JPS6329719A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a zoom lens which has a large zoom and aperture ratios and is super-compact and low in cost, by causing an optical system having four groups of lenses to satify prescribed conditions. CONSTITUTION:The zoom lens of this invention is provided with the 1st lens group which is successively composed of a negative, positive, and positive lenses from the object side and has a positive focal distance as a whole and the 2nd group which is composed of a negative, negative, and positive lenses, has a negative focal distance as a whole, and is movable and conducts variable power at the time of variable power. The zoom lens is also provided with the 3rd group which is composed of two lenses of a lens having a weak refracting power and aspheric surface and a positive lens or three lenses of a lens having a weak refracting power and aspheric surface, positive lens, and negative lens, has a positive focal distance as a whole, is always fixed, and produces an almost afocal state on the light emitting side, and the 4th group which is composed of a positive, positive, and negative lenses, has a positive focal distance as a whole, eliminates variation of focusing position produced at the time of variable power, and is movable for focusing. The lenses of the groups are caused to satisfy inequality I. The fr and fAT of of the inequality are the focal distance of the whole system at the telescoping end and resultant focal distance of the lenses of the 1st-3rd groups at the telescoping end, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a zoom lens, and particularly to a zoom lens preferable for use in a video camera.

[Conventional technology]

Video cameras have not become very popular because they are more expensive and heavier than conventional silver halide still cameras. However, in recent years, they have become much smaller, lighter, and cheaper, and as a result, they are rapidly becoming popular among general users. In particular, portable cameras that have a camera part and a deck part integrated are also appearing.

This is mainly due to the shift to LSI circuitry.
One factor contributing to this is the shift in imaging devices from conventional 2/3-inch tubes to solid-state imaging devices such as 1/2-inch CODs.

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 yet become smaller, lighter, and less expensive. In particular, it is insufficient in terms of reducing the overall length of the lens system, the diameter of the front lens, and the number of lenses.

Conventional examples of zoom lenses for 1/2-inch image size with a zoom ratio of approximately 6 times that relatively satisfy the above requirements are disclosed in Japanese Patent Application Laid-open No. 60-123817 and Japanese Patent Application Laid-open No. 60-1'26618. , JP-A-60-12661, etc. These conventional examples use an aspheric surface, have a short overall length to wide-angle end focal length ratio of 11.7 to 11.8, have a small number of constituent elements at 11 to 12, and have a front lens diameter of around 40 m. It is a zoom lens with relatively good performance. However, the F number at the wide-angle end is 1.33 to 1.4.
5, and F for 1/2 inch image size COD.
A lens system with a brightness of /1 or 2 class is required, and the conventional example described above is unsatisfactory in terms of brightness. Also, this level of F
As a number zoom lens, it cannot be said that the overall length of the lens system and the front lens are small enough to be satisfactory. Furthermore, with these conventional front lens focusing systems, when autofocus or power focus is used to advance the heavy front lens, power consumption increases and the off-axis rays on the short distance side are greatly vignetted. Unless the diameter is increased, it is difficult to focus on the shorter distance side.

[Problem that the invention seeks to solve]

The problems to be solved by the present invention are that the zoom ratio is about 6, the F number at the wide-angle end is about 1.2, the overall length to wide-angle end focal length ratio is about 11.1, and the front lens diameter is 37. ■Large zoom ratio, large aperture ratio, and ultra-compact size with only 11 to 12 images.

The objective is to provide a low-cost zoom lens.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention uses an aspherical surface and also provides a relay system with a role as a compensator and also has a focusing function. It is.

The zoom lens of the present invention includes, in order from the object song u, a negative lens,
The first group is composed of three lenses, a positive lens, and has an overall positive focal length, and the first group is composed of three lenses, a negative lens, and a positive lens, and has an overall negative focal length. a second group that is movable when changing the magnification and is mainly responsible for changing the magnification; a lens having a weak refractive power and an aspherical surface;
Consisting of two positive lenses or a lens with weak refractive power and an aspherical surface, a positive lens, and a negative lens, it has a positive focal length as a whole and is always fixed on the exit side. The third part has the role of making it almost afocal.
It is composed of three lenses: a positive lens, a positive lens, and a negative lens with a slightly larger air distance from the third group, and has a positive focal length as a whole and eliminates the fluctuation of the focal position that occurs when changing the magnification. It is composed of a fourth group that functions as a compensator and is movable for focusing.

In this way, this BJJ focuses on the fact that correction of focal position movement and focusing are the same thing, and uses only three lenses to serve both of the functions of correcting focal position movement and focusing that occur when changing the magnification. It is characterized in that it is concentrated in the fourth group relay lens system consisting of lenses, and that a part of the fixed group of the third group is provided with an aspherical surface.

As mentioned above, by fixing the first group, which is likely to be affected by group eccentricity, it is possible to reduce performance deterioration due to eccentricity.Furthermore, when autofocus is adopted, this can be reduced by a large and heavy first group. By using a lightweight fourth lens group instead of using a conventional lens, it is possible to improve responsiveness and reduce power consumption. Another disadvantage of focusing with the first lens group is that when focusing on a close object point, the off-axis beam is vignetted, making it impossible to get the closest distance, and in order to get it closer, the diameter of the front lens must be increased. This problem can be solved by using the focusing method using the fourth lens group.

In addition, in the conventional example described above, the lens immediately after the variator corrects the focal position fluctuation during zooming, but in the present invention, this function is also provided in the fourth group, so that it is a functionally concentrated type. This also aims to reduce costs. Concentrating the focusing and focal position correction functions in the fourth group brings about various benefits, but the deterioration of imaging performance due to fluctuations in aberrations caused by the movement of the fourth group must be taken into account. It won't happen.

The variation in aberration due to the movement of the fourth lens group is significant in spherical aberration. In order to prevent this, it is necessary to satisfy the following condition (1).

(1) l fT/fATl < 0.6 However, fT
is the focal length of the entire system at the telephoto end, and fAT is the combined focal length of the first to third groups at the telephoto end.

In order to reduce fluctuations in spherical aberration caused by moving the fourth group, it is sufficient if the fluctuations in the axial ray height due to the movement of the fourth group are small. In other words, it is sufficient if the first to third groups are almost afocal. Condition (1) above indicates this afocal degree. If this condition (1) is not met, the fluctuation of spherical aberration due to focusing becomes significant at the focal length near the telephoto end.

Next, the zoom lens of the present invention has a configuration of 11 to 12 lenses.
One of its characteristics is that it is kept in one piece. The most typical zoom lens currently in practical use consists of a compensator, an erector, and the front group of a relay lens system, that is, the lens near the aperture, which consists of a total of 4 to 6 elements. However, in the present invention, it is composed of two to three sheets. The reason why as many as six lenses are used near the aperture in this conventional example is to satisfactorily correct spherical aberration, which tends to be undercorrected. Therefore, if the number of lenses in this area is reduced by three or four at once, the spherical aberration will naturally become insufficiently corrected. Therefore, it can be seen that it is desirable to introduce an aspherical surface into this portion. If the aspherical surface is a diverging surface, it becomes stronger as it goes to the outside of the radius compared to a spherical surface on the optical axis.If it is a convergent surface, it becomes stronger toward the outside of the radius than the spherical surface on the optical axis. The surface should be made so that it becomes weaker. As a result, large negative spherical aberration can be corrected or alleviated.

As mentioned above, the zoom lens system as a whole has a forward direction in which negative spherical aberration is likely to occur. Among the entire lens system, particularly large spherical aberration occurs in the positive lens of the third group. In order to correct this spherical aberration, a material with a relatively high refractive index is used for this positive lens. Therefore, it is not preferable to use an aspheric surface for this lens from the viewpoint of lens processing.

Therefore, in the present invention, a lens (either a positive lens or a negative lens) having a weaker refractive power is added on the incident side than the positive lens, and this lens is provided with an aspherical surface. This lens does not particularly need to use a high refractive index, so it is easy to process, and if it is made of a plastic lens, it will be even easier to process.

Furthermore, if the lens having a weak refractive power is made negative, it is advantageous in correcting the Petzval sum.

By configuring the zoom lens of the present invention as described above, the number of lenses that conventionally required at least 13 can be reduced to 1.
It is possible to reduce the number of lenses to 1 to 12, and achieve smaller size, lighter weight, and higher performance while maintaining a large aperture ratio and a high zoom ratio. Furthermore, by adopting rear focusing, we have achieved lighter focusing, reduced effects of eccentricity of the front group, and easier close-up focusing.

The zoom lens of the present invention satisfies the following conditions (2) to (8).
), a zoom lens with even higher performance can be obtained.

(2) 1.2 < fy/rrvF < 0.11
(110,5<fVrrvR<0.5(4) 2
．． O< l f 7 l/J〒"(s) 0.1
<ci3. /Kei< 0.55(6) 0.53<
(e2wezT)/e2w<0.77(γ)1<f
L81 nB > 1.65 where fy is the composite focal length of the entire system at the wide-angle end, fT
is the combined focal length of the entire system at the telephoto end, fly is the combined focal length of the 4th group, f7 is the focal length of the aspherical lens with weak refractive power in the 3rd group, and d31 is the focal length of the aspherical lens in the 3rd group. The air distance between the lens and the lens, 82w is the distance between the principal points of the second and third groups at the wide-angle end, e2T is the distance between the principal points of the second and third groups at the telephoto end, and rTVF is the distance between the principal points of the fourth group at the wide-angle end. The radius of curvature of the side surface, rlVR, is the radius of curvature of the surface closest to the image side of the fourth group, and nB is the refractive index of the third # strong positive lens.

Each of the above conditions will be explained.

Conditions (2) and (a) define the radius of curvature of the surface closest to the object side and the surface closest to the image side of the fourth group, respectively. These conditions were established in order to minimize coma aberration and slight astigmatism that occur because the longitudinal aberration of the off-axis upper ray changes toward the positive side as the fourth group moves for close-range focusing. These are the conditions. If the upper limit is exceeded under these conditions, the above-mentioned aberrations will occur significantly when focusing on a short-distance object, which is undesirable. When the lower limit is exceeded, spherical aberration and coma aberration tend to be undercorrected in all conditions.

Condition (4) defines the power of the aspherical lens. It is conceivable to use plastic for this aspherical lens because it is most advantageous in terms of processing, but when plastic is used, it is necessary to reduce the influence of focus shift due to temperature changes. For this purpose, the power of the lens must be weakened within the limits shown in the conditions. Therefore, if the range of condition (4) is exceeded, the focus shift due to temperature changes will become large, which is not preferable.

Condition (5) defines the position of the aspherical lens so that the aspherical surface is most effective. In the lens system of the present invention, negative spherical aberration occurs most in the positive lens with strong power in the third group. In order to generate positive spherical aberration to correct the negative spherical aberration generated by this positive lens, it is effective to place the aspherical lens mentioned above at a distance slightly toward the object side from this positive lens. . Therefore, when the lower limit of condition (5) is exceeded, the effect of correcting spherical aberration by the aspherical surface decreases. If the upper limit is exceeded, the movable range of the variator becomes narrower, and aberration fluctuations due to zooming tend to increase.

Condition (6) defines the movable range of the second group variator,
It is something that It is preferable that the wider the variator's movable range, the less aberration fluctuations due to zooming.However, the weaker the variator's power is, and the closer the IJ eater is to the third group, the larger the positive Petzval sum of the entire system. It takes a value of 9, which is unfavorable. This is because, in addition to weakening the negative power of the variator, the positive powers of the third and fourth groups become stronger. Therefore, when the upper limit of condition (6) is exceeded, the Petzval sum tends to take a large positive value, and when the lower limit is exceeded, the power of the variator becomes strong and aberration fluctuations due to zooming tend to become large.

Condition (7) defines the composite focal length of the fourth group. If the upper limit of this condition is exceeded, the lens diameter of the fourth group will increase and the amount of focusing movement will also increase, which is not preferable.

Moreover, if the lower limit is exceeded, the Petzval sum of the entire system increases in the positive direction, which is not preferable.

Condition (8) defines the refractive index of the positive lens with strong power in the third group. When the lower limit of condition (8) is exceeded, the Petzval sum of the entire system tends to increase in the positive direction, and the spherical aberration of the entire system tends to increase in the negative direction.

Next, the aspherical surface used in the zoom lens of the present invention will be explained in detail.

In the present invention, an aspherical surface is provided on the image side surface of the lens closest to the object in the third group, and the lens shape is a meniscus lens with a convex surface facing the object side. The aspheric surface has a radius of curvature on the optical axis that is even-odd toward the image side with respect to the spherical surface, and the amount of even-oddity increases monotonically toward the outside in the radial direction of the lens, satisfying the following condition (9). It is desirable to do so.

(9) y = 0.21f at F31, 2X10
−”< Δx / JT';;”T < 0.18X
10-1 Here, the aspheric surface is expressed by the following formula, where r is the radius of curvature of the paraxial sphere on the optical axis, and ΔX is Ey'
+Fy6+Gy'+Hy'°. Further, fF3 defines the even-odd amount. As mentioned above, in the case of only a spherical system, the occurrence of large negative spherical aberration is corrected or alleviated by the aspheric surface.

When the lower limit of this condition is exceeded, spherical aberration is likely to be under-corrected, and when the upper limit is exceeded, conversely, over-correction is likely to occur, and furthermore, eccentricity during manufacturing of the aspherical lens is likely to cause performance deterioration.

〔Example〕

Next, examples of the zoom lens of the present invention will be shown.

Example 1 f = 9 to 54, F/1.2 to F/1.6, ω = 2
4.0%4.2゜r, =138.5871 d, =1.2000 nl =1.78472
v, =25.68r2 ==47.5057 d2=0.3500 r3 =53.6234 d3=5.400On,2 =1.60311 C2=60.70r4 =-91,5618 d4 =0.3000 r5 = 27.7173 d5 =4,4000 n3 ==L 60311
v3 =60.70r6 =67.4923 d6 =D1 r7 =42.3316 d7 =1.0000 n4 (83400z
=37.16r8 =12.5771 d8 =4.5000 rg ”-16,4261 dg =1,0000 15 =1.69350
115 = 53.23 rlo = 23.1199 dlg = 2,7000 ng = l, 84666
Shiro = 23,78r1, = -66,8174 dll"D2 r12 = 102,3270 d, □ = 1,5000 n7 = 1.49216
v7=57.5Or+3 =39.0772 (Aspherical surface) d, 3 = 5.0000 r14=co (aperture) d, 4 = 3.0000 r, 5 = 26.6547 dl5 = 4.7000 n8 = 1.69680
νB =55,52r 16 =-73,1675 d16 =0.8000 r1□ =1056.0485 d17=1.0000 ng =1.80518
1'g = 25.43r + 8 = 68.4734 dl8"D3 r,, = -757,0535 dl, = 3.200OnIO = 1.77250 ν
,. =49.66r2o =-31,4990 d2o=0.1500 r2□ =22.0561 d21 =6.8000 nll =1.56
873 ν1, =63.16r2□ =-16,2
445 d22=1.0000n02=1.80518ν1゜=
25.43r23=-216,4248 d23'' D4 r24=ω d24=5.5500 n13=1.51633
Sh3=64.15r25″ 0 fD1D2D3D4 9 1.000 25.696 8,827
5.85031.5 15.415 11.28
1 7,7436.93554 25.696
1,000 11.677 3.000r13 aspherical coefficient B = O, Fli =0,43303X10-', F
=0.30701X10-7() =-0,3308
6Xl0-', H=0.18449 xlo-"f
T/fAT=0.1872, fPi"'rfVF
= 0.0324fly/r[Vr=-0,1135
, l fy 1hLF = 5.8732d3□%! =
0.3,629, (e2y-e2T)/e2w=
o, 5934fIv/V/fw-fT=1.1143
, ng = 1.69680y = 8.4858
, 1Δx l/v6 blocks = 0.0119 Actual dance example 2 f = 9~54, Vl, 2~11'/1.6, ω=
24.00~4.2°r, = 140.0595 d, = 1,2000 nl = L 78472
v, = 25,68r, 3 = 54.9266 d3 = 5.9500 n2 = 1.60311
1'z =60.70r4 =-84,7893 d4 =0.2500 r5 =26.9309 d5 =4,3000 n3 =1.60311
v3 = 60.70r6 = 61.4229 d6 = D.

r7 =42.5209 d, =1.0000 n4 =1,83400
ν4 =37.16r8-12. '3908 d8 =4.3000 rg knee 15.6689 d9 =1.0000 n5=1.69350
ν5 = 53.23r, ) = 22.2536 d1o = 2,7000 n6 = 1,84666
Shiro=23.78r, ,=-66,4278 dll” D2 r1□=102.8525 d1□=1,300On7=1,49216
V7 = 57.50r13 = 42.2736 (aspherical surface) d, 3 = 4.6000 r14 = oO (aperture) d14 = 3.0000 r, 5 = 26.9382 d, 5 = 5.3000 n8 = 1,69680
vB =55,52r16 =-53,85
68 dos =0.5000 r1□ =-524,8070 d,, =1.0000 ng =1.80518
v9 = 25.43r1g = 77.2138 dl8” D3 r,g = -444,9998 dl, = 2,8000 nto = 1.77250
ν,. =49.66rzo = 33.7334 d2o =0.1500 r2, =21.8592 d21 =6.9000 n, □ =1,568
73 v1□ =63,16r2゜=-16,06
65 d22=1.0OOCI n12=1,80518
ν12=25.43r23 ”-163,1585 d23 ”' D4 r24 :(1) d24 =5.5500 n13 =1.5163
3 '13 =54.15' r25 : ■ f Dl D2 D3
D49 1.600 25.324
9,310 5,32131.5 15.7
95 11.129 7,982 6,649
54 25.924 1,000 11.
631 3,000r+3 aspheric coefficient B = O," = 0.48999 XIO"', F
=-0,20431X], O-'G =0.39446
X10-8, H=-〇, 91401 xlo-11fT
/fAT-0,2139, fIV/'rrvF =-0
,0570flV/'rrt/R-0,1556,l
f 71Z47ko = 6.6628d31 f, -ff
i = 0.3448, (e2we2T)/e2+, y=
0.6015f+V stone=1.1517, n8=1.
69680y=7.2680, ΔV Liu]〒=0
．． 0061 Implementation% J 3 f=9-54, F/1.2 to F/1.6, ω=24.0
0~4.2゜rl =124.3606 dl-1,2000n, =1.78472 v1=
25.68r2 = 45.1181 d2 = 0.6000 r3 = s4.0934 d3 = 6.2000 n2 = 1.60311 si2 = 60.70r4 = -76, 1604 d4 = 0.2500 r5 = 25.54j7 d5 = 4.0500 n3=1.60311 C3=60.70r6 =49.3267 d6= Dl r7 =41.7487 d, =1.0000 n4=1.83400 V
4=37.16rg =12.5990 d8=4.3000 r9 =-15,2875 dg =1,0000 n5 =1.69350
1'5 = 53.23r, 0 = 22.1064 d, ) = 2,7000 n6 = 1,84666
White = 23.78r, 1 = -77,2551 dll = D2 rl2 = 49.6547 d, □ = 1.3000 n7 = 1.4921
6 1'7 ==57.50r13 =33.397
4 (Valve ball 1Iii) d13 = 4.6000 r work, == co (aperture) d14 = 3.0000 r15 = 25.1392 d, 5 = 5,1000 nB = 1.69680
vB =55.52rts =-87,3442 d16 =0.5000 r1□ Eng49719.5913 at? =1. oooo n9 = 1.80
518 79 =25.43r+s =78.8
472 (its =]) 3 r, g = 31961.3448 d, g = 3,100 Onio = 1.77250
νto =49.66r2o=-32,8055 d2゜=0.1500 r2, =20.8988 d2,=6,9000 nil =1,56873
ν1, =63.16r2□=-15,7316 d22 =1.0000 n,. =1.80518
1/12 =25,43rz3 =-672,5
171 d23 = D4 r24 °c.

d24 =5,5500 n13 =1.5163
3 1'13 =64.15r25 :■ f Dl D2 D3
D49 1.600 25,220
9,926 4.76731.5 15.699
11,122 8.367 6,32654
25.820 1.000 @ ll, 6
93 3,000r13 aspheric coefficient B = 01F = 0.41143 XiO", F' =
-0,15990Xl0-'G =0.46014X
10-8. H=-0, 19482Xl0-10fT/
f4T=0.1861, frV/'r[VF=0
．． 0008fIV/rrvR=-0,0372, l f
71/, /fw-fT=9.6570d3 Otsu 5 vote door=
0.3448, (e2W-e2T)/'e2W =0.
6214ff7te=1.1352, n8=1
．． 69680y =7.0028, Δ6r7
=0.0046 Example 4 f =9~54, F/1.2~F'/1.6, ω=24
．． 00~4.2゜r, = 117.4644 dl = 1.2000 nl' = 1.78472
v1==25.68r2 =42.7622 d2=0.8000 r3 =52.9839 d3 =6.5000 n2 =1.60311
v2=60.70r4 =-68,8451 d4=0.2500 r5 =23.7117 d5 =4.0500 n3 =1.6031
1 ν2 =60.70r5 =43.6883 d6=D.

r7 =35.2282 d7 =1,0000 n= =1.83400
v4 = 37.16rB = 12.2472 d8 = 4.5000 rg = -14,4787 dg = 1.0000 n5 = 1.69350
1'5 = 53.23 r1o = 22.4133 d,. =2,7000 n6 =1.84666
Shiro =23.78r1, =-95,2069 dll ”' D2 r1□=28.5635 d12 =1.300On7 =1.49216
F7 = 57.50r, 3 = 25.4338 (aspherical surface) d, 3 = 4.6000 r14 = oO (aperture) d14 = 3.0000 r, 5 = 23.5302 d, 5 = 4.4000 n4 = 1 .69680
1'g=55.52rts =-270,1245 d16 =0.6000 F1 fu -2+3.4753 d, 7-1,0000 n9 =1,80518
F9 = 25,43r, 8 = 71.1123 d18 :D3 rl, = 306.2786 d, 9 = 3,1000 nl. =1.77250
C1o=49.66r2o=-31,6738 d2o=0.1500 F2,=16.8414 C12t=6.9000 n,,=1.568
73 v,□ =63,16r2□ =-15,4
878 d2°=1,0000 nl. =1.80518
v. =25.43r23 =69.3524 d23 = D4 F24 = ■ d24 =5.5500 n13 =1.5163
3 F13 =64.15r25 =ω f DI D2 D3
D49 1.600 23.710
9,676 4,99931.5 14,7
54 10.556 8,119 6,556
54 24.310 1,000 11.
675 3.000r13 aspheric coefficient B = O, F2 = 0.30709 x 10-', F
=0.77384 xlO-7G =0.22959
X 10-8, H=-0, 12307Xl0-1゜f
T/fAT-0, 1994, frv//rrVF=0.
0795fff/rrVR=0.3510, 1f7
1hFq=24.7922d31Otsumi1■=0.34
48, (e2w-e2T)/e2w=0.6305f■
Early=1.1042, ng=1.69680y=
7.3394, ΔVnE'=o, ous2 implementation row 5 f-9~54, F/1.2~F/1.6, ω=24.O
o~4.20r, =141.2006 d, =L, 2000 nl =1,78472
v, =25,68r2 ==47.2013 d2=0.4500 F3”53.4868 d3 =5.8000 n2 =1.60311
L'2 = 60.70r4 = -95,5930 d4 = 0,2500 F5 = 29.1819 d5 = 4.30 (70n3 = 1.60311 ν
3 =60.70rs =89.1867 d6 =])1 F7 =35.5751 d7 =1,0000 n4 =1.83400
2 = 37.16r3 = 12.4183 d8 = 4.6000 rg = -15,9656 dg = 1.0000 n5 = 1.69350
V5 = 53.23r,. =19.3103 d, (, =2,7000 n5 =1.84666
v6=23.78r,,=-114,8216 d1□=D2 rr2=-44,0758 d12=1,300On7=1.69895
F7, = 30.12r13 = 714.1310
(Aspherical surface) d13 = 4.0000 r14 = oo (aperture) d14 = 2.5000 F15 = 27.7574 d15 ''5,0000 nB = 1.69680
'B = 55.52r16 = -107,921
3 dl6 :D3 r,,=-432,6513 d□,=3.2000 ng=1.77250
V, =49.66r18--34.0843 d18 =0.1500 r19 =19.8572 dlg =7.5000 nio =1.5687
3 ν,. =63.16r2. )=-16,115
3 d2o=1.0000 nl,=1,84666
ν11 =23.78r2, =-289,8674 d21 =D4 r22 °c.

dz. =5,5500 n12 =1.51633
'12 =64,15r23: l f Dl D2 D3
D49 1.600 24,739
11. '444 5.71831.5 15.3
74 10.965 10,248 6.915
54 25.339 1,000 14.
162 3.00Or+3 aspheric coefficient B = O1E = 0.35018 Xl0-', F =-
0,19573Xl0-7G=O,'10783X10
, H=0.15879X10-10fT/f
AT=0.1967, fIV/rIVF=-
0,0599frV/'rlVR= 0.0894
, lhl//jfw・fT=3.0513d31/v”
fy]7 = 0.2949, (e2we2T)/e2w
= 0.5656f "q doors" = 1.1750, n
8=1.69680y=7.5918, Δx//
'fw-fT=0.006 but rl, r2.・
... is the radius of curvature of each lens surface, dl, d2.・・・
・ is the thickness of each lens and the distance between lenses, nl, n2
, ... is the refractive index of each lens, and 1. ν2.・・・
・ is the Atsube number of each lens.

Among the above examples, Implementation EflJ 1 to Example 4 are the first
In the lens configuration shown in the figure, the third lens group is composed of an aspherical lens with weak refractive power, a positive lens, and a negative lens.

In addition, F in the figure is a filter.

Among these examples, f=9.31.5°5 in Example 1
4 and the aberration situation during close-range focusing at the telephoto end are respectively 3rd.
As shown in FIGS. 4, 5, and 6. Similarly, the aberration conditions in each state of Example 2 are shown in FIGS. 7 and 8, respectively.
9 and 10, the aberration situation in each state of Example 3 is shown in FIGS. 11, 12, 13, and 14, respectively, and the aberration situation in each state of Example 4 is shown in FIG. As shown in FIGS. 15, 16, 17, and 18.

In Example 5, the third group is composed of an aspherical lens with weak refractive power and a positive lens. <See Figure 2! ! ) The aberration conditions of Example 5 at f = 9.31, 5.54 and when focusing at close range at the telephoto end are as shown in Fig. 19, Fig. 1, Fig. 21, and Fig. ρ, respectively. .

〔Effect of the invention〕

The zoom lens of the present invention uses an aspherical surface and eliminates the compensator t of conventional zoom lenses by giving that role to the relay lens system of the fourth group, thereby eliminating the need for at least 13 lenses. Further miniaturization with 11 to 12 sheets.

Light weight and high performance were achieved while maintaining a large aperture ratio and high zoom ratio. Rear focusing is also possible with the fourth group, which has the effect of reducing the weight of focusing, reducing the amount of eccentricity of the front lens, and easily enabling close-up focusing. .

[Brief explanation of drawings]

FIG. 1 is a sectional view of embodiments 1 to 4 of the present invention, and FIG.
The figure is a sectional view of Example 5 of the present invention, FIGS. 3 to 6 are aberration curve diagrams of Example 1 of the present invention, and FIGS. 7 to 10 are aberration curve diagrams of Example 2 of the present invention. 11 to 14 are aberration curve diagrams of Example 3 of the present invention, FIG. 15 to 18 are aberration curve diagrams of Example 4 of the present invention, and FIGS. 19 to 22.
The figure is an aberration curve diagram of the embodiment of the present invention. Applicant Olympus Optical Co., Ltd. Agent Hiroshi Mukai - Fig. 2 Fig. 3 Convergence No. 4E Spherical aberration Astigmatism Distortion aberration 3 > Lateral chromatic aberration Comatic aberration Alternating Lateral chromatic aberration Comatic aberration Fig. 5 Fig. 6 Figure 7 Figure 8 Spherical aberration Astigmatism, distortion Chromatic aberration of magnification Comatic aberration Figure 9 Figure 10 Chromatic aberration of magnification Comatic aberration Figure 11 Figure 12 Chromatic aberration of magnification Comatic aberration Figure 13 Figure 14 Figure 1 Su, l:l Let) ri, b-u・)
U, tJ tJb-5,0Go bIJ 1st
5 Figure 16 Chromatic aberration of magnification Comatic aberration Figure 17 Figure 18 Chromatic aberration of magnification Comatic aberration Figure 19 Figure 20 Spherical aberration Astigmatism Distortion Chromatic aberration of magnification Comatic aberration Figure 21 Figure 22 Figure 10' p00 [,),':) (), b
UIJ U-1) -5tl 0.0
＞U magnification chromatic aberration Coya aberration - U, ub uri, U co

Claims (1)

[Claims] (1) A first group consisting of three lenses in order from the object side, a negative lens, a positive lens, and a positive lens, and having a positive focal length as a whole, a negative lens, a negative lens, and a positive lens; The lens consists of three lenses, the second group has a negative focal length as a whole and is movable when changing the magnification and is mainly responsible for changing the magnification, a lens with a weak refractive power and an aspherical surface, and a positive lens. Two lenses or a lens with a weak refractive power and an aspherical surface, a positive lens,
A third group consisting of three lenses, a negative lens, which has a positive focal length as a whole and is always fixed and serves to create an almost afocal on the exit side, a positive lens, a positive lens,
The fourth lens group is composed of three negative lenses, has a positive focal length as a whole, has the role of a so-called compensator to eliminate fluctuations in the focal position that occur when changing the magnification, and is movable for focusing. A zoom lens that satisfies the following condition (1). (1) |f_T/f_A_T|<0.6 where f_T is the focal length of the entire system at the telephoto end, f_A
_T is the combined focal length from the first group to the third group at the telephoto end. (2) A zoom lens according to claim (1) that satisfies the following conditions (2) to (8). (2) −1.2<f_IV/r_IV_F<0.11(3)
−0.5<f_IV/r_IV_R<0.5(4)2.0<
|f_7|/√(f_W・f_T) (5) 0.1<d_
3_1/√(f_W・f_T)<0.55(6)0.5
3<(e_2_W-e_2_T)/e_2_W<0.7
7 (7) 1<f_IV/√(f_W・f_T)<1.3(
8) n_8>1.65 where f_W is the composite focal length of the entire system at the wide-angle end, f
_T is the focal length of the entire system at the telephoto end, f_IV is the combined focal length of the fourth group, f_7 is the focal length of the aspherical lens with weak refractive power in the third group, and d_3_1 is the focal length of the aspherical lens in the third group. The air distance between the lens and the lens, e_2_W, is the distance between the second and third groups.
e_2_T is the principal point distance between the second and third groups at the wide-angle end, r_IV_F is the principal point distance between the second and third groups at the telephoto end,
The radius of curvature of the surface closest to the object side of the group, r_IV_R is the radius of curvature of the surface closest to the image side of the fourth group, and n_8 is the refractive index of the positive lens with strong power in the third group. (3) An aspherical lens with a weak refractive power in the third group has an aspherical surface whose image side surface is biased toward the image side with respect to a spherical surface with a radius of curvature on the optical axis, and which increases monotonically toward the outside in the radial direction of the lens. A zoom lens characterized in that the aspherical surface satisfies the following condition (9) when expressed by the following formula (A). (A)X=y^2/[r+√(r^2-y^2)]+Δ
＿X=y^2/[r+√(r^2-y^2)]+Ey^
4+Fy^6+Gy^8+Hy^1^0 (9) y=0.
0.2×10^-^2<Δ_X/√(f_W・f_T) in 2｜f_F_3|
<0.18×10^-^1 where y is the radial height of the aspherical surface from the optical axis, r is the radius of curvature of the approximate spherical surface on the optical axis of the aspherical surface, and f_F_3 is the front focal position of the third group It is.