JPS63116113A - Telephoto zoom lens - Google Patents

Abstract

PURPOSE:To obtain the titled zoom lens having excellent image forming performance extending over the whole variable power area, by allowing the zoom lens constituted of four groups having a refractive power of positive, negative, positive and positive in order from an object side, to satisfy the prescribed conditions. CONSTITUTION:The titled zoom lens is constituted of a first lens groups G1 being a focusing lens group having a position refractive power a second lens group G2 being a variable power lens group having a negative refractive power, a third group G3 being a correcting group having a positive refractive power, and the fourth lens group G4 being a relay lens group having a positive refractive power, in order from an object side. The second lens group G2 has three negative lens components L2A, L2B and L2C, among which L2A and L2B are stuck to each other, and a fourth lens group G4 has two positive lens components L4A, L4B, an aperture diaphragm S, a negative lens component L4C and a positive lens component L4D, and constituted so as to satisfy the conditions in the expression I - the expression V. In this regard, in the expressions, f1, f2, f3 and f4 : Z : f4AB : nN1 : and nN2 denote focal distances of the first - the fourth lens groups G1-G4, a zoom ratio, a composite focal distance of L4A, L4B in the fourth lens groups G4, the lowest refractive index in the negative lens component of the second lens group G2, and the second lowest refractive index in the negative lens component of the second lens group G2, respectively.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a zoom lens, and particularly to a focusing lens group with positive refractive power, a variable magnification lens group with negative refractive power, and a correction lens group with positive refractive power, in order from the object side. The present invention also relates to a telephoto zoom lens having a four-group configuration consisting of a relay lens group with positive refractive power.

[Conventional technology]

Telephoto zoom lenses with such configurations have been put into practical use with various specifications. There is a growing demand for a compact configuration with a large zoom ratio while maintaining portability.

Conventionally, in this type of zoom lens, when focusing on the fourth lens group G4 as a relay lens group, the aperture stop is set closest to the object side of the fourth lens group G4, and the exit pupil is located far from the image plane. There were many structures. Further, miniaturization of this type of lens system has been carried out in the direction of increasing the refractive power of each lens group.

[Problem that the invention seeks to solve]

For this reason, the back focus became even shorter than the total length of the fourth lens group G4, and the position of the exit pupil tended to be far from the lens surface located closest to the image plane in the fourth lens group G4. As a result, the position where the principal ray with the maximum angle of view passes through the lens surface closest to the image plane in the fourth lens group G4 is far away from the optical axis, and it is difficult to ensure sufficient peripheral light intensity. This has the disadvantage that the effective diameter of the lens closest to the image plane in the lens group G4 must be enlarged, resulting in an increased lens aperture.

On the other hand, in order to solve the above problems and further reduce the aperture diameter of the optical system, if the aperture stop is set in the fourth lens group G4, it is possible to bring the exit pupil closer to the image plane. . However, the refractive power of the fourth lens group G4 is relatively strong, and the entrance pupil position is farthest from the object-side lens surface of the first lens group G1. The position of incidence on the most object-side lens surface of group G is far away from the optical axis, so in order to ensure sufficient peripheral light intensity even in close-range photography, it is necessary to The effective diameter of the lens located closest to the object side must be increased, and in this case as well, there is a problem in that the lens aperture must be increased.

An object of the present invention is to provide a compact telephoto zoom lens that has excellent imaging performance over the entire zooming range.

[Means for solving problems]

The present invention includes, in order from the object side, a first lens group G1 as a focusing lens group with positive refractive power, a second lens group Gz as a variable magnification lens group with negative refractive power, and a second lens group Gz as a correction lens group with positive refractive power. Based on a 4-group zoom lens consisting of a 3rd lens group G3 and a 4th lens group G4 as a relay lens group with positive refractive power, in particular, the specific lens configuration of the 2nd lens group as a variable power group, and the relay lens group. The refractive power and specific lens configuration of the fourth lens group have been devised.

That is, three negative lens components (L!1, L□, L, zc) are arranged as the second lens group Gt, and two of them are
The two negative lens components are laminated together, and the two positive lens components (
L 4A, L 411), aperture stop S, negative lens (
L4c) and a positive lens component (Lan) are arranged. The configuration satisfies the following conditions regarding the refractive power distribution to each lens group, the second lens group Gt, and the fourth lens group G4.

0.38<f4/(f+-Z)<0.48
(t)1.35<lf4/(fg・Z) |<1.
61 (2+0.5 < fa / (fs・Z)
<0.6 +3)0.3 < faam
/fa <0.44 (41 However, fl: Focal length of the first lens group G, rt: Focal length of the second lens group G, f3: Focal length of the third lens group G, f4: Fourth lens group Focal length Z of G4: Zoom ratio f4Al: Synthetic focal length of the two positive lens components (L4A, L41) on the object side in the fourth lens group G4 n: In the negative lens component of the second lens group G , lowest refractive index nNt: This is the second lowest refractive index among the negative lens components of the second lens group Gt.

[Effect]

In such a configuration of the present invention, the aperture stop is set in the fourth lens group G4 as a relay lens group. In addition, the refractive power of the fourth lens group G4 is weaker than that of the conventional one, and a structure with a relatively long bank focus is adopted.As a result, the fourth lens group G4 It has become possible to shorten the distance between the exit pupil and the lens surface located closest to the image plane.

Furthermore, the negative lens component of the second lens group G2 as a variable power group is divided into three parts, and lenses with low refractive indexes are used for these negative lens components. Therefore, the first lens group G as the focusing group can suppress the negative excessive fluctuation of spherical aberration that occurs in close-range shooting conditions, especially in close-distance shooting conditions on the telephoto side.
It becomes possible to strengthen the refractive power of the first lens group Gz and the second lens group Gz as a variable power group, and to reduce the size of the variable power system.

Thereby, the distance between the entrance pupil and the lens surface located closest to the object plane in the first lens group G can be shortened.

As described above, in the present invention, the distance between the lens surface closest to the image plane in the fourth lens group G4 and the exit pupil and the distance between the lens surface closest to the object side in the first lens group G and the entrance pupil are compared. By making the focal length smaller, securing sufficient amount of peripheral light without enlarging the effective diameter of the lens, and realizing miniaturization of the variable power system despite the weak refractive power of the fourth lens group G, We were able to achieve miniaturization of the entire lens system.

Each of the above conditional expressions will be explained below.

Conditional expression Tll to conditional expression (3) is based on the fourth lens group G as a relay lens group in specifications having a sufficient variable power range.
The refractive power (1/f+) distribution of each lens group G5 (i=1.2.3) in the variable magnification system is defined for the refractive power (1/f,) of G.4. If the upper limits of these conditional expressions are exceeded, the refractive power of each lens group G in the variable power system will become stronger than necessary, and an excessive load will be placed on correcting aberrations.
Since the total length of the optical system becomes too long and it becomes difficult to miniaturize the total length of the optical system, it becomes necessary to make the fourth lens group G an extremely telephoto type.On the other hand, each of these conditions (11 to (3)) If the lower limit of the formula is exceeded, the variable magnification system becomes large, which is not preferable as it hinders miniaturization of the overall length of the optical system.

In addition, the refractive power of the fourth lens group G4 becomes too strong, and the back focus cannot be maintained at a sufficient length.
When the principal ray with the maximum angle of view passes through the lens closest to the object side in the first lens group G1 and the lens closest to the image plane in the fourth lens group G4, it passes through a point far away from the optical axis and has a sufficient angle of view. In order to secure the amount of peripheral light, it is necessary to enlarge the effective diameter of the lens closest to the object in the first lens group G and the effective diameter of the lens closest to the image plane in the fourth lens group G. This is inappropriate because it goes against the intent of the present invention.

Conditional expression (4) is based on the second lens from the object side in the fourth lens group G4.
It shows an appropriate distribution of the composite refractive power of the two positive lens components (L4 and L4.).

If the upper limit is exceeded, the aperture diameter of the optical system will increase.
Furthermore, inward coma aberration occurs, which is not desirable in aberration correction. On the other hand, if the lower limit of conditional expression (4) is exceeded, the Petzval sum becomes excessively negative, making it difficult to correct astigmatism.

Conditional expression (5) indicates that the second lens group G! It shows the average value of the lowest refractive index and the next lowest refractive index of the negative lens components.

If the upper limit is exceeded, negative spherical aberration will occur excessively in a short distance state, and the burden of aberration correction on the first lens group G1 will increase. For this reason, it becomes difficult to increase the refractive power of the first lens group G1, which is not preferable for downsizing the lens system. On the other hand, if the lower limit of conditional expression (5) is exceeded, a material with a lower refractive index will be used for the negative lens, and aberration fluctuations due to zooming will likely occur. This makes it difficult to increase the refractive power of the second lens group G2, which is inconvenient for downsizing the lens system.

Furthermore, the Petzval sum also becomes excessively negative, making it difficult to correct astigmatism.

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

0.14 < f*/fig <
0.4 (6)0.2 <
rt/Etc < 0.45 (?) 0.55
<Qtc < 0.95
+810.85 <qla<
1.4 (9) f□: Focal length of the second negative lens component L□ in the second lens group G! tc: Third negative lens component L in the second lens group G!
Focal length qxc of 0: third negative lens component LIC in the second lens group G8
Shape factor qla: Shape factor of the positive lens component La5s located closest to the object side in the fourth lens group G4. The shape factor q is defined as q'' (rb + r, )/ (rb - r,), where r is the radius of curvature of the lens surface on the object side of the lens, and rl is the radius of curvature on the image surface side. .

Equation (6) is the second negative lens component L□ in the second lens group Gi.
It stipulates the appropriate refractive power distribution. If the upper limit is exceeded, astigmatism becomes excessively positive on the telephoto side, and inward coma aberration also occurs, which is inappropriate.

If the lower limit is exceeded, on the contrary, astigmatism becomes excessively negative and extroverted coma aberration occurs, which is inappropriate.

Equation (7) is the third negative lens component in the second lens group Gt,
It shows the appropriate refractive power distribution of c. If the upper limit is exceeded, the spherical aberration becomes excessively positive on the telephoto side, which is inappropriate. If the lower limit is exceeded, negative spherical aberration will be excessively generated, which is inappropriate.

Equation (8) is a condition for making the balance between spherical aberration and astigmatism appropriate. If the upper limit is exceeded, negative spherical aberration will occur excessively on the telephoto side, and astigmatism will also become excessively positive, which is inappropriate. When the lower limit is exceeded, the opposite tendency becomes stronger.

Formula +91 is a condition for appropriately balancing spherical aberration and coma aberration. When the upper limit is exceeded, the spherical aberration becomes excessively negative, and when the lower limit is exceeded, the opposite tendency increases.

Furthermore, in the first to fourth embodiments to be described later, the first lens group G as a focusing group is a positive lens component L laminated from the object side.
It is composed of IA and a single positive lens component L1m. Further desirable conditions for this configuration include the following.

0.4 < qla <
1.0 α・0.3 <
ft/f*A<0.5
011-1.3〈qac〈0.7 Q
B However, qla: first lens group G, laminated lens component LIA inside
Shape factor r zA: second lens group G! The first negative lens component L!
Focal length of A q4. : Shape factor of the negative lens component L4B located closer to the image plane than the aperture stop in the fourth lens group G.

(Example〕 Examples according to the present invention will be described below.

In the first embodiment according to the present invention, the first lens group G is composed of a bonded positive lens component LIA and a single positive lens component L1m, and the second lens group G2 is composed of a positive lens component LIA and a single positive lens component L1m in order from the object side. A negative lens component Lta formed by laminating a biconcave negative lens, a negative lens component L□ formed by laminating a biconcave negative lens and a positive lens, and a single biconcave negative lens component L! It is composed of c. Further, the third lens group G includes a single positive lens component L3A and a bonded positive lens component.

It is made up of. Fourth lens group G having an aperture stop
4, in order from the object side, is a single positive lens component L with a surface with a stronger curvature facing the object side; 4A% A positive lens consisting of a combination of a positive lens and a negative lens with a surface with a stronger curvature facing the object side; Ingredient L4. , an aperture stop S, a negative lens component Lac with a surface of stronger curvature facing the image plane side, and a single positive lens component Lsm.

In Table 1 below, which shows the specifications of the first embodiment, the leftmost number represents the order from the object side, and the refractive index and Atsube number are d
This is the value for the line (λ-587.6n■). (The same applies to the following examples) Table 1 (first example) Focal path jll r -100,0 to 300. OF number 4.6'a / (f+ -Z) -0,43
3I fa / (fg'Z) I =1.553
f4/ < rri ・Z) -0,556 fnam / fa -0,402 (n, B
"nwt) /2-1.6651 Figures 2A to 2C show various aberration diagrams for the first embodiment. Figure 2A is at the wide-angle end (f-100°0), and Figure 2B is at the middle (f-100°0). -200
, 0), and FIG. 2C is a diagram of various aberrations at the telephoto end (f-300, 0).

The second to fourth embodiments according to the present invention have the same lens configuration as the first embodiment, but aberrations are corrected by changing the material or refractive power distribution of the lens components constituting each lens group. This is what was done.

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

Table 2 (Second Example) Focal path @ f -100,0 to 300. OF number
466fa / (f+ 'Z) -0,
433)ra/(rt・Z)l=1.552)s
/ (fs ・Z) =0.556f4□
/ f, =0.401(nu++n++x
)/2=1.66510 Table 3 (Third Example) Focal length f −100,0 to 300. OF number 4
．． 6ra / (f+ -Z) =0.424
1 14 / (It ・Z)l-1,533)4
/ <12 ・Z) -0,549f, □ /
fs =0.366(ns++nNx)/2-1
．． 65980 Table 4 (Fourth Example) Focal length f-100, 0 to 300. OF number 4.
6f4/(f+・Z)=0.4241
ra/<rt・Z)l=1.533r, /
<12 ・Z) -0,549rna* /
r4 = 0.424 (n, +++n5t)/2
=1.661160 Various aberration diagrams for the second to fourth embodiments are shown in Figures 3A, 3B, 30 to 5A, 5B,
Each is shown in Figure 50.

In each aberration diagram, A is at the wide-angle end (f = 100°0),
B is intermediate (f = 200.0), C is telephoto end (f = 300.0)
．． 0) are various aberration diagrams.

From the aberration diagrams for each example, it is clear that all examples maintain excellent imaging performance over the entire zoom range.

〔effect〕

As is clear from the aberration diagrams of the above embodiments, according to the present invention, a telephoto zoom lens having excellent imaging performance over the entire zoom range can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of a first embodiment according to the present invention, FIGS. 2A, 2B, and 20 are various aberration diagrams regarding the first embodiment,
Figures 3A, 3B, and 30 are various aberration diagrams for the second embodiment, Figures 4A, 4B, and 4C are various aberration diagrams for the third embodiment, and Figures 5A, 5B, and 50 are diagrams for the fourth embodiment. It is a diagram of various aberrations. (Explanation of symbols of main parts) G1--...--First lens group Gt--
−−−・−・Second lens group G3'−−−−−
−−−−・−Third lens group G4 ・・〜・・・・・−・
・Fourth lens group s ----------・・---------Single aperture diaphragm Applicant Nippon Kogaku Kogyo Co., Ltd. Agent Patent attorney Takashi Watanabe Figure 1

Claims (1)

[Claims] In order from the object side, a first focusing lens group with positive refractive power;
Lens group G_1, a second variable magnification lens group with negative refractive power
Lens group G_2, the third lens group as a correction lens group with positive refractive power
In a four-group zoom lens consisting of a lens group G_3 and a fourth lens group G_4 as a relay lens group with positive refractive power, the second lens group has three negative lens components (L_2
_A, L_2_B, L_2_C), of which two negative lens components are constructed by lamination, and the fourth
Lens group G_4 includes, in order from the object side, two positive lens components (L_4_A, L_4_B), an aperture stop S, and a negative lens (
L_4_C) and a positive lens component (L_4_B),
A telephoto zoom lens that satisfies each of the following conditions. 0.38<f_4/(f_1・Z)<0.48(1) 1.35<|f_4/(f_2・Z)|<1.61(2
) 0.5<f_4/(f_3・Z)<0.6(3) 0.3<f_4_A_B/f_4<0.44(4) 1.45<(n_N_1+n_N_2)/2<1.67
(5) However, f_1: Focal length of the first lens group G_1 f_2: Focal length of the second lens group G_2 f_3: Focal length of the third lens group G_3 f_4: Focal length Z of the fourth lens group G_4: Zoom ratio f_4_A_B : Combined focal length n_N_1 of the two positive lens components (L_4_A, L_4_B) on the object side in the fourth lens group G_4: Lowest refractive index n_N_2 of the negative lens components in the second lens group G_2: Among the negative lens components, 2
lowest refractive index