JPH01196530A - Astigmatism inspection method and apparatus - Google Patents

Abstract

PURPOSE:To obtain an astigmatism inspection device with a high detection accuracy and excellent operability, by detecting a position on an optical axis at a primary image point of a pinhole chart turning a pupil plane split prism arranged near an exit pupil of a projection lens. CONSTITUTION:A pinhole chart 4 is arranged between a light source 2 and an optical system 3 to be inspected and a primary image formed is projected with a projection lens 5. Moreover, A pupil plane split prism 6 is arranged near an exit pupil of the projection lens 5 and a light receiving element 7 at the position of a reference image surface and the center of gravity or the center position of several secondary images is detected to measure a value of astigmatism. The pupil plane split prism 6 is turned by a rotation mechanism section 8 with respect to the optical system being inspected to detect a position on the optical axis at a primary image point and a difference between the max. and min. thereof is calculated with a computing section 9 to be displayed on a display section 10. This enables highly accurate detection of the value of astigmatism and adjustment thereof with a simple operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an astigmatism testing method and an astigmatism testing device.

[Conventional technology]

In general, resolving power is the most important characteristic of the performance of an optical system, and this resolving power depends on the spherical aberration, astigmatism, and
It is determined by the amount of each aberration such as comatic aberration and chromatic aberration. Among these aberrations, astigmatism can be cited as an aberration that is largely dependent on manufacturing accuracy.

Astigmatism is mainly determined by the degree of surface precision of each optical element and the combination conditions of each surface. Therefore, even with optical elements with relatively poor surface precision, it is possible to significantly reduce the apparent astigmatism by adjusting the combination. Can be done. As a concrete measure,
An adjustment method is known in which astigmatism is reduced by rotating a lens that is highly effective against astigmatism.

On the other hand, as for the method of detecting the amount of astigmatism, there are the following conventional techniques.

(1) Method for evaluating chart images This method uses, for example, a radial chart, and while moving the test lens (test optical system), select the lens that corresponds to the range in which the chart image is in focus in any direction. In this method, the amount of movement is measured as an apparent astigmatism.

(2) Method for evaluating spot images This method uses, for example, a point chart to observe the point images visually or through a television camera while moving the lens under test, and measures the apparent astigmatism of the lens under test. This is the way to do it.

(3) A method of measuring astigmatism using an interferometer.

(4) In addition, as a detection method suitable for focus adjustment, there is a method in which high-speed image processing is added to the image phase difference method using pupil plane division (see Japanese Patent Application No. 61-294250).

[Problem to be solved by the invention]

However, each of the above conventional techniques has the following problems. In other words, the method of evaluating chart images has very poor detection accuracy (the lens must be constantly moved for measurement, making it unsuitable as an adjuster. Also, the method of evaluating spot images has poor detection sensitivity). Although it is relatively high, the measurement accuracy is not very good (it has a drawback.Furthermore, it is not suitable as an adjuster because it involves the movement of the lens.Also, the interferometer method has high detection accuracy, but requires strict placement. Therefore, there is a problem that, for example, after adjusting the lens to be tested, the placement must be adjusted again, and this means is also unsuitable as an adjuster.
The technique described in No. 294250 basically has a problem in that astigmatism cannot be adjusted.

As described above, various conventional techniques have had problems such as poor detection accuracy or poor operability.

The present invention has been made in view of the problems of the prior art described above, and an object of the present invention is to provide an astigmatism testing method and an astigmatism testing device that have high detection accuracy and excellent operability. do.

[Means to solve the problem]

In order to achieve the above object, the present invention forms a primary image of a pinhole chart disposed between a light source and a test optical system in the test optical system, and forms a primary image of the pinhole chart in the test optical system. The image is projected onto the light receiving element as a plurality of secondary images through a projection lens and a pupil plane splitting prism disposed near the exit pupil of the projection lens, and while rotating the pupil plane splitting prism, the primary image point is The amount of astigmatism is measured by detecting the position on the optical axis and calculating the difference between the maximum value and the minimum value of the detected value.

Further, the astigmatism testing device according to the present invention includes a light source, a pinhole chart disposed between the light source and the optical system to be tested, and a pinhole chart formed in the optical system to be tested. a projection lens for projecting the image as a secondary image;
A pupil plane splitting prism disposed near the exit pupil of the projection lens, and a pupil plane splitting prism disposed at a reference image plane position of the projection lens to detect the center of gravity or center position of each of a plurality of secondary images formed by the prism. a rotation mechanism for rotating the pupil plane splitting prism with respect to the optical system to be tested; and a position signal of the secondary image in the light receiving element to calculate an amount of defocus and the calculated value. a calculation unit for calculating the difference between a maximum value and a minimum value per at least 1/2 rotation of the pupil plane dividing prism; and a display unit for displaying the calculation result in the calculation unit. be.

[Effect]

According to the above method and apparatus, astigmatism is eliminated by detecting the position on the optical axis of the primary image point of the pinhole chart while rotating the pupil plane dividing prism disposed near the exit pupil of the projection lens. It is something that can be measured.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

(First Example) FIG. 1 is an explanatory diagram showing the configuration of an astigmatism testing apparatus 1 according to the present invention.

As shown in the figure, the astigmatism testing apparatus 1 includes a light source 2, a pinhole chart 4 disposed between the light source 2 and a test optical system (test lens or lens to be adjusted) 3, a projection lens 5 for projecting the primary image of the pinhole chart 4 formed by the analysis system 3 as a secondary image; a pupil plane splitting prism 6 disposed near the exit pupil of the projection lens 5; A light-receiving element (such as a CCD camera) 7 arranged at the reference image plane position of the projection lens 5 to detect the center of gravity or center position of each of the plurality of secondary images formed by these, and the optical system 3 to be tested. , a rotation mechanism unit 8 for rotating the pupil plane splitting prism 6 and the position signal of the secondary image in the light receiving element 7 are used to calculate the amount of defocusing, and the calculated value is calculated as follows: Both of them are composed of a calculation section 9 for calculating the difference between the maximum value and minimum value per 1/2 rotation, and a display section 10 for displaying the calculation results in the calculation section 9.

The distance between the pinhole chart 4 and the test optical system 3 is
This is given as an adjustment condition, and the rotation mechanism section 8 rotates the pupil plane splitting prism 6 near the exit pupil of the projection lens 5.
It is configured so that it can always rotate with the central axis of the exit pupil as the rotation axis.

As shown in FIG. 2a, the pupil plane splitting prism 6 has two wedge prisms 6a having the same wedge angle α,
6b are brought into close contact with each other on the sides. Therefore, when the primary image of the pinhole chart 4 formed in the test optical system 3 is projected as a secondary image onto the light receiving element 7 via the projection lens 5, the pupil plane dividing prism 6 As a result of this action, the secondary images are projected as a plurality (two) of identically shaped images 11a and 11b, as shown in FIG.

Next, a method for inspecting (measuring) the amount of astigmatism and a method for adjusting astigmatism using the astigmatism inspection apparatus 1 having the above configuration will be described.

The light emitted from the light source 1 is irradiated onto the pinhole chart 4, and the image of the pinhole chart 4 is first formed as a primary image via the optical system 3 to be examined.

The image of this pinhole chart 4 is then projected onto the light receiving element 7 as a secondary image via the projection lens 5. In this case, two secondary images are formed on the light receiving element 7 by the action of the pupil plane splitting prism 6 as shown in FIG.

Here, n is the refractive index of the wedge prisms 6a and 6b, and λ
is the wavelength of the light, f is the focal length of the optical system under test 3, NA is the NA (numerical aperture) of the optical system under test 3, β8 is the magnification of the optical system under test 3, and fo is the focal length of the projection lens 5. , EXP, is the position of the exit pupil of the projection lens 5, β. The magnification of the projection lens 5,
α is the wedge angle of the wedge prisms 6a and 6b, and 2° is the two image points 11a and llb on the light receiving element 7.
If the distance between is fo=2(n 1)(βoro+fo EXPo)
sir+α...(1) NA1. lNA, 1.

Next, consider a case in which the first image point changes to the front on the optical axis (to the right in the figure) in this state. Figure 3a.

b is a diagram showing this state. In this case, the second image point changes to the front of the light-receiving surface of the light-receiving element 7 (to the right in the figure), so the center of gravity of the upper ray bundle is on the upper side, and the center of gravity of the lower ray bundle is on the lower side, so that the light is received. As shown in FIG. 3, the image point position (in this case, the center of gravity of the light beam) on the light-receiving surface of the element 7 changes by an equal distance in the opposite direction to the X direction with respect to the dividing line.

Now, let the difference in the coordinates of these two points 11a and llb in the X direction be δ. Also, as in Figure 2, two points 11a and l in the y direction
Let the difference in the coordinates of lb be 2. In this case as well, the sizes and shapes of the two image points 11a and llb are the same, and their size in the χ direction is dx, and their size in the y direction is dx.
Let ysΔ2 be the amount of change in the first image point.

／″ Rumor q ℃
℃.

Here, when the light-receiving surface of the light-receiving element 7 is placed within the focal depth of the second image point 11, the size and shape of the image point on the light-receiving surface of the light-receiving element 7 are expressed as Δ in the above equation. This is almost the same as when the image point on the light receiving surface of the light receiving element 7 is ignored. Therefore, if Δ2 is in a small range, only δ will change depending on the difference between the imaging point and the light-receiving surface of the light-receiving element 7. Therefore, by detecting this δ, it is possible to detect the shift amount Δ2 of the first imaging point.

In the case of the pupil plane splitting system into two as described above, the maximum sensitivity is for the luminous flux component in the direction perpendicular to the cemented surface of the wedge prisms 6a and 6b, and the luminous flux component parallel to the cemented surface and perpendicular to the optical axis. It is clear from the above explanation that the sensitivity is 0 for .

On the other hand, astigmatism can be considered to be the amount of deviation of the primary image point on the optical axis when the direction of the component light beam is rotated. Therefore, according to this embodiment, the position of the primary image point on the optical axis is detected while rotating the wedge prisms 6a and 6b, and the difference between the maximum value and the minimum value is calculated by the calculation unit 9. ,
The amount of astigmatism can be measured (inspected) with high precision. The calculation result calculated by the calculation unit 9 is displayed on the display unit 10, so that the amount of astigmatism can be visually observed.

Further, by adjusting the optical system 3 to be tested so that the difference between the maximum value and the minimum value of the position of the primary image point on the optical axis becomes O,
It becomes possible to manufacture a lens without astigmatism with simple operations. Similarly, by rotating a specific lens of the optical system 3 to be tested so that the difference between the maximum value and the minimum value becomes 0, in other words, the detected astigmatism value becomes 0. , the astigmatism can be adjusted to a minimum, and highly accurate astigmatism adjustment is possible with simple operations.

Therefore, according to this embodiment, the amount of astigmatism, which is a characteristic of the optical system, can be detected with extremely high precision and ease of operation, and the astigmatism can be adjusted with high precision using simple operations. be.

(Second Embodiment) FIG. 4 shows a second embodiment of an astigmatism testing apparatus 1 for carrying out the astigmatism testing method according to the present invention. The feature of this embodiment is that a detection section 20 for detecting the rotation direction of the pupil plane division prism 6 is arranged between the pupil plane division prism 6 and the calculation section 9.

Therefore, in this embodiment, the configuration of the rotation mechanism section 8 is extremely simplified. For other components, please refer to the
Since it is similar to the embodiment, the same reference numerals are given to the same components as those shown in FIG. 1, and the explanation thereof will be omitted.

According to this embodiment, it is possible to measure the amount of deviation between the two image points 11a and llb on the light receiving element 7 corresponding to each rotation direction of the pupil plane splitting prism 6. For example, the rotation direction of the pupil plane splitting prism 6 is (1), the direction of O9 is (2), 90
If the orientation is 180° (3), then the light receiving surface of the light receiving element 7Φ will have the shape shown in FIG. 5a.

As shown in b and c, images corresponding to each rotational direction are projected, and therefore, the amount of deviation δ of each image point 11a and Ilb in each rotational direction. .

δ90″′, 6180@ can be measured.

Furthermore, by setting the rotation direction more precisely and performing measurements, it is possible to draw an elastic curve of detected values for each rotation direction, as shown in FIG. 5d. This characteristic curve is -180 for boat fishing.
This is a curve representing a periodic function of the ° period, and the amplitude W in this curve is proportional to the astigmatism. The proportionality constant at this time is determined by the magnification of the projection lens 5 and the image-side numerical aperture of the optical system 3 to be tested.

Although not shown, a servo is operated so that the dividing line of the pupil plane dividing prism 6 is always located at the center of the pupil plane of the projection lens 5 (specifically, so that the intensities of a plurality of point images are equal). Through control, even more precise measurements can be achieved. Furthermore, it is not always necessary to display the characteristic curve, and the amplitude per period can be determined using the periodic signal from the detection section 20.
Astigmatism can also be determined by the calculation unit 9.

Further, this embodiment has the advantage that the rotating mechanism section 8 can be made simple and lightweight, and is also inexpensive. For other astigmatism testing methods and astigmatism adjustment methods, please refer to
Since it is the same as the first embodiment, its explanation will be omitted.

(Third Embodiment) FIG. 6 shows a third embodiment of an astigmatism testing apparatus 1 for carrying out the astigmatism testing method according to the present invention. The feature of this embodiment is that the projection lens 5. The pupil plane splitting prism 6 and the light-receiving element 7 such as a CCD camera are integrally rotated around the optical axis to detect astigmatism. Then, as in the first embodiment, the astigmatism can be adjusted to a minimum by, for example, rotating a specific lens of the optical system 3 to be tested so that the detected astigmatism value becomes 0. The settings are as follows. Other constituent parts are the same as those in the first embodiment, so constituent parts similar to those shown in FIG. 1 are given the same reference numerals and their explanations will be omitted.

In this embodiment, the projection lens 5. Since the pupil plane splitting prism 6 and the light-receiving element 7 such as a CCD camera are configured to rotate around the optical axis as a unit, the orientation of the image with respect to the light-receiving element 7 does not change, making image processing easier. At the same time, it is possible to eliminate the influence of astigmatism of the projection lens 5, and there is an advantage that astigmatism can be detected with higher accuracy. Other functions, effects, and astigmatism adjustment methods are the same as those in the first embodiment, so their explanations will be omitted.

Note that the light receiving element 7 in each of the above embodiments may be replaced by a CCD camera, for example, two line sensors or a light position detection element, and the same effect can be achieved in this case as well. In each of the above embodiments, an example is shown in which a two-split pupil plane splitting prism 6 is used, but the invention is not limited to this. For example, a four-split prism may be used, and normally non-rotating, high-precision focus detection can be performed. It may be set so that the astigmatism can be detected and the tW4 adjustment can be performed by rotating it via the rotation mechanism section 8 only when the astigmatism is measured and adjusted.

Furthermore, in each embodiment, by inserting various color filters, interference filters (not shown), etc. on the illumination side, it is of course possible to measure astigmatism for a specific wavelength (or wavelength range).

Furthermore, although the above explanation only describes the measurement of on-axis astigmatism, by arranging the pinhole chart 4 off-axis with respect to the optical system 3 to be tested, off-axis astigmatism can be measured. Of course, it can be set so that it can be measured.

(Effects of the Invention) As described above, the present invention detects the position on the optical axis of the primary image point of the pinhole chart while rotating the pupil plane dividing prism disposed near the exit pupil of the projection lens. Since it measures the amount of astigmatism, it is possible to detect astigmatism, which is a characteristic of an optical system, with extremely high precision and ease of use.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing a first embodiment of the present invention. FIGS. 2 a and b are explanatory diagrams of the main parts of FIG. 1. FIGS. 3 a and b
4 is an explanatory diagram showing the working state of the first embodiment, FIG. 4 is a configuration explanatory diagram showing the second embodiment of the present invention, and FIGS. 5 a, b, c, and d show the operation of the second embodiment. FIG. 6 is an explanatory diagram showing the configuration of the third embodiment of the present invention. 2... Light source 3... Test optical system 4... Pinhole chart 5... Projection lens 6... Pupil plane dividing prism 7... Light receiving element 8... Rotating mechanism unit Patent applicant Olympus Optical Industry Co., Ltd. Figure 3 (b) y

Claims (2)

[Claims] (1) A primary image of a pinhole chart placed between a light source and a test optical system is formed in the test optical system, and the primary image of the pinhole chart is emitted from a projection lens and a projection lens. A plurality of secondary images are projected onto a light receiving element through a pupil plane splitting prism disposed near the pupil, and the position of the primary image point on the optical axis is detected while rotating the pupil plane splitting prism. An astigmatism testing method characterized by measuring the amount of astigmatism by calculating the difference between the maximum value and the minimum value of the detected values. (2) a light source, a pinhole chart disposed between the light source and the optical system to be tested, and a system for projecting an image of the pinhole chart formed by the optical system to be tested as a secondary image; A projection lens, a pupil plane splitting prism disposed near the exit pupil of the projection lens, and a reference image plane position of the projection lens to detect the center of gravity or center position of each of a plurality of secondary images formed by these. a light-receiving element arranged in the
A rotation mechanism unit for rotating the pupil plane splitting prism and a position signal of the secondary image in the light receiving element for the optical system to be tested, and calculating the defocus amount from the pupil plane splitting of the calculated value. Astigmatism characterized by comprising: a calculation section for calculating the difference between the maximum value and the minimum value per at least 1/2 rotation of the prism; and a display section for displaying the calculation result in the calculation section. Aberration inspection device.