JP4592293B2 - Variable magnification lens - Google Patents

Description

  The present invention relates to a variable magnification lens for finite distance imaging, and more particularly to a high performance variable magnification lens suitable for substrate inspection.

In recent years, the size of defect inspection objects using a line CCD camera has been diversified, and various inspection apparatuses corresponding to the sizes have been required. In order to meet such a demand, it is an optical system consisting of a substantially symmetric front group and a rear group across the diaphragm, and the air gap between the front group and the diaphragm and the air gap between the diaphragm and the rear group are changed, A zoom lens that achieves a zoom ratio of about 2.85 times from -0.35 to -1.0 times is disclosed (for example, see Patent Document 1). As a result, the disclosed variable magnification lens balances the image surface by suppressing the spherical aberration from greatly changing to the negative side when focusing from the low magnification side to the same magnification, and corrects the coma aberration. By demonstrating the effect, we are resolving the problem with the whole payout method.
JP 05-273465 A

  However, with the variable magnification lens disclosed in the above publication, when used at a photographing magnification exceeding 1 ×, the spherical aberration increases on the high magnification side and the image surface tilts greatly, and coma occurs on the low magnification side. Becomes larger, and in either case, correction becomes difficult. For this reason, the zoom lens disclosed in the above publication has a problem that it is very difficult to use at a photographing magnification exceeding 1 ×. Furthermore, in the variable power lens disclosed in the above publication, if the magnification from the lowest magnification to the highest magnification is out of the same magnification in focusing, the symmetry of the refractive power of the front group and the rear group is lost, leading to an increase in distortion aberration. However, there is a problem that the variation of the chromatic aberration of magnification becomes large.

  The present invention has been made in view of such a problem, and provides a variable magnification lens that can maintain good performance even when used at a photographing magnification in a wide variable magnification range exceeding 1 ×. Objective.

In order to achieve such an object, a zoom lens according to the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, an aperture stop, , and a third lens group having positive refractive power, the first lens group is configured to include a cemented lens of a positive lens and a negative lens located closest to the object side, the second lens group, The third lens group includes three cemented lenses having negative refractive power with the concave surface facing the object side closest to the object side. The third lens group includes three cemented lenses having negative refractive power. When focusing from the high magnification to the low magnification side, the air gap between the first lens group and the second lens group and the air gap between the second lens group and the third lens group are varies, the focal length of the second lens group and f2, The focal length of the entire lens system at high magnification is f, the combined focal length of the first lens group and the second lens group at the maximum magnification is f12, and the focal length of the third lens group is f3. When the air gap between the first lens group and the second lens group at the magnification is D12, and the air gap between the second lens group and the third lens group at the maximum magnification is D23, −7.05 <f2 / f <−1.54, 1.29 <f12 / f3 <1.91, 0.006 <D12 / f <0.026, 0.028 <D12 / D23 <0.2 It is comprised so that the conditions may be satisfied .

  In the present invention, it is preferable to have a flare stop before and after the aperture stop.

  As described above, according to the zoom lens according to the present invention, the lens has a bright effective F number of about 7.7, and is stable in a wide zoom range of −1.75 to −0.5833 times. In addition, it is possible to achieve a variable power optical system with high resolution and excellent imaging performance.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The zoom lens according to the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, an aperture stop, and a third lens having a positive refractive power. And a lens group. When focusing from the high magnification to the low magnification side, the air gap between the first lens group and the second lens group and the air gap between the second lens group and the third lens group are changed. ing. At this time, it is preferable that the air gap between the first lens group and the second lens group is increased.

  As described above, in the variable power lens according to the present invention, when focusing from the high magnification side to the low magnification side, first, the optical system is divided into the front group and the rear group so as to be substantially symmetrical with the aperture stop interposed therebetween. Further, the front group is divided into a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side, and an air space between the first lens group and the second lens group is set. It is changing. As a result, the variable power lens according to the present invention enables aberration correction in a wide magnification range exceeding the same magnification (that is, a magnification range from the highest magnification to the lowest magnification with the same magnification interposed therebetween), and high performance optical The system is feasible. The reason why the front group and the rear group are substantially symmetrical with the aperture stop interposed therebetween is that the power (refractive power) of the front group and the rear group is almost equal at the same magnification, and distortion aberration and lateral chromatic aberration are reduced. This is because the generation can be corrected to almost zero.

In the zoom lens according to the present invention, the first lens group includes at least one pair of a positive lens and a negative lens that are located closest to the object side, and the second lens group has a negative refractive power. The third lens group includes three cemented lenses having negative refractive power with the concave surface facing the object side closest to the object side .

  As described above, according to the present invention, each lens group of the first lens group to the third lens group includes a cemented lens having an achromatic meaning, thereby suppressing variation in axial chromatic aberration in a wide photographing magnification range. . In particular, the three cemented lenses before and after the aperture stop (specifically, disposed in the second lens group and the third lens group) eliminate the refractive index difference between the positive lens and the negative lens, Further, by combining appropriate dispersion values as in each of the embodiments described later, good aberration correction can be performed even at a high imaging magnification exceeding the same magnification.

  Hereinafter, the variable magnification lens according to the present invention will be described in detail along conditional expressions (1) to (4). The zoom lens according to the present invention preferably satisfies the following expression (1), where f2 is the focal length of the second lens group and f is the focal length of the entire lens system at the maximum magnification.

              −7.05 <f2 / f <−1.54 (1)

  Conditional expression (1) is a condition relating to the refractive power of the second lens group having a negative refractive power, and defines a refractive power arrangement that can exert its effect in the variable power lens according to the present invention. If the upper limit of conditional expression (1) is exceeded, the negative refractive power of the second lens group will be too strong and overcorrected, coma cannot be corrected to the low magnification side, and spherical aberration will increase to the positive side. The resolution decreases. On the other hand, if the lower limit value of conditional expression (1) is not reached, the refractive power of the second lens group becomes weak, and the effect of correcting off-axis coma due to floating between the first lens group and the second lens group is lost. . In addition, the refractive power of the first lens group and the refractive power of the third lens group become relatively very strong, especially the spherical aberration on the high magnification side increases to the negative side, and the field curvature also falls to the negative side. It becomes difficult to ensure good image quality.

  In the variable power lens according to the present invention, when the combined focal length of the first lens group and the second lens group at the maximum magnification is f12 and the focal length of the third lens group is f3, the following formula (2) Is preferably satisfied.

              1.29 <f12 / f3 <1.91 (2)

  The conditional expression (2) defines the refractive power distribution in the front group (consisting of the first lens group and the second lens group) and the rear group (consisting of the third lens group). Maintaining the refractive power in the entire photographing magnification range so that the refractive power of the front group determined by the air space between the first lens group and the second lens group becomes stronger as the magnification is changed from high magnification to low magnification. Change. When the upper limit of conditional expression (2) is exceeded, the refractive power of the rear group consisting of the third lens group becomes relatively strong, and the spherical aberration on the high magnification side becomes overcorrected and increases to the positive side. Therefore, it becomes very difficult to balance the image plane to the low magnification side. On the other hand, if the lower limit value of conditional expression (2) is not reached, the refractive power of the front group (consisting of the first lens group and the second lens group) becomes too strong, so that spherical aberration generated in the front group becomes low magnification. And the symmetry of the refractive power of the front group and the rear group is greatly broken, and it becomes difficult to correct distortion and coma.

  Conditional expressions (3) and (4) described below are used to determine the air gap between the first lens group and the second lens group and the second lens group in order to achieve a wide zoom range by changing the distance between the object images. When the floating method using the air distance between the first lens group and the third lens group is employed, an appropriate air distance (that is, the air distance between the first lens group and the second lens group and the second lens group) Air interval between the second lens group and the third lens group).

  The zoom lens according to the present invention has the following formula when the air distance between the first lens group and the second lens group at the maximum magnification is D12 and the focal length of the entire lens system at the maximum magnification is f. It is preferable to satisfy (3).

              0.006 <D12 / f <0.026 (3)

  Conditional expression (3) defines the air gap between the first lens group and the second lens group. If the upper limit of conditional expression (3) is exceeded, the incident position of off-axis light rays that emerge from the first lens group and enter the second lens group becomes low, so that off-axis coma aberration deteriorates and correction is difficult. become. On the other hand, if the lower limit value of conditional expression (3) is not reached, the air space between the first lens group and the second lens group becomes small, causing mechanical interference.

  In the variable power lens according to the present invention, the air gap between the first lens group and the second lens group at the maximum magnification is D12, and the air gap between the second lens group and the third lens group at the highest magnification is set. When D23, it is preferable to satisfy the following formula (4).

              0.028 <D12 / D23 <0.2 (4)

  Conditional expression (4) corrects spherical aberration and astigmatism in a well-balanced manner over the entire magnification range, so that the air gap between the first lens group and the second lens group, and the second lens group and the third lens group The ratio to the air spacing is determined. When the upper limit value of conditional expression (4) is exceeded, the amount of positive spherical aberration and astigmatism generated by the third lens group increases, and an appropriate distance between the first lens group and the second lens group is increased. The floating effect cannot be obtained. On the other hand, if the lower limit of conditional expression (4) is not reached, it will be difficult to correct spherical aberration on the high magnification side.

  Furthermore, the zoom lens according to the present invention preferably has a flare stop before and after the aperture stop in order to suppress high-order coma. Here, when focusing from the high magnification side to the low magnification side, the aperture stop and the flare stop may be moved together with either the second lens group or the third lens group, or independently. May be. Further, when focusing from the high magnification side to the low magnification side, by changing the aperture diameter at each magnification, a sufficient amount of peripheral light at each magnification can be secured, and high resolution can be achieved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In the accompanying drawings, the image plane is indicated by symbol I.

In the four embodiments of the variable magnification lens according to the present invention to be described below, as shown in FIGS. 1, 5, 9, and 13, all have positive refractive power in order from the object side. A first lens group G1, a second lens group G2 having negative refractive power, an aperture stop S, and a third lens group G3 having positive refractive power, the first lens group G1 being closest to the object side It includes at least one pair of a positive lens and a negative lens , and the second lens group G2 includes three cemented lenses having negative refractive power, and the third lens group G3 is located closest to the object side. The configuration includes three bonded lenses having negative refractive power with the concave surface facing the object side.

  When focusing from the high magnification side to the low magnification side, the object distance (distance from the object side to the first lens group), the air gap between the first lens group G1 and the second lens group G2, and the second The air gap (aperture space) between the lens group G2 and the third lens group G3 is changed. Further, when focusing from the high magnification side to the low magnification side, the aperture stop S moves integrally with the second lens group G2 in any of the embodiments, and the aperture diameter is changed at each photographing magnification. With an effective F number of 7.7, it is possible to secure a sufficient amount of peripheral light.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a lens configuration diagram of a variable magnification lens according to the first example. In the zoom lens HL1 according to the first example, the first lens group G1 includes, in order from the object side, a cemented lens including a positive lens L1 having a convex surface facing the object side and a biconcave lens L2, and a convex surface facing the object side. A lens group having positive refractive power is configured by arranging a cemented lens composed of a negative meniscus lens L3 and a biconvex lens L4. The second lens group G2 includes a cemented lens including a positive meniscus lens L5 having a convex surface facing the object side, a negative meniscus lens L6 having a convex surface facing the object side, and a positive meniscus lens L7 having a convex surface facing the object side. To constitute a lens group having negative refractive power. The third lens group G3 includes a positive meniscus lens L8 having a concave surface facing the object side, a negative meniscus lens L9 having a concave surface facing the object side, and a positive meniscus lens L10 having a concave surface facing the object side. A lens, a cemented lens composed of a positive meniscus lens L11 having a concave surface facing the object side and a negative meniscus lens L12 having a concave surface facing the object side, a biconcave lens L13 and a biconvex lens L14 are arranged to have a positive refractive power. It constitutes a lens group. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

  FIG. 2 is a diagram showing the movement trajectory of each lens group when zooming from the high magnification side (-1.75 times) to the low magnification side (-0.5833 times) with the same magnification (-1.00 times) in between. 2A shows the position of each lens group when the variable magnification lens HL1 is at an imaging magnification of 1.75 times (high magnification side), and FIG. 2B shows the magnification of the variable magnification lens HL1 at an imaging magnification of -1.00 times (equal magnification). 2C shows the position of each lens group, and FIG. 2C shows the position of each lens group when the variable magnification lens HL1 is at an imaging magnification of -0.5833 (on the low magnification side). The aperture stop S moves together with the second lens group G2.

  Next, the specifications of each lens in the first embodiment are shown in Table 1 (however, the unit of length is mm). In this specification table, the first column m is the number of each optical surface from the object side (hereinafter referred to as surface number), the second column r is the radius of curvature of each optical surface, and the third column d is each optical surface. The distance on the optical axis from one to the next optical surface (or image surface), the fourth column ν is the Abbe number, the fifth column n is the refractive index with respect to the d-line (λ = 587.56 nm), and the sixth column is each lens component Respectively. In the table, Fe represents the effective F number, β represents the photographing magnification, and D0 represents the object distance. The description of the table is the same in the other examples.

  In the first embodiment, the surface interval d6 indicated by the surface number 6 (namely, the surface interval between the surface number 6 and the surface number 7) and the surface interval d11 indicated by the surface number 11 (ie the surface between the surface number 11 and the surface number 12). The (interval) changes during focusing. The surface number 11 corresponds to the aperture stop S.

(Table 1)
Fe = 7.7
m r d v n
1 702.0736 8.5000 82.52 1.497820 L1
2 -40.5552 2.4500 64.12 1.516800 L2
3 175.9380 0.2000 1.000000
4 70.0000 4.5000 48.87 1.531720 L3
5 53.1031 9.5000 67.87 1.593189 L4
6 -436.6233 d6 (variable) 1.000000
7 39.0048 6.5000 67.87 1.593189 L5
8 95.5568 2.5000 52.32 1.517420 L6
9 24.3988 5.4000 47.82 1.757000 L7
10 23.7124 14.7500 1.000000
11 Aperture stop S d11 (variable) 1.000000
12 -23.8762 5.4000 50.85 1.570990 L8
13 -18.2210 3.5000 52.32 1.517420 L9
14 -47.0835 6.0000 67.87 1.593189 L10
15 -42.3346 5.0000 1.000000
16 -267.1949 7.0500 67.87 1.593189 L11
17 -31.4666 2.4000 48.87 1.531720 L12
18 -58.3639 0.2000 1.000000
19 -347.2786 2.5500 52.95 1.571350 L13
20 69.8200 8.0000 82.52 1.497820 L14
21 -106.4123 1.000000

(Variable interval in zooming)
β -1.75 -1.00 -0.5833
D0 102.3573 154.5617 244.0704
d6 2.15000 7.00000 10.90000
d11 12.65000 12.30000 10.10000

(Values for conditional expressions)
f2 = -290.500
f = 120.029
f12 = 174.429
f3 = 118.853
D12 = 2.15
D23 = 27.4

(Conditional expression)
(1) f2 / f = -2.42
(2) f12 / f3 = 1.47
(3) D12 / f = 0.018
(4) D12 / D23 = 0.078

  Thus, in the first example, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  3 shows various aberrations when the imaging magnification β is 1.75 times, FIG. 4 shows various aberrations when the imaging magnification β is −1.00 times, and FIG. 5 shows various aberrations when the imaging magnification β is −0.5833 times. In each aberration diagram, d is d line (λ = 587.56 nm), g is g line (λ = 435.83 nm), C is C line (λ = 656.28 nm), and F is F line (λ = 486.13 nm). Respectively. Further, the value of Fe in the spherical aberration diagram is the effective F number, the value of Y in the astigmatism diagram and the distortion diagram is the maximum value of the image height, and the value of Y in the coma aberration diagram is the value of each image height. It is. Further, in the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. The explanation of the above aberration diagrams is the same in the other examples.

  As is apparent from each aberration diagram, in the variable magnification lens HL1 according to the first example, the effective F number is 7.7 in the wide variable magnification range of -1.75 times to -0.5833 times. It can be seen that while having brightness, various aberrations are well corrected and stable and excellent imaging performance is secured.

(Second embodiment)
A second embodiment of the present invention will be described below with reference to FIGS. FIG. 6 is a lens configuration diagram of the variable magnification lens HL2 according to the second example. In the variable magnification lens HL2 according to the second example, the first lens group G1 having a positive refractive power is bonded in order from the object side to the positive lens L1 having a convex surface facing the object side and the biconcave lens L2. A lens group including a negative meniscus lens L3 having a convex surface facing the object side and a biconvex lens L4 is disposed to constitute a lens group having a positive refractive power. The second lens group G2 includes a cemented lens including a positive meniscus lens L5 having a convex surface facing the object side, a negative meniscus lens L6 having a convex surface facing the object side, and a positive meniscus lens L7 having a convex surface facing the object side. To constitute a lens group having negative refractive power. The third lens group G3 includes a positive meniscus lens L8 having a concave surface facing the object side, a negative meniscus lens L9 having a concave surface facing the object side, and a positive meniscus lens L10 having a concave surface facing the object side. A lens, a cemented lens composed of a positive meniscus lens L11 having a concave surface facing the object side and a negative meniscus lens L12 having a concave surface facing the object side, a biconcave lens L13 and a biconvex lens L14 are arranged to have a positive refractive power. It constitutes a lens group. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

  FIG. 7 is a diagram showing the movement trajectory of each lens group when zooming from the high magnification side (-1.75 times) to the low magnification side (-0.5833 times) with the same magnification (-1.00 times) in between. 7A shows the position of each lens group when the variable magnification lens HL2 is at an imaging magnification of 1.75 times (high magnification side), and FIG. 7B shows the magnification of the variable magnification lens HL2 at an imaging magnification of -1.00 times (equal magnification). (C) shows the position of each lens group when the variable magnification lens HL2 is at an imaging magnification of -0.5833 (on the low magnification side). The aperture stop S moves together with the second lens group G2.

  Next, Table 2 shows the specifications of each lens in the second embodiment. In the second embodiment, the surface interval d6 indicated by the surface number 6 (namely, the surface interval between the surface number 6 and the surface number 7) and the surface interval d11 indicated by the surface number 11 (ie the surface number 11 and the surface number 12) The distance between the planes) changes during focusing. The surface number 11 corresponds to the aperture stop S.

(Table 2)
Fe = 7.7
m r d v n
1 197.6374 7.0000 82.52 1.497820 L1
2 -43.6597 3.0000 64.12 1.516800 L2
3 155.6731 3.0000 1.000000
4 67.5879 4.5000 50.85 1.570990 L3
5 36.2191 9.5000 67.87 1.593189 L4
6 -1205.7046 d6 (variable) 1.000000
7 35.4362 5.9911 67.87 1.593189 L5
8 33.8366 2.3043 54.62 1.514540 L6
9 24.2500 4.9772 47.38 1.788000 L7
10 22.0739 13.5951 1.000000
11 Aperture stop S d11 (variable) 1.000000
12 -24.2961 5.4000 50.85 1.570990 L8
13 -16.7185 3.5000 52.32 1.517420 L9
14 -231.8648 6.0000 67.87 1.593189 L10
15 -43.3155 5.0000 1.000000
16 -193.6937 7.0500 67.87 1.593189 L11
17 -29.9223 2.3000 50.85 1.570990 L12
18 -52.3453 3.0000 1.000000
19 -505.3142 2.5000 52.95 1.571350 L13
20 81.3102 8.0000 82.52 1.497820 L14
21 -139.6636 1.000000

(Variable interval in zooming)
β -1.75 -1.00 -0.5833
D0 102.2566 155.4856 245.2328
d6 3.40000 9.65000 10.30000
d11 12.95000 13.05000 11.50000

(Values for conditional expressions)
f2 = -188.34265
f = 120.95503
f12 = 185.91454
f3 = 112.56525
D12 = 3.40
D23 = 26.55

(Conditional expression)
(1) f2 / f = -1.56
(2) f12 / f3 = 1.65
(3) D12 / f = 0.028
(4) D12 / D23 = 0.13

  As described above, in the second embodiment, it is understood that all the conditional expressions (1) to (4) are satisfied. 8 shows various aberration diagrams when the imaging magnification β is 1.75 times, FIG. 9 shows various aberration diagrams when the imaging magnification β is −1.00 times, and FIG. 10 shows various aberration diagrams when the imaging magnification β is −0.5833 times. As is apparent from each aberration diagram, in the variable magnification lens HL2 according to the second example, the effective F number is 7.7 in a wide variable magnification range of -1.75 times to -0.5833 times. It can be seen that while having brightness, various aberrations are well corrected and stable and excellent imaging performance is secured.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to FIGS. FIG. 11 is a lens configuration diagram of the variable magnification lens HL3 according to the third example. In the zoom lens HL3 according to the third example, the first lens group G1 includes, in order from the object side, a cemented lens including a positive meniscus lens L1 having a concave surface facing the object side and a biconcave lens L2, and an object side. A lens group having a positive refractive power is configured by arranging a cemented lens including a negative meniscus lens L3 and a biconvex lens L4 having a convex surface. The second lens group G2 includes a cemented lens including a positive meniscus lens L5 having a convex surface facing the object side, a negative meniscus lens L6 having a convex surface facing the object side, and a positive meniscus lens L7 having a convex surface facing the object side. To constitute a lens group having negative refractive power. The third lens group G3 includes a positive meniscus lens L8 having a concave surface facing the object side, a negative meniscus lens L9 having a concave surface facing the object side, and a positive meniscus lens L10 having a concave surface facing the object side. A lens, a cemented lens composed of a positive meniscus lens L11 having a concave surface facing the object side and a negative meniscus lens L12 having a concave surface facing the object side, a biconcave lens L13 and a biconvex lens L14 are arranged to have a positive refractive power. It constitutes a lens group. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

  FIG. 12 is a diagram showing the movement trajectory of each lens group when zooming is performed from the high magnification side (-1.75 times) to the low magnification side (−0.5833 times) with the same magnification (−1.00 times) in between. 12A shows the position of each lens group when the variable magnification lens HL3 is at an imaging magnification of 1.75 times (high magnification side), and FIG. 12B shows the magnification of the variable magnification lens HL3 at an imaging magnification of -1.00 times (equal magnification). 12C shows the position of each lens group, and FIG. 12C shows the position of each lens group when the variable magnification lens HL3 is at an imaging magnification of -0.5833 (on the low magnification side). The aperture stop S moves together with the second lens group G2.

  Next, Table 3 shows the specifications of each lens in the third example. In the third embodiment, the surface interval d6 indicated by the surface number 6 (ie, the surface interval between the surface number 6 and the surface number 7) and the surface interval d11 indicated by the surface number 11 (ie, the surface number 11 and the surface number 12) The distance between the planes) changes during focusing. The surface number 11 corresponds to the aperture stop S.

(Table 3)
Fe = 7.7
m r d v n
1 -295.8036 8.5000 82.52 1.497820 L1
2 -39.4630 2.4500 64.12 1.516800 L2
3 410.7216 0.2000 1.000000 L3
4 88.4033 4.5000 48.87 1.531720 L4
5 69.3099 9.5000 67.87 1.593189
6 -238.7392 d6 (variable) 1.000000
7 45.3483 7.6541 67.87 1.593189 L5
8 711.4063 2.9439 52.32 1.517420 L6
9 25.8385 6.3588 47.82 1.757000 L7
10 27.9226 17.3690 1.000000
11 Aperture stop S d11 (variable) 1.000000
12 -22.8607 5.4000 50.85 1.570990 L8
13 -18.8613 3.5000 52.32 1.517420 L9
14 -53.0068 6.0000 67.87 1.593189 L10
15 -41.5489 5.0000 1.000000
16 -225.7922 7.0500 67.87 1.593189 L11
17 -33.6739 2.4000 48.87 1.531720 L12
18 -59.2502 0.2000 1.000000
19 -534.0237 2.5500 52.95 1.571350 L13
20 66.1282 8.0000 82.52 1.497820 L14
21 -106.4123 1.000000

(Variable interval in zooming)
β -1.75 -1.00 -0.5833
D0 97.5950 149.1347 238.3698
d6 0.90000 7.40000 14.05000
d11 13.60000 12.55000 9.25000

(Values for conditional expressions)
f2 = -844.664
f = 120.009
f12 = 163.681
f3 = 125.555
D12 = 0.90
D23 = 30.97

(Conditional expression)
(1) f2 / f = -7.04
(2) f12 / f3 = 1.30
(3) D12 / f = 0.0075
(4) D12 / D23 = 0.029

  As described above, in the third example, it is understood that all the conditional expressions (1) to (4) are satisfied. 13 shows various aberrations when the imaging magnification β is 1.75 times, FIG. 14 shows various aberrations when the imaging magnification β is −1.00 times, and FIG. 15 shows various aberrations when the imaging magnification β is −0.5833 times. As is apparent from each aberration diagram, in the variable magnification lens HL3 according to the third example, the effective F number is 7.7 in a wide variable magnification range of −1.75 times to −0.5833 times. It can be seen that while having brightness, various aberrations are well corrected and stable and excellent imaging performance is secured.

(Fourth embodiment)
Hereinafter, a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 16 is a lens configuration diagram of the variable magnification lens HL4 according to the fourth example. In the zoom lens HL4 according to the fourth example, the first lens group G1 includes, in order from the object side, a cemented lens including a positive lens L1 having a convex surface facing the object side and a biconcave lens L2, and a convex surface facing the object side. A lens group having positive refractive power is configured by arranging a cemented lens composed of a negative meniscus lens L3 and a biconvex lens L4. The second lens group G2 includes a cemented lens including a positive meniscus lens L5 having a convex surface facing the object side, a negative meniscus lens L6 having a convex surface facing the object side, and a positive meniscus lens L7 having a convex surface facing the object side. To constitute a lens group having negative refractive power. The third lens group G3 includes a positive meniscus lens L8 having a concave surface facing the object side, a negative meniscus lens L9 having a concave surface facing the object side, and a positive meniscus lens L10 having a concave surface facing the object side. A lens, a cemented lens composed of a positive meniscus lens L11 having a concave surface facing the object side and a negative meniscus lens L12 having a concave surface facing the object side, a biconcave lens L13 and a biconvex lens L14 are arranged to have a positive refractive power. It constitutes a lens group. An aperture stop S is disposed between the second lens group G2 and the third lens group G3. Further, a flare stop FS is disposed on the front and rear sides of the aperture stop S (that is, the most image side of the second lens group and the most object side of the third lens group).

  FIG. 17 is a diagram showing the movement trajectory of each lens group when zooming is performed from the high magnification side (-1.75 times) to the low magnification side (−0.5833 times) with the same magnification (−1.00 times) in between. 17A shows the position of each lens group when the variable magnification lens HL4 is at an imaging magnification of 1.75 times (high magnification side), and FIG. 17B shows the magnification of the variable magnification lens HL4 at an imaging magnification of −1.00 times (equal magnification). ), And FIG. 17C shows the position of each lens group when the variable magnification lens HL4 is at an imaging magnification of −0.5833 (on the low magnification side). The flare stop FS and the aperture stop S located on the image side of the second lens group are moved together with the second lens group G2. Further, the flare stop FS located on the object side of the third lens group G3 is moved integrally with the third lens group G3.

  Next, Table 4 shows the specifications of each lens in the fourth example. In the fourth embodiment, the surface interval d6 indicated by the surface number 6 (namely, the surface interval between the surface number 6 and the surface number 7) and the surface interval d12 indicated by the surface number 12 (ie the surface number 12 and the surface number 13) The distance between the planes) changes during focusing. The surface number 12 corresponds to the aperture stop S. Surface numbers 11 and 13 correspond to the flare stop FS.

(Table 4)
Fe = 7.7
m r d v n
1 702.0736 8.5000 82.52 1.497820 L1
2 -40.5552 2.4500 64.12 1.516800 L2
3 175.9380 0.2000
4 70.2500 4.5000 48.87 1.531720 L3
5 49.6295 9.5000 67.87 1.593189 L4
6 -431.7184 d6 (variable) 1.000000
7 41.1491 6.5000 67.87 1.593189 L5
8 82.4495 2.5000 52.32 1.517420 L6
9 23.1247 5.4000 47.82 1.757000 L7
10 24.6021 4.0000
11 Flare FS 10.7500 1.000000
12 Aperture stop S d12 (variable) 1.000000
13 Flare aperture FS 5.0000 1.000000
14 -23.8681 5.4000 50.80 1.570990 L8
15 -20.6979 3.5000 52.32 1.517420 L9
16 -55.0000 6.0000 67.87 1.593189 L10
17 -45.5235 4.5000
18 -206.9529 7.7500 67.87 1.593189 L11
19 -31.1728 2.4000 48.87 1.531720 L12
20 -54.8123 0.2000
21 -962.1916 2.5500 52.95 1.571350 L13
22 65.5072 8.0000 82.52 1.497820 L14
23 -116.1825

(Variable interval in zooming)
β -1.75 -1.00 -0.5833
D0 102.1346 154.2296 243.4796
d6 1.75000 6.35000 10.35000
d12 8.00000 7.75000 5.55000

(Values for conditional expressions)
f2 = -331.019
f = 119.915
f12 = 163.807
f3 = 122.795
D12 = 1.75
D23 = 27.75

(Conditional expression)
(1) f2 / f = -2.76
(2) f12 / f3 = 1.33
(3) D12 / f = 0.015
(4) D12 / D23 = 0.063

  Thus, in the fourth example, it can be seen that all the conditional expressions (1) to (4) are satisfied. 18 shows various aberrations when the imaging magnification β is 1.75 times, FIG. 19 shows various aberrations when the imaging magnification β is −1.00 times, and FIG. 20 shows various aberrations when the imaging magnification β is −0.5833 times. As is apparent from each aberration diagram, in the variable magnification lens HL4 according to the fourth example, the effective F number is 7.7 in the wide variable magnification range of -1.75 times to -0.5833 times. It can be seen that while having brightness, various aberrations are well corrected and stable and excellent imaging performance is secured.

It is a lens block diagram of the variable magnification lens which concerns on 1st Example of this invention. FIG. 6 is a diagram showing a movement locus of each lens unit when the magnification is changed from the high magnification side (−1.75 times) to the low magnification side (−0.5833 times) in the magnification lens according to the first example. FIG. 6 is a diagram illustrating various aberrations at an imaging magnification of 1.75 times in the first example. FIG. 5 is a diagram illustrating various aberrations at an imaging magnification of −1.00 times in the first example. FIG. 5 is a diagram illustrating various aberrations at an imaging magnification of −0.5833 times in the first example. It is a lens block diagram of the variable magnification lens which concerns on 2nd Example of this invention. FIG. 10 is a diagram illustrating a movement locus of each lens unit when a magnification is changed from a high magnification side (−1.75 times) to a low magnification side (−0.5833 times) in the magnification lens according to the second example. FIG. 12 is a diagram illustrating various aberrations at an imaging magnification of 1.75 times in the second example. FIG. 12 is a diagram illustrating various aberrations at the imaging magnification of −1.00 times in the second example. FIG. 12 is a diagram illustrating various aberrations at the imaging magnification of −0.5833 times in the second example. It is a lens block diagram of the variable magnification lens which concerns on 3rd Example of this invention. FIG. 12 is a diagram illustrating a movement locus of each lens unit when a magnification is changed from a high magnification side (−1.75 times) to a low magnification side (−0.5833 times) in the magnification lens according to the third example. FIG. 11 is a diagram illustrating all aberrations at the imaging magnification of 1.75 times in the third example. FIG. 12 is a diagram illustrating various aberrations at the imaging magnification of −1.00 times in the third example. FIG. 10 is a diagram illustrating all aberrations at the imaging magnification of −0.5833 times in the third example. It is a lens block diagram of the variable magnification lens which concerns on 4th Example of this invention. FIG. 10 is a diagram illustrating a movement locus of each lens unit when a magnification is changed from a high magnification side (−1.75 times) to a low magnification side (−0.5833 times) in a magnification lens according to a fourth example. FIG. 12 is a diagram illustrating various aberrations at the imaging magnification of 1.75 times in the fourth example. FIG. 11 is a diagram illustrating all aberrations at the imaging magnification of −1.00 in the fourth example. FIG. 10 is a diagram illustrating all aberrations at the imaging magnification of −0.5833 times in the fourth example.

Explanation of symbols

G1 First lens group G2 Second lens group G3 Third lens group S Aperture stop FS Flare stop I Image surface

Claims (2)

In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, an aperture stop, and a third lens group having a positive refractive power,
The first lens group is configured to include a cemented lens of a positive lens and a negative lens located closest to the object side,
The second lens group is composed of three bonded lenses having negative refractive power,
The third lens group includes three cemented lenses having negative refractive power with a concave surface facing the object side located closest to the object side,
When focusing from the high magnification to the low magnification side, the air gap between the first lens group and the second lens group and the air gap between the second lens group and the third lens group change ,
The focal length of the second lens group is f2, the focal length of the entire lens system at the highest magnification is f, the combined focal length of the first lens group and the second lens group at the highest magnification is f12, and The focal length of the third lens group is f3, the air gap between the first lens group and the second lens group at the maximum magnification is D12, and the second lens group and the third lens group at the maximum magnification are When the air interval of D23 is D23,
−7.05 <f2 / f <−1.54
1.29 <f12 / f3 <1.91
0.006 <D12 / f <0.026
0.028 <D12 / D23 <0.2
A zoom lens characterized by satisfying the above conditions . The variable power lens according to claim 1 , further comprising a flare stop before and after the aperture stop.

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