JPH0493812A - Variable power lens - Google Patents

Abstract

PURPOSE:To obtain the lens system which has excellent optical performance over the entire power variation range while reduced in overall size by specifying the refracting power and lens constitution of three lens groups. CONSTITUTION:When the power is varied from the wide-angle end to the telephoto end, the respective lens groups I - III are moved to the object side and inequalities I are satisfied. In the inequalities I, elw is the interval between the principal points of the 1st group I and the 2nd group II at the wide-angle end, e2w the principal point interval between the 2nd and 3rd groups I and II, SIGMAD the total lens thickness of the respective lenses, fw the focus curvature of the whole system at the wide-angle end, and Ri a radius of curvature of an (i)th lens surface. Consequently, the number of the lenses is decreased gradually and the lens which has excellent optical performance over the entire power variation range is obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a variable magnification lens suitable for photographic cameras, video cameras, etc., and in particular has a lens group with negative refractive power or three preceding lens groups. The present invention relates to a variable magnification lens having a short overall lens length, a small size, and excellent optical performance, in which magnification is changed by moving these three lens groups.

(Prior art) Conventionally, the lens has three lens groups in order from the object side: a first group with negative refractive power, a second group with positive refractive power, and a third group with negative refractive power. The present applicant has developed a zoom lens in which magnification is changed by moving the lens group, for example, in JP-A-63-27.
This method has been proposed in Japanese Patent Publication No. 1214, Japanese Patent Application Laid-Open No. 64-72114, and the like.

This type of zoom lens is relatively easy to widen the angle of view, so it is often used as a wide-angle imaging system.

In the same bulletin, the first. Second. By moving the third group under certain conditions to change the magnification and by specifying the lens configuration of the three lens groups, a variable magnification ratio with high optical performance that satisfactorily corrects aberration fluctuations associated with changing the magnification. 2-3 times overall 8
A relatively compact zoom lens consisting of ~9 lenses, particularly suitable for lens-shutter cameras, has been achieved.

(Problems to be solved by the invention) The above-mentioned Japanese Patent Application Laid-Open No. 63-27]214 and
[72] In the zoom lens proposed in Publication No. 14, each lens group is composed of two or more lenses, and for example, the total optical length (the 1st 1 Distance from lens surface to imaging plane jI
M) is being shortened.

The present invention utilizes the refractive power arrangement of the zoom lens previously proposed by the applicant, further improves the lens configuration of each lens group,
In particular, an object of the present invention is to provide a variable magnification lens that is suitable for lens shutter cameras, which reduces the number of lenses and has good optical performance over the entire variable magnification range.

(Means for Solving the Problems) The variable power lens of the present invention comprises, in order from the object side, a first group consisting of a negative first lens, a positive second lens, and a positive third lens.
It has three lens groups: a second group consisting of two lenses, and a third group consisting of a negative fourth lens. This is a variable magnification lens that performs focusing by changing the air distance between the two groups, and the distance between the principal points of the first and second groups at the wide-angle end is e1.
w, e2w is the distance between the principal points of the second and third groups, ΣD is the sum of the lens thicknesses of each lens, and fw is the focal length at the wide-angle end of the entire system.
, when Ri is the radius of curvature of the i-th lens surface, 0, 1 < ΣD/fw < 1. 0
---(1) 0.2<e1w/e2w<2.0
It is characterized by satisfying the condition (2).

Alternatively, the present invention provides, in order from the object side, a first group consisting of a negative first lens, a second group consisting of two lenses, a positive second lens and a positive third lens, and a third group consisting of a negative fourth lens. It is a variable magnification lens that has three lens groups, moves the three lens groups to change the magnification, and changes the air distance between the second and third groups to focus. hand,
e1w, which is the distance between the principal points of the first and second groups at the wide-angle end, e2w, which is the distance between the principal points of the second and third groups, ΣD, which is the sum of the lens thicknesses of each lens, and the distance at the wide-angle end of the entire system. When the focal length is fw and the radius of curvature of the i-th lens surface is Ri, 0.1< ΣD/fw <1. 0 ・−・(
1) 0.2<e1w/e2w<2.0...(
2) It is characterized by satisfying the following conditions.

(Example) FIGS. 1 to 4 are lens sectional views of numerical examples 1 to 4 of the present invention, respectively. 1st. FIG. 2 shows the zoom position at the wide-angle end. Third. In Figure 4, (A) is at the wide-angle end, (
B) shows the zoom position at the telephoto end. In the figure, ■ is the first group with negative refractive power, ■ is the second group with positive refractive power, ■ is the third group with negative refractive power, sp is the aperture stop (F number stop), FS
is a flare aperture. Arrows indicate the directions of movement of each lens group, aperture stop, flare stop, etc. when changing magnification from the wide-angle end to the telephoto end.

In the variable power lens according to this embodiment, when changing the power from the wide-angle end to the telephoto end, the zoom lens is moved by moving each lens group toward the object side as shown in each figure. In particular, in this embodiment, the three lens groups are moved independently in the object side direction to effect variable magnification. Further, focusing is performed by moving the third group on the optical axis.

The aperture stop SP is disposed between the second lens and the third lens of the second group, and moves integrally with the second group during zooming.

In Fig. 3, the flare diaphragm FS is placed between the first and second groups, and when changing the magnification from the wide-angle end to the telephoto end, it can be used either integrally with the third group or independently, as shown by the dotted arrow. It is moved towards the object side.

In FIG. 4, a first flare stop FSI is placed between the first group and the second group, and a second flare stop FS2 is placed between the second lens and the third lens. Then, when changing the magnification from the wide-angle end to the telephoto end, the first flare diaphragm FSI is moved integrally or independently with the third group as shown by the dotted arrow, and the second flare diaphragm FS2 is moved by the amount of movement of the second group. It is moved towards the object side.

As shown in FIGS. 1 to 4, the zoom lens of the present invention is composed of three lens groups with negative refractive power, negative refractive power, and negative refractive power in order from the object side. A first group and a third group having negative refractive power are arranged so that the lens structure has a substantially symmetrical lens configuration with a magnification change medium pressure refractive power arrangement.

In particular, a second lens with positive refractive power is placed on the object side across the second group, and a third lens with positive refractive power is placed on the image side, making the lens configuration sandwich the aperture and have a full magnification range. It is constructed so as to be approximately symmetrical as a whole.

By adopting such a substantially symmetrical lens arrangement, chromatic aberrations are corrected in a well-balanced manner for the entire lens system, rather than using the conventional method of correcting chromatic aberrations within each lens group. In other words, the aberrations of the three lens groups cancel each other out.

By satisfying at least one of the above-mentioned conditional expressions (1) and (2) and conditional expression (3) or conditional expression (4), aberration fluctuations can be reduced over the entire zoom range and good optical performance can be obtained. There is.

Next, the technical meaning of each of the above conditional expressions will be explained.

Conditional expression (1) is used to appropriately set the sum of the thicknesses of the four lenses when a variable power lens with a three-group configuration is constructed of four lenses as a whole. If the total lens thickness exceeds the lower limit and becomes too thin, it becomes difficult to maintain a good area density of each lens surface, and if it exceeds the upper limit and becomes too thick, the entire lens system becomes large.

Conditional expression (2) concerns the paraxial refractive power arrangement of each lens group at the wide-angle end when a variable power lens is constructed from three lens groups with negative, positive, and negative refractive powers, and is mainly concerned with miniaturization of the entire lens system. This is to facilitate correction of various aberrations while aiming at the following. If the lower limit is exceeded, the back focus at the wide-angle end becomes short and the effective diameter of the fourth lens increases. On the other hand, if you exceed the upper limit, the hack focus will become longer than necessary and the overall length of the lens will become longer, which is not good.

Conditional expression (3) relates to the lens shape of the negative first lens and is mainly intended to satisfactorily correct spherical aberration. If the lower limit is exceeded, many higher-order spherical aberrations occur, and aberration fluctuations due to changes in surface shape become large. Conversely, when the upper limit is exceeded, spherical aberration becomes under-corrected over the entire zoom range.

Conditional expression (4) relates to the lens shape of the negative fourth lens, and is mainly intended to satisfactorily correct off-axis aberrations over the entire zoom range. When the lower limit value is exceeded, astigmatism increases, and when the upper limit value is exceeded, the meridional image surface becomes overcorrected.

In addition, in particular, in the variable power lens of the present invention, in order to keep the Petzval sum at an appropriate value and to satisfactorily correct the field curvature, when the refractive index of the material of the first lens and the fourth lens is Nl and N4, respectively, It is good if at least one of the following conditional expressions is satisfied.

1.57<Nl (5)1.
72<N4 ・・・・・・・・・(6) Conditional expression (
Anything outside of 5) or (6) is not good, as both result in field curvature or overcorrection.

In the present invention, in order to reduce the weight of the entire lens system, for example, the positive third lens may be made of a plastic material. At this time, in order to prevent changes in imaging performance such as focus movement due to changes in ambient temperature, when the focal length of the third lens is f3, 1 < f 3 / f w < 15 ・----
--- It is preferable to set it as shown in (7).

If the lower limit of conditional expression (7) is exceeded and the positive refractive power of the third lens becomes too strong, focus movement due to temperature changes will increase and the lens barrel structure will become complicated. Conversely, if the upper limit is exceeded and the positive refractive power of the third lens becomes too weak,
This is not good because a lot of spherical aberration occurs from the entire second group.

In the present invention, in order to reduce aberration fluctuations over the entire magnification range and obtain good optical performance, at least one lens surface of the first lens is provided with an aspherical surface whose negative refractive power becomes stronger toward the lens periphery. It is good to apply. Alternatively, at least one lens surface in the second group may be provided with an aspheric surface whose positive refractive power becomes weaker toward the lens periphery.

The variable power lens of the present invention has a 1° angle, a 2° angle, and a 2° angle, as shown in FIGS. Although each of the third groups is independently moved toward the object side, the movement method is not limited to this, as long as a magnification is changed and an in-focus image is obtained as a result.

Figures 9 (A) and (B) are the same strains as Figures 1 to 4; Second. This shows a state in which the third lens group is moved independently to change the power from the power change position z1 to the power change position Z2.

At this time, for example, as shown in FIG. 10 (A) and (B), the first group is moved independently, and the second and third groups are integrally moved toward the object side, and the second group is moved to the variable magnification position z2. Move it to the corresponding position. The third focusing group is moved to correct the focus position fluctuation that occurs at this time, as shown in Figure 10 (C
). The resulting optical arrangement may be the same as the optical arrangement shown in FIG. 9(B). Furthermore, the movement of each lens group during zooming from the zooming position z2 to the zooming position z1 is completely opposite to that described above.

In addition, as shown in FIGS. 11(A), (B), and (C), from the zooming position Z2 to the zooming position z, with the zooming position z2 as a reference.
When changing the magnification to 1, the N3 group is moved independently and the first group and the second group are integrally moved toward the image plane as shown in FIGS. It is moved to a position corresponding to double position Z1. The second focusing group is moved to correct the focus position fluctuation that occurs at this time, as shown in Figure 11 (
Set as shown in C). As a result, Figure 9 (A, )
The optical arrangement may be the same as that of . Furthermore, the movement of each lens group during zooming from the zooming position z1 to the zooming position z2 is completely opposite to that described above.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness and air distance from the object side, Ni
and νi are the refractive index of the i-th lens and a number corresponding to each other in order from the object side.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis,
The traveling direction of the light is positive, R is the paraxial radius of curvature, A, B, C,
When D and E are each aspherical coefficients, it is expressed by the following formula: +DH8+EH''.

Further, Table 1 shows the relationship between each of the above-mentioned conditional expressions and various numerical values in the numerical examples.

Numerical Example f-39,3~67.6 2ω・57.7°~35.5°FNO F1 Near, 0~11.5 Numerical Example 2 f・39J3~67.8 2ω-57,6' ~35.4゜*Rl--44,33 R2-456,87 R3-29,92 R4--29,45 R5・(Aperture) R8--98,00 *R7--30,95 R8--48 ,36 R9-45,85 DI-1,20 D2・Variable D 3-4.00 D 4= 2.43 D 5-5.05 D 6-3.00 D7・Variable D 8-2.0O N I-1,58306v N 2-1.49700 ν N 3-1.4917] ν N 4-1.78590 v 1-30.2 2-81.6 3=57.4 4-44.2 Umbrella RI- -51,31 R2~-384,19 R3 consideration 30.19 R4 proverb -28,23 85・(aperture) R6--8:1.82 Book R7--34,70 R8--42,40 R9-59 ,99 DI-1,20 D2/Variable D 3-4.00 D4 jump 1.09 D5/7.73 06 Rin 3.00 D7/Variable D 8-2.00 FNOI: 5.8-9.7 1-1.69895 N 2~1.4970Q N 3・1.49171 N 4-1.78590 1-30.1 2-81.6 3-san 57.4 4-44.2 R1 surface: Aspheric coefficient A -OB--2,6+3x 10-' D-6,892x 10-" R7 surface: ltospheric coefficient A-OB-2,485x 10 G--8,458X 1O-9 C= 2.16]X 10 R1 surface: Aspherical coefficient A-OB--2,079X 1O-5 D--4,861x10-1 R7 surface: Aspherical coefficient ^-OB・2.627X 1O-5 D-3,187x 10-" C= 2.835X 10-8 9.850X 10-8 Numerical example f-39,19~70.0 2ω-57,8°~34.3" FNO~1:5.8 ~10°0 R8 surface :Aspheric coefficient A-OB-2,672x 1O-5 D-3,187X 10 C~1.021X 10 *R]--5], +2 R2-4]3.89 R3-Flare diaphragm R4-30, 29 R5--28,23 R6-(aperture) R7--83,58 Main R8--34,61 R9--42,16 RIO-59,37 1. 1.20 2. Variable 3 = Variable 4- 4 .00 5~1.17 6-7.80 7-3.00 8.Variable 9-2.0O N I-1,68893ν N 2-1.49700 ν N 3・1.49]71 ν N 4 1.78590 ν R1 surface: Aspheric coefficient A-OB--2,14]x 10-' D--4.861x 10-" -1-31.1 2-81.6 Numerical Example 3 Proverb 57. 4 f-39,32~74.0 2ω~ 57.6°~32.6°FNO-1:5.0 *R]--53,43 4-44,2 R2-658,93 R3-1st Flare diaphragm R4-30,60 85--27°87 R6-(diaphragm) R7-2nd Flare diaphragm R8--82,18 19~-37,49 RIO--37,66 Rli-70,06 D ]- 1,20 D2/Variable 3-Variable 4-4.00 5-1.51 6-Variable D7/Variable D 8-1.50 D9-Variable DIO-2,0O 1-1,69895 2 1.49700 3 -1.49171 4-1.78590 2.000X 10"" 1-30.1 2 San81.6 3-57.4 4-44.2 Table-1 R1 surface: Aspheric coefficient A-OB--2 ,075xlO-5 D--2,222X 10-" R9 surface: Aspheric coefficient ^-OB-2,704x 1O-5 D-4,303x 10-" C--3,025x 10-8 -9.656x 1O-8 (Effects of the Invention) According to the present invention, as described above, by specifying the refractive powers and lens configurations of the three lens groups, the entire lens system can be miniaturized and the entire zoom ratio can be adjusted to about 2. A variable power lens having good optical performance over a wide range can be achieved.

[Brief explanation of the drawing]

Figures 1 to 4 are cross-sectional views of lenses of numerical examples 1 to 4 of the present invention, and Figures 5 to 8 are lens sectional views of numerical example 1 of the present invention, respectively.
4 to 4 and FIGS. 9 to 11 are explanatory diagrams showing the moving states of each lens group of the variable power lens of the present invention. In the lens cross-sectional diagram, I, II, and III are the first, second, and third groups in order, and the arrows indicate the movement direction of each lens group during zooming from the wide-angle end to the telephoto end, and in the aberration diagram (A
), (B), and (C) are aberration diagrams at the wide-angle end, middle, and telephoto end, respectively; d is the d-line, g is the g-line, S and C are the sine conditions, S is the sagittal image plane, and M is the meridional image. It is a surface. Figure (A) Figure (A) Figure (A) Figure (A) Figure (A) Figure (A) Figure (A) Figure (A) Figure (A)

Claims (1)

[Claims] (1) A first group consisting of a negative first lens in order from the object side;
It has three lens groups: a second group consisting of two lenses, a positive second lens and a positive third lens, and a third group consisting of a negative fourth lens. A variable magnification lens that performs magnification and focuses by changing the air distance between the second and third groups, the distance between the principal points of the first and second groups at the wide-angle end being e1w. , the distance between the principal points of the second and third groups is e2w, the sum of the lens thicknesses of each lens is ΣD, the focal length at the wide-angle end of the entire system is fw, and the radius of curvature of the i-th lens surface is Ri. A variable magnification lens that satisfies the following conditions: 0.1<ΣD/fw<1.0 0.2<e1w/e2w<2.0 -6<(R2+R1)/(R2-R1)<6 . (2) a first group consisting of a negative first lens in order from the object side;
It has three lens groups: a second group consisting of two lenses, a positive second lens and a positive third lens, and a third group consisting of a negative fourth lens. A variable magnification lens that performs magnification and focuses by changing the air distance between the second and third groups, the distance between the principal points of the first and second groups at the wide-angle end being e1w. , the distance between the principal points of the second and third groups is e2w, the sum of the lens thicknesses of each lens is ΣD, the focal length at the wide-angle end of the entire system is fw, and the radius of curvature of the i-th lens surface is Ri. It is characterized by satisfying the following conditions: 0.1<ΣD/fw<1.0 0.2<e1w/e2w<2.0 -0.5<(R8+R7)/(R8-R7)<1.1 variable magnification lens.