JPH02294608A - Rear focus type zoom lens - Google Patents

Abstract

PURPOSE:To obtain a compact rear focus type zoom lens where variable magnification ratio is 8 and F number is 1.2 by providing five lens groups and satisfying specific conditions. CONSTITUTION:The zoom lens is constituted of a 1st fixed lens group I with positive refracting power, a 2nd lens group III for power variation which has nagative refracting power, a 3rd lens group III which has negative refracting power and corrects an image plane varying as the power is varied, a 4th lens group IV which has positive refracting power and collimate luminous flux diverged by the 2nd and 3rd lens groups into luminous flux parallel to the optical axis, and a 5th lens group V which has positive refracting power and is variable in focusing operation. Further, requirements shown by inequalities I - V are satisfied. In inequalities I - V, fw is the focal length at the zoom position of a wide-angle end and fI - fV are the focal length values of the 1st - 5th lens groups. Consequently, the rear focus type zoom lens where the variable magnification ratio is 8 including a standard visual field and an about 1.2 F number can be obtained.

Description

[Detailed Description of the Invention] [Field of Application in Industrial Technology] The present inventor has proposed that the curvature radius on the object side of the lens be curved on the image side of the lens used in video cameras and 'l' V cameras. This relates to a zoom lens K which has a curvature radius of tii'Iti*, which is a favorable half radius of curvature.

[Conventional technology]

In recent years, there has been a remarkable increase in the performance and miniaturization of video cameras, and along with this, zoom lenses, which are one of the key devices of video cameras, have become thicker, have higher magnification, are smaller and lighter, and have become smaller and smaller. Furthermore, in order to realize the lightweight /I1 type zoom lens, which has a wide variety of focusing systems suitable for autofocus, it is necessary to reduce the number of elements in the lens. Increasing the diameter of zoom lenses, lwl
+f! K, which actually uses f-magnification, has a large number of lenses.

In addition, the focus of Jubei's zoom lenses was based on the so-called front-element focusing method, which was performed by creating a group of lenses located on the object side. In this lens focusing method, in order to prevent the effective image circle from decreasing when the front lens is 8 yen 9 yen,
This has led to an increase in the effective diameter of the lens system, especially the SJJ lens group. Also, when autofocus is set to row 5, if you press K to create the K front lens group as in manual focus,
Since a large front lens group must be moved on the machine, the center section becomes large and a large amount of electric power is required for the motor that drives the front lens group, which is disadvantageous for miniaturization and weight reduction. Furthermore, the focusable subject distance in the penalty focus method is 1
For a subject K that is closer than 1.m, it is necessary to perform 7 focusing operations using lens groups other than the front lens group. Therefore, the autofocus is worn out at a subject distance of 1F+L up to the thigh, and focusing on a subject closer than 1rrL requires manual focus.

Therefore, we decided to fix the mI lens, and the lens groups other than the front lens group,
Is it possible that the so-called rear focus method, in which focus is performed on a part of the camera, is used?
No. 18 has been proposed.

The publication describes the I lens group, which has a fixed 9-order K from the object side and has a positive refracting power, the younger lens group II, which has a variable negative refracting power, and corrects the image plane that changes as the magnification changes. ■The lens group K having a negative refractive power for the purpose of
Therefore, a 5-group zoom lens has an audience lens group with positive refractive power to make the diverging light beam parallel to the optical axis, and a younger brother V lens group with positive refractive power that is movable during focusing. is proposed.

In this proposal, we would like to use the vertical V located at the rear of the zoom lens
Since focusing is performed by the lens group, at the wide end κ of the zoom lens, the distance from the subject (1) to just in front of the lens (O
It is possible to perform autofocus up to (rm),
Furthermore, since the lightweight lenses 8+- are moved, the driving force for the lens group can be small.

[Problem to be invented or solved]

However, in this proposal, 7 orcuses are carried out using a lens group with a folding action. Therefore, although the tuna aberration at the subject distance ψ time K has been well corrected, the trap aberration during focus fluctuates greatly, and the various aberrations at the sleeping distance are greatly degraded. . Therefore, the resolution of the object image is reduced during focusing.

Furthermore, the proposed zoom lens has a variable power ratio of 6ff,
It wasn't very magnified.

Akira Motokabu responded to the above proposal with a variable magnification ratio of 8 and t.
1.2 and to provide a compact rear focus type zoom lens.

[Failure to solve the problem]

In order to achieve the above objective, in order from the object side, the first lens group has a fixed positive refractive power, the younger lens group has a variable negative refractive power, and the correction surface that changes due to sadness is corrected. A lens group with a negative refractive power for the purpose of focusing, a lens group with a positive refractive power for aligning the nine beams diverged by the above-mentioned first and second lens groups with parallel light beams with respect to the original axis. This lens has five lens groups, the v-th lens group, each having a movable positive refractive power, and also satisfies the following conditions.

5-7 < II /j'r < 6. s
．． ．． ．． (1+-'.5< j■/fW <-1
．． 2 ・(2》-6.0 < f
III/jr <-s. o 15
12.7 < j■/fW < 5.2
(4I2・5 < jv/fy < 5.0
(51 However, j7: Focal length of the wide-angle zoom position jI: Focal length of the younger brother I lens group f■: Focal length of the second lens group f■ Focal length of the second melon lens group j■: The second ■lens Group focal length f■: Focal length of the Vth lens group In addition, in order to achieve a rear focus zoom lens with well-corrected compensation over the entire subject distance,
The above jl41V lens group includes, in order from the object side, the Su IV-1 lens with positive refractive power, the N-2nd lens with positive refractive power, the younger brother IV-5 lens with positive refractive power, and the IV-5 lens with negative refractive power. aGI
The 4-element V-4 lens consists of the above-mentioned V lens group, in order from the object side: a gV-1 lens with positive refractive power, a cumulative V-2 lens with positive refractive power, and an iV-5 lens with negative refractive power. The lens is a four-lens structure consisting of a V-4 lens with positive refractive power, and further satisfies the following conditions.

However, R4y-1l; radius of curvature R on the object side of the IV-1 lens
rv-rx: Half radius of curvature of the image surface of the younger brother FF-1 lens RV
-1 = radius of curvature of the V-th lens on the object side Ry-+j
: Radius of curvature on the image plane side of the V-+ lens [Operation] Figures 1 to 5 are lens wr plane views corresponding to numerical examples 1 to 5, which will be described later, of the present invention, respectively. Figures 1 to 5
Since the configuration of the lens group up to the figure is the same, the lens group E1 will be selected as a representative and will be explained below.

In FIG. 1K, I, II, m, IV, and V are each 81.
Harmony ■． Clothes ■． This is the second lens group.

In the present invention, by making the I-th to V-th lens groups satisfy the above-mentioned conditions, it is possible to achieve a compact rear focus type zoom lens with a variable power ratio (magnification, F number 1.2). ing.

Generally, in order to obtain a compact zoom lens, it is desirable for K to shorten the focal length of each lens group constituting the lens system. However, if the focal length is too short, it becomes difficult to adjust the focal length, leading to an increase in the number of lenses. Therefore,
In this embodiment, since the focal length from the I-th lens group to the V-th lens group is specified, it is more compact and the lens $. It has achieved a rear focus zoom lens with few details.

Next, K, conditional expressions (1) to (5) will be explained.

Conditional expressions (1) and (2) are conditions for the focal lengths of the I-th lens group and the ■-th lens group, and the conditional expressions (t) (2
), it is possible to achieve a compact rear focus type zoom lens with a magnification ratio of 8x. If the upper limit of conditional expression (1) is exceeded, the magnification ratio becomes 8.
In order to obtain the magnification, the moving chamber of the 2nd lens group becomes large, making it insufficiently compact.If the lower limit is exceeded, it becomes disadvantageous in terms of aberration correction, and in the worst case, the number of lenses in the 1st lens group may be required to be 4 or more.

If the upper limit of conditional expression (2) is exceeded, it will be disadvantageous in terms of aberration correction, and in the worst case, the number of lenses in the first lens group will need to be four or more. becomes too large and compaction becomes insufficient.

Conditional expression (5) is a condition for the focal length of the Ⅰ lens group, and if the upper limit is exceeded, it will be disadvantageous in terms of aberration correction, and in the worst case, the number of lenses in the ① lens group will be required to be two or more, and the means for controlling the aKIII lens group. The tolerance for good quality of the lens is very strict, so it becomes difficult to see if the lower limit is exceeded. ■The younger brother is used to correct the image plane, which fluctuates as the magnification changes due to the movement of the lens group. ■The base of the movement of the lens group is thick. Therefore, the compactness becomes insufficient.

The conditional expression (in short) is the condition for the focal length of the lens group,
Outside this range, the axial ray flux incident on the V-th lens, which is movable during focusing, is not parallel to the 9th axis. However, the resolution becomes thicker (deterioration).

Conditional expression (5) is a condition for the focal length of the younger brother V lens group. If the upper limit is exceeded, the movement of the V lens group during focusing will be reduced.
If the lower limit is exceeded, it becomes disadvantageous in terms of aberration correction, and in the worst case, the number of lenses in the ① lens group may be required to be five or more.

Next, the condition κ for achieving a rear focus type zoom lens in which various aberrations are well corrected over the entire K1 object distance will be explained.

General In order to properly correct various convergence over the entire K object distance, it is necessary to correct various aberrations in the V-th lens group alone, which is movable during focusing, and the various aberrations of the lens system from the Elen lens balance to the ■-th lens group. It is desirable that they be independently corrected. In this example, the spherical aberration with an F number of 1.2 and the variable magnification ratio of 8x are achieved by making the ① lens group and the Vth lens group each have a lens configuration of four lenses with a constant Pfr as described above. Comatic aberration and astigmatism are independently corrected by the ① lens group and the lens groups from the Ⅰ lens group to the ① lens group K.

In particular, the No. 1 lens group is a No. IV-1 lens with positive refractive power,
N-2nd lens with positive refractive power, @IV-5 with positive refractive power
The lens is made up of four ilV-4 lenses with negative refractive power to reduce the height of the incident light to the Mv lens group and alleviate the occurrence of various retractions in the V lens group. Furthermore, the coma aberration of the lens system from the I lens group to the IV lens group is calculated by the younger brother N.
This is corrected by making the -5 lens a meniscus-like lens shape with the convex surface facing the object 9111 surface, and astigmatism is corrected by making the IV-4 lens a lens shape with both lens surfaces concave. are doing.

Then, the v-th lens group includes a 14V-1 lens with a positive refractive power, a 14V-2 lens with a positive refractive power, and a V-th lens with a negative refractive power.
By using a four-element configuration including a convex, concave, and concave triplet lens consisting of 5 lenses and a straw V-4 lens with positive refractive power, spherical aberration, coma aberration, and astigmatism are corrected at the same time. In order to reduce coma aberration and astigmatism, which fluctuate the most when moving the V lens, the iV-4 lens has both lens surfaces convex, and the V-5 lens has a concave surface. 9 correction is made by forming the lens into a meniscus-like shape that is directed toward the lens.

&K, congratulations on conditional expressions (6) to (9)K.

Conditional expression (6) is a condition for compressing the coma aberration of the lens system from the I lens group to the lens cup II to all zoom positions, and it is possible to compensate for the coma aberration of the lens system from the I lens group to the lens cup II by applying the lens shape of the younger brother IV-5 lens. If the upper limit of conditional expression 13 is exceeded, coma aberration will be under-corrected, and if the lower limit is exceeded, coma aberration will be over-corrected.

Conditional expression (7) is a condition for protecting and correcting astigmatism of the lens system from the I-th lens group to the ■-th lens group at all zoom positions. This shows the conditions.

If the upper limit of the conditional expression is exceeded, astigmatism or undercorrection will occur, and if the lower limit is exceeded, astigmatism will be overcorrected.

Conditional expression (8) is a condition for correcting astigmatism across all focus positions, and is expressed by the lens shape of the younger brother V-5 lens. Above the conditional expression [
If it exceeds Y, astigmatism will be under-corrected, and if it exceeds the lower limit, it will be astigmatism or over-corrected), ? Condition (9) is a condition for correcting coma aberration by imprinting it directly on the entire focus position, and is expressed by the lens shape of the iV-4 lens. If the upper limit of the conditional expression is exceeded, coma aberration will be undercorrected, and if the lower limit is exceeded, coma aberration will be overcorrected.

In addition, in the present invention, even if each lens of the IV lens float and MV lens group is divided and replaced with two or more lenses, the object of the present invention can be achieved as long as the technical idea of the present invention is not departed from. It goes without saying that it can be done.

[Example]

Hereinafter, examples of the ridge iim of the present invention will be shown. In the example, the R curtain is the radius of curvature of the t-th lens surface 5i, Di is the distance on the optical axis between the lens surface S1 and the lens surface S i+1, N), and are the refractive index and Abbe number of the lens at the IC-th scanning point from the object side, f is the focal length, and L is the object distance.

R and R■ are 7 ace great, a-bass filter, etc.VC. = tL4 dummy glass.

Further, Table 1 shows the relationship between the above-mentioned conditions and the number {i1 actual examples of the present invention.

(Left below) [Numerical Example 1 corresponding to Figure 1 K] j=8.8 ~ 66.5 jF/K=1:1.2 J'
:48.9eN6.9°RD N 〆87.10 0.95 1.84666
25.841. 27 5.80 1
．． 58915 61. 2-141,60
0.20 55.214.05 L58915
61.295.05 Variable 51.5B 0. a5 1.74520
49.511.59 4.57 -16.04 0.8S
L74520 49.514,44
5,25 1.84666
25.8-592.60 (variable) -27.61 0.85 1.69680
55.5-182.00 (OK) 424,80 4,00 1.69
680 55.5-25.54 2
．． 15 (crest) 2.90 59.8B 5,15 1.622
MJ 55.2-55 小(] 0.20 25.54 66.20 -52.70 82,17 50.02 1 gai .60 21.81 164.!10 22.55 10.72 25.22 - 128.70 2,80 2,81 0.85 (variable 3.74 0.20 3.65 0.20 0.85 2,70 3.15 (possible f) 2,76 1.58915 1.84666 1 .66755 1.66892 1.84666 1.65844 1.52507 61.2 25.8 41.9 45.0 25.8 50.9 58.5 [Example 2 corresponding to the straw 2 diagram] f=8. 8-67.Q, F A6=1:1.
2, JV= 48.90y 6.8°SR
D N V1 B7,10
0,95 1.8466625.82 41.2
7 5,80 1.58915 61.2
5 -141.60 0.204
55.21 4.05 1. 5B915
61. 25 95.05 (variable) 6 51.58 b. 85
1.7432Ω 49.57 1
1.59 4.57 8 -16.04 0.85 1,7462
0 49.59 14.44 5.25
1. 846+56 25.81a -s92
．． 6o (variable) 11 -27.61
4), Armor 1.69680 55.5
12-182. DO ('H change) 15 44l
l]. O L38 L696 &) 5
5.514 -25.00 LOI 15 (crest) 2.55 1 6 58.45 5,10 1.62
260 out. 1917 -551.00 0
．． 2o25.41 62.51 -55.51 81.95 29.70 -385.80 21.66 154.50 22.06 10,54 22.54 -187.40 5.10 2.65 0.80 (variable ) 5.60 0.20 5.80 0.20 0.85 2.55 5.10 (variable) 5.90 1.58915 1. 84666 1.66755 1.66892 1.84666 1.65844 1.52!107 61.2 23.8 41.9 45.0 26.8 50.9 58.5 [Example 3 corresponding to Figure 5 K] f=8.8~67.1, FA6=1:1
．． 2, F=as. 9'- 6.8°RD
N V 87.10 0.95 1.84666
25. B41.27 6. Hit 1.5891
5 61.2-141.55 0.2
0 55.21 4.05 1.58915
61.295.05 (variable) 51.5B 0. a5 1.74
520 49.511,59 4.57 -16.04 0.85
1.74520 49.514.44
5.25 1.84666
25.8-592.60 (variable) -27.61 0.85 1.6
9680 55.5-182.00 (
Variable) 556.2 5.7O L696
80 55.5-26.09 2
．． 25 (Aperture) 2.45 45.88 5,50 1.65
B44 50.9-107.04
0.20 24.50 56.86 -52.66 81.97 29.86 -720.86 22.00 181.79 25.57 10.80 25.08 -97.25 5.20 2.95 0. 80 (variable) 4.08 0.21 3.71 0.21 0.97 2.69 (variable) 2.76 1.61271 1.84666 1. 66892 1.66892 1.84666 1.65844 1.52507 58.8 25.8 45.0 45.0 25.8 50.9 58.5 [Numerical Example 4 corresponding to Figure 4 K] f = 8. 6~65.1, F/#6=1: 1,
2, F=49.9'-7. D'RD #
V B6.77 0.95 1.84666
25.8a2. Q2 6. oa 1.5891
5 61.2-142,50 0,
2ro53. a 4.05 1.58915
61.294.51 (variable) 51.58 0.85 1.74400
44.811 ,59 4.57 -16.04 0.85 1.74520
49.5214.44 5.25 1.84
6<46 25.8-592.60 (variable) -29.45 0.85 1.69680
55.5-194.10 (variable) 149,40 5.5D
I. 69680 55.5-55
．． 22 2.25 (Aperture) 2.00 64.55 5,50 1.65844
50.9-53.54 0.20 24.64 62.7B -52.18 86.11 26.91 -455.20 25.64 105.20 21,25 10.52 2 Otsu-231.70 2 .70 2.65 Ω, 80 (K) 3.80 0,20 3,20 0.20 0,90 2.50 2.92 (variable) 2.76 1.66892 1.84666 1.65844 1, 74a0 1.84<566 1.65844 1.52507 45.0 25.8 50.9 44.8 25.8 50.9 58.5 [Example 5 corresponding to Figure 5 K] f=8.8~ 66.5, FAt=1: 1.2,
l/'=45.9°-6.9°SRDN
V 1 B6.77 0.95. 1. B4
666 25. B2 42.02 6.0
0 1.58915 61.25 J
42.51) 0.204 55,55
4,05 1.589L5 61.25
95.62 (variable) 6 51.50 0.85 1.7440
0 44.87 11.55 4.37 8 -16.15 0.85 1.745
2G 49.59 14.44 2.52
1. B4666 25.81o -, a
4 o. oo (possible f) 1 1 -29.45
0.135 1.69680 55.51
2 -194.10 (variable) 15 16
1.40 5.55 1.69680 5
5.514 -54.55 2.6015
(Aperture) 2.05 16 64.50 3. Crime 1.65844
50.91 7 -55.54 0.2
024.65 62.81 -52.09 86.78 26.92 -440.00 25.62 102.40 21. 25 10.54 22,59 -257.00 2.70 2.65 0.85 (variable) 3.80 0,20 3.21 0.20 0#90 2.50 2.92 (variable) 2.76 1.66892 1.84666 L65844 L74400 1.84666 1.65844 1.52507 45.0 26.8 50.9 44.8 25.8 50.9 58.5 Table 1. Relationship between glare conditions and numerical examples of the present invention Figure 6 shows various aberration diagrams of the numerical example 1, and Figure 6 CA) shows the relationship at the wide-angle end (f = 8.76) at the subject distance (self). The aberration at the zoom position is calculated from the center (Image Omtn ) to the periphery (
It is an aberration diagram shown by applying the image 2,2rrLm and 6.5ηa).

At the center (image height Qmm), the aberration has no directionality, so there is only one convergence diagram, but at the periphery, there is omnidirectionality (vertical and horizontal directions), so two are shown as meridional and sagittal.

Figure 6 CB) is the standard for subject distance control (j = 56.7
2) The zoom position [K, Fig. 6 CC) shows the yield at the zoom position of the telephoto dawn (f = 66.54), and how to read it is from the younger brother Fig. 6 ( , f)
It is completely the same as that of .

The younger brother figure 6 (D) is a wide-angle trend at a subject distance of 1.2 m (j = 8
．． 76) at the zoom position t1tK is shown in Figure 6 (A
) is mark 4! The aberration at the zoom position of k (f = 56.72) is shown in Figure 6 CF) at the telephoto end (f = 6
6.54) is an aberration diagram showing the aberrations at the zoom position, and the arrangement is completely the same as that of FIG. 6CA).

Figure 7 shows various pay-off diagrams for Example 2, and the younger brother (Figure 7 CA) shows the take-back at the zoom position at the wide-angle end (j = 8.77) when the subject distance is zero, and Figure 7 CB ) is standard Cj=56.75)
The zoom position of the younger brother 7G CC) is at the telephoto end (
f engineering 66. These are aberration diagrams showing the convergence at the zoom position of OQ), and Fig. 7(l)) shows the aberration at the zoom position of wide-angle m (f = 8.77) when the subject distance is 1.2 m. , Fig. 7(E) shows the hesitation ( j =
56.75 ) aberration at zoom position tK? , Figure 7 CF) is a harvesting diagram showing the harvesting time t at the zoom position of the telescope (f = 66.00), respectively.

Figure 8 shows the various yields of Example 5, younger brother 8 CA) shows the aberrations at the zoom position of a wide-angle field (j' = 8.82) when the object distance is Korean, and Figure 8 CB) shows the aberrations at the zoom position. Quasi (j=56
．． Figure 8 shows the aberrations t at the zoom position at the telephoto end (f = 157.14), and Figure 8 CD
) is the wide angle at the subject distance of 1.2 corners - ( f = 8.82
) at the zoom position K. The younger brother (Fig. 8 CE) is the image Jun (
FIG. 8(F) is an aberration diagram showing the aberration at the zoom position of 56.95) and the convergence at the zoom position of the telephoto end (j' = 67.14).

Figure 9 shows the various aberrations of Numerical Example 4, and Figure 9 (CA) shows the aberrations at the zoom position tlK at the wide-angle end (f = 8.56) when the temporary object distance ψ is shown in Figure 9 (B). is standard Cj=5
Figure 9 is an aberration diagram showing the aberration at the zoom position of 5.62) and the aberration at the zoom position of the telephoto end (f = 65.09), respectively; Figure 9 CD)
is the wide-angle end (f = 8.
Figure 9 (E) shows the aberrations at the zoom position of the standard (j = 55.62) zoom position fl[. K
The aberrations in the telephoto lens (f = 65
．． 09) are aberration diagrams showing aberrations at zoom position.

Figure 10 shows the results of numerical comparison example 5, and Figure 10 (CA) shows the captured scene at the zoom position at the wide-angle end (j' = 8.56) when the object distance is ω. ) is standard ( f
= 55.78) at the zoom position, as the first
Figure 0 is a collection diagram showing the yield at the zoom position at the telephoto end (f = 755.01),
The younger brother (Figure 10 CD) is a wide-angle sea (j =
8.56), Figure 10 (E) shows the aberration at the standard (j = 55.78) zoom position, and Figure 10 (CF) shows the aberration at the zoom position of the far end. FIG.

〔Effect of the invention〕

According to the present invention, it is possible to achieve a rear focus type zoom lens suitable for TV cameras, video cameras, etc. with a variable magnification ratio of about 8 including the standard angle of view and an F number of about 1.2. In particular, the rear focus system achieves excellent aberration correction even when the subject distance is increased by using four elements each for the younger brother IV lens punch and V lens #, and by satisfying certain conditions. A zoom lens has been achieved.

[Brief explanation of drawings]

1 to 5 are schematic diagrams showing lens systems at the wide-angle end zoom position corresponding to Examples 1 to 5K of the present invention, respectively;
Figure 6 shows a practical example of the present invention, the early aberration diagram of Example 1, Figure 7 shows various retrieval diagrams of Example 2 of the present invention, and the retrieval diagram of Example 5 of the present invention. Figure 9 is a diagram of various aberrations of Example 4 of the present invention,
FIG. 10 is a diagram showing various aberrations of Example 5 of the present invention. r, u. m. rv. v-...Respectively younger brother I Niv Lens group porridge 1 figure younger brother 2 figure scabbard figure 5 side figure 5 figure 5f56 figure (C) helmet figure 6 figure (D) closed figure 7 (D) helmet 8 fat (delta drop 66 rero (D Punishment c3 diagram (8) Closed J diagram (D) Scabbard 10 diagram (6) Closed diagram 3 (E) 100 [F (F no.

Claims (1)

[Claims] 1. In order from the object side, a lens group I (I) having a fixed positive refractive power, a lens group II (II) having a negative refractive power for variable power, and a variable power lens. A third lens group (III) with a negative refractive power to correct the image plane that changes as the image surface changes, and a positive refractive power to make the light beam diverged by the above II and III lens groups parallel to the optical axis. It has five lens groups: an IV lens group (IV) with refractive power and a V lens group (V) with positive refractive power that is movable during focusing, and further satisfies the following conditions: A rear focus zoom lens. 5.7<f_ I /f_W<6.3 -1.5<f_II/f_W<-1.2 -6.0<f_III/f_W<-3.0 2.7<f_IV/f_W<3.2 2 .5<f_V/f_W<3.0 However, f_W: Focal length at the zoom position at the wide-angle end f_ I: Sunspot distance of the I-th lens group f_II: Focal length of the II-th lens group f_III: Focal length of the III-th lens group f_IV: Focal length of the IV lens group f_V: Focal length of the V lens group 2, The above-mentioned IV lens group (IV) includes, in order from the object side, the IV-1 lens with positive refractive power, the diaphragm, and the positive refractive power. It is composed of four lenses: the IV-2 lens with refractive power, the IV-3 lens with positive refractive power, and the IV-4 lens with negative refractive power, and the V lens group (V) is , in order from the object side: a V-1 lens with positive refractive power, a V-2 lens with positive refractive power, a V-3 lens with negative refractive power, and a V-4 lens with positive refractive power. 2. The rear focus type zoom lens according to claim 1, comprising four lenses, and further satisfying the following conditions. 1.8<(R_IV-3_A+R_IV-3_B)/(R_
IV-3_A-R_IV-3_B)<2.7 0.3<(R_IV-4_A+R_IV-4_B)/(R_
IV-4_A-R_IV-4_B)<0.5 -3.3<(R_V-3_A+R_V-3_B)/(R
_V-3_A-R_V-3_B)<-2.5 0.5<(R_V-4_A+R_V-4_B)/(R_
V-4_A-R_V-4_B)<0.9 However, R_IV-i_A: Radius of curvature on the object side of the IV-i lens R_IV-i_B: Radius of curvature on the image plane side of the IV-i lens R_V-i_A: Radius of curvature on the image plane side of the IV-i lens Radius of curvature on the object side of the Vi lens R_V-i_B: Radius of curvature on the image plane side of the Vi lens