JP2020126232A - Imaging optical system and image reader device - Google Patents

Abstract

To provide a compact, wide-angle imaging optical system and an image reader device equipped with the same.SOLUTION: An imaging optical system provided herein consists of a single mirror with positive power and a dioptric system with positive power consisting of a plurality of lenses, and is configured to form an intermediate image between the mirror and the dioptric system. The mirror and the dioptric system share a common optical axis and have shapes that are rotationally symmetric about the optical axis. The mirror has an aspherical shape. A first lens located on the most object side in the dioptric system is a positive lens having a concave surface on the object side.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to an imaging optical system and an image reading device.

2. Description of the Related Art There is known a stand-scanner type image reading device that picks up an image of a subject placed within an image reading range from above the subject. As the image forming optical system that can be used in such an image reading apparatus, for example, those described in Patent Documents 1 to 3 below are known. Each of the imaging optical systems of Patent Documents 1 to 3 is configured by combining a refractive optical system including a plurality of lenses and a mirror.

JP, 2016-212149, A Japanese Patent No. 5274030 International Publication No. 2016/125848

The stand scanner type image reading apparatus is mainly installed on a desk and reads a subject placed on the desk. Therefore, the image reading device is required to be as small as possible, and thus the imaging optical system mounted on the image reading device is also required to be small. Further, the imaging optical system mounted on the image reading device is also required to have a wide angle so that an object in a region as wide as possible can be read.

On the other hand, in each of the imaging optical systems of Patent Documents 1 to 3, the lens closest to the object in the refractive optical system is a negative lens. The lens closest to the object side of the refracting optical system is a relatively large lens because light from a wide angle of view is incident on the lens. When the most object-side lens of the refracting optical system is a negative lens, the light flux incident from the mirror exits without being converged, so that the next lens also becomes large, and as a result, the total length of the refracting optical system is expanded. Therefore, it is disadvantageous for downsizing the imaging optical system.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a compact and wide-angle imaging optical system, and an image reading apparatus including the imaging optical system.

An imaging optical system according to an aspect of the present disclosure includes, in order from the object side, one mirror having positive power and a refracting optical system having a plurality of lenses and having positive power. Is an imaging optical system that forms an intermediate image between the mirror and the refraction optical system, and the mirror and the refraction optical system have a common optical axis and have a rotationally symmetric shape with the optical axis as a rotation axis. The first lens, which has an aspherical shape and is the most object-side lens of the refractive optical system, is a positive lens having a concave surface facing the object side.

In the imaging optical system of the above aspect, the distance on the optical axis from the reflecting surface of the mirror to the image forming surface is TTL, the distance on the optical axis from the reflecting surface of the mirror to the object surface is ZOB, and the object of the first lens is When the distance on the optical axis from the side surface to the image forming surface is LL0 and the maximum image height is Ymax, it is preferable to satisfy the conditional expressions (1) and (2). Further, it is more preferable to satisfy at least one of conditional expressions (1-1) and (2-1) after satisfying conditional expressions (1) and (2).
0.8<TTL/ZOB<2.5 (1)
0.85<TTL/ZOB<2 (1-1)
6<LL0/Ymax<15 (2)
7<LL0/Ymax<13 (2-1)

Further, in the imaging optical system of the above aspect, it is preferable that conditional expression (3) is satisfied when the focal length of the first lens is fL1 and the focal length of the refractive optical system is fL0. Further, it is more preferable that the conditional expression (3-1) is satisfied.
3<fL1/fL0<50 (3)
4<fL1/fL0<25 (3-1)

In the image forming optical system of the above aspect, the refracting optical system is composed of, in order from the object side, a front group having a positive power, an aperture stop, and a rear group having a positive power. It is preferable that the first lens, the second lens having a negative power, and the third lens having a positive power be provided successively in order from the object side.

Further, in the image forming optical system of the above aspect, the rear group is provided with a cemented lens having a positive power as a whole and composed of a positive lens and a negative lens on the most image side, and the Abbe number of the positive lens constituting the cemented lens is Is 50 or more, and the Abbe number of the negative lens forming the cemented lens is preferably 40 or less. In addition, the Abbe numbers of the positive lens and the negative lens that form the cemented lens satisfy these conditions, the Abbe number of the positive lens that forms the cemented lens is 55 or more, and the Abbe number of the negative lens that forms the cemented lens. It is more preferable that the number satisfies at least one of 30 or less.

Further, in the image forming optical system of the above aspect, it is preferable that the first lens of the refractive optical system is an aspherical lens and the lenses other than the first lens of the refractive optical system are spherical lenses.

An image reading apparatus according to one aspect of the present disclosure includes the image forming optical system according to the above aspect of the present disclosure.

In the image reading apparatus of the above aspect, it is preferable that the image reading range is set to a region that does not include the optical axis.

In the present specification, "consisting of" and "consisting of" mean, in addition to the listed components, optical elements such as lenses, diaphragms, filters, plane mirrors, and cover glasses that have substantially no power. Is intended to be included. It is also intended that components such as lens flanges, lens barrels, and imaging devices may be included.

Further, “in order from the object side” regarding the arrangement of the constituent elements means in order from the object side along the optical path. Unless otherwise specified, the sign of the refractive power and the surface shape of the aspherical surface will be considered in the paraxial region. The “C line”, “d line”, “e line”, and “g line” described in this specification are bright lines, the wavelength of the C line is 656.27 nm (nanometers), and the wavelength of the d line is The wavelength of 587.56 nm (nanometer), the wavelength of e-line is 546.07 nm (nanometer), and the wavelength of g-line is 435.86 nm (nanometer).

According to the present disclosure, it is possible to provide a compact and wide-angle imaging optical system, and an image reading apparatus including the imaging optical system.

Schematic configuration diagram of an image reading apparatus according to an embodiment of the present disclosure Sectional drawing which shows the structure of the imaging optical system (common to Example 1) which concerns on one Embodiment of this indication. Sectional drawing which shows the structure of the imaging optical system (common to Example 1) which concerns on one Embodiment of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 2 of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 3 of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 4 of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 5 of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 6 of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 7 of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 8 of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 9 of this indication. Sectional drawing which shows the structure of the imaging optical system of Example 10 of this indication. Astigmatism diagram and distortion diagram of the imaging optical system of Example 1 of the present disclosure. Transverse aberration diagram of the imaging optical system of Example 1 of the present disclosure Astigmatism diagram and distortion diagram of the imaging optical system of Example 2 of the present disclosure. Transverse aberration diagram of the imaging optical system of Example 2 of the present disclosure Astigmatism diagram and distortion diagram of the imaging optical system of Example 3 of the present disclosure. Transverse aberration diagram of the imaging optical system of Example 3 of the present disclosure. Astigmatism diagram and distortion diagram of the imaging optical system of Example 4 of the present disclosure. Transverse aberration diagram of the imaging optical system of Example 4 of the present disclosure Astigmatism diagram and distortion diagram of the imaging optical system of Example 5 of the present disclosure. Transverse aberration diagram of the imaging optical system of Example 5 of this indication. Astigmatism diagram and distortion diagram of the imaging optical system of Example 6 of the present disclosure. A lateral aberration diagram of the imaging optical system of Example 6 of the present disclosure. Astigmatism diagram and distortion diagram of the imaging optical system of Example 7 of the present disclosure. A lateral aberration diagram of the imaging optical system of Example 7 of the present disclosure. Astigmatism diagram and distortion diagram of the imaging optical system of Example 8 of the present disclosure. Transverse aberration diagram of the imaging optical system of Example 8 of the present disclosure. Astigmatism diagram and distortion diagram of the imaging optical system of Example 9 of the present disclosure. Transverse aberration diagram of the imaging optical system of Example 9 of the present disclosure. Astigmatism diagram and distortion diagram of the imaging optical system of Example 10 of the present disclosure. Transverse aberration diagram of the imaging optical system of Example 10 of the present disclosure.

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image reading device 10 according to an embodiment of the present disclosure.

The image reading device 10 is a stand-scanner type device that images a subject placed in an image reading range 20 from above the subject, and an imaging optical system 11 and an image sensor 12 are housed in a housing 13. Consists of The imaging optical system 11 is composed of, in order from the object side, one mirror 11a having a positive power and a refracting optical system 11b having a plurality of lenses and having a positive power. The image pickup element 12 is an element that outputs an image pickup signal corresponding to a subject image formed by the image forming optical system 11, and is arranged on the image forming surface of the image forming optical system 11. A CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like can be used as the image sensor 12.

Next, a specific example of the imaging optical system 11 mounted on the image reading device 10 will be described. 2 and 3 are cross-sectional views showing the configuration of the imaging optical system (common to Example 1) according to an embodiment of the present disclosure. The configuration examples shown in FIGS. 2 and 3 are common to the configuration of the image forming optical system of Example 1 described later. In FIG. 2 and FIG. 3, the light flux A near the optical axis and the light flux B with the maximum angle of view are also shown as the light flux. In addition, in FIG. 2, the mirror M1 side is illustrated as the object side along the optical axis Z, and the imaging plane Sim side is illustrated as the image side. Further, FIG. 3 is an enlarged view of the image forming optical system part in FIG. 2, and is shown in a state rotated 90 degrees to the left from the state shown in FIG. The aperture stop St shown in FIGS. 2 and 3 does not show a shape but a position on the optical axis.

This imaging optical system comprises, in order from the object side, one mirror M1 having a positive power and a refracting optical system RO having a plurality of lenses and having a positive power. The mirror M1 and the refracting optical system RO are connected to each other. An intermediate image I is formed in between. 2 and 3, the intermediate image I in the vicinity of the optical axis is simply shown for convenience. As an example, the refraction optical system RO includes, in order from the object side, a front group GF including four lenses L1 to L4, an aperture stop St, and a rear group GR including three lenses L5 to L7. Composed of. By thus forming the intermediate image I in the imaging optical system, it is possible to suppress the expansion of the light flux in the imaging optical system, which is advantageous for downsizing and widening the angle of the imaging optical system. Become.

Further, the mirror M1 and the refracting optical system RO have a common optical axis Z and have a rotationally symmetric shape with the optical axis Z as a rotation axis. With such a configuration, the design of the imaging optical system is facilitated, and the workability and assembly of the optical element forming the imaging optical system are improved. As a result, it is advantageous for improving the performance while suppressing the cost of the imaging optical system.

In the present disclosure, regarding the shapes of the mirror M1 and the refraction optical system RO, the optical axis Z can be used even for a shape in which a region not used for image formation is partially cut from a rotationally symmetric shape with the optical axis Z as the rotation axis. Shall be included in the rotationally symmetric shape with the rotation axis as. The above-mentioned "the mirror M1 and the refractive optical system RO have a rotationally symmetric shape" refers to a surface shape, and the optical surface used for the image formation of the mirror M1 and the refractive optical system RO is a rotationally symmetrical surface. Means that.

The mirror M1 has an aspherical shape. As described above, the mirror M1 arranged on the most object side of the imaging optical system and having a large effective diameter has an aspherical shape, which is advantageous for correction of field curvature, coma aberration, astigmatism, and distortion. Becomes

The first lens L1 which is the most object-side lens of the refractive optical system RO is a positive lens whose concave surface faces the object side. In this way, by making the object side of the first lens L1 a concave surface, a wide angle of view can be taken while suppressing the diameter of the first lens L1. Further, by making the first lens L1 a positive lens, the light flux incident from the mirror M1 is converged and emitted, so that the diameter of the next second lens L2 can be reduced, and the refractive optical system RO can be made smaller. It leads to shortening of the total length. Therefore, it is advantageous for downsizing the imaging optical system.

As described above, the imaging optical system of this embodiment can be a small-sized and wide-angle imaging optical system. Therefore, the image reading apparatus 10 including the image forming optical system according to the present embodiment can also be a small-sized apparatus capable of reading a wide range of images.

Further, the image reading device 10 is configured to be a region that does not include the optical axis Z by using the mirror M1 so that the image reading range 20 can be configured as a stand scanner type device. ..

In the imaging optical system of the present embodiment, the distance on the optical axis Z from the reflecting surface of the mirror M1 to the imaging surface Sim is TTL, and the distance on the optical axis Z from the reflecting surface of the mirror M1 to the object plane Obj. ZOB, if the distance on the optical axis Z from the object-side surface of the first lens L1 to the imaging plane Sim is LL0 and the maximum image height is Ymax, then conditional expressions (1) and (2) may be satisfied. preferable. The maximum image height Ymax means the distance between the optical axis Z and the image point farthest from the optical axis Z. Further, there is no optical power such as a filter or a cover glass between the object plane Obj and the mirror M1, between the mirror M1 and the refractive optical system RO, and/or between the refractive optical system RO and the image plane Sim. When the members are arranged, the value in terms of air is used as the distance for the optical member having no power. For example, when an optical member having no power such as a filter or a cover glass is arranged between the refracting optical system RO and the image forming surface Sim, the most image side of the refracting optical system RO from the reflecting surface of the mirror M1. The sum of the distance to the surface on the optical axis Z and the back focus at the air-equivalent distance of the imaging optical system is TTL.
0.8<TTL/ZOB<2.5 (1)
0.85<TTL/ZOB<2 (1-1)
6<LL0/Ymax<15 (2)
7<LL0/Ymax<13 (2-1)

In order to install the image reading device 10 on the same surface as the document placement table (object surface Obj) or in the vicinity thereof, the mirror M1 for bending the light flux of the reading light is required. By setting the conditional expression (1) so as not to fall below the lower limit, it is possible to prevent the total length of the imaging optical system from becoming too short as compared with the reading range, which is advantageous in correcting aberrations. By not exceeding the upper limit of the conditional expression (1), it is possible to prevent the total length of the imaging optical system from becoming too long as compared with the reading range, which is advantageous for downsizing of the apparatus.

If the lower limit of conditional expression (2) is not exceeded, the total length of the refractive optical system RO does not become too short with respect to the maximum image height Ymax, which is advantageous for aberration correction. If the upper limit of conditional expression (2) is not exceeded, it is advantageous for downsizing the refracting optical system RO, which is advantageous for downsizing the image reading apparatus 10 as a whole.

In addition, if the conditional expressions (1) and (2) are satisfied and then at least one of the conditional expressions (1-1) and (2-1) is satisfied, better characteristics can be obtained. ..

Further, when the focal length of the first lens is fL1 and the focal length of the refractive optical system RO is fL0, it is preferable to satisfy the conditional expression (3). In order to reduce the size of the refractive optical system RO while increasing the effective diameter of the first lens L1, the first lens L1 needs to have an appropriate positive power. However, since the larger effective diameter of the second lens L2 is also advantageous for aberration correction, it is necessary that the positive power of the first lens L1 is not too large. By not falling below the lower limit of the conditional expression (3), the positive power of the first lens L1 can be prevented from becoming too large. By ensuring that the upper limit of conditional expression (3) is not exceeded, an appropriate positive power can be secured for the first lens L1. If the conditional expression (3-1) is satisfied, better characteristics can be obtained.
3<fL1/fL0<50 (3)
4<fL1/fL0<25 (3-1)

The refractive optical system RO is composed of a front group GF having positive power, an aperture stop St, and a rear group GR having positive power in order from the object side. The front group GF is arranged in order from the most object side. It is preferable to continuously include the first lens L1, the second lens L2 having negative power, and the third lens L3 having positive power. In this way, by making the power of the second lens L2 negative, it is possible to avoid sudden convergence of light rays, and further, the first lens L1, the second lens L2, and the third lens having relatively large effective diameters. It is advantageous for correction of coma aberration and field curvature by dispersing the positive and negative effects by making the power arrangement of the three lenses of L3 positive and negative.

Further, the rear group GR is provided with a cemented lens C1 composed of a positive lens and a negative lens and having a positive power as a whole on the most image side, and the Abbe number of the positive lens constituting the cemented lens C1 is 50 or more. The Abbe number of the negative lens forming the lens C1 is preferably 40 or less. In the imaging optical system of this embodiment shown in FIGS. 2 and 3, the positive lens L6 and the negative lens L7 constitute this cemented lens C1. In this way, by disposing the cemented lens C1 including the positive lens and the negative lens having the above Abbe number difference on the image side of the aperture stop St and at the position where the height of the off-axis chief ray becomes high, This is advantageous for correction of lateral chromatic aberration. When the front lens group GF includes a positive lens and a negative lens, the rear lens group GR on the image side of the aperture stop St also includes a positive lens and a negative lens, which is advantageous for correction of field curvature and distortion. Become. In addition, after the Abbe numbers of the positive lens and the negative lens that form the cemented lens C1 satisfy these conditions, the Abbe number of the positive lens that forms the cemented lens C1 is 55 or more, and the negative lens that forms the cemented lens C1. If the Abbe number of the lens satisfies at least one of 30 or less, better characteristics can be obtained.

Further, it is preferable that the first lens L1 of the refractive optical system RO is an aspherical lens, and the lenses other than the first lens L1 of the refractive optical system RO are spherical lenses. Thus, the aberration is effectively corrected by making the first lens L1 located closest to the object side of the refracting optical system RO, having a large effective diameter, and having a small overlap of light beams with respect to different image heights, to have an aspherical shape. be able to. Further, by making all the remaining lenses of the refracting optical system RO spherical lenses, it becomes advantageous to improve the processability and assembling of the optical elements constituting the imaging optical system. As a result, it is advantageous for improving the performance while suppressing the cost of the imaging optical system.

Next, numerical examples of the imaging optical system of the present invention will be described.
[Example 1]
FIG. 3 is a sectional view showing the arrangement of the image forming optical system according to the first embodiment. Since the illustration method of FIG. 3 has been described above, a part of the duplicate description will be omitted here. The illustrated method is basically the same for the second to tenth embodiments.

The imaging optical system of Example 1 is composed of, in order from the object side, one mirror M1 having a positive power and a refracting optical system RO having a plurality of lenses and having a positive power. The refracting optical system RO is composed of, in order from the object side, a front group GF including four lenses L1 to L4, an aperture stop St, and a rear group GR including three lenses L5 to L7. It

Table 1 shows the lens data of the imaging optical system of Example 1, and Table 2 shows the data on the aspherical coefficients. In the following, the meanings of the symbols in the table will be described taking the example of Example 1 as an example, but the same applies to Examples 2 to 10.

In the lens data of Table 1, in the column S, the surface number of the component element closest to the object side is the first, and the surface numbers are sequentially increased toward the image side. In the column R, the radius of curvature of each surface is shown. In the column D, the distance between each surface and the next surface on the optical axis Z is shown. The Nd column shows the refractive index of each optical element at the d line, and the νd column shows the Abbe number of each optical element at the d line. However, the reflective surface has mirror written in the column of Nd. The sign of the radius of curvature is positive when the surface shape is convex on the object side and negative when the surface shape is convex on the image side. A radius of curvature of 0.000 means a plane. The lens data also includes the object plane Obj, the aperture stop St, and the image plane Sim.

In the lens data of Table 1, the surface number of the aspherical surface is marked with *, and the numerical value of the paraxial radius of curvature is shown as the radius of curvature of the aspherical surface. The data on the aspherical surface coefficients in Table 2 show the surface numbers of the aspherical surfaces and the aspherical surface coefficients concerning these aspherical surfaces. “E±n” (n: integer) of the numerical value of the aspherical surface coefficient in Table 2 means “×10 ^±n ”. The aspherical surface coefficient is a value of each coefficient K and RBi in the aspherical surface expression represented by the following expression.

However,
Zd: depth of the aspherical surface (length of a perpendicular line drawn from a point on the aspherical surface having a height h to a plane perpendicular to the optical axis where the aspherical surface abuts)
h: Height (distance from the optical axis)
CC: the reciprocal K of the paraxial radius of curvature, RBi: aspherical surface coefficient, and Σ at the aspherical surface depth Z means the sum of i.

13 and 14 show aberration diagrams of the imaging optical system of Example 1. FIG. 13 shows an astigmatism diagram and a distortion diagram (distortion) in order from the left. In the astigmatism diagram, the aberration at the e-line in the sagittal direction is shown by a solid line, and the aberration at the e-line in the tangential direction is shown by a dotted line. In the distortion diagram, the aberration at the e-line is shown by the solid line. Ω in each aberration diagram means a half angle of view. Note that, in the examples of the present disclosure, the vicinity of the angle of view of 0 degree is outside the use range, and therefore, in the astigmatism diagram and the distortion diagram (distortion), only the use range is shown in the aberration diagram. For the above reason, the spherical aberration diagram is not described in the present disclosure.

FIG. 14 shows a lateral aberration diagram. The left column shows the aberration in the tangential direction, and the right column shows the aberration in the sagittal direction for each angle of view. In the lateral aberration diagram, the aberrations at the e-line, g-line, and C-line are shown by a solid line, a long broken line, and a short broken line, respectively.

The symbols, meanings, description methods, and illustration methods of each data relating to the above-described first embodiment are the same in the following embodiments unless otherwise specified, and therefore, a part of the duplicate description will be omitted below.

[Example 2]
Next, the imaging optical system of Example 2 will be described. FIG. 4 is a sectional view showing the arrangement of the image forming optical system according to the second embodiment. The image forming optical system of the second embodiment has the same number of lenses as the image forming optical system of the first embodiment. Regarding the imaging optical system of Example 2, lens data is shown in Table 3, aspherical coefficient is shown in Table 4, and aberration diagrams are shown in FIGS. 15 and 16.

[Example 3]
Next, the imaging optical system of Example 3 will be described. FIG. 5 is a sectional view showing the arrangement of the image forming optical system according to the third embodiment. The image forming optical system of Example 3 has the same number of lenses as the image forming optical system of Example 1. Regarding the imaging optical system of Example 3, Table 5 shows lens data, Table 6 shows aspherical coefficients, and FIGS. 17 and 18 show aberration diagrams.

[Example 4]
Next, the imaging optical system of Example 4 will be described. FIG. 6 is a sectional view showing the arrangement of the image forming optical system according to the fourth embodiment. The imaging optical system of Example 4 is composed of, in order from the object side, one mirror M1 having a positive power and a refracting optical system RO having a plurality of lenses and having a positive power. The refracting optical system RO is composed of, in order from the object side, a front group GF composed of four lenses L1 to L4, an aperture stop St, and a rear group GR composed of two lenses L5 to L6. It Regarding the image forming optical system of Example 4, lens data is shown in Table 7, aspherical surface coefficients are shown in Table 8, and aberration diagrams are shown in FIGS. 19 and 20.

[Example 5]
Next, the imaging optical system of Example 5 will be described. FIG. 7 is a sectional view showing the arrangement of the image forming optical system according to the fifth embodiment. The image forming optical system of Example 5 has the same number of lenses as the image forming optical system of Example 4. Regarding the imaging optical system of Example 5, Table 9 shows lens data, Table 10 shows aspherical coefficients, and FIGS. 21 and 22 show aberration diagrams.

[Example 6]
Next, the imaging optical system of Example 6 will be described. FIG. 8 is a sectional view showing the arrangement of the image forming optical system according to the sixth embodiment. The imaging optical system of Example 6 is composed of, in order from the object side, one mirror M1 having a positive power and a refracting optical system RO having a plurality of lenses and having a positive power. The refracting optical system RO is composed of, in order from the object side, a front group GF including five lenses L1 to L5, an aperture stop St, and a rear group GR including three lenses L6 to L8. It Regarding the image forming optical system of Example 6, Table 11 shows lens data, Table 12 shows aspherical coefficients, and FIGS. 23 and 24 show aberration diagrams.

[Example 7]
Next, the imaging optical system of Example 7 will be described. FIG. 9 is a sectional view showing the arrangement of the image forming optical system of Example 7. The image forming optical system of Example 7 has the same number of lenses as the image forming optical system of Example 1. Regarding the image forming optical system of Example 7, Table 13 shows lens data, Table 14 shows aspherical coefficients, and FIGS. 25 and 26 show aberration diagrams.

[Example 8]
Next, the imaging optical system of Example 8 will be described. FIG. 10 is a sectional view showing the arrangement of the image forming optical system of Example 8. The imaging optical system of Example 8 is composed of, in order from the object side, one mirror M1 having a positive power and a refracting optical system RO having a plurality of lenses and having a positive power. The refracting optical system RO is composed of, in order from the object side, a front group GF including three lenses L1 to L3, an aperture stop St, and a rear group GR including three lenses L4 to L6. It Table 15 shows lens data, Table 16 shows aspherical coefficients, and FIGS. 27 and 28 show aberration diagrams of the imaging optical system of Example 8.

[Example 9]
Next, the imaging optical system of Example 9 will be described. FIG. 11 is a sectional view showing the arrangement of the image forming optical system of Example 9. The imaging optical system of Example 9 has the same number of lenses as the imaging optical system of Example 1. In the imaging optical system of Example 9, a plane mirror Mp1 for bending the optical path is arranged in the optical path between the mirror M1 and the refracting optical system RO. With respect to the imaging optical system of Example 9, Table 17 shows lens data, Table 18 shows aspherical coefficients, and FIGS. 29 and 30 show aberration diagrams.

[Example 10]
Next, the imaging optical system of Example 10 will be described. FIG. 12 is a sectional view showing the arrangement of the image forming optical system of Example 10. The image forming optical system of Example 10 has the same number of lenses as the image forming optical system of Example 1. With respect to the imaging optical system of Example 10, Table 19 shows lens data, Table 20 shows aspherical coefficients, and FIGS. 31 and 32 show aberration diagrams.

Table 21 shows specifications of the imaging optical systems of Examples 1 to 10, values corresponding to symbols included in conditional expressions (1) to (3), and values corresponding to conditional expressions (1) to (3). Show. Note that Table 21 shows the values when the d line is used as a reference. Further, the maximum angle of view is an angle formed by the principal ray of the light beam B having the maximum angle of view in FIGS. 2 to 12 and the optical axis Z. Further, the magnifications shown in Table 21 are not paraxial magnifications, but magnifications for reading a document.

From the above data, it is understood that all the imaging optical systems of Examples 1 to 10 satisfy the conditional expressions (1) to (3), and are compact and wide-angle imaging optical systems.

Although the technology of the present disclosure has been described above with reference to the embodiments and examples, the technology of the present disclosure is not limited to the above-described embodiments and examples, and various modifications are possible. For example, the radius of curvature, the surface distance, the refractive index, the Abbe number, the aspherical coefficient, etc. of each lens are not limited to the values shown in the above-mentioned numerical examples, and may take other values.

Reference Signs List 10 image reading device 11 imaging optical system 11a mirror 11b refraction optical system 12 imaging element 13 housing 20 reading range A luminous flux B luminous flux C1 cemented lens GF front group GR rear group I intermediate image L1 to L8 lens M1 mirror Mp1 plane mirror Obj Object plane RO Refractive optical system Sim Image plane Ymax Maximum image height Z Optical axis

Claims (13)

In order from the object side, one mirror having a positive power and a refracting optical system having a plurality of lenses and having a positive power are formed, and an intermediate image is formed between the mirror and the refracting optical system. Image optics,
The mirror and the refraction optical system have a common optical axis, and have a rotationally symmetric shape with the optical axis as a rotation axis,
The mirror has an aspherical shape,
The first lens, which is the most object-side lens of the refracting optical system, is a positive lens with a concave surface facing the object side. The distance on the optical axis from the reflecting surface of the mirror to the image plane is TTL,
The distance on the optical axis from the reflecting surface of the mirror to the object surface is ZOB,
The distance on the optical axis from the object side surface of the first lens to the image forming surface is LL0,
If the maximum image height is Ymax,
0.8<TTL/ZOB<2.5 (1)
6<LL0/Ymax<15 (2)
The imaging optical system according to claim 1, wherein the conditional expressions (1) and (2) expressed by are satisfied. The focal length of the first lens is fL1,
When the focal length of the refraction optical system is fL0,
3<fL1/fL0<50 (3)
The imaging optical system according to claim 1 or 2, which satisfies the conditional expression (3) represented by: The refracting optical system comprises, in order from the object side, a front group having a positive power, an aperture stop, and a rear group having a positive power,
4. The front group includes, in order from the most object side, the first lens, the second lens having a negative power, and the third lens having a positive power in succession. The imaging optical system according to the item. The rear group includes a cemented lens, which is composed of a positive lens and a negative lens and has positive power as a whole, on the most image side,
The Abbe number of the positive lens constituting the cemented lens is 50 or more,
The imaging optical system according to claim 4, wherein the negative lens that constitutes the cemented lens has an Abbe number of 40 or less. The first lens of the refractive optical system is an aspherical lens,
The image forming optical system according to claim 1, wherein the lenses of the refractive optical system other than the first lens are spherical lenses. 0.85<TTL/ZOB<2 (1-1)
The imaging optical system according to claim 2, wherein the conditional expression (1-1) expressed by is satisfied. 7<LL0/Ymax<13 (2-1)
The imaging optical system according to claim 2, wherein the conditional expression (2-1) expressed by is satisfied. 4<fL1/fL0<25 (3-1)
The imaging optical system according to claim 3, wherein the conditional expression (3-1) expressed by is satisfied. The imaging optical system according to claim 5, wherein the positive lens that constitutes the cemented lens has an Abbe number of 55 or more. The imaging optical system according to claim 5, wherein the negative lens that constitutes the cemented lens has an Abbe number of 30 or less. An image reading apparatus comprising the image forming optical system according to claim 1. The image reading device according to claim 12, wherein a reading range of the image is set to a region not including the optical axis.