JPS615223A - Zoom lens of wide picture coverage - Google Patents

Abstract

PURPOSE:To extend the picture coverage by arranging a focusing function lens group, a magnification varying function lens group, an image surface compensating function lens group, and an image forming function lens group in order from the object side and designating specific conditions among lenses of the focusing function lens group. CONSTITUTION:A zoom lens system is constituted with the first lens group 1 which has the focusing function and has a positive refracting power, the second lens group 2 which has the magnification varying function and has a negative refracting power, and the third lens group 3 which has the picture compensating function and has a negative refracting power, and the fourth lens group which has the image forming function and has a positive refracting power which are arranged in order from the object side. The first lens group 1 consists of the 1a- th negative meniscus lens projected to the object side, the 1b-th double convex lens having a positive refracting power, and the 1c-th lens having a positive refracting power which are arranged in order from the object side, and conditions of formulas are satisfied to extend the picture coverage. In these formulas, fw, f1, fa, and fc are the shortest focal length of the whole of the system and focal lengths of the first lens group, the 1a-th lens, and the 1c-th lens respectively, and R2 and R3 are radiuses of curvature of the image-side surface of the 1a-th lens and the object-side surface of the 1b-th lens respectively, and nu1-nu3 are Abbe's numbers of the 1a-th - the 1c-th lenses respectively.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a zoom lens for a video camera, and in particular, provides a compact zoom lens that expands the screen encompassing range by devising a method of constituting a focusing lens section. It is.

Conventional Structure and Problems The required screen size of a zoom lens for a video camera is determined by the size of the image sensor, and it is necessary to ensure a sufficient amount of peripheral light at the outermost periphery. When the focusing lens is extended, the amount of peripheral light in a zoom lens that takes close-up shots is lowest at the shortest shooting distance. If you close down the aperture at the shortest shooting distance, the amount of peripheral light will drop off rapidly at the periphery of the screen as you move slightly from the wide-angle end to the telephoto end, making it impossible to secure the required screen size. This phenomenon occurs conspicuously in a zoom lens with a low image height and a so-called single aperture, in which the light beam that forms an image at the periphery is biased to one side of the optical axis at the aperture position. The conventional solution to this problem was to increase the effective diameter of the lens, especially the effective diameter of the focusing lens, to increase the amount of peripheral light. is strongly requested,
There is a growing need for a lens that allows for a wider enclosing screen without making the lens thicker.

Purpose of the Invention Based on this background, the present invention provides a wide screen encompassing range, an F number of approximately 1.2, and a zoom ratio by setting appropriate conditions for the configuration of the lens group that controls the focusing function. The objective is to provide a compact zoom lens for video cameras that is approximately 6 times larger.

Composition of the Invention The composition of the compact zoom lens of the present invention, which has a wide screen encompassing range, consists of, in order from the object side, a first lens group with positive refractive power that controls the focusing function, and a negative refractive lens group that controls the variable magnification function. It consists of a second lens group that has a refractive power, a third lens group that has a negative refractive power that controls the image plane correction function, and a fourth lens group that has a positive refractive power that controls the image forming function. The group consists of, in order from the object side, a negative meniscus-shaped lens 1a with its convex surface facing the object side, a biconvex lens 1b with positive refractive power, and a 10th lens with positive refractive power. and satisfy the following conditions.

4.OfW<f 1<6. Ofw (1)1,
rsfl<1fal<2. ofl(2)1, o
fl<fo<1.1rsf1('41.1<R3/R
1<2.1 (→ν, <35
(When v 2 t ν3 > s o
(''However, fW is the shortest focal length of the entire system,
fl is the focal length of the first lens group S f, is the focal length of the i1a lens, fo is the focal length of the 10th lens, R2
is the radius of curvature of the image-side surface of lens 1a, R3 is the radius of curvature of the object-side surface of lens 1b, and C1. C2. 3 indicates the Atsube numbers of the 1a-th lens, the 1b-th lens, and the 10th lens, respectively.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of a zoom lens having a wide screen encompassing area according to the present invention. In Figure 1, 1 is the first
Lens groups, 2 is the second lens group, 3 is the third lens group, 4 is the fourth lens group, 6 is an equivalent glass plate corresponding to a crystal filter or the face plate of an image pickup tube, and 6 is the 1a
7 indicates the 1b lens, and 8 indicates the 10th lens.

The gist of the present invention, which aims to secure a wide encompassing screen with a compact lens, is to increase the power of the first lens group 1 and increase the 40 magnification of the fourth lens group. By increasing the magnification of the fourth lens group 4 for the image formed through the first lens group 1, second lens group 2, and third lens group 3, the image height at the final image forming plane increases and the screen encompassing range increases. It can be taken widely. On the other hand, the focal length f of the entire system is: the focal length of the first lens group 1 is fl, the magnification of the second lens group 20 is m2, the magnification of the third lens group 3 is m3, and the magnification of the fourth lens group 4 is m4.
Then, the following relational expression holds true.

f ”' fl ”2”3”4 Therefore, while keeping the focal length f of the entire system at a predetermined value,
To increase the magnification m4 of the fourth lens group 4, fl
needs to be made smaller. In order to reduce the focal length of the first lens group 1 without causing collision between the first lens group 1 and the second lens group 2, the power of each group is strengthened, and
Most of the power of the first lens group 1 is given to the tenth lens 8, and the image-side principal point of the first lens group 1 is brought closer to the second lens group side.

Condition 1 is the first condition in order to make the zoom lens compact.
This defines the power of the lens group 1. If the upper limit of condition 1 is exceeded, aberration correction becomes easier, but the lens system becomes larger. If the lower limit of condition 1 is exceeded, the lens can be made compact, but aberrations cannot be corrected well, and it becomes particularly difficult to correct spherical aberration and coma aberration on the telephoto side.

If the upper limit of condition 2 is exceeded, it becomes difficult to correct chromatic aberration while correcting spherical aberration on the telephoto side, and if the lower limit is exceeded,
Comatic aberration worsens.

If the upper limit of condition 3 is exceeded, the image-side principal point of the first lens group 1 will move too far to the object side of the first lens group 1, making it impossible to obtain a wide encompassing screen. If the lower limit of condition 3 is exceeded, the power of the gJ1c lens 8 becomes too strong, making it difficult to satisfactorily correct various aberrations on the telephoto side.

Condition 4 defines the conditions for the air lens formed by the 1st a lens 6 and the 2nd b lens 7. If the upper limit is exceeded, it will be difficult to correct high-order aberrations, especially on the telephoto side, and if the lower limit is exceeded, coma aberration will occur. It becomes difficult to correct.

Conditions 6 and 6 are both necessary for correcting chromatic aberration, and if these ranges are exceeded, it becomes difficult to correct both longitudinal chromatic aberration and lateral chromatic aberration.

Examples that meet these conditions are shown below. R1, R in the table
2... is the radius of curvature of each lens surface counted from the object side, dl, d2... is the wall thickness or air gap between lens surfaces, n1yn2t... is each lens d of
Refractive index for a line, C1. C2. ... is Atsbe's number.

Example 1 Focal length f=8.759~49.508m+n F
Number = 1.25~1.45f1 = 44.596m
rn fa==-75,439mm fc=45.
659mmR=94.549d=1.50n
=1.80518 ν1=25.4R2-56,
690d2=2.20 R6=62.391d3:4.81 n2=1.63
854 Shi2=55.4R4=-248.059 d
4=Q, 17R5=31.792 d5=7.52
n6=1.62041shi3=60.3R6""-23
7,021R6 (variable) R7”299.351 dl
-0,90n4=1.7110 ν4=53.8R8
=14250d8=400 R11-842726d11 (variable) R12=-22,447d, 2=1.00 n7=4
．． 71700 v7=47.9R13=-51,2
74d13 (variable) R14=84.422 d14=
4.00 n8=1.7130 [1shi8=53. QR
--28,206d15=2.0[1Rl6-(3)(
Aperture D) d16=3.00R17"3"93"d
5. BOn 1.69680 ν9==55.
5Rl8>63743d18=1.44 R--22,729d-1,00n1o=1.84
665 ν1o=25.9R2o=-101,729
d2. -113.68R21=85.577 d21
=3.90 n11==1.51635 S11=6
4.1R22"-24,581d2z"", 0-21R
25=23.9D6 d26=4,6On, 12=1
．． 516351/12=64.1R--39,444d
24=t78 R25=”-21,600d25=1.00 n13
==1.84665 v16=25.9R26=-5
5,727d26=5.00R27:oo, d
27=7.40 n14==1.51633 Shira 4
=641R283″ fd6d11d13 8.759. 1.4&21, 26.5
451 1.695024851 17.4
621 5.8069 6.22924
9.508 23.6621 4.89
10. 0.9451 Example 2 Focal length f-8,764~49.582mF%-=
124-1.45f1=44.978wn fa=-
81,682 tan f. =47.526m5R1=
84:979 d, = 1.50 n1 = 1.805
18 Si1=25.4R2=56.785 d2=
2. ．． 0OR3=56.555 d6=5.09. n
2=1.62041 shi2=bo, 6R4=-357
．． 753d4=0.17R5=32.316 d-=
7. Q13 n5=1.62041 shi5=6Q,
3R=-294,211d6 (variable) R7""299.551 d, =0.9[] n4
=1.7130[ν4=53.3R8=14.250
d8=4.0OR9=-17,906d9=0.90
R5””1.69680 ν5=55.5R1o
=15.155 dlo-'2.79 n6=1.
80518 Shiro=25.4R=-842,726(
111 (variable) R12=-21,815d12=1.0
On7='1.69680 5=55.5R15=-
49.829 d13 (variable) R14=76.455
d14=5.50 n8=1.713001/8=
538R15=-28,5G6 d15=1.7GR
16=-00 (aperture) d16=5.00R1723
7-178 d 1y=5.50 Xi q=1.
71500 1'9"'558R19=-21,47
1d19=1. []On1o=1.84665 v1o
=23.9R2o=-113,732d2o=13.7
0R2,=80.097 d21=3.88 n11
=1.51633 Shira1=64.1R22=-24,
620d22=0.21R26=23.613d2
4=4.49 n12=1.51633 si12=64
．． lR24=-41,082d, 5=1.89R-22
,68141,0On 1.84665 C13=
=23.9R26=-52,835d27=5.00R
27=oo d28=7.40 n14=1.5
1633 SI14-64, 1R28-″ f d6 dll d138
．． 764 1.4621- 26.343
1 1.693024.858 17.4621
5.8069 6.229249.58
2 23.6621 4.8910
0.9451 Example 3 Focal length f==8.808~49.888mm F
7<-=1.22-), 4Qf1=46.000mm
fa=-82,918mm f,=52.828
+mmR-84,056d =1.48 n =18
0518 ν1'==25.4R2=36.917
d2=0.86R3=43.499 d3=5.9
5 n2=1.62041 ci2=60:3R4=
-898.640 d4=0.17R5=52.545
d5=6.22 n6=1.62041 C3-6Q, 3R6=4256.341 d6 (variable) R
7=111.409 d7=0.90 n4=1.
71300 ν4=53.8R8=12.991
c18=4.0OR9=-17,123d9=0.9
0 n5=1.69680 ν5=55.5R-1
5,507d1o=2.56 n6=1.80518
White=25.4Rl1=-664,354dll (variable) R--23,283d12=i, 00 n7=1.
69680 Schiff = 55.5P, 13 = -57,469
d16 (variable) R, -76,455d14=3.50
n8=1.713001/8=55.8R--28,
506d15=1.70 Rl6-oo (aperture) d16=3. OOR-5B,
299 d17=3.50 n9=1.71300
ν9=53.8R--49,701d18=1.44 Rl9=-21,164a19=1. oo n1o=
1.84665 ν1o=23.9R2o--112,
147d2o=1670R-76,925, d21=3
．． 88 n11=1.51633 shi, 1-641R2
2--24772d22-0.21R26=22.96
3 d23=4.49 n12=1.51633 ci12=64.1R24=-40.869 624=1.
89R25=-22,765d25=1.0On, 6.
,．． 1.84665 Shira 5=23.9R26--55
122d26-500 R27:oo d -7,4On -
1,516ro6 si14=641R28=o.

fd6d11d13 8.808 1.4621 26.343
1 1.693025.004 1.7.46
21 5.8[]6'? 4.89104
9.888 23.6621 71. a9
1o O, 9451 Figure 2 a, b, c,
Figures 3a, b, and c and Figure 4 a, b, and c show the aberration performance of Example 1 at the wide-angle, standard, and telephoto ends, respectively, and Figure 6 a, b, and c.

Figures 6a, b, and c and Figures 7a, b, and c respectively show the aberration performance of Example 2 at the wide-angle, standard, and telephoto ends;
Figure 8 a, b, c, Figure 9 a, b.

c1 Figure 10 a, b, and a show the aberration performance of Example 3 at the wide-angle, standard, and telephoto ends, respectively. In the diagram of spherical aberration, the solid line shows the spherical aberration for the d-line, and the dashed-dotted line shows the spherical aberration for the q-line. In the diagram of astigmatism, the solid line shows the sagittal curvature of field, and the dotted line shows the meridional curvature of field. It can be seen from the figure that aberrations are well corrected in the zoom lens of the present invention.

Next, the comprehensive screen dimensions of each embodiment will be described.

Each embodiment is a zoom lens for a video camera using a % inch image pickup tube, and the required r step height y is 4 times. 1.2
Examining the relationship between the focal length and the image height, which becomes lopsided at an imaging distance of m, in all examples, the image height is the smallest when the converted focal length is f = 14 g when the object is at infinity. The luminous flux is regulated by the effective diameter of the twelfth lens.

When the effective diameter of the 1a lens is set to 38 mm, the image height of Example 10 in f-14 exposure is y = 4.17
In Example 2, y = 4.1 rings, and in Example 3, y =
It is 4.08 rtan. The image height that becomes one-sided indicates the point where the aperture efficiency becomes 50 when the aperture is stopped down, and in each example, the image height required for a % inch image pickup tube can be secured. In terms of aperture efficiency, the amount of light at four image heights is more than 50%.

Effects of the Invention As is clear from the above explanation, the lens configuration and conditions of the present invention make it possible to realize a zoom lens that is very compact and has a wide screen encompassing range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a zoom lens with a wide screen encompassing range according to an embodiment of the present invention, and FIGS. 2 and 3 show the configuration thereof. FIG. 4 is a diagram of various aberrations of Example 1, FIG. 5, and FIG. 6. FIG. 7 is a diagram of various aberrations of Example 2, FIG. 8, and FIG. 9. FIG. 10 is a diagram showing various aberrations of Example 3. In the diagram of spherical aberration, the solid line indicates the spherical aberration for the d-line, and the dashed-dotted line indicates the spherical aberration for the q-line.
In the diagram of astigmatism, the solid line indicates sagittal curvature of field, and the dotted line indicates meridional curvature of field. 1...First lens group, 2...Second lens group, 3...Third lens group, 4...Fourth lens group
Lens group, 5...Crystal filter. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 5 Figure 8 J (Song @M (%)

Claims (1)

[Claims] (1) In order from the object side, a first lens group with positive refractive power that controls the focusing function, a second lens group with negative refractive power that controls the variable magnification function, and a second lens group that controls the image plane correction function. In a zoom lens consisting of a third lens group with negative refractive power and a fourth lens group with positive refractive power that controls the imaging function, the first lens group is arranged in order from the object side to the object side. A negative meniscus 1a lens with a convex surface, a 1b biconvex lens with positive refractive power, and a 1st lens with positive refractive power.
A zoom lens with a wide screen encompassing range [4.0 f_
W<f_1<6.0f_W 1.5f_1<|f_a|<2.0f_1 1.0f_1<f_c<1.15f_1 1.1<R_3/R_2<2.1 ν_1<35 ν_2, ν_3>50 However, f_W is The shortest focal length of the entire system, f_1 is the focal length of the first lens group, f_a is the focal length of the 1a-th lens,
f_c is the focal length of the 1c lens, R_2 is the radius of curvature of the image side surface of the 1a lens, R_3 is the curvature radius of the object side surface of the 1b lens, and ν_1, ν_2, and ν_3 are the 1a lens and the 1b lens, respectively. Atsube number of lens, 1st c lens. ]