JPS63205629A - Zoom lens of rear focusing type - Google Patents

Abstract

PURPOSE:To obtain a high variable power ratio by moving a 3rd group and 4th group so as to satisfy specific conditions at the time of focusing. CONSTITUTION:The five lens groups; a group I having positive refracting power, 2nd group II having negative refracting power, 3rd group III having positive refracting power, 4th group IV having negative refracting power and 5th group V having positive refracting power are arranged successively from an object side. The focusing from an infinite object to a near distance object is executed by moving the 3rd group III and the 4th group IV to the image plane side to attain 1.5<(betaF<2>-1)/Z<6.0 when the focal length of the entire system at an arbitrary zoom position at the time of focusing to the infinite object is F, the focal length of the entire system at the wide angle end is Fw, the overall imaging magnification of the 3rd group III and the 4th group IV at the focal length F is betaF and Z=F/Fw. The high variable power ratio is thereby obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a rear focus type zoom lens, and in particular, a rear focus type zoom lens suitable for a high zoom ratio zoom lens used in a photographic camera, a video camera, etc. This relates to zoom lenses.

(Prior Art) Conventionally, zoom lenses for photographic cameras, video cameras, etc. have adopted the so-called rear focus system, in which focusing is performed by moving lens groups other than the first lens group on the object side. Various proposals have been made, such as No.-136012.

In general, the rear focus type uses a moving lens group that is relatively small and lightweight, so it has the advantage of requiring less driving force for the lens group and allowing quick focusing.

However, if a rear focus type zoom lens is adopted in which focusing is performed by moving the lens group behind the variable magnification lens group, for example, even for the same object distance, the difference in zoom position, that is, the difference in focal length, causes the focus lens group to The amount of delivery is different, and the amount of delivery may change in a quadratic or discontinuous manner.

In such a zoom lens, if the variable power ratio is increased, a large amount of space must be reserved for movement of the focus lens group on the wide-angle side, resulting in an increase in the size of the lens system. In addition, if a rear focus system similar to that described above is adopted, the amount of extension of the focus lens group for the same object distance may be about 2 to 3 times greater at the telephoto end than at the wide-angle end.

In such a zoom lens, the amount of movement of the image plane relative to the amount of movement of the focus lens group, that is, the sensitivity increases at the telephoto end, and when this value reaches a certain degree of 1k, it becomes mechanically and mechanically difficult to control the movement of the focus lens group. I'm coming.

Also, if the sensitivity at the telephoto end is set to a controllable value, the sensitivity at the wide-angle end will become too small, requiring more space to move the focus lens group, and the lens system will become larger. .

(Problems to be Solved by the Invention) The present invention prevents an increase in the effective diameter of the first group when achieving a high zoom ratio in a zoom lens employing a rear focus system, and at the wide-angle end. The purpose of the present invention is to provide a rear focus type zoom lens which is particularly suitable for a zoom lens having a high zoom ratio, which reduces the difference in sensitivity at the telephoto end, and facilitates mechanical control of a focus lens group.

(Means for solving the problem) From the object side, the first group has positive refractive power, and the second group has negative refractive power.
It has five lens groups: a third group with positive refractive power, a fourth group with negative refractive power, and a fifth group with positive refractive power. While moving the first group toward the object side, the distance between the first group and the second group and the distance between the third group and the fourth group are changed.
This is done by moving each lens group so that the distance between the groups increases, and the distance between the second and third groups, and the distance between the fourth and fifth groups decreases, and the lens group is moved to infinity. The focus from an object to a close object is controlled by the third group and the fourth group. This was done by moving the group toward the image plane.

(Example) FIG. 1 and FIG. 2 each show numerical example 1 of the present invention, which will be described later.
FIG. 2 is a cross-sectional view of the lens of No. 2. Third. 4th゜5th. 6th. FIG. 7 shows paraxial refractive power arrangements of numerical examples 1 to 5 of the present invention, which will be described later. In the figure, (A) shows the wide-angle end, and (B) shows the telephoto end.

Matara is the first group with positive refractive power, ■ is the second group with negative refractive power,
■ is the third group with positive refractive power, ■ is the fourth group with negative refractive power, V
is the fifth group with positive refractive power. S is the aperture.

The arrows indicate the locus of movement of each lens group when changing the magnification from the wide-angle end to the telephoto end. In Numerical Examples 1.3 and 4.5, the first to fourth groups are moved, and in Numerical Example 2, all of the first to fifth groups are moved to change the magnification. The dotted line indicates the third point when focusing on an object distance of 1.6m. Fourth
It shows the position of the group. Note that the third group and the fourth group are moved integrally.

In this embodiment, when changing the magnification from the wide-angle end to the telephoto end, the first
While moving the group toward the object side, the first. By increasing the distance between the second lens group and the second lens group, the power changing effect of the second lens group is increased.

Furthermore, by moving the first group toward the object side, the total lens length at the wide-angle end is shortened, and the total lens length is increased at the telephoto end. This makes it easy to correct various aberrations by increasing the telephoto ratio at the telephoto end while preventing the diameter of the front lens from increasing to secure off-axis rays at the wide-angle end.

In addition, by reducing the distance between the second and third groups and moving the third group toward the object side, the third group also takes part in the zooming action, allowing a high zoom ratio of about 10x. A zoom lens has been achieved.

Furthermore, a fifth group that is fixed or movable during zooming is provided, and the fourth group is moved toward the image plane, that is, the distance between the third and fourth groups is increased, and the distance between the fourth and fifth groups is increased. By reducing the distance, various aberrations are corrected in a well-balanced manner.

In this embodiment, although the movement of the fourth group does not directly contribute to the zooming effect, the lens groups from the third group to the fifth group as a whole have a large aberration correction effect.

In other words, when comparing the wide-angle side and the telephoto side, the 3rd to 5th groups move the 4th group with negative refractive power toward the image plane, which makes the entire lens system more telephoto. It's changing. Especially when viewed as a relay lens system, the third
Since the total length of the lens group up to the fifth group is increased, it is very advantageous in terms of aberration correction.

In addition, good optical performance is achieved by moving the fourth group toward the image plane during zooming from the wide-angle end to the telephoto end, and blocking defective off-axis flare components using the outer diameter of the lens.

Furthermore, in this embodiment, the refractive powers of each lens group are configured so that the refractive powers of adjacent lens groups have opposite signs,
This allows variations in various aberrations to cancel each other out, achieving overall good aberration correction.

In this embodiment, with the above-mentioned lens configuration, focusing as the object distance changes is performed by moving the third and fourth groups.

Generally, in a zoom lens with a high zoom ratio, when focusing is performed using the front lens group (first group), the lens system increases in size. Furthermore, as the zoom ratio becomes higher, if the zoom method or focus method becomes inappropriate, the number of lens systems increases. Furthermore, if the refractive power arrangement is inappropriate, there are problems such as increased aberration fluctuations.

On the other hand, in this embodiment, in the above-mentioned lens configuration, the third and fourth groups are moved to perform focusing, thereby reducing fluctuations in aberrations and shortening the overall length of the lens. At this time, focusing may be performed while changing the distance between the third group and the fourth group, which facilitates sophisticated aberration correction. Further, as in this embodiment, the third group and the fourth group may be integrated to perform focusing, and in this case, there is a feature that the mechanism can be simplified.

Next, a case will be described in which focusing is performed by moving the third group and the fourth group as one unit. Let the sensitivity and imaging magnification of the focus lens group consisting of the third and fourth groups be ES and βF, respectively, and the imaging magnifications of the lens groups arranged closer to the image plane than the focus lens group are Bi, Bi++, - ” aK
Then, the sensitivity ES when focusing near infinity is Cape ES (1-βF2) B+", Bt++"B
x2=(1).

Further, the amount of defocus for the same object distance increases in proportion to approximately the square of the zoom ratio. Therefore, in order to reduce the difference in the amount of edge protrusion of the focus lens group between the wide-angle end and the telephoto end, the sensitivity needs to increase as the magnification changes from the wide-angle end to the telephoto end. Furthermore, in order to achieve a high zoom ratio of a zoom lens, it is preferable to also increase the magnification of the focus lens group when changing the magnification. In consideration of the above, in this embodiment, the imaging magnification βF is set to satisfy 1βF+>1 (2).

In other words, the refractive power arrangement of each lens group is set so that the focus lens group is moved toward the image plane when focusing from an object at infinity to a close object.

Next, the technical meaning of the fifth group arranged closer to the image plane than the focus lens group in this embodiment will be explained.

Now, if the focal lengths of the lens groups placed closer to the object side than the focus lens group are f and B, the focal length 11F of the entire system is F −f, B・βF−J , 81++ −BK −=
(3) becomes. In order to achieve a high zoom ratio of a zoom lens, the sensitivity from the wide-angle end to the telephoto end should be mechanically controllable, and the amount of extension of the focus lens group should be minimized, and the sensitivity between the wide-angle end and the telephoto end should be made as small as possible. It is necessary to ensure that the ratio of sensitivity at is not too large. Specifically, this corresponds to when the amount of edge protrusion of the focus lens group to the same object distance at each focal length remains constant or slightly changes.

According to this, the upper limit of the variable power ratio of the focus lens group is controlled. In other words, when there is no lens group on the image side of the focus lens group, it is necessary to increase the zoom ratio of the lens group on the object side of the focus lens group, and the amount of movement for zooming of the lens group on the object side of the focus lens group. It becomes necessary to increase the number of lens groups or increase the number of lens groups. For this reason, in this embodiment, at least one lens group that is movable or fixed during zooming is arranged closer to the image plane than the focus lens group. In this case, the lens group does not necessarily need to be multiplied when changing the magnification, and may be kept fixed as in Example 1 of 3.4.5 degrees.

In order to perform focusing by moving the third and fourth groups in the above lens configuration, the focal length at any zoom position when focusing on an object at infinity must be F.
, the focal length of the entire system at the wide-angle end is F-1 chain point distance @F
Let βF be the total imaging magnification of the third group and the fourth group in
When Z=F/Fw, 1.5<(β F2-1)/Z<6.0
-(4) It is preferable to satisfy the following condition.

Conditional expression (4) is for defining the range of the amount of extension of the third and fourth groups when performing focusing at each zoom position from the wide-angle end to the telephoto end.

If the imaging magnification βF exceeds the upper limit of conditional expression (4) and becomes too large compared to Z, the sensitivity of the focus lens group will increase, the amount of extension will decrease, and the total length of the lens will be shortened, but the focus lens group will not be mechanically adjusted. It becomes difficult to control accurately.

Furthermore, the refractive power of the third group becomes weaker, and the amount of movement of the third group for changing the magnification becomes larger. For this reason, it is necessary to widen the gap between the second and third groups at the wide-angle end, which increases the overall length of the lens and also to secure off-axis rays.

Therefore, the growth efficiency of the first group increases, which is good, but not good.

Furthermore, if the lower limit of conditional expression (4) is exceeded and the imaging magnification βF becomes too small compared to 2, the sensitivity of the focus lens group becomes small and the amount of extension increases. For this reason, a large moving space must be provided, which is not a good idea since the total length of the lens increases.

In this embodiment, in order to further correct aberrations and to downsize the entire lens system, βFw is the imaging magnification of the focus lens group when focusing on an object at infinity at the wide-angle end.
When −2,3< βF, < −L, S
--It is preferable that the following condition (5) is satisfied. .

If the imaging magnification βF exceeds the upper limit of conditional expression (5) and becomes too large, ΔE1 must be increased to obtain a predetermined variable magnification ratio, and the amount of movement of the first group increases, resulting in The total length of the lens increases. Note that the distance between the first group and the second group at the wide-angle end and the distance at the telephoto end is EIw, respectively.
When E1〒, it is expressed as ΔE I=E +t-E +w.

Furthermore, the amount of movement of the fourth group increases, and the sensitivity at the wide-angle end further decreases, and the total length of the lens at the wide-angle end increases.

If the lower limit of conditional expression (5) is exceeded and the imaging magnification βFw becomes too small, the sensitivity increases and it becomes difficult to mechanically control the focus lens group with high precision.

Figure 10 shows that in Numerical Example 1, which will be described later, the object distance is 16 m and 3 (5
FIG. 12 is an explanatory diagram showing the relationship between the horizontal axis and the zoom ratio, respectively, with the horizontal axis representing the amount of movement of the focus lens group when focusing on lens m. As is clear from the figure, as the focal length increases, the amount of extension of the focus lens group for the same object distance increases.

Next, numerical examples of the present invention will be shown. On the right side of Numerical Example 1.2, R・i is the radius of curvature of the first lens surface from the object side, Di is the thickness and air distance of the i-th lens from the object side, and Ni and νi are each from the object side. These are, in order, the refractive index and Abbe number of the glass of the i-th lens.

In Numerical Examples 3 and 4.5, f is the focal locus of the i-th group counting from the object side, and e1' is the principal point interval between the i-th group and the i+1-th group.

Numerical Example I F-35,9FNo・I: 4~5.6 2ω□ 62~
7.2'RI-114,19D I・3.2ON!・1
．． 805+8 ν 1-25.4B2~78.12
02-9.00 N 2-1.43387 C2-
95. IR3--373,4203-0,10 R4-64,29D 4-5.50 N 3-1.4
9782 ν3-66.1R5・166.17 0
5-3.11~37°82~65.11 R6-128,27D 6-2.00 N 4・1.
88300 υ4・40.8R7-24,49D 7
-8.70 R8--67,30D B-2,50N 5 mushrooms 1.84
866 υ5-23.9R9--52,0009-1
,00N 6-1.88300 White ~ 4G, 8RI
O-140,30010-1,00R11=49.
94 011-6.50 87-1.84666 v
7-23.9RI2- -51.67 012-1.
50R13--39, 11013-1, 50N 8・1
．． 88300 Shi8-40.8RI4- 355.4
8 014-49.99-12. Old ~ 4.24 R15 So Aperture 015-17.15 ~ 8.2 ~ 4
．． 1 R+6- 132.71 Di6-4.00 N
9-1.51633 C9-64. IRI7--12
9.59 017 Seal 0.11RI8- 70.70
018-4.21 Nl0-1.5+633 Silo Fable 64. lR19-47461.89 019-0
．． 11R20=50.35 020-5.26 8
11-1.5+533 v I+-64,1R21-
141,76D21-1.03R22=139.5
0 D221-4.13 8+2-1.84666
v 12-23.9R23-39, 61023-3,
10 R24= 173.01 0g4- 4.13
N13-1.511+8 v 13-51.0
R25--122,88025-0,101126・
84.41 D26-4.1:IN+4-1.
51+18 υ14-51.0R27--746,
49027@5.78~:12.79~81.78 828 dew -88,41028-2,988+5-1.
88:100 Shi15-40.8R29-100,
00029-3,86N+6-1.80518 116
-25.4130 seal -345,13D30-43.1
1 ~ 25.14 ~ 22.21 R31-1472, 04031-6, CION17・1
．． 51633 Si17-64. l832--4
0.27 032-0.10n33・93.85
033-5゜00 N18-1.5+118
Sea18-51.0R34--137,58D34-2
．． 94R35--43,03035-2,00N19 So1.80610 19-40.9R35-75,
27036-0,50 R37-124,66037-5,00N20-1.5
1+18 20-51.01138- -71
．． 07 Numerical Example 2 F= 35.7 FNo+-1: 4-5.62ω-
62.6~7.2°Rl” 98.47 01m3.
50 N l-1,76182v 1-26.68
2- 67.90 02-9.42 N 2-1.4
3387 C2-95. IR3--605,8603
-0,10 R4-72,8704 So 5.45 N 3=1
．． 48749 v 3-70.2n 5-30
5.73 05-3.78~38.49~60.78 R6-140,8306・1.66N4・1.8830
0 Shi4-40.8R7-23,3007-8,81 R8--73,1308-2,94N 5-1.846
66 shi5-23.9R9maro-56,0009den 1
．． 37NS Tan 1.88300 ν 6-40.8R
IO-168,81010-0,50R11-45,1
2DI+-6,46N 7 1.84666 ν
7-23.9112 Maro -55,94012-1,
00RI3- -43.88 013・ 1.37
N 8-1.88300 ν 8-40.
8R14-168, 61014 Tan 59.27-12.0
6 ~2.0 RI5- Aperture Di5・7. Old ~6.9 ~5.08 RI6- 106.07 Di6-4.00 N
9 dew 1.49388 ν9-66, IRI7--21
6.52 017-0.11RI8s69.97 01
8-4.21 Nl0-1.51633 v IQ
-64,11119-238,18019-0,118
20-48, 33D20-4. fi5 NIL-1,
51118 Series-51.0R21-421,7102
1-1,03R22-171,33022-4,14N
12-1.84666 12-23.9R23-3
8,23023-3,10 R24-98,49024 4.14 N+3-1.
511+8 νI3・51,0R25−-105,4
5025-0,10R26= 67.88 026-
4.14 N+4=1.51118 v 14m5
1.0R27-419, 54027・5.91~32.
91 ~53.91 828--118.52 028-2.77 N15
I-1,88300V+5-40.8+129-75
．． 00 D29-3.59 816-1.805+8
υ16-25.4R30-1687, 280:10
-49.07~37.0~34.07 R31-223, 38031-7,00N+7-1.5
1118 Shi17~51.0R32--39,620
:12-0.10R33-118,83033・4.5
0 N18-1.511+8 Shi18-51.0R
34--94, 22D34 2.80R35--39,
56035-2,00N+9 proverbs 1.80+00 ν
19-:15.0R36-741, 19036-2,
00R37-86, 71D37-4.00 N20
-1.50137 Shi2O-51i, 4R38-6
8,40 Numerical Example 3 Numerical Example 4 Numerical Example 5 (Effects of the Invention) According to the present invention, when focusing a zoom lens consisting of five lens groups having a predetermined refractive power and a movement trajectory, the above-mentioned conditions are met. By moving the third and fourth groups to satisfy It is possible to achieve a rear focus type zoom lens suitable for a zoom lens having a high zoom ratio with a reduced diameter and a shortened overall lens length.

[Brief explanation of the drawing]

1st. 2 is a sectional view of the lens of Numerical Examples 1.2 of the present invention, 3rd to □, and 7 are paraxial power distribution diagrams of Numerical Examples 1 to 5 of the present invention, and 8. Figure 9 shows numerical example 1 of the present invention.
, 2 is an aberration diagram. In FIGS. 3 to 7, (A) shows the wide-angle end, and (B) shows the telephoto end. 8th. In Figure 9 (
A) shows the aberration at the wide-angle end, (B) shows the aberration at the center of G, and (C) shows the aberration at the telephoto end. , FIG. 10 is an explanatory diagram showing the relationship between the extension amount of the focus lens group and the zoom ratio in Numerical Example 1 of the present invention. In the figure, I, II, III, TV, and V are the first
．． Second. 3rd, 4th. In the fifth group, S is an aperture, ΔS is a sagittal image plane, and ΔM is a meridional image plane. Patent applicant Canon Co., Ltd. Figure 8 Figure 89 Collar 9 Cloth

Claims (1)

[Claims] (1) In order from the object side, the first group with positive refractive power, the second group with negative refractive power, the third group with positive refractive power, the fourth group with negative refractive power, and the positive refractive power. It has five lens groups, a fifth group having a refractive power of By moving each lens group so that the distance between the third and fourth groups increases and the distance between the second and third groups and the distance between the fourth and fifth groups decrease. A rear focus type zoom lens, characterized in that focusing from an object at infinity to an object at a short distance is performed by moving the third and fourth groups toward the image plane side. (2) A rear focus type zoom lens according to claim 1, characterized in that the third group and the fourth group are moved integrally to perform focusing. (3) Focus on an object at infinity. F is the focal length of the entire system at any zoom position when zooming, F_w is the focal length of the entire system at the wide-angle end, and βF is the total imaging magnification of the third and fourth groups at the focal length F. and Z=F/F
2. A rear focus type zoom lens according to claim 1, which satisfies the following condition: _w, 1.5<(βF^2-1)/Z<6.0.