JPH01179903A - Zoom lens - Google Patents

Abstract

PURPOSE:To remove restrictions on back focus and to make a zoom lens compact and high-performance by not only extending the air interval between first and second lens groups but also shortening that between third and fourth lens groups at the time of zooming to the longest focal length and satisfying a specific condition. CONSTITUTION:In case of zooming from the shortest focal length (S end) to the longest focal length (L end), the first positive lens group and the fourth negative lens group are moved from the image side to the object side and the second negative lens group and the third positive lens group are moved during zooming. Consequently, the air interval between the first positive lens group and the second negative lens group is extended and that between the third positive lens group and the fourth negative lens group is shortened to take partial charge of the power varying effect, and therefore, the amount of movement of each group is reduced. Further, the third group has an aspherical surface in this fundamental constitution and it satisfies an inequality I. Thus, a compact lens system having a short overall length is obtained where the back focus in the S end is equal to or shorter than a half of the screen diagonal length.

Description

[Detailed Description of the Invention] The present invention also 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.

111 Company 01 Box 1 Quantity Conventionally, as a zoom lens for photography that includes a standard area, a negative-leading two-component zoom lens is known, which is composed of two components, negative and positive, in order from the object side. ．． On the other hand, with the recent increase in the magnification of zoom lenses, various forward-leading type so-called multi-component movable zoom lenses have been proposed. However, these zoom lenses mainly
II? Most of them were developed for reflex cameras, and the total length of the lens system (the length from the front of the lens closest to the object to the film surface) is large due to back focus constraints. In addition, as a zoom lens for a camera that does not have constraints on back focus, Japanese Patent Application Laid-open No. 128911/1983 discloses. A positive-leading type two-component zoom is known, such as Japanese Patent Laid-Open No. 57/201213, which is composed of two components, positive and negative, in order from the object side.

However, with this type of zoom lens, the amount of movement of the lens group that is generally moved for zooming is large,
Even if the overall length of the lens system is compact, it becomes large when the lens barrel is included. Furthermore, in the above-mentioned zoom type, the aperture moves during zooming, which is undesirable in, for example, a lens shutter camera, as it increases the size and complexity of the camera body. That is, in a lens shutter camera, not only the aperture diaphragm but also the shutter blades and a driving unit for the shutter blades must be arranged at the aperture position and these must be moved, so the above point can be said to be an extremely serious drawback.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact and high-performance zoom lens suitable for cameras with no restrictions on back focus.

A further object of the present invention is to provide a compact and high-performance zoom lens in which the camera body is made compact and simple.

A further object of the present invention is to provide a zoom lens that has a higher zoom ratio and a larger aperture than that of JP-A-60-57814.

The zoom lens of the present invention that achieves the above-mentioned purpose consists of, in order from the object side, a first positive lens group (I) and a second negative lens group (■).
, a third positive lens group (m) and a fourth negative lens group (IV), and when zooming from the shortest focal length end (S end) to the longest focal length end (L end), the first positive lens group As the fourth negative lens group moves from the image side to the object side,
At least the second negative lens group or the third positive lens group moves during zooming. In the zoom lens of the present invention, based on the above configuration, when zooming from the S end to the S end, the air distance between the first positive lens group and the second negative lens group increases, and the air distance between the first positive lens group and the second negative lens group increases. By reducing the air distance between the lens group and the fourth negative lens group, the zooming effect can be shared, making it possible to reduce the amount of movement of each moving group.

Furthermore, the zoom lens of the present invention has the above configuration,
By having a negative lens group with a relatively strong power closest to the image side, the back focus at the S end is less than 1/2 of the diagonal length of the screen, which constitutes a compact lens system with an extremely short overall length.

Note that, according to an embodiment of the present invention, the zoom lens system includes:
As shown in Figures 1 to 3, by fixing the lens group including the aperture during zooming, zoom lenses for compact cameras such as lens-shutter cameras can be used to downsize and simplify the camera body. I can make a big contribution.

The zoom lens of the present invention is further characterized in that it has an aspherical surface in the third group based on the above basic configuration and satisfies the following conditional expression.

However, X: displacement amount in the optical axis direction at the height Y of the optical axis expressed by the following formula
@10...
Aspheric coefficient C0: Radius of curvature N of the spherical surface that is the reference for the aspheric surface: Refractive index N+ on the object side of the aspheric surface, refractive index on the image side of the aspheric surface If the surface has a negative power, the positive refractive power becomes weaker as the distance from the lens optical axis increases, or if the surface has a negative power, the negative refractive power decreases as the distance from the lens optical axis increases. Note that near the optical axis, where spherical aberration has little influence, even if the above conditional expression is deviated by a small amount, it will still be substantially as specified by the present invention. By using an aspherical surface that satisfies condition ① in the third group, spherical aberrations that occur due to larger apertures, and spherical aberrations that occur due to increased power of each group due to enlarged zoom ratio and compactness, and during zooming. Fluctuations in comatic aberration are well corrected.

Furthermore, it is desirable for the zoom lens system of the present invention to satisfy the following conditions.

0.65<f3/l f41<1.0-1---・
・■0.08<Z/f,<1.50・
-11-- ■ However, f3: Focal length f of the third positive lens group, : Focal length Z of the fourth negative lens group: Zoom ratio Conditional expression (■) is based on the shape of the aspherical surface in conditional expression (■) as well as the large aperture. transformation,
Alternatively, if the lower limit of conditional expression 0 is exceeded, increasing the zoom ratio is a condition for good aberration correction while maintaining compactness. It becomes impossible to correct it completely. Moreover, if the upper limit is exceeded, it becomes difficult to correct aberration fluctuations during zooming, particularly fluctuations in field curvature and coma, in a well-balanced manner.

Conditional expression (■), together with the aspherical shape of conditional expression (■), is a condition for properly correcting the enlargement of the zoom ratio while maintaining compactness.If the upper limit of conditional expression (■) is exceeded, conditional expression (■) is specified. Even if an aspherical surface is used, it is difficult to satisfactorily correct aberration fluctuations during zooming. Moreover, if the lower limit is exceeded, compactness cannot be maintained if the zoom ratio becomes large.

Furthermore, in the zoom lens of the present invention, by providing an aspherical surface on the convex surface toward the object side in the third positive lens group, the converging light beam of the third group having strong positive refractive power is moved away from the lens optical axis. Accordingly, the surface is shaped so that the positive refractive power is moderate, and spherical aberration is well corrected.

Further, in the zoom lens system of the present invention, it is desirable that at least the positive lens in the third positive lens group has an aspherical surface and satisfies the following conditions.

n3-P<1.5. u3-P<6
0 ....-■ However, n3-P: refractive index of the positive lens in the third positive lens group u3-P:
If a plastic lens that satisfies conditional formula (2) is used as the lens having a dispersive aspherical surface of the positive lens in the third positive lens group, it is preferable in terms of manufacturing because it can significantly save labor in the processing process.

Further, as a specific configuration of the zoom lens of the present invention, the following is preferable. That is, the first lens group includes at least a negative lens with a convex surface facing the object side, and a positive lens with a concave surface facing the closest image side. including.

The above configuration reduces fluctuations in various aberrations, especially astigmatism, when the lens group focuses on a nearby object.

Further, the second lens group includes at least one negative lens and one positive lens and corrects chromatic aberration during zooming, particularly the balance of lateral chromatic aberration. And the third lens group is positive and
The negative/positive trip-left type or its modified type is most preferable for correcting spherical aberration and comatic aberration.
The lens group includes at least one negative meniscus lens closest to the image side, which contributes to making the entire system more compact and correcting the image plane near the S end.

Specific examples of the present invention will be described below. 1 to 3 are lens sectional views at the S end and L@ of Examples 1 to 3 of the zoom lens of the present invention, respectively. In the following examples, r is the radius of curvature of the i-th surface from the object side, d is the axial distance of the i-th axis from the object side, N, and ν
i is the refractive index and Abbe number of the i-th lens in order from the object side, respectively. As is clear from each embodiment, the change in the F number is small when the aperture diameter is fixed, and it is also possible to omit the aperture diameter correction mechanism. 4 to 6 are aberration diagrams of Examples 1 to 3 when the object distance is infinite, and in these figures, (M) shows the aberration at an intermediate focal length.

In Examples 1 to 3, the second lens group including the diaphragm (1) is fixed during zooming, but instead of this, the diaphragm may be provided in the third lens group and fixed. good. Furthermore, if mechanical circumstances permit, the second.
Moving the third lens group together is optically easy and does not deviate from the requirements of the present invention as long as it achieves the effect of constructing a compact zoom lens.

Also, the second. The variation in the air gap during zooming of the third lens group is relatively small compared to the variation in other lens groups, so in a lens system with a relatively small zoom ratio or a lens system with a large tolerance for aberrations, the second ．． It is also possible to move the third lens integrally.

<Example 1> f = 39.0-50.0-62. OF-2, 8-3.
1 to 3.2 Plate radius Supervisory plate Plate lid Kei Sarachika Eyuoka r+ 69.083 a, 1.500 N, 1.84666 ν,
23.83rx 29.274 d, 3.500 N, 1.69680 νz
56.47r+ 91.962 ds 0.150 r, 20.681 da 4.200 N31.69680 νz
56.47rs 62.885 ds 2.200~7.032~12.290rh-
68,144 d, 1.100 N, 1.72000 ν,
54.71rt 16.714 d7 1.700 N, 1.84666
νS 23.83rs 29.814 da 6.346~5.370~4.592r,"
19.016 d, 1.781 N, 1.70500 ν,
54.86r1°-329,636 dl. 0.508 rll -398,165 d,, 1.481 N, 1.80518 νt
25.43rt1 26.001 d1□2.262 r, 345.032 d, s 3.050 N@ 1.66446 ν@
35.84r,, -83,202 Poryo Plate Hoshiki Σd= 48.552~45.434~4
3.642rv :Aa -0,27572Xl0-
'Ah = 0.47719xto-7Aa
= 0.40999 xlO-”A,.--0
,72437Xl0−”AI!=0.73952
Xl0-"fs/lfal=0.69 Z/f, =0.066 <Example 2> f=37.0-57.0-77, OF-4, 1-4.
9 ~ 4.9 The number of cases d, 0.150 d, 0.886 1”a 13.366 d++ 0.150 r+z 17.952 d13 0. 906 r,, -41,321 Aspheric coefficient Σd=55.162~54.682~55
．． 834rH:A4=-0,24524xiO-'
A4 =-0,90078xlO-'A a
"0.29760 X 10-" A+.

= -0,28852x IQ-1'A1□=-0,8
2387Xl0-" r+s:A4= 0.20193 Xl0-'
Ah =0.76861 xio-'A, =-0
, 35400X10-' Al. -0,52644x
lO-mouth A1□=-0,12983Xl0-" f3/lf, l=0.73z/f, -0,094 <Example 3> f=37.0~57.0~11.OF- 4,1~4.
9~5.1r, 53.412 d, 0.944 r, -44,599 a, 1.566 Nm 1.84666 νa
23.83r + s 27, 064 d+s 2.860 r+h 81.547 r! . -17,162 Escape 11 Old [Loss Σd=54.133~53.244~5
3.726r1z:A<=0.31815
Xl0-' Ah = 0.21422 Xl
0-'As "' 0.41218 X10-
@Al. = 0.53232 Xl0-”AI!
= 0.14891 Xl0−”r+s:Aa
= 0.38538 Xl0-' Ah= 0
．． 35379 Xl0-”As-0,67620
Xl0-"Ate--0,48971XIQ-"A
l2= 0.12423 Xl0-”r 3/
l f4 j =0.76Z/f,
-0,095

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 each illustrate Example 1 of the present invention. S end of each zoom lens of Example 2 and Example 3,
It is a sectional view of the lens at the L end. FIG. 4, FIG. 5, and FIG. 6 are aberration diagrams showing various aberrations of the zoom lens of each of the above embodiments at each focal length and at an infinite object distance. (1) ...first positive lens group, (■) ...second negative lens group. (1) -.- Third positive lens group, (IV) - Fourth negative lens group. (1) - Aperture.

Claims (1)

[Claims] (1) Consisting of, in order from the object side, a first positive lens group, a second negative lens group, a third positive lens group, and a fourth negative lens group,
When zooming from the shortest focal length end to the longest focal length end, the first positive lens group and the fourth negative lens group move from the image side to the object side, and at least the second negative lens group or the third positive lens group zooms. As a result, when zooming from the shortest focal length end to the longest focal length end, the air distance between the first and second lens groups increases and the air distance between the third and fourth lens groups decreases. death,
and a zoom lens whose back focus at the end of the shortest focal length is 1/2 or less of the diagonal length of the screen, having an aspherical surface in at least the third positive lens group, and satisfying the following conditions. A zoom lens. |X| - |
8+A_1_0Y^1^0+... X_0: Shape of the spherical surface that is the reference for the aspherical surface expressed by the following formula
)^1^/^2} A: Aspherical coefficient C_0: Radius of 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 (2) Furthermore The first one is characterized by satisfying the following conditions.
A zoom lens according to the claims. 0.65<f_3/|f_4|<1.0 However, f_3: Focal length of the third positive lens group f_4: Focal length of the fourth negative lens group (3) Furthermore, it is characterized by satisfying the following conditions. Second
A zoom lens according to the claims. 0.08<Z/f_3<1.50 However, Z: Zoom ratio f_3: Focal length of the third positive lens group (4) The third positive lens group has an aspherical surface on its convex surface toward the object side. The zoom lens according to claim 3, characterized in that: (5) The zoom lens according to claim 3, wherein at least the positive lens in the third positive lens group has an aspherical surface and satisfies the following conditions. n3-P<1.5, u3-P<60 However, n3-P: refractive index of the positive lens in the third positive lens group u3-P:
Dispersion of the positive lens in the third positive lens group (6) The zoom lens according to claim 1, wherein the second negative lens group includes an aperture and is fixed during zooming.