JPH04153612A - Front stop triplet type lens - Google Patents

Abstract

PURPOSE:To excellently compensate various aberrations while securing edge thickness and center thickness sufficiently by composing the lens of a stop, a 1st biconvex lens, a 2nd biconcave lens, and a 3rd positive lens which has a convex surface on the image side in order from the object side and satisfying specific conditions. CONSTITUTION:The lens consists of the stop, the 1st biconvex lens, the 2nd biconcave lens, and the 3rd positive lens which has the convex surface on the image side and inequalities I - III hold. In the inequalities I - III, (f) is the focal length of the whole system, f12 the composite focal length of the 1st and 2nd lenses, and r1, r2, and r3 the radii of curvature of the 1st, 2nd, and 3rd lens surfaces from the object side, respectively. Consequently, the lens is F2.8 or bright although the lens is composed of the three elements in the three groups, the edge thickness of the convex lens and the center thickness of the concave lens are secured sufficiently, and the aberrations are excellently compensated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a triplet type lens that is most suitable for video cameras using solid-state image pickup devices, etc., and particularly relates to a triplet type lens that is most suitable for video cameras and the like that use solid-state image sensors, etc. This relates to a type of triplet lens.

[Conventional technology]

In general, when applying a small camera lens using a silver halide film to a video camera using a solid-state image sensor with a small screen size, simply multiplying the dimensions of the lens system by a proportionality coefficient will not increase the edge thickness of the convex lens or the concave lens. The middle wall thickness becomes too thin, resulting in gaps during processing. Therefore, it is necessary to construct a dedicated lens system.

Conventionally, as a lens for video cameras, JP-A-2-1
91907, etc., but in recent years, the image sensor size has changed from 1/2 inch size with a diagonal length of about 8 mm to 6 mm.
There is a tendency for lenses to become smaller, from 1/3 inch size to about 1/4 mm, and 1/4 inch size to about 4 mm, and even in the case of the above-mentioned prior example, the edge thickness and middle thickness of the lens cannot be said to be sufficient.

[rMME to be solved by the invention The present invention has been made in view of this situation,
The purpose was to solve the above-mentioned problems of the conventional technology, to have only 3 elements in 3 groups, and to be as bright as F2.8. It is an object of the present invention to provide a lens in which the aberrations are sufficiently corrected and aberrations are well corrected.

[Means to solve the problem]

The front aperture triplet type lens of the present invention includes, in order from the object side, the aperture, the second lens of the biconvex lens, and the second lens of the biconcave lens.
The lens consists of a third lens, which is a positive lens with a convex surface facing the image side, where f is the focal length of the entire system, flff is the composite focal length of the first lens, and r, %r2, and F3 are the first lens from the object side. 2. When the radius of curvature of the third lens surface is set, the following conditions (1) to (3) are satisfied.

(1) 0.25<f/f12<1 (2) 0.4< rz /r+ <1.1(3)
0. 7< rz / rs <1.5 [Operation] When a conventional triplet lens is used for a small image sensor for video, various aberrations occur when trying to secure the edge thickness of the convex lens and the middle thickness of the concave lens. In particular, it becomes difficult to satisfactorily correct off-axis aberrations. In the present invention, by configuring the above conditions (1) to (3) to be satisfied, the above-mentioned edge wall thickness and middle wall thickness are sufficiently ensured, while
It becomes possible to satisfactorily correct various aberrations.

These conditions will be explained below.

Condition (1) relates to the composite focal length of the first lens. In other words, by making the composite system of the first and second lenses positive and keeping it within the range of condition (1), the curvature of the meridional image plane toward the positive side at the periphery of the screen is prevented, and the comment last is maintained until the periphery of the screen. However, when the upper limit is exceeded, the Petzval sum increases and the negative curvature of the image plane at the periphery of the screen becomes too large, and when the lower limit is exceeded, the meridial image surface becomes positive. This is undesirable as it causes a sharp curvature to the side.

Condition (2) is defined for the radius of curvature of the first rune, and by making the radius of curvature of the second surface a relatively smaller value than the radius of curvature of the first surface, the meridian image at the periphery of the screen can be improved. Although it is possible to prevent the surface from curving toward the positive side and from increasing coma flare, if the lower limit of condition (2) is exceeded, the Petzval sum will increase, and if the upper limit is exceeded, the above-mentioned aberrations will increase. This is not desirable.

Condition (3) concerns the image-side surface of the second lens and the object-side surface of the second lens, which face each other, and by making the radius of curvature of these two surfaces relatively close, each surface can be It is possible to cancel out higher-order aberrations that occur in If the upper and lower limits of condition (3) are exceeded, it will be difficult to cancel out especially high-order spherical aberration and comatic aberration, and one radius of curvature will become too small, causing total internal reflection, which is not preferable.

Furthermore, regarding the lens thickness, when the sum of the lens thicknesses of all lenses is Σd, it is desirable that the following condition be satisfied as a secondary condition.

(4) 0.6<Σd/f<1 5 If the lower limit of this condition (4) is exceeded, it becomes difficult to ensure the edge and middle thickness of the lens, and if the upper limit is exceeded, Various aberrations, especially the Petzval sum, become too large, making it impossible to obtain a good image plane.

[Example: Examples of the present invention will be shown below. The lens data of the lenses of Examples 1 to 7 will be described later, and Examples 1.2.
1, 2, and 3 show cross sections of the lens 6 only.

A parallel plane plate placed after the third lens represents a cover glass for a solid-state image sensor or the like. Aberration curve diagrams of the lenses of Examples 1 to 7 are shown in FIGS. 4 to 10, respectively. In Examples 5, 6, and 7, an aspheric surface expressed by the following formula is used, thereby achieving even better aberration correction.

x = (y2/r) / [1+ [1-P (y2/r
2)) 172]↑^4y4+^6y6+^aV" However, the optical axis direction is X, the direction perpendicular to the optical axis is y,
r is the paraxial radius of curvature, P is the conic coefficient, and ^4, ^6, and 80 are the aspheric coefficients.

In addition, in the lens data, symbols other than the above, F
xo is the F number, 2ω is the angle of view, rlsr2... is the radius of curvature of each lens surface, d1, dz... is the distance between each lens surface, ndl, nd2... is the dII refractive index of each lens , 1, 2, etc. represent the Atsube number of each lens (cover glass is also treated as a lens).

Example 1 =7 F,.=2.8 2ω=48°ro=oo (aperture) a, =0.8684 r, =4.5998 d, =2.0198 ndl =1.83481
v,, =42.72r 2=-3,2686 d2-0.0531 r, =-2,8653 d,=0.801 n,2=1.69g95ν,,
=30.12r4=3.5059 d = =0.4665 rs =353.6973 d s 49501 rs ”-5,6441 d , =2.5946 r, =OO d□=0.86 rs=o.

n,! =1.78590 n d< =1.51633 νas =44.18 ν,, =64.15 f / f , 2=0.14 r, /r, =0.71 r, l/l r, l = 1.14Σd/f=o
, 68 Example 2 f = 7 F,, = 2.8 2ω = 48° 1o = OO (aperture) d, = 1.4827 r, = 4.2576 = 2.2572 d = 1.81600 νd 46, 62 3.6764 d2 2 =31.08 r (3,2309 d * =0.81767 10.3387 2.0432 nd3"1 , 53 56 r , = -8,2704 d , =1. 9106 0.86 n,,=1.51633 νd(264.15 r s = ■ f/f 2=0.39 /r 1.04 / rco=1.2 Σd/f=0.72 Example 3 f = 7 F,, = 28 2ω = 48° ro = oo (aperture) d o ”O7174 r + = 5.1841 d , = 2 1483 r 2 = -3,7541 d 2 = 0.1774 r , = -2,8636 ds: 0889) r, =4.2148 d, =0 4541 r, knee 38.8412 ds =1.81 r, =-41126 d, =2 797 rri=C test) d7=o , 86 ra= ■ d = 1.81600 n , 2 = 1.68893 ndco : 1 d4 = 1.51633 = 46.62 ν,, =31.08 ν dco = 44.73 νd4=64.15 f / f 12 = 0.30 r 2 / r + = 0.72”z l/
l r3 l =lJ1Σd/f=0.69 Example 4 f =7 F,. =2.8 2ω=48°r0=oo (aperture) d0=0.7934 r I=4.6562 d+=2.0064 n+++ r! =-3,6913 d2 =0.0755 rs =-3,1070 d,;0.8033nd2 r, =3.6849 d, =0.4146 rs =-119,5271 1,68893 =1.81600 νdl =46.62 ν,, =31.08 d s 4.8001 n, = =1.74400 ν,, =44.73 r, =-4,8330 a, =2.8038 rf =OO dt= 0.86 n −4=1.51633 ν,, =64.15 rs=■ f/f,=0.36/r+=0.79/Σ(1/f=0.66 Example 5 =7 F,.=2.8 2ω=48゜ro=■ (Aperture) do=1.26 r, =4.6746 2,0928 d=1.81600 νd=46.62 r 2 =-4,9477 (Non Spherical surface) d2=0.1916 r, =-4,0153 d, =0.8803 r, =3.6981 d, =0.7057 r s =16.8483 a, =t, 8495 r @=-6, 6807 d, = 2.0337 1, = 06 dt = 0.86 r・ = 00 d2 1, 68893 n, s 4.74400 d4 = 1.51633 ν, 2 = 31.08 νd3 44, 73 νd4 64, 15 Aspheric coefficient second surface P=1 ^, = 0.13694 X 10-" ^, = -0,76395
0,48798X 10-”r/r 12=0.
41 r2 /r r2 / r3 nd/f=0.69 Example 6 f=7 Fl. =2.8 2ω=48゜ro=oo (aperture) do =1.080+ r, =4.6468 dl:35 r 2 =-4,887 d, =0.1953 r, -4,0847 (non-diaphragm) Spherical surface) d, = 0.7024 n, 2 = 1.688931
, =3.6563 d , =0.902 r s =6.6738 d s =2.4975 1.23 =1 81600 1.06 d n d co =1.74400 =46.62 Shiro □ =31.08 C s =44. "13 r, = -23,8175 a s = 0.2552 r 7 = ■ d, = 0.86 r6; ■ n,, = 1.51633 ν,, = 64.15 Aspheric coefficient 3rd surface P = 1 ^4=-0,39117X 10 A, = -0,14326X 10 ^= = -0,43579x 10 r/r, =0.59 r2/r+ =1.05r2/l
r, l =1.12Σd/f=0.95 Example 7 f =7 F,. =2.8 2ω=48゜r0=oO (aperture) d O=0.9138 r + =5.1914 d , =2.8398 r 2 = -4,8601 d 2 = 0.2763 r , = -3 ,3869 d3 =0.8041 r4 =3.8545 d, =0.5172 r s 45.7666 d, =2.7 r a =-4,9205 (aspherical surface) d, =1.8262 rt= ■ at=0.86 r! 200d3 d n ,, 4.51633 d2 = 1.81600 1.77250 νd1 46, 62 ν, 2 = 31.08 ν, 3 = 49.66 d4 = 64.15 Aspheric coefficient 6th surface P =1 ^, = 0.94342 X 10-'As=-0,
8995,)X 10-'e = -0,75:19
8 X 1O-5f/f12=0.27 r2 1. / r+ = o 94 r 2 l/ l rs l = 1.43
Σd/f=0.91 [Effect of the invention] The front aperture triplet type lens according to the present invention has a configuration of only 3 elements in 3 groups, and has an F number of 2.8.
It is possible to obtain a lens that is bright, has sufficient edge thickness of the convex lens and middle thickness of the concave lens, and has aberrations well corrected, especially for video cameras.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are Embodiment 1 of the present invention,
Lens sectional views of Examples 2 and 6, and FIGS. 4 to 10 are aberration curve diagrams of Examples 1 to 7, respectively. Applicant Olympus Optical Industry Co., Ltd.

Claims (2)

[Claims] (1) Consisting of, in order from the object side, an aperture, a first lens that is a biconvex lens, a second lens that is a biconcave lens, and a third lens that is a positive lens with a convex surface facing the image side, and is characterized by satisfying the following conditions. Front aperture triplet lens: (1) 0.25<f/f_1_2<1 (2) 0.4<|r_2|/r_1<1.1 (3) 0.
7<|r_2|/|r_3|<1.5, where f is the focal length of the entire system, f_1_2 is the combined focal length of the first and second lenses, and r_1, r_2, and r_3 are the first and second lenses from the object side, respectively. This is the radius of curvature of the second and third lens surfaces.