JP2017078752A - Inner focus optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inner focus optical system which employs an inner focusing system suitable for an autofocus camera, has a small image height change rate when finely vibrating (wobbling) focus lens groups in a direction along an optical axis, is bright with an F number equivalent to 1.4, and has an angle of view of equivalent to 24 mm at conversion focal length of a 35 mm format.SOLUTION: An optical system comprises, in order from an object side to an image side, a first lens group G1 of negative refractive power, an aperture diaphragm, a second lens group G2 of positive refractive power, a third lens group G3 of negative refractive power, and a fourth lens group G4 of positive refractive power. When focusing from an object side infinity to an object side at a short distance, the third lens group G3 is moved toward an image plane side.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical system suitable for a photographic lens used in an imaging apparatus such as a still camera or a video camera, and employs an inner focus system suitable for an autofocus camera, and a focus lens group in a direction along the optical axis. The present invention relates to an inner focus optical system that has a small image height change rate when it is vibrated (wobbling), has a bright F value of 1.4, and has a field angle equivalent to 24 mm at a 35 mm equivalent focal length.

  Conventionally, a wide-angle lens used for a photographic camera or a still video camera has been a retrofocus type. This was to secure a back focus of a certain level or more for a single lens reflex system employing a mirror up mechanism.

  On the other hand, mirrorless interchangeable-lens cameras are often used for movie shooting, so the autofocus system always keeps the focus lens group oscillating slightly in the direction along the optical axis. In many cases, the inner focus method is used. At that time, if the rate of change in image height during wobbling is large, the viewer will perceive fluctuations in the magnification of the subject on the screen and feel it annoying. Yes.

  In response to such a requirement, Patent Document 1 includes a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive refractive power in order from the object side, and is included in the second lens group. Focusing from the infinity object side to the short-distance object side by moving a single lens having a refractive power of at least one positive lens closer to the image side than the single lens having a negative refractive power, By satisfying predetermined conditions, an inner focus lens that achieves a high focusing speed while achieving a large aperture has been achieved.

  In Patent Document 2, the first lens group G1 having a positive refractive power, the second lens group G2 having a negative refractive power, and the third lens group G3 having a positive refractive power are arranged in this order from the object side. A large-aperture lens that is arranged between the first lens group G1 and the second lens group G2 and performs focusing by moving the second lens group G2 to the image plane side can satisfy simple conditions. Although it is configured, it supports autofocus during movie shooting, reduces the weight of the focus lens, reduces aberration fluctuations due to focusing, and can be applied to brightness with an open F value of about 1.4 using the inner focus method. We provide high-performance large-aperture lenses.

  In Patent Document 3, in order from the object side, a first lens group, an aperture stop, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a positive refractive power. The first lens group has at least one negative lens and at least one positive lens, and the second lens group has at least one negative lens and at least one positive lens. The third lens group has at least one negative lens, the fourth lens group has at least one positive lens, and when focusing from an object at infinity to a near object, Inner having good imaging performance by moving the third lens group to the image side and satisfying a predetermined condition so as to widen the distance from the second lens group and narrow the distance from the fourth lens group. A focus lens system is provided.

  Further, in Patent Document 4, in order from the object side, the first lens group G1 having a positive refractive power, the second lens group G2 having a positive refractive power, and the third lens group G3 having a negative refractive power are infinite. During focusing from a distant object to a close object, the second lens group G2 moves to the object side, and the first lens group G1 and the third lens group G3 are fixed with respect to the image plane I, and The first lens group G1 includes a stop S and includes a predetermined lens group, and the third lens group G3 includes a predetermined lens group, and satisfies a predetermined conditional expression, thereby satisfying an imaging optical system, an imaging element, and the like. With a short interval, small size, small F-number, low light emission angle, and excellent correction of various aberrations from infinity to short-distance shooting. An imaging optical system of a degree is provided.

JP 2012-220654 A JP 2013-3324 A JP 2013-130669 A Japanese Patent Laying-Open No. 2015-75501

  However, in the lens system disclosed in Patent Document 1, although there are variations in focal length, since the lens group on the object side of the aperture has a positive refractive power, only a field angle of about 28 mm at a 35 mm equivalent focal length is on the wide angle side. From this configuration, it is difficult to achieve an angle of view of 24 mm at a 35 mm equivalent focal length and an F value of about 1.4.

  In the lens system disclosed in Patent Document 2, since the focus lens group and the stop are adjacent to each other, the focus lens group for autofocus at the time of moving image shooting is slightly vibrated (wobbling) in the direction along the optical axis. Since the change rate of the image height at the time is large, there is a problem that the viewer recognizes a change in the magnification of the subject on the screen and feels uncomfortable. Furthermore, since the first group is composed of a Gaussian type and only an angle of view of about 50 mm is disclosed with a 35 mm equivalent focal length, it is difficult to further widen the angle.

  In the lens system disclosed in Patent Document 3, there is no restriction on the refractive power of the first lens unit that is on the object side of the stop, and the first lens unit of the disclosed embodiment has only a weak negative refractive power. Therefore, only an embodiment having an F angle of about 1.7 at an angle of view of about 32 mm at a focal length of 35 mm as disclosed in the embodiments is disclosed. From this configuration, an image of 24 mm at a focal length of 35 mm is disclosed. It is difficult to achieve an angle and an F value of about 1.4.

  In Patent Document 4, the first lens group G1 having a positive refractive power, the second lens group G2 having a positive refractive power, and the third lens group G3 having a negative refractive power are sequentially arranged from the object side. The second lens group G2 moves to the object side during focusing from an object at infinity to a near object, and the first lens group G1 and the third lens group G3 are fixed with respect to the image plane I. The first lens group G1 includes a stop S and includes a predetermined lens group, and the third lens group G3 includes a predetermined lens group, and satisfies a predetermined conditional expression. Is small, the light emission angle is suppressed, and various aberrations are favorably corrected from infinity shooting to short-distance shooting, but a narrow image with a field angle of about 40 to 60 ° (35 mm equivalent focal length of about 37 mm to 59 mm). It can only be realized at the corners. It is difficult to achieve the angle of view of 24mm in m equivalent focal length.

  Therefore, the present invention adopts an inner focus method suitable for an autofocus camera by the means described below, and an image height change rate when the focus lens group is slightly vibrated (wobbling) in a direction along the optical axis. Provided is an inner focus optical system that is small and bright with an F value of 1.4 and has an angle of view equivalent to 24 mm at a 35 mm equivalent focal length.

In order to solve the above-described problem, the first invention is arranged in order from the object side to the image side, the first lens group G1 having a negative refractive power, the aperture stop, the second lens group G2 having a positive refractive power, The third lens group G3 having a positive refractive power and the fourth lens group G4 having a positive refractive power, and when focusing from the infinity object side to the short distance object side, the third lens group G3 is in the image plane direction. The inner focus optical system is characterized by satisfying the following conditions.
(1) -6.5 <f1 / f <-2.8
(2) -5.6 <f3 / f <-3.0
(3) -0.68 <f2 / f1 <-0.24
Where f: focal length in the infinite focus state of the entire system f1: focal length of the first lens group G1 f2: focal length of the second lens group G2 f3: focal length of the third lens group G3

In order to solve the above-described problem, the second invention is based on the second lens group G2 based on the object side surface of the third lens group G3 when focusing on infinity in the first invention. When the imaging position of the aperture stop is FcEntp, the inner focus optical system satisfies the following conditions.
(4) 0.5 <FcEntp / f3 <0.95
(5) FcEntp / f <−2.0

In order to solve the above-mentioned problem, in a third invention, in the first or second invention, a lens La having a negative refractive power and a lens having a positive refractive power are arranged in order from the object side toward the image plane side of the aperture stop. The lens has a cemented lens in which Lb and a lens Lc having a negative refractive power are cemented, and the focal length and the combined thickness of the lenses La, Lb, and Lc satisfy the following conditions. An inner focus optical system was adopted.
(6) -0.15 <f / fabc <0.06
(7) 0.5 <OALAbc / f <1.5
However, the focal length of the cemented lens of fabc: La, Lb, and Lc OALabc: the combined thickness of the cemented lens of La, Lb, and Lc

In order to solve the above-mentioned problems, the fourth invention is an inner focus optical system characterized in that, in any of the first to third inventions, the following conditions are satisfied.
(8) -1.3 <M4 ² × (1-M3 ² ) <− 0.5
However,
M3: Lateral magnification of the third lens group G3 when the object distance is infinity M4: Lateral magnification of the fourth lens group G4 when the object distance is infinity

  According to the present invention, an inner focus method suitable for an autofocus camera is adopted, and an image height change rate when a focus lens group is slightly vibrated (wobbled) in a direction along the optical axis is small, and an F value is 1.4. An inner focus optical system having a field angle equivalent to 24 mm at a 35 mm equivalent focal length can be provided.

1 is a lens configuration diagram of an inner focus optical system according to Example 1 of the present invention at an infinite shooting distance. FIG. FIG. 6 is a longitudinal aberration diagram at an imaging distance infinite according to Example 1 of the present invention. FIG. 6 is a longitudinal aberration diagram at the photographing magnification of 40 times in Example 1 of the present invention. FIG. 4 is a longitudinal aberration diagram at the shooting distance 200 mm 2 in Example 1 of the present invention. FIG. 5 is a lateral aberration diagram at infinite shooting distance according to Example 1 of the present invention. FIG. 4 is a lateral aberration diagram at the photographing magnification of 40 in Example 1 of the present invention. FIG. 3 is a lateral aberration diagram at the shooting distance 200 mm 2 in Example 1 of the present invention. FIG. 6 is a lens configuration diagram of an inner focus optical system according to Example 2 of the present invention at an imaging distance of infinity. FIG. 6 is a longitudinal aberration diagram at an imaging distance infinite according to Example 2 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging magnification of 40 times in Example 2 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 200 mm in Example 2 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance infinite according to Example 2 of the present invention. FIG. 6 is a lateral aberration diagram at the photographing magnification of 40 in Example 2 of the present invention. FIG. 5 is a lateral aberration diagram at an imaging distance of 200 mm 2 according to Example 2 of the present invention. FIG. 6 is a lens configuration diagram of an inner focus optical system according to Example 3 of the present invention at an imaging distance of infinity. FIG. 7 is a longitudinal aberration diagram at an imaging distance infinite according to Example 3 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging magnification of 40 times in Example 3 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 200 mm in Example 3 of the present invention. FIG. 6 is a lateral aberration diagram at infinite shooting distance according to Example 3 of the present invention. FIG. 6 is a lateral aberration diagram at the photographing magnification of 40 in Example 3 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance of 200 mm 2 in Example 3 of the present invention. FIG. 9 is a lens configuration diagram of an inner focus optical system according to Example 4 of the present invention at an imaging distance of infinity. FIG. 6 is a longitudinal aberration diagram at an imaging distance infinite according to Example 4 of the present invention. FIG. 10 is a longitudinal aberration diagram at an imaging magnification of 40 times in Example 4 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 200 mm in Example 4 of the present invention. FIG. 10 is a lateral aberration diagram at infinite shooting distance according to Example 4 of the present invention. FIG. 6 is a lateral aberration diagram at the photographing magnification of 40 in Example 4 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance of 200 mm in Example 4 of the present invention. FIG. 6 is a lens configuration diagram of an inner focus optical system according to Example 5 of the present invention at an imaging distance of infinity. FIG. 6 is a longitudinal aberration diagram at an imaging distance infinite according to Example 5 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging magnification of 40 times according to Example 5 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 200 mm in Example 5 of the present invention. FIG. 10 is a lateral aberration diagram at infinite shooting distance according to Example 5 of the present invention. FIG. 6 is a lateral aberration diagram at the photographing magnification of 40 in Example 5 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 200 mm in Example 5 of the present invention. FIG. 10 is a lens configuration diagram of an inner focus optical system according to Example 6 of the present invention at an imaging distance of infinity. FIG. 9 is a longitudinal aberration diagram at an imaging distance infinity according to Example 6 of the present invention. FIG. 12 is a longitudinal aberration diagram at an imaging magnification of 40 times in Example 6 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 200 mm in Example 6 of the present invention. FIG. 6 is a lateral aberration diagram at infinite shooting distance according to Example 6 of the present invention. FIG. 11 is a lateral aberration diagram at Example 6 with a shooting magnification of 40 ×. FIG. 12 is a lateral aberration diagram at an imaging distance of 200 mm in Example 6 of the present invention. FIG. 10 is a lens configuration diagram of an inner focus optical system according to Example 7 of the present invention at an imaging distance of infinity. FIG. 10 is a longitudinal aberration diagram at an imaging distance infinite according to Example 7 of the present invention. FIG. 10 is a longitudinal aberration diagram at an imaging magnification of 40 times in Example 7 of the present invention. FIG. 9 is a longitudinal aberration diagram at an imaging distance of 200 mm in Example 7 of the present invention. FIG. 10 is a lateral aberration diagram at infinite shooting distance according to Example 7 of the present invention. FIG. 10 is a transverse aberration diagram at Example 6 with a photographing magnification of 40. FIG. FIG. 12 is a lateral aberration diagram at an imaging distance of 200 mm in Example 7 of the present invention.

  As can be seen from the lens configuration diagrams shown in FIGS. 1, 8, 15, 22, 29, 36, and 43, the inner focus optical system of the embodiment of the present invention has negative refractive power in order from the object side to the image side. 1 lens group G1, an aperture stop, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a positive refractive power. The third lens group G3 moves in the image plane direction when focusing from the object side to the short distance object side.

  Hereinafter, the inner focus optical system of this embodiment will be described. In the present invention, the refractive power arrangement of the optical system is, in order from the object side, the first lens group G1 having negative refractive power, the aperture stop, the second lens group G2 having positive refractive power, and the focus lens group having negative refractive power. A so-called retrofocus type refracting power in which the third lens group G3 and a fourth lens group G4 having a positive refracting power are used, and the entire optical system has a negative refracting power on the object side from the aperture stop and a positive refracting power on the image side from the aperture stop. An optical system having an angle of view equivalent to 24 mm at a 35 mm equivalent focal length is achieved by reducing the image height change rate due to wobbling during focusing.

  The reason why the above configuration is necessary is as follows. That is, by arranging a lens unit having a positive refractive power between the aperture stop and the focus lens group, the image of the aperture stop viewed from the focus group is projected far away, thereby reducing the image height change rate. In addition, by disposing a lens unit having a positive refractive power on the image side of the focus lens group, the principal ray that has passed through the focus lens group is reflected by the effect of the lens unit having the positive refractive power. The incident angle on the surface becomes gradual, which contributes to further reduction in the image height change rate.

  Also, by placing a lens unit with negative refractive power on the object side of the aperture stop, the incident angle with a wide angle of view is relaxed with this lens unit with negative refractive power, and the chief ray angle passing through the aperture stop is moderated. This increases the aberration correction capability for the angle of view. As described above, an optical system having a small image height change rate when the focus lens group is slightly vibrated (wobbling) in the direction along the optical axis and having an angle of view equivalent to 24 mm at a 35 mm equivalent focal length is provided. Is possible.

Furthermore, as described above, the inner focus optical system of the present embodiment satisfies the following conditional expression.
(1) -6.5 <f1 / f <-2.8
(2) -5.6 <f3 / f <-3.0
(3) -0.68 <f2 / f1 <-0.24
Where f: focal length in the infinite focus state of the entire system f1: focal length of the first lens group G1 f2: focal length of the second lens group G2 f3: focal length of the third lens group G3

  As described above, the inner focus optical system according to the present invention is premised on that autofocus by wobbling is possible. That is, the image height change rate during wobbling is small. For this purpose, it is only necessary to reduce the fluctuation of the chief ray height of the focus lens group due to the wobbling, and the image of the aperture stop by the second lens group G2 from the object side surface of the third lens group G3 when focusing on infinity. What is necessary is just to enlarge the distance to a position.

Image height variation due to wobbling can be represented by variation in distortion due to wobbling.
According to Yoshiya Matsui, lens design method, Kyoritsu Shuppan P88, the third-order distortion coefficient V is expressed by the following equation.
V = J ・ IV
When this is developed, the following is obtained, and the third-order distortion coefficient V is proportional to the cube of the paraxial principal ray height H ′.
(Reference formula 1)
V = (H ′ · Q ′) ³ / (H · Q) · H ² · Δ (1 / (n · s)) + P · (H ′ · Q ′) / (H · Q)

In order to reduce the variation in distortion due to the wobbling, the variation in the principal ray height of the focus lens group due to the wobbling may be reduced. Here, the position of the image of the aperture stop by the second lens group G2 and the lateral magnification of the third lens group G3, which is the focus lens group, with respect to the object side surface of the third lens group G3 at the infinite object distance From the lateral magnification of the fourth lens group G4, which is the lens group behind the focus lens group, and the principal ray height in the focus lens group, the variation Δh in the principal ray height of the focus lens group due to wobbling is expressed by the following equation. .
(Reference formula 2)
Δh = h′−h = h · Δs / M4 ² × (1-M3 ² )
However,
FcEntp: The image forming position Δs of the aperture stop by the second lens group G2 with respect to the object side surface of the third lens group G3 at the time of focusing on infinity: Image plane movement amount h at the time of wobbling: Distance infinite Chief ray height h ′ in the focus lens group at the time: chief ray height M3 in the focus lens group at the time of wobbling: lateral magnification M4 of the third lens group G3 at infinity at the object distance: fourth lens group at infinity at the object distance G4 horizontal magnification

  In conditional expression (1), by appropriately defining the ratio of the focal lengths of the first lens group G1 and the entire system at the time of focusing on infinity, the incident angle of light rays with a wide angle of view is relaxed, and the subsequent optical system It becomes possible to make it enter.

  If the upper limit of conditional expression (1) is exceeded and the negative refractive power of the first lens group G1 is increased, the curvature of the concave surface in the first lens group G1 is further increased, which causes negative spherical aberration. Further, since the incident angle and the ray height of the axial ray on the second lens group G2 are increased, it becomes a cause of occurrence of higher-order aberrations and it becomes difficult to correct the aberration. Further, since the back focus becomes longer, the entire length of the optical system becomes longer. On the other hand, when the lower limit of conditional expression (1) is exceeded and the negative refractive power of the first lens group G1 becomes small, the inclination of the principal ray that passes through the aperture stop is not relaxed, so the peripheral rays after the second lens group G2 The height of the light beam becomes higher, and it becomes difficult to correct the coma flare of the upper light beam.

  Regarding conditional expression (1), the lower limit value is desirably limited to −5.0, and the upper limit value is desirably limited to −3.25, whereby the above-described effect can be further ensured.

  In the conditional expression (2), by appropriately defining the ratio of the focal lengths of the third lens group G3, which is the focus lens group, and the first lens group G1, it is possible to suppress aberration fluctuations during focusing.

  If the upper limit of conditional expression (2) is exceeded and the negative refractive power of the third lens group G3 becomes relatively large, the amount of movement of the third lens group G3 during focusing becomes small, which is advantageous in terms of space. It becomes difficult to simultaneously correct the variation in spherical aberration and astigmatism during focusing. On the other hand, if the lower limit of conditional expression (2) is exceeded and the negative refractive power of the third lens group G3 becomes relatively small, the amount of movement of the third lens group G3 at the time of focusing increases, and the total length of the optical system increases. Further, it is not preferable because the amount of amplitude at the time of wobbling must be increased and a load is applied to the actuator.

  Regarding conditional expression (2), the lower limit value is desirably limited to −4.3, and the upper limit value is desirably limited to −3.2, whereby the above-described effect can be further ensured.

  In the conditional expression (3), by appropriately defining the ratio of the focal lengths of the second lens group G2 and the first lens group G1, a wide angle of view can be maintained and a large aperture can be achieved.

  When the upper limit of conditional expression (3) is exceeded and the positive refractive power of the second lens group G2 becomes relatively large, or the negative refractive power of the first lens group G1 becomes small, spherical aberration and coma at the time of increasing the diameter are increased. It becomes difficult to correct aberrations. On the other hand, if the lower limit of the conditional expression (3) is exceeded and the positive refractive power of the second lens group G2 becomes relatively small, or the negative refractive power of the first lens group G1 becomes large, the third lens that is the focus lens group. The overall refractive power cannot be secured unless the negative refractive power of the lens group G3 is weakened. For this reason, the amount of movement of the third lens group G3 at the time of focusing becomes large and the entire length of the optical system becomes long, which is not preferable.

  Regarding conditional expression (3), the lower limit value is desirably limited to −0.52 and the upper limit value is desirably limited to −0.34, whereby the above-described effect can be further ensured.

Further, in the inner focus optical system according to the embodiment of the present invention, the imaging position of the aperture stop by the second lens group G2 is FcEntp with the object side surface of the third lens group G3 at the time of focusing on infinity as a reference. In this case, the following conditional expression is satisfied.
(4) 0.5 <FcEntp / f3 <0.95
(5) FcEntp / f <−2.0

  In conditional expressions (4) and (5), the imaging position of the aperture stop by the second lens group G2 with respect to the object side surface of the third lens group G3 at the time of focusing on infinity and the third lens group G3 The ratio of the focal length and the aperture stop by the second lens group G2 based on the focal length of the entire system at the infinite focus state and the object side surface of the third lens group G3 at the infinite focus state. By appropriately defining the ratio to the image position, it is possible to suppress image height fluctuations during wobbling.

  If the upper limit of conditional expression (4) is exceeded and the distance from the object side surface of the third lens group G3 at the time of focusing on infinity to the imaging position of the aperture stop by the second lens group G2 increases, the total length of the optical system becomes larger. Since it becomes long, it is not preferable. If the negative refractive power of the third lens group G3 is increased, the amount of movement of the third lens group G3 during focusing is reduced, which is advantageous in terms of space, but fluctuations in spherical aberration and astigmatism during focusing. It becomes difficult to correct simultaneously. On the other hand, if the lower limit of the conditional expression (4) is exceeded and the distance from the object side surface of the third lens group G3 to the image forming position of the aperture stop by the second lens group G2 at the time of focusing on infinity becomes small, the wobbling time Since the fluctuation of the principal ray height of the focus lens group becomes large, it becomes difficult to suppress the fluctuation of the image height during wobbling.

  Moreover, the upper limit of conditional expression (5) is exceeded, and the distance from the object side surface of the third lens group G3 to the imaging position of the aperture stop by the second lens group G2 and the focal length of the entire system when focusing on infinity As the ratio increases, similarly, it becomes difficult to suppress fluctuations in image height during wobbling.

  Regarding conditional expression (4), the lower limit value is desirably limited to 0.68, and the upper limit value is preferably limited to 0.87, whereby the above-described effect can be further ensured.

  Regarding conditional expression (5), the above-mentioned effect can be made more reliable by desirably limiting the upper limit value to -2.4.

Further, in the inner focus optical system of the embodiment of the present invention, three lenses of a negative refractive power lens La, a positive refractive power lens Lb, and a negative refractive power lens Lc are cemented on the image plane side of the aperture stop. The focal length and the combined thickness of the cemented lenses of the lenses La, Lb, and Lc satisfy the following conditions.
(6) -0.15 <f / fabc <0.06
(7) 0.5 <OALAbc / f <1.5
However, the focal length of the cemented lens of fabc: La, Lb, and Lc OALabc: the combined thickness of the cemented lens of La, Lb, and Lc

  In conditional expression (6), by appropriately defining the ratio of the focal length of the entire system at the time of focusing on infinity and the focal length of the cemented lens that is joined by three lenses, axial chromatic aberration, field curvature, and astigmatism are reduced. Enables correction and balancing.

  In addition, in conditional expression (7), by appropriately defining the ratio of the combined thickness of the cemented lenses joined by the three lenses and the focal length of the entire system when focused at infinity, in combination with conditional expression (6) By projecting the imaging position of the aperture stop as viewed from the focus group to the distance, it is possible to suppress fluctuations in image height during wobbling without increasing the total length.

  If the upper limit of conditional expression (6) is exceeded and the positive refractive power of the cemented lens with three cemented lenses becomes relatively strong, the Petzval sum shifts positively, and field curvature and astigmatism deteriorate, which is not preferable. On the other hand, if the lower limit of conditional expression (6) is exceeded and the negative refractive power of the three-piece cemented lens becomes relatively strong, the refractive power of the positive lens component following the image plane side of the three-piece cemented lens If is not strengthened, the height of the marginal ray of the focus lens group becomes high, and aberration fluctuations during focusing cannot be suppressed. Further, when the refractive power of the positive lens component is increased, the spherical aberration becomes under and it becomes difficult to increase the diameter. Further, in this specification, the “lens component” is a broad concept including a single lens, a cemented lens, and a group of lenses. Thus, one lens component is the same as one lens group in its broadest concept.

  If the combined thickness of the three cemented lenses exceeds the upper limit of conditional expression (7), the exit pupil is projected far away, so that the effect of suppressing fluctuations in image height increases, but the parallel plane plate As a result, the spherical aberration falls under and the astigmatism falls over, so that a large aperture cannot be achieved. On the other hand, if the lower limit of conditional expression (7) is exceeded and the combined thickness of the three cemented lenses decreases, the exit pupil approaches the image side, so the effect of suppressing fluctuations in image height is weakened. It becomes difficult to suppress high fluctuations. Further, the spherical aberration is over and the astigmatism is over, which is not preferable.

Regarding conditional expression (6), the lower limit value is desirably limited to -0.10, and the upper limit value is preferably limited to 0.03, whereby the above-described effect can be further ensured.
Regarding conditional expression (7), the lower limit value is desirably limited to 0.66 and the upper limit value is preferably limited to 1.15, whereby the above-described effect can be further ensured.

Furthermore, the inner focus optical system of the embodiment of the present invention is characterized in that the following conditional expressions are satisfied.
(8) -1.3 <M4 ² × (1-M3 ² ) <− 0.5
However,
M3: Lateral magnification of the third lens group G3 when the object distance is infinity M4: Lateral magnification of the fourth lens group G4 when the object distance is infinity

  Conditional expression (8) defines the sensitivity of the image plane when the third lens group G3 moves during focusing. By appropriately defining this value, it becomes possible to drive and control the focus lens group within the AF focusing range. Further, as shown in the reference formula (2), the fluctuation Δh of the principal ray height of the focus lens group due to the wobbling increases as this value approaches zero, so that an appropriate range is necessary.

  If the upper limit of conditional expression (8) is exceeded, the chief ray height variation Δh of the focus lens group due to wobbling increases, so the effect of suppressing the image height variation becomes weak, and it is difficult to suppress image height variation during wobbling. become. On the other hand, if the lower limit of conditional expression (8) is exceeded, the amount of movement of the focus lens group decreases, so that the imaging surface moves greatly with a slight movement of the focus lens group, and the focus lens group is within the AF focusing range. It becomes difficult to drive and control the third lens group G3.

  Regarding conditional expression (8), the lower limit value is desirably limited to -1.0, and the upper limit value is desirably limited to -0.7, whereby the above-described effect can be further ensured.

  The inner focus optical system of the present invention is more effective with the configuration described in the following paragraph 0054.

  With this configuration, in the inner focus optical system according to the embodiment of the present invention, the third lens group G3 is constituted by a single lens. However, if there is a margin in the power of the actuator for focus drive, this is used as a cemented lens. Thus, the chromatic aberration is corrected by the focus lens group. As a result, it is also possible to suppress fluctuations in chromatic aberration due to focus movement.

Next, the lens configuration and specific numerical data of each example according to the inner focus optical 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.

  In [Surface Data], the surface number is the number of the lens surface or aperture stop counted from the object side, r is the radius of curvature of each surface, d is the distance between the surfaces, and nd is for the d-line (wavelength λ = 587.56 nm). The refractive index, νd, indicates the Abbe number with respect to the d line. BF represents back focus.

  In the surface number (aperture stop), the radius of curvature ∞ (infinite) with respect to the plane or aperture stop is entered.

In [Aspherical data], each coefficient value giving the aspherical shape of the lens surface marked with * in [Surface data] is shown. The shape of the aspheric surface is such that the displacement in the direction orthogonal to the optical axis is y, the displacement (sag amount) in the optical axis direction from the intersection of the aspheric surface and the optical axis is z, the conic coefficient is K, 4, 6, 8, When tenth-order aspheric coefficients are set as A4, A6, A8, and A10, respectively, the coordinates of the aspheric surface are expressed by the following equations.

  [Various data] shows values such as focal length.

  [Variable interval data] indicates the value of the variable interval and BF (back focus) in each shooting distance state.

  [Lens Group Data] indicates the surface number of the most object side constituting each lens group and the combined focal length of the entire group.

  In all the values of the following specifications, the focal length f, the radius of curvature r, the lens surface interval d, and other length units described 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 the aberration diagrams corresponding to each example, d, g, and C represent d-line, g-line, and C-line, respectively, and ΔS and ΔM represent sagittal image plane and meridional image plane, respectively.

  Further, in the lens configuration diagrams shown in FIGS. 1, 8, 15, 22, 29, 36, and 43, S is an aperture stop, I is an image plane, FL is an optical filter, and an alternate long and short dash line through the center is an optical axis.

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

  The lens of the inner focus optical system in FIG. 1 includes, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens having a negative refractive power. The lens group G3 is composed of a fourth lens group G4 having a positive refractive power.

  The first lens group G1 includes a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side. And a cemented lens composed of a negative meniscus lens having a convex surface facing the object side and a biconvex lens, a negative meniscus lens having a concave surface facing the object side, and a positive meniscus lens having a concave surface facing the object side.

  The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The second lens group G2 includes a three-piece cemented lens including a negative meniscus lens La having a convex surface facing the object side, a biconvex lens Lb, and a negative meniscus lens Lc having a concave surface facing the object side, a biconvex lens, and a biconvex lens. .

  The third lens group G3 is composed of a biconcave lens, and performs focusing from an object at infinity to a short distance object by moving the third lens group G3 along the optical axis toward the image plane side.

  The fourth lens group G4 includes a biconvex lens having a convex surface on the object side and an aspheric surface.

  The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Subsequently, specification values of the inner focus optical system according to Example 1 are shown below.
Numerical example 1
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 111.9995 3.4734 1.51680 64.20
2 1524.0793 0.2000
3 29.0201 1.9987 1.49700 81.61
4 13.4534 4.0281
5 22.5454 1.0000 1.49700 81.61
6 11.6487 4.3971
7 46.6011 1.0000 1.49700 81.61
8 16.6206 2.2002
9 77.0772 0.8000 1.71300 53.94
10 10.1427 5.7221 1.72825 28.32
11 -149.6735 2.9680
12 -12.6023 1.8746 1.54814 45.82
13 -83.6671 3.0363 1.91082 35.25
14 -18.6796 0.2562
15 (Aperture stop) ∞ 3.0577
16 91.3877 0.8000 1.92286 20.88
17 20.2405 6.5216 1.49700 81.61
18 -14.4992 0.8000 1.92286 20.88
19 -28.2236 0.1263
20 106.8761 4.3352 1.49700 81.61
21 -21.9850 0.1263
22 55.6039 2.2692 1.92286 20.88
23 -185.7095 (d23)
24 -193.2853 0.8000 1.48749 70.44
25 24.3139 (d25)
26 * 61.3656 3.6503 1.59349 67.00
27 -29.5797 0.1500
28 ∞ 4.2000 1.51680 64.20
29 ∞ (BF)
Image plane ∞

[Aspherical data]
26
K 0.0000
A4 -2.08326E-05
A6 7.34646E-08
A8 -5.57038E-10
A10 1.83771E-12
[Various data]
INF 40 times 0.2m
Focal length 12.35 12.35 12.32
F number 1.47 1.48 1.50
Full angle of view 2ω 88.12 88.02 87.77
Image height Y 10.82 10.82 10.82
Total lens length 86.00 86.00 86.00
[Variable interval data]
INF 40 times 0.2m
d0 ∞ 477.0000 114.0000

d23 3.0000 3.4324 4.6496
d25 6.5127 6.0802 4.8631
BF 16.6959 16.6960 16.6959
[Lens group data]
Group Start surface Focal length
G1 1 -48.26
G2 16 22.25
G3 24 -44.25
G4 26 34.14

  FIG. 8 is a lens configuration diagram of the inner focus optical system according to Example 2 of the present invention.

  The lenses of the inner focus optical system in FIG. 8 are, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens having a negative refractive power. The lens group G3 is composed of a fourth lens group G4 having a positive refractive power.

  The first lens group G1 includes a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and an image side surface composed of an aspherical surface, and an object A positive meniscus lens having a convex surface facing the side, a positive meniscus lens having a concave surface facing the object side, a cemented lens made up of a biconcave lens and a biconvex lens.

  The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The second lens group G2 includes a three-lens cemented lens including a negative meniscus lens La and a biconvex lens Lb having a convex surface facing the object side, and a negative meniscus lens Lc having a concave surface facing the object side, and a biconvex lens and the image side surface being non-surface. It consists of a biconvex lens consisting of a spherical surface.

  The third lens group G3 is composed of a negative meniscus lens having a convex surface directed toward the object side. The third lens group G3 is moved from the infinity object to the short distance object by moving the third lens group G3 along the optical axis toward the image plane side. It is carried out.

  The fourth lens group G4 includes a biconvex lens having a convex surface on the object side and an aspheric surface.

  The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Subsequently, specification values of the inner focus optical system according to Example 2 are shown below.
Numerical example 2
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 61.9700 3.4526 1.51680 64.20
2 195.1199 0.2000
3 37.6564 1.5000 1.49700 81.61
4 12.5572 5.3354
5 39.4476 1.5000 1.59349 67.00
6 * 12.1147 4.2353
7 60.0604 1.6538 1.84666 23.78
8 ∞ 1.6987
9 -23.8074 8.0047 1.59349 67.00
10 -20.2140 2.5861
11 -15.7726 0.8000 1.59270 35.45
12 28.6832 3.5481 1.84666 23.78
13 -35.0580 0.5000
14 (Aperture stop) ∞ 2.9894
15 89.1013 0.8000 1.80610 33.27
16 14.2443 9.7939 1.59349 67.00
17 -14.0715 0.8000 1.80610 33.27
18 -41.7388 0.1500
19 36.4960 5.4332 1.59349 67.00
20 -26.8525 0.1263
21 225.8417 2.4607 1.59349 67.00
22 * -64.6965 (d22)
23 70.4259 0.8000 1.48749 70.44
24 18.1604 (d24)
25 84.0917 3.5125 1.43700 95.10
26 -30.7754 0.1500
27 ∞ 4.2000 1.51680 64.20
28 ∞ (BF)
Image plane ∞
[Aspherical data]
6 faces 22 faces
K 0.0000 0.0000
A4 -1.45261E-05 3.03245E-05
A6 -3.19713E-07 -2.89377E-08
A8 2.18843E-09 5.44612E-11
A10 -2.26972E-11 2.16299E-13
[Various data]
INF 40 times 0.2m
Focal length 12.33 12.29 12.15
F number 1.47 1.47 1.47
Full angle of view 2ω 88.70 88.69 88.68
Image height Y 10.82 10.82 10.82
Total lens length 89.64 89.64 89.64
[Variable interval data]
INF 40 times 0.2m
d0 ∞ 475.3552 110.3552
d22 2.0000 2.3791 3.4852
d24 5.4424 5.0633 3.9572
BF 15.9715 15.9715 15.9715
[Lens group data]
Group Start surface Focal length
G1 1 -41.81
G2 15 20.61
G3 23 -50.45
G4 25 52.04

  FIG. 15 is a lens configuration diagram of the inner focus optical system according to Example 3 of the present invention.

  The lens of the inner focus optical system in FIG. 15 includes, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens having a negative refractive power. The lens group G3 is composed of a fourth lens group G4 having a positive refractive power.

  The first lens group G1 includes a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and an image side surface composed of an aspherical surface, and an object Consists of a convex lens with a convex surface on the side, a positive meniscus lens with a concave surface on the object side, a biconcave lens, and a triple-junction lens.

  The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The second lens group G2 includes a three-lens cemented lens including a negative meniscus lens La and a biconvex lens Lb having a convex surface facing the object side, and a negative meniscus lens Lc having a concave surface facing the object side, and a biconvex lens and the image side surface being non-surface. It consists of a biconvex lens consisting of a spherical surface.

  The third lens group G3 is composed of a negative meniscus lens having a convex surface directed toward the object side. The third lens group G3 is moved from the infinity object to the short distance object by moving the third lens group G3 along the optical axis toward the image plane side. It is carried out.

  The fourth lens group G4 is composed of a biconvex lens.

  The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Subsequently, specification values of the inner focus optical system according to Example 3 are shown below.
Numerical example 3
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 94.1558 3.2246 1.51680 64.20
2 1200.0836 0.2000
3 48.5901 1.5000 1.49700 81.61
4 12.8100 5.1784
5 34.9609 1.5000 1.59349 67.00
6 * 11.5418 4.4503
7 45.1993 5.1086 1.84666 23.78
8 ∞ 1.7177
9 -21.9447 8.2345 1.55032 75.49
10 -13.2984 0.8000 1.64769 33.84
11 29.1932 3.9912 1.84666 23.78
12 -34.9133 0.5000
13 (Aperture stop) ∞ 2.4666
14 49.8054 0.8000 1.80610 33.27
15 13.9281 9.4493 1.59349 67.00
16 -17.6773 0.8000 1.80610 33.27
17 -60.0201 0.1500
18 30.2427 5.5071 1.59349 67.00
19 -28.5524 0.1263
20 1423.2341 2.1142 1.59349 67.00
21 * -68.3139 (d21)
22 79.7955 0.8000 1.48749 70.44
23 16.9909 (d23)
24 123.6121 3.1473 1.43700 95.10
25 -27.8516 0.1500
26 ∞ 4.2000 1.51680 64.20
27 ∞ (BF)
Image plane ∞
[Aspherical data]
6 faces 21 faces
K 0.0000 0.0000
A4 -1.62249E-05 3.85559E-05
A6 -5.40875E-07 -2.75521E-08
A8 4.78586E-09 -2.94247E-11
A10 -3.92291E-11 6.00352E-13
[Various data]
INF 40 times 0.2m
Focal length 12.41 12.35 12.19
F number 1.46 1.46 1.46
Full angle of view 2ω 88.19 88.13 88.00
Image height Y 10.82 10.82 10.82
Total lens length 88.51 88.51 88.51
[Variable interval data]
INF 40 times 0.2m
d0 ∞ 479.4899 111.4899
d21 2.0000 2.3345 3.3175
d23 5.1375 4.8029 3.8200
BF 15.2563 15.2563 15.2562
[Lens group data]
Group Start surface Focal length
G1 1 -44.55
G2 14 20.51
G3 22 -44.47
G4 24 52.34

  FIG. 22 is a lens configuration diagram of the inner focus optical system according to Example 4 of the present invention.

  The lenses of the inner focus optical system in FIG. 22 are, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens having a negative refractive power. The lens group G3 is composed of a fourth lens group G4 having a positive refractive power.

  The first lens group G1 includes a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side and an image-side surface made of an aspheric surface, and a biconvex lens And a positive meniscus lens having a concave surface facing the object side, and a three-piece cemented lens composed of a biconcave lens and a biconvex lens.

  The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The second lens group G2 includes a three-lens cemented lens including a negative meniscus lens La and a biconvex lens Lb having a convex surface facing the object side, and a negative meniscus lens Lc having a concave surface facing the object side, and a biconvex lens and the image side surface being non-surface. It consists of a biconvex lens consisting of a spherical surface.

  The third lens group G3 is composed of a negative meniscus lens having a convex surface directed toward the object side. The third lens group G3 is moved from the infinity object to the short distance object by moving the third lens group G3 along the optical axis toward the image plane side. It is carried out.

  The fourth lens group G4 is composed of a biconvex lens.

  The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Subsequently, specification values of the inner focus optical system according to Example 4 are shown below.
Numerical example 4
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 84.5939 3.2460 1.51680 64.20
2 797.6103 0.2000
3 66.8147 1.5000 1.49700 81.61
4 12.7398 5.9756
5 41.5116 1.5000 1.59349 67.00
6 * 11.7656 4.3735
7 44.4076 2.0816 1.90366 31.31
8 -281.9358 2.3034
9 -22.9563 6.8396 1.55032 75.50
10 -13.2984 0.8000 1.64769 33.84
11 38.2640 3.3506 1.84666 23.78
12 -30.1874 4.3711
13 (Aperture stop) ∞ 2.5331
14 48.1820 1.4537 1.80610 33.27
15 13.4074 9.4570 1.59349 67.00
16 -14.9377 0.8000 1.80610 33.27
17 -138.4709 0.1500
18 41.8155 4.8143 1.77250 49.62
19 -27.4108 0.1263
20 159.3318 2.4083 1.59349 67.00
21 * -71.0227 (d21)
22 149.4015 0.8000 1.48749 70.44
23 17.7368 (d23)
24 86.9239 3.5702 1.43700 95.10
25 -27.8966 0.1500
26 ∞ 4.2000 1.51680 64.20
27 ∞ (BF)
Image plane ∞
[Aspherical data]
6 faces 21 faces
K 0.0000 0.0000
A4 -3.57723E-05 3.68805E-05
A6 -4.18787E-07 -5.56128E-08
A8 2.34966E-09 3.15561E-10
A10 -3.33633E-11 -8.31317E-13
[Various data]
INF 40 times 0.2m
Focal length 12.22 12.17 12.01
F number 1.46 1.46 1.46
Full angle of view 2ω 89.26 89.23 89.17
Image height Y 10.82 10.82 10.82
Total lens length 88.51 88.51 88.51
[Variable interval data]
INF 40 times 0.2m
d0 ∞ 471.4900 111.4901
d21 2.0000 2.3158 3.2195
d23 5.1062 4.7904 3.8867
BF 14.3993 14.3993 14.3993
[Lens group data]
Group Start surface Focal length
G1 1 -60.32
G2 14 20.39
G3 22 -41.37
G4 24 48.79

  FIG. 29 is a lens configuration diagram of the inner focus optical system according to Example 5 of the present invention.

  The lenses of the inner focus optical system in FIG. 29 are, in order from the object side to the image side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens having a negative refractive power. The lens group G3 is composed of a fourth lens group G4 having a positive refractive power.

  The first lens group G1 includes a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side and an image-side surface made of an aspheric surface, and a biconvex lens And a positive meniscus lens having a concave surface facing the object side, and a three-piece cemented lens composed of a biconcave lens and a biconvex lens.

  The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The second lens group G2 includes a three-lens cemented lens including a negative meniscus lens La and a biconvex lens Lb having a convex surface facing the object side, and a negative meniscus lens Lc having a concave surface facing the object side, and a biconvex lens and the image side surface being non-surface. It consists of a biconvex lens consisting of a spherical surface.

  The third lens group G3 is composed of a negative meniscus lens having a convex surface directed toward the object side. The third lens group G3 is moved from the infinity object to the short distance object by moving the third lens group G3 along the optical axis toward the image plane side. It is carried out.

  The fourth lens group G4 is composed of a biconvex lens.

  The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Subsequently, specification values of the inner focus optical system according to Example 5 are shown below.
Numerical example 5
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 92.7835 3.0140 1.51680 64.20
2 944.7431 0.2000
3 61.5507 1.5000 1.49700 81.61
4 12.6652 6.8120
5 46.9978 1.5000 1.59349 67.00
6 * 11.7745 4.1858
7 46.1775 1.9567 1.90366 31.31
8 -365.5764 2.8857
9 -20.8072 4.0393 1.55032 75.50
10 -10.8701 0.8000 1.64769 33.84
11 40.6050 3.7101 1.84666 23.78
12 -24.3611 4.3990
13 (Aperture stop) ∞ 1.8197
14 48.8138 3.1111 1.80610 33.27
15 13.4037 9.7120 1.59349 67.00
16 -14.2433 0.8000 1.80610 33.27
17 -157.7796 0.1500
18 45.7722 4.7785 1.77250 49.62
19 -26.1471 0.1263
20 234.9351 2.4179 1.59349 67.00
21 * -64.4738 (d21)
22 131.2250 0.8000 1.48749 70.44
23 17.6774 (d23)
24 56.0468 3.9772 1.43700 95.10
25 -29.5065 0.1500
26 ∞ 4.2000 1.51680 64.20
27 ∞ (BF)
Image plane ∞
[Aspherical data]
6 faces 21 faces
K 0.0000 0.0000
A4 -3.48384E-05 3.29882E-05
A6 -4.95711E-07 -4.94954E-08
A8 3.58410E-09 2.79280E-10
A10 -4.44666E-11 -7.30904E-13
[Various data]
INF 40 times 0.2m
Focal length 12.34 12.29 12.16
F number 1.47 1.47 1.47
Full angle of view 2ω 88.55 88.49 88.35
Image height Y 10.82 10.82 10.82
Total lens length 89.01 89.01 89.01
[Variable interval data]
INF 40 times 0.2m
d0 ∞ 475.9851 110.9851
d21 2.0000 2.3357 3.3160
d23 5.2689 4.9332 3.9529
BF 14.7008 14.7008 14.7008
[Lens group data]
Group Start surface Focal length
G1 1 -62.04
G2 14 21.42
G3 22 -42.00
G4 24 44.87

  FIG. 36 is a lens configuration diagram of the inner focus optical system according to Example 6 of the present invention.

  36, in order from the object side to the image side, the first lens group G1 having a negative refractive power, the second lens group G2 having a positive refractive power, and a third lens having a negative refractive power. The lens group G3 is composed of a fourth lens group G4 having a positive refractive power.

  The first lens group G1 includes a biconvex lens, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and both surfaces made of aspheric surfaces, a biconvex lens, and a positive surface having a concave surface facing the object side. It is composed of a three-piece cemented lens composed of a meniscus lens, a biconcave lens, and a biconvex lens.

  The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The second lens group G2 includes a cemented triplet composed of a negative meniscus lens La having a convex surface facing the object side, a biconvex lens Lb, and a negative meniscus lens Lc having a concave surface facing the object side, a biconvex lens, and both sides facing the concave surface on the object side Is a positive meniscus lens having an aspheric surface.

  The third lens group G3 is composed of a negative meniscus lens having a convex surface directed toward the object side. The third lens group G3 is moved from the infinity object to the short distance object by moving the third lens group G3 along the optical axis toward the image plane side. It is carried out.

  The fourth lens group G4 is composed of a biconvex lens.

  The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Subsequently, specification values of the inner focus optical system according to Example 6 are shown below.
Numerical example 6
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 148.0172 2.3711 1.51680 64.20
2 -142366.9122 0.2000
3 65.4978 1.5000 1.49700 81.61
4 13.0033 6.7242
5 * 45.5902 1.5000 1.59349 67.00
6 * 12.1958 4.8171
7 48.5613 2.0527 1.90366 31.31
8 -260.8483 3.6912
9 -21.2467 3.3049 1.55032 75.50
10 -12.7614 0.8000 1.64769 33.84
11 35.9287 3.7451 1.84666 23.78
12 -28.2061 4.4220
13 (Aperture stop) ∞ 1.2399
14 40.2489 2.2389 1.80610 33.27
15 13.8101 10.0558 1.59349 67.00
16 -13.8912 0.8000 1.80610 33.27
17 -488.3151 0.1500
18 40.0072 4.9275 1.77250 49.62
19 -27.8584 0.1263
20 * -2983.7281 2.4541 1.59349 67.00
21 * -45.6636 (d21)
22 148.4414 0.8000 1.48749 70.44
23 17.3319 (d23)
24 50.7900 4.0570 1.43700 95.10
25 -30.7400 0.1500
26 ∞ 4.2000 1.51680 64.20
27 ∞ (BF)
Image plane ∞
[Aspherical data]
5 faces 6 faces 20 faces 21 faces
K 0.0000 0.0000 0.0000 0.0000
A4 -8.29511E-07 -4.30314E-05 -7.15980E-06 2.92706E-05
A6 1.32579E-07 -1.77753E-07 2.02067E-08 -1.14763E-08
A8 -9.99712E-10 -2.39719E-10 1.65705E-09 1.95036E-09
A10 3.83778E-12 -1.47642E-11 -7.40897E-12 -7.97317E-12
[Various data]
INF 40 times 0.2m
Focal length 12.46 12.42 12.28
F number 1.46 1.46 1.47
Full angle of view 2ω 88.37 88.27 87.98
Image height Y 10.82 10.82 10.82
Total lens length 89.02 89.02 89.02
[Variable interval data]
INF 40 times 0.2m
d0 ∞ 482.9801 110.9801
d21 2.0000 2.3167 3.2633
d23 5.2288 4.9121 3.9656
BF 15.4632 15.4632 15.4631
[Lens group data]
Group Start surface Focal length
G1 1 -48.82
G2 14 21.29
G3 22 -40.33
G4 24 44.49

  FIG. 43 is a lens configuration diagram of the inner focus optical system according to Example 7 of the present invention.

  43, in order from the object side to the image side, the first lens group G1 having a negative refractive power, the second lens group G2 having a positive refractive power, and a third lens having a negative refractive power. The lens group G3 is composed of a fourth lens group G4 having a positive refractive power.

  The first lens group G1 includes a biconvex lens, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and both surfaces made of aspheric surfaces, a biconvex lens, and a positive surface having a concave surface facing the object side. It is composed of a three-piece cemented lens composed of a meniscus lens, a biconcave lens, and a biconvex lens.

  The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The second lens group G2 includes a cemented triplet composed of a negative meniscus lens La having a convex surface facing the object side, a biconvex lens Lb, and a negative meniscus lens Lc having a concave surface facing the object side, a biconvex lens, and both sides facing the concave surface on the object side Is a positive meniscus lens having an aspheric surface.

  The third lens group G3 is composed of a negative meniscus lens having a convex surface directed toward the object side. The third lens group G3 is moved from the infinity object to the short distance object by moving the third lens group G3 along the optical axis toward the image plane side. It is carried out.

  The fourth lens group G4 includes a cemented lens including a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens.

  The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Subsequently, specification values of the inner focus optical system according to Example 7 are shown below.
Numerical example 7
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 214.0210 2.4795 1.51680 64.20
2 -459.3514 0.2000
3 57.7775 1.5000 1.49700 81.61
4 11.8460 5.1583
5 * 24.7464 1.5000 1.59349 67.00
6 * 11.7790 5.2477
7 246.2613 1.3749 1.90366 31.31
8 -138.8222 3.6238
9 -17.6844 3.9828 1.55032 75.50
10 -10.7668 0.8000 1.59270 35.45
11 36.7595 4.0829 1.84666 23.78
12 -28.0517 1.6945
13 (Aperture stop) ∞ 2.2258
14 39.5254 2.3574 1.80610 33.27
15 14.1896 11.1402 1.59349 67.00
16 -15.5283 0.8000 1.80610 33.27
17 -131.8122 0.1500
18 46.4965 5.1616 1.77250 49.62
19 -29.2158 0.1263
20 * 549.1239 2.3942 1.59349 67.00
21 * -58.2043 (d21)
22 209.7375 0.8000 1.48749 70.44
23 23.2521 (d23)
24 32.8717 0.8000 1.83481 42.72
25 16.6499 6.5071 1.43700 95.10
26 -29.8402 0.1500
27 ∞ 4.2000 1.51680 64.20
28 ∞ (BF)
Image plane ∞
[Aspherical data]
5 faces 6 faces 20 faces 21 faces
K 0.0000 0.0000 0.0000 0.0000
A4 3.04792E-05 7.94799E-06 1.20612E-05 4.69646E-05
A6 -1.49310E-07 -4.83730E-07 2.40482E-07 2.38747E-07
A8 1.12955E-09 3.15734E-09 -2.91096E-10 -2.27444E-10
A10 -2.41320E-12 -3.27600E-11 -8.66765E-13 -5.28665E-13
[Various data]
INF 40 times 0.2m
Focal length 12.39 12.33 12.17
F number 1.46 1.46 1.46
Full angle of view 2ω 88.34 88.40 88.61
Image height Y 10.82 10.82 10.82
Total lens length 89.02 89.02 89.02
[Variable interval data]
INF 40 times 0.2m
d0 ∞ 480.9801 110.9801
d21 2.0000 2.3699 3.4830
d23 5.4429 5.0730 3.9598
BF 13.1199 13.1199 13.1200
[Lens group data]
Group Start surface Focal length
G1 1 -40.25
G2 14 21.10
G3 22 -53.72
G4 24 61.98

[Values for conditional expressions]
Condition / Example EX1 EX2 EX3 EX4 EX5 EX6 EX7

(1) -6.5 <f1 / f <-2.8 -3.91 -3.39 -3.59 -4.94 -5.03 -3.92 -3.25
(2) -5.6 <f3 / f <-3.0 -3.58 -4.09 -3.58 -3.39 -3.40 -3.24 -4.34
(3) -0.68 <f2 / f1 <-0.24 -0.46 -0.49 -0.46 -0.34 -0.35 -0.44 -0.52
(4) 0.5 <FcEntp / f3 <0.95 0.68 0.82 0.73 0.86 0.87 0.79 0.78
(5) FcEntp / f <-2.0 -2.43 -3.37 -2.63 -2.91 -2.97 -2.55 -3.37
(6) -0.15 <f / fabc <0.06 -0.08 -0.02 0.03 -0.09 -0.10 -0.10 -0.02
(7) 0.5 <OALabc / f <1.5 0.66 0.92 0.89 0.96 1.10 1.05 1.15
(8) -1.3 <M4 ² × (1-M3 ² ) <-0.5 -0.72 -0.82 -0.93 -0.97 -0.93 -0.99 -0.84

G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group La Negative lens Lb composing 3 lens cemented lenses Positive lens Lc composing 3 lens cemented lenses Negative lens S composing 3 lens cemented lenses Aperture stop FL Optical filter I Image plane

Claims (4)

In order from the object side to the image side, the first lens group G1 having a negative refractive power, the aperture stop, the second lens group G2 having a positive refractive power, the third lens group G3 having a negative refractive power, and a positive lens The fourth lens group G4 having a refractive power is characterized in that the third lens group G3 moves in the image plane direction and satisfies the following conditions when focusing from the infinity object side to the near object side. Inner focus optical system.
(1) -6.5 <f1 / f <-2.8
(2) -5.6 <f3 / f <-3.0
(3) -0.68 <f2 / f1 <-0.24
Where f: focal length in the infinite focus state of the entire system f1: focal length of the first lens group G1 f2: focal length of the second lens group G2 f3: focal length of the third lens group G3
When the object side surface of the third lens group G3 at the time of focusing on infinity is used as a reference, and the imaging position of the aperture stop by the second lens group G2 is FcEntp, the following conditions are satisfied: The inner focus optical system according to claim 1, wherein:
(4) 0.5 <FcEntp / f3 <0.95
(5) FcEntp / f <−2.0
A lens having a negative refractive power La, a positive refractive power lens Lb, and a negative refractive power lens Lc are cemented on the image plane side of the aperture stop, and the lenses La and Lb 3. The inner focus optical system according to claim 1, wherein a focal length and a composite thickness of the cemented lens of Lc and Lc satisfy the following conditions.
(6) -0.15 <f / fabc <0.06
(7) 0.5 <OALAbc / f <1.5
However, the focal length of the cemented lens of fabc: La, Lb, and Lc OALabc: the combined thickness of the cemented lens of La, Lb, and Lc
The inner focus optical system according to claim 1, wherein the following condition is satisfied.
(8) -1.3 <M4 ² × (1-M3 ² ) <− 0.5
However,
M3: Lateral magnification of the third lens group when the object distance is infinity M4: Lateral magnification of the fourth lens group when the object distance is infinity

Images