JPH03123310A - Zoom lens - Google Patents

Abstract

PURPOSE:To shorten the overall length of the lens by allowing the zoom lens of a prescribed composition having a first - a fourth lens groups having refracting power of positive, negative, negative and positive, respectively in order from an object side to satisfy a prescribed condition. CONSTITUTION:The zoom lens has the four lens groups of the first group I of positive refracting force for focusing, the second group II of negative refracting force having a displacing function, the third group III of negative refracting force for correcting an image surface fluctuated by displacement, and the fourth group IV of positive refracting force having an image forming function in order from an object side. The first group I has a cemented lens D1 + D2 of positive refracting power having a cemented lens surface R1 whose convex surface is turned to the object side, and a meniscus positive lens D4 whose convex surface is turned to the object side, and a second group II has a negative lens D6 whose strong refracting surface is turned to an image surface side and a cemented lens D7 + D8 + D9 of negative refracting power having a cemented lens surface R7 whose convex surface is turned to the object side. A third group III consists of a negative lens D11 whose concave surface is turned to the object side, and when a focal distance of an i-th group, a focal distance of the whole system in a telephone end, and a variable power ratio are denoted as Fi, FT, and Z, respectively, this lens is allowed to satisfy the conditions of an expression I and an expression II.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a zoom lens, and in particular, to a zoom lens that has a large aperture of F number 1.4 and a high zoom ratio of approximately 12.5, covering the entire zoom lens range. The present invention relates to a zoom lens having a relatively small number of lenses and having a simple structure, which is suitable for photographic cameras, video cameras, etc. and has good optical performance.

(Prior Art) Photographic cameras, video cameras, and the like have traditionally required zoom lenses with large apertures, high zoom ratios, and high optical performance.

Among these, zoom lenses for consumer video cameras, for example, have a spatial frequency of about 50 lines/mm over the entire screen due to the increase in the number of pixels of image pickup devices such as CCDs and improvements in recording methods such as 5-VH3. High resolution is required.

In addition, since the image pickup device of a general video camera has relatively low sensitivity, a zoom lens with a large aperture ratio is required.

In the zoom lens, in order from the object side, there is a 1st group with positive refractive power for focusing, a 2nd group with negative refractive power for zooming, and a positive or 3rd with negative refractive power
The so-called 4-group zoom lens, which consists of four lens groups: a second lens group and a fourth group with positive refractive power for imaging, is used in various cameras because it is easy to achieve relatively high zoom ratios and large aperture ratios. ing.

Among the 4-group zoom lenses, the aperture ratio is approximately 1.4 and the variable power ratio is 12.
A four-group zoom lens with a relatively large aperture and a high variable power ratio has been proposed, for example, in Japanese Patent Laid-Open No. 55-95922 and Japanese Patent Laid-Open No. 59-71015.

Among these, JP-A No. 55-95922 has a lens configuration of 17 elements in 17 groups as a whole, and JP-A No. 59-7
In Japanese Patent No. 1015, the lens structure as a whole is composed of 16 lenses in 14 groups, and each lens is composed of a relatively large number of lenses.

(Problems to be Solved by the Invention) Generally, in a four-group zoom lens, if the refractive power of each lens group and the lens configuration of the first group and the variable power section are not appropriately set, aberration fluctuations will increase over the entire variable power range. It becomes difficult to obtain good optical performance.

For example, in a zoom lens with a high zoom ratio of about 12.5, it is necessary to reduce the size of the entire lens system while properly correcting chromatic aberration over the entire zoom range from the wide-angle end to the telephoto end. While increasing the force and reducing the amount of movement associated with zooming, the third
It is better to configure the group to have a laminated lens. However, if the refractive power of the second group is simply strengthened, aberration fluctuations due to zooming will increase, and if the third group is configured to have a laminated lens, There were problems such as an overall increase in the number of lenses.

The present invention provides a so-called 4-group zoom lens that has an F number of 1.4, a large aperture ratio, and a variable power ratio of 1 by appropriately setting the lens configuration such as the lens shape and refractive power of each lens group.
The purpose of the present invention is to provide a zoom lens having a simple structure with a relatively small number of lenses and having high optical performance over the entire zoom range of about 2.5.

(Means for Solving the Problems) The zoom lens of the present invention includes, in order from the object side, a first group with positive refractive power for focusing, a second group with negative refractive power having a variable magnification function,
It has four lens groups: a third group with negative refractive power that corrects the image plane that changes due to zooming, and a fourth group with positive refractive power that has an imaging function. The second group has a positive refractive power laminated lens having a laminated lens surface with a convex surface facing toward the object side, and a meniscus-shaped positive lens with a convex surface facing the object side, and the second group has a strong refractive surface on the image side. The third group includes a negative lens with a negative refractive power and a bonded lens surface with a convex surface facing the object side. When the focal length of the group is Fi, the focal length of the entire system at the telephoto end is FT, and the variable power ratio is Z, then 0.1 <1F27FT|<0.15... (1) 0.
It is characterized by satisfying the following condition: 45<l F3/FT+<0.61 (2).

(Example) FIG. 1 is a cross-sectional view of the lens of Numerical Example 1 of the present invention.
In the figure, ■ is the first group with positive refractive power for focusing, II is the second group with negative refractive power that moves monotonically toward the image plane when changing magnification from the wide-angle end to the telephoto end, and m is the second group with negative refractive power for zooming. In order to maintain a constant position on the image plane, which changes with
is a fourth group having a positive refractive power that performs a fixed imaging function, and SP is a fixed aperture disposed in the fourth group.

In this embodiment, the lens configurations of the first, second, and third groups are set as described above, and the second lens group. The refractive power of the third group is expressed by the conditional expression (1
), (2), and as a result, it is possible to achieve a relatively small number of lenses (about 14), a large aperture ratio with an F number of about 1.4, and a high zoom ratio of about 12.5. The result is a four-group zoom lens with high optical performance over the entire zooming range, with excellent correction for aberration fluctuations that occur during zooming.

Especially the first one. By providing a bonded lens surface in the second group, chromatic aberration is effectively corrected.

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

Conditional expression (1) sets the negative refractive power of the second group appropriately, easily obtains a predetermined zoom ratio, and mainly reduces the aberration fluctuations associated with zooming while reducing the overall lens length of the zooming section. This is to shorten the time.

When the upper limit is exceeded and the refractive power of the second group becomes weaker, the amount of movement of the second group to ensure a predetermined zoom ratio increases, and the lens length of the zoom unit increases, and the aperture and This is not good because the distance from the first group increases and the lens diameter of the first group increases in order to secure off-axis light flux.

Also, if the refractive power of the second group becomes too strong beyond the lower limit, the amount of movement of the second group to ensure the specified zoom ratio will decrease, and the overall length of the lens will become shorter, but the aberrations associated with zooming will decrease. This is not good because the fluctuations are getting bigger.

Conditional expression (2) relates to the negative refractive power of the third group, and corrects aberration fluctuations in a well-balanced manner when the third group is composed of one negative lens with a concave surface facing the object side.

This is also to prevent the diameter of the front lens of the first group from increasing at the wide-angle end.

If the negative refractive power of the third group exceeds the upper limit and becomes too weak, the amount of movement of the third group due to zooming will increase, the overall length of the lens will become longer, and the diameter of the front lens of the first group at the wide-angle end will increase. It's increasing.

Furthermore, if the lower limit is exceeded and the negative refractive power of the third lens group becomes too strong, the Petzval sum will increase in the negative direction and astigmatism will increase, which is not good.

The zoom lens which is the object of the present invention can be achieved by satisfying the above-mentioned conditions, but it is also necessary to correct the aberration fluctuations caused by zooming in a well-balanced manner over the entire zooming range.
It is preferable that the condition is satisfied when the radius of curvature of the first lens surface of the group is R111i.

Conditional expression (3) relates to the lens shape of the single negative lens constituting the third group, and when the lower limit is exceeded, higher-order spherical aberration increases in the positive direction and extroverted coma aberration increases. So it's not good.

On the other hand, when the upper limit is exceeded, higher-order spherical aberration increases in the negative direction, inward coma aberration increases, and it becomes difficult to obtain high optical performance.

In this Ikemizu invention, in order to reduce the amount of aberration and obtain high optical performance over the entire zoom range, it is preferable to configure the fourth group as follows.

The fourth group consists of two lens groups, the 41st group and the 42nd group, in order from the object side with the widest air gap as the boundary, and the 41st group has a strongly convex refractive surface facing the image side. A positive fourth lens with a strongly convex refractive surface facing the object side.
2 lens, a negative fourth lens with a strongly concave refractive surface facing the object side.
3 lenses, a positive 4th lens with a strongly convex refractive surface facing the object side.
Consisting of four lenses, the 42nd group is a negative 45th lens with a strongly concave refractive surface facing the image side, a positive 46th lens with both lens surfaces convex, and a positive 47th lens. It is preferable to use three lenses, and set the focal length of the fourth group to F4. The focal length of the 41st group and the 429th group are respectively F4-1°F4-2, and the focal length of the 4th group is F4-1°F4-2.
When the focal length of the th lens is f4, i, 0.72
(-E12J-<o, ms...(4)4 The following condition is satisfied.

Conditional expression (4) relates to the 419th refractive power and is mainly intended to satisfactorily correct spherical aberration. If the lower limit is exceeded and the positive refractive power becomes too strong, the annular spherical aberration will increase on the wide-angle side. If the upper limit is exceeded and the positive refractive power becomes too weak, spherical aberration will be overcorrected and the outer diameter of the 42nd lens group will further increase, which is not good.

Conditional expression (5) relates to the ratio of the negative refractive power of the 45th lens to the positive refractive power of the 42nd lens group, and is mainly used to correct off-axis aberrations in a well-balanced manner.

If the negative refractive power of the 45th lens exceeds the lower limit and becomes too strong, high-order astigmatism will occur, and if the upper limit is exceeded and the negative refractive power of the 45th lens becomes too weak, negative This is not good because distortion increases and it becomes difficult to properly correct it.

In the above description, a refractive surface that is strong on the object side means that the refractive power is stronger than that of the other surface, that is, the lens surface on the image plane side. The same applies to a refractive surface that is strongly directed toward the image plane.

Next, numerical examples of the present invention will be shown.
4 is the radius of curvature of the i-th lens surface in order from the object side, D
l is the thickness and air distance of the i-th lens from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side. Note that R27 and R28 are glass blocks such as a face plate and a filter.

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

Numerical Example 1 F=1~12.3 FNO=l:1.45~
2ω=54.2e ~4.861:2.1I RI=16.983 DI=0.3012
N1=1.8051!1 ν 1=25.4
R2=6.599 D2=1.2410
N2=1.60311 ν 2=60.7R3=-
18,88403=0.0241R4:5.473
04=0.5663 N5=1.69680
V3=55.5R5= 12.483 D5=
Variable R6=8.924 D6=0.
1325 N4=1.78590 ν 4=4
4.2R7= 1.849 07= 0.60
60R8=-2,38308=0.1205
N5=1.7+299 ν5=53.8R9
= 2.383 [)9 = 0.4578
N6=1.84666 ν 6=23.9R1O
=-28,0580IO= variable R11=-3,
794DI+=0.1205 N7=1.69
680 ν 7=55.5R12=-24,758
DI2= variable RI3=-502,3720I3=
0.5301 Ng=1.62299 νg=
58. IRI4=-3,153DI4=0.
4217RI5= 4.015 D15=
0.5542 N9=1.63854 ν 9
=55.4R+6=-9,416D16=0.
2087R17=-3,626DI7=0.1
446 Nl0=1.805+8 νlo=
25.4R18= 25.469 018= 0.
0181RI9= 3.054 DI9=
0.5422 NII=1.65844 ν1
1= 50.9R20= -22,612020=
1.7920R21= 10.600 021=
0.1084 N+2=1°83400 ν
12= 37.2R22= 1.683 022
= 0.1389R23= 3.604 023
= 0.3373 N15 = 1.51633
ν13=64. lR24=-5-459024
= 0.0181R25= 2.130 02
5=0.3614 N+4=1.61484
ν14=51.2R26=oo D
26=0.6024R27= (1) D27
= 0.7229 N+5 = 1.51633
ν15=64. lR28; ■ bf=0.644 Total length=17.225 Aperture surface is R1
Numerical example of the position of 0.241 in front of the S plane 2 F = 1 ~ 12.3 FNO = I: 1.45 ~
2ω=54.2＠〜4.8゜! :2.29 R1= 15.583 DI= 0.2787
N1=1.80518 ν l=25.4
R2= 6.113 02= 1.1484
N 2 = 1.60311 ν 2 = 60.7R
3=-17,72903=0.0223R4=
5.048 04= 0.5240 N5=
1.69680 ν 3=55.5R5= 11
．． 471 05= Variable R6= 8.294 D
6=0.1226 N4=1.77250 C4=49.6R7=1.734. 07=
0.5608R8=-2,26608=0.1
115 N5=1.7+299 ν 5= 5
3.8R9= 2.217 09= 0.42
37 N6=1.84666 ν 6-23.
9RIG= 76.475 0IO= Variable R11
= -3,288DI+= 0.1115N
? =1.62374 ν 7=47. lR12=-
13,864012= variable R13=101.371
D13=0.5060 N8=1.62
299 ν 8=58.1 RI4= −2,84
7DI4= 0.4217RI5= 3.648
DI5=0.4819 N9=1.63
854 ν 9=55.4R16=-27,374
DI6= 0.2410R17= -3,524D
I7=0.1325 Nl0=1.80518
SI1O=25.4RI8=-760.008
DI8=0.0181R19=2.935
D19=0.5060 Nl1=1.6
5830 νIl= 53.4R20=-45,6
56020= 1.7470R21= 21.47
6 021= 0.1205 N+2=1.8
3400 ν12= 37.2R22= 1.
648 022= 0.1325R23= 3
．． 396 023= 0.2651 Nl3=
1.5+633 113=64. lR24=
−5,159024= 0.0181R25=
2.294 025= 0.3012 N+4
=1.61484 ν14= 51.2R26=-
13,801026= 0.6024R27=
oo D27=0.7229
N+5-1.51633 y151I 64
．． lR28= ■ bf=0.660 Total length=15.837 Aperture surface is R1
Position of 0.241 in front of S plane (Table 1) (Effects of the invention) According to the present invention, by setting the lens configuration of each lens group as described above, the total lens length can be shortened and the entire lens diameter can be simplified. While achieving this, it is possible to achieve a four-group zoom lens with a large aperture and high zoom ratio, which has a simple structure, is suitable for photographic cameras, video cameras, etc., and has good optical performance over the entire zoom range.

[Brief explanation of drawings]

1st. FIG. 2 is a sectional view of a lens of numerical example 1%2 of the present invention, and FIGS. 3 and 4 are various aberration diagrams of numerical example 1.2 of the present invention, respectively. In the aberration diagram, (A) is at the wide-angle end, (B
) is the aberration diagram at the intermediate position, and (C) is the aberration diagram at the telephoto end.
Il, m, rV are the first . 2nd, 3rd. 4th group, ΔM is meridional image plane, ΔS is sagittal image plane, d
is the d-line, g is the g-line, and sp is the aperture.

Claims (1)

[Claims] (1) In order from the object side, the first group has a positive refractive power for focusing, the second group has a negative refractive power and has a variable magnification function, and corrects the image plane that changes due to variable magnification. It has four lens groups: a third group with negative refractive power and a fourth group with positive refractive power having an imaging function,
The first group includes a bonded lens with positive refractive power having a bonded lens surface with a convex surface facing the object side, and a meniscus-shaped positive lens with a convex surface facing the object side, and the second group includes: It has a negative lens with a strong refractive surface facing the surface side and a bonded lens with negative refractive power having a bonded lens surface with a convex surface facing the object side, and the third group has a concave surface facing the object side. Consisting of a negative lens, the i-th
When the focal length of the group is Fi, the focal length of the entire system at the telephoto end is FT, and the variable power ratio is Z, then 0.1<|F2/FT|<0.15 0.45<|F3/FT|<0 A zoom lens characterized by satisfying the following conditions: .61. (2) The radius of curvature of the i-th lens surface of the third group is R
When IIIi, 1.3<|(RIII2+RIII1)/(RIII2−RIII1
2. The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition: )|<1.7.