JPS6224209A - Telephoto lens - Google Patents

Abstract

PURPOSE:To obtain a telephoto lens for correcting satisfactorily a secondary spectrum which is generated by following a conversion to telephotography, and obtaining a high resolution, by specifying a refractive index of glass, an Abbe number, a partial dispersion ratio, a radius of curvature, and a relation of a focal distance of the whole system, of each lens. CONSTITUTION:The titled lens has four lens groups of the first lens group I of a positive refractive power, the second lens group II of a negative refractive power, the third lens group III having a negative refractive power as a whole by sticking the lenses of positive and negative refractive powers, and the fourth lens group IV of a negative refractive power for focusing, and when a refractive index of glass, an Abbe number, and a partial dispersion ratio of the j-th lens of the first lens group are denoted as Nij, nuij, and thetaij in order, respectively, and a radius of curvature of the j-th lens surface of the i-th lens group, and a focal distance of the whole are denoted as Rij, and (f), respectively, the inequality is satisfied. Provided that the partial dispersion ratio theta is derived by theta=(Ng-Nd)/(NF-NC), when refractive indexes in (d), (g), C, and F lines are denoted as Nd, Ng, NC, and NF, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a telephoto lens, and in particular to a high-resolution telephoto lens that satisfactorily corrects the 4IK secondary spectrum among various aberrations suitable for photographic cameras, video cameras, etc. This relates to telephoto lenses.

(Prior Art) Among the various aberrations, it is important for K to improve the resolution of a telephoto lens having a long focal length to satisfactorily correct chromatic aberration in particular.

In general, even if chromatic aberration is well corrected for light rays of two wavelengths, the correction is not necessarily sufficient for light rays of other wavelengths, and a certain amount of chromatic aberration, a so-called secondary spectrum, often remains. The longer the focal length, the more this secondary spectrum becomes, resulting in color flare and color blurring, which is a factor that greatly reduces the performance of telephoto lenses.

Japanese Unexamined Patent Publication No. 57-64715 discloses a method for reducing the secondary spectrum of a telephoto lens by using an optical glass with anomalous dispersion in the front group of the telephoto lens with positive refractive power. is suggesting.

However, even if anomalous dispersion optical glass is used in the front group of a telephoto lens, if the entire lens system or the front group is moved during focusing, the secondary spectrum will change accordingly.
If there is an increase in On the other hand, Japanese Patent Application Publication No. 50-
Japanese Patent No. 139732 proposes a so-called rear focus type telephoto lens in which focusing is performed by moving a part of the rear lens group of the telephoto lens.

However, in this telephoto lens, secondary spectra remain, and correction of chromatic aberration fluctuations during focusing is not always sufficient.

(Problems to be Solved by the Invention) The present invention is characterized by providing a high-resolution telephoto lens that is suitable for photographic cameras, video cameras, etc. and that satisfactorily corrects the secondary spectrum that occurs as a result of telephoto cameras. The objective is to provide a telephoto lens that is well-corrected for aberration fluctuations, particularly chromatic aberration fluctuations, in 7-focus imaging when focusing is performed by moving some of the lens groups.

(Means for solving the problem) A first lens group having a plurality of lenses in order from the object side and having a positive refractive power as a whole, a second lens group having a negative refractive power, and lenses having positive and negative refractive powers. It has four lens groups as a whole: a third lens group with negative refractive power and a fourth lens group with negative refractive power for focusing, and the refraction of the glass of the i-th lens group O and the j-th lens. When the ratio, number of squares, and partial dispersion ratio are respectively 1cNij, νij, #ij, the radius of curvature of the j-th lens surface of the first lens group is Rlj, and the focal length of the entire system is f... ...(1) The following conditions are satisfied. However, partial dispersion ratio #li
The refractive index at the d, g, C, and F lines is Nd, Ng,
When NC, Ny, a-(N, -N, 1)/(NF
-NC).

Other features are described in the examples. (Implementation row) FIG. 1 and FIG. 2 each show a numerical implementation sequence l, which will be described later.

FIG. 4 is a cross-sectional view of the lens of No. 4. In the figure, t, n, Ilt, and ■ are the first, second, third, and fourth lens groups, respectively.

In this implementation array, the first lens group has multiple lenses, especially three lenses with positive, negative, and positive refractive powers, and is composed of lenses with positive refractive power as a whole to minimize the occurrence of spherical aberration that accompanies telephoto zooming. I'm doing less. In addition, if the third lens group (2) is composed of two lenses with positive and negative refractive powers, and is composed of a laminated lens with negative refractive power as a whole, and is further composed of glass having dispersion as described above, chromatic aberration, especially The secondary spectrum is reduced. A fourth lens group with a negative refractive power is placed at the end of the lens system, and a rear focusing method is adopted in which the fourth lens group is moved toward the image plane when focusing from an object at infinity to an object at a close distance.] , 7. Changes in chromatic aberration, especially lateral chromatic aberration, due to orcasing are reduced.

Conditional expression (11) is used to satisfactorily correct higher-order spherical aberrations and chromatic spherical aberrations regarding the refractive index of the glasses of the two lenses of the third lens group and the curvature half and radius of the bonded lens surfaces. If the radius of curvature of the bonded lens surface increases beyond the upper limit, spherical aberration will be insufficiently corrected and a large amount of higher-order spherical aberration will occur. When it becomes weaker, spherical aberration becomes overcorrected and coma aberration occurs more frequently toward the middle of the screen.

Conditional expression (21) relates to the dispersion of the two glass lenses in the third lens group, and is intended to reduce the secondary spectrum that accompanies telephoto zooming.If the upper limit of 69 is exceeded, the axial chromatic aberration due to the secondary spectrum will increase. If the lower limit is exceeded, the chromatic coma aberration on the wide surface side increases as the secondary spectrum increases.

In this embodiment, in order to reduce aberration fluctuations during focusing and achieve high resolution over a wide range, the fourth lens group is composed of two lenses with positive and negative refractive powers in order from the object side. It is better to set α1(N41-N42(0,3...--(3). Conditional expression +31, (4) is the fourth
This is to reduce curvature of field when focusing is performed by the lens group and to reduce fluctuations in chromatic aberration, especially fluctuations in secondary spectra. If the upper limit of conditional expression (3) is exceeded, the refractive index difference between both lenses becomes too large, and the fluctuation of astigmatism due to orcasing increases.If the lower limit is exceeded, the refractive index difference between both lenses decreases, and the Petzval sum increases. As the curvature of field increases, it becomes difficult to reduce the curvature of field. When the upper limit of conditional expression (4) is exceeded, secondary spectra due to focusing increase, making it difficult to satisfactorily correct chromatic aberration of magnification, and in particular, chromatic aberration of magnification becomes overcorrected. If the lower limit is exceeded, the fluctuation of the chromatic aberration of magnification due to the secondary spectrum becomes large, or the chromatic aberration of magnification becomes insufficiently corrected.

In order to maintain good performance of the entire screen in this implementation array, the second lens was composed of three lenses with positive, negative, and positive refractive powers, and the concave surface of the second lens was directed toward the image plane. It is preferable to use a meniscus-shaped lens.

Further, in the present embodiment fllVc, the lenses with positive and negative refractive powers of the fourth lens group may be bonded together or may be configured independently.

In this embodiment, the total refractive power of the second, third, and fourth lenses is negative, and the lens as a whole constitutes a rear group of a telephoto lens.

Next, numerical implementation sequences of the present invention are shown. R at i in the numerical implementation sequence
1 is the radius of curvature of the tl-th lens surface from the object side, D
l is the first lens thickness and air distance from the object side, Nl
and ν1 are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

Numerical implementation sequence I F=59&95 FNO-116tea-41tR1
-24101Di-2&7ON1 outlet L 43387
C1-1182--20100 0> 481R
3--187,46D3- gL08 N2-177
250 Cito4i6R4-132L14 D4-
2.04R5-22&54 D5-2α5ON>
L 487411 y 3-7α2R6--325
L91 D 8-123.45R7-51L13
D? -6,87N4-L65160 y4S&
6R8-5L 80 D 8-1λ98R-15 32D9-1132 N 5-L50137
Shishibow & 4RIO--10LTo 010-40
6 N 8-L62280 y 6-57.0
all-23a12 Dll-&00R1> 2
7188 Dl2- 7.00 N? -L78
472 y7-2L7R13-501114013
-158 R14-865 & 21 Dl41 & 83
N B-L 61340 ν8→λ8RIS-1
1 & 4G Numerical implementation column 2? -59401FNO-1:46 2ω-411R
l-22a 94 D l-25-70N 1-
L 43387 y 1-9 & IR2--1
99,4402-KanOO R3P-187,22D BP&50 N 2=L
77250y 2m9L 6R4-157a 3
3D 4-IL 20R3-24L93 05-2
α5G N 3-1.48749 C3 Self 7 α2R
60-33 & Is D 6-14 & 56R7-
54070? -400N4-L58913 y44L
.

R8-5118D 8-10.00 R9-1m 06 D 9-1cL50 N S-
L 50137 y 5-5a 4RIG--10
& 24 Dio-t 00 N 6-L 6
5160y ←5&6R11-23&04
Dll-100Iu2-242.18 Di2-
LOG N7”L78472 y7-2&
7R13 fog-246 to 30 013- L50R1
4--133α60 014-150 N 8-L
65412 ShiJl-39L 7R15-11&7
9 Numerical implementation f113 F-77454FNO-1:&9 2a+-3L1daR
1-31a79 Di-2α80 N 1-L
43387 ν 1→! LIR2--261L6
2 D2-1&o:5R3--221L12
DB-498N 2-L? ? 250 ν 2 brutality 4
9.6R4-188LO004-0,56 R5-297,26D 5= la 43 N 3
-L 48749 y 3-7a 2R--401
86D6 2 units R7-5 & 67 D7- R87N4-L69680
ν←5ASR&-5L HD 8-22.77 R9-13λ9B DB-R74N5 bite 1.501
37 ν 5-54L 4RIG--LaO2m
o-4a Ng-L6S830 y←57.3R1
1st eye 214.43 Dll-7,00812-
267,50Di2- R49N7-1.78472
Sear 2 & 7RL3- 415λ84 D
i3- 1.57R14=16230.50 No. 01-3,50N 8-L 61340 y 8-4
3L 8R15-117,47 Numerical implementation sequence 4 F-779,49FNO-1:&9 2ω-118
"R1-317, 35D 1-m 91 N 1
-L 43387 y 14 & IR2-24K
03 D 2-19.09B 3p=225.76
D3! mfL So N 2-L 77250
y 249.6B4-12151192 04-
LnIL &-29&38 D Syla 72
N 3-L 4B? 49y: Th7α2B G-
-40L 78 D←22L 29R7-5N85
07- 7.04 N4-L54771
yr6L9R&-5L74 DB-22,72 B9= 13a 10 D 9- 9.63
N S=L 50137 v bow 6.4axe-
-ti4is oio-: L m N 6-L 6
5830 v 6=57.3all-11&6G
Dll-7, 00812-33 provisional u 012-5.
03 N? -L84666 Sheer Nagi9RL3=7
8a 7S DI3Ma & 52 N &=L 6
1340 y 13=418R14-12421 Next, each conditional expression and numerical implementation sequence 1 in this implementation 13i'lK
Table 1 shows the relationship with the numerical values of ~4.

Table 1 Numerical values of numerical examples (effects of the invention) According to the present invention, it is possible to satisfactorily correct the secondary spectrum that occurs as a result of telephoto zooming, and to achieve a telephoto lens that can obtain high resolution. 4! By moving some of the lens groups in the rear group, it is possible to achieve a high-resolution telephoto lens that reduces fluctuations in chromatic aberration during focusing.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views of lenses of numerical embodiment 1.40 of the present invention, and Figures 3, 4, 5, and 6 are numerical embodiments of the present invention.
It is a diagram of various aberrations of H, 2, 3, and 4. In the aberration diagrams, the figure shows various aberrations for an object at infinity, and the symbol (■) for a short-distance object (represented by the distance from the image plane -1, where f is the focal length). In the figure, d, C, F, and g are d line, C line, and 1'l, respectively.
The aberrations of the rays lA and tllA, m is the meridional surface, S is the sagittal image surface, and Y is the image height.

Claims (1)

[Claims] (1) A first lens group having a plurality of lenses in order from the object side and having a positive refractive power as a whole, a second lens group having a negative refractive power,
It has four lens groups: a third lens group with negative refractive power and a fourth lens group with negative refractive power for focusing, which are made by bonding lenses with positive and negative refractive powers. The refractive index, Abbe number, and partial dispersion ratio of the glass of the j-th lens are respectively Nij, νij, and θij, the radius of curvature of the j-th lens surface of the i-th lens group is Rij, and the focal length of the entire system is f. When 0.5<[f(N32-N31)/|R32|]<1.
0, R32<00.003<(θ31-θ32)/(ν
A telephoto lens characterized by satisfying the following condition: 32-ν31)<0.016. (2) The fourth lens group consists of two lenses with positive and negative refractive powers in order from the object side.0.1<N41-N42<0.3 0.002<(θ41-θ42)/(ν42-ν41 )
The telephoto lens according to claim 1, wherein the telephoto lens satisfies the condition <0.006. (3) The first lens group has positive, negative, and positive refractive powers.
3. The telephoto lens according to claim 2, wherein the second lens group has a meniscus-shaped lens with a concave surface facing toward the image plane.