Measurement optical system and photometric device

Abstract

A measurement optical system 1 includes, in order from the object side, an optical filter 30, a front group 41, an aperture 42, and a rear group 43. The aperture 42 is disposed in the vicinity of a rear focal point f22 of the front group 41 and in the vicinity of a front focal point f31 of the rear group 43. An opening AP of the aperture 42 is formed in a non-point symmetric shape centered on an optical axis Ax1 of the rear group 43, in a plane including the aperture 42.

Description

Measuring optical system and photometric device

[0001] The present disclosure relates to a measurement optical system and a photometric device that include an optical filter.

[0002] There are known photometric devices (e.g., two-dimensional luminance colorimeters, two-dimensional spectrometers, etc.) that measure the luminance, chromaticity, spectral distribution, etc. of light from a measurement target in two dimensions (see, for example, Patent Documents 1 and 2). The measurement optical system used in the photometric device uses optical filters such as linear variable filters whose transmission wavelength range changes depending on the position, and filters corresponding to color matching functions. Examples of optical filters that are used include filters that combine a colored glass filter that absorbs a specific wavelength range with a dye film, and interference filters that utilize the interference effect of a multilayer film (see, for example, Patent Document 3).

[0003] JP 2006-177812 A JP 2017-207406 A JP 2011-220769 A

[0004] However, these optical filters reflect much of the light that does not pass through them, resulting in stray light. For example, when an interference filter is combined with a CMOS or CCD image sensor, both have relatively high reflectance, resulting in a large amount of stray light due to reflection between them. Colored glass filters and dye films also generate stray light, although their reflectance is lower than that of interference filters.

[0005] The present disclosure aims to reduce the amount of stray light.

[0006] In order to achieve the above object, the present disclosure provides a measurement optical system having, in order from the object side, an optical filter, a front group, an aperture, and a rear group, the aperture being disposed at the rear focus of the front group and the front focus of the rear group, and an opening being formed in a plane including the aperture in an asymmetrical shape centered on the optical axis of the rear group.

[0007] According to the present disclosure, the amount of stray light can be reduced.

[0008] 4A is a schematic diagram of a photometric device according to a first embodiment; FIG. 4B is a diagram illustrating an example of a specific shape of an aperture stop according to the first embodiment; FIG. 4C is a diagram illustrating an optical system in which an optical filter is placed immediately before a light-receiving sensor; FIG. 4D is a diagram illustrating an optical system in which an optical filter is tilted; FIG. 4E is a diagram illustrating an optical system in which an optical filter is placed at the position of a first image formed by an objective optical system, and the first image is formed on a sensor surface by a relay optical system; FIG. 4F is a diagram illustrating an optical system using an LVF as an optical filter; FIG. 4G is an enlarged view of the optical filter of FIG. 4A; FIG. 4H is a graph illustrating the spectral transmittance at each point on the optical filter; FIG. 4I is a diagram illustrating the positional relationship between the rear focus of the front group and the aperture; FIG. 4J is a diagram illustrating the positional relationship between the rear focus of the front group and the aperture; FIG. 4J is a diagram illustrating the positional relationship between the front focus of the rear group and the aperture; FIG. 4K is a diagram illustrating the positional relationship between the front focus of the rear group and the aperture; FIG. 10 is a schematic diagram of a case where the second optical axis of the rear group is shifted in the radial direction, where the light beam incident on the aperture is parallel light. FIG. 11 is a schematic diagram of a case where the second optical axis of the rear group is shifted in the radial direction, where the light beam incident on the aperture is diverging light. FIG. 12 is a schematic diagram of a case where the second optical axis of the rear group is shifted in the radial direction, where the light beam incident on the aperture is converging light. FIG. 13 is a schematic diagram of a photometric device according to a third embodiment. FIG. 14 is a diagram showing an example of a specific shape of the aperture according to the third embodiment. FIG. 15 is a light path diagram showing an example of a specific configuration of the photometric device of Example 1. FIG. 16 is a light path diagram showing an example of a specific configuration of the photometric device of Example 2. FIG. 17 is a light path diagram showing an example of a specific configuration of the photometric device of Example 3. FIG. 18 is a light path diagram showing an example of a specific configuration of the photometric device of Example 4. FIG. 19 is a light path diagram showing an example of a specific configuration of the photometric device of Example 5. FIG. 19 is a light path diagram showing an example of a specific configuration of the photometric device of Example 6.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Various limitations are applied to the following embodiments in order to implement the present disclosure, but the scope of the present disclosure is not limited to the following embodiments and illustrated examples.

[0010] <First Embodiment> [Overall Configuration of Measurement Optical System] Fig. 1 is a schematic diagram of a photometric device 100 according to the first embodiment. As shown in Fig. 1, the photometric device 100 two-dimensionally measures the luminance, chromaticity, spectral distribution, etc. of light from a measurement object surface (measurement object) OB. The photometric device 100 includes a light receiving sensor 50 and a measurement optical system 1 that guides light to the light receiving sensor 50.

[0011] The light receiving sensor 50 is, for example, a CMOS or CCD image sensor, and has a light receiving surface (sensor surface) 51 as a photoelectric conversion unit that photoelectrically converts incident light. The light receiving sensor 50 photoelectrically converts the light received by the light receiving surface 51 from the measurement object surface OB, and outputs an electrical signal according to the light intensity.

[0012] The measurement optical system 1 includes, along an optical axis Ax1, an objective optical system 20, an optical filter 30, and a relay optical system 40, in that order from the object side (measurement target surface OB side).

[0013] The objective optical system 20 forms an intermediate image (first image) f1 as an image of the measurement object surface OB. The objective optical system 20 includes at least one lens and has, for example, positive refractive power.

[0014] The optical filter 30 may be, for example, an interference filter, a color balance filter, or a filter using a dye film made of a resin material. The optical filter 30 of this embodiment is an interference filter having a glass or resin substrate and a multilayer film formed on the surface of the substrate. Alternatively, the optical filter 30 may be three switchable interference filters that selectively transmit light of specific wavelengths corresponding to tristimulus values. Alternatively, the optical filter 30 may be a linear variable filter (LVF) for use in a two-dimensional spectroscopic device that performs measurements while sequentially scanning the optical filter 30, and whose transmission wavelength band changes depending on the position of incidence of light. The optical filter 30 is disposed near the first image f1 of the objective optical system 20. Here, "near" the first image f1 where the optical filter 30 is disposed refers to a predetermined range before and after the position of the first image f1 in the optical axis direction, including the position of the first image f1. "Near" the first image f1 means, for example, that the optical filter 30 should ideally be disposed at the first image f1 from a paraxial optical perspective, but in a real optical system, it is disposed at an optimal position near the first image f1 depending on residual aberrations, etc. In the case of a two-dimensional color luminance meter or the like, the optical filter may be located between the objective optical system and the relay optical system. As will be described later, the optical filter may be disposed at an angle. To reduce the error sensitivity to defects on the optical filter surface (e.g., pinholes, bumps, scratches, etc. in the multilayer film), it is preferable to displace the position from the first image.

[0015] The relay optical system 40 relays the first image formed by the objective optical system 20 and forms a second image on the light-receiving sensor 50 (light-receiving surface 51). Specifically, the relay optical system 40 has, in order from the object side, a front group 41, a diaphragm (aperture stop) 42, and a rear group 43. The front group 41 includes at least one lens and has, for example, positive refractive power. The rear group 43 includes at least one lens and has, for example, positive refractive power. The diaphragm 42 has an opening AP that transmits light.

[0016] [Aperture Shape of the Aperture] FIG. 2 shows specific examples of the shape of the aperture 42 (first example: aperture 42a to fifth example: aperture 42e). As shown in FIG. 2, the aperture AP of the aperture 42 is formed asymmetrically about the optical axis Ax1 (of the rear group 43) in a plane including the aperture 42. In other words, the shape of the aperture AP does not match the shape of the inversion portion V (illustrated in the second and third examples) obtained by rotating the aperture AP 180° around the optical axis Ax1. More preferably, the overlap area ratio between the aperture AP and the inversion portion V is 50% or less, and even more preferably 40% or less. The "overlap area ratio" refers to the ratio of the area of ​​the overlapping portion between the aperture AP and the inversion portion V to the total area of ​​the aperture AP. For example, in the apertures 42a, 42d, and 42e of the first, fourth, and fifth examples, the aperture AP and the inversion portion V do not overlap at all (overlap area ratio: 0%). In the aperture 42b of the second example, the overlapping area ratio between the opening AP and the inverted portion V is approximately 39%, and in the aperture 42c of the third example, the overlapping area ratio between the opening AP and the inverted portion V is approximately 33%.

[0017] With this configuration, light reflected from the light-receiving surface 51 of the light-receiving sensor 50 (shown by the thin dashed line in FIG. 1 ) is blocked (blocked) by the light-shielding portion SH (the portion other than the aperture AP) of the aperture 42. Therefore, the reflected light does not return to the optical filter 30. This suppresses the generation of stray light due to reflection between the light-receiving sensor 50 and the optical filter 30. That is, when light reflected from the light-receiving surface 51 returns to the aperture 42, it returns to a position rotated 180° around the optical axis Ax1 (of the rear group 43). In other words, only the light beam from the overlapping portion of the aperture AP and the inverted portion V returns to the optical filter 30, is further reflected by the optical filter 30, and can enter the light-receiving sensor 50 as stray light. Therefore, for example, the apertures 42b and 42c in the second and third examples can reduce stray light by approximately 39% and approximately 33%, respectively, compared to a typical circular aperture. The apertures 42b and 42c in the second and third examples increase stray light compared to the apertures 42a, 42d, and 42e in the first, fourth, and fifth examples, but also increase the amount of measurement light. The number, shape, and arrangement of the apertures AP are not particularly limited. However, it is preferable that the apertures AP be evenly spaced (circumferentially) around the optical axis Ax1, as in the apertures 42c to 42e in the third to fifth examples. This allows the apertures 42c to 42e in the third to fifth examples to suppress bias in the distribution of the angle of incidence of light rays on the optical filter 30 and reduce polarization dependency compared to the apertures 42a and 42b in the first and second examples. However, the apertures 42a and 42b in the first and second examples can reduce polarization dependency by tilting the optical filter 30 so that the angle of incidence of light rays on the optical filter 30 is smaller.

[0018] In this way, the aperture AP of the diaphragm 42 located between the light-receiving sensor 50 and the optical filter 30 is asymmetrical about the optical axis Ax1 of the rear group 43, thereby reducing the amount of stray light generated between the light-receiving sensor 50 and the optical filter 30. Specifically, as shown in FIG. 3A , if an optical filter (interference filter) is placed immediately before the light-receiving sensor, stray light is likely to be generated due to reflection between the light-receiving sensor (sensor surface) and the optical filter. For example, CMOS and CCD image sensors have high surface reflectance, and the reflectance of the optical filter can also be very high depending on the wavelength. For example, assuming the reflectance R of the optical filter = 50% (transmittance T = 50%) and the reflectance Rs of the sensor surface = 10%, the amount of stray light reflected between the sensor surface and the optical filter and incident on the light-receiving sensor is very large, Rs * R = 5%, compared to the amount of light to be measured. In two-dimensional photometric devices, light emitted from one point within the measurement field of view can cause errors in the measurements of other points as stray light, resulting in poor spatial resolution. In this regard, according to this embodiment, stray light can be blocked (light-shielded) by the aperture 42 disposed between the light-receiving sensor 50 and the optical filter 30. Therefore, compared to disposing the optical filter immediately before the light-receiving sensor, the amount of stray light generated between the light-receiving sensor 50 and the optical filter 30 can be reduced, thereby suppressing deterioration of spatial resolution. Furthermore, as shown in FIG. 3B , when suppressing stray light between the light-receiving sensor and the optical filter by tilting the optical filter (interference filter), a large tilt of the optical filter results in a large incident angle of light on the optical filter. As the incident angle of light on the optical filter increases, the spectral transmittance changes depending on the polarization (S-polarized, P-polarized). Therefore, the transmittance of the optical filter changes depending on the polarization state of the measurement light, resulting in measurement errors. Furthermore, a large tilt of the optical filter increases the size of the optical system. In this regard, according to this embodiment, the generation of stray light can be suppressed without tilting the optical filter to increase the incident angle of light. Therefore, unlike the case where the optical filter is tilted to suppress the generation of stray light between the light receiving sensor and the optical filter, it is possible to suppress the generation of stray light and also to suppress the occurrence of measurement errors and the increase in size of the optical system. Also, as shown in Figure 3C, a configuration is conceivable in which an optical filter is placed at the position of the first image formed by the objective optical system, and the first image is formed on the sensor surface by the relay optical system.In this case, if the optical system is aberration-free and the optical filter can be accurately positioned at the first image, stray light between the light-receiving sensor and the optical filter will overlap with the normal measurement light, preventing a deterioration in spatial resolution. However, in reality, the image of the reflected light will broaden due to aberrations, manufacturing errors, and misalignment during optical filter switching or sweeping, resulting in a deterioration in spatial resolution and measurement accuracy. Furthermore, if an optical filter is positioned at the first image, even small defects on the filter surface (e.g., pinholes, bumps, or scratches in the multilayer film) can significantly affect the measurement value. In this regard, this embodiment reduces the amount of stray light generated between the light-receiving sensor 50 and the optical filter 30 without requiring an aberration-free optical system or accurate positioning of the optical filter at the first image. Furthermore, in a spectroscopic device using an LVF as an optical filter, the half-width of the spectral responsivity will widen due to the influence of stray light. In other words, as shown in Figures 4A to 4C, when the LVF is positioned at an angle, the intermediate image (first image) plane and the LVF plane are spaced apart at the periphery of the measurement field of view. As a result, the light beam corresponding to measurement point P on the sensor surface is affected by the spectral transmittance at different positions on the LVF, resulting in a wider half-width. Specifically, the light beam corresponding to measurement point P on the sensor surface is affected by the spectral transmittance at points P1, P2, and P3 on the LVF. In this case, the average spectral transmittance at each of these points has a wider half-width than each of the individual points. A similar effect occurs when the transmission wavelength band of the LVF changes in the direction perpendicular to the plane of the paper in FIG. 4A . In this regard, according to this embodiment, there is no need to tilt the LVF, and the light beam corresponding to any measurement point on the sensor surface 51 is focused at one point on the LVF (optical filter 30), so the half-width does not deteriorate.

[0019] [Position of Aperture] The aperture 42 is disposed at a position on the optical axis Ax1 that corresponds to the rear (image side) focal point f22 of the front group 41 and the front (object side) focal point f31 of the rear group 43. However, the position of the aperture 42 on the optical axis Ax1 may be any position as long as it is within the "vicinity" of each focal point expressed by, for example, the following conditional expressions:

[0020] With regard to the position of the diaphragm 42 on the optical axis Ax1, it is preferable that the measurement optical system 1 satisfy the following conditional expression (1): -0.35 < da / fa < 0.35 (1) where da is the distance on the optical axis Ax1 from the rear focal point f22 of the front group 41 to the diaphragm 42, and fa is the focal length of the front group 41. It is also preferable that the measurement optical system 1 satisfy the following conditional expression (1a): -0.2 < da / fa < 0.2 (1a)

[0021] The above conditional expressions (1) and (1a) define the position of the diaphragm 42 on the optical axis Ax1 relative to the rear focal point f22 of the front group 41 of the relay optical system 40. As shown in Figures 5A and 5B, when da / fa = 0, the light beam on the front side of the front group 41 is telecentric, and the angles of incidence of the light rays on the optical filter 30 are distributed approximately uniformly across the entire measurement field of view. Therefore, by satisfying conditional expressions (1) and (1a), the spectral response becomes nearly uniform across the entire measurement field of view, enabling measurements to be made with higher accuracy.

[0022] Furthermore, it is preferable that the measurement optical system 1 satisfy the following conditional expression (2): -0.35 < db / fb < 0.35 (2) where db is the distance on the optical axis Ax1 from the front focal point f31 of the rear group 43 to the diaphragm 42, and fb is the focal length of the rear group 43. It is also preferable that the measurement optical system 1 satisfy the following conditional expression (2a): -0.2 < db / fb < 0.2 (2a)

[0023] The above conditional expressions (2) and (2a) define the position of the diaphragm 42 on the optical axis Ax1 relative to the front focal point f31 of the rear group 43 of the relay optical system 40. As shown in FIGS. 5C and 5D , when db / fb = 0, the rear side of the rear group 43 is telecentric, and the angles of incidence of light rays on the sensor surface 51 are distributed approximately uniformly across the entire sensor surface 51. This allows stray light to be suitably removed across the entire measurement field of view. Therefore, by satisfying conditional expressions (2) and (2a), the amount of stray light due to reflection between the sensor surface 51 and the optical filter 30 can be reduced.

[0024] [Technical Effects of the First Embodiment] As described above, according to this embodiment, the diaphragm 42 is disposed at the rear focal point f22 of the front group 41. This makes the front side of the relay optical system 40 telecentric, and the angles of incidence of light emitted from each point on the measurement object surface OB onto the optical filter 30 are approximately uniform. Therefore, the spectral response becomes nearly uniform across the entire measurement field of view, enabling measurements to be made with higher accuracy.

[0025] Furthermore, according to this embodiment, the aperture AP of the diaphragm 42 is formed asymmetrically about the optical axis Ax1 of the rear group 43 within a plane including the diaphragm 42. In other words, the shape of the aperture AP does not coincide with the shape of the inversion portion V, which is obtained by rotating the aperture AP 180° around the optical axis Ax1. This allows the diaphragm 42 to block the light beam reflected by the sensor surface 51 and returning to the optical filter 30. Therefore, compared to placing the optical filter immediately before the light receiving sensor, the amount of stray light due to reflection between the light receiving sensor 50 and the optical filter 30 can be reduced. Furthermore, unlike when tilting the optical filter to suppress the generation of stray light, the generation of stray light can be suppressed, and measurement errors and an increase in the size of the optical system can be suppressed. Furthermore, the amount of stray light generated between the light receiving sensor 50 and the optical filter 30 can be reduced without requiring the optical system to be aberrated or the optical filter to be precisely positioned at the position of the first image.

[0026] Furthermore, according to this embodiment, it is preferable that the measurement optical system 1 satisfies the above conditional expression (1), which makes the spectral response nearly uniform over the entire measurement field, enabling more accurate measurements.

[0027] Furthermore, according to this embodiment, it is preferable that the measurement optical system 1 satisfies the above-mentioned conditional expression (2), which makes it possible to reduce the amount of stray light due to reflection between the sensor surface 51 and the optical filter 30.

[0028] Furthermore, according to this embodiment, the aperture AP of the diaphragm 42 has an overlapping area ratio of 50% or less with the inversion portion V, which is formed by rotating the aperture AP 180 degrees about the optical axis Ax1 of the rear group 43. As a result, the diaphragm 42 cuts off more than half of the light beam that is reflected by the sensor surface 51 and returns to the optical filter 30. Therefore, compared to when the optical filter 30 is located immediately before the light receiving sensor 50, for example, the amount of stray light generated by reflection between the light receiving sensor 50 and the optical filter 30 can be reduced to less than half.

[0029] Second Embodiment Fig. 6A is a schematic diagram of a photometric device 100B according to a second embodiment, and Fig. 6B is a diagram showing an example of a specific shape of the aperture 42B provided in the measurement optical system 1B of the photometric device 100B. In the following embodiments, differences from the first embodiment will be mainly described, and the same components as those in the first embodiment will be denoted by the same reference numerals, and their description will be omitted. As shown in Figs. 6A and 6B, the photometric device 100B according to the second embodiment differs from the first embodiment mainly in that the optical axes of the rear group and the light receiving sensor are offset parallel to the optical axis of the front group. Specifically, the photometric device 100B includes a measurement optical system 1B and a light receiving sensor 50B.

[0030] The measurement optical system 1B includes a relay optical system 40B instead of the relay optical system 40 in the first embodiment. The relay optical system 40B includes a diaphragm 42B and a rear group 43B instead of the diaphragm 42 and the rear group 43 in the first embodiment.

[0031] The aperture 42B has a circular opening AP. The center C of the opening AP is located on the first optical axis Ax0 of the measurement optical system 1B, in front of the rear group 43B. The rear group 43B and the light-receiving sensor 50B have second optical axes Ax1 that are offset parallel to the first optical axis Ax0. The distance between the second optical axis Ax1 and the first optical axis Ax0 is equal to the opening radius r of the opening AP. However, this distance only needs to be at least half the opening radius r of the opening AP, and preferably at least the opening radius r.

[0032] With respect to the position of the diaphragm 42B on the second optical axis Ax1, the measurement optical system 1B preferably satisfies the following conditional expression (3): -0.5 < d1 / fa < 0.5 (3) where d1 is the distance on the first optical axis Ax0 (second optical axis Ax1) from the front focal point f21 of the front group 41 to the first image f1 (the image of the measurement object surface OB formed by the objective optical system 20), and fa is the focal length of the front group 41 (see FIGS. 7A and 7B). Preferably, the measurement optical system 1B also satisfies the following conditional expression (3a): -0.25 < d1 / fa < 0.25 (3a)

[0033] The above conditional expressions (3) and (3a) define the distance from the front focal point f21 of the front group 41 of the relay optical system 40B to the first image. As shown in FIGS. 7A and 7B, when d1 / fa = 0, the light beam that exits the front group 41 and enters the aperture 42B is parallel. FIGS. 7C to 7E are schematic diagrams illustrating a case where the second optical axis Ax1 of the rear group 43 is shifted (translated) in the radial direction of the first optical axis Ax0 (a direction perpendicular to the first optical axis Ax0) to cut reflected light from the sensor surface 51 with the aperture 42. In FIG. 7C, the light beam that enters the aperture 42 is parallel, in FIG. 7D, it is diverging, and in FIG. 7E, it is converging. As shown in these figures, when the light beam that enters the aperture 42 is parallel, the reflected light can be completely cut off by setting [the shift amount of the second optical axis Ax1 of the rear group 43 = the aperture radius r of the aperture 42]. However, in the case of converging or diverging light, to completely cut off reflected light, it is necessary to make the following relationship: [shift amount of the second optical axis Ax1 of the rear group 43] > [aperture radius r of the diaphragm 42]. In other words, in this case, the shift amount of the second optical axis Ax1 of the rear group 43 becomes large, and the rear group 43 becomes large. Therefore, by satisfying the above conditional expressions (3) and (3a), the measurement optical system 1 can be made compact. Note that the measurement optical system 1 of the first embodiment may satisfy conditional expressions (3) and (3a).

[0034] The second embodiment described above also achieves the same effects as the first embodiment. Furthermore, according to the second embodiment, the second optical axis Ax1 of the rear group 43B and the first optical axis Ax0 located in front of it are parallel to each other, and the distance between them is equal to or greater than half the aperture radius r of the aperture AP. As a result, light reflected from the sensor surface 51B (shown by the thin dashed line in FIG. 6A ) is blocked by the light-shielding portion SH of the aperture 42B and does not return to the optical filter 30. This reduces the amount of stray light due to reflection between the light-receiving sensor 50B and the optical filter 30.

[0035] Furthermore, according to this embodiment, the measurement optical system 1 satisfies the above-mentioned conditional expression (3), which allows the measurement optical system 1 to be made compact.

[0036] Third Embodiment Fig. 8A is a schematic diagram of a photometric device 100C according to a third embodiment, and Fig. 8B is a diagram showing an example of a specific shape of a diaphragm 42C provided in a measurement optical system 1C of the photometric device 100C. As shown in Figs. 8A and 8B, the photometric device 100C according to the third embodiment differs from the first embodiment mainly in that the optical axes of the rear group and the light receiving sensor are inclined from the optical axis of the front group. Specifically, the photometric device 100C includes a measurement optical system 1C and a light receiving sensor 50C.

[0037] The measurement optical system 1C includes a relay optical system 40C instead of the relay optical system 40 in the first embodiment. The relay optical system 40C includes a diaphragm 42C and a rear group 43C instead of the diaphragm 42 and the rear group 43 in the first embodiment.

[0038] The aperture 42C has a circular opening AP. Its center C is located on the first optical axis Ax0 of the measurement optical system 1B, in front of the rear group 43B. Note that FIG. 8B shows the shape of the aperture 42C as viewed from a direction along the second optical axis Ax1 of the rear group 43B, which is tilted from the first optical axis Ax0, so the opening AP is elliptical. The second optical axis Ax1 of the rear group 43C and the light-receiving sensor 50C is tilted from the first optical axis Ax0. The distance between the intersection of the second optical axis Ax1 and the aperture 42C and the first optical axis Ax0 is equal to the opening radius r of the aperture AP. However, this distance only needs to be at least half the opening radius r of the aperture AP, and preferably greater than or equal to the opening radius r.

[0039] It is preferable that the measurement optical system 1C satisfy the following conditional expression (4): fb tan α / h < 1.0 (4), where fb is the focal length of the rear group 43C, α is the angle between the second optical axis Ax1 and the first optical axis Ax0, and h is the half-width of the sensor surface 51C. If the second optical axis Ax1 of the rear group 43C is significantly tilted beyond the upper limit of conditional expression (4), the rear group 43C will become large. In the case of Example 3 (see FIG. 11 ), which will be described later, α = 3.361°, h = 5.0, and fb = 17.132, and the value of the left side of conditional expression (4) is 0.201.

[0040] The third embodiment described above also achieves the same effects as the first embodiment. Furthermore, according to the third embodiment, the second optical axis Ax1 of the rear group 43C and the first optical axis Ax0 located in front of it are inclined relative to each other. The distance between the intersection of the second optical axis Ax1 of the rear group 43C and the aperture 42C and the first optical axis Ax0 is equal to or greater than half the aperture radius r of the aperture AP. As a result, light reflected from the sensor surface 51C (shown by the thin dashed line in FIG. 8A ) is blocked by the light-shielding portion SH of the aperture 42C and does not return to the optical filter 30. This reduces the amount of stray light due to reflection between the light-receiving sensor 50C and the optical filter 30.

[0041] Although one embodiment of the present disclosure has been described above, embodiments to which the present disclosure can be applied are not limited to the above-described embodiment. The present disclosure can be modified as appropriate without departing from the spirit and scope of the present disclosure.

[0042] For example, the above conditional expressions (1) to (3) may be satisfied by any of the measurement optical systems of the first to third embodiments. Furthermore, the measurement optical system may include other filters, such as an infrared cut filter, an ultraviolet cut filter, or an ND filter, depending on the required characteristics. Furthermore, the measurement optical system of the present disclosure may include at least an optical filter and a relay optical system (front group, aperture, and rear group).

[0043] Examples of the measurement optical system of the present disclosure are shown below. Figures 9 to 14 are optical path diagrams showing specific configuration examples of the measurement optical system of Examples 1 to 6.

[0044] The various numerical values ​​for Examples 1 to 6 are shown in Table 1 below. Symbols or terms in the table are as follows: fa: focal length of the front group [mm] fb: focal length of the rear group [mm] d1: distance on the optical axis (first optical axis) from the front focal point of the front group to the image of the surface to be measured [mm] da: distance on the optical axis (first optical axis) from the rear focal point of the front group to the diaphragm [mm] db: distance on the optical axis (first optical axis) from the front focal point of the rear group to the diaphragm [mm] Aperture radius of the diaphragm: aperture radius of the diaphragm [mm] Shift amount of the optical axis of the rear group: distance between the second optical axis of the rear group and the first optical axis on the front side (in the third example, the distance from the center of the diaphragm aperture to the intersection of the second optical axis of the rear group and the diaphragm surface) [mm] Tilt of the optical axis of the rear group: tilt angle of the second optical axis of the rear group with respect to the first optical axis on the front side [°]

[0045] Example 1 corresponds to the photometric device 100 and measurement optical system 1 according to the first embodiment. Examples 2, 4, and 5 correspond to the photometric device 100B and measurement optical system 1B according to the second embodiment. Example 3 corresponds to the photometric device 100C and measurement optical system 1C according to the third embodiment. Example 6 shows a photometric device 100D and measurement optical system 1D that do not include an objective optical system. In this case, the first image in the above embodiments is the position of (the image of) the measurement target surface.

[0046] When the measurement range is narrow, the configuration of Example 6, which omits the objective optical system, allows for a more compact and cost-effective device. On the other hand, when the measurement range is wide, the optical filter and relay optical system become correspondingly larger. When the measurement range is wide, providing an objective optical system, as in Examples 1 to 5, allows for a wider measurement range. The lateral magnification of the relay optical system may be 1x (fa = fb), a magnification system (fa < fb), or a reduction system (fa > fb). A magnification system reduces the intermediate image, making it easier to miniaturize the objective optical system and the front group of the relay optical system. Inserting and removing an optical filter allows for a smaller size of the optical filter, which also shortens measurement time. A reduction system is advantageous for miniaturizing the rear relay group and allows for the use of a small light-receiving sensor. The magnification of the relay optical system can be optimized to meet the required characteristics.

[0047] As described above, the present disclosure is useful for providing a measurement optical system and a photometric device that can reduce the amount of stray light.

[0048] 100, 100B, 100C, 100D Photometric device 1, 1B, 1C, 1D Measuring optical system 20 Objective optical system 30 Optical filter 40, 40B, 40C, 40D Relay optical system 41, 41D Front group 42, 42B, 42C, 42D Aperture 43, 43B, 43C, 43D Rear group 50, 50B, 50C, 50D Light-receiving sensor 51, 51B, 51C, 51D Light-receiving surface (sensor surface) Ax0 First optical axis Ax1 Second optical axis (optical axis of rear group) f1 Image of measurement object surface formed by objective optical system (first image) f21 Front focus of front group f22 Rear focus of front group f31 Front focus of rear group OB Measurement object surface AP Aperture C Center of aperture r Aperture radius SH Light-shielding part V Inverted part

Claims

1. A measurement optical system having, in order from the object side, an optical filter, a front group, an aperture, and a rear group, the aperture being located at the rear focus of the front group and the front focus of the rear group, and an opening being formed asymmetrically about the optical axis of the rear group within a plane including the aperture.

2. The measuring optical system according to claim 1, which satisfies the following condition: −0.35<da / fa<0.35 (1), where da is the distance on the optical axis from the rear focal point of the front group to the stop, and fa is the focal length of the front group.

3. The measuring optical system according to claim 1, which satisfies the following condition: -0.35<db / fb<0.35 (2), where db is the distance on the optical axis from the front focus of the rear group to the stop, and fb is the focal length of the rear group.

4. The measurement optical system according to claim 1, wherein the aperture of the diaphragm has an overlapping area ratio of 50% or less with respect to an inverted portion obtained by rotating the aperture 180 degrees around the optical axis of the rear group.

5. The measurement optical system according to claim 1, wherein the aperture of the diaphragm is formed in a circular shape, and the optical axis of the rear group and the optical axis in front of the rear group are parallel to each other and the distance between them is equal to or greater than half the aperture radius of the aperture.

6. The measurement optical system according to claim 1, wherein the aperture has a circular opening, the optical axis of the rear group and the optical axis in front of the rear group are inclined relative to each other, and the distance between the intersection of the optical axis of the rear group and the aperture and the front optical axis is equal to or greater than half the aperture radius of the aperture.

7. The measuring optical system according to claim 1, which satisfies the following condition: -0.5 < d1 / fa < 0.5 (3) where d1 is the distance on the optical axis from the front focal point of the front group to the image of the surface to be measured, and fa is the focal length of the front group. The measuring optical system according to claim 1.

8. The measurement optical system according to claim 1, further comprising an objective optical system arranged closer to the object side than the optical filter.

9. The measurement optical system according to claim 1, wherein the optical filter is an interference filter having a substrate made of glass or resin and a multilayer film formed on the surface of the substrate.

10. The measurement optical system according to claim 1, wherein the optical filters are three switchable interference filters that selectively transmit light of specific wavelengths corresponding to tristimulus values.

11. The measurement optical system according to claim 1, wherein the optical filter is a linear variable filter whose transmission wavelength band changes depending on the incident position of a light beam, and is placed at the position of the image of the surface to be measured.

12. A photometric device comprising: a measuring optical system according to any one of claims 1 to 11; and a light-receiving sensor arranged closer to the image side than the rear group.

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