JPH01252917A - 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 2nd lens group (II) 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 with no back focus constraints, positive and negative 2. 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 the miniaturization and simplification of the camera body.

In order to achieve the above object, the zoom lens according to the present invention includes, in order from the object side, a first lens group (1) having a positive refractive power, a first lens group (1) having a positive refractive power, as shown in FIGS. a second lens group (■) having an aspherical surface on at least one surface;
, and a third lens group (Ill) having negative refractive power, and when zooming from the shortest focal length end to the longest focal length end, the first lens group <1) and the third lens group (Ill)
II) moves from ffl[ to the object side, the second lens group (■) moves, the air gap between the first and second lens groups increases, and the air gap between the second and third lens groups increases. is reduced and satisfies the following conditions.

However, here, X is the amount of displacement in the optical axis direction at the height Y from the optical axis expressed by the following formula, X=Xo+A4Y'+iY@+AaY8+Al6Y"+
,,.

Xo is the shape of the spherical surface that is the reference for the aspheric surface expressed by the following formula, 'Xo=CoY2/(1+(1-Co''Y2)l/2
1A is an aspherical coefficient, Co is a curvature of a spherical surface serving as a reference for the aspherical surface, N is a refractive index on the object side of the aspherical surface, and N' is a 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 5 aspherical surface is applied has positive refractive power, the aspherical surface has a surface shape in which the positive refractive power becomes weaker as it moves away from the optical axis of the lens, or If the surface has negative refractive power, this indicates that the surface has a shape in which the negative refractive power becomes stronger 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, only a small amount of spherical aberration is satisfied.
) is substantially defined by the present invention.

Therefore, although the second lens group (II) as a whole has a strong positive refractive power, the aspheric surface provided therein has the condition (
By satisfying 1), it is possible to provide the lens with a relatively loose refractive power at a position away from the optical axis. Therefore, since the axial light beam passes through a relatively high position in the second lens group (U) and the off-axis principal ray passes through a relatively low position, the aspheric surface defined in condition (1) is lens n<
ri>, it is possible to satisfactorily correct spherical aberration and fluctuations in comatic aberration during zooming.

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

However, here, and is the distance from the vertex of the lens surface closest to the object side of the second lens group (II) to the film surface, L2°
is the distance from the vertex of the lens surface closest to the image side of the second lens group (■) to the film surface, 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 longest focal length This is the focal length of the entire system at the edge.

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 short focal length end and the longest focal length end, it becomes difficult to correct especially spherical aberration and field curvature at the intermediate focal length.

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, even if an aspherical surface is used in the second lens group (II), it will be difficult to correct aberration fluctuations during zooming, especially 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.

r.

(4) 0.10<-<0.60 L However, here, f2 is the focal length of the second lens group (II).

Condition (4) appropriately defines the refractive power of the second lens group (II), 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 (ff>
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 (II[) becomes undesirably large.

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

β53 (6) 0.08 < lf3/rLl < 0.4
5(7) 0.25<(D, 2L-D, 2S)/rs
<0.60 However, here, βL is the third lens group (I[[
) is the lateral magnification of the third lens group (I [l), βS is the lateral magnification of the third lens group (I [l) at the shortest focal length end,
), the focal lengths D, , L are the first focal lengths at the longest focal length end.
, the axial distance between the second lens group, and DI28 are the axial distance between the first and second lens groups at the shortest focal length end.

Condition (5) defines the variable power effect of the third lens group (In), and if the upper limit of condition (5) is exceeded, the refractive power of the third lens group (III) becomes stronger or the third lens group The amount of movement of the group (I[l) increases, and in the former case, the third
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. Moreover, if the lower limit of condition (5) is exceeded, the load on the second lens group (I[I) 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 ([
When the refractive power of [I) becomes weaker, the amount of movement of the third lens group (1) becomes larger in order to obtain a predetermined zoom ratio, making it difficult to make the entire system, including the lens barrel configuration, compact. . In addition, if the lower limit of condition (6>) is exceeded, the third lens group (II
When the refractive power of I) becomes stronger, the aberrations generated in the third lens group (I[[) become larger, making it difficult to sufficiently correct distortion and fluctuations in coma aberration during zooming.

Furthermore, condition (7) is that the first lens group (1
) 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, can 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 difficult to maintain the front or rear lens diameter in order to ensure sufficient image illuminance at the very periphery of the screen. becomes too large, making it 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 in processing the aspherical surface.

(8) Nd2 < 1.6. νd2<60 However,
Here, Nd2 is the refractive index of the lens having an aspherical surface in the second lens group (II), and νd2 is the Abbe number of the lens having an aspherical surface in the second lens group (■).

By using a plastic lens that satisfies condition (8) as the lens having an aspherical surface, it is possible to achieve significant labor savings 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 first lens group (1) includes at least one positive lens and one negative lens, relatively strong refractive power is given to the first lens group (1), and the first lens group (+ > can be kept as small as possible.Also, by including the third lens group (■) at least one positive lens and one negative lens, chromatic aberration during zooming, especially lateral chromatic aberration, can be suppressed in a well-balanced manner. When zooming, the first lens group N)
and the third lens group (Ill) move together, and the second lens group (II) also moves separately, which improves the lens barrel structure compared to a structure in which each lens group moves separately. It will be advantageous.

Incidentally, the present invention is basically based on l? Although this is a zoom lens system having the above-mentioned configuration, even if a fixed component with a relatively weak refractive power is added to the most image side thereof, the configuration requirements of the present invention will not be essentially deviated from.

Examples of the present invention are shown below. In each example, rl is the radius of curvature of the i-th lens surface in order from the object side, dl is the first axial distance from the object side, and ni and νi are the object These are the refractive index and number of the i-th lens in order from the side. A surface marked with an asterisk (*) indicates that it is an aspherical surface, and its shape is defined as follows.

X −X o + A 4 Y' + A a Y'
+A a Y ”+ A + o Y ” + ”' Xo=CoY2/N -1-(1-Co2Y2)'/'
) Here, X is the amount of displacement in the optical axis direction at the height Y from the optical axis, Xo is the shape of the spherical surface that is the reference for the aspherical surface, and A
is the aspherical coefficient, and Co is the curvature of the spherical surface, which is the reference for the aspherical surface. The relationship between each example and each condition is shown in Tables 1 and 2.

(Hereinafter, blank space) Example 1 f=36.2-60.0-100. OFNO,=4.6
~6.5~8.2 Radius of curvature Axis spacing Refractive index (Nd) Atsbe number (νd) Σd=45.360~
45.642～48.538
A, = 0.13264xlO-'A
s = -0,14389xlO-'A,. =-
0,77820x 10sOA, = 0.30283x
lO-" r+s: A4 = 0.73124X10-'
As-0,46162xlO-'As =-0,13
250xlO-' A, o= 0.17648x
lO-'A, 2=-0,82995x 10~+2
Example 2 f=36.2-60.0-100. OFNO,=4. Z
~5.8~8,2 Radius of curvature On-axis i7D spacing Refractive index (N, J) Atsbe number (νd) Σd=48.72
4 ~ 48.724 ~ 413.724 nine-bed plate imitation rlO: A < --0, 28476X10"
As=0.21778xlO-'As=-0,1
4027xlO-' A,. =-0,86607
x10-”A, 2= 0.30716x1.0-th r+
i: A4 = 0.73338xlO-' A
, = 0.31545xlO-'A, =-0,12
740xlO-' A,, = 0.17035x
lO-@/'+z=-0.75925X10-"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=46.701~4
6.701~46.7011FM order view r+o: A, =-0,26480X10-'
A, = 0.15451xlO-'As =-0,
14+77xlO-' A1o=-0,6935
1XlO-'OA, , = 0.30671 x
10th rls: A4 = 0.66667XIO-
'/'l = 0.37242xlO-@A,
=-0,13112xtO-F A,.

= 0.16514xlO-raA12=-0,713
39XIO-+2 Example 4 r=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 distance baller value song r,, + A, =-0,32792xlO-'
As =-0,21904xlO-5A, =-0
,10602xlO-'A, o=0
．． 51049xlO - own0A12 = 0.32548x
iO-" rli: A4 = 0.73134xlO-'
As--0,17739xlO-'Aa = 0.
48737xlO-' A,. =-0,4475
1X 10-” Al2=O, t7248X10 odor Example 5 f=36.2~61.6~97.8 FNO,
=5.0~7.5~8.2 Radius of curvature Shaft top surface spacing
Refractive index (Nd) Atsbe number (νd) Σd=41.3
85~40.748~47.468 well spherical admiration 7o: A4 = -0,37480xlO-3A,
=-0,27472X10-'As =-0,125
55xlO-'Al. -0,55780X10
-"A,, = 0.41099xlO-th r, a: A, = 0.69067xlO-'
As =-0,36197xlO-'A, = 0.
36949xfO-'A,,=-0,2925
1xlO port 0A, □=-0,8914+3X10mm Example 6 f=36.2~60.0~100.0 FNO,=4
．． 5-6.4-8.2 Radius of curvature Axis spacing Refractive index (Nd) Atsbe's number (νd) Nine floor painting ratio r+o: A, =-0,25901xlO-'
Ag=0.13633xlO-'A, =-0,1
4519xlO-'A,,=-0,83209
xlO""A, z=0.30009xlO-th r1. : A, = 0.75180xlO-'
A, = 0.40478xlO-'A, =-0
, 12670xfO-F A1゜=0.
18149xlO-9A I2= -0,92009x
to-' 2 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 Ijitsu Kaikisan r + o: A4 = -0,36797X10-3
A, = 0.65573X10-'A
a = -0,14327xlO-' AI. =-
0,69498X 10-” Al2= 0.3058
8X10-" rl@: A4 = 0.55671X10-'
Am = 0.87481xlO-
1Al =-0,13361xlO-'
A. = 0.20500xlO-'Al2=-0
．． 10217X10-” Example 8 f=36.2-61.6-97.8 FNO,=4.
3 to 6.0 to 8.2 Radius of curvature Distance between upper surfaces of the axis Refractive index (Nd) Atsbe number (νd) Σd = 45.988 to
45.988~45, 988
As = 0.68474xlO-'A
, =-0,13033x1. O-'A,,=
-0,20092xlO-AspirationA,2=0.96592
xlO 2 r+a: A4 = 0.45722xlO-'
As ==-0,60189xlO-'As =-0
, 30351xlO-” A+o=0.687
73xlO-”A1□=-0,42398X10-12
Example 9 f=36.2-61.6-97.8 F”NO,=5
．． 1 to 8.2 to 8.2 Radius of curvature Distance between upper surfaces of shaft Refractive index (Nd) Atsbe number (νd) Σd=45.797
~41.732~49.494 trillion ball plate selection rlo: A4 = -0,22872X10-3Al
= 0.87387X10-'As =-0,1149
1xlO-' A+. 20.11307x1.0
-'A I 2 = 0.45618 x 10- ”

[Brief Description of the Drawings] Figures 1 to 9 show lens arrangements 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. The cross-sectional views, FIGS. 10 to 18, show the zoom lenses of each of the above embodiments at the shortest focal length end <S>, intermediate focal length <M>, and longest focal length end <L> at infinite object distance. It is an aberration diagram showing various aberrations. 1: first lens group, (2): second lens group, (2): third lens group. Applicant: Minolta Camera Co., Ltd.

Claims (1)

[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 having an aspherical surface on at least one surface, and a negative refractive power. 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. A compact high-power zoom lens characterized by increasing the air gap between the first and second lens groups and decreasing the air gap between the second and third lens groups, and satisfying the following conditions: System: (|X|-|X_0|/C_0(N'-N))<0 where, =X_0+A_4Y^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 : Focal length of the second lens group. (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 magnification zoom lens system according to claim (4), further satisfying the following conditions: Nd_2<1.6, νd_2<60, where: Nd_2: second lens The refractive index of the lens having an aspherical surface in the group, νd_2: Abbe number of the lens having an aspherical surface in the second lens group.