JPH1038756A - Method and apparatus for measuring aberration of afocal optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and an apparatus for measuring each aberration of an afocal optical system. SOLUTION: The light from a light source 11 is passed through a pattern plate 15 and then passed through a collimate lens 17 to produce a parallel luminous flux. The parallel luminous flux is passed through an afocal optical system to be inspected and introduced to a focus lens system 47 in order to focus the image of the light source on a light receiving element 45. The light from the light source 11 is passed through a filter to produce a monochromatic light which is then focused for a plurality of waveforms. Subsequently, color aberration is measured for the entire optical system based on the moving distance of the light receiving element 45 on the optical axis of the focus lens system 47 and the color aberration is determined for the afocal optical system to be inspected by removing the color aberration component of the focus lens system 47. When the focal position is determined for each point of the image, curvature of the image plane can be determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a technique for measuring aberrations such as chromatic aberration and field curvature of an afocal optical system.

[0002]

2. Description of the Related Art An afocal optical system is an optical system used for a telescope, binoculars, a viewfinder of a camera, and the like.
An optical system in which the set of object points and image points are at infinity "or
It is defined as "optical system without focus." Particularly important as the performance of this afocal optical system are field curvature and chromatic aberration.

However, since an afocal optical system does not form an image by itself, it is not easy to measure aberrations such as chromatic aberration and field curvature as an afocal optical system.
As a conventional measurement method, a method of measuring a curvature of field using a diopter telescope is known, and chromatic aberration is mainly measured by visual observation.

However, the measurement using a diopter telescope is manually performed, takes a long time, and is greatly affected by errors caused by a person who performs the measurement. In addition, since the measurement of chromatic aberration is performed by visual observation, objective evaluation such as numerical value cannot be performed.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a measuring apparatus and a measuring method capable of measuring each aberration of an afocal optical system. .

[0006]

In order to achieve the above object, an apparatus according to the present invention comprises a light source, a collimator for converting a light beam from the light source into a parallel light beam, and an afocal optical system to be examined on which the parallel light beam enters. An object holding means for holding the system, an imaging lens system to which a light beam passing through the afocal optical system to be incident enters, and a light receiving element movably provided in the optical axis direction of the imaging lens system, It is characterized by having.

Further, the light source has a plurality of filters for transmitting monochromatic light for different wavelengths, and the light source can be switched to monochromatic light of a plurality of wavelengths by exchanging the filters. It is desirable to have a configuration having a stop at the focal position on the front side of the image lens.

Alternatively, the light source to the collimator are integrated to constitute a light source device, and the light source device is movable in a Y-axis direction crossing the X-axis as a central axis and is orthogonal to these XY planes. It is also possible to adopt a configuration in which it is rotatable around the Z axis, the above-mentioned imaging lens system and the light receiving element are held by a common holding means, and the holding means is rotatable about the Z axis.

A configuration in which the rotation axis of the holding means overlaps the focal point of the imaging lens system on the light source side, or the imaging lens system has a magnifying lens, and the magnifying lens and the light receiving element are fixed to a holding table. The holding table may be configured to be movable in the optical axis direction.

The measuring method of the present invention comprises the steps of: converting light from a light source into a parallel light beam; passing light from the light source through a filter that transmits only monochromatic light into monochromatic light; Transmitting the image of the light source on the light receiving element through the afocal optical system to be tested and forming an image of the light source on the monochromatic light having a plurality of wavelengths. It is characterized in that the chromatic aberration of the entire optical system is measured based on the distance moved on the optical axis, and the chromatic aberration of the afocal optical system to be measured is obtained excluding the chromatic aberration of the imaging lens.

Alternatively, a step of converting the light from the light source into a parallel light beam, a step of making the parallel light beam incident on an imaging lens system via an afocal optical system to be detected, and forming an image on a light receiving element; A position on the optical axis at which the amount of light received by the light-receiving element is maximized at an arbitrary point on the image is measured, and the field curvature of the entire optical system is measured from the position of the light-receiving element. Except for, the field curvature of the afocal optical system to be measured can be measured. It is desirable to provide an aperture at the front focal position of the imaging lens system and to make the imaging lens system a telecentric optical system.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration example of the measuring device of the present invention. In the light source device 10, a light source lamp 11, a filter member 13, a pattern plate 15, and a collimator lens 17 as a collimator are arranged in a predetermined positional relationship with each other, and are integrated by a housing 19. The filter member 13 is “disc-shaped” and has a plurality of filters that transmit only monochromatic lights having different wavelengths. By rotating the filter member 13, a filter can be selected and a wavelength can be selected. The pattern plate 15 may use a pinhole and a slit.

The filter provided on the filter member 13 is a multi-coated flat glass having a half-width of the transmitted light wavelength of about 10 nm. Light source lamp 11
Is a white light source. When the white light source is turned on, the emitted white light passes through the filter member 13 to become monochromatic light, passes through the pattern plate 15, is converted into a parallel light flux by the collimating lens 17, and is emitted.

The light source device 10 is held by a rotary stage 20, and the rotary stage 20 is attached to an intersection of a cross-shaped stage 30. Stage 30 is
Take the X and Y axes as shown, and
X direction stage 32 extending in the direction (axis parallel to the X axis)
And a Y-direction stage 31 extending in the Y-axis direction orthogonal to the central axis 320 in a “cross” shape, and the rotary stage 20 is movable along a guide line 311 on the Y-direction stage 31. I have. Rotary stage 2
Numeral 0 is rotatable in both forward and reverse directions about an axis 330 parallel to the Z axis orthogonal to the XY plane.

The X direction stage 32 is a subject holding means 32
The object afocal optical system 0 is held by the object holding means 321 such that the optical axis thereof coincides with the central axis 320.

The X-direction stage 32 is also provided with a second rotary stage 322.
One end of the holding means 40 is fixed to 2. The holding means 40 is in the form of a narrow plate having a narrow width, and has on its surface side a stop S and a holding table 48 having a driving device movable in the optical axis direction with respect to the holding means 40. . Holder 4
Numeral 8 holds a magnifying lens 43 and a CCD sensor as a light receiving element 45.

Although not shown, a combination of a rack and pinion and a stepping motor is conceivable as a driving device of the holding table 48. The CCD sensor as the light receiving element 45 is
It is a line sensor or area sensor having at least a scanning function in a direction orthogonal to the optical axis of the imaging lens system 47.

The imaging lens 41 is held by a lens holder 42, and the magnifying lens 43 is held by another lens holder 44. The imaging lens 41 and the magnifying lens 43 form an imaging lens system 47 with the optical axes aligned. In the illustrated state, the optical axes of the imaging lens 41, the magnifying lens 43, and the afocal optical system 0 to be inspected held by the object holding means 321 coincide with each other. The chromatic aberration and curvature of field of the imaging lens system 47 are known.

The stop S is fixedly provided at the front focal position P of the imaging lens system 47, and the rotation axis of the second rotary stage 322 overlaps the focal point P. At the lower end of the X-direction stage, a guide rail 33 is provided in an arc shape centering on the rotation axis P, and a “rotating roller (not shown)” provided on the back side of the free end side of the holding means 40. ”Is related. The second rotary stage 322 and the guide rail 33
And the above-mentioned rotary roller (not shown) constitute a “rotation mechanism that makes the holding means 40 rotatable around the Z axis about the position of the stop S”, and can be rotated by a driving device. As this rotary drive, a combination of a rack & pinion and a stepping motor similar to the holding table 48 can be used.

That is, a rack along the arc is fixed to the guide rail 33, and a stepping motor with a pinion may be fixed to the back side of the holding means 40 so as to mesh with the rack.

FIG. 1 shows a state in which the "performance on the optical axis" of the afocal optical system 0 to be measured is measured. When the afocal optical system 0 to be inspected is set as shown in the figure and the light source lamp 11 is turned on, the emitted light passes through a predetermined filter of the filter member 13, for example, d
The light becomes monochromatic light having a line wavelength, passes through a pinhole of the pattern plate 15, is converted into a parallel light beam by the collimator lens 17, exits from the light source device 10, and enters the afocal optical system 0 to be inspected.

At this time, the optical axis of the light source device 10 coincides with the optical axis of the afocal optical system 0 to be inspected. The light beam emitted from the afocal optical system 0 passes through the stop S, once forms an image of a pinhole by the imaging lens 41, and the enlarged image by the magnifying lens 43 is formed on the light receiving surface 45 A of the light receiving element 45. Imaged. The positional relationship between the light receiving surface 45A of the light receiving element 45 and the magnifying lens 43 is adjusted in advance so as to have a predetermined magnification.

The light receiving element 45 scans and outputs the intensity distribution of the formed image. This output is sent to arithmetic means (microcomputer) not shown. The arithmetic means operates the holding table 4 so that the peak of the "image intensity distribution" becomes maximum.
8 is moved in the optical axis direction. The position of the image plane on the axis of the afocal optical system 0 to be detected can be determined from the position of the holding table 48 when the peak becomes maximum. Although the holding table 48 moves the magnifying lens 43 and the light receiving element 45 together, the holding table 48 may be configured to move only the light receiving element 45.

Next, the wavelength of the monochromatic light is switched by rotating the filter member 13 and passing through another filter, the same measurement is performed, and the position of the holding table 48 when the peak becomes maximum is obtained. The amount of movement of the holding table 48 in the optical axis direction between them becomes axial chromatic aberration. By subtracting the known chromatic aberration of the imaging lens system 47 from the chromatic aberration, the chromatic aberration of the afocal optical system can be obtained.

In the afocal optical system measuring apparatus, the pinhole image is formed into a virtual image by the test afocal optical system, and the virtual image is viewed through the imaging lens system 47. Position of virtual image and imaging lens system 47
When the light receiving surface is moved to match the object position of
Generally, when the effective F number of the imaging lens changes and the illuminance on the light receiving surface becomes maximum, it is impossible to determine that the position of the virtual image coincides with the object position of the imaging lens.

Therefore, in the present invention, the stop S is placed at the position of the front focal point P of the image forming lens system 47 to form a telecentric optical system. With such a configuration, the effective F-number does not change due to a change in the conjugate length, and the virtual image position of the afocal optical system to be detected can be found.

FIG. 2 shows the embodiment shown in FIG. 1 in a direction (off-axis) inclined with respect to the optical axis of the afocal optical system to be measured.
The state when measuring chromatic aberration is shown. When performing off-axis measurement, it is possible to perform measurement by moving only the light receiving surface 45A in parallel in the Y-axis direction. However, in this case, the imaging lens system 47 must cover a large image. In addition, the lens becomes large in diameter due to its large aperture, and it is difficult to eliminate aberrations at a wide angle of view.

Therefore, the present invention has attempted to solve this problem as follows. As shown in FIG.
It is moved along the direction stage 31 in the Y-axis direction. The movement amount LY at this time is, for example, the Y-direction stage 3
It can be measured by engraving a scale on 1. Next, the rotating stage 20 is rotated so that the parallel light beam from the light source device 10 is incident on the afocal optical system 0 to be measured.

Since the distance LX between the guide line 311 and the position of the afocal optical system 0 to be inspected is constant, the angle between the incident parallel light beam and the optical axis of the afocal optical system 0 at this time is θin. Can be known from the relationship tan θin = LY / LX.

The calculating means rotates the holding means 40 so that the image of the pinhole is located near the center of the CCD. From the rotation angles θout and θin, the magnification of the test afocal optical system 0 can be determined. Further, the difference between the positions of the centers of gravity of the "image intensity distribution" on the CCD surface when the measurement is performed while changing the wavelength of the monochromatic light becomes chromatic aberration of magnification.

In the illustrated embodiment, the X-axis and the Y-axis intersect at a right angle. However, even if the X-axis and the Y-axis intersect at an angle other than the right angle, the measurement can be performed in the same manner as described above. With the above configuration, it is possible to set the incident angle of view, automate the finding of the exit angle of view corresponding to the angle of incidence, and reduce the labor of measurement. In addition, it is not necessary to increase the aperture or the angle of view of the imaging lens system, errors during off-axis measurement are reduced, and the apparatus is inexpensive.

It should be noted that in the above-described embodiment, the holding table 4 is set so that the image intensity of the pattern plate 15 is maximized at a plurality of angles of view.
8 is moved, and the amount of this movement is plotted for each angle of view to determine the field curvature. In this case, if the stop S is provided at the front focal point of the imaging lens 41, an error due to a change in the image plane position of the afocal optical system can be eliminated. If the measurement is performed as shown in FIG. It becomes possible.

[0033]

According to the present invention as described above,
A collimator that converts the light beam from the light source into a parallel light beam, an imaging lens system that transmits the parallel light beam through the test afocal optical system, and then enters the collimator, and is provided movably in the optical axis direction of the imaging lens system. And a light receiving element, the image of the afocal optical system to be measured can be formed, the aberration information can be obtained from the image, and the aberration of the afocal optical system can be measured.

If a light source is provided with a filter that transmits only monochromatic light, and the imaging positions are measured at different wavelengths by a plurality of filters, the chromatic aberration and field curvature of the afocal optical system can be measured. it can.

If a stop is provided at the focal position on the light source side of the image forming lens, the F number of the image forming lens can be made constant, and the deviation of the image forming position due to a change in the F number can be taken into consideration. Get better.

The light source to the collimator are integrated to constitute a light source device, and the light source device is movable in the Y-axis direction crossing the X-axis serving as the central axis of the device, and the Z-axis is perpendicular to the XY plane. And a configuration in which the imaging lens system to the light receiving element are held by a common holding unit, and the holding unit is rotatable around an axis parallel to the Z axis. Then, the aperture of the imaging lens system can be made small, and off-axis measurement with low cost and little error can be performed.

If the light source itself is replaced to change the wavelength of the light from the light source, an error is caused because the luminance distribution is different. However, if the light source is switched by the transmission filter, an error due to the luminance distribution occurs. Since there is no measurement, accurate measurement is possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an apparatus for measuring aberration of an afocal optical system to be inspected according to the present invention.

FIG. 2 is a diagram showing a state in which off-axis aberration is measured by the apparatus shown in FIG. 1;

[Explanation of symbols]

 Reference Signs List 0 afocal optical system to be inspected 10 light source device 11 light source 13 filter 17 collimator 40 holding means 45 light receiving element 48 imaging lens system 321 object holding means P front focal point of imaging lens S aperture

Claims (9)

[Claims] 1. A light source, a collimator for converting a light beam from the light source into a parallel light beam, a subject holding unit for holding a test afocal optical system on which the parallel light beam enters, and a test afocal optical system An imaging lens system on which the reflected light beam is incident;
An afocal optical system aberration measuring apparatus, comprising: a light receiving element movably provided in an optical axis direction of the imaging lens system. 2. The light source according to claim 1, wherein the light source has a plurality of filters for transmitting monochromatic light for different wavelengths, and the light source can be switched to monochromatic light of a plurality of wavelengths by exchanging the filters. An aberration measuring device for an afocal optical system according to claim 1. 3. The aberration measuring device for an afocal optical system according to claim 1, wherein the imaging lens has a stop at a front focal position. 4. A light source device is constituted by integrating the light source to the collimator, and the light source device is movable in a Y-axis direction intersecting the X-axis as a central axis, and the XY device is provided.
It is rotatable about a Z-axis perpendicular to the plane, and the components from the imaging lens system to the light receiving element are held by common holding means,
The aberration measuring device for an afocal optical system according to claim 3, wherein the holding means is rotatable around the Z axis. 5. An aberration measuring apparatus for an afocal optical system according to claim 4, wherein a rotation axis of said holding means is at a focal point on a light source side of said imaging lens. 6. The imaging lens according to claim 1, wherein the imaging lens has a magnifying lens, and the magnifying lens and the light receiving element are fixed to a holder, and the holder is movable in an optical axis direction. 6. The aberration measuring device for an afocal optical system according to any one of 1 to 5. 7. A process of converting light from a light source into a parallel light beam;
A step of passing light from the light source through a filter that transmits only monochromatic light into monochromatic light, and transmitting a parallel light beam of monochromatic light through the imaging lens system via the afocal optical system to be tested, and onto the light receiving element. Performing the step of forming an image of the light source with respect to monochromatic light of a plurality of wavelengths, measuring the chromatic aberration of the entire optical system by the distance that the light receiving element moves on the optical axis of the imaging lens, and calculating the chromatic aberration of the imaging lens. A method for measuring aberrations of an afocal optical system, characterized by obtaining chromatic aberration of an afocal optical system to be inspected except for (1). 8. A step of converting light from a light source into a parallel light beam;
A step of causing the parallel light beam to enter the imaging lens system via the afocal optical system to be detected and forming an image on the light receiving element, and that the light receiving amount of the light receiving element is maximized at an arbitrary point on the image formation An aberration measuring method for an afocal optical system, wherein a position on an optical axis is obtained, and a field curvature of the afocal optical system to be measured is measured from the position of the light receiving element. 9. An aberration measuring method for an afocal optical system according to claim 7, wherein an aperture is provided at a front focal position of said imaging lens system, and said imaging lens system is a telecentric optical system.