JPH0658455B2 - Large aperture ratio telephoto zoom lens - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a large aperture ratio telephoto zoom lens, in particular, a focusing lens unit having a positive refractive power, a variable power lens unit having a negative refractive power, and a positive refractive power in order from the object side. The present invention relates to a zoom lens having a four-group configuration including the correction lens group and the positive refracting power relay lens group.

[Background of the Invention]

The telephoto zoom lens having such a configuration can maintain excellent image forming performance, and is therefore put into practical use as a zoom lens having various specifications. Further, it is required to have a specification with a larger aperture ratio while maintaining portability with a compact structure.

Conventionally, since this type of lens requires compactness, the image forming performance as a whole is insufficient. In particular, although the focusing lens group has a complicated lens structure, the imaging performance for a short-distance object is unsatisfactory. This is because with the miniaturization of the optical system, not only spherical aberration but also distortion and chromatic aberration become remarkable, which makes it difficult to correct these. Also, when the optical performance is emphasized, the configuration of the optical system itself becomes large,
The portability was poor and the operability had to decline.

On the other hand, it is required for a zoom lens with a large aperture ratio to have excellent imaging performance even when the aperture is open. However, as the aperture ratio increases, the ring-shaped spherical aberration, coma and astigmatism increase. The occurrence was remarkable, and the correction became more difficult. Then, it becomes difficult to reduce the aberration variation during zooming, and further, the aberration variation that accompanies the change in the object distance also increases, so it is difficult to reduce the close-up distance at which the image can be taken.

[Object of the Invention]

An object of the present invention is to have an excellent imaging performance over the entire zooming range, to make the optical system compact, and to maintain a high imaging performance even for short-distance object photography. It is to provide a large aperture ratio telephoto zoom lens.

[Outline of Invention]

The present invention is basically based on the conventional four-group zoom lens, and in this structure, in particular, the specific lens structure of the second lens group as the variable power lens group, that is, the arrangement of the lens components and the refraction of the lens components. The refractive index distribution is devised in terms of the refractive index distribution, the arrangement of the positive lens group on the object side of the diaphragm in the fourth lens group as the relay lens group, and the refractive index distribution.

That is, the second lens group G ₂ is composed of two cemented negative lens components and a single negative lens component, and an aperture diaphragm S is provided in the fourth lens group G _{4 so} that the second lens group G ₂ is closer to the object side than the diaphragm. Each positive lens component is arranged, and a negative lens component and a positive lens component are arranged behind the diaphragm. And
The power distribution condition for each lens group and the second lens group G ₂ and the fourth lens group G ₄ are configured to satisfy the following conditions.

Where f _{i is} the focal length of the i-th lens group (i = 1,2,3,4) F _{n is} the F-number of the entire system n _{N 1} : The lowest refractive index n in the negative lens component of the second lens group G _{2. N2:} refractive index lower 2nd negative lens component of the second lens group G ₂ n _P1: the lowest refractive index in the positive lens component on the object side of the stop of the fourth lens group G ₄ n _P2: fourth lens It has the second lowest refractive index in the positive lens component on the object side of the stop of the group G ₄ .

In the present invention as described above, the second lens group G as a variable power group
The negative lens component in ₂ has a lower refractive index than the conventional one, and the optical system has been made more compact, resulting in negative overshoot in close-up shooting, especially in close-up shooting on the telephoto side. We have succeeded in suppressing the spherical aberration fluctuation that occurs. As a result, the first lens group G as a focusing group
There is no need to complicate the configuration of _{1 and} the number of lenses is small, and it is possible to make a compact configuration.

Further, by setting an aperture stop in the fourth lens group G ₄ as a relay group, the aperture of the optical system is made thin and the lens configuration of the relay group as in the present invention is adopted.
At the same time as making it compact, it became possible to correct spherical zone spherical aberration and coma sufficiently well. In particular, by using a positive lens forming a positive cemented lens component located closer to the object side than the aperture stop in the fourth lens group G _{4 and} having a low refractive index and low dispersion glass, the curvature of the cemented surface is maximized. It can be loosened to correct chromatic aberration of high-order spherical aberration (in particular, aberration for short wavelength light). Furthermore, by using a low refractive index glass for the positive lens component closer to the object side than the diaphragm of the relay group, the negative Petzval sum generated in the variable power system of the second group is canceled out, and better correction of astigmatism is achieved. did. The above conditional expressions will be described below.

The conditional expressions (1) to (3) are the fourth as the relay group.
It is the ratio of the refracting power (1 / f _i ) of each variable power system group to the refracting power (1 / f ₄ ) of the lens group G ₄ . By dividing this by the F number (F _n ) of the entire system, the refractive power distribution of each group of variable power systems with respect to the brightness is defined. If the upper limits of these conditional expressions are exceeded, the optical system becomes too bright, so it is very difficult to correct various aberrations, and at the same time, the focal length f _{4 of} the fourth lens group G ₄ becomes long and the converging refractive power decreases. However, it is not suitable because the diaphragm diameter of the optical system becomes large. In addition, the total length of the fourth lens group G ₄ inevitably becomes long, and the fourth lens group G ₄
It becomes necessary to make the telescope compact as an extreme telephoto type. As a result, an excessive load is applied to the optical system for aberration correction.

On the other hand, if the lower limit of each of the conditional expressions (1) to (3) is deviated, a dark optical system is produced, which is contrary to the intended purpose of the present invention, which is not suitable. Further, the focal length f _{4 of} the fourth lens group G ₄ becomes shorter than necessary, and the chief ray having the maximum angle of view becomes the first lens group G 4.
When incident on the most object-side lens surface of ₁ , the incident position is largely separated from the optical axis. Therefore, in order to secure a sufficient amount of peripheral light even in the close-up shooting state, the first
Since the effective diameter of the lens located closest to the object in the lens group G ₁ becomes very large, it is difficult to make the configuration small. The focal length _{f 4} of the fourth lens group G ₄
Is shortened, it becomes difficult to secure a sufficient air space between the second lens group G ₂ and the third lens group G ₃ on the telephoto side of the zooming range, and the zooming range is increased. Will be difficult. Further, in this case, the air gap between the first lens group G ₁ and the second lens group G ₂ becomes unnecessarily large at the wide-angle end, which is disadvantageous for downsizing.

Conditional expression (4) represents the average value of the lowest refractive index and the second lowest refractive index of the negative lens component in the second lens group G ₂ .

When the value exceeds the upper limit, negative spherical aberration excessively occurs in the close-up shooting state on the telephoto side, and the burden of aberration correction of the first lens group G ₁ becomes large, making it difficult to achieve a simple configuration. . Moreover, in this case, since a high-dispersion material is used as the negative lens, it is difficult to correct chromatic aberration.

On the other hand, when the value goes below the lower limit of this condition, a material having a lower refractive index is used for the negative lens, so that aberration variation due to zooming is likely to occur, and the Petz-Pearl sum is excessively negative. It becomes difficult to correct the point aberration.

Conditional expression (5) shows the average value of the lowest refractive index and the second lowest refractive index of the positive lens component on the object side of the diaphragm in the fourth lens group G ₄ . If the upper limit is exceeded, the Petzpearl sum will become excessively negative, making it difficult to correct astigmatism.
Furthermore, it becomes difficult to correct chromatic aberration. On the other hand, when the value goes below the lower limit of the conditional expression (5), an excessive annular spherical aberration occurs particularly in the wide-angle side to the middle variable power range, and it becomes difficult to correct coma.

In the configuration of the present invention as described above, there are the following more desirable conditions.

_{0.2 <| f 2 / f 1} | <0.3 (6) 0.3 <| f 2 / f 23 | <0.45 (7) 0.85 <q 4A <1.4 (8) However, f _23: the most image side in the second group Of the negative lens component L ₂₃ of the fourth lens group: q _4A : Form factor of the most object-side positive lens component L ₄₁ in the fourth group, where the shape factor q is the radius of curvature of the object-side lens surface of the lens r _a , its image-side lens surface when a _{r b,} to be defined by _{q = (r b + r a} ) / (r b -r a).

(6) the focal length f ₁ of the first lens group G ₁ exceeds the upper limit becomes short of, the focal length f ₂ of the second lens group G ₂ becomes long, the second lens group G ₂ and the third lens It becomes impossible to secure a sufficient distance on the telephoto side from the group G _3, and the first lens group G ₁
And the distance between the second lens group G ₂ are also the same, which is not desirable. Further, since the focal length f _{1 of} the first lens group G ₁ becomes too short, the load on the brightness of the first lens group G ₁ becomes excessive, which causes fluctuation of spherical aberration and also increases the bending of spherical aberration. Inappropriate. The focal length f ₁ of the first lens group G ₁ Outside lower limit becomes longer,
The principal ray incident on the first lens group G ₁ is incident on a position largely separated from the optical axis. Therefore, the aperture of the first lens group G ₁ must be very large in order to secure a sufficient peripheral light quantity when focusing on a short distance. Further, the amount of extension of the first lens group G ₁ for focusing at a very close distance also increases, which is not suitable. Second lens group G ₂
The focal length f ₂ is the curvature of each lens surface of the second lens group G ₂ becomes strong short, aberration variation is excessively generated, there is a tendency that the astigmatism also it becomes difficult to correct.

Expression (7) is a condition that defines an appropriate distribution of the refractive power of the final lens component of the second lens group G ₂ . If the upper limit is exceeded, spherical aberration becomes excessively positive on the telephoto side, which is unsuitable. If the value goes below the lower limit, negative spherical aberration is excessively generated, which is unsuitable.

Expression (8) is a condition for properly balancing spherical aberration and coma. Above the upper limit, the spherical aberration becomes excessively negative, and above the lower limit, the opposite tendency increases.

In the configuration like the present invention, the third group as the correction group is used.
By changing the shape of the cemented positive lens component on the image side in the lens group G _{3 to} the shape as in the present invention, it is possible to correct the fluctuation of astigmatism due to zooming.

Further, among the first to eighth embodiments described later, desirable conditions in the configuration excluding the eighth embodiment are as follows. That is, f ₂₁ : focal length of the first negative lens component L ₂₁ of the second group f ₂₂ : focal length of the second negative lens component L ₂₂ of the second group q _4C : negative lens just behind the diaphragm of the fourth group Form factor of component L ₄₃ is 0.3 <| f ₂ / f ₂₁ | <0.5 (9) 0.1 <| f ₂ / f ₂₂ | <0.14 (10) −1.3 <q _4C <−0.7 (11) Further, in order to suppress the aberration variation at a short distance, the curvature radius of the lens surface of the first lens group G ₁ closest to the object tends to be small, and the shape factor of the cemented lens component closest to the object is q _1A . In this case, it is desirable that 0.75 < _q1A <1.1 (12).

The following conditions are desirable in the eighth embodiment.

_{0.05 <| f 2 / f 21} | <0.13 (13) 0.3 <| f 2 / f 22 | <0.6 (14) EXAMPLES The examples according to the following the present invention will be described. In the first embodiment according to the present invention, the first lens group G ₁ is composed of a cemented positive lens component L ₁₁ and a single positive lens component L ₁₂ .
The second lens group G ₂ has, in order from the object side, a negative lens component L ₂₁ formed by laminating a positive lens and a biconcave negative lens, and a negative lens formed by laminating a biconcave negative lens and a positive lens. It is composed of a component L ₂₂ and a single biconcave negative lens component L ₂₃ . The third lens group G ₃ is composed of a single positive lens component L ₃₁ and a cemented positive lens component L ₃₂ . The fourth lens group G ₄ having a diaphragm is arranged in order from the object side.
A single positive lens component L ₄₁ with a stronger curvature surface facing the object side, a positive lens component L _{42 with} a stronger curvature surface facing the object side made up of a positive lens and a negative lens cemented together, an aperture, an image It is composed of a negative lens component L ₄₃ and a single positive lens component L ₄₄ whose surface has a stronger curvature.

Table 1 below shows the specifications of the first embodiment. In the table, the numbers at the left end represent the order from the object side, and the refractive index and the Abbe number are values for the d-line (λ = 587.6 nm). In addition, T.
L. Is the total length of the lens system, that is, the distance from the vertex of the lens surface closest to the object to the image plane. (The same applies to the following examples) 2A to 2C are graphs showing various aberrations of the first embodiment.
Shown in the figure. Fig. 2A shows the wide-angle end, Fig. 2B shows the telephoto end,
FIG. C is a diagram of various aberrations in each state of the close-up distance at the wide-angle end, and FIG. 2D is a diagram of various aberrations in each state of the close-up distance at the telephoto end.

The second to fourth examples according to the present invention have the same lens configuration as that of the first example, but aberration correction is performed by changing the material of the lens component forming each lens group. Is.

Tables 2 to 4 below show specifications of the second to fourth examples.

The various aberration diagrams for the second to fourth examples are shown in FIGS.
Figures B, 3C and 3D to 5A, 5B, 5C and 5D are shown respectively.

In each aberration diagram, A is a wide-angle end, B is a telephoto end, C is a close-up distance at the wide-angle end, and D is a close-up distance at the telephoto end.

In the fifth embodiment according to the present invention, as shown in the lens configuration diagram of FIG. 6, the positive lens component closest to the object side on the object side of the diaphragm in the fourth lens group G ₄ is a cemented lens, and 2 The th positive lens component is composed of a single positive lens.

Table 5 below shows specifications of the fifth embodiment.

FIGS. 7A, 7B, 7A and 7B are graphs showing various aberrations of the fifth embodiment.
It is shown in FIGS. 7C and 7D.

In the sixth embodiment according to the present invention, as shown in the lens configuration diagram of FIG. 8, the cemented negative lens component closest to the object side in the second lens group G ₂ has a stronger curvature toward the image side in order from the object side. It is constructed by cementing a negative lens having a surface facing and a positive meniscus lens having a convex surface facing the object side, and the configuration of the other lens groups is almost the same as in the first to fourth embodiments.

Table 6 below shows specifications of the sixth embodiment.

9A, 9B, 9 are graphs showing various aberrations of the sixth embodiment.
It is shown in FIGS.

The seventh embodiment according to the present invention, whose lens structure is shown in FIG. 10, has the same second lens group G ₂ structure as that of the sixth embodiment described above, and is positive on the object side of the diaphragm of the fourth lens group G _4. Like the fifth embodiment shown in FIG. 6, the lens component has a positive lens component closest to the object in the fourth lens group G ₄ as a cemented lens.

Table 7 below shows specifications of the seventh embodiment.

11A, 11B, 11 are graphs showing various aberrations of the seventh embodiment.
Shown in C and 11D.

In the eighth embodiment according to the present invention, as shown in the lens configuration diagram of FIG. 12, two positive lens components of the first lens group G ₁ are both cemented lenses, and the second lens group G ₂ is the object side. In order from, a negative lens component consisting of a cemented lens consisting of a positive lens and a negative lens with a stronger curvature facing the image side, a single biconcave negative lens component, and a biconcave negative lens with a convex surface facing the object side. The cemented lens is composed of a cemented lens with a positive meniscus lens, and a cemented negative lens component having a surface having a stronger curvature toward the object side. The configuration of the fourth lens group G ₄ is almost the same as that of the first to fourth examples.

Table 8 below shows specifications of the eighth embodiment.

FIGS. 13A, 13B, 13 are graphs showing various aberrations of the eighth embodiment.
It is shown in FIG.

From the various aberration diagrams for each of the above examples, each of the examples has excellent imaging performance at the wide-angle end and the telephoto end, and maintains good imaging performance even in the close-range shooting state in each zoom range. It is clear that it has been done.

〔The invention's effect〕

As described above, according to the present invention, while having excellent imaging performance over the entire variable power range, the optical system can be made compact and good imaging performance can be maintained even for a short-distance object. A telephoto zoom lens is achieved.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of the first embodiment according to the present invention, FIGS. 2A, 2B, 2C and 2D are aberration diagrams of the first embodiment, and FIGS. 3A, 3B, 3C and 3D are second embodiment. FIGS. 4A, 4B, 4C, and 4D are aberration diagrams for the third embodiment, and FIGS. 5A, 5B, 5C, and 5D are aberration diagrams for the fourth embodiment. Is a lens configuration diagram of the fifth embodiment, FIGS. 7A, 7B, 7C and 7D are aberration diagrams of the fifth embodiment, FIG. 8 is a lens configuration diagram of the sixth embodiment, 9A, 9B, 9C, FIG. 9D is a diagram of various types of aberration in the sixth example, and FIG. 10 is a lens configuration diagram of the seventh example.
11A, 11B, 11C, and 11D are aberration diagrams for the seventh embodiment, FIG. 12 is a lens configuration diagram of the eighth embodiment, and 13A and 13D.
B, 13C and 13D are aberration diagrams of the eighth embodiment. [Explanation of Signs of Main Parts] G ₁ ...... First lens group G ₂ ...... Second lens group G ₃ ...... Third lens group G ₄ ...... Fourth lens group S ...... Aperture stop

Claims (1)

[Claims] 1. A first lens group G ₁ as a focusing group having a positive refracting power, which is movable in order from the object side along the optical axis for focusing.
Second lens group G ₂ as a variable power group of negative refracting power which is movable on the optical axis for variable power, and correction group of positive refractive power which is movable on the optical axis to keep the image plane position constant. As a third lens group G ₃ and a fourth lens group G ₄ as a positive refractive power relay group
In the four-group zoom lens, the second lens group G ₂ has three negative lens components, of which two negative lens components are cemented together, and the fourth lens group G ₄
Is a large aperture ratio telephoto zoom lens characterized in that it has two positive lens components, an aperture stop, a negative lens component and a positive lens component in order from the object side, and satisfies the following conditions. Where f _{i is} the focal length of the i-th lens group (i = 1,2,3,4) F _{n is} the F-number of the entire system n _N1 : is the lowest refractive index of the negative lens components of the second lens group G _2. n _N2 : second lowest refractive index in the negative lens component of the second lens group G ₂ , n _P1 : lowest refractive index in the positive lens component on the object side of the aperture of the fourth lens group G ₄ , n _P2 : fourth The refractive index is the second lowest in the positive lens component on the object side of the stop of the lens group G ₄ .