the lens 109 to be measured is measured by measuring the angle α _0.
The distance Δx from 10 ′ and the reference image point 110 can be measured. In addition, astigmatism can be measured by measuring the maximum rotation angles of the four point images when the lens 109 to be inspected or the optical system 100 for measurement is rotated. In this case, the reference image point 11 serving as the measurement reference of the distance Δx
The preparation of the position of 0 is carried out by using a preparation jig, and this is removed and used at the time of measurement. Maintenance of the reference image points is performed at appropriate times using this adjusting jig.

[0004]

However, when the lens performance is measured by the method described above, the reference image point 110
Position is difficult to prepare and maintain, which results in distance Δx
There is a problem that the measurement accuracy of is deteriorated. In addition, it is difficult to measure off-axis performance with high accuracy. It is an object of the present invention to provide a lens performance evaluation method and device capable of highly accurately evaluating lens performance including off-axis performance by solving such problems.

[0005]

FIG. 1 shows the basic configuration of the present invention, which includes a first pinhole plate 1, a lens 2 to be tested, a second pinhole plate 3, an imaging lens 4 and a pupil 4. The split prism 5, the light receiving element 6, the image measuring unit 7, and the display unit 8 are arranged in this order on the optical path. As shown in FIG. 2, the first pinhole plate 1 is formed with a plurality of pinholes 1a. The second pinhole plate 3 is the test lens 2
Is arranged at the point image position of the first pinhole plate 1. As shown in FIG. 3, the second pinhole plate 3 has
Although the pinhole 3a is formed, 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-division prism 5 is arranged near the exit pupil of the imaging lens 4, and is formed by side-joining two kinds of wedge prisms 5a and 5b having the same wedge angle, as shown in FIG. Has been done. The pupil 4-division prism 5 and the imaging lens 4 form a 4-division imaging lens A, and the light-receiving element 6 is arranged at the point image position of the 4-division imaging lens A. The image measurement unit 7 measures the position of the center of gravity or the center of each of the four point images formed on the light receiving element 6 (see FIG. 5), and from this measurement value, the amount of in-focus shift or an amount proportional thereto. To calculate. Display 8
Visually displays the output from the image measuring unit 7. In addition,
The second pinhole plate 3, the four-divided imaging lens A and the light receiving element 6 are movable relative to the first pinhole plate 1 and the lens to be inspected in the direction orthogonal to the optical axis.

In the above-mentioned structure, as shown in FIG. 5, the center of gravity or the center of each of the four point images of the pinhole 3a is imaged on the light receiving element 6, and the image measuring unit 7 produces these point images. The amount of out-of-focus or the amount proportional to this is calculated by measuring, and the amount is adjusted so as to be zero. After this preparation, 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 of the pinhole 1a. It is formed at a position corresponding to the position.

Since the size of the pinhole 3a is larger than the size of this image, the second pinhole plate 3, the four-divided imaging lens A and the light receiving element 6 are integrally formed in a direction orthogonal to the optical axis in the plane of the drawing. By moving to, the luminous flux forming the point image P ₁ or P ₂ of the pinhole 1a at an arbitrary position passes through the pinhole 3a without being excluded, and receives no noise light from other pinholes. The same amount as above is detected. This detected value is the amount of deviation of the point image in the optical axis direction from the reference position, the amount of focusing deviation, or an amount proportional thereto. The reference image point can be detected by directly illuminating the pinhole 3a, so that the focus shift amount at this time or the amount proportional thereto can be measured. Therefore, adjustment and maintenance that do not require a preparation jig can be performed.

[0009]

Embodiment 1 FIGS. 6 to 10 show Embodiment 1 of the present invention, in which the same elements as in FIG. 1 are designated by the same reference numerals.
In FIG. 6, 9 is a halogen lamp as a light source, 10
Is a lens, 11 is a mirror, and 12 is a lens. The halogen lamp 9 is fixedly arranged in the lamp house 13,
The lens 10, the mirror 11, and the lens 12 are fixed to a mount 14 that communicates with the lamp house 13 to form an illumination optical system. The pedestal 14 and the lamp house 13 are detachable from each other. Further, a first mounting mount 15 having a mounting screw inside is mounted on the upper part of the pedestal 14, and a second mounting mount 16 is removably mounted on the upper part of the first mounting mount 15. ing. A first rotation mechanism unit 17 and a uniaxial linear motion mechanism unit 1 are sequentially provided on the second mounting mount 16.
8, second rotation mechanism portion 19 and third mounting mount 2
0 are sequentially attached, and hereinafter, these are 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, and the second pinhole plate 3 is attached to the fourth mounting mount 21.
A four-division imaging lens A including an imaging lens 4 and a pupil four-division prism 5 is arranged in order from below, and a light receiving element 6 and a CCD camera 22 are attached to the upper portion thereof.

On the other hand, the lens frame 23 for holding the lens 2 to be inspected is attached by the mount screw inside the first mounting mount 15, and 5 is provided on the outside of the first mounting mount 15. First with pinhole 1a
Pinhole frame 2 held by the pinhole plate 1 (see FIG. 7)
4 is attached. Reference numeral 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 measuring means will be described together with the operation. First, prior to the measurement, as shown in FIG.
Remove the lens frame 23 and the pinhole frame 24 to
The fourth mounting mount 21 is directly mounted on the mounting mount 15 of No. 1 and pre-measurement is performed. That is, by directly illuminating the second pinhole plate 3 with the halogen lamp 9 and the illumination optical system, as shown in FIG.
A four-divided image of a is formed on the light receiving element 6. Image measurement unit 7
Measures the centroid position of each of these four point images. The coordinates are (X ₁ , Y ₁ ), (X ₂ ,
Y ₂ ), (X ₃ , Y ₃ ), (X ₄ , Y ₄ ), calculate the focus shift amount F from the reference position using Equation 1, and display this result on the display unit 8 and store it at the same time. It is stored in the unit 25. Here, k is a coefficient determined by the image-side numerical aperture of the lens under test.

[0013]

[Equation 1]

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

For convenience of explanation, only three point images P ₁ , P ₂ and P ₃ among these point images will be described. Here, P ₁ is the image of the pinhole 1a located at the center (on the axis) of the first pinhole plate, P ₂ is the image of the pinhole 1a on the right side of the center, and P ₃ is the center opposite to P _2. It is an image of the pinhole 1a on the left side. Second pinhole plate 3
Since a pinhole 3a larger than the point images P ₁ , P ₂ and P ₃ is formed at the center (on the axis) of all, all the light flux forming the point image P ₁ passes through the pinhole 3a as shown in the figure. Then
This light flux forms a four-divided image on the light receiving element 6.
On the other hand, the other light flux, that is, the light flux forming the point images P ₂ and P ₃ is blocked by the second pinhole plate 3 and therefore does not reach the light receiving element 6, and noise due to this 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 barycenter position of each of the four point images is measured by the image measuring unit 7 as described above. Then, the coordinates (X ₁ , Y ₁ ), (X ₂ , Y ₂ ),
Using (X ₃ , Y ₃ ) and (X ₄ , Y ₄ ),
The focus shift amount F from the reference position is calculated, and the difference between the F value and the F value of the pre-measurement stored in the storage unit 25 is calculated by the calculation unit 26 and displayed on the display unit 8. To do. This display value is the reference image point position (second pin position) of the image point formed by the lens to be inspected when the object point is arranged at the center (on the axis) of the reference object point position (position of the first pinhole plate 1). The amount of deviation from the position of the hole plate 3, that is, the in-focus deviation is accurately represented.

Next, the second rotation mechanism section 19
While rotating the pinhole plate 3, the 4-division imaging lens A, and the CCD camera 22 as one body, the astigmatism amount B at that time is calculated by the formula 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 is the amount of astigmatism. In addition, the spinning 4
The eccentricity of the point image can also be measured by measuring and displaying the radius gyration of the individual average coordinates. Then, the uniaxial translation mechanism 18 is operated to move the second pinhole plate 3, the four-division imaging lens A and the CCD camera 22 as one body to the right by a predetermined distance as shown in FIG. Then point image P
Only the light flux forming ₂ is passed through the pinhole 3a. Then, the focus shift amount, the astigmatism amount, and the eccentricity amount at this time are measured.

Further, by rotating the portion arranged above the first rotating mechanism portion 17 by 180 ° rotation of the rotating mechanism portion 17, only the light flux forming the point image P ₃ is emitted from the pinhole 3a. Let it pass. Then, the in-focus deviation amount, the non-aberration amount, and the eccentricity amount at this time are measured. The other point images, that is, the point images of the two pinholes 1a other than the pinholes 1a corresponding to the point images P ₁ , P ₂ , and P ₃ , can be measured in the same manner by rotating 90 ° and 270 °.

Although the above description is for the case of using five pinholes 1a, increasing the number of pinholes 1a enables accurate evaluation of the lens to be inspected. That is, it is possible to obtain the distortion aberration by analyzing the measurement group of the eccentricity amount, and it is possible to know the image aberration aberration by analyzing the measurement group of the defocus amount.

In the present embodiment, in addition to the above-mentioned structure, a removable interference filter (not shown) is inserted at an appropriate position between the first pinhole plate 1 and the halogen lamp 9 to measure chromatic aberration. It will be possible. The light source 9 and the illumination optical system are not limited to the illustrated configurations as long as they can uniformly illuminate the first pinhole plate 1.

In this embodiment, since the change of the measuring device is always compensated for the change over time or the change in environment, maintenance is unnecessary.

[0023]

[Embodiment 2] FIG. 11 shows Embodiment 2 of the present invention, in which reference numeral 27 is 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. It is a clamp screw for. The moving mechanism unit in this embodiment includes a first mounting mount 15 and a first rotating mechanism section 1.
7, uniaxial translation mechanism 18 and third mounting mount 20
The other configurations are the same as those in the first embodiment. In this embodiment, similarly to the first embodiment, the moving mechanism unit, the lens frame 23 to be tested and the pinhole frame 24 are removed,
Although the fourth mounting mount 21 is directly mounted on the mounting mount 15 for pre-measurement, unlike the first embodiment, the adjustment frame 27 is attached to the fourth mounting mount 21 so that the focusing deviation F becomes 0. It is rotated to adjust the distance between the four-divided imaging lens A and the light receiving element 6 and then fixed by the clamp screw 28. Then, by arranging as shown in FIG. 11 and measuring the point image P ₁ by the lens 2 under test in the same manner, the in-focus amount is directly obtained without performing the difference calculation. The astigmatism amount and the eccentricity amount on the axis are rotated by the first rotation mechanism unit 17 to obtain the first embodiment.
You can ask for it as well.

Next, the uniaxial translation mechanism 18 is operated to operate the second pinhole plate 3, the 4-divisional imaging lens A and the CCD camera 2.
By moving 2 together as a unit by a predetermined distance, only the light flux forming the point image P ₂ is pinhole 3
It is possible to pass from a, and it is possible to know the focus shift amount and the eccentricity amount at this time. Further, the astigmatic difference between the sagittal direction and the meridional direction can be obtained.

Further, by rotating the portion arranged above the first rotation mechanism portion 17 by the rotation of the rotation mechanism portion 17, the focus shift amount is obtained for each of the other point images including the point image P _3. The eccentricity amount and the astigmatic difference can be sequentially obtained. The distortion and the field curvature can also be obtained in the same manner as in the first embodiment.

In this embodiment as described above, it is possible to perform the measurement in a short time because the preliminary measurement as in the embodiment 1 is not necessary.

[0027]

Third Embodiment FIG. 12 shows a third embodiment of the present invention. The moving mechanism unit in this embodiment is the first mounting mount 1
5, biaxial linear motor groove portion 29 and third mounting mount 20
The other configurations are the same as those of the second embodiment. In this embodiment, when performing off-axis measurement, 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. Incidentally, in Example 2 and Example 3, by rotating the lens frame 23 to be inspected, the amount of astigmatism can be obtained as in Example 1.

[0028]

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

[Brief description of 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 four-division prism.

FIG. 6 is a cross-sectional view of the first embodiment of the present invention.

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

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

FIG. 9 is a front view of an image forming example of 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 four-division prism.

FIG. 15 is a front view of a conventional imaging example.

[Explanation of symbols]

 1 1st pinhole plate 2 Test lens 3 2nd pinhole plate 4 Imaging lens 5 Pupil 4-division prism 6 Light-receiving element 7 Image measurement part A 4-division imaging lens

Claims (5)

[Claims] 1. A point image of a light spot formed by a lens to be inspected is formed by a four-division imaging lens including an imaging lens and a pupil four-division element
In the lens performance evaluation method, which is formed as a plurality of secondary point images, and a focus shift amount or an amount proportional to the focus shift amount is calculated from the measured values of the center of gravity or the center position of each of these point images, A pinhole is arranged at the reference image point, and the pinhole and the four-divisional imaging lens are integrally moved in at least one direction, so that a plurality of light spots arranged on the reference object surface are formed by a plurality of test lenses. A lens performance evaluation method, wherein only a light beam forming an arbitrary one point image of the point images is passed through the pinhole. 2. A focus shift amount of the pinhole is detected,
The lens performance evaluation method according to claim 1, wherein the detected value is subtracted from the in-focus shift amount of the image by the lens to be inspected, and the subtracted value is set as the true in-focus shift amount of the inspected lens. 3. The lens performance evaluation method according to claim 1, wherein the distortion aberration is measured from a measurement group of the decentering amount of the point image formed by the lens to be inspected. 4. The lens performance evaluation method according to claim 1, wherein the field curvature is measured from a measurement group of a focus shift amount of a point image formed by the lens to be inspected. 5. A wedge prism having the same wedge angle, which is arranged in the vicinity of the exit pupil, is side-joined in order to re-image the point image of the light spot by the test lens as four point images. Image forming lens including a prism for dividing the pupil into four, a light receiving element disposed at a reference image plane position of the four image forming lens, and four point images formed on the light receiving element. Each of the center of gravity or the position of the center is measured, and an image measurement unit that calculates a focus shift amount or a proportional amount thereof is provided, and the plurality of light spots are arranged on the reference object surface of the lens under test. 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 the multiple point images of the inspected lens of the pinholes. The pinhole, the four-division imaging lens and the A lens performance evaluation device, wherein the light receiving element and the light receiving element are integrally movable with respect to a lens to be inspected having a plurality of pinholes in a direction orthogonal to the optical axis.