JP2019211703A - Imaging optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system which is small in size, can have a light weight focus lens, can be photographed at a short photographing distance, and has a reduced light emission angle. A first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power are arranged in this order from the object side. When focusing from an object at infinity to a near object, the distance between the first lens group G1 and the second lens group G2 is reduced, and the second lens group G2 and the third lens group G3 are Is widened, the second lens group G2 is moved to the object side, and a specific condition is satisfied. [Selection diagram] Figure 1

Description

  The present invention relates to a compact imaging optical system used in an imaging apparatus such as a digital camera or a video camera.

  In recent years, imaging devices such as digital still cameras and video cameras have become widespread. Among them, in the interchangeable lens digital still camera, a mirror for guiding the light beam to the finder optical system is arranged between the imaging optical system and the image sensor. There is an imaging apparatus in which the distance between the imaging optical system and the imaging element is shortened.

  Among them, a large-sized image pickup device is used, and a downsized image pickup device is widely used. The imaging optical system is also required to be downsized with respect to the downsized imaging apparatus. By increasing the size of the image sensor, even a lens with a large F-number can be photographed with a shallow depth of field and a large amount of background blur. When the distance between the background and the subject increases, the amount of blur in the background increases, so it is preferable that the shooting distance at which shooting can be performed can be shortened.

  In addition, an image sensor widely used in an image pickup apparatus generally has a characteristic that sensitivity decreases with respect to light having a large incident angle on the image sensor. Therefore, when the incident angle on the image sensor is large, a peripheral light amount is reduced. . Therefore, it is necessary to suppress the decrease in sensitivity by suppressing the incident angle to the image sensor, that is, the light emission angle from the imaging optical system.

  In view of the above, there is a demand for an imaging optical system that is compact and can be photographed at a short photographing distance and that has a reduced light emission angle.

  Patent documents relating to the above are disclosed in, for example, Patent Documents 1 to 5.

JP 2013-195587 A WO2013 / 099211 Japanese Patent Laying-Open No. 2015-041012 Japanese Patent Laid-Open No. 06-222260 JP 09-236746 A

  In Patent Documents 1 and 2, the lens used for focusing is larger than the peripheral image height. Therefore, the actuator for moving the focus lens becomes large. In an imaging apparatus having a large imaging element, it is difficult to reduce the size, which is not preferable.

  Patent Document 3 is not preferable because only one lens is used for focusing, and axial chromatic aberration increases when the shooting distance is shortened.

  Patent Documents 4 and 5 are miniaturized by shortening the image circle corresponding to a large image sensor and the total optical length. However, since the light emission angle is large, it is not suitable for a general image sensor.

  The present invention has been made in view of such circumstances, and provides an imaging optical system that is small in size, can be made light in focus lens, can be photographed at a short photographing distance, and has a reduced light emission angle. The purpose is to do.

The first invention for solving the above-described problem is, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a negative refraction. The second lens group G3 includes a third lens group G3 having power, and the distance between the first lens group G1 and the second lens group G2 is reduced when focusing from an object at infinity to an object at a short distance. An imaging optical system characterized in that an interval between the group G2 and the third lens group G3 is widened, the second lens group G2 is moved toward the object side, and the following conditional expression is satisfied.
(1) 1.40 <f / f12 <2.80
(2) 0.020 <G3ΔPgFmax <0.300
(3) 1.80 <G3nd
(4) 0.60 <f1 / f <6.50
f: Focal length of the entire system in the infinite focus state f12: Composite focal length G3ΔPgFmax of the first lens group G1 and the second lens group G2 in the infinite focus state: of the positive lens of the third lens group G3 Of these, the largest ΔPgF value ΔPgF = PgF−0.64833 + 0.00180νd: g, abnormal partial dispersibility between F lines PgF = (ng−nF) / (nF−nC): g, partial dispersion between F lines Ratio ng: Refractive index for g-line (wavelength λ = 435.84 nm) nF: Refractive index for F-line (wavelength λ = 486.13 nm) nC: Refractive index G for C-line (wavelength λ = 656.27 nm) G3nd: Refractive index f1: with respect to the d-line (wavelength λ = 587.56) of the positive lens in the three lens group G3 The focal length of the first lens group G1

In the second invention, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power. The distance between the first lens group G1 and the second lens group G2 is reduced when focusing from an object at infinity to a short distance object, and the second lens group G2 and the third lens group An imaging optical system characterized in that the distance from G3 is widened, the second lens group G2 moves to the object side, and the following conditional expression is satisfied.
(1) 1.40 <f / f12 <2.80
(5) 2.0 <LT / (Ymax) <3.10
(6) 2.00 <K2 <5.00
(9) 0.50 <((D1_2) * K2) / f <1.40
f: Focal length of the entire system in the infinite focus state f12: Composite focal length of the first lens group G1 and the second lens group G2 in the infinite focus state LT: The first lens in the infinite focus state For the sake of convenience, Ymax = (f * tan (w)), which is not defined as the distance between the most object-side surfaces of the group G1 and the image plane Ymax: the maximum image height Ymax and the effective half angle of view w can be discriminated. And
K2: Focus sensitivity of the second lens group G2 in the infinite focus state K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f1 of the second lens group G2 in FIG. 1: Focal length D1_2 of the first lens group G1: The most image-side surface of the first lens group G1 and the most object of the second lens group G2 in the infinite focus state Spacing between side faces

In the third invention, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power. The distance between the first lens group G1 and the second lens group G2 is reduced when focusing from an object at infinity to a short distance object, and the second lens group G2 and the third lens group An imaging optical system characterized in that the distance from G3 is widened, the second lens group G2 moves toward the object side, and the following conditional expression is satisfied.
(1) 1.40 <f / f12 <2.80
(2) 0.020 <G3ΔPgFma <0.300
(3) 1.80 <G3nd
(5) 2.0 <LT / (Ymax) <3.10
f: Focal length of the entire system in the infinite focus state f12: Composite focal length G3ΔPgFmax of the first lens group G1 and the second lens group G2 in the infinite focus state: of the positive lens of the third lens group G3 Of these, the largest ΔPgF value ΔPgF = PgF−0.64833 + 0.00180νd: g, abnormal partial dispersibility between F lines PgF = (ng−nF) / (nF−nC): g, partial dispersion between F lines Ratio ng: Refractive index for g-line (wavelength λ = 435.84 nm) nF: Refractive index for F-line (wavelength λ = 486.13 nm) nC: Refractive index G for C-line (wavelength λ = 656.27 nm) G3nd: Refractive index LT with respect to the d-line (wavelength λ = 587.56) of the positive lens in the third lens group G3: from the most object-side surface to the image plane of the first lens group G1 in the infinite focus state For the sake of convenience, it is assumed that Ymax = (f * tan (w)) where the effective half field angle w is not defined because the maximum image height Ymax is not defined.

In the fourth invention, in order from the object side, a first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power. The first lens group G1 is fixed with respect to the image plane, and the third lens group G3 is fixed with respect to the image plane when focusing from an object at infinity to an object at a short distance. The imaging optical system is characterized in that the second lens group G2 moves to the object side and satisfies the following conditional expression.
(1) 1.40 <f / f12 <2.80
(2) 0.020 <G3ΔPgFmax <0.300
(5) 2.0 <LT / (Ymax) <3.10
(6) 2.00 <K2 <5.00
f: Focal length of the entire system in the infinite focus state f12: Composite focal length G3ΔPgFmax of the first lens group G1 and the second lens group G2 in the infinite focus state: of the positive lens of the third lens group G3 Of these, the largest ΔPgF value ΔPgF = PgF−0.64833 + 0.00180νd: g, abnormal partial dispersibility between F lines PgF = (ng−nF) / (nF−nC): g, partial dispersion between F lines Ratio ng: Refractive index for g-line (wavelength λ = 435.84 nm) nF: Refractive index for F-line (wavelength λ = 486.13 nm) nC: Refractive index for C-line (wavelength λ = 656.27 nm) LT: Infinity In the in-focus state, the definition of the surface interval Ymax: maximum image height Ymax from the most object-side surface of the first lens group G1 to the image surface is not made, and an effective half field angle w can be determined. For convenience, and Ymax = (f * tan (w)) of.
K2: Focus sensitivity of the second lens group G2 in the infinite focus state K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f1 of the second lens group G2 at: a focal length of the first lens group G1

According to a fifth aspect of the present invention, there is provided the imaging optical system according to the second aspect, wherein the following condition is satisfied.
(2) 0.020 <G3ΔPgFmax <0.300
G3ΔPgFmax: The largest ΔPgF value among positive lenses in the third lens group G3 ΔPgF = PgF−0.64833 + 0.00180νd: g, anomalous partial dispersion PgF between F lines = (ng−nF) / (nF -NC): Partial dispersion ratio between g and F lines ng: Refractive index for g line (wavelength λ = 435.84 nm) nF: Refractive index for F line (wavelength λ = 486.13 nm) nC: C line (wavelength λ = 656.27 nm) refractive index G3nd: refractive index with respect to d-line (wavelength λ = 587.56) of the positive lens of the third lens group G3

According to a sixth aspect of the present invention, there is provided the imaging optical system according to any one of the second, fourth and fifth aspects, wherein the following condition is satisfied.
(3) 1.80 <G3nd
G3nd: refractive index with respect to d-line (wavelength λ = 587.56) of the positive lens of the third lens group G3

An image forming optical system according to any one of the second to sixth inventions, wherein the seventh invention satisfies the following condition.
(4) 0.60 <f1 / f <6.50
f: focal length of the entire system in the infinitely focused state f1: focal length of the first lens group G1

According to an eighth aspect of the present invention, there is provided the imaging optical system according to the first aspect, wherein the following condition is satisfied.
(5) 2.0 <LT / (Ymax) <3.10
LT: The distance between the most object side surface of the first lens group G1 in the infinite focus state and the image plane Ymax: the maximum image height Ymax is not defined, and an effective half field angle w can be discriminated. For convenience, it is assumed that Ymax = (f * tan (w)).

According to a ninth aspect of the present invention, there is provided the imaging optical system according to any one of the first, third, seventh and eighth aspects, wherein the following conditions are satisfied.
(6) 2.00 <K2 <5.00
K2: Focus sensitivity of the second lens group G2 in the infinite focus state K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f of the second lens group G2 in FIG. 5: focal length of the entire system in the infinite focus state f12: combined focus f1 of the first lens group G1 and the second lens group G2 in the infinite focus state f1: Focal length of the first lens group G1

An image forming optical system according to any one of the first to ninth aspects, wherein the tenth aspect satisfies the following condition.
(7) 0.30 <f2 / f <0.95
f2: focal length of the second lens group G2 f: focal length of the entire system in the infinitely focused state

An eleventh aspect of the present invention is the imaging optical system according to any one of the first to tenth aspects of the present invention, wherein the following conditions are satisfied.
(8) 0.30 <| f3 / f | <1.40
f3: focal length of the third lens group G3 f: focal length of the entire system in the infinitely focused state

The twelfth invention satisfies the following conditions, and the imaging optical system according to any one of the first invention, the third invention, the fourth invention, and the seventh to eleventh inventions system.
(9) 0.50 <((D1_2) * K2) / f <1.40
D1_2: the distance between the most image side surface of the first lens group G1 in the infinite focus state and the most object side surface of the second lens group G2 K2: the second lens group G2 in the infinite focus state Focus sensitivity K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f of the second lens group G2 in FIG. 5: focal length f1 of the entire system in the infinitely focused state f1: focal length f12 of the first lens group G1: the first lens group G1 in the infinitely focused state and the above Composite focal length of the second lens group G2

  In a thirteenth aspect of the invention, the first lens group G1 is fixed with respect to the image plane and the third lens group G3 is fixed with respect to the image plane when focusing from an object at infinity to an object at a short distance. The imaging optical system according to any one of the first to third inventions and the fifth to twelfth inventions, characterized in that:

  In a fourteenth aspect of the invention, the aperture stop S is adjacent to the image side of the first lens group G1 and is fixed in the optical axis direction during focusing. The imaging optical system according to any one of the above.

The fifteenth aspect of the present invention is the image forming optical system according to any one of the first to fourteenth aspects of the present invention, which satisfies the following conditional expression.
(10) 1.60 <| EXP / Ymax | <3.50
EXP: Distance from exit pupil position to image plane in infinite focus state Ymax: Maximum image height Ymax is not defined and effective half angle of view w can be determined for convenience.
Ymax = (f * tan (w)).

  According to a sixteenth aspect of the invention, the first lens group G1 includes a positive lens L1 and a negative lens L2 in order from the object side, and has a positive refractive power as a whole. The imaging optical system according to any one of the above.

  In a seventeenth aspect, the second lens group G2 includes a negative lens L3, a positive lens L4, and a positive lens L5 in order from the object side, and has a positive refractive power as a whole. The imaging optical system according to any one of 16 inventions.

  In an eighteenth aspect of the invention, the third lens group G3 includes a negative lens L6, a negative lens L7, and a positive lens L8 in order from the object side, and has a negative refractive power as a whole. The imaging optical system according to any one of the seventeenth inventions.

  The present invention can provide an imaging optical system that is small in size, can be made light in focus lens, can be photographed at a short photographing distance, and has a reduced light emission angle.

It is a lens block diagram at the time of infinity focusing which concerns on Example 1 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 1 of this invention. It is a lateral aberration diagram at the time of focusing on infinity according to Example 1 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 240 mm according to Example 1 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance of 240 mm according to Example 1 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 2 of this invention. It is a longitudinal aberration diagram at the time of focusing on infinity according to Example 2 of the present invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 2 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 240 mm according to Example 2 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance of 240 mm according to Example 2 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 3 of this invention. It is a longitudinal aberration diagram at the time of focusing on infinity according to Example 3 of the present invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 3 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 200 mm according to Example 3 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance of 200 mm according to Example 3 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 4 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 4 of this invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 4 of the present invention. It is a longitudinal aberration figure in photographing distance 220mm concerning Example 4 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 220 mm according to Example 4 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 5 of this invention. It is a longitudinal aberration figure at the time of infinity focusing which concerns on Example 5 of this invention. It is a lateral aberration figure at the time of infinity focusing based on Example 5 of this invention. FIG. 10 is a longitudinal aberration diagram at an imaging distance of 210 mm according to Example 5 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 210 mm according to Example 5 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 6 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 6 of this invention. It is a lateral aberration figure at the time of infinity focusing which concerns on Example 6 of this invention. It is a longitudinal aberration figure in photographing distance 260mm concerning Example 6 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 260 mm according to Example 6 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 7 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 7 of this invention. It is a lateral aberration diagram at the time of focusing on infinity according to Example 7 of the present invention. It is a longitudinal aberration figure in photographing distance 260mm concerning Example 7 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 260 mm according to Example 7 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 8 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 8 of this invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 8 of the present invention. It is a longitudinal aberration figure in shooting distance 290mm concerning Example 8 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 290 mm according to Example 8 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 9 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 9 of this invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 9 of the present invention. FIG. 12 is a longitudinal aberration diagram at an imaging distance of 240 mm according to Example 9 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 240 mm according to Example 9 of the present invention. It is a longitudinal aberration figure in photographing distance 150mm concerning Example 9 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 150 mm according to Example 9 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 10 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 10 of this invention. It is a lateral aberration figure at the time of infinity focusing based on Example 10 of this invention. It is a longitudinal aberration figure in photographing distance 290mm concerning Example 10 of the present invention. It is a lateral aberration figure in photographing distance 290mm concerning Example 10 of the present invention.

  In order from the object side, the first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power, are arranged at infinity. When focusing from an object to a short-distance object, the distance between the first lens group G1 and the lens group G2 is reduced, and the distance between the second lens group G2 and the third lens group G3 is increased. The second lens group G2 is configured to move toward the object side.

  By using the first lens group G1 having a positive refractive power, the diameter of the light beam passing through the image-side lens can be reduced in order to reduce the size of the entire system lens.

  By disposing the aperture stop S between the first lens group G1 and the second lens group G2, the exit pupil position can be brought closer to the object side, and the light exit angle can be reduced.

  By using the second lens group G2 having a positive refractive power and satisfying the conditions described later, aberration correction at the time of focusing and downsizing of the entire lens system can be performed.

  By setting the third lens group G3 having negative refractive power and satisfying the conditions described later, it is possible to balance the enlargement of the image circle, the miniaturization of the entire lens system, and the correction of aberrations.

  In the present invention, the distance between the second lens group G2 and the third lens group G3 is widened when focusing from an object at infinity to an object at a short distance, thereby reducing the amount of lens movement. Can do.

The following conditional expressions are satisfied.
(1) 1.40 <f / f12 <2.80
(2) 0.020 <G3ΔPgFmax <0.300
(3) 1.80 <G3nd
(4) 0.60 <f1 / f <6.50
f: Focal length of the entire system in the infinite focus state f12: Composite focal length G3ΔPgFmax of the first lens group G1 and the second lens group G2 in the infinite focus state: of the positive lens of the third lens group G3 Of these, the largest ΔPgF value ΔPgF = PgF−0.64833 + 0.00180νd: g, abnormal partial dispersibility between F lines PgF = (ng−nF) / (nF−nC): g, partial dispersion between F lines Ratio ng: Refractive index for g-line (wavelength λ = 435.84 nm) nF: Refractive index for F-line (wavelength λ = 486.13 nm) nC: Refractive index G for C-line (wavelength λ = 656.27 nm) G3nd: Refractive index f1: with respect to the d-line (wavelength λ = 587.56) of the positive lens in the three lens group G3 The focal length of the first lens group G1

  When focusing from an object at infinity to an object at a short distance, the distance between the second lens group G2 and the third lens group G3 is increased, and in accordance with the conditional expression (1), the lens is moved during focusing. A focus method with a small amount can be adopted. Therefore, it is possible to reduce the size of the entire system and to perform shooting at a short shooting distance, and it is possible to satisfactorily correct lateral chromatic aberration by combining with conditional expression (2).

  Conditional expression (1) defines the lateral magnification of the third lens group G3 as a preferable condition for increasing the image circle, downsizing the entire lens system, and balancing aberration correction.

  If the lateral magnification of the third lens group G3 exceeds the upper limit of the conditional expression (1), the residual aberration of the combined system of the first lens group G1 and the second lens group G2 is enlarged, which is not preferable. If the lateral magnification of the third lens group G3 becomes smaller than the lower limit of conditional expression (1), the image circle becomes smaller and the amount of lens movement at the time of focusing also increases, making it difficult to downsize the entire lens system. Become. If only the movement amount of the lens at the time of focusing is reduced, the photographing distance becomes longer, which is not preferable.

  Regarding conditional expression (1), desirably, the lower limit value is preferably set to 1.55 and the upper limit value is set to 2.50, so that the above-described effect can be further ensured.

  Conditional expression (2) defines an anomalous partial dispersion of the medium used for the positive lens of the third lens group G3 as a preferable condition for correcting the chromatic aberration of magnification.

  In the light beam passing through the third lens group G3 of the present invention, the axial light beam passes near the center of the third lens group G3, and the off-axis light beam passes near the periphery of the third lens group G3. The closer the image plane in the third lens group G3 is, the more noticeable the difference between the passing points of the on-axis light beam and the off-axis light beam is. Therefore, it is possible to separately correct the lateral chromatic aberration due to the off-axis light beam depending on the condition of the medium.

  If the upper limit of conditional expression (2) is exceeded and the anomalous partial dispersibility increases, the chromatic aberration of g-line will increase underly, making it difficult to correct lateral chromatic aberration. If the lower limit of conditional expression (2) is exceeded and the anomalous partial dispersion becomes small, especially the chromatic aberration of g-line becomes excessively large, and it becomes difficult to correct lateral chromatic aberration.

  Regarding conditional expression (2), preferably, the lower limit value is preferably set to 0.025 and the upper limit value is set to 0.100, so that the above-described effect can be further ensured.

  Conditional expression (3) defines the refractive index of the positive lens of the third lens group G3 as a preferable condition for correcting astigmatism.

  If the lower limit of conditional expression (3) is exceeded and G3nd is reduced, the radius of curvature must be reduced in order to obtain the refractive power of G3, and astigmatism increases, which is not preferable.

  Regarding conditional expression (3), preferably, the lower limit value is preferably set to 1.90, whereby the above-described effect can be further ensured.

  Conditional expression (4) defines the ratio of the focal length of the first lens group G1 to the entire system as a preferable condition for downsizing and aberration correction of the entire lens system.

  If the upper limit of conditional expression (4) is exceeded and the refractive power of the first lens group G1 becomes small, it becomes difficult to downsize the entire lens system. If the lower limit of conditional expression (4) is exceeded and the refractive power of the first lens group G1 increases, the balance of aberration correction with the second lens group G2 is lost, which is not preferable.

  Regarding conditional expression (4), preferably, the lower limit value is desirably set to 0.95 and the upper limit value is defined to be 4.50, whereby the above-described effect can be further ensured.

The present invention is configured to satisfy the following conditional expression.
(5) 2.00 <LT / (Ymax) <3.10
LT: The distance between the most object side surface of the first lens group G1 in the infinite focus state and the image plane Ymax: the maximum image height Ymax is not defined, and an effective half field angle w can be discriminated. For convenience, Ymax = (f * tan (w)).

  Conditional expression (5) defines the relationship between the length of the entire lens system and the maximum image height as a preferable condition for the balance between the downsizing of the entire lens system and aberration correction.

  When the upper limit of conditional expression (5) is exceeded, it exceeds 1.5 times the image circle, and it cannot be said that the image circle is downsized, and the object of the present invention cannot be achieved. When the lower limit of conditional expression (5) is exceeded, the entire lens system becomes small, and the amount of aberration generated by the increase in the refractive power of each group increases, making it difficult to correct aberrations satisfactorily.

  Regarding conditional expression (5), desirably, the lower limit value is preferably set to 2.45, and the upper limit value is specified to be 3.05, whereby the above-described effect can be further ensured.

The present invention is configured to satisfy the following conditional expression.
(6) 2.00 <K2 <5.00
K2: Focus sensitivity of the second lens group G2 in the infinite focus state K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification of the second lens group G2 at f: Focal length of the entire system in the infinite focus state f12: Composite focal length of the first lens group G1 and the second lens group G2 in the infinite focus state

  Conditional expression (6) defines the focus sensitivity of the second lens group as a preferable condition for the balance between the miniaturization of the entire lens system and aberration correction.

  If the upper limit of conditional expression (6) is exceeded and the refractive power of each group increases, the amount of aberration generated increases, making it difficult to perform good aberration correction. Further, since the focus sensitivity is increased, it becomes difficult to satisfy the drive accuracy required at the time of focusing. If the lower limit of conditional expression (6) is exceeded and the amount of movement of the second lens group G2 increases, it becomes difficult to reduce the size of the entire lens system.

  Regarding conditional expression (6), preferably, the lower limit value is preferably set to 2.30 and the upper limit value is set to 4.80, whereby the above-described effect can be further ensured.

The present invention is configured to satisfy the following conditional expression.
(7) 0.30 <f2 / f <0.95
f2: Focal length of the second lens group G2
f: focal length of the entire system in the infinitely focused state

  Conditional expression (7) defines the ratio between the focal length of the second lens group G2 and the entire system as a preferable condition for reducing the size of the entire lens system, enabling shooting at a short shooting distance, and correcting aberrations. It is.

  When the upper limit of conditional expression (7) is exceeded and the refractive power of the second lens group G2 is reduced, the focus sensitivity is reduced, making it difficult to achieve both downsizing of the entire lens system and shooting at a short shooting distance. If the lower limit of conditional expression (7) is exceeded and the refractive power of the second lens group G2 is increased, aberration fluctuations during focusing increase, and the balance of aberration correction with the second lens group G2 is lost.

  Regarding conditional expression (7), preferably, the lower limit value is desirably set to 0.35 and the upper limit value is defined to be 0.70, whereby the above-described effect can be further ensured.

The present invention is configured to satisfy the following conditional expression.
(8) 0.30 <| f3 / f | <1.40
f3: focal length of the third lens group G3 f: focal length of the entire system in the infinitely focused state

  Conditional expression (8) defines the ratio of the focal lengths of the third lens group G3 and the entire system as preferable conditions for increasing the image circle, downsizing the entire lens system, and correcting aberrations.

  When the upper limit of conditional expression (8) is exceeded and the refractive power of the third lens group G3 is reduced, the lateral magnification is reduced, so that it is difficult to achieve both enlargement of the image circle and downsizing of the entire lens system. Exceeding the lower limit of conditional expression (8) is not preferable because aberrations occurring in the first lens group G1 and the second lens group G2 are significantly enlarged and the balance of aberration correction is lost.

  Regarding conditional expression (8), desirably, the lower limit value is desirably set to 0.45 and the upper limit value is defined to be 1.30, whereby the above-described effect can be further ensured.

The present invention is configured to satisfy the following conditional expression.
(9) 0.50 <((D1_2) * K2) / f <1.40
D1_2: the distance between the most image side surface of the first lens group G1 in the infinite focus state and the most object side surface of the second lens group G2 K2: the second lens group G2 in the infinite focus state Focus sensitivity K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f of the second lens group G2 in FIG. 5: focal length f1 of the entire system in the infinitely focused state f1: focal length f12 of the first lens group G1: the first lens group G1 in the infinitely focused state and the above Composite focal length of the second lens group G2

  Conditional expression (9) indicates that the entire lens system can be miniaturized, that photographing can be performed at a short photographing distance, and the balance between the first lens G1 and the second lens group G2 and the focus are preferable conditions for aberration correction balance. It defines the relationship of sensitivity.

  If the upper limit of conditional expression (9) is exceeded and the distance between the first lens G1 and the second lens group G2 is increased, it is difficult to reduce the size of the entire lens system. When the lower limit of the conditional expression (9) is exceeded and the distance between the first lens G1 and the second lens group G2 is reduced, the first lens group G1 and the aperture stop S interfere with each other in a focused state at a short shooting distance. Therefore, it is not preferable because shooting at a short shooting distance becomes impossible.

  Regarding conditional expression (9), preferably, the lower limit value is preferably set to 0.60 and the upper limit value is set to 1.25, whereby the above-described effect can be further ensured.

  In the present invention, the first lens group G1 is fixed with respect to the image plane, and the third lens group G3 is fixed with respect to the image plane when focusing from an object at infinity to an object at a short distance. It has a configuration.

  By fixing the first lens group G1 related to the appearance structure to the image plane, it is possible to reduce the weight of the lens group that moves during focusing. As a result, the focus actuator is reduced in size, and the size of the product can be reduced.

  By fixing the third lens group G3, which is the lens group having the largest lens system in the entire system, to the image plane, the amount of lens movement during focusing can be reduced, and the focus group can be reduced in weight. Therefore, it is possible to reduce the size of the entire system and to perform shooting at a short shooting distance.

  Focus sensitivity can be increased by fixing the third lens group G3 having a large lateral magnification during focusing. For this reason, the amount of movement of the focus group for focusing on a short-distance object is small, and photographing at a short photographing distance is possible.

  In the present invention, the first lens group G1 is fixed with respect to the image plane, and the third lens group G3 is fixed with respect to the image plane when focusing from an object at infinity to an object at a short distance. Take.

  The effects are as described above. By adopting this configuration, it is possible to efficiently adopt a focusing method with a small amount of lens movement during focusing. The entire lens system can be downsized and shooting can be performed at a short shooting distance. Can be made possible.

  In the present invention, the aperture stop S is adjacent to the image side of the first lens group G1 and is fixed in the optical axis direction when focused.

  The aperture stop S is adjacent to the image side of the first lens group G1 and is fixed in the optical axis direction during focusing, thereby reducing the weight of the mechanism that moves during focusing. As a result, the focus actuator is reduced in size, and the size of the product can be reduced. In order to make the aperture mechanism used for adjusting the amount of light, it is desirable to dispose the first lens group G1 on the image side in order to reduce the size of the entire lens system.

The present invention is configured to satisfy the following conditional expression.
(10) 1.60 <| EXP / Ymax | <3.50
EXP: Distance from exit pupil position to image plane in infinite focus state Ymax: Maximum image height Ymax is not defined and effective half angle of view w can be determined for convenience.
Ymax = (f * tan (w)).

  Conditional expression (10) defines the ratio between the exit pupil position and the maximum image height as a preferable condition for the light exit angle reaching the periphery of the image circle.

  If the upper limit of conditional expression (10) is exceeded and the EXP is increased, the length of the entire lens system and the diameter of the lens disposed on the image side are increased, making it difficult to reduce the size of the entire lens system. When the lower limit of conditional expression (10) is exceeded and the EXP becomes smaller, the light emission angle reaches a steep angle with respect to the image plane. When an image sensor used for a digital still camera or the like is used, it is not preferable because the sensitivity at the periphery of the image circle is reduced and the amount of peripheral light is significantly reduced.

  Regarding conditional expression (10), the lower limit value is desirably limited to 1.80, and the upper limit value is preferably limited to 2.80, whereby the above-described effect can be further ensured.

  In the present invention, the first lens group G1 includes a positive lens L1 and a negative lens L2 in order from the object side, and has a configuration having a positive refractive power as a whole.

  The positive lens L1 and the negative lens L2 are configured in order from the object side to the first lens group G1 in order from the object side, so that the positive lens L1 can reduce the luminous flux and contribute to downsizing of the entire lens system. To do. The balance of aberration correction with the second lens group G2 can be achieved by relaxing the ray angle of the marginal ray with respect to the optical axis by the negative lens L2 thereafter. At this time, it is desirable that the positive lens L1 and the negative lens L2 are not cemented in order to increase the surfaces used for aberration correction, and the positive lens L1 is a convex meniscus lens or negative lens with a convex surface facing the object side in order to reduce manufacturing error sensitivity. L2 is preferably a concave meniscus lens having a convex surface facing the object side. In order to reduce the size of the entire lens system, it is desirable to dispose the aperture mechanism used for adjusting the light amount on the image side of the first lens group G1.

  It is more desirable to use an aspherical surface for the first lens group G1. This makes it possible to appropriately correct spherical aberration and coma. It is most effective for aberration correction to use a double-sided aspheric surface for the positive lens L1.

  In the present invention, the second lens group G2 includes a negative lens L3, a positive lens L4, and a positive lens L5 in this order from the object side, and has a positive refracting power as a whole.

  The negative lens L3, the positive lens L4, and the positive lens L5 are configured in order from the object side to form the second lens group G2, and have positive refractive power as a whole, thereby increasing the focus sensitivity and reducing the weight of the focus lens. Manufacturing error sensitivity can be reduced. In order to balance aberration with the first lens group G1, one negative lens is required for the second lens group, but the negative lens L3 whose lens thickness is thicker at the peripheral portion is arranged at a position where the beam diameter is small. Become. Further, in order to bring the exit pupil position closer to the object side, it is desirable to dispose the negative lens L3 closer to the object side. The positive lens L4 is desirably adjacent to correct the chromatic aberration of the negative lens L3, and the negative lens L3 and the positive lens L4 may be cemented to reduce the manufacturing error sensitivity between the adjacent positive lens L4. desirable. Further, by arranging the positive lens L5 on the image plane side, the optical system is symmetric with the first lens group G1, and aberration correction is balanced. At this time, the cemented lens, that is, the cemented lens composed of the negative lens L3 and the positive lens L4, has a meniscus having a concave surface directed toward the object side in order to reduce manufacturing error sensitivity between the positive lens L5 adjacent to the image surface side. It is desirable to have a shape.

  From the above, it is possible to increase both the focus sensitivity and the effects of correcting aberrations and reducing manufacturing error sensitivity from the configuration of the second lens group G2.

  The positive lens L5 tends to have a large lens diameter because off-axis rays pass through a position away from the optical axis. Therefore, it is desirable to use a material with a low specific gravity.

  It is more desirable to use an aspheric surface for the second lens group G2. This makes it possible to appropriately correct spherical aberration and astigmatism during focusing. Use of a double-sided aspheric surface for the positive lens L5 is most effective for aberration correction.

  In the present invention, the third lens group G3 includes a negative lens L6, a negative lens L7, and a positive lens L8 in order from the object side, and has a negative refracting power as a whole.

  The negative lens L6, the negative lens L7, and the positive lens L8 are configured in order from the object side to form the third lens group G3 so as to have a negative refracting power as a whole, so that the image circle can be enlarged and the entire lens system can be downsized. Can do. The negative lens L6 has a lens diameter equivalent to that of the positive lens L5, so that the marginal ray on the upper side of the off-axis light beam is substantially parallel to the optical axis, thereby reducing the manufacturing error sensitivity with the second lens group G2 and focusing. It is possible to reduce both aberration fluctuations. In addition, it is desirable that the lens is a concave meniscus lens having a convex surface facing the object side in order to reduce the strong negative refractive power for expanding the image circle and the aberration fluctuation during focusing. The negative lens L7 is preferably a concave meniscus lens that is used for correction of astigmatism, is disposed at a position close to the image plane where the axial ray height is low, and has a concave surface facing the object side. For the positive lens L8, it is desirable to use a medium having a high refractive index, high dispersion, and anomalous partial dispersion. It is desirable to be close to the image plane for use in correcting off-axis lateral chromatic aberration, astigmatism, and distortion.

Next, a lens configuration of an example according to the imaging optical system of the present invention is 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 lens surface, d is the distance between the lens surfaces, and nd is for the d-line (wavelength 587.56 nm). The refractive index, vd is the Abbe number with respect to the d-line, PgF is the partial dispersion ratio between the g-line and the F-line, and the effective diameter is the effective lens diameter.

  The * (asterisk) attached to the surface number indicates that the lens surface shape is an aspherical surface. BF represents back focus.

  The (diaphragm) attached to the surface number indicates that the aperture stop is located at that position. ∞ (infinity) is entered in the radius of curvature for a plane or aperture stop.

[Aspherical data] indicates the values of the coefficients that give the aspherical shape of the lens surface marked with * in [Surface data]. The shape of the aspherical surface is expressed by the following formula. In the following equation, y is the displacement from the optical axis in the direction perpendicular to the optical axis, z is the displacement (sag amount) in the optical axis direction from the intersection of the aspherical surface and the optical axis, and r is the radius of curvature of the reference spherical surface. The conic coefficient is represented by K. The fourth, sixth, eighth, tenth, twelfth, fourteenth, sixteenth, and twentieth aspherical coefficients are represented by A4, A6, A8, A10, A12, A14, A16, A18, and A20, respectively.

  [Various data] shows values such as the focal length when focusing on infinity.

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

  [Lens Group Data] indicates the lens surface number closest to the object side constituting each lens group and the combined focal length of the entire lens 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 in proportional expansion and proportional reduction, and the present invention is not limited to this.

  FIG. 1 is a lens configuration diagram at the time of focusing on infinity of the imaging optical system according to Example 1 of the present invention.

  In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and a biconvex lens L5 that is a double aspheric surface. The third lens group G3 having a negative refractive power includes a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a biconvex lens L8, and is infinite. When focusing from a distant object to a close object, the first lens group G1, the aperture stop S, and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 moves toward the object side. .

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 1 are shown below.
Numerical example 1
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 23.3681 3.7585 1.77250 49.50 0.5519 20.01
2 * 144.1153 0.3080 18.30
3 45.1236 0.8000 1.51742 52.15 0.5589 16.74
4 16.3472 4.6499 14.58
5 (Aperture) ∞ (d5) 12.90
6 -12.2130 0.8000 1.69895 30.05 0.6028 12.85
7 55.6607 4.2213 1.87070 40.73 0.5682 14.54
8 -18.8353 0.1500 15.60
9 * 37.4761 4.7493 1.58913 61.25 0.5373 17.90
10 * -23.9712 (d10) 18.50
11 109.6497 0.9857 1.67300 38.26 0.5757 18.97
12 21.1832 8.7012 19.20
13 -19.7354 0.8000 1.75211 25.05 0.6191 21.87
14 -29.9543 0.1500 23.66
15 95.8651 2.5968 1.98612 16.48 0.6656 28.20
16 -580.7065 16.3216 28.72
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞

[Aspherical data]
1 side 2 sides
K 0.7548 0.0000
A4 -1.0943E-05 -2.3116E-06
A6 -9.0526E-08 1.4773E-07
A8 3.3856E-09 -4.0502E-09
A10 -6.8374E-11 7.7863E-11
A12 7.5676E-13 -9.6225E-13
A14 -4.8496E-15 6.3690E-15
A16 1.5425E-17 -2.0898E-17
A18 -1.8709E-20 2.6920E-20
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -2.3178 -2.6500
A4 -2.4796E-06 -4.7357E-06
A6 -9.6746E-09 1.5970E-08
A8 -5.6804E-10 3.7484E-10
A10 3.7440E-11 -1.2512E-11
A12 -7.5858E-13 2.6612E-13
A14 7.5576E-15 -3.0274E-15
A16 -3.5787E-17 1.8357E-17
A18 6.4474E-20 -4.2619E-20
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 240
Focal length 43.93 36.81
F number 2.90 3.02
Full angle of view 2ω 51.10 49.90
Statue height Y 21.63 21.63
Total lens length 63.57 63.57

[Variable interval data]
INF 240
d0 ∞ 172.6297
d5 8.3114 4.8314
d10 1.7666 5.2466
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 98.79
G2 6 22.68
G3 11 -39.36
G12 1 24.39
G23 6 54.90

FIG. 6 is a lens configuration diagram of the imaging optical system according to Example 2 of the present invention when focusing on infinity.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side, and a negative meniscus shape having an aspheric surface on the object side and a convex surface facing the object side. The aperture stop S is adjacent to the image side of the first lens group G1 and has a positive refracting power. The cemented lens L2 includes a lens made of resin or the like and a negative meniscus lens having a convex surface facing the object side. The lens group G2 includes a cemented lens including a biconcave lens L3 and a biconvex lens L4, and a biconvex lens L5 that is a double-sided aspheric surface. The third lens group G3 having negative refractive power has a convex surface directed toward the object side. A negative meniscus lens L6, a negative meniscus lens L7 having a concave surface facing the object side, and a biconvex lens L8. When focusing from an infinite object to a close object, the first lens group G1 and the aperture stop S are used. And third len Group G3 is fixed to the image plane, the second lens group G2 moves toward the object side.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 2 are shown below.
Numerical example 2
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 25.0272 3.6286 1.77250 49.62 0.5503 19.60
2 148.6155 0.1500 17.88
3 * 44.5784 0.1188 1.51840 52.10 0.5538 16.79
4 35.9682 0.8000 1.51742 52.15 0.5589 16.45
5 18.3624 3.6611 14.90
6 (Aperture) ∞ (d6) 13.28
7 -11.8564 0.8000 1.69895 30.05 0.6028 13.05
8 74.0878 4.2582 1.87070 40.73 0.5682 14.70
9 -17.7220 0.1500 15.70
10 * 43.7832 4.3575 1.58913 61.25 0.5373 18.00
11 * -26.0653 (d11) 18.57
12 100.0000 0.8000 1.64769 33.84 0.5923 19.27
13 22.6971 9.6164 19.38
14 -20.0973 0.8000 1.67270 32.17 0.5962 22.62
15 -33.0792 0.1500 24.58
16 120.8436 2.5285 1.98612 16.48 0.6656 28.58
17 -317.4586 16.1672 29.10
18 ∞ 2.5000 1.51633 64.14 0.5353
19 ∞ (BF)
Image plane ∞

[Aspherical data]
3 sides 10 sides 11 sides
K -0.5947 -4.1801 -2.6057
A4 -3.1404E-06 3.2870E-07 -3.7190E-06
A6 -1.9502E-07 -1.7897E-08 1.2815E-08
A8 8.0064E-09 -4.0774E-09 -1.3261E-09
A10 -1.4668E-10 1.6733E-10 1.5502E-11
A12 1.2804E-12 -3.0256E-12 2.6614E-13
A14 -4.1538E-15 2.8060E-14 -7.3721E-15
A16 0.0000E + 00 -1.3039E-16 5.6089E-17
A18 0.0000E + 00 2.4152E-19 -1.3703E-19
A20 0.0000E + 00 0.0000E + 00 0.0000E + 00

[Various data]
INF 240
Focal length 44.27 37.14
F number 2.90 3.00
Full angle of view 2ω 50.75 49.99
Statue height Y 21.63 21.63
Total lens length 63.57 63.57

[Variable interval data]
INF 240
d0 ∞ 174.9301
d6 9.4838 5.6659
d11 1.6000 5.4179
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 89.60
G2 7 24.41
G3 12 -43.26
G12 1 25.50
G23 7 58.75

FIG. 11 is a lens configuration diagram at the time of focusing on infinity of the imaging optical system according to Example 3 of the present invention.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The aperture stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having a positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and a biconvex lens that is a double aspherical surface. The third lens group G3 having a negative refractive power and a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a concave surface facing the object side A positive meniscus lens L8, and the first lens group G1, the aperture stop S, and the third lens group G3 are fixed with respect to the image plane when focusing from an object at infinity to an object at a short distance. 2 lens group G2 is an object To move to.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 3 are shown below.
Numerical example 3
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 40.0578 1.9199 1.72903 54.04 0.5446 17.97
2 * 1035.9646 0.1500 17.19
3 35.3446 0.8000 1.51823 58.96 0.5441 15.51
4 21.8772 3.9211 14.20
5 (Aperture) ∞ (d5) 11.81
6 -11.9037 0.8000 1.69895 30.05 0.6028 12.14
7 33.6044 4.8000 1.87070 40.73 0.5682 14.18
8 -18.2410 0.1500 15.40
9 * 38.2460 4.6535 1.58913 61.25 0.5373 17.60
10 * -23.7324 (d10) 18.30
11 36.1340 0.8000 1.51742 52.15 0.5589 19.30
12 17.4730 6.9149 19.08
13 -18.7936 0.8000 1.64769 33.84 0.5923 19.93
14 -52.5631 0.1500 22.15
15 -160.7300 1.9252 1.92286 20.88 0.6388 23.30
16 -65.0696 15.3702 24.11
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞

[Aspherical data]
1 side 2 sides
K 2.2440 0.0000
A4 -4.7931E-06 3.5362E-06
A6 -1.1561E-06 -1.2927E-06
A8 3.9457E-08 5.9642E-08
A10 -5.1536E-10 -1.1713E-09
A12 -3.6010E-14 8.3976E-12
A14 7.2185E-14 4.6761E-14
A16 -7.2860E-16 -1.0681E-15
A18 2.3716E-18 4.6152E-18
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -3.5035 -2.7645
A4 -5.9110E-06 -6.8076E-06
A6 -2.5290E-09 1.9360E-08
A8 3.4621E-10 3.2163E-10
A10 4.9236E-13 1.3592E-12
A12 0.0000E + 00 1.9007E-15
A14 0.0000E + 00 0.0000E + 00
A16 0.0000E + 00 0.0000E + 00
A18 0.0000E + 00 0.0000E + 00
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 200
Focal length 37.01 31.09
F number 2.90 3.02
Full angle of view 2ω 59.14 58.03
Statue height Y 21.63 21.63
Total lens length 57.27 57.27

[Variable interval data]
INF 200
d0 ∞ 142.7325
d5 8.0119 4.7646
d10 1.6000 4.8473
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 110.04
G2 6 21.04
G3 11 -34.64
G12 1 21.48
G23 6 45.56

FIG. 16 is a lens configuration diagram at the time of focusing on infinity of the imaging optical system according to Example 4 of the present invention.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The aperture stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having a positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and a biconvex lens that is a double aspherical surface. The third lens group G3 having a negative refractive power and a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a concave surface facing the object side A positive meniscus lens L8, and the first lens group G1, the aperture stop S, and the third lens group G3 are fixed with respect to the image plane when focusing from an object at infinity to an object at a short distance. 2 lens group G2 is an object To move to.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 4 are shown below.
Numerical example 4
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 27.9565 2.1228 1.85135 40.10 0.5694 20.03
2 * 68.1371 0.1500 19.12
3 19.1686 0.8000 1.55298 55.07 0.5447 16.74
4 13.0798 5.4212 15.00
5 (Aperture) ∞ (d5) 12.38
6 -12.8045 0.8000 1.69895 30.05 0.6028 12.61
7 26.7275 4.8000 1.87070 40.73 0.5682 14.71
8 -20.8226 0.1500 15.80
9 * 42.5418 4.5045 1.58913 61.25 0.5373 17.90
10 -24.4535 (d10) 18.54
11 34.5567 1.4070 1.67300 38.26 0.5757 19.43
12 18.8436 10.2837 19.10
13 -17.0132 0.8000 1.75211 25.05 0.6191 21.82
14 -32.5270 0.1500 24.42
15 -626.8220 2.9061 1.98612 16.48 0.6656 27.60
16 -60.7974 14.8183 28.43
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞

[Aspherical data]
1 side 2 sides
K 1.4127 0.0000
A4 -1.6186E-05 -1.0510E-05
A6 -9.2237E-08 1.9241E-08
A8 1.9145E-09 2.9174E-09
A10 2.2312E-11 -2.4662E-11
A12 -6.4984E-13 -2.1752E-13
A14 3.6410E-15 2.6677E-15
A16 0.0000E + 00 0.0000E + 00
A18 0.0000E + 00 0.0000E + 00
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -4.3611 -2.2863
A4 -4.9661E-06 -7.4309E-06
A6 5.1598E-09 2.2351E-08
A8 -3.8894E-10 -1.5640E-10
A10 4.9734E-12 2.4462E-12
A12 0.0000E + 00 1.5323E-14
A14 0.0000E + 00 0.0000E + 00
A16 0.0000E + 00 0.0000E + 00
A18 0.0000E + 00 0.0000E + 00
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 220
Focal length 40.00 34.53
F number 2.90 3.08
Full angle of view 2ω 55.84 53.58
Statue height Y 21.63 21.63
Total lens length 63.57 63.57

[Variable interval data]
INF 220
d0 ∞ 156.4295
d5 8.3569 4.4610
d10 1.6000 5.4959
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 154.41
G2 6 23.51
G3 11 -48.02
G12 1 24.61
G23 6 43.75

FIG. 21 is a lens configuration diagram of the imaging optical system according to Example 5 of the present invention when focusing on infinity.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The aperture stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having a positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and a biconvex lens that is a double aspherical surface. The third lens group G3 having a negative refracting power is composed of a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a biconvex lens L8. When focusing from an object at infinity to an object at a short distance, the first lens group G1, the aperture stop S, and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 moves toward the object side. Moving.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 5 are shown below.
Numerical example 5
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 21.0823 3.4782 1.76802 49.24 0.5515 21.16
2 * 99.2280 0.1608 20.07
3 47.5622 0.8000 1.51742 52.15 0.5589 18.94
4 19.4504 4.4894 16.80
5 (Aperture) ∞ (d5) 14.80
6 -15.0441 0.8000 1.69895 30.05 0.6028 14.30
7 21.1179 4.7971 1.87070 40.73 0.5682 15.72
8 -26.2651 0.1870 16.20
9 * 45.2265 4.2577 1.58913 61.25 0.5373 17.80
10 * -27.0031 (d10) 18.39
11 1450.3022 1.3351 1.67300 38.26 0.5757 19.13
12 25.6487 8.1008 19.40
13 -17.7190 0.8004 1.75211 25.05 0.6191 21.66
14 -51.2250 0.1502 25.06
15 1000.0000 4.3333 1.98612 16.48 0.6656 28.40
16 -42.8968 14.0137 29.54
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞

[Aspherical data]
1 side 2 sides
K 0.6876 12.9030
A4 -1.3213E-05 -9.8307E-07
A6 3.2013E-07 1.2898E-07
A8 -1.8639E-08 -8.8793E-09
A10 5.2041E-10 3.1773E-10
A12 -8.2976E-12 -6.4386E-12
A14 7.5237E-14 7.2797E-14
A16 -3.6261E-16 -4.3185E-16
A18 7.1284E-19 1.0386E-18
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -2.4143 -4.0616
A4 -5.0885E-06 -6.7662E-06
A6 -1.4701E-08 3.9183E-08
A8 -1.9852E-09 2.3073E-08
A10 9.1678E-11 -1.2237E-09
A12 -1.1699E-12 2.9740E-11
A14 2.3893E-15 -3.7929E-13
A16 5.7896E-17 2.4731E-15
A18 -3.1362E-19 -6.4997E-18
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 210
Focal length 50.72 34.65
F number 2.90 2.98
Full angle of view 2ω 44.98 44.39
Statue height Y 21.63 21.63
Total lens length 64.52 64.52

[Variable interval data]
INF 210
d0 ∞ 144.4762
d5 10.6925 5.0552
d10 1.6281 7.2654
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 65.48
G2 6 26.88
G3 11 -38.63
G12 1 27.64
G23 6 107.03

FIG. 26 is a lens configuration diagram of the imaging optical system according to Example 6 of the present invention when focusing on infinity.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The aperture stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having a positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and a biconvex lens that is a double aspherical surface. The third lens group G3 having a negative refractive power and a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a biconvex lens L8, When focusing from an infinite object to a close object, the first lens group G1, the aperture stop S, and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 moves toward the object side. To do.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 6 are shown below.
Numerical example 6
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 21.0987 3.3398 1.77250 49.50 0.5519 19.88
2 * 54.6445 0.7934 18.16
3 29.1842 0.8000 1.48749 70.44 0.5306 16.60
4 17.2858 3.6525 15.68
5 (Aperture) ∞ (d5) 15.00
6 -13.4041 0.8000 1.69895 30.05 0.6028 14.41
7 30.1667 4.7697 1.87070 40.73 0.5682 16.18
8 -20.0313 0.1500 16.80
9 * 26.9679 4.4763 1.58913 61.25 0.5373 17.80
10 * -37.7416 (d10) 18.16
11 138.9423 0.8000 1.95375 32.32 0.5901 18.22
12 22.4583 10.0862 18.00
13 -16.4066 0.8000 1.70154 41.15 0.5769 21.66
14 -29.7489 0.1500 24.39
15 178.9531 3.4842 1.98612 16.48 0.6656 29.30
16 -81.0895 15.1006 30.05
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞

[Aspherical data]
1 side 2 sides
K 2.1022 10.6169
A4 -1.5287E-05 7.0189E-06
A6 -2.1976E-07 1.8322E-07
A8 -4.4936E-10 -1.5319E-08
A10 2.1212E-10 7.5207E-10
A12 -6.3286E-12 -1.7441E-11
A14 8.8011E-14 2.2713E-13
A16 -6.0800E-16 -1.5745E-15
A18 1.7022E-18 4.6288E-18
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -2.1665 -4.9007
A4 5.0447E-06 4.5712E-06
A6 -1.3519E-08 1.2052E-08
A8 2.6215E-09 3.3008E-09
A10 -7.1467E-11 -8.7446E-11
A12 7.7627E-13 9.2023E-13
A14 -3.2966E-15 -3.7697E-15
A16 0.0000E + 00 0.0000E + 00
A18 0.0000E + 00 0.0000E + 00
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 260
Focal length 51.30 40.89
F number 2.90 2.94
Full angle of view 2ω 44.52 44.28
Statue height Y 21.63 21.63
Total lens length 64.57 64.57

[Variable interval data]
INF 260
d0 ∞ 195.4280
d5 9.2671 6.2340
d10 1.6000 4.6331
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 73.81
G2 6 22.28
G3 11 -29.05
G12 1 23.90
G23 6 102.38

FIG. 31 is a lens configuration diagram of the imaging optical system according to Example 7 of the present invention when focusing on infinity.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The aperture stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having a positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and a biconvex lens that is a double aspherical surface. The third lens group G3 having a negative refractive power, which includes L5, includes a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a biconvex lens L8. When focusing from an object at infinity to an object at a short distance, the first lens group G1, the aperture stop S, and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 is located on the object side. Move to.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 7 are shown below.
Numerical example 7
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 20.6620 3.1514 1.85135 40.10 0.5694 19.63
2 * 47.5814 0.4460 17.95
3 23.7152 0.8000 1.67300 38.26 0.5757 16.60
4 15.8076 3.7525 15.65
5 (Aperture) ∞ (d5) 15.03
6 -13.7424 0.8000 1.69895 30.05 0.6028 14.56
7 33.2777 4.8000 1.87070 40.73 0.5682 16.30
8 -19.2935 0.1895 17.00
9 * 23.9858 4.5111 1.58913 61.25 0.5373 17.50
10 * -45.1305 (d10) 17.74
11 141.4802 0.8000 1.95375 32.32 0.5901 17.66
12 21.0998 10.5351 17.50
13 -17.0176 0.8000 1.83400 37.35 0.5789 21.74
14 -28.6516 0.1500 24.22
15 208.3778 3.5796 1.98612 16.48 0.6656 29.20
16 -72.4839 14.9309 30.01
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞

[Aspherical data]
1 side 2 sides
K 2.0719 11.2100
A4 -1.8102E-05 2.1864E-06
A6 -2.5741E-07 -6.4336E-08
A8 5.6331E-10 -2.6344E-09
A10 1.5449E-10 3.4042E-10
A12 -4.5910E-12 -8.8147E-12
A14 6.3669E-14 1.1928E-13
A16 -4.4851E-16 -8.4905E-16
A18 1.3183E-18 2.6669E-18
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -1.8995 -5.1449
A4 8.2067E-06 8.1730E-06
A6 -1.1855E-08 7.2803E-09
A8 2.6173E-09 2.4921E-09
A10 -7.3732E-11 -7.1060E-11
A12 8.0300E-13 7.6064E-13
A14 -3.4811E-15 -3.2809E-15
A16 0.0000E + 00 0.0000E + 00
A18 0.0000E + 00 0.0000E + 00
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 260
Focal length 51.21 40.91
F number 2.90 2.95
Full angle of view 2ω 44.59 44.29
Statue height Y 21.63 21.63
Total lens length 64.39 64.39

[Variable interval data]
INF 260
d0 ∞ 195.6050
d5 9.0455 6.3188
d10 1.6000 4.3267
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 79.67
G2 6 21.04
G3 11 -27.24
G12 1 22.82
G23 6 93.77

FIG. 36 is a lens configuration diagram of the imaging optical system according to Example 8 of the present invention when focusing on infinity.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The aperture stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having a positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and both aspheric surfaces. The third lens group G3 including a convex lens L5 and having negative refractive power includes a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a biconvex lens L8. When focusing from an object at infinity to an object at a short distance, the first lens group G1, the aperture stop S, and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 is located on the object side. Move to.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 8 are shown below.
Numerical example 8
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 19.2943 4.3849 1.77250 49.50 0.5519 21.91
2 * 83.4557 0.4474 20.13
3 37.3406 0.8000 1.64769 33.84 0.5923 18.60
4 17.8608 3.9704 17.25
5 (Aperture) ∞ (d5) 16.38
6 -17.4689 0.8000 1.67270 32.17 0.5962 15.46
7 18.5228 4.7563 1.87070 40.73 0.5682 16.88
8 -37.3036 0.1500 17.20
9 * 61.4797 3.6234 1.58913 61.25 0.5373 17.10
10 * -27.3796 (d10) 17.71
11 108.5223 0.8000 1.88300 40.81 0.5654 18.75
12 28.8108 8.2602 18.80
13 -17.3629 0.8000 1.83400 37.35 0.5789 21.12
14 -33.0352 0.1500 23.51
15 159.5584 2.9136 1.98612 16.48 0.6656 27.52
16 -112.0386 15.6000 28.23
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞

[Aspherical data]
1 side 2 sides
K 1.2865 3.6433
A4 -2.2596E-05 4.5240E-06
A6 -9.5381E-08 4.9414E-08
A8 -9.9329E-10 1.1435E-09
A10 6.9611E-11 -2.6295E-11
A12 -1.8807E-12 1.4369E-13
A14 2.3787E-14 4.2434E-15
A16 -1.4812E-16 -6.1675E-17
A18 3.6682E-19 2.5658E-19
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -12.4781 -3.2159
A4 -6.8969E-06 -4.7966E-06
A6 -2.7438E-08 2.8670E-08
A8 -1.6769E-09 2.9749E-09
A10 1.8763E-11 -1.0572E-10
A12 8.9135E-14 1.3762E-12
A14 -1.0850E-15 -5.7279E-15
A16 0.0000E + 00 0.0000E + 00
A18 0.0000E + 00 0.0000E + 00
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 290
Focal length 58.00 44.21
F number 2.90 2.95
Full angle of view 2ω 39.82 39.34
Statue height Y 21.63 21.63
Total lens length 64.57 64.57

[Variable interval data]
INF 290
d0 ∞ 225.4298
d5 11.0138 5.9218
d10 1.6000 6.6920
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 63.49
G2 6 32.00
G3 11 -33.78
G12 1 31.29
G23 6 440.27

FIG. 41 is a lens configuration diagram of the imaging optical system according to Example 9 of the present invention when focusing on infinity.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The aperture stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having a positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and a biconvex lens L5 that is a double-sided aspheric surface. The third lens group G3 having a negative refractive power includes a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a biconvex lens L8, and is infinite. At the time of focusing from a distant object to a close object, the third lens group G3 is fixed with respect to the image plane, and the first lens group G1, the aperture stop S, and the second lens group G2 are united toward the object side. Move and second Group's moves further toward the object side.

  The power for moving the first lens group G1, the aperture stop S, and the second lens group G2 together may use an actuator with a large torque, or as a mechanical extension mechanism independent of the actuator, dedicated for close-up photography. Although a lens system may be used, it is desirable to use a small actuator for driving the second lens group G2 so that micro driving is possible in the optical axis direction. At this time, the second lens group G2 moves toward the object side, so that it is possible to focus on an object at a shorter distance.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 9 are shown below.
Numerical example 9
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 23.3681 3.7585 1.77250 49.50 0.5519 20.01
2 * 144.1153 0.3080 18.30
3 45.1236 0.8000 1.51742 52.15 0.5589 16.74
4 16.3472 4.6499 14.58
5 (Aperture) ∞ (d5) 12.90
6 -12.2130 0.8000 1.69895 30.05 0.6028 12.85
7 55.6607 4.2213 1.87070 40.73 0.5682 14.54
8 -18.8353 0.1500 15.60
9 * 37.4761 4.7493 1.58913 61.25 0.5373 17.90
10 * -23.9712 (d10) 18.50
11 109.6497 0.9857 1.67300 38.26 0.5757 18.97
12 21.1832 8.7012 19.20
13 -19.7354 0.8000 1.75211 25.05 0.6191 21.87
14 -29.9543 0.1500 23.66
15 95.8651 2.5968 1.98612 16.48 0.6656 28.20
16 -580.7065 16.3216 28.72
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞



[Aspherical data]
1 side 2 sides
K 0.7548 0.0000
A4 -1.0943E-05 -2.3116E-06
A6 -9.0526E-08 1.4773E-07
A8 3.3856E-09 -4.0502E-09
A10 -6.8374E-11 7.7863E-11
A12 7.5676E-13 -9.6225E-13
A14 -4.8496E-15 6.3690E-15
A16 1.5425E-17 -2.0898E-17
A18 -1.8709E-20 2.6920E-20
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -2.3178 -2.6500
A4 -2.4796E-06 -4.7357E-06
A6 -9.6746E-09 1.5970E-08
A8 -5.6804E-10 3.7484E-10
A10 3.7440E-11 -1.2512E-11
A12 -7.5858E-13 2.6612E-13
A14 7.5576E-15 -3.0274E-15
A16 -3.5787E-17 1.8357E-17
A18 6.4474E-20 -4.2619E-20
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 240 150
Focal length 43.93 37.82 32.28
F number 2.90 3.07 3.26
Full angle of view 2ω 51.10 48.96 46.43
Image height Y 21.63 21.63 21.63
Total lens length 63.57 67.10 67.10

[Variable interval data]
INF 240 150
d0 ∞ 168.8040 85.1913
d5 8.3114 8.3114 4.8314
d10 1.7666 5.2940 8.7740
BF 2.0000 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 98.79
G2 6 22.68
G3 11 -39.36
G12 1 24.39
G23 6 54.90

FIG. 46 is a lens configuration diagram of the imaging optical system according to Example 10 of the present invention when focusing on infinity.
In order from the object side, the first lens group G1 having a positive refractive power includes a positive meniscus lens L1 having a convex surface facing the object side which is a double-sided aspheric surface, and a negative meniscus lens L2 having a convex surface facing the object side. The stop S is adjacent to the image side of the first lens group G1, and the second lens group G2 having positive refractive power includes a cemented lens composed of a biconcave lens L3 and a biconvex lens L4, and a biconvex lens L5 that is a double-sided aspheric surface. The third lens group G3 having negative refractive power includes a negative meniscus lens L6 having a convex surface facing the object side, a negative meniscus lens L7 having a concave surface facing the object side, and a biconvex lens L8. When focusing from an object at infinity to an object at a short distance, the distance between the first lens group G1 and the second lens group G2 is reduced, and the distance between the second lens group G2 and the third lens group G3 is reduced. 1st review 'S group G1 and the aperture stop S and the second lens group G2 and the third lens group G3 moves separately to the object side.

  As the distance between the first lens group G1 and the second lens group G2 is reduced, an increase in the total optical length is suppressed, and as the distance between the second lens group G2 and the third lens group G3 is increased, astigmatism is appropriately corrected. This makes it possible to correct the curvature of field.

  As the power for moving each lens group, an actuator having a large torque may be used. However, for the driving of the second lens group G2, a small actuator may be used so as to enable minute driving in the optical axis direction. desirable.

  A filter F that is a plane-parallel plate is disposed between the third lens group G3 and the image plane. The position of the filter F on the optical axis does not affect the aberration anywhere between the third lens group G3 and the image plane.

Subsequently, specification values of the imaging optical system according to Example 10 are shown below.
Numerical example 10
Unit: mm
[Surface data]
Surface number rd nd vd PgF Effective diameter Object surface ∞ (d0)
1 * 23.3681 3.7585 1.77250 49.50 0.5519 20.01
2 * 144.1153 0.3080 18.30
3 45.1236 0.8000 1.51742 52.15 0.5589 16.74
4 16.3472 4.6499 14.58
5 (Aperture) ∞ (d5) 12.90
6 -12.2130 0.8000 1.69895 30.05 0.6028 12.85
7 55.6607 4.2213 1.87070 40.73 0.5682 14.54
8 -18.8353 0.1500 15.60
9 * 37.4761 4.7493 1.58913 61.25 0.5373 17.90
10 * -23.9712 (d10) 18.50
11 109.6497 0.9857 1.67300 38.26 0.5757 18.97
12 21.1832 8.7012 19.20
13 -19.7354 0.8000 1.75211 25.05 0.6191 21.87
14 -29.9543 0.1500 23.66
15 95.8651 2.5968 1.98612 16.48 0.6656 28.20
16 -580.7065 (d16) 28.72
17 ∞ 2.5000 1.51633 64.14 0.5353
18 ∞ (BF)
Image plane ∞

[Aspherical data]
1 side 2 sides
K 0.7548 0.0000
A4 -1.0943E-05 -2.3116E-06
A6 -9.0526E-08 1.4773E-07
A8 3.3856E-09 -4.0502E-09
A10 -6.8374E-11 7.7863E-11
A12 7.5676E-13 -9.6225E-13
A14 -4.8496E-15 6.3690E-15
A16 1.5425E-17 -2.0898E-17
A18 -1.8709E-20 2.6920E-20
A20 0.0000E + 00 0.0000E + 00

9 faces 10 faces
K -2.3178 -2.6500
A4 -2.4796E-06 -4.7357E-06
A6 -9.6746E-09 1.5970E-08
A8 -5.6804E-10 3.7484E-10
A10 3.7440E-11 -1.2512E-11
A12 -7.5858E-13 2.6612E-13
A14 7.5576E-15 -3.0274E-15
A16 -3.5787E-17 1.8357E-17
A18 6.4474E-20 -4.2619E-20
A20 0.0000E + 00 0.0000E + 00

[Various data]
INF 240
Focal length 43.93 38.38
F number 2.90 3.18
Full angle of view 2ω 51.10 48.07
Statue height Y 21.63 21.63
Total lens length 63.57 66.23

[Variable interval data]
INF 240
d0 ∞ 169.9704
d5 8.3114 4.8314
d10 1.7666 4.2180
d16 16.3216 20.0097
BF 2.0000 2.0000

[Lens group data]
Group Start surface Focal length
G1 1 98.79
G2 6 22.68
G3 11 -39.36
G12 1 24.39
G23 6 54.90

The conditional expression corresponding values corresponding to the above-described embodiments are shown above.
Conditional expression / Example EX1 EX2 EX3 EX4 EX5
1.40 <f / f12 <2.80 1.80 1.74 1.72 1.63 1.84
0.020 <G3ΔPgFmax <0.300 0.047 0.047 0.028 0.047 0.047
1.80 <G3nd 1.99 1.99 1.92 1.99 1.99
0.60 <f1 / f <6.50 2.25 2.02 2.97 3.86 1.29
2.00 <LT / (Ymax) <3.10 2.94 2.94 2.65 2.94 2.98
2.00 <K2 <5.00 3.05 2.77 2.85 2.57 2.77
0.30 <f2 / f <0.95 0.52 0.55 0.57 0.59 0.53
0.30 <| f3 / f | <1.40 0.90 0.98 0.94 1.20 0.76
0.50 <((D1_2) * K2) / f <1.40 0.90 0.82 0.92 0.89 0.83
1.60 <EXP / Ymax <3.50 2.43 2.55 2.14 2.49 2.51

Condition / Example EX6 EX7 EX8 EX9 EX10
1.40 <f / f12 <2.80 2.15 2.24 1.85 1.80 1.80
0.020 <G3ΔPgFmax <0.300 0.047 0.047 0.047 0.047 0.047
1.80 <G3nd 1.99 1.99 1.99 1.99 1.99
0.60 <f1 / f <6.50 1.44 1.56 1.09 2.25 2.25
2.00 <LT / (Ymax) <3.10 2.99 2.98 2.99 2.94 2.94
2.00 <K2 <5.00 4.12 4.62 2.60 3.05 3.05
0.30 <f2 / f <0.95 0.43 0.41 0.55 0.52 0.52
0.30 <| f3 / f | <1.40 0.57 0.53 0.58 0.90 0.90
0.50 <((D1_2) * K2) / f <1.40 1.04 1.16 0.67 0.90 0.90
1.60 <EXP / Ymax <3.50 2.40 2.40 2.19 2.43 2.43

G1 First lens group G2 Second lens group G3 Third lens group I Image plane F Filter S Aperture stop

Claims (18)

In order from the object side, the first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power,
When focusing from an object at infinity to an object at a short distance, the distance between the first lens group G1 and the second lens group G2 is reduced, and the distance between the second lens group G2 and the third lens group G3 is reduced. And the second lens group G2 moves to the object side,
An imaging optical system satisfying the following conditional expression:
(1) 1.40 <f / f12 <2.80
(2) 0.020 <G3ΔPgFmax <0.300
(3) 1.80 <G3nd
(4) 0.60 <f1 / f <6.50
f: Focal length of the entire system in the infinite focus state f12: Composite focal length G3ΔPgFmax of the first lens group G1 and the second lens group G2 in the infinite focus state: of the positive lens of the third lens group G3 Of these, the largest ΔPgF value ΔPgF = PgF−0.64833 + 0.00180νd: g, abnormal partial dispersibility between F lines PgF = (ng−nF) / (nF−nC): g, partial dispersion between F lines Ratio ng: Refractive index for g-line (wavelength λ = 435.84 nm) nF: Refractive index for F-line (wavelength λ = 486.13 nm) nC: Refractive index G for C-line (wavelength λ = 656.27 nm) G3nd: Refractive index f1: with respect to the d-line (wavelength λ = 587.56) of the positive lens in the three lens group G3 The focal length of the first lens group G1
In order from the object side, the first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power,
When focusing from an object at infinity to an object at a short distance, the distance between the first lens group G1 and the second lens group G2 is reduced, and the distance between the second lens group G2 and the third lens group G3 is reduced. And the second lens group G2 moves to the object side,
An imaging optical system satisfying the following conditional expression:
(1) 1.40 <f / f12 <2.80
(5) 2.0 <LT / (Ymax) <3.10
(6) 2.00 <K2 <5.00
(9) 0.50 <((D1_2) * K2) / f <1.40

f: Focal length of the entire system in the infinite focus state f12: Composite focal length of the first lens group G1 and the second lens group G2 in the infinite focus state LT: The first lens in the infinite focus state For the sake of convenience, Ymax = (f * tan (w)), which is not defined as a surface interval Ymax from the surface closest to the object side of the group G1 to the image surface, and the maximum image height Ymax is not defined. And
K2: Focus sensitivity of the second lens group G2 in the infinite focus state K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f1 of the second lens group G2 in FIG. 1: Focal length D1_2 of the first lens group G1: The most image-side surface of the first lens group G1 and the most object of the second lens group G2 in the infinite focus state Spacing between side faces

In order from the object side, the first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power,
When focusing from an object at infinity to an object at a short distance, the distance between the first lens group G1 and the second lens group G2 is reduced, and the distance between the second lens group G2 and the third lens group G3 is reduced. And the second lens group G2 moves to the object side,
An imaging optical system satisfying the following conditional expression:
(1) 1.40 <f / f12 <2.80
(2) 0.020 <G3ΔPgFma <0.300
(3) 1.80 <G3nd
(5) 2.0 <LT / (Ymax) <3.10
f: Focal length of the entire system in the infinite focus state f12: Composite focal length G3ΔPgFmax of the first lens group G1 and the second lens group G2 in the infinite focus state: of the positive lens of the third lens group G3 Of these, the largest ΔPgF value ΔPgF = PgF−0.64833 + 0.00180νd: g, abnormal partial dispersibility between F lines PgF = (ng−nF) / (nF−nC): g, partial dispersion between F lines Ratio ng: Refractive index for g-line (wavelength λ = 435.84 nm) nF: Refractive index for F-line (wavelength λ = 486.13 nm) nC: Refractive index G for C-line (wavelength λ = 656.27 nm) G3nd: Refractive index LT with respect to the d-line (wavelength λ = 587.56) of the positive lens in the third lens group G3: from the most object-side surface to the image plane of the first lens group G1 in the infinite focus state For the sake of convenience, it is assumed that Ymax = (f * tan (w)) where the effective half field angle w is not defined because the maximum image height Ymax is not defined.
In order from the object side, the first lens group G1 having a positive refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power,
The first lens group G1 is fixed with respect to the image plane, the third lens group G3 is fixed with respect to the image plane, and the second lens group G3 is fixed to the image plane during focusing from an object at infinity to an object at a short distance. The lens group G2 is configured to move toward the object side,
An imaging optical system satisfying the following conditional expression:
(1) 1.40 <f / f12 <2.80
(2) 0.020 <G3ΔPgFmax <0.300
(5) 2.0 <LT / (Ymax) <3.10
(6) 2.00 <K2 <5.00
f: Focal length of the entire system in the infinite focus state f12: Composite focal length G3ΔPgFmax of the first lens group G1 and the second lens group G2 in the infinite focus state: of the positive lens of the third lens group G3 Of these, the largest ΔPgF value ΔPgF = PgF−0.64833 + 0.00180νd: g, abnormal partial dispersibility between F lines PgF = (ng−nF) / (nF−nC): g, partial dispersion between F lines Ratio ng: Refractive index for g-line (wavelength λ = 435.84 nm) nF: Refractive index for F-line (wavelength λ = 486.13 nm) nC: Refractive index for C-line (wavelength λ = 656.27 nm) LT: Infinity In the in-focus state, the definition of the surface interval Ymax: maximum image height Ymax from the most object-side surface of the first lens group G1 to the image surface is not made, and an effective half field angle w can be determined. For convenience, and Ymax = (f * tan (w)) of.
K2: Focus sensitivity of the second lens group G2 in the infinite focus state K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f1 of the second lens group G2 at: a focal length of the first lens group G1
The imaging optical system according to claim 2, wherein the following condition is satisfied.
(2) 0.020 <G3ΔPgFmax <0.300
G3ΔPgFmax: The largest ΔPgF value among positive lenses in the third lens group G3 ΔPgF = PgF−0.64833 + 0.00180νd: g, anomalous partial dispersion PgF between F lines = (ng−nF) / (nF -NC): Partial dispersion ratio between g and F lines ng: Refractive index for g line (wavelength λ = 435.84 nm) nF: Refractive index for F line (wavelength λ = 486.13 nm) nC: C line (wavelength λ = 656.27 nm) refractive index G3nd: refractive index with respect to d-line (wavelength λ = 587.56) of the positive lens of the third lens group G3
6. The imaging optical system according to claim 2, wherein the imaging optical system satisfies the following condition.
(3) 1.80 <G3nd
G3nd: refractive index with respect to d-line (wavelength λ = 587.56) of the positive lens of the third lens group G3
The imaging optical system according to claim 2, wherein the following condition is satisfied.
(4) 0.60 <f1 / f <6.50
f: focal length of the entire system in the infinitely focused state f1: focal length of the first lens group G1 The imaging optical system according to claim 1, wherein the following condition is satisfied.
(5) 2.0 <LT / (Ymax) <3.10
LT: The distance between the most object side surface of the first lens group G1 in the infinite focus state and the image plane Ymax: the maximum image height Ymax is not defined, and an effective half field angle w can be discriminated. For convenience, it is assumed that Ymax = (f * tan (w)).
9. The imaging optical system according to claim 1, wherein the imaging optical system satisfies the following conditions.
(6) 2.00 <K2 <5.00
K2: Focus sensitivity of the second lens group G2 in the infinite focus state K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f of the second lens group G2 in FIG. 5: focal length of the entire system in the infinite focus state f12: combined focus f1 of the first lens group G1 and the second lens group G2 in the infinite focus state f1: Focal length of the first lens group G1
The imaging optical system according to claim 1, wherein the following condition is satisfied.
(7) 0.30 <f2 / f <0.95
f2: focal length of the second lens group G2 f: focal length of the entire system in the infinitely focused state
The imaging optical system according to claim 1, wherein the following condition is satisfied.
(8) 0.30 <| f3 / f | <1.40
f3: focal length of the third lens group G3 f: focal length of the entire system in the infinitely focused state
The imaging optical system according to claim 1, wherein the imaging optical system satisfies the following condition.
(9) 0.50 <((D1_2) * K2) / f <1.40
D1_2: the distance between the most image side surface of the first lens group G1 in the infinite focus state and the most object side surface of the second lens group G2 K2: the second lens group G2 in the infinite focus state Focus sensitivity K2 = | Δdef / Δx |
= | (Β3 ^ 2) * (1-β2 ^ 2) |
= | ((F / f12) ^ 2) * (1- (f12 / f1) ^ 2) |
Δdef: amount of movement of the minute image plane in the infinitely focused state Δx: amount of movement of the minute focus lens in the infinitely focused state β3: lateral magnification of the third lens group G2 in the infinitely focused state β2: infinitely focused state Lateral magnification f of the second lens group G2 in FIG. 5: focal length f1 of the entire system in the infinitely focused state f1: focal length f12 of the first lens group G1: the first lens group G1 in the infinitely focused state and the above Composite focal length of the second lens group G2
The first lens group G1 is fixed with respect to the image plane and the third lens group G3 is fixed with respect to the image plane when focusing from an object at infinity to a short-distance object. The imaging optical system according to any one of claims 1 to 3, and 5 to 12.
14. The imaging optical system according to claim 1, wherein the aperture stop S is adjacent to the image side of the first lens group G1 and is fixed in the optical axis direction during focusing. system.
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
(10) 1.60 <| EXP / Ymax | <3.50
EXP: Distance from exit pupil position to image plane in infinite focus state Ymax: Maximum image height Ymax is not defined and effective half angle of view w can be determined for convenience.
Ymax = (f * tan (w)).
16. The imaging optical system according to claim 1, wherein the first lens group G1 includes a positive lens L1 and a negative lens L2 in order from the object side, and has a positive refractive power as a whole. system.
17. The connection according to claim 1, wherein the second lens group G <b> 2 includes a negative lens L <b> 3, a positive lens L <b> 4, and a positive lens L <b> 5 in order from the object side, and has a positive refractive power as a whole. Image optics.
  18. The connection according to claim 1, wherein the third lens group G <b> 3 includes a negative lens L <b> 6, a negative lens L <b> 7, and a positive lens L <b> 8 in order from the object side, and has a negative refractive power as a whole. Image optics.

Images