JP2000241128A - Plane-to-plane space measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for measuring the thickness of a lens or a plane-to-plane space nondestructively and noncontactingly at a high accuracy. SOLUTION: The apparatus comprises a low-coherence light source 101, a beam dividing element 102 for dividing a beam emitted from the light source 101, a reflection mirror 103 for changing the optical path length of one beam divided by the dividing element 102 and reflecting the beam, and a photoelectric detector 105 for detecting an interference signal produced by superposing a light which is reflected from an object 104 after another beam divided by the dividing element 102 is incident on an object 104, on a light reflected from the mirror 103. A signal from the photoelectric detector 105 and information from the reflection mirror 103 are arithmetically processed to measure the distance between (a) and (b).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface distance measuring apparatus for measuring the thickness and the surface distance of a lens.

[0002]

2. Description of the Related Art As a conventional surface distance measuring device, there is known a method of detecting a reflection image from the top of an optical element such as a lens and measuring the surface distance. There is also a method in which a cross section of an optical system is photographed using X-rays, and a distance between elements is obtained from an X-ray photograph.

[0003]

However, in the above-mentioned conventional measuring instrument, the measuring accuracy of the surface distance is about 5/100 mm, and there is a demand for measuring at about 1/100 mm with the improvement of the accuracy of the optical system. Are not responding to the demand.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a non-destructive, non-contact, surface distance measuring device capable of measuring a lens thickness and a surface distance with high accuracy. To provide.

[0005]

According to the present invention, there is provided an apparatus for measuring a surface interval, comprising: (1) a low coherence light source having a short spatial coherence length; and a light beam for splitting a light beam emitted from the low coherence light source. A splitting means, an optical path length changing means having means for changing the optical path length of one of the light beams split by the light beam splitting device and reflecting the light beam, and the other light beam split by the light beam splitting device being an object. Light intensity detecting means for detecting an interference signal generated by superimposing reflected light incident and reflected on an optical system and reflected light from the optical path length changing means, wherein a signal from the light intensity detecting means and the optical path A method and an apparatus for measuring a surface interval, wherein an interval is measured by arithmetically processing information from a length changing means.

(2) Light beam shaping means for converting light emitted from the low coherence light source into a substantially parallel light beam, polarization state converting means for converting the substantially parallel light beam into an arbitrary polarization state, and a light beam for dividing the substantially parallel light beam Splitting means for converting the polarization state of one of the light beams split by the light beam splitting means;
Polarization state conversion means, reflection means for reflecting the light beam whose polarization state has been changed by the second polarization state conversion means, movement means for moving the reflection means, and movement amount for measuring the movement amount of the reflection means Measuring means, light collecting means for condensing the other light beam split by the light beam splitting means, a pinhole arranged at a light collecting position by the light collecting means, and a light beam from the pinhole should be measured. An optical element having an adjusting means for guiding the light to an object having a surface interval and condensing the light on an arbitrary surface of the object, and a light beam combining means for superimposing the two light beams split by the light beam splitting means And photoelectric conversion means for converting the light intensity of the light flux superimposed by the light flux synthesis means into an electric signal, and signal processing means for processing a signal from the photoelectric conversion means and information from the movement amount measurement means. Specially It said to be (1) surface distance measuring method and apparatus according to item.

(3) As the low coherence light source,
The method and apparatus according to the above mode (1), wherein a super luminescent diode is used.

(4) As the low coherence light source,
2. The method and apparatus according to claim 1, wherein a semiconductor laser operated at a threshold current or less is used.

(5) As the low coherence light source,
The method and apparatus for measuring a surface interval according to the above mode (1), wherein a pulse laser is used.

(6) As the low coherence light source,
The method and apparatus for measuring a surface interval according to the above mode (1), wherein infrared light is used.

(7) As the low coherence light source,
The method and apparatus for measuring a surface interval according to the above mode (1), wherein visible light is used.

(8) The method and apparatus according to the above (1), wherein a photodiode, a photomultiplier, a line sensor, or a solid-state image sensor is used as the photoelectric conversion means.

(9) As the means for reflecting one of the light beams split by the light beam splitting means, an optical system having a configuration optically equivalent to the test object is used. 4. The method and apparatus for measuring a surface distance according to claim 1.

(10) The method and apparatus for measuring a surface interval according to the above item (1), wherein an optical system of a zoom lens is used as an optical system composed of a plurality of optical elements to be inspected. .

(11) The method and apparatus for measuring a surface interval according to the above (1), wherein a digital camera is used for alignment of the optical system.

(12) A method for adjusting the distance between lenses using the method and apparatus for measuring the distance between surfaces in the process of assembling the optical system of various optical instruments according to the above (1) to (11).

(13) A low coherence light source having a short spatial coherence length, light beam splitting means for splitting a light beam emitted from the low coherence light source, and changing the optical path length of one of the light beams split by the light beam splitting device The other light beam split by the light beam splitting device is incident on an optical system as a test object, and the reflected light or transmitted light from the optical system and the light beam passing through the light path length changing device. And an apparatus for detecting an interference signal generated by superimposing the distance and measuring the distance from the information from the optical path length changing means.

(14) A light beam shaping means for converting light emitted from the low coherence light source into a substantially parallel light beam, a polarization state converting means for converting the substantially parallel light beam into an arbitrary polarization state, and a light beam for dividing the substantially parallel light beam Splitting means, second polarization state converting means for converting the polarization state of one of the light beams split by the light beam splitting means, and reflecting means for reflecting the light beam whose polarization state has been changed by the second polarization state converting means Moving means for moving the reflecting means; moving amount measuring means for measuring the moving amount of the reflecting means; and third polarization state conversion for converting the polarization state of the other light beam split by the light beam splitting means. Means for guiding the light flux whose polarization state has been changed by the third polarization state conversion means to an optical system as a test object having a surface interval to be measured, toward a substantially spherical center or a surface top of the surface to be measured. Luminous flux An optical element with an adjusting device such that the light beam enters, a light beam combining device for superimposing the two light beams split by the light beam splitting device, and converting the light intensity of the light beam superimposed by the light beam combining device into an electric signal. The method and apparatus according to (13), wherein the distance between the surfaces is measured from the photoelectric conversion means, and the signal from the photoelectric conversion means and the information from the movement amount measuring means.

(15) A light beam shaping device for converting light emitted from the low coherence light source into a substantially parallel light beam, a light beam dividing device for dividing the substantially parallel light beam, and reflecting one of the light beams divided by the light beam dividing device. Reflecting means, a moving means for moving the reflecting means, a moving amount measuring means for measuring a moving amount of the reflecting means, and an object having a surface interval for measuring the other light beam divided by the light beam dividing means. Light intensity detecting means for detecting an interference signal generated by superimposing reflected light reflected from an arbitrary surface of the test object and reflected light from the front light distribution path length changing means, leading to an optical system serving as an inspection object; And (13) a photoelectric conversion means for converting the light intensity into an electric signal; and measuring a surface interval from a signal from the photoelectric conversion means and information from the movement amount measuring means.
The method and apparatus for measuring a surface distance according to the description.

(16) a light beam shaping means for shaping light emitted from the low coherence light source into a light beam having a desired shape; a polarization state converting means for converting the light beam into a desired polarization state;
Light beam splitting means, second polarization state conversion means for converting the polarization state of one of the light beams split by the light beam splitting means, and reflection for reflecting the light beam whose polarization state has been changed by the second polarization state conversion means Means, moving means for moving the reflecting means, moving amount measuring means for measuring the moving amount of the reflecting means, and third polarization state for converting the polarization state of the other light beam split by the light beam splitting means. Conversion means;
The light beam whose polarization state has been changed by the third polarization state conversion means is guided to an optical system which is a test object having a surface interval to be measured, and an adjusting means is provided so that the light beam enters the surface to be measured. Optical element, a light beam combining means for superimposing two light beams split by the light beam splitting means, a photoelectric conversion means for converting the light intensity of the light beam superposed by the light beam combining means into an electric signal, and the photoelectric conversion means The method and apparatus according to (13), wherein the surface distance is measured from a signal from the means and coasting information from the movement amount measuring means.

(17) A light beam emitted from a light source having a short coherence length is split by a light beam splitting element, one of which is reflected by a reflecting member as reference light, and the other of which is to be measured and whose distance and thickness are to be measured as measurement light. The reference light and the measurement light are superimposed on each other by the light beam splitting element, and the optical path length difference between the reflected light from one surface of the test object and the reflected light from the reflecting member is the coherence length of the light source. When the interference signal generated when the interference signal is detected, and the interference signal is obtained by changing the optical path length by moving the reflection member with respect to the reflected light from the other surface of the test object, moving the reflection member A method or apparatus for determining a surface distance of an optical element, an optical system, or an optical device, wherein the distance between the test objects is measured from an amount.

(18) The light beam emitted from the low coherence light source is split into reference light and measurement light incident on the test object, and the measurement light reflected from the test object and the reference light interfere with each other. A method or apparatus for determining a surface interval from an interference signal.

(19) A light beam emitted from a light source having a short coherence length is split by a light beam splitting means, one of which is guided as a reference light, and the other is guided as a measurement light to a test object whose interval is to be measured. A method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines by superimposing measurement light with a measurement light.

(20) An interferometer using a light source having a short coherence length, and a test object arranged in an optical path of the interferometer to cause interference, thereby causing an optical element, an optical system, an optical device, or a surface of various machines. The method or device for determining the interval.

(21) a light source having a short coherence length;
A measuring light beam path and a reference light beam path; light from the light source is incident on the object to be measured; and the emitted light and the light in the reference light beam path interfere with each other to form an optical element or an optical system or an optical device or various machines. Method or device for determining the surface spacing of

(22) The surface spacing of an optical element, an optical system, an optical device, or various machines according to any one of (19) to (21), wherein the surface to be measured includes a non-planar surface. Method or equipment.

(23) At least one lens is included in an optical path incident on the object to be measured (19).
(21) A method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines according to any one of (21) to (21).

(24) The optical element, the optical system, the optical device, or the surface of various machines according to any one of (19) to (21), wherein at least one lens is included in the common optical path. The method or device for determining the interval.

(25) The surface spacing of an optical element, an optical system, an optical device, or various machines according to any one of (19) to (21), wherein the object to be measured includes a zoom lens. Method or equipment.

(26) When measuring the lens thickness, the group refractive index is used (19) to (21).
A method or apparatus for determining a surface interval of an optical element, an optical system, an optical device, or various machines according to any one of the preceding claims.

(27) Any one of (19) to (21), wherein the interference fringes are observed on a TV monitor.
A method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines according to the item.

(28) The optical element, the optical system, the optical device, or various machines according to any one of (19) to (21), wherein concentric interference fringes or a part thereof are viewed. Method or device for determining the surface spacing of

(29) The optical element, the optical system, the optical device, or the various machines according to any one of (19) to (21), wherein a non-parallel light beam is incident on the test object. A method or device for determining the surface spacing.

(30) The method according to (19), wherein the angle of the light beam with respect to the optical axis when the measuring light is incident near the spherical center or near the surface top is within ± 15 ° with respect to the theoretical optical value. (21) A method or apparatus for determining a surface interval of an optical element, an optical system, an optical device, or various machines according to any one of (21).

(31) The surface of an optical element, an optical system, an optical device, or various machines according to any one of (19) to (21), wherein the test object is an optical element being processed. The method or device for determining the interval.

(32) After giving a plurality of different optical path lengths to a light beam from a light source having a short coherence length, the light beam is made incident on a test object, and the interference light of the reflected light is examined to determine an optical element, an optical system, or an optical device. Or a method or device for determining the surface spacing of various machines.

(33) A light beam from a light source having a short coherence length is divided into a plurality of light beams, each having a different optical path length, and then incident on a test object, and the interference light of the reflected light is examined to determine the optical element or the optical element. A method or device for determining the surface spacing of a system or optical device or various machines

(34) A light beam from a light source having a short coherence length is divided into a plurality of light beams, each having a different optical path length, and then integrated. The light beam is incident on a test object, and the interference light intensity of reflected light, Alternatively, a method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines by examining the contrast of interference fringes.

(35) An interferometer using a light source having a short coherence length, and a method or an apparatus for arranging a test object in an optical path of the interferometer and obtaining a surface interval causing interference. This is to measure the thickness and interval of each element composed of a plurality of optical elements.

(36) A light source having a short coherence length,
A method or apparatus comprising a measurement light path and a reference light path, wherein light from the light source is incident on an object to be measured, and the emitted light and the light on the reference light path interfere with each other to determine a surface interval.

(37) A light beam emitted from the low coherence light source is split by a light beam splitting element, one of which is reflected by a reflecting mirror as reference light, and the other is guided to a test object whose interval is to be measured as measurement light, The optical path length of the reference light is variable, and the reference light and the measurement light are overlapped by the light beam splitting element, and the reflected light from any surface of the test object and the light from the reflecting mirror. If the optical path difference with the reflected light is within the coherence length of the light source, interference occurs, the interference signal is detected by the photoelectric detector, and then, for reflected light from another surface of the test object, When an interference signal is obtained by the photoelectric detector by changing the optical path length by moving the reflecting mirror,
A method and apparatus for measuring a surface distance, wherein a distance between the two surfaces is obtained by measuring a moving distance of the reflecting mirror.

(38) A light beam is emitted from the low coherence light source, the light beam is split into a measuring beam and a reference beam by a light beam splitting element, and an object to be measured on the measuring beam side is to measure a surface interval of a plurality of lens surfaces. A barrel lens is placed, and a reflecting mirror is installed on the reference light side.The reference light side is adjusted so that the optical path difference between the reference light side optical path and the measurement light side optical path can be adjusted within the coherence length of the light source. The optical path length of the optical path is variable, the measuring light side optical path and the reference light side optical path are overlapped, the overlapping optical path is received by a photoelectric detector, and the interference fringes due to the optical path difference within the coherence length of the light source. First, an interference fringe is detected on one of the lens surfaces to be detected, and then the other lens to be detected is detected on another lens surface to be detected. Optical path length difference to the optical path length of the measuring light side optical path due to the surface The optical path length of the reference light side optical path is changed so as to be within the coherence length of the light source, interference fringes are detected on the other lens surface to be measured, and the amount of change in the optical path length of the reference light side optical path at this time is A surface distance measuring method and apparatus for measuring a surface distance between the lens surface to be measured and the another lens surface to be measured.

(39) The diameter (R ₀ ) of the light beam on the measurement light side optical path is smaller than the diameter (R _s ) of the lens surface to be measured so as to reduce the measurement error due to the curved surface of the lens surface to be measured. An optical element (for example, an opening arranged near the light source or near the collimator lens) that changes the light flux diameter so as to be ／ or less (3R ₀ <2R _s ) is arranged in the optical path (38). 2) The method and apparatus for measuring a surface interval described in the above.

(40) In order to change the optical path length of the reference light side optical path so that the optical path length difference with respect to the optical path length of the measurement light side optical path is within the coherence length of the light source, it is arranged in the reference light side optical path. The method and apparatus according to (38), wherein the set reflecting mirror is set so as to be movable along an optical path.

First, a basic configuration of the method and apparatus for measuring a surface distance according to the present invention will be described with reference to FIG. The light beam emitted from the low coherence light source 101 is
02, one of which is reflected by the reflecting mirror 103 as reference light, and the other is an object 1 whose interval is to be measured as measurement light.
It is led to 04. Here, the optical path length of the reference light is made variable. The reference beam and the measuring beam are divided by the beam splitter 1
02, the optical path length difference between the reflected light from the surface a of the test object 104 and the reflected light from the reflecting mirror 103 is within the coherence length of the light source.
, An interference signal is detected. Next, with respect to the reflected light from another surface b of the test object 104, the reflecting mirror 103 is moved to change the optical path length, and when an interference signal is obtained by the photoelectric detector 105, the reflecting mirror 103 is moved. If the distance is measured, ab
Are obtained.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the method and apparatus for measuring a surface distance according to the present invention will be described below. (First Embodiment) FIG. 2 is a diagram showing a configuration of a first embodiment of the present invention. The light beam emitted from the low coherence light source 1 becomes parallel light by the collimator lens 2 and becomes linearly polarized light by the polarizer (polarizer) 3. Next, when this linearly polarized light is split by the polarizing beam splitter (PBS) 4,
The polarizer 3 is set so that the amount of transmitted light and the amount of reflected light are substantially equal.
The azimuth of the transmission axis is set in advance. Among the light beams split by the polarization beam splitter 4, the reflected light is used as reference light.
The light becomes circularly polarized light by the quarter-wave plate 5, is reflected by the reflecting mirror 6, becomes linearly polarized light again through the quarter-wave plate 5, passes through the polarization beam splitter 4, is condensed by the lens 7, and is collected by the photoelectric detector. (Photodetector) 8. The reflecting mirror 6 can be moved by a linear guide or the like, and its moving distance can be accurately measured by the length measuring device 9.

On the other hand, the transmitted light split by the polarization beam splitter 4 passes through the second quarter-wave plate 10 to become circularly polarized light as measurement light, and is then condensed on the pinhole 12 by the lens 11. The light transmitted through the pinhole 12 passes through the lens 13, and the lens 1 to be measured whose surface distance and thickness are to be measured.
4 is incident. Here, if the lens 13 and the test lens 14 are adjusted so that the condensing position of the measurement light is located at the top of the surface of the lens whose surface distance and thickness are to be measured,
The reflected light from the lens surface is the lens 13, the pinhole 12,
The light passes through the lens 11 and the quarter-wave plate 10, is reflected by the polarization beam splitter 4, is condensed by the lens 7, and is incident on the photoelectric detector 8. As the photoelectric detector 8, a solid-state imaging device such as a CCD may be used in addition to the photodiode.
Here, since the lens 11, the pinhole 12, the lens 13, and the test lens 14 constitute a confocal optical system,
The reflected light from the surface of the lens to be measured other than the surface to be measured is blocked by the pinhole.

In the photoelectric detector 8, the light reflected by the reflecting mirror 6 (reference light) and the light reflected by the lens to be measured (measurement light)
When the optical path length difference between the two is within the range of the coherence length of the light source, interference occurs and an interference signal is observed.
At this time, if a low coherence light source having a coherence length of about several tens of μm is used as the light source, an interference signal is observed when the optical path length difference between the reference light and the measurement light falls within the range of the coherence length. If you want to increase the contrast of the interference signal,
In order to make the intensities of the reference light and the measurement light as equal as possible, use a mirror whose reflectance is close to that of the lens to be measured or change the azimuth angle of the polarizer 3 to change the light amount ratio between the reflected light and the transmitted light. Or a light amount adjusting element such as an ND filter may be placed in front of the reference mirror 6.

In the actual measurement of the distance between the lenses, first, the position of the lens 13 is adjusted so that the light from the light source is focused on one of the lens surfaces a of the lens surfaces to be measured of the lens 14 to be measured. In this state, the counter of the length measuring device 9 is reset. Next, the lens 13 is adjusted so that light is condensed on the other lens surface vertex b of the lens surface interval of the lens 14 to be measured. Here, the reference mirror 6 is moved until an interference signal appears in the output of the photoelectric detector 8. In the case of a low coherence light source, the coherence length of the light source is about several tens of μm, and the position where the peak of the interference signal appears is the position where the optical path lengths of the reference light and the measurement light are almost equal. At this time,
A signal processing unit 15 for correcting the lens magnification, the optical path length of the glass, and the aberration component generated in the lens to be inspected from the value obtained by the length measuring device 9 is provided, and the correction operation is performed. The desired lens surface distance a-b can be accurately obtained.

As a low coherence light source, a super luminescent diode having a coherence length of several tens of μm is well known, but a similar effect can be obtained by operating a single mode oscillation semiconductor laser at a threshold current or less. . Further, a short pulse laser may be used.

When the alignment of the optical system is performed, if the light source is invisible light, a visualization device having sensitivity to the wavelength of the light source is used. For example, a commercially available digital camera with a liquid crystal monitor may be used instead. Generally, an infrared cut filter is incorporated immediately before an image pickup device of a digital camera. However, a beam is captured because near infrared light of about 800 nm is somewhat sensitive. Therefore, if the digital camera has a function that can directly display the captured image of the camera on the LCD monitor in real time, it is easy to adjust the optical system without using an expensive visualization device by monitoring the beam using this function Can be done. (Second Embodiment) Next, a second embodiment of the present invention is shown in FIG. In the present embodiment, the reflecting mirror 6 in the first embodiment is used.
Instead of using a lens reference lens frame having a configuration optically equivalent to the lens to be inspected, the lens interval and the thickness being strictly adjusted, and the values thereof being known, are used as the reference optical system. That is, in the first embodiment, an optical system having a configuration similar to that of the lens 14 to be measured is used as a reference optical system.

As in the first embodiment, the light beam emitted from the low coherence light source 1 becomes parallel light by the collimator lens 2 and becomes linearly polarized light by the polarizer 3. One of the two luminous fluxes, reflected and transmitted by the polarization beam splitter 4, is circularly polarized by the 板 wavelength plate 5 as reference light, and condensed on the pinhole 21 by the lens 20. The light transmitted through the pinhole 21 passes through a lens 22 and enters a reference lens 23 having a known lens surface distance. Reference lens 2
If there is one lens surface vertex of the reference lens 23 at the condensing position of the light that has entered the lens 3, the light reflected therefrom is
The light passes through the pinhole 21, the lens 20 and the quarter-wave plate 5, passes through the polarization beam splitter 4, is condensed by the lens 7, is incident on the photoelectric detector 8, and is reflected by the reflected light from the lens to be measured. Overlapping, if the optical path length difference between the two is within the coherence length of the light source, an interference signal is observed.

The actual measurement in this embodiment is as follows.
First, the lens 13 or 14 is moved so that the measurement light is converged on one lens surface a of the lens surface interval of the lens 14 to be measured, and reflected light from the surface a is obtained. Similarly,
In the reference lens 23, the reflected light is obtained by condensing the light on the surface a 'of the lens corresponding to the surface a of the test lens. Where 2
The two light beams are superimposed on each other and adjusted by moving the lens 22 or 23 so that the interference signal is observed by the photoelectric detector 8.

Next, the lens 13 is adjusted so that the reflected light from the other lens surface top b at the interval to be measured of the lens to be measured is obtained. Then, by moving the lens 22, b
Is adjusted so as to obtain the reflected light from the surface vertex b ′ of the reference lens 23 corresponding to the above. At this time, if the moving distances of the lens 13 and the lens 22 are equal, it is understood that the distance between a and b is equal to the distance between a ′ and b ′. When the distance between a and b is different from the distance between a ′ and b ′, the lens 1
From the difference between the movement amount of the lens 3 and the movement amount of the lens 14, the distance between the lens surfaces of the test lens can be obtained by calculation.

In this embodiment, since the reference light and the measuring light pass through optical systems which are optically substantially equivalent, even if aberration occurs in each optical system, the reference light and the measuring light are equally affected and canceled. Therefore, correction for aberration generated in the lens system is almost unnecessary. (Third Embodiment) FIG. 4 shows the configuration of a third embodiment of the present invention. In FIG. 4, a light beam emitted from the low coherence light source 1 becomes substantially parallel light by the collimator lens 2,
The polarizer (polarizer) 3 converts the light into linearly polarized light. A microscope objective lens may be used as the collimator lens 2.

The linearly polarized light is converted into a polarization beam splitter (P
When the light is divided by the BS) 4, by changing the azimuth of the transmission axis of the polarizer 3, the light amount ratio between the transmitted light and the reflected light can be arbitrarily changed. Of the light beams split by the polarizing beam splitter 4, the reflected light is the first quarter of the light beam as the reference light.
After being converted into circularly polarized light by the wave plate 5 and reflected by the reflecting mirror 6, the light again passes through the quarter-wave plate 5, becomes linearly polarized light, passes through the polarization beam splitter 4, and enters the photoelectric detector 8. Reflector 6
Can be moved by a linear guide or the like, and the movement distance can be accurately measured by the length measuring device 9. As the length measuring device 9, a magne scale, a glass scale, a laser measuring device, or the like may be used.

On the other hand, the transmitted light split by the polarization beam splitter 4 is converted into circularly polarized light passing through the second quarter-wave plate 10 as measurement light, and the optical system 14 to be measured for the spacing and thickness of the surfaces is to be measured. The position of the lens 30 disposed on the incident side of the test optical system 14 is adjusted so that light is incident toward the spherical center or the top of one surface a to be measured. By adjusting in this way, the light beam reflected by the surface a becomes substantially parallel light within ± 10 ° with respect to the optical axis by the lens 30, for example. Then, the reflected light becomes linearly polarized light by the 板 wavelength plate 10, is reflected by the polarization beam splitter 4, and enters the photoelectric detector 8.

As the photoelectric detector 8, a one-dimensional or two-dimensional solid-state imaging device, an imaging tube, a photodiode, or the like can be used. If a two-dimensional photoelectric conversion element is used, reflected images from each surface of the test optical system 14 to be measured can be confirmed on the CRT, and thus there is an advantage that the test lens can be easily positioned.

Here, the optical system to be inspected 14 includes a camera, a zoom lens of a digital camera, a single focus lens, a microscope, a lens of an endoscope, a spectacle lens, a contact lens, and the like.

In the photoelectric detector 8, for example, a photodiode, a CCD, a C-MOS sensor, an imaging tube, a photomultiplier, a line sensor, a CdS, etc., the light reflected by the reflecting mirror 6 (reference light) and the test light The light reflected by the lens (measurement light) overlaps, and if the optical path length difference between them is within the range of the coherence length of the light source, interference occurs and an interference signal is observed. If a low coherence light source having a coherence length of about several tens of μm is used as the light source 1, an interference signal is observed when the optical path length difference between the reference light and the measurement light falls within the range of the coherence length.

As the low coherence light source 1, a light source having a coherence length of 0.1 μm to 200 μm in full width at half maximum or 1 nm to 500 nm in full width at half maximum of wavelength can be used. For example, a superluminescent diode (S
Although LD) is well known in recent years, a semiconductor laser may be operated at a threshold current or less, or a short pulse laser, a halogen lamp, an LED, or the like may be used.

In this state, the display value of the length measuring device 9 is recorded or reset.

Next, the position of the lens 30 is adjusted so that light enters the spherical center or the top of the other surface b of the optical system 14 to be measured. It is made to enter the detector 8. Then, the position of the reflecting mirror 6 is changed to obtain a position at which an interference signal is obtained.

The position of the reflecting mirror 6 at this position is read from the value of the length measuring device 9. By subtracting this value from the value obtained on the surface a, an interval to be obtained can be obtained.

Since the value obtained here is an air conversion length, if the medium between the intervals to be measured is air, the display value of the length measuring device 9 becomes the interval to be obtained almost as it is. In the case of a dense medium, the actual distance can be obtained by dividing the medium by the refractive index of the medium.

Here, since a low coherence light source such as an SLD is used, the wavelength of the light source has a wide range. Therefore, when the medium has chromatic dispersion, an accurate interval can be obtained by using the group refractive index in consideration of the dispersion.

The group refractive index _ng is represented by the following equation.

[0068] Here _{n g = n p -λ (dn} p / dλ) ··· Equation 1, represents the phase refractive index at n _p, lambda represents a wavelength.
This concept can be used throughout the present invention.

At this time, the position of the reflection mirror 6 may be calculated in advance when the refractive index and the surface interval of the optical system 14 to be measured are known.

The position z _{j + 1} of the reflecting mirror 6 where the interference fringes occur can be approximately calculated by the following equation.

[0071] Here, z _{j + 1} is a position of the reflecting mirror 6 at which an interference fringe generated by the j-th reflected light is generated. N _gi is a group refractive index of a known medium between the i-th surface and the (i + 1) -th surface. . t _i is the known spacing between the i-th and (i + 1) -th surfaces. C varies depending on where the origin is taken in a constant term.

In this embodiment, the photoelectric detector is used for detecting the interference fringes. However, the interference fringes may be projected on a screen such as a ground glass and observed directly with the naked eye. further,
The interference fringes may be observed with the naked eye on a CRT using a TV camera as a photoelectric detector, or the signals may be observed with a waveform monitor, an oscilloscope, or the like.

A polarizer 31 is provided in front of the photoelectric detector 8 to make the polarization states of the reference light and the measurement light uniform, thereby improving the contrast of interference fringes.

When it is desired to increase the contrast of the interference signal, the azimuth of the polarizer 3 is changed, and the ratio of the amount of reflected light to the amount of transmitted light in the polarizing beam splitter 4 is changed. By making the intensities uniform, the contrast of interference fringes is improved. In order to improve the accuracy, it is preferable that the light amount ratio between the reference light and the measurement light be approximately equal, that is, 1:20 to 20: 1. For this purpose, a filter or the like may be appropriately inserted into the optical path, or a reflecting mirror having a different reflectance may be used.

It is to be noted that the lens 30 may be omitted, and the collimator lens 2 may be appropriately moved in the optical axis direction so that the measuring light is made to enter near the spherical center or near the top of the measuring surface. Even in this manner, the surface interval measurement is possible.

The lens 30 or the collimator lens 2 may be appropriately replaced depending on the test object.

As the measurement object, in addition to the surface distance of the zoom lens, the distance between the lens surface and the film surface, the lens surface and the pressure plate, the distance between the lens surface and the CCD imaging surface, the surface distance between the prisms of the camera finder, and the like are measured. You may.

In the first embodiment, the signal processing means 15
May not be required. In that case, the processing performed by the signal processing means 15 may be manually calculated and performed by a calculator. At this time, some calculation processing such as correction of lens magnification and aberration components may be omitted.

Hereinafter, what can be said in common to the present invention will be described.

When a solid-state image pickup device is used as the photoelectric detector 8, the output of the photoelectric detector 8 is observed with an oscilloscope, a waveform monitor, a television display, or the like, and the intensity of the interference signal reaches a peak or the contrast of the interference fringes. Alternatively, the position of the reflecting mirror at which the peak becomes may be obtained, and the lens surface interval may be obtained.

The allowable range when the measuring light is made to enter the vicinity of the spherical center or the top of the surface is such that even if there is an error of about ± 15 ° with respect to the optical axis of the incident light or the emitted light to the surface to be measured. Good. In the case of precise measurement, the error may be within ± 10 °. This is because the interference fringes generated near the optical axis may be used for the measurement. At this time, in most cases, the interference fringes are concentric, but the contrast is relatively easy to see, which is convenient.

Further, the present invention can be used for measuring the plane distance of an optical element that is not a plane or an optical system including the optical element. In these cases, it is important to perform more accurate measurement. That is, the light beam incident on the test object is non-parallel. This is effective for causing the light beam to enter the vicinity of the spherical center or the top of the surface of the non-planar surface to be measured.

The present invention can also be used for inspecting the thickness of an optical element during processing. When the optical element is a lens, the term "under processing" means that during the polishing and shaving (fine grinding) of the refracting surface of the lens, during the centering of one lens (during edge cutting), and during the assembly of a plurality of lenses. Surface spacing adjustment and eccentricity adjustment (centering of two or more lenses), lens thickness management after cemented lens (centering of cemented lens, lens thickness of cemented lens, adhesive thickness, in case of air space joining) Air spacing, alignment of both lenses).

FIG. 5 shows an example in which the interferometer shown in FIG. 4 is used to measure the thickness of the center of the lens 41 being polished on the polishing plate 40 during polishing. The b surface of the lens 41 may be a rough surface after sanding before polishing or a surface after polishing. The surface a may be a surface through which light is transmitted to some extent. In the figure, reference numeral 42 denotes a pitch, and the polishing dish 40 and the lens 41 are fixed by the pitch 42.

FIG. 6 shows another configuration of the interferometer. In this configuration, the light emitted from the low coherence light source 1 is split into two polarized lights by the first polarizing beam splitter 4,
Light 1 (dotted line) having a vibration direction perpendicular to the paper surface enters the movable prism 43, and enters the second polarizing beam splitter 4B.
Then, the light m (solid line) having the vibration direction in the paper becomes one again.

At this time, by moving the position of the movable prism 43 in the x-axis direction of the coordinates shown in the figure, the difference Δ between the optical path of the light m and the optical path of the light 1 can be changed freely. The expected average thickness of the test lens 41 is represented by t _s , and the test lens 41
When the group index of the a _{n gs, 2n gs · (t} s -2e) ≦ Δ ≦ 2n gs · (t s + 2e) to be changed optical path difference delta movable prism 43 so as to satisfy Equation 3 Keep it. Δ only needs to include the range of Equation 3, and may exceed the range of Equation 3. Here, e is the amount of variation in the thickness of the test lens 41.

The light united by the second polarizing beam splitter is converted into linearly polarized light by the polarizer 3,
Through the lens 30 and enters the lens to be tested 41 via the lens 30. The light reflected on the surfaces a and b of the test lens 41 enters the photoelectric detector 8 via the lens 30, the half prism 44, and the lens 45, and the interference light intensity is displayed on the TV monitor 46.

Here, focusing on the light reflected on the b-plane of the light m and the light reflected on the a-plane of the light 1, the light 1 is delayed by Δ from the light m, and the wave packet is changed to the lens to be measured. 41 I incident on it, the light l is to reflect in front of a plane, the optical path difference shrinks by about 2n _gs · t _s is the light m after reflection by the light l and b face after reflection at a surface, Δ = _2ngs · t ₄₁ ... Equation 4 When the following expression is _satisfied , the intensity of the interference light becomes maximum. Where t
₄₁ is the true thickness of the test lens 41.

Therefore, in the range of Expression 3 or in the vicinity thereof, Δ
If the intensity of the interference light or the contrast of the interference fringes is maximized by changing the value of t, t ₄₁ can be obtained from Equation 4.

In this example, the lens 30 and the test lens 41
Even if the distance is changed between, for that is the light l, common optical path of m, it is superior in that it does not affect the measurement of t _41. The light incident on the lens 41 to be measured may be incident using the lens 30 so as to converge on the middle of the a and b surfaces of the lens 41 to be measured. If you do that,
Since the light is incident near the tops of the surfaces a and b, an easily visible interference fringe can be obtained.

The object to be measured in the example shown in FIG. 6 is not limited to the lens 41, but can also be used to measure objects such as a zoom lens, a single focus lens, and the like as described in the other embodiments of the present invention. In particular, it is effective for measuring the surface interval of an optical system including a plurality of lenses.

Further, as can be said in common to the present invention, in addition to the above-mentioned objects to be measured, various machines, that is, optical device manufacturing devices, optical device manufacturing devices, etc. Or the surface spacing of machines other than optics. The present invention is effective for optical elements, optical systems, optical devices, and various machines, particularly when the surface shape is non-planar. In the case where the surface shape is an aspherical surface, the above description may be applied to a tangent spherical surface or an approximate spherical surface near the light beam incident point. For example, as the “sphere center”, a sphere center of a tangent spherical surface or an approximate spherical surface may be applied.

[0093] Although the above has mainly described an example of a Twyman-Green interferometer, it may be constituted by a Mach-Zehnder type, a Fizeau type or an interferometer using a fiber.

As an application example of the surface distance measuring method and apparatus of the present invention, there is a lens group distance measurement of a zoom lens. In a zoom lens, there is a strong demand to accurately measure the amount of movement of each lens group according to a change in zoom state.
At this time, if the zoom lens whose interval is to be measured is the test lens and the reference optical barrel having the same configuration as the test lens on the reference side and the lens interval corresponding to each zoom state is accurately known is used, By measuring the difference from the optical system by the method of the present invention, the lens group interval can be accurately obtained.

In the manufacturing process of the optical system of various optical instruments, it is often necessary to check whether the lens spacing is as designed, but if the surface spacing measuring device of the present invention is used when assembling the optical system. Since the distance between the lenses can be easily measured, the adjustment can be easily performed.

[0096]

As is apparent from the above description, the method and apparatus for measuring the surface distance of the present invention makes it possible to measure the surface distance of optical elements such as lenses, mirrors, prisms, etc. in a non-destructive, non-contact and highly accurate manner. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a surface distance measuring method of the present invention.

FIG. 2 is a diagram showing a first embodiment of the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a third embodiment of the present invention.

5 is a diagram showing an example of measuring the thickness of the center of a lens affixed to a polishing plate during polishing using the interferometer shown in FIG. 4;

FIG. 6 is a diagram showing another configuration of the interferometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 101 ... Low coherence light source 2 ... Collimator lens 3 ... Polarizer (polarizer) 4, 4B ... Polarization beam splitter 5, 10 ... 1/4 wavelength plate 6,103 ... Reflection mirror 7, 11, 13, 20, 22, Reference numerals 30, 45: Lens 8, 105: Photoelectric detector 9: Length measuring device 12, 21, Pinhole 14, 41: Lens to be inspected (optical system to be inspected) 15: Signal processing means 23: Reference lens 31: Polarizer ( 40: Polishing plate 42: Pitch 43: Movable prism 44: Half prism 46: TV monitor 102: Light beam splitting element 104: Test object

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Fumi, Imamura 2-43-2, Hatagaya, Shibuya-ku, Tokyo F-term (reference) 2F065 AA22 AA30 BB05 CC22 DD03 FF51 FF61 FF67 GG02 GG04 GG07 HH03 HH13 JJ03 JJ18 JJ26 LL04 LL06 LL09 LL12 LL13 LL21 LL33 LL36 LL37 QQ13 SS13 UU07

Claims (40)

[Claims] 1. A low coherence light source having a short spatial coherence length, a light beam splitting means for splitting a light beam emitted from the low coherence light source, and changing an optical path length of one of the light beams split by the light beam splitting device. An optical path length changing means having a means for reflecting a light beam, and reflected light reflected by the other light beam split by the light beam splitting device incident on an optical system serving as a test object and reflected light from the light path length changing device. And a light intensity detecting means for detecting an interference signal generated by superimposing the optical path length, and an interval is measured by arithmetically processing a signal from the light intensity detecting means and information from the optical path length changing means. Surface distance measuring method and apparatus. 2. A light beam shaping means for converting light emitted from the low coherence light source into a substantially parallel light beam, a polarization state converting means for converting the substantially parallel light beam into an arbitrary polarization state, and a light beam splitting device for splitting the substantially parallel light beam Means, second polarization state conversion means for converting the polarization state of one of the light beams split by the light beam splitting means, and reflection means for reflecting the light beam whose polarization state has been changed by the second polarization state conversion means. Moving means for moving the reflecting means; moving amount measuring means for measuring the moving amount of the reflecting means; condensing means for condensing the other light beam divided by the light beam dividing means; With a pinhole arranged at a light condensing position, and adjusting means for guiding a light beam from the pinhole to a test object having a surface interval to be measured and condensing the light beam on an arbitrary surface of the test object. Optics and front A light beam combining means for superimposing the two light beams split by the light beam dividing means, a photoelectric conversion means for converting the light intensity of the light beam superposed by the light beam combining device into an electric signal, and a signal from the photoelectric conversion means. 2. The method and apparatus according to claim 1, further comprising signal processing means for processing information from the movement amount measuring means. 3. The method and apparatus according to claim 1, wherein a super luminescent diode is used as the low coherence light source. 4. The method and apparatus according to claim 1, wherein a semiconductor laser operated at a threshold current or less is used as the low coherence light source. 5. The method and apparatus according to claim 1, wherein a pulse laser is used as the low coherence light source. 6. The method and apparatus according to claim 1, wherein infrared light is used as the low coherence light source. 7. The method and apparatus according to claim 1, wherein visible light is used as the low coherence light source. 8. The method and apparatus according to claim 1, wherein a photodiode, a photomultiplier, a line sensor, or a solid-state image sensor is used as the photoelectric conversion unit. 9. The apparatus according to claim 1, wherein an optical system having a configuration optically equivalent to a test object is used as a unit for reflecting one of the light beams split by the light beam splitting unit. Surface distance measuring method and apparatus. 10. The method and apparatus according to claim 1, wherein an optical system of a zoom lens is used as an optical system including a plurality of optical elements to be inspected. 11. The method and apparatus according to claim 1, wherein a digital camera is used for alignment of the optical system. 12. A method for adjusting the distance between lenses using the surface distance measuring method and apparatus according to claim 1 in an assembling step of an optical system of various optical devices. 13. A low coherence light source having a short spatial coherence length, a light beam splitting means for splitting a light beam emitted from the low coherence light source, and changing an optical path length of one of the light beams split by the light beam splitting device. Light path length changing means, the other light beam split by the light beam splitting means is incident on the optical system as the test object, reflected light or transmitted light from the optical system, and the light beam passing through the light path length changing means And an apparatus for detecting an interference signal generated by superimposing the distance and measuring an interval from the information from the optical path length changing means. 14. A light beam shaping means for converting light emitted from the low coherence light source into a substantially parallel light beam, a polarization state converting means for converting the substantially parallel light beam into an arbitrary polarization state, and a light beam splitting device for splitting the substantially parallel light beam Means, second polarization state conversion means for converting the polarization state of one of the light beams split by the light beam splitting means, and reflection means for reflecting the light beam whose polarization state has been changed by the second polarization state conversion means. Moving means for moving the reflecting means; moving amount measuring means for measuring the moving amount of the reflecting means; and third polarization state converting means for converting the polarization state of the other light beam split by the light beam splitting means. And guiding the light beam whose polarization state has been changed by the third polarization state conversion means to an optical system as a test object having a surface interval to be measured, and toward the substantially spherical center or the top of the surface to be measured. Is incident An optical element having an adjusting means for performing the operation, a light beam combining means for superimposing two light beams split by the light beam dividing means, and a photoelectric device for converting the light intensity of the light beam superposed by the light beam combining means into an electric signal. 14. The method and apparatus according to claim 13, wherein a plane distance is measured from a conversion unit, a signal from the photoelectric conversion unit, and information from the movement amount measuring unit. 15. A light beam shaping device for converting light emitted from the low coherence light source into a substantially parallel light beam, a light beam splitting device for splitting the substantially parallel light beam, and reflecting one of the light beams split by the light beam splitting device. A reflecting means, a moving means for moving the reflecting means, a moving amount measuring means for measuring a moving amount of the reflecting means, and a test object having a surface interval for measuring the other light beam divided by the light beam dividing means. A light intensity detecting means for detecting an interference signal generated by superimposing the reflected light reflected on an arbitrary surface of the test object and the reflected light from the pre-distribution path length changing means. The photoelectric conversion device for converting the light intensity into an electric signal, and a surface interval is measured from a signal from the photoelectric conversion device and information from the movement amount measurement device. Surface spacing measurement method and And equipment. 16. A light beam shaping device for shaping light emitted from the low coherence light source into a light beam having a desired shape, a polarization state converting device for converting the light beam into a desired polarization state, a light beam splitting device, and the light beam splitting device. Second polarization state conversion means for converting the polarization state of one of the light beams split by
Reflecting means for reflecting a light beam whose polarization state has been changed by the polarization state converting means, moving means for moving the reflecting means, moving amount measuring means for measuring the moving amount of the reflecting means, and splitting by the light beam dividing means. To the third polarization state conversion means for converting the polarization state of the other light beam, and the optical system as the test object having a surface interval to measure the light beam whose polarization state has been changed by the third polarization state conversion means. And an optical element with an adjusting unit that allows the light beam to enter the surface to be measured, a light beam combining unit that superimposes the two light beams split by the light beam dividing unit, and a light beam combining unit that overlaps the two light beams. 2. A photoelectric conversion means for converting the light intensity of the light beam into an electric signal, and a surface interval is measured from a signal from the photoelectric conversion means and coast information from the movement amount measuring means. Surface distance measuring method and apparatus according. 17. A light beam emitted from a light source having a short coherence length is split by a light beam splitting element, one of which is reflected by a reflecting member as reference light, and the other is an object to be measured whose distance or thickness is to be measured as measuring light. And the reference light and the measurement light are overlapped by the light beam splitting element, and the optical path length difference between the reflected light from one surface of the test object and the reflected light from the reflecting member is within the coherence length of the light source. The interference signal generated at the time of is detected, and the reflected light from the other surface of the test object is moved to move the reflecting member to change the optical path length, and when the interference signal is obtained, the moving amount of the reflecting member A method or apparatus for determining a surface distance of an optical element, an optical system, or an optical device, wherein the distance between the test objects is measured from the distance. 18. A light beam emitted from a low coherence light source is split into reference light and measurement light incident on a test object, and the measurement light reflected from the test object and the reference light interfere with each other, and the interference occurs. A method or device for determining the surface spacing from a signal. 19. A light beam emitted from a light source having a short coherence length is split by a light beam splitting unit, one of which is guided as a reference beam, and the other is guided as a measuring beam to an object to be measured. A method or apparatus for superimposing measurement light to determine the surface spacing of an optical element, an optical system, an optical device, or various machines. 20. An interferometer using a light source having a short coherence length, and a test object arranged in an optical path of the interferometer to cause interference, thereby causing an optical element, an optical system, an optical device, or a surface interval between various machines. Method or device to seek. 21. A light source having a short coherence length, a measurement light path, and a reference light path, wherein light from the light source is incident on an object to be measured, and the emitted light and the light on the reference light path interfere with each other. A method or an apparatus for determining a surface interval of an optical element or an optical system or an optical device or various machines. 22. A method or apparatus for determining a surface interval of an optical element, an optical system, an optical device, or various machines according to claim 19, wherein the surface to be measured includes a non-planar surface. . 23. An optical element, an optical system, an optical device, or various machines according to claim 19, wherein at least one lens is included in an optical path incident on the object to be measured. Method or device for determining the surface spacing of 24. The method according to claim 19, wherein at least one lens is included in the common optical path.
A method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines according to the item. 25. A method or apparatus for determining a surface interval of an optical element, an optical system, an optical device, or various machines according to claim 19, wherein the object to be measured includes a zoom lens. . 26. The surface spacing of an optical element, an optical system, an optical device, or various machines according to claim 19, wherein a group refractive index is used when measuring a lens thickness. Method or device to seek. 27. The method according to claim 19, wherein the interference fringes are observed on a TV monitor. apparatus. 28. The method according to claim 19, wherein the concentric interference fringes or a part thereof are viewed.
A method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines according to the item. 29. An optical element, an optical system, an optical device, or various machines according to claim 19, wherein a non-parallel light beam is made incident on the test object. The method or device to be sought. 30. The method according to claim 19, wherein the angle of the light beam with respect to the optical axis when the measuring light is incident near the spherical center or near the surface top is within ± 15 ° with respect to the theoretical optical value. A method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines according to any one of the preceding claims. 31. The surface spacing of an optical element, an optical system, an optical device, or various machines according to claim 19, wherein the test object is an optical element being processed. Method or equipment. 32. After giving a plurality of different optical path lengths to a light beam from a light source having a short coherence length, the light beam enters a test object,
A method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines by examining interference light of reflected light. 33. A light beam from a light source having a short coherence length is divided into a plurality of light beams, and different light path lengths are given.
A method or apparatus for determining the surface spacing of an optical element, an optical system, an optical device, or various machines by investigating interference light of reflected light that is incident on a test object. 34. A light beam from a light source having a short coherence length is divided into a plurality of light beams, each having a different optical path length, and
A method or apparatus that integrates the light flux, enters the test object, and checks the interference light intensity of reflected light or the contrast of interference fringes to determine the surface spacing of an optical element, an optical system, an optical device, or various machines. 35. An interferometer using a light source having a short coherence length, and a method or an apparatus for arranging a test object in an optical path of the interferometer and obtaining a surface interval causing interference. 36. A light source having a short coherence length, a measurement light path, and a reference light path, wherein light from the light source is made incident on an object to be measured, and emitted light and light in the reference light path are caused to interfere with each other. A method or device for determining the surface spacing. 37. A light beam emitted from the low coherence light source is split by a light beam splitting element, one of which is reflected by a reflecting mirror as reference light, and the other is guided to a test object to be measured as a measuring light, and the distance is measured. The optical path length of the reference light can be changed, the reference light and the measurement light are overlapped by the light beam splitting element, and the reflected light from any surface of the test object and the reflection from the reflecting mirror are reflected. If the optical path length difference with light is within the coherence length of the light source, interference occurs, the interference signal is detected by the photoelectric detector, and then, for reflected light from another surface of the test object, When a reflection mirror is moved to change an optical path length and an interference signal is obtained by the photoelectric detector, a distance between the two surfaces is obtained by measuring a movement distance of the reflection mirror. Measurement method and device. 38. A light beam is emitted from a low coherence light source, and the light beam is split into a measuring beam and a reference beam by a beam splitting element. A lens is arranged, a reflecting mirror is installed on the reference light side, and the reference light side optical path is adjusted so that the optical path difference between the reference light side optical path and the measurement light side optical path can be adjusted within the coherence length of the light source. The measurement optical side optical path and the reference optical side optical path are overlapped, and the overlapped optical path is received by the photoelectric detector, and the interference fringes due to the optical path difference within the coherence length of the light source are obtained. First, an interference fringe is detected on one lens surface of the lens surface to be detected, and then the other lens surface to be detected is detected on another lens surface to be detected. Optical path length difference with respect to the optical path length of the measuring light side optical path The optical path length of the reference light side optical path is changed so as to be within the coherence length of the reference light path, interference fringes are detected on the other lens surface to be measured, and the amount of change in the optical path length of the reference light side optical path at this time is changed. A method and apparatus for measuring a surface distance between an inspection lens surface and the another lens surface to be measured. 39. The diameter (R ₀ ) of the luminous flux of the optical path on the measurement light side with respect to the diameter (R _s ) of the lens surface to be measured so as to reduce the measurement error due to the curved surface of the lens surface to be measured.
39. An optical element (for example, an opening arranged near a light source or a collimator lens) for changing a light beam diameter so as to be ２ or less (3R ₀ <2R _s ) is arranged in an optical path. The method and apparatus for measuring a surface distance according to the description. 40. An optical path provided in the reference light side optical path for changing the optical path length of the reference light side optical path so that the optical path length difference with respect to the optical path length of the measurement light side optical path is within the coherence length of the light source. 39. The method and apparatus according to claim 38, wherein the reflecting mirror is set so as to be movable along an optical path.