JPH09184784A - Measurement of anamorphic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the shape of an anamorphic lens by making a light source converge toward the center of curvature of one principal meridian in the anamorphic lens on a mounting table, separating the flux of reflection light with a beam splitter to form its line picture on the light receiving surface, and observing the picture when the mounting table is slid parallel to the light flux. SOLUTION: An anamorphic lens AL has different curvatures on horizontal and vertical sections, to the light flux is allowed to converge at the center of curvature in the principal meridian's direction so as to form a line picture. The minimum line width is measured in order to obtain a difference between the curve and true round in one principal meridian's direction. A cylinder prototype is fitted on a five feed mounting table 20 at such a position that a line picture is formed on a light receiving surface 39. Then, the prototype is removed and the table 20 with the lens AL loaded is moved to the position where the line picture is formed on the light receiving surface 39. In such a position, an incident light is also directed toward the center of curvature of the lens AL, and the reflected light returns through the same light passage as that in the prototype, so that the difference of curvature radius can be obtained in the basis of the moving quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the shape of an anamorphic lens having different curvatures in the vertical and horizontal directions.

[0002]

2. Description of the Related Art Hitherto, as a means for measuring the shape of a lens, a method using an interference fringe has been widely used, and particularly in a spherical lens, a method using a Newton plate is used as a simple method.

[0003]

However, when inspecting an anamorphic lens, the Newton's ring to be detected does not become a perfect circle even if a Newton's plate is used. It was difficult to do.

The present invention has been made in view of the above problems, and an object thereof is to provide a method capable of accurately measuring the shape of an anamorphic lens.

[0005]

In order to achieve the above-mentioned object, the invention described in claim 1 is an anamorphic lens which is an object in which a light beam emitted from a light source is attached to a stage through a condenser lens. Converging toward the center of curvature of one of the main meridians, separating the light beam reflected by the anamorphic lens by a beam splitter, and forming a line image on the light receiving surface provided at a position substantially conjugate with the center of curvature. 1
And a second step of observing the image formed on the light receiving surface while sliding the object stage in a direction parallel to the traveling direction of the light flux before and after the line image is formed. It is characterized by

According to the above method, a line image is formed on the light receiving surface, and before and after the line image is formed, it is formed on the light receiving surface while sliding the stage in a direction parallel to the traveling direction of the light beam. Observe the image. In this case, if the anamorphic lens is a good product, a uniform bright portion is formed on the light-receiving surface in the defocused state before and after the line image is formed. A line image is formed inside.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 6 show an embodiment of the present invention. FIG. 1 shows a specific configuration of an apparatus used to implement the method according to the invention.

This apparatus comprises a substrate 10, a fine movement stage 20 which is slidably provided on the substrate and on which an object to be inspected is placed, and the following optical elements. 30
Is a helium neon laser tube as a light source, and the light flux emitted from this laser tube is incident on the beam expander 33 via the first mirror 31 and the second mirror 32.
The parallel light flux emitted from the beam expander 33 is split into two optical paths by the beam splitter 34. The light flux that has traveled straight and passed through the beam splitter 34 reaches the anamorphic lens AL, which is the object to be inspected, set as the focused light on the fine movement stage 20 via the condenser lens 35. The light beam reflected by the anamorphic lens AL returns to the beam splitter 34, and a part of it reaches the CCD camera 39 provided on the light receiving surface via the third mirror 37 and the imaging lens 38.

2A and 2B, the anamorphic lens AL is mounted on the fine movement mount 20 so that the light flux emitted from the condenser lens 35 is focused on the center of curvature of the anamorphic lens AL in one main meridian direction. It shows the state of placing
(A) is in the same plane as FIG. 1 (hereinafter referred to as horizontal section),
(B) shows an optical path in a plane perpendicular to the plane (hereinafter referred to as a vertical section).

If the reflecting surface is a spherical surface, the reflected light returns along the same optical path as the incident light by setting the incident light flux to be focused on the center of curvature, and forms a point image on the light receiving surface 39a. However, since the anamorphic lens AL has different curvatures in the horizontal cross section and the vertical cross section, when the light flux is focused on one of the main meridian curvature centers as shown in (B), as shown in (A). Has a spread in the other main meridian direction,
A line image will be formed as a whole. However, if the main meridian direction in the vertical cross section is not a circle, the line image is thick. Therefore, the difference between the curve in one main meridian direction and a perfect circle can be measured by measuring the minimum line width.

Next, a method of measuring an anamorphic lens using the above apparatus will be described. << Measurement of radius of curvature >> The radius of curvature of the toric surface in the direction of the main meridian or the radius of curvature of the cylinder surface is measured by taking the difference from the reference cylinder prototype. FIG. 3 shows the principle for measuring the radius of curvature. That is, the light to be reflected by the reference cylinder prototype having a predetermined accurate radius of curvature R and the light to be reflected by the lens to be inspected 40 are set so as to take the same optical path, and the amount of movement A between them is determined to obtain the lens to be inspected. The radius of curvature R ′ along one of the main meridians 40 can be determined by R ′ = RA.

Specifically, first, the cylinder prototype is attached to the fine motion stage 20 and set at a position where a line image is formed on the light receiving surface 39a. After that, the prototype is removed, the lens 40 to be inspected is attached, and the fine movement stage 20 is moved to a position where a line image is formed on the light receiving surface 39a. Similarly, the position where the line image is formed is the case where the incident light is directed to the center of curvature of the lens 40 to be inspected and the reflected light returns on the same optical path as in the case of the standard device. , The difference in radius of curvature from the prototype can be obtained.

The cylinder lens is suitable for use as a prototype because it can be processed with relatively high precision. According to the above means, the radius of curvature can be similarly detected even when the surface to be detected is concave.

<< Measurement of Eccentricity >> Next, a method of measuring the eccentricity of the anamorphic lens will be described. FIG. 4 shows the principle of eccentricity measurement. The solid line shows the incident light and the broken line shows the reflected light. Also in this case, the amount of eccentricity is measured by comparison with the reference cylinder prototype. Here, the eccentricity of the lens means that the position of the center of curvature with respect to the contact surface of the lens that contacts the stage 20 is displaced from the position of the center of curvature of the prototype.

As shown in FIG. 4, the light collection position of the reflected light by the reference cylinder prototype is stored, and the prototype and the lens 40 to be tested are replaced with each other to collect the reflected light from the lens 40 to be tested. To detect. Amount B'of deviation of these condensing positions
And the magnification of the optical system, the eccentricity B along one main meridian of the lens 40 to be measured can be obtained.

<< Measurement of Main Meridian Inclination >> Next, a means for measuring the inclination of the main meridian of the toric surface will be described with reference to FIG. FIG. 5 shows a horizontal section similar to FIGS. 1 and 2 (A). When measuring the inclination of the main meridian of the toric surface in the horizontal sectional direction, first, the lens 40 to be inspected is rotatably set on the fine motion stage 20 while being attached to the circular dish 50, and is shown by a broken line in FIG. As described above, the dish 50 is adjusted so that one end of the lens becomes the measurement point (near the intersection with the optical axis of the device). The center of rotation of the dish 50 is the center of curvature of the main meridian in the horizontal cross section of the lens 40 to be tested. Then, the lens 4 to be inspected
The fine movement table 20 is adjusted to a position where the light flux converges toward the center of curvature in the vertical cross-sectional direction so that the reflected light from 0 forms a line image on the light receiving surface 39a, and the dish 50 is moved as shown by an arrow in the figure. Rotate to scan the entire surface of the lens.

Since the lens 40 to be inspected is rotated about the center of curvature of the main meridian in the horizontal section, the center of curvature of the intersecting curve of the vertical section including the optical axis of the apparatus and the toric surface is the optical axis. It will be located in the vertical section that contains. Therefore, if the main meridian in the horizontal cross section is not inclined, the light receiving surface 3
The line image formed on 9a does not move even if the light beam scans.

If the main meridian is inclined due to the deviation of the polishing of the lens, etc., at the point where the actual main meridian is away from the ideal main meridian, the eccentricity of the center of curvature in the direction of the vertical cross section is not eccentric. The line image is formed at a position different from the position where the line image is formed.

If the main meridian has an inclination, the amount of eccentricity at each point changes, so that the position of the line image formed on the light receiving surface 39a moves as the light beam is scanned. Therefore, by observing the movement of the line image, the inclination of the main meridian in the horizontal sectional direction can be measured.

<< Measurement of Surface Accuracy >> In measuring the surface accuracy, the lens 40 to be inspected is set on the fine movement stage 20, and the fine stage 20 is slid before and after forming a line image to receive the light receiving surface 39a. Inspect the image that appears above.

Specifically, the light beam is converged toward the center of curvature of one main meridian of the lens 40 to be inspected mounted on the fine movement stage 20, and the light beam reflected by the lens 40 to be inspected is reflected by the beam splitter 34. Then, a line image is formed on the light receiving surface 39a (first step). Then, before and after the line image is formed, the image formed on the light receiving surface 39a is observed while sliding the fine movement stage 20 in a direction parallel to the traveling direction of the light flux (second step).

FIG. 6 shows the observation result, and is an explanatory view showing the result of inspecting the surface accuracy of the toric surface. In the case of a non-defective product, a line image is formed on both sides in a defocused state before and after the formation of the line image due to surface droop outside the effective luminous flux diameter of the toric surface, and the inside of the line image becomes uniformly bright, and the line image At the time of formation, one thin line image is formed.

Since the defective product has fine irregularities on its surface, the radius is locally different. Therefore, even if the radii of curvature are substantially the same, a line image due to a local difference in the radius of curvature is formed in a bright portion in a defocused state, and flare appears around the line image even when the line image is formed.

Therefore, by evaluating the state of the image detected by the above inspection, it is possible to discriminate between a good product and a defective product concerning the surface accuracy.

[0025]

As described above, according to the measuring method of the present invention, by observing the image formed on the light receiving surface, it is possible to easily determine whether the surface accuracy of the anamorphic lens is a good product or a defective product. Can be identified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of an apparatus for realizing an anamorphic lens measuring method according to the present invention.

FIG. 2A is a diagram showing a horizontal cross section of the optical type shown in FIG.
(B) is a view showing a vertical cross section of the optical system of FIG. 1.

FIG. 3 is an explanatory diagram showing the principle of curvature radius measurement.

FIG. 4 is an explanatory diagram showing the principle of eccentricity measurement.

FIG. 5 is an explanatory diagram showing the measurement of the inclination of the main meridian.

FIG. 6 is an explanatory diagram of an image formed on a light receiving surface.

[Explanation of symbols]

 20 Micro-moving stage 30 Light source 33 Beam expander 34 Beam splitter 35 Condensing lens 39a Light receiving surface 40 Test lens

Claims (1)

[Claims] 1. A light flux emitted from a light source is converged through a condenser lens toward a center of curvature of one main meridian of an anamorphic lens which is an object to be inspected and is reflected by the anamorphic lens. The first stage in which a light beam is split by a beam splitter to form a line image on a light-receiving surface provided at a position substantially conjugate to the center of curvature; and before and after the line image is formed, A second step of observing an image formed on the light receiving surface while sliding in a direction parallel to the traveling direction, the measuring method of the anamorphic lens.