JPH02158708A - wide angle zoom lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a wide-angle zoom lens suitable for photographic cameras, video cameras, etc. The present invention relates to a wide-angle zoom lens having a large aperture, short overall length, and good optical performance, in which magnification is changed by moving these three lens groups.

(Prior art) Conventionally, the front group (first I
It has two lenses JT, TJ and a rear group with positive refractive power (tjS2 group), and both lens groups are moved to change the magnification.
Various 712-group zoom lenses have been proposed that have relatively large apertures and wide angles of view.

In addition, in order to downsize the entire lens system while maintaining a predetermined angle of view, variable magnification ratio, and aperture ratio in a two-group zoom lens, the first group is combined with a second group with positive refractive power and a second group with negative refractive power. 3rd group 2
For example, a so-called three-group zoom lens, which is divided into two lens groups and is composed of three lens groups as a whole, and which changes the magnification by moving these three lens groups under predetermined conditions, was developed in Japanese Patent Laid-Open No. 57 -5023 publication and JP-A-58-75108
It is proposed in the publication.

In these three-group zoom lenses, when changing power from the wide-angle end to the telephoto end, the air gap between the second and third groups is increased, and the combined focal length of the second and third groups becomes longer than the telephoto end compared to the wide-angle end. It becomes longer at the end so that the principal point position of the composite system moves to the object side,
Compared to a two-group zoom lens, the amount of movement of the first and second groups is reduced, thereby shortening the overall length of the lens.

(Problem to be solved by the invention) However, these three-group zoom lenses have an F number of about 4,
It was not necessarily bright enough.

That is, in JP-A-57-5023, since the refractive power of the second group is weaker than that of the first and third groups,
The effect of the negative refractive power of the group and the third group is strong, and the height of incidence of axial rays on the second group becomes high, making it extremely difficult to obtain a large aperture ratio at the telephoto end, and it is difficult to obtain a large aperture ratio at the telephoto end. there were.

Also, Japanese Patent Application Laid-Open No. 5875108 (earlier disclosed by the applicant)
Since the purpose of the publication is to achieve high zoom ratio and miniaturization, each lens group has strong refractive power, and it is extremely difficult to increase the aperture. The problem was that it was difficult to use the lens, and it was only around F4 at the telephoto end.

The present invention utilizes the refractive power arrangement of a so-called three-group zoom lens proposed in the applicant's earlier Japanese Patent Application Laid-open No. 75108/1983, and by appropriately setting the refractive power of each lens group, a wide angle of view can be achieved. The object of the present invention is to provide a French painting zoom lens which has a shortened overall lens length and a large aperture ratio of about 28 while maintaining the same image quality, and has high optical performance over the entire zoom range.

(Means for solving the problem) From the object side, the first group has negative refractive power, and the second group has positive refractive power.
It has three lens groups: a group and a third group with negative refractive power,
When changing the magnification by moving these three lens groups, when changing the magnification from the wide-angle end to the telephoto end, the air gap between the second and third groups is moved toward the object side. When the focal length of the entire system at the wide-angle end and the telephoto end is respectively fw and fT, and the focal length of the first group is fi, 0.08 <+f21'/IfI ・f3)
<0.16...(1)<(fil"/ffw-
fT]<1.75----(21 conditions are satisfied.

(Example) Figures 1 to 3 are cross-sectional views of lenses of numerical examples 1 to 3 of the present invention.
2 indicates the second lens group with positive refractive power, ▪ indicates the third lens group with negative refractive power, and arrows indicate the movement direction of each lens group when changing the magnification from the wide-angle side to the telephoto side.

When changing magnification from the wide-angle end to the telephoto end, the zoom lens according to this embodiment moves the first group monotonically or reciprocally toward the image plane side, and moves the second and third groups toward the image plane as shown in each figure. Both groups are moved so that the distance between the second group and the third group increases in the object side direction, that is, the second group is moved more than the third group.

Then, the refractive power of each lens group is determined by the above-mentioned conditional expressions (11, (2
), the overall length of the lens is shortened, and the zoom ratio is 2°F number 28, and the shooting angle of view at the wide-angle end with a large aperture ratio is approximately 64 degrees over the entire zoom range. It has high optical performance.

In particular, the movement state and refracting power of each lens group are appropriately set so that the movement m of the second group is smaller than that of a so-called two-group zoom lens, and this reduces the maximum aperture diameter at the telephoto end. This effectively reduces the size of the entire lens system.

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

Conditional expression (1) is intended to satisfactorily correct various aberrations while keeping the refractive powers of the first, second, and third groups well-balanced and downsizing the entire lens system.

When the square value of the focal length of the second group exceeds the upper limit of conditional expression (1) and becomes longer than the product of the focal lengths of the first and third groups, that is, the refraction of the second group If the force becomes too weak, the amount of movement of the second group due to zooming will increase, and the overall length of the lens will become longer.

In particular, when changing the magnification from the wide-angle end to the telephoto end, the second group is moved toward the object side, so the distance between the second group and the image becomes longer at the telephoto end, and the outer diameter of the second group increases. This is not a good idea because the entire lens system becomes larger.

Furthermore, in general, in order to increase the aperture ratio of a zoom lens, it is necessary to satisfactorily correct spherical aberration on the telephoto side. However, as the outer diameter of the second lens group with positive refractive power increases, a large amount of spherical aberration occurs in one direction, and it is difficult to properly correct the spherical aberration that tends to undershoot at the telephoto end. It's coming.

For this reason, in the present invention, the refractive power of the second group is made not to exceed the upper limit of conditional expression (1), thereby effectively correcting spherical aberration when increasing the aperture ratio to approximately F2.8. There is.

On the other hand, if the lower limit of conditional expression (1) is exceeded and the refractive power of the first and third groups becomes too weak compared to the refractive power of the second group, the refractive power of the first and third groups becomes weaker due to zooming. As the amount of movement increases, the outer diameter of the first group lens increases accordingly, and negative distortion increases at the wide-angle end, making it difficult to correct this well.

Conditional expression (2) relates to the ratio of the product of the focal lengths of the entire system at the wide-angle end and the telephoto end to the focal length of the first group.

If the focal length of the first group exceeds the upper limit of conditional expression (2) and the focal length of the first group becomes too long, that is, the refractive power of the first group becomes weak, the first group needs to be This is not good because the amount of movement of the lens increases and the size of the entire lens system increases.

On the other hand, if the lower limit of conditional expression (2) is exceeded and the refractive power of the first group becomes too strong, the entire lens system will be downsized, but distortion will increase in the negative direction on the wide-angle side. Also, the second
The refractive power of the group tends to become stronger, and spherical aberration tends to be undercorrected at the telephoto end, making it difficult to achieve a large aperture ratio.

In addition, in this example, while trying to shorten the total lens length,
Furthermore, high optical performance is achieved over the entire zoom range (the first
The group includes a single or bonded meniscus-shaped negative lens with a convex surface facing the object side, a negative lens with concave surfaces on both lens surfaces, and at least one positive lens on a meniscus with a convex surface facing the object side, The second group has two positive lenses, a cemented lens made by bonding a positive lens and a negative lens, a negative lens, and a positive lens with both lens surfaces being convex, and the third group has a negative lens and a positive lens bonded together. It is preferable to have a negative cemented lens.

Next, numerical examples of the present invention will be shown.
i is the radius of curvature of the first lens surface from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

Numerical Example F=35~70 Rl=55.0S R2=26.08 1+3=-207,66 R4=81.27 R5=55.27 +16=74.49 R7=56.73 R8=187.99 1 (9 = 118.03 RIO = -377,27 RIl = 39.54 R12 = 129.35 Old 3 = 32.72 RI4 = +65.47 R15 = 41.3O R+6 = 785.80 R17 = 21.89 R18 = 47.34 +119= -64,08 1120= -93,25 R21= 28.27 122= -58,90 FNO=l :2.8 DI=2.25 02= 10.00 03=2.0O D4 = 2.00 05 = 2.25 06 = 1.00 07 = 3.50 D8/Variable D9 = 3.00 01O = 0.10 D11 = 3.50 DI2 = 0.10 013 = 7.00 014 = 3 .00 DI5 = 5.00 DI6 = 1゜50 DI7 = 4.00 018 = 3.50 019 = Variable D20 = 1.50 021 = 7.00 2ω = 63.4' ~ 34.3'' N l = 1 .7725 ν l= 49.6O
N2=1.8830 ν2=40.8ON
3=1.76+8 ν 3=27.1ON
4=1.7847 ν 4=26.2ON 5
=1.8348 ν 5= 42.7ON 6
=1.816 ν 6= 46.6ON 7=
1.6968 ν 7= 55.5088=1
．． 8467 ν 82 23.9ON 9=1
．． 8467 C 9= 23.9O NIO=1.835 νlo= 42.7O Nll=1.7725 N12=1.6034 νll= 49.60 ν12= 38.00 Numerical Example Numerical Example F; 35~70 Rl= 38.75 R2 = 22.61 R3 = -176,84 R4 = 72.56 R5 = 45.41 R6 = 163.39 R7 = 107.72 R8 = = 377, 70 R9 = 45.15 R1O = 92.11 R11 = 34.57 R12 -129,85 R13 = -288,65 R14 = -62,81 R15 = 24.35 R16 is 96.51 R17 = -38,30 R18 = -33,67 R19 = 31.82 R20= -30,02 2ω=63.4' ~ 34.3'' N l=1.7440 ν l= 44.7
9FNO=1・28 DI=2.20 D2=11.00 D3=2.00 D4=3.0O D5=4.25 D6・Variable D 7=2.50 84=1.772508=0
．． 15 D9=3.45 DlO= 0.15 Dll= 7.70 D12= 2.88 DI3= 4.50 D14= 1.50 D15= 2.20 DI6= 4.00 DI7= Variable D18= 1.50 DI9 = 6.33 N 2 = 1.834O N 9 = 1.883O N 8 = 1.8052 NIO = 1.7725 Nll = 1.5673 N 6 = 1.6968 N? = 1.8467 N 5 = 1.7725 N 3 = 1.7847 2 = 37.20 3 = 26.20 4 49.60 5 = 49.60 ν 6 = 55.50 ν 7 = 23.90 8 = 25.40 9= 40.80 νlO= 49.60 νl+= 42.80 F; 35~70 R+=41.40 R2= 74.88 R3= 23. +3 R4=-184,42 R5= 71.45 R6= 60.46 R7= 76.67 R8= 48.00 R9= 109.73 R1O= 112.06 Old 1=-191,67 RI2= 38.78 R13 = 9050 It14= 28.74 RI5= 122. +4 R16= 38.54 R17= 136.19 R18= 19.6O R+9= 37.01 1120= , -77,06 R21= -55,74 R22= 28.57 R23= -35,44 FNO=1・2 .8 1) l=6.24 02=2.0O D3=8.23 04=2.00 05=3. Old D 6 = 1.96 D7 = 0.58 D8 = 3.06 09. Variable DIO = 3.37 D11 = 0.15 DI2 = 3.66 DI3 = 0.15 D14 = 6.44 D15 = 1.83 D16= 5.28 DI7= 1.50 DI8=339 DI9= 4.31 D20: Variable D2+= 1.50 022= 5.49 2ω=63.4@ ~34.3″ N l=1.5+63 ν l = 64.1O
N2=1.7725 ν2=49.6ON
3=1.81130 3=40.8O N 4=1.7847 4=25.71 N 5=1.7618 5=26.6O N 6=1.8160 66O N 7=1.7725 ? = 49.6O N 8 = 1.713O N 9 = 1.8052 ν 8 = 53.80 ν 9 = 25.4O NIO = 1.8052 ν10 1.8348 27O NI2 = 1.7725 N13 = 1.5318 ν12 = 49 60 ν13= 48.90 [fi・+31 (fw4T) (Effect of the invention) According to the present invention, three lens groups with predetermined refractive powers are
By specifying and changing the magnification as described above, it is possible to achieve high optical performance over the entire magnification range with a short lens length, a zoom ratio of 2, an angle of view of 63 4'' to 34, 3'', and a 0 diameter ratio of approximately 2°8. A compact wide-angle zoom lens can be achieved.

[Brief explanation of the drawing]

Figures 1 to 3 (21 are lens cross-sectional views of numerical examples 1 to 3 of the present invention; Figures 4 to 6 are various aberration diagrams of numerical examples 1 to 3 of the present invention; A) is the aberration diagram at the wide-angle end (B) is the intermediate aberration diagram, and (C) is the aberration diagram at the telephoto end. Indicates the direction of movement of the group.

Claims (1)

[Claims] (1) It 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, and these three lens groups can be moved. When changing the magnification from the wide-angle end to the telephoto end, the second and third groups are moved toward the object side so that the air distance between them increases. When the focal lengths of the entire system at the wide-angle end and the telephoto end are respectively fw and fT, and the focal length of the i-th group is fi, 0.08<(f2)^2/(f1・f3)<0.161
A wide-angle zoom lens that satisfies the following condition: <(f1)^2/(fw·fT)<1.75.