JPS62178917A - Zoom lens - Google Patents

Abstract

PURPOSE:To make the titled zoom lens small in size and light in weight, irrespective of a large aperture by using an aspherical lens, and also making the fourth group have a part as a compensator to omit a negative compensator. CONSTITUTION:The titled zoom lens is constituted of the first group having a positive focal distance, the second group of a variator which has a negative focal distance and can move only at the time of variable power, the third group which is always fixed and has a positive focal distance, and the fourth group which is an image forming system and also movable, the first group is made to have a focusing function, and also, the fourth group is made to have a function for correcting a variation of a focal position, generated at the time of zooming. In order to set the number of pieces for constituting the lens to 10 pieces, it is the most desirable that three pieces, three piece, one piece and three pieces are distributed to the first group, the second group, the third group, and the fourth group, respectively. A spherical aberration of a negative large value which is generated due to a fact that the number of pieces of the constitution has been eliminated in this way and the overall length has been shortened extremely can be dissolved by introducing an aspherical lens to the third group or the fourth group.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a large-diameter zoom lens that uses an aspherical surface and has a short overall length.

[Conventional technology]

Video cameras have not been as popular because they are more expensive and heavier than conventional silver-halide still cameras, but they have recently become much smaller, lighter, and cheaper, and are rapidly becoming popular among general users. . In particular, portable cameras that have a camera part and a deck part integrated are starting to appear. This is mainly due to the shift to LSI circuitry, and the shift in imaging devices from the conventional 3-inch tube to 14-inch solid-state image sensors such as CCDs also played a role. There is.

As described above, while the electrical systems of video cameras are becoming much more compact and cost-effective, the current situation is that the electrical systems have not made any progress in reducing the size, weight, and cost of lens systems. In particular, as a conventional example of a zoom lens with a zoom ratio of about 6x for a 0.1A inch image size, which is insufficient in terms of the overall length of the lens system, the size of the front lens diameter, and the number of constituent elements, JP-A No. 60-123817,
JP 60-126618, JP 60-12661
There are No. 9 etc. These conventional examples use an aspheric surface and have a short focal length at the wide-angle end of 11.7 to 11.8 (the number of constituent elements is also small at 11 to 12 elements, and the front lens diameter is around 40 mm, so the performance is small. However, the F number at the wide-angle end is 1.33 to 1.45, which is unsatisfactory considering that a CCD with an IA inch image size requires Vl, 2 class brightness. The example uses a conventional 4-group zoom lens in which the second group is a variator and the third group is a compensator, so even if an aspherical surface is used, the number of elements can be further reduced and a high-performance zoom lens can be obtained. That is difficult.

[Problem that the invention seeks to solve]

The present invention uses an aspherical surface with a zoom ratio of about 6 and a wide-angle end of F.
The number is about 1.2, the focal length ratio of the total length to the wide-angle end is about 11.5, the diameter of the front lens is about 40 mm, and the number of elements is limited to 10, making it a large zoom ratio, large aperture ratio, and ultra compact. The purpose is to provide a low-cost zoom lens.

[Means for solving problems]

In order to achieve the above object, the present invention is characterized in that an aspherical surface is used and the fourth group has a role as a compensator.

That is, the zoom lens of the present invention consists of, in order from the object side, a first group having a positive focal length, a second group of variators having a negative focal length and movable only when changing the magnification, and a variator group that is always fixed and has a positive focal length. It consists of a third group with a focal length of , and a movable fourth group which is an imaging system. It is a lens system characterized by having a function to correct fluctuations, and by introducing an aspheric surface, the number of constituent elements can be reduced to 1.
This makes it possible to keep the number of sheets to about 0.

Furthermore, instead of providing the focusing function to the first group as described above, the first group is fixed at all times and the fourth group is provided with the focusing function, thereby giving this group both the function of a compensator and the focusing function. This also makes it possible to use it as a concentrated zoom lens. In this way, by fixing the first group, which is easily affected by group eccentricity, it is possible to reduce performance degradation due to eccentricity.Furthermore, when autofocus is adopted, this is done by the large and heavy first group. (By using the lightweight fourth lens group, it is possible to improve responsiveness and reduce power consumption.Also, when focusing on a short-distance object point, which is a drawback of focusing using the first lens group, the axis By using this focusing method using the fourth lens group, it is possible to solve the problem of not being able to make the closest distance closer due to the vignetting of the external light flux, and of having to increase the diameter of the front lens to make it closer. O When performing focusing using the fourth group in this way,
Ratio fS between the focal length fA and the focal length fS at the wide-angle end from the first group to the third group; 4. By keeping the value within the range of the following condition (1), fluctuations in spherical aberration during focusing by the fourth group can be suppressed to a small value.

(1) 1.9 < fS/fA < 1.9 However, fS is the focal length of the entire system at the wide-angle end and the telephoto end, respectively.
When W and fT are given, fS=lNT is the value expressed.

If the upper and lower limits of the above condition (1) are exceeded, fluctuations in spherical aberration during focusing due to movement of the fourth group will increase, which is not preferable.

In the zoom lens of the present invention as described above (both the first group focusing and the fourth group focusing), the fourth group is extended toward the object side at the wide-angle end.

Furthermore, in order to make the number of lens elements 10 in the zoom lens of the present invention, the first group is divided into three elements, the second group is divided into three elements, the third group is divided into one element, and the fourth group is divided into three elements. is most preferable.

The large negative value of spherical aberration that occurs when the number of constituent elements is removed and the overall length is extremely shortened can be eliminated by introducing an aspherical surface into the third or fourth group. The most desirable O
It is preferable that the aspherical surface used here satisfy the following conditions (2) and (3) because better spherical aberration can be achieved.

cutting) |Δx|≦3. OX 10-3・fS (y=0.5y1) (3) 1.2 X 10-L f
S≦Δx≦4.8X10 *fS (where y=y1) Under the above conditions, Δx is the deviation of the aspherical surface from the reference spherical surface, y is the ray height, and yl is the height at which the axial marginal ray cuts the aspherical surface.

When the upper limit of this condition (2) is exceeded, astigmatism worsens.

Moreover, if the lower limit of condition (3) is exceeded, the marginal ray of spherical aberration will be under-corrected, and if the upper limit is exceeded, the correction may be made on the object side surface of the sphere, or on any surface of the fourth group, especially on any one surface of the positive lens. Even if it is provided, aberrations can be sufficiently corrected. In addition to this aspherical surface, it is extremely effective to make the image side surface of the negative lens in the fourth group aspherical to reduce fluctuations in spherical aberration when rear focus is used. If an aspherical surface is introduced into the surface, the correction can be made even better.

In the zoom lens of the present invention described above, the first group is composed of three lenses in order from the object side: a negative lens with a convex surface facing the object side, a positive lens, and a positive lens; Consists of three lenses in order: a negative lens, a negative lens, and a positive lens, the third group consists of one positive lens, and the fourth group consists of a negative lens, a positive lens, and a positive lens in order from the object side. Consisting of three lenses or a positive lens, a negative lens, and a positive lens, and further under the following conditions (4), (5), (6),
If (7) is satisfied, an even better zoom lens can be obtained.

(4) 0.2 < D/fS < 0.6 (5)
0.35 < t! z48<0.77(6) 5.
3 < fI/fW < 6.8 (7) 1.55 <
``u'/fW< 2. D is the relationship between the surface of the fourth group closest to the object and the surface closest to the image of the optical component closest to the object side of that surface when focusing on the object point at infinity at the wide-angle end. Distance on the optical axis, t
l is the distance from the surface of the first group closest to the object side to the surface of the first group closest to the image side, and fl and fH are the combined focal lengths of the first group and the second group, respectively.

Condition (4) is that when focusing on an object point at infinity at the wide-angle end, the object side surface of the fourth group and the closest optical component (e.g. half prism, diaphragm) placed closest to the object side. This specifies the distance D on the optical axis from the image side surface, and if D exceeds the lower limit of the condition, there will likely be insufficient movement space when focusing with the 4th group, and the upper limit will be exceeded. The total length of the Tonzu type tends to become long, which is undesirable.

Condition (5) defines the distance J on the optical axis from the surface closest to the object side of the first group to the surface closest to the image side of the first group, and L
If l exceeds the upper limit of condition (4), the entrance pupil position will move away from the first surface toward the image side, and if the diameter of the first group is not increased, the peripheral illumination will likely be insufficient at 0 or t1, which satisfies condition (5). If the lower limit is exceeded, even if the diameter of the first group is made smaller, it is unlikely to cause a lack of peripheral light, but if you want to increase the radius of curvature of each lens in the first group to ensure a good fit, increasing the radius of curvature will cause chromatic aberration. This is not preferable because the correction becomes insufficient and the overall length becomes longer.

Conditions (6) +' (7) define the ratios fI//fW and fVfW of the focal lengths of the first and second groups, respectively, to the focal length of the entire system at the wide-angle end. 0 The lower limit of these conditions If it exceeds , the inclination angle of the chief ray from the first group to the second group becomes large, and the height of the chief ray in the first group tends to become high, or the aberration fluctuation during zooming or focusing becomes large.

Moreover, if the upper limits of these conditions are exceeded, the total length tends to become long.

〔Example〕

Examples of the zoom lens of the present invention explained above are shown below.

Example 1 f = 8.78~49.02 F/1.23~
F/1.45ω= 24.5°~47°rl=ω d+ =2.500On+ ”1.51633 91=
6415r2 =ω d2=0.7000 r, =127.7145 d3 =1.4000 n2=1.76182 si2=26.52r, =45.1571 d, =0.7000 rs=49.7009 ds=7. 6000 n3=1.49216 1/3
=57.50r6 ==85.4537 d, =0.1000 r7=32.6390 d7=5.7000 n4 =1.49216
174 = 57.50 r8 = 181.9150 d8 = 1.1000 (variable) re ” 184.8264 do = 1.0000 n5 = 1.77250
5 = 49.66 rho = 16.7610 d, o = 3.6000 rn = 24.0264 d,,”1.0000 na = 1.67790
Shea=55.33r, 2=23.7490 d+2=2.8000 17=1.84666
Shift = 23.78r13 = 455.1834 d13 = 30.2540 (variable) r14 = ω (aperture) d++ = 1. ooooo.

r15 = 11.5669 d+s ”3.7000 nB = 1.46450
νa =65.94r+a =30.5865
(Aspherical surface) a, 6 = 8.5766 (variable) r, 7 = 43.6724 +: 1 + 7 = 1.0000 n mini 1.80518
sig=25.43r,,=14.1578 d,8=1.1000 rlQ=19.8805 d,9=4.6000 n,,)=1.60311
νto = 60.70r2o = 47.746
7 d2o = 0.1500 r21=21.9500 d21=5.5000 n11=1.60311
C, □=60.70r22=35.2839 d2□=4.1200 (variable) r23:0 d23 ”7.300On, 2 =1.51633
711 =64.15r24=''' f 8.78 20.746 49
．． 02 (for zooming) d, 1.100 18.040 30.35
4d+330.254 13.314 1.000
d,, 8.577 7.192 9.7
03d22 4.120 5.510 3.0
00 (for focusing by the first group) a, H4,
49321, 43433, 74s (for focusing by 4th group) dll 8.500 6.7
90 7.573d i/2 4.197 5.
912 5.130fVfA=0.416,
Δx(y=0.571)=0.036Δx(y=y
1)=0.68. D/f8=0.414t1/f8=0
．． 747, 1 piece, = 5.763fI! /fW=-1.6
96, y, = 8.4 Aspheric coefficient (16th surface) P = 1, E = 0.11429
X10=F=-0,60778X10-8 G=0.44632X10-8 Example 2 f=8.78-49.02, F/1.23
~F/1.4 r.

ω=24.5°~47°r, =ω dt =2.5000 n, =1.51633
! '1 = 64.15 r2 200 d2 = 0.7000 r3 = 166.4713 d3" 1.4000 n2 = 1.80518
ν2 =25.43r4=48.8032 d4=0.7500 rs=61.0792 ds=5.3000 n3=1.62012 1
/3=49.661-a: 190.5370 d620.1000 rv=36.9349 d7=5.3000 n4 =1.61405
1/4 = 54.95r, = 572.9049 d8 = (variable) rg = 80.8811 do ” 1.00On5 = 1.80610 ν
5=40.95r, )=13.5524d,. =4.7000 rn = 18.5165 dll = 1.0000 na = 1.658
44 1/6 = 50.86r1□ = 48.090
3 d1□=0.3000 r, 3=36.3053 d13=2.9000 n7=1.84666
3'? ``23.78r,, ''-61,0233 d14= (variable) r15=ω (aperture) dl, = 1.0OOO r16 = 13.0806 d46 = 4.5000 na = 1.46450
shi8=65.94r1t=68.2078 (
Aspheric surface) dx7= (variable) r18 =5559.5073 d, 8=1.0000 no=1.84666
1'g=23.88rlo =22.3039 (Aspherical surface) d+o = 1.0000 r2o=22.6034 d2o=3.5000 n4o"1.60311
C, o=60.70r2+ = 192.759
2 ci2. =0.1 so.

r2□=25.5326 d2□=5.7000 nl,=1.60311
,, =60.70r2s =-20,8908 d23=(variable) r24=''' d2+ =7.3000 n12 =1.5163
3 shi, 2=54.15r2v:o.

f 8.78 20.746
49.02 (for zooming) a, 1.100 18.880 31.23
4d1431.134 13.354 1.000
d1□ 8.517 7.247 10.184d
234.667 5.937 3.000 (for focusing by the first group) d, < 4467
22.247 34.601 (for focusing by 4th group) dQ'r 8.436
6.830 7.944d i'3 4.748
6.354 5.240fS/fA= 0.6
69, Δx(y=0.5y1)=0.016Δ
x(y-')'1)=0.32, D/f8=0.
411tI/f8=0.619, fshi=6
．． 452fl! /fW"1.908,'l+
=&7 Aspheric coefficient (17th surface) P=1, E=0.41064
X10-'F=0.24444X10""6 G=0.68693X10-9 (19th surface) P=1, E=0.79964
X10-'F=0.26528X10-6 G=0.50673 X10-9 Example 3 f=8.78-49.02, F/1.2
3~F/1.44ω=245~4.7 r, =■ d, =2.500On+ =1.51633 1/,
=64.15r2 =■ d2=0.7000 r3=102.1899 d3=1.4000 n2=1.80518 '2
=25.43r4=48.7165 d4=0.9000 r5=64.1435 ds =4.5000 n3 ”1.60311
v3=60.70re: 398.7165 d, =0.1000 r7=36.3349 d7=5.6000 n4 =1.60311
1'4 =60.70r@=413.5654 d8=(variable) re" 368.0803 do"1.0000 n5=1.80610 1
/! I=40.95r,. =13.7439 d,. =4.4500 ro = 18.9571 do=1.0000 n6=1.67790
White=55.33r+2=208.0719 d1□=0.3000 r13=74.2664 (Aspherical surface) du=3.0OOOn7=1.84666 J/
7 =23.78r14= 34.8063 d1+ = (variable) rl, =ω (aperture) d+5 = 1.0000 rl6 = 13.5839 d+a =4.7000 na =1.46450
shi8=65.94r17=92.1144 (
Aspherical surface) d+7= (variable) r+s= 117.1111 d48=1.0OOOno =1.84666 , =23.88rlQ =24.1916 (Aspherical surface)
d, Q=1. ooooo.

r2o=20.9782 d2o=6.0O00neo=1.60311
C, o=5Q, 7Qr21= 19.9371 d2. =0.1500 r22=31.1855 d2□=2.9000 no =1.60311
ro = 60.70r23 = 161.32
05 d23= (variable) r24 :″ d24=7.300o n+z=1.51633
! '+2=64.15r25 :l f 8.78 20.746 49
．． 02 (for zooming) d, 1.100 19.167 31.50
9d,, 31.409 13.342 1.0
00d+78.550 7.393 10.511
du4.960 6.118 3.000←In case of focusing by 1st group) a7 4.490
22.557 34.899 (for focusing by 4th group) dr'+ 8.468
6.970 8.227d i', 5.043
6.541 5.284fS/fA=0,7
29. Δx(y=0.5yt)=0.025Δx(y=
y1)=0.41. D/f8=0.412tI/f8=
0.603, fI//fW=6.471f
1.960, y, = 3.7 Aspheric coefficient (13th surface) p = 1, E = 0.28342
X10-'F=-○, 52424X10=G=0.51263X10-8 (17th surface) P=1, E=O167902
X 10-'F = 0.83874 X 10-7G
=-0,42857xlO-9 (19th surface) P=1, E=0.46013
X10-4F=0.23885X10-6 G=-0,36653X10-9 In the above data, rl r r2 r... is the radius of curvature of each lens surface, dlld21 is the thickness of each lens and the lens spacing, n1p n2 +・... is the refractive index of each lens, ν.

ν2. ... is the Atsube number of each lens, f is the focal length of the entire system, aa is the lens distance when focusing at a short distance with the 1st group, d ('a + dA is the distance when focusing at a short distance with the 4th group) This is the lens spacing when .

The aspherical surface used in each of the above embodiments is expressed by the following equation when the y-axis is taken in the optical axis direction and the y-axis is taken in the direction perpendicular to the optical axis.

However, C is the reciprocal of the radius of curvature of the circle that touches the aspherical surface near the optical axis, P is a parameter expressing the shape of the aspherical surface, B, E,
F, G, . . . are second-order, fourth-order, sixth-order, eighth-order, . . . aspheric coefficients, respectively.

Example 1 has the lens configuration shown in FIG. 1, and the 16th surface is an aspherical surface, and the aspherical coefficients are shown in the data.

The aberration situation in this example is as shown in Figures 1 to 12, of which Figures 4 to 6 show aberration curves at wide angle, intermediate angle of view, and telephoto when focusing on an object at infinity, respectively. 7 to 9 are aberration curve diagrams at wide angle, intermediate angle of view, and telephoto when focusing at a short distance with the first group, and FIGS. 10 to 12 are aberration curve diagrams at the 4th angle, respectively.
FIG. 4 is an aberration curve diagram at wide angle, intermediate angle of view, and telephoto when focusing on a short distance using a group.

Example 2 has the lens configuration shown in FIG. 2, in which the 17th and 19th surfaces are aspherical, and their aspherical coefficients are shown in the data. The aberration situation in this example is shown in Figures 13 to 2.
As shown in Fig. 1, Figs. 13 to 15 show aberration curve diagrams at wide angle, intermediate angle of view, and telephoto when focusing on an object at infinity, and Figs. 16 to 18
The figure shows aberration curves at wide angle, intermediate angle of view, and telephoto when focusing at a short distance with the first lens group. Figures 19 to 21 show aberration curves at wide angle, intermediate angle, and telephoto when focusing on a short distance with the fourth group, respectively. It is an aberration curve diagram at the angle of view and telephoto.

Example 3 has the lens configuration shown in FIG.
The 19th surface is an aspherical surface, and their aspherical coefficients are shown in the data. The aberration situation in this example is as shown in Figs. 22 to 30, of which Figs. 22 to 24 show aberration curve diagrams at wide angle, intermediate angle of view, and telephoto when focusing on an object at infinity, respectively. , Figures 25 to 27 are aberration curve diagrams at wide angle, intermediate angle of view, and telephoto when the first group focuses 7 times at a short distance, respectively, and Figure 28
30 to 30 are aberration curve diagrams at wide angle, intermediate angle of view, and telephoto when focusing at a short distance using the fourth group, respectively.

〔Effect of the invention〕

The zoom lens of the present invention is compact despite its large aperture, as it uses an aspherical surface and eliminates the need for a negative compensator by giving the fourth lens group the role of a compensator. , lightweight.

For example, a conventional spherical lens requires at least 13 lenses, and even when an aspherical lens is used, 11 lenses are required, but it can be constructed with 10 lenses. In addition, rear focusing (focusing with the fourth group) is possible, which is advantageous in autofocus because there is less deterioration during focusing due to eccentricity and the weight of the focusing itself can be reduced. It also has the advantage of being able to achieve close focus.

[Brief explanation of drawings]

1 to 3 are embodiments 1 to 3 of the present invention, respectively.
FIGS. 4 to 12 are aberration curve diagrams of Example 1, and FIGS. 13 to 21 are aberration curve diagrams of Example 2.
2 to 30 are aberration curve diagrams of Example 3.

Claims (1)

[Claims] (1) In order from the object side, the first group of the focusing group has a positive focal length, is immovable when changing the magnification, and is movable only when focusing, and has a negative focal length. The second variator group is movable only when changing magnification, the third group has a positive focal length and is always fixed, and the imaging system corrects fluctuations in focal position that occur when changing magnification. A lens system consisting of a fourth group that also has the role of a compensator,
A zoom lens including at least one aspherical surface in the third or fourth group. (2) In order from the object side, the first group has a positive focal length and is always fixed, the second variator group has a negative focal length and is movable only when changing the magnification, and the positive focal length. It consists of a third group that has a distance and is always fixed, and a fourth group that is an imaging system and is movable for correcting the focal position that occurs when focusing or changing the magnification. A zoom lens that includes at least one aspherical surface in the fourth group and satisfies the following condition (1). (1) −1.9<(f_S/f_A)<1.9 where f
_S is the focal length expressed as √(f_W・f_T), where f_W is the focal length of the entire system at the wide-angle end and f_T is the focal length at the telephoto end, and f_A is the combined focus of the first to third groups. It is distance. (3) A zoom lens according to claim (1) or (2), characterized in that extremely close-up photography is performed by extending the fourth group toward the object side at the wide-angle end. (4) Claims (1) in which the first group consists of three lenses, the second group consists of three lenses, the third group consists of a single lens, and the fourth group consists of three lenses. ) or (2)
zoom lens. (5) A zoom lens according to claim (3) in which an aspherical surface is used in the third group. (6) The image side surface of the third group is made aspherical and the following condition (2) is met.
The zoom lens according to claim (5), which satisfies (3). (2) |Δx|≦3.0×10^-^3・f_S(y=
0.5y_1) (3) 1.2×10^-^2・f_S≦
Δx≦4.8×10^-^2・f_S (y=y_1) However, Δx is the amount of deviation of the aspherical surface from the reference spherical surface, and f_S is the focal length of the entire system at the wide-angle end as f_W, and the focal length of the entire system at the telephoto end. When the focal length of the system is f_T, the focal length is expressed as √(f_W·f_T), y is the ray height, and y_1 is the axial marginal ray height.