JPS63318513A - Variable power lens - Google Patents

Abstract

PURPOSE:To shorten the whole length and to expand an aperture ratio by constituting the lens group of three groups and satisfying the lens system with specific conditions. CONSTITUTION:The lens system consists of a positive 1st group, a negative 2nd group and a positive 3rd group which are successively arranged from the object side, the 3rd group is constituted of a front group and a rear group, and at the time of power variable, the 1st group is moved, the 2nd group is fixed and the rear group in the 3rd group is moved in order to correct the variation of an image face due to the variable power. The lens system is satisfied with conditions shown by inequalities. In the inequalities, f1 and f2 are the focal distances of the 1st and 2nd groups, f31, f32 are the focal distances of the front and rear groups in the 3rd group and fw is the focal distance of the whole system at a wide angle end. Consequently, the power variable lens shortening the whole length of the lens system at the wide angle end and having a large aperture ratio can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable magnification lens, and particularly to a telephoto variable magnification lens suitable for electronic still cameras and video cameras.

[Conventional technology]

In electronic still cameras and video cameras, since the sensitivity of the imaging device is relatively low, it is desirable that the photographing lens has a large aperture ratio. However, as the aperture ratio of the photographic lens increases, various aberrations are disturbed, and in order to correct this a large number of lenses are required, and the overall length of the lens system tends to become longer.

As a conventional example of a telephoto variable magnification lens for electronic still cameras and video cameras as mentioned above, Japanese Patent Application Laid-Open No. 62-436
There is one shown in Publication No. 15.

This conventional example consists of a positive first group for focusing, a negative second group for zooming, a positive third group for correcting fluctuations in the image plane due to zooming, a front group, and a rear group. This is a lens system consisting of a fixed fourth group for imaging. This zoom lens has 13 to 14 lenses and an aperture ratio of '/2.9.

Therefore, a lens system with fewer lenses, a shorter overall length, and a larger aperture ratio is desired.

[Problem that the invention seeks to solve]

The present invention is a telephoto variable magnification lens that is suitable for electronic still cameras and video cameras, and that changes magnification within a field angle (2ω) range of 15° to 45°. The object of the present invention is to provide a variable power lens having a shorter overall length and a larger aperture ratio.

[Means to solve problems]

The variable power lens of the present invention includes, in order from the object side, a positive first group;
It consists of a negative second group and a positive third group, and the third group consists of a front group and a rear group, and when changing magnification, the first group moves and the second group is fixed. , a lens system in which the rear group in the third group moves in order to correct image plane fluctuations due to zooming, and satisfies the following conditions (1), (2), and (3). .

(1) 0.3 < lf2/f, l < 0.9 (
2) -0,2<fvf,1<0.6(3)
−0,2< f32/f3. < 0.6 but f+,
f2 is the focal length of the first group and the second group, respectively, f3++f32
are the focal lengths of the front and rear groups of the third group, respectively, and fW is the focal length of the entire system at the wide-angle end.

In the conventional example described above, the first group consists of four groups, the first group to the fourth group.
The group and the fourth group are fixed, and the second group and the third group are moved.

In the present invention, in order to reduce the number of lens components and shorten the total length of the lens system, a configuration is adopted in which the total length of the lens system changes during zooming. Specifically, the role of the third group in the conventional example described above is made part of the fourth group, eliminating the third group, and furthermore, by fixing the second group and moving the first group toward the object side. The lens is configured to change the magnification towards the telephoto side.

In other words, as described above, the variable power lens of the present invention includes the first group,
It is composed of three groups, the second group and the third group, and when changing magnification, the second group is fixed and the first group is moved toward the object side to change the magnification toward the telephoto side. 3rd to correct for fluctuations
The rear group in the group was moved.

With this configuration, the overall length of the lens system becomes the shortest at the wide-angle end where the first group approaches the second group, making it possible to make the lens system compact.

Furthermore, the third group of the conventional example was omitted, and the above condition (1
), (2), and (3), the number of constituent elements could be reduced by appropriately arranging the refractive power of each group.

Next, each of the above conditions will be explained.

Condition (1) stipulates the ratio of the refractive powers of the first group and the second group, and if the lower limit of this condition is exceeded and the refractive power of the second group becomes stronger than that of the first group, aberrations due to zooming will occur. As a result, negative distortion increases especially on the wide-angle side, and inward coma aberration increases on the telephoto side.

Furthermore, if the upper limit is exceeded and the refractive power of the second group becomes weak, the amount of movement of the first group during zooming becomes large and the total length of the lens system on the telephoto side becomes large, which is not preferable.

Condition (2) concerns the refractive power of the third group; if the lower limit is exceeded and the third group becomes negative and the refractive power becomes strong, spherical aberration will be overcorrected, especially on the wide-angle side, and it will be difficult to increase the aperture ratio. Become. Furthermore, if the positive refractive power becomes strong beyond the upper limit, spherical aberration will be insufficiently corrected over the entire magnification range, and similarly, the aperture ratio will not be able to be increased.

Condition (3) relates to the ratio of the refractive powers of the front group and the rear group of the third group. If the lower limit of the condition is exceeded, the meridional image plane will tilt toward the plus side of the sagittal image plane, increasing astigmatism, and the back focus will become longer than necessary, increasing the total length from the first surface to the image plane, which is undesirable. When the upper limit is exceeded, the meridional image plane falls to the minus side of the sagittal image plane, and inward coma aberration increases. Furthermore, the desired back focus cannot be obtained, and it becomes impossible to arrange optical members such as an optical low-pass filter or an optical path splitting mirror that guides light to the finder after the lens system.

〔Example〕

Next, embodiments of the variable power lens of the present invention described above will be shown.

Example 1 f=30~85, F/28, 2ω=15.6°~
5.4゜r+=5319435 d+=4.800On+=3148749v
, =70.20rt=279°3766 d2=0.2000 r3=55.7547 da” 46000 n2=3148749
J/2 = 70.2 Or, = 260.6617 d4 = 0.3273 rs = 340.3336 ds”2.0000 n3 = 3180518
ν3=25.43ra=142.4011 do"D+ ry"19.5117 d7=31500On+=3151633 J'4=
64.15ra=16.0334 d8=3.0O00 r, = 29.4529 do "315000 ns"'315163
3 I's =64.15r,. =25.4678 d+o ”2.0000 na =31.805
18 shi, = 25.43r++ = 75.8329 do = 314545 rl□200 (aperture) dot = 20.7026 r+3 = 24.2699 d+: + = 315000 n d = 3176
182 Schiff =26.55r+4 =29.7
306 d,, = 3161315 r+5=80.6510 d,5=3.1000 1s=3172000 1
/3=50.25r+a=-17,4809 d+a=Dt r+7=19.4834 dr7=3.2000 no=3151633
shi, =54.15r+a=88.3914 f 30 50.5 85D,
' 0.436 19.618 28.881
D2 3.000 8.970 17.709f
l=70.755, f2=-46,249f3
1=5131021, f32=33123
5 Total length at wide-angle end = 85.3 (= 2.8 fW)
Example 2 f=30~85, F/2.8.2ω=15.4°~5
．． 4°r+ =56.2685 d+=4. oooo n, =3148749
C, =70.2Or2=2187.8600 d2=0.2000 r3=46.7059 d,=4.7000 12=3148749 C2
=70.2Or, = 218.4412 d4=0.2000 ri:: 362.9391 d5=2.0000 n:+”3192286
shi, ==20.88re ”207.6720 da=D+ r7=75.3686 d7=3.2000 n+=3172825 shi,=28.46 shi,=-25,3869 da=314545 n5= 3153172
shi, =48.90ro=20.7632 d, =s, 4545 r+o = 14.5856 (aspherical surface) d+o =
315000 na = 3149216 White = 57.50ro = 66.2025 dot = 314545 r12 = ■ (aperture) d + 2 = 15.2928 r, a:: 78.0540 d + s = 315000 17 = 3178472
j/7=25.71r+4=33.9009 dot=315200 r+5=114.8046 d+s=3.600o n==3160311
1'a=60.70r+a=18.0109 d+a=D2 r+1 =19.7993 d+7=4.0000 no=3148749
νo=70.20r+s= 95.0066 f 30 50.5 85D+
0.436 19.239 28.33
1D2 2.9 9.163 18.
542 Aspheric coefficient P=310000, B=O, E=-0, 58125x
tOzuF=-0,23569X10-', G=0.40
271X10-'f+=67.458, f2=-29,
732f3+=102.782, f3□=33.99
9 Total length at wide-angle end=85.1 (=2.8fW) Example 3 f=30~85, F/2.0.2ω=15.4°~5
．． 4゜r+=62.2320 d+=5.9000 nI=3148749
=70.20r2=495.4467 d2=0.2000 rs ”48.7371 d3 =6.7000 n2='3148749
2 = 70.20r + = 277.9439 d, = 0.3273 rs ” 326.2820 ds = 2.0000 13 = 3184666
ν3=23.88ra "226.7799 da"D+ r7=27.2985 dfu =315000 n,=314921
6 j/+=57.50r8 ” 13.736
9 da"6.5891 r, = -20,2072 do = 315000 n, = 3153172
1/1=48.9°rIO=42.1818 d+o=3.9273 16=3176182
White = 26.55rn = -54,7702 do = 314545 r12-○○ (aperture) dx2 = 14.6927 r+s = -45,0302 do3 = 315000 n7 = 3178472 1
/7 =25.71rn=36.6253 d1+ = 315067 r15=85.5565 d+a=4.7273 na=3164100
sig=56.93r18 =-19,6342 d+a=D2 r+7=22.1671 dty=5. oooOn Mini 3148749 J/
, =70.20r+s=84.4751 f 30 50.5 85D+
0.436 19.069 28.29
6D2 2.883 8.997 18.4
91fl=68.822, f2=-44,14
2fs+=145.842, f3□=36.
582 Total length at wide-angle end = 9315 (=3.tfW)
Example 4 f=30~85, F/2.0, 2ω=15.4°~5
．． 3°rt=63.2198 d+=6. oooo n+=3148749
! /+=70.20rt= 44311091 d2=0.2000 r3=48.9546 d3=7.0000 nz=3148749
! 72=70.20r4=265.8749 d+=0.2000 rs=-334,5678 ds=2.0000 n3=3192286
1/3=20.88ra=238.5499 da=Dr ry=84.9063 d7=4.5000 n4=3174077
! '4 =27.79ra" 24.2474 da"314545 n5=3153172 1
15=48.90ro=18.7987 d,=5.4545 r+o=-13,8896 (aspherical surface) d+o=315
000 na=3149216 1/a=57.
50ru = -40,4543 do = 314545 r, 2 = ω (aperture) do2 = 12.9355 rI3: 35.5996 do3 = 315000 17 = 3178472
V7=25.71r+<=42.3370 d++=315086 r+5=63.3790 do5=5.4000 na=3164100
! 's =56.93r+6=20.5922 d+a=D2 rt? =46.1 980 drr=3.2000 no=3148749
=70.2Or+s=147.0955 do8=0.2000 r19 =26.6211 dxo =4.0O00nlO=3148749 ν
to = 70.20r2o = -8884,3675 f 30 50.5 85Dl
0.436 19.1 28.179D
2 2.9 8.958 17.773 Aspheric coefficient P=310OOO, B=O, E=-0,70617X1
0-5F=-0,40315X10-? , G=0.10
475X10-'f+=69.982, f2=-30,
203fss” 149.18, f 32 = 331
56 Example 5 f=30~85, F/2.0.2ω=15.3°~5.
4゜r+=58.9194 do=5.800On+=3148749 M+
=70.20r2=850.8648 d, =0.2000 r3=45.9326 ds ”7.300On2=3148749 1'2
=70.2Or+= 259.9939 d4=0.2000 rs= 320.5336 d5=2. oooo n,=3184666 1
/3=23.88r6 "174.4801 da"n+ r7=26.3544 d7 =31500On+=3151742
shi,=52.41rs” 1318316 ds=6.5455 ro=24.7383 do”315000 n1=3153172 3
/5=48.9゜r+o=20.5039 doo ”3.9273 na =3175520
C, = 27.51ru = 103.2497 do = 314545 r12 = CI) (aperture) do2 = 17.8377 r + 3 = 3317632 do3 = 315000 n7 = 3178472
Schiff = 25.71rn = 44.2687 d++ = 315473 r+5 = 64.8852 doi = 5.2000 ns = 316410
0 j/s = 56.93r+a= 20.67
97 11a=Dz r17 =70.2356 d+t=2.5840 no=31487
49 yo =70.20r18 =-214
,2150 d,,=0.2000 r+g=3318678 d4(1=3.5398 n+o=31487
49 ν+o = 70.2 Or2. =-166,
0850 f 30 50.5 85D
, 0.436 19.14 28.71
3D2 2.909 8.693 17.5
59f, = 69.898, f2 = -39,14
2fsI=209.171, fsz=37
．． 039 Total length at wide-angle end = 1013 (= 3.4
fW) where rl+r2+... is the radius of curvature of each lens surface, d.

, d2. ... is the thickness of each lens, rl+1 ”2
r... is the refractive index of each lens, C31C2. ... is the Atsube number of each lens.

These Examples 1 to 5 have lens structures shown in FIGS. 1 to 5, respectively.

In all of the above embodiments, the rear group in the third group is composed of only positive lenses. It is desirable that the value (divided by the number of sheets) be 55 or more. This allows almost all chromatic aberrations to be corrected within the rear group, making it possible to keep chromatic aberrations small over the entire zoom range.

Among these Examples, Examples 2 and 4 use an aspheric surface expressed by the following formula, where the optical axis direction is X1 and the direction perpendicular to the optical axis is y.

However, C is the curvature at the apex of the aspherical surface, P, B, E, F.

G, . . . are all aspheric coefficients.

In each of these embodiments, the number of lenses is very small, 9 to 10, and the lens system is even more compact.

〔Effect of the invention〕

The variable magnification lens of the present invention is suitable for electronic still cameras and video cameras, and is a telephoto variable magnification lens that has an angle of view (2ω) of about 15° to 5.4°. However, in a lens system with an aperture ratio of F/2.8, the value for the focal length at the wide-angle end is smaller than the conventional example of about 3.2, and even if the aperture ratio is larger than F/2.0, the focal length at the wide-angle end is This is a lens system with a short overall length, which is comparable to the conventional example.

[Brief explanation of the drawing]

1 to 5 are embodiments 1 to 5 of the present invention, respectively.
6, 7, and 8 are aberration curve diagrams at the wide-angle end, intermediate focal length, and telephoto end of Example 1, respectively. Aberration curve diagrams at the wide-angle end, intermediate focal length, and telephoto end of Example 2, FIG.
FIGS. 13 and 14 are aberration curve diagrams at the wide-angle end, intermediate focal length, and telephoto end of Example 3, and FIGS. 15 and 16, respectively.
17 are aberration curve diagrams and FIG. 18 at the wide-angle end, intermediate focal length, and telephoto end of Example 4, respectively. FIGS. 19 and 20 are aberration curve diagrams at the wide-angle end, intermediate focal length, and telephoto end of Example 5, respectively.

Claims (1)

[Claims] A first group having positive refractive power as a whole, which is composed of a first group having positive refractive power, a second group having negative refractive power, a front group and a rear group in order from the object side. It is a lens system with three groups, in which the first group moves when changing magnification, the second group is fixed, and the rear group of the third group moves to correct image field fluctuations that occur when changing magnification. A variable power lens that satisfies the following conditions (1), (2), and (3). (1) 0.3<|f_2/f_1|<0.9(2)-0
．． 2<f_W/f_3_1<0.6(3)-0.2<f
_3_2/f_3_1<0.6 where f1 and f_2 are the focal lengths of the first group and second group, respectively, f_3_1 and f_3_2
are the focal lengths of the front and rear groups of the third group, respectively, and f_W is the focal length of the entire system at the wide-angle end.