JPS62247318A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a large aperture zoom lens of simple constitution and well corrected aberration by specifying refracting power of the fourth lens group and the shape of lenses in four-group zoom lens. CONSTITUTION:The lens is provided with the first lens group I for focusing having positive refracting power, the second lens group II for variable power having negative refracting power, the third lens group III of positive refracting power that moves with convex locus to image face side to correct the image face changed by variable power, an aperture and fixed fourth lens group IV of positive refracting power for image forming from the object side in order. The fourth lens group IV has four lenses of positive, negative, positive, positive refracting power in order and when focal length of the i-th lens is F4i, radius of curvature and focal length are R4i, f4i respectively, lens thickness or air space is D4i and focal length of the whole system at the wide angle end if fW, conditions shown in inequalities I-VI are satisfied. Thereby, various aberrations that occur with enlarging of aperture ratio of the whole lens system can be corrected satisfactorily.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a zoom lens suitable for video cameras, photographic cameras, etc., and particularly to a zoom lens suitable for video cameras, photographic cameras, etc., and in particular, to reduce the number of lenses and simplify the lens configuration at a large aperture ratio. This is about the zoom lens in the shed.

(Conventional technology) Recent video cameras have improved the performance of image pickup tubes and CODs, and the entire camera has been made into a shed.) Along with this, the lens system has been made brighter and has a high zoom ratio, while shortening the overall length of the lens. A compact lens system is required.

Many types of zoom lenses are used in video cameras, and because it is relatively easy to achieve a high zoom ratio of 1 and a large aperture ratio, for example, A four-group zoom lens, as proposed in Japanese Patent No. 60-186817, is often used. This four-group zoom lens consists of, in order from the object side, a first lens group for focusing, a second lens group for variable magnification, a third lens group for correcting the image plane that changes as the magnification changes, and a constant aperture. It consists of four lens groups: a fourth lens group for image formation.

However, these zoom lenses have an F number of 20.
It's a little dark and has a relatively large number of lenses, 13 in total, so the total length of the lens is probably only one. tended to be longer.

Generally speaking, if you try to configure a lens system with a 4-group zoom lens with a brightness of about F+:/A-L4, the 4th lens group's brightness will be
The number of lens elements must be increased to about 6 to 7 lenses, and as a result, the lens structure becomes complicated, the overall length of the lens becomes longer, and the overall lens system tends to become larger.

(Problems to be Solved by the Invention) The present invention provides a 4#P zoom lens by appropriately setting the lens configuration of the fourth lens group to S% to achieve a magnification ratio of 38 degrees for a 1F nanoparse L4. The number of sheets/zu is the overall Kl
The overall object of the present invention is to provide a zoom lens of a simple construction in which the number of lens elements in the fourth zoom lens group is reduced to about one.

(Means for solving the problem) A first lens with a positive refractive power for focusing in the order from the object side (Details) A second lens group with a negative refractive power for zooming 3rd lens #1 diaphragm with positive refractive power that moves with a convex locus toward the image plane to correct the image, and 4 lenses in the 4th lens group with positive refractive power for constant image formation. has a group,
The fourth lens group has four lenses having positive refractive power (one negative, one positive, and one positive), and the focal length of the first lens is F, the radius of curvature of the i-th lens surface, and the focal point. Let the distance be R, /, and the first lens thickness or air distance t-DS.If the focal length of the entire system at wide-angle lens m is 54 (1 (F, □ 10 F43 + F44) / F411... −・・・・・・(1) 0<R41/R41kuα4
・・・・・・－・・・(2) LX < lR4:
l/R441< 11 --・= (3) L3
<|f44//wl < 11 --------
- (41α4 <D43/'/W< 0.6
・・−−(51α04 < 744/ (
/, 5+74. ) < 0.4 ・・・・・・・・・
...(6) is to be satisfied.

The features of this shrub invention are described in the Examples.

(Example) FIG. 1 is a sectional view of a lens according to a first embodiment of the present invention.

In the figure, I shows the details of the first lens group with positive refractive power for focusing, and I shows the details of the second lens group SI with negative refractive power for zooming to correct the gR surface that changes with zooming. A third lens group moves to have a convex locus toward the image plane side, (2) is a fourth lens group having a positive refractive power for constant image formation, and (ST) is an aperture. The arrows indicate the direction of movement of each lens group when changing magnification from wide-angle to telephoto.

In this embodiment, as described above, the zoom lens is changed by moving the second and s3 lens details, and the fourth lens group is composed of four lenses, thereby simplifying the fourth lens detail. We are trying to downsize the entire system.

By setting the refractive power and lens shape of the four lenses in the fourth lens group so as to satisfy conditional expressions (1) to (6), various aberrations that occur due to the large diameter ratio can be effectively corrected. are doing.

Conditional expression (1) concerns the refractive power ratio between the positive refractive power lens and the negative refractive power lens when the fourth lens is composed of four lenses in the order of positive refractive power, negative refractive power, positive refractive power, and positive refractive power. This is for electricians to fully correct spherical aberration near F number L4. If the lower limit value is exceeded, spherical aberration will be under-corrected, and conversely, if the upper limit value is exceeded, the spherical aberration will be over-corrected.

Conditional expression (2) relates to the lens shape of the fourth lens, and conditional expression (3) relates to the lens shape of the C-th lens, both of which are intended to satisfactorily correct comatic aberration of the entire screen. Conditional expression (
If the lower limit of 2) or the upper limit II of conditional expression (3) is exceeded, a large amount of inward comatic aberration will occur. Also, conditional expression (2)
If the upper limit of or the lower limit of conditional expression (3) is exceeded, a large amount of outward coma aberration will occur, which is not good.

Conditional expression (4) is set to 6 in order to appropriately maintain the refractive power of the lens surface on the image plane side of the 42nd lens and to reduce the Petzval sum. Conditional expression (5) is used to appropriately set the lens thickness of the 42nd lens and maintain a good field curvature. If the lower limit of conditional expression (4) or conditional expression (51) is exceeded, the image plane will be greatly curved toward the object side; It becomes curved.

Conditional expression (6) is the refractive power of the object-side lens surface of the 43rd lens and the refractive power of the object-side lens surface of the 43rd lens relative to the refractive power of the lens surface with negative refractive power on the image side of the 42nd lens. This is mainly for the purpose of satisfactorily correcting distortion aberration with respect to the ratio to the sum of . If the lower limit of conditional expression (6) is exceeded, the distortion becomes large in the positive direction on the telephoto side51, and if the upper limit is exceeded, the distortion becomes large in the negative direction on the wide-angle side, which is not preferable.

In this embodiment, in order to achieve even better aberration correction, the fourth lens has a meniscus shape with the convex surface facing the object side.
The 43rd lens has a concave lens shape, the 43rd lens has a meniscus shape with a convex surface facing the image plane, and the 4th lens has a concave lens shape.
It is preferable that the four lenses are constructed in a lens shape in which the lens surface on the object side has a stronger refractive power than the lens surface on the image side.

Next, the number of the present invention (1! An example will be shown. In the numerical example, Ri is the radius of curvature of the first lens surface in the order of p from the object side. Di is the thickness and air distance of the first lens from the object side. , Nl and νl are the refractive index and Atbe number of the glass of the 1st lens (on the object side, respectively). Furthermore, R22, R
23 is an optical member such as a low-pass filter.

Numerical Example I F-(1,55~2&08 F'N0-1:L4 2
ω-4&gi~16. τR1= 12a99D
1-100 N 1-1.8Q518 v 1
-2 & 4 liters 2= 39.99 D 2-
9.00 N 2-1.60311 y
2-60.7R3--7L15 D 3- 0.1
0R4-2N49 D 4- 5.30 N
3-1.62299y 3-58.2R5
-'132 D 5- 177~15.50R6-
238 & 25 D 6- 1.00 N
4-L77250 v 4-49.6R7-14
0407-180 R8--1 & 20 0 8 1.00'J5 L69
680 ν 5-5 & 5R9-1 & 20 D
9-λ40 N 6-L84666 ν
6-2U9RIO--17G, 55 010-15
．． 7l-430R11-49,0Or)11-R5
0N 7-L60311 y 7-6α7R12
--49,00Di2- 4.80~4.48R13-
Aperture 013-110 R14= 1198 Di4- 120 N
8”L71300 w 8-518115-
1581.07 015-1.90R16= -1
9,54016-! h50 N 9-1.805
18y 9-25.4R17-15,64Di
7- 1.30R18--48,72018-2,40
Nl0-1.65160 Shi1G-511.6R1
9--11, 90Di9- 0.10R20= 14
65 r120- 140 Ni1-1.7725
0 &l1l-416R21 Mausoleum-239,9302
1-100R22--022-5, 50N12-1.5
1633 &112-641R23-(To) Numerical Example 2 F-9,55"!&08 F'N0-1:1.4 2
ω-4&r-1a2″R1= 119.35 D 1
- ZOON 1-1.80518 &+ 1-25
．． 4R2-41,58D 2- &00 N
2-1.60311 ν 2-6α7R3--8&
07 D 3- 0.10R4-2151D
4- &2Q N 3-1.62299 ν
3-5112R5-5L75 D 5- 1.2
5~15.00R6= 5a24 D 6-
1.00 N 4-L77250 v
4-49.6R7-11,7107-160 R8= -1163D B-0,90N 5-L
69680y 5-5&5R9-19,460
9-270N 6-1.84666 ν 6-2
λ9RIO--10126DlG-1a62~422R
11-4! L89 Dil-R10N 7-1.
60311y 7-6α7R12--5L68
Di2-480~445R13-Aperture Re D
i3- 1.10R14-IL56 Di4- 12
0 N 8-1.71300 v 8-5λ
8R15-13473015-L90 R16--2163Di6- 5.50 N 9-
1.80518y 9-25.4R17-14
26DI? -1,30 R18--59,62Di8- 140 Nl0-
t65160 Shi10-5&6R19--11,9
8Di9ko Q, 10R20-IL75 020-
140 Ni1-1.77250 yll-4
9,6R21-14&94 D21-100R22-
■ D22- &50 Nl2-15163
3 ν12-6 Melon 1123 ω Numerical Example 3 F-9,55~2EL08 FNO-1:1.4 2
ω-45,5″~1aτR1= 118.27 D
1-! 00 N 1-1.80518 y 1-
2N4R2= 4L30 D 2- N00 N
2=L60311 y 2-6(L7R3--90
,50D 3-0.10 R4-2189D 4= N20 N 3-L622
99 w 3-5&2R5-56,00D 5-12
7~15.02R6-53,6206-1,00N 4
-L77250 Shi4-49.6R7-11,690
7-3,60 R8--15,7808-0,90N 5-L6968
0 C5-5&5R9=1&87 D 9-1
70 N 6-L84666 y 6”2&9RI
O--116, 68010-16, 70-129R11
-44,97r) 11-210 N 7-L6031
1 v 7-60.7R12--53,95D12-
480~445R13-Aperture Re D13- 1.
10R14-10, 90D14- N20 N 8-
L71300 Shi8-5λ8R15-34,6701
5-1,90 R16--25,03D16- N50 N 9-L
80518 v 9-2&4R17-1160D17
-130 R1g-207,70018-5L40 Nl0-L
69680 Shi1o-5&5R19--12-300
19-α10 R20 1α43 02G-140N11-L7
7250 1111-49.6R21-2a36 0
21- LOQ R22= -e D22-! L50 N1
2"L51633 12-641R23-# (Effects of the Invention) As described above, according to the present invention, in a 4#-zoom lens, by specifying the refractive power and lens shape of the fourth lens group as described above, the F number can be adjusted. This zoom lens has a large aperture of L4, has a simple construction with a small number of lenses in the @4 lens group, and has well-corrected aberrations.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the lens of Numerical Embodiment 1 of the present invention. Figs. End S@ is an aberration diagram of a telephoto pot. In the figure, the 11th, 2nd, 31st, and 4th lens groups 1ST, diaphragm S8, sagittal image plane 1M, and meridional image plane are respectively indicated by 1.1°.

Claims (1)

[Claims] In order from the object side, a first lens group with positive refractive power for focusing, a second lens group with negative refractive power for zooming, and a lens group for correcting the image plane that changes due to zooming. It has four lens groups: a third lens group with positive refractive power that moves with a convex trajectory toward the image plane, an aperture, and a fourth lens group with positive refractive power for constant image formation,
The fourth lens group has four lenses having positive, negative, positive, and positive refractive powers in order, and the focal length of the first lens is F_4_i, and the radius of curvature and focal length of the first lens surface are F_4_i. 5.4<|(F_4_1
+F_4_3+F_4_4)/F_4_”_2|<6.
40<R_4_1/R_4_2<0.4 1.1<|R_4_3/R_4_4|<2.11.3<
|f_4_4/f_W|<2.1 0.4<D_4_3/f_W<0.6 0.04<f_4_4/(f_4_5+f_4_7)<
A zoom lens characterized by satisfying a condition of 0.4.