JP2005148485A - Zoom lens and imaging device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which has good optical performance over the entire variable magnification range from a wide-angle-end to a telephoto-end and over the total object range from a point of infinity object to a near range object. <P>SOLUTION: The zoom lens is provided with a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having negative refractive power, a fourth lens group having positive refractive power and a fifth lens group having positive refractive power in the successive order from an object side to an image side. For zooming, the second and the third lens groups are moved and for focusing, the fifth lens group is moved. The fifth lens group consists of one negative lens G51 and two positive lenses G52 and G53 in the successive order from the object side to the image side. When the focal distance at the zoom position of the wide-angle-end of the total system is standardized to be 1, the incident conversion tilt angle of on-axis marginal light beams to the fifth lens group is set at α5, the average value of the Abbe's number of the material of positive lenses G2 and G3 is set at ν5p and the Abbe's number of the material of a negative lens G1 is set at ν5n. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a zoom lens and an imaging apparatus using the same, and is suitably used for electronic cameras such as video cameras and digital still cameras, film cameras, broadcast cameras, and the like.

  2. Description of the Related Art Conventionally, zoom lenses for television cameras, video cameras, and the like have been required to have a small lens system, a large aperture ratio, a high zoom ratio, and a wide angle as the entire camera is downsized.

  In order from the object side of the zoom lens, a first lens group with positive refractive power for focusing (focusing movement group and focusing lens group), and a second lens group with negative refractive power for zooming (magnification) Moving group, zoom lens group), positive or negative third lens group (correcting lens group) for correcting an image plane that fluctuates with zooming, an aperture stop, and a positive lens for imaging The so-called four-group zoom lens, which is composed of four lens groups of the fourth lens group (relay lens group) having a refractive power, is small in size and easy to achieve high magnification and high performance. It is often used in professional zoom lenses. Among these four-group zoom lenses, zoom lenses having a relatively simple configuration of the fourth lens group are known (for example, Patent Documents 1 to 5).

  The front focus method, which places the in-focus movement group on the object side of the variable magnification movement group, is advantageous over the manual focus method because the amount of extension of the in-focus movement group does not change even if the magnification is changed if the object distance is constant. Therefore, it is widely used in broadcast zoom lenses and professional zoom lenses that place emphasis on manual operation.

  The rear focus method in which the focusing movement group is arranged on the image side of the variable magnification movement group is advantageous for reducing the size and weight of the focusing group, and is therefore widely used in autofocus zoom lenses.

  In view of these points, in a four-unit zoom lens having positive, negative, negative, and positive refractive powers, an image side lens unit is used for autofocusing and a zooming unit for manual focusing. A zoom lens using a lens group on the object side is known (for example, Patent Document 6).

  In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a positive refractive power The fifth lens group includes five lens groups, and the second lens group is moved toward the image plane side to perform zooming from the wide-angle end to the telephoto end. There is known a rear focus type zoom lens in which the lens group is moved for correction, and the fourth lens group is moved on the optical axis to perform focusing (for example, Patent Document 7).

Further, in order from the object side, a first lens unit having a positive refractive power fixed during zooming, a second lens unit having a negative refractive power for zooming, a third lens unit having a positive refractive power, and a negative refractive power. The fourth lens group and five lens groups of a fifth lens group having a positive refracting power for correcting image plane variation accompanying zooming, and at least the third lens group and the fourth lens group during zooming. A rear focus type zoom lens is known in which one lens is moved and a fifth lens group is moved during focusing (for example, Patent Document 8).
Japanese Patent Laid-Open No. 2-118510 JP-A-2-208618 JP-A-3-123310 Japanese Patent Laid-Open No. 3-145615 JP-A-4-138407 Japanese Utility Model Publication No. 62-43286 JP-A-8-146295 JP-A-5-215967

  In the four-group zoom lens disclosed in Patent Documents 1 to 5, the fourth lens group is composed of one negative lens and two positive lenses in order from the object side. Since the incident conversion inclination angle α4 of the axial ray is large, when the fourth lens group is focused, the change in the incident height h4 of the axial ray becomes large, and fluctuations in axial aberrations such as spherical aberration and axial chromatic aberration occur. Tended to be larger.

  In Patent Document 6, the fourth lens group includes one negative lens and two positive lenses in order from the object side. However, the Abbe number ν4n of the negative lens material and the Abbe number ν4p of the positive lens material are disclosed. Because of this, the curvature of each lens in the fourth lens group increases to increase the off-axis aberration fluctuation during focusing, and the weight of the fourth lens group increases to increase the required driving force for focusing. As a result, the power consumption tends to increase and the driving mechanism tends to increase in size.

  Further, since the refractive power of the fourth lens group is suppressed to be small, a lens group having a positive refractive power must be newly disposed on the object side of the stop for converging the divergent light beam from the third lens group. There was a problem. Alternatively, the refractive power of the third lens group must be weakened to reduce the divergence of the light flux from the third lens group, and as a result, the amount of movement during zooming of the third lens group increases and the lens There was a tendency for the overall length to become longer.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens in which the entire lens system is small in aberration variation and field angle change due to focusing, and an image pickup apparatus having the same.

  In addition to this, the present invention uses the front lens focus method and the rear focus method to cover the entire zooming range from the wide-angle end to the telephoto end, and over the entire object distance from the infinity object to the near object, An object of the present invention is to provide a zoom lens having good optical performance.

The zoom lens according to the first aspect of the invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a positive lens group. A fourth lens group having a refractive power and a fifth lens group having a positive refractive power;
During zooming, the second lens group and the third lens group move,
In the zoom lens in which the fifth lens group moves at the time of focusing, the fifth lens group is composed of one negative lens G51 and two positive lenses G52 and G53 in order from the object side to the image side. When the focal length at the zoom position at the end is normalized to 1, the incident conversion inclination angle of the axial marginal ray to the fifth lens group is α5, the average value of the Abbe numbers of the materials of the positive lenses G52 and G53 is ν5p, When the Abbe number of the material of the negative lens G51 is ν5n,
0 <α5 <0.35
1.85 <ν5p / ν5n
It is characterized by satisfying.

  According to the present invention, good optical performance can be obtained over the entire zoom range from the wide-angle end to the telephoto end and over the entire object distance from an infinitely distant object to a close object.

  Embodiments of the zoom lens of the present invention and an image pickup apparatus having the same will be described below.

  FIG. 1 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the first exemplary embodiment of the present invention.

  In the following aberration diagrams and examples in FIGS. 2 to 6, 8 to 12, and FIGS. 16 to 20, values when numerical examples described later are expressed in mm units are used as references. f is a focal length. The object distance is the distance measured from the image plane.

FIG. 2 is an aberration diagram of Example 1 at f = 7.6 mm and an object distance of 2.5 m.
FIG. 3 is an aberration diagram of Example 1 at f = 29.1 mm and an object distance of 2.5 m.
FIG. 4 is an aberration diagram of Example 1 at f = 111.5 mm and an object distance of 2.5 m.
FIG. 5 is an aberration diagram of Example 1 at f = 111.5 mm at an object distance of infinity.
FIG. 6 is an aberration diagram of Example 1 at f = 111.5 mm and an object distance of 0.5 m.
FIG. 7 is a cross-sectional view at the wide-angle end of the zoom lens according to Example 2 of the present invention;
FIG. 8 is an aberration diagram of Example 2 at f = 7.6 mm and an object distance of 2.5 m.
FIG. 9 is an aberration diagram of Example 2 at f = 29.1 mm and an object distance of 2.5 m.
FIG. 10 is an aberration diagram of Example 2 at f = 111.5 mm and an object distance of 2.5 m.
FIG. 11 is an aberration diagram of Example 2 at f = 111.5 mm at an object distance of infinity.
FIG. 12 is an aberration diagram of Example 2 at f = 111.5 mm and an object distance of 0.5 m.
FIG. 13 is a conceptual diagram of the arrangement of the fifth lens group in the zoom lens according to the present invention.
FIG. 14 is a conceptual diagram of the arrangement of the fourth lens group in the zoom lens according to the present invention.
FIG. 15 is a cross-sectional view at the wide-angle end of the zoom lens according to Example 3 of the present invention;
FIG. 16 shows aberration diagrams of Example 3 at f = 7.6 mm and an object distance of 2.5 m.
FIG. 17 is an aberration diagram of Example 3 at f = 29.1 mm and an object distance of 2.5 m.
FIG. 18 is an aberration diagram of Example 3 at f = 111.5 mm and an object distance of 2.5 m.
FIG. 19 is an aberration diagram of Example 3 at f = 111.5 mm at an object distance of infinity.
FIG. 20 is an aberration diagram for Example 3 at f = 111.5 mm and an object distance of 0.5 m.

  FIG. 21 is a schematic view of a main part of a video camera (imaging device) including the zoom lens of the present invention.

  FIG. 22 is a schematic diagram of a main part of a digital camera (imaging device) including the zoom lens of the present invention.

  The zoom lens of each embodiment is a photographing lens system used in an imaging apparatus. In the lens cross-sectional view, the left side is the subject side (front) and the right side is the image side (rear). In the lens cross-sectional view, L1 is a first lens group having a positive refractive power (optical power = reciprocal of focal length), L2 is a second lens group having a negative refractive power, and L3 is a third lens group having a negative refractive power. , L4 is a fourth lens group having a positive refractive power, and L5 is a fifth group having a positive refractive power. SP is an aperture stop, which is located on the object side of the fourth lens unit L4.

  P is an optical block corresponding to an optical filter, a face plate color separation prism, or the like. IP is an image plane, and when used as a photographing optical system for a video camera or a digital still camera, when the imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is a silver salt film camera Corresponds to the film surface.

  In the aberration diagrams, d and g are represented by d-line and g-line, respectively, ΔM and ΔS are represented by meridional image surface, sagittal image surface, and lateral chromatic aberration are represented by g-line.

Next, features of the zoom lens of the present invention will be described.
◎ During zooming, the second lens unit L2 and the third lens unit L3 move,
At the time of focusing, the fifth lens unit L5 is moved. The fifth lens unit L5 is composed of one negative lens G51 and two positive lenses G52 and G53 in order from the object side to the image side. When the focal length at the zoom position at the wide angle end of the entire system is normalized to 1, As shown in FIG. 13, the incident conversion inclination angle of the axial marginal ray to the fifth lens unit L5 is α5, the average value of the Abbe number of the materials of the positive lenses G52 and G53 is ν5p, and the Abbe of the material G51 of the negative lens When the number is ν5n,
0 <α5 <0.35 (1)
1.85 <ν5p / ν5n (2)
Is satisfied.

  Conditional expressions (1) and (2) suppress aberration fluctuations in a small size and light weight by appropriately defining the configuration of the fifth lens unit L5, the Abbe number ratio of the lens material, and the incident angle of inclination α5 of the axial ray. It is a condition to do. As shown in the conceptual diagram of the fifth lens unit L5 in FIG. 13, by disposing the negative lens G51 closest to the object side, the incident height hn5 of the on-axis light beam to the negative lens G51 is increased and the refractive power is reduced. Thus, it is possible to correct chromatic aberration in the fifth lens unit L5. As a result, the curvature of each lens surface in the fifth lens unit L5 is reduced, and the weight is reduced while suppressing the occurrence of aberration in the fifth lens unit L5.

  If the negative lens G51 is arranged further on the image side, the incident height hn5 becomes small, so that a large refracting power is required for chromatic aberration correction, and the curvature of each lens surface becomes large, resulting in aberration fluctuation accompanying focusing. The number increases or the number of components increases.

Conditional expression (1) achieves focusing with a small driving force and a small stroke while reducing the sensitivity and securing of the back focus of the fifth lens unit L5, and suppressing aberration fluctuations due to focusing. It is a condition to do. Assuming that the incident converted tilt angle of the axial ray of the fifth lens unit L5 is α5 and the outgoing converted tilt angle is α5 ′, the back focus sensitivity Δsk of the fifth lens unit L5 is:
Δsk = α5 ′ ² −α5 ² = 1−α5 ² (7)
It is represented by If the refractive power of the fifth lens unit L5 increases and exceeds the lower limit value of the conditional expression (1), the curvature of each lens constituting the fifth lens unit L5 increases, and various aberrations deteriorate or focus. The accompanying aberration variation becomes large. If the upper limit value of conditional expression (1) is exceeded, the refractive power of the fifth lens unit L5 becomes small and the entire lens system can be reduced in weight, but the incident height h5 of the axial ray of the fifth lens unit L5 is the same. It changes greatly with the focal point, and the fluctuation of axial aberration such as spherical aberration and axial chromatic aberration becomes large.

  Conditional expression (2) defines the refractive power of each component lens of the fifth lens unit L5 by defining the ratio of the Abbe numbers of the materials of the positive lenses G52 and G53 and the negative lens G51 constituting the fifth lens unit L5. This is a condition for suppressing and reducing the variation of off-axis aberration accompanying focusing and reducing the weight.

When the lower limit value of conditional expression (2) is exceeded, | φ5p | and | φ5n | increase, the curvature of each lens surface increases, and the weight of the fifth lens unit L5 increases. In addition, since the fifth lens unit L5 is away from the stop and the incident height hb5 of the off-axis principal ray is high, when the curvature of each lens surface increases, the axis of curvature of field, astigmatism, etc. accompanying focusing is increased. External aberration fluctuations increase.
When the focal length at the wide-angle end zoom lens position of the entire system is standardized by fw (mm) and the refractive power φw = 1 / fw at the wide-angle end zoom lens position of the entire system in the focused state of the object at infinity When the refractive power of the fifth lens unit L5 is φ5, the outgoing conversion inclination angle of the off-axis principal ray of the fifth lens unit L5 is αb5 ′, and the incident height of the off-axis principal ray of the fifth lens unit L5 is hb5,
0 (mm) <− {(hb5-1) / αb5 ′ + hb5 / (αb5′−φ5 · hb5)}
fw / 30 <1 (mm) (3)
Is satisfied.

Conditional expression (3) is a condition for defining the refractive power φ5 of the fifth lens unit L5 and the emission condition of the off-axis principal ray to suppress the change in the angle of view accompanying focusing. The angle of view change Δy when the amount of movement of the sub-system i in the optical axis direction is Δx is the refractive power of the sub-system φi, the incident height of the off-axis chief ray is hbi, and the off-axis chief ray is incident / exited The converted tilt angles are αbi and αbi ′, respectively.
Δy = αbi ′ · φi · Δx · (Δx + δ)
δ = − (hbi−1) / αbi′−hbi / (αbi−φi · hbi) (8)
It is represented by Here, δ corresponds to the difference between the apparent distance a from the stop to the sub-system i and the apparent distance b from the sub-system i to the image plane. If the conditional expression (3) is not satisfied, δ in the expression (8) becomes a large value, and the change in the angle of view accompanying the focusing of the fifth lens unit L5 increases, which may cause a framing problem or the fifth lens unit L5. When the wobbling operation is performed for determining the in-focus state, the image around the screen greatly vibrates periodically, resulting in an image that is difficult to see.
The fourth lens unit L4 has at least two positive lenses and one negative lens, and the average value of the Abbe number and refractive index of the materials of the two positive lenses is ν4p and N4p, respectively. When the Abbe number and refractive index of the material are ν4n and N4n, respectively,
1.0 <ν4p / ν4n <1.7 (4)
0.18 <N4n-N4p (5)
Is satisfied.

  Conditional expressions (4) and (5) show the configuration of the fourth lens unit L4, the Abbe number ratio and the refractive index difference between the materials of the two positive lenses and one negative lens constituting the fourth lens unit L4. By defining, it is a condition for controlling the chromatic aberration correction and Petzval sum of the fourth lens unit L4 in the positive direction to improve the off-axis performance. The Petzval sum P is expressed as follows: when the refractive power of the i-th surface and the refractive index of the material between the i-th surface and the i + 1-th surface are φRi and Ni, respectively.

It is represented by In the four-group zoom lens, in order to reduce the size and increase the zoom ratio, it is necessary to increase the negative refractive power φ2 of the second lens unit L2. Therefore, the Petzval sum P tends to increase in the negative direction from the equation (9), and this tendency becomes remarkable as the size is reduced and the zoom ratio is increased. Therefore, in order to improve field curvature and astigmatism over the entire zoom range, it is necessary to positively increase the shared value of the Petzval sum of the fourth lens unit L4 and the fifth lens unit L5 having positive refractive power. It becomes important. However, in this embodiment, since the refractive power of the constituent lenses of the fifth lens unit L5 is suppressed, it is difficult to obtain the Petzval sum in the fifth lens unit L5. Therefore, in the present invention, in particular, the refractive index difference and the Abbe number ratio of the materials of the constituent lenses of the fourth lens unit L4 are set appropriately, and the share value P4 of the Petzval sum of the fourth lens unit is increased in the positive direction. Therefore, the peripheral performance over the entire zoom range is made good. Exceeding the lower limit of the conditional expression (4) is advantageous for controlling the Petzval sum P4 in the positive direction, but the refractive power of each lens becomes too large and various aberrations become large. If the upper limit of conditional expression (4) is exceeded, it becomes difficult to control the Petzval sum P4 in the positive direction. If the lower limit of conditional expression (5) is exceeded, the difference in refractive index between the negative lens and positive lens materials will decrease, making it difficult to control the Petzval sum P4 in the positive direction.
The fourth lens unit L4 is composed of one or more positive lenses, one negative lens, and one positive lens in order from the object side to the image side.

In the embodiment of the present invention, the arrangement of the positive lens and the negative lens of the fourth lens unit L4 is defined so that the sharing value P4 of the Petzval sum of the fourth lens unit L4 can be more easily controlled in the positive direction. As shown in the conceptual diagram of the fourth lens unit L4 in FIG. 14, by placing the negative lens Gn closer to the object side, the incident height hn of the axial ray on the negative lens Gn becomes smaller. As a result, the required refractive power for axial chromatic aberration correction increases, and the Petzval sum is controlled in the positive direction under the condition that the refractive index of the material of the negative lens Gn is higher than the refractive index of the materials of the positive lenses GP1 and GP2. It becomes easy. However, since the light flux from the third lens unit L3 is divergently incident, it is not preferable to dispose the negative lens Gn closest to the object side because the fourth lens unit L4 becomes large and various aberrations increase. Therefore, it is arranged between the positive lenses GP1 and GP2. Various aberrations can be further improved by increasing the number of constituent elements of the fourth lens unit L4.
When the refractive power of the fourth lens unit L4 when normalized by the refractive power φw (1 / mm) at the zoom position at the wide-angle end of the entire system is φ4,
0.023 (1 / mm) <φ4 / fw (6)
Is satisfied.

Conditional expression (6) is a condition for appropriately setting the refractive power φ4 of the fourth lens unit L4 to configure the entire zoom lens with a small number of lenses. When the lower limit of conditional expression (6) is exceeded, the refractive power of the fourth lens unit L4 becomes small, and it becomes difficult to converge the divergent light beam from the third lens unit L3. Therefore, it is necessary to newly arrange a positive lens unit on the object side of the fourth lens unit L4 for convergence of the light beam, and the number of constituent lenses increases, and the third lens unit L3 reduces the divergence from the third lens unit L3. The refracting power of the lens unit L3 must be weakened. As a result, the movement amount of the third lens unit L3 increases and the total lens length becomes long.
The fifth lens unit L5 is moved in the optical axis direction during automatic focusing, and the first lens unit L1 is moved in the optical axis direction during manual focusing.

  In each embodiment, the first lens unit L1 can be moved for manual focusing, and the operability during manual focusing is good. In the optical system at the focal length f, when the imaging point at the infinite object distance is i0 and the imaging point with respect to the object distance obj is i (obj), the amount of change Δsk = i (obj) − i0 is expressed by the following equation from Newton's formula.

Δsk = f ² / (obj−f) (10)
Therefore, when the focusing operation is performed on the sub-system B1 closer to the object side than the variable magnification moving group, the change amount ΔskB1 of the imaging point at the object distance obj is
ΔskB1 = fB1 ² / (obj−fB1) (11)
And is constant regardless of magnification.

  Therefore, the feed amount ΔxFF of the focusing sub-system FF in the sub-system B1 does not change regardless of the zooming state.

  However, on the image side of the zoom movement group, the image formation point shift ΔskB1 in the sub-system B1 is enlarged or reduced in the zoom movement sub-system B2, and is approximately expressed by the following equation.

ΔskB2 = {fB1 ² / (obj−fB1)} βB2 ² (12)
Accordingly, when focusing is performed in the focusing sub-system FR in the image-side sub-system B3 with respect to the zooming movement group, the feed amount ΔxFR increases in proportion to the square of the imaging magnification βB2 of the zooming movement group. .

  Therefore, if the first lens unit L1 is used for focusing, there is no change in the amount of extension due to zooming. Therefore, an electric driving means is unnecessary, and a focusing mechanism with good operability and followability in manual operation is provided. Can be easily achieved.

  Next, specific features of each embodiment will be described.

  FIG. 1 is a lens cross-sectional view at the wide angle end according to Numerical Embodiment 1 of the present invention.

  In FIG. 1, L1 is a front lens group having a positive refractive power as the first lens group. L2 is a variator having a negative refractive power for zooming as the second lens group, and is zoomed from the wide-angle end (wide) to the telephoto end (tele) by monotonically moving on the optical axis to the image plane side. The zoom is done. L3 is a compensator having a negative refractive power as the third lens group, and moves in a non-linear manner with a convex locus toward the object side on the optical axis in order to correct image plane fluctuations accompanying zooming. ing. The variator L2 and the compensator L3 constitute a variable power system.

  SP is a stop, and L4 is a relay group which is fixed during zooming of the positive refractive power as the fourth lens group. L5 is a focusing unit having a positive refractive power as the fifth lens unit.

  Next, features of the fifth lens unit L5 in Numerical Example 1 will be described. The fifth lens unit L5 is a rear focus lens unit having a positive refractive power as a whole, and moves on the optical axis toward the object side when focusing on a short-distance object. In this embodiment, when the closest distance is 0.5 m, the extension amount of the fifth lens unit L5 is −13.24 mm with the sign of the amount of movement to the image side being positive, and is normalized by the refractive power φw at the wide angle end. In this case, the extension amount Δx of the fifth lens unit L5 is −1.742.

  The fifth lens unit L5 has a three-element configuration of negative, positive, and positive lenses in order from the object side to the image side. By disposing the negative lens G51 closest to the object side, the on-axis light beam is incident on the negative lens G51. The height is increased to enable correction of chromatic aberration with a smaller refractive power, thereby reducing the weight while suppressing the occurrence of various aberrations in the fifth lens unit L5.

Table 1 shows paraxial tracking values when the focal length at the wide-angle end in Numerical Example 1 is normalized to 1. From Table 1, the incident conversion inclination angle α5 of the fifth lens unit L5 is 0.29, which satisfies the conditional expression (1). The back focus sensitivity Δsk of the fifth lens unit L5 is
Δsk = 1−α5 ² = 0.916 (13)
Thus, the back focus sensitivity of the fifth lens unit L5 is ensured and focusing with a small stroke is possible.

The Abbe number ν5n of the material of the negative lens G51 of the fifth lens unit L5 is 30.1, the average value ν5p of the Abbe number of the material of the positive lens is 64.1, and the value of the equation (2) is
ν5p / ν5n = 2.13 (14)
In this case, the refractive power of each component lens of the fifth lens unit L5 is suppressed to suppress fluctuations in off-axis aberrations associated with focusing and to reduce the weight.

  From Table 1, the refractive power φ5 of the fifth lens unit L5 is 0.149445, the incident height hb5 of the off-axis principal ray is 0.859734, the outgoing conversion inclination angle αb5 is −0.029542, and the value of the expression (3) is 0. .175 satisfies the conditional expression (3) and suppresses a change in the angle of view due to focusing.

  Next, features of the fourth lens unit L4 in Numerical Example 1 will be described. The fourth lens unit L4 is a fixed lens unit having a positive refractive power as a whole. The fourth lens unit L4 in the present embodiment has a three-lens configuration in order from the object side, that is, positive, negative, and positive lenses. By arranging the positive lens closer to the object side, the Petzval in the fourth lens unit L4 is arranged. The sum is easily controlled in the positive direction.

The refractive index Nn of the negative lens material of the fourth lens unit L4 is 1.81078, the Abbe number ν4n is 40.9, the average refractive index Np of the positive lens material is 1.60548, and the average Abbe number ν4p is 60.6, the values of equations (4) and (5) are
ν4p / ν4n = 1.48 (15)
N5n-N5p = 0.205 (16)
Conditional expressions (4) and (5) are satisfied, and the Petzval sum of the fourth lens unit L4 is increased in the positive direction to suppress field curvature and astigmatism over the entire zooming range. The performance is good.

From Table 1, the refractive power φ4 of the fourth lens unit L4 is 0.252140, and the value of the equation (6) is fw = 7.6 (mm),
φ4 / fw = 0.033 (1 / mm) (17)
Thus, conditional expression (6) is satisfied, and the entire zoom lens system is made compact.

  In this embodiment, it is also possible to move the first lens unit L1 on the optical axis using the focusing lens unit. If the first lens unit L1 is used for manual focusing, there is no change in the amount of extension due to zooming, so an electric drive means is unnecessary, and a focusing mechanism with good operability and tracking in manual operation is easy. Can be achieved.

  FIG. 7 is a lens cross-sectional view at the wide angle end according to Numerical Embodiment 2 of the present invention.

  In FIG. 7, L1 is a front lens group having a positive refractive power as the first lens group. L2 is a variator having negative refractive power for zooming as the second lens group, and zooming from the wide-angle end (wide) to the telephoto end (tele) by monotonically moving on the optical surface side on the optical axis. The position is zoomed. L3 is a compensator having a negative refractive power as the third lens group, and moves in a non-linear manner with a convex locus toward the object side on the optical axis in order to correct image plane fluctuations accompanying zooming. ing. The variator L2 and the compensator L3 constitute a variable power system.

  SP is a stop, and L4 is a relay group fixed as a fourth lens group during zooming of positive refractive power. L5 is a focusing unit having a positive refractive power as the fifth lens unit.

  Next, features of the fifth lens unit L5 in Numerical Example 2 will be described. The fifth lens unit L5 is a rear focus lens unit having a positive refractive power as a whole, and moves on the optical axis toward the object side when focusing on a short-distance object. In this embodiment, when the closest distance is 0.5 m, the extension amount of the fifth lens unit L5 is −12.55 mm with the sign of the amount of movement toward the image side being positive, and is normalized by the refractive power φw at the wide angle end. In this case, the extension amount Δx of the fifth lens unit L5 is −1.651.

  The fifth lens unit L5 has a three-element configuration of negative, positive, and positive lenses in order from the object side to the image side. By disposing the negative lens G51 closest to the object side, the on-axis light beam is incident on the negative lens G51. The height is increased to enable correction of chromatic aberration with a smaller refractive power, thereby reducing the weight while suppressing the occurrence of various aberrations in the fifth lens unit L5.

Table 2 shows paraxial tracking values when normalized with the refractive power φw at the wide angle end in Numerical Example 2. From Table 2, the incident conversion inclination angle α5 of the fifth lens unit L5 is 0.004, which satisfies the conditional expression (1). The back focus sensitivity Δsk of the fifth lens unit L5 is
Δsk = 1−α5 ² = 1.000 (18)
Thus, the back focus sensitivity of the fifth lens unit L5 is ensured and focusing with a small stroke is possible.

The Abbe number of the material of the negative lens G51 of the fifth lens unit L5 is 25.4, the average Abbe number of the materials of the positive lenses G52 and G52 is 50.9, and the value of the expression (2) is
ν5p / ν5n = 2.00 (19)
In this case, the refractive power of each component lens of the fifth lens unit L5 is suppressed to suppress fluctuations in off-axis aberrations associated with focusing and to reduce the weight.

  From Table 2, the refractive power φ5 of the fifth lens unit L5 is 0.170427, the incident height hb5 of the off-axis principal ray is 1.282568, the outgoing conversion inclination angle αb5 is 0.048333, and the value of the expression (3) is 0. The condition is satisfied at 418, and the change in the angle of view due to focusing is suppressed.

  Next, features of the fourth lens unit L4 in Numerical Example 2 will be described. The fourth lens unit L4 is a fixed lens unit having a positive refractive power as a whole. The fourth lens unit L4 of the present embodiment has a three-lens configuration in order from the object side to the image side, that is, a positive lens, a negative lens, and a positive lens. By disposing the positive lens closer to the object side, the fourth lens unit L4 is arranged. The Petzval sum is easily controlled in the positive direction.

The refractive index Nn of the negative lens material of the fourth lens unit L4 is 1.82017, the ν4n Abbe number is 46.6, the average refractive index Np of the positive lens material is 1.61671, and the average of the Abbe number ν4p is 54. .1, and the values of equations (4) and (5) are
ν4p / ν4n = 1.16 (20)
N5n-N5p = 0.203 (21)
Conditional expressions (4) and (5) are satisfied, and the Petzval sum of the fourth lens unit L4 is increased in the positive direction to suppress field curvature and astigmatism over the entire zooming range. The performance is good.

From Table 1, the refractive power φ4 of the fourth lens unit L4 is 0.202056, and the value of equation (6) is fw = 7.6 (mm)
φ4 / fw = 0.0266 (1 / mm) (22)
Thus, conditional expression (6) is satisfied, and the entire zoom lens system is made compact.

  In this embodiment, it is also possible to move the first lens unit L1 on the optical axis using the focusing lens unit. If the first lens group is used for manual focusing, there is no change in the amount of extension that accompanies zooming, so there is no need for electrical drive means, and a focusing mechanism with good operability and tracking in manual operation is easy. Can be achieved.

  FIG. 15 is a lens cross-sectional view at the wide-angle end according to Numerical Embodiment 3 of the present invention.

  In FIG. 15, L1 is a front lens group having a positive refractive power as the first lens group. L2 is a variator having a negative refractive power for zooming as the second lens unit, and is zoomed from the wide angle end (wide) to the telephoto end (tele) by monotonically moving on the optical axis to the image plane side. The zooming is done. L3 is a compensator having a negative refractive power as the third lens group, and moves in a non-linear manner with a convex locus toward the object side on the optical axis in order to correct image plane fluctuations accompanying zooming. ing. The variator L2 and the compensator L3 constitute a variable power system.

  SP is a stop, and L4 is a relay group fixed as a fourth lens group during zooming of positive refractive power. L5 is a focusing lens unit having a positive refractive power as the fifth lens unit.

  Next, features of the fifth lens unit L5 in Numerical Example 3 will be described. The fifth lens unit L5 is a rear focus lens unit having a positive refractive power as a whole, and moves on the optical axis toward the object side when focusing on a short-distance object. In this embodiment, when the object at a close distance is 0.5 m, the amount of extension of the fifth lens unit L5 is −12.48 mm with the sign of the amount of movement to the image side being positive, and is specified by the refractive power φw at the wide angle end. The fifth lens group L5 feed amount Δx when it is changed to −1.642.

  The fifth lens unit L5 has a three-element configuration of negative, positive, and positive lenses in order from the object side to the image side. By disposing the negative lens G51 closest to the object side, the on-axis light beam is incident on the negative lens G51. The height is increased to enable correction of chromatic aberration with a smaller refractive power, thereby reducing the weight while suppressing the occurrence of various aberrations in the fifth lens unit L5.

Table 3 shows paraxial tracking values when the focal length at the wide-angle end in Numerical Example 3 is normalized to 1. From Table 2, the incident conversion inclination angle α5 of the fifth lens unit L5 is 0.158, which satisfies the conditional expression (1). The back focus sensitivity Δsk of the fifth lens unit L5 is
Δsk = 1−α5 ² = 0.975 (23)
Thus, the back focus sensitivity of the fifth lens unit L5 is ensured and focusing with a small stroke is possible.

The Abbe number of the material of the negative lens G51 of the fifth lens unit L5 is 23.8, the average Abbe number of the materials of the positive lenses G52 and G53 is 70.2, and the value of the expression (2) is
ν5p / ν5n = 2.950 (24)
In this case, the refractive power of each component lens of the fifth lens unit L5 is suppressed to suppress fluctuations in off-axis aberrations associated with focusing and to reduce the weight.

  From Table 3, the refractive power φ5 of the fifth lens unit L5 is 0.170381, the incident height hb5 of the off-axis principal ray is 0.939728, the outgoing conversion inclination angle αb5 is −0.012198, and the value of the expression (3) is 0. .130 satisfies the conditional expression (3) and suppresses a change in the angle of view due to focusing.

  Next, features of the fourth lens unit L4 in Numerical Example 3 will be described. The fourth lens unit L4 is a fixed lens unit having a positive refractive power as a whole. The fourth lens unit L4 of the present embodiment has a four-lens configuration of positive, positive, negative, and positive lenses in order from the object side to the image side. By arranging two positive lenses on the most object side, spherical aberration and Correction of axial chromatic aberration and coma aberration is made easier.

The refractive index Nn of the negative lens material of the fourth lens unit L4 is 1.83945, the Abbe number ν4n is 42.7, the average refractive index Np of the positive lens material is 1.55432, and the average Abbe number ν4p is In 57.2, the values of equations (4) and (5) are
ν4p / ν4n = 1.340 (25)
N4n-N4p = 0.285 (26)
Conditional expressions (4) and (5) are satisfied, and the Petzval sum of the fourth lens unit L4 is increased in the positive direction to suppress field curvature and astigmatism over the entire zooming range. The performance is good.

From Table 3, the refractive power φ4 of the fourth lens unit L4 is 0.234409, and the value of equation (6) is fw = 7.6 (mm)
φ4 / fw = 0.031 (1 / mm) (27)
Thus, conditional expression (6) is satisfied, and the entire zoom lens system is made compact.

  In this embodiment, it is also possible to move the first lens unit L1 on the optical axis using the focusing lens unit. If the first lens unit L1 is used for manual focusing, there is no change in the amount of extension due to zooming, so an electric drive means is unnecessary, and a focusing mechanism with good operability and tracking in manual operation is easy. Can be achieved.

  In each embodiment, it is more preferable to set the numerical values of the conditional expressions (1) to (6) as follows.

0 <α5 <0.3 (1a)
ν5p / ν5n> 1.9 (2a)
0 (mm) <− {(hb5-1) / αb5 ′ + hb5 / (αb5′−φ5 · hb5)}
・ Fw / 30 <0.8 (mm) (3a)
1.1 <ν4p / ν4n <1.5 (4a)
Nn-Np> 0.19 (5a)
0.02 (1 / mm) <φ4 / fw (6a)
As described above, in the embodiments of the present invention, the second lens unit L2 and the third lens unit L3 are used for zooming movement with the lens unit configuration of positive, negative, negative, positive, and positive refractive power, and the fifth lens. In a rear focus type zoom lens in which the group L5 is a focusing lens group, by appropriately setting the configuration and various constants of the fourth lens group L4 and the fifth lens group L5, the optical performance is high in magnification and compact. Has achieved a good zoom lens.

  The numerical examples 1 to 3 corresponding to the examples 1 to 3 are shown below. In each embodiment, i indicates the order of the surfaces from the object side, ri is the radius of curvature of each surface, di is the member thickness or air spacing between the i-th surface and the i + 1-th surface, and ni and νi are respectively The refractive index and Abbe number for the d-line are shown. In Numerical Examples 1 to 3, the three surfaces closest to the image are planes corresponding to glass blocks. f indicates a focal length, fno indicates an F number, and ω indicates a half angle of view. The table shows the relationship between the above-mentioned conditional expressions (1) to (6) and various numerical values in the numerical examples.

  Next, embodiments of a video camera and a digital video camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIGS.

  In FIG. 21, 10 is a video camera body, 11 is a photographing optical system constituted by the zoom lens of the present invention, 12 is a solid-state imaging device (photoelectric conversion) such as a CCD sensor or a CMOS sensor that receives a subject image by the photographing optical system 11. (Element), 13 is a memory for storing information corresponding to the subject image photoelectrically converted by the image sensor 12, and 14 is a finder for observing the subject image displayed on a display element (not shown). The display element is constituted by a liquid crystal panel or the like, and a subject image formed on the image sensor 12 is displayed.

  In FIG. 22, reference numeral 20 denotes a camera body, 21 denotes a photographing optical system constituted by the zoom lens of the present invention, 22 denotes a CCD sensor or CMOS sensor built in the camera body and receiving a subject image formed by the photographing optical system 21. A solid-state image sensor (optical conversion element) such as 23, a memory 23 for recording information corresponding to the subject image photoelectrically converted by the solid-state image sensor 22, and a liquid crystal display panel 24 are formed on the solid-state image sensor 22. It is a finder for observing the subject image.

  Thus, by applying the zoom lens of the present invention to an imaging apparatus such as a video camera or a digital still camera, an imaging apparatus having a small size and high optical performance can be realized.

Sectional view at the wide-angle end of Numerical Example 1 Aberration diagram of Numerical Example 1 at f = 7.6 mm and object distance of 2.5 m Aberration diagram of Numerical Example 1 at f = 29.1 mm and object distance of 2.5 m Aberration diagram of Numerical Example 1 at f = 111.5 mm and an object distance of 2.5 m Aberration diagram of Numerical Example 1 at f = 111.5 mm at an object distance of infinity Aberration diagram of Numerical Example 1 at f = 111.5 mm and an object distance of 0.5 m Sectional view at the wide-angle end of Numerical Example 2 Aberration diagram of Numerical Example 2 at f = 7.6 mm and an object distance of 2.5 m Aberration diagram of Numerical Example 2 at f = 29.1 mm and object distance of 2.5 m Aberration diagram of Numerical Example 2 at f = 111.5 mm and an object distance of 2.5 m Aberration diagram of Numerical Example 2 at f = 111.5 mm at an infinite object distance Aberration diagram of Numerical Example 2 at f = 111.5 mm and object distance of 0.5 m Schematic diagram of arrangement of fifth group for zoom lens according to the present invention 4 is a conceptual diagram of the arrangement of the fourth group in the zoom lens according to the present invention. Sectional view at the wide-angle end of Numerical Example 3 Aberration diagram of Numerical Example 3 at f = 7.6 mm and an object distance of 2.5 m Aberration diagram of Numerical Example 3 at f = 29.1 mm and an object distance of 2.5 m Aberration diagram of Numerical Example 3 at f = 111.5 mm and an object distance of 2.5 m Aberration diagram of Numerical Example 3 at f = 111.5 mm and an object distance of infinity Aberration diagram of Numerical Example 3 at f = 111.5 mm and an object distance of 0.5 m Schematic when the zoom lens of the present invention is applied to a video camera Schematic when the zoom lens of the present invention is applied to a digital camera

Explanation of symbols

L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group SP Aperture IP Image plane P Glass block d d line g g line ΔS Sagittal image plane ΔM Meridional image plane Fno F number f Focal length ω Semi Angle of view

Claims (8)

In order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, a fourth lens group having a positive refractive power, and a positive lens A fifth lens unit having refractive power;
During zooming, the second lens group and the third lens group move,
In the zoom lens in which the fifth lens group moves at the time of focusing, the fifth lens group is composed of one negative lens G51 and two positive lenses G52 and G53 in order from the object side to the image side. The incident conversion inclination angle of the axial marginal ray to the fifth lens group when normalized by the refractive power φw at the zoom position at the end is α5, the average value of the Abbe numbers of the materials of the positive lenses G52 and G53 is ν5p, When the Abbe number of the material of the negative lens G51 is ν5n,
0 <α5 <0.35
1.85 <ν5p / ν5n
A zoom lens characterized by satisfying When the focal length at the zoom position at the wide-angle end of the entire system is normalized by fw (mm) and the refractive power φw (1 / mm) at the zoom position at the wide-angle end of the entire system in the focused state of the object at infinity, When the refractive power of the fifth lens group is φ5, the outgoing conversion inclination angle of the off-axis principal ray of the fifth lens group is αb5 ′, and the incident height of the off-axis principal ray of the fifth lens group is hb5,
0 (mm) <− {(hb5-1) / αb5 ′ + hb5 / (αb5′−φ5 · hb5)}
・ Fw / 30 <1 (mm)
The zoom lens according to claim 1, wherein: The fourth lens group has at least two positive lenses and one negative lens, and the Abbe number and refractive index average values of the materials of the two positive lenses are ν4p and N4p, respectively, and the material of the negative lens When the Abbe number and refractive index of ν4n and N4n
1.0 <ν4p / ν4n <1.7
0.18 <N4n-N4p
The zoom lens according to claim 1, wherein the zoom lens according to claim 1 is satisfied. 4. The zoom according to claim 1, wherein the fourth lens group includes one or more positive lenses, one negative lens, and one positive lens in order from the object side to the image side. lens. When the refractive power of the fourth lens group is φ4 when normalized by the refractive power φw at the zoom position at the wide-angle end of the entire system,
0.023 (1 / mm) <φ4 / fw
The zoom lens according to claim 1, wherein the zoom lens according to claim 1 is satisfied. 6. The method according to claim 1, wherein the fifth lens group is moved in the optical axis direction during automatic focusing, and the first lens group is moved in the optical axis direction during manual focusing. Zoom lens of the term. The zoom lens according to claim 1, wherein an image is formed on a solid-state image sensor. An imaging apparatus comprising: the zoom lens according to claim 1; and a solid-state imaging device that receives an image formed by the zoom lens.