JPS60184221A - Zoom lens having rear focus mechanism - Google Patents

Abstract

PURPOSE:To reduce the weight of a focusing operation mechanism by forming a converter system so that it is approximately afocal and feeding a focusing lens system to the object side along the optical axis to focus a lens on a close-distance object point from an infinity object point. CONSTITUTION:A zoom lens is in the F/2.0 class and has a long back focus which is >=0.9-fold length of a geometrical mean fs between the shortest focal length and the longest focal length, and this zoom lens consists of a converter system A and a focusing lens system B consisting of <=3 lenses. This converter system A consists of the first fixed positive group I , the second movable negative group II having a variable power function, the third movable group which is used mainly for keeping the focus position constant, and the fourth positive fixed group IV. The converter system A is so formed that it is approximately afocal. When the focal length of the system A is denoted as fA and the geometrical means between the shortest focal length and the longest focal length of the whole of the zoom lens system is denoted as fs, fA is so determined that -0.5<fs/fA<0.35 is true.

Description

TECHNICAL FIELD The present invention relates to a bright, high-performance zoom lens having a rear focus mechanism.

Prior Art Conventionally, most focusing operations in zoom lenses have been performed by extending the front lens group, which has a large diameter and is heavy. In the case of such a focusing method, there is a drawback that the fluctuation of spherical aberration and dichromatic aberration is likely to be large among the fluctuations of the difference when focusing on a short-distance sales point, especially on the long focal length side. Furthermore, this focusing method also has problems such as the necessity to increase the closest shooting distance or increase the diameter of the front lens due to vignetting of the lower rays by the front lens on the short distance side.

In order to eliminate these drawbacks, it is desirable to adopt a rear focus method as a focusing method. A zoom lens employing this focusing method is described in Japanese Patent Application Laid-open No. 71583/1983. However, although this conventional example has advantages especially in autofocus, etc., the first embodiment has large aberration fluctuations, especially astigmatism fluctuations when focusing at short distances, which is unfavorable in terms of performance, and the second embodiment is not suitable for telephoto systems. This is applicable only to zoom lenses that are dark at F15.6 and have a dim back focus. In other words, this conventional example has a short focal length, which is the objective of the present invention, at F/2.0 class or above, and the bank focus is 0 of the geometric mean f8 of the shortest focal length and the longest focal length.
Aberration fluctuation when focusing at close range while increasing i'ifl'j by 9 times or more! 1) Certain conditions for reducing fluctuations in spherical aberration, coma aberration, and astigmatism are not met.

Purpose The present invention reduces aberration fluctuations during close-range focusing.1] There is no shortage of peripheral light due to vignetting of the light beam, and the front lens is prevented from becoming huge in order to ensure insufficient peripheral light. The object of the present invention is to provide a zoom lens having a simple frame structure for focusing, light focusing operation, and a rear focusing mechanism that is effective for autoraocous.

Another object of the present invention is to provide a zoom lens that has a short focal length and a rear focus mechanism that has a long back focus.

Summary In order to achieve the above-mentioned object, the zoom lens of the present invention is designed to have a long back focus of 09 times or more the geometric mean f8 of the shortest focal length and the longest focal length, especially in the F/2.0 class. The lens configuration is as follows. In other words, the convergence system A and 3 shown in FIG. This system consists of a focusing lens system B having a number of lenses. The converter system A is formed to be almost afocal, and the focusing lens system B is extended along the optical axis toward the object f111 to focus from an object point at infinity to a near object point. be.

This structure makes it possible to reduce the weight of the lens group for focusing, and also to reduce the weight of the focusing operation. In particular, if autofocus is adopted, this has great advantages in terms of quick response and power savings. However, when focusing in the above manner, aberrations may vary, and certain conditions must be set, especially in a bright F/20 zoom lens as in the present invention. Therefore, in the present invention, the converter system A is made to be almost afocal as described above. Moreover, the focal length of this system A is fA.

Zoom l, when the geometric mean of the shortest focal length and longest focal length of the entire lens system is f8, the following condition (1) is 61? . It is desirable to set f so that it adds up.

(1) −0,5<1ζ×O35 Although the right-hand side can also be set to 05 to achieve the above-mentioned purpose, it is desirable to set it to 0.35 or less in order to lengthen the back focus.

If the limit of this condition is exceeded, it becomes difficult to lengthen the back focus, and if you try to lengthen it forcibly, the power of focusing lens system B will weaken and the amount of extension during focusing will have to be increased. So I don't like it. Moreover, when the lower limit is exceeded, fluctuations in spherical aberration and comatic aberration become large.

As long as the above conditions are satisfied, a single lens is sufficient for focusing lens system B. However, considering fluctuations in astigmatism, it should be constructed with two or three positive lenses, with the positive lens closest to the object being the It is preferable to use Kokichi in which the image side surface is negative and has a strong curvature. It is also preferable that the positive lens closest to the image side has a convex surface on the object side with a clearly stronger curvature than on the image side.

(2) 0.42 fs < lfN, 4 < 0.64
f3(3) tB < 0.45 fs (4) 1.4 fs< f4 < 2.0 f3(5
) 0.4 fs <1ful< 0.7 fs (6)
013fs<D<05f8 where fFan is the focal length of the negative lens component closest to the object in the fourth group, and tB is the total thickness of the focusing lens system, including the air gap, from the surface closest to the object side of this lens system. distance to the image side surface), fI.

fl is the focal length of the first group 2 and second group 1], and D is the air distance between the converter system A and the focusing lens system B.

Focusing lens system B has two or three lenses as described above.
It is preferable to use a positive lens.

However, in order to reduce the weight of this system B that moves during focusing, which is the greatest objective of the present invention, the above condition (3) is set to 41r.
You need to add 0. If it deviates from this condition, it will be light: 11-
cannot be converted into

The zoom lens of the present invention is a lens system that has a brightness of F/2.0 or more, a high zoom ratio of 3 or more -1, a rear focus mechanism, and small aberration fluctuations. However, even if short-range performance can be improved, the focal length of the lens component is still specified. This lens component has the shortest focal length σ
Since the influence on each aberration is uniformly large from j[1 to the longest focal length, it is advantageous for aberration correction to make the power looser. When the lower limit of condition (2) is exceeded, the spherical aberration bulges out at the shininal part and tends to take a large positive value at the marginal part. On the other hand, if the upper limit is exceeded, it becomes difficult to extend the focus.

Condition (4) stipulates the focal length of the first group (■); if the upper limit of condition (4) is exceeded, the total length of the zoom section tends to become longer; if the lower limit is exceeded, the focal length of each lens surface of this group increases. Since the radius of curvature becomes small, it becomes difficult to secure the effective diameter of the lens and correct each aberration ρ.

Condition (5) defines the focal length of the second group 11, and if the lower limit of this condition is exceeded, the total length of the zoom section is shortened (
-1- is desirable, but aberration fluctuations during zooming tend to become too large, and if the upper limit is exceeded, the total length of the zoom section becomes long. The lower limit of conditions (4) and (5) is F/
This is designed to ensure a brightness of 20 or higher, and it may be darker than this.'' There is no problem with slightly exceeding this lower limit for gifts. For example, in condition (4), 1.
If it is greater than 0, there is no problem.

If the lower limit of condition (6) is exceeded, sufficient distance necessary for focusing cannot be obtained, and if the upper limit is exceeded, the total length becomes too long.

Example 411 The rear focusing mechanism of the present invention described above is
Examples of sheets and lenses are shown below.

Example 1 f2=14-2.425-42, F/2.0r
l = 145.4.589 dl-1-, 1600nl -.], 80518 ci,
=25.43r2228.8038 d2"" 7.3000 n2= ], 6201.2
ν2 ” 49.66r, knee 1.24.4191 d,, = 0.1700 r, = 28.0380 d, + = 5.6000 n; + = 1.6204
5 shi, = 38.12r, = 194.2344 d5 ” 0.6000~q, 404-~16.075
r11 = 27', 2667 rI+ = 1.0400 n, l = 1.78590
C4=44.18r7=10.3892 d723.9500 r8: 15.8056 ds ””1. ．． 0400 ns-”i, 701
54 shi, = 41.21 rfl = 13.5487 dp = 3.4000 no = 1.84666
shi,,=23.88r10 knee 92.7796 d+o=17.4871~8.20+~243+r
,,=-11,9646 do ”' 1.0000 n7= 1..71300
Schiff=53.84r12=42.5665 d+z=1.2558~1-725 A-0,8e
;Sr knee 85.6664 d+a = 2.7002 n9 = 1.59270
ν8=35.291+< = 17.944.9 d+, + = 0.8553 r, 5-(Xll (aperture) d, ffi = 2.0000 1+1.l== 21.1736 d+6" 4.5115 ng" ” 1.62230
C, =53.20r1゜=-27,2639 d,? = 0.2100 r18 = 14.3135 d+'s = 3.1600 nlo = 1.51.
742 νto = 52.411J: 115.78
20 d+o = 1. ．． 2000 r,, o=-25,5498 d,, o= 1.6617 nN == 1.8466
6 ν,, = 23.88r2+ = 15.215
0 ・ dz+ = 8.5579 r22 = 2332.0237 d22 = 4.2478 n+2” ], 5111
2 shi, 2 = 60.48r2. == 20.850
1 d2:+ -" 0.1342 r24-33.8590 d2s "' 4.6445 n+, = 1.4874
9 ν13=70.15r2s=61.6882 fB,=23.3 Example 2 f-14~24.25~42. F/2. .

r+ = 84.1276 d, = 1.1'600 nl = 1.80518
shi, =25.4.3r2= 29.0902 d2-73000 n2-1,62012 sear 49
66r3"' 273.1915 d3 = 0.1700 r, = 287778 4, = 5.6000 n3-1..62012 Si3
=49.66ri =, 203.0683d, -0,6000~8,83δ~14.867ro=
29.7145 d++ ” ], 0400 n<-1,73400ν
4=51. ．． 49rt = 11. ．． 3398 d7=3.9500 r8=-21,5403 da "" 1.0400 n*=1. ．． 6935
0'! I = 53.23ro ” 15.9303 do = 3.IQOOn6 = 1..84666 Shiro = 23.88r1o = 1554.6274 d+o = 12.9984~F;, 073~2.82
8rl+ = -14,7944 dll = 1.000On? -1,69680v7
= 55.52r12 = --36,0319 d12""4.9325~4ぢq8~0854"l:
1 = 50.3787 d,,, = 2.6753 113=1. ．． 7495
0 shi8235271'+4 = -29,8033 d, 4 = 0.6469 1 B'-value aperture) dlfi = 2.0000 rllll = 20.2193 d+++ -5,3125n*, = ], 6935
0 ν. =53.23r17 = 440.8891 d+7"" 0.8000 r+s= 25.3662 d+g-1,,4008neo-1,,84666νI
11 = 23.88rlo218.0976 do+ = 1.8984 r26 = 104.9452 d2o = 3.0000 no ”' 1.5687
3 νo' = 63,16r,, = -33,8872 d2+ = 6.0137 122 = 1877.6563 d22 ''' 3.6497 n+2''' 1.487
49 shi...=70.15rv:+=18.16
73 d2:+ ”' 0.1342 r2i = 27.7264 d2.+ = 3.3156 n+J= 1.4874
9 ν13 = 70.15r, = -111,,3
84.7 fB = 2.3.3 Example 3 f-14~2425~42, E/2. Qr, = 8
2.8380 d, = 1.1600 n, = 1.80518 ν
I = 25.43r2 = 28.9584 d2 = 7.3000 nz ” 1.62012 Shi2 = 49.66r -243,9198 di = Oj, 700 r,, = 28.9601 cL - -5,6000n: + "" 1.62374
C3=47.1Or6=203.8797 d,=0.600□88647勺14.52'? 1++
= 29.0358 dn = 1.040On4 =' 1.73400
ν+”'51.49r7 == 11.4509 d723.9.500 r8 = 21.5434 d8= 1.0400 nfi = 1.69680
ν, = 55.52r, = 16.1419 do = 3.1000 no = 1.84666
Shi6223.881r+o == 327.0857 d102127201~Dou (15B N2.84-91
rn =' 15.1829 dH"' 1.0000 n7" 1.6-9680
Schiff = 55.52r1□ = -38,3036 a, 2 = 4.8880 ~ +, EQ4 ~ '08541'
+3 = 50.2085 d,, = 2.6726 nB = 1.76200
v8= 40.1Or+4 ”” 29.8907 d+, + = 0.6433 r+i2ol) (aperture) d,, = 2.0000 r16 ”’ 2 o1914 d+6= 5.5367 n9”” 1..69680
ν0=55.52r1. "" 2178.6990 d, 7= 0.8000 r, 8= -, 25, 1867 dos " 1.4025 n+o " 1-. 846
66 ν+o ”” 23.88rho = 18;2
541 dto = 1.8967 r20 = 89.3959 d2o = 3.0000 no = 1.62041
'n = 60.27r2. Knee 41.7577 (12, = 6.1391 r22 = 2160.7673 d22 ” 3.6490 n12 = 1.5687
3 ν,, = 63.16r2:+ = 20.10
24 d2s20.134-2 r,,, = 28.7.875 d-z<-3,3002n+++ ”” 1.4874
9 ν13 = 70.15 to r2 = -98,5889 fB2233 Example 4 f-14~2425~42, F/2. Or, = 8
3.0383 d+-1,160On+-1,,80518shi,=25
．． 43r, : = , 29.14-00 dz = 7.3000 n2 = 1.62012 Si2 = 49.66rx = 253.1450 d++ = 0.1700 r4 = 28.6874 d4” 5.6000 n3” 1.62012 1'
3"49.6'6r (= 210.2929 d5=0.6000~8.6:IF1~14.534-
r, = 30.3630 d6 = 1.0400 n4 = 1.73400 ci,
, = 51.49 r7 2 11.3638 d7 = 3.9500 r8 knee 21.4761 d8 = 1.0400 ni = 1.69350 v
, = 53.23r, = 17.0207 dq = 3.1000 n++ = 1. ．． 8466
6 shi, = 23.88r+o = 1069.1825 dto = 13.0418~5. '272~2.78
9To = 141675 d,, = 1. ．． 0000 n7””],,6968
0 Schiff = ・55.52r12 = -36,27
00 dI2 = /1.5289~4243~0.85 tor
, 3 = 55.6389 dzs -2,6729ns = 1.74950 ν
s = 35.27r+< = 31.9536 d+<20.6353 rls-ω (aperture) dlTh=2.0000 ra6= 21.0858 den = 5.0173 no = 1.6935Q
νn””53.23rl? == 708.9650 d+7 = 0.8000 r+s = 27.0343 d, 8-14021 n,. =1.84666 ν+o
= 23.88rII+ = 19.195 O d4g = 1. ．． 9053 r2o = 45.3739 d2o ” 3.0000 no = 1.56873
νn = 63.16r2+ = 24.8871 d2+ = 6.6760 rt2= 119.5541 d2□= 3.6491 n+2= 1.48749.
l'+2-70.15r23'= 20.3750 dz3= 0.1342 r24= 28.5509 d24. =3.300411+3=1.48749+
3-=70-15r2. --144.4908 fB = 23.3 Example 5 f-14~2425~42, F/2, Orl =
82.6129 d, = 1.1600 nl = 1.80518
νl", 25.43r2, = 29.2181 d2" 7.300On2 = 1.62012 ν2
= 49.66r3'' -246,0953 d3=0.1700 r4 = 28.4664 da = 5.6000' n3 := 1.620
12 shi3=49.66ra=217.2658 ds=0.6000~B516~t4.296r,
: = 311.0022 (Lt = 1.0400 n, t = 1.73400
shi,=51.491"7-11.4972 d7-39500 r8=--20Q 045 d8ko=1.0400 old=1.69350 shi,=5
323r+1=16.3829 small+=3. H) 00 no == 1. ．． 8466
6 νo” 23.881・.-64fi, 645
4 d111:128886~5.006~286Srl+
knee 14.2623 do = 1.0000 n7 2 1.69680 Schiff = 55.52r12 knee 30.9806 d1 = 4.5295~4484-~08ri4r11
” 5 (17675 d1s ”” 2.6656 n8”” 1.7495
0! 's = 35.27rM = -30,653
9 d+<= 0.5921 r, 5-L): l (aperture) d4i=2.0000 r, 6 = 19.184- O d,, = 5.6618 n, = 1.69350
v,, = 53.231+7 == 3649.83
66 d, 7' 0.8000 r, 8 = -24,4207 d47 "" 1.4073 nl. = '1.846
66 ν,. =23.88r,9218.4904 d,, =38044 r2o280.9804 d,,o=3.0OQOnu: 1.56873
νo ”6:'3.16ry+ ”=-23,6
744 dz+ = 4.3200 r2゜=-81,,0091 d:2” 3.6442 n42= 1.48749
L'+2 = 70.1.5r23: 19.676
4 d2320, 1342 r2. = 28.3524 d24. = 3.3101 11+3= 1.487
49 ν,,, = 70.15r25 = 150.
6774 f11=233 where r+ + r2 +... is the radius of curvature of each surface of the V lens, dl l d2r... is the thickness and air gap of each lens, nl r 12 +...- is the refractive index of each lens,
C7. C2. . is the Abbe number of each lens, f is the focal length of the entire system, and f]1 is the back focus.

The amount of extension of the focusing lens system B when focusing on a close distance in each of the above embodiments is as follows.

f214 f”2'1.25 f=42 Example 1 0.
181 0.538], 627 actual 627 implementation 0.
183 0.542 1.633 Example 3 0.186
0.552 1.672 Example 4 0.173 0.
510 1.505 Example 5 0.173 0.510
1.499'' Among the examples described in 1, Example 1 has the lens configuration shown in FIG. It consists of a lens. The aberration situation in this example is as shown in FIGS. 3 to 8. Of these, Figures 3 and 4 are wide objects, respectively, and show the object point at infinity.

When focusing on an object point of 1 or 2 m, 5th
Figures 6 and 6 are standard object points at infinity.

Figures 7 and 8 are for an object point at 1 and 2 m, respectively, for an object point at infinity in telephoto mode and an object point at 1.2 tFl.

Examples 2 to 5 all consist of positive lenses as shown in FIG.

The aberration situation of Example 2 is shown in FIGS. 9 to 14. Of these, Figures 9 and 10 are wide and for an object point at infinity and an object point at 12 m, respectively, and Figures 11 and 12
The figures are for a standard object point at infinity and an object point at 12 m, and Figures 13 and 14 are for a telephoto object point at infinity +1.2y+z.

The aberration situation of Example 3 is shown in Figs. 15 to 20, and Figs. 15 and 16 respectively show wide, infinite object point, 1.2y
nO object point, Figures 17 and 18 are standard and infinite object points, ], 2 m object points, Figures 19 and 20 are telephoto and infinite object points, :1. , for an object point of 2 m.

The aberration situation in Example 4 is as shown in Figs. 21 to 26, and Figs. 21 and 22 show a wide object point at infinity,
The object point at 1.2 m, Figures 23 and 24 are standard, the object point at infinity + the object point at 1.2 m, and Figures 25 and 26 are the object point at infinity, the object point at 12 m. It is something.

The aberration situation of Example 5 is shown in FIGS. 27 to 32. Of these, Figures 27 and 28 are wide, with an object point at infinity + 1.2 m, and Figure 29.

Figure 30 is a standard object point at infinity and a 1.2m object point, and Figures 31 and 32 are a telephoto object point at infinity.

This is an object point of 1 or 2 m.

As an effect of the invention, the zoom lens with the rear focus mechanism of the present invention performs focusing without moving the huge front lens, especially with fast lenses of F/2.0 or higher, making focusing extremely light. obtain. Furthermore, aberration fluctuations due to focusing are small, and even if the focal length is short, it is possible to make the back focus sufficiently long.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of Example 1 of the present invention, FIG. 2 is a cross-sectional view of Example 2 to Example 5 of the present invention, FIGS. 3 to 8 are aberration curve diagrams of Example 1, and FIG. 15 to 20 are aberration curve diagrams of Example 2, FIGS. 21 to 26 are aberration curve diagrams of Example 4,
FIG. 27 to FIG. 32 are aberration curve diagrams of Example 5. Applicant Olympus Optical Industry Co., Ltd. Agent Akiji Mukai Figure 1 Figure 2 Figure 3 Spherical aberration Astigmatism Distortion Figure 4 Spherical aberration Astigmatism Distortion 11+ J-reverse Figure 5 Spherical aberration Astigmatism Distortion Aberrations Figure 6 Spherical Aberration Astigmatism Distortion Figure 7 Spherical Aberration Astigmatism Distortion FI2.0 7.9° 7,9'' Figure 8 Spherical Aberration Astigmatism Distortion Figure 9 Spherical Aberration Astigmatism Distortion Aberration Figure 10 Spherical Aberration Astigmatism Distortion Aberration Figure 11 Spherical Aberration Astigmatism Distortion Aberration Ft2.o +4.5° 145° Figure 12 Spherical Aberration Astigmatism Distortion Aberration Figure 13 Spherical Aberration Astigmatism Distortion 1111 JIV difference Fig. 14 rl Surface aberration Astigmatism Distortion +111 Jl! Difference No. 16
Spherical aberration Astigmatism Distortion tube 17, Spherical aberration Astigmatism Distortion 1'- F12D 14.5° 14.5° Fig. 18 Spherical aberration Astigmatism Distortion Fig. 19 Spherical aberration Non-no,'' , 1, Aberration Distortion +1V difference F/2,
0 7.9° 7.9a Figure 20 Spherical aberration Astigmatism Distortion l11+ IIV difference Figure 21 Spherical aberration Astigmatism Distortion F/2.0 22.5'22.5" Figure 22 Spherical aberration Astigmatism Aberration Distortion 11+ ll5L difference Fig. 23 Spherical aberration Astigmatism Distortion aberration Fig. 24 Spherical aberration Astigmatism Distortion 111 Distortion Fig. 25 Spherical aberration Astigmatism □dj l+II
Figure 6 Spherical aberration Astigmatism Distortion 1111 JIV, difference Figure 27 Spherical aberration Astigmatism Distortion aberration 1, j, 11ii liV, ;:2 Astigmatism Cup aberration Figure 29 Spherical aberration p: ), 'j, I [Also;, α Strain + Il
+il Distortion II Chamfering Discrepancy Astigmatism Distortion Jllj Difference Figure 31 Spherical Aberration Astigmatism Distortion Aberration Spherical Surface 111 (Difference Astigmatism 79" Difference Distortion + lI + JIV, Difference 79")

Claims (1)

[Claims] A fixed and positive first group, a movable and negative second group that mainly has a variable power function, and a movable third group that mainly has a function of keeping the focal position constant; It consists of a fixed positive converter system that forms an almost afocal lens and a movable focusing lens system, and when focusing from an object point at infinity to a near object point A zoom lens having an afocus mechanism, characterized in that the focusing lens system is extended toward the object side along the optical axis and satisfies the following condition (1): (1) -0,5 <)ζ<035 where f8 is the geometric mean of the shortest focal length and longest focal length of the entire zoom lens system, and fA is the focal length of the converter system.