JP2007155976A - Fisheye lens and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fisheye lens capable of obtaining a central fovea optical system that is a single wide-angle optical system, extremely compact and wide in visual field and, moreover, has high resolution over the entire visual field and illuminance kept uniform as far as the periphery. <P>SOLUTION: The fisheye lens includes: a front group including three groups, which are, in order from the object side, two concave lenses 1 and 2, the concave faces of which are directed toward the object, and a doublet 3, the concave face of which is directed toward the object and which has convex or concave refractive power as a whole; and a rear group including three groups, which are convex lenses 4, 5, and 6. In the fisheye lens, the front group has one or more doublets and the rear group has two or more doublets. The first face of the first concave lens of at least the front group is an aspherical face and a fisheye lens that satisfies specific conditions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fisheye lens and an imaging apparatus using the fisheye lens.

  The foveal optical system is an optical system that mimics the function of the human eye, and has an extremely wide field of view, and can obtain high resolving power when focusing on the center of the field of view. . Such optical systems are described in, for example, Japanese Patent Application Laid-Open Nos. 2004-354572 and 2000-221391.

JP 2004-354572 A JP 2000-221391 A JP 2003-167195 A JP 2004-354572 A

  Various schemes are known for optical systems similar to the function of foveal optics. In a multiple optical system that combines a telephoto lens with a narrow angle of view and a wide-angle lens, the complexity and size of the system are crucial defects. If this is realized with a twin-lens optical system, parallax with the subject also becomes a problem.

  Although it is possible to use a zoom lens, it is difficult to satisfy a wide field of view and high resolution at the same time. There is always a characteristic that only one of the time lapses due to zooming can be confirmed instantly, and that is the difficulty. In general, it is a major drawback that the length and size of the lens cannot be avoided.

  JP-A-2003-167195 also proposes a catadioptric optical system. However, in the catadioptric optical system, the central portion, which is the most important point in the field of view, becomes a blind spot, and only a donut shape can be observed. In general, processing accuracy is difficult and high resolution is not obtained. The center part of the catadioptric optical system is made transmissive, and only the center part is magnified, but the wide-angle and telephoto images are discontinuous, making it extremely difficult to build a system. Met.

  Japanese Patent Application Laid-Open No. 2004-354572 describes a method for realizing a foveal optical system with a single wide-angle optical system. This optical system is a lens that reduces the distortion of an image at the center of the visual field and generates a negative barrel-shaped distortion as it approaches the periphery. However, this foveal lens also does not reach a wide field of view up to about 180 degrees, and because it gives priority to distortion, resolution is partially insufficient, and another important characteristic for the eye That is, there is a problem that the lens is dark in the periphery, and therefore the field of view is substantially narrower, due to the fact that the sensitivity is as uniform as possible to the periphery of the field of view or the sensitivity is as high as possible.

  The present invention has been made in view of such circumstances, and is a single wide-angle optical system that has a very small and wide field of view, and also has high resolution over the entire field of view and illuminance to the periphery. It is an object of the present invention to provide a fisheye lens capable of realizing a tilted foveal optical system, and an imaging device using the fisheye lens.

The first means for solving the above-mentioned problems includes two concave lenses having a concave surface facing the image side from the object side, a cemented lens having a convex or concave refractive power as a whole, with the concave surface facing the image side, A fisheye lens composed of a front group consisting of a total of three groups and a rear group consisting of three convex lenses, including at least one pair of cemented lenses in the front group and two or more pairs in the rear group, The first surface of the first concave lens is a fish-eye lens having an incident angle of 60 degrees or more, which is an aspherical surface and satisfies the following conditions.
(1) The first surface aspheric surface of the front group first concave lens is expressed by

In the range of Y _max >Y> 0.5f, dx / dY> 0
However, in the aspherical expression, X represents the optical axis direction, Y represents the coordinate in the direction perpendicular to the optical axis, the intersection of the optical axis and the first surface vertex of the first concave lens is the origin, and the optical axis is the rotation center. Rotating aspheric surface. Y _max is the maximum effective radius of the lens, R 1 is the radius of curvature of the first surface of the first concave lens, f is the focal length of the entire lens system, and κ, A, B, C, D, E, and F are constants. It is.
(2) When h = f * sinω is taken as a reference scale for the lens projection function, the distortion amount V when the incident angle ω = 60 degrees is −10% ≧ V ≧ −16%.
However, V = (H−h) * 100 / h (%), and H represents the height of the image from the optical axis when the incident angle ω = 60 degrees.

  In the present specification and claims, the lens number and the surface number are counted in order from the object side.

  The three lenses in the front group have a function of passing incident light from a wide incident angle little by little to a small angle along the optical axis and passing through the aperture position. Since light rays from a large incident angle pass through the end of the lens, in order to minimize the meridional field curvature that occurs positively, it is necessary that all lenses have a concave surface on the image side, and Since at least one lens located closest to the object side has a particularly large incident angle, a meniscus shape is preferable.

  The use of the third lens group in the front group is necessary in order to prevent sudden occurrence of meridional field curvature and to prevent occurrence of uneven field curvature relative to image height. If the number of sheets is small, the unevenness of the location becomes large, and if the number of sheets is large, the size becomes too large.

  The reason why at least one pair of cemented lenses is placed in the front group is that they are indispensable for correcting both axial chromatic aberration and lateral chromatic aberration in combination with the rear group cemented lens. All single lenses have chromatic dispersion, so the front lens group has positive axial chromatic aberration and negative lateral chromatic aberration for shorter wavelength light. On the other hand, when only a convex single lens is disposed in the rear group, as a function of only the rear group, negative axial chromatic aberration and negative lateral chromatic aberration are generated with respect to light having a shorter wavelength. Therefore, if it is assumed that the front group and the rear group are composed of only a single lens, the longitudinal chromatic aberration can be canceled and corrected because the signs are opposite to each other, but the lateral chromatic aberration is negative and cannot be corrected.

  Having a negative refractive power component with relatively large dispersion in the rear group is effective for correcting chromatic aberration, and is a necessary condition, but it alone cannot correct axial chromatic aberration and lateral chromatic aberration in a well-balanced manner. A component having a positive refractive power with relatively large dispersion is necessarily required for a group. The first lens group and the second lens group are of the junction type because they do not like that the outer periphery of the field of view of the image plane is colored because the incident angle of the light beam passing through the edge of the lens is slightly different for each wavelength. It is also effective to use an achromatic lens. Specifically, the Abbe number νd> 55 is desirable for both the first lens group and the second lens group.

  The aspherical surface is mainly used to obtain the negative distortion characteristics of the foveal lens, but it has the least influence on the spherical aberration at the place farthest from the stop, that is, the first surface of the first concave lens. Met. Although it is possible to use aspheric surfaces for a plurality of surfaces, the balance of spherical aberration, meridional field curvature and distortion cannot be corrected well unless at least the first surface of the first concave lens is aspherical.

  The reason why three positive lenses are arranged in the rear group is that if the number of lenses is two or less, high-order aberrations, particularly negative spherical aberration and a sharp increase in the vicinity of the field of view, due to the burden of the refractive power of each lens being too strong. This is because the field curvature aberration cannot be corrected. More importantly, in order to satisfy the telecentric optical system, with respect to only the rear group, the vicinity of the focal position when the ray is traced from the image side is the stop position, but the spherical aberration must not be excessive. In the case of this lens, if the combined focal length of the rear three groups is assumed to be fB, about 1.2f <fB <1.5f is desirable, but in this combined focal length range, the F-number when the back ray tracing is performed is 0.7. This is because at least three groups of convex lenses are necessary in order to make the lens extremely bright and reduce spherical aberration as much as possible. If four or more lens groups are arranged, the spherical aberration is reduced, but the lens thickness becomes too thick and the front back F of the rear lens group becomes negative and cannot be a telecentric optical system. It was.

  As described above, the rear group needs a concave lens in order to correct chromatic aberration. However, when a single concave lens is used, it is convenient to use a concave lens as a biconcave lens for chromatic aberration, spherical aberration, and coma. It turns out that it can correct well. However, the image-side surface of the biconcave lens becomes a concave surface having a slightly larger radius of curvature than the image surface, and the reflection between the surface of a parallel flat member such as a filter on the image side and the concave surface returns to the imaging surface and becomes a flare. I knew I would get it.

  Therefore, when the aberration balance was adjusted again by increasing the number of cemented lenses, the radius of curvature of the concave surface could be somewhat reduced, and the corresponding flare could be reduced. As a result of this study, it was found that, as long as this foveal characteristic is obtained, a lens having less flare and good aberration correction can be realized by using at least two cemented lenses in the rear group.

  In this means, the front group has a concave refractive power and the rear group has a convex refractive power, which belongs to a so-called retrofocus type. In general, the retrofocus lens can be expected to maintain the peripheral light amount, and the curvature of the image surface tends not to be large for a wide field of view. By arranging a negative lens on the object side (referred to as the front group) and a positive lens on the image side (referred to as the rear group), the principal ray crosses the optical axis between the front group and the rear group. Both the front group and the rear group cause negative distortion. As a result, strong negative distortion is obtained in the entire lens system.

  However, it is generally empirically that the distortion aberration amount thus obtained has a projection function close to y = f * ω. The required specification is a distortion characteristic in which the negative distortion is small in a small incident angle range and the negative distortion is extremely large in a large incident angle range. In order to achieve this, optical arrangement with insufficient negative distortion is still used as basic data, and it is devised to further increase the tendency of distortion of light rays with a large incident angle that mainly pass through the periphery of the lens. I have to do it.

  Specifically, one means is to use aspherical lenses for the front group and the rear group. The front group uses an aspherical surface that has the effect of increasing the refractive action of the concave lens so that light rays with a large incident angle at the lens periphery are guided into the lens. In order to reduce the image height of the collected rays, an aspheric surface that has as much convergence as possible around the lens is used. There were several side effects when actually tracing the rays.

  The first side effect is that the telecentricity of the lens is lost. In particular, when the positive refracting power is increased at the periphery of the rear lens group, the light rays that are focused on the periphery of the screen converge. As a result, even if the chief rays of the light rays gathering inward in the screen are arranged in a divergent manner, an image is formed so that the chief rays of light rays gathering outside in the screen converge.

  That is, the telecentricity is lost, and the direction in which the chief ray travels is convergent or divergent depending on the location. This results in two problems. One is that the compatibility with the electronic image pickup device is deteriorated, resulting in uneven sensitivity. The electronic image pickup device has high sensitivity to vertically incident light, and the sensitivity is reduced to obliquely incident light. Therefore, when telecentricity is lost, sensitivity unevenness occurs.

  The second problem is that the distortion of the image may change in a complex manner when there is a focusing error using the lens. Even if this does not have a great influence on the visual observation of the image, there is a great possibility that inconvenience is caused when information on the object side is obtained from the result of position measurement in the image.

  As a result of the above examination, no aspherical surface is used to increase the distortion of the rear group. However, the use of an aspherical surface for correcting other aberrations such as spherical aberration and coma aberration and reducing the number of sheets is not excluded.

  The second side effect is that the aperture ratio of the ambient light is deteriorated and the ambient light is diminished. In particular, in the front group, the chief ray of a large incident angle incident on the fisheye lens travels near the edges of a plurality of lenses having wedge angles, but is thin so that it passes through the prism spectrograph. Parallel light travels while gradually decreasing the incident angle, and passes through the optical axis at the stop position. In order to make the negative distortion of a light beam with a large incident angle particularly strong, it is necessary to further increase the apex angle of the prism, but eventually the surface of the first surface of the lens comes into contact with the incident light beam, The limit is coming. This is because when the light ray comes into contact with the first surface, the cross-sectional area of the incident light beam that can pass through the stop becomes 0, and therefore the peripheral light amount incident on the lens theoretically disappears.

  Asphericalization is performed on the first surface of the first lens in a range where these side effects do not exceed the limit of the required specifications. Although we tried to make multiple surfaces aspherical, the incident light quantity of light with a large incident angle started to decrease from a smaller angle, and it was found that it was impossible to maintain a wide incident angle, so only one surface was eventually I will keep it on. And the 1st surface of a 1st lens is formed according to (1) Formula which is the general shape of an aspherical lens.

The restriction of conditional expression (1) is a very useful condition. When dx / dY> 0 cannot be satisfied in the range of Y _max >Y> 0.5f, the amount of incident light on the lens at an angle of view of 60 ° or more is drastically reduced. Even the surrounding illuminance is insufficient. When Y is 0.5f or less, only a light beam with a relatively small incident angle contributes, so it hardly contributes to excess or deficiency of illuminance due to this reason. Therefore, the constraint that dx / dY> 0 is unnecessary. It is.

  The second conditional expression (2) will be described. A projection method of H = f * sinω is known as a lens having illuminance uniformity. This equation is applied in the case of an ideal state in which the loss of the light amount due to the reflection of each surface of the lens, the internal transmittance of the lens, and the loss of the cross-sectional area of the incident light beam are not included. Actually, these effects cause peripheral dimming.

  In order to minimize this influence, it is desirable to have a further negative distortion with respect to the projection method of H = f * sinω, and in order to maintain the illuminance, the range of condition (2) should be maintained. is necessary. When the value of V exceeds −10%, the decrease in the amount of peripheral light due to the projection function at an incident angle ω = 60 ° is certainly not bad toward 0%. When ω> 60 °, by providing a further negative distortion characteristic, the incident light beam becomes sharply thin and the peripheral light amount becomes insufficient. That is, the tendency that the peripheral light amount is insufficient cannot be removed. When the value of V is smaller than -16%, the projection function is in the direction of further increase of the peripheral light amount, but the luminous flux incident on the lens becomes sharply thin, so that the peripheral image plane illuminance is still insufficient. . Eventually, the peripheral image surface illuminance is not insufficient when the distortion amount V when ω = 60 degrees is −10% ≧ V ≧ −16%.

The second means for solving the problem is the first means, characterized by satisfying the following (3) and (4).
(3) When the focal length of the front group is set to fF, -0.8f>fF> -1.5f
(4) The curvature radius R of the cemented surface of the second group convex lens in the rear group is 1.0f <R <1.4f.
Under the condition (3), when the value of fF is −0.8 f or more, the concave power becomes too strong and the Petzval sum becomes too negative. On the other hand, when the value of fF is −1.5 f or less, the back ef becomes too short, and it becomes difficult to actually realize the optical system due to dimensional restrictions.

  The condition (4) is a condition for preventing the occurrence of harmful ghosts. In some cases, the return light from the parallel plane member located on the CCD surface of the camera or the back surface of the lens is reflected by the concave joint surface and returns to the CCD surface. This condition is for preventing this. When the value of R is 1.4 f or more, there is a high possibility of harmful ghosts. When the value of R is 1.0 f or less, no harmful ghost is generated, but the action of the concave lens is too strong, and in particular, the color coma is rapidly deteriorated. In addition, the cemented surface of the second group convex lens has a function of diverging light rays, and works to correct the internal coma aberration generated in the rear group well by diverging the light rays passing through the vicinity of the lens edge more strongly. Also have.

  The third means for solving the problem is the first means or the second means, wherein the second convex lens in the rear group is a cemented lens of concave and convex two lenses in order from the object side, The concave lens is a lens made of a transmissive member having a higher refractive index and higher dispersion than the convex lens on the image side. When the focal length of the concave lens is fou, -1.5f <fou <-0.8f. is there.

  This is to provide a function of a concave lens having a diverging action in the rear group. Therefore, the negative spherical aberration of the rear group is corrected by setting the refractive index of the concave lens higher than that of the convex lens. When the spherical aberration of the rear group is corrected, the chief rays emitted from the center of the (aperture) stop become parallel to reach the image plane, and the telecentricity on the image side is improved. When the refractive index of the concave lens is lower than that of the convex lens, the telecentricity on the image side cannot be maintained. Further, by using a highly dispersive material for the concave lens, both axial chromatic aberration and lateral chromatic aberration that occur in the rear group can be improved.

  When fou is −1.5 f or less, the action of the concave lens becomes too small, and the spherical aberration of the entire system becomes negative and cannot be corrected. When fou is −0.8 f or more, the divergent action is too strong, so that the meridional field curvature becomes positive, and particularly the upper coma aberration is increased, thereby deteriorating the aberration balance.

  The fourth means for solving the problem is the first means or the second means, wherein the third convex lens in the rear group is a cemented lens of two lenses that are convex and concave in order from the object side, The concave lens is a lens made of a transmissive member having a higher refractive index and higher dispersion than a convex lens.

  This means has a function of further satisfactorily correcting negative spherical aberration, axial chromatic aberration, and lateral chromatic aberration that have not been corrected by the second convex lens in the rear group. When the condition of this means is not satisfied, the correction is insufficient.

  A fifth means for solving the above-mentioned problems has a fisheye lens of any one of the first to fourth means, and has a function of acquiring an image by an electronic imaging device, and further a pan mechanism, An imaging apparatus having at least one of a tilt mechanism and a rotation mechanism and capable of being operated by an electric signal or by a mechanical means.

  The foveal optical system has a distribution in the ability to observe the subject in detail, and the center of the field of view has a high resolution, so if necessary, the pan, tilt, and rotation mechanisms can be used to capture the target in the center of the field of view. May be desired. Since this lens has an extremely wide angle, is bright up to the periphery, and has a high resolving power, a combination with a pan mechanism, a tilt mechanism, and a rotation mechanism is more effective than a conventional optical system. Note that the combination of the pan mechanism, the tilt mechanism, and the rotation mechanism can be realized by appropriately applying a known technique.

  A sixth means for solving the problem includes the fisheye lens according to any one of the first to fourth means, and further includes an electronic imaging device, and further captures an image, time, direction, and self An imaging apparatus having a function of recording or storing at least one of coordinates, a function of identifying a subject, and a function of directing a target near the center of the field of view according to a self signal or an external signal.

  The extremely wide-angle foveal optical system of this lens has a distribution in the ability to observe the subject in detail, and the center of the field of view has a high resolving power, so if necessary, make full use of the pan, tilt, and rotation mechanisms. When an object is captured in the center of the field of view, the possibility of identifying the subject is further increased from the periphery to the center. Taking advantage of the adaptability of the taking lens, it is possible to achieve the target more perfectly near the center of the field of view. A function that records or stores at least one of the captured image, time, direction, and own coordinates, a function that identifies the subject, and a function that directs the target near the center of the field of view according to the self signal or an external signal Can be realized by appropriately applying known techniques.

  A seventh means for solving the above-mentioned problem is a fish-eye lens of any one of the first to fourth means, using a plurality of the same fish-eye lens, and using a parallax to at least a specific place distance An imaging apparatus characterized in that information can be acquired.

  Wide-angle lenses generally tend not to capture parallax, but the foveal optical system is superior in capturing parallax because the central focal length is relatively long. Using the lens of the present invention, it is particularly advantageous to acquire distance information of at least a specific place using parallax.

  An eighth means for solving the above-mentioned problem is an imaging apparatus using a plurality of any of the fish-eye lenses of the first to fourth means, and having multiple eyes with a convergence mechanism.

  According to the present invention, a fish-eye lens that can realize a foveal optical system that has a very small and wide field of view with a single wide-angle optical system, and that has a high resolving power over the entire field of view and that maintains illuminance to the periphery. And an imaging apparatus using the fisheye lens can be provided.

  Examples of the fisheye lens of the present invention are shown below. In each table, men is a surface number and counted from the object side, r is a radius, d is a distance between surfaces, νd is an Abbe number, and nd is a refractive index of the wavelength of the d-line. Further, f is the overall focal length, R1 is the radius of curvature of the first surface, and ω is the maximum incident angle. Further, K represents κ, C4, C6, C8, and C10 in the formula (1), and A, B, C, and D in the formula (1), respectively. In each embodiment, E and F in formula (1) are zero.

  In the aberration diagrams, the maximum value of the vertical axis of spherical aberration (H) is H (the height of incident light), the maximum value of the vertical axis of field curvature (Distortion) is ω, The maximum value of the horizontal axis of coma aberration (Ray Aberration) is H. In the field curvature, thick lines indicate sagittal and thin lines indicate tangential. The unit of dimension is mm.

[Example 1]
A fisheye lens as shown in FIG. 1 was designed. In FIG. 1, 1 is a first lens, a concave meniscus lens having a concave surface facing the image side, 2 is a second lens, a concave lens having a concave surface facing the image side, and 3 is a third lens. A cemented lens having a convex or concave refractive power, and the first lens 1, the second lens 2, and the third lens 3 constitute a front group. Reference numeral 4 denotes a fourth lens, 5 denotes a fifth lens, which is a cemented lens, and 6 denotes a sixth lens, which is a cemented lens. The fourth lens 4, the fifth lens 5, and the sixth lens 6 constitute a rear group. is doing. 7 is a filter, and 8 is an image plane. The light rays indicate an incident angle of 0 and a maximum (the same applies to the following lens diagrams).

  The design data of this fisheye lens is shown in Table 1, and the aberration diagram is shown in FIG. A parallel plane member having an integrated function such as a color filter, a CCD cover glass, and a low pass filter is included in the vicinity of the focal point (17th and 18th surfaces). The positions after the 16th surface are not defined. When focusing is required, the entire payout or 1 to 16 faces may be drawn. In each table, surface number 8 is an aperture stop (not shown). R = 0 indicates a plane.

In this fisheye lens, the above-mentioned conditions (1) to (4) and fou were as follows.
dx / dY = 0.135
V = -12.168%
fF = -0.912f
R = 1.198f
fou = -1.298f
As shown in FIG. 2, all the aberrations except for the distortion aberration are in a very small range, and the distortion aberration increases rapidly as the incident angle increases and has good performance as a fisheye lens. You can see that
(Table 1)

[Example 2]
A fisheye lens as shown in FIG. 3 was designed. In the drawings showing the following lens systems, the respective reference numerals are the same as those shown in FIG. In FIG. 3, the fourth lens 4 is also a cemented lens. The shape of the filter 7 differs depending on each figure. The design data of this fisheye lens is shown in Table 2, and the aberration diagram is shown in FIG. Near the focal point (18 to 20 surfaces) are a color filter, a CCD cover glass, and a low pass filter. The positions of these parallel plane members in the optical axis direction and changes in thickness, refractive index, dispersion, etc. are not significantly different in terms of aberration performance. There is no big difference even if all or part is missing. The positions of the parallel plane members after the 17th surface are not defined. When focusing is required, the entire payout or 1 to 17 faces may be drawn.

In this fisheye lens, the above-mentioned conditions (1) to (4) and fou were as follows.
dx / dY = 0.144
V = -12.877%
fF = -0.986f
R = 1.082f
fou = -1.019f
As can be seen from FIG. 4, all the aberrations except for the distortion are in a very small range, and the distortion increases sharply on the negative side as the incident angle increases and has good performance as a fisheye lens. You can see that
(Table 2)

[Example 3]
A fisheye lens as shown in FIG. 5 was designed. The design data of this fisheye lens is shown in Table 3, and the aberration diagram is shown in FIG.

In this fisheye lens, the above-mentioned conditions (1) to (4) and fou were as follows.
dx / dY = 0.143
V = -12.200%
fF = -0.930f
R = 1.215f
fou = -1.239f
As can be seen from FIG. 6, all the aberrations except distortion are within a very small range, and the distortion increases sharply on the negative side as the incident angle increases and has good performance as a fisheye lens. You can see that
(Table 3)

[Example 4]
A fisheye lens as shown in FIG. 7 was designed. The design data of this fisheye lens is shown in Table 4, and the aberration diagram is shown in FIG. In this fisheye lens, the conditions (1) to (4) and fou described above were as follows.
dx / dY = 0.071
V = -11.832%
fF = -0.940f
R = 1.270f
fou = -1.317f
As can be seen from FIG. 8, all the aberrations except for the distortion are within a very small range, and the distortion increases sharply on the negative side as the incident angle increases and has good performance as a fisheye lens. You can see that
(Table 4)

[Example 5]
A fisheye lens as shown in FIG. 9 was designed. The design data of this fisheye lens is shown in Table 5, and the aberration diagram is shown in FIG. In this fisheye lens, the above-mentioned conditions (1) to (4) and fou were as follows.
dx / dY = 0.060
V = -11.718%
fF = -0.908f
R = 1.309f
fou = -1.363f
As can be seen from FIG. 10, all the aberrations except distortion are within a very small range, and the distortion increases sharply on the negative side as the incident angle increases and has good performance as a fisheye lens. You can see that
(Table 5)

  In each of the above embodiments, a single wide-angle optical system has a very small field of view and a wide field of view exceeding 180 degrees, and on top of that, high resolving power is maintained over the entire field of view and the illuminance is maintained to the periphery. A lens suitable for foveal optics with a brightness of about F2.8 was realized.

It is sectional drawing of the lens system which is 1st Example of this invention. It is an aberration diagram of the first embodiment of the present invention. It is sectional drawing of the lens system which is 2nd Example of this invention. It is an aberration diagram of the second embodiment of the present invention. It is sectional drawing of the lens system which is 3rd Example of this invention. It is an aberration diagram of the third embodiment of the present invention. It is sectional drawing of the lens system which is 4th Example of this invention. It is an aberration diagram of the fourth embodiment of the present invention. It is sectional drawing of the lens system which is 5th Example of this invention. It is an aberration diagram of the fifth example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st lens, 2 ... 2nd lens, 3 ... 3rd lens, 4 ... 4th lens, 5 ... 5th lens, 6 ... 6th lens, 7 ... Filter, 8 ... Image plane

Claims (8)

A front group consisting of a total of three groups of two concave lenses having a concave surface facing the image side from the object side, and a cemented lens having a convex or concave refractive power as a whole, with the concave surface facing the image side, and three groups A fish-eye lens composed of a rear group consisting of convex lenses, including one or more pairs of cemented lenses in the front group and two or more groups in the rear group, and at least the first surface of the first concave lens in the front group is an aspheric surface, A fisheye lens having an incident angle of 60 degrees or more, which satisfies the following conditions.
(1) The first aspherical surface of the front group first concave lens is expressed by

In the range of Y _max >Y> 0.5f, dx / dY> 0
However, in the aspherical expression, X represents the optical axis direction, Y represents the coordinate in the direction perpendicular to the optical axis, the intersection of the optical axis and the first surface vertex of the first concave lens is the origin, and the optical axis is the rotation center. Rotating aspheric surface. Y _max is the maximum effective radius of the lens, R 1 is the radius of curvature of the first surface of the first concave lens, f is the focal length of the entire lens system, and κ, A, B, C, D, E, and F are constants. It is.
(2) When h = f * sinω is taken as a reference scale for the lens projection function, the distortion amount V when the incident angle ω = 60 degrees is −10% ≧ V ≧ −16%.
However, V = (H−h) * 100 / h (%), and H represents the height of the image from the optical axis when the incident angle ω = 60 degrees. The fisheye lens according to claim 1, wherein the following (3) and (4) are satisfied.
(3) When the focal length of the front group is set to fF, -0.8f>fF> -1.5f
(4) The curvature radius R of the cemented surface of the second group convex lens in the rear group is 1.0f <R <1.4f. The second convex lens in the rear group is a cemented lens of concave and convex two lenses in order from the object side, and the concave lens is a lens made of a transmissive member having a higher refractive index and higher dispersion than the convex lens on the image side. The fisheye lens according to claim 1 or 2, wherein -1.5f <fou <-0.8f when fou is satisfied. The third lens in the rear group is a cemented lens composed of two concave lenses in order from the object side, and the concave lens is a lens made of a transmissive member having a higher refractive index and higher dispersion than the convex lens. The fisheye lens according to claim 2. A fisheye lens according to any one of claims 1 to 4, having a function of acquiring an image with an electronic imaging device, and at least one of a pan mechanism, a tilt mechanism, and a rotation mechanism. An imaging device having a mechanism and capable of being operated by an electrical signal or by mechanical means. A fisheye lens according to any one of claims 1 to 4, further comprising an electronic imaging device, and further recording or storing at least one of captured images, time, direction, and own coordinates. An image pickup apparatus having a function, a function of identifying a subject, and a function of directing a target near the center of the field of view according to a self signal or an external signal. 5. The imaging according to claim 1, wherein a plurality of fish-eye lenses having the same specification are used, and at least distance information of a specific place can be acquired using parallax. apparatus. An imaging apparatus using a plurality of fisheye lenses according to any one of claims 1 to 4, wherein the multi-eye has a convergence mechanism.

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