JPH03140911A - Variable power lens - Google Patents

Abstract

PURPOSE:To obtain the variable power lens for video cameras which is fixed in aperture position, is simple in the constitution of a lens frame and does not change an F-number at the time of variable power by fixing a 1st lens group, 4th lens group and aperture position at the time of the variable power with a lens system which makes the variable power by changing the spacings between the respective lens groups. CONSTITUTION:The 1st lens group is constituted of the combined lens of a negative lens and a positive lens, the 2nd lens group of the combined lens of positive and negative lenses, the 3rd lens group of the combined lens of positive and negative lenses, and the 4th lens group of negative and positive lenses, respectively. A diaphragm is disposed on the object side of the 4th lens group and a spherical faces are used for the face on the extreme image side of the 1st lens group and the face on the extreme image side of the 4th lens group, respectively. The 2nd lens group and the 3rd lens group move and the rest are fixed at the time of the variable power. The lens system which has about 3 to 4 variable power ratio, about F/2.0 to F/4.0 aperture ratio, is fixed in the diaphragm, allows the simple construction of the lens frame and does not change the F-number at the time of the variable power is obtd. in this way.

Description

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

[Prior art] Currently, lenses for consumer video cameras have a zoom ratio of 6.
Zoom lenses with an aperture ratio of F/1.2 to F72.0 are mainstream. This is because the above specifications are extremely efficient in terms of design and needs.

Many of the above-mentioned zoom lenses are generally referred to as four-group zoom lenses, such as those disclosed in, for example, Japanese Patent Laid-Open No. 58-102208 and Japanese Patent Laid-Open No. 58-153913.

These zoom lenses generally have, in order from the object side, a 21st group that has a positive refractive power and is fixed during zooming and has a focusing function, and a 21st group that has a negative refractive power and is movable and has a zooming function. A second lens group, a third lens group that moves to correct the movement of the image plane due to zooming, a permanently fixed aperture, and a fourth lens that has positive refractive power and is always fixed and has an imaging function. It consists of a group.

This type of four-group zoom lens is suitable for achieving high variable power and large aperture. However, since the first (21) group has positive power, it is not suitable for widening the angle of view, and the angle of view at the wide end is limited to about 50°.

In addition to the 4-group zoom, there is a 2-group zoom. It consists of a first (21) lens group with negative refractive power and a second lens group with positive refractive power in order from the object side, and magnification is changed by changing the relative spacing between these lens groups. be.

This two-group zoom lens has a negative lens group in front, so it is suitable for wide angles, but it is not suitable for high zoom ratios and large apertures, and the zoom ratio is generally around 2. It is.

Further, in this two-group zoom lens, the aperture is generally located in the second lens group and moves together with the second lens group when changing the magnification. Moving the diaphragm in this manner is undesirable because it increases the cost of the lens frame structure.

Furthermore, as a zoom lens for a video camera aiming at a wider angle of view, Japanese Patent Application Laid-Open No. 63-292106 and Japanese Patent Application Laid-Open No. 1-1
A lens system described in Japanese Patent No. 91820 is known.

The former is a zoom lens consisting of three lens groups, negative, positive, and positive, but the aperture is located in the second lens group or on the object side and moves together with the second lens group, resulting in high cost due to the lens frame structure. Become. Furthermore, the F number changes as the magnification changes, which is not preferable.

The latter zoom lens has a negative, positive, and positive three-group configuration, and each lens group is movable, and the aperture is divided between the second lens group and the third lens group.
Although it is fixed between the lens groups, the variable power ratio is small at 2 to 3, and the F number changes as the power is varied.

Furthermore, there is a zoom lens having a negative, positive, and positive three-group structure, which is described in Japanese Patent Laid-Open No. 40913/1983.

In this lens system, the aperture and the third lens group are fixed, and the F number does not change when changing the magnification, but the maximum angle of view at the wide end is about 45 degrees, which cannot be said to be a wide angle of view.

[Problems to be Solved by the Invention] The present invention was made in order to solve the problem that the conventional variable magnification lens for video cameras has a narrow angle of view at the wide end, as described above. Angle of view at the edge is 60
Above the degree, the variable power ratio is 3 to 4, and at the degree, the aperture ratio is F.
To provide a variable magnification lens for a video camera, which has an aperture position of about /20 to F74.0, has a fixed aperture position, has a simple lens frame configuration, and whose F number does not change when changing.

[Means for Solving the Problems] The variable magnification lens of the present invention includes, in order from the object side, a first (21) group having a negative refractive power, and a second (21) group each having a positive refractive power. This lens system consists of a third lens group, a fourth lens group, and an aperture placed behind the third lens group, and changes the distance between each lens group to change the magnification. group and fourth
The lens group and the aperture position are fixed.

Generally, in a zoom lens, when the lens group behind the aperture is moved during zooming, the F number (aperture ratio) changes as the zoom lens changes magnification. In this case, in order to keep the F number constant, the diameter of the aperture must be changed as the magnification is changed, which increases costs.

Furthermore, in order to prevent the total length of the lens system from changing during zooming, it is necessary to keep the first (21) group fixed.

In other words, in order to keep the overall length of the lens system constant and the F number constant without changing the aperture diameter, in the case of a 4-group zoom lens, the aperture should be placed behind the third lens group. However, the positions of the 1st) 21st lens group, the 4th lens group, and the aperture stop may be fixed.

The present invention is based on a negative and positive two-group zoom lens as shown in FIG. 38 in order to achieve a wide angle. That is, the 1st) 21st lens group (Il) was made to have negative power, and the second to fourth lens groups (II [+1V) were made to have positive power as a whole.Here, in order to fix the 21st lens group fIl, , from the second lens group to the fourth lens group (II II
IIV) may be constructed so that the virtual image I formed by the first 21st group (1) is used as an object point and the distance from there to the image I' is kept constant and relayed. Since the second lens group to the fourth lens group have positive power as a whole,
In order to keep the fourth lens group fixed and maintain strong positive power as a whole while achieving a large variable power effect, the second lens group must be fixed.
It is desirable that the lens group and the third lens group each have positive powers.

In Figure 38, the absolute value of the overall imaging magnification of the second to fourth lens groups is small at the wide end and large at the telephoto end, so the entire system from the second to fourth lens groups The main point moves forward as you go from wide to tele. By the way, in order to fix the aperture near the fourth lens group as mentioned above, the aperture has to be configured to be far away from the second lens group to the rear from the principal point of the entire fourth lens group on the telephoto side. . Therefore, the entrance pupil on the telephoto side becomes far away, making it difficult to correct aberrations on the telephoto side. Furthermore, since the principal point of the entire system from the second lens group to the fourth lens group moves forward, if the F number is kept constant, the ray height of the marginal ray on the telephoto side will increase, and furthermore, the aberration correction on the telephoto side will become more difficult. It becomes difficult.

In order to correct this, it is desirable to satisfy the following conditions (1) and (21).

(1) -0.6<β2i4<-0.2 (21-0.
1<fw/f, <0.5 where β234 is the second .fw/f at the wide end. Third. The magnification of the entire fourth lens group, fw is the focal length of the entire system at the wide end, and f4 is the focal length of the fourth lens group.

When the lower limit of the condition fi+ is exceeded, the imaging magnification of the second to fourth lens groups at the telephoto end also becomes a large negative value, and the principal point of the second to fourth lens groups moves forward at the telephoto end. , the entrance pupil becomes too far away, which worsens off-axis aberrations on the telephoto side, which is undesirable. Furthermore, the ray height of the marginal ray on the telephoto side also increases, which is undesirable because spherical aberration and coma aberration worsen on the telephoto side. If the upper limit of condition (1) is exceeded, the first)
The negative power of the 21st group becomes large, and the aberrations generated in the 21st group (1) cannot be corrected completely, which is not preferable.

Condition (2) defines the power of the fourth lens group, and if the lower limit of this condition is exceeded, the power of the fourth lens group will be reduced to the second lens group on the telephoto side. Third
The ray height of the marginal ray in the lens group becomes too high, making it difficult to correct aberrations on the telephoto side. If the upper limit of condition (2) is exceeded, the positive power of each of the second lens group and the third lens group becomes weaker, the variable magnification effect decreases, and the occurrence of aberrations in the fourth lens group increases.

Since the second lens group and the third lens group have a large zooming effect, it is necessary to reduce the occurrence of chromatic aberration in these lens groups. For this purpose, it is desirable that the second lens group or the third lens group include at least one negative lens that satisfies the following condition (3).

(3)　νn〈50 However, Schiff is the Atsube number of the above negative lens.

If this condition (3) is exceeded, the fluctuation of chromatic aberration due to zooming becomes large, which is not preferable.

If condition (1) is satisfied, the negative power of the 1st lens group increases, and off-axis aberrations tend to occur in the 1st) 21st lens group. In this case, in order to perform good aberration correction, it is desirable to provide at least one aspherical surface in the first lens group whose negative refractive power decreases as the distance from the optical axis increases.

This aspherical surface is
When the axis is taken as the y-axis in the direction perpendicular to the optical axis, it is expressed by the following equation.

However, r is the radius of curvature of the reference sphere, P is the conic constant, Ait
is the aspheric coefficient.

The above aspherical surface used in the present invention satisfies the following condition (4):
It is desirable that it satisfies the following.

(4) Σ1Δxl/h< o, 2 (3'
= '/wc) where ΔX is the amount of displacement of the aspherical surface from the reference spherical surface, h is the maximum image height, y is the height from the optical axis, and Vtt
c is the chief ray height at the maximum angle of view at the wide end of this surface.

Also, Σ1Δx1 is 1 for all aspheric surfaces in the 21st group. This means calculating the sum of the absolute values of ΔX.

If the range of condition (4) is exceeded, distortion will be overcorrected and coma will also increase, which is not preferable.

In the lens system of the present invention, focusing can be performed by extending only the 1st 21st group, as in a normal zoom lens. In this case, compared to a variable magnification lens that uses pressure power first, there is less vignetting of the light ray when it exits the lens group, and less variation in aberrations. This is because it is nearly parallel to the axis.

Furthermore, in the lens system of the present invention, focusing can also be performed by extending the entire fourth lens group or a portion thereof. In general, when focusing is performed by extending the first (1) 21st lens group, it has the advantage that the amount of extension during focusing does not change even when the magnification is changed, but it has the disadvantage that the lens to be extended is heavy.

On the other hand, when focusing is performed using four lens groups,
It has the advantage that the lens is lightweight and the load during focusing is small. Therefore, it is extremely effective for increasing the focusing speed in autofocus.

In the variable power lens of the present invention, it is desirable to set the power of the fourth lens group within the range of condition (2) as described above, but it is also possible to make it powerless within this range.

Furthermore, in a special case, the fourth lens group can be omitted.

As mentioned above, when the fourth lens group is omitted, the lens system consists of, in order from the object side, the 1st) 21st lens group with negative refractive power, the second lens group with positive refractive power, and the second lens group with positive refractive power. 3rd with
It consists of a lens group and an aperture, and magnification is changed by changing the distance between each lens group.It is characterized in that the position of the first (21) group and the aperture are fixed when changing the magnification. .

With this variable power lens, the explanation for the 4-group zoom lens described above also holds true; however, since the 4th lens group is omitted, the 2nd... Since the ray height of the marginal ray in the third lens group becomes high, this is not suitable for making the lens system brighter, but since the number of lenses can be reduced by 2, it is very advantageous for reducing costs.

In the case of a configuration in which the fourth lens group is omitted as described above, it is desirable that the lens system having the three-group configuration satisfies the following conditions.

+5) -0.6<βti<-0.2 (6) Shift<50 However, β23 is the imaging magnification of the composite system of the second and third lens groups, and νn is the second and third lens groups. This is the Abbe number of at least one negative lens in the group.

When the lower limit of condition (5) is exceeded, the imaging magnification of the entire system of the second and third lens groups at the telephoto end becomes a large negative value, and the imaging magnification of the entire system of the second and third lens groups at the telephoto end increases. The principal point moves forward and the entrance pupil becomes too far away, which worsens off-axis aberrations on the telephoto side, which is undesirable.Also, the ray height of the marginal ray on the telephoto side also increases, causing spherical aberration and coma aberration on the telephoto side. If the upper limit of 0 condition (5) is exceeded, the negative power of the first (21) lens group becomes large and the aberrations generated in the lens group 4 cannot be corrected completely, which is not preferable.

If the range of condition (6) is exceeded, the fluctuation of chromatic aberration becomes excessive, which is not preferable.

In the case of these three structures as well, it is effective to use an aspheric surface in the first (1) 21st lens group for the same reason as stated in the case of the lens system with the four group structure.

[Example] Next, 6 Example 1 showing each example of the variable magnification lens of the present invention f = 7 ~ 21, F / 2.8, maximum image height 42ω = 61.9 @ ~ 20.9 ° r, = 44.5660 d1= 1.2000 n+ = 1.72916
17+ = 54.68ra: 21.0144 d, = 1.9000 r, = 52.6896 d, = 5.000 On, = 1.804), (5) 8
vw = 25.43r, = -26,934
6 d4” 1.2000 ns= 1.77250
vs = 49.665 rs = 18.3715 (aspherical surface) d, = D, (variable) ra = 30.3953 do” 3.8000 n4 = 1.72916
rt = -39,8855 d7 = 1.0000 ns = 1.804),
(5) 8re=294.7054 ds=oz (variable) r, = 31.1464 d*= 5.2000 1a= 1.72916r
+o = -18,5539 d+o = 1.0000 nt = 1.804)
, (5)8r+1 =-41,5452dz=Ds(
variable) j, 2:00 (aperture) d,, = 1.8000 r+* = -6,1842 d+i = 1.0000 1a = 1.72342
rz =-13,3193 d,, =0.2000 6 = 54.68 = 25.43 =54.68 = 25.43 =37.95 r+s =-28,3790 d,, =2.800On, =1 .72916
v, =54.68r+6 =-7,0616 (aspherical surface) Aspherical coefficient (fifth surface) P = 1.0000, A4 = -0.828
39x 10-'A, = -0.64078x 10-" (16th side) P = 1.000 (1, A4 = 0.24487X
10-"A, = 0.41822x 10-' f 7 12 21 D, 31.060 12.586 2.400
D, 0.600 1). 469 8.654D
, 1.000 8.606 21.605β,
, 4=-0.31, f, /f4=0.27Σ1Axl/
h=0.008 Example 2 f=6~24, F/2.8, maximum image height 42ω=70.3'~18.2°r+=67.0952 d, =1.200On, =1.72916r , = 13
．． 4535 (aspherical surface) d, = 2.6000 r, = 24.0199 ds = 5.4000 n2 = 1.804),
(5) 8r4= -29,8765 d4= 1.200On-= 1.7725Or, =
15.5623 (Aspherical surface) d@=mouth, (variable) re” 44.8181 ds= 4.800On4= 1.72916r-=-
16,8876 dt = 1.0 (1001s = 1.8 (14), (5
)8re=-54,3473 ds=oz (variable) r*=28.3527 d*= 5.200On-= 1.72916tho
=-19,7 lens d+o = 1.0000 nt= 1.804
), (5)8rt+ =-47,6410=54.
68 = 25.43 = 49.66 = 54.68 = 25.43 :54.68 = 25.43 di, = D3 (variable) rl. = cx) (aperture) d, 2 = 2.2000 rls = -4,6298 d, 3 = 1.0000 mouth, = 1.72342
ν, =37.95r+4 =-7,13
22 d,, =2.0374 no=1.72916
v, ”=5448r+a=-4,932
1 (Aspherical surface) Aspherical coefficient (second surface) P = 1.0000, A, = 0.5544
5x 10-'A, = 0.34), (5) 60x 1
0-? (5th side) P = 1.0000 A4 = -0.63693
x 10-'A, = -0.27231x 10-'(
15th side) P=1.0000, A,=0.42528X
10""A, = 0.26975x 10-' f 6 12 24 D+ 30.180 10.932 2.400
9 D2 0.600 D3 1.000 βzs4=-0.36 Σ 1Δx/h=0.064 Example 3 f=7~28, F/2.8 2ω=62.3″~15.5°rl= 26.7650 d, = 1.100 On, = 1.69680172 =
1). 5080 (Aspherical surface) d, = 4.0000 rs = -21,9263 d, = 1.1000 r4 = 17454.2482 d, = 0.7000 rr, = 329.6909 d, = 1.7818 1”6 = -65,4528 d, = D, (variable) ry” 55.6324 n 2 = 1, 69680 na ” 1, 804), (5) 81).209
3.875 9.639 25.505 f, /f, = 0.19 0 Maximum image height = 56.49 56.49 = 25.43 d7 = 2.4 [100n4 = 1.72916r, =
-65,1509 d, = D, (variable) rs = 23.961) d- = 1.0000 ns = 1.804),
(5) 8r+o = 13.3441d,, =
5.2000 1a= 1.6968Or,, =-
104,0234 dz=03 (variable) rl2 "Flash dia" 1.6000 rlx = -5,4348 d, 3 = 1.3133 na = 1.72916
4 ν5 = 54.68 = 25.43 White = 56.49 νa = 54.68 rz = -6,3666 d, 4 = 3.4), (5) 78 rls = 12.9207 (Aspherical surface) dis =
0.8[100n,=1.7847Orye=5.
9133 dis "0.9500 rly =9.8846 1 νa "26.22 dly =2.3498 r,, knee 30.7105 Aspheric coefficient (second surface) P=1.0000, A, = A, = 0 .18308X 10-' (5th surface) P=1.0000, A4=A, = 0.57100x 10-' 7 D, 27.991 Da 0.800 Da 0.800 βI$4=-0.35.

Σ1Δxi/h = 0.033 Example 4 f=7 to 21, F/3,0 2 ω=61.4" to 20.6" rl = 49.9638 dl = 1.2084 n9 = 1.77250 n r = 1, 69680 2 4 8.728 10.083 to, 780 fw/f4= 0.25 = 49.66 0.32926x 10-' A, = 0.34804x 10-"0.36432
X 10-” A, = 0.32459 21,1)86 d3=1.2297 1”4 knee 1339.3852 d,=1.0001 r5=-258,5732 d5=1.8669 n,=1.804
), (5) 8r6 = -32,8734 d, = D, (variable) rt = 38.6070 d, = 2.8220 re = -230.6438 d, = D, (variable) r, = 24.8829 d, = 1.1) 63 1) 2 = 1.69680 Q4 = 1.72916 jl, = 1.804), (5) 8 rl.

12.2105 d. = 6.0000 1a = 1.69680
r,, =-74,5630 d,, =D, (variable) 3 ν2 White 649 = 25.43 = 54.68 = 25.43 =56.49 r, 2 = ■ (aperture) d1□ = 2. 8000 rla = -5,3756 d, 3'' 1.3696 Q, = 1.7291
6r,, =-6,2765 d,, =3.7000 r, 5=1). 3897 (Aspherical surface) d, 5” 0
．． 800On, = 1.7847゜rls = 5.6
137 d,, =0.8000 rly ”8.3643 d,7 =2.200One=1.7725Or+a
=-43,9605 Aspheric coefficient = 54.68 = 26.22 = 49.66 (second surface) P = 1.0000, A, = -0.425
09x 10-'Aa=-0.26444xlO-'
, A, = -0.25545xlO-" (15th surface) P = 1.0000, A4 = 0.31) 7
3x 10-"A, = 0.90524xlO-',
A, = O, 15060xlO-'4 f 7 12D 2
2.761 7.905D2 3.626
9.4), (5)0D3 0.8000 10
．． 072β234=-Q,36,f,/f4=o,3
1Σ1Δx1/h=0.030 Example 5 f=7~21, F/2.8 2ω=61.4°~20.96 r, = 158.1643 (Aspherical surface) d+"5.
400On, = 1.72825rz = -18,98
47 d2= 1.3540 Q2= 1.72916r
s= 14.4361 di=DI (variable) "4=23.7197 d<= 5.0000 ns= 1.72916
rs = -20.9506 d5 = 1.0000 n4 = 1.804), (5) 8 r6 = 2794.8349 F1 1 O,800 159 24,528 Maximum image height 4 rl ν2 = 28.46 =54.68 =54.68 25.43 da"Da r7= 41.5540 d," 3.2000 n5= 1.67790
v5=55.33r8==-57,797
0 da = 03 (variable) r9 = oo (aperture) d9 = 4.5548 rlo = -4,0736 d,, ” 0.8000 n6 = 1.784
70 Shiro =26.22r,, =-7,8
349 d,, =0.5306 r,□ =-17,6719 d,2 =1.900On, =1.78590
v, =44.18r+a =-5,3395 (aspherical surface) Aspherical coefficient (first surface) P=1.0000, A4=0.36146x
lO-5A, = 0.89973xlO-', A
, = -0.41081xlO-9 (13th surface) P = 1.0000, A, = 0.3615
8X 10-36 A, = 0.10982xlO-', A,
=f 7 12DI
28.945 14.886D, 0.80
0 6.834D, 1.000 9
．． 025β234=-〇,,32,f,/f
4=0.37Σ Δxl/h=0.026 Example 6 f=7~21, F/4.0 2ω=60.6'~21.8°r, = 14.3307 d, = 1.0000 n , = 1.77250
ra=9.2878 d, = 3.4000 rs=22.3754 (aspherical surface) d, = 3.6000 n,” 1.8 (14)
, (5)8r4=182.6498d,=1.000On,=1.77250rs=9
．． 6921 d-” DI (variable) 7 0.59604 2. Il! (10G ry = -94,204), (5) dt = Dz (possible t) r, = 32.2391 d8 = i, ooo.

r9= 12.4066 d+a= 5.8000 r+o =-21,7625 dl. =D3 (variable) rll = ■ (aperture) d,, =3.0000 r1□ = -5,9364 dos =1.6000 rrs = -6,8832 Aspheric coefficient P = 1.0000, A, = 0. 49237
xlO-'A, = 0.4), (5)699x 10-
'7 D, 32.632 12 21 16.134 4.507 8 n mini 1.49216 n <= 1.6 (131) ns = 1.804), (5) 8 na" 1.69680 = 60.70 = 25.43 = 55.52 = 57.50 D, (1,6001), δ93na
o, aoo 6.004βzs4= -0.5
0, fw/f4=-0.04ΣΔx/h=0.
061 Example 7 f=7~28, F/2.8 2ω=62.3'~15.6°r+=44.9788 d, = 1.0000 il, = 1.6968O
r, = 12.8493 (aspherical surface) d, = 4.0000 rl knee 20.8212 dm = 1.0000 n* = 1.69680r
4 = -858,0492 d, = 0.7000 rs = -60.4314 da" 1.8000 n, = 1.804), (
5) 8ra = -28,3267 d, =D, (Township Ory:: 92.1) 38 12.940 16.584 Maximum image height ν1 = 56.49 ν2 = 56.49 ν3 = 25.43 d , = 2.6000 r-= -52,8923 da"D*(possible t) r, = 21.7443 d, = 1.0000 r+o = 12.7098 d,, = 5.6000 r,, = -101 ,6235 d++ = Da (possible r1□ = -5,8903 d+, = 1.3000 nt = 1.729
16r1m = -6,5936 d,, =0.8000 r14 =QQ (aperture) d,, =5.0758 rrs =9.7260 (aspherical surface) dos = 1.0000 n*= 1.784
7Or+a: 5.243G d,, = 0.9000 rlt = 8.2226 n, = 1.72916 n mini 1.804), (5) 8 na = 1.69680 = 54.68 Tomi 25.43 = 56. 49 = 54.68 = 26.22 Q 0 d+y = 2.4000 ns = 1.772
50ve = 49.66r+8 = 16
1.8048 Aspheric coefficient (second surface) P=1.0000, A4=-0.24), (5
)60XlO-'Ai=-0.4231)X10-'
, As=0.50898X 10-” (15th
surface) P = 1.0000, A = 0.30929X
10-3A6=0.18672X 10-',
A6=-0.1)931X 10-'f 7
14 28 D, 27.898 7.991 0.600
D20.600 10.349 0.600D,
1.600 1). 758 28.8986.34=
-0.38, f, /f, = 0.20ΣΔx /h = 0
．． 027 Example 8 f=7~21, F/4.0, maximum image height 42ω=61.5'~22.0' r, = 15.8324 d, 1.000 On, = 1.77250 v,
=49.661 r2=9.3824 d2= 3.4000 r3= 28.881) (Aspherical surface) d 3” 3
, 600 On 2= ] , 804), (5) 8r
4= -71,9406 d4= 1.0000 (13= 1.7725
0 ['5 = 12.5437 d5 = D, I cute) r, = 39.1309 d a ” 2, 8000 n 4 = 1,
6031) rr=-59,5657 d, =D, (possible T) ra=39.8143 d8= 1.000On, = 1.804), (5) 8
re=13.3682 d-=5.8000 na=1.6968O
r,, =-21,5480 d,. =D3 (possible t) r++ =-6,14), (5)5 dll = 1.6000 nt = 1.49216
2 = 25 49.66 = 60.70 = 25.43 = 55.52 = 57.50 r+2 = -6,7778 d1□ = 1.0000 r,,::OO (aperture) Aspheric coefficient P = 1. 0000, A4=A6=0.5
5529x 10-' 7 D, 33.24), (5) D20.600 D, 1.600 βxi4=-o, 47°ΣΔx/h=0.044 Example 9 f=7~21 2ω=61.3゜r, = 16.8825 d, = 1.0000 r2 = 7.4074 d, = 4.6000 rs = -38,8946 (aspherical surface) 3 F/4.0 n+ = 1.72916 2 16.473 12 .040 6.938 f, /f4= -0.01 ~ 21.8" 0.22391x 10-' 1 4.4), (5) 8 12.967 17.965 Maximum image height 4 = 54.68 ds ” 1.000 [1nz= 1.7?250
ν2 = 49.66r4 = 28.4674 d4 = 2.4000 n3 = 1.804), (
5) 8 V3 = 25.43r5 = -101
,6261 (aspherical surface) d5=D, (variable) ra=26.6577 d, =2.800On, =1.65844 1/4
=50.86r, =-661,1244 d, =D, (curtain) r, = 24.5819 (aspherical) da = 1.0
000 1s= 1.804), (5)8
v5=25.43re=IO,9050d,=6. Rolo 00 n, = 1.69680
V6 =56.49r+a =-41,2
706 dl. = 03 (town t) r1) = (capital) (aperture) Aspheric coefficient (3rd surface) P = 1.0000, A, = 0.1063
3X 1O-3A, = 0.14749x 10-' 4 (5th surface) P = 1.0000, A4 = 0.
39726x 10-'A6=-0.59156x 1
0-' (8th side) P = 1.0000, A4 = -0.953
59x 1O-5A, = 0.13027x 1O-6 f 7 12
21D, 29.833 13.843 2
．． 994D20.600 10.846 10.210
D3 0.800 6.544 18
．． 029β23 = -0.45, Σ 8x /h =
0.053 but rl, r2. ... is the radius of curvature of each lens surface, dl, d2. . . . is the wall thickness and air spacing of each lens, +1 + +n2. -... is the refractive index of each lens. C2. ... is the Atsube number of each lens.

Example 1 has the lens configuration shown in FIG. 1, in which the 1st) 21st group is a negative lens and a cemented lens of a positive lens and a negative lens, the 2nd lens group is a cemented lens of a positive lens and a negative lens, and the 3rd lens group is a cemented lens of a positive lens and a negative lens. is a cemented lens of a positive lens and a negative lens, and the fourth lens is composed of a negative lens and an Ellen 5 lens. Further, the diaphragm is arranged on the object side of the fourth lens group. The aspheric surfaces are used for the most image-side surface of the 21st lens group (first) and the most image-side surface of the fourth lens group. When changing the magnification, the second lens group and the third lens group move, and the rest remain fixed.

The aberration conditions at wide, standard, and telephoto for the object point at infinity in Example 1 are as follows: The 10th lens group is a negative lens and a cemented lens of a positive lens and a negative lens, and the 2nd lens group is a cemented lens of a positive lens and a negative lens. The third lens group is composed of a cemented lens of a positive lens and a negative lens, and the fourth lens group is composed of a cemented lens of a negative lens and a positive lens.The aperture is arranged on the object side of the fourth lens group. Further, aspherical surfaces are used for the second surface and the surface closest to the image side of the first lens group 21, and the surface closest to the image side of the fourth lens group, respectively. The angle of view at the wide end of this embodiment is as wide as 70.3°.

The aberration situations in wide, standard, and telephoto for the object point at infinity in Example 2 are as shown in FIGS. 13, 14, and 15, respectively.

Embodiment 3 has a lens configuration shown in FIG.
The lens group consists of one positive lens, the third lens group consists of a cemented lens of a negative lens and a positive lens, and the fourth lens group consists of three lenses: a negative lens, a negative lens, and a positive lens.The aperture is the fourth lens group. It is placed on the object side of the lens group. Also, the aspherical surface is the first
) They are used for the second surface of the 21st lens group and the third surface of the fourth lens group. The lens closest to the object in the fourth lens group is a meniscus lens with a concave surface facing the object side and having almost no power. This lens allows axial aberrations to be controlled without changing off-axis aberrations, and is effective in correcting axial aberrations over the entire zoom range. Furthermore, the height of the axial ray can be increased, which is also effective for lengthening the back focus. The variable power ratio of this embodiment is 4, which is large.

The aberration situations in wide, standard, and telephoto with respect to an object point at infinity in this embodiment are as shown in FIGS. 16, 17, and 18, respectively.

Example 4 has a lens configuration shown in FIG.
The 21st group consists of three lenses: a negative lens, a negative lens, a positive lens, and a second lens.
The lens group consists of one positive lens, the third lens group is a cemented lens of a negative lens and a positive lens, and the fourth lens group consists of three lenses: a negative lens, a negative lens, and a positive lens.The aperture is in the fourth lens group. is on the object side. The aspherical surfaces are used for the second surface of the first lens group (21) and the third surface of the fourth lens group, respectively. The meniscus lens on the object side of the fourth lens group has the same effect as that of the third embodiment. The F number of this lens system is 2.0
It has a large diameter.

The aberration situations in wide, standard, and telephoto for the object point at infinity in Example 4 are shown in Figures 19 and 20, respectively.
As shown in FIG.

Example 5 has the lens configuration shown in FIG. 5, where the 1st) 21st lens group is a cemented lens of a positive lens and a negative lens, the 2nd lens group is a cemented lens of a positive lens and a negative lens, and the 3rd lens group is a positive lens. The fourth lens group consists of two lenses, a negative lens and a positive lens, and the aperture is located on the object side of the fourth lens group. The aspheric surfaces are used for the surface closest to the object side of the first lens group (21) and the surface closest to the image side of the fourth lens group, respectively. This lens system has seven lenses, which is a very small number of lenses.

The aberration situations in wide, standard, and telephoto for the object point at infinity in this example are shown in Fig. 25, Fig. 23, and Fig. 2, respectively.
As shown in Figure 4.

Example 6 has a lens configuration shown in FIG. 6, in which the 1st) 21st lens group is a negative lens and a cemented lens of a positive lens and a negative lens, the 2nd lens group is a single positive lens, and the 3rd lens group is a negative lens. The fourth lens group, which is a cemented lens of positive lenses, is composed of one negative lens, and the aperture is located on the object side of the fourth lens group. The aspherical surface is used for the third surface of the 21st group (first). This example is
Unlike the previous embodiments, the fourth lens group has very weak negative power. By weakening the power of the fourth lens group, the aberrations generated in this group can be reduced, and the number of lenses in the fourth lens group can be reduced. be.

The aberration situations in wide, standard, and telephoto with respect to an object point at infinity in this embodiment are as shown in FIGS. 25, 26, and 27, respectively.

Example 7 is as shown in FIG. The cemented lens, the fourth lens group, is composed of three lenses: a negative lens, a negative lens, and a positive lens, and the aperture is located in the fourth lens group. The lens closest to the object in the fourth lens group is a meniscus lens with almost no power, with its concave surface facing the object side. This lens also has the same effect as the meniscus lens of Example 3. This embodiment is a lens system with a very large variable power ratio of 4.

The aberration situations in wide, standard, and telephoto with respect to an object point at infinity in this embodiment are as shown in FIGS. 28, 29, and 30, respectively.

Example 8 has a lens configuration shown in FIG. 8, in which the 1st) 21st lens group is a negative lens and a tangent of a positive lens and a negative lens, the 2nd lens group is a single positive lens, and the 3rd lens group is a negative lens. and a positive lens, and the fourth lens group is composed of one negative lens, and the aperture is located on the image side of the fourth lens group. The aspherical surface is used for the third surface of the 21st group (first). In this embodiment, the fourth lens group has very weak negative power. By weakening the power of the fourth lens group, the aberrations generated in this group can be reduced (possibly, the number of elements in the fourth lens group can be reduced, and it is composed of only one lens. This lens also has the same structure as in Example 3. It is a meniscus lens.

The aberration situations in wide, standard, and telephoto with respect to an object point at infinity in this embodiment are as shown in FIGS. 31, 32, and 33, respectively.

Embodiment 9 has the configuration shown in FIG. 9, and the entire lens system consists of three groups. The 1st) 21st lens group is composed of a negative lens and a cemented lens of a negative lens and a positive lens, the second lens group is composed of one positive lens, and the third lens group is composed of a cemented lens of a negative lens and a positive lens. The aspherical surfaces are used for the third surface of the 21st lens group, the surface closest to the image side, and the object side surface of the third lens group. By omitting the fourth lens group and configuring the entire lens system with three groups as in Example 1, the number of lenses can be reduced.

The aberration situations in wide, standard, and telephoto with respect to an object point at infinity in this embodiment are as shown in FIGS. 34, 35, and 36, respectively.

[Effects of the Invention] The variable power lens of the present invention has an angle of view at the wide end of about 60° or more, a variable power ratio of about 3 to 4, and an aperture ratio of F/2.0 to F/4.
．． It is a lens system with 0 degrees, a fixed aperture, a simple lens frame, and the F number does not change when changing the magnification.

[Brief explanation of the drawing]

1 to 9 show Example 1 of the variable power lens of the present invention, respectively.
10 to 12 are aberration curve diagrams of Example 1, FIGS. 13 to 15 are aberration curve diagrams of Example 2, and FIGS. 16 to 18 are sectional views of Example 9. 3, FIGS. 19 to 21 are aberration curve diagrams of Example 4, and FIGS. 22 to 24 are aberration curve diagrams of Example 5 of the present invention,
252 to 27 are aberration curve diagrams of Example 6, FIG. 28 to 30 are aberration curve diagrams of Example 7, and FIGS. 31 to 33.
The figure is an aberration curve diagram of Example 8, FIGS. 34 to 36 are aberration curve diagrams of Example 9, FIG. 37 is a diagram showing the configuration when the second lens group and subsequent lens groups are made into one group, and FIG. The figure is a diagram showing the basic configuration of the present invention.

Claims (1)

[Claims] (1) In order from the object side, a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with positive refractive power, and a third lens group with positive refractive power. This lens system consists of four lens groups and an aperture located behind the third lens group, and performs magnification by changing the distance between each lens group.
A variable magnification lens in which the lens group, the fourth lens group, and the aperture position are fixed. (2) The variable magnification lens according to claim (1), wherein the following conditions (1), (2), and (3) are satisfied. (1)-0.6<β_2_3_4<-0.2(2)-0
．． 1<f_w/f_4<0.5 (3) νn<50 where β_2_3_4 is the combined magnification of the combined system of the second lens group, third lens group, and fourth lens group at the wide end,
f_w is the focal length of the entire system at the wide end, f_4 is the focal length of the fourth lens group, and νn is the Abbe number of at least one negative lens included in the second and third lens groups. (3) The variable magnification lens according to claim (1) or (2), wherein at least one surface of the first lens group is an aspheric surface whose negative refractive power decreases as the distance from the optical axis increases. . (4) In order from the object side, each lens group consists of a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with positive refractive power, and an aperture. A variable power lens is a lens system that performs power change by changing the distance between the lenses, and is characterized in that the first lens group and the aperture position are fixed during power change. (5) The variable power lens according to claim (4), which satisfies the following conditions (4) and (5). (5) -0.6<β_2_3<-0.2 (6) νn<50 where β_2_3 is the imaging magnification of the composite system of the second and third lens groups, and νn is the second and third lens groups. This is the Abbe number of at least one negative lens included in the lens group.