JP4629372B2 - Lens wavefront aberration inspection method and lens wavefront aberration inspection apparatus used therefor - Google Patents

Description

The present invention relates to a method for inspecting characteristics of a non-converging lens that emits non-converging light or diffused light without spot-condensing parallel light, or a non-converging lens that does not emit light from a point light source as parallel light , particularly wavefront aberration The present invention also relates to a lens wavefront aberration inspection apparatus used therefor.

  In recent years, lenses that emit non-converged light or diffused light without spotting parallel light or lenses that do not emit light from a point light source as parallel light are important due to the widespread use of digital still cameras, DVD devices, etc. Therefore, the number of production is also increasing. There is also a demand for a miniaturized high-precision lens. Such lenses are usually used in combination of a plurality of lenses.

Conventionally, inspecting characteristics of such a lens, for example, a non-converging lens (test lens) , in particular, wavefront aberration , forms an optical system in combination with a correction lens called a null lens, and interference of light passing through the optical system. It was performed by measuring (refer patent document 1). In addition, the characteristics of the test lens are inspected by measuring the shape of the test lens with a stylus type three-dimensional measuring device.

  However, the null lens takes time to accurately align with the test lens, and must be prepared for each type of test lens. As a result, the inspection cost of the test lens increases. was there. In addition, since the null lens is also a non-converging lens, it is necessary to inspect the characteristics. In that case, a further null lens is necessary.

  In addition, the shape measurement of the test lens by the three-dimensional measuring device is performed only on a part of the plurality of test lenses produced because it takes time, and in addition, the inside of the test lens cannot be measured. there were.

Therefore, the present invention does not require a correction lens called a null lens, and is a lens wavefront aberration inspection method and a lens wavefront aberration inspection apparatus used therefor, which can inspect wavefront aberrations in particular in a short time, easily and inexpensively, particularly as a characteristic of a lens to be examined. It is an issue to provide.

A lens wavefront aberration inspection method of the present invention that solves the above-described problem is a method for inspecting the wavefront aberration of a non-converging lens, wherein at least two diffused lights diffracted from a transmission diffraction grating and traveling in different directions are emitted. Capturing the interference fringe image formed by condensing at least two diffused light beams that have interfered in the non-converging lens and transmitted through the non-converging lens; Inspecting the wavefront aberration of the non-converging lens from the interference fringe image.

The lens wavefront aberration inspection apparatus used in the lens wavefront aberration inspection method of the present invention is a non-convergent lens wavefront aberration inspection apparatus, wherein the non-converging lens is detachably held, and the non-converging lens transmits light. a light incident means for entering at least two diffused light traveling in different directions emitted by the diffraction from the diffraction grating, condensing at least two diffuse light passed through the non-converging lens interfere in the non-converging lens An interference fringe image capturing unit that captures the interference fringe image formed in this manner ; and a lens wavefront aberration inspection unit that inspects the wavefront aberration of the non-converging lens from the interference fringe image.

According to the present invention, it is possible to inspect the wavefront aberration of a test lens easily and inexpensively in a short time without the need for a correction lens called a null lens, and as a result, the wavefront for all manufactured test lenses. It is also possible to inspect aberrations .

FIG. 1 schematically shows a conceptual or basic optical system necessary for a lens characteristic inspection method (lens wavefront aberration inspection method) capable of inspecting the wavefront aberration of a lens according to the present invention. The optical system includes a test lens 10 to be inspected for lens characteristics, a diffraction grating 12 that is a light splitting unit that splits one light into a plurality of lights, and a plurality of lights emitted from the test lens 10. Interference fringe image capturing means 14 for capturing an interference fringe image is provided on the optical axis 16. The interference fringe image capturing means 14 is an imaging device such as a CCD camera or a screen, which will be described later.

As shown in FIG. 2 in which the area A of FIG. 1 is enlarged, the diffraction grating 12 has a plurality of grooves arranged in parallel in a direction perpendicular to the direction of the optical axis 16 having a grating pitch p and a grating depth d of the order of submicrons. . Two lights emitted from the diffraction grating 12 and traveling in different directions, the + 1st order diffracted light L _{+ 1} and the -1st order diffracted light L- ₁ are incident on the lens 10 to be examined. Subsequently, the two lights are refracted and emitted by the test lens 10 to form an interference fringe image 18 on the interference fringe image capturing means 14. The interference fringe image 18 is called a shearing interference fringe, and the characteristics of the interference fringe image 18, for example, the lens characteristics of the lens 10 to be examined, such as aberration, can be inspected from the pitch and number of the fringes.

A lens characteristic inspection device (lens wavefront aberration inspection device) that can inspect the wavefront aberration of a lens and that is based on this optical system and that corresponds to several types of test lenses will be described below.

First embodiment:
A lens characteristic inspection apparatus 110 according to the first embodiment will be described with reference to FIG. 3 showing a schematic configuration. The lens characteristic inspection apparatus 110 serves as a light incident means, a laser apparatus 112 that outputs light, an objective lens 114 that emits diffused light by expanding the diameter of the light output from the laser apparatus 112, and an output from the objective lens 114. The filter 118 having a pinhole 116 that removes an excess component of the diffused light and expands the emission angle of the diffused light to emit spherical light, and the spherical wave light from the pinhole 116 is incident. The collimator lens 120 that emits parallel light and the parallel light emitted from the collimator lens 120 are incident, and the grating pitch that emits + 1st order diffracted light L _{+ 1} and -1st order diffracted light L- ₁ (two lights) p and a diffraction grating 122 having a grating depth d.

  In addition, the lens characteristic inspection device 110 includes a test lens 124 into which two lights from the diffraction grating 122 are incident. In addition, the lens characteristic test apparatus 110 is refracted and emitted from the test lens 124 as an interference fringe image capturing unit. A condenser lens 126 that collects two lights and collects them on a CCD image sensor of a CCD camera, which will be described later, and a CCD camera 128 that images an interference fringe formed from the two lights emitted from the condenser lens 126 as an image. Have

  Further, the lens inspection apparatus 110 includes a holder 130 that is a means for holding the diffraction grating 122 and a chuck 132 that is a means for holding the lens 124 to be removed. One of the holder 130 and the chuck 132 is configured as a means for rotating around the optical axis 134 while holding the diffraction grating 122 or the test lens 124 by a rotation driving means 136 such as a motor (FIG. 3). In FIG. 2, the rotation driving means 136 is drivingly connected to the holder 130.)

The design of the diffraction grating 122 differs depending on the laser device 112 used, the desired interference fringe image, in other words, the diffraction angle θ of ± first-order diffracted light that forms the interference fringe image, for example, the wavelength of the output light When a He—Ne laser device having λ of 532.8 nanometers (nm) is used, and the diffraction angle θ of the two lights, the + 1st order diffracted light L _{+ 1} and the −1st order diffracted light L− ₁ , is ± 5 ° The grating pitch p of the diffraction grating is determined to be 6113 nm. The lattice pitch p can be obtained by the equation (1).

The grating depth d of the diffraction grating 122 is determined so that the 0th-order diffracted light is not emitted toward the test lens 124. The grating depth d can be obtained from the refractive index n of the diffraction grating and the refractive index 1 in the atmosphere (approximate value) by the equation shown in Equation 2.

  When the diffraction grating 122 is quartz glass having a refractive index n = 1.45625, the grating depth d is determined to be 694 nm.

  The distance between the diffraction grating 122 and the test lens 124 and the distance between the condenser lens 126 and the CCD camera 128 are determined by holding the chuck 132 and the condenser lens 126 and holding the chuck 132 and the condenser lens 126 in the optical axis direction 136. The distance is adjusted by parallel movement, for example, adjusted by distance adjusting means 138 and 140 composed of an actuator or the like. These distances are determined by the desired interference fringe image. Specifically, the distance between the diffraction grating 122 and the test lens 124 is determined so that the shearing rate is as large as possible, and the distance between the condenser lens 126 and the CCD camera 128 is determined by the CCD imaging of the CCD camera 128. It is determined so that an interference fringe image is formed as large as possible on the entire element surface.

  As shown in the CCD camera image shown in FIG. 4, the interference fringe image obtained in this way is formed in a region 142 where substantially circular projection lights formed by the two lights overlap each other. Characteristics such as aberration of the lens 124 to be examined are inspected from the characteristics of the interference fringe image.

By rotating either the holder 130 holding the diffraction grating 122 or the chuck 132 holding the test lens 124 by the rotation driving means 134, a plurality of different interference fringe images can be obtained. For example, a holder 130 that holds the diffraction grating 122 is shown in FIG. The holder 130 shown in the drawing is rotated by the rotation driving means 134 around the optical axis 134 in the direction of the arrow 144, thereby detecting two lights (+ 1st order diffracted light L _{+ 1} and −1st order diffracted light L- ₁ ). The incident direction with respect to the lens 124 is changed. As a result, a plurality of interference fringe images having different incident directions of the two lights are obtained, and aberrations in different directions (radiation directions) of the lens 124 to be measured, for example, 0 ° and 90 ° directions (orthogonal) from the plurality of interference fringe images. It is possible to evaluate aberration components (wavefront aberrations that vary depending on the radiation direction) of the lens 124 in the two radiation directions). A method for evaluating the wavefront aberration of a lens from an interference fringe image is described in Japanese Patent Application No. 11-212170.

  The evaluation of aberration components in different radial directions in the test lens 124 may be performed by rotating the test lens 124 held by the chuck, in which the rotation driving unit 134 is drivingly connected to the chuck 132.

Second embodiment:
The lens characteristic inspection apparatus according to the second embodiment is intended for a lens having an extremely small focal length, for example, a convex lens having a small curvature radius and having a focal length of 0 mm to 10 mm. The light emitted from such a lens converges or diverges immediately after emission. Therefore, it is necessary to dispose interference fringe image capturing means such as an imaging lens and a CCD camera close to the lens to be examined. However, the interference fringe image capturing means cannot be placed close to the subject lens because of its shape. In other words, if the interference fringe image catching means is placed close to the interference fringe image capturing means, the interference fringe image capturing means and the subject lens come into contact with each other. The present embodiment is a lens characteristic inspection apparatus for solving this.

A lens characteristic inspection apparatus 210 according to the second embodiment is schematically shown in FIG. The lens characteristic inspection apparatus 210 includes, as light incident means, a laser apparatus 212 that outputs light, an objective lens 214 that condenses the light output from the laser apparatus 212, and a focal point of light collected by the objective lens 214. disposed near the focal point, + 1 emits a diffracted light L ₊₁ and -1 order diffracted light L _-1, and a diffraction grating 216 having a grating pitch p and grating depth d.

  The lens characteristic inspection apparatus 210 has a test lens 218 into which two lights from the diffraction grating 216 are incident. Further, as the interference fringe image capturing unit, the lens characteristic test apparatus 210 is refracted and emitted from the test lens 218. A condensing lens 220 that collects two lights and collects them on a CCD element surface of a CCD camera, which will be described later, and a CCD camera 222 that captures an interference fringe formed from two lights emitted from the condensing lens 220 as an image. Have. In addition, a holder 224 for holding the diffraction grating 216 and a chuck 226 for detachably holding the lens 218 to be tested are provided.

The grating pitch p and the grating depth d of the diffraction grating 216 are determined by the laser device 212 and the desired negotiation fringe image, as in the first embodiment. Further, the distance between the diffraction grating 216 and the lens 218 to be examined and the distance between the condenser lens 220 and the CCD camera 222 are also held in the optical axis direction by holding the chuck 226 and the condenser lens 220 as in the first embodiment. The distance is adjusted by moving the chuck 226 and the condensing lens 220 in parallel to 228. For example, the distance is adjusted by distance adjusting means 230 and 232 including an actuator. These distances are determined by the desired interference fringe image. However, the condensing angle φ of the condensing light emitted from the objective lens 214 must be larger than the diffraction angle θ of the + 1st order diffracted light L _{+ 1} and the −1st order diffracted light L- ₁ (two lights). This is because when the condensing angle φ is smaller than the diffraction angle θ, an interference fringe image formed by overlapping two lights is not formed.

  Further, since the light incident on the diffraction grating 216 is not parallel light, the interference fringe image obtained in the present embodiment has a substantially circular shape of + 1st order diffracted light and 0th order diffracted light as shown in the CCD camera image shown in FIG. It is formed in a region 240 where projection light overlaps and a region 242 where substantially circular projection light of −1st order diffracted light and 0th order diffracted light overlaps. From at least one feature of the interference fringe images formed in the two regions 240 and 242, characteristics such as aberration of the lens 218 to be examined are inspected.

  In this embodiment, similarly to the first embodiment, either the holder 224 or the chuck 226 is centered on the optical axis 228 in a state where the diffraction grating 216 or the test lens 218 is held by the rotation driving means 234 such as a motor. (In FIG. 6, the rotation driving means 234 is drivingly connected to the holder 224).

  According to the lens characteristic inspection apparatus 210 of the second embodiment as described above, the characteristic of a lens to be tested having an extremely small focal length, for example, a convex lens having a small curvature radius and a focal length of 0 mm to 10 mm is inspected. be able to.

Third embodiment:
The lens characteristic inspection apparatus according to the third embodiment has a lens with an extremely small focal length, for example, a convex lens with a small radius of curvature and a focal length of 0 mm to 10 mm, and an extremely small focal length. A target lens, for example, a concave lens having a small radius of curvature and having a radius of −10 mm to 0 mm is targeted.

  FIG. 8 schematically shows a lens characteristic inspection apparatus 310 according to the third embodiment. The components of the lens characteristic inspection apparatus 310 are the same as those of the lens characteristic inspection apparatus 110 of the first embodiment, except for the screen 342 disposed between the lens 324 to be examined and the condenser lens 326. . Therefore, the same component is shown with the code | symbol which added 200 to the code | symbol of the component of 1st Embodiment. Moreover, description is abbreviate | omitted about the component same.

  In the lens characteristic inspection apparatus 310 according to the present embodiment, a semi-transparent planar screen 342 such as ground glass on which two lights emitted from the test lens 324 are projected is near the test lens 324. Is arranged. On the screen 342, an interference fringe image formed by overlapping two lights is projected. The condensing lens 326 condenses the interference fringe image projected on the screen onto the CCD image sensor surface of the CCD camera 328.

  Further, as shown in the figure, the screen 342 is arranged so that the plane of the screen 342 is substantially orthogonal to the optical axis 334, but the arrangement is not necessarily limited to such an arrangement. For example, the screen 342 may be disposed such that its plane intersects the optical axis 334 at a predetermined angle. In such a case, the CCD camera does not need to capture the interference fringe image projected on the semi-translucent screen from the side facing the test lens through the screen. The CCD camera can also capture an interference fringe image projected on a non-translucent screen from the same side as the lens to be examined.

  According to the lens characteristic evaluation apparatus 310 of the third embodiment, the characteristic can be inspected even with a test lens whose focal length is extremely small positively or negatively.

Finally, in the embodiment, the two lights (+ 1st order diffracted light L _{+ 1} and -1st order diffracted light L- ₁ ) incident on the lens to be examined are separated from one light by the diffraction grating. However, not only the diffraction grating but also a half mirror may be used as the light splitting means. In addition, although one light is divided to form two lights, the two lights may be output from, for example, two laser devices. Furthermore, the number of light incident on the test lens is not necessarily limited to two. For example, four lights pass through each of two lights at substantially the same angle with respect to the optical axis of the test lens and on two orthogonal planes including the optical axis of the test lens. If the light is incident on the test lens, aberration components in different radiation directions of the test lens can be inspected at a time, similarly to the result obtained by rotating the diffraction grating in the above embodiment.

It is a figure which shows the basic optical system of the lens characteristic inspection apparatus which concerns on this invention. It is a figure which shows the diffraction grating which expanded the part shown by A of FIG. 1 shows an optical system of a lens characteristic inspection apparatus according to a first embodiment. It is a figure which shows the interference fringe image captured by the lens characteristic inspection apparatus of 1st Embodiment. It is a figure which shows a diffraction grating holder. The optical system of the lens characteristic inspection apparatus of 2nd Embodiment is shown. It is a figure which shows the interference fringe image captured by the lens characteristic inspection apparatus of 2nd Embodiment. 7 shows an optical system of a lens characteristic inspection apparatus according to a third embodiment.

Explanation of symbols

10: lens to be examined, 12: diffraction grating, 14: interference fringe image capturing means, 16: optical axis, 18: interference fringe image,
110: Lens characteristic inspection device, 112: Laser device, 114: Objective lens, 116: Pinhole, 118: Filter, 120: Collimator lens, 122: Diffraction grating, 124: Test lens, 126: Condensing lens, 128: CCD camera, 130: holder, 132: chuck, 134: rotation drive means, 136: optical axis, 138: distance adjustment means, 140: distance adjustment means, 142: region, 144: direction,
210: lens characteristic inspection device, 212: laser device, 214: objective lens, 216: diffraction grating, 218: lens to be tested, 220: condenser lens, 222: CCD camera, 224: holder, 226: chuck, 228: light 230, distance adjusting means, 232: distance adjusting means, 234: rotation driving means, 240: region, 242: region,
310: Lens characteristic inspection device, 312: Laser device, 314: Objective lens, 316: Pinhole, 318: Filter, 320: Collimator lens, 322: Diffraction grating, 324: Test lens, 328: CCD camera, 330: Holder 332: Chuck, 334: Rotation drive means, 336: Optical axis, 338: Distance adjustment means, 340: Distance adjustment means, 342: Screen

Claims (2)

A method for inspecting the wavefront aberration of a non-converging lens,
Entering at least two diffused lights diffracted from the transmission diffraction grating and traveling in different directions into the non-converging lens;
Capturing an interference fringe image formed by condensing at least two diffused light beams that interfered in the non-converging lens and transmitted through the non-converging lens;
A method of inspecting the wavefront aberration of the non-converging lens from the captured interference fringe image. A non-converging lens wavefront aberration inspection device,
Lens holding means for detachably holding the non-converging lens;
A light incident means for causing the non-converging lens to enter at least two diffused lights diffracted from the transmission diffraction grating and traveling in different directions;
Interference fringe image capturing means for capturing an interference fringe image formed by condensing at least two diffused light beams that interfere with each other in the non-converging lens and pass through the non-converging lens;
A lens wavefront aberration inspection apparatus comprising: a lens wavefront aberration inspection unit that inspects the wavefront aberration of the non-converging lens from the interference fringe image.

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