阅读说明：本技术 摄像光学系统 (Image pickup optical system ) 是由 坂上典久 于 2019-03-26 设计创作，主要内容包括：提供一种用于实现足够小型、足够广角、足够高分辨率的内窥镜、不使用接合透镜的5片透镜的摄像光学系统。一种摄像光学系统,具有从物体侧到像侧依次配置的、具有负屈光力且物体侧的面为平面或凸面的第1透镜、具有正屈光力且为双凸透镜的第2透镜、光圈、具有正屈光力且为双凸透镜的第3透镜、具有负屈光力且为双凹透镜的第4透镜、具有正屈光力的第5透镜,各透镜不是接合透镜,其中,用f5表示该第5透镜的焦距,用f表示整体的焦距,则满足2.6<f5/f<7。(Provided is an imaging optical system for realizing a sufficiently small, wide and high-resolution endoscope, which is provided with 5 lenses without using a cemented lens. An imaging optical system includes, arranged in order from an object side to an image side, a 1 st lens having a negative refractive power and an object side surface being a flat surface or a convex surface, a 2 nd lens having a positive refractive power and being a biconvex lens, a diaphragm, a 3 rd lens having a positive refractive power and being a biconvex lens, a 4 th lens having a negative refractive power and being a biconcave lens, and a 5 th lens having a positive refractive power, wherein each of the lenses is not a cemented lens, and wherein a focal length of the 5 th lens is represented by f5, and a total focal length is represented by f, and 2.6< f5/f <7 is satisfied.)

1. An imaging optical system includes the following parts arranged in order from an object side to an image side: a 1 st lens having a negative refractive power and an object-side surface being a flat surface or a convex surface, a 2 nd lens having a positive refractive power and being a biconvex lens, a diaphragm, a 3 rd lens having a positive refractive power and being a biconvex lens, a 4 th lens having a negative refractive power and being a biconcave lens, and a 5 th lens having a positive refractive power, each of the 5 lenses being not a cemented lens,

when f5 denotes the focal length of the 5 th lens and f denotes the overall focal length, 2.6< f5/f <7 is satisfied.

2. The imaging optical system according to claim 1, wherein all surfaces of the 1 st lens other than the object-side surface are aspheric surfaces.

3. The image pickup optical system according to claim 1 or 2, wherein the 5 th lens is a biconvex lens.

4. The imaging optical system according to any one of claims 1 to 3,

the imaging optical system satisfies 4< f5/f < 7.

5. The imaging optical system according to any one of claims 1 to 4,

when the abbe number of the 2 nd lens is v 2, the abbe number of the 3 rd lens is v 3 and the abbe number of the 4 th lens is v 4, the following conditions are satisfied:

|ν2－ν3|<10

ν4<ν2

ν4<ν3。

6. the imaging optical system according to any one of claims 1 to 5,

when the distance from the vertex of the object-side surface of the 1 st lens to the image plane is TTL, 5.5< TTL/f <6.5 is satisfied.

7. The imaging optical system according to any one of claims 1 to 6,

when the aperture value is Fno, 4.0< Fno <6.5 is satisfied.

Technical Field

The present invention relates to an imaging optical system, and more particularly to an imaging optical system for an endoscope.

Background

As endoscopes used in the medical field, there are insertion endoscopes and capsule endoscopes. An image pickup optical system, i.e., an objective lens, at the distal end portion of a typical insertion endoscope is connected to an image pickup device located at a remote position via an optical fiber or a relay lens. In an imaging optical system of such a general insertion endoscope, telecentricity is required in order to reduce light quantity loss. In addition, some insertion endoscopes include an image pickup optical system and an image pickup element at a distal end portion thereof, and display an image on a display device located at a remote position. The capsule endoscope includes an imaging optical system and an imaging element in a capsule. Therefore, the imaging optical system of the capsule endoscope and the electronic endoscope is not required to have telecentricity. On the other hand, any type of endoscope requires a small size, a wide angle, and a high resolution. In order to achieve high resolution, it is necessary to reduce aberrations of the image pickup optical system. In addition, from the viewpoint of cost, it is preferable not to use a cemented lens.

Patent document 1 discloses an imaging optical system for an endoscope that does not use 5 lenses joined to lenses. However, astigmatism of the imaging optical system is relatively large, and the resolution thereof cannot be sufficiently satisfied.

Thus, an imaging optical system of 5 lenses without using a cemented lens has not been developed for realizing a sufficiently small, sufficiently wide-angle, and sufficiently high-resolution endoscope.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2006 and 276779

Disclosure of Invention

Problems to be solved by the invention

Therefore, there is a need for an image pickup optical system having 5 lenses without using a cemented lens to realize an endoscope small enough, wide enough, and high enough resolution. The invention provides an imaging optical system of 5 lenses without using a cemented lens for realizing a sufficiently small, sufficiently wide-angle, and sufficiently high-resolution endoscope.

Means for solving the problems

An imaging optical system of the present invention includes a 1 st lens having a negative refractive power and an object-side surface being a flat surface or a convex surface, a 2 nd lens having a positive refractive power and being a biconvex lens, a diaphragm, a 3 rd lens having a positive refractive power and being a biconvex lens, a 4 th lens having a negative refractive power and being a biconcave lens, and a 5 th lens having a positive refractive power, which are arranged in order from an object side to an image side, wherein each of the lenses is 5 lenses other than a cemented lens, and wherein a focal length of the 5 th lens is represented by f5, and a focal length of the entire lens is represented by f, and 2.6< f5/f <7 is satisfied.

The imaging optical system of the present invention is an optical system in which each lens is not a 5-piece lens of a cemented lens. By not using a cemented lens, a small-sized and low-cost image pickup optical system can be provided.

The imaging optical system according to the present invention includes a 1 st lens having a negative refractive power and a plane or a convex surface on an object side, a 2 nd lens having a positive refractive power and being a biconvex lens, a diaphragm, and a 3 rd lens having a positive refractive power and being a biconvex lens, which are arranged from the object side to the image side. The configuration of the lens includes a 1 st lens having a negative refractive power, a 2 nd lens having a positive refractive power, and a 3 rd lens having a positive refractive power, which are arranged from the object side to the image side, and various aberrations at a wide angle are easily corrected.

Since the object-side surface of the 1 st lens is a flat surface or a convex surface, it is possible to prevent liquid droplets from staying on the lens surface and causing a decrease in resolution.

The chromatic aberration of magnification of the 2 nd lens having positive refractive power before the aperture and the chromatic aberration of magnification of the 3 rd lens having positive refractive power after the aperture cancel each other out, and the chromatic aberration of magnification is reduced.

The imaging optical system of the present invention includes a 4 th lens having a negative refractive power and being a biconcave lens, and a 5 th lens having a positive refractive power, wherein a focal length of the 5 th lens is represented by f5, and when the focal length is represented by f as a whole, 2.6< f5/f <7 is satisfied.

By setting f5/f smaller than the upper limit of the above equation, the power of the 5 th lens can be maintained relatively high, and an increase in field curvature and a decrease in the peripheral light amount ratio can be suppressed. By making f5/f larger than the lower limit of the above equation, the power of the 5 th lens is not excessively large, and an increase in astigmatism can be suppressed.

In the imaging optical system according to embodiment 1 of the present invention, all surfaces of the 1 st lens other than the object-side surface are aspherical surfaces.

By making all surfaces of the 1 st lens other than the object-side surface thereof aspheric, it is possible to reduce aberration and obtain a good resolution.

In the imaging optical system according to embodiment 2 of the present invention, the 5 th lens is a lenticular lens.

By using the 5 th lens element as a lenticular lens element, it is possible to reduce the field curvature while suppressing a decrease in the peripheral light amount ratio, and to obtain good resolution.

The imaging optical system according to embodiment 3 of the present invention further satisfies 4< f5/f < 7.

By making f5/f larger than the lower limit of equation 4< f5/f <7, the distance from the exit pupil position of the optical system to the image plane can be easily set to about 1.5mm, corresponding to a small and high-resolution sensor having a large incident angle of light rays at the peripheral edge.

In the imaging optical system according to embodiment 4 of the present invention, when the abbe number of the 2 nd lens is ν 2, the abbe number of the 3 rd lens is ν 3, and the abbe number of the 4 th lens is ν 4, | ν 2- ν 3| <10, ν 4< ν 2, and ν 4< ν 3 are satisfied.

When the above conditions are satisfied, chromatic aberration can be reduced by using only a high dispersion resin having a small abbe number as a material of the 4 th lens. Therefore, it is advantageous from the viewpoint of cost to reduce the number of lenses of the highly dispersed resin.

In the imaging optical system according to embodiment 5 of the present invention, TTL is defined as a distance from a vertex of the object-side surface of the 1 st lens to the image plane, and 5.5< TTL/f <6.5 is satisfied.

By making TTL/f larger than the lower limit of the above formula, the peripheral light amount ratio is easily made to be equal to or larger than a predetermined value, and by making TTL/f smaller than the upper limit, the optical system can be easily made compact.

In the imaging optical system according to embodiment 5 of the present invention, 4.0< Fno <6.5 is satisfied when the aperture value is Fno.

When Fno is larger than the lower limit value of the above equation, the depth of field of the optical system is increased, and thus, the imaging system can cope with a wide range of imaging. By making Fno smaller than the upper limit value of the above equation, the resolution of the sensor that can cope with a small pixel size can be maintained, and the sensor can also be miniaturized.

Drawings

Fig. 1 is a diagram showing a configuration of an imaging optical system according to embodiment 1.

Fig. 2 is a diagram showing spherical aberration of the imaging optical system according to embodiment 1.

Fig. 3 is a diagram showing distortion aberration of the imaging optical system of example 1.

Fig. 4 is a diagram showing astigmatism of the imaging optical system according to example 1.

Fig. 5 is a diagram showing chromatic aberration of magnification of the imaging optical system of embodiment 1.

Fig. 6 is a diagram showing a configuration of an imaging optical system according to embodiment 2.

Fig. 7 is a diagram showing spherical aberration of the imaging optical system of example 2.

Fig. 8 is a diagram showing distortion aberration of the imaging optical system of example 2.

Fig. 9 is a diagram showing astigmatism of the imaging optical system according to example 2.

Fig. 10 is a diagram showing chromatic aberration of magnification of the imaging optical system of example 2.

Fig. 11 is a diagram showing a configuration of an imaging optical system according to embodiment 3.

Fig. 12 is a diagram showing spherical aberration of the imaging optical system of example 3.

Fig. 13 is a diagram showing distortion aberration of the imaging optical system of example 3.

Fig. 14 is a diagram showing astigmatism of the imaging optical system according to example 3.

Fig. 15 is a diagram showing chromatic aberration of magnification of the imaging optical system according to embodiment 3.

Fig. 16 is a diagram showing a configuration of an imaging optical system according to embodiment 4.

Fig. 17 is a diagram showing spherical aberration of the imaging optical system of example 4.

Fig. 18 is a diagram showing distortion aberration of the imaging optical system of example 4.

Fig. 19 is a diagram showing astigmatism of the imaging optical system according to example 4.

Fig. 20 is a diagram showing chromatic aberration of magnification of the imaging optical system according to embodiment 4.

Fig. 21 is a diagram showing a configuration of an imaging optical system according to embodiment 5.

Fig. 22 is a diagram showing spherical aberration of the imaging optical system of example 5.

Fig. 23 is a diagram showing distortion aberration of the imaging optical system of example 5.

Fig. 24 is a diagram showing astigmatism of the imaging optical system according to example 5.

Fig. 25 is a diagram showing chromatic aberration of magnification of the imaging optical system according to embodiment 5.

Detailed Description

Fig. 1 is a diagram showing a configuration of an imaging optical system according to an embodiment (example 1 described later) of the present invention. The imaging optical system includes a 1 st lens 101 having a negative refractive power and a plane or a convex surface on an object side, a 2 nd lens 102 having a positive refractive power and being a biconvex lens, a stop 103, a 3 rd lens 104 having a positive refractive power and being a biconvex lens, a 4 th lens 105 having a negative refractive power and being a biconcave lens, and a 5 th lens 106 having a positive refractive power, which are arranged from the object side to the image side. The imaging optical system is an optical system in which each lens is not a 5-piece lens joined with a lens. The light beam passing through the above-described lens is converged on an image plane 108 after passing through an optical member 107. The optical member 107 is a glass cover of a sensor or the like. In the present specification and claims, a lens having a negative refractive power means a lens having a negative refractive power with respect to a light flux entering a range of an angle of field in an optical system, that is, a light flux passing through a pupil, and a lens having a positive refractive power means a lens having a positive refractive power with respect to the light flux.

The following describes features of an imaging optical system according to an embodiment of the present invention.

The imaging optical system according to the embodiment of the present invention is an optical system in which each lens is not a 5-piece lens joined with a lens. By not using a cemented lens, a small-sized and low-cost image pickup optical system can be provided.

An imaging optical system according to an embodiment of the present invention includes a 1 st lens having a negative refractive power and a plane or a convex surface on an object side, a 2 nd lens having a positive refractive power and being a biconvex lens, a diaphragm, and a 3 rd lens having a positive refractive power and being a biconvex lens, which are arranged from the object side to the image side. The configuration of the lens includes a 1 st lens having a negative refractive power, a 2 nd lens having a positive refractive power, and a 3 rd lens having a positive refractive power, which are arranged from the object side to the image side, and various aberrations at a wide angle are easily corrected. From the viewpoint of telecentricity, it is advantageous to dispose the diaphragm between the 1 st lens and the 2 nd lens. From the viewpoint of downsizing, widening the angle, and increasing the resolution, it is advantageous to dispose the diaphragm between the 2 nd lens and the 3 rd lens. In the present invention, since importance is placed on miniaturization, a wider angle, and higher resolution than telecentricity, the diaphragm is disposed between the 2 nd lens and the 3 rd lens.

Since the object-side surface of the 1 st lens is a flat surface or a convex surface, the retention of liquid droplets on the lens surface and the resulting decrease in resolution can be prevented.

An imaging optical system according to an embodiment of the present invention includes a 4 th lens having a negative refractive power and being a biconcave lens, and a 5 th lens having a positive refractive power, and a focal length of the 5 th lens is represented by f5, and when the focal length is represented by f as a whole, 2.6< f5/f <7 (1) is satisfied.

By making the upper limit of the f5/f ratio formula (1) small, the power of the 5 th lens can be maintained relatively large, and an increase in field curvature and a decrease in the peripheral light amount ratio can be suppressed. By making f5/f larger than the lower limit value of expression (1), the refractive power of the 5 th lens is not excessively large, and an increase in astigmatism can be suppressed.

Further, by making f5/f larger than the lower limit of formula 4< f5/f <7 (2), the distance from the exit pupil position of the optical system to the image plane can be easily set to about 1.5mm in accordance with a small and high-resolution sensor having a large incident angle of light rays on the peripheral edge.

The chromatic aberration can be reduced by a configuration in which a 2 nd lens having a positive refractive power and being a biconvex lens, a diaphragm, a 3 rd lens having a positive refractive power and being a biconvex lens, and a 4 th lens having a negative refractive power and being a biconcave lens are arranged.

The chromatic aberration of magnification of the 2 nd lens having positive refractive power before the aperture and the chromatic aberration of magnification of the 3 rd lens having positive refractive power after the aperture cancel each other out, and the chromatic aberration of magnification is reduced.

If the Abbe number of the 2 nd lens is upsilon 2, the Abbe number of the 3 rd lens is upsilon 3, and the Abbe number of the 4 th lens is upsilon 4, the requirement is met

|ν2－ν3|<10 (3)

ν4<ν2 (4)

ν4<ν3 (5)

In the case of (3), chromatic aberration can be reduced by using only a high dispersion resin having a small abbe number as the material of the 4 th lens.

TTL is the distance from the apex of the object side surface of the 1 st lens to the image plane, and the TTL/f ratio is set to be

5.5<TTL/f<6.5 (6)

The lower limit of (2) is larger, and the peripheral light amount is easily made larger than a predetermined value, and smaller than the upper limit, so that the optical system can be easily miniaturized.

When f is Fno, the depth of field of the optical system is increased by increasing Fno to a value greater than the lower limit of 4.0< Fno <6.5 (7), and thus, it is possible to cope with a wide range of imaging. By making Fno smaller than the upper limit value of equation (7), it is possible to maintain the resolution of the sensor that can cope with a small pixel size, and also to cope with miniaturization of the sensor.

The following describes embodiments of the present invention.

The material of the 1 st lens, the 2 nd lens, the 3 rd lens and the 5 th lens in each example was a cycloolefin polymer (grade: E48R). The material of the 4 th lens of each example was polycarbonate (grade: EP 5000). The material of the sensor cover (optical component 105) is N-BK 7.

Each surface of each lens is represented by the following formula.

[ mathematical formula 1]

[ mathematical formula 2]

[ mathematical formula 3]

The z-axis is a line connecting the centers of curvature of both surfaces of each lens. z is a coordinate indicating a position in the z-axis direction of a point on the lens surface, which is positive on the image side, with respect to the intersection of each lens surface and the z-axis. h represents the distance from the z-axis to a point on the lens surface. R is the signed radius of curvature of the apex of the lens face, i.e. the signed center radius of curvature. c is the signed curvature of the apex of the lens surface, i.e. the signed center curvature. The absolute value of c is the curvature of the apex of the lens surface, i.e., the center curvature, and the sign is positive when the lens surface is convex toward the object side and negative when the lens surface is convex toward the image side. k is the conic constant. Ai are aspherical coefficients. i and m are integers.

The uniform principal axis of each lens is taken as the optical axis.

The aberrations of the imaging optical system in each example are represented by an F-line (wavelength 486.1nm), a d-line (wavelength 587.56nm), and a C-line (wavelength 656.27 nm).

The length of [ radius of curvature ] and [ spacing ] in the table below are in millimeters.

Example 1

Fig. 1 is a diagram showing a configuration of an imaging optical system according to embodiment 1. The imaging optical system includes a 1 st lens 101 having a negative refractive power and a plane or a convex surface on an object side, a 2 nd lens 102 having a positive refractive power and being a biconvex lens, a diaphragm 103, a 3 rd lens 104 having a positive refractive power and being a biconvex lens, a 4 th lens 105 having a negative refractive power and being a biconcave lens, and a 5 th lens 106 having a positive refractive power, which are arranged from the object side to the image side. The imaging optical system is an optical system in which each lens is not a 5-piece lens joined with a lens. The light beam passing through the above-described lens is converged on an image plane 108 after passing through an optical member 107.

Table 1 shows the surface intervals of the optical elements, the properties of the materials of the optical elements, and the shapes of the surfaces of the optical elements. Surfaces 1-4 respectively represent the object-side surface of the 1 st lens 101, the image-side surface of the 1 st lens 101, the object-side surface of the 2 nd lens 102, and the image-side surface of the 2 nd lens 102. The surface interval corresponding to the surface 1 indicates an interval between the image-side surface of the 1 st lens 101 and the object-side surface of the 2 nd lens 102. The refractive index and abbe number corresponding to the surface 1 indicate the refractive index and abbe number of the 1 st lens 101.

[ Table 1]

Table 2 shows the central curvature radius, conic constant and aspherical surface coefficient of equation (8) for surfaces 2-4 and 6-11.

[ Table 2]

	R	k	A4	A6
					2 noodles	0.424604	-0.53477	-3.415E-01	8.528E-04
3 side of flour	3.107207	0	-4.931E-01	1.120E-01
					4 sides	-0.84564	0	2.790E-01	-7.810E-02
6 noodles	1.144051	0	4.112E-01	0.000E+00
					7 noodles	-0.60091	-2.00778	-6.572E-01	0.000E+00
8 noodles	-0.67064	-0.96092	－1.085E+00	0.000E+00
					9 noodles	2.296324	0	2.012E-01	-1.444E-01
10 noodles	2.056713	0	3.610E-01	－1.583E+00
					11 noodles	-15.2077	0	3.459E-01	-7.598E-01

Fig. 2 is a diagram showing spherical aberration of the imaging optical system of embodiment 1. The horizontal axis represents the coordinates of the optical axis direction of the imaging position. 0 on the horizontal axis represents the position of the image plane. The vertical axis represents the relative value of the distance of a ray parallel to the optical axis from the optical axis. 0 denotes a ray coincident with the optical axis, and 1 denotes a ray passing through the aperture edge of the aperture.

Fig. 3 is a diagram showing distortion aberration of the imaging optical system of example 1. The horizontal axis represents distortion aberration. The vertical axis represents the angle of the chief ray with the optical axis.

Fig. 4 is a diagram showing astigmatism of the imaging optical system of example 1. The horizontal axis represents the positions of the meridional image plane and the sagittal image plane of the F line, the d line, and the C line in the optical axis direction. In the figure, Tan denotes a meridional image plane, and Sag denotes a sagittal image plane. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

Fig. 5 is a diagram showing chromatic aberration of magnification of the imaging optical system of embodiment 1. The horizontal axis represents chromatic aberration of magnification of the F-line and the C-line with respect to the d-line. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

The focal length, aperture value (Fno.), half field angle, distance from the vertex of the object-side surface of the 1 st lens to the image plane (TTL), distance from the image plane to the exit pupil in the object-side direction (exit pupil position), and ratio of illuminance at the periphery of the image plane to illuminance on the optical axis (peripheral light amount ratio) in the imaging optical system of example 1 are as follows.

Focal length 0.693mm

Fno.5

Half field angle of 60 degrees

TTL 4.081mm

Exit pupil position 1.491mm

The light intensity at the periphery is 55%

Example 2

Fig. 6 is a diagram showing a configuration of an imaging optical system according to embodiment 2. The imaging optical system includes a 1 st lens 201 having a negative refractive power and a plane or a convex surface on an object side, a 2 nd lens 202 having a positive refractive power and being a biconvex lens, a stop 203, a 3 rd lens 204 having a positive refractive power and being a biconvex lens, a 4 th lens 205 having a negative refractive power and being a biconcave lens, and a 5 th lens 206 having a positive refractive power, which are arranged from the object side to the image side. The imaging optical system is an optical system in which each lens is not a 5-piece lens joined with a lens. The light flux passing through the above-described lens passes through the optical member 207 and is then converged on the image plane 208.

Table 3 shows the surface intervals of the optical elements, the properties of the material of the optical elements, and the surface shapes of the optical elements. Surfaces 1 to 4 respectively represent the object side surface of the 1 st lens 201, the image side surface of the 1 st lens 201, the object side surface of the 2 nd lens 202, and the image side surface of the 2 nd lens 202. The surface interval corresponding to the surface 1 indicates an interval between the image side surface of the 1 st lens 201 and the object side surface of the 2 nd lens 202. The refractive index and abbe number corresponding to the surface 1 indicate the refractive index and abbe number of the 1 st lens 201.

[ Table 3]

Table 4 shows the central curvature radius, conic constant and aspherical surface coefficient of equation (8) for surfaces 2 to 4 and surfaces 6 to 11.

[ Table 4]

Fig. 7 is a diagram showing spherical aberration of the imaging optical system of example 2. The horizontal axis represents the coordinates of the optical axis direction of the imaging position. 0 on the horizontal axis represents the position of the image plane. The vertical axis represents the relative value of the distance of a ray parallel to the optical axis from the optical axis. 0 denotes a ray coincident with the optical axis, and 1 denotes a ray passing through the aperture edge of the aperture.

Fig. 8 is a diagram showing distortion aberration of the imaging optical system of example 2. The horizontal axis represents distortion aberration. The vertical axis represents the angle of the chief ray with the optical axis.

Fig. 9 is a diagram showing astigmatism of the imaging optical system of example 2. The horizontal axis represents the positions of the meridional image plane and the sagittal image plane of the F line, the d line, and the C line in the optical axis direction. In the figure, Tan denotes a meridional image plane, and Sag denotes a sagittal image plane. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

Fig. 10 is a diagram showing chromatic aberration of magnification of the imaging optical system of example 2. The horizontal axis represents chromatic aberration of magnification of the F-line and the C-line with respect to the d-line. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

The focal length, aperture value (Fno.), half field angle, distance from the vertex of the object-side surface of the 1 st lens to the image plane (TTL), distance from the image plane to the exit pupil in the object-side direction (exit pupil position), and ratio of illuminance at the periphery of the image plane to illuminance on the optical axis (peripheral light amount ratio) in the imaging optical system of example 2 are as follows.

Focal length 0.693mm

Fno.5

Half field angle of 60 degrees

TTL 4.096mm

Exit pupil position 1.469mm

The light intensity at the periphery is 53%

Example 3

Fig. 11 is a diagram showing a configuration of an imaging optical system according to embodiment 3. The imaging optical system includes a 1 st lens 301 having a negative refractive power and a plane or a convex surface on an object side, a 2 nd lens 302 having a positive refractive power and being a biconvex lens, a stop 303, a 3 rd lens 304 having a positive refractive power and being a biconvex lens, a 4 th lens 305 having a negative refractive power and being a biconcave lens, and a 5 th lens 306 having a positive refractive power, which are arranged from the object side to the image side. The imaging optical system is an optical system in which each lens is not a 5-piece lens joined with a lens. The light beam passing through the above-described lens is converged on an image plane 308 after passing through an optical member 307.

Table 5 shows the surface intervals of the optical elements, the properties of the materials of the optical elements, and the shapes of the surfaces of the optical elements. Surfaces 1-4 respectively represent the object side surface of the 1 st lens 301, the image side surface of the 1 st lens 301, the object side surface of the 2 nd lens 302, and the image side surface of the 2 nd lens 302. The surface interval corresponding to the surface 1 indicates an interval between the image side surface of the 1 st lens 301 and the object side surface of the 2 nd lens 302. The refractive index and abbe number corresponding to the surface 1 indicate the refractive index and abbe number of the 1 st lens 301.

[ Table 5]

Table 6 is a table showing the central radius of curvature, conic constant, and aspherical surface coefficient of equation (8) for surfaces 2 to 4 and surfaces 6 to 11.

[ Table 6]

Fig. 12 is a diagram showing spherical aberration of the imaging optical system of example 3. The horizontal axis represents the coordinates of the optical axis direction of the imaging position. 0 on the horizontal axis represents the position of the image plane. The vertical axis represents the relative value of the distance of a ray parallel to the optical axis from the optical axis. 0 denotes a ray coincident with the optical axis, and 1 denotes a ray passing through the aperture edge of the aperture.

Fig. 13 is a diagram showing distortion aberration of the imaging optical system of example 3. The horizontal axis represents distortion aberration. The vertical axis represents the angle of the chief ray with the optical axis.

Fig. 14 is a diagram showing astigmatism of the imaging optical system according to example 3. The horizontal axis represents the positions of the meridional image plane and the sagittal image plane of the F line, the d line, and the C line in the optical axis direction. In the figure, Tan denotes a meridional image plane, and Sag denotes a sagittal image plane. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

Fig. 15 is a diagram showing chromatic aberration of magnification of the imaging optical system according to embodiment 3. The horizontal axis represents chromatic aberration of magnification of the F-line and the C-line with respect to the d-line. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

The focal length, aperture value (Fno.), half field angle, distance from the vertex of the object-side surface of the 1 st lens to the image plane (TTL), distance from the image plane to the exit pupil in the object-side direction (exit pupil position), and ratio of illuminance at the periphery of the image plane to illuminance on the optical axis (peripheral light amount ratio) in the imaging optical system of example 3 are as follows.

Focal length 0.692mm

Fno.5

Half field angle of 60 degrees

TTL 4.077mm

Exit pupil position 1.506mm

The light intensity at the periphery is 56%

Example 4

Fig. 16 is a diagram showing a configuration of an imaging optical system according to embodiment 4. The imaging optical system includes a 1 st lens 401 having a negative refractive power and a plane or a convex surface on an object side, a 2 nd lens 402 having a positive refractive power and being a biconvex lens, a diaphragm 403, a 3 rd lens 404 having a positive refractive power and being a biconvex lens, a 4 th lens 405 having a negative refractive power and being a biconcave lens, and a 5 th lens 406 having a positive refractive power, which are arranged from the object side to the image side. The imaging optical system is an optical system in which each lens is not a 5-piece lens joined with a lens. The light beam passing through the lens passes through the optical member 407 and is converged on the image plane 408.

Table 7 shows the surface intervals of the optical elements, the properties of the materials of the optical elements, and the shapes of the surfaces of the optical elements. Surfaces 1-4 respectively represent the object side surface of the 1 st lens 401, the image side surface of the 1 st lens 401, the object side surface of the 2 nd lens 402, and the image side surface of the 2 nd lens 402. The surface interval corresponding to the surface 1 indicates an interval between the image side surface of the 1 st lens 401 and the object side surface of the 2 nd lens 402. The refractive index and abbe number corresponding to the surface 1 indicate the refractive index and abbe number of the 1 st lens 401.

[ Table 7]

Table 8 shows the central radius of curvature, conic constant, and aspherical surface coefficient of equation (8) for surfaces 2 to 4 and surfaces 6 to 11.

[ Table 8]

	R	k	A4	A6
					1 side	25	0	-	-
2 noodles	0.426301	-0.49165	-2.997E-01	-5.887E-02
					3 side of flour	4.010181	0	-5.135E-01	1.198E-01
4 sides	-0.82682	0	3.097E-01	-9.007E-02
					6 noodles	1.130368	0	4.315E-01	0.000E+00
7 noodles	-0.5989	-1.77407	-5.313E-01	0.000E+00
					8 noodles	-0.66806	-1.12215	－1.121E+00	0.000E+00
9 noodles	2.257062	0	2.620E-01	-2.704E-01
					10 noodles	2.051253	0	3.552E-01	－1.584E+00
11 noodles	-22.1343	0	2.858E-01	-6.924E-01

Fig. 17 is a diagram showing spherical aberration of the imaging optical system of example 4. The horizontal axis represents the coordinates of the optical axis direction of the imaging position. 0 on the horizontal axis represents the position of the image plane. The vertical axis represents the relative value of the distance of a ray parallel to the optical axis from the optical axis. 0 denotes a ray coincident with the optical axis, and 1 denotes a ray passing through the aperture edge of the aperture.

Fig. 18 is a diagram showing distortion aberration of the imaging optical system of example 4. The horizontal axis represents distortion aberration. The vertical axis represents the angle of the chief ray with the optical axis.

Fig. 19 is a diagram showing astigmatism of the imaging optical system according to example 4. The horizontal axis represents the positions of the meridional image plane and the sagittal image plane of the F line, the d line, and the C line in the optical axis direction. In the figure, Tan denotes a meridional image plane, and Sag denotes a sagittal image plane. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

Fig. 20 is a diagram showing chromatic aberration of magnification of the imaging optical system according to embodiment 4. The horizontal axis represents chromatic aberration of magnification of the F-line and the C-line with respect to the d-line. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

The focal length, aperture value (Fno.), half field angle, distance from the vertex of the object-side surface of the 1 st lens to the image plane (TTL), distance from the image plane to the exit pupil in the object-side direction (exit pupil position), and ratio of illuminance at the periphery of the image plane to illuminance on the optical axis (peripheral light amount ratio) in the imaging optical system of example 4 are as follows.

Focal length 0.693mm

Fno.5

Half field angle of 60 degrees

TTL 4.051mm

Exit pupil position 1.48mm

The light intensity at the periphery is 56%

Example 5

Fig. 21 is a diagram showing a configuration of an imaging optical system according to embodiment 5. The imaging optical system includes a 1 st lens 501 having a negative refractive power and a plane or a convex surface on an object side, a 2 nd lens 502 having a positive refractive power and being a biconvex lens, a stop 503, a 3 rd lens 504 having a positive refractive power and being a biconvex lens, a 4 th lens 505 having a negative refractive power and being a biconcave lens, and a 5 th lens 506 having a positive refractive power, which are arranged from the object side to the image side. The imaging optical system is an optical system in which each lens is not a 5-piece lens joined with a lens. The light flux passing through the above-described lens is converged on an image plane 508 after passing through the optical member 507.

Table 9 shows the surface intervals of the optical elements, the properties of the materials of the optical elements, and the shapes of the surfaces of the optical elements. Surfaces 1-4 respectively represent the object side surface of the 1 st lens 501, the image side surface of the 1 st lens 501, the object side surface of the 2 nd lens 502, and the image side surface of the 2 nd lens 502. The surface interval corresponding to the surface 1 indicates an interval between the image side surface of the 1 st lens 501 and the object side surface of the 2 nd lens 502. The refractive index and abbe number corresponding to the surface 1 indicate the refractive index and abbe number of the 1 st lens 501.

[ Table 9]

Table 10 shows the central radius of curvature, conic constant, and aspherical surface coefficient of equation (8) for surfaces 2 to 4 and surfaces 6 to 11.

[ Table 10]

	R	k	A4	A6
					2 noodles	0.418117	-0.52668	-2.491E-01	2.784E-02
3 side of flour	0.885091	0	-2.310E-01	-9.553E-03
					4 sides	-1.87067	0	-1.779E-01	9.756E-02
6 noodles	1.383282	0	-7.045E-01	0.000E+00
					7 noodles	-0.57818	-0.01235	-2.628E-01	0.000E+00
8 noodles	-0.47721	-0.51236	-6.654E-02	0.000E+00
					9 noodles	5.011886	0	1.297E-01	-4.476E-01
10 noodles	1.501162	0	8.030E-02	-3.219E-01
					11 noodles	-2.56615	0	7.080E-01	-5.641E-01

Fig. 22 is a diagram showing spherical aberration of the imaging optical system of example 5. The horizontal axis represents the coordinates of the optical axis direction of the imaging position. 0 on the horizontal axis represents the position of the image plane. The vertical axis represents the relative value of the distance of a ray parallel to the optical axis from the optical axis. 0 denotes a ray coincident with the optical axis, and 1 denotes a ray passing through the aperture edge of the aperture.

Fig. 23 is a diagram showing distortion aberration of the imaging optical system of example 5. The horizontal axis represents distortion aberration. The vertical axis represents the angle of the chief ray with the optical axis.

Fig. 24 is a diagram showing astigmatism of the imaging optical system according to example 5. The horizontal axis represents the positions of the meridional image plane and the sagittal image plane of the F line, the d line, and the C line in the optical axis direction. In the figure, Tan denotes a meridional image plane, and Sag denotes a sagittal image plane. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

Fig. 25 is a diagram showing chromatic aberration of magnification of the imaging optical system according to embodiment 5. The horizontal axis represents chromatic aberration of magnification of the F-line and the C-line with respect to the d-line. The vertical axis represents an angle of a principal ray of the light beam incident on the imaging optical system with respect to the optical axis. The maximum value of the angle of the longitudinal axis corresponds to the half field angle.

The focal length, aperture value (Fno.), half field angle, distance from the vertex of the object-side surface of the 1 st lens to the image plane (TTL), distance from the image plane to the exit pupil in the object-side direction (exit pupil position), and ratio of illuminance at the periphery of the image plane to illuminance on the optical axis (peripheral light amount ratio) in the imaging optical system of example 5 are as follows.

Focal length 0.694mm

Fno.5

Half field angle of 60 degrees

TTL 4.1mm

Exit pupil position 1.907mm

The light intensity at the periphery is 58%

Features of the embodiments

Table 11 shows the characteristics of the examples.

[ Table 11]

According to Table 11, examples 1 to 5 satisfied formula (1) and formulas (6) to (7), and examples 1 to 4 satisfied formula (2). In addition, examples 1 to 5 satisfy formulas (3) to (5) according to tables 1, 3, 5, 7 and 9. The exit pupil positions (the distance from the image plane to the exit pupil in the object-side direction) of examples 1 to 5 were less than 2mm, and the peripheral light amount ratio was 53% or more.

In addition, according to the aberration diagrams of the respective embodiments, the magnitudes of the respective aberrations are as follows. Regarding spherical aberration, the imaging position on the optical axis is in the range of ± 5 μm from the image plane. Regarding astigmatism, the positions of the meridional image plane and the sagittal image plane of the three wavelengths in the optical axis direction are within ± 20 micrometers from the image plane in all embodiments, and within ± 10 micrometers in embodiments 1, 3, and 4. Distortion aberration is ± 50% or less. The chromatic aberration of magnification of the F-line and the C-line with respect to the d-line is within. + -. 1 μm in all the examples, and within. + -. 0.5 μm in examples 1 to 4.

Thus, the aberrations in embodiments 1 to 5 are very small, and a high-resolution imaging optical system is realized.