JPS61195328A - Interferometer with semispherical lens - Google Patents

Abstract

PURPOSE:To make possible the separate observation of symmetrical and non- symmetrical components of the aberration of the lens to be inspected by disposing a semispherical lens having the radius of curvature at the focal point of the lens. CONSTITUTION:When observing the symmetrical components of the aberration, that is, when desired to see the interference stripes of waves (a) and (b), the semispherical lens 3 is shifted in a direction perpendicular to the optical axis. The reflected light or wave (c) from a spherical surface 3'' is condensed at a position offset from the center on a spatial filter surface 8. This rays of light are cut so that only the symmetrical aberration of the lens to be inspected is observed. When observing non-symmetrical aberration components, that is, when it is desired to see the interference stripes of the waves (b) and (c), a plane surface primary standard 1 is tilted slightly. At this time, the reflected light or a wave (a) from the standard 1 is cut by the spatial filter 8 so that only the non-symmetrical aberration of the lens to be inspected is observed. When observing the overall aberration, that is, when it is desired to see the interference stripes of the waves (a) and (c), the standard 1 and the lens 3 are inclined by the same angle and the spatial filter 8 is moved therewith so that only the wave (b) is cut by the filter 8 so as to permit the observation of the overall aberration.

Description

Detailed Description of the Invention: a. Technical Field The present invention relates to an interferometric measurement device for measuring aberrations of general lenses, and particularly for measuring symmetrical aberrations such as unispherical aberration and asymmetrical aberrations such as coma aberration. This relates to an interferometer that separately observes aberrations.

b. Prior Art and its Problems Conventionally, as a means for measuring the aberration of a general lens, a Fizeau type or Twyman type interferometer, in which a plane mirror or a concave mirror is arranged at the focal point of the lens to be tested, has been used. This interferometer has the advantage of being relatively easy and inexpensive to construct, but the observed lens aberrations are symmetrical aberrations such as spherical aberration and astigmatism, or coma with these symmetrical aberrations. It is a comprehensive aberration that includes asymmetrical aberrations such as aberrations, and it is not possible to measure only asymmetrical aberrations. Therefore, in the case of centering work in lens assembly where the goal is to cancel coma aberration, there is a possibility that spherical aberration or astigmatism will be adjusted incorrectly.

Additionally, a digital interferometer is a device that can output aberrations separated into symmetrical and asymmetrical components.
This equipment is quite expensive.

C0 Purpose The present invention was made in order to solve the above-mentioned conventional problems.In an interferometer that superimposes a reference wave and a test wave,
The object of the present invention is to provide an interferometer that can output separated symmetrical and asymmetrical components of aberration at low cost by placing a hemispherical lens having a center of curvature at the focal point of a lens to be measured.

d. Configuration of Embodiment In order to achieve the above object, the present invention provides an interferometer for measuring the performance of a general lens in which a reference wave and a test wave are made to interfere with each other. It is configured to locate the center of the lens, and observes the interference fringes obtained by interfering the reflected waves from the test lens and the hemispherical lens.

This method measures the various aberrations of the lens separately.

FIG. 1 is a block diagram of the main parts of the present invention. This figure shows the interferometer's planar prototype (reference body) 1, the test lens 2°, and the hemispherical lens 3, which is the reference lens. Parallel light is incident on the flat prototype 1.

■, ■, ■ indicate three lights to be caused to interfere.

■ represents the reference wave reflected on the reference surface 1' of the flat prototype 1, ■ represents the test wave that passed through the test lens 2 and was reflected on the flat surface 3' of the hemispherical lens 3, and the reflection point is on the flat surface 3'. Therefore, when the wave is reflected, the positions of the incident ray and the reflected ray are swapped. Also, ■ is a test wave that passes through the test lens 2 and is reflected by the spherical surface 3'' of the hemispherical lens 3;
Since the focal point of the hemispherical lens 3 is aligned with the center of the hemispherical lens 3, the reflected light follows the same optical path as the incident optical path in the opposite direction.

In the interference between ■ waves and ■ waves, only the symmetrical component of aberration is caused by the exchange of the chief ray and lower ray of ■ waves.
That is, it can be seen that the interference fringes at this time represent spherical aberration and astigmatism.

In the interference between the ■ wave and the ■ wave, a comprehensive aberration that is a combination of symmetrical aberration and asymmetrical aberration is generated by superimposing a plane wave (ie, a reference wave) and a general test wave reflected by a spherical surface.

In addition, in the interference of ■ waves and ■ waves, the light that has passed through the test lens is superimposed, and the principal ray and lower ray of one wave ■ are switched, and the other wave ■ is the same light that is reflected. This interference pattern is created by

It can be seen that asymmetrical aberrations such as coma are suppressed.

An embodiment of the present invention having the above configuration will be described below. FIG. 2 is an explanatory diagram showing the interferometer of the present invention. Explaining according to the optical path, the light source 4 is an (a-N e laser), and its light is expanded by a beam expander 5 and enters a flat prototype (reference body) 1 through a beam spiriter 6. A part of the light incident on the device 1 is reflected by the reference surface 1' of the flat prototype device and becomes a reference wave (■ wave) and guided to the observation surface 9, and the remaining light passes through and enters the test lens 2.
reach. Furthermore, this light passes through the lens 2 to be tested.

The light reaches the hemispherical lens 3, which is arranged so that its center of curvature is at the focal point of the test lens 2, and is divided into light that is reflected on the flat surface 3' of the hemispherical lens and light that is reflected on the spherical surface 31, each of which is different. It becomes a test wave (■ wave, ■ wave) with characteristics.

Then, those reflected lights pass through the test lens 2 and the flat prototype l again, are split into an outgoing path by the beam spiriter 6, and pass through the imaging lens 7 to form interference fringes on the observation surface 9. At this time, Between the imaging lens 7 and the observation surface 9, three types of aberrations, symmetrical aberration, comprehensive aberration, and asymmetrical aberration, are generated on the observation surface 9 using the working example shown in FIG. A method of observing (distinguishing) the interference fringes, that is, each of the above-mentioned aberrations, will be explained. FIG. 3 shows the optical system for reflected light from the hemispherical lens 3 to the observation surface 9.

When observing the symmetrical component of the aberration, that is, when observing the interference fringes of the ■wave and ■wave, the hemispherical lens 3 is shifted in a direction perpendicular to the optical axis. At this time, the reflected light from the spherical surface 3' (■ wave)
is focused on a location shifted from the center by the spatial filter 8 surface, and this light is cut.

Therefore, only symmetrical aberrations of the lens to be tested can be observed.

When measuring the asymmetric component of the aberration w4, that is, when looking at the interference fringes of the ■ wave and ■ wave, the flat prototype 1 is slightly tilted. At this time, the reflected light (■ wave) from the flat prototype 1 is cut by the spatial filter 8 as described above. Therefore, only the asymmetric aberration of the lens to be tested can be observed.

When observing comprehensive aberrations, that is, when looking at the interference fringes of the ■wave and ■wave, use the flat prototype 1. Both hemispherical lenses 3 are tilted at the same angle, and the spatial filter 8 is also moved accordingly, so that only the ■ wave is cut by the spatial filter 8.

This makes it possible to observe the overall aberration of the lens to be tested. In the above embodiment, a spatial filter 8 is provided between the imaging lens 7 and the observation surface 9, but as is clear from the description of FIG. 1, this is not necessarily necessary. In other words, unnecessary light is caused by the amount of inclination of the hemispherical lens 3 or the flat prototype 1,
By appropriately adjusting the amount of deviation, it is possible to prevent the light from entering the imaging lens system.

f. Effect As explained above, according to the present invention, by using a hemispherical lens in the interferometer, it is possible to separate and observe the symmetrical component and the asymmetrical component of the aberration in the lens to be tested. Therefore, when centering a lens, there is no need to worry about being confused by spherical aberration or astigmatism, and the work can be easily done while observing the aberrations. In addition, since it is possible to easily switch to and view symmetrical aberrations, it is now possible to assemble lenses that involve centering and feed back the work to lens processing that requires correction of spherical aberrations. It has extremely high industrial utility value for actual lens production.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of the present invention, FIG. 2 is an explanatory diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing a method for distinguishing three types of interference fringes. 1: Planar prototype (reference body) 2: Test lens 3: Hemispherical lens 4: Laser light source 5: Beam expander 6: Beam splitter 7: Condenser lens 8: Spatial filter (spatial
filter) 9:11 Side ■: Reference wave ■: Test wave (reflection on the plane of the hemispherical lens) ■= Test wave (
Reflection on the spherical surface of a hemispherical lens) Patent applicant: Asahi Kogaku Kogyo Co., Ltd. No. 2 I Co-procedural correction belt November 27, 1985 Patent Application No. 1987-38087 16 Name of the invention Interferometer using a hemispherical lens 3, Relationship with the person making the amendment Patent applicant address 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Name (0
52) Asahi Kogaku Kogyo Co., Ltd. Representative: Tori Matsumoto 1 Agent residence: Asahi Kogaku Kogyo Co., Ltd., 2-36-9 Maeno-cho, Itabashi-ku, Tokyo 6, "Detailed description of the invention" in the specification subject to amendment Column, \Otsu. Contents of the amendment (1) In the "Detailed Description of the Invention" section of the specification, "symmetrical" in the third line of page 2 is amended to "symmetrical in the i'180'direction." (2) "Asymmetric" in the 5th line of the second page is corrected to "asymmetric in the 180° direction." (3) In the first line of page 7, "tilt both i'3 at the same angle," is corrected to "move the reflected image of 1i'3 by the same amount."

Claims (1)

[Claims] 1. In an interferometer that observes interference fringes by superimposing a reference wave obtained by reflection from a reference surface and a test wave obtained by passing through a test lens, the center of curvature is set at the focal point of the test lens. An interferometer characterized by a hemispherical lens.