JPS61138227A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a compact, high-power zoom lens by dividing the 2nd lens group into a lens group 2-1 with a stop and a lens group 2-2, and moving the lens group 2-2 to an image plane side for the 2nd power variation. CONSTITUTION:A zoom lens has the 1st lens group I with negative refracting power and the 2nd lens group II with positive refracting power successively from the object side; the gap between both lens groups I and II is varied for the 1st power variation and the 1st lens group I is moved for focusing. An infinite-distance object is focused through the 1st lens group I at the wide-angle zooming end. The 2nd lens group II is divided into the 2-1 lens group IIa with the stop and the 2-2 lens group IIb and at least the 2-2 lens group IIb is moved toward the image plane side for the 2nd power variation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, and more particularly to a high-power zoom lens suitable for isobaric still cameras, cine cameras, and video cameras.

Recently, zoom lenses with high zoom ratios have been required not only for high-end cameras but also for general cameras. For example, K, which aims to increase the magnification of a zoom lens, increases the amount of movement of the variable magnification lens group9.
Another method is to strengthen the refractive power of the variable power lens group or increase the number of movable lens groups in the variable power lens group.

However, these methods have drawbacks such as the total length of the lens becomes long and it is difficult to perform good aberration correction. For example, in Japanese Patent Application Laid-Open No. 53-34539, there are two lens groups, a gi lens group with negative refractive power and a second lens group with positive refractive power, in order from the object @, and the distance between both lens groups can be changed. A so-called two-group zoom lens that performs variable magnification.
Then, the second lens group is divided into three lens groups with positive, negative, and positive refractive powers, and the negative lens group is moved relative to the two positive lens groups to achieve a high zoom ratio. Nine zoom lenses are disclosed.

However, in this method, when performing thermal point alignment with the first lens, the lens outer diameter of the first lens group is increased to allow the light beam from the closest object distance to enter the first lens group without clanking at the wide-angle end zoom position. Moreover, the overall length of the lens also tended to be longer.

An object of the present invention is to provide a compact zoom lens with a high zoom ratio.

The main feature of the zoom lens for achieving the object of the present invention is that it has two lens groups, a first lens group with a negative refractive power and a second lens group with a positive refractive power, in order from the object side. A first magnification change is performed by changing the interval between the lens groups, and the details of the second lens are set at the wide-angle end ox-5 position on a zoom lens that performs focusing by moving the first lens group. Focusing on a finite-distance object in a state of mind, dividing the second lens group into a 2-1 lens group having an aperture and a 2-2 lens group, and moving the 2-2 lens group toward the image plane side. In particular, the second change in magnification was performed when the image was moved.

Next, features of the zoom lens of the present invention will be explained using the respective figures.

First of all, Figure 1 shows the conventional 2! A schematic diagram of a thin paraxial arrangement of an Flk zoom lens is shown. In the figure, ■ indicates the first lens group with negative refractive power, ■ indicates the second lens group with positive refractive power, and W and T indicate the zoom position at the wide-angle end and telephoto end, respectively, and can be changed by moving as shown by the arrows. We're doing double that. In order to achieve a high zoom ratio on the wide-angle side in a two-group zoom lens, it is sufficient to increase the amount of movement of both lens groups as shown by the dotted line in the figure. However, as the amount of lens movement increases, the total length of the lens increases, and the distance between the first lens group and the 22nd lens, which often has an aperture, increases. Since the NO. diameter of each lens must be increased by 7, it becomes difficult to make the zoom lens smaller.

FIG. 2 is an explanatory diagram of the optical path of off-axis rays leading to the maximum image height when focusing is performed by moving the first lens of the conventional 21FF zoom lens.

In FIG. 1 IC, for simplicity, the aperture is made to coincide with the principal plane of the second lens I. As is clear from the figure (when the first lens group K is extended as shown by the dotted line and focused from infinity to a short distance, the light aS at the maximum angle of view for an object at infinity is
1. Determine the diameter of the first lens by ensuring the maximum angle of view of light a52t for a close object. In particular, in many cases, the diameter of the first lens group I is determined by securing the light ray S2 at the maximum angle of view of a close object at the zoom position at the wide-angle end. Rather than employing the above-described configuration, the present invention aims to reduce the increasing diameter of the first lens group as much as possible when expanding the zoom range from the wide-angle end zoom position in the first zoom range to an ultra-wide angle. This makes it possible to achieve a high magnification ratio by making the lens small.

FIG. 3 shows a schematic diagram of an embodiment of a thin paraxial arrangement of a zoom lens according to the present invention. ■ In the same figure.

The lenses are the first and second lens groups with negative and positive refractive powers, respectively.
is the 2-1st vy tin group, Ib is the 2nd-2nd vy tin group, S is the aperture, W and T are the zoom positions of the wide-angle layer and the telephoto end, respectively, and WW is the zooming further from the wide-angle end W to the wide-angle end. The zoom position at the super wide-angle end, region C1B, indicates the first and second zooming ranges, respectively.

The first magnification change is performed by integrally moving the first lens group (2) and the second lens group IIf having an aperture within the region C. Focusing is also performed by moving the first lens group l.

Next, the zoom position AC at the wide-angle end W, and the ultra-wide angle ym of wide-angle A
When performing the second magnification change to WW, extend the second lens detail I to focus on a finite distance object, and use the $2-2 lens group I.
Ibt-Move to the image plane side. At this time, the details of the 2-1 lens are fixed.

At this time, the finite distance object that was in focus changes, and the image plane position is set so that, for example, an object at infinity is in focus.

FIG. 4 shows a paraxial optical arrangement and an optical path diagram of off-axis rays at the ultra-wide-angle end ww tc when the second magnification is changed.

2-1 lens group 11 having an aperture at 8g2 variable power
Rather than leaving m on the object side, the 2-1st lens group (
Light rays from an object at an infinite distance and a short distance object pass through the center of M and S, compared to the case where 1 m is moved as one, and the first lens group of S2! The first step is to lower the shooting height of each
We are working to reduce the diameter of the lens group.

Note that when performing thermal point alignment from an object at infinity to an object at a finite distance at the super wide-angle end WW, the 2-2nd lens detail ib may be moved toward the object side.

Even in this case, the light ray that enters the highest position on the optical axis of the first lens group IK is an off-axis ray from an object at infinity. Therefore, by reducing the height of the light beam incident on the first lens group I at the ultra-wide-angle end as in this embodiment, it is possible to efficiently downsize the zoom lens.

In this way, if you secure off-axis rays from an object at infinity at the ultra-wide-angle end, even if you move the 2nd-2nd lens group to adjust the focus, the maximum off-axis ray will remain between the wide-angle end W and the ultra-wide-angle end WW. Sufficient light can also be secured.

In this example, in the first zooming, two lens groups are moved to reduce aberration fluctuations in each lens group, especially aberration fluctuations on the telephoto side, and in the second zooming, two lens groups are moved. The simple structure of dividing the lens into two groups and moving one of them reduces aberration fluctuations caused by each lens group. 5Z-, which has an aperture in the second magnification changer.
By fixing the T lens group, fluctuations in off-axis aberrations can be reduced compared to K.

In this example, the row in which the 2-2nd lens group is moved in the second magnification change to conveniently use only the zoom position at the ultra-wide-angle end is shown, but the 2-2nd lens group and the 1st lens group or the 2nd
-Move the 1st lens group and use any zoom position of the 2nd magnification variable from K! 5tC may be used.

Although the object of the present invention is achieved with the above configuration, it is also desirable to further downsize the zoom lens and reduce aberration fluctuations during the first and second magnification changes to achieve good aberration correction. It is preferable that the following conditions be satisfied.

The focal length at the wide-angle end and the telephoto end in the first variable magnification are respectively /w, fT, the focal length at the super wide-angle end in the second variable magnification is f, the focal length S of the first lens group is f The focal lengths of the 2-1 lens group and the 2-2 lens group are respectively 'la ``Ib ' The resulting magnification of the second lens group at the telephoto end of the first variable power is β2T % The focal length of the second lens group at the telephoto end of the first variable power is When the distance between the 1st lens detail and the 2nd lens group is 4q, and the equivalent V value of the 2-1st lens group is V, then 1a /W < 11. l < a85 fT ・
・−= (1) 0 (/4 < 02 fw−−−−−
−・−+211<1βzT+ (z −・
...-...(3)"/W</'ww≦fg
・-=・(4) 0 (fIN, X, fIN,
-----------f5) 5 degrees. ,
...--(It is set as 71.

Conditional expression (1) is a condition for limiting the refractive power, that is, the focal length of the first lens group. When the upper limit is exceeded, the amount of extension when focusing with the first lens group increases, and when securing off-axis light #lt- at the wide-angle end for close-range objects,
The diameter of the front lens increases. Also, when changing the magnification from the wide-angle end to the ultra-wide-angle end, the amount of movement of the first lens group increases, and in order to secure off-axis light at the ultra-wide-angle end, the diameter of the first lens group increases. come. If the lower limit l[t- is exceeded, the refractive power of the first lens group becomes too strong and the fluctuation of spherical aberration at the telephoto end increases. Furthermore, distortion is insufficiently corrected at the wide-angle end and the ultra-wide-angle end, and it becomes difficult to correct it satisfactorily.

Conditional expression (2) relates to the V-lens spacing between the first lens group and the second lens group at the telephoto end.

If the upper limit is exceeded, unnecessary space will increase at the telephoto end (at the wide-angle end), the distance between the first lens group and the second lens group will increase, and the distance between the first lens group and the second lens group will increase to ensure off-axis rays. The diameter increases. Also, if the lower limit is exceeded, the first lens group and the second lens group will interfere with each other, which is not preferable.

Conditional expression (3) defines the magnification at the telephoto end of the second lens group, which mainly performs the zooming action in the first zooming. Exceeding the upper limit means that the magnification at the telephoto end of the second lens group deviates by a large amount from the same magnification (βv-1).
The aberration fluctuations caused by the second lens group are very large), and the spherical aberration fluctuations especially at the telephoto end become large. When the lower limit is exceeded, the second lens group and the first
The amount of movement of the lens group becomes large, and as a result, the distance between the first and second lens groups at the wide-angle end becomes large (for the reason mentioned above), and the diameter of the front lens becomes large.

Conditional expression (4) defines the focal length of the entire system at the wide-angle end and the ultra-wide-angle end. The upper limit value indicates the starting point for changing the focal length at the wide-angle end of the present invention. The lower limit value indicates the relationship between the focal length of the wide-angle end of the normal zoom range and the ultra-wide-angle end according to the present invention, and if this value is exceeded, it is necessary to secure a ray of light with the maximum angle of view that will fall to the ultra-wide-angle end for an object at infinity. This is not preferable because it becomes extremely difficult to do so and causes an increase in the diameter of the front lens.

Conditional expressions (51, +61 are conditions for dividing the second lens group t into two lens groups.

Conditional expression (5) is a condition for dividing the f142 lens group into two lens groups, both of which have positive refractive power.

If the 412-1 lens group has a negative refractive power, the lens diameters from the 2-2 lens group onward will increase, and the fluctuation of spherical aberration on the telephoto side will increase. Furthermore, if the 2-2nd lens group has a negative refractive power, it is not preferable that the 2nd-2nd lens group will not change its magnification even if it is moved toward the image side when transitioning from the wide-angle end to the super-telephoto end.

Conditional expression (6) relates to the division of refractive power when the second lens is divided into two lens groups. If the lower limit is exceeded, the refractive power of the 2nd-2nd lens group will be weaker, and the amount of movement of the 2nd-2nd lens group will increase when transitioning to the ultra-wide-angle end, and the Lens length becomes longer. If the upper limit is exceeded, the refractive power of the 2nd-1st lens group will be too weak, and the height of the axial rays incident on the 2nd-2nd lens group will increase, resulting in large fluctuations in spherical aberration at the telephoto end. It's coming. Also, at the ultra-wide-angle end, the 2nd-2nd lens, which has a strong refractive power, moves away from the aperture, so the fluctuations in the curvature of field become large.

Conditional expression (7) is a condition for correcting chromatic aberration. If color correction is performed in the normal zoom range and set to the ultra-wide-angle end, the lateral chromatic aberration at wavelength gM will be overcorrected.

Therefore, in order to correct the overcorrection of the color of the magnification of the wavelength g line due to the movement of the 2-2 lens group, the color correction in the 2-2 lens group is over-corrected in the 2-1 lens group, and the color correction is overcorrected in the 2-1 lens group. The 2-2 lens group may be undercorrected. Conditional expression (7) appropriately performs the above viewpoint LFJ color correction.

Next, FIG. 5 shows a developed view of cam grooves provided in the cam barrel of the lens barrel for moving each lens group in this embodiment row. In the figure, 11 + 12 and 13 are cam grooves for the first lens group, 2-1 lens group, and 2-2 lens group, respectively, and an actual cam barrel has three cam grooves like this. 3
It is a set. W, T, and WW are the same as those explained in FIG. 3 and 9. Area C is the area of the first magnification change, B
The area CB is an area for the second variable power, and the area CB is an area for moving the first lens group and smoothly transitioning each lens group from the first variable power to the second variable power.

In region C, the 2-1st lens group and the 2-2nd lens group move integrally, so the cam grooves 12 and 13 are parallel. The cams @12 and 13 are linear or non-linear. Although the cam groove 11 for the first lens group is non-linear, it may be linear if the cam grooves 12 and 13 are non-linear.

In region B, the cam groove is configured such that the first lens group and the 2-1st lens group are fixed on the optical axis, and the 2-2nd lens group moves toward the image plane side.

It should be noted that during the second zooming, the first lens group is extended to a finite distance object, so a cam groove l] is formed so that the first lens group moves along the optical axis between regions CB.

By providing such a region CB, it becomes easy to control the amount of extension of the first lens group during the second magnification change.

Note that between the regions C1, the 2-1st lens group and the 2-2nd lens group may be fixed on the optical axis or may be moved.

The cam grooves 11 and 12 are made non-linear between the regions 8, for example, S
By moving the first lens group and the second-first lens group to control the position of the diaphragm near the wide-angle end and the telephoto end, the distortion and aberration fluctuations of the first lens group are controlled. It's okay.

FIG. 6 is a developed view of the cam grooves of the modified row of FIG. 5. FIG. In the figure, w', 'r', and ww' indicate the wide-angle end, telephoto end, and ultra-wide-angle end, respectively. Further, 21 is a cam groove of the first lens group, and 22 is a cam groove of the 2-1st lens group and the 2-2nd lens group.

The first lens group and the 2-1st lens group are in areas C and CB.
, Bt-, and the second-second lens group is in the area CI, C/
The first and second magnification changes are performed using B/ and B/, respectively.

During the first transformation, the first lens group moves from W to T in area C, the 2-1 lens group moves from W to T in area C, and the 2-2 lens group moves from W' to W' in area Cl. Move to T'.

During the second magnification change, the first lens group is in the area Bl, $2-1
The lens group uses area B', and the 2-2nd lens group uses area B'.

Also, in order to smoothly transition the details of each V lens from the first variable magnification to the second variable magnification, as shown in FIG. For details, area C'B
'I will set up each.

According to the embodiment shown in FIG. 6, the movement of the different moving lens groups, ie, the 2-1 lens detail and the 2-2 lens group, can be controlled by a single cam groove in the 181-trajectory portion, and the mechanism is simplified. can be achieved.

In the embodiments shown in FIGS. 5 and 6, the cam #II may be configured to move the first lens group toward the object side at the ultra-wide-angle end WW. This is preferable because the luminous flux can be easily secured. In addition, the cam grooves in area B in FIG. 5 and area B' in FIG.
The diameters of the first lens group and the first lens group may be controlled.

The above implementation row describes a zoom lens having two lens details 1 and 1, but when changing the magnification, a movable or fixed tIIE3v nozzle is placed at the image plane VK of the second lens group and the same procedure is performed. The objectives of the present invention can be achieved.

Next, numerical examples of the present invention will be shown. B in numerical examples
1 is the curvature half set of the first lens surface in order from the object side, D
l is the first lens thickness and air distance from the object side, Nl
and vi are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

In numerical value implementation row 1.2, the third lens group, which is fixed during zooming, is arranged on the image plane side of the second lens group to better correct the aberrations of the entire screen.

Numerical implementation sequence I F-2487~29.0~53.8 FNO-1:
, i52ω-82σ~737~4&t R1= 11494- 0 1-124
N 1-L 65844 w 1-50.9R
2-61L 88 D 2-a2R3-170,8
8D 3-L 43 N 2=L 8061
y 2-4a 9R4-L&Q9D←&78 R5-111L 08 D 5-1.28 N 3
=1.804 y 3=4a 6R6 thin 3L 99
D 6-201 R7-26, 53D7-149 N 4-L 8
0518 ν 4 fog 2 rods 4R8-72, 71D
IS-09 R9-95,5909=Z6 N5=1.60311
y5=6a7RIO--5L 13 01G-
L 45R11-(Squeeze) Dll-R1 to IJL 39 D12ml ON 6-L
713 v 6-5 & 8R13-67,05
Dl3-44 R1←-4& 06 014-& 8 N 7
-L 84666 y 7-219R1 2α8
4 Dis-L 4R16-19413D16=L
7 N 8-L 62004 w 8-
3a 3R17--5a 09 017-0.1R1
8-145,47DlB-17N 9=L 62004
y 9-31L 3R19--2a 33
DlG-variable R2G-47,18D2G-L 5
NIO Akebono L 48749 ν1O-7(L
2R21-3 78 /1--3&5 /Ia-sa61 / l1b-
6L37β2T--L27 Numerical implementation fI12? -2 Tables 35-29-53 λ for F'NO-
52ω-8&τ~7&I~47.4゜R1-11168D1-λ24 N 1-L 65
844 Shi1-5α9FL 2-57a 19
D 2-0.20R3-33G, 80 D
3=L 43 N > L 80610 v
2→α9R4-19,42D4-&7B R5= 20L 07 D 5p=L 28
N 3=L 80400 v 344
6R6-3440D6426 R7-2&20 D7-&49 N4”L
80518 y44&4R8-141,780
8-J & R9= 21a 94 D h2.60 N S=
L 65844 y 540.9R1O--31,
94010-L 00 N←1゜76182
v 6=2a 6R11--5&00 Dl
l-L4GR1 (aperture) D13-variable R13m 2 & 17 Di3- & Go
N? -L 65844 v 7-5α9R
14-546ff 014-alGR15= 1
& 57 D15=L Do N 8=L 5
6013y 8-47. OR1← 67.65
DI reward 3L15R17--89,60017-&
80 N to L field 66 ν9→λ9R18-
1&44 018-L70 R19-70,89019-470Nl0-L 647
69 Shi10-3λ8R2G--23L 56
D2G-Variable R21-5132D21-1.50 R22 3&26 f□--3&5 7 II, -77,17lIb-
50,4βzT--1,25 In numerical examples 1 and 2, in order to achieve good aberration correction over the entire zoom range, the first lens group t? E, 11th, 12th, negative, negative and positive refractive power;
Consists of four lenses, the 13th and 14th lenses, and the 2nd -
1 lens details: Single or laminated f with positive refractive power
421 lenses, the 2-2nd lens group is made up of three or four lenses with positive, negative, positive or positive, positive, negative, and positive refractive powers, and the third lens group has a convex surface toward the object side. It is preferable that the lens be constructed of a meniscus-shaped 31st lens having a refractive power of a tiger fish.

In particular, by making the 12th L/lens and the 13th lens a meniscus shape with negative refractive power with convex surfaces facing the object side, and making the @0 lens a biconvex lens, negative distortion on the wide-angle side is better corrected than K. are doing.

Further, by making the 14th lens a meniscus shape with a positive refractive power with a convex surface facing the object side, spherical aberration can be corrected better than K.

Regarding the details of the 2-1 lens, six lenses may be used as a single lens, but it is preferable to use a combination of lenses because chromatic aberration can be corrected satisfactorily over the entire zoom range. Since the 31st lens has a meniscus shape with a negative refractive power, the curvature of field of the entire screen is reduced compared to K.

Note that during the second magnification change, the first lens group is moved toward the object side by 8.4 and &9 degrees in Numerical Examples 1 and 2, respectively, but the amount of movement at this time is less than half the focal length at the wide-angle end. This is preferable in order to keep the diameter of the first lens group small.

In this embodiment, if the entire second lens group is moved toward the object side at the wide-angle end zoom position, macro photography can be performed while maintaining good aberrations.

As described above, according to the present invention, it is possible to achieve a compact zoom lens having a first variable power and a second variable power and a high variable power.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams of a thin paraxial arrangement of a conventional two-group zoom lens; Figures 3 and 4 are explanatory diagrams of a thin paraxial arrangement of a zoom lens of the present invention; FIG. 6 is an explanatory diagram of one embodiment of the cam groove when moving the lens group according to the present invention, and FIGS. 7 and 9 are numerical embodiments 1 and 2 of the present invention, respectively.
8 and 10 are aberration diagrams of numerical embodiments i and z of the present invention, respectively. In Figures 8 and 10 ^), (B), (C)
, CD) are various aberration diagrams at the ultra-wide-angle end, wide-angle end, intermediate, and telephoto end, respectively. In the aberration diagram, ΔS is the sagittal image plane, and 6M is the meridional image plane. Figure 1 Hem 3 ■ 夷 4 Figure 5 Notebook Φ Diagram JNJxie 9, 'Ill' (jl
tlEνm (%) Note δ Illustration Note 10

Claims (1)

[Claims] (1) It has two lens groups, a first lens group with negative refractive power and a second lens group with positive refractive power, in order from the object side, and performs the first magnification change by changing the interval between both lens groups, In a zoom lens in which focusing is performed by moving the first lens group,
At the wide-angle end zoom position, the first lens group is focused on a finite distance object, and the second lens group is composed of two lenses, a 2-1 lens group and a 2-2 lens group, each having an aperture. The second lens group is divided into groups and moved at least the 2-2nd lens group toward the image plane side.
A zoom lens characterized by variable magnification.