JP2016153912A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus in which various aberrations can be excellently corrected even in an optical system which has a wide angle of view and is bright and which can obtain high image formation performance.SOLUTION: The imaging apparatus includes an imaging surface IMG having a concave shape toward an object side and an imaging optical system forming an object image on the imaging surface. The imaging optical system includes a plurality of lenses and an aperture diaphragm STO. A lens G3 on the most image side among the plurality of lenses is a meniscus lens having a convex surface toward an image side. A lens adjacent to the lens G3 on the most image side includes an emission surface having a convex shape toward the image side. The focal length of the imaging optical system and a distance from the exit pupil of the imaging optical system to the imaging surface are set to be almost equal. The curvature radius of the imaging surface is set to be almost equal to the focal length of the imaging optical system.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging apparatus in which a curved imaging surface is disposed in the vicinity of an image plane of an imaging optical system. In particular, the present invention relates to an imaging apparatus suitable for a digital still camera, a digital video camera, a mobile phone camera, a surveillance camera, and the like.

  Several examples of an imaging apparatus using such a curved imaging surface are disclosed.

  A spherical lens in which concentric spheres are formed by a spherical shell lens and a spherical lens inside the lens has been proposed (Patent Document 1).

  This spherical lens can satisfactorily correct spherical aberration and chromatic aberration. In addition, since it is a point-symmetric configuration, it is easy to widen the angle of view, and it is suitable for an imaging optical system of an imaging apparatus that requires a wide angle and high resolution.

  In this spherical lens, an example is disclosed in which an aperture stop is provided on a plane passing through the spherical center of the spherical lens in order to block harmful light such as flare and obtain good imaging performance.

  Disclosed is an optical system for use in an inexpensive camera with a curved image surface, consisting of only two single lens members, with an aperture stop between them, and one of the lens members being double aspheric. (Patent Document 2).

  This optical system is an imaging device for a disposable camera that has a total field angle of at least 62.5 degrees and is configured to image on a curved film surface.

JP 63-081413 A JP-A-8-338944

Patent Document 1 discloses an example in which an imaging device having a wide angle of view is realized using a spherical lens.
The main embodiment is an F / 2.8 imaging optical system, in which spherical aberration and axial chromatic aberration are well corrected.

  On the other hand, an embodiment brighter than F / 2.8 is also disclosed. For example, although an F / 2.0 or F / 1.4 imaging optical system is disclosed, large spherical aberration occurs and sufficient imaging performance is not obtained.

  That is, the spherical lens disclosed in Patent Document 1 has a problem in that spherical aberration cannot be corrected and imaging performance deteriorates.

  In the optical system of Patent Document 2, the image surface is curved, and the two single lens members are aspherical, so that the imaging performance is improved over a wide angle.

  However, this optical system reduces the amount of generation of spherical aberration by narrowing down to F / 8.0.

  In this optical system, an aspherical surface that is displaced from the reference spherical surface to the image side is provided on the most object side surface, and an aspherical surface that is displaced from the reference spherical surface to the object side is provided on the most image side surface.

That is, the aspherical surface is displaced from the reference spherical surface to the inside of the imaging optical system at the periphery of the outermost lens surface of the imaging optical system.
This aspherical surface corrects coma and astigmatism.
For this reason, spherical aberration cannot be corrected satisfactorily.

  An object of the present invention is to provide an imaging apparatus that can satisfactorily correct various aberrations even in a bright optical system with a wide angle of view and obtain high imaging performance.

An imaging apparatus according to an aspect of the present invention is an imaging apparatus including an imaging surface that is concave toward the object side, and an imaging optical system that forms an object image on the imaging surface. The lens closest to the image side is a meniscus lens having a convex surface facing the image side, and the lens adjacent to the lens closest to the image side is the image side lens. When the focal length of the imaging optical system is f_sys, the distance from the exit pupil of the imaging optical system to the imaging surface is d_pup, and the radius of curvature of the imaging surface is R_img The following expression is satisfied.
0.8 ≦ f_sys / d_pup ≦ 1.5
0.8 ≦ | R_img | /f_sys≦1.5

  According to the present invention, it is possible to realize an imaging apparatus capable of satisfactorily correcting various aberrations even in a wide-angle and bright optical system and obtaining high imaging performance.

FIG. 2 is a diagram illustrating a configuration example of an imaging apparatus according to Embodiment 1 of the present invention. (A) is a figure which shows the aspherical shape of the lens surface of the most object side of the imaging device in Example 1 of this invention, (b) is a figure which shows the aspherical amount of the lens surface of the most object side. (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference spherical surface in the lens surface of the most object side of the imaging device in Example 1 of this invention, (b) is a figure which shows the 2nd-order differential value of an aspherical component. . FIG. 3 is a longitudinal aberration diagram of the imaging optical system according to Example 1 of the present invention. FIG. 3 is a lateral aberration diagram of the imaging optical system according to Example 1 of the present invention. FIG. 6 is a diagram illustrating a configuration example of an imaging apparatus according to a second embodiment of the present invention. (A) is a figure which shows the aspherical shape of the lens surface of the most image side of the imaging device in Example 2 of this invention. FIG. 6B is a diagram illustrating the aspheric amount of the lens surface closest to the image side. (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference spherical surface in the lens surface of the most image side of the imaging device in Example 2 of this invention. (B) is a figure which shows the 2nd-order differential value of an aspherical component. FIG. 6 is a longitudinal aberration diagram of the image pickup optical system according to the second embodiment of the present invention. FIG. 6 is a lateral aberration diagram of the image pickup optical system according to the second embodiment of the present invention. FIG. 6 is a diagram illustrating a configuration example of an imaging apparatus according to a third embodiment of the present invention. (A) is a figure which shows the aspherical shape of the lens surface of the most object side of the imaging device in Example 3 of this invention, (b) is a figure which shows the aspherical amount of the lens surface of the most object side. (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference | standard spherical surface in the lens surface of the most object side of the imaging device in Example 3 of this invention, (b) is a figure which shows the 2nd-order differential value of an aspherical component. . (A) is a figure which shows the aspherical shape of the lens surface of the most image side of the imaging device in Example 3 of this invention. FIG. 6B is a diagram illustrating the aspheric amount of the lens surface closest to the image side. (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference spherical surface in the lens surface of the most image side of the imaging device in Example 3 of this invention. (B) is a figure which shows the 2nd-order differential value of an aspherical component. FIG. 6 is a longitudinal aberration diagram of the imaging optical system according to Example 3 of the present invention. FIG. 6 is a lateral aberration diagram of the image pickup optical system according to the third embodiment of the present invention. FIG. 6 is a diagram illustrating a configuration example of an imaging apparatus according to a fourth embodiment of the present invention. (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference | standard spherical surface in the lens surface of the most object side of the imaging device in Example 4 of this invention, (b) is a figure which shows the 2nd-order differential value of an aspherical component. . (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference | standard spherical surface in the lens surface of the most object side of the imaging device in Example 4 of this invention, (b) is a figure which shows the 2nd-order differential value of an aspherical component. . (A) is a figure which shows the aspherical shape of the lens surface of the most image side of the imaging device in Example 4 of this invention. FIG. 6B is a diagram illustrating the aspheric amount of the lens surface closest to the image side. (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference spherical surface in the lens surface of the most image side of the imaging device in Example 4 of this invention. (B) is a figure which shows the 2nd-order differential value of an aspherical component. FIG. 10 is a longitudinal aberration diagram of the imaging optical system according to Example 4 of the present invention. FIG. 10 is a lateral aberration diagram of the imaging optical system according to Example 4 of the present invention. FIG. 10 is a diagram illustrating a configuration example of an imaging apparatus according to a fifth embodiment of the present invention. (A) is a figure which shows the aspherical shape of the lens surface of the most image side of the imaging device in Example 5 of this invention. FIG. 6B is a diagram illustrating the aspheric amount of the lens surface closest to the image side. (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference spherical surface in the lens surface of the most image side of the imaging device in Example 5 of this invention. (B) is a figure which shows the 2nd-order differential value of an aspherical component. FIG. 10 is a longitudinal aberration diagram of the imaging optical system according to Example 5 of the present invention. FIG. 12 is a lateral aberration diagram of the imaging optical system according to Example 5 of the present invention. FIG. 10 is a diagram illustrating a configuration example of an imaging apparatus according to a sixth embodiment of the present invention. (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference spherical surface in the lens surface of the most object side of the imaging device in Example 6 of this invention, (b) is a figure which shows the 2nd-order differential value of an aspherical component. . (A) is a figure which shows the 2nd-order differential value of the aspherical surface and reference spherical surface in the lens surface of the most object side of the imaging device in Example 6 of this invention, (b) is a figure which shows the 2nd-order differential value of an aspherical component. . FIG. 10 is a longitudinal aberration diagram of the imaging optical system according to Example 6 of the present invention. FIG. 10 is a lateral aberration diagram of the imaging optical system according to Example 6 of the present invention. FIG. 3 is an optical path diagram schematically showing an image formation state of an axial light beam in the imaging apparatus according to the embodiment of the present invention. FIG. 3 is an optical path diagram schematically showing an image formation state of an axial light beam in the imaging apparatus according to the embodiment of the present invention. The figure which shows the imaging relationship at the time of arrange | positioning the object plane of the imaging device in embodiment of this invention in a finite distance. FIG. 5 is a diagram illustrating a relationship between a focus position and an imaging surface shape during focus adjustment of the imaging device according to the embodiment of the present invention.

  A configuration example of the imaging device according to the embodiment of the present invention will be described.

  First, the overall configuration will be described.

  The imaging apparatus of the present embodiment includes an imaging optical system having a plurality of lenses, and has an imaging surface curved with a concave surface facing the object side in the vicinity of the image plane of the imaging optical system. The Petzval image plane can be corrected.

  Furthermore, by bringing the imaging optical system closer to a point-symmetric optical system, the occurrence of off-axis aberrations such as coma, astigmatism, distortion, and lateral chromatic aberration is suppressed, and the correction target aberrations are spherical aberration, axial chromatic aberration, etc. Limited to axial aberrations only.

  Making the imaging optical system closer to a point-symmetric optical system restricts the lens shape and reduces the degree of freedom in optical design, but it has the advantage that the aberration to be corrected can be limited only to axial aberration. Is more important.

  As a result, it is possible to realize an imaging apparatus having a bright and high imaging performance over a wide angle of view.

  Therefore, in the imaging apparatus of the present invention, the focal length of the imaging optical system is set to be approximately equal to the distance from the exit pupil of the imaging optical system to the imaging surface, and the radius of curvature of the imaging surface is set to be approximately equal to the focal length of the imaging optical system. By doing so, the imaging optical system is brought close to a point-symmetric optical system.

  In particular, it is important that the optical system on the image side is closer to point symmetry than the aperture stop of the imaging optical system.

  By setting the focal length of the imaging optical system to be approximately equal to the distance from the exit pupil of the imaging optical system to the imaging surface, the image-side principal point and the exit pupil of the imaging optical system can be aligned at substantially the same position.

  This is because the incident height of the viewing angle light beam is lowered, so that the viewing angle light beam can be handled in the same way as the axial light beam, and the optical system on the image side is closer to point symmetry than the aperture stop of the imaging optical system. be able to.

  Specifically, as described below, it may be configured to satisfy the expression (1) (the conditional expression of the circled number 1 shown in the following table).

  Thereby, it is possible to satisfactorily correct off-axis aberrations such as coma, astigmatism, distortion, and lateral chromatic aberration over a wide angle of view.

  In addition, by setting the radius of curvature of the imaging surface to be approximately equal to the focal length of the imaging optical system, it is possible to favorably correct curvature of field.

  Specifically, as described below, it may be configured to satisfy the expression (2) (the conditional expression of the circled number 2 shown in the following table).

  Astigmatism can be satisfactorily corrected by the configuration of the imaging optical system, so that the curvature of field can be limited to only the Petzval image surface, and the Petzval image surface can be corrected by curving the imaging surface, so that all off-axis aberrations can be corrected. Generation can be suppressed. That is, the remaining aberration can be limited to axial aberration.

  Furthermore, when the present invention adopts a configuration that satisfies the expressions (1) and (2) as follows, at least one of the most object side lens surface or the most image side lens surface in the imaging optical system is provided. By using an aspherical surface provided with an aspherical amount that shifts from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface, spherical aberration can be corrected well even in a wide optical field and a bright optical system. It is configured to be able to.

That is, in an imaging apparatus having an imaging optical system having a plurality of lenses and an imaging surface curved with a concave surface facing the object side in the vicinity of the image plane of the imaging optical system,
The imaging optical system has an aperture stop,
An aspherical surface in which at least one of the most object-side lens surface or the most image-side lens surface in the imaging optical system is given an aspherical amount that displaces from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface age,
The focal length of the imaging optical system and the distance from the exit pupil of the imaging optical system to the imaging surface are set to be substantially equal, and the radius of curvature of the imaging surface is from the exit pupil of the imaging optical system to the imaging surface. Is set to be approximately equal to the distance.

At this time, when the focal length of the imaging optical system is f_sys, the distance from the exit pupil of the imaging optical system to the imaging surface is d_upp, and the radius of curvature of the imaging surface is R_img, the following equations (1) and (2) Can be configured to satisfy.
0.8 ≦ f_sys / d_pup ≦ 1.5 (1)
0.8 ≦ | R_img | /f_sys≦1.5 (2)

  Note that the imaging surface in the imaging apparatus of the present invention is a curved electronic imaging element or a light transmission means whose entrance surface is curved.

  As the curved electronic imaging device, for example, an electronic imaging device formed on a shape-variable substrate or a small planar electronic imaging device arranged in an array shape to have a concave shape can be considered.

  The light transmission means may be, for example, an image plate formed by bundling optical fibers into a plate shape, and one end is processed into a concave shape and the other end is processed into a flat surface.

  Then, it is possible to adopt a configuration in which an incident surface of the optical transmission means is curved with the concave surface facing the object side as an imaging surface, and a flat emission surface is connected to an electronic imaging device to form an imaging unit.

  Next, at least one of the most object-side lens surface or the most image-side lens surface of the imaging optical system is given an aspheric amount displaced from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface. The operation of the aspherical configuration will be described.

  An aspheric surface provided with an aspheric amount displaced from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface mainly acts on spherical aberration correction.

The imaging optical system has a positive power as a whole, and generally the spherical aberration is under.
From the viewpoint of the optical path length from the object point to the image point, this is due to the fact that the optical path length of the light beam at a high incident height with respect to the axial light beam is short.

  From the viewpoint of the wavefront, the reason is that the phase of the light beam at a high incident height with respect to the optical axis is advanced.

  Therefore, a non-spherical amount in which at least one of the lens surface closest to the object side of the imaging optical system or the lens surface closest to the image side is displaced from the reference spherical surface to the outside of the imaging optical system at the peripheral portion of the lens surface is given. It consists of a spherical surface.

  The most object-side lens surface or the most image-side lens surface of the imaging optical system is the outermost lens surface of the lens surfaces included in the imaging optical system, and the inside of the lens surface is optical glass, the lens surface The outside is filled with air.

  In general, the refractive index of optical glass is Nd = 1.45 to 2.15, which is higher than the refractive index of air Nd = 1.0.

  At this time, a portion of the optical path of the light beam passing through the peripheral portion of the lens surface is made from the air to the optical glass by the aspheric surface provided with the aspheric amount displaced from the reference spherical surface to the outside of the imaging optical system in the peripheral portion of the lens surface. It is possible to substantially increase the optical path length. Alternatively, the wavefront phase can be delayed. Thereby, spherical aberration can be corrected satisfactorily.

  From the viewpoint of power, the power at the periphery of the lens surface is shifted in the negative direction by the aspheric surface to which the aspheric surface displaced from the reference spherical surface to the outside of the imaging optical system is provided at the periphery of the lens surface. An aspheric surface can be constructed.

  When the reference spherical surface has positive power, an aspherical surface in which the positive power in the peripheral portion is weaker than on the optical axis can be configured.

  As a result, the power received by the light beam at a high incident height can be weakened relative to the power received by the principal light beam, and the under spherical aberration can be corrected well.

  FIG. 35 is an optical path diagram schematically showing the state of the imaging of the axial light beam in the imaging apparatus of the present invention, and FIG. 36 is an optical path diagram schematically showing the state of the imaging of the field angle light beam.

In FIGS. 35 and 36, and a state in which an image is formed of angle beam BEM from an object point _{PNT OBJ} on the object plane OBJ by the imaging optical system SYS to an image point _{PNT IMG} on an image plane IMG shown schematically .

When the object point PNT _OBJ is on the optical axis AXI of the imaging optical system SYS as shown in FIG. 35, the axial light beam is shown. As shown in FIG. 36, the object point PNT _OBJ is other than the optical axis AXI of the imaging optical system SYS. Is defined as a field angle luminous flux.

The axial light flux and the field angle light flux are limited by the aperture stop STO. The light beam that passes through the aperture center STO _CNT of the aperture stop is the principal ray RAY _PRI , and the light beam that passes through the aperture top STO _UP Ray _UP , a ray passing through the lower end STO _LOW of the opening is defined as a lower ray RAY _LOW .

In FIG. 35, the on-axis light beam BEM _ON is refracted by the most object side lens surface _RMSTOBJ , the light beam width is limited by the aperture stop STO, is refracted by the most image side lens surface _RMSTIMG , and is connected to the imaging surface IMG. I image.

The arrival position of each ray on the most object side lens surface _RMSTOBJ is as follows. The principal ray RAY _PRI is on the optical axis AXI, the upper ray RAY _UP is near the upper peripheral portion, and the lower ray RAY _LOW is on the lower peripheral portion. The closest object side lens surface _RMSTOBJ is the surface having the widest beam width in the imaging optical system SYS.

  Spherical aberration is characterized by being easily affected by the power of a surface with a high incident height h (a surface with a wide light flux width). According to the third-order aberration coefficient, the spherical aberration is strongly influenced by the power of the lens surface in proportion to the fourth power of the incident height h.

Therefore, if the most object side lens surface _RMSTOBJ is formed of an aspheric surface, the action of the aspheric surface can be effectively exhibited.

Also, by using an aspherical surface with weaker peripheral power than the optical axis, the power in the upper ray RAY _UP and lower ray RAY _LOW with a high incident height can be weaker than on the optical axis, so it becomes under. The spherical aberration can be corrected well.

  Further, since the influence on spherical aberration is great, the amount of spherical aberration to be applied can be kept small.

As shown in FIG. 36, when the object point PNT _OBJ is below the optical axis of the imaging optical system SYS, the optical path length of the upper ray RAY _UP (from the object point PNT _OBJ to the aperture stop opening) The upper end STO _{UP of the} part becomes longer than the optical path length of the principal ray RAY _PRI (from the object point PNT _OBJ to the opening center STO _{CNT of the} aperture stop).

Therefore, in the light flux of the upper beam RAY _UP side of the principal ray RAY _PRI, that incident height in the direction along the principal ray RAY _PRI is higher than the incidence height of the axial light flux, a large spherical aberration occurs It becomes a problem. The problem becomes more prominent as the angle of view becomes wider.

On the other hand, the point of reaching the lens surface _{R MSTIMG} the ray _{RAY UP} on the angle beam BEM most image side, located close to the periphery of the most image-side lens surface _{R MSTIMG} than arrival point of the principal ray _{RAY PRI} It is.

Therefore, if the most image side lens surface _RMSTIMG is configured as an aspherical surface in which the peripheral power is weaker than the optical axis, weak power can be given to the light beam on the upper ray RAY _UP side than the principal ray RAY _PRI. Possible lens surfaces can be constructed.

As a result, it is possible to satisfactorily correct spherical aberration that has occurred greatly in the light beam on the upper ray RAY _UP side of the principal ray RAY _PRI of the field angle beam.

In addition, spherical aberration also occurs in the light beam on the lower ray RAY _LOW side of the principal ray RAY _PRI of the field angle beam.

That lower ray _{RAY LOW} of angle beam BEM reaches the most object side lens surface on _{R MSTOBJ} is a position close to the periphery of the lens surface _{R MSTOBJ} the most object side of the arrival point of the principal ray _{RAY PRI} .

Therefore, when the most object side lens surface _RMSTOBJ is configured as an aspherical surface in which the peripheral power is weaker than the optical axis, weak power can be given to the light beam on the lower ray RAY _LOW side than the principal ray RAY _PRI. Possible lens surfaces can be constructed.

This makes it possible to satisfactorily correct the generated spherical aberration in the light beam on the lower light ray RAY _LOW side of the main light ray RAY _PRI of the field angle light beam.

  Furthermore, if both the lens surface closest to the object side and the lens surface closest to the image side are formed of an aspheric surface in which the power at the periphery is weaker than the optical axis, the upper ray side is more than the principal ray of the axial beam and the field angle beam. It is possible to achieve an optimum configuration for a light beam on a lower light beam side than the principal light beam of the light beam and the field angle light beam.

  In an imaging optical system with a bright F-number of the optical system, it is difficult to correct spherical aberration with only a spherical lens, but spherical aberration can be corrected satisfactorily using the effects of the present invention.

In particular, in an imaging apparatus using an extremely bright imaging optical system of F / 1.4 or more, the imaging performance can be greatly improved by correcting the spherical aberration by the effect of the present invention.
If the bonding surface is aspherical, there is a disadvantage that it is difficult to process the two surfaces into the same aspherical shape. The most object-side lens surface or the most image-side lens surface of the imaging optical system is aspherical. In this case, there is an advantage that manufacturing is easy.

  Since the imaging optical system is an optical system close to point symmetry, the same aberration remains between the on-axis light beam and each off-axis light beam, and the aberration can be corrected well by the common phase difference distribution shape.

  That is, if a wavefront control element is arranged in the vicinity of the aperture stop surface of an imaging optical system that is close to point symmetry, aberration can be corrected well over a wide field angle even in a bright optical system exceeding F / 2.0. Can do. Furthermore, the same effect can be exhibited even in an extremely bright optical system exceeding F / 1.4.

  In addition, since the imaging optical system having a bright F value has a narrow depth of field, it is possible to take a picture with a blurred background other than the focus plane even though it is a compact camera.

  In addition, the bright F-number imaging optical system can shorten the exposure time in proportion to the square of the F-number, so that camera shake, subject blur, and shot noise can be greatly reduced, resulting in high-quality images. An imaging device that can be provided can be provided.

  Next, the effect | action which improves peripheral light quantity fall is demonstrated.

  In a general imaging optical system, it is known that the peripheral light amount ratio is reduced according to the cos ω4 power law with respect to the field angle (incident angle) ω.

  Therefore, the peripheral part of the photographed image becomes very dark and an image with uniform illuminance cannot be obtained.

  Some recent digital cameras and digital video cameras digitally correct peripheral light loss by significantly increasing the sensitivity at the periphery, but noise increases with a low contrast, so Compared with the image quality is considerably degraded.

  The peripheral light loss causes such a serious problem. This tendency becomes more prominent with an imaging optical system with a wide angle of view, and is one of the elements necessary to realize an imaging optical system with a wide angle of view.

The breakdown of the cos ω4 power law of the peripheral light ratio is
(A) The apparent focal length is increased according to the angle of view, so that the square of cos ω
(B) The apparent aperture diameter is reduced according to the angle of view, so that the first power of cos ω
(C) The angle of incidence on the imaging surface is increased according to the angle of view, which is the first power of cos ω.

  In the imaging optical system in the imaging apparatus of the present invention, the radius of curvature of the imaging surface is set to be approximately equal to the focal length of the imaging optical system, and the apparent focal length can be made substantially the same at all angles of view.

  As a result, the peripheral light amount ratio can be improved by the square of cos ω.

  By satisfying the expression (2), a corresponding effect can be obtained.

  That is, the peripheral light amount ratio can be improved from the fourth power of cosω to the second power of cosω.

  To provide an imaging device capable of significantly improving the peripheral light amount ratio of an imaging optical system having a wide angle of view, and capable of shooting a high-quality image with high contrast and low noise over a wide angle of view. Can do.

  Next, the significance of the above formulas (1) and (2) will be described in more detail.

  Equation (1) is a condition for setting the focal length f_sys of the imaging optical system and the distance d_pup from the exit pupil of the imaging optical system to the imaging surface to be substantially equal, and is an optical system on the image side with respect to the aperture stop of the imaging optical system. Can have a configuration close to point symmetry.

  If the expression (1) is satisfied, off-axis aberrations such as coma, astigmatism, distortion, and lateral chromatic aberration can be corrected well.

  If the upper limit of the expression (1) is exceeded, the point symmetry of the optical system on the image side with respect to the aperture stop of the imaging optical system cannot be secured, and off-axis aberrations such as coma, astigmatism, distortion, and lateral chromatic aberration will occur. It occurs and becomes a problem.

  If the lower limit of the expression (1) is exceeded, the point symmetry of the optical system on the image side with respect to the aperture stop of the imaging optical system cannot be secured, and off-axis aberrations such as coma, astigmatism, distortion, and lateral chromatic aberration occur. It occurs and becomes a problem.

  Expression (2) is a condition for setting the radius of curvature of the imaging surface to be approximately equal to R_img and the focal length f_sys of the imaging optical system, and is a condition for satisfactorily correcting field curvature and astigmatism.

  If the expression (2) is satisfied, the image plane shape of the imaging apparatus can be brought close to the Petzval image plane, so that field curvature can be corrected without generating astigmatism over a wide angle of view.

  When the upper limit of the expression (2) is exceeded, the deviation from the Petzval image plane becomes large at the periphery of the imaging surface, the field curvature occurs, and the imaging performance deteriorates.

  If the lower limit of the expression (2) is exceeded, the deviation from the Petzval image plane increases at the periphery of the imaging surface, and field curvature occurs, resulting in degradation of imaging performance.

  In the case of an imaging optical system with a bright F value, the allowable depth of field curvature is narrow because the depth of focus is narrow, and it is necessary to correct field curvature with high accuracy.

  When the imaging surface is not spherical but is aspherical or stepped, the radius of curvature of the imaging surface is defined as follows.

  First, when the shape of the imaging surface is an aspherical surface, the radius of curvature of the reference spherical surface is defined as “the radius of curvature of the imaging surface”.

  An aspherical surface can be expressed by an α equation, and the reciprocal of the curvature c on the optical axis of the α equation is the radius of curvature.

  Here, z is the sag amount (mm) in the optical axis direction of the aspherical shape, c is the curvature (1 / mm) on the optical axis, r is the distance (mm) from the optical axis in the radial direction, A, B, C, and D are fourth-order, sixth-order, eighth-order, and tenth-order coefficients, respectively.

  Even if the imaging surface is aspherical, the radius of curvature of the reference curved surface can be obtained by measuring the radius of curvature on the optical axis.

  Next, the case where the shape of the imaging surface is stepped will be described.

  Strictly speaking, the imaging surface has a staircase shape when a small electronic imaging device is configured as an array or when an imaging surface curved by bundling optical fibers is configured.

  In that case, a curved surface connecting one pixel of the electronic image sensor or one central point of the optical fiber can be regarded as an imaging surface.

  If the curvature radius of the reference curved surface is calculated from the result of fitting the curved surface by the above-described α equation by the least square method, the curvature radius of the imaging surface can be obtained.

  The imaging apparatus of the present invention adjusts the focus position by changing the distance between the imaging optical system and the imaging surface.

  FIG. 37A and FIG. 37B show an imaging relationship when the object plane is arranged at a finite distance.

  In FIG. 37A, OBJ is an object plane, SYS is an imaging optical system, IMG is an image plane, and the imaging optical system SYS forms an object point on the object plane OBJ on an image point on the image plane IMG. ing.

  As shown in FIG. 37A, the imaging optical system SYS forms an object point equidistant from the imaging optical system SYS on the Petzval image plane, so that the object plane OBJ at this time has a curved shape. Become.

  However, in the imaging optical system, the object plane OBJ is preferably a flat surface.

  As shown in FIG. 37B, an object point other than on the optical axis is not a curved object surface indicated by a broken line but a plane object surface indicated by a solid line. Then, as indicated by an arrow A in FIG. 37B, the object point moves away from the imaging optical system SYS. Also, as indicated by the arrow B, the image point moves from the Petzval image plane indicated by the broken line to the image plane IMG indicated by the solid line in a direction approaching the imaging optical system SYS.

  An example of the amount of movement on the image plane side as a defocus amount in the light beam traveling direction is shown in the graph of FIG. 38 in the imaging optical system model of FIG.

  FIG. 38 shows the relationship between the focus position and the imaging surface shape during focus adjustment in an example.

  In this example, the focal length of the imaging optical system is f_sys = 12.0 (mm), the radius of curvature of the imaging surface is R_img = 12.0 (mm), and the parameters from the exit pupil to the imaging surface of the imaging optical system are as follows. The distance is d_pup = 12.0 (mm), the object distance is S = −300 (mm), and the field angle is ω = 60 (deg).

  As described above, when the object plane is a plane, the focus position of each light beam at each angle of view is defocused from the Petzval image plane to the imaging optical system side.

  The defocus amount in the traveling direction of the light beam is displayed on the graph of the focus position indicated by the circled number 1.

  Further, the radius of curvature of the imaging surface is set equal to the focal length of the imaging optical system, which corresponds to the Petzval image surface shape when the object distance is infinity.

  It is natural that the object position is infinite and the focus position of the circled numeral 1 and the imaging surface shape of the circled numeral 2 coincide with each other, but FIG. 38 shows that the circled numeral 1 is even when the object distance is reduced to S = −300 (mm). It shows that the focus position and the imaging surface shape of the circled number 2 are exactly the same.

  This means that the plane object surface can be focused without causing field curvature at any distance from infinity to S = −300 (mm).

  Further, the above can be realized in a wide range of angle of view from −60 to +60 (deg).

  If the focal length of the imaging optical system is set approximately equal to the distance from the exit pupil of the imaging optical system to the imaging surface, and the radius of curvature of the imaging surface is set approximately equal to the focal length of the imaging optical system, the shape of the imaging surface changes. Without adjusting, it is possible to adjust the focus only by changing the distance between the imaging optical system and the imaging surface.

  Therefore, it is important to satisfy the expressions (1) and (2).

  An imaging optical system having an extremely bright F value like the imaging apparatus of the present invention has a very narrow depth of focus, so that it is extremely important for the imaging apparatus that high-precision focus adjustment can be easily realized.

  Examples of the present invention will be described below.

[Example 1]
As Example 1, a configuration example of an imaging apparatus to which the present invention is applied will be described.
As shown in FIG. 1, the image pickup optical system used in the image pickup apparatus according to the present embodiment includes three lenses G1, G2, and G3 and an aperture stop STO.

  In order from the object side, the first lens G1 is a planoconvex lens having a convex surface facing the object side, the second lens G2 is a planoconvex lens having a convex surface facing the image side, and a meniscus lens having a convex surface facing the image side. Three lenses G3 are arranged.

  The exit surface of the first lens G1 is bonded to the incident surface of the second lens G2, and an aperture stop STO is configured by disposing a light shielding member at an ineffective portion of the bonded surface.

  IMG in FIG. 1 is an imaging surface.

  As shown in FIG. 1, in the imaging apparatus according to the present embodiment, the incident surface of the light transmission means OTM formed in a spherical shape is the imaging surface IMG, and the curved shape of the imaging surface is made to follow the curvature of field of the imaging optical system. Thus, good imaging performance is realized over the entire area of the imaging surface IMG.

  The optical transmission means OTM of the image pickup apparatus in the present embodiment is an image fiber formed by bundling optical fibers having a pitch of several microns, and plays a role of transmitting an image formed on the image pickup surface to the electronic image pickup element ICD.

  The exit surface of the optical transmission means OTM is formed in a plane, and an image is transmitted to the electronic image sensor ICD by being brought into close contact with the electronic image sensor ICD.

  Thus, in the imaging apparatus of the present embodiment, the imaging unit ICU is configured by the optical transmission means OTM and the electronic imaging element ICD.

  Table 1 shows the configuration of the image pickup apparatus of this embodiment.

  Surface number 1 is the entrance surface of the first lens G1, surface number 2 is the bonding surface of the exit surface of the first lens G1 and the second lens G2, and surface number 3 is the exit surface of the second lens G2 and the third lens G3. Surface number 4 is the exit surface of the third lens G3.

  An aperture stop STO is configured by disposing a light-shielding member on the ineffective portion of the bonding surface of the first lens G1 having surface number 2 and the second lens G2.

  Surface number 5 is the imaging surface IMG, which is the incident surface of the optical transmission means OTM. The exit surface of the optical transmission means OTM (not shown) is connected to the electronic image pickup device ICD to constitute the image pickup unit ICU.

  In the table, R is the radius of curvature (mm), d is the surface separation (mm), Nd is the refractive index of the d-line, and νd is the Abbe number. The surface with “*” is an aspherical surface.

  The aspherical surface in the image pickup apparatus of the present embodiment is a rotationally symmetric aspherical surface with the optical axis as the center, and is expressed by a polynomial expression (3).

  Here, z is the sag amount (mm) in the optical axis direction of the aspherical shape, c is the curvature (1 / mm) on the optical axis, r is the distance (mm) from the optical axis in the radial direction, A, B, C, and D are fourth-order, sixth-order, eighth-order, and tenth-order coefficients, respectively.

  Table 2 shows the aspherical coefficient of the first surface in the imaging apparatus of the present embodiment.

  The first-order partial value obtained by first-order differentiation of the aspherical polynomial of equation (3) with respect to the distance r from the optical axis in the radial direction is obtained by equation (4).

  This first-order differential value represents the inclination of the lens surface.

  The second-order partial value obtained by second-order differentiation of the aspherical polynomial of equation (3) with respect to the distance r from the optical axis in the radial direction is obtained by equation (5).

Differential value of the second derivative value of the lens surface inclination, i.e. represents a curvature in the radial direction, the power phi _r and (6) a relationship of.

  Here, N is the refractive index of the medium on the object side of the lens surface, and N ′ is the refractive index of the medium on the image side of the lens surface.

  In the imaging apparatus of the present embodiment, only the lens surface closest to the object among the lens surfaces of the imaging optical system is an aspherical surface.

  2A shows the aspherical shape of the lens surface closest to the object side, and FIG. 2B shows the aspherical amount of the lens surface closest to the object side. FIG. 3A shows the second-order differential values of the aspheric surface and the reference sphere, and FIG. 3B shows the second-order differential values of the aspheric component.

  As shown in FIG. 2A, the most object side lens surface of the present embodiment is a lens surface in which the sag amount increases in the positive direction from the optical axis toward the periphery, and the convex surface faces the object side. Lens surface.

  The sag amount is a displacement amount in the optical axis direction, and FIG. 2A shows how much other positions of the lens surface are displaced in the optical axis direction with respect to the optical axis. The reference spherical surface is a spherical surface with a convex surface facing the object side having a radius of curvature R = 3.1146 (mm).

FIG. 2B shows the aspheric amount. The aspherical amount is a sag amount ΔZ _ASP in which the aspherical surface is displaced from the reference curved surface in the optical axis direction, and is obtained by subtracting the sag amount of the spherical surface from the sag amount of the aspherical polynomial expressed by equation (3). .

  Specifically, it is expressed by equation (7).

  As shown in FIG. 2B, in this embodiment, the aspheric amount is displaced in the negative direction, and is an aspheric surface displaced from the reference spherical surface to the object side, that is, outside the imaging optical system.

  As the distance from the optical axis increases, the amount of aspherical surface displaced outward from the imaging optical system is gradually increased to give the maximum amount of aspherical surface at the periphery of the lens surface.

  In FIG. 3A, the second-order differential value of the aspherical surface is indicated by a solid line, and the second-order differential value of the reference sphere is indicated by a broken line.

  Both the second-order differential value of the aspherical surface and the second-order differential value of the reference sphere gradually increase in the positive direction as the distance from the optical axis increases.

  FIG. 3B shows the second-order differential value of the aspheric component. This is obtained by subtracting the second order differential value of the reference sphere from the second order differential value of the aspherical surface.

  The second-order differential value of the aspheric component is gradually increased in the negative direction as the distance from the optical axis increases.

  As described above, the second-order differential value in the peripheral portion of the lens surface is weaker than that of the reference sphere by giving an aspherical component whose second-order differential value is negative to the reference spherical surface having a positive second-order differential value.

  Equation (6) shows the relationship between the second-order differential value and power.

  In the lens surface closest to the object side of the imaging optical system, since the medium on the object side of the lens surface is air, N = 1.0000, and the medium on the image side of the lens surface is optical glass and N ′ = 1.87801, (N′−N) has a positive value.

  Therefore, the lens surface closest to the object has a positive power on the optical axis, and has a lens surface shape in which the positive power gradually decreases as the distance from the optical axis increases.

  Thereby, spherical aberration can be corrected satisfactorily.

  FIG. 4 shows a longitudinal aberration diagram in the imaging optical system of the present embodiment, and FIG. 5 shows a lateral aberration diagram.

  As shown in FIG. 4, spherical aberration, axial chromatic aberration, astigmatism, field curvature, and chromatic spherical aberration are corrected well. Here, the spherical aberration of color is defined as the difference between the spherical aberration amount of each wavelength (for example, C line, F line, g line, etc.) with respect to the spherical aberration amount of the reference wavelength (for example, d line).

  In particular, the spherical aberration can be condensed on the image plane in the entire region from a light beam having a low incident height to a light beam having a high incident height, and can be corrected very well.

  In addition, axial chromatic aberration and chromatic spherical aberration can be corrected very well, and high imaging performance is obtained.

  As shown in FIG. 5, good performance is obtained even at each angle of view, and coma, field curvature, and lateral chromatic aberration are corrected well.

  Table 3 shows the specifications of the image pickup apparatus of the present embodiment.

  The image pickup apparatus of the present embodiment has a bright F value of F / 1.2 and an ultra wide angle of view of 120.0 (deg) while keeping the total length to 6.229 (mm) and compact. This is an example of an imaging apparatus that simultaneously achieves brightness, high resolution, an ultra-wide field angle, and compactness.

  Table 4 shows values of the expressions (1) and (2) in the imaging apparatus of the present embodiment.

  The value of the formula (1) is 1.03, which satisfies the range of the formula (1). As a result, the optical system on the image side from the aperture stop of the imaging optical system can be configured to be nearly point-symmetric, and coma, astigmatism, and lateral chromatic aberration can be favorably corrected.

  The value of formula (2) is 1.02, which satisfies the range of formula (2). Thereby, it is possible to satisfactorily correct field curvature and astigmatism over a wide field angle of 120.0 (deg).

  By satisfying equations (1) and (2), it is possible to adjust the focus from infinity to the closest distance by simply changing the distance between the imaging optical system and the imaging surface without changing the shape of the imaging surface. Become.

  In the imaging apparatus of the present invention, the radius of curvature of the imaging surface is set to be approximately equal to the distance from the exit pupil of the imaging optical system to the imaging surface.

The following equation (8) is a condition for setting the radius of curvature of the imaging surface to be approximately equal to the distance from the exit pupil of the imaging optical system to the imaging surface.
0.8 ≦ | R_img | /d_pup≦1.5 (8)
If Expression (8) is satisfied, the imaging optical system can be configured to be closer to point symmetry.

  In the imaging apparatus of the present embodiment, focus adjustment is performed by changing the distance between the imaging optical system and the imaging surface. At that time, by satisfying the equation (8), the field curvature due to the focus adjustment can be suppressed to be very small at a wide range of object distances from infinity to the closest distance, and high-resolution imaging is possible.

  In the image pickup apparatus of the present embodiment, the value of equation (8) is 1.05, which satisfies the range of equation (8).

  As a result, the imaging optical system has a configuration close to point symmetry, and coma, astigmatism, distortion, and lateral chromatic aberration are corrected well. Furthermore, focus adjustment is possible while maintaining high resolution in a wide range of focus adjustment from infinity to close range.

  Next, the effect | action which improves peripheral light quantity fall is demonstrated.

  In the imaging optical system in the imaging apparatus of the present embodiment, the radius of curvature of the imaging surface is set to be substantially equal to the focal length of the imaging optical system, and the focal length can be made substantially the same at all angles of view.

  As a result, the peripheral light amount ratio can be improved by the square of cos ω.

In this embodiment, the maximum half angle of view ω = 60.0 (deg). When cos ⁴ ω = 0.0625, cos ² ω = 0.25 can be obtained, and the peripheral light amount can be improved four times.

  By satisfying the expression (2), a corresponding effect can be obtained.

  Furthermore, in the imaging optical system in the imaging apparatus of the present embodiment, the radius of curvature of the imaging surface is set to be substantially equal to the distance from the exit pupil of the imaging optical system to the imaging surface, and the incident angle on the imaging surface is set to be substantially vertical. Can be set.

  As a result, the peripheral light amount ratio can be improved by the first power of cos ω.

In this embodiment, the maximum half angle of view ω = 60.0 (deg). When cos ⁴ ω = 0.0625, cos ³ ω = 0.125 can be obtained, and the peripheral light amount can be improved by a factor of two.

  By satisfying the expression (6), a corresponding effect can be obtained.

  By simultaneously satisfying the expressions (2) and (6), the peripheral light amount ratio can be improved by the third power of cos ω, and the peripheral light amount can be increased to eight times the conventional amount.

  As a result, the peripheral light amount ratio of the imaging optical system with a wide angle of view can be greatly improved. Therefore, an imaging apparatus that can capture high-quality images with high contrast and low noise over a wide angle of view. Can be provided.

  As described above, by using the effect of the present invention, it is possible to realize an imaging apparatus having a good imaging performance over a wide angle of view even with an F value brighter than F / 2.0, with a compact configuration.

  In addition, the drop in the amount of light from the periphery can be greatly improved, and a very bright imaging optical system can be realized over a wide field angle.

  As a result, the exposure time can be greatly shortened, so that it is possible to provide an imaging apparatus capable of capturing a high-quality image with favorable reduction of camera shake, subject blur, and noise.

  In addition, it is possible to provide an imaging optical system capable of giving a large blur to a defocused subject with a compact configuration.

  In addition, the above-described high-performance imaging optical system can be adjusted in focus in a wide range from infinity to a close range with a simple configuration with almost no deterioration in imaging performance.

[Example 2]
As a second embodiment, a configuration example of an imaging apparatus having a different form from the first embodiment will be described.

  As shown in FIG. 6, the image pickup optical system used in the image pickup apparatus of this embodiment includes three lenses G1, G2, G3 and an aperture stop STO.

  In order from the object side, the first lens G1 is a planoconvex lens having a convex surface facing the object side, the second lens G2 is a planoconvex lens having a convex surface facing the image side, and a meniscus lens having a convex surface facing the image side. Three lenses G3 are arranged.

  IMG in FIG. 6 is an imaging surface.

  As shown in FIG. 6, the imaging surface IMG of the imaging apparatus in the present embodiment is an incident surface of the light transmission means OTM formed in a spherical shape and follows the curvature of field of the imaging optical system, so that the imaging surface IMG Good imaging is realized over the entire area.

  The optical transmission means OTM of the image pickup apparatus in this embodiment is an image fiber formed by bundling optical fibers with a pitch of several microns, and plays a role of transmitting an image formed on the image plane of the image pickup optical system to the electronic image pickup device ICD.

  The exit surface of the optical transmission means OTM is formed in a flat surface, and the image pickup unit ICU is configured by being brought into close contact with the electronic image pickup device ICD.

  Table 5 shows the configuration of the image pickup apparatus of the present embodiment.

  Surface number 1 is the incident surface of the first lens G1. Surface number 2 is a bonding surface of the exit surface of G1 and the entrance surface of the second lens G2, and an aperture stop STO is configured by disposing a light shielding member at an ineffective portion thereof.

  Surface number 3 is a bonding surface of the exit surface of the second lens G2 and the entrance surface of the third lens G3. Surface number 4 is the exit surface of the third lens G3, and has a rotationally symmetric aspherical shape expressed by the polynomial equation (3).

  Surface number 5 is the imaging surface IMG, which is the incident surface of the optical transmission means OTM. An emission surface of the optical transmission means OTM not shown is connected to the electronic image sensor ICD.

  In the table, R is the radius of curvature (mm), d is the surface separation (mm), Nd is the refractive index of the d-line, and νd is the Abbe number. The surface with “*” is an aspherical surface.

  Table 6 shows the aspheric coefficient of surface number 4 in the imaging apparatus of the present embodiment.

  In the image pickup apparatus of the present embodiment, the lens surface closest to the image is configured as an aspherical surface.

  FIG. 7A shows the aspherical shape of the most image side lens surface, and FIG. 7B shows the aspherical amount of the most image side lens surface. FIG. 8A shows the second-order differential values of the aspheric surface and the reference sphere, and FIG. 8B shows the second-order differential values of the aspheric component.

  As shown in FIG. 7A, the lens surface closest to the image side in this embodiment is a lens surface in which the sag amount increases in the negative direction from the optical axis toward the peripheral portion, and the convex surface faces the image side. Lens surface.

  The reference spherical surface of this lens surface is a spherical surface having a convex surface facing the image side with a radius of curvature R = -2.9424 (mm).

  FIG. 7B shows the aspheric amount.

  As shown in FIG. 7B, in this embodiment, the aspheric amount is displaced in the positive direction, and is an aspheric surface displaced from the reference spherical surface to the image side, that is, outside the imaging optical system.

  As the distance from the optical axis increases, the amount of aspherical surface displaced outward from the imaging optical system is gradually increased to give the maximum amount of aspherical surface at the periphery of the lens surface.

  In FIG. 8A, the second-order differential value of the aspheric surface is indicated by a solid line, and the second-order differential value of the reference sphere is indicated by a broken line.

  Both the second-order differential value of the aspheric surface and the second-order differential value of the reference sphere have negative values.

  FIG. 8B shows the second-order differential value of the aspheric component.

  The second-order differential value of the aspheric component is gradually increased in the positive direction as the distance from the optical axis increases.

  As described above, the second-order differential value in the peripheral portion of the lens surface is weaker than that of the reference sphere by providing the reference spherical surface having a negative second-order differential value with an aspherical component having a positive second-order differential value.

  Equation (6) shows the relationship between the second-order differential value and power.

  In the lens surface closest to the image side of the imaging optical system, the medium on the object side of the lens surface is optical glass, N = 2.170, and the medium on the image side of the lens surface is air, so N ′ = 1.0000. (N′−N) has a negative value.

  Therefore, the lens surface closest to the image has a positive power on the optical axis, and has a lens surface shape in which the positive power gradually decreases as the distance from the optical axis increases.

  Thereby, spherical aberration can be corrected satisfactorily.

  In particular, when the lens surface closest to the image side is an aspherical surface provided with an aspherical amount displaced from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface, Spherical aberration can be corrected satisfactorily.

  FIG. 9 is a longitudinal aberration diagram in the imaging optical system of the present embodiment, and FIG. 10 is a transverse aberration diagram. As shown in FIG. 9, spherical aberration, axial chromatic aberration, astigmatism, field curvature, and chromatic spherical aberration are corrected well. In particular, the spherical aberration can be condensed on the image plane in the entire region from a light beam having a low incident height to a light beam having a high incident height, and can be corrected very well.

  In addition, axial chromatic aberration and chromatic spherical aberration can be corrected very well, and high imaging performance is obtained.

  As shown in FIG. 10, good performance is obtained for each light flux at each angle of view, and coma aberration, curvature of field, and lateral chromatic aberration are corrected well.

  Table 7 shows the specifications of the image pickup apparatus of the present embodiment.

  The imaging apparatus of the present embodiment has a bright F value of F / 1.2 and an ultra wide angle of view of 120.0 (deg), while keeping the total length to 6.437 (mm) and compact. This is an example of an imaging apparatus that simultaneously achieves brightness, high resolution, an ultra-wide field angle, and compactness.

  Table 8 shows the values of the expressions (1) and (2) in the image pickup apparatus of the present embodiment.

  The value of the formula (1) is 0.89, which satisfies the range of the formula (1). Thereby, the optical system on the image side from the aperture stop of the imaging optical system can be configured to be nearly point-symmetric, and coma, astigmatism, distortion, and lateral chromatic aberration can be corrected well.

  The value of formula (2) is 1.02, which satisfies the range of formula (2). Thereby, it is possible to satisfactorily correct field curvature and astigmatism over a wide field angle of 120.0 (deg).

  By satisfying equations (1) and (2), it is possible to adjust the focus from infinity to the closest distance by simply changing the distance between the imaging optical system and the imaging surface without changing the shape of the imaging surface. Become.

  The value of equation (8) is 0.90, which satisfies the range of equation (8).

  As a result, the imaging optical system has a configuration close to point symmetry, and coma, astigmatism, distortion, and lateral chromatic aberration are corrected well.

  Furthermore, focus adjustment is possible while maintaining high resolution in a wide range of focus adjustment from infinity to close range.

[Example 3]
As a third embodiment, a configuration example of an imaging apparatus having a different form from the above embodiments will be described.
As shown in FIG. 11, the image pickup optical system used in the image pickup apparatus of this embodiment includes three lenses G1, G2, G3 and an aperture stop STO.

  In order from the object side, a first lens G1 that is a meniscus lens having a convex surface facing the object side, a second lens G2 that is a plano-convex lens having a convex surface facing the image side, and a meniscus lens having a convex surface facing the image side. Three lenses G3 are arranged.

  IMG in FIG. 11 is an imaging surface.

  As shown in FIG. 11, the imaging surface IMG of the imaging apparatus in the present embodiment is an incident surface of the light transmission means OTM formed in a spherical shape, and follows the curvature of field of the imaging optical system, so that the imaging surface IMG Good imaging is realized over the entire area.

  The optical transmission means OTM of the image pickup apparatus in this embodiment is an image fiber formed by bundling optical fibers with a pitch of several microns, and plays a role of transmitting an image formed on the image plane of the image pickup optical system to the electronic image pickup device ICD.

  The emission surface of the optical transmission means OTM is formed in a plane, and the imaging unit ICU is configured by being in close contact with and connected to the electronic imaging element ICD.

  Table 9 shows the configuration of the imaging apparatus of the present embodiment.

  Surface number 1 is the entrance surface of the first lens G1, and has a rotationally symmetric aspherical shape expressed by the polynomial shown in equation (3).

  Surface number 2 is a bonding surface of the exit surface of G1 and the entrance surface of the second lens G2, and an aperture stop STO is configured by disposing a light shielding member at an ineffective portion thereof. Surface number 3 is the bonding surface of the exit surface of the second lens G2 and the entrance surface of the third lens G3, and surface number 4 is the exit surface of the third lens G3, which is expressed by the polynomial shown in equation (3). It has a rotationally symmetric aspherical shape.

  Surface number 5 is the imaging surface IMG, which is the incident surface of the optical transmission means OTM. An emission surface of the optical transmission means OTM not shown is connected to the electronic image sensor ICD.

  In the table, R is the radius of curvature (mm), d is the surface separation (mm), Nd is the refractive index of the d-line, and νd is the Abbe number. The surface with “*” is an aspherical surface.

  Table 10A shows the aspherical coefficient of surface number 1 and Table 10B shows the aspherical coefficient of surface number 4 in the imaging apparatus of the present embodiment.

  In the imaging apparatus of the present embodiment, the lens surface closest to the object and the lens surface closest to the image are aspherical.

  12A shows the aspherical shape of the lens surface closest to the object side, FIG. 12B shows the amount of aspherical surface of the lens surface closest to the object side, and FIG. The second order differential value of the reference spherical surface is shown, and FIG. 13B shows the second order differential value of the aspherical component.

  As shown in FIG. 12A, the lens surface closest to the object in this embodiment is a lens surface in which the sag amount increases in the positive direction from the optical axis toward the periphery, and the convex surface faces the object side. Lens surface.

  The reference spherical surface of this lens surface is a spherical surface with a convex surface facing the object side having a radius of curvature R = 3.24633 (mm).

  FIG. 12B shows the aspheric amount.

  As shown in FIG. 12B, in this embodiment, the aspheric amount is displaced in the negative direction, and is an aspheric surface displaced from the reference spherical surface to the object side, that is, outside the imaging optical system.

  As the distance from the optical axis increases, the amount of aspherical surface displaced outward from the imaging optical system is gradually increased to give the maximum amount of aspherical surface at the periphery of the lens surface.

  In FIG. 13A, the second-order differential value of the aspheric surface is indicated by a solid line, and the second-order differential value of the reference sphere is indicated by a broken line.

  Both the second-order differential value of the aspherical surface and the second-order differential value of the reference sphere have positive values.

  FIG. 13B shows the second-order differential value of the aspheric component.

  The second-order differential value of the aspheric component is gradually increased in the negative direction as the distance from the optical axis increases.

  As described above, the second-order differential value in the peripheral portion of the lens surface is weaker than that of the reference sphere by giving an aspherical component whose second-order differential value is negative to the reference spherical surface having a positive second-order differential value.

  Equation (6) shows the relationship between the second-order differential value and power.

  In the lens surface closest to the object side of the imaging optical system, since the medium on the object side of the lens surface is air, N = 1.0000, and the medium on the image side of the lens surface is optical glass and N ′ = 1.880202, (N′−N) has a positive value.

  Therefore, the lens surface closest to the object has a positive power on the optical axis, and has a lens surface shape in which the positive power gradually decreases as the distance from the optical axis increases.

  Thereby, spherical aberration can be corrected satisfactorily.

  In particular, when the lens surface closest to the object is an aspheric surface provided with an aspheric amount displaced from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface, the axial luminous flux and the image in the vicinity of the axial surface are obtained. The spherical aberration of the angular light beam can be corrected well.

  FIG. 14A shows the aspherical shape of the most image side lens surface, and FIG. 14B shows the aspherical amount of the most image side lens surface. FIG. 15A shows the second-order differential values of the aspheric surface and the reference sphere, and FIG. 15B shows the second-order differential values of the aspheric component.

  As shown in FIG. 14A, the lens surface closest to the image side in this embodiment is a lens surface in which the sag amount increases in the negative direction from the optical axis toward the peripheral portion, and the convex surface faces the image side. Lens surface.

  The reference spherical surface of this lens surface is a spherical surface having a convex surface facing the image side having a radius of curvature R = −2.9174 (mm).

  FIG. 14B shows the aspheric amount.

  As shown in FIG. 14B, in this embodiment, the aspheric amount is displaced in the positive direction, and is an aspheric surface displaced from the reference spherical surface to the image side, that is, outside the imaging optical system.

  As the distance from the optical axis increases, the amount of aspherical surface displaced outward from the imaging optical system is gradually increased to give the maximum amount of aspherical surface at the periphery of the lens surface.

  In FIG. 15A, the second-order differential value of the aspheric surface is indicated by a solid line, and the second-order differential value of the reference sphere is indicated by a broken line.

  Both the second-order differential value of the aspheric surface and the second-order differential value of the reference sphere have negative values.

  FIG. 15B shows the second-order differential value of the aspheric component.

  The second-order differential value of the aspheric component is gradually increased in the positive direction as the distance from the optical axis increases.

  As described above, the second-order differential value in the peripheral portion of the lens surface is weaker than that of the reference sphere by providing the reference spherical surface having a negative second-order differential value with an aspherical component having a positive second-order differential value.

  In the lens surface closest to the image side of the imaging optical system, the medium on the object side of the lens surface is optical glass, N = 2.270, and the medium on the image side of the lens surface is air, so N = 1.0000. N′−N) has a negative value.

  Therefore, the lens surface closest to the image has a positive power on the optical axis, and has a lens surface shape in which the positive power gradually decreases as the distance from the optical axis increases.

  Thereby, spherical aberration can be corrected satisfactorily.

  In particular, when the lens surface closest to the image side is an aspherical surface provided with an aspherical amount displaced from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface, Spherical aberration can be corrected satisfactorily.

  FIG. 16 shows a longitudinal aberration diagram in the imaging optical system of the present embodiment, and FIG. 17 shows a lateral aberration diagram.

  As shown in FIG. 16, spherical aberration, axial chromatic aberration, astigmatism, field curvature, and color spherical aberration are corrected well. In particular, the light beam can be condensed on the image plane over the entire range from a light beam having a low incident height to a high light beam, and the spherical aberration can be corrected very well.

  In addition, axial chromatic aberration and chromatic spherical aberration can be corrected very well, and high imaging performance is obtained.

  As shown in FIG. 17, good performance is obtained for each field angle light beam, and coma aberration, curvature of field, and lateral chromatic aberration are corrected well.

  As in this embodiment, both the most object-side lens surface and the most image-side lens surface are aspherical surfaces to which an aspherical amount obtained by displacing the reference spherical surface from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface This makes it possible to correct spherical aberration with high accuracy over a wide angle of view.

  Table 11 shows the specifications of the image pickup apparatus of the present embodiment.

  The image pickup apparatus of the present embodiment has a bright F value of F / 1.2, an ultra wide angle of view of 120.0 (deg), and a compact overall length of 6.371 (mm). This is an example of an imaging apparatus that simultaneously realizes high resolution, an ultra-wide angle of view, and compactness. Table 12 shows the values of the expressions (1) and (2) in the image pickup apparatus of the present embodiment.

  The value of the formula (1) is 0.96, which satisfies the range of the formula (1). Thereby, the optical system on the image side from the aperture stop of the imaging optical system can be configured to be nearly point-symmetric, and coma, astigmatism, distortion, and lateral chromatic aberration can be corrected well.

  The value of equation (2) is 0.99, which satisfies the range of equation (2). Thereby, it is possible to satisfactorily correct field curvature and astigmatism over a wide field angle of 120.0 (deg).

  The value of the formula (8) is 0.95, which satisfies the range of the formula (8).

  As a result, the imaging optical system has a configuration close to point symmetry, and coma, astigmatism, distortion, and lateral chromatic aberration are corrected well.

  Furthermore, in the imaging apparatus of the present embodiment, focus adjustment is performed by changing the distance between the imaging optical system and the imaging surface.

  Since the expression (8) is satisfied, focus adjustment can be performed while maintaining high resolution in a wide focus adjustment range from infinity to the close range.

[Example 4]
As a fourth embodiment, a configuration example of an imaging apparatus having a different form from the above embodiments will be described.

  As shown in FIG. 18, the image pickup optical system used in the image pickup apparatus according to the present embodiment includes four lenses G1, G2, G3, and G4 and an aperture stop STO.

From the object side,
A first lens G1, which is a meniscus lens having a convex surface facing the object side;
A second lens G2, which is a plano-convex lens having a convex surface facing the object side,
A third lens G3 which is a plano-convex lens having a convex surface facing the image side;
A fourth lens G4, which is a meniscus lens having a convex surface facing the image side, is disposed.

  IMG in FIG. 18 is an imaging surface.

  As shown in FIG. 18, the image pickup surface IMG of the image pickup apparatus in the present embodiment is obtained by making the electronic image pickup element ICD produced on a substrate having a variable shape into a spherical shape.

Table 13 shows the configuration of the imaging apparatus of the present embodiment.
Surface number 1 is the entrance surface of the first lens G1, and has a rotationally symmetric aspherical shape expressed by the polynomial shown in equation (3).

  Surface number 2 is a bonding surface of the exit surface of G1 and the entrance surface of the second lens G2. Surface number 3 is a bonding surface of the exit surface of the second lens G2 and the entrance surface of the third lens G3. A light shielding member is disposed on the ineffective portion to constitute an aperture stop STO.

  Surface number 4 is a bonding surface of the exit surface of the third lens G3 and the entrance surface of the fourth lens G4. Surface number 5 is the exit surface of the third lens G3, and has a rotationally symmetric aspherical shape expressed by the polynomial shown in equation (3).

  Surface number 6 is the imaging surface IMG, which is the incident surface of the curved electronic imaging device.

  In the table, R is the radius of curvature (mm), d is the surface separation (mm), Nd is the refractive index of the d-line, and νd is the Abbe number. The surface with “*” is an aspherical surface.

  Table 14A shows the aspheric coefficient of surface number 1 and Table 14B shows the aspheric coefficient of surface number 5 in the imaging apparatus of the present embodiment.

  In the imaging apparatus of the present embodiment, the lens surface closest to the object and the lens surface closest to the image are aspherical.

  FIG. 19A shows the aspherical shape of the lens surface closest to the object, and FIG. 19B shows the aspherical amount of the lens surface closest to the object. FIG. 20A shows the second-order differential values of the aspheric surface and the reference sphere, and FIG. 20B shows the second-order differential values of the aspheric component.

  As shown in FIG. 19A, the lens surface closest to the object in this embodiment is a lens surface in which the sag amount increases in the positive direction from the optical axis toward the periphery, and the convex surface faces the object side. Lens surface.

  The reference spherical surface of this lens surface is a spherical surface with a convex surface facing the object side having a radius of curvature R = 3.0198 (mm).

  FIG. 19B shows the aspheric amount.

  As shown in FIG. 19B, in this embodiment, the aspheric amount is displaced in the negative direction, and is an aspheric surface displaced from the reference spherical surface to the object side, that is, outside the imaging optical system.

  As the distance from the optical axis increases, the amount of aspherical surface displaced outward from the imaging optical system is gradually increased to give the maximum amount of aspherical surface at the periphery of the lens surface.

  In FIG. 20A, the second-order differential value of the aspherical surface is indicated by a solid line, and the second-order differential value of the reference sphere is indicated by a broken line.

  Both the second-order differential value of the aspherical surface and the second-order differential value of the reference sphere have positive values.

  FIG. 20B shows the second-order differential value of the aspheric component.

  The second-order differential value of the aspheric component is gradually increased in the negative direction as the distance from the optical axis increases.

  As described above, the second-order differential value in the peripheral portion of the lens surface is weaker than that of the reference sphere by giving an aspherical component whose second-order differential value is negative to the reference spherical surface having a positive second-order differential value.

  The relationship between the second-order differential value and power is shown in equation (6).

  In the lens surface closest to the object side of the imaging optical system, since the medium on the object side of the lens surface is air, N = 1.0000, and the medium on the image side of the lens surface is optical glass and N ′ = 2.00060, (N′−N) has a positive value.

  Therefore, the lens surface closest to the object has a positive power on the optical axis, and has a lens surface shape in which the positive power gradually decreases as the distance from the optical axis increases.

  Thereby, spherical aberration can be corrected satisfactorily.

  In particular, when the lens surface closest to the object is an aspheric surface provided with an aspheric amount displaced from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface, the axial luminous flux and the image in the vicinity of the axial surface are obtained. The spherical aberration of the angular light beam can be corrected well.

  FIG. 21A shows the aspherical shape of the most image side lens surface, and FIG. 21B shows the aspherical amount of the most image side lens surface.

  FIG. 22A shows the second-order differential values of the aspheric surface and the reference sphere, and FIG. 22B shows the second-order differential values of the aspheric component.

  As shown in FIG. 21A, the lens surface closest to the image side in this embodiment is a lens surface in which the sag amount increases in the negative direction from the optical axis toward the peripheral portion, and the convex surface faces the image side. Lens surface.

  The reference spherical surface of this lens surface is a spherical surface having a convex surface facing the image side with a radius of curvature R = −2.9057 (mm).

  FIG. 21B shows the aspheric amount.

  As shown in FIG. 21B, in this embodiment, the aspheric amount is displaced in the positive direction, and is an aspheric surface displaced from the reference spherical surface to the image side, that is, outside the imaging optical system.

  As the distance from the optical axis increases, the amount of aspherical surface displaced outward from the imaging optical system is gradually increased to give the maximum amount of aspherical surface at the periphery of the lens surface.

  In FIG. 22A, the second-order differential value of the aspheric surface is indicated by a solid line, and the second-order differential value of the reference sphere is indicated by a broken line.

  Both the second-order differential value of the aspheric surface and the second-order differential value of the reference sphere have negative values.

  FIG. 22B shows the second-order differential value of the aspheric component.

  The second-order differential value of the aspheric component is gradually increased in the positive direction as the distance from the optical axis increases.

  As described above, the second-order differential value in the peripheral portion of the lens surface is weaker than that of the reference sphere by providing the reference spherical surface having a negative second-order differential value with an aspherical component having a positive second-order differential value.

  In the lens surface closest to the image side of the imaging optical system, the medium on the object side of the lens surface is optical glass and N = 2.00060, and the medium on the image side of the lens surface is air, so N = 1.0000. N′−N) has a negative value.

  Therefore, the lens surface closest to the image has a positive power on the optical axis, and has a lens surface shape in which the positive power gradually decreases as the distance from the optical axis increases.

  Thereby, spherical aberration can be corrected satisfactorily.

  In particular, when the lens surface closest to the image side is an aspherical surface provided with an aspherical amount displaced from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface, Spherical aberration can be corrected satisfactorily.

  FIG. 23 shows a longitudinal aberration diagram in the imaging optical system of the present example, and FIG. 24 shows a lateral aberration diagram.

  As shown in FIG. 23, spherical aberration, axial chromatic aberration, astigmatism, field curvature, and color spherical aberration are corrected fairly well. In particular, the light beam can be condensed on the image plane over the entire range from a light beam having a low incident height to a high light beam, and the spherical aberration can be corrected very well.

  In addition, axial chromatic aberration and chromatic spherical aberration can be corrected very well, and high imaging performance is obtained.

  As shown in FIG. 24, good performance is obtained for each field-angle light beam, and coma aberration, field curvature, and lateral chromatic aberration are corrected fairly well.

As in this embodiment, both the most object-side lens surface and the most image-side lens surface are aspherical surfaces to which an aspherical amount obtained by displacing the reference spherical surface from the reference spherical surface to the outside of the imaging optical system at the periphery of the lens surface; This makes it possible to correct spherical aberration with high accuracy over a wide angle of view.
Table 15 shows the specifications of the image pickup apparatus of the present embodiment.

  The imaging apparatus according to the present embodiment has a bright F value of F / 1.2 and an ultra wide angle of view of 120.0 (deg), and the overall length is 6.044 (mm) and is compact. This is an example of an imaging apparatus that simultaneously achieves brightness, high resolution, an ultra-wide field angle, and compactness.

  Table 16 shows the values of the expressions (1) and (2) in the image pickup apparatus of the present embodiment.

  The value of the formula (1) is 0.96, which satisfies the range of the formula (1). Thereby, the optical system on the image side from the aperture stop of the imaging optical system can be configured to be nearly point-symmetric, and coma, astigmatism, distortion, and lateral chromatic aberration can be corrected well.

  The value of formula (2) is 1.01, which satisfies the range of formula (2). Thereby, it is possible to satisfactorily correct field curvature and astigmatism over a wide field angle of 120.0 (deg).

  The value of equation (8) is 0.97, which satisfies the range of equation (8).

  As a result, the imaging optical system has a configuration close to point symmetry, and coma, astigmatism, and lateral chromatic aberration are corrected well.

  Furthermore, in the imaging apparatus of the present embodiment, focus adjustment is performed by changing the distance between the imaging optical system and the imaging surface. Since the expression (8) is satisfied, focus adjustment can be performed while maintaining high resolution in a wide focus adjustment range from infinity to the close range.

[Example 5]
As a fifth embodiment, a configuration example of an imaging apparatus having a different form from the above embodiments will be described.

  As shown in FIG. 25, the image pickup optical system used in the image pickup apparatus of the present embodiment includes four lenses G1, G2, G3, and G4 and an aperture stop STO.

From the object side,
A first lens G1, which is a meniscus lens having a convex surface facing the object side;
A second lens G2, which is a plano-convex lens having a convex surface facing the object side,
A third lens G3 which is a plano-convex lens having a convex surface facing the image side;
A fourth lens G4, which is a meniscus lens having a convex surface facing the image side, is disposed.

  Further, as in the first embodiment, an image pickup unit ICU composed of an optical transmission means OTM and a flat electronic image pickup element ICD is used.

  In the present embodiment, only the lens surface closest to the image in the imaging optical system is an aspherical surface.

  Table 17 shows the configuration of the image pickup apparatus of the present embodiment.

  In the table, R is the radius of curvature (mm), d is the surface separation (mm), Nd is the refractive index of the d-line, and νd is the Abbe number. The surface with “*” is an aspherical surface.

  Table 18 shows the aspheric coefficients of surface number 5 in the imaging apparatus of the present example.

  FIG. 26A shows the aspherical shape of the lens surface closest to the image, and FIG. 26B shows the aspherical amount. FIG. 27A shows the second-order differential values of the aspheric surface and the reference sphere, and FIG. 27B shows the second-order differential values of the aspheric component.

  As shown in FIG. 26 (a), the most image side lens surface (surface number 5) of this example is a lens surface in which the sag amount increases in the negative direction from the optical axis toward the peripheral portion. This is a lens surface with a convex surface facing the side. This lens surface has a spherical surface with a radius of curvature R = −3.0745 (mm) as a reference spherical surface.

  Further, as shown in FIG. 26B, the aspherical amount is displaced in the positive direction, and is constituted by an aspherical surface displaced from the reference spherical surface to the image side, that is, outside the imaging optical system. As the distance from the optical axis increases, the amount of aspherical surface displaced outward from the imaging optical system is gradually increased to give the maximum amount of aspherical surface at the periphery of the lens surface.

  In FIG. 27 (a), the second-order differential value of the aspherical surface is shown by a solid line, and the second-order differential value of the reference sphere is shown by a broken line. Both have negative values.

  FIG. 27B shows the second-order differential value of the aspheric component.

  The second-order differential value of the aspheric component is gradually increased in the positive direction as the distance from the optical axis increases.

  In this way, by adding an aspheric surface in which the second-order partial value of the reference sphere is negative and the second-order differential value of the aspheric component is positive, the second-order differential value in the peripheral portion of the lens surface is obtained from the reference sphere. Is also weakening.

  That is, the power of the lens surface is gradually weakened from the optical axis of the lens surface toward the peripheral portion with the positive power of the reference spherical surface and the aspherical component as negative power.

  Thereby, since the spherical aberration in the light beam with the angle of view can be corrected satisfactorily, it is possible to provide an imaging apparatus having a good imaging performance over a wide angle of view.

  In particular, in a wide-angle imaging optical system in which the peripheral ray (upper ray) of the light beam with the maximum angle of view passes below the optical axis on the lens surface closest to the object in the imaging optical system. The effects of the present invention are fully exhibited.

  Table 19 shows the specifications of the image pickup apparatus of the present embodiment.

  The imaging apparatus of the present embodiment has a bright F value of F / 1.2 and an ultra wide angle of view of 120.0 (deg), while keeping the total length of 6.384 (mm) compact. This is an example of an imaging apparatus that simultaneously achieves brightness, high resolution, an ultra-wide field angle, and compactness.

  Table 20 shows the values of the expressions (1) and (2) in the image pickup apparatus of the present embodiment.

  The value of equation (1) is 0.95, which satisfies the range of equation (1). Thereby, the optical system on the image side from the aperture stop of the imaging optical system can be configured to be nearly point-symmetric, and coma, astigmatism, distortion, and lateral chromatic aberration can be corrected well.

  The value of formula (2) is 1.03, which satisfies the range of formula (2). Thereby, it is possible to satisfactorily correct field curvature and astigmatism over a wide field angle of 120.0 (deg).

  The value of equation (8) is 0.97, which satisfies the range of equation (8).

  As a result, the imaging optical system has a configuration close to point symmetry, and coma, astigmatism, distortion, and lateral chromatic aberration are corrected well.

  FIG. 28 shows a longitudinal aberration diagram in the imaging optical system of the present example, and FIG. 29 shows a lateral aberration diagram.

  Furthermore, in the imaging apparatus of the present embodiment, focus adjustment is performed by changing the distance between the imaging optical system and the imaging surface.

  Since the expression (8) is satisfied, focus adjustment can be performed while maintaining high resolution in a wide focus adjustment range from infinity to the close range.

[Example 6]
As a sixth embodiment, a configuration example of an imaging apparatus having a different form from the above embodiments will be described.

  As shown in FIG. 30, the imaging optical system used in the imaging apparatus of the present embodiment includes four lenses G1, G2, G3, G4 and an aperture stop STO.

From the object side,
A first lens G1, which is a meniscus lens having a convex surface facing the object side;
A second lens G2, which is a plano-convex lens having a convex surface facing the object side,
A third lens G3 which is a plano-convex lens having a convex surface facing the image side;
A fourth lens G4, which is a meniscus lens having a convex surface facing the image side, is disposed.

  Further, as in the first embodiment, an image pickup unit ICU composed of an optical transmission means OTM and a flat electronic image pickup element ICD is used.

  In this embodiment, only the lens surface closest to the object in the imaging optical system is an aspherical surface.

Table 21 shows the configuration of the image pickup apparatus of the present embodiment.
In the table, R is the radius of curvature (mm), d is the surface separation (mm), Nd is the refractive index of the d-line, and νd is the Abbe number. The surface with “*” is an aspherical surface.

  Table 22 shows the aspherical coefficients of surface number 5 in the imaging apparatus of the present example.

  FIG. 31A shows the aspherical shape of the lens surface closest to the object side, and FIG. 31B shows the amount of aspherical surface. FIG. 32A shows the second-order differential values of the aspheric surface and the reference sphere, and FIG. 32B shows the second-order differential values of the aspheric component.

  As shown in FIG. 31A, the most object side lens surface (surface number 1) of this embodiment is a lens surface whose sag amount increases in the positive direction from the optical axis toward the periphery. This is a lens surface with a convex surface facing the side. This lens surface uses a spherical surface with a radius of curvature R = 3.1360 (mm) as a reference spherical surface.

  As shown in FIG. 31B, the aspheric amount is displaced in the negative direction, and is constituted by an aspheric surface displaced from the reference spherical surface to the object side, that is, outside the imaging optical system.

  As the distance from the optical axis increases, the amount of aspherical surface displaced outward from the imaging optical system is gradually increased to give the maximum amount of aspherical surface at the periphery of the lens surface.

  In FIG. 32 (a), the second order differential value of the aspherical surface is indicated by a solid line, and the second order differential value of the reference sphere is indicated by a broken line. Both have positive values.

  FIG. 32B shows the second-order differential value of the aspheric component.

  The second-order differential value of the aspheric component is gradually increased in the negative direction as the distance from the optical axis increases.

  In this way, by adding an aspheric surface in which the second-order partial value of the reference sphere is positive and the second-order differential value of the aspheric component is negative, the second-order differential value in the peripheral portion of the lens surface is obtained from the reference sphere. Is also weakening.

  That is, the power of the lens surface is gradually weakened from the optical axis of the lens surface toward the peripheral portion with the positive power of the reference spherical surface and the aspherical component as negative power.

  Thereby, since the spherical aberration in the axial light beam can be corrected satisfactorily, it is possible to provide an imaging device having a good imaging performance.

  Table 23 shows the specifications of the image pickup apparatus of the present embodiment.

  The imaging apparatus of the present embodiment has a bright F value of F / 1.2 and an ultra wide angle of view of 120.0 (deg), while keeping the total length to 6.281 (mm) and compact. This is an example of an imaging apparatus that simultaneously achieves brightness, high resolution, an ultra-wide field angle, and compactness.

  Table 24 shows the values of the expressions (1) and (2) in the image pickup apparatus of the present embodiment.

  The value of the formula (1) is 1.09, which satisfies the range of the formula (1). Thereby, the optical system on the image side from the aperture stop of the imaging optical system can be configured to be nearly point-symmetric, and coma, astigmatism, distortion, and lateral chromatic aberration can be corrected well.

  The value of formula (2) is 1.04, which satisfies the range of formula (2). Thereby, it is possible to satisfactorily correct field curvature and astigmatism over a wide field angle of 120.0 (deg).

  The value of the formula (8) is 1.13, which satisfies the range of the formula (8).

  As a result, the imaging optical system has a configuration close to point symmetry, and coma, astigmatism, distortion, and lateral chromatic aberration are corrected well.

  FIG. 33 is a longitudinal aberration diagram in the imaging optical system of the present embodiment, and FIG. 34 is a transverse aberration diagram.

  Furthermore, in the imaging apparatus of the present embodiment, focus adjustment is performed by changing the distance between the imaging optical system and the imaging surface. Since the expression (8) is satisfied, focus adjustment can be performed while maintaining high resolution in a wide focus adjustment range from infinity to the close range.

  The configuration of the present invention including each of the embodiments described above can be used for products using an imaging device such as a digital camera, a digital video camera, a mobile phone camera, and a surveillance camera.

G1, G2, G3 Lens STO Aperture stop Asph Aspherical surface IMG Imaging surface OTM Optical transmission means ICD Electronic imaging device ICU Imaging unit

Claims (13)

An imaging apparatus comprising an imaging surface that is concave toward the object side, and an imaging optical system that forms an object image on the imaging surface,
The imaging optical system includes a plurality of lenses and an aperture stop,
Among the plurality of lenses, the lens closest to the image side is a meniscus lens having a convex surface facing the image side, and the lens adjacent to the lens closest to the image side includes a convex exit surface toward the image side. ,
When the focal length of the imaging optical system is f_sys, the distance from the exit pupil of the imaging optical system to the imaging surface is d_upp, and the radius of curvature of the imaging surface is R_img, the following equation is satisfied: An imaging device.
0.8 ≦ f_sys / d_pup ≦ 1.5
0.8 ≦ | R_img | /f_sys≦1.5   The imaging apparatus according to claim 1, wherein a refractive index of the lens closest to the image side is larger than a refractive index of a lens adjacent to the lens closest to the image side.   The imaging apparatus according to claim 1, wherein an entrance surface of the lens closest to the image side and an exit surface of a lens adjacent to the lens closest to the image side have negative power.   The imaging apparatus according to claim 1, wherein a lens closest to the object among the plurality of lenses includes a convex incident surface.   The imaging apparatus according to claim 4, wherein the lens closest to the object side and the lens adjacent to the lens closest to the image side are cemented with each other.   Among the plurality of lenses, the lens closest to the object side is a meniscus lens having a convex surface facing the object side, and the lens adjacent to the lens closest to the object side includes an incident surface convex toward the object side. The imaging apparatus according to claim 1 or 2, wherein   The imaging apparatus according to claim 6, wherein the lens adjacent to the lens closest to the object side and the lens adjacent to the lens closest to the image side are cemented with each other.   8. The lens according to claim 1, wherein among the plurality of lenses, a lens closest to the object side and a lens closest to the image side are joined to each other via the aperture stop. Imaging device.   The lens surface closest to the object among the plurality of lenses is an aspherical surface having a spherical surface convex toward the object side as a reference surface and a peripheral portion displaced to the object side with respect to the reference surface. The imaging apparatus according to claim 1, wherein the imaging apparatus is characterized.   The lens surface closest to the image side among the plurality of lenses is an aspherical surface having a spherical surface convex toward the image side as a reference surface and a peripheral portion displaced to the image side with respect to the reference surface. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is characterized.   The portion closer to the object side than the aperture stop in the imaging optical system and the portion closer to the image side than the aperture stop in the imaging optical system have mutually different positive powers. The imaging device according to any one of the above. The imaging apparatus according to claim 1, wherein the following expression is satisfied.
0.8 ≦ | R_img | /d_pup≦1.5   13. The imaging apparatus according to claim 1, further comprising: an optical transmission unit including the imaging surface; and an imaging element that receives light from the optical transmission unit.

Images