JPH02296208A - Wide angle zoom lens - Google Patents

Abstract

PURPOSE:To obtain the zoom of a long back focus at an ultra wide angle of view by forming the zoom lens into two-group constitution consisting, successively from an object side, a front group having a negative refracting power and a rear group having a positive refracting power, dividing the rear group to three groups; positive, negative and positive, successively from the object side, and changing the relative positions of the respective groups. CONSTITUTION:This lens has, successively from the object side, the 1st lens group having the negative refracting power, the 2nd lens group having the positive refracting power, the 3rd lens group having the negative refracting power, and the 4th lens having the positive refracting power. The 1st lens group, the 2nd lens group and the 4th lens group are so moved as to respectively decrease, increase and decrease the spacing between the 1st lens group and the 2nd lens group, the spacing between the 2nd lens group and the 3rd lens group and the spacing between the 3rd lens group and the 4th lens group at the time of zooming from the wide angle end to the telephoto end diameter. In addition, the lens is so constituted as to satisfy equation I when the focal length of the 1st lens group is designated as f1, the focal length of the 2nd lens group as f2, the focal length of the 3rd lens group as f3, the focal length of the 4th lens group as f4, the focal length of at the wide angle end of the entire system as Fw, and the focal length at the telephoto end of the entire system as Ft. The zoom lens having the long back focus while having the ultra-wide angle aperture diameter is obtd. in this way.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an ultra-wide-angle zoom lens for a 35 rhm Leica version camera, and has a wide range of applications as an ultra-wide-angle zoom lens for video cameras, still cameras, etc. be.

Particularly preferably, the angle of view 2ω is 92.8° to 64.6°Fn
This relates to o2.8 class zoom.

[Prior art]

Conventionally, this type of ultra-wide-angle zoom was disclosed in Japanese Patent Application Laid-open No. 57-19091.
There is No. 7, which is a two-group zoom lens consisting of a front group with negative refractive power and a rear group with positive refractive power from the object side. In the embodiment, the Fno is about 3.5, and if the aperture is made even larger, it tends to become difficult to secure the back focus. In order to achieve such high zoom magnification, the second lens group is divided into three groups, positive, negative, and positive, resulting in a four-group configuration, as disclosed in Japanese Patent Application Laid-Open No. 55-14403 and U.S. Patent Specification No. 4. , No. 759,617, JP-A-57-11
No. 315 and Japanese Patent Application Laid-open No. 63-241511. These are examples where the wide-angle end is applied to a relatively wide-angle zoom with an angle of view of 2ω = 75°4°, but with the current configuration, the back focus is still insufficient for the ultra-wide-angle large-aperture zoom that is the purpose of this application. There is a risk that it will not be possible to secure the

Furthermore, as an example of application to a wider-angle zoom, there is a product 24-40 mm 7 released by Tokina Optical.
There are 2 and 8.

Even with this zoom, the angle of view at the wide-angle end is 2ω = 84°.

These lenses employ a four-group zoom system to increase the zoom aperture.

[Problem that the invention seeks to solve]

The present invention provides a zoom lens with a small lower number while having an extremely wide angle of view, and in the examples described later, a lens with an angle of view 2ω of 92.8° to 64.6° and an F number of 2.8 is disclosed. ing.

A further object of the present invention is to provide a zoom lens with a long back focus while having an ultra-wide angle and large aperture.

[Means for solving problems]

The super wide-angle zoom lens of the present invention includes, from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a third lens group having a positive refractive power. When zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group, the distance between the second lens group and the third lens group, and the distance between the third lens group and the fourth lens the first so that the interval between the groups decreases, increases, and decreases, respectively.
The lens group, the second lens group, and the fourth lens group are assumed to be movable, and the focal length of the first lens group is f1, the focal length of the second lens group is f2, and so on. The focal length of the third lens group is set to f3. Fourth
The focal length of the lens group is f4. The focal length of the entire system at the wide-angle end is Fw.

When the focal length of the entire system at the telephoto end is Ft, 0.6
< ifl/Ft l <1.20.6 < jf2
/Ft l <1.10.8 < 1f3/Ft l
<1.40.95< l f4/Ft 1< 1.6
satisfies the following conditions.

〔Example〕

Examples of the present invention will be described in detail below.

The present invention is based on a zoom lens with a two-group configuration: a front group with a negative refractive power from the object side, and a rear group with a positive refractive power from the object side. divided into
By changing the relative position of each group, the efficiency of zooming is increased and a large-diameter, ultra-wide-angle zoom lens is realized.

In particular, by optimizing its paraxial arrangement, the first lens group,
The lens configuration of the second lens group has been simplified, the lens configuration in front of the aperture has been simplified, and the filter diameter has been reduced (
This makes it possible to do this and at the same time ensure sufficient back focus.

The specific zoom movement locus is as shown in Fig. 1. From the object side, the first lens group 1 has a negative refractive power, the second lens group 2 has a positive refractive power, and the second lens group has a negative refractive power. It has three lens groups 3 and a fourth lens group 4 with positive refractive power, and when zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group, and the distance between the second lens group and the third lens The first lens group, the second lens group, so that the distance between the groups and the distance between the third lens group and the fourth lens group decrease, increase, and decrease, respectively.
The fourth lens group moves along movement trajectories A, B, C, and D.

The second to fourth lens groups serve as the rear group, increasing the variable power effect and increasing the degree of freedom in refractive power distribution, making it possible to secure the necessary back focus.

In addition to such a zoom configuration, it is necessary to satisfy the following conditions.

Here, the focal length of the first lens group is f1, the focal length of the second lens group is f2. The focal length of the third lens group is set to f3. The focal length of the fourth lens group is set to f4. If the focal length at the wide-angle end of the entire system is Fw, and the focal length at the telephoto end of the entire system is Ft, the following equation is satisfied.

0.6 < 1fl/Ft l <1.2
(1) 0.6 < ] f2/Ft l <1.1
(2) 0.8 < 1f3/Ft l <
1.4 (3) 0.95< 1f4/Ft
l <1.6 (4) Next, the meaning of the extreme value of the condition will be explained.

Conditional expression (1) relates to the refractive power distribution of the first lens group. If the upper limit is exceeded, the refractive power arrangement of the first lens group becomes weak, and in an ultra-wide-angle zoom lens such as the one according to the present invention, the filter diameter increases. In addition, the disadvantage of increasing the movement stroke for zooming and increasing the size of the lens system is noticeable, and the tendency for the back focus to become short is noticeable. This corresponds to a significant increase in

This is advantageous in terms of paraxial arrangement in terms of filter diameter, compactness, and ensuring back focus as mentioned earlier. However, since the refractive power arrangement of the first lens group becomes stronger, the structure of the lens group must be made more complicated, which results in an increase in the size of the first lens group, resulting in an increase in the filter diameter and an increase in the size of the lens. . Therefore, in particular, it becomes impossible to adopt a simple lens configuration as shown in the embodiment of the present application.

Conditional expression (2) relates to the refractive power distribution of the second lens group. If the upper limit is exceeded, the refractive power arrangement of the second lens group becomes weaker, which is advantageous for securing back focus. However, there is a strong tendency for the overall length of the lens to become long, which is a significant disadvantage for compactness. Furthermore, the height of the axial rays exiting the second lens group becomes large, making it difficult to correct spherical aberration in the third lens group, and the disadvantage of increasing the aperture diameter becomes significant.

Exceeding the lower limit significantly strengthens the distribution of refractive power in the second lens group. Increasing the refractive power of the second lens group is advantageous for compactness, but in the case of an ultra-wide-angle lens like the one in this application, it becomes difficult to secure the back focus. In addition, since the refractive power arrangement of the second lens group becomes stronger, the structure of the lens group must be complicated, which results in the disadvantage that the second lens group becomes thicker. In the case of the zoom configuration of this example, it is advantageous in terms of optical performance to place the diaphragm between the second and third lens groups, but if the second lens group is thick (the maximum image at the wide-angle end In order to secure a high luminous flux, the lens diameter of the first lens group increases, and the filter diameter also increases, making it difficult to adopt a simple lens configuration.

Conditional expression (3) relates to the refractive power distribution of the third lens group.

With ultra-wide-angle zoom lenses, it is extremely difficult to secure back focus because the focal length is extremely short. It is advantageous for the refractive power arrangement of the third lens group to be weak in terms of aberration correction, but if it is weakened beyond the upper limit, it is very difficult to secure the back focus. Exceeding the lower limit corresponds to significantly strengthening the refractive power distribution of the third lens group. This is advantageous in terms of paraxial arrangement for securing the back focus mentioned earlier. However, since the refractive power arrangement of the third lens group becomes strong, the structure of the lens group must be complicated in order to correct aberrations. In particular, it becomes difficult to correct spherical aberration and curvature of field due to zooming.

Conditional expression (4) relates to the refractive power distribution of the fourth lens group. If the upper limit is exceeded, the refractive power arrangement of the fourth lens group becomes weak, which is advantageous for compactness. However, securing back focus becomes extremely difficult. Exceeding the lower limit corresponds to significantly strengthening the refractive power distribution of the fourth lens group. Increasing the refractive power of the fourth lens group is advantageous for securing back focus, but since the refractive power arrangement of the fourth lens group is strengthened, there is a drawback that the configuration of the lens group must be complicated. It's coming.

A detailed explanation will be given below using numerical examples.

In the numerical examples, Ri is the radius of curvature of the i-th lens surface from the object, Di is the thickness and air distance of the first lens from the object, and Ni and νi are the d-lines of the glass of the i-th lens from the object, respectively. are the refractive index and Atsube number of

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis,
The traveling direction of light is positive, R is the paraxial radius of curvature, B, C,
When D and E are each aspheric coefficients, it is expressed by the following formula.

Numerical Example 1 is shown below. A cross section of the lens is shown in FIG. 1, along with the locus of movement of each lens group due to zooming. Also, at the wide-angle end at infinite object distance, intermediate focal position,
Aberration diagrams at the telephoto end are shown in Figures 3 (a), (b), and (C), respectively.

From the object side, the first lens group 1 has a negative refractive power, the second lens group 2 has a positive refractive power, and the third lens group has a negative refractive power.
It has a lens group 3 and a fourth lens group 4 having positive refractive power. When zooming from the wide-angle end to the telephoto end,
The distance between the lens group and the second lens group, the distance between the second lens group and the third lens group, and the distance between the third lens group and the fourth lens group are
The first lens group, the second lens group decrease, increase, and decrease, respectively.
The lens group and the fourth lens group move. Specifically, the first lens group 1 moves toward the image side on the wide-angle side, and slightly moves toward the object side on the telephoto side. The second lens group, the third lens group, and the fourth lens group move toward the object side.

In this example, in order to simplify the mechanical structure, the second lens group and the fourth lens group are configured to move together.

The first lens group l includes, from the object side, a concave meniscus lens with a convex surface facing the object side, a counter pressure lens, a biconcave l lens, and a positive lens. The second lens group 2 includes a bonded lens and a positive meniscus lens. The third lens group 3 includes a negative lens and a laminated lens. In the present invention, since the first lens group, the second lens group, and the third lens group have relatively weak refractive powers, it is possible to correct aberrations with a simple lens configuration. For the second lens group, if a more advanced aberration correction is required or the refractive power is to be strengthened, a positive lens may be added to the second lens group. In the third lens group, a laminated lens is arranged with the convex surface of the laminated surface facing the object side. It is also possible to arrange a bonded lens on the lens on the object side, but the spherical aberration of the g-line on the telephoto side will be somewhat worse, so the configuration shown in the example is more advantageous in the case of a paraxial arrangement as in the present application. be.

In this embodiment, focusing to a finite distance is performed by moving the third lens G3 and fourth lens G4 of the first lens group together.

On the other hand, the entire first lens group 1 is extended, or the first lens group is focused and the third lens group is focused at the same time. Fourth lens G3.
Paying out G4 faster (floating)
This makes it possible to focus on finite objects with high performance. In this embodiment, the diaphragm is arranged between the second lens group and the third lens group. Particularly during zooming, it is moved together with the third lens group.

Numerical Example 2 is shown below. A cross section of the lens is shown in FIG. 2, and the locus of movement of each lens group due to zooming is also shown. Also, at the wide-angle end at infinite object distance, intermediate focal position,
Figure 4(a) shows the aberration diagram at the telephoto end.

(b) and (C) respectively.

From the object side, the first lens group 1 has a negative refractive power, the second lens group 2 has a positive refractive power, and the third lens group has a negative refractive power.
It has a lens group 3 and a fourth lens group 4 having positive refractive power. When zooming from the wide-angle end to the telephoto end,
The distance between the lens group and the second lens group, the distance between the second lens group and the third lens group, and the distance between the third lens group and the fourth lens group are
The first lens group, the second lens group decrease, increase, and decrease, respectively.
The lens group and the fourth lens group move. Specifically, the first lens group 1 moves toward the image side on the wide-angle side, and slightly moves toward the object side on the telephoto side. The second lens group, the third lens group, and the fourth lens group move toward the object side.

The first lens group 1 includes, from the object side, a concave meniscus lens with a convex surface facing the object side, a counter pressure lens, a biconcave lens, and a positive lens. The second lens group 2 includes a laminated lens,
It has a positive meniscus lens. The third lens group 3 is
It has a negative lens and a laminated lens. In the present invention, since the first lens group, the second lens group, and the third lens group have relatively weak refractive powers, it is possible to correct aberrations with a simple lens configuration. For the second lens group, if a more advanced aberration correction is required or the refractive power is to be strengthened, a positive lens may be added to the second lens group. In the third lens group, a laminated lens is arranged with the convex surface of the laminated surface facing the object side. It is also possible to place a bonded lens on the object side lens, but
Since the spherical aberration of the g-line on the telephoto side becomes somewhat worse, the configuration shown in the embodiment is more advantageous in the case of a paraxial arrangement as in the present application.

In this embodiment, focusing to a finite distance is performed by moving the third lens G3 and fourth lens G4 of the first lens group together.

Also, the entire first lens group can be extended, or the third lens group can be focused at the same time as the first lens group. Fourth lens G3. G
It is possible to focus on a finite object by letting out 4 faster (floating). In this embodiment, the diaphragm is arranged between the second lens group and the third lens group. Particularly during zooming, it is moved together with the third lens group.

0f 0　　　　　o　.

-× -8 dimension )＾ For A) For Yu )))) For λ λλ
q) o o 〇−X + , -1 large? co ≧ ≧ ：′″ ) λ＾ uni ) yu
)) λ ＾ λtame〆kumei2α
0 mm -35 mm % Angle of view 2ω is 92.8° ~
We were able to achieve a high-performance zoom with a long back focus of 64°6” and Fno2.8.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing lens cross sections and zoom trajectories corresponding to Numerical Examples 1 and 2, respectively. Figure 3(a). (b), (C), and Fig. 4 (a), (b),
(C) is an aberration diagram at the wide-angle end, intermediate focal position, and telephoto end at an infinite object distance. In the figure, 1 is the first lens group, 2 is the second lens group, and 3 is the third lens group.
Lens group 4 is the fourth lens group. (shi) ω= :lR,,'l" 5・υυ All M (n one) 200FNO/Otsu 3 Shoyo Kaniigyu Cpu32,3'ω=32.3" -A, OQ Distorted Sen ('A) Old, 00

Claims (1)

[Claims] (1) From the object side, the first lens group has a negative refractive power, the second lens group has a positive refractive power, the third lens group has a negative refractive power, and the fourth lens has a positive refractive power. However, when zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group, the distance between the second lens group and the third lens group, and the distance between the third lens group and the fourth lens group are , decrease, increase, decrease, the first lens group, the second lens group,
The fourth lens group is assumed to be movable, and the focal length of the first lens group is f1, the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the focal length of the fourth lens group is f4.
, when the focal length at the wide-angle end of the entire system is Fw, and the focal length at the telephoto end of the entire system is Ft, 0.6<|f1/Ft|<1.
2 Characterized by satisfying the following conditions: 0.6<|f2/Ft|<1.1 0.8<|f3/Ft|<1.4 0.95<|f4/Ft|<1.6 Wide angle zoom lens.