JPH0443311A - Zoom lens - Google Patents

Abstract

PURPOSE:To make the power variation ratio large and to decrease the number of lens elements by using an aspherical surface which decreases in refracting power with the distance from the optical axis as at least one surface among the lens surfaces of a 4th group composed of a single positive or two positive lenses. CONSTITUTION:A 3rd group consists of a positive and a negative lens and the 4th group consists of a single positive lens; and the object-side surface of the 4th group is aspherical and the surface of the 3rd group which is closest to the object side is also aspherical. Thus, the negative lens is arranged in the 3rd group to compensate an on-axis chromatic aberration and a power chromatic aberration sufficiently and this negative lens compensates even a negative spherical aberration. Further, the 3rd group is given sufficient refracting power, the principal point of the 3rd group is set as forward as possible, and a positive lens whose object-side surface is convex is arranged on the most object side to provide two or three positive lenses including the positive lens. The 4th group is used as a focusing group. Consequently, the small-sized lens system which has a high power variation ratio and a large aperture ratio and consists of a small number of lens elements is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a zoom lens mainly used in video cameras.

[Background Art] In recent years, video cameras have rapidly become smaller, lower in price, and higher in image quality. In line with this, zoom lenses for video cameras are also desired to be smaller, lower in cost, and have higher resolution.

Conventionally, zoom lenses for video cameras with a high zoom ratio of 6x or more have a four-group configuration from the object side: positive, negative, negative, and positive.
Most commonly, the second group performs magnification change and the third group corrects the image position. However, in recent years, this third group has been omitted, and the fourth group has been divided into a front group and a rear group, and one of them has an image position correction function, thereby reducing the number of lenses and making the lens system more compact. Something is being devised. Such conventional examples include JP-A-62-206516 and JP-A-2-5.
There are those described in Publication No. 3017.

[Problems to be Solved by the Invention] Among the above conventional examples, the former has a small zoom ratio of about 3 and the number of elements in the third group is large, making it difficult to achieve low cost. The force is small and the miniaturization of the lens system is not sufficient.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-performance zoom lens that is compact, has a small number of lenses, and has a large zoom ratio.

[Means for Solving the Problems] The zoom lens of the present invention has, in order from the object side, a first group that has positive refractive power and is fixed during zooming, and a first group that has negative refractive power and is movable during zooming. a second group having a variable power function;
It consists of a third group that has positive refractive power and is fixed during zooming, and a fourth group that has positive refractive power and is movable during zooming and has the function of mainly correcting the image position. It is composed of four or less lenses, including a positive lens whose object side surface is a convex surface and at least one negative lens, and a fourth lens.
The lens group is composed of a single positive lens or two positive lenses, and at least one of the lens surfaces of the fourth group is an aspheric surface whose refractive power becomes weaker as the distance from the optical axis increases. It is said that

In the case of a lens system like the present invention, in order to smoothly correct aberrations that occur after reducing size, cost reduction, and eliminating unnecessary space, lenses with low effectiveness are eliminated as much as possible and the minimum number of lenses is required. It is desirable to configure the number of sheets.
In order to achieve this, the construction of the third and fourth groups, which mainly have an imaging function, requires the most ingenuity.

In order to satisfactorily correct chromatic aberration, it is necessary to use at least one negative lens in the third and fourth groups.In the present invention, as described above, a negative lens is placed in the third group. Color aberration and chromatic aberration of magnification are corrected at the same time. Furthermore, this negative lens also corrects negative spherical aberration. In addition, in order to downsize the lens system, the third group should be given sufficient refractive power, the principal point of the third group should be placed as far forward as possible, and the third group should be designed to minimize (suppress) the occurrence of spherical aberration. Two or three positive lenses including a positive lens whose object side surface is convex are placed closest to the object side.

A lens with a larger size is not preferable because the cost and length of the lens system are greater than the effectiveness.

It is also possible to use only one positive lens by making at least one surface of the positive lens in the third group an aspheric surface to correct spherical aberration, as in the embodiment shown below.

It is desirable that the positive lens closest to the object side of the third group described above satisfies the following conditions.

-1,2<(R,+RIl/(R1-R1+<-0,
2. However, R, , R, is calculated using the radius of curvature of the object side and image plane of the positive lens closest to the object in the third group, respectively, and when the lens surface is aspheric, the paraxial radius of curvature is used.

If the lower limit of the above conditions is exceeded, spherical aberration cannot be corrected, and if the upper limit is exceeded, miniaturization of the lens system cannot be achieved.

Further, it is preferable that all the negative lenses in the third group be located closer to the image side than all the positive lenses, because this is preferable for downsizing the lens system and correcting chromatic aberration.

It is preferable that the 3rd nth lens be configured with three lenses (positive, positive, and negative) or four lenses (positive, positive, positive, and negative) because the number of lenses can be reduced.

Furthermore, if the two lenses closest to the image side of the third group are configured with a positive lens with a strongly convex surface facing the object side and a negative lens with a strongly concave surface facing the image side, the number of lenses can be reduced.

As mentioned above, the three groups are positive, positive, negative or positive, positive, positive, negative, and then the two lenses closest to the image are a positive lens with a strongly convex surface facing the object side, and a positive lens with a strongly concave surface facing the image side. It is more desirable if the lens is configured with a negative lens directed toward the lens.

As mentioned above, in the zoom lens of the present invention, since the Hosotchi chromatic aberration and 1x lateral chromatic aberration are simultaneously corrected by the negative lens in the third group, the fourth group can omit the negative lens and consist only of positive lenses. 6 In the present invention, in order to correct astigmatism, coma, and negative distortion that occurs at the wide-angle end, at least one surface in the fourth group is moved from the optical axis to the periphery of the lens (accordingly, the refractive power is The lens has an aspherical surface that reduces the number of lenses.This allows us to successfully correct various aberrations with a minimum number of lenses, resulting in a more compact lens system.

In the zoom lens of the present invention, if the fourth group is used as a focusing group, there is no need to provide a new movable group for focusing, and the distance to the nearest object can be shortened compared to focusing by the first group. I can do it.

[Example] Next, embodiments of the zoom lens of the present invention will be shown.

Example 1 f=8.76-65.96, F/2.0-F/2.
62ω=50.2'''~7.2°r+=51.4795 d,=t,0000 r,=23.9639 d2=5°6000 r,=-71,1147 d,=0.150O r,= 17.8414 d, = 3.8000 rs = 33.3216 d, = D, (variable) rs = 37-2001 d, = 1.1026 r, = 7.3340 d7 = 2.000O r, = -10, 3299 d, = 1.0000 rs = 9.5724 d, = 2.000O rls = 469.3178 d+o” mouth 2 (variable) n+ = 1.80518 n, = 1.60311 n, = 1.60311 n, = = 1.69680 ng=1.69680 ns=1.80518 ν, =25.43 si! = 60.70 s: 60.70 ν, = 55.52 ν, = 55-52 ν, = 25.43 rz = (capital) (aperture) d = 1.5000 r,, = 7.9854 (non- Spherical surface) d, 2”” 3.500On, = 1.6968Or,
, =-37,1999 d, 3= 1.8644 r,, =42.6275 d+4=1.2104 jl, :: t, gos
tsr+s = 6.7517 d+5=Di (variable) rls = lO, 1365 (aspherical surface) d,, = 3.3000 no” 156384
r,, =-33,5763 d,, =D, (variable) r18 = (to) d,, =5.100On,, =1.54771r,
, :00 d, , = 1.2100 ν, = 55.52 ν, = 25.43 ci9=60.69 ν,. = 62.83 rzo ” ■ d,.=0.6000 n.

= 1.48749 shi, , = 70.20r, , =
OO Aspheric coefficient (12th surface) E = -0,25435x 10-", F = G
= -0,46594X 10-' (16th surface) E = -0,22509x 10-" G = -0,91309x 10-'f 8.7
6 24.04 D 1.000 9.497 D, 15.916 7.420 D36.391 3.500 D47.067 9.958 Example 2 f=6.49-48.90, F/1.42ω= 51
．． 8”~7.4゜r = 57.3585 d+” 1.0000 n1 = 1.80518r
x = 23.7370 d-=5.6 (1000==1.60311~F/2.
2 F = 0.35300 0, +4404x 10-' 65.96 15.916 1, Mouth 00 11.458 2.000 = 25.43 νz=60.70 r, =-71,5301 ds=0.1500 r4 = 17.1706 d, = 3.8000 rs = 43.6355 ds = D + (variable) rs = 1140.8303 d, = 1.1026 r- = 6.8647 dt = z, ooo.

r,=-9,8125 ds=1.0000 r,=L1232 d,=2.6000 rl. = 735.9093 d,. =D, (variable) r,, =oo (aperture) d,, =1.5000 r,, = 13.4774 d+*= 3.4000 n7 = 1.6031
1 nm = 1.60311 n mini 1.69680 na = 1.69680 n mini 1.80518 si 1 = 60.70 ν, = 55.52 ν5 = ss, sz si, = 25.43 ν, = 1io, 7° rlt = -65,0959 d+, = 0.30 r, 4 = 16.4183 d,, = 2.5000 is = 141.9059 a,, = 0.3000 r,, = 8.6800 d,, = 2.4000 rlt = 17.8996 d, t = 0.7000 rl. = -28,6777 d,, = 1.2104 rlm = 8.6110 d,, =D, (variable) r,. = 8.9305 (aspherical surface) d*o= 3.300On+ 1 rat = -ta, 5ost di+=04 (variable) rwx = flash d**= 5.1000 n, = 1.60311 n, = 1.60311 = 1.80518 = 1.56384 = 1.54771 shi, = 60.70 shi9 = 60.70 ν1゜ = 25.43 shi,, = 60.69 ν1□ = 62.83 r■'':o.

d, 1 = 1.2100 rTomi4=OO d,,=0.60roO rwx =■ Aspheric coefficient E = -0,37686x 10-”G=O D.

D two the law of nature.

Example 3 f=6.49-48.90, F/1.52ω=5
1.8@〜7.4@r+ ” 49.2800 t+, = t, 0000 r*= 23.1954 d, = 5.2000 F = -0,16869x 10-' = 1.487
49 17.82 9.287 6.332 3.500 5.431 71, = 1.60311 il, = 1.80518 6.49 1.000 14.619 6.351 2.580 si, m=70.20 48.90 14.619 1.000 6.931 2.000 ~F/2.2 ν1=25.43 Sig=60.70 rs" -104,9168 dz=0.1500 "4= 18.4142 da = 3.7500 rs = 58.6398 a, = O, (variable) ra = 60.7724 ds = = 1.1026 ry = 6.6301 d, = 2.0000 rs knee 9.8199 ds = 1.000On- = 1 r*= 11.1626 d, = 2.40 rl.: -73,9440 C+,, = O, (variable) r, = cX: + (aperture) d,, = 1.5000 rlt = 8.9570 d1□=4.2000 n mini 1 n mini 1 j14= 1.69680 ny” 1.69680 si, = 60.70 ν, = 55.52 ν, = 55.52 si, = 25.43 ν , =55.52 r,, =-97,9282 rzs = (fund) d,, = 0.8990 r,, =-18,4246 d+4 = 1.2000 ns = 1.80518 rls =9.9456 d, , = 0.5000 rls = 16.4456 d, 6 = 2.400On, = 1.6968Or,,
=-31,7035 d+t=Ds (variable) r,, =9.9286 (aspherical surface) d+s=4.1000 n+a =1.563
84r,, =-29,2366 d+*=04 (variable) r3゜ = flash d,, ==5.100on,, =1.54
771r21 = ■ dl, == 1.2100 r mouth = flash diz = 0.600 Ofi2 = 1.48749ν. =
25.43 ν@=55.52 ν1゜= 60.69 , , = 62.83 ν1□: 70.20 Aspherical coefficient E = -〇, 22999x 10-"G=O Example 4 f=6. 49-4g, 89.

2ω=51.8°~7.41 rl = 61.1461 d, = 1. (1000Q,: 1.80518r*
= 25.5792 d, = 5.2000 r, = -82,8557 d*= 0.1500 r, = 18.9721 d4=3.7500 ~F/2.1 F = -0,97968x 10-'17 .82 9.552 6.843 2.500 7.528 F/1. s jl, = 1.60311 ns = 1.60311 6.49 1.300 15.095 3.764 6.264 48.90 14.895 ? , 591 2.437 s, = 25.43 s 2 = 60 sm = 60.70 rs = 50.8855 d% = D, (variable) rg: 293.8083 d, = 1.1026 r, = 7. 3631 d, = 2.0000 rs: -10,8606 dll = 1.0QOO r, = 9.0391 d, = 2.4000 rlo = -479,7696 d,, = D, (variable) rll = (capital) (Aperture) d,, = 1.5000 rli = 11.1400 d,, = 4.2000 rlx = -43,8310 d,, = 0.3000 rl4 = 8.2915 d, 4 = 2.4000 jl,: 1.696
8011, :1.69680 n4=1.69680 fi,=1.69680 n,=1.80518 ν4=55.52 ν,=55.52 νg=25.43 ci,=55.52 νm=55.52 rls =19.0091 d,, = 0.6044 r,6 knee 271999 d,,” 1.2104 Q, = 1.8051
8r,, Near, 3325 d+y=Ds (variable) rls =9.6114 (Aspherical) d,, =4.1
000 n,, ”1.56384rI*
=-15,3541 d,, =D, (variable) "20:o.

d,,=5. ID0D n,, =1.547
71 "21:■ di+=1.2100 rag" ■ da-= 0.6000 nl-= 1.487
491, =25.43 o"60.69, =62゜83 1□=70.20 rzs" (fund) Aspherical coefficient E =-0,39357x 10-" F =-0,40862X 10 G= 0 f 6.49 D, 1.300 D, 16.688 Ih 4.934 D, 3.660 Example 5 f=6.49-48.90.

2ω = 51.8' ~ 7.46 r, = 62.6591 d, = 1.0000 rg = 25.6867 d, = 5.2[100 rs'' -88,1045 d, = 0.1500 r, = 19.1934 d, = 3.7500 rs" 58.7953 ds=D+(variable) rs" -157,6505 da= 1.1026 i, = 1.80518 ni=1.60311 jl, = 1.60311 n, =1.69680 17.82 10.119 7.869 2.472 6.123 F/1.6 48.89 16.488 1.500 6.157 2.437 ~F/2.2 ν1=25.43 si, = 60.70 si, = 60.70 ν, = 55.52 ry = 7.6914 d, = 2.0000 rs"-13,7250 d, = 1.0000 r* = 8.3911 d9 = 2 .4000 rl. = 204.9580 dl. ;D2 (variable) r□, =oo (aperture) d,, = 1.5000 rlz = 11.4645 d,, = 4.2m mouth On- = 1.69680rIz
=-41,1109 d,,=0.3(100 r,4 =9.3876 d,,=2.4000 rlg =28.3293 d,,=0.4948 r,,=-24,6734 d+s= 1.2104 ns=1.69680 ns" 1.69680 ns" 1.80518 ns" 1.-80518 psi, = 55.52 νg"25.43 si, = 55.52 ν, = 55.52 ν, = 25.43 r,, =8.4053 d, 7=03 (variable) r 1m = 24.2967 d, s: 2.000On+.

r, 9 = -36,3424 d,, = 0.10 (10 r2゜ = 1 mouth, 7 B 65 (-tk shrine u crime) d
, o=2.0000 n++ r,, = 70.0000 d,, =04 (variable) r22 =■ daz= 5.1000 n1zr23 :■ dai=1.2100 r24 :oO da4= 0.600On+5 r15 :'') Aspheric coefficient E = -0,17524x 10-"G = -0,2
3328x 10-' = 1.60311 = 1.60311 = 1.54771 = 1.48749 F = 0.70866 o = 60.70, = 60.70! =62.83, =70.20 X to-' f 6.49 17.82 48.9
0D, 1.300 10.352 1
6.336D, 16.536 1483
1.500Di 5.837 3.797
7.805D4 3.467 5.507
1.500 but r+, r2. -. is the radius of curvature of each lens surface, d,, d, . . . is the wall thickness and air spacing of each lens, nn2. ... is the refractive index of each lens, 1. C2. -... is the Atsube number of each lens.

Embodiment 1 has a lens configuration shown in FIG. 1, in which the third group is composed of a positive lens and a negative lens, and the fourth group is composed of a positive single lens, and the object side surface (r, , 1 of the fourth group is It is an aspherical surface.
The surface of the group closest to the object ("1□") is also an aspheric surface.

The aberration conditions at the wide-angle end, intermediate focal length, and telephoto end of Example 1 are as shown in FIGS. 6, 7, and 8, respectively.

Embodiment 2 has the configuration shown in FIG. 2, in which the third group consists of three positive lenses and one negative lens, the fourth group consists of a single positive lens, and the object side surface (r ,.) is an aspheric surface.

The aberration situations at the wide-angle end, intermediate focal length, and telephoto end of Example 2 are as shown in FIGS. 9, 10, and 11, respectively.

Embodiment 3 has the configuration shown in FIG. 3, in which the third group is made up of a positive lens, a negative lens, and a positive lens, and the fourth group is made up of a positive single lens, and the object side surface fr of the fourth group is -1 is an aspherical surface.

The aberration conditions at the wide-angle end, intermediate focal length, and telephoto end of Example 3 are as shown in FIGS. 12, 13, and 14, respectively.

Embodiment 4 has the configuration shown in FIG. 4, in which the third group consists of two positive lenses and a negative lens, and the fourth group consists of a single positive lens. It is aspherical.

The aberration conditions at the wide-angle end, intermediate focal length, and telephoto end of Example 4 are as shown in FIGS. 15, 18, and 17, respectively.

Embodiment 5 has the configuration shown in FIG. 5, in which the third group consists of two positive lenses and a negative lens, and the fourth group consists of two positive lenses. The object side surface of the lens (.

) is an aspheric surface.

The aberration conditions at the wide-angle end, intermediate focal length, and telephoto end of Example 5 are as shown in FIGS. 18, 19, and 20, respectively.

The shape of the aspherical surface used in these Examples is expressed by the following formula, where the optical axis direction is the X axis and the direction perpendicular to the optical axis is the Y axis.

However, r is the radius of curvature of the reference sphere, E, F, G.

-... is an aspheric coefficient.

[Effects of the Invention] The zoom lens of the present invention is a compact lens system with a high variable power ratio, a large aperture ratio, and a small number of lenses.

[Brief explanation of drawings]

1 to 5 are cross-sectional views of embodiments 1 to 5 of the zoom lens of the present invention, respectively, and FIGS. 6 to 8 are sectional views of embodiment 1 of the zoom lens of the present invention.
, FIGS. 9 to 11 are aberration curve diagrams of Example 2, FIGS. 12 to 14 are aberration curve diagrams of Example 3,
15 to 17 are aberration curve diagrams of Example 4, and FIG.
20 to 20 are aberration curve diagrams of Example 5. Applicant Olympus Optical Industry Co., Ltd. Agent Hiroshi Mukai Figure 3 Figure 6 Figure 7 Figure 1O Figure 11 Figure 8 Figure 9 Figure 12 Figure 13 Figure 14 Figure 15 Figure 18 Figure 19 Figure 16 Figure 17

Claims (1)

[Claims] In order from the object side, the first group has positive refractive power and is fixed during zooming, the second group has negative refractive power and is movable during zooming and has a variable power function, and the second group has positive refractive power and is fixed during zooming. It consists of a fixed third group and a fourth group that has positive refractive power and is movable during zooming and has the function of mainly correcting the image position, and the third group has a convex surface on the object side closest to the object side. It is composed of four or less lenses including a certain positive lens and at least one negative lens, and the fourth group is composed of a single positive lens or two positive lenses, and at least one of the lens surfaces of the fourth group
A zoom lens is an aspherical surface whose refractive power decreases as the surface moves away from the optical axis.