JP2842861B2 - How to measure anamorphic lens - 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 for measuring the shape and the like of an anamorphic lens having different curvatures in a vertical direction and a horizontal direction.

[0002]

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

[0003]

However, when inspecting an anamorphic lens, since the detected Newton ring does not become a perfect circle even if a Newton plate is used, it is examined whether or not a predetermined accuracy has been reached. It was difficult to do.

[0004] The present invention has been made in view of the above problems, and has as its object to provide a method capable of accurately measuring the shape of an anamorphic lens.

[0005]

According to one aspect of the present invention, there is provided an anamorphic lens which is a test object in which a light beam emitted from a light source is mounted on a stage via a condenser lens. Converging toward the center of curvature of one of the main meridians, separating a light beam reflected by the anamorphic lens by a beam splitter, and forming a line image on a light receiving surface provided at a position substantially conjugate with the center of curvature. 1
And a second step of observing an image formed on the light receiving surface while sliding the stage in a direction parallel to a traveling direction of the light beam before and after the line image is formed. It is characterized by the following.

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

[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 for realizing the method according to the present invention.

The apparatus comprises a substrate 10, a finely movable stage 20 slidably mounted on the substrate and on which a test object is mounted, and the following optical elements. 30
Denotes a helium neon laser tube as a light source, and a light beam emitted from the laser tube enters a beam expander 33 via a first mirror 31 and a second mirror 32.
The parallel light beam emitted from the beam expander 33 is split into two light paths by a beam splitter 34. The luminous flux that travels straight and passes through the beam splitter 34 reaches the anamorphic lens AL, which is an object set on the fine moving stage 20, as converged light via the condenser lens 35. The light beam reflected by the anamorphic lens AL returns to the beam splitter 34, and a part of the light beam reaches the CCD camera 39 provided on the light receiving surface via the third mirror 37 and the imaging lens 38.

FIGS. 2A and 2B show the anamorphic lens AL mounted on the fine moving stage 20 such that the light beam emitted from the condenser lens 35 is focused on the center of curvature in one main meridian direction of the anamorphic lens AL. It shows the state where it was placed,
(A) is in the same plane as that of FIG.
(B) shows an optical path in a plane perpendicular to this (hereinafter referred to as a vertical section).

If the reflecting surface is spherical, setting the incident light beam to converge at the center of the curvature causes the reflected light to return along the same optical path as the incident light and form 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 condensed at the center of curvature in one main meridian direction as shown in (B), as shown in (A). Has a spread in the other main meridian direction,
A line image is 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, by measuring the minimum line width, the difference between the curve in one main meridian direction and a perfect circle can be measured.

Next, a method of measuring an anamorphic lens using the above apparatus will be described. << Measurement of Radius of Curvature >> The radius of curvature in one principal meridian direction of the toric surface 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 reflected light from the reference cylinder prototype having a predetermined accurate radius of curvature R and the reflected light from the test lens 40 are set to take the same optical path, and the amount of movement A between them is determined to obtain the test lens. The radius of curvature R 'along one of the main meridians of R.40 can be determined by R' = R-A.

More specifically, first, a cylinder prototype is mounted on the fine moving table 20 and set at a position where a line image is formed on the light receiving surface 39a. Thereafter, the prototype is removed, the lens 40 to be inspected is attached, and the fine moving 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 where the incident light is directed to the center of curvature of the lens 40 to be measured and the reflected light returns along the same optical path as in the case of the prototype, so that the amount of movement is measured. , The difference in radius of curvature from the prototype can be determined.

[0013] A 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 the eccentricity measurement. The solid line indicates the incident light, and the broken line indicates 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 abutting on the mounting table 20 is shifted from the position of the center of curvature of the prototype.

As shown in FIG. 4, the position where the light reflected by the reference cylinder prototype is condensed is stored, and the position of the light reflected by the lens 40 is changed by replacing the prototype and the lens 40 to be tested. Is detected. The shift amount B 'of these light-condensing positions
And the magnification of the optical system, the amount of eccentricity B along one main meridian of the test lens 40 can be obtained.

<< Measurement of Main Meridian Tilt >> Next, means for measuring the inclination of the main meridian on 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 in the horizontal sectional direction of the toric surface, first, the test lens 40 is set to be rotatable on the fine moving stage 20 while being stuck on the circular dish 50, and is indicated by a broken line in FIG. As described above, the plate 50 is adjusted so that one end of the lens is located at the measurement point (near the intersection with the optical axis of the apparatus). The rotation center of the plate 50 is the center of curvature of the main meridian in the horizontal section of the lens 40 to be measured. Then, the test lens 4
The fine moving stage 20 is adjusted to a position where the light beam converges toward the center of curvature in the vertical cross section direction so that the reflected light by 0 forms a line image on the light receiving surface 39a, and the plate 50 is indicated by an arrow in the figure. To scan the entire surface of the lens.

Since the test lens 40 is rotated about the center of curvature of the main meridian in the horizontal section, the center of curvature of the intersection curve between the vertical section including the optical axis of the apparatus and the toric surface is defined by the optical axis. Will be located in the vertical cross-section that includes the Therefore, if the main meridian in the horizontal section direction 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 has an inclination due to the deviation of the polishing of the lens or the like, at the point where the actual main meridian departs from the ideal main meridian, the eccentricity of the center of curvature in the vertical cross-sectional direction is determined if there is no eccentricity. 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 scans. 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 surface accuracy, the lens 40 to be inspected is set on the fine moving stage 20 and the fine moving stage 20 is slid before and after forming a line image to form a light receiving surface 39a. Inspect the image that appears above.

More specifically, the light beam is converged toward the center of curvature of one main meridian of the test lens 40 attached to the fine moving table 20, and the light beam reflected by the test lens 40 is converted into a beam splitter 34. To form a line image on the light receiving surface 39a (first stage). Thereafter, before and after the line image is formed, the fine moving stage 20 is slid in a direction parallel to the traveling direction of the light beam, and an image formed on the light receiving surface 39a is observed (second stage).

FIG. 6 is an explanatory view showing the result of the observation and the result of inspection of 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 is uniformly bright, and the line image is uniformly formed. At the time of formation, one thin line image is formed.

Defective products have fine irregularities on the surface, and therefore have locally different radii. 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.

Thus, by evaluating the state of the image detected by the above-mentioned inspection, it is possible to discriminate a non-defective product from a non-defective product with respect to 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 easy to determine whether the surface accuracy of the anamorphic lens is good or defective. Can be identified.

[Brief description of the drawings]

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

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

FIG. 3 is an explanatory diagram illustrating 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 measurement of inclination of a main meridian.

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

[Explanation of symbols]

 Reference Signs List 20 fine movement stage 30 light source 33 beam expander 34 beam splitter 35 condensing lens 39a light receiving surface 40 lens to be inspected

Claims (1)

(57) [Claims] 1. A light beam emitted from a light source is converged toward a center of curvature of one main meridian of an anamorphic lens, which is a test object, mounted on a stage via a condenser lens, and reflected by the anamorphic lens. A first step of separating a light beam by a beam splitter to form a line image on a light receiving surface provided at a position substantially conjugate with 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.