JPH01252916A - Compact high-variable magnification zoom lens system - Google Patents

Abstract

PURPOSE:To obtain the compact high-variable magnification zoom lens which is suitable for cameras having no restrictive conditions for back focusing and has high performance by constituting the lens system consisting of 3 groups so as to satisfy specific conditions. CONSTITUTION:This lens consists of the 3 groups including the 3rd lens group III having an aspherical face on at least one face. The 1st lens group I and the 3rd lens group III move from an image side to an object side and the 2nd lens group II moves at the time of zooming from the shortest focal length end to the longest focal length end. The air spacing between the 1st and 2nd lens groups increases and the air spacing between the 2nd and 3rd lens groups decreases; in addition, the conditions expressed by the equation I are satisfied. In the equation, X is the displacement quantity in the optical axis direction at the height Y from the optical axis expressed by the equation II; X0 is the shape of the spherical face which is the reference of the aspherical face expressed by the equation III; A is the coefft. of the aspherical face; C0 is the curvature of the spherical face which is the reference of the aspherical face; N is the refractive index on the object side from the aspherical face; N' is the refractive index on the image side from the aspherical face. The compact high-variable magnification zoom lens which is suitable for the cameras having no restrictive conditions for back focusing and has the high performance is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a camera with no constraints on back focus;
The present invention relates to a compact zoom lens suitable for, for example, a lens shutter camera.

Conventionally, as a camera zoom lens that does not have constraints on back focus, positive and negative focal lengths are applied sequentially from the object side, as proposed in JP-A-56-128911 and JP-A-57-20 Lens No. 3. A two-component positive pressure folding edge type zoom lens is known, which is composed of two components. Furthermore, regarding the three-component zoom lens described in JP-A-58-137813 and JP-A-58-184915, the four-component zoom lens described in JP-A-60-57814, and other types. Various proposals have also been made. However, most of these zoom lenses have relatively small zoom ratios, and no zoom lens with a zoom ratio exceeding 3 has been realized.

On the other hand, relatively compact zoom lenses for -eye reflex cameras with a zoom ratio exceeding 3 are disclosed in Japanese Patent Laid-Open No. 54-30855 and Japanese Patent Laid-Open No. 55-156.
Although various proposals have been made, such as in Japanese Patent No. 912 and Japanese Patent Application Laid-open No. 57-169716, the total length of the lens system (the length from the front surface of the lens closest to the object side to the film surface) is large due to back focus constraints. It has become a thing.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a compact, high-performance, high-power zoom lens that is suitable for cameras with no restrictions on back focus.

A further object of the present invention is to provide a zoom lens that has a simplified zoom format and a higher zoom ratio than the zoom lens described in Japanese Patent Application Laid-Open No. 60-57814.

A further object of the present invention is to provide a compact, high-performance, high-power zoom lens that takes into account miniaturization and simplification of the camera body.

In order to achieve the above object, the zoom lens according to the present invention has a lens group (+) having a positive refractive power, a lens group (+) having a positive refractive power, a lens group having a positive refractive power, and a third lens group (III) having a negative refractive power and an aspherical surface on at least one surface, and when zooming from the shortest focal length end to the longest focal length end. Group (1) and third lens group (II
I) moves from the image side to the object side, and the second lens group (
II) is moved so that the air distance between the first and second lens groups increases, and the air distance between the second and third lens groups decreases, and the following conditions are satisfied: It is.

However, here, X is the displacement amount in the optical axis direction at the height Y from the optical axis, which is expressed by the following formula, X = X o + A 4 Y 噌 + A, Y'+
AaY'+A,. Y16+... Xo is the shape of the spherical surface that is the reference for the aspherical surface expressed by the following formula, Xo=CoY"/(1+(1-Co"Y")'/"IA
is the aspherical coefficient, Co is the standard curvature of the spherical surface,
N is the refractive index on the object side of the aspherical surface, and N' is the refractive index on the image side of the aspherical surface.

The present invention will be explained in detail below.

Condition (1) is that if the surface to which the aspherical surface is applied has positive refractive power, the aspherical surface has a surface shape in which the positive refractive power becomes stronger as the distance from the lens optical axis increases, or
If the surface has a negative refractive power, this indicates that the surface has a shape in which the negative refractive power becomes weaker as the distance from the optical axis of the aspherical lens increases. In addition, in the vicinity of the optical axis where spherical aberration has little effect, the above condition (1) is satisfied only by a minute amount.
Even if the above is omitted, the present invention is substantially defined.

Therefore, although the third lens group (III) as a whole has a strong negative refractive power, the aspherical surface provided therein satisfies condition (1), so that it is relatively It is possible to give it a moderate refractive power. Therefore, the axial principal ray passes through a relatively low position in the third lens group (U) except for the longest focal length end, and the off-axis principal ray passes through a relatively high position, so condition (1) is satisfied. By applying this aspherical surface to the third lens group (Iff), it is possible to satisfactorily correct positive distortion at the longest focal length end and fluctuations in coma aberration during zooming.

Furthermore, in the present invention, it is desirable that the following conditions are also satisfied.

However, here, L is the distance from the vertex of the lens surface closest to the object side of the second lens group (■) to the film surface, and L2'' is the vertex of the lens surface closest to the image side of the second lens group (II). FM is the diagonal length of the screen, fS is the focal length of the entire system at the shortest focal length end, and fL is the focal length of the entire system at the longest focal length end.

Condition (2) is a condition for maintaining the compactness of the entire system without increasing the zoom ratio.If the upper limit of condition (2) is exceeded, the overall length becomes longer and the compactness that is the objective of the present invention is maintained. This becomes difficult. - On the other hand, if the lower limit of condition (2) is exceeded, as the zoom ratio increases, the back focus becomes shorter, the diameter of the third lens group increases, or the second and third lens groups become extremely thin. , the degree of freedom for correcting aberration fluctuations during zooming is reduced. When this degree of freedom decreases, in a zoom lens that includes a wide angle and has a relatively large zoom ratio like the present invention, even if aberrations are corrected at the shortest focal length end and the longest focal length end, the intermediate focal length In particular, it becomes difficult to correct spherical aberration and curvature of field.

Condition (3) is a condition for maintaining the compactness of the entire system while maintaining high performance under condition (2). As the thickness increases, it becomes difficult to realize a compact optical system. Conversely, if the lower limit of condition (3) is exceeded, aberration fluctuations during zooming,
In particular, it is difficult to correct spherical aberration and coma aberration in a well-balanced manner.

Furthermore, in the present invention, in addition to the above conditions (1) to (3), it is desirable that the following conditions are also satisfied.

2 (4) 0.10<-<0.60 L However, here, f is the focal length of the second lens group (II).

Condition (4) appropriately defines the refractive power of the second lens group (IF), and when the refractive power of the second lens group (n) becomes weaker than the upper limit of condition (4), the refractive power of the third lens group (III)
The axial luminous flux incident on the lens becomes high, the back focus becomes long, and compactness tends to be impaired.

Conversely, if the lower limit of condition (4) is exceeded, the second lens group (11)
If the refractive power becomes too strong, the aberrations generated in the second lens group <n> will become large, making it difficult to sufficiently correct spherical aberration, especially at the end of the shortest focal length, and the back focus will become too short. Therefore, if an attempt is made to ensure sufficient image plane illuminance at the shortest focal length end, the diameter of the third lens group (I[l) will become undesirably large.

Furthermore, it is desirable that the zoom lens system of the present invention satisfies the following conditions.

(6) 0.08 < lf, /fLl < 0.
45(7) 0.25<(DI2L o12s>/
rs<o, 60, where βL is the lateral magnification of the third lens group (Iff) at the longest focal length end, βS is the lateral magnification of the third lens group (Ill) at the shortest focal length end, r, is the focal length of the third lens group (III), D12L
is the axial distance between the first and second lens groups at the longest focal length end, and D+2S is the axial distance between the first and second lens groups at the shortest focal length end.

Condition (5) stipulates the variable power effect of the third lens group (■). If the upper limit of condition (5) is exceeded, the refractive power of the third lens group (lft) becomes stronger or The amount of movement of the lens group (III) increases, and in the former case, the amount of movement of the lens group (III) becomes large.
It becomes impossible to realize the lens group (III) with a relatively simple configuration. Furthermore, in the latter case, aberration fluctuations during zooming increase and the overall length at the longest focal length end becomes longer, making it difficult to make the entire system including the lens barrel configuration compact. Furthermore, if the lower limit of condition (5) is exceeded, the load on the second lens group (Iff) for zooming becomes too strong.

Condition (6) defines the refractive power of the third lens group (-III), and the refractive power of the third lens group (-III) exceeds the upper limit of condition (6).
When the refractive power of III) becomes weaker, the amount of movement of the third lens group (I Become. Furthermore, when the refractive power of the third lens group (III) becomes stronger beyond the lower limit of condition (6), the third lens group (It
), the aberrations occurring in the third lens group (II
) Even if an aspherical surface is used for the lens, it is difficult to sufficiently correct distortion and fluctuations in comatic aberration during zooming.

Furthermore, condition (7) is the first lens group (1) due to zooming.
and the second lens group (It), and if the upper limit of condition (7) is exceeded, aberration fluctuations due to zooming, especially spherical aberration and coma aberration, cannot be well corrected. At the same time, the distance between the first and second lens groups at the shortest focal length end becomes too large, making it necessary to change the front or rear lens diameter to ensure sufficient image illuminance at the very edge of the screen. It becomes too large and it becomes difficult to ensure compactness. Furthermore, if the lower limit of condition (7) is exceeded, the change in the distance between both lens groups during zooming becomes small, making it difficult to increase the zoom ratio.

Furthermore, in the present invention, it is desirable that the following conditions be satisfied.

(8) Nd, < 1.6. νd, <60 However, here, Nd is the refractive index of the lens having an aspherical surface in the third lens group (III), and νd is the refractive index of the lens having an aspherical surface in the third lens group (III).
i) is the Abbe number of the lens with an aspherical surface in

By using a plastic lens that satisfies condition (8) as the lens having an aspherical surface in the third lens group (III), a large amount of labor can be saved in the processing process, which is preferable in terms of manufacturing.

In the present invention, the following is desirable as a specific configuration of each lens group.

Since the 1st lens group (1) includes at least one positive lens and one negative lens, it is possible to give the 1st lens group (1) a relatively strong refractive power, so that the 1st lens group (1) can be used for zooming.
) can be kept as small as possible. Furthermore, since the third lens group <II[) includes at least one positive lens and one negative lens, chromatic aberration during zooming, particularly lateral chromatic aberration, can be corrected in a well-balanced manner. During zooming, the first lens group (1) and the third lens group (Ill) move together, and the second lens group (II) also moves separately, so that each lens group moves independently. This is advantageous in terms of lens barrel configuration compared to a moving configuration.

Although the present invention is basically a zoom lens system having a three-group configuration, even if a component with a fixed relatively weak refractive power is added to the most image side, it does not essentially meet the requirements of the present invention. Never.

In the following examples of the present invention, 1 is the radius of curvature of the first lens surface from the object side, di is the i-th axial distance from the object side, Ni, ν; These are the refractive index and Atsube number of the i-th lens in order from the object side.The surface marked with (*) indicates that it is an aspheric surface, and its shape is defined as follows.

X = X o + A 4 Y' + A a Y
' 10 A @ Y ”+ A lo Y ” 10... Xo=CoY2/(If(I Co2Y”)'/2)
However, where, It is curvature. The relationship between each example and each condition is shown in Tables 1 and 2.

(Hereinafter, blank space) Example 1 f=38.2-60.0-100. OFNO,=4.6
~6.5~8.2 Radius of curvature Axis spacing Refractive index (Nd) Atsube number (νd) Σd=45.380~4
5.642~48.538 nine beds and rho: A-=-0,25261xlO-3As=
0.13264xlO-'As =-0,14389
X10-'A,. =-0,77820xlO-
"A+x=0.30283xtO-" rli :A<=0.73124xlO-'
As-0,46162xlO-'Am =-0,13
250xlO-'A,. = 0.17848x
lO-'A+2=-0,82995X10-tatami=1 Example 2 f=36.2~60.0~100. OF'NO,=4.
2~5.8~8.2 Radius of curvature Between top surfaces of axis @ Refractive index (Nd) Atsbe number (νd) Σd=46.724~
46.724～46.724匪■blood wound rlo: A4 =-0,28476xlO-ko
A, = 0.21778xlO-'A
s=-0,14027xlO-' A+e=-
0,66607X10-”A12=0.30716X
10-”rlo:A4=0.73338xlO-'
As = 0.31545X10-'A, =-0,
12740xlO-' A,, = 0.1703
5x10-A l 2 = -0,75925X 1
0-”Example 3 f=36.2-60, 0-100.OFNO,=4.4
~6.0~8.2 Radius of curvature Axis spacing Refractive index (Nd) Atsbe number (νd) Σd=48.701~4
6.701～46.701匪■Kekkisanr. :A==-0,28480X10-'
As = 0.15451X10-5A, =-0,1
4177x10-@A,,=-0.89351xlO-
■.

Alt=0.30671xlO-"r+4:A4=0.66687X10-'
Aa = 0.37242xfO-'A, =-0,
13112xlO-' A,, = 0.1651
4xlO-@A+a=-0.71339xlO-" Example 4 f=37.0~63.0~100.OFNO,=4.9
~7.2~8.2 Radius of curvature Axis spacing Refractive index (Nd) Atsbe number (νd) Σd=41.959~4
2.044~47.646 Nine blood injury rho: A4 = -0,32792X10-'
As =-0,21904xlO-'A, =-0,
10602xlO-' A,, = 0.5104
9xlO"■OA+2=0.32546X10-"rla:A4=0.73134X10-'
Al=-0,17739xlO-'As=0.4
8737X10-” A+o=-0,44751
X10-IOA+z=0.17248xlO-' Example 5 f=36.2-61.6-97.8 FNO,=5.
0 to 7.5 to 8.2 Radius of curvature Axial surface spacing Refractive index (Nd) Atsbe number (νd) Σd = 41.385 to
40.748 ~ 47.468 Shodoko plate style rlo: A4 = -0,37480X10-co
As =-0,27472xlOzuAs
=-0,12555xlO-' A+o=0.
55780xlO-”Alz= 0.41099xlO
-”rH:A4 = 0.69067xlO-'A
s = -0,36197X10-'A, = 0.36
949xlO-”A,,-0,29251x
lO-'.

A + 2 = -0,89148X 10-''Example 6 f=36.2~60.0~100.OFNO,=4.5
~6.4~8.2 Radius of curvature Axis spacing Refractive index (Nd) Atsbe number (νd) Σd=48.423~6
3.395 ~ 84.805 Sho ball plate sho: A4 = -0,25901X10-co
As = 0.13633xlO-'A
s = -0,14519xlO-' A,. =-
0,83209x 10-” Al2= 0.3000
9X10-"rho:Aa=0.75180X10-'
Aa-0,40478xlO-@As =-0,1
2670xlO-7A+o=0.18149xlO
-@A4z=-0,92009X10-12 Example 7 f=36.2~60.0~97.8 FNO,=4.
5 ~ 6.1 ~ 8.2 Radius of curvature Axis top surface spacing Refractive index (Nd) Atsbe number (νd) Σd = 44.482 ~
44.481 ~ 44.482 Nine-ball master's salary rlo: Al = -0,36797X10-'
An = 0.65573xlO-'As =-0,
14327X10-' A+o=-0,6949
8X10-”Al2=0.30588X10-”rl@: A4=0.556F1x10-'
A, = 0.87461xlO-
7As −=−0,13381xlO−′ Ag
o = 0.20500xlO-'A+t=-0.10
217×10-th Example 8 f=38.2-61.6-97.8 FNO,=4.
3 to 8.0 to 8.2 Radius of curvature Distance between upper surfaces of shaft Refractive index (Nd) Atsbe number <νd) Σd=45.988 to
45.988 to 45.988
A, = 0.68474xlO-'A
,=-0.13033X10-' A+o=-0
,20092X10-'Al2=0.96592xlO
-self2 r, ,: A, = 0.45722xlO-'
A, =-0,60189xlO-'A
s=-0,30351xlO-"A1o=
0.68773X10-”A, 2=-0,42398x
lO-12 Example 9 f=37.0~83.0~100.0 FNO,=
5.1~7.8~8.2 Radius of curvature Shaft top surface spacing
Refractive index (Nd) Atsbe number (νd) Id=44.80
6 ~ 43.087 ~ 49.070 trillion yen faction r,,: A, = 0.48419xlO-'
At =-0,20970xlO-'A, = 0.
35583xlO-”A,,=-0,22888
xlO-"At2=0.20713xlO-"

[Brief explanation of the drawing]

1 to 9 are cross-sectional views showing the lens arrangement at the shortest focal length end (S end) and longest focal length end (L end) of the zoom lenses of Examples 1 to 9 of the present invention, respectively, and FIGS. FIG. 18 is an aberration diagram showing various aberrations of the zoom lens of each of the above embodiments at the shortest focal length end <S>, intermediate focal length <M>, and longest focal length end <L> when the object distance is infinite. It is. 1; 2nd lens group; 2nd lens group; 3rd lens group. Applicants: Minolta Camera Co., Ltd.

Claims (1)

[Scope of Claims] (1) In order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a second lens group having a negative refractive power and having an aspherical surface on at least one surface. When zooming from the shortest focal length end to the longest focal length end, the first lens group and the third lens group move from the image side to the object side, and the second lens group moves to 1. A compact high-power zoom lens system characterized by increasing the air gap between the second lens group and decreasing the air gap between the second and third lens groups, and satisfying the following conditions. : (|X|-|X_0|/C_0(N'-N)>0 where, X: displacement in the optical axis direction at height Y from the optical axis expressed by the following formula, ^4+A_6Y^6+A_8Y^
8+A_1_0Y^1^0+... X_0: Shape of the spherical surface that is the reference for the aspheric surface expressed by the following formula, X_0=C_0Y^2/{1+(1-C_0^2Y^2
)^1^/^2} A: aspherical coefficient, C_0: curvature of the spherical surface that is the reference for the aspherical surface, N: refractive index on the object side of the aspherical surface, N': refractive index on the image side of the aspherical surface, and be. (2) The compact high magnification zoom lens system according to claim (1), further satisfying the following conditions: 0.20<(L_2/FM)・(fS/fL)<0.5
00.15<(L_2-L_2'/FM)<0.45, where, L_2: Distance from the vertex of the lens surface closest to the object side of the second lens group to the film surface, L_2': Second lens group The distance from the vertex of the lens surface closest to the image side to the film surface, FM: Screen diagonal length, fS: Focal length of the entire system at the shortest focal length end, fL: Focal length of the entire system at the longest focal length end , is. (3) The compact high magnification zoom lens system according to claim (2), further satisfying the following condition: 0.10<f_2/fL<0.60, where, f_2: th The focal length of the two lens groups is: (4) The compact high-power zoom lens system according to claim (3), further satisfying the following condition: 1.60<(βL_3/βS_3<5.000.08<
|f_3/fL|<0.45 0.25<(D_1_2L-D_1_2S)/fS<0
．． 60 However, here, βL_3: Lateral magnification of the third lens group at the longest focal length end, βS_3: Lateral magnification of the third lens group at the shortest focal length end, f_3: Focal length of the third lens group, D_1_2L: Longest focal length The axial distance between the first and second lens groups at the distance end, D_1_2S: The axial distance between the first and second lens groups at the shortest focal length end. (5) The compact high-power zoom lens system according to claim (4), further satisfying the following conditions: Nd_3<1.6, νd_3<60, where: Nd_3: third lens The refractive index of the lens having an aspherical surface in the group, νd_3: Abbe number of the lens having an aspherical surface in the third lens group.