JP7214376B2 - OPTICAL SYSTEM, IMAGING DEVICE AND IMAGING SYSTEM INCLUDING THE SAME - Google Patents

Description

The present invention relates to an optical system used in an imaging apparatus that obtains image information by dispersing a luminous flux from an object, and is suitable for evaluation and inspection in industrial fields such as agriculture, food, and medicine.

2. Description of the Related Art Conventionally, an optical system is known that splits a light beam from a test object (object) into a plurality of light beams having different wavelengths and converges the light beams at different positions. Patent Literature 1 describes an optical system in which a light beam reflected by a cylindrical mirror is split by a diffraction grating and each light beam is condensed by a lens.

U.S. Pat. No. 7,199,877

However, in the optical system described in Patent Document 1, since the incident angles of the light beams with respect to the lens are different from each other, different coma aberrations occur for each wavelength. In order to correct such coma aberration that differs for each wavelength, it is necessary to use a large number of lenses, which complicates the configuration of the optical system.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical system capable of correcting different aberrations for each wavelength with a simple configuration, and an imaging device and an imaging system including the optical system.

An optical system as one aspect of the present invention for achieving the above object is an optical system comprising a front group, a light shielding member, and a rear group arranged in order from an object side to an image side, wherein the light shielding member includes , a long aperture is provided in a first direction, and the front group does not form an image of an object on the aperture in a first cross section parallel to the first direction; An intermediate image of the object is formed on the aperture in the second vertical section, and the rear group disperses the light flux passing through the aperture in the second cross section into a plurality of light fluxes having different wavelengths. and an anamorphic optical surface for condensing the plurality of light beams at different positions on the second cross section, wherein the axis normal to the origin of the anamorphic optical surface is the x axis, and the first and _{perpendicular} to the _x -axis at the origin is the y-axis; , the radius of curvature at the origin of the anamorphic optical surface in the second cross section is r, the sagittal change coefficients are E2 _and E4 , and the shape of the anamorphic optical surface in the _second cross section is given by When expressed by a formula, the curvature on one side with respect to the x-axis of the shape defined by the formula becomes smaller as it goes off-axis, and the curvature on the other side with respect to the x-axis goes off-axis It is characterized by increasing according to

Advantageous Effects of Invention According to the present invention, it is possible to provide an optical system capable of correcting different aberrations for each wavelength with a simple configuration, and an imaging apparatus and an imaging system having the optical system.

FIG. 2 is a schematic diagram of the essential parts in the XY cross section of the optical system according to the embodiment; FIG. 2 is a schematic diagram of a main part in the ZX cross section of the optical system according to the embodiment; FIG. 2 is a schematic diagram of a main part of a diffractive optical element according to an embodiment; The figure which shows the partial curvature in the zx cross section of the 4th reflective surface which concerns on embodiment. FIG. 4 is a diagram showing a condensed state of light beams having different wavelengths according to the embodiment; FIG. 10 is a diagram showing a condensed state of light beams having different wavelengths according to a comparative example; 4 is a diagram showing the MTF of the optical system according to Example 1. FIG. FIG. 7 is a schematic diagram of a main part of an optical system according to Example 2; FIG. 10 is a diagram showing the MTF of the optical system according to Example 2; FIG. 10 is a schematic diagram of a main part of an optical system according to Example 3; FIG. 11 is a diagram showing the MTF of the optical system according to Example 3; FIG. 10 is a schematic diagram of a main part of an optical system according to Example 4; FIG. 11 is a diagram showing the MTF of the optical system according to Example 4; 1 is a schematic diagram of a principal part of an imaging system as usage example 1 of the optical system according to the embodiment; FIG. FIG. 2 is a schematic diagram of a principal part of an imaging system as usage example 2 of the optical system according to the embodiment;

Preferred embodiments of the present invention will be described below with reference to the drawings. Each drawing may be drawn on a scale different from the actual scale for the sake of convenience. Moreover, in each drawing, the same reference numerals are given to the same members, and redundant explanations are 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 direction axis (optical axis) at the vertex (origin) of each optical surface, the y-axis is parallel to the Y-axis and perpendicular to the x-axis at the origin, and the z-axis is the x-axis and It is the axis perpendicular to the y-axis. In addition, 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 section and the xy section are the first section (reading section), the ZX section and The zx section is also called a second section (spectral section).

1 and 2 are schematic diagrams of essential parts of an optical system 10 according to an embodiment of the present invention, with FIG. 1 showing a first cross section and FIG. 2 showing a second cross section. 1 and 2 show the shape of each member in a cross section including the optical axis, and in FIG. 1, each member is shown on the same page for the sake of convenience. 1 and 2, the diffraction grating on the diffraction surface is omitted for the sake of convenience. In this embodiment, it is assumed that the test object is placed 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 placed on the image plane of the optical system 10. do. It is also assumed that the test object is illuminated with white light (light having multiple wavelength components) such as sunlight.

An optical system 10 according to this embodiment includes a front group 11, a light shielding member (slit member) 4, and a rear group 12, which are arranged in order from the object side to the image side. The optical system 10 forms an image of the test object on a light receiving surface (image plane) 7 by condensing a light beam from the test object (not shown) positioned on the -X side. The front group 11 has a stop 1 , a first reflecting surface 2 and a second reflecting surface 3 . The rear group 12 also has a third reflecting surface (diffractive surface) 5 and a fourth reflecting surface 6 . A cover glass G is arranged immediately before the light-receiving surface 7, but it is treated as something that does not contribute to image formation.

The diaphragm 1 is a member for regulating the width in the second direction of the light flux from the test object, and is arranged so that its aperture surface 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 entrance (aperture 1) and exit (light-receiving surface 7) of the optical system 10 are arranged on opposite sides of each optical surface. As a result, when the optical system 10 is applied to an imaging apparatus, it is possible to easily avoid blocking of the light flux from the subject by the imaging element, wiring, or the like.

The light shielding member 4 is provided with an opening (slit) elongated in the first direction. The light blocking member 4 functions as a diaphragm that limits the width of the light beam in the first direction while limiting the angle of view in the second section of the optical system 10 to block unnecessary light. The width of the opening of the light shielding member 4 is determined according to the required light amount, resolution, and the like. The width of the opening of the light shielding member 4 in the second direction is shorter than the width (several millimeters) in the first direction, and is preferably several μm to several hundred 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 will be reduced. It is more preferably 10 μm or more and 0.2 mm or less.

Areas other than the apertures of the diaphragm 1 and the light shielding member 4 are light shielding surfaces through which at least light in the wavelength band used (designed wavelength band) of the optical system 10 does not pass. As the diaphragm 1 and the light shielding member 4, it is possible to adopt a plate metal with a hole or a glass plate whose surface is vapor-deposited with chromium. By adopting such a light shielding member 4, the optical system 10 can form an image of a linear reading area (test area) long in the first direction.

The first reflecting surface 2, the second reflecting surface 3, and the fourth reflecting surface 6 are reflecting surfaces obtained by applying a reflecting coating to a base surface having a free-form surface shape. The base surface of each reflective 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 spectral reflection characteristics that enable sufficient energy efficiency (light utilization efficiency) to be achieved in the wavelength band used. Note that the reflective coating may be omitted if the base surface has a sufficient reflectance in the wavelength band used.

In this embodiment, each of the first reflecting surface 2, the second reflecting surface 3, and the fourth reflecting surface 6 is an anamorphic optical surface (anamorphic reflection surface) having a different curvature (power) between the first cross section and the second cross section. surface). Thereby, different optical actions can be produced between the first cross section and the second cross section. In particular, in the second cross section, the fourth reflecting surface 6 has a smaller curvature on one side of the optical axis toward the off-axis direction, and a curvature on the other side of the optical axis toward the off-axis direction. It has a shape that makes it bigger. This makes it possible to satisfactorily correct coma aberration that differs for each wavelength (details will be described later).

Each reflecting surface of the front group 11 may not be an anamorphic optical surface. For example, each reflecting surface may be spherical and an anamorphic refractive surface may be provided instead. However, in order to reduce the number of optical surfaces in the front group 11, it is desirable that at least one of the first reflecting surface 2 and the second reflecting surface 3 be an anamorphic optical surface. Also, the rear group 12 may have at least one diffractive surface and at least one anamorphic optical surface arranged on the image side thereof.

However, in order to suppress the occurrence of aberration by sharing the power between the optical surfaces, it is more preferable to make all the optical surfaces of the front group 11 and the rear group 12 anamorphic optical surfaces. If the diffractive surface 5 is provided in the front group 11 , only part of the wavelengths of light can pass through the opening of the light shielding member 4 . Therefore, it is necessary to provide the diffractive surface 5 in the rear group 12 .

In the present embodiment, all the optical surfaces are made reflecting surfaces, so that the optical path is bent and the size of the optical system 10 is reduced 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. Placement is desirable. At least one optical surface may be a refractive surface (transmissive surface) as required.

However, especially in the rear group 12, since a holding member and wiring (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 sufficient space could be secured, a plurality of refracting optical elements would need to be arranged in order to correct chromatic aberration satisfactorily, resulting in an increase in the size of the entire system. Therefore, it is desirable that at least all optical surfaces included in the rear group 12 are reflecting surfaces. Furthermore, it is more preferable that all the optical surfaces included in the front group 11 are reflecting surfaces.

As described above, the configuration of the optical system 10 is not limited to the present embodiment. For example, the front group 11 may be configured with one or three or more optical surfaces, or the rear group 12 may be configured with three or more optical surfaces. You may That is, the front group 11 should have at least one reflecting surface or refractive surface, and the rear group 12 should have at least two reflecting surfaces or refractive surfaces (one of which is a diffractive surface). At this time, a configuration in which a reflective surface and a refracting surface are combined may be used as necessary. However, in order to reduce the size of the entire system and reduce the number of parts, it is desirable to configure each of the front group 11 and the rear group 12 with two reflecting surfaces as in this embodiment.

3A and 3B are schematic diagrams of essential parts 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 direction). The diffraction surface 5 is composed of a base surface 51 and a diffraction grating 52 provided on the base surface 51 . In FIG. 3, only a portion of the diffraction grating 52 is shown enlarged for the sake of convenience.

The base surface 51 of the diffractive surface 5 has a free-form surface shape like the other reflecting surfaces. The diffraction grating 52 is composed of a plurality of gratings (projections) arranged at a pitch on the order of submicrons to microns, and the height of each grating is also on the order of submicrons to microns. As the diffraction grating 52, the shape of the zx cross section can be a stepped shape, a rectangular uneven shape, a blaze shape, a SIN wave shape, or the like. 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 blaze shape is adopted, which relatively easily achieves both improvement in diffraction efficiency and simplification of manufacturing. In the blaze-shaped diffraction grating, the part farthest in the x-direction from the base surface 51 is the grating vertex, the part that reflects (diffracts) the incident light is the blaze surface (grating surface), and the adjacent blaze surface contributes to the diffraction. The part not covered is called the lattice wall surface. The diffraction 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, the short-wavelength light flux is incident on the +Z side of the light-receiving surface 7 in FIG. 2, and the long-wavelength light flux is incident on the -Z side.

Base surface 51 is formed in a manner similar to the other reflective surfaces described above. The diffraction grating 52 can be formed by processing the base surface 51 by cutting or polishing, but the diffraction grating 52 may be formed at the same time as the base surface 51 is formed. For example, the diffractive optical element 50 provided with the diffraction grating 52 may be manufactured by forming a fine concave-convex structure on the surface of a mirror piece forming a mold, and molding using the mold. In addition, in order to improve the diffraction efficiency, the surface of the diffraction grating 52 may be coated with a reflective coating.

Further, as shown in FIG. 3B, it is desirable to configure the diffraction grating 52 so that a plurality of ridgelines corresponding to the vertices of each grating on the zx cross section are parallel to each other. Furthermore, it is more preferable to keep the intervals between the ridge lines of the diffraction grating 52 constant. Thereby, processing of the base surface 51 by cutting or polishing can be facilitated. However, if necessary, the intervals between the ridges may be non-constant. For example, in order to achieve a higher degree of aberration correction in the optical system 10, the distance between each ridge line may be changed in the z direction.

The base surface 51 of the diffraction surface 5 is desirably an anamorphic surface having different curvatures in the xy section and the zx section. This makes it possible to share the power with other anamorphic optical surfaces, thereby facilitating correction of aberrations. In this embodiment, the base surface 51 of the diffractive surface 5 is an anamorphic surface, but the base surface 51 may be formed of a flat surface or a spherical surface, emphasizing ease of manufacturing the diffraction grating 52 .

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

A luminous flux emitted from the object to be inspected passes through the opening of the stop 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 form an image of the test object on the opening of the light shielding member 4 in the first cross section (XY cross section), and does not form an image on the opening of the light shielding member 4 in the second cross section (ZX cross section). forms an intermediate image of the object. That is, the front group 11 is constructed so that the focal position does not coincide with the object plane in the first cross section. As a result, a linear intermediate image (line image) long in the first direction is formed on the opening of the light shielding member 4 . Here, "on the aperture" is not limited to the exact position of the aperture, but includes the vicinity of the aperture (substantially above the aperture) that is slightly away from the position of the aperture in the optical axis direction.

The luminous flux that has passed through the opening of the light shielding member 4 is split into a plurality of luminous fluxes with different wavelengths by the diffraction surface 5 on the second cross section. At this time, as shown in FIG. 3, since the diffraction grating 52 on the diffraction surface 5 is composed of a plurality of gratings (ridge lines) arranged in the z direction, the light flux incident on the diffraction surface 5 undergoes spectral action only in the z direction. It receives no spectroscopic effect in the y-direction.

A plurality of light beams from the diffraction surface 5 are reflected by the fourth reflecting surface 6 and enter the light receiving surface 7 arranged on the image plane. At this time, the 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 can be formed on the light receiving surface 7 for each wavelength, 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 produces different optical effects between the first cross section including the reading direction and the second cross section including the spectroscopic direction. Specifically, in the first cross section, the object to be inspected is not once imaged on the opening of the light shielding member 4, but is imaged on the light receiving surface 7, but in the second cross section, the object to be inspected is imaged on the light shielding member 4. image is once formed on the aperture of , and then imaged again on the light-receiving surface 7 . That is, the first cross-section images the test object once, while the second cross-section images the test object twice.

According to this configuration, since the convergence state of the light flux passing through the opening of the light shielding member 4 is not restricted in the first cross section, the degree of freedom in designing the optical system 10 can be improved. Therefore, the power can be appropriately shared between the front group 11 and the rear group 12 to form an image of the test object on the light receiving surface 7, which facilitates correction of various aberrations. It is possible to achieve both widening of the area and high definition of the captured image.

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 luminous flux passing through the opening of the light shielding member 4 can be non-parallel. This makes it easier to achieve a wide angle of view in the first cross section. If the luminous flux passing through the aperture of the light shielding member 4 were parallel rays, it would be necessary to dispose a large number of optical elements in the rear group 12 in order to widen the angle of view of the optical system 10. The system becomes large. In this embodiment, a wide angle of view is achieved by diverging the light flux passing through the opening of the light shielding member 4. However, if necessary, the light flux passing through the opening of the light shielding member 4 may be regarded as convergent light.

Further, when the subject is once imaged on the opening of the light shielding member 4 in the first cross section as well, each of the front group 11 and the rear group 12 must correct aberrations independently. Therefore, it becomes difficult to widen the angle of view of the optical system 10 because the degree of freedom in designing each optical surface is reduced, such as the need to increase the power of each optical surface. On the other hand, since it is not necessary to widen the angle of view in the second cross section, it is possible to increase the NA by forming an image of the test object once on the opening of the light shielding member 4 .

In the configuration described above, the front group 11 and the rear group 12 have different powers in the first section and the second section. In order to realize this configuration, it is necessary to provide anamorphic optical surfaces in each of the front group 11 and the rear group 12 . At this time, the anamorphic optical surfaces included in the front group 11 should positively have power (the absolute value of the curvature should be larger than 0) not only in the second cross section but also in the first cross section. desirable.

In the second section, the front group 11 and the rear group 12 have positive power in order to form an image of the subject once on the opening of the light shielding member 4 and then re-image it on the light receiving surface 7. need to let On the other hand, in the first cross section, it is not necessary to form an image of the test object on the opening of the light shielding member 4. Therefore, in order to further widen the angle of view, the front group 11 is provided with negative power. , the rear group 12 preferably has positive power. As a result, the optical system 10 becomes a retrofocus type in the first section, so that the focal length of the entire system is shortened and a wide angle of view can be achieved. However, if the subject is sufficiently far away from the optical system 10, the front group 11 is given positive power and the rear group 12 is given negative power, so that the optical system 10 can be used as a telescopic optical system. good too.

A state in which a light beam is dispersed by the diffraction surface 5 will be described with reference to FIG. Here, it is assumed that a white luminous flux emitted from one point of the object is divided into luminous fluxes of wavelengths λ1 [nm], λ2 [nm], and λ3 [nm] (λ2 < λ1 < λ3). . However, FIG. 2 shows only the chief ray and the marginal ray among the respective light beams.

The principal ray L1P and the marginal rays L1U and L1L in the white light beam emitted from the test object pass through the diaphragm 1, the first reflecting surface 2, and the second reflecting surface 3 and form a line-shaped intermediate beam on the opening of the light shielding member 4. form an image. The principal ray L2P and the marginal rays L2U and L2L that have passed through the opening of the light shielding member 4 are divided by the diffraction surface 5 into light rays L3P, L3U and L3L of wavelength λ1, light rays L4P, L4U and L4L of wavelength λ2, and light rays of wavelength λ3. It is split into L5P, L5U, and L5L. The light beams of wavelength λ1, wavelength λ2, and wavelength λ3 are condensed at a first position 73, a second position 74, and a third position 75 on the light receiving surface 7, respectively.

Next, the shape and action of the fourth reflecting surface 6 will be described in detail.

FIG. 4 shows the partial curvature (aspheric amount) of the fourth reflecting surface 6 in the second cross section. In FIG. 4, the horizontal axis indicates the position [mm] in the z direction with respect to the origin of the local coordinate system of the fourth reflecting surface 6, and the vertical axis indicates the partial curvature 1/R _z [1/mm] of the fourth reflecting surface 6. is shown. _Rz is the partial radius of curvature of the fourth reflecting surface 6 in the second cross section. In FIG. 4, the solid line, dashed line, and dashed-dotted line represent y = 0.0 [mm], y = -6.0 [mm], and y = -10.0 [mm] in the local coordinate system. It shows a graph at position.

As can be seen from FIG. 4, the partial curvature 1/R _z is asymmetric on the -z side and +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. Furthermore, the partial curvature 1/ _Rz changes differently (asymmetrically) on the -z side and the +z side with respect to the optical axis. In this embodiment, the partial curvature 1/R _z increases off-axis on the -z side and decreases off-axis on the +z side. Also, the partial curvature 1/ _Rz increases with increasing distance from the position of y=0 [mm].

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

5(a), 5(b), and 5(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 diffraction surface 5 The curvature on the side (closer side) decreases toward the off-axis direction. On the other hand, the curvature of the -z side of the fourth reflecting surface 6 with respect to the optical axis, that is, the side opposite to the vertex 54 of the base surface of the diffractive surface 5 (far side) increases toward the off-axis direction. As a result, the marginal ray L3L incident on the +z side of the fourth reflecting surface 6 and the marginal ray L3U incident on the -z side of the fourth reflecting surface 6 are each reflected so as to approach the principal ray L3P. As can be seen from FIG. 5, the coma aberration on the light receiving surface 7 is well corrected for the light beams of any wavelength.

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

The fourth reflecting surface 6 according to the comparative example is obtained by setting a part of the aspheric coefficients in the expression representing the shape of the second cross section of the fourth reflecting surface 6 according to this embodiment to zero. Specifically, the values of the aspheric coefficients M01, M21, M41, M03, M23, M43, M05, M25, and M45 in the later-described formula (Formula 2) are set to zero. However, the values of M01, M05, M25 and M45 are also 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 symmetrical with respect to the optical axis, unlike the present embodiment.

FIG. 6 shows, in the same manner as FIG. 5, the state of convergence of light beams of different wavelengths on the light receiving surface 7 in the second cross section including the optical axis according to the comparative example. 6(a), 6(b), and 6(c) show that the principal ray and the marginal ray of each wavelength of λ1=700 nm, λ2=400 nm, and λ3=1000 nm reach the light receiving surface 7. shows the optical path of As shown in FIGS. 6(a), 6(b), and 6(c), in the comparative example, the condensing positions of the principal ray and the marginal ray of each wavelength on the light-receiving surface 7 do not coincide. and coma is not well corrected.

As described above, in this embodiment, in the second cross section, the curvature of the anamorphic optical surface arranged on the image side of the diffraction surface 5 decreases as the curvature on one side of the optical axis goes off-axis. The shape is such that the curvature on the other side with respect to the axis increases toward the outside of the axis. As a result, since the marginal rays of the light beams of each wavelength can be condensed so as to approach the principal ray, coma aberration which differs for each wavelength can be satisfactorily corrected.

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 diffracts with respect to the optical axis. The curvature of the surface 5 on the side opposite to the vertex of the base surface is configured to increase toward the off-axis direction. Note that the curvature of both sides of the fourth reflecting surface 6 with respect to the optical axis changes according to the direction of deflection of the light flux by the diffraction surface 5 and the fourth reflecting surface 6 (orientation of each optical surface). It may be configured to have the relationship of However, in the second cross section, the optical path from the light shielding member 4 to the diffraction surface 5 and the optical path from the fourth reflection surface 6 to the light receiving surface 7 should intersect, which is advantageous for miniaturization of the entire system. , it is desirable to configure as in this embodiment.

As described above, according to the optical system 10 according to the present embodiment, it is possible to correct different aberrations for each wavelength with a simple configuration.

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

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

The combined focal lengths of the front group 11 and the rear group 12 in the first cross section according to this embodiment are −16.27 mm and 28.30 mm, respectively, and the combined focal lengths of the front group 11 and the rear group 12 in the second cross section are 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 intermediate processing in the second cross section, while widening the angle of view (reading) by adopting the retrofocus type in the first cross section. area) has been achieved.

Here, expressions of the surface shape of each optical surface of the optical system 10 according to the present embodiment will be described. The expressions for the surface shape of each optical surface are not limited to those described later, and each optical surface may be designed using another expression if necessary.

Shapes (generatrix shapes) of base surfaces of the first reflecting surface 2, the second reflecting surface 3, the third reflecting surface (diffraction surface) 5, and the fourth reflecting surface 6 according to the present embodiment in the first cross section is represented by the following formula in each local coordinate system.

However, R _y is the radius of curvature (radius of curvature of the generatrix) in the xy section, and K _y , B ₂ , B ₄ and B ₆ are the aspherical coefficients in the xy section. The aspherical coefficients B ₂ , B ₄ and B ₆ may have different numerical values on both sides of the x-axis (−y side and +y side), if necessary. As a result, the generatrix shape can be made asymmetrical in the y direction with respect to the x axis. Although second to sixth order aspherical coefficients are used in this embodiment, higher order aspherical coefficients may be used if necessary.

Further, the shape (sagittal line shape) of the base surface of each optical surface according to the present embodiment in the second cross section at an arbitrary position in the y direction is represented by the following formula.

However, K _z and M _jk are the aspheric coefficients on the zx section. Also, r' is the radius of curvature (sagittal curvature radius) in the zx cross section at a position away from the optical axis by y in the y direction, and is expressed by the following equation.

However, r is the sagittal curvature radius on the optical axis, and E ₂ and E ₄ are sagittal variation coefficients. If r=0 in the formula (3), the first term on the right side of the formula (2) is treated as zero. Note that the sagittal line variation coefficients E ₂ and E ₄ may have different numerical values on the -y side and the +y side, if necessary. This makes it possible to make the sagittal shape aspheric amount asymmetrical in the y direction. Also, although the formula (Formula 3) includes only even terms, odd terms may be added as necessary. Also, higher order sagittal variation coefficients may be used if desired.

Note that the first-order term of z in the formula (Equation 2) is a term that contributes to the amount of tilt of the optical surface (the amount of sagittal line tilt) in the zx section. Therefore, by setting M _jk to different numerical values on the -y side and the +y side, the sagittal line tilt amount can be changed asymmetrically in the y direction. However, the sagittal beam tilt amount may be changed asymmetrically by using an odd term. Also, the second-order term of z in the formula (Equation 2) is a term that contributes to the sagittal curvature radius of the optical surface. Therefore, in order to simplify the design of each optical surface, only the quadratic term of z in Equation (2) instead of Equation (3) may be used to give the optical surface the sagittal radius of curvature.

Moreover, the shape of the diffraction grating on the diffraction surface 5 is not particularly limited as long as it can be represented 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 grating has one diffraction order.
φ=(2π/λ)×(C1×z)

The fundamental wavelength here is the wavelength for determining the height of the diffraction grating, and the spectral characteristics of the illumination light with respect to the test object, the spectral reflectance of the reflecting surfaces other than the diffraction surface 5, and the imaging including the light receiving surface 7 It is determined based on the spectral sensitivity of the element, the required diffraction efficiency, and the like. In other words, the fundamental wavelength corresponds to the wavelength to be emphasized in detection by the light-receiving surface 7 . In this embodiment, by setting the fundamental wavelength λ to 542 nm, it is possible to focus on observation in the visible region in the working wavelength band. However, for example, by setting the fundamental wavelength to about 850 nm, it is possible to focus on observing the near-infrared region, and by setting the fundamental wavelength to about 700 nm, it is possible to observe the visible region to the near-infrared region in a well-balanced manner. good too.

Table 1 shows the position of the vertex of each optical surface of the optical system 10 according to this embodiment, the direction of the normal line at the vertex, and the radius of curvature at 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 (x-axis) is the X-axis in the ZX cross section including the optical axis. is indicated by an angle θ [deg] with respect to . Further, d [mm] indicates the interval (surface interval) between the optical surfaces, d′ [mm] indicates the interval between the reflection points of the principal rays on each optical surface, and R _y and R _z [mm] Each indicates the radius of curvature in the XY section and the ZX section at the reflection point of the principal ray. 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 shape of each optical surface of the optical system 10 according to this embodiment. In Table 2, each unit of R _y , r, and λ is [mm]. As shown in Table 2, the fourth reflecting surface 6 according to the present embodiment has an aspheric shape that is symmetrical with respect to the zx section in the y direction, and an aspherical shape that is asymmetrical with respect to the xy section in the z direction. It has a spherical shape.

Table 3 shows the diameters [mm] of the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the light receiving surface 7 in the y direction and z direction. In this embodiment, the aperture of the diaphragm 1, the aperture of the light blocking member 4, and the light receiving surface 7 are all rectangular.

FIG. 7 shows the MTF (Modulated Transfer Function) of the optical system 10 according to this embodiment. In FIG. 7, 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 area is Y = 0, 30, 60, 90, 120, 150 are shown for each of the As shown in FIG. 7, the spatial frequencies [lines/mm] for each wavelength of the imaging element including the light receiving surface 7 are 27.8, 41.7, and 55.6. As can be seen from FIG. 7, aberrations are well corrected over the entire reading area, and a sufficient depth of focus is ensured.

[Example 2]
An optical system 10 according to Example 2 of the present invention will be described below. In the optical system 10 according to the present embodiment, description of the same configuration as that of the optical system 10 according to the first embodiment is omitted.

8A and 8B are schematic diagrams of essential parts of an optical system 10 according to an embodiment of the present invention, in which FIG. 8A shows a first cross section and FIG. 8B shows a second cross section. Compared with the optical system 10 according to the first embodiment, 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, and further miniaturization of the entire system is realized.

In this embodiment, the distance from the 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 on the first cross section is ±24.46°. Further, 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 2.7 mm. The combined focal lengths of the front group 11 and the rear group 12 in the first cross section according to this embodiment are −14.21 mm and 16.69 mm, respectively, and the combined focal lengths of the front group 11 and the rear group 12 in the second cross section are The focal lengths are 19.33 mm and 11.01 mm, respectively.

As in Example 1, Table 4 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 6 shows the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7. However, regarding the shape of the second cross section of the third reflecting surface 5, the local After defining the coordinate system, it is represented by the above-described formula (Equation 2). The reason why the values of the radius of curvature _Ry in Tables 4 and 5 do not match is that the values of the radius of curvature in Table 4 take into consideration the tilt angle in the second cross section.

FIG. 9, like FIG. 7, shows the MTF of the optical system 10 according to this embodiment. As can be seen from FIG. 9, aberrations are well corrected over the entire reading area and a sufficient depth of focus is ensured.

[Example 3]
An 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, description of the same configuration as that of the optical system 10 according to the first embodiment is omitted.

10A and 10B are schematic diagrams of essential parts of an optical system 10 according to an embodiment of the present invention, in which FIG. 10A shows a first cross section and FIG. 10B shows a second cross section. The optical system 10 according to the present embodiment has a smaller (brighter) Fno on the exit side (image side) than the optical system 10 according to the first embodiment. Specifically, while the Fno on the exit side of the optical system 10 according to Example 1 is 4.7 and 4.0 in the first and second cross sections, respectively, the optical system according to this example The exit side Fno of 10 is 4.1 and 3.5 in the first and second cross sections, respectively.

In this embodiment, the distance from the 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 on 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 area in the second direction on the light receiving surface 7 is 2.64 mm. The combined focal lengths of the front group 11 and the rear group 12 in the first cross section according to this embodiment are −14.46 mm and 26.85 mm, respectively, and the combined focal lengths of the front group 11 and the rear group 12 in the second cross section are The focal lengths are 19.34 mm and 24.98 mm, respectively.

As in Example 1, Table 7 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 9 shows the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7.

FIG. 11, like FIG. 7, shows the MTF of the optical system 10 according to this example. As can be seen from FIG. 11, aberrations are well corrected over the entire reading area and a sufficient depth of focus is ensured.

[Example 4]
An 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, description of the same configuration as that of the optical system 10 according to the first embodiment is omitted.

12A and 12B are schematic diagrams of essential parts of an optical system 10 according to an embodiment of the present invention, FIG. 12(a) showing a first cross section and FIG. 12(b) showing a second cross section. Compared with the optical system 10 according to the first embodiment, 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, and further miniaturization of the entire system is realized.

In this embodiment, the distance from the 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 on the first cross section is ±24.49°. In this embodiment, the wavelength band used is 400 nm to 1000 nm, and the width of the imaging area in the second direction on the light receiving surface 7 is 2.37 mm. The combined focal lengths of the front group 11 and the rear group 12 in the first cross section according to this embodiment are −13.23 mm and 16.78 mm, respectively, and the combined focal lengths of the front group 11 and the rear group 12 in the second cross section are The focal lengths are 17.53 mm and 11.25 mm, respectively.

As in Example 1, Table 10 shows the position of the vertex of each optical surface of the optical system 10 according to the present example, the direction of the normal line at the vertex, and the radius of curvature at each cross section. , and Table 12 shows the aperture of the diaphragm 1, the aperture of the light shielding member 4, and the diameter of the light receiving surface 7. The reason why the values of the radius of curvature _Ry do not match between Tables 10 and 11 is that the values of the radius of curvature in Table 10 take into account the tilt angle in the second cross section.

In this embodiment, the sagittal shape of the first reflecting surface 2, the second reflecting surface 3, the third reflecting surface 5, and the fourth reflecting surface 6 is expressed by the following equation instead of the above-described equation (equation 3). is represented using Further, the sagittal line shape of the third reflecting surface 5 is represented by the above-described formula (Equation 2) after determining different local coordinate systems for each position on the generatrix as in the second embodiment.
r'=r( ¹ + ^E2y2 _{+ E4y4} )

FIG. 13, like FIG. 7, shows the MTF of the optical system 10 according to this example. As can be seen from FIG. 13, aberrations are well corrected over the entire reading area and a sufficient depth of focus is ensured.

[Imaging system]
An imaging device (spectral reading device) and an imaging system (spectral reading system) will be described below as examples of using the optical system 10 according to the above-described embodiment.

14 and 15 are schematic diagrams of essential parts of imaging systems 100 and 200 according to embodiments of the present invention. The imaging systems 100 and 200 include an imaging device 101 and 201 having an optical system 10 and an imaging device for receiving an image formed by the optical system 10, and a transport device for changing the relative positions of each imaging device and the subject 103 and 203. and a portion 102, 202. Note that each imaging system preferably has an image processing section that generates an image based on image information obtained from the imaging device. The image processing unit is, for example, a processor such as a CPU, and may be provided inside or outside each imaging device.

According to the imaging devices 101 and 201, a plurality of image information (one-dimensional images) corresponding to a plurality of wavelengths are obtained by once imaging the linear reading regions 104 and 204 long in the first direction (Y direction). can be obtained. At this time, it is desirable to configure each imaging device as a multispectral camera capable of acquiring image information corresponding to four or more wavelengths, which is more than a general camera. Furthermore, it is more preferable to configure each imaging device as a hyperspectral camera capable of acquiring 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 employed as an imaging element in each imaging device. The imaging element may be configured to photoelectrically convert not only visible light but also infrared light (near-infrared light and far-infrared light). Specifically, an imaging element using materials such as InGaAs and InAsSb may be employed depending on the wavelength band used. Moreover, it is desirable to determine the number of pixels of the imaging device based on the required resolution in the reading direction and the spectral direction.

As shown in FIG. 14, the transport unit 102 in the imaging system 100 is means for moving 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 shown in FIG. 15, the transport unit 202 in the imaging system 200 is means for moving the imaging device 201 in the second direction. A multicopter, an airplane, an artificial satellite, or the like can be used as the transport unit 202 . 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, or for a test object that is difficult to move. .

According to the imaging systems 100 and 200, each imaging device sequentially images the reading region while changing the relative position of each imaging device and each test object in each transport unit, thereby obtaining a plurality of positions in the second direction. can acquire a plurality of image information corresponding to . A two-dimensional image corresponding to a specific wavelength can be generated by performing rearrangement, arithmetic processing, and the like on the plurality of picked-up images by the image processing unit. Since each piece of image information represents grayscale information in the first direction, the spectral distribution may be generated by the image processing unit based on the grayscale information for each wavelength at a specific position in the second direction.

Note that each transport unit may be configured to move both each imaging device and each test object. Further, each transportation unit may be configured to be able to adjust the relative position between each imaging device and each test object in the optical axis direction (X direction). Alternatively, a drivable optical member (focusing member) may be placed inside or outside the optical system 10, and the position of the optical member may be adjusted so that the subject can be focused.

Although preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist.

4 light shielding member 5 third reflecting surface (diffraction surface)
6 fourth reflecting surface (anamorphic optical surface)
7 Light-receiving surface (image surface)
10 optical system 11 front group 12 rear group

Claims (20)

An optical system comprising 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 an opening long in a first direction,
The front group does not image an object on the opening in a first cross section parallel to the first direction, and the object is imaged on the opening in a second cross section perpendicular to the first direction. forms an intermediate image of
The rear group includes a diffraction surface that disperses the light flux passing through the aperture on the second cross section into a plurality of light fluxes having different wavelengths, and a diffraction surface that converges the plurality of light fluxes on different positions on the second cross section. an anamorphic optical surface;
The axis normal to the origin of the anamorphic optical surface is the x-axis, the axis parallel to the first direction and orthogonal to the x-axis at the origin is the y-axis, and the axis orthogonal to the x-axis and the y-axis is Let the z-axis be the aspheric coefficients in the second section, _Kz and _Mjk be the aspheric coefficients , r be the radius of curvature at the origin of the anamorphic optical surface in the second section, _and E2 and E4 be the _sagittal change coefficients. and the shape of the anamorphic optical surface in the second cross section is

When expressed by the following formula, the curvature on one side with respect to the x-axis of the shape defined by the formula becomes smaller as it goes off-axis, and the curvature on the other side with respect to the x-axis becomes off-axis An optical system characterized by increasing in size as it goes. In the second cross section, the curvature of the anamorphic optical surface on the same side as the vertex of the base surface of the diffractive surface with respect to the x -axis decreases as it goes off-axis, and is opposite to the vertex with respect to the x-axis . 2. The optical system according to claim 1, wherein the curvature of the side increases toward off-axis. 3. The optical system according to claim 1, wherein the curvature of said anamorphic optical surface changes in said second cross section so that a marginal ray of a light beam from said diffractive surface approaches a principal ray. 4. The optical system according to any one of claims 1 to 3, wherein said anamorphic optical surface is a reflective surface. 5. The optical system according to claim 1, wherein the base surface of said diffraction surface is an anamorphic surface. 6. The optical system according to any one of claims 1 to 5, wherein a plurality of ridgelines of the diffraction grating of said diffraction surface are parallel to each other. 7. The optical system according to claim 6, wherein intervals between the plurality of ridge lines are constant. 8. The optical system according to claim 1, wherein said diffraction surface is a reflecting surface. 9. The optical system according to claim 1, wherein all optical surfaces included in said front group and said rear group are reflecting surfaces. 10. The optical system according to claim 1 , wherein said front group and said rear group have positive power in said second section . 11. The optical system according to any one of claims 1 to 10, wherein the front group has negative power and the rear group has positive power in the first cross section. 12. The optical system according to any one of claims 1 to 11, wherein the light shielding member restricts the width of the light flux from the object in the first direction. 13. The optical system according to any one of claims 1 to 12, wherein the front group has a diaphragm that regulates the width of the light flux from the object in a second direction perpendicular to the first direction. system. An imaging apparatus comprising: the optical system according to any one of claims 1 to 13; and an imaging device for receiving an image formed by the optical system. 15. The imaging apparatus according to claim 14, further comprising an image processing section that generates an image based on image information obtained from the imaging device. 16. An imaging system comprising: the imaging device according to claim 14 or 15; and a conveying unit that changes the relative positions of the imaging device and the object. 17. The imaging system according to claim 16, wherein said transporter moves said object in a direction perpendicular to said first direction. 17. The imaging system according to claim 16, wherein the transport section moves the imaging device in a direction perpendicular to the first direction. Image processing for generating an image of the object based on a plurality of pieces of image information acquired by causing the imaging device to image the object while changing the relative positions of the imaging device and the object by the transport unit. 19. An imaging system according to any one of claims 16 to 18, comprising a unit. 20. The imaging system according to claim 19, wherein the image processing section generates an image for each wavelength corresponding to the plurality of luminous fluxes.

Images