JP2006065034A - Zoom lens and imaging apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which gets along with a small number of constituent lenses and is compact while maintaining the zoom ratio of three times or more and the excellent optical performance. <P>SOLUTION: The zoom lens has a first lens group having negative refractive power, a second lens group having positive refractive power and a third lens group having positive refractive power in order from the object side to the image side, wherein spaces between respective groups are changed upon zooming. The first lens group L1 is composed of one sheet of negative lens and one sheet of positive lens, the second lens group L2 is composed of a 2a lens group L2a having one sheet of positive lens/one sheet of negative lens and a 2b lens group L2b which is arranged on the image side of the 2a lens group and has at least one sheet of positive lens, and the third lens group is composed of at least one sheet of positive lens. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zoom lens, and is particularly suitable as a photographing optical system for a small digital still camera or video camera.

  Recently, with the enhancement of functionality of imaging devices (cameras) such as video cameras and digital still cameras using solid-state imaging devices (photoelectric conversion devices) such as CCD and CMOS sensors, the optical system used for them includes a wide angle of view. There is a need for a zoom lens with a large aperture ratio.

  This type of camera requires a lens system with a relatively long back focus because various optical members such as a low-pass filter and a color correction filter must be arranged between the rearmost lens of the photographing optical system and the image sensor. Required. Furthermore, in the case of a color camera using an image pickup device for color images, in order to avoid color shading, an optical system with good telecentric characteristics on the image side is desired.

  Conventionally, a so-called short zoom type wide angle of view that consists of two lens groups, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and performing zooming by changing the distance between the two lenses. Various two-group zoom lenses have been proposed. In these short zoom type optical systems, zooming is performed by moving the second lens group having a positive refractive power, and image positions associated with zooming are moved by moving the first lens group having a negative refractive power. Compensation for fluctuations. In the lens configuration composed of these two lens groups, the zoom magnification (zoom ratio) is about twice.

  Furthermore, in order to bring the entire lens into a compact shape while having a high zoom ratio of 2 times or more, a third lens group having negative or positive refractive power is arranged on the image side of the second group zoom lens to increase the zoom ratio. A so-called three-group zoom lens that corrects various aberrations that accompany the above is proposed (Patent Documents 1 and 2).

  Further, as a three-group zoom lens, a wide-angle three-group zoom lens system that satisfies back focus and telecentric characteristics is also known (Patent Documents 3 and 4).

  In order to make the three-group zoom lens compact, a three-group zoom lens in which the first lens group has two negative and positive lens configurations and a cemented lens is effectively arranged in the second lens group is also known. (Patent Documents 5 to 8).

  A three-group zoom lens having a high zoom ratio of 3 times or more is also known (for example, Patent Documents 9 and 10).

Further, a three-group zoom lens having a relatively small number of lenses while having a high zoom ratio of 3 times or more is also known (Patent Documents 11 to 13).
Japanese Patent Publication No. 7-3507 Japanese Patent Publication No. 6-40170 JP-A 63-135913 Japanese Patent Laid-Open No. 7-261083 JP 2002-196240 A JP 2002-350726 A Japanese Patent Laid-Open No. 2003-222797 Japanese Patent Application No. 2004-148893 US Pat. No. 4,828,372 JP-A-4-217219 JP-A-10-213745 JP 2002-277740 A Japanese Patent Laid-Open No. 2003-21783

  The above-mentioned three-group zoom lens designed for 35 mm film photography has a too long back focus and poor telecentric characteristics for a camera using a solid-state image sensor. It is difficult to use as it is for a camera.

  On the other hand, in recent years, in order to achieve both compactness of the camera and high zoom ratio of the zoom lens, the interval between the lens groups has been reduced to a different interval from the shooting state when not shooting (when the camera is turned off). A so-called collapsible zoom lens in which the protruding amount of the lens is reduced is widely used.

  In general, if the number of lenses in each lens group constituting a zoom lens is large, the length of each lens group on the optical axis becomes long, and if the amount of movement of each lens group in zooming and focusing is large, the total lens length becomes long. Thus, the desired retractable length cannot be achieved, making it difficult to use the retractable zoom lens.

  The present invention has been made in view of the above-described conventional example. An object of the present invention is to provide a compact and novel zoom lens having a small number of constituent lenses while maintaining a desired zoom ratio and desired optical performance.

The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. In the zoom lens in which the distance between each group varies, the first lens group is composed of one negative lens and one positive lens, and the second lens group is composed of one positive lens and one negative lens. The second lens group is composed of a second lens group that is arranged on the image side of the second lens group, and includes at least one positive lens. The third lens group is composed of at least one positive lens. Yes. The imaging magnification at the wide-angle end of the second lens group is β2w, the imaging magnification at the telephoto end is β2t, the distance between the first lens group and the second lens group at the wide-angle end is L1w, When the distance L2t at the telephoto end of the third lens group is set,
4.5 <(β2t · L2t) / (β2w · L1w) <10.0
It is characterized by satisfying the following conditions.

  With such a configuration, it is possible to realize a compact zoom lens with a small number of constituent lenses while maintaining a desired zoom ratio (for example, three times or more) and desired optical performance.

  Embodiments of the zoom lens according to the present invention will be described below with reference to the drawings. The zoom lens of this embodiment is used as a photographing optical system such as a video camera or a digital still camera.

  1, 3 and 5 are lens cross-sectional views of the zoom lenses of Examples 1 to 3, respectively. 2, 4 and 6 are aberration diagrams of the zoom lenses of Examples 1 to 3, respectively. (A) is in the wide-angle end state, (b) is in the intermediate zoom position state, and (c) is in the telephoto end. State.

  In each lens cross-sectional view, the left side is the subject side (front), and the right side is the image side (rear). L1 is a first lens group having negative refractive power (optical power = reciprocal of focal length), L2 is a second lens group having positive refractive power, and L3 is a third lens group having positive refractive power. L2a is a second a lens unit disposed on the object side in the second lens unit L2, and is composed of one positive lens and one negative lens. L2b is a second b lens group having at least one positive lens disposed on the image side of the second a lens group L2a. SP is an aperture stop (F number determining member), G is an optical low-pass filter, an infrared cut filter, a glass block designed to correspond to a parallel plate existing in the optical path such as a cover glass, IP is a CCD sensor, This is an image plane on which a photosensitive surface of a solid-state imaging device (photoelectric conversion device) such as a CMOS sensor is located. The aperture stop SP is a member that determines the F-number light beam on the axis when opened.

  In each aberration diagram, d and g are d-line and g-line, respectively, ΔM and ΔS are meridional image surfaces, sagittal image surfaces, and lateral chromatic aberration are represented by g-lines.

  In the zoom lens of the present embodiment, a first lens group L1, a second lens group L2, and a third lens group L3 are arranged in order from the object side to the image side. During zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves substantially reciprocally along a locus convex to the image side, the second lens unit L2 moves to the object side, and the third lens unit L3 moves to the image side. Thus, the interval between the lens groups is changed.

  The zoom lens according to the present embodiment performs main zooming by moving the second lens unit L2 during zooming, and zooms by moving the first lens unit L1 back and forth and moving the third lens unit L3 in the image side direction. It compensates for the fluctuations in the image position that accompany.

  In the present embodiment, an aperture stop SP as an F-number determining member is disposed on the object side of the second lens unit L2, and the distance between the entrance pupil on the wide angle side and the first lens unit L1 is shortened, whereby the first lens While suppressing an increase in the outer diameter of the lenses constituting the group L1, the number of constituent lenses is increased by canceling off-axis aberrations between the first lens group L1 and the third lens group L3 across the aperture stop SP. Good optical performance is obtained.

  As is clear from the lens cross-sectional views shown in FIGS. 1, 3, and 5, the aperture stop SP is the lens on the object side of the lens disposed closest to the object side of the second lens unit L2 in coordinates in the optical axis direction. It is arranged between the vertex of the surface and the intersection of this lens surface and the lens end surface (so-called edge surface). The lens aperture length is shortened by disposing the aperture stop SP closer to the image side than the object-side vertex of the lens disposed closest to the object side of the second lens unit L2.

  The reason why the lens retractable length can be shortened by such an arrangement of the aperture stop SP will be described.

  In a conventional short zoom type three-group zoom lens, a diaphragm member for determining an open F-number is generally disposed between the first lens group and the second lens group. In general, a meniscus positive lens having a concave surface facing the image side is disposed closest to the image side of the first lens unit of the short zoom type.

  When trying to reduce the distance between the first lens group and the second lens group from the shooting state when the lens is retracted, the meniscus positive lens closest to the image side of the first lens group has a concave surface facing the image side. The lens outer peripheral portion of the meniscus positive lens interferes with the diaphragm member, and the distance from the image-side vertex of the meniscus positive lens to the lens outer peripheral portion cannot shorten the lens retractable length.

  Further, the distance between the aperture member and the object side apex of the lens disposed closest to the object side of the second lens group is also a certain distance when the aperture member is disposed between the first lens group and the second lens group. This is another factor that makes it impossible to shorten the lens retractable length.

  In the present embodiment, as described above, the F-number determining member (aperture stop SP) serving as the diaphragm member includes the object-side vertex of the lens disposed closest to the object side of the second lens unit L2, and the object side of this lens. By disposing the lens between the first lens unit L1 and the lens end surface, a member that mechanically interferes when retracted is eliminated from between the first lens unit L1 and the second lens unit L2, and the first lens unit L1 when the lens is retracted. And the distance between the second lens unit L2 and the second lens unit L2.

  Next, the configuration of each lens group will be described in more detail.

  The first lens unit L1 includes, in order from the object side, two lenses, a meniscus negative lens having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side.

  The first lens unit L1 has a role of focusing the off-axis chief ray on the center of the aperture, and especially on the wide-angle side, since the amount of refraction of the off-axis chief ray is large, various off-axis aberrations, particularly astigmatism. And distortion is likely to occur.

  Therefore, in the present embodiment, as with a normal wide-angle lens, the negative lens and the positive lens are configured to suppress the increase in the lens diameter closest to the object side.

  Astigmatism is achieved by making the lens surface on the object side of the negative meniscus lens an aspheric surface that has a positive refractive power in the periphery and an aspheric surface on the image side that has a negative refractive power in the periphery. In addition, the distortion aberration is corrected in a well-balanced manner, and the first lens unit L1 is configured with a small number of two, which contributes to making the entire lens compact.

  Each lens constituting the first lens unit L1 has a shape close to a concentric sphere centered on a point where the aperture stop SP intersects the optical axis in order to suppress the occurrence of off-axis aberration caused by refraction of the off-axis principal ray. Have taken.

  The second lens unit L2 includes, in order from the object side, a second lens unit L2a configured by a cemented lens of a positive lens having a convex surface facing the object side and a negative lens having a concave surface facing the image side, and a convex surface facing the object side Consists of a total of four or three lenses of the second b lens unit L2b composed of a cemented lens of a negative meniscus lens and a positive lens having convex surfaces on both sides, or a positive lens having convex surfaces on both surfaces Has been.

  The second lens unit L2 has a shape in which a positive lens is disposed closest to the object side, reduces the refraction angle of the off-axis principal ray emitted from the first lens unit L1, and does not cause off-axis aberrations.

  Further, the positive lens arranged closest to the object side is a lens having the highest height of the on-axis light beam, and is a lens mainly involved in correction of spherical aberration and coma aberration. Therefore, in the present embodiment, spherical aberration and coma are favorably corrected by making the object side surface of the positive lens disposed closest to the object side an aspherical surface in which the positive refractive power becomes weak in the periphery.

  In addition, by making the image side surface shape of the negative lens arranged on the image side of the positive lens arranged closest to the object side with the concave surface facing the image side, the positive lens arranged closest to the object side Aberrations occurring on the object side surface are canceled.

  Furthermore, the positive lens arranged closest to the object side and the negative lens arranged on the image side of the positive lens have approximately the same amount of sensitivity to the tilt of the image plane caused by the lens decentering with respect to the optical axis. In addition, focusing on the fact that the signs are different from each other, the positive lens and the negative lens are cemented to cancel the tilt of the image plane as the entire cemented lens, and the lens configuration has little performance deterioration with respect to manufacturing errors.

  The third lens unit L3 is composed of one positive lens whose both lens surfaces are convex.

  The third lens unit L3 shares the increase in the refractive power of each lens unit constituting the zoom lens accompanying the downsizing of the image sensor, and the refraction of the short zoom system configured by the first and second lens units L1 and L2. By reducing the force, it is possible to suppress the generation of aberrations particularly in the lenses constituting the first lens group and achieve good optical performance. In addition, image-side telecentric imaging necessary for a photographing apparatus using a solid-state imaging device or the like is achieved by making the third lens unit L3 serve as a field lens.

Here, when the back focus is sk ′, the focal length of the third lens unit L3 is f3, and the imaging magnification of the third lens unit L3 is β3,
sk ′ = f3 (1-β3)
The relationship is established.

However,
0 <β3 <1.0
It is.

  Here, when zooming from the wide-angle end to the telephoto end, if the third lens unit L3 is moved to the image side, the back focus sk ′ is decreased, and the imaging magnification β3 of the third lens unit L3 is set to the telephoto side. Will increase. Then, as a result, the third lens unit L3 shares the variable magnification, and the amount of movement of the second lens unit L2 is reduced, and the space for this can be saved, contributing to the miniaturization of the lens system.

  When photographing a short-distance object using the zoom lens according to the present embodiment, it is possible to obtain good performance by moving the first lens unit L1 toward the object side and performing focusing. It is better to focus by moving the third lens unit L3 to the object side.

  This occurs when the first lens unit L1 arranged on the most object side is moved by focusing, the increase of the front lens diameter, and the load on the actuator by moving the first lens unit L1 with the heaviest lens weight. This is because an increase can be prevented. Further, since the first lens unit L1 is not moved for focusing, the first lens unit L1 and the second lens unit L2 can be simply linked by a cam or the like to move during zooming, and the mechanical structure is improved. Simplification and improved accuracy can also be achieved.

  When focusing is performed by the third lens unit L3, the third lens unit at the telephoto end having a large focusing movement amount is obtained by moving the third lens unit L3 to the image side during zooming from the wide-angle end to the telephoto end. Since the position of L3 can be arranged on the image side compared to the wide-angle end, the total amount of movement of the third lens unit L3 required for zooming and focusing can be minimized, and the lens system is compact. It is effective for conversion.

  Next, in the zoom lens according to the present embodiment, preferable conditions will be described in order to obtain good optical performance or to reduce the size of the entire lens system.

(A) In order to shorten the lens retractable length and the lens outer diameter, it is preferable to satisfy the following conditions.
4.5 <(β2t · L2t) / (β2w · L1w) <10.0 (1)
Here, β2w is the imaging magnification at the wide-angle end of the second lens unit L2, β2t is the imaging magnification at the telephoto end of the second lens unit L2, and L1w is the wide-angle of the first lens unit L1 and the second lens unit L2. The distance L2t is the distance between the second lens unit L2 and the third lens unit L3 at the telephoto end.

  Exceeding the lower limit value of conditional expression (1) is preferable because the distance between the first lens unit L1 and the second lens unit L2 at the wide-angle end is relatively increased, and the lens diameter of the first lens unit L1 is increased. Absent. If the upper limit of conditional expression (1) is exceeded, the total lens length at the telephoto end is relatively long with respect to the wide-angle end, and the retractable length cannot be sufficiently shortened.

More preferably, the numerical range of conditional expression (1) should be as follows.
5.0 <β2t · L2t / (β2w · L1w) <8.0 (1a)
(B) In order to shorten the lens retractable length, it is preferable to satisfy the following conditions.
0.2 <D2S / D2R <0.9 (2)
Here, D2S is the distance in the optical axis direction between the object-side vertex of the lens disposed closest to the object side of the second lens unit L2 and the F-number determining member (aperture stop SP), and D2R is the most of the second lens unit L2. This is the distance in the optical axis direction between the object-side apex of the lens arranged on the object side and the intersection of the object-side surface of the lens and the lens end surface (edge surface).

  If the lower limit value of conditional expression (2) is exceeded, the lens surface on the image side of the positive meniscus lens disposed closest to the image side of the first lens unit L1 and the object side surface of the lens barrel of the second lens unit L2 interfere with each other. Therefore, it is not preferable because a sufficient reduction in the retractable length cannot be achieved. If the upper limit value of conditional expression (2) is exceeded, the distance from the F-number determining member to the first lens unit L1 becomes long, and the lens diameter of the first lens unit L1 increases, which is not preferable.

More preferably, the numerical range of conditional expression (2) should be as follows.
0.3 <D2S / D2R <0.8 (2a)
(C) In order to shorten the total lens length, it is preferable that the following conditions are satisfied.
4.5 <√ (ft / L1t) <10.0 (3)
Here, ft is the focal length at the telephoto end of the entire system, and L1t is the distance between the first lens unit L1 and the second lens unit L2 at the telephoto end.

  Exceeding the lower limit of conditional expression (3) is not preferable because the distance between the first lens unit L1 and the second lens unit L2 at the telephoto end increases, and the entire lens length increases. When the upper limit of conditional expression (3) is exceeded, the distance between the first lens unit L1 and the second lens unit L2 becomes too close at the telephoto end, and the first lens unit L1 and the second lens unit L2 are Is not preferable because of the possibility of mechanical interference.

  More preferably, the numerical range of conditional expression (3) should be as follows.

5.0 <√ (ft / L1t) <8.0 (3a)
(D) In order to increase the zoom ratio and shorten the lens retractable length, it is preferable to satisfy the following conditions.
1.0 <β3t / β3w <1.3 (4)
Here, β3w is the imaging magnification at the wide-angle end of the third lens unit L3, and β3t is the imaging magnification at the telephoto end of the third lens unit L3. Note that the imaging magnification is that when an object at infinity is in focus.

  Exceeding the lower limit value of conditional expression (4) is not preferable because the zoom ratio multiplication effect of the third lens unit L3 is lost and the zoom ratio is disadvantageous for higher magnification. If the upper limit of conditional expression (4) is exceeded, the amount of movement of the third lens unit L3 from the wide-angle end to the telephoto end increases. Since it becomes a disadvantageous direction for shortening the length, it is not preferable.

More preferably, the numerical range of conditional expression (4) should be as follows.
1.0 <β3t / β3w <1.2 (4a)
(E) In order to shorten the total lens length, it is preferable that the following conditions are satisfied.
−0.7 <(R2f + R2r) / (R2f−R2r) <− 0.35 (5)
Here, R2f is the paraxial radius of curvature of the object side surface of the lens disposed closest to the object side of the second lens unit L2, and R2r is the image side of the lens disposed closest to the image side of the second lens unit L2. The paraxial radius of curvature.

  Exceeding the lower limit of conditional expression (5) is not preferable because spherical aberration is insufficiently corrected. If the upper limit value of conditional expression (5) is exceeded, it is not preferable because the back focus at the telephoto end cannot be secured.

More preferably, the numerical range of conditional expression (5) should be as follows.
−0.65 <(R2f + R2r) / (R2f−R2r) <− 0.4 (5a)
As described above, by making each lens group have a lens configuration that achieves both desired refractive power arrangement and aberration correction, the lens system can be made compact while maintaining good performance.

  Next, numerical data of numerical examples 1 to 3 corresponding to the first to third examples will be shown. In the numerical examples, f is a focal length, Fno is an F number, and ω is a half angle of view. i indicates the order counted from the object side, Ri is the radius of curvature of the i-th surface, Di is the axial distance between the i-th surface and the (i + 1) -th surface, and Ni and νdi are the i-th surface, respectively. The refractive index and the Abbe number based on the d-line of the second material.

  In the aspherical shape, the traveling direction of light is positive, X is the amount of displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k Is a conic constant, and B to E are aspherical coefficients, respectively.

なる式で表している。なお「ｅ±Ｚ」は「×１０^±Ｚ」を意味する。

It is expressed by the following formula. “E ± Z” means “× 10 ^{± Z} ”.

  Table 1 shows the relationship between the above-described conditional expressions and numerical examples.

(Numerical example 1)
f = 4.715-16.774 Fno = 2.85-5.97 2ω = 73.9 ° -23.9 °
R 1 = 50.030 D 1 = 1.35 N 1 = 1.88300 νd1 = 40.8
R 2 = 4.759 D 2 = 2.24
R 3 = 8.594 D 3 = 1.60 N 2 = 1.92286 νd2 = 18.9
R 4 = 16.681 D 4 = Variable
R 5 = Aperture D 5 = -0.50
R 6 = 4.338 D 6 = 2.00 N 3 = 1.77250 νd3 = 49.6
R 7 = 8.707 D 7 = 0.50 N 4 = 1.64769 νd4 = 33.8
R 8 = 3.832 D 8 = 0.48
R 9 = 9.572 D 9 = 0.50 N 5 = 1.76182 νd5 = 26.5
R10 = 3.897 D10 = 2.00 N 6 = 1.60311 νd6 = 60.6
R11 = -11.842 D11 = variable
R12 = 12.540 D12 = 1.60 N 7 = 1.60311 νd7 = 60.6
R13 = 89.899 D13 = variable
R14 = ∞ D14 = 1.40 N 8 = 1.51633 νd8 = 64.1
R15 = ∞

Aspheric coefficient (first surface)
k = 0.00000e + 00
B = 4.56667e-04 C = -7.14952e-06 D = 4.76420e-08
(Second side)
k = -1.53849e + 00
B = 1.59706e-03 C = 1.32234e-05 D = -3.93707e-07 E = 1.11975e-09
(Sixth surface)
k = -4.37828e-01
B = -2.86734e-06 C = 8.92384e-06

(Numerical example 2)
f = 6.005-21.002 Fno = 2.62-5.60 2w = 61.2 ° -19.2 °
R 1 = 14.916 D 1 = 1.20 N 1 = 1.88300 νd1 = 40.8
R 2 = 4.222 D 2 = 1.34
R 3 = 6.744 D 3 = 1.90 N 2 = 1.84666 νd2 = 23.9
R 4 = 12.586 D 4 = Variable
R 5 = Aperture D 5 = -0.65
R 6 = 4.347 D 6 = 2.00 N 3 = 1.88300 νd3 = 40.8
R 7 = 63.098 D 7 = 0.60 N 4 = 1.80518 νd4 = 25.4
R 8 = 3.531 D 8 = 0.64
R 9 = 12.745 D 9 = 1.40 N 5 = 1.69680 νd5 = 55.5
R10 = -18.733 D10 = variable
R11 = 17.228 D11 = 1.40 N 6 = 1.69680 νd6 = 55.5
R12 = -97.710 D12 = variable
R13 = ∞ D13 = 1.90 N 7 = 1.51633 νd7 = 64.1
R14 = ∞

Aspheric coefficient (first surface)
k = 0.00000e + 00
B = -5.40012e-04 C = 1.51938e-05 D = -1.52986e-07
(Second side)
k = -1.34784e + 00
B = 6.88013e-04 C = 1.50185e-05 D = 5.06277e-07
(Sixth surface)
k = -2.84476e-01
B = -6.29759e-05 C = -8.41757e-06

(Numerical Example 3)
f = 6.048-21.255 Fno = 2.71-5.74 2w = 73.2 ° -23.9 °
R 1 = 71.340 D 1 = 1.60 N 1 = 1.88300 νd1 = 40.8
R 2 = 5.719 D 2 = 2.75
R 3 = 10.800 D 3 = 1.70 N 2 = 1.92286 νd2 = 18.9
R 4 = 22.275 D 4 = Variable
R 5 = Aperture D 5 = -0.50
R 6 = 5.049 D 6 = 2.30 N 3 = 1.80610 νd3 = 40.7
R 7 = -60.222 D 7 = 0.50 N 4 = 1.69895 νd4 = 30.1
R 8 = 4.267 D 8 = 0.70
R 9 = 10.417 D 9 = 0.50 N 5 = 1.76182 νd5 = 26.5
R10 = 5.329 D10 = 2.20 N 6 = 1.51633 νd6 = 64.1
R11 = -12.663 D11 = variable
R12 = 12.931 D12 = 1.80 N 7 = 1.60311 νd7 = 60.6
R13 = 58.859 D13 = Variable
R14 = ∞ D14 = 1.40 N 8 = 1.51633 νd8 = 64.1
R15 = ∞

Aspheric coefficient (first surface)
k = 0.00000e + 00
B = 2.58911e-04 C = -2.62258e-06 D = 1.30274e-08
(Second side)
k = -1.21325e + 00
B = 6.70859e-04 C = 5.95470e-06 D = -5.54523e-08 E = 1.33713e-10
(Sixth surface)
k = -3.46473e-01 B = -8.50982e-05 C = 4.56506e-07

  As described above, the zoom lens according to the present embodiment is compact with a small number of constituent lenses, particularly suitable for an imaging system using a solid-state imaging device, and particularly suitable for a retractable zoom lens. A zoom lens having excellent optical performance with a zoom ratio of 3 times or more can be achieved.

  Further, by effectively introducing an aspheric surface into the lens group, it is possible to effectively correct off-axis aberrations, particularly astigmatism / distortion aberration and spherical aberration when the aperture ratio is increased.

  Next, an embodiment of a digital still camera (imaging device) using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG.

  In FIG. 7, reference numeral 20 denotes a camera body, 21 denotes a photographing optical system constituted by any one of the zoom lenses described in the first to third embodiments, and 22 denotes a subject image formed by the photographing optical system 21 built in the camera body. A solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives light, a memory 23 for recording information corresponding to a subject image photoelectrically converted by the solid-state imaging device 22, and a liquid crystal display panel 24. 2 is a viewfinder for observing a subject image formed on the solid-state image sensor 22.

  In this way, by applying the zoom lens of the present invention to an imaging apparatus such as a digital still camera, a compact imaging apparatus having high optical performance can be realized.

2 is a lens cross-sectional view of a zoom lens of Example 1. FIG. FIG. 6 is an aberration diagram of the zoom lens according to Example 1; 6 is a lens cross-sectional view of a zoom lens according to Example 2. FIG. FIG. 6 is an aberration diagram of the zoom lens according to Example 2; 5 is a lens cross-sectional view of a zoom lens according to Example 3. FIG. FIG. 6 is an aberration diagram of the zoom lens according to Example 3; It is a principal part schematic diagram of a digital still camera.

Explanation of symbols

L1 1st lens group L2 2nd lens group L3 3rd lens group L2a 2a lens group L2a 2b lens group SP Aperture stop (F-number determining member)
IP image plane G glass block d d line g g line S sagittal image plane M meridional image plane

Claims (12)

In order from the object side to the image side, there are a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, and the distance between the groups changes during zooming. In the zoom lens, the first lens group includes one negative lens and one positive lens, and the second lens group includes a second a lens group including one positive lens and one negative lens. The second lens group includes a second b lens group that is disposed on the image side of the second a lens group and has at least one positive lens. The third lens group includes at least one positive lens, and the second lens group includes: The imaging magnification at the wide-angle end is β2w, the imaging magnification at the telephoto end is β2t, the distance between the first lens group and the second lens group at the wide-angle end is L1w, the second lens group and the third lens group When the distance at the telephoto end is L2t,
4.5 <(β2t · L2t) / (β2w · L1w) <10.0
A zoom lens characterized by satisfying the following conditions:   A light beam having an open F number between the object-side vertex of the positive lens disposed closest to the object side in the second lens group and the intersection of the object-side surface of the positive lens and the end surface of the positive lens. 2. The zoom lens according to claim 1, further comprising an F-number determining member for determining The distance in the optical axis direction between the object-side apex of the positive lens disposed closest to the object side in the second lens group and the F-number determining member is D2S, and is disposed closest to the object side in the second lens group. When the distance in the optical axis direction between the object-side vertex of the positive lens, the object-side surface of the positive lens, and the end surface of the positive lens is D2R,
0.2 <D2S / D2R <0.9
The zoom lens according to claim 2, wherein the following condition is satisfied.   During zooming from the wide-angle end to the telephoto end, the first lens group moves along a convex locus toward the image side, the second lens group moves monotonously toward the object side, and the third lens group moves toward the image side. The zoom lens according to claim 1, wherein the zoom lens moves.   5. The zoom lens according to claim 1, wherein the negative lens in the first lens group has an aspheric shape on both the object side and the image side.   The zoom lens according to claim 1, wherein the second lens group is a cemented lens in which a positive lens and a negative lens are cemented. When the focal length at the telephoto end of the entire system is ft, and the distance between the first lens group and the second lens group at the telephoto end is L1t,
4.5 <√ (ft / L1t) <10.0
The zoom lens according to claim 1, wherein the following condition is satisfied. When the imaging magnification at the wide-angle end of the third lens group is β3w and the imaging magnification at the telephoto end is β3t,
1.0 <β3t / β3w <1.3
The zoom lens according to claim 1, wherein the following condition is satisfied. R2f is the paraxial radius of curvature of the object side surface of the lens arranged closest to the object side in the second lens group, and is the paraxial radius of curvature of the lens side arranged closest to the image side in the second lens group. When R2r,
−0.7 <(R2f + R2r) / (R2f−R2r) <− 0.35
The zoom lens according to claim 1, wherein the following condition is satisfied.   The zoom lens according to claim 1, wherein the third lens group is moved toward the object side to perform focusing from an object at infinity to an object at a short distance.   The zoom lens according to claim 1, wherein an image is formed on the photoelectric conversion element. An image pickup apparatus comprising: the zoom lens according to claim 1; and a photoelectric conversion element that receives an image formed by the zoom lens.

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