JP2000305016A - Rear focus type zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To have satisfactory performance and a high variable power ratio over all zoom areas and all object distance ranges by composing a zoom lens of plural lens groups and making the focal length of a lens or the like satisfy specified formulas. SOLUTION: This lens has a first lens group L1 having a positive refracting power, a second lens group L2 having a negative refracting power, a third lens group L3 having a positive refracting power and a fourth lens group L4 having a positive refracting power successively from the side of an object. The first lens group L1 is composed of a 11th lens having a negative refracting power, a 12th lens having a positive refracting power and 13th lens having a positive refracting power from the object side and the second lens group L2 is composed of three negative lenses and one positive lenses. When the focal length of the 12th lens is defined as f12, a focal length at the telescopic end of all systems is defined as Ft, the Abbe number of the 12th lens is defined as ν12 and the focal length of an i-th lens group is defined as Fi, the conditions of 0.95<f12/Ft<1.5, 75.0<ν12 and 150<F3/F4<4.00 are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type (inner focus type) zoom lens,
It has a high zoom ratio of 0x or more, but has a long back focus, especially where a color separation prism is inserted between the lens and the image plane (CCD), and a long exit pupil position. The present invention relates to a very compact rear-focusing zoom lens which is used for a camera and the like and has a very long back focus and is small as a whole.

[0002]

2. Description of the Related Art In recent years, as home video cameras and the like have become smaller and lighter, remarkable progress has been made in miniaturization of zoom lenses for image pickup. Efforts are being made to reduce the diameter of the ball and simplify the lens configuration. In addition, with the advancement of performance (digitalization) of video decks, the quality of video cameras has been improved. As one of the methods, high image quality is achieved by image separation by a color separation optical system. One means for achieving these objects is to move a lens group other than the first lens group on the object side to focus. , A so-called rear focus type zoom lens is known.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens which performs focusing by moving the first lens group.
The size of the entire lens system can be easily reduced. In addition, close-up photography, particularly extremely close-up photography, can be performed. Further, since the relatively small and light lens group is moved, the driving force of the lens group is small and quick focusing can be performed.

[0004] Such a rear focus type zoom lens is disclosed in, for example, JP-A-6-51199 and JP-A-6-51199.
337353, JP-A-6-347697,
JP-A-7-199069, JP-A-7-27068
4, JP-A-7-318804, JP-A-9-
281390, JP-A-9-281391,
It is proposed in Japanese Patent Application Laid-Open No. 9-304698.

[0005]

Generally, in a zoom lens, in order to achieve a reduction in the front lens diameter and the size of the entire system, a so-called rear focus method is more preferable than a distance adjustment (focusing) by the first lens group. Are suitable.

In the zoom lenses proposed in the above-mentioned publications, a long back focus is secured assuming a three-color separation prism, but in many of the embodiments, the zoom ratio is about 10 times. .

The present invention maintains a long back focus in which an optical element such as a prism for color separation or an optical element for protecting a zoom lens unit enters, and provides good optical performance over the entire zoom range and the entire object distance range. An object of the present invention is to provide a rear focus type zoom lens having a high zoom ratio of 20 times or more while providing performance.

[0008]

According to a first aspect of the present invention, there is provided a rear focus type zoom lens having a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a positive lens unit. A third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, wherein at least the second lens group and the fourth lens group are moved to perform zooming, and the fourth lens group The fourth lens group is moved so as to draw a locus convex toward the object side during zooming from the wide-angle end to the telephoto end, and the first lens group is negatively refracted from the object side. An eleventh lens having power, a twelfth lens having positive refractive power, and a thirteenth lens having positive refractive power. The second lens group includes three negative lenses and one positive lens, The twelfth
The focal length of the lens is f12, the focal length at the telephoto end of the entire system is Ft, the Abbe number of the twelfth lens is ν12,
Assuming that the focal length of the lens group is Fi, 0.95 <f12 / Ft <1.5 (1) 75.0 <ν12 (2) 1.50 <F3 / F4 <4.00 (3) It is characterized by satisfying the conditions.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 4, 7, and 10 show numerical examples 1 to 4 of a rear focus type zoom lens according to the present invention.
4 is a lens cross-sectional view, and FIGS. 2 and 3 are various aberration diagrams at a wide-angle end and at a telephoto end in Numerical Example 1 described later of the present invention. 5 and 6 are various aberration diagrams at a wide angle end and a telephoto end of a numerical example 2 described later of the present invention. 8 and 9 are graphs showing various aberrations at a wide angle end and a telephoto end of a numerical example 3 described later of the present invention. FIGS. 11 and 12 are various aberration diagrams at the wide-angle end and at the telephoto end of Numerical Example 4 described later of the present invention.

In the drawing, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, L3 is a third group having a positive refractive power, and L4 is a fourth group having a positive refractive power. . SP denotes an aperture stop, which is arranged in front of the third lens unit L3. The stop SP changes the stop diameter as the magnification changes. G is a glass block such as a face plate and a filter color separation prism provided as needed. IP is an image plane on which an image sensor such as a CCD is arranged.

In this embodiment, the second lens unit is moved to the image plane side as indicated by an arrow at the time of zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming is partly or entirely included in the fourth lens unit. In the present embodiment, all of them are corrected while moving along a convex locus toward the object side.

Also, a rear focus system in which a part or the whole of the fourth unit (all in the present embodiment) is moved on the optical axis to perform focusing is adopted. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. The first and third units are fixed during zooming and focusing.

In the present embodiment, the fourth unit is moved to correct the image plane fluctuation caused by zooming, and the fourth unit is moved to perform focusing. In particular, as shown by the curves 4a and 4b in the same figure, at the time of zooming from the wide-angle end to the telephoto end, the lens is moved so as to have a convex locus toward the object side. Thus, the space between the third and fourth units is effectively used, and the overall length of the lens is effectively reduced.

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end, the fourth unit is moved forward as indicated by a straight line 4c in FIG.

In this embodiment, the second lens group has the same lateral magnification β2 from the wide-angle end to the telephoto end at the same magnification (β2 =
-1), so that a high zoom ratio can be obtained.
By moving the lens group so as to draw a convex locus toward the object side, a high zoom ratio is obtained while increasing the space efficiency and shortening the diameter of the first lens group.

As described above, the first lens unit is a negative lens,
By using a positive lens and a positive lens, the principal point position is made as close as possible to the second lens group side, and the principal point interval between the first lens group and the second lens group on the wide-angle side is made short so that it can be easily set. One lens group is downsized. By making the second lens group three negative lenses and one positive lens, fluctuations in chromatic aberration due to zooming are reduced. By arranging the third lens group as described above, the exit pupil can be lengthened, the beam diameter can be increased with the third lens group, and the back focus can be lengthened without overdoing the fourth lens group. It is possible to take.

Further, as described above, by controlling the stop diameter of the stop SP in accordance with zooming, harmful light fluxes serving as flare components are cut, and uneven illuminance on the image plane is reduced.
At this time, the control of the aperture diameter is preferably controlled by an electric means such as an actuator, and the control information is preferably taken out from a storage means such as a memory. At this time, in order to simplify the lens barrel structure, the third
Although it is desirable to fix the lens group, the third lens group may be moved so that the third lens group is equally-divided. By doing so, it is possible to provide a high zoom ratio while further reducing the size.

According to the present invention, by adopting the above configuration, a zoom lens which achieves a very high performance while securing a long back focus for entering a color separation prism while providing a high zoom ratio is achieved. I have.

Next, the technical meanings of the conditional expressions (1) to (3) will be described.

Conditional expression (1) relates to the refractive power of the twelfth lens, and particularly to the refractive power of a lens having anomalous dispersion. If the refractive power of the twelfth lens is increased beyond the lower limit of the conditional expression (1), there arises a problem that the spherical aberration near the telephoto end deteriorates. Conversely, if the refractive power is weakened, there arises a problem that the correction of chromatic aberration near the telephoto end becomes insufficient.

Conditional expression (2) relates to the dispersion value of the glass material of the twelfth lens. A glass material that satisfies this conditional expression has anomalous dispersibility, and by using this, it is easy to remove a secondary spectrum that is problematic in a lens having a super-telephoto focal length as in the present invention. . If the Abbe number νd becomes smaller than the lower limit of the conditional expression (2), the correction of chromatic aberration near the telephoto end becomes insufficient, and there arises a problem that a blurred image is colored.

Conditional expression (3) relates to the ratio of the focal length of the third lens unit to the focal length of the fourth lens unit. This is for maintaining the optical performance. If the focal length of the third lens unit is shorter than the lower limit, it becomes difficult to correct a change in spherical aberration due to zooming or during focusing. In addition, problems such as difficulty in securing a sufficient back focus, shortening of the exit pupil at the intermediate zoom position, and an increase in the amount of movement of the fourth lens unit, resulting in a large variation in aberrations during zooming and focusing. . Conversely, if the focal length of the third lens group becomes longer than the upper limit, the divergence of the light beam emitted from the third lens group will increase, and the effective diameter of the fourth lens group will increase, making the lens heavier. Problems such as the inability to do so occur. In order to achieve good aberration correction with a small size while having a high zoom ratio, the numerical ranges of the conditional expressions (1) to (3) are preferably set as follows.

0.98 <f12 / Ft <1.30 (1a) 81.0 <ν12 (2a) 2.00 <F3 / F4 <3.50 (3a) In the present embodiment, as described above. By setting the lens configuration, high optical performance is obtained over the entire zoom range and over the entire object distance, while maintaining a high zoom ratio of 20.

In the rear focus type zoom lens according to the present invention, in order to obtain better optical performance, it is preferable to satisfy at least one of the following conditions.

(A-1) The third lens group is composed of a negative lens and a positive lens in order from the object side.

(A-2) An aperture is provided on the object side of the third lens group, and the aperture diameter of the aperture varies depending on the positions of the second lens group and the fourth lens group on the optical axis.

(A-3) The focal length at the wide-angle end of the entire system is F
w, the distance between the third lens unit and the fourth lens unit at the wide-angle end when focused on infinity is D4w,

[0028]

(Equation 2)

The following condition must be satisfied.

Conditional expression (4) defines the range of movement of the fourth lens group which performs the correction and the focusing action on the image plane fluctuation caused by zooming. If the lower limit is exceeded, it becomes difficult to perform focusing on a sufficiently close object. If the upper limit is exceeded, focusing can be performed relatively easily, but the entire lens is undesirably large.

Conditional expression (5) relates to the ratio of the focal length of the first lens unit to the focal length of the second lens unit, and achieves good optical performance with a long back focus while achieving high zoom ratio and compactness. It is for maintaining. When the focal length of the second lens group is longer than the lower limit and the focal length of the first lens group is shorter, the amount of movement of the second lens group increases, making it difficult to reduce the overall length of the lens and the diameter of the front lens. Become.
In addition, a problem arises in that the amount of movement of the fourth lens group near the telephoto end increases, and the fluctuation of aberration during zooming increases. Conversely, if the upper limit is exceeded, it becomes difficult to satisfactorily correct various aberrations such as distortion.

Condition (6) relates to the focal length of the second lens group. If the focal length of the second lens group is shorter than the lower limit, the Petzval sum becomes large under, and it becomes difficult to correct aberration such as image plane tilt. Conversely, if the focal length of the second lens group becomes longer than the lower limit, the amount of movement of the second lens group increases, and the diameter of the front lens becomes too large.

In order to further improve aberration correction, it is preferable to set the numerical ranges of the conditional expressions (4) to (6) as follows.

[0034]

(Equation 3)

(A-4) The focal length of the i-th lens unit is Fi, the average value of the refractive index of the material of the negative lens in the second lens unit is NA2, and the focal length of the wide-angle end and the telephoto end of the entire system is Fw,
Ft,

[0036]

(Equation 4)

The following condition must be satisfied.

Condition (7) relates to the focal length of the fourth lens group. When the value exceeds the upper limit, the amount of movement of the fourth lens unit increases, and aberration fluctuation during zooming or focusing increases. Conversely, if the lower limit is exceeded, the sensitivity of the fourth lens group will increase, making control difficult. Further, it is difficult to correct various aberrations, and it is difficult to obtain a sufficient back focus.

Condition (8) relates to the refractive index of the material of the negative lens in the second lens group. When the limit is exceeded,
When there is no glass suitable for chromatic aberration correction, and below the lower limit, the Petzval sum tends to increase negatively, making it difficult to satisfactorily flatten the image surface.

It is more preferable to set the numerical ranges of the conditional expressions (7) and (8) as follows.

[0041]

(Equation 5)

(A-5) A meniscus negative lens having a convex surface directed toward the object side from the object side, a negative lens having a concave lens surface on the object side, a positive lens having both lens surfaces convex from the object side,
Then, it is constituted by a negative lens having a concave surface facing the object side. Thus, the object-side principal point of the second group is positioned in the first group, the distance between the principal points of the first group and the second group is reduced, and the size of the lens system is reduced. Also, the variation in chromatic aberration due to zooming is reduced.

(A-6) The third unit L3 is composed of a negative lens having a concave surface facing the object side and a positive lens having both lens surfaces convex in order from the object side.

(A-7) The fourth unit is composed of a positive lens having both convex lens surfaces, a cemented lens in which a negative meniscus lens having a convex surface facing the object side and a positive lens having both convex lens surfaces are joined. It is to be.

Next, numerical examples of the present invention will be described.

In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, and Di is the i-th lens surface from the object side.
The second lens thickness, the air gap, and Ni and νi are the refractive index and Abbe number of the glass of the ith lens in order from the object side.

In the numerical examples, the last three lens surfaces are glass blocks such as a face plate and a filter. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

The aspherical surface has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R represents a paraxial radius of curvature, and K, B, C, D, and E represent aspherical shapes. Assuming spherical coefficients,

[0049]

(Equation 6)

This is represented by the following equation. “E-0x” means “10 ^−X ”.

Numerical Example 1 f = 1 to 22.05 Fno = 1.65 to 3.04 2ω = 63.0 ° to 3.2 ° R 1 = 16.126 D 1 = 0.40 N 1 = 1.846660 ν 1 = 23.8 R 2 = 9.692 D 2 = 0.35 R 3 = 15.330 D 3 = 1.15 N 2 = 1.455999 ν 2 = 90.3 R 4 = -31.987 D 4 = 0.05 R 5 = 7.259 D 5 = 1.07 N 3 = 1.603112 ν 3 = 60.6 R 6 = 43.668 D 6 = Variable R 7 = 12.089 D 7 = 0.17 N 4 = 1.882997 ν 4 = 40.8 R 8 = 1.720 D 8 = 0.78 R 9 = -5.331 D 9 = 0.17 N 5 = 1.882997 ν 5 = 40.8 R10 = 81.961 D10 = 0.12 R11 = 3.496 D11 = 0.65 N 6 = 1.846660 ν 6 = 23.8 R12 = -10.852 D12 = 0.15 N 7 = 1.804000 ν 7 = 46.6 R13 = 6.959 D13 = Variable R14 = Aperture D14 = 1.00 R15 = -4.562 D15 = 0.20 N 8 = 1.696797 ν 8 = 55.5 R16 = -21.590 D16 = 0.05 R17 = 12.210 D17 = 0.75 N 9 = 1.583126 ν 9 = 59.4 R18 = -4.614 D18 = Variable R19 = 5.935 D19 = 0.62 N10 = 1.583126 ν10 = 59.4 R20 = -17.925 D20 = 0.30 R21 = 11.615 D21 = 0.20 N11 = 1.846660 ν11 = 23.8 R22 = 4.212 D22 = 0.95 N12 = 1.487490 ν12 = 70.2 R23 = -7.023 D23 = 0.75 R24 = ∞ D24 = 0.95 N13 = 1.516330 ν13 = 64.1 R25 = ∞ D25 = 3.50 N14 = 1.589130 ν14 = 61.2 R26 = ∞ ＼ Focal length 1.00 4.83 22.05 OK Spacing ＼ D6 0.20 6.23 9.07 D13 9.19 3.16 0.33 D18 4.29 3.10 4.47 Aspheric coefficient R17 k = 1.85796e + 01 B = -3.87345e-03 C = -1.26374e-04 D = 2.06665e-05 E = -4.35282e- 06 F = -8.38294e-08 R19 k = 8.06182e-01 B = -2.41262e-03 C = -1.07907e-05 D = 3.15906e-06 E = -9.05328e-07 Numerical example 2 f = 1 ~ 21.03 Fno = 1.65 ~ 2.82 2ω = 64.3 ° ~ 3.4 ° R 1 = 15.334 D 1 = 0.40 N 1 = 1.846660 ν 1 = 23.8 R 2 = 9.338 D 2 = 0.42 R 3 = 15.264 D 3 = 1.23 N 2 = 1.433870 ν 2 = 95.1 R 4 = -32.556 D 4 = 0.05 R 5 = 7.338 D 5 = 1.28 N 3 = 1.603112 ν 3 = 60.6 R 6 = 57.435 D 6 = Variable R 7 = 7.620 D 7 = 0.18 N 4 = 1.882997 ν 4 = 40.8 R 8 = 1.616 D 8 = 0.84 R 9 = -5.312 D 9 = 0.18 N 5 = 1.882997 ν 5 = 40.8 R10 = 15.461 D10 = 0.13 R11 = 3.635 D1 1 = 0.62 N 6 = 1.846660 ν 6 = 23.8 R12 = -6.705 D12 = 0.15 N 7 = 1.834807 ν 7 = 42.7 R13 = 11.245 D13 = Variable R14 = Aperture D14 = 0.87 R15 = 9.995 D15 = 0.21 N 8 = 1.712995 ν 8 = 53.9 R16 = 3.956 D16 = 0.77 N 9 = 1.583126 ν 9 = 59.4 R17 = -19.890 D17 = Variable R18 = 5.567 D18 = 0.62 N10 = 1.583126 ν10 = 59.4 R19 = 12.846 D19 = 0.38 R20 = 15.721 D20 = 0.18 N11 = 1.84666 0 ν11 = 23.8 R21 = 4.458 D21 = 0.85 N12 = 1.487490 ν12 = 70.2 R22 = -5.808 D22 = 0.77 R23 = ∞ D23 = 0.97 N13 = 1.516330 ν13 = 64.1 R24 = ∞ D24 = 3.59 N14 = 1.589130 ν14 = 61.2 R25 = ∞ ＼Focal length 1.00 4.72 21.03 variable interval＼ D6 0.21 6.16 8.96 D13 9.11 3.16 0.36 D17 4.36 3.19 4.36 Aspherical coefficient R17 k = 5.34332e + 00 B = 4.92928e-04 C = 8.42897e-05 D = 1.81683e-05 E = -5.60146e-06 R18 k = 1.38922e-01 B = -2.99278e-03 C = -2.22815e-05 D = 2.69176e-05 E = -2.70834e-06 F = -1.02645e-06 Numerical example 3 f = 1 ~ 20.13 Fno = 1.65 ~ 3.02 2ω = 60.5 ° ~ 3.3 ° R 1 = 15.126 D 1 = 0.36 N 1 = 1.846660 ν 1 = 23.8 R 2 = 9.134 D 2 = 0.27 R 3 = 13.518 D 3 = 1.12 N 2 = 1.433870 ν 2 = 95.1 R 4 = -29.374 D 4 = 0.05 R 5 = 6.900 D 5 = 0.98 N 3 = 1.603112 ν 3 = 60.6 R 6 = 39.747 D 6 = Variable R 7 = 10.966 D 7 = 0.19 N 4 = 1.882997 ν 4 = 40.8 R 8 = 1.594 D 8 = 0.67 R 9 = -5.553 D 9 = 0.17 N 5 = 1.882997 ν 5 = 40.8 R10 = 17.933 D10 = 0.12 R1 1 = 3.346 D1 1 = 0.62 N 6 = 1.846660 ν 6 = 23.8 R12 = -8.513 D12 = 0.14 N 7 = 1.772499 ν 7 = 49.6 R13 = 8.513 D13 = Variable R14 = Aperture D14 = 1.00 R15 = -5.538 D15 = 0.21 N 8 = 1.712995 ν 8 = 53.9 R16 = -29.450 D16 = 0.48 R17 = 11.227 D17 = 0.76 N 9 = 1.583126 ν 9 = 59.4 R18 = -5.242 D18 = Variable R19 = 6.027 D19 = 0.60 N10 = 1.583126 ν10 = 59.4 R20 = -23.813 D20 = 0.24 R21 = 11.156 D21 = 0.19 N11 = 1.846660 ν11 = 23.8 R22 = 4.047 D22 = 0.93 N12 = 1.487490 ν12 = 70.2 R23 = -7.157 D23 = 0.71 R24 = ∞ D24 = 0.90 N13 = 1.516330 ν13 = 64.1 R25 = ∞ D25 = 3.33 N14 = 1.589130 ν14 = 61.2 R26 = ∞ ＼focal length 1.00 4.57 20.13 variable interval＼ D6 0.19 5.90 8.59 D13 8.74 3.03 0.35 D18 4.35 3.22 4.34 Aspheric coefficient R17 k = 1.62861e + 01 B = -3.52395e-03 C = -2.71319e-04 D = 4.54558e-05 E = -6.82063e-06 R19 k = -1.63048e + 00 B = -8.32415e-04 C = 9.62576e-05 D =- 1.35923e-05 E = 2.97984e-07 Numerical example 4 f = 1 ~ 20.26 Fno = 1.65 ~ 3.11 2ω = 60.5 ° ~ 3.3 ° R 1 = 14.452 D 1 = 0.39 N 1 = 1.846660 ν 1 = 23.8 R 2 = 8.459 D 2 = 0.40 R 3 = 16.467 D 3 = 0.95 N 2 = 1.496999 ν 2 = 81.5 R 4 = -35.959 D 4 = 0.05 R 5 = 6.570 D 5 = 1.10 N 3 = 1.603112 ν 3 = 60.6 R 6 = 62.494 D 6 = Variable R 7 = 8.108 D 7 = 0.17 N 4 = 1.882997 ν 4 = 40.8 R 8 = 1.500 D 8 = 0.72 R 9 = -4.151 D 9 = 0.17 N 5 = 1.834807 ν 5 = 42.7 R10 = 21.404 D10 = 0.12 R1 1 = 3.601 D1 1 = 0.60 N 6 = 1.846660 ν 6 = 23.8 R12 = -9.891 D12 = 0.14 N 7 = 1.772499 ν 7 = 49.6 R13 = 15.398 D13 = Variable R14 = ∞ D14 = 0.81 R15 = 11.051 D15 = 0.19 N 8 = 1.719995 ν 8 = 50.2 R16 = 4.050 D16 = 0.09 R17 = 4.349 D17 = 0.76 N 9 = 1.583126 ν 9 = 59.4 R18 = -9.041 D18 = Variable R19 = 6.346 D19 = 0.64 N10 = 1.583126 ν10 = 59.4 R20 = -10.177 D20 = 0.31 R21 = 13.761 D21 = 0.19 N11 = 1.846660 ν1 1 = 23.8 R22 = 4.160 D22 = 0.76 N12 = 1.487490 ν12 = 70.2 R23 = -6.370 D23 = 0.71 R24 = ∞ D24 = 0.90 N13 = 1.516330 ν13 = 64.1 R25 = ∞ D25 = 3.33 N14 = 1.589130 ν14 = 61.2 R26 = ∞ ＼ Focal length 1.00 4.57 20.26 Variable interval＼ D6 0.17 5.71 8.32 D13 8.49 2.95 0.34 D18 4.30 3.17 4.41 Aspheric coefficient R17 k = -7.92534e-01 B = 6.04010e-04 C = -3.57324e-06 D = 1.86818e-05 E = -4.09155e-06 F =- 1.17171e-06 R19 k = 2.79281e-01 B = -2.48262e-03 C = -1.22638e-05 D = 2.65202e-06 E = 1.32918e-06 F = -4.72329e-07

[0052]

[Table 1]

[0053]

According to the present invention, by setting the refractive power of each lens group as described above, the front lens diameter is small, the field angle is wide, and the zoom ratio is 20 times while reducing the size of the entire lens system. Achieving good aberration correction over the entire zoom range despite the high zoom ratio described above, and achieving a large aperture ratio rear-focusing zoom lens with sufficiently long back focus with little aberration fluctuation during focusing Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is an aberration diagram at a wide angle end according to Numerical Embodiment 1 of the present invention.

FIG. 3 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 4 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 5 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention;

FIG. 7 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 8 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 10 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 11 is an aberration diagram at a wide angle end according to Numerical Embodiment 4 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

[Explanation of symbols]

 L1: first lens group L2: second lens group L3: third lens group L4: fourth lens group SP: stop d: d-line g: g-line ΔM: meridional image plane ΔS: sagittal image plane

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA01 MA15 PA09 PA10 PA19 PA20 PB12 QA02 QA07 QA17 QA21 QA25 QA34 QA42 QA45 RA05 RA12 RA13 RA32 RA41 RA42 SA23 SA27 SA29 SA32 SA63 SA65 SB04 SB15 SB23 SB34

Claims (4)

[Claims] 1. A first lens having a positive refractive power in order from the object side.
A second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. The second lens group and the fourth lens At least the group is moved to perform zooming, and the fourth lens group is moved to perform focusing.
The lens unit is moved so as to draw a locus convex toward the object side during zooming from the wide-angle end to the telephoto end. The first lens unit includes an eleventh lens having a negative refractive power from the object side and a positive refractive power. The second lens group includes three negative lenses and one positive lens, the focal length of the twelfth lens is f12, and the entire system 0.95 <f12 / Ft <1.5 75.0 <ν12 1.50 where Ft is the focal length at the telephoto end, ν12 is the Abbe number of the twelfth lens, and Fi is the focal length of the ith lens group. <F3 / F4 <4.00 A rear focus type zoom lens characterized by satisfying the following condition: 2. The rear focus type zoom lens according to claim 1, wherein said third lens group comprises a negative lens and a positive lens in order from the object side. 3. An aperture stop on the object side of the third lens group, the aperture diameter of which varies depending on the positions on the optical axis of the second lens group and the fourth lens group. 1 or 2 rear focus type zoom lens. 4. The focal length at the wide-angle end of the entire system is Fw,
When the distance between the third lens unit and the fourth lens unit at the wide-angle end when focusing on infinity is D4w, 4. The rear focus type zoom lens according to claim 1, wherein the following condition is satisfied.