JP6594576B1 - Optical system, imaging apparatus and imaging system including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system capable of suppressing the bending of a locus of a light beam in a slit, and an imaging apparatus and an imaging system provided with the optical system. An optical system 10 includes a front group 11, a light shielding member 4, and a rear group 12 arranged in order from an object side to an image side. The light shielding member 4 is provided with a long opening in a first direction. The front group 11 has aspheric surfaces 2 and 3, and in the first cross section parallel to the first direction, an object is not imaged on the aperture, and the second group perpendicular to the first direction In the cross section, an intermediate image of the object is formed on the aperture, and the rear group 12 has a diffractive surface 5 that splits the light beam that has passed through the aperture in the second cross section into a plurality of light beams having different wavelengths. A plurality of light beams are condensed at different positions in the two cross sections, and the tilt angles of the aspherical surfaces 2 and 3 in the second cross section change in the first direction. [Selection] Figure 2

Description

  The present invention relates to an optical system used in an imaging apparatus that acquires image information by splitting a light beam from an object, and is suitable for inspection and evaluation in industrial fields such as manufacturing, agriculture, and medicine.

  2. Description of the Related Art Conventionally, an optical system that splits a light beam from a test object (object) into a plurality of light beams having different wavelengths and condenses each light beam at different positions is known. Patent Document 1 describes an optical system in which a light beam from an object is condensed on a slit that is long in one direction by a cylindrical mirror and then dispersed by a diffraction grating.

US Pat. No. 7,1998,877

  Here, with respect to the optical system described in Patent Document 1, in order to realize a wide angle of view in a cross section including the longitudinal direction of the slit, it is conceivable that the cylindrical mirror has a curvature (power) in the cross section.

  However, when the cylindrical mirror has a curvature in a cross section including the longitudinal direction of the slit, the locus of the light beam reflected by the cylindrical mirror is curved in the short direction of the slit. Therefore, there is a possibility that a part of the light beam is shielded without passing through the slit.

  An object of the present invention is to provide an optical system that can suppress the curvature of the locus of a light beam in a slit, an imaging apparatus including the optical system, and an imaging system.

  In order to achieve the above object, an optical system according to one aspect of the present invention is an optical system including a front group, a light shielding member, and a rear group arranged in order from the object side to the image side. A long opening is provided in the first direction, the front group has an aspherical surface and does not form an object on the opening in a first cross section parallel to the first direction; In the second cross section perpendicular to the first direction, an intermediate image of the object is formed on the opening, and the rear group has the wavelength of light beams that have passed through the opening in the second cross section. A diffraction surface for splitting into a plurality of different light fluxes, the light fluxes are condensed at different positions in the second cross section, and a tilt angle of the aspherical surface in the second cross section It changes in the direction of 1.

  ADVANTAGE OF THE INVENTION According to this invention, the optical system which can suppress the curve of the locus | trajectory of the light beam in a slit, an imaging device provided with it, and an imaging system can be provided.

The principal part schematic in the XY cross section of the optical system which concerns on embodiment. The principal part schematic in the ZX cross section of the optical system which concerns on embodiment. FIG. 2 is a schematic diagram of a main part of a diffractive optical element according to an embodiment. The schematic diagram for demonstrating the effect by a tilt change surface. The figure which shows the tilt amount and tilt change amount of the tilt change surface which concern on embodiment. The figure which shows the spot diagram on opening of the light shielding member which concerns on embodiment. The figure which shows the curvature radius in the 2nd cross section of the 1st, 2nd reflective surface which concerns on embodiment. The figure which shows the curvature radius in the 2nd cross section of the 3rd, 4th reflective surface which concerns on embodiment. The figure which shows the partial curvature in the zx cross section of the 4th reflective surface which concerns on embodiment. The figure which shows the condensing state of the light beam of a several different wavelength which concerns on embodiment. The figure which shows the condensing state of the light beam of a several different wavelength which concerns on a comparative example. FIG. 3 is a diagram illustrating an MTF of the optical system according to the first embodiment. FIG. 6 is a schematic diagram of a main part of an optical system according to a second embodiment. FIG. 6 is a diagram showing an MTF of an optical system according to Example 2. FIG. 6 is a schematic diagram of a main part of an optical system according to a third embodiment. FIG. 6 is a diagram showing an MTF of an optical system according to Example 3. FIG. 7 is a schematic diagram of a main part of an optical system according to a fourth embodiment. FIG. 10 is a diagram showing an MTF of an optical system according to Example 4. FIG. 10 is a diagram showing a spot diagram on an opening of a light shielding member according to Example 5; The principal part schematic of the imaging system as the usage example 1 of the optical system which concerns on embodiment. The principal part schematic of the imaging system as the usage example 2 of the optical system which concerns on embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Each drawing may be drawn on a different scale for the sake of convenience. Moreover, in each drawing, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

  In the following description, an XYZ coordinate system is defined as an absolute coordinate system, and an xyz coordinate system is defined as a local coordinate system for each optical surface. In the local coordinate system, the x axis is the normal axis (optical axis) at the apex (origin) of each optical surface, the y axis is parallel to the Y axis and orthogonal to the x axis at the origin, the z axis is the x axis, and It is an axis orthogonal to the y-axis. Further, the Y direction and the y direction are the first direction (reading direction), the Z direction and the z direction are the second direction (spectral direction), the XY cross section and the xy cross section are the first cross section (read cross section), the ZX cross section, and The zx cross section is also referred to as a second cross section (spectral cross section).

  1 and 2 are schematic views of a main part of an optical system 10 according to an embodiment of the present invention. FIG. 1 shows a first cross section, and FIG. 2 shows a second cross section. 1 and 2 show the shape of each member in a cross section including the optical axis. In FIG. 1, each member is shown in the same sheet for convenience. In FIGS. 1 and 2, the diffraction grating on the diffraction surface is omitted for convenience. In the present embodiment, the test object is disposed at a position near Z = 0 on the object plane parallel to the YZ plane, and the light receiving surface 7 of the image sensor is disposed on the image plane of the optical system 10. To do. In addition, it is assumed that the test object is illuminated with white light (light having a plurality of wavelength components) such as sunlight.

  The optical system 10 according to the present embodiment includes a front group 11, a light shielding member (slit member) 4, and a rear group 12 arranged in order from the object side to the image side. The optical system 10 forms an image of the test object on the light receiving surface (image surface) 7 by collecting a light beam from a test object (not shown) located on the −X side. The front group 11 includes a diaphragm 1, a first reflection surface 2, and a second reflection surface 3. The rear group 12 has a third reflecting surface (diffraction surface) 5 and a fourth reflecting surface 6. Note that a cover glass G is disposed immediately before the light receiving surface 7, but this is treated as not contributing to image formation.

  The diaphragm 1 is a member for regulating the width of the light beam from the test object in the second direction, and is arranged so that the opening surface thereof is perpendicular to the X direction. However, the diaphragm 1 may be provided outside the optical system 10. As shown in FIGS. 1 and 2, it is desirable that the light beam entrance (aperture 1) and the light exit (light receiving surface 7) in the optical system 10 be disposed on opposite sides of each optical surface. Thereby, when the optical system 10 is applied to an imaging device, it is possible to easily avoid that the light beam from the test object is blocked by the imaging element, wiring, or the like.

  The light shielding member 4 is provided with a long opening (slit) in the first direction. The light shielding member 4 serves as a stop for restricting the width of the light beam in the first direction while restricting the angle of view in the second cross section of the optical system 10 to shield unnecessary light. Note that the width of the opening of the light shielding member 4 is determined according to the required light quantity, resolution, and the like. The width of the opening of the light shielding member 4 in the second direction is preferably shorter than the width (several mm) in the first direction and is several μm to several 100 μm. If the width of the opening of the light shielding member 4 in the second direction is too large, the resolution on the light receiving surface 7 is lowered, and if it is too small, the effective light beam contributing to image formation is easily shielded. More preferably, it is 10 μm or more and 0.2 mm or less.

  The region other than the aperture in the aperture stop 1 and the light shielding member 4 is a light shielding surface that does not transmit light in at least the use wavelength band (design wavelength band) of the optical system 10. As the diaphragm 1 and the light shielding member 4, it is possible to employ one having a hole in a sheet metal or one having a chromium vapor deposited on the surface of a glass plate. By adopting such a light shielding member 4, the optical system 10 can form an image of a linear reading region (test region) that is long in the first direction.

  The 1st reflective surface 2, the 2nd reflective surface 3, and the 4th reflective surface 6 are reflective surfaces obtained by giving a reflective coating to the base surface which has a free-form surface shape. The base surface of each reflecting surface is formed by processing (cutting, polishing, molding with a mold, etc.) a block material made of glass, resin, metal or the like. The reflective coating desirably has a spectral reflection characteristic that can realize sufficient energy efficiency (light utilization efficiency) in the used wavelength band. When the base surface has a sufficient reflectance in the used wavelength band, the reflective coating may be omitted.

  In the present embodiment, each of the first reflecting surface 2, the second reflecting surface 3, and the fourth reflecting surface 6 is an aspherical surface, and specifically, the curvature (power) between the first cross section and the second cross section. Are different anamorphic optical surfaces (anamorphic reflecting surfaces). Thereby, different optical actions can be generated in the first cross section and the second cross section. In particular, the first reflecting surface 2 and the second reflecting surface 3 are tilt changing surfaces in which the tilt angle (tilt amount) in the second cross section changes in the first direction. Thereby, the incident positions of the axial principal ray and the most off-axis principal ray in the light shielding member 4 can be brought close to each other in the second direction, and the bending of the light flux in the opening can be suppressed (details will be described later). . Here, the tilt angle indicates an angle with respect to the x-axis (xy cross section) of the normal line at the vertex in the zx cross section of each reflecting surface.

  The front group 11 only needs to have at least one tilt changing surface. For example, one of the first reflecting surface 2 and the second reflecting surface 3 is a spherical surface or an anamorphic reflecting surface that is not a tilt changing surface. Alternatively, either one of them may be removed. However, in order to easily obtain the effects of the present invention, it is desirable that both the first reflecting surface 2 and the second reflecting surface 3 be tilt change surfaces.

  The rear group 12 may have at least one diffractive surface. For example, the base surface of the diffractive surface 5 may be an anamorphic surface, and the fourth reflecting surface 6 may be a spherical surface or may be removed. However, in order to satisfactorily correct coma aberration and the like generated for each wavelength generated by the diffractive surface 5, it is desirable to provide an optical surface other than the diffractive surface 5 in the rear group 12, and the diffractive surface 5 as in the present embodiment. It is more preferable to dispose an anamorphic optical surface on the image side. When the diffractive surface 5 is provided in the front group 11, only a part of the light beams having a certain wavelength can pass through the opening of the light shielding member 4. Therefore, the diffractive surface 5 needs to be provided in the rear group 12.

  Further, in the optical system 10, in order to suppress the occurrence of aberration by sharing power between the optical surfaces, it is more preferable that all the optical surfaces of the front group 11 and the rear group 12 are anamorphic optical surfaces. The configurations of the front group 11 and the rear group 12 are not limited to those described above, and the optical surfaces in each group may be increased or decreased. However, in order to realize downsizing of the entire system and reduction in the number of parts, it is desirable that each of the front group 11 and the rear group 12 is constituted by two reflecting surfaces as in this embodiment.

  In the present embodiment, since all the optical surfaces are reflecting surfaces, the optical path is bent to realize downsizing of the optical system 10 while suppressing the occurrence of chromatic aberration. At this time, in order to reduce the size of the optical system 10, as shown in FIG. 2, the reflecting surfaces are arranged so that the optical paths intersect in each of the front group 11 and the rear group 12 (so that it becomes a character of 4). It is desirable to arrange. If necessary, a prism or an internal reflection mirror may be used as a reflection member including a reflection surface. However, in order to suppress the occurrence of chromatic aberration as described above, the reflection member is an external reflection mirror, and the reflection surface is It is desirable to be configured to be adjacent to air. Further, if necessary, at least one optical surface may be a refractive surface (transmission surface).

  However, particularly in the rear group 12, since holding members and wirings (not shown) are arranged around the light shielding member 4 and the light receiving surface 7, it is difficult to secure a sufficient space for arranging the refractive optical element. . Even if a sufficient space can be secured, it is necessary to arrange a plurality of refractive optical elements in order to correct chromatic aberration satisfactorily, so that the entire system becomes large. Therefore, it is desirable that at least all optical surfaces included in the rear group 12 are reflective surfaces. Furthermore, it is more preferable that all the optical surfaces included in the front group 11 are reflecting surfaces.

  3A and 3B are schematic views of a main part of a diffractive optical element (reflective optical element) 50 including the diffractive surface 5 according to the present embodiment, FIG. 3A is a perspective view, and FIG. 3B is a front view (+ x). Figure viewed from the direction). The diffraction surface 5 includes a base surface 51 and a diffraction grating 52 provided on the base surface 51. In FIG. 3, only a part of the diffraction grating 52 is shown enlarged for convenience.

  The base surface 51 in the diffractive surface 5 has a free-form surface shape like other reflective surfaces. The diffraction grating 52 is composed of a plurality of gratings (convex portions) arranged at a pitch on the order of submicron to micron, and the height of each grating is also on the order of submicron to micron. As the diffraction grating 52, one having a step shape, a rectangular uneven shape, a blazed shape, a SIN wave shape, or the like in the zx section can be adopted. The shape of the diffraction grating 52 is selected in consideration of the required diffraction efficiency and ease of manufacture.

  In the present embodiment, a blazed shape is employed, in which it is relatively easy to improve both diffraction efficiency and ease of manufacture. In the blazed diffraction grating, the portion farthest in the x direction with respect to the base surface 51 is the lattice vertex, the portion that reflects (diffracts) incident light is the blazed surface (lattice surface), and contributes to diffraction adjacent to the blazed surface. The part which is not called is called a lattice wall surface. The diffractive surface 5 according to this embodiment is arranged so that the blaze surface faces the light receiving surface 7 side (image side) and the grating wall surface faces the object side. As a result, a short wavelength light beam enters the + Z side of the light receiving surface 7 in FIG. 2, and a long wavelength light beam enters the -Z side.

  The base surface 51 is formed by the same method as the other reflective surfaces described above. The diffraction grating 52 can be formed by processing the base surface 51 by cutting or polishing. However, the diffraction grating 52 may be formed at the same time when the base surface 51 is formed. For example, the diffractive optical element 50 in which a fine concavo-convex structure is provided on the surface of a mirror piece constituting the mold and the diffraction grating 52 is provided by molding using the mold may be manufactured. In order to improve the diffraction efficiency, a reflective coating may be applied to the surface of the diffraction grating 52.

  Further, as shown in FIG. 3B, it is desirable to configure the diffraction grating 52 so that a plurality of ridge lines corresponding to the vertices of each grating in the zx section are parallel to each other. Furthermore, it is more preferable that the intervals between the ridge lines of the diffraction grating 52 be constant. Thereby, the process of the base surface 51 by cutting or grinding | polishing can be made easy. However, the intervals between the ridge lines may be non-constant if necessary. For example, in order to realize more advanced aberration correction in the optical system 10, the interval between the ridge lines may be changed in the z direction.

  As with the other reflecting surfaces, the base surface 51 of the diffractive surface 5 is preferably an aspheric surface, and specifically, an anamorphic surface having different curvatures in the xy section and the zx section. This makes it possible to share power with other anamorphic optical surfaces, thus facilitating correction of aberrations. In the present embodiment, the base surface 51 of the diffractive surface 5 is an anamorphic surface. However, the base surface 51 may be configured as a flat surface or a spherical surface in consideration of the ease of manufacturing the diffraction grating 52.

  The operation of the optical system 10 will be described with reference to FIGS. 1 and 2.

  The light beam emitted from the test object passes through the aperture of the diaphragm 1, is reflected by the first reflecting surface 2 and the second reflecting surface 3, and reaches the light shielding member 4. At this time, the front group 11 does not image the test object on the opening of the light shielding member 4 in the first cross section (XY cross section), and on the opening of the light shielding member 4 in the second cross section (ZX cross section). An intermediate image of the test object is formed in That is, the front group 11 is configured such that the focal position does not coincide with the object plane in the first cross section. Thus, a line-shaped intermediate image (line image) that is long in the first direction is formed on the opening of the light shielding member 4. Here, “on the opening” is not limited to the exact position of the opening, but also includes the vicinity (substantially above the opening) of the opening slightly separated from the position of the opening in the optical axis direction.

  The light beam that has passed through the opening of the light shielding member 4 is split into a plurality of light beams having different wavelengths from each other by the diffraction surface 5 in the second cross section. At this time, since the diffraction grating on the diffraction surface 5 is composed of a plurality of gratings (ridge lines) arranged in the z direction, the light beam incident on the diffraction surface 5 is subjected to spectral action only in the z direction and spectral action in the y direction. I do not receive it. The plurality of light beams from the diffractive surface 5 are reflected by the fourth reflecting surface 6 and enter the light receiving surface 7 disposed on the image surface. At this time, a plurality of light beams having different wavelengths are condensed at different positions on the light receiving surface 7 in the second cross section. That is, according to the optical system 10 according to the present embodiment, since a plurality of images for each wavelength can be formed on the light receiving surface 7, the light receiving surface 7 can acquire a plurality of image information for each wavelength.

  As described above, the optical system 10 according to the present embodiment generates different optical effects in the first cross section including the reading direction and the second cross section including the spectral direction. Specifically, in the first cross section, the test object is imaged on the light receiving surface 7 without being imaged once on the opening of the light shielding member 4, but in the second cross section, the test object is imaged on the light shielding member 4. The image is once formed on the aperture and then re-imaged on the light receiving surface 7. That is, the test object is imaged once in the first cross section, while the test object is imaged twice in the second cross section.

  According to this configuration, since the convergence state of the light beam (light beam incident on the opening) passing through the opening of the light shielding member 4 is not limited in the first cross section, the degree of freedom in designing the optical system 10 can be improved. it can. Accordingly, the front group 11 and the rear group 12 can appropriately share the power to form an image of the test object on the light receiving surface 7, and various aberrations can be easily corrected. Wide area) and high definition of captured images.

  Specifically, by configuring the front group 11 so that the focal position in the first cross section does not coincide with the object plane, the light beam passing through the opening of the light shielding member 4 can be made non-parallel light. Thereby, it becomes easy to realize a wide angle of view in the first cross section. If the light beam passing through the opening of the light shielding member 4 is parallel light, it is necessary to arrange a large number of optical elements in the rear group 12 in order to increase the angle of view of the optical system 10. The system becomes larger. In the present embodiment, a wide angle of view is realized by using a divergent light as a light beam passing through the opening of the light shielding member 4. However, a light beam passing through the opening of the light shielding member 4 as necessary. May be convergent light.

  Further, in the first cross section, when the test object is once imaged on the opening of the light shielding member 4, each of the front group 11 and the rear group 12 must independently correct the aberration. Therefore, it is necessary to increase the power of each optical surface, for example, the degree of freedom in designing each optical surface is lowered, and it is difficult to increase the angle of view of the optical system 10. On the other hand, in the second cross section, since it is not necessary to widen the angle of view, it is possible to increase the NA by once imaging the test object on the opening of the light shielding member 4.

  In the configuration described above, each of the front group 11 and the rear group 12 has different powers in the first cross section and the second cross section. In order to realize this configuration, it is necessary to provide an anamorphic optical surface for each of the front group 11 and the rear group 12. At this time, the anamorphic optical surface included in the front group 11 should be positively given power not only to the second cross section but also to the first cross section (make the absolute value of curvature larger than 0). desirable. In the first cross section, it is more preferable that the power code of the front group 11 and the power code of the rear group 12 are different from each other.

  Specifically, in the second cross section, a positive power is applied to the front group 11 and the rear group 12 in order to form an image once on the opening of the light shielding member 4 and then re-image the light receiving surface 7. It is necessary to have. On the other hand, in the first cross section, since it is not necessary to once form an image of the test object on the opening of the light shielding member 4, in order to realize a further wide angle of view, the front group 11 is given negative power. It is desirable to give the rear group 12 positive power. Thereby, since the optical system 10 becomes a retro focus type in the first cross section, the focal length of the entire system is shortened, and a wide angle of view can be realized. However, when the test object is sufficiently separated from the optical system 10, the optical system 10 is made a telephoto optical system by giving the front group 11 positive power and giving the rear group 12 negative power. Also good.

  The manner in which the light beam is split by the diffractive surface 5 will be described with reference to FIG. Here, a case is considered in which a white light beam emitted from one point of the test object is split into light beams having respective wavelengths of λ1 [nm], λ2 [nm], and λ3 [nm] (λ2 <λ1 <λ3). . However, in FIG. 2, only the chief ray and the marginal ray are shown among the light beams.

  The chief ray L1P and the marginal rays L1U and L1L in the white light beam emitted from the test object are line-shaped intermediately on the opening of the light shielding member 4 via the stop 1, the first reflecting surface 2, and the second reflecting surface 3. Form an image. The principal ray L2P and the marginal rays L2U, L2L that have passed through the opening of the light shielding member 4 are caused by the diffraction surface 5 to have rays L3P, L3U, L3L of wavelength λ1, rays L4P, L4U, L4L of wavelength λ2, and rays of wavelength λ3. Spectroscopy into L5P, L5U, and L5L. Then, each of the light beams having the wavelength λ1, the wavelength λ2, and the wavelength λ3 is condensed at the first position 73, the second position 74, and the third position 75 on the light receiving surface 7.

  Next, the shapes and functions of the first reflecting surface 2 and the second reflecting surface 3 will be described in detail.

  FIG. 4 is a schematic diagram for explaining the effect of the change in the tilt direction of the reflecting surface in the first direction. In FIG. 4, the principal ray (axial principal ray) 501 of the light beam from the on-axis object point and the principal rays (off-axis principal ray) 502 and 503 of the light beam from the most off-axis object point are reflected by the reflecting surface. The state when passing through the opening 401 of the light shielding member is shown. 4A shows the reflecting surface 510 whose tilt angle is not changed, and FIG. 4B shows the reflecting surface 520 obtained by changing the tilt angle with respect to the planar reflecting surface. FIG. 4C shows a reflecting surface 530 obtained by giving a change in tilt angle similar to that of the reflecting surface 520 in FIG. 4B to the reflecting surface 510 in FIG. 4A.

  As shown in FIG. 4A, among the light rays reflected by the reflecting surface 510, the axial principal ray 501 is incident on the position of the opening 401 of the light shielding member in the z direction. On the other hand, the most off-axis chief rays 502 and 503 are incident on a position (a light shielding surface) separated from the opening 401 of the light shielding member by a shift amount 511. As described above, when the reflection surface 510 is not a tilt change surface, the incident position of each principal ray reflected by the reflection surface 510 with respect to the light shielding member is greatly different between the on-axis and the off-axis. As a result, the locus 512 of the light beam from the test object is greatly curved in the z direction, and the light beam from the off-axis object point cannot pass through the opening 401.

  When the reflecting surface is a plane, the trajectory of the light beam reflected by the plane reflecting surface is not curved in the z direction, so that each ray from the on-axis object point to the most off-axis object point passes through the opening 401. Will pass. On the other hand, as shown in FIG. 4B, the locus 522 of the light beam from the test object is intentionally changed in the z direction by continuously changing the tilt angle in the zx section of the plane reflecting surface in the y direction. Can be curved.

  Therefore, as shown in FIG. 4C, the same change in tilt angle as that of the reflection surface 520 is given to the reflection surface 510, whereby the axial principal ray 501 and the most off-axis principal rays 502, 503 in the light shielding member. Can be brought closer to each other in the z direction. As a result, the amount of deviation 511 of the most off-axis chief rays 502 and 503 with respect to the opening 401 can be reduced, and the locus 532 of the light beam can be substantially matched with the shape of the opening 401. Therefore, by using the tilt change surface, it is possible to prevent a part of the light beam from being blocked by the light blocking member without passing through the opening 401.

  As described above, since the first reflecting surface 2 and the second reflecting surface 3 according to the present embodiment are tilt change surfaces, the incident positions of the axial principal ray and the most off-axis principal ray at the opening of the light shielding member 4 are set to the first positions. The two directions can be close to each other. Thereby, the curvature of the light beam in the opening can be suppressed, and each light beam from the on-axis object point to the off-axis object point can pass through the opening. Therefore, according to the optical system 10 according to the present embodiment, a part of the light beam is shielded by the light shielding member 4 while realizing a wide angle of view by giving power to each reflecting surface in the first cross section. It becomes possible to suppress deterioration of the optical performance due to this.

  FIG. 5 shows the tilt angles of the first reflecting surface 2 and the second reflecting surface 3 according to this embodiment and the amount of change. In FIG. 5, the solid line graph indicates the first reflecting surface 2, and the broken line graph indicates the second reflecting surface 3. In FIG. 5A, the horizontal axis indicates the position [mm] in the y direction with respect to the origin in the local coordinate system of each reflection surface, and the vertical axis indicates the tilt angle (tilt amount) [deg] of each reflection surface. In FIG. 5B, the horizontal axis indicates the position [mm] in the y direction with respect to the origin in the local coordinate system of each reflective surface, and the vertical axis indicates the amount of change in tilt angle (tilt change amount) of each reflective surface. [Deg / mm] is shown. The tilt change amount corresponds to a first-order differential value of the tilt amount, and is expressed by dT / dy, where T is the tilt amount.

  As shown in FIG. 5A, the tilt amounts of the first reflecting surface 2 and the second reflecting surface 3 change in the y direction, and the change is symmetric with respect to the z axis. At this time, in order to facilitate the design and manufacture of each reflecting surface, it is desirable to change the tilt amount of each reflecting surface monotonously (continuously) as shown in FIG. If the change in the tilt amount of each reflecting surface is not monotonous, an inflection point is generated on each reflecting surface, which not only makes it difficult to manufacture each reflecting surface, but also tends to cause wavefront aberration near the inflection point. End up.

Further, as shown in FIG. 5B, the tilt change amounts of the first reflecting surface 2 and the second reflecting surface 3 are close to the same object point. Thus, by making the tilt change amounts of the regions through which light beams from the same object point pass on the respective tilt change planes close to each other, the curvature of the light beam from the same object point can be satisfactorily reduced. Specifically, when the tilt change amounts of the regions where the light beams from the same object point pass through the first reflecting surface 2 and the second reflecting surface 3 are | dT ₁ / dy | and | dT ₂ / dy | It is desirable to satisfy the following conditional expression (1).
1.00 ≦ | dT ₁ / dy | / | dT ₂ /dy|≦1.50 (1)

If the upper limit value of conditional expression (1) is exceeded, the difference in tilt change between the first reflecting surface 2 and the second reflecting surface 3 becomes too large, and the curvature of the light beam from the same object point can be satisfactorily reduced. Becomes difficult. Conditional expression (1) assumes that the tilt change amount of the first reflecting surface 2 is equal to or greater than the tilt change amount of the second reflecting surface 3 (| dT ₁ / dy | ≧ | dT ₂ / dy |). Yes. If the tilt change amount of the first reflecting surface 2 is smaller than the tilt change amount of the second reflecting surface 3, the tilt change amount of the first reflecting surface 2 is | dT ₂ / dy | The amount of change may be read as | dT ₁ / dy |.

In the present embodiment, the difference between the tilt amount on the axis of the first reflection surface 2 and the tilt amount outside the most axis is 1 deg, and the difference between the tilt amount on the axis of the second reflection surface 3 and the tilt amount outside the most axis. Is 0.4 deg. Further, the amount of tilt change in the region where the light beam from the most off-axis object point passes on the first reflecting surface 2 and the second reflecting surface 3 is 0.26 deg / mm and 0.20 deg / mm, respectively, | dT ₁ Since / dy | / | dT ₂ /dy|=1.30, the conditional expression (1) is satisfied. Furthermore, it is more preferable that the following conditional expression (1a) is satisfied.
1.00 ≦ | dT ₁ / dy | / | dT ₂ /dy|≦1.35 (1a)

  FIG. 6 shows the distribution (spot diagram) of the light flux from each object height on the opening of the light shielding member 4 according to the present embodiment. In FIG. 6, the horizontal axis indicates the position [mm] in the z direction (short direction) in the opening of the light shielding member 4, and the vertical axis indicates the position [mm] in the y direction (longitudinal direction) in the opening of the light shielding member 4. Each point represents an intersection of the opening of the light shielding member 4 and the light beam.

  Since the width of the opening of the light shielding member 4 according to the present embodiment in the y direction is 3.6 mm, the light flux on the opening reaches a range of 3.6 mm (± 1.8) in the y direction as shown in FIG. It has spread. As described above, it can be seen that the curvature in the z direction of the light flux distribution is sufficiently reduced by using the first reflecting surface 2 and the second reflecting surface 3 as tilt change surfaces. At this time, since the width of the opening of the light shielding member 4 in the z direction is 0.05 mm and sufficiently large with respect to the diameter of the light beam, the light beam passes through the opening without being shielded by the light shielding member 4 in the z direction. You can see that

  As described above, according to the optical system 10 according to the present embodiment, by providing the tilt change surface in the front group 11, it is possible to suppress the curvature of the locus of the light beam at the opening of the light shielding member 4. Good optical performance can be realized.

  At least one of the first reflecting surface 2 and the second reflecting surface 3 is a sub-curvature curvature changing surface in which the radius of curvature in the second cross section is different between the on-axis position and the most off-axis position in the first direction. desirable. Thereby, it is possible to satisfactorily correct the curvature of field at the opening of the light shielding member 4, and it is possible to prevent a part of the light beam from being blocked by the light shielding surface of the light shielding member 4. In general, when the optical system has a wide angle of view, field curvature is prominent. Therefore, it is easy to widen the angle of view by adopting a ray curvature changing surface. This will be described in detail below.

FIG. 7 is a diagram showing the radius of curvature in the second cross section (zx cross section) of each reflecting surface in the front group 11. 7A and 7B show the radii of curvature of the first reflecting surface 2 and the second reflecting surface 3, respectively. In FIG. 7, the horizontal axis indicates the position [mm] in the y direction with respect to the origin in the local coordinate system of each reflecting surface, and the vertical axis indicates the curvature radius R _z [mm] of the second cross section of each reflecting surface.

  As shown in FIG. 7, the first reflecting surface 2 and the second reflecting surface 3 according to this embodiment both have a radius of curvature in the second cross section between the on-axis position and the most off-axis position in the first direction. It is a different surface curvature change surface. Thereby, in the second cross section, it is possible to correct the curvature of field that the converging position of the light flux is shifted in the optical axis direction between the on-axis position and the most off-axis position in the opening of the light shielding member 4. Therefore, for example, the light beam reflected at the most off-axis position of the second reflecting surface 3 is collected before and after the opening of the light shielding member 4, and a part thereof is prevented from being shielded by the light shielding surface of the light shielding member 4. It becomes possible.

  At this time, as shown in FIG. 7, it is desirable to change the curvature radii of the first reflecting surface 2 and the second reflecting surface 3 from the on-axis position toward the most off-axis position. Thereby, the field curvature in the second cross section can be corrected well in the entire region from the on-axis position to the most off-axis position in the first direction. That is, the condensing position on the second cross section of the light beam can be aligned on the opening of the light shielding member 4 in the entire region from the on-axis position to the most off-axis position. At this time, as shown in FIG. 7, it is desirable to change the radius of curvature of each reflecting surface monotonously (continuously). If the change in the radius of curvature of each reflecting surface is not monotonous, an inflection point occurs on each reflecting surface, which not only makes it difficult to manufacture each reflecting surface, but also tends to cause wavefront aberration near the inflection point. End up.

  In order to correct the curvature of field at the opening of the light shielding member 4, the radius of curvature may be different between the on-axis position and at least one of the most off-axis positions. However, in order to correct the field curvature more satisfactorily, it is desirable to make the radius of curvature different between the on-axis position and the two (at both ends) off-axis positions as in this embodiment. At this time, the magnitude relationship (direction of change) of the curvature radius between the on-axis position and one of the most off-axis positions and the magnitude relation between the curvature radius of the on-axis position and the other most off-axis position can be equal to each other. preferable. That is, the radius of curvature at both off-axis positions is increased relative to the radius of curvature at the on-axis position, or the radius of curvature at both off-axis positions is decreased relative to the radius of curvature at the on-axis position. It is preferable.

  The front group 11 only needs to have at least one sub-linear curvature changing surface. For example, one of the first reflecting surface 2 and the second reflecting surface 3 is a spherical surface or is not an anamorphic surface that is not a concentric-line curvature changing surface. It may be an optical surface, or one of them may be removed. In particular, it is desirable that the optical surface having the smallest radius of curvature (the largest power) in the second cross section in the front group 11 be a subsurface curvature changing surface. In the present embodiment, since the radius of curvature of the second reflecting surface 3 is smaller than the radius of curvature of the first reflecting surface 2, at least the second reflecting surface 3 can be easily changed into a sub-curvature curvature changing surface. Curvature can be corrected. However, in order to easily obtain the effect of the present invention, it is desirable that both the first reflecting surface 2 and the second reflecting surface 3 be the surface curvature changing surfaces.

  In the case where a plurality of sub-curvature curvature changing surfaces are provided, it is desirable to determine the amount of change in the curvature radius according to the size of the curvature radius of each reflecting surface. In the present embodiment, as shown in FIG. 7, the amount of change in the radius of curvature of the second reflective surface 3 having a small curvature radius is smaller than the amount of change in the radius of curvature of the first reflective surface 2 having a large radius of curvature. ing. In the second cross section, the radius of curvature of the first reflecting surface 2 decreases from the on-axis position toward the most off-axis position, and the curvature radius of the second reflecting surface 3 increases from the on-axis position toward the most off-axis position. Is getting bigger. Thereby, the condensing position in the 2nd cross section of the light beam from the 2nd reflective surface 3 substantially corresponds to the position of the opening of the light shielding member 4 in the whole region from the on-axis position to the most off-axis position in the first direction. Can be made. However, the method of changing the radius of curvature of each reflecting surface is not limited to that shown in the present embodiment, and it is desirable to determine according to the design of the entire optical system.

  FIG. 8 shows the radius of curvature in the second cross section of each reflecting surface in the rear group 12 as in FIG. Each of FIG. 8A and FIG. 8B shows the curvature radius of the base surface of the third reflecting surface 5 and the fourth reflecting surface 6. As shown in FIG. 8, not only the front group 11 but also the rear group 12 is provided with a child-curvature changing surface, so that the field curvature in the second cross section of the light receiving surface 7 can be corrected. In this embodiment, as shown in FIG. 8, the curvature radii of the third reflecting surface 5 and the fourth reflecting surface 6 are changed so as to decrease from the on-axis position toward the most off-axis position.

  As shown in FIG. 8A, the radius of curvature of the base surface of the third reflecting surface 5 is large in the vicinity of the most off-axis position, but this portion does not contribute to image formation (ineffective region). It is. That is, the radius of curvature of the portion (effective region) that contributes to the image formation on the base surface of the third reflecting surface 5 is monotonously decreased from the on-axis position toward the most off-axis position. As in the case of the front group 11, the method of changing the radius of curvature of each reflecting surface is not limited to that shown in the present embodiment, and it is desirable to determine according to the design of the entire optical system.

  In the present embodiment, as shown in FIG. 8A, the third reflection surface 5 has a curvature radius of the base surface that is different between the on-axis position and the most off-axis position. The power (refractive power) due to refraction of the surface 5 is made different between the on-axis position and the most off-axis position. On the other hand, it is desirable that the power (diffraction power) by diffraction of the third reflecting surface 5 is equal to each other at the on-axis position and the most off-axis position. When the diffraction power is different between the on-axis position and the most off-axis position, the spectral performance differs between the on-axis position and the most off-axis position, and there is a possibility that good spectral information (image information) cannot be obtained. . In the present embodiment, as described above, since the diffraction grating on the third reflecting surface 5 is composed of a plurality of gratings (ridge lines) arranged in the z direction, the diffraction power is equal at the on-axis position and the most off-axis position. Yes. However, “equal” here includes not only exact matching but also substantially matching (substantially equal).

  In the optical system described in Patent Document 1 described above, since the incident angles of the respective light beams with respect to the lens are different from each other, coma aberration that differs depending on the wavelength occurs. In order to correct such coma aberration that differs for each wavelength, it is necessary to use a large number of lenses, and the configuration of the optical system becomes complicated. Therefore, it is desirable to devise the shape of the fourth reflecting surface 6 in order to realize an optical system that corrects different aberrations for each wavelength while having a simple configuration. This will be described in detail.

FIG. 9 shows the partial curvature (aspheric amount) of the fourth reflecting surface 6 in the second cross section. In FIG. 9, the horizontal axis indicates the position [mm] in the z direction with respect to the origin of the fourth reflecting surface 6 in the local coordinate system, and the vertical axis indicates the partial curvature 1 / R _z [1 / mm] of the fourth reflecting surface 6. Is shown. In addition, _Rz is the partial curvature radius of the 4th reflective surface 6 in a 2nd cross section. In FIG. 9, the solid line, the broken line, and the alternate long and short dash line indicate y = 0.0 [mm], y = −6.0 [mm], and y = −10.0 [mm] in the local coordinate system, respectively. The graph in position is shown.

As can be seen from FIG. 9, the partial curvature 1 / R _z is asymmetric on the −z side and the + z side with respect to the optical axis (x axis). Specifically, the partial curvature 1 / R _z is larger on the −z side than on the + z side. Further, the partial curvature 1 / R _z has different changes (asymmetric changes) on the −z side and the + z side with respect to the optical axis. In the present embodiment, the partial curvature 1 / _Rz increases as it goes off-axis on the −z side, and decreases as it goes off-axis on the + z side. Further, the partial curvature 1 / _Rz increases as the distance from the position of y = 0 [mm] increases.

  FIG. 10 shows a light condensing state on the light receiving surface 7 in the second cross section (y = 0 [mm]) including the optical axis of light beams having different wavelengths according to the present embodiment. 10 (a), 10 (b), and 10 (c), the principal rays and the marginal rays of the light beams having the wavelengths of λ1 = 700 nm, λ2 = 400 nm, and λ3 = 1000 nm reach the light receiving surface 7, respectively. The optical path is shown. In the present embodiment, it is designed so that a chief ray having a wavelength λ1 = 700 nm is incident on the optical axis (x axis) of the fourth reflecting surface 6. In FIG. 10, the reference numerals of the light beams of the respective wavelengths are the same as those shown in FIG. 2, and the diffraction grating on the diffraction surface 5 is omitted as in FIG.

  10 (a), 10 (b), and 10 (c), the + z side with respect to the optical axis of the fourth reflecting surface 6, that is, the same as the vertex 54 of the base surface of the diffractive surface 5 is used. The curvature on the side (near side) becomes smaller toward the off-axis. On the other hand, the curvature on the −z side with respect to the optical axis of the fourth reflecting surface 6, that is, on the side opposite to the apex 54 of the base surface of the diffractive surface 5 (the far side) increases toward the off-axis. Thereby, each of the marginal ray L3L incident on the + z side of the fourth reflection surface 6 and the marginal ray L3U incident on the −z side of the fourth reflection surface 6 is reflected so as to approach the principal ray L3P. As can be seen from FIG. 10, the coma aberration on the light receiving surface 7 is well corrected for the light flux of any wavelength.

  Here, in order to explain the effect of the fourth reflecting surface 6 according to the present embodiment, a comparative example in which only the fourth reflecting surface 6 in the optical system 10 is changed will be considered.

The fourth reflecting surface 6 according to the comparative example is obtained by setting a part of the aspheric coefficient in the expression representing the shape of the second cross section of the fourth reflecting surface 6 according to the present embodiment to zero. Specifically, the values of aspherical coefficients M ₀₁ , M ₂₁ , M ₄₁ , M ₀₃ , M ₂₃ , M ₄₃ , M ₀₅ , M ₂₅ , and M ₄₅ in formula (Equation 2) described later are set to zero. . However, the values of M ₀₁ , M ₀₅ , M ₂₅ , and M ₄₅ are zero in this embodiment. These aspheric coefficients relate to the symmetry of the fourth reflecting surface 6 with respect to the optical axis. That is, the partial curvature 1 / _Rz of the fourth reflecting surface 6 according to the comparative example is a target with respect to the optical axis unlike the present embodiment.

  FIG. 11 shows the condensing state on the light receiving surface 7 in the second cross section including the optical axis of the light beams having different wavelengths according to the comparative example, as in FIG. 11 (a), 11 (b), and 11 (c), the principal rays and the marginal rays of the light beams having the wavelengths of λ1 = 700 nm, λ2 = 400 nm, and λ3 = 1000 nm reach the light receiving surface 7, respectively. The optical path is shown. As shown in FIG. 11A, FIG. 11B, and FIG. 11C, in the comparative example, the condensed positions of the principal ray and the marginal ray at each wavelength on the light receiving surface 7 do not match. The coma is not corrected well.

  Thus, in the present embodiment, in the second cross section, the anamorphic optical surface disposed on the image side of the diffractive surface 5 becomes smaller as the curvature on one side with respect to the optical axis goes off-axis, The shape is such that the curvature on the other side with respect to the shaft increases as it goes out of the shaft. Thereby, since the marginal ray of the light flux of each wavelength can be condensed so as to be close to the principal ray, it is possible to satisfactorily correct the coma aberration that differs for each wavelength.

  Specifically, in the present embodiment, the curvature of the fourth reflecting surface 6 on the same side as the vertex of the base surface of the diffractive surface 5 with respect to the optical axis becomes smaller as it goes off-axis, and is diffracted with respect to the optical axis. The curvature of the surface 5 opposite to the vertex of the base surface is configured to increase as it goes off-axis. The method of changing the curvature of both sides with respect to the optical axis of the fourth reflecting surface 6 is opposite to that of the present embodiment in accordance with the direction of deflection of the light beam (direction of each optical surface) by the diffractive surface 5 and the fourth reflecting surface 6. You may comprise so that it may become the relationship of these. However, it is advantageous for downsizing the entire system that the optical path from the light shielding member 4 to the diffractive surface 5 and the optical path from the fourth reflecting surface 6 to the light receiving surface 7 intersect in the second cross section. It is desirable to configure as in the present embodiment.

  Here, the F value of the optical system 10 according to the present embodiment will be described. In the case of an optical system having different optical performances required for the first cross section and the second cross section, as in the optical system 10 according to the present embodiment, it is desirable to appropriately set the F value in each cross section. Specifically, it is desirable to make the F value on the image side of the optical system 10 different between the first cross section and the second cross section.

In general, by increasing the F value on the image side of the optical system, the imaging performance at the aperture of the light shielding member 4 can be improved, and the depth of field can be increased while downsizing the entire system. The amount of light on the surface 7 decreases, and the SN ratio of the signal output from the image sensor decreases. Therefore, in order to achieve both a wide angle of view and a sufficient amount of light at the light receiving surface 7 while miniaturizing the entire system of the optical system 10, the F value on the image side in the first cross section is set to F1, the second cross section. It is desirable that the following conditional expression (2) is satisfied when the F value on the image side in F2 is F2.
1.00 <F1 / F2 (2)

  Conditional expression (2) indicates that the image-side F value in the first section is larger than the image-side F value in the second section. By satisfying conditional expression (2), the F value in the first cross section becomes sufficiently large (dark), and a wide angle of view and good correction of various aberrations can be realized. On the other hand, since the F value in the second cross section is sufficiently small (bright), it is possible to secure a sufficient amount of light on the light receiving surface 7 and improve the resolution. If the lower limit of conditional expression (2) is not reached, it is difficult to achieve both a wide angle of view in the first cross section and securing a sufficient amount of light on the light receiving surface 7 while downsizing the entire system.

Furthermore, it is desirable to satisfy the following conditional expression (2a). Exceeding the upper limit value of conditional expression (2a) is not preferable because the F value on the image side in the first cross section becomes too large and it becomes difficult to secure a sufficient amount of light in each pixel of the light receiving surface 7.
1.00 <F1 / F2 <4.50 (2a)

It is more preferable to satisfy the following conditional expressions (2b) and (2c) in order.
1.00 <F1 / F2 <2.00 (2b)
1.03 <F1 / F2 <1.50 (2c)

On the other hand, by reducing the F value on the image side of the optical system, the amount of light on the light receiving surface 7 can be improved, but aberration correction becomes difficult. Therefore, in order to improve the ability to distinguish a plurality of light beams having different wavelengths (wavelength resolution) or to widen the angle of view, it is necessary to increase the number of optical elements, which increases the size of the entire system. . Therefore, in order to achieve both high wavelength resolution and securing a sufficient amount of light at the light receiving surface 7 while downsizing the entire system, it is desirable to satisfy the following conditional expression (3).
1.00 <F2 / F1 (3)

  Conditional expression (3) indicates that the image-side F value in the second section is larger than the image-side F value in the first section. By satisfying conditional expression (3), the F value in the second cross section becomes sufficiently large (dark), and high wavelength resolution can be realized. On the other hand, since the F value in the first cross section is sufficiently small (bright), it is possible to secure a sufficient amount of light on the light receiving surface 7. If the lower limit of conditional expression (3) is not reached, it is difficult to achieve both high wavelength resolution in the second cross section and securing sufficient light quantity on the light receiving surface 7 while downsizing the entire system.

Furthermore, it is desirable to satisfy the following conditional expression (3a). When the upper limit value of conditional expression (3a) is exceeded, the F value on the image side in the second cross section becomes too large, and there is a possibility that the light beam exceeds the diffraction limit at the opening of the light shielding member 4. In this case, the width in the second direction of the light beam that has passed through the opening of the light shielding member 4 becomes large, and it is difficult to obtain good imaging performance on the light receiving surface 7, which is not preferable.
1.00 <F2 / F1 <5.50 (3a)

Moreover, it is more preferable to satisfy the following conditional expression (3b).
1.00 <F2 / F1 <2.00 (3b)

  In addition, what is necessary is just to select according to the performance calculated | required whether the optical system 10 is comprised so that either of conditional expression (2) or (3) mentioned above may be satisfied.

  Next, the power of each optical surface will be described in detail.

  The optical system 10 according to the present embodiment includes four reflecting surfaces having power in the first cross section, thereby realizing a wide angle of view and good optical performance in the first cross section. At this time, in the front group 11, it is desirable that the power signs in the first cross section of the first reflecting surface 2 and the second reflecting surface 3 be the same. Thereby, it is possible to prevent a part of the light flux from each object height from being blocked by the light blocking surface of the light blocking member 4. In the present embodiment, each of the first reflecting surface 2 and the second reflecting surface 3 is a convex surface in the first cross section, and each has a negative power.

  Specifically, when the first reflecting surface 2 is a convex surface, the light beam from the off-axis object height (off-axis light beam) is reflected more on the image side than the light beam from the on-axis object height (axial light beam). Will be. Therefore, the reflection point of the off-axis light beam on the first reflection surface 2 is located on the −Z side with respect to the reflection point of the on-axis light beam shown in FIG. At this time, if the second reflecting surface 3 is a flat surface or a concave surface, the off-axis ray is reflected on the + X side with respect to the on-axis ray. In this case, the incident position of the axial ray with respect to the light shielding member 4 is shifted in the second direction with respect to the incident position of the axial ray, and a part of the off-axis ray may not pass through the opening. .

  On the other hand, in the present embodiment, since the second reflecting surface 3 is convex like the first reflecting surface 2, the reflection point of the off-axis light beam on the second reflection surface 3 is on the image side than the reflection point of the axial light beam ( -X side). That is, the displacement of the reflection point position of the on-axis ray and the off-axis ray caused by the first reflecting surface 2 can be canceled by the second reflecting surface 3. Thereby, since the condensing positions of the on-axis light beam and the off-axis light beam in the second direction can be brought closer, it is possible to allow all the light beams from each object height to pass through the opening of the light shielding member 4. Become. The same applies when each of the first reflecting surface 2 and the second reflecting surface 3 is a concave surface.

Here, since the second reflecting surface 3 is disposed closer to the light shielding member 4 than the first reflecting surface 2, the interval between the reflection points of the on-axis rays and the off-axis rays on the second reflecting surface 3 is as follows. The distance between the reflection points of the on-axis ray and the off-axis ray on the first reflecting surface 2 becomes smaller. Therefore, in the first cross section, it is not preferable to make the power of the second reflecting surface 3 extremely small with respect to the power of the first reflecting surface 2. Accordingly, it is desirable that the following conditional expression (4) is satisfied when the power in the first cross section of each of the first reflecting surface 2 and the second reflecting surface 3 is φ1m and φ2m.
0.90 <φ2m / φ1m (4)

  Conditional expression (4) represents that the power of the second reflecting surface 3 in the first cross section is equal to or higher than the power of the first reflecting surface 2. By satisfying conditional expression (4), it is possible to satisfactorily correct the positional deviation between the on-axis light beam and the off-axis light beam as described above.

Furthermore, it is more preferable to satisfy the following conditional expressions (4a) and (4b) in order. When the upper limit value of conditional expressions (4a) and (4b) is exceeded, the power of the second reflecting surface 3 in the first cross section becomes too large, and it may be difficult to correct aberrations well. Further, there is a possibility that it is difficult to realize a wide angle of view by arranging the main plane of the front group 11 in the first cross section on the object side.
0.90 <φ2m / φ1m <15 (4a)
0.92 <φ2m / φ1m <10 (4b)

For the same reason, it is desirable that the third and fourth reflecting surfaces 5 and 6 in the rear group 12 have the same power sign in the first cross section. Thereby, the shift | offset | difference in the 2nd direction of the condensing position in the light-receiving surface 7 of the light beam which passed the opening of the light shielding member 4 can be suppressed. In the present embodiment, each of the third reflecting surface 5 and the fourth reflecting surface 6 is a concave surface in the first cross section, and each has a positive power. At this time, when the power in the first cross section of each of the third reflecting surface 5 and the fourth reflecting surface 6 is φ3m and φ4m, it is desirable that the following conditional expression (5) is satisfied, and the conditional expression (5a) , (5b) are more preferably satisfied in order.
1.0 <φ3m / φ4m (5)
1.0 <φ3m / φ4m <15 (5a)
1.5 <φ3m / φ4m <8.0 (5b)

  However, the effect obtained by making the signs of the powers of the reflecting surfaces of the front group 11 and the rear group 12 the same is that the optical paths of the front group 11 and the rear group 12 cross each other as described above. This is a case where each reflecting surface is arranged. When the optical paths do not intersect in each of the front group 11 and the rear group 12, for example, when each optical path is like a letter Z, the sign of the power of each reflecting surface of the front group 11 and the rear group 12 is set as necessary. It may be different.

  In order to realize a reduction in size and cost of the optical system 10, it is desirable to reduce the number of optical elements constituting the optical system 10 as much as possible. Therefore, in the present embodiment, only the first reflecting surface 2, the second reflecting surface 3, the third reflecting surface 5, and the fourth reflecting surface 6 are the reflecting surfaces having power in the first cross section. That is, in the first cross section, only the first reflecting surface 2 and the second reflecting surface 3 have power among the reflecting surfaces included in the front group 11, and the power among the reflecting surfaces included in the rear group 12 is power. Only the third reflecting surface 5 and the fourth reflecting surface 6 are provided. In this way, the entire system can be downsized by configuring the optical system 10 with a minimum number of reflecting surfaces necessary for obtaining good optical performance.

  In the present embodiment, in the first cross section, the first reflecting surface 2 and the second reflecting surface 3 are each given negative power, thereby giving the front group 11 negative power, and the third reflecting surface 5 and By giving each of the fourth reflecting surfaces 6 positive power, the rear group 12 is given positive power. Thereby, as described above, the optical system 10 becomes a retrofocus type in the first cross section, and a wide angle of view can be realized.

Further, when the power in the second cross section of each of the first reflecting surface 2 and the second reflecting surface 3 is φ1s and φ2s, it is desirable that the following conditional expression (6) is satisfied.
φ1s / φ2s <1.0 (6)

  Conditional expression (6) represents that the power of the second reflecting surface 3 in the second cross section is larger than the power of the first reflecting surface 2. By satisfying conditional expression (6), it is possible to bring the second reflecting surface 3 having higher power closer to the light shielding member 4 that is the intermediate imaging position in the second section. As a result, it is easy to reduce the magnification of the front group 11 to obtain a reduction system, and it is possible to increase the depth of field. When exceeding the upper limit value of the conditional expression (6), the first reflecting surface 2 arranged on the object side has a large power, and it becomes difficult to make the front group 11 a reduction system.

Furthermore, it is more preferable to satisfy the following conditional expression (6a). When the lower limit value of conditional expression (6a) is not reached, the power of the second reflecting surface 3 in the second cross section becomes too large, making it difficult to correct aberrations favorably, and a part of the light beam is part of the light shielding member 4. There is a possibility that it becomes impossible to pass through the opening.
0.0 <φ1s / φ2s <1.0 (6a)

Similarly, when the power in the second cross section of each of the third reflecting surface 5 and the fourth reflecting surface 6 is φ3s and φ4s, it is desirable that the following conditional expression (7) is satisfied.
1.0 <φ3s / φ4s (7)

  The width of the image formed on the light receiving surface 7 in the second direction is determined by the width of the opening of the light shielding member 4 in the second direction. At this time, if the width of the image formed on the light receiving surface 7 is increased, the wavelength resolution (spectral performance) is lowered, which is not desirable. Therefore, it is desirable to use the rear group 12 as a reduction system and reduce the magnification. By satisfying conditional expression (7), the rear group 12 can be easily reduced.

Furthermore, it is more preferable to satisfy the following conditional expressions (7a) and (7b) in order. If the lower limit value of the conditional expressions (7a) and (7b) is not reached, the width of the light beam incident on the fourth reflecting surface 6 and the power of the fourth reflecting surface 6 become too large in the second section, and the light receiving surface. 7 becomes difficult to control appropriately the condensing position of the light flux of each wavelength. On the other hand, if the upper limit value of conditional expressions (7a) and (7b) is exceeded, the fourth reflecting surface 6 approaches the plane in the second cross section and its power becomes too small, and the optical path length of the light flux of each wavelength It becomes difficult to reduce the difference. In other words, it becomes difficult to reduce the shift in the optical axis direction of the condensing position of the light flux of each wavelength.
1.5 <φ3s / φ4s <8.0 (7a)
2.0 <φ3s / φ4s <5.0 (7b)

In this embodiment, since the base surface of the third reflecting surface 5 that is a diffraction surface is an anamorphic surface, astigmatism occurs when an arrangement error such as rotation around the optical axis of the third reflecting surface 5 occurs. Will lead to a decrease in the depth of field and depth of field. In particular, in the rear group 12, the spread of the light flux is the largest when it enters the third reflecting surface 5, so that the influence of the arrangement error of the third reflecting surface 5 becomes significant. Therefore, it is desirable to satisfy the following conditional expression (8).
0.5 <φ3s / φ3m <2.0 (8)

  Conditional expression (8) represents that the power in the first cross section and the second cross section of the third reflecting surface 5 is not significantly different. By satisfying conditional expression (8), it is possible to suppress the occurrence of astigmatism and a decrease in the depth of field due to the arrangement error of the third reflecting surface 5. When the conditional expression (8) is not satisfied, the power difference between the first cross section and the second cross section of the third reflecting surface 5 becomes too large, and the influence of the arrangement error of the third reflecting surface 5 is reduced. Becomes difficult.

Furthermore, it is more preferable to satisfy the following conditional expressions (8a) and (8b) in order.
0.6 <φ3s / φ3m <1.8 (8a)
0.8 <φ3s / φ3m <1.3 (8b)

  In the second cross section, it is desirable to give the fourth reflecting surface 6 positive power. As shown in FIG. 2, the optical path lengths of the light beams L4P and L5P from the third reflecting surface 5 to the light receiving surface 7 are longer than the optical path length of the light beam L3P from the third reflecting surface 5 to the light receiving surface 7. At this time, by making the fourth reflection surface 6 concave in the second cross section, the optical path length difference of the light flux of each wavelength from the third reflection surface 5 can be easily reduced.

[Example 1]
The optical system 10 according to Example 1 of the present invention will be described below. The optical system 10 according to the present example has the same configuration as the optical system 10 according to the above-described embodiment.

  In this embodiment, the distance (object distance) from the test object to the diaphragm 1 is 300 mm, the width of the reading area in the first direction is 300 mm, and the angle of view in the first cross section is ± 24.17 °. In the present embodiment, the wavelength band used is 400 nm to 1000 nm, and the width of the image forming area (incident area) of the light beam on the light receiving surface 7 in the second direction is 2.7 mm.

  The composite focal lengths in the first cross section of the front group 11 and the rear group 12 according to this example are -16.27 mm and 28.30 mm, respectively, and the composite focal lengths in the second cross section of the front group 11 and the rear group 12 are respectively. The focal lengths are 19.99 mm and 25.76 mm, respectively. As described above, the optical system 10 according to the present embodiment improves the imaging performance by performing the intermediate in the second cross section, while widening the angle of view (reading) by adopting the retrofocus type in the first cross section. Realization of wide area).

  Here, the expression of the surface shape of each optical surface of the optical system 10 according to the present embodiment will be described. In addition, the expression of the surface shape of each optical surface is not limited to that described later, and each optical surface may be designed using another expression as necessary.

  The shape (bus shape) of the first reflecting surface 2, the second reflecting surface 3, the third reflecting surface (diffraction surface) 5, and the fourth reflecting surface 6 in the first cross section of the first reflecting surface 2, the second reflecting surface 3, and the fourth reflecting surface 6 according to the present embodiment. Is expressed by the following expression in each local coordinate system.

Here, R _y is a radius of curvature (bus curvature radius) in the xy section, and K _y , B ₂ , B ₄ , and B ₆ are aspheric coefficients in the xy section. The numerical values of the aspheric coefficients B ₂ , B ₄ , and B ₆ may be different from each other on both sides of the x axis (−y side and + y side) as necessary. As a result, the bus shape can be asymmetric in the y direction with respect to the x axis. In the present embodiment, secondary to sixth-order aspheric coefficients are used, but higher-order aspheric coefficients may be used as necessary.

  In addition, the shape (sub-wire shape) in the second cross section at an arbitrary position in the y direction of each base surface of each optical surface according to the present embodiment is expressed by the following expression.

However, K _z and M _jk are aspheric coefficients in the zx section. Further, r ′ is a radius of curvature (sub-wire curvature radius) in the zx section at a position separated by y from the optical axis in the y direction, and is represented by the following equation.

Here, r is the radius of curvature of the strand on the optical axis, and E ₂ and E ₄ are the strand changing coefficients. When r = 0 in Expression (Expression 3), the first term on the right side of Expression (Expression 2) is treated as zero. Note that the numerical values of the child line change coefficients E ₂ and E ₄ may be different from each other on the −y side and the + y side, if necessary. As a result, the aspherical amount of the child wire shape can be made asymmetric in the y direction. Moreover, although the equation (Equation 3) includes only even terms, odd terms may be added as necessary. Further, a higher order strand change coefficient may be used as necessary.

Note that the first-order term of z in the equation (Equation 2) is a term that contributes to the tilt amount (child tilt amount) of the optical surface in the zx section. Therefore, by setting M _jk to different values on the −y side and the + y side, it is possible to asymmetrically change the sub-line tilt amount in the y direction. However, the amount of sub-line tilt may be changed asymmetrically by using odd terms. In addition, the quadratic term of z in the equation (Equation 2) is a term that contributes to the radius of curvature of the optical surface. Therefore, in order to simplify the design of each optical surface, the subsurface curvature radius may be given to the optical surface using only the quadratic term of z in Expression (Expression 2) instead of Expression (Expression 3).

The shape of the diffraction grating on the diffraction surface 5 is not particularly limited as long as it is expressed by a phase function based on a known diffractive optical theory. In this embodiment, when the fundamental wavelength (design wavelength) is λ [mm] and the phase coefficient in the zx section is C1, the shape of the diffraction grating on the diffraction surface 5 is defined by the following phase function φ. However, in this embodiment, it is assumed that the diffraction order of the diffraction grating is 1.
φ = (2π / λ) × (C1 × z)

  Note that the fundamental wavelength here is a wavelength for determining the height of the diffraction grating, the spectral characteristics of the illumination light with respect to the object to be examined, the spectral reflectance of the reflective surface other than the diffraction surface 5, and the imaging including the light receiving surface 7. It is determined based on the spectral light receiving sensitivity of the element, the required diffraction efficiency, and the like. In other words, the fundamental wavelength corresponds to a wavelength that is desired to be emphasized during detection by the light receiving surface 7. In this embodiment, by setting the fundamental wavelength λ to 542 nm, the visible range in the used wavelength band can be intensively observed. However, for example, by setting the fundamental wavelength to about 850 nm, the near infrared region can be intensively observed, or by setting the fundamental wavelength to about 700 nm, the near infrared region can be observed in a balanced manner from the visible region. Also good.

Table 1 shows the position of the vertex of each optical surface of the optical system 10 according to the present embodiment, the direction of the normal line at the vertex, and the radius of curvature in each cross section. In Table 1, the position of the vertex of each optical surface is indicated by the distance X, Y, Z [mm] from the origin in the absolute coordinate system, and the direction of the normal line (x axis) is the X axis in the ZX section including the optical axis. Is represented by an angle θ [deg]. Further, d [mm] represents an interval (surface interval) between optical surfaces, d ′ [mm] represents an interval between reflection points of chief rays on each optical surface, and R _y and R _z are principal components. The curvature radii in the XY cross section and the ZX cross section at the reflection point of the light beam are shown. In addition, when the value of the radius of curvature of each reflecting surface is positive, it indicates a concave surface, and when it is negative, it indicates a convex surface.

  Table 2 shows the surface shapes of the optical surfaces of the optical system 10 according to this example.

  Table 3 shows the diameter [mm] in the y direction and the z direction of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the light receiving surface 7 when the conditional expression (2) is satisfied (Example 1a). Table 4 shows the diameter [mm] in the y direction and the z direction of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the light receiving surface 7 when the conditional expression (3) is satisfied (Example 1b). In the present embodiment, all of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the light receiving surface 7 are rectangular.

  FIG. 12 shows an MTF (Modulated Transfer Function) of the optical system 10 according to the present embodiment. In FIG. 12, the MTF for each wavelength of 700 nm (frq1), 400 nm (frq2), and 1000 nm (frq3) is obtained when the object height [mm] in the reading region is Y = 0, 30, 60, 90, 120, 150. Shows about each of them. As shown in FIG. 12, the spatial frequency [lines / mm] for each wavelength of the imaging device including the light receiving surface 7 is 27.8, 41.7, 55.6. As can be seen from FIG. 12, the aberration is satisfactorily corrected over the entire reading region, and a sufficient depth of focus is ensured.

[Example 2]
Hereinafter, the optical system 10 according to Embodiment 2 of the present invention will be described. In the optical system 10 according to the present embodiment, the description of the configuration equivalent to that of the optical system 10 according to Embodiment 1 described above is omitted.

  FIGS. 13A and 13B are schematic views of a main part of the optical system 10 according to the embodiment of the present invention. FIG. 13A shows a first cross section, and FIG. 13B shows a second cross section. The optical system 10 according to the present embodiment has a shorter optical path length from the stop 1 to the light receiving surface 7 than the optical system 10 according to the first embodiment, thereby realizing further downsizing of the entire system.

  In this embodiment, the distance from the test object to the diaphragm 1 is 300 mm, the width of the reading region in the first direction is 300 mm, and the angle of view in the first cross section is ± 24.46 °. In this embodiment, the used wavelength band is 400 nm to 1000 nm, and the width of the imaging region in the second direction on the light receiving surface 7 is 2.7 mm. The composite focal lengths in the first cross section of the front group 11 and the rear group 12 according to the present embodiment are respectively -14.21 mm and 16.69 mm, and the composite focal lengths in the second cross section of the front group 11 and the rear group 12 are respectively. The focal lengths are 19.33 mm and 11.01 mm, respectively.

  As in Example 1, Table 5 shows the position of the vertex of each optical surface of the optical system 10 according to this example, the direction of the normal at the vertex, and the radius of curvature at each cross section, and Table 6 shows each optical surface. The surface shape of is shown. Table 7 shows the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7 when the conditional expression (2) is satisfied (Example 2a). Table 4 satisfies the conditional expression (3). In this case, the diameter of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7 in Example 2b is shown.

However, as for the shape of the third reflecting surface 5 in the second cross section, the local line that differs from position to position so that the normal line at each position on the generatrix represented by the equation (Equation 1) matches the x axis. After defining the coordinate system, it is expressed by the above equation (Equation 2). The reason why the values of the curvature radii _Ry do not match between Table 5 and Table 6 is that the values of the curvature radii in Table 5 take into account the tilt angle in the second cross section.

  FIG. 14 shows the MTF of the optical system 10 according to the present embodiment as in FIG. As can be seen from FIG. 14, the aberration is satisfactorily corrected over the entire reading region, and a sufficient depth of focus is ensured.

[Example 3]
The optical system 10 according to Example 3 of the present invention will be described below. In the optical system 10 according to the present embodiment, the description of the configuration equivalent to that of the optical system 10 according to Embodiment 1 described above is omitted.

  15A and 15B are schematic views of a main part of the optical system 10 according to the embodiment of the present invention. FIG. 15A shows the first cross section, and FIG. 15B shows the second cross section. The optical system 10 according to the present embodiment has a configuration in which the emission side (image side) Fno is smaller (brighter) than the optical system 10 according to the first embodiment. Specifically, the Fno on the emission side of the optical system 10 according to the first embodiment is 4.7 and 4.0 in the first and second cross sections, respectively, whereas the optical system according to the present embodiment. Fno on the exit side of 10 is 4.1 and 3.5 in the first and second cross sections, respectively.

  In this embodiment, the distance from the test object to the diaphragm 1 is 300 mm, the width of the reading region in the first direction is 300 mm, and the angle of view in the first cross section is ± 24.44 °. In this embodiment, the wavelength band used is 400 nm to 1000 nm, and the width of the imaging region in the second direction on the light receiving surface 7 is 2.64 mm. The combined focal lengths in the first cross section of the front group 11 and the rear group 12 according to the present embodiment are -14.46 mm and 26.85 mm, respectively, and the combined focal lengths in the second cross section of the front group 11 and the rear group 12 are respectively. The focal lengths are 19.34 mm and 24.98 mm, respectively.

  As in Example 1, Table 9 shows the position of the vertex of each optical surface of the optical system 10 according to this example, the direction of the normal at the vertex, and the radius of curvature at each cross section. Table 10 shows each optical surface. The surface shape of is shown. Table 11 shows the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7 when the conditional expression (2) is satisfied (Example 3a), and Table 12 satisfies the conditional expression (3). In this case, the diameter of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7 in Example 3b is shown.

  FIG. 16 shows the MTF of the optical system 10 according to the present embodiment, similarly to FIG. As can be seen from FIG. 16, the aberration is satisfactorily corrected over the entire reading area, and a sufficient depth of focus is ensured.

[Example 4]
The optical system 10 according to Example 4 of the present invention will be described below. In the optical system 10 according to the present embodiment, the description of the configuration equivalent to that of the optical system 10 according to Embodiment 1 described above is omitted.

  FIGS. 17A and 17B are schematic views of a main part of the optical system 10 according to the embodiment of the present invention. FIG. 17A shows a first cross section, and FIG. 17B shows a second cross section. The optical system 10 according to the present embodiment has a shorter optical path length from the stop 1 to the light receiving surface 7 than the optical system 10 according to the first embodiment, thereby realizing further downsizing of the entire system.

  In this embodiment, the distance from the test object to the diaphragm 1 is 300 mm, the width of the reading region in the first direction is 300 mm, and the angle of view in the first section is ± 24.49 °. In this embodiment, the used wavelength band is 400 nm to 1000 nm, and the width of the imaging region in the second direction on the light receiving surface 7 is 2.37 mm. The composite focal lengths in the first cross section of the front group 11 and the rear group 12 according to the present embodiment are -13.23 mm and 16.78 mm, respectively, and the composite focal lengths in the second cross section of the front group 11 and the rear group 12 are respectively. The focal lengths are 17.53 mm and 11.25 mm, respectively.

As in Example 1, Table 13 shows the position of the vertex of each optical surface of the optical system 10 according to this example, the direction of the normal line at the vertex, and the radius of curvature at each cross section, and Table 14 shows each optical surface. The surface shape of is shown. Table 15 shows the aperture of the diaphragm 1, the aperture of the light shielding member 4 and the diameter of the light receiving surface 7 when the conditional expression (2) is satisfied (Example 4a), and Table 16 satisfies the conditional expression (3). In this case, the diameter of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the light receiving surface 7 in Example 4b is shown. The reason why the values of the curvature radii _Ry do not match between Table 13 and Table 14 is that the values of the curvature radii in Table 13 take into account the tilt angle in the second cross section.

In the present embodiment, the sub-wire shapes of the first reflecting surface 2, the second reflecting surface 3, the third reflecting surface 5, and the fourth reflecting surface 6 are the following formulas instead of the above formula (Equation 3). It is expressed using Further, the shape of the sub-line of the third reflecting surface 5 is expressed by the above formula (Equation 2) after defining a different local coordinate system for each position on the bus line as in the second embodiment.
r ′ = r (1 + E ₂ y ² + E ₄ y ⁴ )

  FIG. 18 shows the MTF of the optical system 10 according to the present embodiment as in FIG. As can be seen from FIG. 18, the aberration is satisfactorily corrected over the entire reading region, and a sufficient depth of focus is ensured.

[Example 5]
The optical system 10 according to Example 5 of the present invention will be described below. The optical system 10 according to the present embodiment is different from the optical system 10 according to the first embodiment in that the tilt angle of the first reflecting surface 2 is not changed in the first direction. In the optical system 10 according to the present embodiment, the description of the same configuration as the optical system 10 according to the first embodiment is omitted.

  The composite focal lengths in the first cross section of the front group 11 and the rear group 12 according to the present embodiment are −17.01 mm and 28.56 mm, respectively, and the composite focal lengths in the second cross section of the front group 11 and the rear group 12 are respectively. The focal lengths are 19.31 mm and 25.91 mm, respectively.

In the present embodiment, the tilt angle of the first reflecting surface 2 is changed by setting the aspherical coefficients M ₀₁ , M ₂₁ , and M ₄₁ for the first-order term of z in the above equation (Equation 2) to zero. Is missing. Thereby, the surface shape of the 1st reflective surface 2 can be simplified and it can be made easy to manufacture. In particular, when the first reflective surface 2 is formed by molding, the degree of difficulty in processing the mold is reduced, so that the time required for the processing can be greatly shortened.

  As in Example 1, Table 17 shows the position of the vertex of each optical surface of the optical system 10 according to this example, the direction of the normal line at the vertex, and the radius of curvature at each cross section, and Table 18 shows each optical surface. The surface shape of is shown.

  FIG. 19 shows the distribution of the light flux from each object height on the opening of the light shielding member 4 according to the present embodiment, as in FIG. As can be seen from FIG. 19, it can be seen that the curvature in the z direction of the distribution of the light flux from each object height can be sufficiently reduced.

  Table 19 shows the image side F value F1 in the first cross section, the image side F value F2 in the second cross section, and the value of the conditional expression (1) of the optical system 10 according to Examples 1a to 4a. . As shown in Table 19, conditional expression (1) is satisfied in any of the examples. Table 20 shows the image side F value F1 in the first cross section, the image side F value F2 in the second cross section, and the value of the conditional expression (2) of the optical system 10 according to Examples 1b to 4b. Indicates. As shown in Table 20, conditional expression (2) is satisfied in any of the examples.

  Table 21 shows the power value of each reflecting surface according to each example and the value of each conditional expression described above.

[Imaging apparatus and imaging system]
Hereinafter, an imaging apparatus (spectral reading apparatus) and an imaging system (spectral reading system) as examples of use of the optical system 10 according to the above-described embodiment will be described.

  20 and 21 are schematic views of main parts of the imaging systems 100 and 200 according to the embodiment of the present invention. The imaging systems 100 and 200 are configured to change the relative positions of the imaging system 101 and 201 having an optical system 10 and an image sensor that receives an image formed by the optical system 10, and each imaging apparatus and the test objects 103 and 203. Sections 102 and 202. Each imaging system desirably has an image processing unit that generates an image based on image information obtained from the imaging element. The image processing unit is a processor such as a CPU, for example, and may be provided inside or outside each imaging apparatus.

  According to the imaging devices 101 and 201, a plurality of pieces of image information (one-dimensional images) corresponding to a plurality of wavelengths are obtained by imaging the linear reading regions 104 and 204 that are long in the first direction (Y direction) once. Can be obtained. At this time, it is desirable to configure each imaging device as a multispectral camera that can acquire image information corresponding to four or more types of wavelengths more than a general camera. Furthermore, it is more preferable to configure each imaging device as a hyperspectral camera that can acquire image information corresponding to 100 or more wavelengths.

  A CCD (Charge Coupled Device) sensor, a CMOS (Complementary Metal Oxide Semiconductor) sensor, or the like can be used as an imaging element in each imaging apparatus. The imaging device may be configured to photoelectrically convert not only visible light but also infrared light (near infrared light or far infrared light). Specifically, an image sensor using a material such as InGaAs or InAsSb may be employed according to the wavelength band used. In addition, the number of pixels of the image sensor is desirably determined based on the resolution required in the reading direction and the spectral direction.

  As illustrated in FIG. 20, the transport unit 102 in the imaging system 100 is a unit that moves the test object 103 in the second direction (Z direction). A belt conveyor or the like can be employed as the transport unit 102. On the other hand, as illustrated in FIG. 21, the conveyance unit 202 in the imaging system 200 is a unit that moves the imaging device 201 in the second direction. As the transport unit 202, a multicopter, an airplane, an artificial satellite, or the like can be employed. By using the transport unit 202, it is possible to perform imaging at a plurality of positions in the second direction even for a large test object that cannot be transported by a belt conveyor or the like that is difficult to move. .

  According to the imaging systems 100 and 200, a plurality of positions in the second direction can be obtained by causing each imaging device to sequentially image the reading area while changing the relative position of each imaging device and each test object in each transport unit. A plurality of pieces of image information corresponding to can be acquired. A two-dimensional image corresponding to a specific wavelength can be generated by performing rearrangement or arithmetic processing of the plurality of captured images by the image processing unit. In addition, since each image information represents the grayscale information in the first direction, the image processing unit generates a spectral distribution (spectrum information) based on the grayscale information for each wavelength at a specific position in the second direction. Also good.

  In addition, you may comprise each conveyance part so that both each imaging device and each test object may be moved. Moreover, you may enable it to adjust the relative position in the optical axis direction (X direction) of each imaging device and each test object by each conveyance part. Alternatively, an optical member (focusing member) that can be driven inside or outside the optical system 10 is arranged, and the position of the optical member may be adjusted so that the object can be focused.

[Inspection method and manufacturing method]
Hereinafter, an object (test object) inspection method and article manufacturing method using the optical system 10 according to the above-described embodiment will be described. The optical system 10 is suitable for inspection (evaluation) in industrial fields such as manufacturing, agriculture, and medicine.

  In the first step (imaging step) in the inspection method according to the present embodiment, image information of an object is acquired by imaging the object via the optical system 10. At this time, an imaging apparatus or an imaging system as described above can be used. That is, it is possible to acquire image information of the entire object by imaging the object while changing the relative positions of the object and the imaging device. In addition, image information of a plurality of objects can be acquired sequentially (continuously). In the first step, a plurality of pieces of image information corresponding to the wavelengths of the plurality of light beams emitted from the optical system 10 may be acquired.

  In the next second step (inspection step), the object is inspected based on the image information acquired in the first step. At this time, for example, the user (inspector) confirms (determines) the presence or absence of foreign matter or scratches in the image information, or the control unit (image processing unit) detects the foreign matter or scratches in the image information and notifies the user. May be. Or you may employ | adopt the control part which controls the manufacturing apparatus of the articles | goods mentioned later according to the determination result of the presence or absence of a foreign material or a crack.

  In the second step, the object may be inspected based on the spectral distribution of the object acquired using a plurality of pieces of image information for each wavelength. By using the image information acquired via the optical system 10, it is possible to detect unique spectral information of the object to be inspected, and thereby to identify the component of the object. For example, the image processing unit may generate image information in which coloring or the like is enhanced for each spectrum distribution, and the user may perform inspection based on the image information.

  The inspection method according to the present embodiment can be applied to a method for manufacturing an article such as a food, a medicine, or a cosmetic. Specifically, the material (object) for manufacturing the article can be inspected by the inspection method described above, and the article can be manufactured using the inspected material. For example, when it is determined in the second step that the material has foreign matter or scratches, the user (manufacturer) or the manufacturing apparatus removes the foreign matter from the material, or discards the foreign matter or scratched material. can do.

  Moreover, you may use the said inspection method for the abnormality detection of a manufacturing apparatus. For example, the presence or absence of an abnormality may be determined based on the image information of the manufacturing apparatus, and the driving of the manufacturing apparatus may be stopped or the abnormality may be corrected according to the determination result.

  The preferred embodiments and examples of the present invention have been described above, but the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes can be made within the scope of the gist.

2 First reflecting surface (first aspherical surface)
3 Second reflecting surface (second aspherical surface)
4 light shielding member 5 third reflecting surface (diffraction surface)
7 Light receiving surface (image surface)
10 optical system 11 front group 12 rear group

Claims (20)

An optical system composed of a front group, a light shielding member, and a rear group arranged in order from the object side to the image side,
The light shielding member is provided with a long opening in the first direction,
The front group has an aspherical surface, and in the first cross section parallel to the first direction, the object is not imaged on the opening, and in the second cross section perpendicular to the first direction. Forming an intermediate image of the object on the aperture;
The rear group has a diffractive surface for splitting the light beam that has passed through the opening in the second cross section into a plurality of light beams having different wavelengths, and the plurality of light beams are collected at different positions in the second cross section. Light
The optical system according to claim 1, wherein a tilt angle of the aspheric surface in the second cross section changes in the first direction.   The tilt angle of the aspherical surface in the second cross section changes so that the incident positions of the axial principal ray and the most off-axis principal ray in the light shielding member approach each other in a second direction perpendicular to the first direction. The optical system according to claim 1.   3. The optical system according to claim 1, wherein a tilt angle of the aspheric surface in the second cross section changes monotonously in the first direction. 4.   The said front group has the 1st and 2nd aspherical surface in which the tilt angle in the said 2nd cross section changes in the said 1st direction, The Claim 1 thru | or 3 characterized by the above-mentioned. Optical system. When the tilt change amounts of the first and second aspheric surfaces in the region where the light beam from the same object point passes are | dT ₁ / dy | and | dT ₂ / dy |
1.00 ≦ | dT ₁ / dy | / | dT ₂ /dy|≦1.50
The optical system according to claim 4, wherein the following condition is satisfied.   6. The optical system according to claim 1, wherein a base surface of the diffractive surface is an aspherical surface.   7. The optical system according to claim 1, wherein, in the first cross section, the front group has a negative power, and the rear group has a positive power. 8.   The optical system according to claim 1, wherein the light shielding member regulates a width of the light beam from the object in the first direction.   The optical system according to any one of claims 1 to 8, wherein a width of the opening in the second cross section is 0.2 mm or less.   The optical system according to claim 1, wherein all optical surfaces included in the front group and the rear group are reflecting surfaces.   An imaging apparatus comprising: the optical system according to claim 1; and an imaging element that receives an image formed by the optical system.   An imaging system comprising: the imaging apparatus according to claim 11; and a transport unit that changes a relative position between the imaging apparatus and the object.   The imaging system according to claim 12, further comprising an image processing unit that generates image information for each wavelength corresponding to the plurality of light beams. A first step of acquiring image information of the object by imaging the object via an optical system;
And a second step of inspecting the object based on the image information,
The optical system is composed of a front group, a light shielding member, and a rear group arranged in order from the object side to the image side,
The light shielding member is provided with a long opening in the first direction,
The front group has an aspherical surface, and in the first cross section parallel to the first direction, the object is not imaged on the opening, and in the second cross section perpendicular to the first direction. Forming an intermediate image of the object on the aperture;
The rear group has a diffractive surface for splitting the light beam that has passed through the opening in the second cross section into a plurality of light beams having different wavelengths, and the plurality of light beams are collected at different positions in the second cross section. Light
The inspection method according to claim 1, wherein a tilt angle of the aspheric surface in the second cross section changes in the first direction.   The inspection method according to claim 14, wherein the first step includes a step of imaging the object while moving the object in a direction perpendicular to the first direction.   16. The inspection method according to claim 14, wherein the first step includes a step of acquiring a plurality of pieces of image information corresponding to the wavelengths of the plurality of light beams.   17. The method according to claim 14, wherein the second step includes a step of inspecting the object based on a spectral distribution of the object acquired using the plurality of pieces of image information. Inspection method described in 1.   The inspection method according to any one of claims 14 to 17, wherein the second step includes a step of determining the presence or absence of a foreign substance in the object. Inspecting the object by the inspection method according to any one of claims 14 to 18,
And a step of manufacturing an article using the object inspected in the step.   The manufacturing method according to claim 19, wherein the step of manufacturing the article includes a step of removing foreign substances in the object.

Images