JPH04186213A - Zoom lens having high variable power - Google Patents

Abstract

PURPOSE:To obtain a 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. When air space of both the (i)th group and the (i + 1)th group at 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 in equations I - IV. When focal distances of the first, the second and the fifth lens groups 1, 2 and 5 are set respectively as f1, f2 and f3, and when focal distance at the tele edge of whole points is set as fT, zooming is carried out so as to satisfy conditions in equations V-VII. 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 about 10 times with a five-group configuration of negative, positive, negative, and positive.

[Problems to be solved by the invention] 'However, the above-mentioned zoom lens has a relatively large front lens diameter (first group) and optical total length (distance from the first lens surface to the image plane), and is particularly Publication No. 57-164710, JP-A-60
Publication No. 39613 had a low variable power ratio, and could not be said to be sufficient in view of the recent demand for zoom lenses with higher zoom ratios. JP-A-1-191819 discloses a zoom lens with a high zoom ratio, but the overall optical length is long and the diameter of the front lens is also considerably 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. From the wide-angle end to the telephoto end, when the third lens group has a refractive power of When zooming, w<D, from 2W>D 2T D! This is done by satisfying the condition W < D 3□ D 4w > D (T) and also satisfying the following conditional expression.

0.26<f, /f<0.88 - (1) 0.
11<l f, l/f, <0.31- (2) 0.0
8<f5/fT<0.3...(3) Note that f...
f is the focal length of the first lens group and the fifth lens group, respectively. Further, f□ is the focal length of the entire system at the telephoto end.

〔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. 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 combined refractive power (f, □) of the first lens group and the second lens group is made negative (f, 2<O). Collection 2, 3
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 a negative sixth lens group, the back focus is shortened and the overall length is shortened.The sixth lens group 5. The outer diameter of the sixth lens group is 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. This structure is designed to shorten the overall length of the lens.

Next, making the lens outer diameter more compact will be explained. Generally, in a high-power zoom lens including a wide-angle lens, the lens group with the largest outer diameter is the first lens group. Here, as shown in FIG. 1, the factors that determine the outer diameter of the first lens 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 F9° beam is D,
When the focal length of the entire system is f, the formula FN0=- holds true, and the effective diameter of the first lens group at the telephoto end is automatically determined by the height of the axial FNo ray. However, the effective diameter at the wide-angle end, including the wide-angle range, depends on the off-axis rays incident on the first lens group, and the inclination of this ray is very large. It has become difficult to keep the outer diameter of the lens group small. On the other hand, in this embodiment, the combined negative refractive power of the first lens group and the second lens group is made stronger, that is, the negative refractive power of the second lens group is made stronger. Further, the lens interval D2W at the wide-angle end is made as small as possible so that off-axis rays pass as low as possible in the first lens group.

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.

Next, the meaning of the conditional expressions related to the present invention will be explained.

Conditional expression (1) defines the focal length of the first lens group relative to the focal length of the entire system at the telephoto end, and if the lower limit is exceeded and the positive refractive power of the first lens group becomes strong, the overall length will be shortened. However, in order to secure off-axis light flux on the wide-angle side, the lens outer diameter of the first lens group is increased,
Furthermore, it becomes difficult to correct aberrations. If the upper limit is exceeded and the positive refractive power of the first lens group becomes weak, the outer diameter of the lens of the first lens group becomes small, but the overall length becomes long (which is not preferable).

Conditional expression (2) defines the focal length of the second lens group relative to the focal length of the first lens group under conditional expression (1), and if the negative value of the second lens group exceeds the lower limit, If the refractive power of the first lens group becomes stronger, the outer diameter of the first lens group can be made smaller, but the back focus becomes longer than necessary and the overall length becomes longer.

Furthermore, it becomes difficult to correct various aberrations, especially spherical aberration and distortion, occurring in the second lens group in a well-balanced manner. If the negative refractive power of the second lens group becomes weaker by exceeding the upper limit value, it is preferable for correcting aberrations, but the outer diameter of the lens of the first lens group increases, making it difficult to achieve compactness.

Conditional expression (3) defines the focal length of the fifth lens group relative to the focal length of the entire system at the telephoto end. When the refractive power of the fifth lens group becomes stronger beyond the lower limit, the fifth lens group
Although this is advantageous in making the outer diameter of the sixth lens group compact, various aberrations generated in the fifth lens group become too large, making it difficult to correct them with other groups. When the positive refractive power of the fifth lens group becomes weaker than the upper limit, the fifth lens group
, the outer diameter of the lens of the sixth lens group increases, and the total length of the lens also increases, which is not preferable. In addition, preferably D
It is preferable to move the sixth lens group so as to satisfy the conditional expression s w > D 5 .

Although the object of the present invention can be achieved with the above configuration, it is more preferable that the following conditional expressions be satisfied.

1.1 < fs/l f21 < 3.7
...(4) 0.15 < (DIT -D,
w) /f, < 0.3 - (5) Q, Q7 <
(D2W D2A) /ft < 0.2...
(6) Note that f3 is the focal length of the third lens group.

Conditional expression (4) is based on the third focal length of the second lens group.
This defines the focal length of the lens group, and if the lower limit is exceeded and the positive refractive power of the third lens group becomes stronger, the overall length of the lens and the outer diameter of the lenses of the 4th, 5th and 6th lens groups become more compact. Although this is advantageous, various aberrations generated in the third lens group increase, making it difficult to correct them. If the upper limit is exceeded and the positive refractive power of the third lens group becomes weak (if this happens, the overall lens length and the lens outer diameters of the fourth, fifth, and sixth lens groups will increase, which is not preferable).

Conditional expression (5) is based on the first and second focal lengths at the telephoto end.
This defines the difference in the air spacing between the lens groups between the telephoto end and the wide-angle end, that is, the amount of change in the distance between the first and second lens groups during zooming. , the magnification effect of the second lens group becomes smaller, and in order to obtain a predetermined magnification ratio, it becomes necessary to greatly change the air distance between the other groups, and at the wide-angle end, space is reserved for this purpose. (As a result, the total lens length at the wide-angle end increases.If the distance change exceeds the upper limit, the magnification change effect of the second lens group will increase,
Although this is advantageous for increasing magnification, if an attempt is made to ensure sufficient off-axis light flux at the telephoto end, the outer diameters of the lenses in the first lens group or the fourth, fifth, and sixth lens groups will increase.

Conditional expression (6) is the difference in air spacing between the second and third lens groups between the wide-angle end and the telephoto end with respect to the focal length at the telephoto end, that is, the change in the distance between the second and third lens groups during zooming. It stipulates the amount. If the distance change becomes smaller than the lower limit, it is advantageous to reduce the outer diameter of the first lens group, but in order to obtain a predetermined zoom ratio, the fourth lens group,
It becomes necessary to greatly change the air space between the fifth lens group, and this space must be secured in advance at the wide-angle end. In order to secure the external light flux, the outer diameter of the lens of the fifth lens group increases. If the amount of interval change increases beyond the upper limit, it is advantageous for high multiplication, but
This means that the distance between the second and third lens groups at the wide-angle end becomes wider, which is not preferable because the outer diameter of the first lens group becomes larger in order to secure off-axis light flux.

Furthermore, the second lens group is a lens group having a stronger negative refractive power than the focal length of the entire system at the telephoto end. Therefore, in order to reduce various aberrations occurring in the second lens group, the second lens group should be composed of at least two negative lenses and at least one positive lens, and in particular, the object of the negative lens should be located closest to the object side. When the radii of curvature on the side and image side are r21 and r2□, lr2□/r2□1<0.23 ・
...It is good to satisfy (7). Conditional expression (7) defines the ratio of the radius of curvature of the lens closest to the object in the second lens group, and the fact that r22 becomes looser than r21 beyond the upper limit is due to the negative This means that the refractive power becomes weaker, and for this reason, in order to give the second lens group a predetermined refractive power, the radius of curvature of the other negative lenses becomes tighter, or the number of lenses increases; in the former case, The occurrence of various aberrations becomes significant, and in the latter case, the second lens group becomes thicker, so that the outer diameter of the first lens group increases in order to secure an off-axis beam on the wide-angle side.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and νl 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=36-342.5 FNO=1:3
．． 4～5.7 2 ω= jba, va= ljb
, Ue+F+D33 = 3.00
N+ 9 = 1.78472R34 = 32° ~ 7.2' ν 1 = 37.2 ν 2 = 81.6 C 3 = 81.6 C 4 = 42.7 C 5 = 46.6 C 6 = 23.9 ν 7 = 46.6 C 8-60.7 C 9 = 70.2 ν 10 = 23.9 ν 19 = 25.7 Numerical Example 2 - F = 36 to 341.9 FNO = 1: 3
．． 4 ~ 5.72ω = 62° ~ 7.2゜ν 3 = 64.1 ν 4 = 42.7 C 5 = 46.6 C 6 = 23.9 ν 7 = 46.6 C 8 = 63.4 Numerical value Example 3 F=36-341.6 FNO=l: 3.4-5.
7 2ω=626) to d==4t1.
15j~7.2' ν 1=37.2 ν 2= 81.6 C 3= 81.6 C 4= 42.7 C 5=46.6 C 6=23.9 ν 7= 46.6 C B =60.7 C9=70.2 ν10=23.9 Table 1 [Effects of the Invention] As explained above, according to the present invention, a compact zoom lens with high performance and high zoom ratio is provided. can do.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the paraxial arrangement of the present invention. 2 to 4 are lens sectional views at the wide-angle end of numerical examples 1 to 3, respectively. Figures 5 to 7 are aberration diagrams for object 1 in Numerical Examples 1 to 3, respectively, and (A) to (C) are the wide-angle end, middle, and wide-angle end, respectively.
This is an aberration diagram at the telephoto end, where S is the magnifying image plane and M is the meridional image plane. Figure (A) FNO/3.4 W2319
W=31' Spherical aberration Astigmatism Distortion (%) Sine condition Fho14. '? Z w = '? ,／'
w = 9.7' Sine condition Figure 5 (C) FNO15, '15 W = 3.6'
VJ=3.6' spherical aberration
Non-emerging aberration Distortion (%) Sine condition FNO/3.4 W=31'
W=:31' sine condition Figure 6 (8) FNO/4. BZ W= q, /'
W=9. /' Spherical aberration Astigmatism Distortion (%) Sine condition FNo/, 5.7 VJ=3.6""
W = 3.6' Spherical aberration Astigmatism Distortion (%) Sine condition FNO/3.44 W = 37'
W=3+″ Spherical aberration Astigmatism
Distortion (%) Sine condition FNO/4. '? 2W=9.1°
W=9.1゜Sine condition FNO15,'l W=3,l)'
W=3.6° Spherical aberration Astigmatism Distortion (%) Sine condition

Claims (1)

[Claims] (1) In order from the object side: a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a negative refractive power. a fourth lens group with power,
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 di_w, respectively.
When di_t, zooming from the wide-angle end to the telephoto end is performed while satisfying 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 the first lens group, the second lens group, and the fifth lens Let the focal length of each group be f_
1, f_2, f_5, when the focal length of all points at the telephoto end is f_T, 0.26<f_1/f_T<0.88 0.11<|f_2|/f_1<0.31 0.08<f_5/ A high variable power zoom lens that satisfies the following condition: f_T<0.3. (2) When the focal length of the third lens group is f_3, 1
．． 1<f_3/|f_2|<3.7 0.15<(D_1_T−D_1_W/f_T<0.3
0.07<(D_2_W−D_2_T)/f_T<0.
A high-power zoom lens according to claim 1, which satisfies the following two conditional expressions.