JPH0810177B2 - Astigmatism inspection method and astigmatism inspection apparatus - Google Patents

Description

The present invention relates to an astigmatism inspection method and an astigmatism inspection apparatus.

[Conventional technology]

Generally, the resolving power is the most important characteristic for the performance of an optical system, and the resolving power is determined by the amount of each aberration such as spherical aberration, astigmatism, core aberration, chromatic aberration and the like of the optical system.
Among these aberrations, astigmatism can be cited as an aberration that greatly depends on the manufacturing accuracy.

Astigmatism is mainly determined by the degree of surface accuracy of each optical element and the combination condition of each surface. Therefore, even if the optical element has relatively poor surface accuracy, the astigmatism should be significantly reduced by combination adjustment. You can As a concrete means, there is known an adjusting method for reducing the astigmatism by rotating a lens having a great effect on the astigmatism. On the other hand, as for the method of detecting the amount of astigmatism, there are the following conventional techniques.

(1) Method of Evaluating Chart Image This method uses, for example, a radial chart, and a lens corresponding to a range in which the chart image in any direction is in focus while moving the lens to be inspected (optical system to be inspected). This is a method of measuring the amount of movement of as an apparent astigmatism.

(2) Method for evaluating spot image In this method, for example, a point chart is used, and the point image is observed visually or through a television camera while moving the lens to be inspected, and the apparent astigmatism of the lens to be inspected is measured. Is the way to do it.

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

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

[Problems to be Solved by the Invention]

However, each of the above conventional techniques has the following problems. That is, the method of evaluating the chart image has a very poor detection accuracy and requires the lens to be constantly moved for measurement, and is not suitable as an adjuster. Further, although the method of evaluating the spot image has relatively high detection sensitivity, it has a drawback that the measurement accuracy is not so good.
Furthermore, it is not suitable as an adjuster because it involves movement of the lens. Further, the method using an interferometer has a high detection accuracy, but since the arrangement needs to be strict, there is a problem that the arrangement must be readjusted after adjusting the lens to be inspected,
This means is also unsuitable as an adjuster. Also, Japanese Patent Application Sho 61
The technique described in -294250 basically has a problem that the astigmatism cannot be adjusted.

As described above, the various conventional techniques have a problem that the detection accuracy is poor or the operability is extremely poor.

The present invention has been made in view of the above-mentioned problems of the conventional technology, and an object thereof is to provide an astigmatism inspection method and an astigmatism inspection apparatus that have high detection accuracy and are excellent in operability. To do.

[Means for Solving the Problems] In order to achieve the above object, the present invention forms a primary image of a pinhole chart arranged between a light source and a test optical system by the test optical system. 1 of the pinhole chart
The secondary image is projected onto the light receiving element as a plurality of secondary images through the projection lens and the pupil plane splitting prism disposed near the exit pupil of the projection lens, and the plurality of secondary planes are rotated while rotating the pupil plane splitting prism. The amount of astigmatism is measured by detecting the position of the primary image point on the optical axis by each position on the light receiving element of the image and calculating the difference between the maximum value and the minimum value of the detected values. is there.

Further, the astigmatism inspection apparatus according to the present invention includes a light source, a pinhole chart arranged between the light source and the optical system to be inspected, and a pinhole chart formed by the optical system to be inspected. A projection lens for projecting the primary image as a secondary image, a pupil plane splitting prism arranged near the exit pupil of the projection lens, and the position of the center of gravity or the center of each of a plurality of secondary images formed by these. The light receiving element disposed at the reference image plane position of the projection lens to detect the optical axis, a rotation mechanism section for rotating the pupil plane splitting prism with respect to the optical system to be measured, and the secondary element in the light receiving element. The deviation amount of the image point of the primary image is calculated from the difference in the coordinates of the image point position of the image, and the difference between the calculated value and the maximum value and the minimum value per at least 1/2 rotation of the pupil plane division prism is calculated. The calculation unit for calculating and the calculation unit That the operation result is a more configuration and display unit for displaying.

[Action]

According to the above method and apparatus, the position of the primary image point on the optical axis of the pinhole chart on the optical axis is detected while rotating the pupil plane splitting prism arranged near the exit pupil of the projection lens. The quantity can be measured.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

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

As shown in the figure, the astigmatism inspection apparatus 1 includes a light source 2, a pinhole chart 4 arranged between the light source 2 and an optical system under test (lens under test or lens to be adjusted) 3, A projection lens 5 for projecting a primary image of the pinhole chart 4 formed by the optical analysis system 3 as a secondary image, and a pupil plane splitting prism 6 arranged near the exit pupil of the projection lens 5.
A light receiving element (CCD camera or the like) 7 arranged at the reference image plane position of the projection lens 5 to detect the position of the center of gravity or the center of each of the plurality of secondary images formed by these, and the optical system 3 to be tested. On the other hand, the focus shift amount is calculated from the rotation mechanism unit 8 for rotating the pupil plane dividing prism 6 and the position signal of the secondary image in the light receiving element 7, that is, the coordinates of the image point position of the secondary image. Of the displacement of the image point of the primary image, and at least the calculated value of the pupil plane splitting prism 6 is calculated.
It is composed of a calculation unit 9 for calculating the difference between the maximum value and the minimum value per 1/2 rotation, and a display unit 10 for displaying the calculation result of the calculation unit 9.

The distance between the pinhole chart 4 and the optical system 3 to be inspected is given as an adjustment condition, and the rotation mechanism section 8 includes the pupil plane splitting prism 6 near the exit pupil of the projection lens 5.
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 division prism 6 includes two wedge prisms 6a, 6 having the same wedge angle α.
The b is closely attached on the side. Therefore, when the primary image of the pinhole chart 4 formed by the optical system 3 to be tested is projected as a secondary image on the light receiving element 7 via the projection lens 5, the pupil plane splitting prism 6 splits the image. By the action, the secondary image is projected as a plurality (two) of the same-shaped images 11a and 11b as shown in FIG. 2b.

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

The light emitted from the light source 1 is applied to the pinhole chart 4, and the image of the pinhole chart 4 is first detected by the optical system 3 to be measured.
Is imaged as a primary image via the. Then, the image of the pinhole chart 4 is projected as a secondary image on the light receiving element 7 via the projection lens 5. In this case, the light receiving element 7
Two secondary images are formed on the upper side by the action of the pupil plane dividing prism 6, as shown in FIG.

Here, n is the refractive index of the wedge prisms 6a and 6b, λ is the wavelength of light, f _w is the focal length of the optical system 3 to be tested, NA _w is NA (numerical aperture) of the optical system 3 to be tested, and β _w is Magnification of the optical system 3 to be tested, f _o
Is the focal length of the projection lens 5, EXP _o is the position of the exit pupil of the projection lens 5, β _o is the magnification of the projection lens 5, α is the wedge angle (wedge angle) of the wedge prisms 6a and 6b, and l _o is the light receiving element 7. two image point 11a above, when the distance between _{11b, l o = 2 (n} -1) (β o f o + f o -EXP o) sinα ... (1) Becomes

Next, consider a case where the first image point changes forward (on the right side in the drawing) on the optical axis in this state. 3A and 3B are diagrams showing this state. In this case, the second image point changes to the front (right side in the figure) of the light receiving surface of the light receiving element 7, so that 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. The position of the image point on the light receiving surface of the element 7 (in this case, the position of the center of gravity of the bundle of rays) changes by an equal distance in the x direction in the opposite direction with respect to the dividing line, as shown in FIG. 3b. Now these 2 points 11
Let δ be the difference in the x-direction coordinates of a and 11b. Similarly to FIG. 2b, the difference between the coordinates of the two points 11a and 11b in the y direction is l.
In this case also, the size and shape of the two image points 11a and 11b are exactly the same, the size in the x direction is dx, the size in the y direction is dy, and Δ _z is the change of the first image point. The amount.

l = l _o (5) Becomes

Here, when the light-receiving surface of the light-receiving element 7 is placed within the depth of focus 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 by equation (6) and Since Δ _z can be ignored in the equation (7), it becomes almost equal to that when the image points coincide with each other on the light receiving surface of the light receiving element 7. Therefore, if Δ _z is in a minute range, only δ changes depending on the difference between the image forming point and the light receiving surface of the light receiving element 7. That is, if the first image point exists to the extent that the second image point 11 enters the depth of focus, only δ changes corresponding to the position of the first image point on the optical axis. Therefore, by detecting this δ, it is possible to detect the shift amount Δ _z of the first image formation point.

In the case of the two-division method of the pupil plane as described above, it has the maximum sensitivity to the luminous flux component of the direction orthogonal to the joint surface of the wedge prisms 6a and 6b, and the luminous flux component parallel to the joint surface and perpendicular to the optical axis. It is clear from the above description that the sensitivity is 0 for.

On the other hand, the astigmatism can be considered as the amount of deviation of the primary image point on the optical axis when the azimuth of the component light flux is rotated. Therefore, according to the present embodiment, while the wedge prisms 6a and 6b are being rotated, the position of the primary image point on the optical axis is detected by each position on the light receiving element of the plurality of secondary images, and the maximum value By calculating the difference between the minimum values by the calculation unit 9, the amount of astigmatism can be measured (inspected) with high accuracy. Then, 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 checked.

Also, by adjusting the optical system 3 to be inspected 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 0, a lens without astigmatism can be manufactured by a simple operation. It becomes possible to do. Similarly, by rotating a specific lens of the non-detection optical system 3 so that the difference between the maximum value and the minimum value becomes 0, in other words, the astigmatism detection value becomes 0. The astigmatism can be adjusted so as to be the minimum, and the astigmatism can be adjusted with high accuracy by a simple operation.

Therefore, according to the present embodiment, the amount of astigmatism, which is a characteristic of the optical system, can be detected with extremely high accuracy and good operability, and high-precision astigmatism adjustment can be performed with a simple operation. is there.

Second Example FIG. 4 shows a second example of the astigmatism inspection apparatus 1 for carrying out the astigmatism inspection method according to the present invention. The feature of the present embodiment is that a detection unit 20 for detecting the rotational azimuth of the pupil plane division prism 6 is arranged between the pupil plane division prism 6 and the calculation unit 9. Therefore, in this embodiment, the structure of the rotation mechanism portion 8 is extremely simplified. Since the other components are the same as those in the first embodiment, the same components as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

According to the present embodiment, it is possible to measure the amount of deviation between the two image points 11a and 11b on the light receiving element 7 corresponding to each rotation direction of the pupil plane division prism 6. For example, the pupil plane division prism 6
The rotation direction of (1), 0 ° direction, (2) .90 ° direction,
(3) If the azimuth is 180 °, an image corresponding to each rotational azimuth is projected on the light receiving surface of the light receiving element 7 as shown in FIGS. The amount of displacement of each image point 11a, 11b in each direction of rotation δ _o °, δ 90 °, δ 180
Can be measured. Further, if the rotational azimuth is set and measured more finely, a characteristic curve of the detected value for each rotational azimuth can be drawn as shown in FIG. 5d. This characteristic curve is generally a curve representing a periodic function of 180 ° cycle, and the amplitude W in this curve is a quantity proportional to astigmatism. The proportional constant at this time is the projection lens 5
And the image-side numerical aperture of the non-detection optical system 3 are determined.

Although illustration is omitted, the division line of the pupil plane dividing prism 6 should always be positioned at the center of the pupil plane of the projection lens 5 (specifically, the intensities of a plurality of point images should be equal).
By performing servo control, more accurate measurement can be realized. Also, it is not always necessary to display the characteristic curve,
It is also possible to obtain the amplitude per one cycle by the periodic signal from the detector 20 and the astigmatism in the calculator 9.

Further, in the present embodiment, there is an advantage that the rotation mechanism portion 8 can be simple and lightweight and can be inexpensive. The other astigmatism inspection method and the astigmatism adjustment method are the same as those in the first embodiment, and the description thereof will be omitted.

Third Example FIG. 6 shows a third example of the astigmatism inspection apparatus 1 for carrying out the astigmatism inspection method according to the present invention. The feature of the present embodiment is that the projection lens 5, the pupil surface splitting prism 6, and the light receiving element 7 such as a CCD camera are integrally rotated around the optical axis via the rotation mechanism portion 8 so that astigmatism can be detected. It is the point configured in. Then, as in the first embodiment, the astigmatism can be adjusted to be the minimum by rotating a specific lens of the optical system 3 to be detected so that the detected astigmatism detection value becomes zero. Is set. Since the other components are the same as those in the first embodiment, the same components as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the projection lens 5 and the pupil plane dividing prism
6, and the light receiving element 7 such as a CCD camera is integrally rotated around the optical axis, so that the orientation of the image does not change with respect to the light receiving element 7, image processing is facilitated, and the projection lens 5 The effect of the astigmatism can be eliminated, and the astigmatism can be detected with higher accuracy. The other actions and effects and the method of adjusting astigmatism are the same as those in the first embodiment, and the description thereof will be omitted.

The light receiving element 7 in each of the above embodiments may use, for example, two line sensors or optical position detecting elements other than the CCD camera, and the same effect can be obtained in this case as well. Further, in each of the above-mentioned embodiments, the example in which the two-division pupil surface division prism 6 is used is shown, but the present invention is not limited to this, and it is set to, for example, a four-division prism, and usually non-rotation and high-precision focus detection are performed. It may be set so that the astigmatism can be detected and adjusted by rotating it via the rotation mechanism portion 8 only when the astigmatism is measured and adjusted.

Also, in each embodiment, various color filters on the illumination side,
By inserting an interference filter (not shown),
Of course, astigmatism can be measured for a specific wavelength (or wavelength range).

Further, in the above description, only the measurement of the on-axis astigmatism is described, but by disposing the pinhole chart 4 off-axis with respect to the optical system 3 to be measured, off-axis astigmatism can be reduced. Of course, it can be set to be measurable.

〔The invention's effect〕

As described above, the present invention detects the amount of astigmatism by detecting the position on the optical axis of the primary image point of the pinhole chart while rotating the pupil plane splitting prism arranged near the exit pupil of the projection lens. As a result, the astigmatism, which is a characteristic of the optical system, can be detected with extremely high accuracy and operability.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing a first embodiment of the present invention, FIGS. 2a and 2b are explanatory views of the main part of FIG. 1, and FIGS. 3a and 3b are of the first embodiment. FIG. 4 is an explanatory view showing a working state, FIG. 4 is a configuration explanatory view showing a second embodiment of the present invention, and FIGS. 5A, 5B, 5C and 5D are explanatory views showing a working state of the second embodiment. FIG. 6 is a configuration explanatory view showing a third embodiment of the present invention. 2 ... Light source 3 ... Optical system to be inspected 4 ... Pinhole chart 5 ... Projection lens 6 ... Pupil plane division prism 7 ... Light receiving element 8 ... Rotation mechanism section

Claims (2)

[Claims] 1. A primary image of a pinhole chart disposed between a light source and a test optical system is formed by the test optical system, and the primary image of the pinhole chart is projected by a projection lens and a projection lens. Of the plurality of secondary images on the light receiving element while projecting as a plurality of secondary images on the light receiving element through the pupil surface dividing prism disposed near the exit pupil of the plurality of secondary images. The astigmatism inspection method is characterized in that the amount of astigmatism is measured by detecting the position of the first-order image point on the optical axis and calculating the difference between the maximum value and the minimum value of the detected values. . 2. A light source, a pinhole chart arranged between the light source and an optical system to be inspected, and a primary image of the pinhole chart formed by the optical system to be inspected as a secondary image. A projection lens for projecting, a pupil plane dividing prism arranged near the exit pupil of the projection lens, and a position of the center of gravity or center of each of a plurality of secondary images formed by these prisms of the projection lens for detecting the position. A light receiving element arranged at the reference image plane position, a rotation mechanism section for rotating the pupil plane splitting prism with respect to the optical system to be measured, and a coordinate of the image point position of the secondary image in the light receiving element. An arithmetic unit for calculating the deviation amount of the image point of the primary image from the difference and for calculating the difference between the calculated value and the maximum value and the minimum value per at least ½ rotation of the pupil plane division prism; The calculation result in the calculation unit is displayed. Astigmatism inspection apparatus for a display unit, wherein more by being configured.