JPH04186211A - Zoom lens having high variable power - Google Patents

Abstract

PURPOSE:To obtain a compact zoom lens having high variable power ratio by satisfying a prescribed condition in an optical system equipped with six lens groups having positive, negative, positive, negative, positive and negative refractive powers in order from an object side. CONSTITUTION:The first lens group I having positive refractive power, the second lens group II having negative refractive power, the third lens group III having positive refractive power, the fourth lens group IV having negative refractive power, the fifth lens group V having positive refractive power and sixth lens group VI having negative refractive power are provided in order from an object side. Furthermore, when air space of both the (i)th group and the (i + 1)th group in the wide angle edge and the tele edge are set respectively as Diw and DiT, zooming from the wide angle edge to the tele edge is carried out so as to satisfy conditions of equations I-IV, and focusing is carried out by moving the sixth lens group VI. Thereby, in spite of a compact type, a zoom lens having high performance and high variable power ratio can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a zoom lens suitable for single-lens reflex cameras, video cameras, etc., particularly a zoom lens that includes a wide-angle range and has an extremely high variable power ratio of 10x. Regarding lenses.

[Prior art]

Conventionally, as zoom lenses ranging from wide-angle to telephoto, for example, Japanese Patent Application Laid-Open No. 164710/1983 and Japanese Patent Application Laid-Open No. 60-1989
It is known from Publication No. 39613 and the like.

In these publications, a zoom ratio of 3 to 5 times is obtained with a zoom lens having five groups, positive, negative, positive, negative, and positive, in order from the object side.

On the other hand, in JP-A-1-191819, similarly,
A zoom lens is disclosed that has a zoom ratio of approximately 10 times with a five-group configuration of negative, positive, negative, and positive groups.

[Problem that the invention seeks to solve]

However, the zoom lens described above has a front lens diameter (first group) and an optical total length (distance from the first lens surface to the image plane).
is relatively large, and especially in JP-A-57-164710 and JP-A-60-39613, the variable power ratio is low;
In recent years, there has been a demand for zoom lenses with higher zoom ratios, and this was not sufficient. Japanese Patent Publication No. 1-191
Publication No. 819 discloses a zoom lens with a fairly high zoom ratio, but the overall optical length is long and the diameter of the front lens is also quite large.

In view of these problems, it is an object of the present invention to provide a zoom lens that has a zoom ratio of about 10 times, has a shortened overall optical length, and has good optical performance.

[Means and configuration for solving the problem] The present invention is characterized by: in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a positive refractive power. The third lens group has a refractive power of Zooming to DIW <DIT D2w> D2T Dsw < DOT D <w> D a is performed while satisfying the following condition, and focusing is performed to the sixth
A high variable power zoom lens that is characterized by moving the lens group.

〔Example〕

1 to 4 show cross-sectional views of a zoom lens according to the present invention. In particular, FIG. 1 shows the paraxial arrangement of the zoom lens and the optical paths of the axial and off-axis rays according to the present invention.

■ is the first lens group with positive refractive power, ■ is the second lens group with negative refractive power, ■ is the third lens group with positive refractive power, and ■ is the fourth lens group with negative refractive power. The group ■ indicates a fifth lens group having a positive refractive power, and ■ indicates a sixth lens group having a negative refractive power. Zooming from the wide-angle end to the telephoto end is performed by moving on the optical axis following a movement locus shown by dotted lines or arrows. Also, focusing is performed by moving the sixth lens group. Further, S indicates an aperture. This aperture SP has a fixed relationship with the third lens group (2).

As configured above, the present invention first brings the positive first lens group and the negative second lens group closest to each other at the wide-angle end,
The composite refractive power (f, ) of the first lens group and the second lens group is made negative (f, □<0), and the second and third lens groups
The distance between the lens groups is the largest, the distance between the third and fourth lens groups is the closest, the fifth lens group is placed at a distance on the image plane side, and the sixth lens group is placed further apart. . In addition, the positive third lens group is made so that the combined refractive power of the first lens group and the second lens group is negative, and the refractive power of the positive third lens group and the negative fourth lens group is relatively weak. The 5th lens group and the negative 6th lens group constitute a retro type as a whole. Furthermore, by arranging the negative sixth lens group, the back focus is shortened and the overall length is shortened.At the same time, this sixth lens group The outer diameters of the fifth and sixth lens groups are made small.

Next, at the telephoto end, the distance between the positive first lens group and the second lens group is widest, and the distance between the negative second lens group and the positive third lens group is widest.
If you look at the lens group as a whole by setting the distance between the lens groups to the smallest and placing the negative 4th lens group, positive 5th lens group, and negative 6th lens group closest to each other, the telephoto type is strong. The lens is designed to shorten the overall length of the lens.

Next, making the lens outer diameter more compact will be explained. Generally, the lens group with the largest outer diameter in a high-power zoom lens including a wide-angle lens is the 1121st lens group. Here, as shown in FIG. 1, the elements that determine the outer diameter of the 1121st group include an off-axis ray at the wide-angle end and an on-axis FNo ray at the telephoto end. The open F number is FNo, the diameter of the axial FNo ray is D,
When the focal length of the entire system is f, the following formula holds: FN0=-, and the effective diameter of the 1121st lens group at the telephoto end is automatically determined by the height of the axial F No ray. However, the effective diameter at the wide-angle end, including the wide-angle range, depends on the off-axis rays incident on the 1121st group, and the inclination of this ray is very large. It is difficult to keep the outer diameter of the In contrast, in this embodiment, the combined negative refractive power of the 1121st lens group and the second lens group is strengthened, that is, the negative refractive power of the second lens group is strengthened. Furthermore, the lens interval D2W at the wide-angle end is made as small as possible so that off-axis rays pass as close to the 1121st group as possible.

By the way, if the negative refractive power of the second lens group is strengthened, the lens system becomes a retro type, especially at the wide-angle end, and the back focus becomes longer than necessary. ) tends to become longer.

In the present invention, forcing is performed by reducing the diameter of the 1121st lens group and moving the sixth lens group having negative refractive power along the optical axis so that focusing can be performed at close range.

In this embodiment, even when zooming from the wide-angle end to the telephoto end, the sixth lens group is moved toward the object side so as to satisfy Dsw > Ds. The sensitivity of the 6th lens group is increased on the telephoto side so that the amount of extension for focusing is smaller than when the 6th lens group is fixed during zooming.

In this example, the distance from the final lens surface to the image plane when focusing on an infinite object at the wide-angle end is D6w, and the focal length of the sixth lens group is D6w when focusing on an infinite object at the wide-angle end. When the distance from the final lens surface to the image plane when focusing is D8, 0.65<l f, l/D8W<2.6 (1
)0.5<Ds, /If, l<2.6 - (2) is satisfied.

Conditional expression (1) is based on the distance from the lens surface closest to the image side of the sixth lens group at the wide-angle end to the image plane.
This defines the focal length of the lens group, and if the focal length of the sixth lens group becomes shorter than the lower limit of conditional expression (1), the sensitivity of the sixth lens group increases, and Although the smaller space is advantageous for making the overall length more compact, various aberrations occurring in the sixth lens group, especially spherical aberration, become larger, making it difficult to suppress aberration fluctuations during focusing. Conditional expression (1)
When the focal length of the sixth lens group increases beyond the upper limit of , the aberration fluctuation during focusing becomes smaller, but the telephoto type tendency of the entire lens system weakens, and the overall length becomes longer.

Conditional expression (2) is based on conditional expression (1) and defines the object beauty and the distance from the most image-side surface of the sixth lens group at the telephoto end to the image plane with respect to the focal length of the sixth lens group. Therefore, when the distance D6T becomes smaller beyond the lower limit of conditional expression (2), the sensitivity of the sixth lens group at the telephoto end becomes smaller, and the amount of focus extension increases. If the distance D6□ increases beyond the upper limit, the sensitivity of the sixth lens group at the telephoto end will increase, and the amount of focus extension can be reduced, but positioning accuracy during autofocus will become difficult.

Next, numerical examples of the present invention will be shown. In numerical examples R
1 is the radius of curvature of the first lens surface from the object side, D
l is the first lens thickness and air distance 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 1 F=36 FNO=1: 3.4-57R
34 = 00 2ω = 62° ~ 72° 3 = 1.49700 3 = 81.6 4 = 1.83481 ν 4 =
42.75= 1.80400 ν
5=46.65=1.84666
ν 622397= 1.80400
ν 7= 46.68= 1.60311
ν 8=60.79=1.78472
C19=25.7 Numerical Example 2 F=36 FNO=1: 3.4-57
2ω=63=14 4=18 5=18 6=18 8=16 H=1.8 K3:6=4v, tυΦ2° ~7
2°, 34.00 ν 1=37.2
9700 ν 2= 81.697
00 ν 3= 81.6・348
1 ν 4=42.7.0400
ν 5= 46.614666
ν 6=23.910400
ν 7= 46.6.0311 and 8=
60.7:0400, 1B=46.6 Numerical Example 3 F=36 FNO=1:3.4-5.7 2ω
=62°~72aν 1=37.2 ν 2=81.6 3=81.6 C 4=42.7 C 5=46.6 C 6=23.9 ν 7=46.6 C 8=60 .7 Shi 9 = 81.6 Shi 0 = 23.9 Table 1 [Effects of the Invention] As explained above, according to the present invention, although it is a comparator, it is possible to achieve high performance and high zoom ratio. can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the paraxial arrangement of the present invention. 2 to 4 are wide-angle lens sectional views of numerical examples 1 to 3, respectively. 5 to 7 are object aberration diagrams of numerical examples 1 to 3, respectively, (A) to (C) are various aberration diagrams at the end, middle, and telephoto end, respectively, and S is the image plane , M is the meridional image plane. FNO/3.42 W= 3/'
W=31" Spherical aberration Non-outgoing aberration Distortion (%) Sine condition FNO/4.9.5 W='?, I'
W-9,1″ Spherical aberration Non-emerging aberration
Distortion (%) sine condition FNO15-7W=36° vv=3.
6” Spherical aberration Achromatic aberration Distortion (%
) Sine condition FHO/3.35 W= 31°
W-31゜Sine condition FNO/4.87 W= q, /'
W-De,! ″Spherical aberration Non-Ichi aberration
Distortion (%) sine condition FNO/, 5. VW=3.69
W=3. A' sine condition FNO/3.4 W -= 37
'''W-,,57' spherical aberration
Unfortunate 15! Difference Distortion (%) Sine condition FNO/4.8t W= Q, I'
W='? , I' sine condition Figure 7 (C) FNO/J, 7 W = 3, l
” W-J, 6m spherical aberration
Unoccupied aberration Distortion (%) sine condition

Claims (2)

[Claims] (1) In order from the object side, the first lens group has a positive refractive power, the second lens group has a negative refractive power, the third lens group has a positive refractive power, and the fourth lens has a negative refractive power. group,
It has a fifth lens group having a positive refractive power, a sixth lens group having a negative refractive power, and the i-th lens group at the wide-angle end and the telephoto end.
The air spacing between the group and the (i+1) group is D_i_W, respectively.
, D_i_T, zooming from the wide-angle end to the telephoto end satisfies the following conditions: D_1_W<D_1_T D_2_W>D_2_T D_3_W<D_3_T D_4_W>D_4_T, and focusing is performed by moving the sixth lens group. A high variable power zoom lens. (2) The focal length of the sixth lens group is f_5, the distance from the final lens surface to the image plane when focusing on an infinite object at the wide-angle end is D_5_W, and when focusing on an infinite object at the telephoto end When the distance from the final lens surface to the image plane is D_5_T, 0.65<|f_
5|/D_5_W<2.60.5<D_5_T/|f_
5|<2.6 The high variable power zoom lens according to claim 1, wherein the zoom lens satisfies the following condition: 5|<2.6.