JP3042007B2 - Zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens. In particular, zoom tube lenses for microscopes, etc.
The present invention relates to a zoom lens in which an entrance pupil is located closer to the object side than a first surface of the lens, and a change 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, for example, in Japanese Patent Publication No. 2-54925. This is a zoom lens composed of a lens group having positive, negative, negative and positive refractive power or a lens group having positive, negative and positive refractive power in order from the object side. The lens group moved. or,
A four-group zoom lens widely used as a photographic zoom lens is disclosed, for example, in Japanese Patent Application Laid-Open No. 2-66509. This is because the fourth lens group moves toward the object side during zooming from the wide-angle side to the telephoto side.

[0003]

In the prior art as described above, when the entrance pupil is located closer to the object side than the first lens surface closest to the object side, the exit pupil fluctuates due to zooming. When used as a zoom tube lens, the position of the eye point of the eyepiece changes due to zooming. Further, when the relay optical system is inserted after the zoom tube lens and used, the entrance pupil entering the relay optical system fluctuates due to zooming, so that the configuration of the relay optical system is complicated.

[0004] The present invention has been made in view of such conventional problems,
It is an object of the present invention to provide a zoom lens in which an entrance pupil is located on the object side of the first surface of the lens and fluctuations of the exit pupil due to zooming are extremely small.

[0005]

According to the present invention, there is provided a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. And a zoom lens including a fourth lens group having a positive refractive power, the fourth lens group moves to 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 distance between the lenses is increased.

On the basis of the above basic configuration, the axial lens distance between the first lens group and the second lens group at the telephoto end is d _12T and the distance between the first lens group and the second lens group at the wide angle end is d _12T . When the on-axis lens interval is d _12W , the back focus at the wide-angle end is Bf _W , and the back focus at the telephoto end is Bf _T , 0 <(d _12T −d _12W ) / (Bf _W −Bf _T ) ≦ 1, Bf it is desirable to satisfy the condition of _W> Bf _T. Further, when the magnification of the second lens unit at the wide-angle end is β _2w , it is more preferable to satisfy either of the following conditional expressions: β _2w > 1 or β _2w ≦ −1.

[0007]

[Action] The zoom lens of the present invention, for example, as shown in FIG. 1, condenses the parallel light beam of the first objective lens O ₁ Toko to collimate light flux emitted from the test object M spatial image (intermediate image ) I
And an aspherical image (intermediate image) I composed of a second objective lens O ₂ forming the eye point position E. P. In the microscope having an eyepiece lens E for magnifying observation at, in which the second objective lens O ₂ and the zoom lens of. Here, in making the second objective lens O ₂ into a zoom lens, if the focal length of the second objective lens O ₂ is simply changed, the position change between the entrance pupil and the exit pupil of the objective lens O during zooming, that is, The fluctuation of the exit pupil of the objective lens O increases, and as a result,
E. Eyepoint of microscope P. Greatly fluctuates,
Not only is the specimen M difficult to observe, but also the optical performance of the microscope itself is degraded. Therefore, according to the present invention, the second objective lens O ₂ (hereinafter simply referred to as a zoom lens) is defined as positive, negative,
It is based on a configuration including four lens groups, positive and positive. In the present invention, at the time of zooming from the wide-angle end to the telephoto end, the fourth lens group moves to the image side, and the first lens group and the second lens group move together.
By using a novel zooming method in which the lens interval between lens groups is increased, fluctuation of the exit pupil due to zooming is suppressed to a very small extent while zooming is performed.

Hereinafter, the conditions under which the exit pupil does not change due to zooming will be described in detail. FIG. 2 shows the refractive power arrangement of the zoom lens. In Figure 2 (a) is a refractive power arrangement diagram when the focal length of the zoom lens is f at the wide-angle end, FIG. 2 (b) the refractive power arrangement when the zoom lens focal length f _z at the telephoto end FIG. _{H 0} is front principal point in the zoom lens at the wide angle end in FIG. 2 (a), _{H 1} is a rear principal point, S is a principal point interval, beta pupil magnification _{(D 1 / D 0),} f is focal length of the zoom lens at the wide angle end, D ₀ is the distance from the front principal point to the entrance pupil, D ₁ is the distance from the rear principal point to the exit pupil. In the zoom lens at the telephoto end in FIG. 2B, H ₀ ′ is a front principal point, H ₁ ′ is a rear principal point, S ′ is a principal point interval, and β ′ is a pupil magnification (D ₁ ′ / D ₀ ′ ), Z is the zoom ratio (zoom ratio), Zf is the focal length of the zoom lens at the telephoto end, D ₀ ′ is the distance from the front principal point to the entrance pupil, D ₁
'Indicates the distance from the rear principal point to the exit pupil.

The condition for making the exit pupil position B equal to the entrance pupil position A at an arbitrary zoom magnification with respect to the entrance pupil position A is a constant distance between the two. Therefore, FIGS. The following equation is obtained from the following equation. −D ₀ + S + D ₁ = −D ₀ ′ + S ′ + D ₁ ′ (1) Further, as is clear from FIGS. 2A and 2B, the following equation is obtained. D ₁ ′ = D ₁ + Zf−f (2) From the lens imaging formula, in the zoom lens at the telephoto end in FIG. 2B, the following pupil imaging relationship holds. 1 / D ₁ ′ = 1 / Zf + 1 / D ₀ ′ (3) Then, by substituting equation (2) into equation (3) and rearranging, the following equation is obtained. D ₀ ′ = Zf {D ₁ + f (Z−1)} / (f−D ₁ ) (4) The relationship between the pupil magnification β ′ at the telephoto end and D ₀ ′, D ₁ ′ is given by the following equation. Is shown. β ′ = D ₁ ′ / D ₀ ′ (5) Therefore, the following equation can be derived by substituting the equations (2) and (4) into the equation (5). β ′ = {D ₁ + Zf−f} / [Zf ｛D ₁ + f (Z−1)} / (f−D ₁ )] = (f−D ₁ ) / Zf = [1 / Z] · [(f −D ₁ ) / f] (6) From the Newton imaging formula, β = (f−D ₁ ) / f is satisfied in the zoom lens at the wide-angle end in FIG. The above equation (6) becomes as the following equations (7) and (7). β ′ = β / Z (7) β ′ / β = 1 / Z (7 ′) Equation (7 ′) indicates that the ratio of the zoom ratio to the pupil magnification is inversely proportional.

The following formula is obtained for the zoom lens at the wide-angle end in FIG. 1 / D ₁ = 1 / f + 1 / D ₀ (8) D ₁ = fD ₀ / (f + D ₀ ) (8 ′) Here, equation (2), equation (4) and equation (8 ′) are converted into equation (1). And rearranging yields: S′−S = (Z−1) ｛D ₀ (Z + 1) + f (Z−1)｝ (9) Expression (9) is a condition for making the positions of the exit pupils equal at an arbitrary zoom ratio Z. Because the present invention considers the case where the entrance pupil is some distance to the object side from the first surface of the zoom lens, wherein, when the entrance pupil to the front principal point H ₀ is located more than the focal length at the wide angle end think about. That is, considering the case of D ₀ ≦ −f (10), the following equation is derived by substituting equation (10) into equation (9) and rearranging. S′−S ≦ −2f (Z−1) <0 (11) where f> 0 and Z> 1 . The formula (10) and f from the formula (11), on the object side entrance pupil from the front principal point _{H 0}
When the distance is greater than (focal length at the wide-angle end), the principal point distance S 'at the telephoto end must be shorter than the principal point distance S at the wide-angle end as a condition for keeping the exit pupil unchanged. It can be understood. Here, as an example, the focal length f at the wide angle end
Is 200, the zoom ratio is 2, and the distance D ₀ from the entrance pupil to the front principal point H _{0 is} −250. From the above equation (9), S′−S ≦ −550. That is, in this case, in order to make the exit pupil unchanged, the principal point distance S 'at the telephoto end needs to be shorter than the principal point distance S at the wide angle end by 550.

The following equation is obtained from equation (7). D ₁ ′ / D ₀ ′ = (1 / Z) (D ₁ / D ₀ ) D ₀ / D ₀ ′ = (1 / Z) (D ₁ / D ₁ ′) Z> 1, and FIG. As is clear from FIG.
'Since> is _{D 1, D 0 / D 0} ' 1 becomes <1. At this time, since D ₀ ′ <0 and D ₀ <0, the following equation is obtained. D ₀ > D ₀ ′ (12) Further, since D ₀ ′ <0 and D ₀ <0 are both negative numbers, the following equation is obtained. | D ₀ | <| D ₀ ′ | (13) According to Expression (13) , the distance from the entrance pupil position A at the zoom ratio Z to the front principal point H ₀ ′ must be longer than that at the wide-angle end. . In other words, this indicates that the position of the front principal point must be moved in the image direction when zooming from the wide-angle side to the telephoto side.

As described above, under the condition that the exit pupil does not fluctuate due to zooming, when zooming from the wide-angle end to the telephoto end, the principal point interval of the optical system is reduced and the front principal point position is moved in the image direction. That is.

As described above, in view of the conditions for suppressing pupil fluctuation, the present invention relates to a zoom lens including four lens units 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 reducing the distance between principal points, and by moving the fourth lens group in the image direction, the front principal point position is moved in the image direction. I found that I could do it. In other words, the present invention is used for zooming from the wide-angle end to the telephoto end.
The principle is to suppress the fluctuation of the exit pupil while zooming by using a new zooming method that moves the fourth lens group toward the image side while increasing the distance between the first lens group and the second lens group. It was made possible. It is preferable that the zoom lens according to the present invention further satisfies the following condition (101) based on the above-described zooming method. _{0 <(d 12T -d 12W)} / (Bf w -Bf T) ≦
1, Bf _w > Bf _T (101) where, d _12W : the axial lens distance between the first lens group and the second lens group at the wide angle end d _12T : the first lens group and the second lens group at the telephoto end Bf _w : Back focus of the zoom lens at the wide-angle end Bf _T : Back focus of the zoom lens at the telephoto end. When the value exceeds the upper limit of Expression (101), the amount of change in the axial lens unit interval between the first lens unit and the second lens unit increases during zooming from the wide-angle end to the telephoto end. It is advantageous to obtain a ratio (zoom ratio).
However, since the amount of movement of the fourth lens group toward the image side is too small compared to the increase in the distance between the on-axis lens groups of the first lens group and the second lens group, the amount of movement of the principal point of the zoom lens is smaller than the amount of decrease. The amount of movement of the front principal point of the zoom lens to the image side is too small. As a result, it becomes difficult to correct the variation of the exit pupil. On the other hand, if the lower limit of the expression (101) is exceeded, an increase in the axial lens unit interval between the first lens unit and the second lens unit at the time of zooming from the wide-angle end to the telephoto end is eliminated. For this reason, it is not only difficult to obtain a sufficient zoom ratio (zoom ratio), but also the distance between the principal points at the telephoto end cannot be made sufficiently smaller than that at the wide-angle end. As a result of this,
It becomes difficult to suppress the fluctuation of the exit pupil.

In the present invention, when the magnification of the second lens unit at the wide-angle end is β _2w , it is preferable that the following condition is satisfied. β _2w > 1, β _2w ≦ −1 (102) When exceeding the range of the expression (102), the following is obtained. −
When 1 <β _2w <0, the jump 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 is difficult to reduce the size of the lens system. When 0 ≦ β _2w ≦ 1,
A real image is formed between the first lens group and the second lens group,
The re-imaging system has to be constituted by the second and subsequent lens groups. As a result, the overall length of the optical system becomes extremely long.

The zoom lens according to 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 β _4w , it is preferable that the following condition is satisfied. -1 <β _4w <1 (103) When the value exceeds the range of Expression (103), when zooming from the wide-angle end to the telephoto end, the fourth lens unit moves in the object direction, and the moving form is different from that of the present invention. Therefore, the fluctuation of the exit pupil due to zooming becomes extremely large.

[0016]

In order to reduce the amount of movement of the fourth lens unit in the image direction when zooming the zoom lens from the wide-angle end to the telephoto end, a first focus is required.
This can be achieved by moving the lens group toward the object. On the other hand, when the first lens group is fixed to the image plane to secure the back focus, it is desirable to satisfy the following expression. β _4w <1.8-0.8Z (104) If this condition is not satisfied, it becomes difficult to secure a sufficient back focus at the telephoto end, and if it is forcibly secured, the configuration of the fourth lens unit becomes complicated. I have no choice.
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 the fluctuation of the exit pupil.

[0018]

Next, an embodiment will be described. FIGS. 3 to 8 show the lens configuration diagrams of the first to sixth embodiments according to the present invention, respectively. FIG. 3A to FIG. 8A show the wide-angle end (minimum focal length state), FIG. 2B shows a lens configuration at the intermediate focal length state, and FIG. 2C shows a lens configuration at the telephoto end (longest focal length state). With the zoom lens of each embodiment,
As can be seen from the lens configuration diagrams of FIGS. 3 to 8, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group having a positive refractive power.
Lens group G3 and fourth lens group G4 having a positive refractive power
When zooming from the wide-angle end to the telephoto end, the on-axis air gap between the most image side surface of the first lens group G1 and the most object side surface of the second lens group G2 is increased, and the fourth lens The group G4 is moved to the image side. With such a movement form, it is possible in principle to suppress the fluctuation of the exit pupil in a well-balanced manner while performing magnification. Next, a lens configuration and a moving mode for each embodiment will be described. First, in the first embodiment, the first lens group G1 having a positive refractive power is composed of a biconvex positive lens and a negative meniscus lens joined to the positive lens and having a convex surface facing the image side. The second lens group G2 includes a positive meniscus lens having a convex surface facing the image side, a negative lens cemented to the positive meniscus lens, and a biconcave negative lens. The third lens group G3 and the fourth lens group G4 are composed of a biconvex positive lens and a negative lens joined thereto. In the moving mode of the first embodiment based on the above lens configuration, the first lens group G1 and the third lens group G3 are fixed to the image plane when zooming from the wide-angle end to the telephoto end. The second lens group G2 and the fourth lens group G4 are moved to the image side while increasing the axial air gap between the most image side surface of the second lens group G2 and the most object side surface of the fourth lens group G4. As is apparent from FIG. 3, the entrance pupil is located at a position 150 mm from the first surface of the first lens unit toward the object, and the exit pupil is f = 2 from the image plane.
312.5, respectively, in the order of 00, 300, 400 mm
At the position of 403.6, 323.1 mm, it can be seen that the fluctuation of the exit pupil upon zooming from the wide-angle end to the telephoto end is 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 lens surface interval, ν _d is the Abbe number, _nd is the d line (λ =
587.6n), f is the focal length of the entire system.
Note that, in each of the embodiments described below, values of specifications are shown in the same format as that of the present embodiment. Specifications (first _{embodiment) No r d ν d n d} 1 105.5724 6.0000 67.87 1.593189 2 -60.2393 2.5000 35.19 1.749501 3 -168.7267 d 3 1.000000 4 -116.6589 3.5000 23.01 1.860741 5 -44.6231 1.6000 58.90 1.518230 6 200.6085 2.4000 1.000000 7 - 188.2477 1.6000 55.60 1.696800 8 50.9322 d ₈ 1.000000 9 150.9884 6.5000 60.14 1.620409 10 -130.0730 3.0000 23.01 1.860741 11 -265.8200 d ₁₁ 1.000000 12 193.7822 8.0000 67.87 1.593189 13 -81.7527 3.0000 23.01 1.860741 14 -121.7309 Bf 1.000000 Distance between the first example _{) f = 200 300 400 d 3} 44.15413 68.83672 74.38978 d 8 33.79640 9.11381 3.56075 d 11 30.66645 101.04194 150.90573 Bf 159.48675 89.11127 39.24747 pupil magnification of -1.562 -1.345 -0.808 condition corresponding value (the first embodiment) (d _12T -d _12W) / (Bf _W -Bf _T ) = 0.251 β _2w = −1.54 β _4w = −0.1

Next, a second embodiment will be described with reference to FIG. FIG. 4 is a lens arrangement diagram of the second embodiment. A description of the same or similar points as in the first embodiment will be omitted. The first lens group is fixed, the second lens group is moving, the third lens group is moving,
The fourth lens group moves. The entrance pupil is the first lens group
At a position of 150 mm from the surface to the object, and the exit pupil is 31 in the order of f = 200, 300, and 400 mm from the image plane.
2.5, 314.7, 313.0 mm. The correction of the variation of the exit pupil by the movement of the third lens group is more strictly performed than in the first embodiment.

The specifications are as follows. Specifications (second _{embodiment) No r d ν d n d} 1 105.5724 6.0000 67.87 1.593189 2 -60.2393 2.5000 35.19 1.749501 3 -168.7267 d 3 1.000000 4 -116.6589 3.5000 23.01 1.860741 5 -44.6231 1.6000 58.90 1.518230 6 200.6085 2.4000 1.000000 7 - 188.2477 1.6000 55.60 1.696800 8 50.9322 d ₈ 1.000000 9 150.9884 6.5000 60.14 1.620409 10 -130.0730 3.0000 23.01 1.860741 11 -265.8200 d ₁₁ 1.000000 12 193.7822 8.0000 67.87 1.593189 13 -81.7527 3.0000 23.01 1.860741 14 -121.7309 Bf 1.000000 _{) f = 200 300 400 d 3} 44.15413 70.94020 74.73168 d 8 33.79640 10.09640 6.79648 d 11 30.66645 100.04722 149.62641 Bf 159.48675 78.01988 36.95930 pupil magnification of -1.562 -1.049 -0.783 condition corresponding value (second embodiment) (d _12T -d _12W) / (Bf _W -Bf _T ) = 0.249 β _2w = −1.54 β _4w = −0.1

Next, a third embodiment will be described with reference to FIG. FIG. 5 is a lens arrangement diagram of the third embodiment. A description of the same or similar points as in the first embodiment will be omitted. The first lens group is fixed, the second lens group is moving, the third lens group is moving,
The fourth lens group moves, and this embodiment has the same movement mode as the second embodiment. The entrance pupil is located at a position 150 mm from the first surface of the first lens unit toward the object, and the exit pupil is f = 2 from the image plane.
310.3, respectively, in the order of 00, 300, 400 mm
309.4 and 309.8. The correction of the variation of the exit pupil by the movement of the third lens group is more strictly performed than in the first embodiment.

The specifications are as follows. Specifications (Third _{Embodiment) No r d ν d n d} 1 105.5724 6.0000 67.87 1.593189 2 -60.2393 2.5000 35.19 1.749501 3 -168.7267 d 3 1.000000 4 -116.6589 3.5000 23.01 1.860741 5 -44.6231 1.6000 58.90 1.518230 6 200.6085 2.4000 1.000000 7 - 188.2477 1.6000 55.60 1.696800 8 75.9411 d ₈ 1.000000 9 200.0000 6.5000 60.14 1.620409 10 -130.0730 3.0000 23.01 1.860741 11 -369.7622 d ₁₁ 1.000000 12 193.7822 8.0000 67.87 1.593189 13 -81.7527 3.0000 23.01 1.860741 14 -122.1353 Bf 1.000000 Distance between planes ) F = 200 300 400 d ₃ 46.98934 68.07221 69.31558 d ₈ 38.81539 18.81539 3.81539 d ₁₁ 30.30581 106.85922 161.42866 Bf 125.67279 48.03649 7.22368 Pupil magnification -1.549 -1.031 -0.775 Conditional value (third embodiment) (d _12T -d _12W ) / (Bf _W -Bf _T ) = 0.188 β _2w = −4.33 β _4w = 0.133

Next, a fourth embodiment will be described with reference to FIG. FIG. 6 is a lens arrangement diagram of the fourth embodiment. A description of the same or similar points as in the first embodiment will be omitted. The first lens group is fixed, the second lens group is moving, the third lens group is moving,
The fourth lens group moves. The entrance pupil is the first lens group
At a position 150 mm from the surface in the object direction, the exit pupil is 29 in the order of f = 200, 300, and 400 mm from the image plane.
3.0, 295.2, 296.4. The correction of the variation of the exit pupil by the movement of the third lens group is more strictly performed than in the first embodiment.

The specifications are as follows. Specifications (Fourth _{Embodiment) No r d ν d n d} 1 105.5724 6.0000 67.87 1.593189 2 -60.2393 2.5000 35.19 1.749501 3 -168.7267 d 3 1.000000 4 -116.6589 3.5000 23.01 1.860741 5 -44.6231 1.6000 58.90 1.518230 6 200.6085 2.4000 1.000000 7 - 188.2477 1.6000 55.60 1.696800 8 37.5395 d ₈ 1.000000 9 150.9884 6.5000 60.14 1.620409 10 -130.0730 3.0000 23.01 1.860741 11 -173.8523 d ₁₁ 1.000000 13 193.7822 8.0000 67.87 1.593189 14 -81.7527 3.0000 23.01 1.860741 15 -113.6289 Bf 1.000000 _{) f = 200 300 400 d 3} 46.39362 74.96337 80.18432 d 8 28.15501 16.15501 4.65501 d 11 31.38065 92.71984 136.52271 Bf 175.56714 97.65820 60.14336 magnification pupil -1.463 -0.984 -0.741 condition corresponding value (fourth embodiment) (d _12T -d _12W) / (Bf _W -Bf _T ) = 0.293 β _2w = −1 β _4w = −0.297

Next, a fifth embodiment will be described with reference to FIG. FIG. 7 is a lens arrangement diagram of the fifth embodiment. A description of the same or similar points as in 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 at a position 150 mm from the first surface of the first lens unit in the object direction, and the exit pupil is f =
312. 200, 300, and 400 mm, respectively.
6, 303.0, 288.5. The back focus Bf at the telephoto end is 50.1 mm, which is longer than the back focus Bf of the second embodiment due to the movement of the first lens group toward the object side.

The specifications are as follows. Specifications (Fifth _{Embodiment) No r d ν d n d} 1 105.5724 6.0000 67.87 1.593189 2 -60.2393 2.5000 35.19 1.749501 3 -168.7267 d 3 1.000000 4 -116.6589 3.5000 23.01 1.860741 5 -44.6231 1.6000 58.90 1.518230 6 200.6085 2.4000 1.000000 7 - 188.2477 1.6000 55.60 1.696800 8 50.9322 d ₈ 1.000000 9 150.9884 6.5000 60.14 1.620409 10 -130.0730 3.0000 23.01 1.860741 11 -265.8208 d ₁₁ 1.000000 12 193.7822 8.0000 67.87 1.593189 13 -81.7527 3.0000 23.01 1.860741 14 -121.7309 Bf 1.000000 _{) f = 200 300 400 d 3} 44.15413 68.80962 72.48519 d 8 33.79640 17.79640 6.79640 d 11 30.66645 110.38910 163.46280 Bf 159.48675 86.80325 50.05353 pupil magnification of -1.562 -0.961 -0.690 condition corresponding value (fifth embodiment) (d _12T -d _12W) / (Bf _W -Bf _T ) = 0.259 β _2w = −1.54 β _4w = −0.1

Next, a sixth embodiment will be described with reference to FIG. FIG. 8 is a lens arrangement diagram of the sixth embodiment. A description of the same or similar points as in 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 at a position 150 mm from the first surface of the first lens unit in the object direction, and the exit pupil is 33 at f, 200, 300, and 400 mm in order from the image plane.
2.3, 332.4, 332.4. The movement in the image direction of the third lens group strictly corrects the fluctuation of the exit pupil.

The specifications are as follows. Specifications (Sixth _{Embodiment) No r d ν d n d} 1 105.5724 6.0000 67.87 1.593189 2 -60.2393 2.5000 35.19 1.749501 3 -168.7267 d 3 1.000000 4 -116.6589 3.5000 23.01 1.860741 5 -44.6231 1.6000 58.90 1.518230 6 200.6085 2.4000 1.000000 7 - 188.2477 1.6000 55.60 1.696800 8 50.9322 d ₈ 1.000000 9 150.9884 6.5000 60.14 1.620409 10 -130.0730 3.0000 23.01 1.860741 11 -236.0883 d ₁₁ 1.000000 12 193.7822 8.0000 67.87 1.593189 13 -81.7527 3.0000 23.01 1.860741 14 -124.1565 Bf 1.000000 F = 200 300 400 d ₃ 44.17310 70.90362 74.24344 d ₈ 31.23069 17.65277 5.58476 d ₁₁ 31.01067 100.78910 150.47905 Bf 155.19381 72.26278 31.30183 Magnification of pupil -1.661 -1.108 -0.831 Conditional value (sixth embodiment) (d _12T -d _12W ) / (Bf _W -Bf _T ) = 0.243 β _2w = −1.54 β _4w = −0.0497

[0030]

According to the present invention, a zoom lens having an entrance pupil on the object side from the first surface of the lens and having a very small change in the exit pupil due to zooming can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a principle diagram of a zoom lens according to 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 Second lens group G3 Third lens group G4 Fourth lens group H ₀ , H ₀ ′ Front principal point H ₁ , H ₁ ′ Rear principal point S, S ′ Principal point interval β, β ′ distance magnification pupil Z variable power ratio (zoom ratio) f, from Zf focal length D _{0, D 0} rear principal point 'distance D _{1, D 1} from the front principal point to the entrance pupil' to the exit pupil

Claims (4)

(57) [Claims] 1. A first lens having a positive refractive power in order from the object side.
Lens group, second lens group having negative refractive power, positive refraction
Third lens group having a positive power and fourth lens group having a positive refractive power
When zooming from the wide-angle end to the telephoto end, the fourth lens group moves to the image side
A lens that moves and is between the first lens group and the second lens group
Characterized by increased spacingAnd at the telephoto end
The axial lens distance between the first lens group and the second lens group
d _12T , First lens group and second lens group at wide-angle end
D is the on-axis lens distance between _12W At the wide-angle end
Focus on Bf _W , Back focus at the telephoto end
To Bf _T And when 0 <(d _12T -D _12W ) / (Bf _W -Bf _T ) ≤
1, Bf _W > Bf _T A zoom lens characterized by satisfying the following conditional expression. 2. The magnification of the second lens group at the wide-angle end is
when a beta _2W, claims, characterized by satisfying the beta _2W> 1, or beta _2W ≦ -1, either conditional expression
2. The zoom lens according to 1. 3. The magnification of the fourth lens group at the wide-angle end is
beta when a _4W, -1 <β _4W <claim 1 or claim, characterized by satisfying a conditional expression
Item 12. A zoom lens according to item 2. 4. The zoom lens system according to claim 1 , wherein said first lens is used for zooming from a wide-angle end to a telephoto end.
4. The lens system according to claim 1, wherein the lens unit is fixed with respect to the image plane, and a conditional expression of β _4W <1.8-0.8Z (where Z is a zoom ratio) is satisfied.
Item 11. The zoom lens according to any one of items 3.