JP2003241088A - Rear-focus zoom lens and image pickup device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfactorily secure distances in front of and behind a diaphragm, and to attain a high performance, in a zoom lens equipped with a color separation prism and having a long back focus. <P>SOLUTION: In the rear-focus zoom lens having four groups, i.e., positive, negative, positive and positive groups, a 3rd group is constituted of three negative, positive and positive lenses, and the shape of the lens closest to the image side of the 3rd group is limited by a conditional expression (the curvature on the R1 surface is sharp). Preferably, a distance between the 2nd group and the 3rd group, and the Abbe number of optical glass constituting the 3rd group are limited by the conditional expression. <P>COPYRIGHT: (C)2003,JPO

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 zoom lens, and more particularly to a front lens with a high zoom ratio while ensuring a long back focus such that a color separation prism is inserted between the lens and the CCD. The present invention relates to a rear focus type zoom lens having a small diameter and a large diameter.

[0002]

2. Description of the Related Art Recently, as home video cameras have become smaller and lighter, remarkable progress has been made in the downsizing of zoom lenses for image pickup. Especially, the overall length is shortened, the front lens diameter is reduced, and the configuration is simplified. Is focused on.

As one means for achieving these objects, there is known a so-called rear focus type zoom lens in which focusing is performed by moving a lens group other than the first lens group on the object side.

Generally, in a rear focus type zoom lens, the effective diameter of the first lens group is smaller than that of a zoom lens in which the first lens group is moved for focusing.
It is easy to downsize the entire lens system. In addition, close-up photography, especially extremely close-up photography, is possible, and since the relatively small and lightweight lens group is moved, the driving force of the lens group is small and quick focusing is possible.

As such a rear focus type zoom lens, for example, JP-A-62-206516, JP-A-62-215225, and JP-A-62-24213.
In the publication, etc., a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group are provided in this order from the object side, and the second lens group is moved to change the magnification. A zoom lens for performing focusing by correcting the image plane variation due to zooming in the fourth lens group is disclosed.

Further, JP-A-4-43311, JP-A-4-153615, JP-A-5-19165, JP-A-5-27167, and JP-A-5-6.
Japanese Patent No. 0973 discloses an example in which the fourth lens group is configured by one convex lens or two convex lenses. Further, JP-A-5-60974 discloses a zoom lens in which the fourth lens group is composed of two concave and convex elements.

Further, JP-A-55-62419, JP-A-62-24213, and JP-A-62-21522.
5, JP-A-56-114920, JP-A-3
-200113, Japanese Patent Application Laid-Open No. 4-242707, Japanese Patent Application Laid-Open No. 4-343313, Japanese Patent Application Laid-Open No. 5-297.
In the publications such as Japanese Patent No. 275, the third group, the fourth group
It is disclosed that each group is composed of two lenses, a positive lens and a negative lens.

Further, as the performance of a video deck becomes higher (digitalization), the picture quality of a video camera is being improved.
As one of the methods, high image quality is achieved by separating an image with a color separation optical system. And as a lens suitable for it, Japanese Patent Application Laid-Open No. 5-72474 and Japanese Patent Application Laid-Open No. 6-3
47697, Japanese Patent Application Laid-Open No. 7-199069, Japanese Patent Application Laid-Open No. 7-270684, Japanese Patent Application Laid-Open No. 9-281390.
There is a gazette such as a gazette.

[0009]

As described above, in general, in a zoom lens, in order to achieve a reduction in the front lens diameter and the entire system, the so-called rear focus method is used rather than the distance adjustment by the first lens group. Is more suitable.

However, in JP-A-4-026811 and JP-A-4-88309, it was difficult to dispose the color separation prism in that structure.

Further, JP-A-4-43311, JP-A-4-153615, JP-A-5-19165, JP-A-5-27167, and JP-A-5-6.
In these zoom lenses disclosed in Japanese Patent Publication No. 0973, the zoom ratio is about 6 to 8 times, and in the case of a high-power zoom lens having a zoom ratio higher than this, the variation due to the variation of the chromatic aberration becomes too large to be corrected and sufficient optical performance is obtained. It was difficult to make the most of it. Further, even in the example disclosed in Japanese Patent Laid-Open No. 5-60974, the zoom ratio is still in the 8 × class, which is still not sufficiently high.

Furthermore, JP-A-55-62419, JP-A-56-114920, and JP-A-3-20011
In the example disclosed in Japanese Patent No. 3, the first group or the third group
Since the lens group also moves with zooming, the lens barrel structure becomes complicated, which is not suitable for achieving miniaturization. Further, in the examples disclosed in JP-A-4-242707, JP-A-4-343313 and JP-A-5-297275, the third group has a large air gap, and the third group is further formed. Since the refractive power of the negative lens in the inside is weak, it is not a type that can sufficiently correct the chromatic aberration occurring in the third lens group in order to apply it to a high zoom lens. Furthermore, in the example proposed in JP-A-5-297275, the third
Since the concave meniscus lens in the group has a structure with a strong concave surface facing the image side, it is effective for telephoto conversion, but it is not suitable for receiving high-order flare components generated by the convex lens with the concave lens. Therefore, it is a type unfavorable for a large-diameter, high-magnification zoom lens.

Further, even in the examples disclosed in JP-A-5-72474, JP-A-6-347697, and JP-A-7-199069, the zoom ratio is about 10 times in each of the embodiments. After all, sufficient multiplication was not achieved.

On the other hand, when the resolution frequency required as the density of CCD increases, the image deterioration due to diffraction cannot be ignored especially when the aperture diameter is small or when the aperture is far from a perfect circle.

As a method of solving this, a method of suppressing the influence of diffraction to the minimum by adopting an iris diaphragm or inserting an ND filter in the optical path is conceivable. There is a drawback that the optical system tends to become large due to the increase in the axial distance required.

For example, in the examples proposed in Japanese Patent Laid-Open Nos. 7-270684 and 9-281390, it cannot be said that a sufficient front-rear spacing of the aperture is secured.

An object of the present invention is to improve the drawbacks of the above-mentioned conventional example, to sufficiently secure a back focus space in which an optical element such as a prism for color separation or an optical element for the purpose of protecting a zoom lens portion is secured. We provide a rear focus type zoom lens that has a large aperture and a zoom ratio of about 12 times while maintaining good optical performance over the entire zoom range and object distance, while ensuring a sufficient front and rear spacing. Another object is to provide a video camera using the zoom lens.

[0018]

A rear focus type zoom lens according to the present invention has a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a positive refractive power in order from the object side. A third lens group having a fourth lens group having a positive refractive power
A rear focus type zoom lens having a lens group, wherein the second lens group and the fourth lens group are moved for zooming and the fourth lens group is moved for focusing. Is a biconcave lens third
1 lens, a 32nd lens that is a biconvex lens, and a 33rd lens that is a biconvex lens. When the curvature of the object side surface of the 33rd lens is r3a and the radius of curvature of the image side surface is r3b,
-0.6 <(r3a + r3b) / (r3a-r3b) <
It is characterized in that the conditional expression 0 is satisfied.

Further, when the distance on the optical axis at the telephoto end of the second lens unit and the third lens unit is D23 and the focal length of the entire zoom system at the wide angle end is fw, 1.0 <D23 / f
It is characterized in that the conditional expression w <1.5 is satisfied.

Further, when the Abbe numbers of the respective lenses of the third lens group are ν31, ν32 and ν33, ν32 <ν3
It is characterized in that the conditional expression 1 <ν33 is satisfied.

Further, the third lens group has a cemented lens of the 31st lens and the 32nd lens, and a 33rd lens having an aspherical surface.
It is characterized by being composed of a lens.

Alternatively, the image pickup apparatus is characterized by having a rear focus type zoom lens, and a color separation optical system and an electric image pickup element on the image plane side thereof.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Next, specific examples of the present invention will be described.

1 to 8 are lens cross-sectional views of Numerical Examples 1-4 of the rear focus type zoom lens of the present invention, which will be described later, and FIGS. 5 to 8 are aberration diagrams of the respective Examples. In each aberration diagram, A is an aberration diagram at the wide-angle end, B is an intermediate aberration diagram, and C is various aberration diagrams at the telephoto end.

In the figure, L1 is the first lens unit having a positive refractive power, L1.
Reference numeral 2 is a second lens group having a negative refractive power, L3 is a third lens group having a positive refractive power, and L4 is a fourth lens group having a positive refractive power.
SP is an aperture stop, which is arranged immediately before the third lens unit L3. GB is a glass block such as a color separation prism, a CCD face plate, and a low-pass filter.

In the present embodiment, the second lens group is moved to the image plane side as indicated by the arrow when the magnification is changed from the wide-angle end to the telephoto end, and the fourth lens group is moved due to the image plane variation due to the magnification change. Correcting. Further, a rear focus type is adopted in which the fourth lens group is moved on the optical axis for focusing. In particular, as shown by the curves 4a and 4b in FIG. 1, when the magnification is changed from the wide-angle end to the telephoto end, the object side is moved so as to have a convex locus. As a result, the space between the third lens group and the fourth lens group is effectively used, and the total lens length is effectively shortened. The solid curve 4a and the dotted curve 4b of the fourth lens group shown in the figure are image planes associated with zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a near object, respectively. The movement locus for correcting the fluctuation is shown. The first lens group and the third lens group are fixed during zooming and focusing.

In Numerical Example 1-4, the third lens group is composed of a cemented lens having negative refractive power of negative and positive and a single lens having positive refractive power, and is a retro-type positive lens group as a whole. Are configured. In the cemented lens having a negative refractive power, the lens surface on the object side has a concave surface facing the object side. In this way, the role of moving the principal point position of the third lens group away from the second lens group is given, which contributes to lengthening the back focus. In particular, a stronger negative power (having a shorter radius of curvature) is applied to the object side than to the image side, so that the principal point position is located further rearward.

On the other hand, in the single lens having the positive refracting power, the lens surface on the object side has a stronger refracting surface (having a shorter radius of curvature) than the surface on the image side, and this cemented lens similarly has the third lens group. It plays the role of keeping the principal point position away from the second lens group,
This contributes to making the focal length of the fourth lens group long and thus the back focus long.

With the above constitution, the object of the present invention can be achieved for the time being, but it is more preferable to satisfy the following conditions.

When the most object-side curvature of the 33rd lens having a positive refractive power is r3a and the radius of curvature of the image side surface is r3b, -0.6 <(r3a + r3b) / (r3a-r3b) <0 ...・ It is necessary to satisfy the condition (1).

Conditional expression (1) relates to the shape of the lens closest to the image side in the third lens group. When the 33rd lens is a biconvex lens, if the lower limit of conditional expression (1) is exceeded and the curvature on the image side becomes gentle, it becomes difficult to shorten the total lens length.

On the other hand, if the upper limit is exceeded and the curvature on the image side becomes tight, it becomes difficult to secure a sufficient back focus and it becomes difficult to correct high-order coma aberration.

When the distance on the optical axis at the telephoto end between the second lens group and the third lens group is D23 and the focal length of the third lens group is fw, 1.0 <D23 / fw <1.5 It is preferable that the condition (2) is satisfied.

More preferably, when the Abbe numbers of the respective lenses of the third lens group are ν31, ν32, ν33, the condition of ν32 <ν31 <ν33 (3) is satisfied.

Conditional expression (2) is a conditional expression for restricting the front-rear distance of the diaphragm. If the lower limit is exceeded, a sufficient distance cannot be ensured, so that only a diaphragm mechanism having a simple structure can be adopted. Beyond the upper limit, the front and back of the aperture will be too wide,
It adversely affects the miniaturization of the total lens length.

Conditional expression (3) is a conditional expression regarding correction of chromatic aberration of the three groups. In particular, by composing the thirty-second lens having a positive refractive power with a glass material having the smallest Abbe number, the high-order aberration occurring in the third lens group is corrected and the chromatic aberration of magnification is well balanced in the entire zoom range. I keep it.

Now, in order to sufficiently correct the chromatic aberration at the telephoto end, the second group may be composed of at least two negative lenses and at least one positive lens, but in this embodiment, as described above. Further, in order to enlarge the principal point distance between the second lens group and the third lens group, a negative lens is arranged closest to the image surface side of the second lens group, which contributes to further lengthening the back focus.

In order to further correct aberrations, in particular, chromatic aberrations, the third lens group should have at least one cemented lens. As described above, with the improvement in image quality of video cameras, chromatic aberration, which has not been a serious problem in the past, in particular chromatic aberration of magnification, becomes a problem, and this is well corrected.

Further, in this embodiment, the aperture stop is arranged immediately before the third lens group in order to make the image of the first lens group small, but the present invention is not limited to this position, and the third lens group and the fourth lens group are not limited to this position. Or between the lenses of the third lens group.

In the present embodiment, the third lens group is made negative and positive in order, the exit pupil is made longer, and the state of the light rays emitted from the zoom lens is made substantially telecentric.
By making the angle of the light ray incident on the color separation prism arranged behind it, the change in the reflection characteristics due to the wavelength of the color separation system is eliminated, color separation is faithfully performed, and the color reproducibility of the image is made very good. ing.

Further, in a high-magnification lens such as this lens, the focal length at the telephoto end becomes very long, and the performance at the telephoto end and its vicinity is greatly affected by the second lens group. If an aspherical surface is introduced into this second lens group, it becomes possible to improve the optical performance.

Since the aspherical surface is basically intended to correct spherical aberration, it is desirable that the aspherical surface has a shape in which the positive refracting power becomes weaker toward the peripheral portion of the lens.

Numerical examples of the present invention will be described below.

In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap in order from the object side, and Ni and νi are in order from the object side, respectively. It is the refractive index and Abbe number of the glass of the i-th lens. Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

The aspherical shape has an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a positive traveling direction, and R is a radius of curvature of the gold axis.
When A, B, C, D, and E are aspherical coefficients, respectively

[Outer 1]

It is expressed by the following equation.

For example, the display of "e-0X" is "10-
Means "X"

[0048]   (Numerical Example 1) f = 1.00 to 11.59 fno = 1: 1.6 to 2.4 2ω = 55.1 to 5.2 r1 = 12.303 d1 = 0.30 n1 = 1.84660 ν1 = 23.9 r2 = 6.849 d2 = 1.07 n2 = 1.48749 ν2 = 70.2 r3 = -38.212 d3 = 0.05 r4 = 5.893 d4 = 0.67 n4 = 1.69680 ν4 = 55.5 r5 = 17.344 d5 = variable r6 = 14.258 d6 = 0.16 n6 = 1.83481 ν6 = 42.7 r7 = 1.560 d7 = 0.68 r8 = -4.312 d8 = 0.14 n8 = 1.83400 ν8 = 37.2 r9 = 51.218 d9 = 0.10 r10 = 3.730 d10 = 0.65 n10 = 1.84666 ν10 = 23.8 r11 = -3.539 d11 = 0.14 n11 = 1.80610 ν11 = 40.9 r12 = 15.784 d12 = variable r13 = 0.000 (aperture) d13 = 1.04 r14 = -4.208 d14 = 0.16 n14 = 1.77250 ν14 = 49.6 r15 = 14.893 d15 = 0.37 n15 = 1.69895 ν15 = 30.1 r16 = -8.335 d16 = 0.23 * r17 = 6.684 d17 = 0.60 n17 = 1.58313 ν17 = 59.4 r18 = -7.007 d18 = variable * r19 = 4.489 d19 = 0.63 n19 = 1.58313 ν19 = 59.4 r20 = -10.658 d20 = 0.03 r21 = 9.512 d21 = 0.16 n21 = 1.84666 ν21 = 23.9 r22 = 2.822 d22 = 0.80 n22 = 1.48749 ν22 = 70.2 r23 = -6.458 d23 = 0.70 r24 = 0.000 d24 = 4.50 n24 = 1.51633 ν25 = 64.1 r25 = 0.000 f 1.00 3.41 11.59 d5 0.18 3.86 5.96 d12 6.20 2.53 0.43 d21 2.02 1.45 2.02 d25 0.70 1.26 0.69 Aspherical coefficient R17 k = 1.03799e + 1 B = -7.71275e-3 C = -4.78061e-4 D = -2.60670e -Four R19 k = -2.05760e-1 B = -3.94789e-3 C = -3.64999e-5 D = 1.57026e- 4 E = -3.52610e-5

[0049]   (Numerical example 2) f = 1.00 to 11.59 fno = 1: 1.6 to 2.4 2 ω = 56.3 to 5.2 r1 = 12.711 d1 = 0.31 n1 = 1.84660 ν1 = 23.9 r2 = 7.009 d2 = 1.10 n2 = 1.48749 ν2 = 70.2 r3 = -38.827 d3 = 0.05 r4 = 6.163 d4 = 0.69 n4 = 1.69680 ν4 = 55.5 r5 = 18.334 d5 = variable r6 = 9.875 d6 = 0.17 n6 = 1.80400 ν6 = 46.6 r7 = 1.478 d7 = 0.69 r8 = -3.684 d8 = 0.14 n8 = 1.83481 ν8 = 42.7 r9 = 14.194 d9 = 0.10 r10 = 3.792 d10 = 0.67 n10 = 1.84666 ν10 = 23.9 r11 = -5.911 d11 = 0.14 n11 = 1.80400 ν11 = 46.6 r12 = 32.764 d12 = variable r13 = 0.000 (aperture) d13 = 0.50 r14 = -4.592 d14 = 0.17 n14 = 1.77250 ν14 = 49.6 r15 = 14.426 d15 = 0.38 n15 = 1.69895 ν15 = 30.1 r16 = -10.063 d16 = 0.24 * r17 = 6.569 d17 = 0.62 n17 = 1.67790 ν17 = 54.9 r18 = -11.076 d18 = variable * r19 = 4.628 d19 = 0.64 n19 = 1.58313 ν19 = 59.4 r20 = -10.658 d20 = 0.04 r21 = 8.814 d21 = 0.17 n21 = 1.84666 ν21 = 23.9 r22 = 2.805 d22 = 0.82 n22 = 1.48749 ν22 = 70.2 r23 = -6.369 d23 = 0.70 r24 = 0.000 d24 = 4.50 n24 = 1.51633 ν25 = 64.1 r25 = 0.000 f 1.00 3.41 11.59 d5 0.19 4.09 6.36 d12 6.69 2.79 0.52 d21 2.05 1.37 2.04 d25 0.70 1.38 0.71 Aspherical coefficient R17 k = 9.36804 B = -7.15542e-3 C = -1.18499e-4 D = -2.96481e-4 R19 k = -1.36499 B = -2.27205e-3 C = -4.01587e-4 D = 2.54039e-4   E = -3.77117e-5

[0050]   (Numerical example 3)  f = 1.00 to 12.76 fno = 1: 1.6 to 2.4 2ω = 55.1 to 4.7 r1 = 11.996 d1 = 0.30 n1 = 1.84660 ν1 = 23.9 r2 = 6.794 d2 = 1.07 n2 = 1.48749 ν2 = 70.2 r3 = -46.719 d3 = 0.05 r4 = 5.997 d4 = 0.67 n4 = 1.69680 ν4 = 55.5 r5 = 17.222 d5 = variable r6 = 8.724 d6 = 0.16 n6 = 1.88300 ν6 = 40.8 r7 = 1.572 d7 = 0.68 r8 = -4.258 d8 = 0.14 n8 = 1.83400 ν8 = 37.2 r9 = 7.612 d9 = 0.10 r10 = 3.377 d10 = 0.60 n10 = 1.84666 ν10 = 23.9 r11 = -3.795 d11 = 0.05 r12 = -3.152 d12 = 0.14 n12 = 1.77250 ν12 = 49.6 r13 = -301.153 d13 = variable r14 = 0.000 (aperture) d14 = 0.70 r15 = -3.425 d15 = 0.16 n15 = 1.77250 ν15 = 49.6 r16 = 18.809 d16 = 0.37 n16 = 1.69895 ν16 = 30.1 r17 = -4.354 d17 = 0.37 * r18 = 6.320 d18 = 0.26 n18 = 1.67790 ν18 = 54.9 r19 = -23.202 d19 = variable * r20 = 4.534 d20 = 0.63 n20 = 1.58313 ν20 = 59.4 r21 = -7.390 d21 = 0.07 r22 = 20.459 d22 = 0.16 n22 = 1.84666 ν22 = 23.9 r23 = 3.012 d23 = 0.80 n23 = 1.48749 ν23 = 70.2 r24 = -6.212 d24 = 0.70 r25 = 0.000 d25 = 4.50 n25 = 1.51633 ν25 = 64.1 r26 = 0.000 f 1.00 3.41 11.59 d5 0.19 4.00 6.23 d12 6.53 2.71 0.49 d21 1.60 0.88 1.42 d25 0.70 1.43 0.88 Aspherical coefficient R18 k = 8.22976 B = -6.17987e-3 C = -3.32774e-4 D = -2.45969e-4 R20 k = -5.65432e-1 B = -4.34271e-3 C = -5.04194e-4 D = 3.81215e- 4 E = -6.84216e-5

[0051]   (Numerical example 4) f = 1.00 to 12.76 fno = 1: 1.6 to 2.4 2ω = 55.1 to 4.7 r1 = 11.756 d1 = 0.30 n1 = 1.84660 ν1 = 23.9 r2 = 6.657 d2 = 1.07 n2 = 1.48749 ν2 = 70.2 r3 = -42.996 d3 = 0.05 r4 = 5.897 d4 = 0.67 n4 = 1.69680 ν4 = 55.5 r5 = 17.716 d5 = variable r6 = 13.312 d6 = 0.16 n6 = 1.88300 ν6 = 40.8 r7 = 1.549 d7 = 0.68 r8 = -4.334 d8 = 0.14 n8 = 1.83400 ν8 = 37.2 r9 = 12.849 d9 = 0.10 r10 = 3.397 d10 = 0.65 n10 = 1.84666 ν10 = 23.9 r11 = -3.334 d11 = 0.14 n11 = 1.80400 ν11 = 40.9 r12 = 18.784 d12 = variable r13 = 0.000 (aperture) d13 = 0.77 r14 = -4.601 d14 = 0.16 n14 = 1.80610 ν14 = 40.9 r15 = 18.025 d15 = 0.37 n15 = 1.76182 ν15 = 26.5 r16 = -8.194 d16 = 0.16 * r17 = 6.352 d17 = 0.61 n17 = 1.58313 ν17 = 59.4 r18 = -8.560 d18 = variable * r19 = 4.577 d19 = 0.63 n19 = 1.58313 ν19 = 59.4 r20 = -11.224 d20 = 0.03 r21 = 10.837 d21 = 0.16 n21 = 1.84666 ν21 = 23.9 r22 = 2.841 d22 = 0.81 n22 = 1.51633 ν22 = 64.1 r23 = -6.494 d23 = 0.70 r24 = 0.000 d24 = 4.50 n24 = 1.51633 ν25 = 64.1 r25 = 0.000 f 1.00 3.41 11.59 d5 0.19 3.91 6.02 d12 6.32 2.60 0.49 d21 2.16 1.50 2.17 d25 0.70 1.36 0.69 Aspherical coefficient R17 k = 8.92673 B = -7.55209e-3 C = -4.03564e-4 D = -2.51174e-4 R19 k = 2.46972e-1 B = -4.34442e-3 C = -1.73802e-4 D = 1.71858e- 4 E = -3.67776e-5

[0052]

[Table 1]

[0053]

With the configuration as described above, the FNo. While maintaining a large aperture of around 1.6, while maintaining a back focus space for optical elements such as color separation prisms and a space for a complicated diaphragm mechanism, it is excellent over the entire zoom range and object distance. It is possible to provide a rear-focus type zoom lens having performance, and it is possible to realize a compact, lightweight, and high-performance image pickup apparatus using this zoom lens.

[Brief description of drawings]

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

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

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

FIG. 4 is a lens cross-sectional view at a wide-angle end according to Numerical Example 4 of the present invention.

FIG. 5 is a diagram of various types of aberration in Numerical example 1 of the present invention.

FIG. 6 is a diagram of various types of aberration in Numerical example 2 of the present invention.

FIG. 7 is a diagram of various types of aberration in Numerical example 3 of the present invention.

FIG. 8 is a diagram of various types of aberration 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 d d line g g line ΔM meridional image surface ΔS Sagittal image surface aberration diagram (A) is wide-angle end, (B) is zoom intermediate ,
(C) is the telephoto end.

Continued front page    F-term (reference) 2H087 KA03 MA15 NA02 PA09 PA10                       PA16 PA20 PB13 QA02 QA07                       QA17 QA21 QA25 QA34 QA42                       QA45 RA05 RA12 RA32 RA41                       SA23 SA27 SA29 SA32 SA63                       SA65 SA72 SA74 SB04 SB15                       SB24 SB34

Claims (5)

[Claims] 1. 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, and a third lens group having a positive refractive power in order from the object side. A rear focus type zoom lens having four lens groups, wherein the second lens group and the fourth lens group are moved for zooming and the fourth lens group is moved for focusing. The group is the 31st lens which is a biconcave lens,
The 32nd lens which is a biconvex lens, the 3rd which is a biconvex lens
It has 3 lenses and the curvature of the object side surface of the 33rd lens is r3.
a, and the radius of curvature of the image side surface is r3b, -0.6 <(r3a + r3b) / (r3a-r3b) <
A rear-focus type zoom lens that satisfies the conditional expression 0. 2. 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, and a third lens group having a positive refractive power in order from the object side. A rear focus type zoom lens having four lens groups, wherein the second lens group and the fourth lens group are moved to perform zooming and the fourth lens group is moved to perform focusing. When the distance on the optical axis at the telephoto end between the lens unit and the third lens unit is D23, and the focal length of the entire zoom system at the wide-angle end is fw, the conditional expression 1.0 <D23 / fw <1.5 must be satisfied. Rear focus type zoom lens. 3. When the Abbe numbers of the respective lenses of the third lens group are ν31, ν32, and ν33, the conditional expression of ν32 <ν31 <ν33 is satisfied. Rear focus zoom lens. 4. The third lens group includes a 31st lens and a 3rd lens.
4. The rear focus type zoom lens according to claim 1, wherein the rear focus type zoom lens is composed of a cemented lens of two lenses and a 33rd lens having an aspherical surface. 5. An image pickup device comprising the rear-focus type zoom lens according to claim 1, and a color separation optical system and an electric image pickup device on the image plane side. apparatus.