JPH0835908A - Apparatus and method for measuring eccentricity of lens - Google Patents

Abstract

PURPOSE:To provide an eccentricity measuring apparatus by which a spot image by a lens to be inspected can be captured surely and by which an eccentricity amount can be measured at low costs and with high accuracy without providing a rotation mechanism. CONSTITUTION:An eccentricity measuring apparatus 10 is composed of a light source 3 used to project light onto a lens 1 to be inspected, of an imaging element 6 which is arranged on an image formation face in order to detect a formed spot image as an electric signal, of an image processor 7 which processes an image signal taken into by the imaging element 6 and of a computer 9 which operates an eccentricity amount and an eccentricity direction on the basis of the output of the image processor 7. The eccentricity measuring apparatus 10 is provided with a magnification-variable optical system 21 by which the magnification of an image formed by the lens 1 to be inspected can be set arbitrarily and with a movement means 22 which moves the imaging element to a desired position. When the magnification-variable optical system 21 and the imaging-element movement means 22 are installed, the spot image by the lens to be inspected is formed surely on the imaging element 6 even when the eccentricity of the lens to be inspected is large. In addition, when the distribution operation of a coma is used for a measuring method, the eccentricity amount can be found without turning the lens 1 to be inspected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eccentricity measuring device and an eccentricity measuring method for measuring the eccentricity of a lens.

[0002]

2. Description of the Related Art Various proposals have been made for a method of measuring eccentricity, and there is an eccentricity measuring device described in Japanese Patent Laid-Open No. 4-138333. The principle of this measuring device will be described with reference to FIG.

As shown in the figure, this apparatus is provided with a lens 1 to be measured, which is an object to be measured, and the lens 1 to be tested is rotatably held by a lens frame 2 to be tested. Light from the light source 3 is made incident on the lens 1 to be inspected as parallel light through the collimator lens system 4. The light transmitted through the lens 1 to be inspected is projected onto the focal position of the lens 1 to be inspected to form a spot image, which is magnified through the magnifying lens system 5 and imaged on the image sensor 6. The X and Y voltages from the image pickup device 6 are divided into two, one is inputted to the computer 9 through the image processing device 7, and the other is fed through the feedback circuit 8 so that the maximum light amount becomes constant. Are controlling.

According to the configuration of the conventional eccentricity measuring device described above, the eccentricity amount of the lens 1 under test with respect to the lens frame 2 under test is measured as described below. That is, in the configuration of the eccentricity measuring device shown in FIG. 1, when the lens 1 under test is rotated with the lens frame 2 under test as a reference, the lens 1 under test is eccentric with respect to the lens frame 2 under test. Then, the spot image focused on the image pickup device 6 draws a circle. Therefore,
The output of the image sensor 6 changes when the spot image draws a circle, and the computer 9 calculates the output to determine the decentering amount of the lens 1 under test.

[0005]

According to the conventional eccentricity adjustment method described above, the eccentricity amount can be obtained numerically, but there are the following problems.

(1) Since the eccentricity of the rotating mechanism of the lens under test is added to the amount of eccentricity of the lens under test, a measurement error occurs.

(2) Since the rotation mechanism for the lens under test is required, the apparatus becomes expensive.

(3) When the eccentricity is large, an image may not be formed on the image pickup element.

The present invention is intended to solve the above-mentioned problems of the prior art. It reliably captures a spot image formed by a lens to be inspected, and is inexpensive and highly accurate in eccentricity without a rotating mechanism. It is an object of the present invention to provide an eccentricity measuring device capable of measuring.

[0010]

In order to achieve the above object, in a lens eccentricity measuring apparatus of the present invention according to claim 1, a light source for projecting light on a lens to be inspected and a spot image formed are formed. An image sensor arranged on the image forming plane for detection as an electric signal, an image processing device for processing the image signal captured by the image sensor, and an eccentricity amount and an eccentric direction from the output of the image processing device. An eccentricity measuring device including a computer is characterized by having a variable magnification optical system capable of arbitrarily setting a magnification of an image formed by a lens to be inspected and a moving means for moving an image pickup element to a desired position. .

According to a second aspect of the present invention, there is provided a lens eccentricity measuring method according to the first aspect, wherein the image processing device and the computer according to the first aspect provide a distribution of areas due to coma aberration appearing in an image formed by the lens to be inspected, or The eccentricity amount and the direction of the eccentricity are calculated based on the shift amount of the center of gravity position.

[0012]

In the configuration of the eccentricity measuring device of the present invention, the light from the light source is projected onto the lens to be inspected through the lens system. Then, the light transmitted through the lens to be inspected is imaged through the variable magnification optical system, the spot image thus formed is taken out as an electric signal, and this electric signal is inputted to the image processing apparatus. At this time, it is reduced by a variable magnification optical system so that the spot image is located on the image sensor, the position of the spot image is detected by the output of the image processing device, and the image sensor is positioned so that the spot image is located in the center of the image sensor. To move. After that, the spot image is magnified by the variable magnification optical system to an appropriate magnification (the size of the image is about 10% to 20% of the number of pixels of the image pickup element. The same applies hereinafter). As a result, the spot image always appears on the image sensor. A coma aberration appears in the enlarged spot image when it is decentered. The distribution of this aberration is calculated by a computer to obtain the eccentricity.

As described above, by providing the variable magnification optical system and the image pickup device moving means, the spot image by the lens to be inspected is surely formed on the image pickup device even if the eccentricity of the lens to be inspected is large. . Further, by using the coma aberration distribution calculation as the measuring method, the eccentricity amount can be obtained without rotating the lens under test.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the following description, the same components as those shown in the prior art of FIG. 1 are designated by the same reference numerals.

(Embodiment 1) FIG. 2 is a schematic view showing an eccentricity measuring device 10 according to the present invention. The eccentricity measuring apparatus 10 shown in FIG. 2A includes a lens 1 to be measured which is a body to be measured, and the lens 1 to be measured is held by a lens frame 2 to be measured.
The light generated from the light source 3 is incident on the lens 1 to be inspected as parallel light through the collimator lens system 4. The light transmitted through the lens to be inspected 1 is condensed at the focal position of the lens to be inspected 1 to form a spot image, and this spot image is set to be imaged on the image sensor 6 via the variable magnification optical system 21.

The variable magnification optical system 21 comprises a magnifying lens 81 and a zoom lens 82, and the zoom lens 8
By moving 2 on the optical axis, the image by the lens under test 1 is enlarged or reduced.

The image pickup device 6 is installed on the image pickup device moving means 22 and is movable in the direction perpendicular to the optical axis. The image pickup device moving means 22 is composed of an X stage 101 and a Y stage 102, and includes a stage driver 6
6 are driven respectively. A detailed view is shown in FIG. The spot image captured by the image pickup device 6 is input to the image processing device 7, and the image information is input to the computer 9. The signal from the image sensor is divided into two, and the other is controlled by the feedback circuit 8 to control the light source 3 so that the intensity of the light focused on the image sensor 6 is always constant.

(Operation) Next, the eccentricity measuring device 10 described above.
The operation of measuring the amount of eccentricity of the lens 1 to be inspected will be described based on the above configuration.

First, the light source 3 is caused to emit light, and the light from the light source 3 is projected through the collimating lens system 4 as parallel light onto the lens 1 to be inspected. The transmitted light from the lens 1 to be inspected is condensed at the focal position of the lens 1 to be inspected to form a spot image. When the eccentricity of the lens 1 to be inspected is large, a spot image is formed off the optical axis and does not form an image on the image sensor 6. Therefore, the variable magnification optical system 21 reduces the spot image, The deviation of the image forming point from the optical axis is apparently made small so that the image is formed on the image pickup element 6 reliably.

The position of the image information of the spot image captured by the computer 9 through the image processing device 7 is detected by the computer 9, and the spot image is positioned at the center of the image pickup element 6 based on the position information. The position of the image sensor 6 is adjusted by the image sensor moving means 22. afterwards,
The variable magnification optical system 21 magnifies the spot image to an appropriate magnification.

The other output of the image pickup device 6 is controlled by the feedback circuit 8 so that the intensity of the spot image formed on the image pickup device 6 is always appropriate and constant.

The enlarged spot image is used as an image processing device 7.
It is taken into the computer 9 via the. This image is shown in Figure 3.
This will be described below. The figure schematically shows a photograph of a spot image, which is a black-and-white inverted negative image in which bright portions are indicated by black dots. When the eccentricity of the lens 1 to be inspected is small, a circular image is formed in the center and a ring image is concentrically surrounded by a ring image in the periphery as shown in FIGS. When the eccentricity of the lens 1 to be inspected is large,
Due to the influence of coma, the ring image forms an ellipse or an incomplete circle as shown in FIGS. This aberration is characteristic of eccentricity, and the amount of eccentricity can be obtained from the state of the aberration. The computer 9 extracts the feature amount according to the state of the image and calculates the eccentricity amount.

The concept of obtaining the eccentricity will be described below with reference to FIG. The captured image is binarized by the image processing device 7 with a certain threshold value. A main beam component 41 and a sub beam component 42 appear in the image at this time (see FIG. 4).
(A) and FIG.4 (b)). Main beam component 4 now
The center of gravity G0 of 1 is obtained, and four quadrants centering on the center of gravity G0 are hypothesized as shown in FIGS. 4 (c) and 4 (d), and the areas of the respective quadrants are S1 to S4. When the distribution of the sub-beam component 42 is uniform with respect to the center of gravity G0 of the main beam component 41, the eccentricity of the lens 1 to be inspected is small (FIG. 4C), and the areas S1 to S4 of each quadrant are shown. Have the following relationships.

[0024]

[Equation 1] S1≈S2≈S3≈S4

When the distribution of the sub-beam component 42 is not uniform with respect to the center of gravity G0 of the main beam component 41, it means that the lens 1 to be measured has a large eccentricity (FIG. 4).
(D)) The eccentricity amount δ and its direction θ have the following relationship.

[0026]

## EQU2 ## δ = K1 (X ² + Y ² ) θ = tan ^-1 (X / Y) where K1 is a constant determined by the lens to be inspected.

However,

[0028]

(3) X = S1 + S2 Y = S3 + S4

[0029] By calculating this area ratio, the eccentricity amount and the eccentricity direction of the lens 1 under test can be obtained.

FIG. 5 is a flowchart of the actual measurement process.
Shown in First, in order to calculate the center of gravity G0, the spot image is binarized at SL0, which is a threshold value capable of detecting only the main beam component 41, and the center of gravity G0 is calculated (121). Next, four quadrants centering on the center of gravity G0 are hypothesized (FIGS. 4 (c) and 4 (d)) and set as a window (122). Binarization is performed using SL1, which is the threshold value for detecting the sub-beam component 42 (123), and the area of each quadrant, S1 to S4, is calculated (124). The above-described calculation is performed on the obtained area of each quadrant, S1 to S4 (125), and the eccentricity amount δ and its direction θ are obtained.

As described above, in this embodiment, the decentering amount can be obtained without rotating the lens 1 to be tested by using the decentering amount calculation method using the coma aberration distribution of the spot image. . Further, by using the image pickup device moving means, the image forming position can be always located at the center of the image pickup device 6, so that the image pickup device 6 can be moved even if the eccentricity is large.
The reliable measurement can be performed without deviating from the imaging range of.
Therefore, the object of the present invention is to accurately capture the spot image by the lens to be inspected, and it is possible to configure at low cost, and it is possible to perform highly accurate measurement without adding the error due to rotation to the measured eccentricity amount. A device can be provided.

(Second Embodiment) FIG. 6 is an explanatory view showing a second embodiment of the eccentricity measuring device according to the present invention. In the present embodiment, the configuration of the device is the same as that of the first embodiment, and therefore, the same constituent elements will be denoted by the same reference numerals as those in FIG. 2 and redundant description will be omitted.

As shown in FIG. 6, a half prism 61 is arranged between the lens frame 2 to be tested and the variable magnification optical system 21, and the optical path is divided into a first optical path 62 and a second optical path 63. ing. The light in the first optical path enters the image sensor 6 as in the first embodiment. The light of the second optical path 63 is arranged so as to form an image on the optical position detection element 65 via the imaging lens 64. The output of the optical position detection element 65 is the stage driver 66.
The image pickup device moving means 22 is driven according to the input.

(Operation) Similar to the first embodiment, the light from the light source 3 passes through the lens 1 to be inspected. The light passing through the lens 1 to be inspected is split into two light paths by the half prism 61.
The optical path 62 enters the variable magnification optical system and forms an image on the image sensor 6 as in the first embodiment. The second optical path 63 is imaged on the optical position detection element 65 by the imaging lens 64. Since the output from the optical position detection element 65 is the center of gravity of the transmitted light of the lens 1 to be inspected, this center of gravity is used as the stage driver 6
6, the image pickup element moving means 2 is calculated based on the position information.
2 is driven and moved so that a spot image is formed at the center of the image sensor 6. As a result, the spot image on the image sensor 6 always appears at the center of the image sensor 6.

The calculation method for obtaining the eccentricity amount can be obtained by the same method as in the first embodiment.

As described above, in this embodiment, since the optical path is divided and the position of the spot image is constantly detected,
According to the effect of the first embodiment, it is possible to reduce the measurement work and shorten the measurement time.

(Embodiment 3) In this embodiment, a method of calculating the eccentricity amount from the obtained image information will be described. Although details of the apparatus are not mentioned, each component will be described based on FIG. 6. An explanatory view of the measuring method is shown in FIG.

An image is formed by the lens 1 to be inspected, and the image pickup element 6 is formed.
The spot image obtained by the above is as shown in FIG. Now, the brightness distributions on the X and Y axes of this spot image are as shown in FIGS. 7 (a) and 7 (b). In this figure, the main beam component 41 is the sub beam component 4
Since it is sufficiently larger than 2, it is binarized by a threshold SL0 that can extract only the main beam component 41, and its center of gravity G0 (X0, Y0) is obtained (FIGS. 7C and 7C).
(D)). Next, the main beam component 41 is masked and the sub-beam component 42 is extracted by binarization with SL1, which is a threshold value, and the center of gravity G1 (X1, Y1) thereof is obtained (FIG. 7).
(E) and FIG. 7 (f)). Where sub-beam component 4
When the distribution of 2 appears uniformly with respect to the center of gravity G0 of the main beam component 41, the eccentricity is small, and G0,
The relationship of G1 is as in the following formula.

[0039]

[Equation 4] | G0-G1 | ≈0

When the sub-beam component 42 is not uniform with respect to the center of gravity G0 of the main beam component 41, the eccentricity is large, and the eccentricity amount δ and the eccentricity direction θ are given by the following equations. become.

[0041]

## EQU5 ## δ = (X ² + Y ² ) δ = tan ^-1 (X / Y) where K1 is a constant determined by the lens under test.

In addition,

[0043]

## EQU6 ## X = K1 (X1-X0) Y = K1 (Y1-Y0)

It is assumed that

FIG. 8 is a flowchart of the actual measurement process.
Shown in First, in order to calculate the center of gravity G0, the spot image is binarized at SL0, which is a threshold value capable of detecting only the main beam component 41, and the center of gravity G0 is calculated (141). Next, a threshold value SL1 for detecting the sub-beam component 42
Then, binarization is performed (142), the main beam component is masked (143), and the center of gravity of the obtained image (sub-beam component) is calculated (144). The above-described calculation is performed on the obtained center of gravity (145) to obtain the eccentricity amount δ and its direction θ.

As described above, in this embodiment, by using the method of calculating the amount of eccentricity and the direction of eccentricity using the distribution of the coma aberration of the spot image, the lens 1 under test can be rotated without rotating. The amount of core and the direction of eccentricity can be obtained. Therefore, it is possible to provide an apparatus which is an object of the present invention and which can be configured at a low cost and enables highly accurate measurement in which an error due to rotation is not added to the measured eccentricity amount.

[0047]

As described above, according to the present invention, the spot image formed by the lens to be inspected can be reliably captured, and the eccentricity amount can be measured with high accuracy at low cost without a rotating mechanism. At the same time, since it is not necessary to rotate the lens to be inspected, the measurement time can be shortened.

[Brief description of drawings]

FIG. 1 is a schematic view showing a conventional lens eccentricity measuring device.

FIG. 2 is a schematic diagram showing a lens eccentricity measuring device according to a first embodiment of the present invention.

FIG. 3 is a diagram schematically showing a photograph of a spot image.

FIG. 4 is a diagram for explaining how to determine the amount of eccentricity by the apparatus of the first embodiment.

FIG. 5 is a flowchart of a measuring process showing a lens decentering measuring method according to the first embodiment.

FIG. 6 is a schematic diagram showing a lens eccentricity measuring device according to a second embodiment of the present invention.

FIG. 7 is a diagram for explaining a lens eccentricity measuring method according to a third embodiment of the present invention.

FIG. 8 is a flow chart of a measurement process showing a lens eccentricity measurement method according to a third embodiment.

[Explanation of symbols]

1 Lens to be inspected 2 Lens frame to be inspected 3 Light source 4 Collimating lens system 5 Magnifying lens system 6 Image sensor 7 Image processing device 8 Feedback circuit 9 Computer 10 Decentering measuring device 21 Magnification variable optical system 22 Image sensor moving means 41 Main beam component 42 Sub-beam component 61 Half prism 62 First optical path 63 Second optical path 64 Imaging lens 65 Optical position detection element 66 Stage driver 81 Magnifying lens 82 Zoom lens 101 X stage 102 Y stage 103 X axis motor 104 Y axis motor 121 Binarization , Center of gravity G0 calculation (only main beam detected) 122 window set 123 binarization (also detects sub beam) 124 each quadrant area calculation 125 eccentricity amount, direction calculation 141 binarization, center of gravity G0 calculation (only main beam detected) 142 Binarization (sub 143 main beam component mask 144 center of gravity calculation 145 eccentricity amount and direction calculation SL0 threshold SL1 threshold G0 center of gravity G1 center of gravity K1 constant δ eccentricity determined by lens to be measured θ eccentric direction S1 phantom Area S2 Elephant area S3 Elephant area S4 Elephant area

Claims (2)

[Claims] 1. A light source for projecting light onto a lens to be inspected, an image pickup device arranged on an image forming plane for detecting a formed spot image as an electric signal, and an image signal taken in by the image pickup device. In an eccentricity measuring device consisting of an image processing device that processes the image and a computer that calculates the amount of eccentricity and the direction of eccentricity from the output of the image processing device, the magnification of the image formed by the lens under test can be set arbitrarily. An eccentricity measuring device comprising: a variable magnification optical system capable of moving; and a moving means for moving an image sensor to a desired position. 2. The image processing apparatus and the computer according to claim 1, wherein an eccentricity amount and an eccentricity are caused by a distribution of areas due to coma aberration appearing in an image formed by a lens to be inspected or a displacement amount of a center of gravity position. An eccentricity measuring method characterized by calculating a direction.