JPH0450910A - Wide angle lens - Google Patents

Abstract

PURPOSE:To reduce the lens diameter of a front lens and to sufficiently assure a prescribed back focus by consisting the lens of a 1st group having a negative refracting power and a 2nd group having a positive refracting power and specifying the lens constitution of the 1st group and the 2nd group. CONSTITUTION:The 1st group I having the negative refracting power as a whole is constituted of two negative 1st, 2nd lenses and one positive 3rd lens and focusing is executed by moving the 2nd group II having the positive refracting power on the optical axis. The lens is so constituted as to satisfy the conditions expressed by equation I, equation II when the focal distance of the 1st group I and the 2nd group II are respectively designated as f1, f2, the focal length of the entire system is designated as f and the back focus as bf. The lens diameter of the front lens is reduced in this way while the long back focus is maintained.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a wide-angle lens that has a shooting angle of view of about 100 degrees and an F number of about 35, and which aims to downsize the entire lens system. This invention relates to a wide-angle lens that is suitable for cameras such as TTL-type eye reflex cameras and video cameras, which require a long and time-intensive camera system, to guide an optical path to an observation optical system using a rotating reflector.

(Prior art) Conventionally, it is well known that a lens group with negative refractive power or a so-called reverse telephoto type (retrofocus type) wide-angle lens is used as a wide-angle lens with a French angle of view that has a long pack focus compared to the focal length. There is.

For example, in Japanese Patent Application Laid-Open No. 49-121527, the shooting angle of view 1
A reverse telephoto lens with a long back focus of 00 degrees and an F number of about 35 has been proposed.

In general, a reverse telephoto type photographing lens has an asymmetrical lens configuration as a whole, with a lens group with negative refractive power in the front and a lens group with positive refractive power in the rear.

For this reason, the amount of various aberrations such as spherical aberration, coma aberration, distortion aberration, and astigmatism increases, and in order to ensure a long back focus, the absolute value of the negative refractive power of the front lens group must be increased. As a result, the amount of various aberrations generated also increases, and it is generally very difficult to properly correct these various aberrations in a well-balanced manner.

Furthermore, aberration fluctuations due to auto-sync also increase, making it extremely difficult to obtain high optical performance over the entire object distance range.

(Problems to be Solved by the Invention) Recently, as camera bodies have become smaller, there has been a demand for smaller lens systems for photographic lenses used in photographic cameras, video cameras, and the like.

For example, as a reverse telephoto lens, if you try to reduce the diameter of the front lens with a shooting angle of view of about 100 degrees and an F number of about 3.5, but you also try to downsize the entire lens system, distortion, astigmatism, etc. will occur. The amount of various aberrations that occur increases rapidly.

- In order to satisfactorily correct various aberrations caused by stiff shells and obtain high optical performance, it is necessary to increase the number of lenses, which leads to the problem that the entire lens system becomes larger.

The present invention has a shooting angle of view that has a long back focus by appropriately setting the lens configuration, and also reduces the diameter of the front lens, thereby reducing the size of the entire lens system that can be attached to various filters. About 100 degrees, F→-nha 3.
The purpose of the present invention is to provide a wide-angle lens having a wide angle of view of about 5.5 mm, and having high optical performance with small aberration fluctuations during focusing and excellently correcting various aberrations of the entire screen.

(Means for solving the problem) The wide-angle lens of the present invention includes, in order from the object side, a negative first lens,
The lens is composed of a first group with negative refractive power and a second group with positive refractive power, consisting of a negative second lens and a positive third lens, and focusing is performed by moving the second group on the optical axis. At the same time, the focal lengths of the first group and the second group are set to f1.
, f2, focal length of the entire system is f, back focus is bf
When -3,5<fl/f2<-2,2...(1) 2f<
bf...It is characterized by satisfying the condition (2).

(Example) FIGS. 1 to 4 are lens sectional views of numerical examples 1 to 4, which will be described later.

In the figure, I is wSLIT with negative refractive power, II is the second group with positive refractive power, and sp is the aperture.

In this embodiment, the 1117th is the two negative first,
It is composed of a second lens and one positive third lens, and focusing is performed by moving the second lens along the optical axis.

Furthermore, the overall lens structure is of an inverted telephoto type, so that sufficient back focus can be easily obtained.

In addition, in the wide-angle lens of this embodiment, the angle of incidence near 100 degrees is large due to the two negative meniscus lenses on the object side of the first group and one positive third lens. The light beam is gradually refracted to reduce the angle it makes with the optical axis. This makes it possible to reduce the diameter of the front lens while minimizing the occurrence of various aberrations such as distortion, astigmatism, and higher-order aberrations.

By appropriately setting the lens configuration of the second group having positive refractive power as described later, various aberrations of the entire screen are corrected in a well-balanced manner.

In this way, in this embodiment, by specifying the lens 4J4 composition of the first group as described above and performing focus sync with the second group, the back focus is secured to be approximately twice the focal length of the entire system. Preventing the front lens diameter from increasing,
It also achieves high optical performance over the entire range of object distances, from objects at infinity to objects at close range.

In particular, in this embodiment, the focal pressure fif of the first group and the second group is
1. By setting f2 as shown in conditional expression (1), sufficient back focus is ensured, that is, the focal length of the entire system is
While ensuring the back focus bf to satisfy conditional expression (2), ! Fluctuations in aberrations, especially fluctuations in astigmatism, when focusing is performed by moving the i12 group on the optical axis are well corrected.

If conditional expressions (1) and (2) are not satisfied, it becomes difficult to maintain good optical performance of the entire screen over the entire object distance while ensuring a predetermined back focus.

In addition, in this embodiment, in order to effectively correct the distortion counting especially at the periphery of the screen, the convex surface of at least one negative lens on the object side of the two negative lenses in the first group is arranged so as to move toward the periphery of the lens. It would be good to use an aspherical surface with a shape that increases the refractive power of ■.

In this example, in order to obtain good optical performance over the entire screen with a shooting angle of view of 100 degrees and an F number of about 35, both the first and second lenses in the i@1 group had their convex surfaces facing the object side. It is preferable to have a meniscus shape, and the third lens to have a shape in which both cis surfaces are convex.

In addition, the second lens group includes, in order from the object side, a meniscus-shaped negative fourth lens with a convex surface facing the object side, a meniscus-shaped positive fifth lens with a convex surface facing the object side, and a single lens with a convex surface on both sides. Single or cemented positive 6th lens, diaphragm, single or cemented 7th lens, negative 8th lens with both concave lens surfaces, meniscus positive 9th lens with convex surface facing the image side, image It may be constructed from a meniscus-shaped positive 10th lens with the convex surface facing the surface side.

As shown in the numerical examples described later, the wide-angle lens according to the present invention has a focal length of 24.5 mm and both 'l' angles of 50 degrees, so the effective both sides reach a length of +(!60 mm), resulting in an effective screen larger than the size of the Leica version. In addition, while high-resolution images can be obtained by using a large-area film, it is also possible to take tilt-shift photographs using a Leica version camera.

Next, numerical examples of the present invention will be shown. In numerical examples R
1 is the radius of curvature of the first lens surface from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and ν1 are the refractive index and Abbe number of the glass of the first 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 the light is positive, R is the paraxial radius of curvature, A, B, C,
The equation is expressed when D and E are each aspherical coefficients.

Numerical Example 1 F-211,5FNO Example 1:3. SR+=47.05 DI-2,2082-
27,83D2- 6.29 83- 45.00 D3- 2゜20R4-23
,04D41:1.43 R5-89,98D5- 4.71 86-1000.97 D 6- Variable R7=
:19.27 D7- 1.0088- 15.
18 D8- 5.74R9= :l! 1.11
D9= 3.14R1O= 437.17
DIO-2,91RI+=20:],77 Dl
l-10,14RI2- -24.95 Di2-
2.6 (aperture) R]3 = -48,76Di3- 5.442ω-1
00+ N I=1.60311 ν l-60,7N
2 to 1.60311 ν 2= 60.7N 3
-1.59551 ν 3-39.2N 4-1
．． 7+299 ν 4・538115, ], 8
0518 ν 5= 25.4N 6-1.5
1633 ν 6-64°N7-1.83+10
0 ν 7= 37.2R] 6= 117.
06 DI6= 0.70817= -66,9
4Di7- 2.47R] 8- -20.31 DI
8= [1,1SR+9=-66,07Di9-
2.39R20= -25,4:I D6 , 4.5 (object Cx3) N 9 = 1.6968O N10 - 1.69680 ν 9 = 55.5 νIO = 55.5 3rd surface is aspheric" Spherical coefficient B=4.218 xlo-' C=], 09S xlO-Io D=5.8:11 xlO-" E-5,50:l XIO" Numerical Example 2 Numerical Example 3 2ω-100'' N l- 1,589+3 ν I= 61.2
124.5 FNO=I :3.5H1
・ 57.46 DI= 2.30R2=
23.12 D2=]3.23R3=286
．． 29 D 3= 2.20R4= 27.1
7 D 4 Snow 645R5= 30.2] D 5
-8.29R6--221,55D 6= variable 1'
l 7= 32.70 D 7= 1.00R
8= 12.12 D8- L36R9=
19.78 D9- 2.86RIO-25,45
DIO=0.99R1+-:17.50D11
= 9.73R12= -23,36DI2=
2.8 (aperture) R]3=-69,89DI3=5.51R]4
- -29.89-D14=0.12R]5--2
5.04 D15= 6.5717161!65.
[i4 DI6- 0.91R17=-58,1
5DI7-2.36R]8--20.00DI
8- 0.15R19--80,24019-2,16
N10-1.69680R20--31,31 D6, 4.5 (object (1)) N 2-1.58913 14 3J, 532SF+ N 4-1.71299 N 57 1.805+8 11 6=1.53172 N 7=1.7200O N 8=1.80518 N 9=1.69680 First surface is aspherical Aspherical coefficient A=O B= 313 xlO-6 C--9,20xlO-' D-2,80xlO-1 :l E-7,04Xl0-" ν 2= 51.2 ν 3= 45.9 ν 4= 53.8 ν 5= 25.4 ν 6-48.9 R9-19, 49D9= 2.56 R] 0=24.38 DlO=1.058
11= :11.66 Dll-1,0OR+2
〒 16.10 DI2- 9. +6 old 3- -2
2.19 DI3- 2.80ν 7-43.7 Shi 8- 25.4 ν 9= 55.5 ν10- 55.5 R15= -33,67DI5- 2.5SR+6=
966.27 DI6- 0.4SR+7=-
107,66DI7= :1.76R1B-67,9
3D18=1.04R]9--50.29D
I9- 2.34820- -19. +8 D20-
0.15R21-1981,27D2]-2,10R2
2= -51,38 D6 ; 4.5C object cx)) First surface is aspheric Aspheric coefficient B-3J3 Xl [l-6 C--9,2xlO-" D-2,8x 10"" E- 7,4xlO-+6 N 5=1.8O5+8 N 6=1.6968O N 7-L, S: 1172 N 9=1.80518 N10=1.80518 N11-1.64168O N+2=1.69680 5e 25.4 ν 6 = 55.5 ν 7 = 48.9 9- 25.4 ν10-25.4 νlI = 55.5 ν12-55.5 Numerical Example 4 F-24,5FNO-]: 3.S R+-5813DI -2,30 R2-23,57D2-13.+8 R3 cloud 350.92 D 3- 2.20R4-2
7,61D4- 6.56 R5-co], 64D5 805 H6= -224,93D 6- Variable R7= 3
1.43 D7 Fable 1.00R8= 11°95
D8- 4.37R9=20. :15D
9-2.94R]D1125.51 DIO-1,
42R11-35,47Dll-9,76 R12--23,64DI2- 2.8 (aperture) R13--107,79DI3 depth 5.49RI4-
-37.70 DI4- 1.95R15-294,
85DI5-1. +3R16--100.09D
I5- 3.04R17-71,04DI7- 0.7
2RI8- -81.8:l DI8- 2.488
19- -19.63 DI9- 0.15R20-
-270,79D20= 1.95821- -51
．． 38 D6; 4.5 (Object ■) First surface is aspherical Aspherical coefficient B-3,3xlO-'C--9,2xlO-" Dll2.8 xlO-" E=7. OxlO-16 2ω-1oo” N ]=1.58913 ν ]-61,2N
2-1.58913 2-61.2 N 3-1.53256 3 Tsumugi 45.9 N 4-1.71299 ν 4-53.8 N 5-1.80518 5-25.4 N 6-1.53172 6-48.9 N 7=1.70225 N 8-1.80518 ν 7-40.9 18= 25.4 N 9-1.80518 9-25.4 N10=1.69680 ν10-55.5 NI 1-1.69680 νII=55.5 (Effects of the Invention) According to the present invention, by specifying the lens configurations of the first group and the second group as described above, the diameter of the front lens can be reduced and the overall lens system can be improved. Shooting angle of view 1 that can ensure a sufficient back focus while reducing the size of the camera.
It is possible to achieve a wide-angle lens that has high optical performance over the entire screen with an F number of about 3.5 degrees.

[Brief explanation of the drawing]

1 to 4 are lens cross-sectional views of numerical examples 1 to 4 of the present invention, and Figures 5 to 8 are various aberration diagrams of numerical examples 1 to 4 of the present invention. In the aberration diagram, (A) shows the aberration for an object at infinity, and (B) shows the aberration when the image plane is 60 m. In the figure, I is the first group II, @2 group SP is the aperture, and the sagittal image plane M is the meridional image plane.

Claims (3)

[Claims] (1) Consisting of a negative first lens, a negative second lens, and a positive third lens in order from the object side, the whole consists of a first group with negative refractive power and a second group with positive refractive power, When focusing is performed by moving the second group on the optical axis, and the focal lengths of the first and second groups are respectively f1 and f2, the focal length of the entire system is f, and the back focus is bf -3. A wide-angle lens that satisfies the following conditions: 5<f1/f2<-2.2 2f<bf. (2) The first lens and the second lens both have a meniscus shape with a convex surface facing the object side, and the third lens has both lens surfaces having a convex shape. Wide-angle lens described in 1. (3) The second group includes, in order from the object side, a meniscus-shaped negative fourth lens with a convex surface facing the object side, a meniscus-shaped positive fifth lens with a convex surface facing the object side, and both lens surfaces having convex surfaces. A single or cemented positive sixth lens, an aperture, a single or cemented seventh lens, a negative eighth lens with both concave lens surfaces, and a meniscus positive ninth lens with a convex surface facing the image plane. 3. The wide-angle lens according to claim 2, further comprising a meniscus-shaped positive tenth lens with a convex surface facing toward the image plane.