JPH0389309A - Zoom lens - Google Patents

Abstract

PURPOSE:To enable the zoom lens whose variable power ration is 3 - 3.5 folds to give a high performance and to miniaturize it by constituting it of three lens groups, and specifying image forming magnification of a telephone end of a second lens group and image forming magnification of a telephoto end of a third lens group. CONSTITUTION:The zoom lens consists of a first lens group 1 having positive refracting power, a second lens group 2 having negative refracting power, and a third lens group 3 having positive refracting power, and at the time of variable power extending from a wide angle end to a telephoto end, it is executed by moving a second lens group and a third lens group to an image surface side and an object side, respectively, and when photographing magnifications in the respective telephoto ends of a second lens group and a third lens group are denoted as beta2T and beta3T, respectively, expressions I, II are satisfied. In this case, at the time of zooming extending from the wide angle side to the telephoto side, each lens group is moved so that moving local of a second lens group 2 and a third lens group 3 are drawn on an optical axis in the reverse direction and while allowing each moving lens group to share variable power, a high variable power ratio is obtained. In such a way, while miniaturizing the whole lens system, and also, by correcting aberration fluctuation at the tie of varying power, a high optical performance can be maintained extending over the whole variable power range.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a zoom lens, and is particularly suitable for photographic cameras, video cameras, etc., and is capable of achieving miniaturization while maintaining a high zoom ratio and good optical performance. Regarding the zoom lens.

[Prior art]

Conventionally, as a zoom lens that can obtain a relatively high zoom ratio, the zoom lens system 4 is composed of lens groups, and during zooming, the second lens group moves on the optical axis to change the magnification, and the third lens group moves on the optical axis to change the power. A zoom lens is known in which a lens group moves on an optical axis to perform image plane correction. -Example: Tokuko Sho 39-6
Publication No. 128, Special Publication No. 39-13841, USP
There are 2.847, 907, etc. These eliminate aberration fluctuations caused by zooming in the 1st degree 2.3 lens group,
Aberrations that do not depend on zooming, so-called bias component aberrations, are fixed during zooming, and are corrected by the fourth lens group, which mainly performs an imaging function. In this way, a zoom lens with a four-lens group configuration can relatively easily correct aberrations, but on the other hand, because the fourth lens group relays the image plane to the rear,
It had the disadvantage of being longer in overall length. Furthermore, since the diaphragm is generally placed in front of the fourth lens group, the diameter of the front lens also increases.

On the other hand, for example, in Japanese Patent Publication No. 58-32684, the structure is composed of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. discloses a relatively compact zoom lens. The zoom lens proposed in the publication has a variable power ratio of only about 2.5 times.

[Problem that the invention seeks to solve]

The present invention is composed of three lens groups as a whole, and solves the problem of large fluctuations in aberrations when achieving a high variable power ratio of about 3, thereby reducing the size of the entire lens system. It is an object of the present invention to provide a zoom lens that maintains high optical performance over the entire zooming range by properly correcting aberration fluctuations during zooming.

[Means for solving problems]

The zoom lens of the present invention has, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, and from the wide-angle side. When changing the magnification toward the telephoto side, the second lens group is moved toward the image side and the third lens group is moved toward the object side, and the second lens group and the third lens group are photographed at their respective telephoto ends. Set the magnification to β, 7. When β3a, 0.7kuβ2a/βsT<1.25...(1)-
1,4<β2? < -0, 7... It is characterized by satisfying the conditional expression (2).

〔Example〕

The present invention will be explained below based on the drawings.

FIG. 1 shows a schematic diagram of a zoom lens according to the invention.

In FIG. 1, 1 is a first lens group having positive refractive power;
2 is a second lens group with negative refractive power, S is an aperture stop, 3 is a third lens group with positive refractive power, 4 is a correction plate including a crystal filter and an infrared cut filter that perform a low-pass effect, and F is a correction plate Indicates the image plane.

In this embodiment, when zooming from the wide-angle side to the telephoto side, the movement trajectories of the second lens group 3 having negative refractive power and the third lens group 3 having positive refractive power move toward the optical axis in opposite directions. A high variable power ratio is achieved by moving each lens group as shown above and assigning each moving lens group the responsibility of variable power.

In the present invention, the above-mentioned conditional expression (1) is used.

While satisfying (2) at the same time and reducing the size of the zoom lens, the second lens group and the third lens group correct aberration fluctuations during zooming in a well-balanced manner.

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

Conditional expressions (1) and (2) are the second. This is to appropriately set the imaging magnification at the telephoto end of the third lens group.

As shown in conditional expression (1), by making the imaging magnifications β2T and β3T of the second and third lens groups almost equal at the telephoto end, the amount of aberration generated by each group is shared, thereby reducing the amount of aberration caused by zooming. The amount of aberration fluctuation is reduced. If the lower limit of conditional expression (1) is exceeded, the spherical aberration tends to be overcorrected, and furthermore, the curvature of field tends to be overcorrected at the telephoto end, which is undesirable. Also, the conditional expression (
Exceeding the upper limit of 1) is not preferable because the fluctuation of distortion during zooming becomes large and the fluctuation of astigmatism also becomes large.

Furthermore, in conditional expression (2), if the upper limit is exceeded, spherical aberration tends to be overcorrected and field curvature tends to be undercorrected, which is not preferable. Furthermore, if the lower limit is exceeded, both the overall length and the front lens become large, which is undesirable.

As described above, by setting the imaging magnification of each lens group, it is possible to achieve a zoom lens that is the object of the present invention, and more preferably, to satisfy the following conditions.

In other words, if the focal length of the entire system at the wide-angle end is fW%, and the focal length of the third lens group is f, then 0.5< fw/f
The conditional expression is m<0.7 − (3).

When the upper limit of conditional expression (3) is exceeded, field curvature and coma aberration occur significantly, especially on the wide-angle side, while when the lower limit is exceeded, it becomes difficult to correct spherical aberration.

Furthermore, the lens configuration of the third lens group is as follows from the object side:
Biconvex first lens, positive second lens with strongly convex surface facing the object side
The lens has a negative third lens with a strongly concave surface facing the image side, and a biconvex fourth lens.The air distance between the second and third lenses is dma, and the refractive index of the second lens is nm2. When o < d II 4 / f < 0.15
...(4) 1, 6<n Tomi 2
・・・
・It is preferable to satisfy the following conditional expression (5).

Conditional expression (4) is a condition for correcting axial aberrations and off-axis aberrations in a well-balanced manner; if the upper limit is exceeded, comatic aberration will occur significantly, and if the lower limit is exceeded, both spherical aberration and field curvature will occur. This makes it difficult to correct aberrations.

Conditional expression (4) is intended to satisfactorily correct spherical aberration, and when the lower limit is exceeded, zonal spherical aberration increases and resolving power decreases.

Note that the first lens group of the zoom lens in this example is as follows:
In order to make the lens system more compact, it is fixed during zooming and moves during focusing.

In addition, since the zoom lens of the present invention has a 3-lens group configuration in order from the object side, and aberrations must be corrected with a small number of lens groups, the amount of aberration fluctuation due to zooming in each lens group is It is necessary to keep it as small as possible. Therefore, in this embodiment, the second lens group is formed of a concave meniscus lens with a strongly concave surface facing the image side, a concave lens, a convex lens with a strongly convex surface facing the object side, or a concave lens with a strongly convex surface facing the object side, in order from the object side. If the lens is composed of three lenses, each consisting of a laminated convex lens, which is oriented toward the lens, aberration fluctuations, mainly distortion and coma, can be easily suppressed. Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface from the object side, Di is the thickness and air gap of the i-th lens from the object side, and Ni and υi are the curvature radius of the i-th lens surface from the object side, respectively. These are the refractive index and Atsube number of glass.

(1) of R20, R21, and R22 is an optical low-pass filter, an IR cut filter, or the like.

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

Example 1 F=8° 24000~23° 92° 19° 71° 38° 84 64 90 24 7 FNO=1: 2~2° R7=　　　　14.118 R8=　　　　-11,793 R9=　　　　　7.468 D7=2.00 D8=0.80 D9=2.50 R13= R14= R15= R16= R17= -25° 7゜ -57° -24° 5゜ 03 35 55 01 36 D13= D14= D15= D16= D17= R21= o, oo.

2W = 51° 8° ~ 19° 3° 1 = 1° 1633 ν11 = 64° (optical LPF, iR#t filter) fm = 11° 96 b, f = 3.46 Example 2 F = 7° 64215 ~ 25゜55 FNO=1: 2゜R1= R2= R3= R4= R5= R6= R7= R8= R9= l0 R11= R12= R13= R14= R15= R16= R17= R18= R19= R20= R21= R22= 9 3〇261 1 4 151 8 1 1 5 〇345 15 74 18 2 14 44 33 67 09 96 25 70 12 46 00 24 000 (aperture) 31 34 61 04 59 73 87 89 00 00 D1=1.30 D2=4.00 D3=0.15 D4=2.90 D5=variable D6=1.0O D7=1.73 D8=0.80 D9=1.27 D10=1.80 D11=variable D12=variable D13 = 2.50 D14 = 0.15 D15 = 2.50 016 = 1.50 D17 = 4.80 D18 = 0.78 D19 = 2.40 D20 = variable D21 = 6.45 5~3゜2W = 55゜3゜~17゜7゜-N: f2-1l N11=1゜1633 ν11=64゜(optical LPF, iRh foot filter)b.

f=1° 5 Example 3 F=7゜ 54027-256 113° 38° -109° 22゜ 98 19 88 78 05 FNO=1: 2゜ R7= R8= R9= R10= 7゜ 150° 11° 11° 80 39 45 95 D 7= D 8= D 9= D10= R14= R15= R16= R17= R18= R19= =18° 9゜ -181° -38° 6゜ 21° 17 27 58 23 70 87 D14= D15= D16= D17= D18= D19= R22= o, oo.

5~3° 2W=55° 9°～17° 6″ N11= 1゜ 1633 ν11= 64° (Optical LPF, iR capto filter) b.

f = 3゜5 As explained above, in a zoom lens composed of three lens groups having positive, negative, and positive refractive powers in order from the object side, the refraction of the second and third lens groups that have a variable magnification effect By optimizing the force arrangement and lens shape, a variable power ratio of 3 to 3.
It becomes possible to combine a 5x zoom lens with high performance and into a compact size.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a zoom lens with a three-group configuration according to the present invention, FIGS. 2 to 4 are cross-sectional views of lenses of first to third embodiments of the present invention, and FIGS. ~A longitudinal aberration diagram of the third example is shown. In Figures 5 to 7, (A) is the focal length at the wide-angle end, and (B) is the focal length at the wide-angle end.
) indicates the intermediate focal length, (C) indicates the telephoto end focal length, 69g indicates the spherical aberration of the d-line and 2g-line, ΔM indicates the meridional image surface, and ΔS indicates the sagittal image surface. 1 is the first lens group, 2 is the second lens group, S is the aperture, 3 is the third lens group, 4 is the correction plate, and F is the imaging plane. Figure 5 (A) T: ND/2 Ikamaro-← Ikari 1+4 f%M- Mochi diagram (C) Prize diagram (A) 86 ㎓ζB') FND/2.9 Ikashi 16 Toi Ikaini & 4- 44 Tofusuen (CF/10/2.6 Kai 7 Cause (A) 19da, 4 Imiyama Jui% I% + 4 Fig. 7<E3”) Fig. 7 ( C)

Claims (1)

[Claims] (1) Consisting of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a third lens group having a positive refractive power. In a zoom lens that changes magnification from a wide-angle end to a telephoto end by moving the second lens group from the object side to the image side and moving the third lens group from the image side to the object side, the second lens group When the imaging magnification at the telephoto end of is β_2_T and the imaging magnification at the telephoto end of the third lens group is β_3_T, 0.7<β_2_T/β_3_T<1.25-1.4<
A zoom lens characterized by satisfying the following conditional expression: β_2_T<-0.7. (2) The lens satisfies the following conditional expression: 0.5<f_w/f_m<0.7, where the focal length of the third lens group and the focal length of the entire system at the wide-angle end are f_m and f_w, respectively. A zoom lens according to claim 1. (3) The third lens group includes, in order from the object side, a biconvex first lens, a second lens with positive refractive power with a strongly convex surface facing the object side, and a negative lens with a strongly concave surface facing the image side. It consists of a third lens having refractive power and a biconvex fourth lens, and the air distance between the second lens and the third lens in the third lens group is d.
_m4, the refractive index of the second lens in the third lens group is n_m
2. The zoom lens according to claim 2, wherein the following conditional expressions are satisfied: 0<d_m4/f_m<0.15 1.6<n_m_2.