Observation optical system and measurement device

Abstract

Provided are: an observation optical system suitable for observation / measurement of the inner diameter of a pore even when the diameter thereof is narrow; and a measurement device suitable for using the optical system.　This observation optical system according to the present invention comprises, in order from the object side, at least: a reducing lens system that has an angle of view of at least 120 degrees and that comprises a first lens group having a negative refractive power and a second lens group having a positive refractive power; and a magnifying lens system that magnifies an object image from the reducing lens system and forms an image on an imaging element, and that comprises a third lens group having a positive refractive power and a fourth lens group having a negative refractive power. The magnifying lens system is characterized by: generating pincushion distortion that cancels barrel distortion generated in the reducing lens system; and restricting the distortion generated by the entire observation optical system, in a range from 70% to 80% of the maximum image height, to within ± 5%.

Description

Observation optical system and measuring device

[0001] The present invention relates to a probe that uses a wide-angle optical system to obtain a side view of a pore in at least the peripheral field of view.

[0002] There has been a need for observing and measuring the side surface (inner surface) of a pore. To meet this need, a suitable method is to insert a wide-angle optical system (for example, a total angle of view of 120° or more) into the pore to capture an image of the inside of the pore.

[0003] As a wide-angle optical system, it is conceivable to use an optical system equipped with an irregular optical component at the tip, as disclosed in, for example, Patent Document 1 and Patent Document 2. Such an optical system is suitable for observing the inner surface of a hole, but since the irregular component tends to be large, the probe tip becomes enlarged and is not suitable for application to a small hole. Furthermore, the smaller the irregular component, the more difficult it is to process, and there are also problems with processability. Furthermore, these factors make the optical system expensive.

[0004] Although the optical system disclosed in Patent Document 3 has a sufficiently wide angle (total angle of view: 134°), it suffers from a large barrel distortion (approximately 60%), which compresses the image of the peripheral region within the image, which is important for observing the inner surface of the pore, resulting in less information about the detailed structure of the inner surface of the pore. Specifically, the information contained per pixel is approximately 40% of that contained in the center. In other words, the information contained in approximately 2.5 central pixels is compressed into one peripheral pixel and imaged. Therefore, no matter what kind of image processing is used to correct the distortion, it is impossible to recover the information about the lost detailed structure. Therefore, the optical system of Patent Document 3 is not optimally configured for observing pores.

[0005] On the other hand, the optical system disclosed in Patent Document 4 has relatively small distortion, but is not wide-angle to begin with; even the largest example has a total angle of view of approximately 94°. Therefore, even if such an optical system is used to capture an image of the inside of a micropore, the image contains relatively little information about the inner surface of the micropore. Particularly when the subject is the side of the micropore, the small total angle of view results in the observation of the observation surface from an oblique angle, resulting in the image being compressed. Specifically, if the half angle of view measured from the optical axis is ω, the observation image is compressed radially in proportion to cos(90°-ω), which also makes it difficult to recover information about the detailed structure. Therefore, while the optical system disclosed in Patent Document 4 is suitable for central observation, it is not suited to the purpose of acquiring an image of the inner surface of a micropore in the peripheral field of view, and is not an optimal configuration for pore observation.

[0006] JP 2020-197713 A JP 2023-088412 A JP 2020-140052 A Japanese Patent No. 6029159

[0007] In view of the above circumstances, an object of the present invention is to provide an optical system that is suitable for observing and measuring the inner diameter of a small hole, even though the diameter is small, and a measuring device that is suitable for using the optical system.

[0008] In order to solve the above-mentioned problems, an observation optical system according to an embodiment of the present invention includes, in order from the object side, at least a reduction lens system having a total angle of view of 120° or more, which is composed of lenses from a first lens group having a negative refractive power and a second lens group having a positive refractive power, and an enlargement lens system which enlarges the object image formed by the reduction lens system and forms the image on an image sensor, which is composed of a third lens group having a positive refractive power and a fourth lens group having a negative refractive power. The enlargement lens system generates pincushion distortion that offsets barrel distortion generated in the reduction lens system, and limits distortion generated by the entire observation optical system within a range of 70% to 80% of the maximum image height to within ±5%.

[0009] In the present invention, it is preferable to further provide a relay lens system between the reduction lens system and the magnification lens system, and the relay lens system may be composed of a GRIN lens.

[0010] In the present invention, it is preferable that focus adjustment is performed at a location where off-axial rays become approximately telecentric when an intermediate image is formed. Also, a color correction filter or an optical path splitter may be disposed at a location where off-axial rays become approximately telecentric when an intermediate image is formed.

[0011] In the present invention, the maximum value of barrel distortion occurring only in the reduction lens system may be 50% or more at the maximum field of view.

[0012] In the present invention, the reduction lens system and the magnification lens system may be configured using a common lens and may have a completely symmetrical configuration.

[0013] A measurement device according to an embodiment of the present invention includes a probe and an information processing unit. The probe is inserted into a micropore to be measured and captures an image of the inner surface of the micropore. The probe includes at least a light source that emits illumination light to illuminate the interior of the micropore, a reduction lens system having at least a full angle of view of 120° or more, and an observation optical system having a different angle of view depending on the wavelength. The observation optical system includes a reduction lens system having a full angle of view of 120° or more and a relay lens system that relays the intermediate image formed by the reduction lens system on a first intermediate imaging plane and forms the intermediate image on a subsequent imaging plane. The observation optical system has a different angle of view depending on the wavelength. The information processing unit analyzes the image data output by the image processing unit and calculates the distance from the center of the observation optical system to the inner surface of the micropore based on the amount of color shift in the captured image.

[0014] In the present invention, the observation optical system further includes a magnifying lens system that magnifies the image formed by the relay lens system and forms the image on the imaging surface of the imaging element, and the magnifying lens system generates pincushion distortion that offsets the barrel distortion generated in the reduction lens system, and it is preferable that the distortion generated by the entire observation optical system within a range of 70% to 80% of the maximum image height is within ±5%.

[0015] The present invention may further include a light guide member disposed on the outer periphery of the observation optical system, for transmitting illumination light from the light source to the tip of the probe and for emitting the illumination light from the tip. It is particularly preferable that the light guide member has a light-condensing effect and forms at least one ring-shaped condensing pattern on the illumination light.

[0016] In the present invention, the image sensor has a configuration in which red, green, and blue pixels are arranged in a Bayer array, and outputs image data for an image dispersed for each wavelength band of each color, and the information processing unit calculates the amount of color shift of the dispersed image at each position and calculates the distance based on the calculated amount of color shift.

[0017] In the present invention, the light source may be configured to have a variable emission color, and the image sensor may be a monochrome image sensor. In such a configuration, the color of the illumination light emitted by the light source may be changed sequentially, and the image sensor may capture an image at the timing when the illumination light of each color is emitted and output image data. The information processing unit may calculate, at each position, the amount of color shift of the image output by the image sensor under the illumination light of each color, and calculate the distance based on the calculated amount of color shift.

[0018] In the present invention, the observation optical system may further include a spectroscopic device that separates the image formed by the observation optical system into a plurality of wavelengths, and a plurality of image pickup elements may be provided corresponding to the wavelengths separated by the spectroscopic device, and image data may be output for the images of the corresponding wavelengths. The information processing unit may then calculate the amount of color shift of the separated images at each position, and calculate the distance based on the calculated amount of color shift.

[0019] The present invention may further include a beam splitter disposed in the observation optical system, and a light source disposed in the optical path branched by the beam splitter to configure coaxial epi-illumination. The present invention may further include a light-attenuating member disposed between the light source and the beam splitter, the light-attenuating member having a non-uniform transmittance distribution in the radial direction with the transmittance decreasing toward the center. The light-attenuating member may have a slit-shaped region of high transmittance at a specific radius.

[0020] The light-reducing member may have a region in the center where the transmittance changes discontinuously, and the information processing unit may analyze the image data and detect, based on the contrast of the image in the region where the transmittance changes discontinuously, that the tip of the probe has approached a predetermined distance to the subject captured in the center of the field of view.

[0021] A measurement device according to another embodiment of the present invention includes a probe and an information processing unit, and measures a pore by capturing an image of the inner surface of the pore while the probe is inserted into the pore. In the measurement device, the probe includes at least a light source that emits light, a beam splitter, a reference mirror, an observation optical system having a full angle of view of at least 120° or more, and an image sensor. The beam splitter splits light from the light source into a reference light directed toward the reference mirror and a measurement light directed toward the observation optical system, and emits a composite wave of the reference light returning from the reference mirror and the measurement light returning from the observation optical system toward the image sensor. The observation optical system expands the measurement light from the beam splitter over a wide angle and emits it into the pore, and also collects the measurement light reflected or scattered by the inner surface of the pore and emits it toward the beam splitter. The reference mirror unit includes a reference mirror that reflects the reference light from the beam splitter and returns it to the beam splitter, and a drive mechanism that moves the reference mirror so that the optical path length of the reference light path from the beam splitter via the reference mirror and returning to the beam splitter is approximately equal to the optical path length of the measurement light path from the beam splitter via the observation optical system and the inner surface of the orifice and returns to the beam splitter. The image sensor captures an interference image of the composite wave formed on the imaging surface and outputs image data in a state where the optical path length of the reference light path is approximately equal to the optical path length of the measurement light path, and the information processing unit analyzes the image data of the interference image output by the image sensor and calculates the distance from the center of the observation optical system to the inner surface of the orifice based on the position of the reference mirror and the interference intensity at the position of each pixel in the image.

[0022] In the present invention, the reference mirror is provided with a relay lens, which is a double-telecentric lens with the reference mirror side as a magnifying system, between the beam splitter and the reference mirror, and the drive mechanism moves the relay lens in the opposite direction to the movement of the reference mirror in synchronization with the movement of the reference mirror so that the reference light is always focused near the reflecting surface of the reference mirror.

[0023] A measurement device according to yet another embodiment of the present invention includes a light source that emits light, an optical path length difference generating unit that splits light from the light source into two optical paths with relatively different optical path lengths and then recombines the split light, a probe, and an information processing unit. The measurement device measures the pore by capturing an image of the inner surface of the pore with the probe inserted into the pore. The probe includes at least a beam splitter surface, an observation optical system with a full angle of view of 120° or more, and an image sensor. The beam splitter surface splits light from the optical path length difference generating unit into reference light and measurement light directed toward the observation optical system, and emits a combined wave of the reference light and measurement light returning from the observation optical system toward the image sensor. The observation optical system expands the measurement light from the beam splitter surface over a wide angle and emits it into the pore, which is the measurement target, and also collects the measurement light reflected or scattered by the inner surface of the pore and emits it toward the beam splitter surface. The optical path length difference generating unit is configured to adjust the optical path length difference between the two optical paths. The imaging element captures an interference image of the composite waves formed on the imaging surface and outputs image data in a state in which the combined optical path length of one of the two optical paths and the optical path length of the reference optical path split by the beam splitter surface is approximately equal to the combined optical path length of the other of the two optical paths and the optical path length of the measurement optical path that returns to the beam splitter surface via the beam splitter surface via the observation optical system and the inner surface of the pore. The information processing unit analyzes the image data of the interference image output by the imaging element and calculates the optical path length difference between the two optical paths in the optical path length difference generation unit and the distance from the center of the observation optical system to the inner surface of the pore based on the interference intensity at the position of each pixel in the image.

[0024] The present invention may further include a beam splitter disposed in the observation optical system, and a light source disposed in the optical path branched by the beam splitter to configure coaxial epi-illumination. The present invention may further include a light-attenuating member disposed between the light source and the beam splitter, the light-attenuating member having a non-uniform transmittance distribution in the radial direction with the transmittance decreasing toward the center. The light-attenuating member may have a slit-shaped region of high transmittance at a specific radius.

[0025] The light-reducing member may have a region in the center where the transmittance changes discontinuously, and the information processing unit may analyze the image data and detect, based on the contrast of the image in the region where the transmittance changes discontinuously, that the tip of the probe has approached a predetermined distance to the subject captured in the center of the field of view.

[0026] 1 is a schematic diagram illustrating the configuration of a measurement device 1 to which the observation optical system according to the first embodiment is applied. An observation optical system 5A is shown, which is an example of the configuration of the observation optical system 5. 3(a) is an aberration diagram illustrating distortion in a conventional optical system (which does not cancel distortion), and FIG. 3(b) is an aberration diagram illustrating distortion in the observation optical system 5A of this embodiment. 4(a) is an optical image captured using a conventional optical system of a microhole H having a striped pattern drawn at an equal pitch on its inner surface, and FIG. 4(b) is an optical image captured using the conventional observation optical system 5A. An example of a symmetric observation optical system is shown. An observation optical system 5B is shown, which is another example of the configuration of the observation optical system 5. An example is shown in which the relay lens system 53 in the observation optical system 5B is a GRIN lens. An observation optical system 5C is shown, which is yet another example of the configuration of the observation optical system 5. An observation optical system 5C is shown, which is yet another example of the configuration of the observation optical system 5. An example of the configuration of the light-guiding member 4 is shown. Magnification chromatic aberration characteristics in the observation optical system 5B are shown. An image obtained when a hole with a reference diameter is observed is schematically shown. 13(a) is a schematic diagram illustrating an image obtained when observing a hole having an inner diameter relatively smaller than the reference diameter. FIG. 13(b) is a schematic diagram illustrating an image obtained when observing a hole having an inner diameter relatively larger than the reference diameter. FIG. 13(a) is a schematic diagram illustrating the configuration of a second modified example of the measuring apparatus 1A according to the second embodiment. FIG. 13(b) is a schematic diagram illustrating the configuration of a third modified example of the measuring apparatus 1A according to the second embodiment. FIG. 13(b) is a schematic diagram illustrating the configuration of a fourth modified example of the measuring apparatus 1A according to the second embodiment. FIG. 13(b) is a schematic diagram illustrating the configuration of a measuring apparatus 1B according to the third embodiment. FIG. 13(b) is a schematic diagram illustrating an example of an interference image obtained by the measuring apparatus 1B according to the third embodiment. FIG. 13(b) is a schematic diagram illustrating the effect of adjusting the optical path length in a reference optical path including a relay lens 111. FIG. 13(b) is a schematic diagram illustrating the configuration of a measuring apparatus 1C according to a modified example of the third embodiment. FIG. 13(b) is a schematic diagram illustrating an example of the configuration of the optical path length difference generating unit 20. FIG. 13(b) is a diagram illustrating four optical paths in the measuring apparatus 1C. FIG. 10 is a schematic diagram showing another example of the configuration of the optical path length difference generating unit 20.

[0027] First Embodiment Hereinafter, an observation optical system 5 according to an embodiment of the present invention will be described with reference to the drawings, together with a measurement device to which the observation optical system 5 is applied. In the following description, the same components will be assigned the same reference numerals, and a description of a component that has already been described will be omitted as appropriate.

[0028] (Configuration of Measuring Apparatus) Fig. 1 is a schematic diagram illustrating the configuration of a measuring apparatus 1 to which the observation optical system according to this embodiment is applied. The measuring apparatus 1 according to this embodiment is an apparatus that captures an optical image with a probe 2 inserted into a pore H that is a measurement target, observes the properties of the inner surface of the pore H based on the obtained optical image, and measures dimensions related to the inner surface of the pore H based on the image. As shown in Fig. 1, the measuring apparatus 1 includes the probe 2 and an information processing unit 8.

[0029] The probe 2 includes a light source 3, a light-guiding member 4, an observation optical system 5, and an imaging element 6. The light source 3, the light-guiding member 4, the observation optical system 5, and the imaging element 6 are covered with a sheath 7 except for the distal ends of the light-guiding member 4 and the observation optical system 5. The light source 3 emits illumination light that illuminates the inside of the pore H that is the measurement target. The light source 3 may be, for example, a ring LED.

[0030] The light-guiding member 4 faces the emission end of the light source 3 and is disposed so as to surround the outer periphery of the observation optical system 5. The light-guiding member 4 guides the illumination light emitted by the light source 3 to the tip of the probe 2, where it emits a ring-shaped illumination light. The observation optical system 5 is formed with a small diameter so that it can be inserted into the inside of the pore H, which is the measurement target. The observation optical system 5 collects the illumination light reflected from the inner surface and forms an image of the inner surface of the pore H, which is the measurement target, on the imaging surface of the imaging element 6. The configuration of the observation optical system 5 will be described in detail later. The imaging element 6 is a two-dimensional imaging element such as a CCD or CMOS sensor, and converts the image formed on the imaging surface of the imaging element 6 by the observation optical system 5 into image data. The image data converted by the imaging element 6 is input to the information processing unit 8.

[0031] The information processing unit 8 is a processing device such as a computer, and controls each part of the measuring device 1 (e.g., the light source 3, the image sensor 6, etc.) based on a predetermined program, acquires image data from the image sensor 6 and displays it, analyzes the image, and performs measurements.

[0032] Next, an example of the configuration of the observation optical system 5 suitable for observing and measuring the inner surface of such a fine hole H will be described.

[0033] (Configuration example 1 of optical system) Fig. 2 shows an observation optical system 5A, which is one example of the configuration of the observation optical system 5. As shown in Fig. 2, the observation optical system 5A includes, in order from the object side, a negative lens group 511, a positive lens group 512, a positive lens group 521, and a negative lens group 522. The negative lens group 511, the positive lens group 512, the positive lens group 521, and the negative lens group 522 correspond to the first lens group, the second lens group, the third lens group, and the fourth lens group in the present invention, respectively.

[0034] The negative lens group 511 and the positive lens group 512 constitute the reduction lens system 51. The reduction lens system 51 forms a reduced object image (intermediate image) on a first intermediate image plane. The negative lens group 511 has negative refractive power, and the positive lens group 512 has positive refractive power. The reduction lens system 51 formed by the negative lens group 511 and the positive lens group 512 has a total angle of view of 120° or more. By providing a wide total angle of view of 120° or more with this configuration, it is possible to obtain a large amount of information about the lateral side (the inner surface of the narrow hole H into which the observation optical system 5 is inserted) while suppressing the diameter of the tip side (object side) of the observation optical system 5, and to obtain an image suitable for observing and measuring the inner diameter of the narrow hole.

[0035] The positive lens group 521 and the negative lens group 522 constitute the magnifying lens system 52. The magnifying lens system 52 magnifies the intermediate image formed on the first intermediate image plane by the reduction lens system 51 and re-images it on the imaging plane of the image sensor 6. The positive lens group 521 has positive refractive power, and the negative lens group 522 has negative refractive power. The magnifying lens system 52 formed by the positive lens group 521 and the negative lens group 522 has a greater effect of correcting distortion as the angle of incidence onto the imaging plane of the image sensor 6 at the outermost periphery of the screen (near the maximum image height) increases.

[0036] It is preferable that at least some of the lenses constituting the reduction lens system 51 and the magnification lens system 52 are common (i.e., have the same shape and characteristics). For example, it is preferable that the cemented lenses of the positive lens group 512 and the positive lens group 521 are common lenses.

[0037] The intermediate image formed by the reduction lens system 51 is distorted, but the magnifying lens system 52 generates distortion when enlarging and forming the intermediate image on the imaging plane so as to cancel out the distortion caused by the reduction lens system 51. For example, if the reduction lens system 51 generates barrel distortion in the intermediate image, which is characteristic of an inverted telephoto lens arrangement, the magnifying lens system 52 may generate pincushion distortion when enlarging and forming the intermediate image on the imaging plane of the image sensor 6, thereby canceling out the distortion caused by the reduction lens system 51. The magnifying lens system 52 generates pincushion distortion that cancels out the barrel distortion caused by the reduction lens system 51, and the distortion caused by the entire observation optical system 5 in a range of 70 to 80 percent of the maximum image height (i.e., a range where the inner surface of the pore, which is the target area for measurement and observation, is mainly captured) may be within ±5%.

[0038] FIG. 3(a) is an aberration diagram showing distortion in a conventional optical system (without distortion cancellation), and FIG. 3(b) is an aberration diagram showing distortion in the observation optical system 5A of this embodiment. In FIG. 3, + indicates pincushion-shaped distortion, and − indicates barrel-shaped distortion. FIG. 4(a) is an optical image of a micropore H with a uniformly spaced stripe pattern painted on its inner surface, captured using a conventional optical system, and FIG. 4(b) is an optical image captured using the conventional observation optical system 5A. The arrows in FIGS. 4(a) and 4(b) indicate ranges of the same length in the depth direction of the micropore H. As is clear from FIG. 4, in the conventional optical system, the peripheral image is compressed, resulting in relatively little information about the peripheral image. In contrast, in the observation optical system 5A of this embodiment, the proportion of the peripheral image in the image is increased, making it suitable for analyzing the inner surface (side surface) of a micropore, etc. In other words, the observation optical system 5A of this embodiment prevents the loss of peripheral visual field information necessary for observing and measuring the inner surface of a micropore, thereby improving accuracy and detection rate.

[0039] Alternatively, as shown in FIG. 5 , the observation optical system 5 may have a completely symmetrical configuration. That is, the negative lens group 511 and the negative lens group 522 may be a common negative lens group (having the same shape and characteristics), and the positive lens group 512 and the positive lens group 521 may be a common positive lens group. In the example shown in FIG. 3 , the total angle of view is 140°, making it difficult to avoid significant distortion in each of the reduction lens system 51 and the magnification lens system 52. With such a completely symmetrical configuration, the distortion in the reduction lens system 51 and the distortion in the magnification lens system 52 are completely canceled out, ideally eliminating distortion in the image formed on the imaging surface of the image sensor 6. This maintains peripheral information well while allowing for the use of common lenses, contributing to lower costs. Automating the processing and assembly of small lenses is particularly difficult, and manual assembly is often required. In this case, limiting the types of components is also highly effective in reducing the risk of misassembly due to component mix-up.

[0040] (Configuration Example 2 of Optical System) Fig. 6 shows an observation optical system 5B, which is another example of the configuration of the observation optical system 5. As shown in Fig. 6, the observation optical system 5B includes, in order from the object side, a reduction lens system 51, a relay lens system 53, and a magnification lens system 52. In other words, the observation optical system 5B is configured such that the relay lens system 53 is sandwiched between the reduction lens system 51 and the magnification lens system 52 in the observation optical system 5A.

[0041] The relay lens system 53 re-images the intermediate image formed on the first intermediate image plane by the reduction lens system 51 onto a subsequent second intermediate image plane. The magnification of the relay lens system 53 is optional, but it is preferable to set the magnification of the relay lens system 53 to 1x or less to prevent the outer diameter of the relay lens system 53 from exceeding the outer diameter of the reduction lens system. While FIG. 6 shows a configuration in which relaying (i.e., re-imaging of the intermediate image) is performed once, the relay lens system 53 may perform relaying multiple times. In other words, the observation optical system 5B may have three or more intermediate image planes, and the intermediate image formed on the first intermediate image plane by the reduction lens system 51 may be re-imaged on a second or subsequent intermediate image plane by the relay lens system 53. The magnifying lens system 52 enlarges the final intermediate image formed by the relay lens system 53 and forms it on the imaging plane of the image sensor 6.

[0042] For the observation of deep pores H, it may be preferable to maintain a small lens diameter while maintaining a long overall length. The observation optical system 5B is suitable for observing and measuring deep pores H because its length can be extended by using the relay lens system 53. Furthermore, even if the lens system and image sensor are made smaller to accommodate pore observation, there may be cases where a substrate or the like attached to the rear of the image sensor interferes with the pore, making it impossible to observe or measure the deep pore; however, this situation can be avoided by extending the overall length of the observation optical system 5 using the relay lens system 53.

[0043] 7, in the observation optical system 5B, the relay lens system 53 may be a GRIN (Gradient INdex; gradient index) lens. It is particularly preferable for the GRIN lens to have a refractive index distribution that decreases in proportion to the square of the radius from the center to the periphery.

[0044] If multiple lenses are used in the relay system, each lens is expensive and susceptible to manufacturing errors such as decentering. In contrast, if a GRIN lens is used as the relay lens system 53, it is possible to realize the relay lens system 53 with a single component. This makes it possible to simultaneously extend the overall length of the observation optical system 5 and achieve robustness against manufacturing errors. Furthermore, since the number of interfaces with air is reduced, this is advantageous in suppressing the reflection loss of light that remains even after anti-reflection coating is applied.

[0045] 8 and 9 show an observation optical system 5C, which is yet another example of the configuration of the observation optical system 5. Similar to the observation optical system 5B, the observation optical system 5C includes, in order from the object side, a reduction lens system 51, a relay lens system 53, and a magnification lens system 52.

[0046] In the observation optical system 5C, the off-axis chief ray of the intermediate image forming section (which may be an image relayed by the relay lens system 53) is telecentric, and focus adjustment is performed at this section. Note that focus adjustment may be performed by adjusting this section during assembly and fixing it to an optimal position, or by providing a control mechanism and driving it during use to adjust the focus (so-called autofocus). For example, focus adjustment may be performed by switching between a plurality of predetermined focal lengths (for example, two, one for close distances and one for long distances).

[0047] For example, as shown in Fig. 8, the entire system including the intermediate image formation unit by the reduction lens system to the image sensor 6 may be configured to be moved relative to the reduction lens system 51 for focus adjustment. Alternatively, as shown in Fig. 9, if the relay lens system 53 is double-telecentric, only the relay lens system 53 may be moved relative to the reduction lens system 51 and the magnification lens system 52 for focus adjustment.

[0048] In a measurement device 1 equipped with a magnifying lens system 52, the off-axis incident angle (particularly the incident angle at the very periphery of the screen) on the image sensor 6 tends to be steep, so adjusting the focus by changing the lens spacing immediately before the image sensor 6 (for example, within the negative lens group 522) results in a significant change in the field of view. Furthermore, since the image sensor 6 may have shading characteristics, it is desirable to strictly manage the field of view and the angle of incidence. In the observation optical system 5C, these problems can be solved and stable quality can be obtained by adjusting the focus at a point where the chief ray is telecentric.

[0049] It may be desirable to place a filter element such as a color correction filter in the optical path to correct the color of the resulting image, or to place an optical path splitter element in the optical path to accommodate coaxial epi-illumination. To meet these requirements, the observation optical system 5C may include an optical path splitter element or a filter element in a location where the chief ray is telecentric. In the present invention, the off-axis incident angle to the image sensor tends to be steep, so if an optical path splitter element or a filter element is inserted immediately before the image sensor, the characteristics are likely to differ between the center and the periphery. In the observation optical system 5C, the optical path splitter element or the filter element is provided in a telecentric location where the angles of the chief ray of the axial light beam and the peripheral light beam are roughly the same. Therefore, the optical path splitter element or the filter element inserted in this location tends to provide stable characteristics from the center to the periphery.

[0050] The observation optical system 5 may be a combination of the features of each of the configuration examples described above.

[0051] The observation optical system 5 described above can form an image with little distortion while suppressing the outer diameter of the probe 2. When an image of the inner surface of the fine hole H is captured by the measuring device 1 equipped with such an observation optical system 5, the image of the peripheral region within the image is less likely to be compressed, and detailed information about the inner surface of the fine hole H can be included in the image.

[0052] Second Embodiment The measuring device 1 according to the first embodiment described above is an device that takes an optical image of the inner surface of the pore H, which is the measurement target, with the probe 2 inserted into the pore H, and observes and measures the inner surface of the pore H based on this optical image. In contrast, the measuring device 1A according to this embodiment uses an observation optical system 5 having chromatic aberration of magnification to measure the distance from the center of the observation optical system 5 to the inner surface of the pore H, which is the measurement target, instead of (or in addition to) observing and measuring using an optical image. Details thereof will be described below.

[0053] The measuring device 1A according to this embodiment generally includes a probe 2 and an information processing unit 8, similar to the measuring device 1 according to the first embodiment shown in Fig. 1, and the probe 2 includes a light source 3, a light-guiding member 4, an observation optical system 5, and an image sensor 6. In order to enable measurement using the observation optical system 5 having chromatic aberration of magnification, the measuring device 1A differs in its configuration from the measuring device 1 according to the first embodiment. The following description will focus on the differences from the measuring device 1 according to the first embodiment, and will omit descriptions of parts that are common to the measuring device 1 as appropriate.

[0054] The observation optical system 5B, which is the observation optical system 5 used in the measurement device of this embodiment, has at least a wide-angle reduction lens system (objective lens) 51 and a relay lens system 53. The observation optical system 5 may further include a magnification lens system 52 downstream of the relay lens system 53. The observation optical system 5 configured in this manner has an angle of view that varies depending on the wavelength. A lens system provided at the end of the observation optical system 5B opposite the reduction lens system 51 forms an image of the inner surface of the pore H, which is the measurement target, on the imaging surface of the imaging element 6. A cylindrical light-guiding member 4 is disposed on the outer periphery of the observation optical system 5B, and the periphery of the light-guiding member 4 is covered by a sheath (cover) 7.

[0055] A ring-shaped light source 3 is disposed on the light-guiding member 4, facing the end face opposite to the tip (object side) of the probe 2. The light source 3 may be, for example, a ring LED. The light-guiding member 4 is configured to transmit white light emitted by the light source 3 to the tip of the probe 2, and emits ring-shaped illumination light from the tip.

[0056] The illumination light does not need to be uniformly irradiated over a wide area. When observing or measuring the inner surface or diameter of a featureless pore, the image becomes uniform, making it difficult in principle to detect color shifts. Therefore, it is preferable to irradiate the illumination light locally (e.g., to a narrow region in the depth direction of the pore) so that the only light detected is light reflected or scattered at the irradiated area. To achieve such localized illumination, for example, the end surface of the light-guiding member 4 may be curved to focus light into a specific shape ( FIG. 10( a) ). The sheath 7 and the light-guiding member 4 may be molded integrally. The light-guiding member 4 may also be composed of two parts. For example, the cross section of the end surface of the first light-guiding member 41 may be flat, and the second light-guiding member 42 may be curved to focus light into a predetermined shape ( FIG. 10( b) ). In this case, it is even better if the second light-guiding member 42 is molded integrally with the sheath 7.

[0057] Alternatively, as shown in FIG. 10( c), a slit 43 may be provided at the exit end of the light-guiding member 4, projecting a pattern onto the inner surface of the pore H to be measured. The slit 43 may be formed, for example, by vapor-depositing a light-blocking material onto the exit end. The slit 43 may be a thin ring-shaped slit extending circumferentially, and multiple slits may be provided to simultaneously irradiate multiple regions in the depth direction of the pore H with illumination light. This makes it possible to simultaneously detect color shifts in multiple regions irradiated with illumination light, thereby improving measurement throughput. When monochromatic light is used as illumination light, a diffraction pattern (interference fringes) may be used by narrowing the slit pitch. Alternatively, a hologram may be engraved on the exit end to guide light waves in a specific direction.

[0058] The light emitted from the tip of the light-guiding member 4 is reflected or scattered by the object to be measured (i.e., the inner surface of the pore), enters and propagates through the observation optical system 5B, and is captured by the image sensor 6 provided at the other end of the observation optical system 5B, where it is converted into image data. In this example, the image sensor 6 has RGB pixels arranged in a so-called Bayer array, and the images dispersed for each RGB wavelength band are converted into electrical signals and transmitted as image data to the information processing unit 8. The information processing unit 8 analyzes the image data from the image sensor 6, calculates the amount of color shift (i.e., the amount of chromatic aberration of magnification) of the dispersed images at each position, and uses this information to calculate distance information.

[0059] The calculation of distance information will be described. Regarding the characteristic that the observation optical system 5B has different angles of view depending on the wavelength, in the following description, as shown in FIG. 11, the observation optical system 5B is assumed to have a reference angle of green (G), a relatively narrow angle of red (R), and a relatively wide angle of blue (B). In addition, the best focus distance L ＢＦ At the maximum angle of view, the field of view for each wavelength of RGB is assumed to be the same. Therefore, when observing the inner diameter corresponding to this distance, there is no color shift, and R, G, and B are imaged at the same position on the image sensor as shown in Figure 12, and are observed as a white image.

[0060] Consider a case where the diameter at this point is taken as the reference diameter and a hole with an inner diameter relatively smaller than the reference diameter is observed. Because the angle of view differs for each wavelength, color shift occurs, and images are formed on the imaging surface of the image sensor in the order of R, G, and B from the periphery of the field of view (FIG. 13(a)). Conversely, when a hole with an inner diameter relatively larger than the reference diameter is observed, images are formed on the imaging surface of the image sensor in the order of B, G, and R from the periphery (FIG. 13(b)).

[0061] By analyzing this color shift, distance information from the center of the lens to the inner surface of the pore being measured can be obtained. Since the greater the difference from the reference diameter, the greater the amount of this shift, analyzing the amount of shift allows the distance from the center of the observation optical system 5B to the inner surface to be calculated. For example, if a circular pore is imaged and a ring of each color is captured in the image, the luminance profile of each color can be obtained in the radial direction (from the center to the periphery), and the peak position of each color obtained can be determined using an algorithm such as Gaussian fitting to obtain the peak position. The difference in distance from the center to the peak position of each color can then be calculated as the amount of color shift in the radial direction. The distance to the inner surface in the radial direction can then be calculated from the amount of color shift. Images (optical images) at each diameter can be acquired in advance, and the inner diameter can be calculated based on the degree of agreement with these data (so-called pattern matching).

[0062] To improve the accuracy of calculating distance from the amount of color shift using the above method, it is preferable to increase the resolution of the color shift in the image, in other words, to be able to image the color shift over a range that spans many pixels. Therefore, it is preferable to enlarge the intermediate image reduced by the relay system, or to provide a magnifying lens system after the relay system, so that the enlarged image is formed on the imaging surface of the imaging element.

[0063] Conventional pore measurement methods include using a beam directed at the inner surface of the pore and rotating the beam to measure the distance around the entire circumference of the inner surface, and using a component (such as a cone mirror) with an oblique conjugate plane. However, the former requires measuring each point while rotating the beam, which poses challenges in terms of measurement simultaneity, alignment of the rotation axis, and axial wobble during rotation. Furthermore, the latter poses the problem that irregularly shaped components such as cone mirrors are not only difficult to machine with high precision, but also generate astigmatism as the angle of reflection and refraction increases, which can easily reduce measurement accuracy. Furthermore, both methods share the problem of being unable to observe the forward direction (i.e., the depth direction of the pore).

[0064] In contrast, with the measuring device 1A configured as described above, the small-diameter probe 2 can simultaneously capture images of the inner surface of the small hole H, thereby achieving an inner diameter measurement function that does not cause problems with simultaneity. Furthermore, since a high-speed rotation mechanism is not required, there is no axial wobble during rotation, and there are no problems with noise. Furthermore, since inexpensive, commercially available image sensors can be used, the device can be configured inexpensively.

[0065] In addition, forward observation is possible, making alignment easy and eliminating the need for time-consuming positioning adjustments. Even if the pore being measured is a blind hole, it is possible to prevent the probe from colliding with the object and damaging the probe itself. Furthermore, the algorithm for converting color shift into distance is not complex, allowing for high-speed processing.

[0066] Next, several modified examples of the measurement device 1A of the second embodiment will be described.

[0067] (Variation 1 of the Second Embodiment) In a first variation, in the measurement device 1A, the light source 3 is a light source whose emitted light color can be changed, such as a color-changing ring LED, and a monochrome image sensor 6 is used. The illumination light is then changed sequentially (for example, in the order of R, G, and B), and the image sensor captures an image at the timing when the illumination light of each color is irradiated. In this manner, the position where the light of each color is focused on the imaging surface of the image sensor 6 is acquired in a time-division manner. The magnitude of color shift is then calculated from the image-focusing positions acquired in a time-division manner, and the distance to the inner surface is further determined. In this variation, the illumination does not need to be three colors; four or more colors may be used.

[0068] This modified configuration is useful when the color (wavelength) of the illumination light and the image capture can be performed at high speed. In a color image sensor with pixels arranged in a Bayer array, images are output by interpolation at the positions of pixels of different colors. However, the configuration of this modified configuration uses all pixels, eliminating the need for interpolation, thereby improving measurement accuracy. Furthermore, the color of the illumination light is not limited to the three colors of RGB, and may include other colors in addition to RGB, such as infrared (IR), purple, yellow, and amber. This increases information about chromatic aberration of magnification (color resolution), further improving measurement accuracy.

[0069] 14 , in the second modification, a plurality of image sensors 6 are provided for each wavelength band to be dispersed, and a spectroscopic device 63 such as a dichroic prism is used to disperse the image formed by the observation optical system 5 into a plurality of wavelengths, and the dispersed images for each wavelength are converted into image data by separate image sensors. This modification has a configuration as simple as the second embodiment, yet can improve measurement accuracy in the same way as in the first modification.

[0070] (Variation 3 of the Second Embodiment) In a third variation, as shown in FIG. 15 , illumination may be achieved by passing illumination light through the wide-angle observation optical system 5. In this case, the passing illumination light may be refracted by components within the wide-angle observation system. For example, in the example shown in FIG. 15 , a GRIN lens is used as a relay lens 53, and light refracted by the GRIN lens is emitted as illumination light. In this case, the sheath may have a window-like or slit-like structure with high transmittance at the point where the illumination light exits. Note that, although the configuration shown in FIG. 15 is configured so that the illumination light passes through a GRIN lens, if a rod lens element with a uniform refractive index is used in the observation optical system 5, the illumination light may be transmitted through the rod lens element. The rod lens may be included in the imaging lens rather than the relay lens.

[0071] In this modified example, there is no light-guiding member 4 surrounding the observation optical system 5, and the number of parts at the tip is reduced, so that the diameter can be made even thinner, enabling the measurement and observation of even smaller pores. Furthermore, when observing or measuring a measurement object with a relatively high reflectance, if there is a light-emitting point near the tip, the image of the light source may be reflected on the measurement object, causing flare, but irradiating the illumination light from a position away from the tip has the effect of reducing this effect.

[0072] (Variation 4 of the Second Embodiment) In a fourth variation, as shown in FIGS. 16 and 17 , a beam splitter 9 is disposed in a wide-angle observation optical system 5, and a light source 3 is disposed in the branched optical path, forming a so-called coaxial epi-illumination system. The light source 3 may be a spot-type LED, a COB (Chip On Board) LED, or the like. Alternatively, light may be guided from an external light source using an optical fiber bundle or the like. In this variation, there is no light-guiding member 4 surrounding the observation optical system 5, and the number of components at the tip is reduced, allowing for a further reduction in diameter, enabling the measurement and observation of even thinner pores. The observation optical system 5C described in Configuration Example 3 of the optical system of the first embodiment may be used as the observation optical system 5, and a beam splitter 9 may be disposed at a telecentric location.

[0073] The beam splitter 9 may be of a type that splits light by polarization, in which case it is advisable to place a quarter-wave plate between the reduction lens system 51 and the beam splitter 9. This reduces the loss of light used for detection. The light source 3 may be composed of multiple monochromatic laser light sources. In this case, the effects of color mixing can be reduced even when a color imaging element with pixels arranged in a Bayer array is used as the image sensor.

[0074] Because this configuration can detect light from the center of the field of view, it may be configured so that an image of the light-emitting surface of the light source 3 is clearly formed on the imaging surface of the imaging element at a specific working distance from the measurement object. For example, as shown in FIG. 17 , a light-attenuating plate 10 may be placed between the light source and the measurement object, and an image of the light-attenuating plate 10 may be projected onto the measurement object via the observation optical system 5. The light-attenuating plate 10 and the imaging element 6 are configured to be conjugate with each other along the path from the light source 3 to the measurement object at a specific working distance (e.g., near point depth) where the reflected light is imaged on the imaging surface of the imaging element 6. A region 10a with discontinuously varying transmittance (preferably a region that completely blocks light) is provided in the center of the light-attenuating plate 10, and the shape of this region 10a (in the example of FIG. 17 , an "x" symbol) is projected. With this configuration, when the tip of the observation optical system 5 reaches the specific working distance, a clear image of the region 10a (i.e., the "x" symbol) is formed on the imaging surface of the imaging element 6. Therefore, by constantly analyzing the contrast of the image captured by the imaging element 6, it is possible to detect, based on the contrast reaching a specific level (higher than a predetermined threshold), that the probe 2 has approached the subject captured in the center of the field of view (the deepest part of the blind hole if the pore to be measured is a blind hole) to a predetermined distance (i.e., a distance corresponding to the depth of the observation optical system 5). The measuring device 1B may be configured to warn of the risk of contact when it detects that the probe has approached the subject captured in the center of the field of view to a predetermined distance. This makes it possible to prevent the probe from approaching beyond the predetermined distance and colliding with the subject captured in the center of the field of view.

[0075] The light-reducing plate 10 may be configured to be darker (lower transmittance) toward the center and brighter (higher transmittance) toward the periphery, or a slit-shaped area of ​​high transmittance may be provided at a specific radius. At the center, the illumination light and the optical axis of the observation optical system 5 are parallel, resulting in near-specular reflection and easy return of light. However, the specular reflection component decreases as the distance from the center increases, reducing the amount of light that can be recovered. Therefore, only the center of the field of view tends to be bright, making it difficult to obtain a uniform image. By configuring the light-reducing plate 10 to be darker toward the center and brighter toward the periphery, the above characteristics can be canceled out and the phenomenon of localized brightness in the center can be prevented. If a slit-shaped area of ​​high transmittance is provided at a specific radius, the configuration of this example can also achieve localized illumination suitable for distance measurement using color shift. The light-reducing plate 10 may also be positioned at multiple depths. It may also be positioned so that clear patterns appear at near and far points.

[0076] A measuring device 1B according to a third embodiment measures the distance from the center of an observation optical system 5 to the inner surface of a pore H, which is the object of measurement, by utilizing the principles of an optical interferometer, instead of (or in addition to) observation and measurement using optical images as in the measuring device 1 of the first embodiment. Details thereof will be described below.

[0077] The configuration of the measurement apparatus 1B according to this embodiment is generally the same as that of the measurement apparatus 1 according to the first embodiment, and includes a probe 2 and an information processing unit 8. In order to enable measurement using the principle of an optical interferometer, the measurement apparatus 1B differs in its configuration from the measurement apparatus 1 according to the first embodiment. The following description will focus on the differences from the measurement apparatus 1 according to the first embodiment, and will omit descriptions of parts that are common to the measurement apparatus 1 as appropriate.

[0078] As shown in FIG. 18, the probe 2 of the measuring device 1B includes a light source 3, an observation optical system 5, an image pickup element 6, a beam splitter 9, and a reference mirror unit 11.

[0079] The light source 3 is preferably a light source that outputs broadband light having many wavelength components across a wide band and low coherency, and is preferably a white light source such as a halogen or LED (Light Emitting Diode). The light emitted from the light source 3 is converted into a parallel beam by a collimator lens 31 and enters the beam splitter 9.

[0080] The beam splitter 9 splits the light from the light source 3 , reflecting part of the light toward the reduction lens system 51 of the observation optical system 5 and transmitting the other part of the light toward the reference mirror unit 11 .

[0081] The reduction lens system 51 of the observation optical system 5 expands the light from the beam splitter 9 over a wide angle and emits it into the pore H, which is the measurement object. The light reflected by the inner surface of the pore H enters the observation optical system 5 and is emitted toward the beam splitter 9. The optical path along which the light reflected by the beam splitter 9 passes through the measurement object and returns to the beam splitter 9 is called the measurement optical path. For example, the observation optical system 5 may employ the light guiding member 4C described in configuration example 3 of the optical system of the first embodiment, and the beam splitter 9 may be disposed in a telecentric position.

[0082] On the other hand, the light from the light source 3 that has passed through the beam splitter 9 passes through the relay lens 111 in the reference mirror unit 11, is incident on the reference mirror 112, is reflected, and returns to the beam splitter 9 via the relay lens 111 again. The optical path along which the light that has passed through the beam splitter 9 passes through the reference mirror unit 11 and returns to the beam splitter 9 is called the reference optical path.

[0083] As described above, the beam splitter 9 splits the light from the light source 3 into light that travels along the measurement optical path (measurement light) and light that travels along the reference optical path (reference light). The measurement light and reference light are combined by the beam splitter 9 into a composite wave, which is then emitted toward the image sensor 6.

[0084] The composite wave is focused by the imaging lens 61 onto the imaging surface of the imaging element 6. The imaging element 6 is a two-dimensional imaging element such as a CCD or CMOS sensor, and captures the interference image of the composite wave. The captured image data is input to the information processing unit 8.

[0085] The reference mirror unit 11 includes a driver 113 that moves the relay lens 111 and the reference mirror 112. The driver 113 moves the relay lens 111 and the reference mirror 112 in the optical axis direction in response to commands from the information processing unit 8. Here, interference is maximized when the optical path lengths of the reference optical path and the measurement optical path are equal (i.e., when the optical path length difference is zero), and the intensity of interference varies depending on the difference in optical path length near this distance. Therefore, during measurement, the information processing unit 8 controls the driver 113 to move the reference mirror 112 in the optical axis direction so that the optical path length difference is approximately zero, depending on the diameter of the pore H to be measured.

[0086] With the optical path length difference thus reduced to approximately zero, the image sensor 6 captures an interference image. Image data of the interference image captured by the image sensor 6 is input to the information processor 8, and the distance from the center of the observation optical system 5 to the inner surface is calculated as information on the inner diameter of the hole H based on the position information of the reference mirror 112 and the brightness (i.e., the strength of interference) for each position within the measurement field of view. For example, the distance for each pixel position within the image can be calculated by fitting the signal peak position for each pixel from multiple images acquired while changing the optical path length difference. FIG. 19 shows an example of an interference image obtained in this manner. The measurement device 1B may also capture an optical image in addition to the interference image, and perform observation and measurement based on the interference image and the optical image.

[0087] In this case, as shown in FIG. 20 , it is preferable to use a double-telecentric lens with a magnifying system on the reference mirror 112 side as the relay lens 111 disposed in the reference light path. FIG. 20 schematically illustrates a case where a double-telecentric lens with a magnification of 6x is used as the relay lens 111. The double-telecentric lens is then moved in synchronization with the reference mirror 112 and in the opposite direction to the movement of the reference mirror 112 so that the reference light is always focused near the reflecting surface of the reference mirror 112. In this way, if only the reference mirror 112 is moved as shown in FIG. 20( b ) based on the state shown in FIG. 20( a ), the position of the reference mirror 112 will be shifted from the focal position of the relay lens 111, resulting in a decrease in the amount of returned reference light. In contrast, as shown in FIG. 20( c ), by moving the relay lens 111 in the opposite direction to the movement of the reference mirror 112 and maintaining the focal position near the reflecting surface of the reference mirror 112, it is possible to suppress the decrease in the amount of returned light and prevent a decrease in sensitivity to interference fringes. Therefore, the range of diameters that can be measured can be made wider compared to when only the reference mirror 112 moves. Large lens movements generally result in a reduction in the amount of light due to aberrations and vignetting of light rays. By configuring the relay lens 111 as a magnifying, double-telecentric lens, the amount of movement of the reference mirror 112 can be made larger than the amount of movement of the relay lens 111, thereby keeping the amount of movement of the relay lens 111 small. Specifically, the focal position moves at a vertical magnification equal to the square of the magnification (horizontal magnification) of the relay lens 111. Therefore, a configuration can be achieved that can accommodate large changes in the optical path length while suppressing the effects of aberrations.

[0088] The measuring device 1B configured as described above can measure the inner diameter of the hole H all at once using a small-diameter probe by utilizing optical interference, thereby realizing an inner diameter measurement function that does not cause problems with simultaneity. Furthermore, since a high-speed rotation mechanism is not required, there is no axial wobble during rotation, and there are no problems with noise. Furthermore, since a commercially available, inexpensive image sensor can be used, the device can be configured inexpensively.

[0089] Furthermore, since forward observation is also possible, alignment is easy and position adjustments do not require much time. The aforementioned working distance detection method may be combined. That is, a light-reducing plate 10 having a region in the center where transmittance changes discontinuously may be placed in the optical path from the light source 3 to the beam splitter 9, and the contrast of the image captured by the image sensor 6 may be continuously analyzed. When a specific contrast (higher than a predetermined threshold) is reached, it is detected that the probe has approached a predetermined distance from the object captured at the center of the field of view. This prevents damage to the object or breakage of the probe due to a collision with the probe, even when the ore being measured is a blind hole. The aforementioned inner diameter measurement method may also be combined with working distance detection. Specifically, an interference signal also appears in the forward observation image, and a method can be used to analyze this to determine the distance to the object. While the above description assumes that the reference mirror 112 is a single mirror, the mirror may be divided into multiple parts. For example, by using separate mirrors near the optical axis and in the peripheral area of ​​the field of view, interference signals of the distance to the subject and the inner diameter of the pore H, which have different optical path lengths, may be obtained simultaneously.

[0090] Next, several modified examples of the measurement device 1B of the third embodiment will be described.

[0091] (Variation of the Third Embodiment) Like the measurement apparatus 1B of the third embodiment, the measurement apparatus 1C of this variation utilizes the principle of an optical interferometer to measure the distance from the center of the observation optical system 5 to the inner surface of the pore H that is the measurement target, but differs from the measurement apparatus 1B in that it has an optical path length difference generating unit 20 and a fixed reference mirror provided on the probe 2. The following description will focus on the differences from the measurement apparatus 1B of the third embodiment, and will omit descriptions of parts that are common to the measurement apparatus 1B as appropriate.

[0092] Fig. 21 is a schematic diagram illustrating the configuration of a measurement apparatus 1C. As shown in Fig. 21 , the measurement apparatus 1C according to this modification includes a probe 2, a light source 3, an optical path length difference generation unit 20, and an information processing unit 8. The light source 3 and the optical path length difference generation unit 20 are connected by an optical fiber 30, and the optical path length difference generation unit 20 and the probe 2 are connected by an optical fiber 31.

[0093] Fig. 22 is a schematic diagram showing an example of the configuration of the optical path length difference generation unit 20. As shown in Fig. 22, the optical path length difference generation unit 20 includes a beam splitter 21, a fixed mirror 22, and a movable mirror 23. Light emitted from a light source 3 enters the optical path length difference generation unit 20 via an optical fiber 30 and is irradiated onto the beam splitter 21. The beam splitter 21 splits the light from the light source 3, reflecting a portion of the light toward the fixed mirror 22 and transmitting the other portion of the light toward the movable mirror 23.

[0094] The fixed mirror 22 is a reflective mirror that is fixed so that the distance from the beam splitter 21 does not change. The fixed mirror 22 reflects the light from the beam splitter 21 toward the beam splitter 21. The optical path along which the light reflected by the beam splitter 21 passes through the fixed mirror 22 and returns to the beam splitter 21 is called a fixed-length optical path.

[0095] The movable mirror 23 is a reflecting mirror whose distance from the beam splitter 21 can be changed under the control of the information processing unit 8. The movable mirror 23 reflects the light from the beam splitter 21 toward the beam splitter 21. The optical path along which the light that has passed through the beam splitter 21 returns to the beam splitter 21 via the movable mirror 23 is called a variable-length optical path. In this example, the optical path length of the variable-length optical path is longer than the optical path length of the fixed-length optical path.

[0096] The light that has passed through the fixed-length optical path and the light that has passed through the variable-length optical path are combined into a composite wave by the beam splitter 21 and emitted to the probe 2 via the optical fiber 31. In this way, the light emitted from the optical path length difference generating unit 20 contains light of two phases having a phase difference according to the optical path length difference between the fixed-length optical path and the variable-length optical path.

[0097] In this example, the probe 2 includes an observation optical system 5, an image sensor 6, a beam splitter 9, and a fixed reference mirror 12. Light from an optical path length difference generating unit 20 enters the probe 2 via an optical fiber 31. The light from the optical path length difference generating unit 20 is converted into a parallel beam by a collimator lens 31 and enters the beam splitter 9.

[0098] The beam splitter 9 splits the light from the light source 3 , reflecting part of the light toward the reduction lens system 51 of the observation optical system 5 and transmitting the other part of the light toward the fixed reference mirror 12 .

[0099] The reduction lens system 51 of the observation optical system 5 expands the light from the beam splitter 9 over a wide angle and emits it into the pore H, which is the measurement object. The light reflected by the inner surface of the pore H enters the observation optical system 5 and is emitted toward the beam splitter 9. The optical path along which the light reflected by the beam splitter 9 passes through the measurement object and returns to the beam splitter 9 is called the measurement optical path. For example, the observation optical system 5 may employ the light guiding member 4C described in configuration example 3 of the optical system of the first embodiment, and the beam splitter 9 may be disposed in a telecentric position.

[0100] On the other hand, the light from the light source 3 that has passed through the beam splitter 9 is reflected by the fixed reference mirror 12 and returns to the beam splitter 9. The optical path along which the light that has passed through the beam splitter 9 passes through the fixed reference mirror 12 and returns to the beam splitter 9 is called the reference optical path. In this example, the optical path length of the measurement optical path is longer than the optical path length of the reference optical path.

[0101] As described above, the beam splitter 9 splits the light from the optical path length difference generating unit 20 into light that travels along an optical path that passes through the measurement object and light that passes through the fixed reference mirror 12. The light that returns to the beam splitter 9 along these two optical paths becomes a composite wave at the beam splitter 9 and is emitted toward the image sensor 6.

[0102] Here, the optical path of the light emitted by the light source 3 until it enters the image sensor 6 is assumed to be four different optical paths, which are a combination of two types of optical paths within the optical path length difference generation unit 20 (i.e., a fixed-length optical path and a variable-length optical path) and two types of optical paths within the probe 2 (i.e., a measurement optical path and a reference optical path). FIG. 23 is a diagram showing these four optical paths. In FIG. 23, (a) is an optical path that passes through a fixed-length optical path within the optical path length difference generation unit 20 and an optical path that passes through the measurement object within the probe 2, and the optical path length changes depending on the distance from the observation optical system 5 to the measurement object. (b) is an optical path that passes through a fixed-length optical path within the optical path length difference generation unit 20 and an optical path that passes through the fixed reference mirror 12 within the probe 2, and the optical path length is constant and is the shortest of the four optical paths. (c) is an optical path that passes through a variable-length optical path in the optical path length difference generating unit 20 and an optical path that passes through the measurement object in the probe 2, and its optical path length is the longest among the four optical paths. (d) is an optical path that passes through a variable-length optical path in the optical path length difference generating unit 20 and an optical path that passes through the fixed reference mirror 12 in the probe 2, and its optical path length changes depending on the position of the movable mirror 23.

[0103] In the measurement apparatus 1C, an interference image is captured by the image sensor 6, focusing on the interference between the light passing through the optical path (a) in FIG. 23 and the light passing through the optical path (d) in FIG. 23 . Specifically, the position of the movable mirror 23 is adjusted so that the difference in optical path length between the optical paths (a) and (d) in FIG. 23 is approximately zero, causing interference between the light passing through both optical paths, and the image sensor 6 captures the interference image. In other words, the image sensor 6 captures an interference image of the composite wave focused on the imaging plane and outputs image data in a state in which the combined optical path length of the fixed-length optical path and the reference optical path is approximately equal to the combined optical path length of the variable-length optical path and the measurement optical path. A method for calculating the distance from the obtained interference image can be similar to that described in relation to the measurement apparatus 1B, except that information corresponding to the optical path length difference generated by the optical path length difference generating unit 20 (e.g., the position (drive distance) of the movable mirror 23) is used instead of the position of the reference mirror 111. In addition, since the optical paths (b) and (c) in Figure 23 have different optical path lengths from the other optical paths, no interference occurs between the light that has passed through these optical paths and the light that has passed through optical paths other than these optical paths, and therefore the interference image is not affected.

[0104] According to the measuring device 1C described above, the mirror drive mechanism, which tends to be large, can be disposed outside the probe 2, and the reference mirror provided inside the probe 2 can be fixed. As a result, the probe 2 can be made smaller.

[0105] [Modifications of the Embodiment] While the present embodiment and its modifications have been described above, the present invention is not limited to these examples. For example, in the modification of the third embodiment, the optical path length difference generating unit 20 is configured as a Michelson interferometer using two reflecting mirrors (22, 23). However, the configuration of the optical path length difference generating unit 20 is not limited to this. For example, at least one of the reflecting mirrors may be a retroreflector mirror or a corner cube. Furthermore, the beam splitter may be a polarizing beam splitter, with a wave plate appropriately inserted in the optical path. Furthermore, the optical path length difference generating unit 20 may not be a Michelson type, but may be a Mach-Zehnder type configured with two fiber couplers. Specifically, as shown in FIG. 24 , the light from the light source 3 may be split and merged by fiber couplers 24 and 25, with the optical path length of one of the splits being variable. The couplers may have an air gap between them to allow light to propagate, or the air gap may be variable. In short, the optical path length difference generating unit 20 may have any configuration as long as it splits the light from the light source 3 into two optical paths with relatively different optical path lengths and then recombines the split light. Furthermore, the light source may be a swept-type variable wavelength light source that acquires signals in a time-division manner (so-called full-field type SS-OCT; see, for example, D. Hillmann, H. Spahr, C. Hain, H. Sudkamp, ​​G. Franke, C. Pfaffle, C. Winter, and G. Huttmann, “Aberration-free volumetric high-speed imaging of in vivo retina,” Sci. Rep. 6(1), 35209 (2016)).

[0106] Furthermore, in the third embodiment and its variations, the branching and merging of the optical path within the probe 2 is achieved using a plate-type beam splitter 9 disposed at an angle to the optical path, but this function may be achieved in other ways. For example, a reduction lens system or a relay lens may be used with a beam splitter coating on some of its surfaces. For example, a beam splitter coating may be applied to the surface of a GRIN lens. These configurations reduce the number of parts compared to when a plate-type beam splitter is used, contributing to compactness and lower costs.

[0107] Furthermore, any combination of the features of the above-described embodiments, in which a person skilled in the art appropriately adds, deletes, or modifies components, is also included within the scope of the present invention, as long as it includes the gist of the present invention.

[0108] REFERENCE SIGNS LIST 1 Measuring device 2 Probe 3 Light source 4 Light guide member 5 Observation optical system 6 Imaging element 7 Sheath (cover) 8 Information processing unit

Claims

1. A reduction lens system having a total angle of view of 120° or more, comprising lenses of a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side, and an enlargement lens system comprising a third lens group having a positive refractive power and a fourth lens group having a negative refractive power, which enlarges the object image formed by the reduction lens system and forms an image on the imaging surface of an imaging device, the enlargement lens system generating a spiral distortion that cancels out the barrel distortion generated in the reduction lens system, and the distortion generated in the entire observation optical system in the range of 70% to 80% of the maximum image height being within ±5%.

2. The observation optical system according to claim 1, further comprising a relay lens system between the reduction lens system and the enlargement lens system.

3. The observation optical system according to claim 2, wherein at least a part of the relay lens system is constituted by a GRIN lens.

4. The observation optical system according to claim 1 or 2, wherein focusing is performed at a position where off-axis light rays become substantially telecentric during intermediate image formation.

5. The observation optical system according to claim 1 or 2, wherein a color correction filter or an optical path splitting member is disposed at a position where off-axis light rays become substantially telecentric during intermediate image formation.

6. The observation optical system according to claim 1 or 2, wherein the maximum value of the barrel distortion generated only by the reduction lens system is 50% or more in the maximum field of view.

7. The observation optical system according to claim 1 or 2, wherein the reduction lens system and the enlargement lens system are constituted by common lenses and have a completely symmetric configuration.

8. A measuring device comprising a probe and an information processing unit, which images the inner surface of a pore while inserting the probe into the pore to be measured, and measures the pore, wherein the probe includes at least: a light source that emits illumination light for illuminating the inside of the pore; an observation optical system having a reduction lens system with a total angular field of view of at least 120° or more, and a relay lens system that relays an intermediate image formed by the reduction lens system on a first intermediate imaging surface and forms an image on a subsequent imaging surface, the observation optical system having different angular fields of view depending on the wavelength; and an image sensor that images an image of the inner surface of the pore formed by the observation optical system in a state where the illumination light emitted by the light source irradiates the inside of the pore and outputs image data. The information processing unit analyzes the image data output by the image sensor and calculates a distance from the center of the observation optical system to the inner surface of the pore based on the amount of color deviation in the captured image.

9. The observation optical system further includes an enlargement lens system that enlarges an image formed by the relay lens system and forms an image on the imaging surface of the image sensor. The enlargement lens system generates a thread-winding type of distortion that cancels out the barrel type of distortion generated in the reduction lens system, so that the distortion generated in the entire observation optical system within a range of 70% to 80% of the maximum image height is within ±5%. The measuring device according to claim 8.

10. The measuring device according to claim 8 or 9, further comprising a light guide member disposed on the outer periphery of the observation optical system, which propagates illumination light from the light source to the tip of the probe and emits the illumination light from the tip.

11. The measuring device according to claim 10, wherein the light guide member has a condensing action, and the illumination light forms at least one ring-shaped condensing pattern.

12. The image sensor has a configuration in which pixels that respectively spectrally detect at least three wavelength bands are arranged in a Bayer array, outputs image data for an image spectrally separated for each wavelength band, and the information processing unit calculates the amount of color deviation in the spectrally separated image at each position and calculates a distance based on the calculated amount of color deviation. The measuring device according to claim 8 or 9.

13. The light source has a variable emission color, the imaging device is a monochrome imaging device, while sequentially changing the color of the illumination light emitted by the light source, the imaging device performs imaging at the timing when each color of illumination light is irradiated and outputs image data, and the information processing unit calculates the amount of color shift of the image with respect to each color of illumination light output by the imaging device at each position, and calculates the distance based on the calculated amount of color shift. The measuring device according to claim 8 or 9, characterized in that.

14. The measuring device further includes a spectroscopic device that spectroscopically analyzes the image formed by the observation optical system into a plurality of wavelengths, a plurality of imaging devices are provided corresponding to each wavelength spectroscopically analyzed by the spectroscopic device, and outputs image data for the image of the corresponding wavelength, and the information processing unit calculates the amount of color shift of the spectroscopically analyzed image at each position, and calculates the distance based on the calculated amount of color shift. The measuring device according to claim 8 or 9, characterized in that.

15. The measuring device further includes a beam splitter disposed in the observation optical system, and the light source is disposed in the optical path branched by the beam splitter to constitute coaxial epi-illumination. The measuring device according to claim 8 or 9, characterized in that.

16. The measuring device according to claim 15, further comprising a light attenuation member having a non-uniform transmittance distribution in the radial direction in which the transmittance is lower toward the center, and disposed between the light source and the beam splitter.

17. The measuring device according to claim 16, wherein the light attenuation member has a region with a high transmittance in a slit shape at a specific radius.

18. The light attenuation member has a region where the transmittance changes discontinuously at the central portion, and the information processing unit analyzes the image data and, based on the contrast of the image of the region where the transmittance changes discontinuously, detects that the tip of the probe has approached a subject imaged at the center of the field of view to a predetermined distance. The measuring device according to claim 16, characterized in that.

19. A measuring device comprising a probe and an information processing unit, which images the inner surface of a pore while inserting the probe into the pore to be measured, and measures the pore. The probe includes at least a light source that emits light, a beam splitter, a reference mirror unit, an observation optical system having a total angular field of view of 120° or more, and an imaging device. The beam splitter branches the light from the light source into reference light directed to the reference mirror unit and measurement light directed to the observation optical system, and emits a combined wave of the reference light returning from the reference mirror unit and the measurement light returning from the observation optical system toward the imaging device. The observation optical system expands the measurement light from the beam splitter at a wide angle and emits it into the pore to be measured, and condenses the measurement light reflected or scattered by the inner surface of the pore and emits it toward the beam splitter. The reference mirror unit includes a reference mirror that reflects the reference light from the beam splitter and returns it to the beam splitter, and a drive mechanism that moves the reference mirror so that the optical path length of the reference optical path returning from the beam splitter via the reference mirror to the beam splitter is substantially equal to the optical path length of the measurement optical path returning from the beam splitter via the observation optical system and the inner surface of the pore to the beam splitter. The imaging device images an interference image of the combined wave formed on the imaging surface in a state where the optical path length of the reference optical path is substantially equal to the optical path length of the measurement optical path, and outputs image data. The information processing unit analyzes the image data of the interference image output by the imaging device, and calculates the distance from the center of the observation optical system to the inner surface of the pore based on the position of the reference mirror and the interference intensity at the position of each pixel in the image. A measuring device characterized by the above.

20. The reference mirror is provided with a relay lens, which is a bilateral telecentric lens with an expansion system on the reference mirror side, between the beam splitter and the reference mirror. The drive mechanism moves the relay lens in a direction opposite to the movement of the reference mirror in synchronization with the movement of the reference mirror, so that the reference light always focuses near the reflection surface of the reference mirror. The measuring device according to claim 19, characterized by the above.

21. A measuring device comprising a light source that emits light, an optical path length difference generating unit that divides the light from the light source into two optical paths with different optical path lengths relative to each other and recombines them, a probe, and an information processing unit. The measuring device images the inner surface of a pore, which is a measurement target, with the probe inserted into the pore to perform measurement of the pore. The probe includes at least a beam splitter surface, an observation optical system having a total viewing angle of 120° or more, and an imaging element. The beam splitter surface branches the light from the optical path length difference generating unit into reference light and measurement light directed toward the observation optical system, and emits the combined wave of the reference light and the measurement light returning from the observation optical system toward the imaging element. The observation optical system expands the measurement light from the beam splitter surface at a wide angle and emits it into the pore, which is the measurement target, and condenses the measurement light reflected or scattered by the inner surface of the pore and emits it toward the beam splitter surface. The optical path length difference generating unit is configured to be able to adjust the optical path length difference between the two optical paths. The imaging element images the interference image of the combined wave formed on the imaging surface in a state where the optical path length obtained by combining the optical path length of one of the two optical paths and the optical path length of the reference optical path branched by the beam splitter surface is substantially equal to the optical path length obtained by combining the optical path length of the other of the two optical paths and the optical path length of the measurement optical path that returns from the beam splitter surface via the observation optical system and the inner surface of the pore, and outputs image data. The information processing unit analyzes the image data of the interference image output by the imaging element, and calculates the distance from the center of the observation optical system to the inner surface of the pore based on the optical path length difference between the two optical paths in the optical path length difference generating unit and the interference intensity at the position of each pixel in the image.

22. The measuring device according to any one of claims 19 to 21, further comprising a light attenuation member having a non-uniform transmittance distribution in the radial direction in which the transmittance is lower toward the center, and disposed between the light source and the beam splitter.

23. The measuring device according to claim 22, wherein the light attenuation member has a region with a high transmittance in a slit shape at a specific radius.

24. The dimming member has a region where the transmittance changes discontinuously at the center, and the information processing unit analyzes the image data and detects that the tip of the probe has approached a subject imaged at the center of the field of view to a predetermined distance based on the contrast of the image of the region where the transmittance changes discontinuously. The measuring device according to claim 23, characterized in that.

Images