Optical property measurement optical system and optical property measurement device

Abstract

To provide an optical characteristic measuring optical system and an optical characteristic measuring apparatus that can obtain a two-dimensional image close to a viewed image as well as measuring optical characteristics of an object to be measured.SOLUTION: An optical characteristic measuring optical system has a first optical system (11) which captures an infinite conjugate image and a second optical system (12) which captures a conjugate image of an object to be measured. The first optical system (11) and second optical system (12) share a first lens group (G1), and are arranged on two optical axes divided by an optical element (5) deflecting an optical axis respectively to constitute one measurement optical system. Further, the second optical system (12) has its aperture diaphragm arranged nearby intermediate image formation. Here, -1.0<Δp / f1<3.0 holds for the distance Δp from an image-side paraxial focus of a first lens group (G1) to the aperture diaphragm and the focal length f1 of the first lens group.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical property measurement optical system and an optical property measurement device.

Background Art

[0002] In recent years, in ICT products typified by smartphones or industrial products such as automobiles, coating technologies and decoration technologies have been evolving due to the need to improve design. For example, coating technologies that exhibit complex reflection characteristics, such as metallic coatings for automobile exteriors, which look different depending on the viewing angle or the direction of incident light, have been developed.

[0003] When evaluating the appearance of a surface having such reflection characteristics, it is difficult to say that the appearance of the surface can be sufficiently evaluated because conventional colorimeters or gloss meters can only evaluate under certain conditions. For the evaluation of complex reflection characteristics, it is necessary to evaluate the BRDF (Bidirectional Reflectance Distribution Function), which represents the reflection angle characteristics depending on the illumination angle or the light receiving angle. By evaluating the BRDF, the difference in appearance depending on the way light hits and the observation direction can be quantitatively evaluated.

[0004] Furthermore, in the evaluation of metallic coatings, there is a demand to evaluate the distribution of the brightening material (such as aluminum flakes) contained in the paint. For this reason, it is required not only to be able to evaluate the reflection characteristics of the coating surface, but also to be able to acquire a two-dimensional image of the coating surface.

[0005] A goniophotometer is commonly used as a device for measuring BRDF. However, when measuring BRDF, it is necessary to move the illumination unit and the measurement unit of the goniophotometer. Therefore, there are problems in measuring BRDF with a goniophotometer, such as 1) it takes time to measure, 2) the measurement of discrete illumination angles and light-receiving angles, and 3) the measuring device is large. There is a need for a measuring instrument that can measure BRFD in a short time and is small in size. Furthermore, it is also required that the measuring instrument can acquire a two-dimensional image of the measurement object.

[0006] As an invention corresponding to these requirements, International Publication No. 2006 / 050978 (Patent Document 1) discloses a reflection angle characteristic device using a relay-type Fourier transform optical system. According to this invention, the BRDF of the measurement object can be measured in one shot. Furthermore, Example 4 (Figure 5) of International Publication No. 2006 / 050978 discloses an optical system capable of acquiring a two-dimensional image of the measurement object surface.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the device disclosed in International Publication No. 2006 / 050978, there is a problem that the image of the measurement object acquired by the optical system for two-dimensional image acquisition deviates from the appearance when a person visually observes the measurement object. According to International Publication No. 2006 / 050978, a lens 3 having a positive power and a lens 13 having a positive power are arranged so as to sandwich an intermediate imaging position (Fourier plane 9). These lenses 3 and 13 are common lenses between the BRDF measurement optical system and the optical system for two-dimensional image acquisition. Also, the intermediate imaging position corresponds to the focal position of the lens 3.

[0009] If there is an aperture stop at the focal position of lens 3, the chief ray becomes parallel to the optical axis on the measurement object side. Therefore, the optical system for two-dimensional image acquisition becomes a so-called object-side telecentric optical system. However, according to WO 2006 / 050978, the aperture stop in the optical system for two-dimensional image acquisition is located at a position far from the intermediate imaging position. As a result, since the optical system for two-dimensional image acquisition is not an object-side telecentric optical system, the observation angle greatly inclines at the peripheral part of the measurement area. On the other hand, when a person looks at an object, the person generally sees light that is nearly parallel to the line of sight. Therefore, the image captured by the optical system disclosed in WO 2006 / 050978 deviates from the appearance when viewed visually.

[0010] The present invention has been made in view of such problems, and an object thereof is to provide an optical property measurement optical system and an optical property measurement apparatus capable of acquiring a two-dimensional image close to visual observation in addition to measuring the optical properties of a measurement object.

Means for Solving the Problems

[0011] In order to solve the above problems, an optical property measurement optical system according to an aspect of the present invention is an optical property measurement optical system for measuring reflected light from a measurement object, and includes a first optical system and a second optical system that measure a common measurement object. The first optical system includes, in order from the object side, a first lens group having positive power, a second lens group having positive power, an aperture stop, a first imaging device, and an illumination light source, and is a relay optical system that forms an intermediate image between the first lens group and the second lens group. The aperture stop is arranged in the second lens group so that its entrance pupil is on the object side of the first lens group. The measurement object is arranged near the entrance pupil of the aperture stop. The first imaging device is arranged conjugate with the object side infinity. The second optical system includes, in order from the object side, a first lens group common to the first optical system, a third lens group having positive power, and a second imaging device. The second imaging device is arranged at a position conjugate with the measurement object. Let the distance in the optical axis direction from the paraxial focal point on the image side of the first lens group to the aperture stop be Δp, and the focal length of the first lens group be f1. Then, the following conditional expression (1) is satisfied: -1.0 < Δp / f1 < 3.0 ···(1) The first optical system and the second optical system share the first lens group. The optical property measurement optical system further has an optical element that deflects the optical axis on the image side of the first lens group. The optical axis is branched into two directions by the optical element. The first optical system is arranged in the first direction of the two directions, and the second optical system is arranged in the second direction of the two directions.

[0012] Preferably, the optical property measurement optical system includes an intermediate imaging by the first lens group, another optical element that deflects the optical axis between the intermediate imaging and the first imaging element, and another optical element that can emit light from an arbitrary minute region on the surface at a position conjugate to the other object-side infinite distance where the optical axis is deflected.

[0013] Preferably, when the distance between the first lens group and the second lens group is L and the effective diameter of the largest lens in the first lens group is φ1, the following conditional expression (2) is satisfied.

[0014] 0.4 < L / φ1 < 3.0 ···(2) Preferably, in the first optical system, when the angle of the light ray reflected from the center of the measurement object is θ and the position where the light ray reaches the imaging element is Y(θ), θ and Y(θ) are in a substantially proportional relationship. When the maximum image height is Ymax and the maximum light ray angle is θmax, the following conditional expression (3) -0.1 < (Y(θmax / 2) - Ymax / 2) / Ymax < 0.1 ···(3) is satisfied.

[0015] Preferably, the optical property measurement optical system further has a light source that is arranged around the aperture stop of the second optical system and can illuminate the measurement object when imaging the measurement object by the second optical system.

[0016] Preferably, when the back focus of the first optical system is fB and the effective diameter of the most image-side surface of the second lens group is φ2, fB / φ2 satisfies the following conditional expression (4).

[0017] 1.0 < fB / φ2 < 3.0 ···(4) In another aspect of the present invention, the optical property measurement apparatus includes the optical property measurement optical system described in any of the above, and has a function of measuring the optical properties of the measurement object and a function of imaging the measurement object.

Effects of the Invention

[0018] According to the present disclosure, it is possible to provide an optical property measurement optical system and an optical property measurement apparatus capable of acquiring a two-dimensional image similar to visual observation in addition to measuring the optical properties of a measurement object.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6A

Figure 6B

Figure 7

Modes for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The optical property measurement optical system according to the embodiments of the present invention includes a first optical system that images an infinite conjugate image and a second optical system that images a conjugate image of a measurement object. The first optical system and the second optical system share a first lens group and are respectively arranged on two optical axes separated by an optical element that deflects the optical axis, and are configured as one measurement optical system.

[0021] Furthermore, the aperture stop of the second optical system is arranged near the intermediate image formation. Specifically, if the distance in the optical axis direction from the paraxial focal point on the image side of the first lens group to the aperture stop is Δp and the focal length of the first lens group is f1, then Δp / f1 satisfies the following conditional expression.

[0022] -1.0 < Δp / f1 < 3.0 By satisfying the above conditional expression, the aperture stop of the second optical system is arranged near the intermediate image formation, so that the observation angle of the second optical system can be made closer to parallel. Therefore, in addition to measuring the optical properties of the measurement object, it is possible to acquire a two-dimensional image close to visual observation.

[0023] More specifically, the optical property measurement optical system according to the embodiments of the present invention is an optical property measurement optical system for measuring the reflected light from a measurement object, and includes a first optical system and a second optical system for measuring a common measurement object. The first optical system includes, in order from the object side, a first lens group having a positive power, a second lens group having a positive power, an aperture stop, a first imaging element, and an illumination light source, and is a relay optical system that forms an intermediate image between the first lens group and the second lens group. The aperture stop is arranged in the second lens group so that its entrance pupil is on the object side of the first lens group. The measurement object is arranged near the entrance pupil of the aperture stop. The first imaging element is arranged conjugate with the object side infinity. The second optical system includes, in order from the object side, a first lens group common to the first optical system, a third lens group having a positive power, and a second imaging element. The second imaging element is arranged at a position conjugate with the measurement object.

[0024] Let Δp be the distance in the optical axis direction from the paraxial focus on the image side of the first lens group to the aperture stop, and f1 be the focal length of the first lens group. Then, the following conditional expression is satisfied.

[0025] -1.0 < Δp / f1 < 3.0 ···(1) The first optical system and the second optical system share the first lens group. The optical characteristic measurement optical system further has an optical element that deflects the optical axis on the image side of the first lens group. The optical axis is branched into two directions by the optical element. The first optical system is arranged in the first direction of the two directions, and the second optical system is arranged in the second direction of the two directions.

[0026] Since the first optical system has the above configuration, the first imaging element is arranged at an infinite conjugate position, and the first optical system is an optical system (i.e., a Fourier transform optical system) in which the coordinates on the imaging surface of the first imaging element are determined according to the light ray angle incident from the object side. Due to this characteristic, the angular distribution of the reflected light from the measurement object can be imaged on the imaging surface of the first imaging element. Furthermore, by arranging the aperture stop so that the entrance pupil is located closest to the object side and arranging the measurement object near the entrance pupil, it is possible to measure substantially the same position for all reflection angles.

[0027] Since the first lens group images very wide-angle light rays of about 80°, it is difficult to correct various aberrations, particularly the field curvature and distortion aberration that increase with wide angles, only with the first lens group. By using the first optical system as a relay optical system, the aberrations generated in the first lens group can be corrected by the second lens group, so that good aberration performance can be maintained.

[0028] Furthermore, by configuring the second optical system as described above, the second imaging element can capture a two-dimensional image of the measurement target. By arranging the aperture stop so as to satisfy the conditional expression (1), the aperture stop can be arranged near the intermediate imaging position and the entrance pupil is separated from the measurement target, so that the second optical system has a configuration close to object-side telecentricity. In an object-side telecentric optical system, the chief ray becomes parallel to the optical axis on the measurement target side. Since a person generally sees light that is nearly parallel to the line of sight when looking at an object, it becomes possible to acquire a two-dimensional image similar to visual observation.

[0029] Furthermore, the first optical system and the second optical system share the first lens group, the optical axis is branched into two by an optical element, and the first optical system and the second optical system are arranged in respective directions, whereby two different optical systems can be configured for the same measurement position. As a result, the reflection angle distribution and the two-dimensional image can be acquired simultaneously or continuously, enabling measurement in a short time.

[0030] More preferably, the value Δp / f1 satisfies the following conditional expression (1)'. -0.8 < Δp / f1 < 2.0 ···(1)' Even more preferably, the value Δp / f1 satisfies the following conditional expression (1)''.

[0031] -0.6 < Δp / f1 < 1.5 ···(1)'' In an embodiment of the present invention, the optical property measurement optical system may include another optical element that deflects the optical axis between the intermediate imaging by the first lens group and the first imaging element, and a light source that can emit light to an arbitrary minute region on the surface at a position conjugate to the other object-side infinity with the optical axis deflected by the other optical element.

[0032] Since the optical system on the object side also functions as an illumination optical system rather than an additional optical element, there is no need to separately provide an optical system for illumination. Therefore, simplification of the optical system can be achieved. Furthermore, by having a light source capable of emitting light from an arbitrary minute area on the surface at a position conjugate to infinity on the object side, the measurement target can be illuminated with parallel light having an angle corresponding to the position where the light is emitted. As a result, since the measurement target can be illuminated at an arbitrary angle, it becomes possible to measure the BRDF in more detail.

[0033] In an embodiment of the present invention, when the distance between the first lens group and the second lens group is L and the effective diameter of the largest lens in the first lens group is φ1, it is preferable to satisfy the following conditional expression (2).

[0034] 0.4 < L / φ1 < 3.0 ···(2) When the value of L / φ1 exceeds the lower limit of the conditional expression (2), the distance between the first lens group and the second lens group can be sufficiently increased, so that it becomes easier to arrange an optical element for deflecting the optical axis and an aperture stop between the first lens group and the second lens group. On the other hand, when the value of L / φ1 is below the upper limit of the conditional expression (2), it is possible to avoid the overall optical length becoming unnecessarily large, so that an increase in the size of the measuring device can be prevented.

[0035] More preferably, the value of L / φ1 satisfies the following conditional expression (2)'. 0.5 < L / φ1 < 2.5 ···(2)' Even more preferably, the value of L / φ1 satisfies the following conditional expression (2)''.

[0036] 0.6 < L / φ1 < 2.0 ···(2)'' Also, in the first optical system, when the angle of the light ray reflected from the center of the measurement target is θ and the position where the light ray reaches the imaging element is Y(θ), θ and Y(θ) are in a substantially proportional relationship. When the maximum image height is Ymax and the maximum light ray angle is θmax, the following conditional expression (3) -0.1 < (Y(θmax / 2) - Ymax / 2) / Ymax < 0.1 ···(3) is preferably satisfied.

[0037] θ and Y(θ) satisfy a substantially proportional relationship, and by satisfying the upper and lower limits of the range determined by conditional expression (3) for (Y(θmax / 2) - Ymax / 2) / Ymax, the angular distribution of the reflection from the measurement target is imaged substantially as it is as the illuminance distribution on the imaging element. Therefore, the correction calculation for converting the position on the imaging element to the angle of the reflection from the measurement target becomes easy.

[0038] More preferably, (Y(θmax / 2) - Ymax / 2) / Ymax satisfies the following conditional expression (3)'.

[0039] -0.08 < (Y(θmax / 2) - Ymax / 2) / Ymax < 0.08 ···(3)' Even more preferably, (Y(θmax / 2) - Ymax / 2) / Ymax satisfies the following conditional expression (3)''.

[0040] -0.05 < (Y(θmax / 2) - Ymax / 2) / Ymax < 0.05 ···(3)'' In an embodiment of the present invention, the optical characteristic measurement optical system may be disposed around the aperture stop of the second optical system and have a light source capable of illuminating the measurement target during imaging of the measurement target by the second optical system. Thereby, since the entire imaging range of the second optical system can be uniformly illuminated, an image closer to visual observation can be obtained.

[0041] In an embodiment of the present invention, assuming that the back focus of the first optical system is fB and the effective diameter of the most image-side surface of the second lens group is φ2, it is preferable that fB / φ2 satisfies the following conditional expression (4).

[0042] 1.0 < fB / φ2 < 3.0 ···(4) The conditional expression (4) is a condition for arranging an optical element between the intermediate imaging by the first lens group and the first image sensor, and in the back focus section of the first optical system. By satisfying the conditional expression (4), all of the first optical system can also be used as an illumination optical system, so that an additional lens becomes unnecessary. Therefore, the configuration of the optical system can be further simplified.

[0043] When fB / φ2 exceeds the lower limit of the conditional expression (4), the back focus becomes long. Thereby, it is possible to minimize the vignetting of light rays and to arrange an optical element. On the other hand, when fB / φ2 is below the upper limit of the conditional expression (4), it is possible to avoid the overall optical length becoming unnecessarily large, so that the measuring device can be miniaturized.

[0044] More preferably, fB / φ2 satisfies the following conditional expression (4)'. 1.3 < fB / φ2 < 2.8 ···(4)' Even more preferably, fB / φ2 satisfies the following conditional expression (4)''.

[0045] 1.6 < fB / φ2 < 2.6 ···(4)'' In an embodiment of the present invention, it is preferable that the optical property measuring device includes the optical property measuring optical system described in any of the above, and has a function of measuring the optical property of a measurement object and a function of imaging the measurement object. Thereby, in addition to measuring the optical property (reflection property) of the measurement object, it becomes possible to acquire a two-dimensional image close to visual observation. In addition, it is possible to avoid the optical property measuring device from becoming large-sized.

[0046] (Configuration of the optical property measuring optical system) The configuration of the optical property measuring optical system according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6B. FIGS. 1 to 6B are diagrams each showing the configuration of the optical property measuring optical system according to the first to third embodiments. In FIGS. 1 to 6B, the first to third embodiments are denoted as "EX1", "EX2", and "EX3", respectively.

[0047] (First Embodiment) As shown in FIGS. 1 to 2B, the optical property measurement optical system according to the first embodiment includes a first optical system 11 and a second optical system 12 that measure a common measurement target M. FIG. 2A is a diagram showing only the first optical system 11, and FIG. 2B is a diagram showing only the second optical system 12.

[0048] The first optical system 11 includes, in order from the object side, a first lens group G1 having positive power, a second lens group G2 having positive power, an aperture stop S 2 and a first image sensor (not shown) and an illumination light source (not shown).

[0049] The first lens group G1 consists of lenses L1, L2, and L3. The second lens group G2 consists of lenses L4, L5, L6, L7, L8, and L9. The first optical system 11 is a relay optical system that forms an intermediate image between the first lens group G1 and the second lens group G2.

[0050] The aperture stop S 2 is arranged in the second lens group G2. The aperture stop S For 2 The entrance pupil is directed toward the object side of the first lens group G1. The measurement target M is Entrance pupil arranged in the vicinity of.

[0051] The first image sensor is arranged conjugate with the object side infinity. Therefore, the first optical system 11 is an optical system that images the infinite conjugate image of the measurement target M. In FIG. 1, an image plane IM1 is shown instead of the first image sensor (the same applies to the figures described later). A light shielding stop S3 is provided in front of the first image sensor (image plane IM1).

[0052] The second optical system 12 includes, in order from the object side, the first lens group G1, a third lens group G3 having positive power, and a second image sensor (not shown). The first lens group G1 is common to the first optical system 11. The third lens group G3 consists of a lens L11, a lens L12, and L13.

[0053] The second imaging element is arranged at a position conjugate to the measurement object. Therefore, the second optical system images the conjugate image of the measurement object M. In FIG. 1, an image plane IM2 is shown instead of the second imaging element.

[0054] The aperture stop S1 is arranged near the intermediate imaging position so as to satisfy the conditional expression (1). In the first embodiment, the aperture stop S1 is located on the object (measurement object M) side of the intermediate imaging position. Thereby, the second optical system 12 has a configuration close to object-side telecentricity. Therefore, it becomes possible to acquire a two-dimensional image close to visual observation.

[0055] The optical property measurement optical system further includes an optical element 5 that deflects the optical axis AX on the image side of the first lens group G1. Specifically, the optical element 5 branches the optical axis AX into an optical axis AX1 and an optical axis AX2. The direction of the optical axis AX1 and the direction of the optical axis AX2 are different from each other. The first optical system 11 is arranged in the direction of the optical axis AX1, and the second optical system 12 is arranged in the direction of the optical axis AX2.

[0056] The type of the optical element 5 is not particularly limited. For example, a beam splitter, a half mirror, or the like can be applied as the optical element 5. The optical element 5 may be a mirror having the size of the aperture of the aperture stop S1 and being insertable and removable. This mirror is removed during imaging by the first optical system 11 and inserted during imaging by the second optical system 12. Alternatively, the optical element 5 may be a beam splitter having an enhanced reflection film formed on the size of the aperture of the aperture stop S1. In FIG. 1, the aperture stop S1 and the optical element 5 are shown at substantially the same position. However, when the optical element 5 is an insertable and removable mirror, the optical element 5 and the aperture stop S1 may be arranged so as not to prevent the movement of the optical element 5.

[0057] The optical property measurement optical system may further include an optical element 7 and a light source 8. The optical element 7 deflects the optical axis AX1 between the intermediate imaging by the first lens group G1 and the first image sensor. In FIG. 1, the optical axis AX3 corresponds to the optical axis deflected by the optical element 7 from the optical axis AX1. The position of the light source 8 is a position conjugate with the object-side infinity on the optical axis AX1 (i.e., the optical axis AX3) deflected by the optical element 7. Although the optical element 7 and the light source 8 are shown in FIG. 1, it should be noted that their positions in FIG. 1 may not necessarily be accurate.

[0058] The optical element 7 may be, for example, a beam splitter, a half mirror, or the like. The light source 8 is an element capable of emitting light from an arbitrary minute region on the surface. Although not particularly limited, for example, the light source 8 may be a microdisplay.

[0059] The optical property measurement optical system may further include a light source 9 disposed around the aperture stop S1 of the second optical system 12 and illuminating the measurement object during imaging of the measurement object by the second optical system 12. The light source 9 may be, for example, a ring illumination. The light source 9 uniformly illuminates the entire imaging range of the second optical system 12. Although the light source 9 is shown in FIG. 1, it should be noted that the position of the light source 9 in FIG. 1 may not necessarily be accurate.

[0060] According to the first embodiment, with the above configuration, in addition to measuring the optical properties of the measurement object, it is possible to acquire a two-dimensional image similar to a visual image.

[0061] (Second Embodiment) As shown in FIGS. 3 to 4B, the optical property measurement optical system according to the second embodiment includes a first optical system 11 and a second optical system 12 that measure a common measurement object M. FIG. 4A is a diagram showing only the first optical system 11, and FIG. 4B is a diagram showing only the second optical system 12.

[0062] The first optical system 11 includes, in order from the object side, a first lens group G1 having positive power, a second lens group G2 having positive power, and an aperture stop S 2It consists of a first imaging device (not shown) and an illumination light source (not shown).

[0063] The first lens group G1 consists of lenses L1, L2, L3, and L4. The second lens group G2 consists of lenses L5, L6, L7, L8, and L9. In this regard, the second embodiment is different from the first embodiment.

[0064] The aperture stop S1 is arranged near the intermediate imaging position so as to satisfy the conditional expression (1). In the second embodiment, the aperture stop S1 is located on the object (measurement target M) side with respect to the intermediate imaging position. Note that the aperture stop S1 is located on the object (measurement target M) side with respect to the optical element 5. In this regard, the second embodiment is different from the first embodiment. However, since the aperture stop S1 is arranged so as to satisfy the conditional expression (1), similar to the first embodiment, the second optical system 12 has a configuration close to object-side telecentricity. Therefore, also in the second embodiment, it is possible to acquire a two-dimensional image close to visual observation.

[0065] In the second embodiment, the aperture stop S1 and the optical element 5 are inserted and removed together. During imaging by the first optical system 11, both the aperture stop S1 and the optical element 5 are retracted from the optical path. During imaging by the second optical system 12, both the aperture stop S1 and the optical element 5 are inserted. In the second embodiment, a beam splitter or a mirror can be used for the optical element 5.

[0066] Regarding other configurations of the optical property measurement optical system according to the second embodiment, since they are the same as the configuration of the optical property measurement optical system according to the first embodiment, the following description will not be repeated. Also in the second embodiment, in addition to measuring the optical properties of the measurement target, it is possible to acquire a two-dimensional image close to visual observation. Although the optical element 7, the light source 8, and the light source 9 are not shown in FIG. 3, these elements can also be added in the optical property measurement optical system according to the second embodiment.

[0067] (Third Embodiment) As shown in FIGS. 5 to 6B, the optical property measurement optical system according to the third embodiment includes a first optical system 11 and a second optical system 12 that measure a common measurement target M. FIG. 6A is a diagram showing only the first optical system 11, and FIG. 6B is a diagram showing only the second optical system 12.

[0068] The first optical system 11 includes, in order from the object side, a first lens group G1 having a positive power, a second lens group G2 having a positive power, an aperture stop S 2 a first imaging element (not shown), and an illumination light source (not shown). Similar to the first embodiment, the first lens group G1 includes lenses L1, L2, and L3. The second lens group G2 includes lenses L4, L5, L6, L7, L8, and L9.

[0069] In the third embodiment, an opening formed in the housing 15 of the first optical system 11 is used as the aperture stop S1. The aperture stop S1 is arranged in the vicinity of the intermediate imaging position so as to satisfy the conditional expression (1). In the third embodiment, the aperture stop S1 is located on the image side with respect to the intermediate imaging position. The aperture stop S1 is arranged on the image side with respect to the optical element 5. Specifically, the aperture stop S1 is arranged on the second optical axis (optical axis AX2). In these respects, the third embodiment is different from the first and second embodiments. However, since the aperture stop S1 is arranged so as to satisfy the conditional expression (1), similar to the first and second embodiments, the second optical system 12 has a configuration close to object-side telecentricity. Therefore, also in the third embodiment, it is possible to acquire a two-dimensional image close to visual observation. In the third embodiment, a beam splitter or an insertable / removable mirror can be used as the optical element 5. When the optical element 5 is an insertable / removable mirror, the optical element 5 is retracted from the optical path during imaging by the first optical system 11 and inserted during imaging by the second optical system 12.

[0070] Regarding other configurations of the optical property measurement optical system according to the third embodiment, since they are the same as the configurations of the optical property measurement optical systems according to the first and second embodiments, the following description will not be repeated. Also in the third embodiment, in addition to measuring the optical properties of the measurement target, it is possible to acquire a two-dimensional image close to visual observation. Although the optical element 7, the light source 8, and the light source 9 are not shown in FIG. 5, these elements can also be added in the optical property measurement optical system according to the third embodiment.

Example

[0071] Hereinafter, the configuration and the like of the optical property measurement optical system according to the embodiment of the present invention will be described more specifically with reference to the construction data of the examples and the like. Examples 1 to 3 (EX1 to 3) given here are numerical examples corresponding to the first to third embodiments described above, and the lens configuration diagrams (FIGS. 1 to 6B) representing the first to third embodiments respectively show the optical configurations (lens arrangements, lens shapes, etc.) of the corresponding Examples 1 to 3.

[0072] In the construction data of each example, as surface data, in order from the left column, the surface number, radius of curvature (mm), axial surface interval (mm), refractive index with respect to the d-line (wavelength 587.56 nm), Abbe number with respect to the d-line, and effective radius (mm) are shown. Note that "inf" in the table is an abbreviation of "infinity".

[0073] [Numerical Example 1] <The First Optical System> The lens data and characteristics (various values) of the first optical system are shown in Table 1 and Table 2. Note that the surface numbers in Table 1 are assigned in order from the object side (the same applies to the tables described later).

[0074]

Table 1

[0075]

Table 2

[0076] <Second optical system> The lens data and characteristics (various values) of the second optical system are shown in Tables 3 and 4.

[0077] [Table 3]

[0078] [Table 4]

[0079] [Numerical Example 2] <First optical system> The lens data and characteristics (various values) of the first optical system are shown in Tables 5 and 6.

[0080] [Table 5]

[0081] [Table 6]

[0082] <Second optical system> The lens data and characteristics (various values) of the second optical system are shown in Tables 7 and 8.

[0083] [Table 7]

[0084] [Table 8]

[0085] [Numerical Example 3] <First optical system> The lens data and characteristics (various values) of the first optical system are shown in Tables 9 and 10.

[0086]

Table 9

[0087]

Table 10

[0088] <Second Optical System> The lens data and characteristics (various values) of the second optical system are shown in Table 11 and Table 12.

[0089]

Table 11

[0090]

Table 12

[0091] (Configuration of Optical Characteristic Measuring Device) FIG. 7 is a schematic configuration diagram of an optical characteristic measuring device including an optical characteristic measuring optical system according to an embodiment of the present invention. As shown in FIG. 7, the optical characteristic measuring device 100 includes an optical characteristic measuring optical system 101. The optical characteristic measuring optical system 101 has a first optical system 11 and a second optical system 12. The optical characteristic measuring optical system 101 can have the configuration of the optical system according to any one of the first to third embodiments.

[0092] The first optical system 11 has an illumination device 3, a first lens group G1, an aperture stop S1, a second lens group G2, and a first imaging element 21. The illumination device 3 is a device for illuminating the measurement object M. Further, the first optical system 11 can have the optical elements 7 and the light source 8 shown in FIG. 1.

[0093] The second optical system 12 includes a first lens group G1, a third lens group G3, an optical element 5, and a second imaging element 22. The first lens group G1 is common to the first optical system 11 and the second optical system 12. Note that the second optical system 12 may have a light source 9 shown in FIG. 1.

[0094] The optical property measurement apparatus 100 further includes a control unit 50, an input unit 51, an output unit 52, an IF (interface) unit 53, and a storage unit 54. The control unit 50 controls the optical property measurement apparatus 100. For example, the control unit 50 processes an image signal from the first imaging element 21. Thereby, the control unit 50 obtains the BRDF. Further, the control unit 50 processes an image signal from the second imaging element 22 to generate image data of the measurement object M.

[0095] The input unit 51 is connected to the control unit 50. For example, the input unit 51 is a device that inputs various commands such as a command for instructing the measurement object M and various setting information necessary for measuring the optical properties into the optical property measurement apparatus 100.

[0096] The output unit 52 is connected to the control unit 50. The output unit 52 outputs commands and data input by the input unit 51 under the control of the control unit 50. Further, the output unit 52 outputs the optical property (reflection property) of the measurement object M measured by the optical property measurement apparatus 100.

[0097] For example, the output unit 52 may be a display or a printer. When the output unit 52 is a display, the output unit 52 displays an image of the measurement object M photographed by the optical property measurement apparatus 100 in addition to the optical property of the measurement object M. The input unit 51 and the output unit 52 may be realized by a touch panel.

[0098] The IF unit 53 is connected to the control unit 50. The IF unit 53 is a circuit that performs data input / output with an external device under the control of the control unit 50. The standard for data communication is not limited to a specific standard.

[0099] The storage unit 54 is connected to the control unit 50. The storage unit 54 is controlled by the control unit 50 to store various predetermined programs and various predetermined data. The programs stored in the storage unit 54 can include, for example, a control program for controlling each part of the optical property measurement device 100, an arithmetic program for calculating the reflection property (BRDF), and the like. Further, the storage unit 54 stores, for example, the image data of the measurement object M acquired by the first image sensor 21 and the image data of the measurement object M acquired by the second image sensor 22.

[0100] Also, the above embodiments can be variously modified. Modification examples included in the embodiments of the present invention are shown below.

[0101] (1) In the optical property measurement device 100 according to the embodiment of the present invention, the BRDF may be measured for each wavelength.

[0102] For this reason, it is preferable that the illumination device 3 (light source) included in the first optical system 11 can emit light at a plurality of different spectra. Alternatively, the first image sensor 21 of the first optical system 11 may be able to separately receive a plurality of different spectra. The first image sensor 21 may be, for example, an RGB sensor. In front of the first image sensor 21, filters having a plurality of different band-pass characteristics may be arranged so as to be replaceable.

[0103] (2) In the optical property measurement device 100 according to the embodiment of the present invention, a configuration for increasing the illumination light amount and the received light amount may be adopted.

[0104] For example, a surface light source may be adopted as the illumination device 3 of the first optical system 11, and a microlens array may be disposed on the object side of the surface light source. For example, a microdisplay can be used as the light source for the illumination device 3. However, since the microdisplay has broad light distribution characteristics, only a part of the light emission amount of the microdisplay can be utilized as illumination light. By combining the microlens array with the microdisplay, directivity can be imparted to the light, so that the utilization efficiency of the light emitted from the microdisplay can be increased.

[0105] Alternatively, the optical element 5 that branches the optical axes of the first optical system 11 and the second optical system 12 may be a mirror arranged to be insertable and removable on its optical axis. If the optical element 5 that branches the optical axes is, for example, a half mirror with a reflectivity of 50%, the amount of illumination light is halved by the half mirror. When the reflected light passes through the half mirror, the amount of light is further halved. As a result, the amount of received light becomes 1 / 4 or less of the amount of illumination light. Therefore, the optical element 5 may be a mirror that is insertable and removable on the optical axis as described above. When measuring the BRDF by the first optical system 11, the mirror is removed, and when imaging by the second optical system 12, the mirror is inserted. Thereby, since the loss of the amount of light as described above can be substantially eliminated, the amount of illumination light and the amount of received light can be increased.

[0106] (3) In the optical property measurement apparatus 100 according to the embodiment of the present invention, a configuration for shortening the measurement time may be adopted.

[0107] For example, the illumination device 3 may be configured to emit light simultaneously from light emission positions corresponding to a plurality of angles. The illumination device 3 may be a surface light emitting element configured to emit light simultaneously from an arbitrary plurality of regions on the light emitting surface.

[0108] When the glossiness of the measurement target increases, the diffusibility of the reflected light decreases. However, by simultaneously emitting light from the light emission positions of the illumination device 3 corresponding to a plurality of angles, the reflection characteristics at a plurality of angles can be measured simultaneously. Thereby, the measurement time can be shortened.

[0109] (4) In the optical property measuring apparatus 100 according to the embodiment of the present invention, a configuration for performing measurements corresponding to various industrial standards may be adopted.

[0110] For example, the illumination device 3 may be configured to emit light from all positions corresponding to an illumination angle of 45° in all directions. In this case, the illumination device 3 performs annular illumination of 45°. By measuring the amount of reflected light in the 0° direction at that time, the same measurement as colorimetry of 45°c:0° geometry defined in standards such as JIS can be performed.

[0111] Although the embodiments and examples of the present invention have been described, the embodiments disclosed this time should be considered illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

Explanation of Reference Numerals

[0112] 3 Illumination device, 5, 7 Optical elements, 8, 9 Light sources, 11 First optical system, 12 Second optical system, 15 Housing, 21 First image pickup element, 22 Second image pickup element, 50 Control unit, 51 Input unit, 52 Output unit, 53 IF unit, 54 Storage unit, 100 Optical property measuring apparatus, 101 Optical property measuring optical system, AX, AX1, AX2, AX3 Optical axes, G1 First lens group, G2 Second lens group, G3 Third lens group, IM1 Image plane, L1 to L9, L11, L12 Lenses, M Measurement object.

Claims

1. An optical property measurement optical system for measuring reflected light from a measurement object, comprising a first optical system and a second optical system for measuring a common measurement object, wherein the first optical system includes, in order from the object side, a first lens group having a positive power, a second lens group having a positive power, and a first image sensor, wherein the second lens group has a first aperture stop, and is a relay optical system that forms an intermediate image between the first lens group and the second lens group, wherein the first aperture stop is disposed in the second lens group such that the entrance pupil of the first optical system is on the object side of the first lens group, wherein the measurement object is disposed near the entrance pupil, wherein the first image sensor is disposed in conjugate with the object side infinity, wherein the second optical system includes, in order from the object side, the first lens group common to the first optical system, a second aperture stop, a third lens group having a positive power, and a second image sensor, wherein the second image sensor is disposed at a position conjugate to the measurement object, wherein, when the distance in the optical axis direction from the paraxial focus on the image side of the first lens group to the second aperture stop is Δp and the focal length of the first lens group is f1, the following conditional expression (1) is satisfied, −1.0 < Δp / f1 < 3.0... (1) wherein the first optical system and the second optical system share the first lens group, wherein the optical property measurement optical system further includes an optical element that deflects the optical axis on the image side of the first lens group, and the optical axis is branched into two directions by the optical element, wherein the first optical system is disposed in a first direction of the two directions, and the second optical system is disposed in a second direction of the two directions. An optical property measurement optical system.

2. Another optical element that deflects the optical axis between the intermediate image formed by the first lens group and the first image sensor, and a light source capable of emitting light from an arbitrary minute region on a plane at a position conjugate to the other object side infinity whose optical axis has been deflected by the another optical element. The optical property measurement optical system according to claim 1.

3. When the distance between the first lens group and the second lens group is L and the effective diameter of the largest lens in the first lens group is φ1, the following conditional expression (2) 0.4 < L / φ1 < 3.0... (2) is satisfied. The optical property measurement optical system according to any one of claims 1 to 2.

4. In the first optical system, when the angle of the light beam reflected from the center of the measurement object is θ and the position where the light beam reaches the imaging device is Y(θ), θ and Y(θ) are in a substantially proportional relationship. When the maximum image height is Ymax and the maximum light beam angle is θmax, the following conditional expression (3) -0.1 < (Y(θmax / 2) - Ymax / 2) / Ymax < 0.1... (3) is satisfied. The optical characteristic measurement optical system according to any one of claims 1 to 3.

5. The optical characteristic measurement optical system according to any one of claims 1 to 4, further comprising a light source arranged around the second aperture stop arranged in the second optical system and capable of illuminating the measurement object when imaging the measurement object by the second optical system.

6. When the back focus of the first optical system is fB and the effective diameter of the most image-side surface of the second lens group is φ2, the following conditional expression (4) 1.0 < fB / φ2 < 3.0... (4) is satisfied. The optical characteristic measurement optical system according to any one of claims 2 to 5.

7. An optical characteristic measurement device comprising the optical characteristic measurement optical system according to any one of claims 1 to 6, having a function of measuring the optical characteristics of the measurement object and a function of imaging the measurement object.

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