JPH04304409A - zoom lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens. Among them, zoom tube lenses for microscopes, etc.
The present invention relates to a zoom lens in which the entrance pupil is located closer to the object side than the first surface of the lens, and the variation in the exit pupil due to zooming is extremely small.

0002

2. Description of the Related Art A conventional zoom lens of this type is disclosed in Japanese Patent Publication No. 2-54925, for example. This applies to a zoom lens that consists of lens groups having positive, negative, negative, and positive refractive powers, or lens groups having positive, negative, and positive refractive powers in order from the object side, and both the second lens group and the third lens group. The lens group was moved. or,
A zoom lens having a four-group structure that is widely used as a photographic zoom lens is disclosed in, for example, Japanese Patent Laid-Open No. 2-66509. This is because the fourth lens group moves toward the object side when changing power from the wide-angle side to the telephoto side.

0003

[Problems to be Solved by the Invention] In the conventional technology as described above, when the entrance pupil is located closer to the object side than the first surface of the lens closest to the object side, the exit pupil changes due to zooming. When used as a zoom tube lens, the position of the eyepoint of the eyepiece changes due to zooming. Furthermore, when a relay optical system is used by inserting it after a zoom tube lens, the entrance pupil entering the relay optical system changes due to zooming, so there is a problem that the configuration of the relay optical system becomes complicated.

[0004] In view of these conventional problems, the present invention
To provide a zoom lens whose entrance pupil is located closer to the object side than the first surface of the lens, and whose exit pupil changes due to zooming are extremely small.

[0005]

Means for Solving the Problems The present invention provides, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. and a zoom lens including a fourth lens group having positive refractive power, in which the fourth lens group moves toward the image side during zooming from the wide-angle end to the telephoto end, and the first lens group and the second lens group The structure is such that the distance between the lenses increases.

Based on the above basic configuration, the axial lens distance between the first lens group and the second lens group at the telephoto end is d12T, and the distance between the first lens group and the second lens group at the wide-angle end is d12T.
When the axial lens distance between the lens groups is d12W, the back focus at the wide-angle end is BfW, and the back focus at the telephoto end is BfT, then 0<(d12T - d12W)/(BfW
It is desirable to satisfy the following conditional expressions: -BfT)≦1 and BfW>BfT. Furthermore, when the magnification of the second lens group at the wide-angle end is β2w, β2w>1, or β
It is more desirable to satisfy one of the following conditional expressions: 2w≦−1.

[0007]

[Operation] As shown in FIG. 1, for example, the zoom lens of the present invention includes a first objective lens O1 that converts the light beam from the object M into a parallel light beam, and condenses the parallel light beam to form an aerial image (intermediate image).
The objective lens O is composed of a second objective lens O2 that forms an eye point position E. P. In a microscope having an eyepiece E for magnified observation, the second objective lens O2 is made into a zoom lens. Here, the second objective lens O2
When converting into a zoom lens, the second objective lens O
2. If the focal length of lens 2 is simply changed, the positional change between the entrance pupil and the exit pupil of the objective lens O, that is, the fluctuation of the exit pupil of the objective lens O, will be large during zooming.
As a result, the microscope eye point E. P. The position of the microscope changes significantly, which not only makes it difficult to observe the object M but also causes deterioration of the optical performance of the microscope itself. Therefore, the present invention is based on a configuration in which the second objective lens O2 (hereinafter simply referred to as a zoom lens) includes four lens groups: positive, negative, positive, and positive. In the present invention, the fourth lens group moves toward the image side when changing power from the wide-angle end to the telephoto end, and the lens distance between the first lens group and the second lens group increases. This method suppresses fluctuations in the exit pupil due to zooming to an extremely small level while performing zooming.

The conditions under which there is no change in the exit pupil due to zooming will be described in detail below. FIG. 2 shows the refractive power arrangement of the zoom lens. (a) of FIG. 2 is a refractive power arrangement diagram when the focal length of the zoom lens is f at the wide-angle end, and (a) of FIG.
b) is a refractive power arrangement diagram when the zoom lens focal length is fz at the telephoto end. In the zoom lens at the wide-angle end in Fig. 2(a), H0 is the front principal point, H1 is the rear principal point, S is the principal point interval, β is the pupil magnification (D1 /D0),
f is the focal length of the zoom lens at the wide-angle end, D0 is the distance from the front principal point to the entrance pupil, and D1 is the distance from the rear principal point to the exit pupil. In the zoom lens at the telephoto end in Fig. 2(b), H0' is the front principal point, H1' is the rear principal point, S' is the principal point interval, and β' is the pupil magnification (D1'/
D0 ), Z is the variable magnification ratio (zoom ratio), Zf is the focal length of the zoom lens at the telephoto end, D0' is the distance from the front principal point to the entrance pupil, and D1' is the distance from the rear principal point to the exit pupil. Show distance.

Here, the condition for the position B of the exit pupil to be equal to the position A of the entrance pupil at any zoom magnification is that the distance between them is constant. The following equation is obtained. -D0+S+D1=-D0'+S'+D1'
(1) Also, (a) and (
b) As is clearer, the following equation is obtained. D1'=D1+Zf-f
(2) From the lens imaging formula, in the zoom lens at the telephoto end shown in FIG. 2(b), the following pupil imaging relationship holds true. 1/D1'=1/Zf+1/D0'
(3) Then, by substituting equation (2) into equation (3) and rearranging, the following equation is obtained. D0'=Zf{D1+f(Z-1)}/(f-D1
) (4) Also, the magnification β' of the pupil at the telephoto end is
The relationship between D0' and D1' is expressed by the following equation. β' = D1'/D0'
(5) Therefore, by substituting equation (2) and equation (4) into equation (5) and rearranging, the following equation can be derived. β' = {D1+Zf-f}/[Zf{D1+f(
Z-1)}/(f-D1)] =(f-D
1)/Zf = [1/Z]・[(f-D1)/f]
(6) Here, according to Newton's imaging formula, β = (f - D1) / f holds true for the zoom lens at the wide-angle end shown in (a) of Fig.
) becomes as shown in the following equations (7) and (7). β' = β/Z
(7)
β'/β=1/Z
(7')
Equation (7') shows that the ratio between the zoom ratio and the pupil magnification is inversely proportional.

From the image formation formula of the lens, the following equation can be obtained for the zoom lens at the wide-angle end shown in FIG. 2(a). 1/D1=1/f+1/D0
(8) D1=f
D0/(f+D0)
(8') Here, equation (2), equation (4
) and equation (8') into equation (1) and rearranging, the following equation is obtained. S'-S=(Z-1) {D0(Z+1)+f(Z-
1)}(9) Equation (9) is a condition for the positions of the exit pupils to be equal at any zoom ratio Z. In the present invention, we are considering the case where the entrance pupil is a certain distance from the first surface of the zoom lens toward the object side, so here we will consider the case where the distance from the entrance pupil to the front principal point H0 is longer than the focal length at the wide-angle end. think. In other words, D0≦−f
(
Considering case 10), by substituting equation (10) into equation (9) and rearranging, the following equation is derived. S'-S≦-2f(Z-1)<0
(11) However, f>0,
Z>0. From equations (10) and (11) above, if the entrance pupil is more than f (focal length at the wide-angle end) from the front principal point H0 to the object side, the telephoto It can be understood that the principal point distance S' at the end must be shorter than the principal point distance S at the wide-angle end. As an example, if we consider the case where the focal length f at the wide-angle end is 200, the zoom ratio is 2, and the distance D0 from the entrance pupil to the front principal point H0 = -250, then from the above equation (9), S'- S≦−550. That is, in this case, in order to keep the exit pupil unchanged, the principal point distance S' at the telephoto end must be 5
It needs to be shortened by 50.

Further, the following equation is obtained from equation (7). D1
'/D0'=(1/Z)(D1/D0)D0/D0'=
(1/Z) (D1/D1') Z>1, and as is clear from FIGS. 1 and 2, D1'>D1, so D0/D0'<1. At this time, since D0'<0 and D0<0, the following equation is obtained. D0>D0'
(1
2) Furthermore, since D0'<0 and D0<0 are both negative numbers, the following equation is obtained. |D0|<|D0'|
(13) Formula (
12) From entrance pupil position A to front principal point H at zoom ratio Z
The distance to 0' must be longer than that at the wide-angle end. In other words, when changing the magnification from wide-angle to telephoto,
Indicates that the position of the front principal point must be moved toward the image direction.

As mentioned above, the condition that the exit pupil does not change due to zooming is such that when zooming from the wide-angle end to the telephoto end, the distance between the principal points of the optical system is reduced and the front principal point position is moved toward the image direction. That's true.

As described above, from the viewpoint of the conditions for suppressing pupil fluctuations, the present invention provides a zoom lens including four lens groups having positive, negative, positive, and positive refractive powers. By increasing the distance between the lens group and the second lens group, zooming is performed while decreasing the principal point distance, and by moving the fourth lens group in the image direction, the front principal point position is moved in the image direction. I found out that it is possible. In other words, in the present invention, when changing the magnification from the wide-angle end to the telephoto end,
The principle is to suppress fluctuations in the exit pupil while changing the magnification by using a new magnification changing method that moves the fourth lens group toward the image side while increasing the distance between the first and second lens groups. This made it possible. Further, it is desirable that the zoom lens according to the present invention satisfies the following condition (101) based on the variable magnification system as just described. 0<(d12T −d12W)/(BfW
−BfT )≦1, BfW >BfT

(10
1) However, d12W: On-axis lens distance between the first and second lens groups at the wide-angle end d12T: On-axis lens distance between the first and second lens groups at the telephoto end BfW: Wide-angle end Back focus BfT of the zoom lens at: Back focus of the zoom lens at the telephoto end. If the upper limit of equation (101) is exceeded, the amount of change in the axial lens group spacing between the first and second lens groups will increase when zooming from the wide-angle end to the telephoto end, resulting in large power changes. It is advantageous to obtain a zoom ratio. However, the amount of movement of the fourth lens group toward the image side becomes too small compared to the amount of increase in the distance between the axial lens groups of the first and second lens groups, so the distance between the principal points of the zoom lens is compared to the amount of decrease. , the amount of movement of the front principal point of the zoom lens toward the image side is too small. As a result, it becomes difficult to correct variations in the exit pupil. On the other hand, when the lower limit of equation (101) is exceeded, there is no increase in the axial lens group spacing between the first lens group and the second lens group when zooming from the wide-angle end to the telephoto end. For this reason, it is not only difficult to obtain a sufficient variable magnification ratio (zoom ratio), but also it is not possible to make the interval between principal points at the telephoto end sufficiently smaller than at the wide-angle end. As a result of this,
It becomes difficult to suppress fluctuations in the exit pupil.

Further, in the present invention, when the magnification of the second lens group at the wide-angle end is β2w, it is preferable that the following condition is satisfied. β2w>1, β2w≦−1
(
102) When the range of equation (102) is exceeded, the following occurs. When −1<β2w<0, the bounce of off-axis rays by the second lens group becomes large, and the diameters of the third lens group and the fourth lens group become excessively large. As a result, it becomes difficult to make the lens system more compact. 0≦β2w≦
1, a real image is formed between the first lens group and the second lens group, and a re-imaging system must be constructed from the second and subsequent lens groups. As a result, the total length of the optical system becomes extremely long.

Furthermore, the zoom lens of the present invention has a special movement mode in which the fourth lens group moves in the image direction when zooming from the wide-angle end to the telephoto end, as described above. When the magnification of the fourth lens group is β4w, it is preferable that the following condition is satisfied. −1<β4w<1
(103) When exceeding the range of equation (103), when zooming from the wide-angle end to the telephoto end, the fourth lens group moves toward the object, resulting in a movement mode different from that of the present invention, so the exit pupil due to zooming fluctuation becomes extremely large.

[0016]

By the way, in order to secure the back focus by reducing the amount of movement of the fourth lens group in the image direction when zooming the zoom lens from the wide-angle end to the telephoto end, it is necessary to
This can be achieved by moving the lens group toward the object. On the other hand, when securing the back focus by fixing the first lens group to the image plane, it is desirable to satisfy the following equation. β4w<1.8-0.8Z (
104) If this condition is not satisfied, it will be difficult to secure a sufficient back focus at the telephoto end, and if you try to forcefully secure it, the configuration of the fourth lens group will have to be complicated. Note that when zooming the zoom lens of the present invention from the wide-angle end to the telephoto end, it is desirable to move the third lens group in order to more completely suppress fluctuations in the exit pupil.

[0018]

[Example] Next, an example will be explained. Lens configuration diagrams of the first to sixth embodiments according to the present invention are shown in FIGS. 3 to 8 in order, and (a) in FIGS. (b) shows the lens configuration at an intermediate focal length state, and (c) shows the lens configuration at the telephoto end (longest focal length state). With the zoom lens of each example,
As can be seen from the lens configuration diagrams in FIGS. 3 to 8, in order from the object side, the first lens group G1 has a positive refractive power, the second lens group G2 has a negative refractive power, and the third lens group has a positive refractive power.
Lens group G3 and fourth lens group G4 having positive refractive power
When zooming from the wide-angle end to the telephoto end, the axial air distance between the closest image side of the first lens group G1 and the closest object side of the second lens group G2 is increased, and the second lens The fourth lens group G4 is moved toward the image side while increasing the axial air distance between the closest image side of the group G2 and the closest object side of the fourth lens group G4. Such a movement mode makes it possible in principle to suppress fluctuations in the exit pupil in a well-balanced manner while changing the magnification. Next, we will look at the lens configuration and movement form for each example. First, in the first embodiment,
The first lens group G1 with positive refractive power is composed of a biconvex positive lens and a negative meniscus lens cemented to the positive lens with a convex surface facing the image side, and the second lens group G2 with negative refractive power is composed of , consists of a positive meniscus lens with a convex surface facing the image side, a negative lens cemented to the positive meniscus lens, and a biconcave negative lens. Then, the third lens group G3 and the fourth lens group G
4 is composed of a biconvex positive lens and a negative lens cemented to the positive lens. The movement mode of the first embodiment based on the above lens configuration is such that when changing the magnification from the wide-angle end to the telephoto end, the first lens group G1 and the third lens group G3 are fixed to the image plane, and the first lens group G3 is fixed to the image plane. The second lens group G2 and the fourth lens group G4 are moved toward the image side while increasing the axial air distance between the closest image side of the second lens group G2 and the closest object side of the fourth lens group G4. As is clear from FIG. 3, the entrance pupil is 15 mm from the first surface of the first lens group toward the object.
The exit pupil is f=200, 3 from the image plane.
00, 400mm, respectively 312.5, 403.
6.323.1 mm, and it can be seen that fluctuations in the exit pupil when changing magnification from the wide-angle end to the telephoto end are suppressed.

The specifications are as follows. However, the leftmost number represents the order from the object side, r is the radius of curvature of the lens surface,
d is the distance between lens surfaces, νd is the Abbe number, and nd is the d-line (
λ=587.6n), f is the focal length of the entire system. Note that in each of the examples described below, the values of specifications are shown in the same format as in this example. Specifications (1st example) No r d
νd nd 1 105.572
4 6.0000 67.87 1.59
31892 -60.2393 2.5
000 35.19 1.7495013
-168.7267 d3
1.0000004 -116.658
9 3.5000 23.01 1.
8607415 -44.6231 1
．． 6000 58.90 1.5182306
200.6085 2.4000
1.0000007 -188.2
477 1.6000 55.60
1.6968008 50.9322
d8 1.0000009
150.9884 6.5000
60.14 1.62040910 -130.
0730 3.0000 23.01
1.86074111 -265.8200
d11 1.0000001
2 193.7822 8.0000
67.87 1.59318913 -
81.7527 3.0000 23.0
1 1.86074114 -121.730
9 B. f. 1.0
00000 Distance between surfaces (1st example) f=200
300 400
d3 44.15413
68.83672 74.3897
8 d8
33.79640 9.11381
3.56075 d11
30.66645 101.04
194 150.90573 B
．． f. 159.48675
89.11127 39.24747
Pupil magnification -1.562
-1.345 -0.808
Condition corresponding value (first example)
(d12T −d12W )/(BfW −BfT
)=0.251 β2w=-1.54 β4w=-0.1

Next, a second embodiment will be explained with reference to FIG. FIG. 4 is a lens arrangement diagram of the second embodiment. Description of points that are the same as or similar to the first embodiment will be omitted. The first lens group is fixed, the second lens group is movable, and the third lens group is movable.
The fourth lens group moves. The entrance pupil is the first lens of the first lens group.
The position is 150 mm from the surface toward the object, and the exit pupil is 312 mm from the image plane at f = 200, 300, and 400 mm, respectively.
．． 5, 314.7, and 313.0 mm. Third
The first correction is for changes in the exit pupil due to movement of the lens group.
It is implemented more strictly than the example.

The specifications are as follows. Specifications (Second Example) No r d
νd nd 1 105.572
4 6.0000 67.87 1.59
31892 -60.2393 2.5
000 35.19 1.7495013
-168.7267 d3
1.0000004 -116.658
9 3.5000 23.01 1.
8607415 -44.6231 1
．． 6000 58.90 1.5182306
200.6085 2.4000
1.0000007 -188.2
477 1.6000 55.60
1.6968008 50.9322
d8 1.0000009
150.9884 6.5000
60.14 1.62040910 -130.
0730 3.0000 23.01
1.86074111 -265.8200
d11 1.0000001
2 193.7822 8.0000
67.87 1.59318913 -
81.7527 3.0000 23.0
1 1.86074114 -121.730
9 B. f. 1.0
00000 Distance between surfaces (2nd example) f=200
300 400
d3 44.15413
70.94020 74.7316
8 d8
33.79640 10.09640
6.79648 d11
30.66645 100.04
722 149.62641 B
．． f. 159.48675
78.01988 36.95930
Pupil magnification -1.562
-1.049 -0.783
Condition corresponding value (second example)
(d12T −d12W )/(BfW −BfT
)=0.249 β2w=-1.54 β4w=-0.1

Next, a third embodiment will be explained with reference to FIG. FIG. 5 is a lens arrangement diagram of the third embodiment. Description of points that are the same as or similar to the first embodiment will be omitted. The first lens group is fixed, the second lens group is movable, and the third lens group is movable.
The fourth lens group moves, and this embodiment has the same movement form as the second embodiment. The entrance pupil is located 150 mm from the first surface of the first lens group in the object direction, and the exit pupil is located at f= from the image plane.
310.3 for 200, 300, and 400mm respectively
, 309.4, and 309.8. By moving the third lens group, correction for changes in the exit pupil is performed more strictly than in the first embodiment.

The specifications are as follows. Specifications (3rd example) No r d
νd nd 1 105.572
4 6.0000 67.87 1.59
31892 -60.2393 2.5
000 35.19 1.7495013
-168.7267 d3
1.0000004 -116.658
9 3.5000 23.01 1.
8607415 -44.6231 1
．． 6000 58.90 1.5182306
200.6085 2.4000
1.0000007 -188.2
477 1.6000 55.60
1.6968008 75.9411
d8 1.0000009
200.0000 6.5000
60.14 1.62040910 -130.
0730 3.0000 23.01
1.86074111 -369.7622
d11 1.0000001
2 193.7822 8.0000
67.87 1.59318913 -
81.7527 3.0000 23.0
1 1.86074114 -122.135
3 B. f. 1.0
00000 Distance between surfaces (3rd example) f=200
300 400
d3 46.98934
68.07221 69.3155
8 d8
38.81539 18.81539
3.81539 d11
30.30581 106.85
922 161.42866 B
．． f. 125.67279
48.03649 7.22368
Pupil magnification -1.549
-1.031 -0.775
Condition corresponding value (third example)
(d12T −d12W )/(BfW −BfT
)=0.188 β2w=-4.33 β4w= 0.133

Next, a fourth embodiment will be explained with reference to FIG. FIG. 6 is a lens arrangement diagram of the fourth embodiment. Description of points that are the same as or similar to the first embodiment will be omitted. The first lens group is fixed, the second lens group is movable, and the third lens group is movable.
The fourth lens group moves. The entrance pupil is the first lens of the first lens group.
The position is 150 mm from the surface toward the object, and the exit pupil is 293 f = 200, 300, and 400 mm from the image plane, respectively.
．． They are located at positions 0, 295.2, and 296.4. By moving the third lens group, correction for changes in the exit pupil is performed more strictly than in the first embodiment.

The specifications are as follows. Specifications (4th example) No r d
νd nd 1 105.572
4 6.0000 67.87 1.5
931892 -60.2393 2.
5000 35.19 1.7495013
-168.7267 d3
1.0000004 -116.65
89 3.5000 23.01 1
．． 8607415 -44.6231
1.6000 58.90 1.5182306
200.6085 2.4000
1.0000007 -188.
2477 1.6000 55.60
1.6968008 37.5395
d8 1.000000
9 150.9884 6.5000
60.14 1.62040910 -130
．． 0730 3.0000 23.01
1.86074111 -173.8523
d11 1.000000
13 193.7822 8.0000
67.87 1.59318914
-81.7527 3.0000 23.
01 1.86074115 -113.62
89 B. f. 1.
000000 Distance between surfaces (
Fourth embodiment) f=200
300 400
d3 46.39362
74.96337 80.184
32 d8
28.15501 16.15501
4.65501 d11
31.38065 92.7
1984 136.52271
B. f. 175.56714
97.65820 60.14336
Pupil magnification -1.463
-0.984 -0.741
Condition corresponding value (4th example)
(d12T −d12W )/(BfW −Bf
T )=0.293 β2w=-1 β4w=-0.297

Next, a fifth embodiment will be explained with reference to FIG. FIG. 7 is a lens arrangement diagram of the fifth embodiment. Description of points that are the same as or similar to the first embodiment will be omitted. The first lens group, the second lens group, the third lens group, and the fourth lens group all move during zooming. The entrance pupil is located 150 mm from the first surface of the first lens group in the object direction, and the exit pupil is located at f= from the image plane.
312.6 respectively for 200, 300, and 400mm
, 303.0, and 288.5. The back focus Bf at the telephoto end is 50.1 mm, which is longer due to the movement of the first lens group toward the object side compared to the back focus Bf of the second embodiment.

The specifications are as follows. Specifications (fifth example) No r d
νd nd 1 105.572
4 6.0000 67.87 1.59
31892 -60.2393 2.5
000 35.19 1.7495013
-168.7267 d3
1.0000004 -116.658
9 3.5000 23.01 1.
8607415 -44.6231 1
．． 6000 58.90 1.5182306
200.6085 2.4000
1.0000007 -188.2
477 1.6000 55.60
1.6968008 50.9322
d8 1.0000009
150.9884 6.5000
60.14 1.62040910 -130.
0730 3.0000 23.01
1.86074111 -265.8208
d11 1.0000001
2 193.7822 8.0000
67.87 1.59318913 -
81.7527 3.0000 23.0
1 1.86074114 -121.730
9 B. f. 1.0
00000 Distance between surfaces (fifth example) f=200
300 400
d3 44.15413
68.80962 72.4851
9 d8
33.79640 17.79640
6.79640 d11
30.66645 110.38
910 163.46280 B
．． f. 159.48675
86.80325 50.05353
Pupil magnification -1.562
-0.961 -0.690
Condition corresponding value (5th example)
(d12T −d12W )/(BfW −BfT
)=0.259 β2w=-1.54 β4w=-0.1

Next, a sixth embodiment will be explained with reference to FIG. FIG. 8 is a lens arrangement diagram of the sixth embodiment. Description of points that are the same as or similar to the first embodiment will be omitted. During zooming, the first lens group is fixed, and the second, third, and fourth lens groups move. The entrance pupil is located 150 mm from the first surface of the first lens group in the object direction, and the exit pupil is located at f = 200, 300, and 400 mm from the image plane, respectively.
They are located at 2.3, 332.4, and 332.4. By moving the third lens group in the image direction, correction for exit pupil fluctuations becomes more precise.

The specifications are as follows. Specifications (6th example) No r d
νd nd 1 105.572
4 6.0000 67.87 1.59
31892 -60.2393 2.5
000 35.19 1.7495013
-168.7267 d3
1.0000004 -116.658
9 3.5000 23.01 1.
8607415 -44.6231 1
．． 6000 58.90 1.5182306
200.6085 2.4000
1.0000007 -188.2
477 1.6000 55.60
1.6968008 50.9322
d8 1.0000009
150.9884 6.5000
60.14 1.62040910 -130.
0730 3.0000 23.01
1.86074111 -236.0883
d11 1.0000001
2 193.7822 8.0000
67.87 1.59318913 -
81.7527 3.0000 23.0
1 1.86074114 -124.156
5 B. f. 1.0
00000 Distance between surfaces (6th example) f=200
300 400
d3 44.17310
70.90362 74.2434
4 d8
31.23069 17.65277
5.58476 d11
31.01067 100.78
910 150.47905 B
．． f. 155.19381
72.26278 31.30183
Pupil magnification -1.661
-1.108 -0.831
Condition corresponding value (6th example)
(d12T −d12W )/(BfW −BfT
)=0.243 β2w=-1.54 β4w=-0.0497

[0030]

According to the present invention, a zoom lens is obtained in which the entrance pupil is located closer to the object side than the first surface of the lens, and the variation in the exit pupil due to zooming is extremely small.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the general functions of a zoom lens according to the present invention.

FIG. 2 is a diagram showing the principle of the zoom lens of the present invention.

FIG. 3 is a lens arrangement diagram of the first embodiment.

FIG. 4 is a lens arrangement diagram of a second embodiment.

FIG. 5 is a lens arrangement diagram of a third embodiment.

FIG. 6 is a lens arrangement diagram of a fourth embodiment.

FIG. 7 is a lens arrangement diagram of a fifth embodiment.

FIG. 8 is a lens arrangement diagram of a sixth embodiment.

[Explanation of symbols]

G1 First lens group G2
2nd lens group G3 3rd
Lens group G4 4th lens group H0
, H0' Front principal point H1, H1' Back principal point S, S' Principal point interval β, β' Pupil magnification Z Magnification ratio (zoom ratio) f,
Zf focal length

Claims (3)

[Claims] Claim 1: In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a third lens group having a positive refractive power. In a zoom lens that includes four lens groups, when changing power from the wide-angle end to the telephoto end, the fourth lens group moves toward the image side, and the lens distance between the first lens group and the second lens group increases. A zoom lens characterized by: 2. The axial lens distance between the first lens group and the second lens group at the telephoto end is d12T, the axial lens distance between the first lens group and the second lens group at the wide-angle end is d12W, and wide-angle Bf the back focus at the edge
W, and when the back focus at the telephoto end is BfT, 0<(d12T - d12W)/(
The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditional expressions: BfW - BfT )≦1 and BfW > BfT. 3. When the magnification of the second lens group at the wide-angle end is β2w, the following conditional expression is satisfied: β2w>1 or β2w≦−1. The zoom lens described in