JPH01154111A - Inner focus type photographic lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an inner focus type photographic lens suitable for photographic cameras, video cameras, etc. This invention relates to an inner focus type photographic lens that performs focusing and has a large aperture ratio and a relatively wide angle of view.

(Prior Art) Recently, photographic lenses for photographic cameras, video cameras, etc. are required to have high optical performance, a large aperture ratio, and a lens system that can be easily and quickly focused.

A photographing lens with a large aperture ratio can provide a fast shutter speed, and has the advantage of preventing image blur when taking pictures indoors, for example.

In addition, if the focus lens group is small and lightweight and can easily obtain a fast shutter speed, it is possible to reduce the torque of the motor used to drive the focus lens group when applied to an autofocus photography system, for example. There are advantages such as being able to

For this reason, various so-called inner focus type photographic lenses have been proposed in which focusing is performed by moving a part of the lens group with a relatively wide angle of view h1 inside the lens system.

For example, JP-A-59-1.7519 and JP-A-59-
65821, it consists of three lens groups in order from the object side: a first group with positive refractive power, a second group with negative refractive power, and a third group with positive refractive power, and the 7g2 group is moved. JI JJ2 with inner focus type
The lens is disclosed.

However, when attempting to achieve a large aperture ratio and a TFFL shadow angle of view of 20 degrees or more in an inner focus type photographic lens, aberration fluctuations during focusing increase, making it generally very difficult to obtain high optical performance.

(Problems to be Solved by the Invention) The present invention has a large aperture ratio of F number 1.4, and has little aberration fluctuation during focusing when the shooting angle of view is about 30 degrees.
The purpose of the present invention is to provide an inner focus type photographing lens which has high optical performance over a wide photographing distance range and is particularly suitable for photographic cameras, video cameras, etc.

(Means for solving the problem) From the object side, the first group has positive refractive power, and the second group has negative refractive power.
The second group is moved along the optical axis to perform focusing, and the lens 1A closest to the image plane of the first group is located on the image plane. It has a shape with a concave surface on the side, the radius of curvature of the lens surface on the image side of the lens 1A is R1A, and the refractive index of the material of the lens 1A is N1A.
, the lens 3A closest to the object side of the third group has a shape with a concave surface facing the object side, R3A is the radius of curvature of the lens surface on the object side of the lens 3A, and the refractive index of the material of the lens 3A is N3A, where the focal length of the second group is f2, and the focal length of the entire system is f...-(1) is to satisfy the following condition.

(Example) 1st. Second. Third. Figure 4 shows numerical example 1 of the present invention.
4 is a sectional view of the lens. In the figure, ■ is the first group with positive refractive power, II is the second group with negative refractive power, and ■ is the third group with positive refractive power.

This embodiment employs an inner focus type in which focusing is performed by moving the second group on the optical axis.

The lens 1A closest to the image plane of the first group has a lens shape with a concave surface facing the image side, and the lens 3A closest to the object side of the third group has a lens shape with a concave surface facing the object side. The radius of curvature of the lens surface on the image side of , the radius of curvature of the lens surface on the object side of lens 3A, and the radius of curvature of the lens surface on the object side of lens 1A and lens 3.
By setting the refractive index of the material A as shown in the above conditional expression (+), aberration fluctuations when focusing by moving the second group can be reduced, and a wide object distance from an object at infinity to a close object can be achieved. High optical performance is achieved over a wide range.

Furthermore, conditional expression (1) reduces aberration fluctuations during focusing, corrects various aberrations in a well-balanced manner, and achieves high optical performance over the entire screen.

If the upper limit of conditional expression (1) is exceeded, spherical aberration will be insufficiently corrected, and it will be difficult to reduce the Petzval sum, resulting in deterioration of image surface characteristics. Furthermore, when the lower limit of conditional expression (1) is exceeded, the Petzval sum becomes relatively small and spherical aberration can be corrected relatively well, but off-axis aberrations, especially coma aberration, and higher-order word count differences occur. This is not good because the image quality will be greatly degraded as a result.

In this embodiment, focusing from an object at infinity to a close object is achieved by moving the second group toward the image plane. For this reason, the height of incidence of the axial ray that enters the second group is lower for a close object than for an object at infinity, and spherical aberration tends to be undercorrected.

Therefore, by specifying the lens shape and material of the lens 1A closest to the image plane in the first group as described above, the Petzval sum can be reduced while the spherical aberration, which tends to be under-corrected, can be corrected in the direction of over-correction. It has been corrected in a well-balanced manner.

In addition, by specifying the lens shape and material of the lens 3A closest to the object side of the third group as described above, ``the negative refractive power in the third group is directed toward the object side, and the positive refractive power is directed toward the image plane side. Trying to locate in the direction.

As a result, the angle of incidence of off-axis rays entering the third group is made gentler, and while off-axis aberrations are well corrected, the aperture diameter can be prevented from increasing due to a large aperture ratio, and the overall lens system can be made more compact. ing.

In this example, the second group is configured to have one positive lens and two negative lenses, and the second group reduces aberration fluctuations when focusing and provides high optical performance over a wide object distance range. I am getting .

In addition, the second group consists of three lenses in order from the object side: a meniscus-shaped lens with negative refractive power with a convex surface facing the object side, a negative lens with concave surfaces on both lens surfaces, and a positive lens with convex surfaces on both lens surfaces. A positive lens with convex surfaces on both surfaces, a negative lens with concave surfaces on both surfaces, and a negative lens with concave surfaces on both surfaces reduce aberration fluctuations during focusing and improve the overall This is preferable for performing good aberration correction.

Furthermore, in order to better correct aberration fluctuations during focusing, the focal length f2 of the second group should be set to 0, 45<I f2/f l<1.4 (
It is best to set it as shown in 2).

If the lower limit of conditional expression (2) is exceeded and the refractive power of the second group becomes stronger, the amount of movement of the second group during focusing will decrease, which is advantageous in shortening the overall lens length, but Image plane correction at the angle of view becomes difficult.

Furthermore, when the upper limit of conditional expression (2) is exceeded and the refractive power of the second group becomes weaker, the amount of movement of the second group during focusing increases, the total lens length increases, and the Petzval sum further increases. It's not good because it becomes difficult to make it smaller.

Further, in this embodiment, when the focal lengths of the first group and the third group are f1 and f3, respectively, 0.7< f1/f <1.5 - (3
)0.4< f3/f <0.8 ・------
Setting as in (4) is preferable in order to achieve high optical performance over the entire screen while reducing the size of the entire lens system.

Conditional expression (3) relates to the refractive power of the first group, and when the refractive power of the first group exceeds the lower limit and becomes stronger, the difference in the number of words occurring in the first group increases, and aberration fluctuations due to focus increase. It's not good because it comes. In particular, if a glass with a high refractive index is used for the positive lens in the first group in order to properly correct aberrations in the first group, especially spherical aberration, it will inevitably be limited to lenses with large dispersion, so it will be difficult to focus. This is not a good idea because the associated variation in lateral chromatic aberration increases.

When the upper limit of conditional expression (3) is exceeded and the refractive power of the first group becomes weaker, the total length of the lens increases, and accordingly, the diameter of the front lens increases in order to secure sufficient off-axis light flux. It's not good because it will come.

Conditional expression (4) relates to the refractive power of the third group, and as the refractive power of the third group exceeds the lower limit and becomes stronger, it becomes difficult to reduce the Petzval sum.

Also, if the upper limit of conditional expression (4) is exceeded and the refractive power of the third group becomes weaker, the aperture diameter must be increased in order to secure a predetermined F number, and the lens outer diameter increases. However, the entire lens system becomes larger, which is not good.

In the present invention, in order to further improve the optical performance of the entire screen, the first group is a positive lens, two meniscus-shaped positive lenses with a convex surface facing the object side, and a meniscus-shaped positive lens with a convex surface facing the object side. Consists of four negative lenses,
The third group is a cemented lens made by bonding negative and positive lenses together.
It is preferable to use two positive lenses.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness and air distance from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

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, A, B, C
, D, E, etc. are each aspherical coefficients, it is expressed by the formula +DH8+El+'' +....

Furthermore, Table 1 shows the relationship between each of the above-mentioned conditional expressions and each numerical example.

Numerical actual hK example I F= 100 FNo-1: 1.4 2ω
-28,8'rl I-135,32D I-8,30
N 1-1.60311ν 1-60.7R2-909
,5402-0,18 R3-62,0103-8,83N 2-1.696
80 ν 2-55.5R4-190,63D 4
- 0.18R5= 44.91 D 5-10.
67 N 3-1.74400shi 3-44.8R6-
99,4506-1,19 R7-125,9807-1,78N 4 1.805
+8ν4-25.4R8-32,3308-9,72 R9-106+i,72 D 9= 1.78 85
-1.57250shi5~57.8RIO-47,61D
IO-5,93 R11-138,94Dll-1,78N 6-1.6
2606shi6-39.2812-118.52 Di
2-5.93 N 7-1.76182 Sear 26.
6RI3-347.51 Di3-20.18RI4
--38.90 DI4= 2.37 88-1.7
5520shi8-27.5R]5=-592,62015
-7,11N 9=1.77250ν9-49.6RI
6--56.84 016-0.24R17-254,
19017-4,95N10-1.78590shi10-
44.2818--64.89 018-0.2'
IRI9- 66.72 019-6.62 N11
-1.69680υ11-55.5820-642.7
1 Numerical Example 2 F= 100 FNo-1: 1.4 2ω
-33,8'R1= 211.97 D l-10,
24N]-1,62299v 1-58.21+
2-757.79 D 2-0.21R3-97,0
303-8,42N 2-1.69680υ2-55.
5R4= 338.97 04= 0.21R5-53
,0105-14,03N 3-1.74400ν 3
=44.8R6-168,3606-2,10N 4-
1.78472ν 4-25.787- 43.02
07-9.82 R8-301,8908-2,10N 5-1.572
50shi5-57.8n 9-50.40 09-9.
12RIO--66, 22DIO-2, 10N 6-1
．． 53172υ6-48.91 (+1-126.27
Dll-7,02N 7-1.74950 sear 35
．． 3RI2=-120,13012-21,74RI3
--16.66 013-2.10 N 8-1.8
0518ν8=25.4RI4--1122.45 0
14-10.52 N 9 = 1.80400 v 9
=46.68I5--65.15 015-0.28R
I6--636.65 Di6-5.33 N10
-1.80400ν10-46.61117--87.
56 0I7=0.28R18-93,72018=7
．． 02 N11-1.69880shi11-55.5F
+19-1674.70 R5: Aspheric coefficient A = 0. OB −-7,718x 10-'C=
3.568 X 10-” D --6,291X
10-” Numerical Example 3 F= 100 FNo=1:1.4 2ω
= 26.5°R] = 90.01 D 1-8.
70 N l=1.60311ν 1=60.7n
2-2578.31 D 2= 0.16It 3=
60.23 D 3 = 8.80 N 2J,
69680 v 2-55.5R4= 152.46
04=0.16R5-40,70D 5-9.78
83-1.72000shi3-50.2R6=92.
95 D 6-1.09R7= 120.41 D
7-1.63 84=1.76182ν4-26.6
R8-28, 59D 13-9.24 R9-102, 31D 9-1.63 N 5=1.
62280shi5-57.0RIO-39,61010-
6,52 1111=-97,19Dll-1,63N 6=1
．． 62174 Jiro 47. IRI2-108.69
D12=5.43 N 7-1.75520 sear 27.5R13=-445, 20DI3=18.591
114--36.34 D14-2.17 N 8
-1.72825shi8-28.5R15=-326,0
6D15-6.52 N 9-1.77250 v
9-49.6R16--51.63 D16 dew 0.2
2R17-145, 51017-4, 54N10-1.
78590shi10-44.2R18--60,9301
8-0,22R19~ 63.21 019-6.07
N11-1.69680ν11 surprise 55.5R20=
2004.59 Numerical Example 4 F-100FNo=l:1.4 2ω-30,2
゜RI-162,85D I-9,95N l-1,6
0311ν ]-]60.782--481.46 D
2 = 0.19R3 attack 69.84 03-8.71
N 2-1.69680ν2-55.5It 4-
183.45 04-0.19R5-57,27D 5
J1. ]9 N 3-1.74400ν 3-44.
8R6-141,9106= 1.24 R7-202,94D 7= 1.87 N 4-1
．． 78472ν4-25.7R8 43.52 D
8-9.08R9 359.82 D 9
- 6.22 N 5 irises 1.83400 ν
5 fable 37, 2 RIO-124, 35010-1, 87
N 6-1.69680 Jiro 55.5R11-303
,48Dll-3,73Rj2-215.52 D1
2= 1.87 87-1.61720 sear 54. O
n+3- 51.69 013-24.251114-
-45.96 014= 2.49. N 8-1.
78472ν8-25.7RI5-621.79 01
5-7.46 N 9-1.77250ν9-49.
6RI6=-62,39016-0,251117--
443.75 DI7=5.19 N10-1.7
8590shi10-44.28I8--79.47 01
8=0.25RI9 electric 71-66 D19-6.9
5 N11-1.691i80shi11-55.5R2
0--554,43 Table 1 (Effects of the Invention) According to the present invention, each lens group is configured as described above, and focusing is performed by moving the second group on the optical axis, thereby easily and It allows for quick focusing, and in a wide object distance range from infinity to close objects.
It is possible to achieve an inner focus type photographic lens suitable for photographic cameras, video cameras, etc. with a relatively wide angle of view and a large aperture ratio that provides high optical performance.

[Brief explanation of the drawing]

1 to 4 are cross-sectional views of lenses of numerical examples 1 to 4 of the present invention, respectively, and Figures 5 to 8 are lens sectional views of numerical examples 1 to 4 of the present invention, respectively.
4 is a word count difference diagram for an object at infinity. In the cross-sectional view of the lens, I, II, m are 1st. Second. 3rd group,
On the right side of the aberration diagram, S is the sagittal image plane, and M is the meridional image plane. Patent Applicant Canon Co., Ltd. Agent Yukio Takanashi t', -, 1 Akira 1 Rin T Akira 2 Figure 3 Ki 4 Figure 5 Shu 7 Koi 8 Figure

Claims (1)

[Claims] (1) It has three lens groups, in order from the object side: a first group with positive refractive power, a second group with negative refractive power, and a third group with positive refractive power; Focusing is performed by moving the second group on the optical axis, and the lens 1A closest to the image plane of the first group has a concave surface facing the image plane side, and the lens 1A on the image plane side of the first group The radius of curvature of the surface is R1A, the refractive index of the material of the lens 1A is N1A, the lens 3A closest to the object in the third group has a shape with a concave surface facing the object side; 1.0<1/f[{R1A/ (N1A-1)}+{R3
An inner focus type photographing lens characterized by satisfying the following condition: A/(N3A-1)}+|f2|]<3.0. (2) The inner focus type photographing lens according to claim 1, wherein the second group has one positive lens and two negative lenses. (3) The inner focus type photographing lens according to claim 1, wherein the second group satisfies the following condition: 0.45<|f2/f|<1.4. (4) The focal lengths of the first group and the third group are f1 and f3, respectively.
An inner focus type photographing lens according to claim 3, which satisfies the following conditions: 0.7<f1/f<1.5 0.4<f3/f<0.8 .