JP5833357B2 - Super wide-angle lens system - Google Patents

Description

  The present invention relates to a lens used in a digital camera, a silver salt camera, a video camera, and the like, and is a super wide-angle lens system having a shooting angle of view exceeding 120 °, but has a long back focus and a large image circle. The present invention relates to an ultra-wide-angle lens system that employs a high-performance inner focus method that is suitable for an interchangeable lens and has a small aberration variation due to focusing.

  Conventionally, an ultra-wide-angle lens system having an angle of view exceeding 120 ° is described in, for example, the following patent documents.

  Patent Document 1 discloses a wide-angle lens having an angle of view exceeding 120 °.

  Patent Documents 2 and 3 disclose an ultra-wide-angle lens system that employs an inner focus and has an angle of view exceeding 120 °.

JP 2001-124985 A

JP 2005-106878 A

Japanese Patent Application No. 2010-093913 (unpublished)

  The wide-angle lens described in Patent Document 1 has a problem that the back focus is too short to be adapted as a lens system for a single-lens reflex camera.

  The super wide-angle lens system described in Patent Document 2 has a problem that the peripheral light amount becomes insufficient when applied to a digital camera.

  In order to improve the shortage of peripheral light, it is generally necessary to increase the lens diameter.

  However, the super wide-angle lens system described in Patent Document 2 does not employ a large-aperture aspherical lens for the first lens group with a large incident angle, and it is difficult to correct aberrations in peripheral performance. Since the decentering sensitivity of the four lens groups is large and it is difficult to increase the lens diameter of the fourth lens group, there remains a problem that a sufficient amount of peripheral light cannot be secured.

  Further, the super wide-angle lens system described in Patent Document 2 has a problem that the decentering sensitivity of the fourth lens group and the like is large, and it is not easy to assemble the lens frame.

  The super wide-angle lens system described in Patent Document 2 is a super-wide-angle zoom lens, and at the wide-angle end side, it is intended to reduce the performance degradation at the periphery of the screen. As a result of emphasizing the correction of lateral chromatic aberration, the problem of insufficient correction of axial chromatic aberration remained.

  Similarly, Patent Document 3 is an ultra-wide-angle lens system with an angle of view exceeding 120 °, and the lens system is compact as a whole, and is characterized by little aberration fluctuation due to focusing.

  Of course, the present invention can be applied to a 35 mm format interchangeable lens having a large image circle. However, the APS-C format is also intended to be compact while being high performance.

  In addition, by appropriately controlling the ratio of the focal lengths of the first A lens group and the first B lens group, an optical system has been realized in which the entire length is made compact, the aberration fluctuation due to focusing is small, and the shooting distance is short. When applied to a 35 mm format interchangeable lens having a large circle, it has been difficult to achieve a sufficiently high performance when, for example, realizing a wide field angle with a field angle exceeding 120 °.

  The present invention solves the above-described problems, and is an ultra-wide-angle lens system having a shooting angle of view exceeding 120 °, but is suitable for a 35 mm format interchangeable lens having a long back focus and a large image circle. An object is to provide a high-performance ultra-wide-angle lens system.

In order to achieve the above object, the super wide-angle lens system embodying the present invention comprises, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power. The lens group G1 includes a first A lens group G1A having a negative refractive power and a first B lens group G1B having a negative refractive power. The first A lens group G1A is a first negative meniscus lens in order from the object side. Lens L
1. The first B lens group G1B includes a negative meniscus lens L3 having at least one aspheric surface on the most object side, and the second lens group G2 includes a second A lens group G2A, a second B lens group G2B, The second lens group G2C is configured to move the first B lens group G1B to the object side during focusing and perform the first lens group G1 and the second A lens during zooming from the wide-angle end side to the telephoto end side. The distance between the group G2A decreases, the distance between the second A lens group G2A and the previous second B lens group G2CB decreases, and the distance between the previous second B lens group G2B and the second C lens group G2C increases.
The following conditions are satisfied.
(1) 1.5 <| f1A / fw | <2.5
(2) 3.0 <f1B / f1A <6.0
(3) 2.0 <f2 / fw <5.0
However,
fw: focal length of the entire lens system at the wide angle end f1A: focal length of the first A lens group G1A f1B: focal length of the first B lens group G1B f2: focal length of the second lens group G2 at the wide angle end

The super wide-angle lens system according to the present invention further includes a positive single lens L2asp having at least one aspheric surface on the most image plane side in the second lens group G2 in the above invention. It is characterized by satisfying.
(4) 1.0 <f2asp / f2 <7.0
However,
f2asp: focal length of positive single lens L2asp having an aspheric surface on at least one surface in second lens group G2 f2: focal length of second lens group G2 at the wide angle end

Furthermore, the super wide-angle lens system embodying the present invention is characterized in that, in the above invention, the following conditions are satisfied.
  (5) 2.0 <f2A / fw <5.0
  (6) 5.0 <| f2C / fw |
However,
  fw: focal length of the entire lens system at the wide-angle end
  f2A: focal length of the second A lens group G2A
  f2C: focal length of the second C lens group G2C

Further, in the super wide-angle lens system according to the present invention, in the above-described invention, the second A lens group G2A is divided into a front second A lens group front group G2AF sandwiching the aperture unit, and a rear second A lens group rear group G2AR. The following conditions are satisfied.
  (7) 2.5 <| f2AF / f1 | <10.0
  (8) 1.0 <S / D <10.0
However,
  fw: focal length of the entire lens system at the wide-angle end
  f1: Focal length of the first lens group G1
  f2AF: focal length of front group G2AF
  D: Aperture aperture diameter
  S: Distance between principal points of front group G2AF and rear group G2AR

Furthermore, the super wide-angle lens system embodying the present invention is characterized in that, in the above invention, the following conditions are satisfied.
  (9) 2.0 <f2B / fw <10.0
However,
  fw: focal length of the entire lens system at the wide-angle end
  f2B: Focal length of the second B lens group G2B

Furthermore, in the super wide-angle lens system according to the present invention, in the above invention, the second C lens group G2C includes a cemented negative lens unit L2CJoin including at least one negative lens and at least one positive lens, and the following conditions are satisfied. It is characterized by satisfying.
  (10) -15.0 <f2CJoin / fw <-2.0
However,
  fw: focal length of the entire lens system at the wide-angle end
  f2CJoin: focal length of the cemented negative lens unit L2CJoin in the second C lens group G2C

Furthermore, the super wide-angle lens system embodying the present invention is characterized in that, in the above invention, the following conditions are satisfied.
  (11) Nd2CN> 1.8
  (12) Vd2CP> 80
However,
  Nd2CN: Refractive index of at least one negative lens in the cemented negative lens unit L2CJoin
  Vd2CP: Abbe number of at least one positive lens in the cemented negative lens unit L2CJoin

  According to the super wide-angle lens system embodying the present invention, it is a lens system used for a digital camera, a silver salt camera, a video camera, etc. Therefore, it is possible to provide an ultra-wide-angle lens system that is suitable for an interchangeable lens having a long image circle and a large image circle, and that employs a high-performance inner focus system that has little aberration fluctuation due to focusing.

Cross-sectional view of the super wide-angle lens system of Reference Example 1 at infinity Longitudinal aberration diagram of the super wide-angle lens system of Reference Example 1 at infinity Longitudinal aberration diagram of the super wide-angle lens system of Reference Example 1 at a magnification of 1:40 Transverse aberration diagram at infinity of the super wide-angle lens system of Reference Example 1 Lateral aberration diagram of the super wide-angle lens system of Reference Example 1 at an imaging magnification of 1:40 Lens cross-sectional view at infinity at the wide-angle end of the super-wide-angle lens system of Example 2 Longitudinal aberration diagram at infinity of the wide-angle end of the super-wide-angle lens system of Example 2 Longitudinal aberration diagram of the super wide-angle lens system of Example 2 at an imaging magnification of 1:40 at the wide-angle end Longitudinal aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 2 Longitudinal aberration diagram at the intermediate focal length photographing magnification of 1:40 in the super wide-angle lens system of Example 2 Longitudinal aberration diagram at infinity of the telephoto end of the super wide-angle lens system of Example 2 Longitudinal aberration diagram at the telephoto end of the super wide-angle lens system of Example 2 at a magnification of 1:40 Lateral aberration diagram of the super-wide-angle lens system of Example 2 at infinity at the wide-angle end Lateral aberration diagram of the super wide-angle lens system of Example 2 at an imaging magnification of 1:40 at the wide-angle end Transverse aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 2 Lateral aberration diagram of the super wide-angle lens system of Example 2 at an intermediate focal length at an imaging magnification of 1:40 Transverse aberration diagram at infinity at the telephoto end of the super wide-angle lens system of Example 2 Lateral aberration diagram of the super wide-angle lens system of Example 2 at a magnification of 1:40 at the telephoto end Lens cross-sectional view at infinity at the wide-angle end of the super-wide-angle lens system of Example 3 Longitudinal aberration diagram at infinity of the wide-angle end of the super-wide-angle lens system of Example 3 Longitudinal aberration diagram at the wide-angle end photographing magnification of 1:40 in the super-wide-angle lens system of Example 3 Longitudinal aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 3 Longitudinal aberration diagram of the super wide-angle lens system of Example 3 at an intermediate focal length at an imaging magnification of 1:40 Longitudinal aberration diagram of the super wide-angle lens system of Example 3 at infinity at the telephoto end Longitudinal aberration diagram at the telephoto end of the super wide-angle lens system of Example 3 at a magnification of 1:40 Lateral aberration diagram of the super wide-angle lens system of Example 3 at infinity at the wide-angle end Lateral aberration diagram of the super-wide-angle lens system of Example 3 at an imaging magnification of 1:40 at the wide-angle end Transverse aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 3 Lateral aberration diagram of the super wide-angle lens system of Example 3 at an intermediate focal length at an imaging magnification of 1:40 Transverse aberration diagram at infinity of the telephoto end of the super wide-angle lens system of Example 3 Lateral aberration diagram of the super wide-angle lens system of Example 3 at a telephoto end at a magnification of 1:40 Lens cross-sectional view at infinity at the wide-angle end of the super-wide-angle lens system of Example 4 Longitudinal aberration diagram at infinity of the wide-angle end of the super-wide-angle lens system of Example 4 Longitudinal aberration diagram at the photographing magnification of 1:40 at the wide angle end of the super wide angle lens system according to Example 4 Longitudinal aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 4 Longitudinal aberration diagram at the intermediate focal length photographing magnification of 1:40 in the super wide-angle lens system of Example 4 Longitudinal aberration diagram at infinity of the telephoto end of the super wide-angle lens system of Example 4 Longitudinal aberration diagram at the telephoto end of the super wide-angle lens system of Example 4 at a magnification of 1:40 Lateral aberration diagram of the super wide-angle lens system of Example 4 at infinity at the wide-angle end Lateral aberration diagram of the super wide-angle lens system of Example 4 at a magnification of 1:40 at the wide-angle end Transverse aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 4 Lateral aberration diagram of the super wide-angle lens system of Example 4 at an intermediate focal length at an imaging magnification of 1:40 Lateral aberration diagram of the super wide-angle lens system of Example 4 at infinity at the telephoto end Lateral aberration diagram of the super wide-angle lens system of Example 4 at a magnification of 1:40 at the telephoto end Lens cross-sectional view at infinity at the wide-angle end of the super-wide-angle lens system of Example 5 Longitudinal aberration diagram at infinity of the wide angle end of the super wide angle lens system according to Example 5 Longitudinal aberration diagram at the wide-angle end photographing magnification of 1:40 in the super-wide-angle lens system of Example 5 Longitudinal aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 5 Longitudinal aberration diagram of the super wide-angle lens system of Example 5 at an intermediate focal length at an imaging magnification of 1:40 Longitudinal aberration diagram at infinity of the telephoto end of the super wide-angle lens system of Example 5 Longitudinal aberration diagram at the telephoto end of the super wide-angle lens system of Example 5 at a magnification of 1:40 Transverse aberration diagram at infinity of the wide-angle end of the super-wide-angle lens system of Example 5 Lateral aberration diagram of the super wide-angle lens system of Example 5 at a magnification of 1:40 at the wide-angle end Transverse aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 5 Lateral aberration diagram of the super wide-angle lens system of Example 5 at an intermediate focal length at an imaging magnification of 1:40 Transverse aberration diagram at infinity of the telephoto end of the super wide-angle lens system of Example 5 Lateral aberration diagram of the super wide-angle lens system of Example 5 at a magnification of 1:40 at the telephoto end Lens cross-sectional view at infinity at the wide-angle end of the super-wide-angle lens system of Example 6 Longitudinal aberration diagram at infinity of the wide-angle end of the super-wide-angle lens system of Example 6 Longitudinal aberration diagram at the wide-angle end photographing magnification of 1:40 in the super-wide-angle lens system of Example 6 Longitudinal aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 6 Longitudinal aberration diagram at the intermediate focal length photographing magnification of 1:40 in the super wide-angle lens system of Example 6 Longitudinal aberration diagram at infinity of the telephoto end of the super wide-angle lens system of Example 6 Longitudinal aberration diagram at the telephoto end of the super wide-angle lens system of Example 6 at a magnification of 1:40 Lateral aberration diagram of the super wide-angle lens system of Example 6 at infinity at the wide-angle end Lateral aberration diagram of the super wide-angle lens system of Example 6 at a wide-angle end photographing magnification of 1:40 Transverse aberration diagram at infinity of the intermediate focal length of the super wide-angle lens system of Example 6 Lateral aberration diagram of the super wide-angle lens system of Example 6 at an intermediate focal length at an imaging magnification of 1:40 Transverse aberration diagram at infinity at the telephoto end of the super wide-angle lens system of Example 6 Lateral aberration diagram of the super wide-angle lens system of Example 6 at a magnification of 1:40 at the telephoto end

  As can be seen from the lens configuration diagrams shown in FIGS. 1, 6, 19, 32, 45, and 58, the super wide-angle lens system of the present invention is a first lens having a negative refractive power in order from the object side. The first lens group G1 includes a first lens group G1A having a negative refractive power, a first B lens group G1B having a negative refractive power, and further includes a second lens group G2 having a positive refractive power. The first A lens group G1A is composed of, in order from the object side, a first lens L1 of a negative meniscus lens and a second lens L2 of a negative meniscus lens having an aspheric surface on at least one surface, and the first B lens group G1B is the most object A negative meniscus lens L3 having an aspheric surface on at least one surface is provided on the side, and the first B lens group G1B is moved to the object side during focusing.

  An object of the present invention is to provide a super wide-angle lens system having an angle of view exceeding 120 °, and it is important to appropriately guide a light beam having a large incident angle at a peripheral angle of view.

  In addition, in the ultra-wide-angle lens system, a retrofocus type is preferable in order to ensure sufficient back focus, and it is necessary to increase the negative refractive power of the negative lens group located in front.

  Furthermore, it is necessary to set an appropriate inclination angle of the lens surface at the periphery of the lens in order to cope with the incident angle and the emission angle of the light beam having a large inclination at the peripheral field angle.

  Therefore, in the present invention, in the two negative meniscus lenses constituting the first A lens group G1A, appropriate refractive power is distributed, and as a whole, sufficient negative refractive power is obtained, and generation of astigmatism is suppressed. Aimed at a configuration that can.

  In addition, the first A lens group G1A is composed of only two negative meniscus lenses, so that the entire lens system can be made compact.

  Furthermore, an aspherical surface is adopted for at least one surface of the second lens L2 constituting the first A lens group G1A.

  Here, the setting of the refractive power of the negative meniscus lens will be described.

  In general, in a negative meniscus lens, a sufficient negative refractive power can be obtained by reducing the paraxial curvature of the convex surface on the object side and increasing the paraxial curvature of the concave surface on the image side. However, in the present invention, if the paraxial curvature of the object side lens surface of the second lens L2 is made too small, the incident angle with respect to the peripheral light beam at the periphery of the lens surface cannot be reduced, which is disadvantageous in aberration correction. Become.

  Therefore, in the present invention, while maintaining the paraxial curvature of the convex surface on the object side small, an aspheric surface is adopted for this lens surface, and by giving a strong positive refractive power toward the periphery of the lens diameter, An appropriate tilt angle of the lens surface with respect to the peripheral luminous flux at the lens peripheral portion can be obtained, and both negative refracting power and aberration correction effects can be obtained.

  In general, in order to increase the negative refractive power of the negative meniscus lens, it is effective to increase the paraxial curvature of the concave surface on the image plane side. However, if the negative refractive power of the negative meniscus lens is increased by increasing the paraxial curvature of the concave surface on the image surface side, the tilt angle of the lens surface at the periphery of the lens becomes tight, so the workability of the negative meniscus lens is reduced. Getting worse.

  Therefore, in the present invention, by adopting an aspherical surface on the image surface side of the negative meniscus lens, it is possible to appropriately control the tilt angle of the lens peripheral portion and correct aberrations appropriately for the peripheral luminous flux, The processability of the lens can be improved.

  Here, on the contrary, in order to weaken the refractive power of the negative meniscus lens, it is effective to increase the paraxial curvature of the convex surface on the object side. However, when the paraxial curvature of the object side lens surface is increased, the tilt angle of the lens surface with respect to the peripheral light flux at the lens peripheral portion is reduced, so that the processability of the lens is deteriorated.

  Therefore, in the present invention, by adopting an aspherical surface on the object side lens surface, the lens peripheral portion suitable for the peripheral luminous flux is obtained by bringing the inclination angle of the lens surface with respect to the luminous flux at the lens peripheral portion close to a vertical angle. The tilt angle of the lens surface can be obtained, and the workability can be improved while appropriately correcting the aberration with respect to the peripheral light flux.

  As described above, in the negative meniscus lens, by adopting an aspherical surface on either the object side or the image side, it is possible to appropriately control the negative refractive power and at the periphery of the lens with respect to the peripheral luminous flux. An appropriate inclination angle of the lens surface can be obtained, and appropriate aberration correction and lens processability can be taken into consideration.

  Further, in the present invention, among the lenses included in the first B lens group G1B used for focusing, the third lens L3 arranged closest to the object side also has a negative meniscus lens, like the first lens L1 and the second lens L2. Is adopted.

  An object of the present invention is to provide a super-wide-angle lens system having an angle of view exceeding 120 °, and two negative meniscus lenses of the first A lens group G1A for guiding a light beam to a peripheral light beam having a large inclination of an incident light beam. Is not sufficient, and the exit angle of the peripheral ray from the first A lens group G1A remains large. Therefore, it is necessary to further reduce the inclination of the incident light beam in the first B lens group G1B.

  Therefore, as with the first lens L1 and the second lens L2, a negative meniscus lens having a convex surface facing the object side is also adopted for the third lens L3.

  In this way, the incident angle with respect to the peripheral luminous flux can be reduced, and the aberration of the peripheral luminous flux can be sufficiently corrected while the focusing angle is changed with respect to the change in the incident angle of the light beam due to different shooting distances. A lens system with small aberration fluctuations can be obtained.

  Furthermore, in the third lens L3 as well as the second lens L2, by adopting an aspheric surface on at least one surface of the negative meniscus lens, an appropriate lens surface inclination angle with respect to the peripheral luminous flux is obtained. Aberration correction of the peripheral luminous flux can be sufficiently performed.

  In addition, an optical system with small aberration fluctuations can be obtained with respect to a change in the incident angle of a light beam due to a difference in shooting distance during focusing.

  An object of the present invention is to provide an ultra-wide-angle lens system having an angle of view exceeding 120 °, and appropriately balances aberrations at the center of the screen where the incident angle of the light greatly changes, the intermediate angle of view of the screen, and the periphery of the screen. This is very important.

  Therefore, in the present invention, by appropriately controlling the lens shape and the aspherical coefficient of the two negative meniscus lenses included in the first A lens group G1A, aberration variation due to focusing is achieved while maintaining aberration balance over the entire photographing screen. Take measures to reduce.

Therefore, the present invention is characterized in that the following conditional expressions (1) and (2) are satisfied.
(1) 1.5 <| f1A / fw | <2.5
(2) 3.0 <f1B / f1A <6.0
However,
fw: focal length of the entire lens system at the wide angle end f1A: focal length of the first A lens group G1A f1B: focal length of the first B lens group G1B

  Conditional expression (1) defines the ratio of the focal length of the first A lens group G1A to the focal length fw of the entire system of the retrofocus type wide-angle lens system in the super wide-angle lens system of the present invention.

  However, when the present invention is applied to a zoom lens, the focal length of the entire lens system at the zoom wide-angle end is adopted as the focal length of the entire lens system.

  Exceeding the lower limit of conditional expression (1) increases the negative refractive power of the first lens unit G1A, which is effective for making the entire lens system compact, but makes it difficult to correct field curvature. Since the thickness difference between the central portion and the peripheral portion tends to increase in the two lenses L2, the workability of the aspherical lens is deteriorated.

  When the upper limit of conditional expression (1) is exceeded, the negative refractive power of the first A lens group G1A becomes weak, and the lens diameter of the second lens L2 becomes large. As a result, in the second lens L2, the tilt angle becomes large at the peripheral part of the aspheric surface, so that the workability of the aspherical lens is deteriorated in order to perform sufficient aberration correction to the peripheral part of the screen.

  In particular, as the angle of view of the lens system is increased, the inclination angle of the second lens L2 is significantly increased in the periphery of the aspheric surface. Therefore, it is necessary to appropriately set the negative refractive power of the first A lens group G1A. is there.

  In the focusing of the super wide-angle lens system of the present invention, it is necessary to dispose a large-diameter negative meniscus lens in the first A lens group G1A. In addition, the occurrence of curvature of field due to focusing becomes a problem. By adopting an inner focus for focusing, an aberration correction effect due to floating is added.

  Conditional expression (2) defines the ratio between the focal length of the first A lens group G1A and the focal length of the first B lens group G1B in the super wide-angle lens system of the present invention.

  If the lower limit of conditional expression (2) is exceeded, the refractive power of the first B lens group G1B will increase, so that aberration fluctuations due to focusing will increase.

  In addition, the refractive power of the first A lens group G1A is reduced, the necessary and sufficient refractive power for appropriately refracting incident light having an angle of view exceeding 120 ° cannot be obtained, and the lens diameter of the second lens L2 is increased. Therefore, in order to perform sufficient aberration correction up to the periphery of the screen, the tilt angle becomes large at the periphery of the aspheric surface in the second lens L2, and the workability of the aspheric lens is deteriorated.

  In particular, as the angle of view of the lens system is increased, the inclination angle of the second lens L2 is significantly increased in the periphery of the aspheric surface. Therefore, it is necessary to appropriately set the negative refractive power of the first A lens group G1A. is there.

  If the upper limit of conditional expression (2) is exceeded, the refractive power of the first B lens group G1B decreases, and the focus movement amount during close-up shooting of the first B lens group G1B increases. As a result, it is necessary to increase the lens interval between the first A lens group G1A and the first B lens group G1B.

  By satisfying conditional expression (1) and conditional expression (2) simultaneously, the focal length of the first A lens group G1A and the focal length of the first B lens group G1B are appropriately controlled with respect to the focal length of the entire lens system. This makes it possible to reduce aberration fluctuations due to focusing while taking lens processing conditions into consideration, and sufficiently correct aberrations up to the periphery of the screen.

  In addition, since the super wide-angle lens system of the present invention is compatible with a camera system that requires sufficient back focus, such as a digital single-lens reflex camera, it is necessary to appropriately set the focal length of the second lens group G2. is there.

Therefore, the present invention is characterized in that the following conditional expression (3) is satisfied.
(3) 2.0 <f2 / fw <5.0
However,
fw: focal length of the entire lens system at the wide angle end f2: focal length of the second lens group G2 at the wide angle end

  Conditional expression (3) defines the ratio of the focal length of the second lens group G2 to the focal length of the entire lens of the retrofocus type wide-angle lens system in the super-wide-angle lens system.

  Here, when the present invention is applied to a zoom lens, the focal length fw of the entire lens system employs the focal length of the entire lens system at the zoom wide-angle end, and the focal length f2 of the second lens group G2 The focal length of the second lens group G2 at the wide angle end is adopted.

  If the lower limit of conditional expression (3) is exceeded, the focal length of the second lens group G2 is shortened, which is effective for making the entire lens system compact. However, since the curvature of each lens surface increases, the super-wide-angle lens system As a result, it becomes difficult to correct aberrations such as astigmatism and coma.

  If the upper limit of conditional expression (3) is exceeded, the focal length of the second lens group G2 becomes long, which is advantageous for aberration correction, but it is difficult to make the entire lens system compact.

  Furthermore, in the super wide-angle lens system of the present invention, the second lens group G2 is composed of a second A lens group G2A, a second B lens group G2B, and a second C lens group G2C, and the first lens group G1 and the second A lens group G2A. The distance between the second A lens group G2A and the second B lens group G2B is decreased, and the distance between the second B lens group G2B and the second C lens group G2C is increased. It is desirable to achieve zooming from the side to the telephoto end side.

Furthermore, in the present invention, in order to perform sufficient aberration correction, an aspherical surface is adopted as at least one surface of the positive single lens L2asp closest to the image plane in the second lens group G2, and the following conditional expression (4) It is desirable to satisfy
(4) 1.0 <f2asp / f2 <7.0
However,
f2asp: focal length of the positive single lens L2asp that is located closest to the image plane in the second lens group G2 and has an aspheric surface on at least one surface f2: focal length of the second lens group G2 at the wide angle end

  Here, when the present invention is applied to a zoom lens, the focal length f2 of the second lens group G2 is the focal length of the second lens group G2 at the zoom wide-angle end.

  In Patent Document 2, the lens unit closest to the image plane employs an aspherical surface in an optical system having a strong negative refractive power, thereby enabling effective aberration correction.

  However, since the second lens group G2 as a whole has a strong positive refractive power, if the lens unit closest to the image plane is a negative lens unit having an aspherical surface, the assembly accuracy of the lens barrel is increased due to the increased decentration sensitivity. Is difficult to maintain, and productivity problems arise.

Therefore, in the present invention, the lens unit closest to the image plane is a positive single lens L2asp having an aspheric surface on at least one surface, and its refractive power is appropriately set, so that a sufficient aberration correction effect can be obtained and the polarization can be obtained. It became possible to obtain a lens system with low core sensitivity.

Conditional expression (4) indicates that the focal length of the positive single lens L2asp having the most aspherical surface in the second lens group G2 with respect to the focal length of the second lens group G2 in the super wide-angle lens system of the present invention. The ratio is specified.

Condition (4) The focal length of the positive single lens L2asp becomes shorter than the lower limit of the refractive power of the positive single lens L2asp increases, since the refractive effect of peripheral light becomes strong, marginal rays by the aspherical surface The aberration correction effect is insufficient.

When the focal length of the positive single lens L2asp is increased beyond the upper limit of the conditional expression (4), the refractive power of the peripheral light beam emitted from the optical system positioned in front of the positive single lens L2asp increases. with respect to the optical beam, beam tilt change in exit angle and the incident angle when passing through the positive single lens L2asp increases, eccentricity sensitivity of the positive single lens L2asp increases.

  In the super wide-angle lens system of the present invention, the focal length of the second A lens group G2A is appropriately set, and the strong divergent light beam from the first lens group G1 is converged, so that the exit angle from the second A lens group G2A is substantially reduced. By setting afocal, it is possible to cut the upper light flare with an appropriate light height from the intermediate range by using the second A lens group G2A without cutting the peripheral light on the wide-angle end side.

  Furthermore, by appropriately setting the focal length of the second C lens group G2C, it is possible to appropriately control the eccentricity sensitivity of the second C lens group G2C while obtaining sufficient optical performance over the entire zoom range.

Therefore, it is desirable that the present invention further satisfies the following conditional expressions (5) and (6).
(5) 2.0 <f2A / fw <5.0
(6) 5.0 <| f2C / fw |
However,
fw: focal length of the entire lens system at the wide-angle end f2A: focal length of the second A lens group G2A f2C: focal length of the second C lens group G2C

  Conditional expression (5) defines the ratio of the focal length of the second A lens group G2A to the focal length of the entire lens system at the wide angle end in the super wide-angle lens system of the present invention.

  If the lower limit of conditional expression (5) is exceeded and the focal length of the second lens group G2A becomes shorter, it becomes necessary to increase the negative refractive power of the first lens group G1, making it difficult to correct coma and astigmatism. Become.

  When the focal length of the second A lens group G2A is increased beyond the upper limit of the conditional expression (5), the focal length of the second A lens group G2A is increased. Flare cut effect cannot be obtained.

  Conditional expression (6) defines the ratio of the focal length of the second C lens group G2C to the focal length of the entire lens system at the wide-angle end in the super wide-angle lens system of the present invention.

  In the conditional expression (6), when the second C lens group G2C has a positive refractive power, if the lower limit is exceeded, the positive refractive power of the second C lens group G2C becomes strong, and thus the curvature of each lens surface increases. By increasing the decentering sensitivity of the lens unit in the second C lens group G2C, the accuracy required for lens processing is extremely increased.

  In the conditional expression (6), when the second C lens group G2C has a negative refractive power, if the lower limit is exceeded, the negative refractive power of the second C lens group G2C becomes strong, and therefore the entire eccentricity of the second C lens group G2C. Sensitivity increases and productivity in assembling the lens barrel deteriorates.

Further, in the super wide-angle lens system of the present invention, the second A lens group G2A is divided into a front second A lens group front group G2AF and a rear second A lens group rear group G2AR with the aperture unit interposed therebetween. It is desirable to satisfy 7) and conditional expression (8).
(7) 2.5 <| f2AF / f1 | <10.0
(8) 1.0 <S / D <10.0
However,
fw: focal length of the entire lens system at the wide angle end f1: focal length of the first lens group G1 f2AF: focal length of the front group G2AF D: aperture stop diameter S: distance between principal points of the front group G2AF and the rear group G2AR

  An exit aperture is arranged between the front group G2AF and the rear group G2AR by appropriately setting the exit angle of the central light beam from the second group A front lens group G2AF and the optical path length of the second group A rear lens group G2AR. It is desirable.

  Conditional expression (7) defines the ratio of the focal length of the front group G2AF to the focal length of the first lens group G1 in the super wide-angle lens system of the present invention.

  If the lower limit of conditional expression (7) is exceeded, it becomes necessary to increase the distance between the first lens group G1 and the front group G2AF on the wide-angle side, leading to an increase in the total lens length.

  If the upper limit of conditional expression (7) is exceeded, the distance between the first lens group G1 and the front group G2AF becomes smaller on the wide angle side, which is advantageous for making the entire lens system compact, but the focus of the first lens group G1 Since the distance tends to decrease, there is a problem that sufficient performance cannot be obtained.

  Conditional expression (8) defines the distance between the principal points of the front group G2AF and the rear group G2AR in the super wide-angle lens system of the present invention.

  In the entire zoom range, the maximum light beam diameter of the lower light beam and the F number light beam are limited to the same height in the front group G2AF, and the maximum light beam diameter of the upper light beam and the F number light beam are equal in the rear group G2AR. By limiting to the above, appropriate flare cutting can be performed on each lens surface without reducing the peripheral light amount.

  Furthermore, by arranging the aperture stop at an appropriate position, the aperture stop can be arranged at the most appropriate position in the entire zoom range, so that it is possible to expect an improvement in the amount of peripheral light at the time of narrowing down.

  If the lower limit of conditional expression (8) is exceeded, a sufficient space cannot be secured before and after the aperture stop, and a sufficient optical path length cannot be secured for the peripheral luminous flux. The peripheral performance is degraded.

  If the upper limit of conditional expression (8) is exceeded, the optical path length increases between the front group G2AF and the rear group G2AR, leading to an increase in the total lens length.

Furthermore, in the super wide-angle lens system of the present invention, it is preferable that the following conditional expression (9) is satisfied.
(9) 2.0 <f2B / fw <10.0
However,
fw: focal length of the entire lens system at the wide-angle end f2B: focal length of the second B lens group G2B

  Conditional expression (9) defines the ratio of the focal length of the second lens group G2B to the focal length of the entire lens system at the wide-angle end in the super wide-angle lens system of the present invention.

  When the lower limit of conditional expression (9) is exceeded, the positive refractive power of the second B lens group G2B becomes strong, and the decentering sensitivity of the second B lens group G2B increases.

  When the upper limit of conditional expression (9) is exceeded, the refractive power of the second B lens group G2B becomes weak, the peripheral rays incident on the second C lens group G2C become high, and the eccentricity sensitivity of each lens unit in the second C lens group G2C is high. The degree is increased.

  Furthermore, in the super wide-angle lens system of the present invention, it is desirable that the second C lens group G2C has a cemented negative lens unit L2CJoin composed of at least one negative lens and at least one positive lens.

  In the super wide-angle lens system of the present invention, in order to correct aberrations such as chromatic aberration, it is indispensable to dispose a negative lens in the second C lens group G2C.

  However, if a negative lens is arranged in the second C lens group G2C where the exit angle of the peripheral luminous flux is large, the refractive power of the negative lens tends to be strong for aberration correction, and the decentering sensitivity of the negative lens increases. End up. In addition, the refractive power of the positive lens must be increased accordingly, and the decentering sensitivity of the positive lens also increases at the same time.

  Therefore, it is possible to reduce the decentration sensitivity while obtaining a sufficient aberration correction effect by cementing a negative lens having a strong refractive power and a positive lens and appropriately setting the focal length of the entire cemented negative lens unit. .

Therefore, it is desirable that the present invention further satisfies the following conditional expression (10).
(10) -15.0 <f2CJoin / fw <-2.0
However,
fw: focal length of the entire lens system at the wide-angle end f2CJoin: focal length of the cemented negative lens unit L2CJoin in the second C lens group G2C

  Conditional expression (10) defines the ratio of the focal length of the entire cemented negative lens unit L2CJoin in the second C lens group G2C to the focal length of the entire lens system at the wide angle end in the super wide-angle lens system of the present invention. is there.

  When the lower limit of conditional expression (10) is exceeded, the negative refractive power of the cemented negative lens unit L2CJoin becomes small, and the aberration correction effect becomes insufficient.

  When the upper limit of conditional expression (10) is exceeded, the negative refractive power of the cemented negative lens unit L2CJoin becomes strong, and the decentering sensitivity increases.

Furthermore, in the super wide-angle lens system of the present invention, it is desirable that the cemented negative lens unit L2CJoin in the second C lens group G2C satisfies the following conditional expressions (11) and (12).
(11) Nd2CN> 1.8
(12) Vd2CP> 80
However,
Nd2CN: Refractive index of at least one negative lens in the cemented negative lens unit L2CJoin Vd2CP: Abbe number of at least one positive lens in the cemented negative lens unit L2CJoin

  Conditional expression (11) defines the refractive index of the negative lens constituting the cemented negative lens unit L2CJoin in the second C lens group G2C, and conditional expression (12) is the negative junction in the second C lens group G2C. This defines the Abbe number of the positive lens constituting the lens unit L2CJoin.

  By making the refractive power of the negative lens constituting the cemented negative lens unit L2CJoin in the second C lens group G2C within the range of the conditional expression (11), the curvature of each lens surface is reduced while maintaining the refractive power of the negative lens. can do.

  Further, by setting the Abbe number of the positive lens constituting the cemented negative lens unit L2CJoin in the second C lens group G2C within the range of the conditional expression (12), it is possible to correct the lateral chromatic aberration which is a problem in the wide-angle lens. . Furthermore, while maintaining the refractive power of the cemented negative lens unit L2CJoin, the curvature of the cemented surface can be reduced, and the refractive power of each of the positive lens and the negative lens can be reduced.

Next, a lens configuration of an example according to the super wide-angle lens system of the present invention will be described. In the following description, the lens configuration is described in order from the object side to the image side.
Reference example 1

FIG. 1 is a lens configuration diagram of an imaging optical system according to Reference Example 1 of the present invention.

  The first lens group G1 includes a first A lens group G1A and a first B lens group G1B, and has a negative refractive power as a whole.

  The first A lens group G1A includes a negative meniscus lens L1 having a convex surface facing the object side and a negative meniscus lens L2 having a convex surface facing the object side, and has a negative refractive power as a whole.

  The object side lens surface of the negative meniscus lens L2 has a predetermined aspherical shape.

  The first B lens group G1B includes a negative meniscus lens L3 having a convex surface directed toward the object side, a biconcave lens L4, and a positive meniscus lens L5 having a convex surface directed toward the object side, and has a negative refracting power as a whole. Have. The first B lens group G1B moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, the object side lens surface of the negative meniscus lens L3 and the object side lens surface of the biconcave lens L4 each have a predetermined aspheric shape.

  The second lens group G2 includes an aperture stop, a positive meniscus lens L6 having a convex surface facing the object side, a cemented lens including a biconcave lens L7 and a biconvex lens L8, and a positive meniscus lens L9 having a concave surface facing the object side. A negative meniscus lens L10 having a negative meniscus lens L10 having a concave surface facing the object side and having a positive refractive power as a whole, a positive meniscus lens L11 having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side The lens includes a cemented lens having a negative refractive power as a whole, and a negative meniscus lens L14 having a concave surface facing the object side, and has a positive refractive power as a whole. .

  The object side lens surface of the negative meniscus lens L14 has a predetermined aspherical shape. In the present invention, the negative meniscus lens L14 is defined as L2asp.

  FIG. 6 is a lens configuration diagram of the imaging optical system according to Example 2 of the present invention.

  The first lens group G1 includes a first A lens group G1A and a first B lens group G1B, and has a negative refractive power as a whole.

  The first A lens group G1A includes a negative meniscus lens L1 having a convex surface facing the object side and a negative meniscus lens L2 having a convex surface facing the object side, and has a negative refractive power as a whole.

  In addition, both lens surfaces of the negative meniscus lens L2 have a predetermined aspherical shape.

  The first lens group G1B includes a negative meniscus lens L3 having a convex surface directed toward the object side, a biconcave lens L4, and a biconvex lens L5, and has a negative refracting power as a whole. The first B lens group G1B moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, both side lens surfaces of the negative meniscus lens L3 and both side lens surfaces of the biconcave lens L4 have predetermined aspherical shapes.

  The second lens group G2 includes a second A lens group G2A including a front group G2AF, an aperture stop, and a rear group G2AR, a second B lens group G2B, and a second C lens group G2C. Has negative refractive power.

  The front group G2AF includes a positive meniscus lens L6 having a convex surface directed toward the object side, and has a positive refractive power as a whole.

  The rear group G2AR includes a biconvex lens L7 and a negative meniscus lens L8 having a concave surface directed toward the object side. The cemented lens having negative refractive power as a whole, and a negative meniscus lens having a biconvex lens L9 and a concave surface directed toward the object side. And a cemented lens having a positive refractive power as a whole, and has a positive refractive power as a whole.

  The second B lens group G2B is composed of a biconvex lens L11 and a negative meniscus lens L12 having a concave surface facing the object side, and is composed of a cemented lens having a positive refractive power as a whole and a biconvex lens L13. Has positive refractive power.

  The second C lens group G2C includes a negative meniscus lens L14 having a convex surface directed toward the object side and a positive meniscus lens L15 having a convex surface directed toward the object side. The cemented lens having negative refractive power as a whole, and a concave surface facing the object side. And a positive meniscus lens L17 having a concave surface facing the object side, and has a negative refractive power as a whole.

  A predetermined compound aspherical lens is used for the object side lens surface of the positive meniscus lens L17. In the present invention, a cemented lens including the negative meniscus lens L14 and the positive meniscus lens L15 is defined as L2CJoin, and the positive meniscus lens L17 is defined as L2asp.

  FIG. 19 is a lens configuration diagram of the imaging optical system according to Example 3 of the present invention.

  The first lens group G1 includes a first A lens group G1A and a first B lens group G1B, and has a negative refractive power as a whole.

  The first A lens group G1A includes a negative meniscus lens L1 having a convex surface facing the object side and a negative meniscus lens L2 having a convex surface facing the object side, and has a negative refractive power as a whole.

  The object side lens surface of the negative meniscus lens L2 has a predetermined aspherical shape.

  The first B lens group G1B includes a negative meniscus lens L3 having a convex surface directed toward the object side, a biconcave lens L4, and a positive meniscus lens L5 having a convex surface directed toward the object side, and has a negative refracting power as a whole. Have. The first B lens group G1B moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, the object side lens surface of the negative meniscus lens L3 and the object side lens surface of the biconcave lens L4 each have a predetermined aspheric shape.

  The second lens group G2 includes a second A lens group G2A including a front group G2AF, an aperture stop, and a rear group G2AR, a second B lens group G2B, and a second C lens group G2C. Has positive refractive power.

  The front group G2AF includes a positive meniscus lens L6 having a convex surface directed toward the object side, and has a positive refractive power as a whole.

  The rear group G2AR includes a biconvex lens L7 and a negative meniscus lens L8 having a concave surface directed toward the object side. The cemented lens having negative refractive power as a whole, and a negative meniscus lens having a biconvex lens L9 and a concave surface directed toward the object side. And a cemented lens having a positive refractive power as a whole, and has a positive refractive power as a whole.

  The second B lens group G2B is composed of a biconvex lens L11 and a negative meniscus lens L12 having a concave surface facing the object side, and is composed of a cemented lens having a positive refractive power as a whole and a biconvex lens L13. Has positive refractive power.

  The second C lens group G2C includes a negative meniscus lens L14 having a convex surface directed toward the object side and a positive meniscus lens L15 having a convex surface directed toward the object side. The cemented lens having negative refractive power as a whole, and a concave surface facing the object side. And a positive meniscus lens L17 having a concave surface facing the object side, and has a negative refractive power as a whole.

  A predetermined compound aspherical lens is used for the object side lens surface of the positive meniscus lens L17. In the present invention, a cemented lens including the negative meniscus lens L14 and the positive meniscus lens L15 is defined as L2CJoin, and the positive meniscus lens L17 is defined as L2asp.

  FIG. 32 is a lens configuration diagram of the imaging optical system according to Example 4 of the present invention.

  The first lens group G1 includes a first A lens group G1A and a first B lens group G1B, and has a negative refractive power as a whole.

  The first A lens group G1A includes a negative meniscus lens L1 having a convex surface facing the object side and a negative meniscus lens L2 having a convex surface facing the object side, and has a negative refractive power as a whole.

  The object side lens surface of the negative meniscus lens L2 has a predetermined aspherical shape.

  The first B lens group G1B includes a negative meniscus lens L3 having a convex surface directed toward the object side, a biconcave lens L4, and a positive meniscus lens L5 having a convex surface directed toward the object side, and has a negative refracting power as a whole. Have. The first B lens group G1B moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, the object side lens surface of the negative meniscus lens L3 and the object side lens surface of the biconcave lens L4 each have a predetermined aspheric shape.

  The second lens group G2 includes a second A lens group G2A including a front group G2AF, an aperture stop, and a rear group G2AR, a second B lens group G2B, and a second C lens group G2C. Has positive refractive power.

  The front group G2AF includes a positive meniscus lens L6 having a convex surface directed toward the object side, and has a positive refractive power as a whole.

  The rear group G2AR includes a biconvex lens L7 and a negative meniscus lens L8 having a concave surface facing the object side. The cemented lens having negative refractive power as a whole, and a positive meniscus lens L9 having a convex surface facing the object side and the object side And a negative meniscus lens L10 having a concave surface facing the lens, and a cemented lens having a positive refractive power as a whole, and has a positive refractive power as a whole.

  The second B lens group G2B is composed of a biconvex lens L11 and a negative meniscus lens L12 having a concave surface facing the object side, and is composed of a cemented lens having a positive refractive power as a whole and a biconvex lens L13. Has positive refractive power.

  The second C lens group G2C includes a negative meniscus lens L14 having a convex surface directed toward the object side and a positive meniscus lens L15 having a convex surface directed toward the object side. The cemented lens having negative refractive power as a whole, and a concave surface facing the object side. And a positive meniscus lens L17 having a concave surface facing the object side, and has a positive refractive power as a whole.

  A predetermined compound aspherical lens is used for the object side lens surface of the positive meniscus lens L17. In the present invention, a cemented lens including the negative meniscus lens L14 and the positive meniscus lens L15 is defined as L2CJoin, and the positive meniscus lens L17 is defined as L2asp.

  FIG. 45 is a lens configuration diagram of the imaging optical system according to Example 5 of the present invention.

  The first lens group G1 includes a first A lens group G1A and a first B lens group G1B, and has a negative refractive power as a whole.

  The first A lens group G1A includes a negative meniscus lens L1 having a convex surface facing the object side and a negative meniscus lens L2 having a convex surface facing the object side, and has a negative refractive power as a whole.

  The object side lens surface of the negative meniscus lens L2 has a predetermined aspherical shape.

  The first B lens group G1B includes a negative meniscus lens L3 having a convex surface directed toward the object side, a biconcave lens L4, and a positive meniscus lens L5 having a convex surface directed toward the object side, and has a negative refracting power as a whole. Have. The first B lens group G1B moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, both side lens surfaces of the negative meniscus lens L3 and the object side lens surface of the biconcave lens L4 have predetermined aspherical shapes.

  The second lens group G2 includes a second A lens group G2A including a front group G2AF, an aperture stop, and a rear group G2AR, a second B lens group G2B, and a second C lens group G2C. Has positive refractive power.

  The front group G2AF includes a positive meniscus lens L6 having a convex surface directed toward the object side, and has a positive refractive power as a whole.

  The rear group G2AR includes a biconvex lens L7 and a negative meniscus lens L8 having a concave surface directed toward the object side. The cemented lens having negative refractive power as a whole, and a negative meniscus lens having a biconvex lens L9 and a concave surface directed toward the object side. And a cemented lens having a positive refractive power as a whole, and has a positive refractive power as a whole.

  The second B lens group G2B is composed of a biconvex lens L11 and a negative meniscus lens L12 having a concave surface facing the object side, and is composed of a cemented lens having a positive refractive power as a whole and a biconvex lens L13. Has positive refractive power.

  The second C lens group G2C includes a concave lens L14 having a flat surface facing the object side and a positive meniscus lens L15 having a convex surface facing the object side. The cemented lens having negative refractive power as a whole, and the concave surface facing the object side. The positive meniscus lens L16 and the positive meniscus lens L17 having a concave surface facing the object side have a positive refractive power as a whole.

  A predetermined compound aspherical lens is used for the object side lens surface of the positive meniscus lens L17. In the present invention, a cemented lens including the concave lens L14 and the positive meniscus lens L15 is defined as L2CJoin, and the positive meniscus lens L17 is defined as L2asp.

  FIG. 58 is a lens configuration diagram of the imaging optical system according to Example 6 of the present invention.

  The first lens group G1 includes a first A lens group G1A and a first B lens group G1B, and has a negative refractive power as a whole.

  The first A lens group G1A includes a negative meniscus lens L1 having a convex surface facing the object side and a negative meniscus lens L2 having a convex surface facing the object side, and has a negative refractive power as a whole.

  The object side lens surface of the negative meniscus lens L2 has a predetermined aspherical shape.

  The first lens group G1B includes a negative meniscus lens L3 having a convex surface directed toward the object side, a biconcave lens L4, and a biconvex lens L5, and has a negative refracting power as a whole. The first B lens group G1B moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, both side lens surfaces of the negative meniscus lens L3 and both side lens surfaces of the biconcave lens L4 have predetermined aspherical shapes.

  The second lens group G2 includes a second A lens group G2A including a front group G2AF, an aperture stop, and a rear group G2AR, a second B lens group G2B, and a second C lens group G2C. Has positive refractive power.

  The front group G2AF includes a positive meniscus lens L6 having a convex surface directed toward the object side, and has a positive refractive power as a whole.

  The rear group G2AR includes a biconvex lens L7 and a negative meniscus lens L8 having a concave surface facing the object side. The cemented lens having negative refractive power as a whole, and a positive meniscus lens L9 having a concave surface facing the object side and the object side And a negative meniscus lens L10 having a concave surface facing the lens, and a cemented lens having a positive refractive power as a whole, and has a positive refractive power as a whole.

  The second B lens group G2B includes a convex lens L11 having a plane facing the object side and a negative meniscus lens L12 having a concave surface facing the object side, and includes a cemented lens having a positive refractive power as a whole and a biconvex lens L13. And has a positive refractive power as a whole.

  The second C lens group G2C includes a negative meniscus lens L14 having a convex surface facing the object side and a biconvex lens L15. The cemented lens having negative refractive power as a whole, and a positive meniscus lens L16 having a concave surface facing the object side. And a positive meniscus lens L17 having a concave surface facing the object side, and has a positive refractive power as a whole.

  The object side lens surface of the positive meniscus lens L17 has a predetermined aspheric shape. In the present invention, a cemented lens including the negative meniscus lens L14 and the positive meniscus lens L15 is defined as L2CJoin, and the positive meniscus lens L17 is defined as L2asp.

  Specific numerical data of numerical examples corresponding to the respective embodiments described above are shown below.

  In [Overall specifications] of each numerical example, f indicates a focal length, Fno indicates an F number, 2ω indicates a full angle of view, and D indicates an open aperture diameter.

  In [Lens Specifications], the first column number is the lens surface number from the object side, the second column r is the radius of curvature of each lens surface, the third column d is the lens surface spacing, and the fourth column nd is The refractive index for the d-line (wavelength 587.56 nm), Vd indicates the Abbe number for the d-line (wavelength 587.56 nm).

  * (Asterisk) attached to the lens surface number in the first row indicates that the lens surface shape is an aspherical surface. The “aperture stop” in the second row represents the position of the stop surface, and Bf in the third row represents the back focus.

  In [Variable interval for zooming at infinity shooting] and [Variable interval for zooming equivalent to 40x shooting], the focal length f is the focal length at INF, Bf is the back focus, and dn is the lens spacing on each surface. D0 represents the distance from the subject to the lens first surface.

  [Aspheric coefficient] indicates an aspheric coefficient that gives the aspheric shape of the lens surface marked with * in [Lens Specifications]. The shape of the aspheric surface is y for the displacement from the optical axis in the direction perpendicular to the optical axis, z for the displacement (sag amount) from the intersection of the aspheric surface and the optical axis in the optical axis direction, and r for the radius of curvature of the reference spherical surface. When the conic coefficient is K, the fourth order, the sixth order, the eighth order, the tenth order, and the twelfth order aspherical coefficient are set as A4, A6, A8, A10, and A12, the coordinates of the aspherical surface are expressed by the following equations. Shall be.

  In addition, in the values of all the following specifications, the stated focal length f, radius of curvature r, lens surface interval d, and other length units are in millimeters (mm) unless otherwise specified. In the system, the same optical performance can be obtained even in proportional expansion and proportional reduction, and the present invention is not limited to this.

  In addition, a list of values of conditional expressions in the respective embodiments described above is shown below.

Numerical example 1
Unit: mm
[Overall specifications]
INF 1:40
f 12.45 12.41
Fno 4.64 4.63
2ω 122.63 121.85
D 11.00 11.00

[Lens Specifications]
rd nd Vd
[0] d0
[1] 36.7940 1.9000 1.91082 35.25
[2] 24.6540 9.5940
[3] * 67.2540 2.5000 1.83441 37.20
[4] 20.2300 d4
[5] * 27.7900 1.5000 1.69350 53.20
[6] 17.6000 6.6000
[7] * -200.0000 1.4000 1.49710 81.56
[8] 45.3190 0.5200
[9] 35.4500 3.1080 2.00099 29.14
[10] 66.8830 d10
[11] (Aperture stop) 1.2400
[12] 13.5460 3.0060 1.43700 95.10
[13] 99.9010 0.5690
[14] -742.8420 0.8000 1.77250 49.62
[15] 13.8350 3.4410 1.71736 29.50
[16] -43.9900 2.5440
[17] -39.4510 8.2000 1.43700 95.10
[18] -10.3780 0.8500 2.00099 29.14
[19] -33.7400 4.9610
[20] 21.9660 3.9190 1.43700 95.10
[21] 45.6630 0.2300
[22] 29.1280 0.9000 2.00099 29.14
[23] 18.1000 8.5480 1.43700 95.10
[24] -90.5440 2.6870
[25] * -89.3380 3.0280 1.49710 81.56
[26] -26.0180 Bf

[Variable interval when shooting distance changes]
d0 INF 478.81
d4 11.7420 10.9419
d10 28.8970 29.6972
Bf 38.30 38.30

[Aspherical data]
3 surfaces 5 surfaces 7 surfaces 25 surfaces
K 0.0000 -0.1570 0.0000 0.0000
A4 2.3055E-05 -3.2954E-05 2.8341E-05 -3.1920E-05
A6 -3.7379E-08 1.6412E-07 -1.4913E-07 -6.2522E-08
A8 3.6994E-11 1.8549E-10 4.2131E-10 2.4721E-10
A10 -1.3811E-14 -1.9095E-12 -3.6457E-13 -1.5352E-12
A12 4.8126E-19 3.7368E-15 0.0000E + 00 0.0000E + 00

Numerical example 2
Unit: mm
[Overall specifications]
f 11.38 15.03 21.30
Fno 4.66 5.07 5.88
2ω 126.82 111.71 89.18
D 10.30 10.30 10.30

[Lens Specifications]
rd nd Vd
[0] d0
[1] 36.8930 1.6000 2.00060 25.46
[2] 23.2270 10.3800
[3] * 73.6570 2.5000 1.77250 49.62
[4] * 19.1300 d4
[5] * 1000.0000 1.3000 1.69350 53.20
[6] * 37.0300 5.7860
[7] * -1000.0000 1.1000 1.77250 49.62
[8] * 32.3480 0.5000
[9] 46.1710 4.2300 2.00099 29.14
[10] -130.4180 d10
[11] 18.3590 1.7200 1.60342 38.00
[12] 40.0840 8.2100
[13] (Aperture stop) 1.8900
[14] 118.9580 2.5500 1.48749 70.44
[15] -15.2960 0.8000 2.00099 29.14
[16] -96.7270 0.7900
[17] 233.4960 4.4100 1.84666 23.78
[18] -12.8420 0.8000 1.91082 35.25
[19] -45.2170 d19
[20] 80.5330 8.5700 1.43700 95.10
[21] -16.7130 0.8500 1.91082 35.25
[22] -27.7850 0.1500
[23] 48.0950 3.4310 1.43700 95.10
[24] -84.9420 d24
[25] 110.3500 0.9000 2.00099 29.14
[26] 21.0000 4.5800 1.43700 95.10
[27] 144.6150 1.9700
[28] -43.6500 2.7200 1.43700 95.10
[29] -24.6860 0.8000
[30] * -31.6040 0.1000 1.51840 52.09
[31] -28.0360 2.4800 1.48749 70.44
[32] -21.9190 Bf

[Variable interval when shooting distance changes]
f 11.38 15.03 21.30
d0 ∞ ∞ ∞
d4 13.1200 13.1200 13.1200
d10 26.0500 12.7000 1.3500
d19 5.6900 3.7600 0.7000
d24 0.9000 4.2700 8.4500
Bf 38.30 42.95 52.23

[Variable interval for zooming when shooting 40x equivalent]
f 11.38 15.03 21.30
d0 435.84 578.11 829.01
d4 12.0747 12.3265 12.5631
d10 27.0953 13.4935 1.9069
d19 5.6900 3.7600 0.7000
d24 0.9000 4.2700 8.4500
Bf 38.30 42.95 52.23

[Aspherical data]
3 sides 4 sides 5 sides 6 sides
K 0.0000 0.0000 0.0000 0.0000
A4 4.9905E-05 1.6733E-05 9.4415E-05 1.3612E-04
A6 -1.9231E-07 2.5433E-08 -5.0799E-07 -1.1426E-06
A8 3.3694E-10 -8.5534E-10 1.4846E-09 3.7229E-09
A10 -2.3482E-13 1.9591E-12 -5.9157E-13 -3.2547E-12
A12 4.7370E-17 0.0000E + 00 0.0000E + 00 0.0000E + 00
7 faces 8 faces 30 faces
K 0.0000 0.0000 3.0593
A4 -3.3595E-05 -5.7731E-05 -6.9664E-06
A6 -3.0116E-07 -2.7421E-08 4.1535E-08
A8 1.6562E-09 9.4315E-10 -1.2677E-10
A10 -2.1413E-12 -1.7178E-12 1.4419E-12
A12 0.0000E + 00 0.0000E + 00 0.0000E + 00

Numerical example 3
Unit: mm
[Overall specifications]
f 12.40 16.82 23.11
Fno 4.66 5.14 5.87
2ω 122.81 104.52 84.55
D 10.86 10.86 10.86

[Lens Specifications]
rd nd Vd
[0] d0
[1] 41.1370 1.9000 1.91082 35.25
[2] 23.3920 9.8350
[3] * 76.2000 2.5000 1.69350 53.20
[4] 20.2730 d4
[5] * 45.2500 1.5000 1.69350 53.20
[6] 19.5880 6.5230
[7] * -200.3370 1.4000 1.69350 53.20
[8] 34.5320 0.1500
[9] 27.4560 4.7180 2.00099 29.14
[10] 126.1280 d10
[11] 17.5850 1.6990 1.58144 40.89
[12] 33.0890 8.1600
[13] (Aperture stop) 1.7580
[14] 62.1430 3.1360 1.43700 95.10
[15] -14.5810 0.8000 2.00099 29.14
[16] -55.9430 1.7460
[17] 448.7760 3.1780 1.84666 23.78
[18] -16.9890 0.8000 1.91082 35.25
[19] -39.2300 d19
[20] 185.2160 8.2000 1.43700 95.10
[21] -17.1830 0.8500 1.91082 35.25
[22] -28.9800 0.1500
[23] 67.5010 3.1200 1.43700 95.10
[24] -87.7470 d24
[25] 310.7830 0.9000 1.88300 40.80
[26] 20.7000 5.6690 1.43700 95.10
[27] 600.0000 0.8600
[28] -103.4040 3.6990 1.43700 95.10
[29] -32.0430 0.6930
[30] * -49.0700 0.1000 1.51840 52.09
[31] -46.2470 2.5540 1.48749 70.44
[32] -31.9010 Bf

[Variable interval when shooting distance changes]
f 12.40 16.82 23.11
d0 ∞ ∞ ∞
d4 11.8310 11.8310 11.8310
d10 25.0270 11.5680 1.7500
d19 7.9930 6.7010 3.3120
d24 0.9000 6.6000 11.1500
Bf 38.43 42.42 52.58

[Variable interval for zooming when shooting 40x equivalent]
f 12.40 16.82 23.11
d0 474.23 649.37 902.79
d4 11.0398 11.2481 11.4088
d10 25.8182 12.1509 2.1722
d19 7.9930 6.7010 3.3120
d24 0.9000 6.6000 11.1500
Bf 38.43 42.42 52.58

[Aspherical data]
3 surfaces 5 surfaces 7 surfaces 30 surfaces
K 0.0000 5.7763 0.0000 0.0000
A4 3.4915E-05 -2.5719E-05 1.9988E-06 -7.9119E-06
A6 -1.1987E-07 4.3089E-07 -1.8797E-07 1.8639E-09
A8 2.8317E-10 -2.3752E-09 1.5831E-09 9.1886E-11
A10 -3.5981E-13 5.6218E-12 -4.1824E-12 5.4784E-15
A12 1.9381E-16 -4.5118E-15 0.0000E + 00 0.0000E + 00

Numerical example 4
Unit: mm
[Overall specifications]
f 12.40 16.78 23.10
Fno 4.66 5.14 5.87
2ω 122.89 104.68 84.55
D 10.40 10.40 10.40

[Lens Specifications]
rd nd Vd
[0] d0
[1] 40.4080 1.9000 1.91082 35.25
[2] 23.5490 9.7890
[3] * 70.0930 2.5000 1.69350 53.20
[4] 20.2010 d4
[5] * 42.1040 1.5000 1.69350 53.20
[6] 19.7220 6.3780
[7] * -199.8140 1.4000 1.69350 53.20
[8] 34.2810 0.1500
[9] 26.9830 4.5500 2.00099 29.14
[10] 102.1150 d10
[11] 17.8850 1.6460 1.58144 40.89
[12] 33.8760 7.1240
[13] (Aperture stop) 1.9530
[14] 292.4180 2.9550 1.43700 95.10
[15] -13.4260 0.8000 2.00099 29.14
[16] -38.6850 0.8720
[17] -465.6870 3.0230 1.84666 23.78
[18] -16.8560 0.8000 1.91082 35.25
[19] -34.2500 d19
[20] 3907.2720 8.2000 1.43700 95.10
[21] -16.4710 0.8500 1.91082 35.25
[22] -25.8870 0.1500
[23] 77.7660 3.0700 1.43700 95.10
[24] -107.3810 d24
[25] 115.4820 0.9000 1.88300 40.80
[26] 20.7000 6.1900 1.43700 95.10
[27] 600.0000 1.0310
[28] -95.8780 3.8470 1.43700 95.10
[29] -32.3770 0.5020
[30] * -51.7620 0.1000 1.51840 52.09
[31] -50.3160 2.6010 1.48749 70.44
[32] -34.2720 Bf

[Variable interval when shooting distance changes]
f 12.40 16.78 23.10
d0 ∞ ∞ ∞
d4 11.8370 11.8370 11.8370
d10 23.8800 11.2590 1.7500
d19 9.9080 8.2310 3.6080
d24 0.9000 8.3000 13.8910
Bf 38.43 41.31 51.01

[Variable interval for zooming when shooting 40x equivalent]
f 12.40 16.78 23.10
d0 472.27 647.34 901.15
d4 11.0441 11.2531 11.4145
d10 24.6729 11.8429 2.1725
d19 9.9080 8.2310 3.6080
d24 0.9000 8.3000 13.8910
Bf 38.43 41.31 51.01

[Aspherical data]
3 surfaces 5 surfaces 7 surfaces 30 surfaces
K 0.0000 4.8440 0.0000 0.0000
A4 3.1944E-05 -2.3565E-05 2.9531E-06 -6.7483E-06
A6 -1.0692E-07 3.8815E-07 -1.9483E-07 5.2819E-09
A8 2.4018E-10 -1.9574E-09 1.6360E-09 7.1281E-11
A10 -2.8710E-13 3.7049E-12 -4.1345E-12 2.9748E-14
A12 1.4777E-16 -1.7197E-15 0.0000E + 00 0.0000E + 00

Numerical example 5
Unit: mm
[Overall specifications]
f 12.45 16.85 23.09
Fno 4.66 5.11 5.85
2ω 122.62 104.48 84.56
D 10.60 10.60 10.60

[Lens Specifications]
rd nd Vd
[0] d0
[1] 39.9040 1.9000 1.91082 35.25
[2] 23.4930 10.2050
[3] * 96.3950 2.5000 1.69350 53.20
[4] 19.1540 d4
[5] * 45.2500 1.5000 1.69350 53.20
[6] * 25.2180 6.2910
[7] * -177.2800 1.4000 1.69350 53.20
[8] 35.0940 0.3740
[9] 28.9910 4.2310 2.00099 29.14
[10] 97.6950 d10
[11] 19.9790 1.6300 1.68893 31.16
[12] 39.4350 8.2890
[13] (Aperture stop) 1.8850
[14] 124.1430 2.7570 1.43700 95.10
[15] -14.7220 0.8000 2.00099 29.14
[16] -44.6130 1.1970
[17] 375.3020 3.0490 1.84666 23.78
[18] -17.7820 0.8000 1.91082 35.25
[19] -45.6920 d19
[20] 93.5260 6.7530 1.43700 95.10
[21] -15.2070 0.8500 1.91082 35.25
[22] -24.4280 0.1500
[23] 42.5690 3.1400 1.43700 95.10
[24] -68.3810 d24
[25] 0.0000 0.9000 1.88300 40.80
[26] 18.1480 3.9490 1.43700 95.10
[27] 73.8560 2.1420
[28] -34.8150 2.8330 1.43700 95.10
[29] -20.9720 0.5310
[30] * -32.6770 0.1000 1.51840 52.09
[31] -30.0390 2.2660 1.48749 70.44
[32] -22.5710 Bf

[Variable interval when shooting distance changes]
f 12.45 16.85 23.09
d0 ∞ ∞ ∞
d4 11.4080 11.4080 11.4080
d10 24.6010 11.2750 1.7500
d19 3.3520 2.4080 0.7000
d24 0.9000 3.7770 6.4760
Bf 38.30 42.84 51.37

[Variable interval for zooming when shooting 40x equivalent]
f 12.41 16.76 22.93
d0 476.02 650.87 900.87
d4 10.5024 10.7400 10.9222
d10 25.5066 11.9430 2.2358
d19 3.3520 2.4080 0.7000
d24 0.9000 3.7770 6.4760
Bf 38.30 42.84 51.37

[Aspherical data]
3 sides 5 sides 6 sides
K 0.0000 6.1870 0.0000
A4 4.0792E-05 -1.7318E-05 2.3223E-05
A6 -1.5138E-07 8.9191E-07 6.1480E-07
A8 3.7347E-10 -5.3559E-09 -3.0889E-09
A10 -4.8793E-13 1.1825E-11 1.9032E-12
A12 2.7030E-16 -1.0220E-14 0.0000E + 00
7 faces 30 faces
K 0.0000 0.0000
A4 6.2368E-06 -1.6065E-05
A6 -1.4452E-07 -3.1460E-08
A8 1.6483E-09 4.0358E-10
A10 -5.1929E-12 -5.5794E-13
A12 0.0000E + 00 0.0000E + 00

Numerical example 6
Unit: mm
[Overall specifications]
f 12.45 16.75 23.09
Fno 4.64 5.09 5.83
2ω 122.63 105.39 84.57
D 10.50 10.50 10.50

[Lens Specifications]
rd nd Vd
[0] d0
[1] 38.7230 1.9000 1.91082 35.25
[2] 24.0060 9.4060
[3] * 52.5940 2.5000 1.77250 49.47
[4] 19.9520 d4
[5] * 45.2500 1.5000 1.49710 81.56
[6] * 16.7070 5.7300
[7] * -199.5840 1.4000 1.82080 42.71
[8] * 43.0030 0.1500
[9] 36.8990 4.2150 2.00099 29.14
[10] -1569.7390 d10
[11] 15.4340 1.4680 1.56732 42.84
[12] 21.2080 7.3680
[13] (Aperture stop) 1.7940
[14] 69.1970 3.0640 1.43700 95.10
[15] -13.7290 0.8000 2.00099 29.14
[16] -36.7380 0.6110
[17] -376.8910 2.2040 1.84666 23.78
[18] -16.7150 0.8000 1.91082 35.25
[19] -37.2810 d19
[20] 0.0000 5.7210 1.43700 95.10
[21] -21.1820 0.8500 1.77250 49.62
[22] -36.7020 0.1500
[23] 119.2020 2.3140 1.43700 95.10
[24] -184.0430 d24
[25] 148.0410 0.9000 1.90366 31.32
[26] 25.3010 7.0530 1.43700 95.10
[27] -88.4200 0.5000
[28] -61.9340 2.3080 1.43700 95.10
[29] -39.0820 0.8200
[30] * -63.9180 3.2840 1.49710 81.56
[31] -30.8770 Bf

[Variable interval when shooting distance changes]
f 12.45 16.75 23.10
d0 ∞ ∞ ∞
d4 13.8880 13.8880 13.8880
d10 25.0200 11.6440 1.7500
d19 16.3840 9.5070 0.7000
d24 0.9000 9.9230 18.4610
Bf 38.29 42.93 51.94

[Variable interval for zooming when shooting 40x equivalent]
f 12.43 16.69 22.96
d0 473.71 646.30 899.45
d4 12.9281 13.1779 13.3741
d10 25.9799 12.3541 2.2639
d19 16.3840 9.5070 0.7000
d24 0.9000 9.9230 18.4610
Bf 38.29 42.93 51.94

[Aspherical data]
3 side 5 side 6 side
K 0.0000 -2.3934 0.0000
A4 2.3072E-05 -7.3797E-05 -7.7994E-05
A6 -9.1780E-08 5.2336E-07 -5.0044E-07
A8 2.5332E-10 -3.0769E-09 2.0627E-09
A10 -3.7157E-13 1.3234E-11 4.5903E-13
A12 2.2434E-16 -1.8229E-14 0.0000E + 00
7 faces 8 faces 30 faces
K 0.0000 0.0000 0.0000
A4 -7.9516E-06 -1.3863E-05 -1.1823E-05
A6 -3.6565E-07 -7.8254E-08 1.0925E-08
A8 1.8433E-09 6.4336E-10 -2.8557E-11
A10 -2.4167E-12 -1.2813E-12 7.2882E-14
A12 0.0000E + 00 0.0000E + 00 0.0000E + 00

[Values for conditional expressions]
Conditional Example Example 1 Example 2 Example 3 Example 4 Example 5 Example 6
(1) 1.5 <| f1A / fw | <2.5 1.89 1.79 1.80 1.87 1.67 2.01
(2) 3.0 <f1B / f1A <6.0 3.15 4.17 3.25 3.08 4.49 3.05
(3) 2.0 <f2 / fw <5.0 3.05 3.60 3.32 3.30 3.01 3.48
(4) 1.0 <f2asp / f2 <7.0 1.91 3.24 4.30 4.83 3.67 2.68
(5) 2.0 <f2A / fw <5.0 4.90 3.70 3.83 3.65 3.95
(6) 5.0 <| f2C / fw | 40.23 50.68 53.75 8.03 11.47
(7) 2.5 <| f2AF / f1 | <10.0 3.67 4.20 4.18 3.84 5.58
(8) 1.0 <S / D <10.0 7.63 2.31 2.43 2.35 1.96
(9) 2.0 <f2B / fw <10.0 3.71 4.53 4.84 2.95 7.03
(10) 15.0 <f2CJoin / fw <-2.0 -4.21 -4.14 -5.53 -2.60 -11.37
(11) 1.8 <Nd2CN 2.00 1.88 1.88 1.88 1.90
(12) 80 <Vd2CP 95.08 95.08 95.08 95.08 95.08

G1 1st lens group G1A 1A lens group G1B 1B lens group G2 2nd lens group G2A 2A lens group G2AF 2A lens group front group G2AR 2A lens group back group G2B 2B lens group G2C 2C lens group G3 Third lens group L2CJoin A cemented negative lens unit L2asp in the second C lens group A positive single lens having an aspheric surface on at least one surface in the second lens group

Claims (7)

In order from the object side, the first lens unit G1 has a negative refractive power and the second lens unit G2 has a positive refractive power.
The first lens group G1 includes a first A lens group G1A having a negative refractive power and a first B lens group G1B having a negative refractive power.
Further, the first A lens group G1A is composed of, in order from the object side, a first lens L1 of a negative meniscus lens and a second lens L2 of a negative meniscus lens having an aspheric surface on at least one surface.
The first B lens group G1B has a negative meniscus lens L3 having at least one aspheric surface on the most object side,
The second lens group G2 includes a second A lens group G2A, a second B lens group G2B, and a second C lens group G2C.
At the time of focusing, the first B lens group G1B is moved to the object side,
During zooming from the wide-angle end side to the telephoto end side, the distance between the first lens group G1 and the second A lens group G2A decreases, and the distance between the second A lens group G2A and the second B lens group G2B decreases. The distance between the second B lens group G2B and the second C lens group G2C increases,
An ultra-wide-angle lens system that satisfies the following conditions.
(1) 1.5 <| f1A / fw | <2.5
(2) 3.0 <f1B / f1A <6.0
(3) 2.0 <f2 / fw <5.0
Where fw: focal length of the entire lens system at the wide angle end f1A: focal length of G1A of the first A lens group f1B: focal length of G1B of the first B lens group f2: focal length of the second lens group G2 at the wide angle end
2. The super lens according to claim 1, further comprising: a positive single lens L <b> 2 </ b> asp having at least one aspheric surface on the most image plane side in the second lens group G <b> 2 and satisfying the following condition. Wide angle lens system.
(4) 1.0 <f2asp / f2 <7.0
However,
f2asp: focal length of the positive single lens L2asp having an aspheric surface on at least one surface in the second lens group G2 f2 focal length of the second lens group G2 at the wide angle end
The super-wide-angle lens system according to claim 1 or 2, wherein the following condition is satisfied.
  (5) 2.0 <f2A / fw <5.0
  (6) 5.0 <| f2C / fw |
However,
  fw: focal length of the entire lens system at the wide-angle end
  f2A: focal length of the second A lens group G2A
  f2C: focal length of the second C lens group G2C
The second A lens group G2A is divided into a front second A lens group front group G2AF and a rear second A lens group rear group G2AR with an aperture unit interposed therebetween, and satisfies the following conditions: The super-wide-angle lens system according to claim 3.
  (7) 2.5 <| f2AF / f1 | <10.0
  (8) 1.0 <S / D <10.0
However,
  fw: focal length of the entire lens system at the wide-angle end
  f1: Focal length of the first lens group G1
  f2AF: focal length of front group G2AF
  D: Aperture aperture diameter
  S: Distance between principal points of front group G2AF and rear group G2AR
The super-wide-angle lens system according to any one of claims 1 to 4, wherein the following conditions are satisfied.
  (9) 2.0 <f2B / fw <10.0
However,
  fw: focal length of the entire lens system at the wide-angle end
  f2B: Focal length of the second B lens group G2B
The second C lens group G2C has a cemented negative lens unit L2CJoin composed of at least one negative lens and at least one positive lens, and satisfies the following conditions. An ultra-wide-angle lens system according to any one of the above.
  (10) -15.0 <f2CJoin / fw <-2.0
However,
  fw: focal length of the entire lens system at the wide-angle end
  f2CJoin: focal length of the cemented negative lens unit L2CJoin in the second C lens group G2C
The super-wide-angle lens system according to claim 6, wherein the following condition is satisfied.
  (11) Nd2CN> 1.8
  (12) Vd2CP> 80
However,
  Nd2CN: Refractive index of at least one negative lens in the cemented negative lens unit L2CJoin
  Vd2CP: Abbe number of at least one positive lens in the cemented negative lens unit L2CJoin

Images