JP5646287B2 - Imaging optical system and imaging apparatus using the same - Google Patents

Description

  The present invention relates to an optical system used for an imaging apparatus and the like, and more particularly to an imaging optical system suitable for a single focus interchangeable lens in a mirrorless type camera and an imaging apparatus using the imaging optical system.

  2. Description of the Related Art Conventionally, there has been known an imaging optical system that keeps the entire length constant, adopts an inner focus method, and is advantageous for dustproofing and soundproofing during a focusing operation. The imaging optical systems disclosed in Patent Document 1 and Patent Document 2 are, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, an aperture stop, and a positive refractive power. The first lens group and the third lens group are always fixed, and the second lens group having negative refractive power is moved to the image side during focusing from a long distance to a short distance. In addition, the imaging optical systems disclosed in Patent Documents 3, 4, and 5 are arranged in order from the object side, a first lens unit having a positive refractive power, an aperture stop, a second lens group having a positive refractive power, and a positive lens unit. It consists of a third lens group with refractive power, and the first lens group and the second lens group are always fixed, and the second lens group with positive refractive power is moved to the object side during focusing from a long distance to a short distance. is there. With such a configuration, an imaging optical system having favorable optical performance while being advantageous for dustproof and soundproofing.

JP-A-11-160617 JP-A-2005-321574 JP 2009-244696 A JP 2009-244697 A JP 2009-244699 A

  However, the imaging optical systems disclosed in Patent Literature 1 and Patent Literature 2 have a configuration in which a first lens group and a movable second lens group during focusing are arranged on the object side of the aperture stop. The distance between the first lens group and the aperture stop is large, and as a result, the diameter of the first lens group is large. In the imaging optical systems disclosed in Patent Documents 3, 4 and 5, an aperture stop is disposed between the first lens group and the second lens group, but on the image side of the aperture stop. In this configuration, a plurality of positive lens groups are arranged, and off-axis aberration is likely to occur.

  The present invention has been made in view of the above-described problems, and provides an imaging optical system that is advantageous for soundproofing and dustproofing, can easily suppress the radial direction, and easily secure optical performance, and an imaging apparatus using the same. It is intended to do.

  In order to solve the above problems, an imaging optical system according to the present invention is as follows.

  In order from the object side to the image plane side, the first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, and from the object side surface of the first lens group An aperture stop is disposed between the object side surfaces of the second lens group, the first lens group and the third lens group are always fixed, and the second lens group is focused when focusing from a long distance to a short distance. Only the lens group moves in the optical axis direction, and the third lens group includes a front sub-lens group having a positive refractive power disposed on the object side across the largest axial air interval in the third lens group. And a rear sub-lens group having negative refractive power disposed on the image side.

  Hereinafter, the reason and effect | action which took such a structure are demonstrated.

  First, by setting the most object-side lens and the most image-side lens of the imaging optical system to be fixed at all times, and an inner-focus imaging optical system that moves only the second lens group in the optical axis direction during focusing, This is advantageous for securing dustproof and soundproofing properties.

  By disposing the aperture stop closer to the object side than the second lens group, the effective diameter of the first lens group that most affects the size of the imaging optical system can be reduced, and the radial size of the optical system can be reduced. It becomes easy to make it smaller.

  In addition, by suppressing the radial size of the first lens group, it is easy to reduce the axial thickness of the first lens group having positive refractive power. This is advantageous for downsizing the imaging optical system and improves portability.

  On the other hand, since the aperture stop is closer to the object side than the second lens unit, the third lens unit having a positive refractive power is separated from the aperture stop. Since both the second lens group and the third lens group on the image side of the aperture stop have positive refracting power, in order to perform correction including distortion, on-axis aberration and off-axis aberration are used in the third lens group. It is preferable to adopt a configuration that takes both of these into consideration.

  In the present invention, the object side is a front sub-lens group having positive refractive power across the largest axial air interval in the third lens group, and the image side of the axial air interval is a rear sub-lens group having negative refractive power. It is said.

  In this way, by arranging the rear sub lens group having negative refractive power in the third lens group on the image side relative to the front sub lens group having positive refractive power in the third lens group, the front sub lens having positive refractive power is arranged. While maintaining the function of canceling the on-axis aberration in the group, increasing the off-axis ray incident height is advantageous for securing the function of canceling the off-axis aberration (particularly distortion aberration).

  In addition, as a whole, a telephoto lens group is arranged, which is advantageous for shortening the overall length.

  Therefore, the above-described configuration is advantageous for soundproofing and dustproofing, and provides an imaging optical system that is advantageous for downsizing and ensuring optical performance.

  In the above-described invention, it is preferable that at least one of the following configurations is further satisfied.

The third lens group preferably satisfies the following conditional expression (1).
−0.5 <f3r / f3G <−0.05 (1)
However,
f3r is a focal length of the rear sub lens group,
f3G is the focal length of the third lens group,
It is.

  By securing the negative refractive power of the rear sub-lens group so as not to fall below the lower limit value of the conditional expression (1), it becomes more advantageous for correction of on-axis aberrations and off-axis aberrations (particularly distortion aberration). In addition, the imaging optical system as a whole becomes a telephoto type, which leads to shortening of the overall length of the optical system.

  Excessive correction can be suppressed by appropriately suppressing the negative refractive power of the rear sub lens unit so as not to exceed the upper limit value of conditional expression (1). In addition, the exit pupil is easily separated from the image plane, which is advantageous for reducing shading.

In addition, it is preferable that the first lens group satisfies the following conditional expression (2).
4.0 <f1G / f <10.0 (2)
However,
f1G is the focal length of the first lens group,
f is a focal length of the imaging optical system,
It is.

  While correcting the off-axis aberrations such as field curvature and coma aberration, the positive refractive power of the first lens unit is appropriately secured so as to be within the range of the upper limit value and the lower limit value of conditional expression (2). This is advantageous in ensuring a function of canceling off-axis aberration between the first lens group and the third lens group.

The second lens group preferably satisfies the following conditional expression (3).
0.85 <f2G / f <3.0 (3)
However,
f2G is a focal length of the second lens group,
f is a focal length of the imaging optical system,
It is.

  By suppressing the excess of the positive refractive power of the second lens group so as not to fall below the lower limit of conditional expression (3), it is possible to suppress the refractive power of the second lens group as the focus group and to suppress aberration fluctuations associated with focusing. Become.

  Ensuring the positive refractive power of the focus group so as not to exceed the upper limit value of conditional expression (3) is advantageous in reducing the amount of movement associated with focusing.

Further, it is preferable that the third lens group satisfies the following conditional expression (4).
3.0 <f3G / f <9.0 (4)
However,
f3G is the focal length of the third lens group,
f is a focal length of the imaging optical system,
It is.

  By appropriately securing the positive refracting power of the third lens group so as to be within the range of the upper limit value and the lower limit value of conditional expression (4), such as field curvature and coma generated in the first lens group This is advantageous for distortion correction while correcting off-axis aberrations.

In addition, it is preferable that the third lens group satisfies the following conditional expression (5).
0.01 <D3Gfr / f3G <0.5 (5)
However,
D3Gfr is the axial distance between the image side surface of the front sub lens group and the object side surface of the rear sub lens group in the third lens group,
f3G is the focal length of the third lens group,
It is.

  By securing an appropriate distance between the front sub-lens group and the rear sub-lens group so as not to fall below the lower limit of conditional expression (5) and above the upper limit, both on-axis aberrations and off-axis aberrations can be obtained. This is advantageous for correction.

Moreover, it is preferable that the following conditional expression (6) is satisfied.
0.14 <D2G3G / D1Gf3G <0.5 (6)
However,
D2G3G is the axial distance between the image side surface of the second lens group and the object side surface of the third lens group;
D1Gf3G is the axial distance between the object side surface of the first lens group and the object side surface of the third lens group;
It is.

  By securing an on-axis distance between the second lens group and the third lens group so as not to fall below the lower limit value of conditional expression (6), it is easy to cancel off-axis aberrations occurring in the first lens group. Become. This is also advantageous for reducing the weight of the imaging optical system.

  By appropriately restraining the axial distance between the second lens group and the third lens group so as not to exceed the upper limit value of conditional expression (6), it becomes easy to make the imaging optical system small, particularly as an interchangeable lens. This is advantageous for downsizing.

  Moreover, it is preferable that the axial distance between the second lens group and the third lens group is the largest among the axial air distances in the imaging optical system.

  Ensuring an axial distance between the second lens group and the third lens group is advantageous for correcting off-axis aberrations.

  The second lens group that performs focusing is preferably configured as follows.

  The second lens group preferably comprises two or less lenses.

  The lens group that moves during focusing can be reduced in weight, which is advantageous in reducing the power consumption during the wobbling operation and focusing operation, and in improving the AF speed and accuracy.

In addition, it is preferable that the second lens group includes one positive lens component and moves to the object side during focusing from a long distance to a short distance.
However, the lens component is a lens body in which only the object side surface and the image side surface are in contact with air, and means a single lens or a cemented lens.

  Such a configuration is advantageous for reducing the weight of the second lens group.

  Further, the positive lens component is preferably a single lens.

  Since the positive lens component is a single lens, it is further advantageous for weight reduction.

  Further, when performing moving image shooting or high-speed AF, the focusing lens group is preferably light. For this reason, the following should be performed for the aperture stop.

  It is preferable that the brightness stop is disposed closer to the image side than the most object side lens in the first lens group.

  While the first lens group is made smaller, the focusing lens group is disposed in the vicinity of the aperture stop, which is advantageous for reducing the size and weight of the first lens group and the second lens group.

  Further, it is preferable that the brightness stop is disposed between a plurality of lenses in the first lens group.

  Disposing the aperture stop between the plurality of lenses in the first lens group is advantageous for reducing the diameter of the first lens group.

  Moreover, it is preferable that the brightness stop is always fixed together with the first lens group.

  Since the aperture stop does not move during the focusing operation, the weight of the moving member during focusing can be reduced. Therefore, it is advantageous for reducing the power consumption and improving the AF speed and accuracy during the AF operation, the wobbling operation, and the high-speed AF operation during moving image shooting.

  Furthermore, it is preferable that the first lens group has the following configuration.

  The first lens group preferably includes two positive lenses and at least one negative lens disposed on the object side of the brightness stop.

  Sharing a positive refractive power among a plurality of positive lenses and using a negative lens is advantageous in correcting spherical aberration, coma aberration, and chromatic aberration.

In addition, the first lens group includes a first sub lens group having a positive refractive power, a second sub lens group having a negative refractive power, and a third sub lens group having a positive refractive power.
The largest air gap in the second sub lens group is the largest air gap in the first lens group,
The lens immediately before the object side with the largest air gap in the second sub lens group is a lens having a concave surface directed to the image side,
It is preferable that the lens immediately after the image side with the largest air interval in the second sub lens group is a lens having a concave surface directed toward the object side.

  Distributing the positive refractive power between the object side and the image side in the first lens group, and disposing a lens group having a negative refractive power therebetween, is advantageous for correcting spherical aberration, coma aberration, and chromatic aberration. In particular, it is more advantageous for adjusting the Petzval sum and correcting various aberrations by disposing the lens so that a biconvex space having a large axial distance is formed in the second lens group.

Moreover, it is preferable that the following conditional expression (7) is satisfied.
−0.01 <SFair <−0.99 (7)
However,
SFair = (RairO + RairI) / (RairO-RairI),
RairO is the paraxial radius of curvature of the image side surface of the lens immediately before the object side with the largest air gap in the second sub lens group,
RairI is the paraxial radius of curvature of the object side surface of the lens immediately after the image side of the second sub lens group with the largest air gap.

  Conditional expression (7) specifies a preferable shape of the biconvex space.

  By appropriately sharing the negative refracting power on the concave surfaces before and after the biconvex space so as not to fall below the lower limit value of the conditional expression (7) and above the upper limit value, the optical power of the imaging optical system This will ensure both performance and miniaturization.

  By controlling the negative refractive power of the concave surface on the image side of the space so as not to fall below the lower limit value of the conditional expression (7), it is possible to reduce higher-order aberrations.

  By ensuring the negative refractive power of the concave surface on the image side of the space so as not to exceed the upper limit value of conditional expression (7), it leads to axial aberration correction and the like.

Moreover, it is preferable that the following conditional expression (8) is satisfied.
−0.3 <fair / f1G <−0.01 (8)
However,
f1G is the focal length of the first lens group,
fair = 1 / (φairO + φairI−Dair × φairO × φairI),
And
φairO is the refractive power of the image side surface of the lens immediately before the object side with the largest air gap in the second sub-lens group,
φairI is the refractive power of the object side surface of the lens immediately after the image side with the largest air spacing in the second sub-lens group,
Dair is the distance on the optical axis between the lens surface immediately before the object side and the lens surface immediately after the image side of the largest sub-air group in the second sub lens group,
And
The refractive power φ of the surface is expressed by φ = (nI−nO) / ROI where nO is the refractive index of the incident side of the surface, nI is the refractive index of the exit side of the surface, and ROI is the paraxial radius of curvature of the surface. .

  Conditional expression (8) specifies the preferable combined refractive power of the object-side concave surface and the image-side concave surface that sandwich the largest air gap in the second sub-lens group.

  Ensuring the divergence of the air lens so that it does not fall below the lower limit value of conditional expression (8) is advantageous for securing an aberration correction function by the air lens.

  By suppressing the excess of the diverging force of the air lens so as not to exceed the upper limit value of conditional expression (8), it becomes easy to suppress the enlargement of the imaging optical system.

  The first sub lens group preferably includes a plurality of positive lenses, the second sub lens group includes a plurality of negative lenses, and the third sub lens group preferably includes a positive lens.

  This leads to a reduction in higher-order aberrations in the first sub-lens group and the second sub-lens group, and is more advantageous for ensuring both brightness and optical performance.

  Furthermore, it is preferable that the third lens group has the following configuration.

  It is preferable that the front sub lens group in the third lens group includes two lenses, and the rear sub lens group in the third lens group includes one lens component having a negative refractive power.

  Constructing the front sub-lens group with a plurality of lenses is advantageous in reducing aberrations by sharing the positive refractive power or canceling out aberrations. Further, the rear sub lens group is made into one lens component, which is advantageous for weight reduction.

  These imaging optical systems are effective when used in an imaging apparatus such as a digital camera because the exit pupil is easily separated from the image plane and the performance is easily improved.

  An imaging apparatus having an imaging optical system and an imaging element having an imaging surface that is disposed on the image side of the imaging optical system and converts an optical image into an electrical signal. An imaging optical system is preferable.

  Unless otherwise specified, each of the above-described configurations is a configuration in which the farthest distance is in focus. It is more preferable that a plurality of the above-described configurations are satisfied simultaneously.

  Furthermore, in each conditional expression, it is preferable that the lower limit and / or the upper limit be further reduced to ensure the effect.

For conditional expression (1), it is more preferable to set the lower limit value to −0.4, more preferably −0.3.
More preferably, the upper limit value is -0.04, more preferably -0.03, and even more preferably -0.22.

For conditional expression (2), it is more preferable to set the lower limit to 4.5, and more preferably to 5.0.
It is more preferable that the upper limit value is 9.0, more preferably 8.0.

In conditional expression (3), the lower limit value is more preferably 0.9, and even more preferably 0.92.
More preferably, the upper limit value is 2.0, more preferably 1.5, and even more preferably 1.25.

In conditional expression (4), it is more preferable to set the lower limit to 4.0, further 4.5, and even 4.8.
More preferably, the upper limit value is 8.9, more preferably 8.8.

In conditional expression (5), it is more preferable to set the lower limit to 0.012, and further to 0.014.
More preferably, the upper limit value is 0.3, more preferably 0.2.

In conditional expression (6), the lower limit value is more preferably 0.18, and even more preferably 0.22.
More preferably, the upper limit value is 0.4, more preferably 0.3.

In conditional expression (7), it is more preferable to set the lower limit to −0.04, more preferably −0.06.
More preferably, the upper limit value is -0.7, more preferably -0.5.

For conditional expression (8), it is more preferable to let the lower limit value to be −0.2, more preferably −0.15.
More preferably, the upper limit value is -0.03, more preferably -0.05.

  According to the present invention, it is possible to provide an imaging optical system that is advantageous for soundproofing and dustproofing and is easy to secure optical performance while being small in size. Furthermore, it is possible to provide an imaging apparatus using such an imaging optical system.

2 is a cross-sectional view of the optical system of Example 1. FIG. 6 is a cross-sectional view of an optical system according to Example 2. FIG. 6 is a sectional view of an optical system according to Example 3. FIG. FIG. 6 is a diagram illustrating various aberrations of the optical system of Example 1 in an infinitely focused state. FIG. 6 is a diagram illustrating various aberrations of the optical system of Example 2 in an infinitely focused state. FIG. 6 is a diagram illustrating various aberrations of the optical system according to Example 3 in an infinitely focused state. It is sectional drawing of the lens interchangeable camera which used the lens of this invention as an interchangeable lens. It is a front perspective view which shows the external appearance of the digital camera by this invention. It is a rear view of the digital camera of FIG. It is a cross-sectional view of the digital camera of FIG. FIG. 9 is a configuration block diagram of an internal circuit of a main part of the digital camera of FIG. 8.

  Examples 1 to 3 of the present invention will be described. 1 to 3 are sectional views of the optical system of each embodiment. In addition, in each figure, five parallel plates change the pixel pitch from the object side while keeping the dust-proof filter F1 that splashes dust away by ultrasonic vibration, the IR-cut filter F2 with IR cut coating, and the flange back constant. The adjustment parallel plate F3, the low-pass filter F4, and the cover glass C that cancel the change in the thickness of the low-pass filter accompanying the above.

  FIG. 1 is a sectional view of the optical system according to the first embodiment. 1A is a cross-sectional view of the optical system at the time of focusing on infinity according to the first embodiment, and FIG. 1B is a cross-sectional view of the optical system at the time of focusing close to the first embodiment.

  As shown in FIG. 1, the optical system of Example 1 includes, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a first lens group having a positive refractive power. It consists of three lens groups G3. Moreover, it has the aperture stop S arrange | positioned at the 1st lens group G1.

  The first lens group G1, in order from the object side, includes a biconvex positive lens L11, a positive meniscus lens L12 with a convex surface facing the object side, a negative meniscus lens L13 with a convex surface facing the object side, and a biconcave negative lens L14. And an aperture stop S and a positive meniscus lens L15 having a convex surface facing the image side.

  The second lens group G2 is composed of a positive meniscus lens L21 having a convex surface directed toward the object side.

  The third lens group G3 includes a front sub lens group G3F having a positive refractive power and a rear sub lens group G3R having a negative refractive power. The front sub lens group G3F includes a cemented lens SU31 of a biconcave negative lens L31 and a biconvex positive lens L32. The rear sub lens group G3R includes a negative meniscus lens L33 having a convex surface directed toward the image side.

  The first lens group G1 and the third lens group G3 are always fixed. The second lens group G2 moves toward the object side with respect to focusing from infinity to the close.

  FIG. 2 is a sectional view of the optical system according to the second embodiment. 2A is a cross-sectional view of the optical system when focusing on infinity according to the second embodiment, and FIG. 2B is a cross-sectional view of the optical system when focusing close to the second embodiment.

  As shown in FIG. 2, the optical system according to the second embodiment includes, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a first lens group having a positive refractive power. It consists of three lens groups G3. Moreover, it has the aperture stop S arrange | positioned at the 1st lens group G1.

  The first lens group G1, in order from the object side, includes a positive meniscus lens L11 having a convex surface directed toward the object side, a positive meniscus lens L12 having a convex surface directed toward the object side, a negative meniscus lens L13 having a convex surface directed toward the object side, It comprises a biconcave negative lens L14, an aperture stop S, and a positive meniscus lens L15 having a convex surface facing the image side.

  The second lens group G2 is composed of a positive meniscus lens L21 having a convex surface directed toward the object side.

  The third lens group G3 includes a front sub lens group G3F having a positive refractive power and a rear sub lens group G3R having a negative refractive power. The front sub lens group G3F includes a cemented lens SU31 of a biconcave negative lens L31 and a biconvex positive lens L32. The rear sub lens group G3R includes a negative meniscus lens L33 having a convex surface directed toward the image side.

  The first lens group G1 and the third lens group G3 are always fixed. The second lens group G2 moves toward the object side with respect to focusing from infinity to the close.

  FIG. 3 is a sectional view of the optical system according to the third embodiment. 3A is a cross-sectional view of the optical system at the time of focusing on infinity according to the third embodiment, and FIG. 3B is a cross-sectional view of the optical system at the time of focusing close to the third embodiment.

  As shown in FIG. 3, the optical system of Example 3 includes, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a first lens group having a positive refractive power. It consists of three lens groups G3. Moreover, it has the aperture stop S arrange | positioned at the 1st lens group G1.

  The first lens group G1, in order from the object side, includes a positive meniscus lens L11 having a convex surface directed toward the object side, a positive meniscus lens L12 having a convex surface directed toward the object side, a negative meniscus lens L13 having a convex surface directed toward the object side, It comprises a biconcave negative lens L14, an aperture stop S, and a positive meniscus lens L15 having a convex surface facing the image side.

  The second lens group G2 includes a biconvex positive lens L21 and a cemented lens SU21 of a negative meniscus lens L22 having a convex surface directed toward the image side.

  The third lens group G3 includes a front sub lens group G3F having a positive refractive power and a rear sub lens group G3R having a negative refractive power. The front sub lens group G3F includes a cemented lens SU31 of a biconcave negative lens L31 and a biconvex positive lens L32. The rear sub lens group G3R includes a negative meniscus lens L33 having a convex surface directed toward the image side.

  The first lens group G1 and the third lens group G3 are always fixed. The second lens group G2 moves toward the object side with respect to focusing from infinity to the close.

Below, the numerical data of Examples 1-3 are shown. In the numerical data of Examples 1 to 3, r is the radius of curvature of the lens surface, d is the lens thickness and air spacing, nd and νd are the refractive index and Abbe number at the d-line (λ = 587.6 nm), and f is Focal length, Fno is an F number, ω is a half field angle (°), fb (in air) is an air-converted back focus, and IH is an image height.

Numerical example 1
Unit mm

Surface data surface number r d nd νd
1 46.683 4.07 1.81600 46.62
2 -566.229 0.10
3 22.734 3.34 1.60311 60.64
4 36.923 2.45
5 227.015 1.00 1.64769 33.79
6 18.649 5.32
7 -22.020 1.00 1.58144 40.75
8 85.186 1.95
9 (Aperture) ∞ 1.80
10 -178.530 3.15 1.77250 49.60
11 -24.688 d11
12 22.938 3.50 1.45650 90.27
13 354.826 d13
14 -133.961 2.07 1.80 100 34.97
15 35.821 4.59 1.77250 49.60
16 -33.831 6.33
17 -16.924 1.00 1.51742 52.43
18 -34.022 8.99
19 ∞ 0.65 1.51633 64.14
20 ∞ 0.85
21 ∞ 0.82 1.00000 70.86
22 ∞ 0.76 1.00000 61.08
23 ∞ 1.08 1.00000 70.86
24 ∞ 0.45
25 ∞ 0.80 1.00000 63.38
26 ∞ 0.75
Image plane ∞

Infinity close
d11 4.36 0.99
d13 11.81 15.17

Various data
f 44.32 44.06
Fno 1.84 1.82
2ω (angle of view (°)) 28.36 26.71

fb (in air) 13.73
Total length (in air) 71.57
IH 11.15

Each group focal length first lens group 233.14
Second lens group 53.54
Third lens group 384.50

Distance between objects at close focus 85cm

Numerical example 2
Unit mm

Surface data surface number r d nd νd
1 34.681 4.45 1.81600 46.62
2 872.454 0.10
3 20.365 3.46 1.60311 60.64
4 41.023 1.09
5 95.648 1.00 1.64769 33.79
6 15.426 5.30
7 -26.564 1.00 1.58144 40.75
8 51.406 2.22
9 (Aperture) ∞ 2.78
10 -59.129 2.24 1.77250 49.60
11 -23.954 d11
12 21.250 3.87 1.45650 90.27
13 1466.207 d13
14 -68.559 1.00 1.69895 30.13
15 128.545 3.19 1.77250 49.60
16 -27.585 4.47
17 -15.886 1.00 1.51742 52.43
18 -31.871 8.99
19 ∞ 0.65 1.51633 64.14
20 ∞ 0.85
21 ∞ 0.82 1.00000 70.86
22 ∞ 0.76 1.00000 61.08
23 ∞ 1.08 1.00000 70.86
24 ∞ 0.45
25 ∞ 0.80 1.00000 63.38
26 ∞ 0.75
Image plane ∞

Infinity close
d11 4.29 0.99
d13 11.69 14.99

Various data
f 44.26 44.17
Fno 1.84 1.83
2ω (angle of view (°)) 28.46 26.62

fb (in air) 13.73
Total length (in air) 66.89
IH 11.15

Each group focal length first lens group 265.11
Second lens group 47.19
Third lens group 260.76

Distance between objects at close focus 85cm

Numerical example 3
Unit mm

Surface data surface number r d nd νd
1 33.305 5.06 1.81600 46.62
2 240.584 0.10
3 20.030 4.14 1.60311 60.64
4 33.505 1.51
5 61.496 1.00 1.64769 33.79
6 14.552 5.86
7 -30.006 1.00 1.58144 40.75
8 56.949 2.18
9 (Aperture) ∞ 2.11
10 -62.195 1.98 1.78800 47.37
11 -27.548 d11
12 21.710 5.22 1.45650 90.27
13 -63.753 1.00 1.76182 26.52
14 -132.399 d14
15 -74.420 1.00 1.53172 48.84
16 401.206 2.75 1.77250 49.60
17 -29.141 3.94
18 -16.745 1.00 1.49700 81.61
19 -40.363 8.99
20 ∞ 0.65 1.51633 64.14
21 ∞ 0.85
22 ∞ 0.82 1.00000 70.86
23 ∞ 0.76 1.00000 61.08
24 ∞ 1.08 1.00000 70.86
25 ∞ 0.45
26 ∞ 0.80 1.00000 63.38
27 ∞ 0.75
Image plane ∞

Infinity close
d11 5.06 0.99
d14 11.33 15.39

Various data
f 48.49 48.56
Fno 1.84 1.83
2ω (angle of view (°)) 26.05 23.90

fb (in air) 13.73
Total length (in air) 68.96
IH 11.15

Each group focal length first lens group 365.30
Second lens group 45.73
Third lens group 238.74

Distance between objects at close focus 85cm

  4 to 6 are various aberration diagrams of the optical systems of Examples 1 to 3. FIG. In each drawing, (a) shows various aberrations in the infinite focus state, and (b) shows various aberrations in the closest focus state. Spherical aberration and lateral chromatic aberration are numerical values at respective wavelengths of 435.8 nm (g line: one-dot chain line), 587.6 nm (d line: solid line), and 656.3 nm (C line: wavy line). Astigmatism, the solid line indicates the sagittal image plane, and the dotted line indicates the meridional image plane. FNO represents the F number, and IH represents the image height.

Next, the values of conditional expressions (1) to (8) in the above embodiments will be shown.

Conditional Example Example 1 Example 2 Example 3
(1) -0.173 -0.240 -0.245
(2) 5.261 5.990 7.533
(3) 1.208 1.066 0.943
(4) 8.676 5.892 4.923
(5) 0.016 0.017 0.016
(6) 0.269 0.269 0.238
(7) -0.083 -0.265 -0.345
(8) -0.102 -0.087 -0.063

  FIG. 7 is a cross-sectional view of a single-lens mirrorless camera as an electronic image pickup apparatus using a lens of the present invention and using a small CCD or CMOS as an image pickup device. In FIG. 7, 1 is a single-lens mirrorless camera, 2 is a photographic lens system disposed in the lens barrel, 3 is a lens barrel mount that allows the photographic lens system 2 to be attached to and detached from the single-lens mirrorless camera 1, and a screw Type mounts and bayonet type mounts are used. In this example, a bayonet type mount is used. Reference numeral 4 denotes an image sensor surface, and 5 denotes a back monitor.

  As the photographing lens system 2 of the single-lens mirrorless camera 1 having such a configuration, for example, the lens of the present invention shown in the first to third embodiments is used.

  According to the present invention as described above, as an interchangeable lens suitable for a single-lens mirrorless type digital camera, various aberrations such as distortion, chromatic aberration, and curvature of field are well corrected, and a small number of compact lenses that ensure telecentricity. It becomes possible to provide a simple optical system.

  8 to 10 are conceptual diagrams of the configuration of another imaging apparatus according to the present invention in which a lens is incorporated in the photographing optical system 41. FIG. 8 is a front perspective view showing the appearance of the digital camera 40, FIG. 9 is a rear view thereof, and FIG. 10 is a schematic cross-sectional view showing the configuration of the digital camera 40.

  In this example, the digital camera 40 includes a photographic optical system 41 positioned on the photographic optical path 42, a finder optical system 43 positioned on the finder optical path 44, a shutter button 45, a pop-up flash 46, a liquid crystal display monitor 47, and the like. In addition, when a shutter button 45 disposed on the upper portion of the camera 40 is pressed, photographing is performed through the photographing optical system 41, for example, the lens of the first embodiment, in conjunction therewith. The object image formed by the photographing optical system 41 is formed on the image pickup surface (photoelectric conversion surface) of the CCD 49 as an image pickup element provided in the vicinity of the image forming surface. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera or the finder image display element 54 via the processing means 51. Further, a recording means 52 is connected to the processing means 51 so that a photographed electronic image can be recorded.

  The recording unit 52 may be provided separately from the processing unit 51, or may be configured to perform recording and writing electronically using a flexible disk, a memory card, an MO, or the like. Further, it may be configured as a silver salt camera in which a silver salt film is arranged in place of the CCD 49.

  Further, a finder eyepiece lens 59 is disposed on the finder optical path 44. The object image displayed on the finder image display element 54 is magnified by the finder eyepiece lens 59 and adjusted to a diopter that is easy for the observer to see, and is guided to the observer eyeball E. A cover member 50 is disposed on the exit side of the finder eyepiece lens 59.

  FIG. 11 is a block diagram showing the internal circuitry of the main part of the digital camera 40. In the following description, the processing unit 51 includes, for example, the CDS / ADC unit 24, the temporary storage memory 17, the image processing unit 18, and the like, and the storage unit 52 includes, for example, the storage medium unit 19 and the like.

  As shown in FIG. 11, the digital camera 40 is connected to the operation unit 12, the control unit 13 connected to the operation unit 12, and the control signal output port of the control unit 13 via buses 14 and 15. An imaging drive circuit 16, a temporary storage memory 17, an image processing unit 18, a storage medium unit 19, a display unit 20, and a setting information storage memory unit 21 are provided.

  The temporary storage memory 17, the image processing unit 18, the storage medium unit 19, the display unit 20, and the setting information storage memory unit 21 are configured to be able to input or output data with each other via the bus 22. The imaging drive circuit 16 is connected with a CCD 49 and a CDS / ADC unit 24.

  The operation unit 12 includes various input buttons and switches, and is a circuit that notifies the control unit of event information input from the outside (camera user) via these input buttons and switches. The control unit 13 is a central processing unit composed of, for example, a CPU, and has a built-in program memory (not shown). The control unit 13 is input by a camera user via the operation unit 12 according to a program stored in the program memory. This circuit controls the entire digital camera 40 in response to the instruction command.

  The CCD 49 receives an object image formed via the photographing optical system 41 according to the present invention. The CCD 49 is an image pickup element that is driven and controlled by the photographing drive circuit 16 and converts the light amount of each pixel of the object image into an electrical signal and outputs it to the CDS / ADC unit 24.

  The CDS / ADC unit 24 amplifies the electric signal input from the CCD 49 and performs analog / digital conversion, and temporarily generates the raw video data (Bayer data, hereinafter referred to as RAW data) that has just been subjected to the amplification and digital conversion. It is a circuit that outputs to the memory 17.

  The temporary storage memory 17 is a buffer made of, for example, SDRAM or the like, and is a memory device that temporarily stores the RAW data output from the CDS / ADC unit 24. The image processing unit 18 reads out the RAW data stored in the temporary storage memory 17 or the RAW data stored in the storage medium unit 19, and performs various corrections including distortion correction based on the image quality parameter designated by the control unit 13. It is a circuit that performs image processing electrically.

  The storage medium unit 19 detachably mounts a card-type or stick-type recording medium made of, for example, a flash memory, and RAW data transferred from the temporary storage memory 17 to the card-type or stick-type flash memory. It is a control circuit of an apparatus that records and holds image data processed by the image processing unit 18.

  The display unit 20 includes a liquid crystal display monitor 47 and a finder image display element 54, and is a circuit that displays an image, an operation menu, and the like on the liquid crystal display monitor 47 and the finder image display element 54. The setting information storage memory unit 21 stores a ROM unit in which various image quality parameters are stored in advance, and an image quality parameter selected by an input operation of the operation unit 12 among the image quality parameters read from the ROM unit. RAM section is provided. The setting information storage memory unit 21 is a circuit for controlling input / output to / from these memories.

  According to the present invention, the digital camera 40 configured in this manner is compact with a small number of components, in which various aberrations such as chromatic aberration and curvature of field are corrected well, and telecentricity is ensured while performing distortion correction to some extent. An imaging apparatus using a wide-angle optical system can be provided.

  The present invention may be applied not only to a so-called compact digital camera that photographs a general subject as described above, but also to a surveillance camera or the like that requires a wide angle of view.

G1 ... 1st lens group SG1 ... 1st sub lens group SG2 ... 2nd sub lens group SG3 ... 3rd sub lens group G2 ... 2nd lens group G3 ... 3rd lens group G3F ... Front sub lens group G3R ... Rear sub lens Group S ... Brightness stop F1 ... Dust-proof filter F2 ... IR cut filter F3 ... Adjusting parallel plate F4 ... Low-pass filter C ... Cover glass I ... Image plane 1 ... Lens interchangeable camera 2 ... Shooting lens system 3 ... Mount part 4 Image pickup device surface 5 Back monitor 12 Operation unit 13 Control units 14 and 15 Bus 16 Image pickup drive circuit 17 Temporary storage memory 18 Image processing unit 19 Storage medium unit 20 Display unit 21 Setting information storage Memory section 22 ... Bus 24 ... CDS / ADC section 40 ... Digital camera 41 ... Shooting optical system 42 ... Shooting optical path 43 ... Viewfinder optical system 44 ... Viewfinder light 45 ... shutter button 46 ... pop-up strobe 47 ... liquid crystal display monitor 49 ... CCD
DESCRIPTION OF SYMBOLS 50 ... Cover member 51 ... Processing means 52 ... Recording means 54 ... Image display element 59 for finder ... Eyepiece for finder

Claims (20)

In order from the object side to the image plane side,
A first lens unit having positive refractive power;
A second lens group having positive refractive power;
It consists of a third lens group with positive refractive power,
An aperture stop disposed between the object side surface of the first lens group and the object side surface of the second lens group;
The first lens group and the third lens group are always fixed,
During focusing from a long distance to a short distance, only the second lens group moves in the optical axis direction,
The third lens group includes a front sub-lens group having a positive refractive power disposed on the object side and a negative refractive power disposed on the image side with the largest axial air interval in the third lens group interposed therebetween. a rear sub-lens group, Ri Tona,
The image forming optical system according to claim 3, wherein the third lens group satisfies the following conditional expression (4) .
3.0 <f3G / f <9.0 (4)
However,
f3G is the focal length of the third lens group,
f is a focal length of the imaging optical system,
It is. The imaging optical system according to claim 1, wherein the third lens group satisfies the following conditional expression (1).
−0.5 <f3r / f3G <−0.05 (1)
However,
f3r is a focal length of the rear sub lens group,
f3G is the focal length of the third lens group,
It is. The imaging optical system according to claim 1, wherein the first lens group satisfies the following conditional expression (2).
4.0 <f1G / f <10.0 (2)
However,
f1G is the focal length of the first lens group,
f is a focal length of the imaging optical system,
It is. The imaging optical system according to any one of claims 1 to 3, wherein the second lens group satisfies the following conditional expression (3).
0.85 <f2G / f <3.0 (3)
However,
f2G is a focal length of the second lens group,
f is a focal length of the imaging optical system,
It is. The imaging optical system according to any one of claims 1 to 4 , wherein the third lens group satisfies the following conditional expression (5).
0.01 <D3Gfr / f3G <0.5 (5)
However,
D3Gfr is the axial distance between the image side surface of the front sub lens group and the object side surface of the rear sub lens group in the third lens group,
f3G is the focal length of the third lens group,
It is. The following conditional expression (6) imaging optical system according to any one of claims 1 to 5, characterized in that satisfies.
0.14 <D2G3G / D1Gf3G <0.5 (6)
However,
D2G3G is the axial distance between the image side surface of the second lens group and the object side surface of the third lens group;
D1Gf3G is the axial distance between the object side surface of the first lens group and the object side surface of the third lens group;
It is. Axial distance between the second lens group and the third lens group, one of the claims 1 to 6, wherein the largest of the axial air gap distance in the imaging optical system The imaging optical system as described in any one. The imaging optical system according to any one of claims 1 to 7 , wherein the second lens group includes two or less lenses. 9. The imaging optical system according to claim 8 , wherein the second lens group includes one positive lens component and moves to the object side during focusing from a long distance to a short distance.
However, the lens component is a lens body in which only the object side surface and the image side surface are in contact with air, and means a single lens or a cemented lens. The imaging optical system according to claim 9 , wherein the positive lens component is a single lens. The aperture stop imaging optical system according to any one of claims 1 to 10, characterized in that arranged on the image side of the most object side lens in the first lens group . The imaging optical system according to claim 11 , wherein the brightness stop is disposed between a plurality of lenses in the first lens group. The aperture stop imaging optical system according to any one of claims 1 to 12, characterized in that it is always fixed with the first lens group. The first lens group, any one of claims 1 to 13 characterized in that it has at least one negative lens and two positive lenses disposed on the object side of the aperture the brightness The imaging optical system described. The first lens group includes a first sub lens group having a positive refractive power, a second sub lens group having a negative refractive power, and a third sub lens group having a positive refractive power.
The largest air gap in the second sub lens group is the largest air gap in the first lens group,
The lens immediately before the object side with the largest air gap in the second sub lens group is a lens having a concave surface directed to the image side,
The lens according to any one of claims 1 to 14 , wherein the lens immediately after the image side having the largest air interval in the second sub-lens group is a lens having a concave surface directed toward the object side. Image optics. The imaging optical system according to claim 15 , wherein the following conditional expression (7) is satisfied.
−0.99 <SFair <−0.01 (7)
However,
SFair = (RairO + RairI) / (RairO-RairI),
RairO is the paraxial radius of curvature of the image side surface of the lens immediately before the object side with the largest air gap in the second sub lens group,
RairI is the paraxial radius of curvature of the object side surface of the lens immediately after the image side of the second sub lens group with the largest air gap. The imaging optical system according to claim 15 or 16 , wherein the following conditional expression (8) is satisfied.
−0.3 <fair / f1G <−0.01 (8)
However,
f1G is the focal length of the first lens group,
fair = 1 / (φairO + φairI−Dair × φairO × φairI),
And
φairO is the refractive power of the image side surface of the lens immediately before the object side with the largest air gap in the second sub-lens group,
φairI is the refractive power of the object side surface of the lens immediately after the image side with the largest air spacing in the second sub-lens group,
Dair is the distance on the optical axis between the lens surface immediately before the object side and the lens surface immediately after the image side of the largest sub-air group in the second sub lens group,
And
The refractive power φ of the surface is expressed by φ = (nI−nO) / ROI where nO is the refractive index of the incident side of the surface, nI is the refractive index of the exit side of the surface, and ROI is the paraxial radius of curvature of the surface. . The first sub lens group includes a plurality of positive lenses,
The second sub-lens group includes a plurality of negative lenses;
The third sub lens group imaging optical system according to any one of claims 15 to 17, characterized in that it has a positive lens. The front sub-lens group in the third lens group includes two lenses, and the rear sub-lens group in the third lens group includes one lens component having a negative refractive power. The imaging optical system according to any one of claims 1 to 18 . The imaging optical system according to any one of claims 1 to 19 ,
And an imaging device having an imaging surface disposed on the image side of the imaging optical system and converting an optical image into an electrical signal.

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