JPS59170811A - Telephoto lens - Google Patents

Abstract

PURPOSE:To obtain a telephoto lens which has short overall length and aberrations compensated excellently by providing a lens group with positive refracting power and a lens group with negative refracting power in order from a subject side, and satisfying specific requirements. CONSTITUTION:This lens system consists of the 11th lens group with positive refracting power and the 12th lens group with negative refracting power in order from the subject side, and the 12th lens group includes one negative lens and one positive lens. Some lens group of the 2nd lens group is moved for focusing, and the 2nd lens group has a stop, has a lens group 21 with negative refracting power and a lens group 22 with positive refracting power on the image surface side of the stop, and meet requirements shown by inequalities I and II, wherein nu21 and nu22 are mean Abbe numbers of both leng groups and nu11 is the mean Abbe number of the 11th lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a telephoto lens, and more particularly to a telephoto lens in which a part of the lens group at the rear of the telephoto lens is moved to perform nookashing.

Conventionally, in a telephoto lens consisting of a second lens group with a refractive power of two and a second lens group with a refractive power, instead of performing focusing by moving the entire lens, all or part of the second lens group is moved. Telephoto lenses that use so-called rear focus, which performs focusing by moving the subject, have been proposed frequently. This rear focus has advantages such as ease of lens operation and less lens driving force.

However, in the case of rear focusing, in which focusing is performed by moving a part of the lens, multiple aberrations occur, making it difficult to correct these aberrations.
In order to downsize the lens system of a telephoto lens, it is effective to strengthen the refractive power of each lens group. However, when the refractive power of each lens group is strengthened, the Petzval sum increases in the negative direction, and spherical aberration also increases, making it difficult to adequately correct all of these aberrations.

An object of the present invention is to provide a telephoto lens that has a short overall lens length, achieves good correction of aberrations, and employs a zoom lens.

The features of the lens configuration for achieving the purpose of the present description include two lens groups, a first lens group having a positive refractive power and a second lens group having a negative refractive power, in the order of υ from the object side. The lens group consists of, in order from the object side, a first lens group with positive refractive power and a 12-lens group with negative refractive power, and the 12th lens group has at least one lens each with negative and positive refractive powers. It has a lens of
Focusing is performed by moving some of the lens groups of the second lens group, and the second lens group has an aperture, and a lens 2 having a negative refractive power is disposed on the image plane side of the aperture.
The average Atsube number of the 21st lens group and the 22nd lens group is 21. C, 2. When the average Atsube number of the first lens group is ν11, the following conditions are satisfied: (1) ν21>ν22 (2) νu>60.

In the telephoto lens according to the present invention, by dividing the lens group into the first lens group with positive refractive power and the 12th lens group with page refractive power, the rear principal point of the lens group is moved toward the object side. The overall length of the lens is shortened without increasing the refractive power of the valley lens group. Even if focusing is performed by moving part of the second lens group by K, the amount of aberrations generated can be reduced.

On the other hand, the lens group consists of two lenses #r with positive and positive refractive powers.
(Divided into two, chromatic aberration and double-height chromatic aberration occur in large quantities, and spherical aberration is caused by excessive pressure. Therefore, it is preferable to correct spherical aberration by configuring the 12th lens group with at least one lens with negative and positive refractive powers. Conditional expression (2)
By doing the following, the Hosochi chromatic aberration is corrected. If conditional expression (2) is exceeded, the correction of Hosochi chromatic aberration becomes insufficient. The chromatic aberration of magnification is well corrected by setting the Abbe numbers of the glasses of the negative and positive refractive power lenses behind the aperture of the second lens group as shown in conditional expression (1). If Conditional Expression (1) is not satisfied, it becomes difficult to satisfactorily correct the chromatic aberrations of the chromatic aberrations.

The telephoto lens according to the present invention can be achieved with the lens configuration described above, and in order to better achieve the object of the present invention, it is preferable that the following conditions be satisfied. The focal lengths of the first lens group and the 12th lens group are respectively FILe F
It is necessary to satisfy the condition when t□.

By setting the focal lengths of the first lens group and the twelfth lens group in this way, it is possible to shorten the overall lens length and reduce the occurrence of various aberrations, especially chromatic aberration. When the lower limit of conditional expression (3) is exceeded, the divergence of the twelfth lens group decreases, and the correction of spherical aberration becomes insufficient.

Also, if the upper limit is exceeded, the effect of the telephoto type, which is composed of two lens groups with positive and negative refractive powers in the first lens group, where the focal length of the first lens group is large, will be reduced, and the overall length of the lens will be shortened. It becomes difficult to adapt.

In addition, in the telephoto lens of the present invention, the 11th lens group and the 12th lens group
The distance between the lens groups and the focal length of the entire Iri lens system are [
1) 4 (410,036<-<0.07 If the maximum value is exceeded, the overall length of the lens will be shortened, but it will be difficult to correct aberrations, which is not preferable.

In addition, focusing is performed on the lens surface R in the embodiments described below.
1,~lens] Output H・1. Although this is done by moving the lens groups in one direction, it is also possible to move the other lens groups in one direction.

Akira Motomoto is able to achieve a compact W, 4 lens with a short overall lens length using the above lens configuration.

Next, an example of Akira Motomoto's number 11 will be shown. Numerical Example V (
=, R7 is the first lens surface or the four radius of the reflecting mirror in order from the 9-monme body 1 rule, I)i is the lens thickness and air spacing of the first scan from the object side, N1 and ν1 are the refractive index and Abbe's number of the glass of the first lens at 111 from the object side, respectively.

) ≧ A ≧ A
≧ ≧ ≧ \≧ to
))) ≧ MU ≧ )≧
≧ A ≧ ≧ A
, h'h A

[Brief explanation of the drawing]

, 7! Figures 1 to 3 are cross-sectional views of lenses of Examples 1 to 3 of the present invention, Figures 4 and 5 are Figures 6 of Example 1 of the present invention, and Figure 7 is implementation of the present invention. FIGS. 8 and 9 of Example 2 are diagrams of various aberrations in Example 3 of the present invention when the object is at infinity and when the object distance is 10 times the focal length, respectively. Flood bow Gen Otoi Chimasa Bow master Fui Chimasa Gou Genshi, I Chimasa 3 Ki Ax, Igyu

Claims (2)

[Claims] (1) It has two lens groups in order from the object side: the first lens group with positive refractive power and the second lens group with Sada's JI8 refractive power,
The first lens group includes, in order from the object side, a first lens group with a stop refractive power and a twelfth lens group with a negative refractive power.
The second lens l\ has at least 14)i lenses with negative and positive refractive powers, and performs all focusing by moving a part of the front gTh second lens group, r''
l: J The second lens group has an aperture, and IMII
ijl,',I From the pattern, 1st lens K I'i has a lens 21 with a negative refractive power, and a lens 2251 with a positive refractive power. A telephoto lens that satisfies the following condition: When the average Atsube numbers of the self-lenses 22 and 22R are respectively ν22.ν22° and the average Atsube numbers of the first lens group are ν8, then the following conditions are satisfied: . (2) The telephoto lens according to claim 1, wherein the telephoto lens satisfies a condition when the focal lengths of the first lens group and the twelfth lens group are each F11*FI2.