JP4542933B2 - 5-group zoom lens - Google Patents

Description

  The present invention relates to a zoom lens used in a video camera, a digital camera or the like using a light receiving element such as a CCD or a CMOS. In particular, the present invention relates to a zoom lens that has a high resolution, a small size, and a light weight while having a large aperture with an F number of about 2.0 and a zoom magnification of about 30 times.

  2. Description of the Related Art Conventionally, zoom lenses used in video cameras and digital cameras include a first lens group having a positive refractive power and a second lens group having a negative refractive power from the object side toward the image plane. A third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power are arranged in this order. Yes. Such zoom lenses having a positive, negative, positive, and positive five-group configuration are disclosed in Patent Documents 1 to 5.

Patent Documents 1 and 2 disclose a magnification of about 6 times, Patent Document 3 discloses a magnification of about 8 to 10 times, and Patent Document 4 discloses a magnification of about 10 times. Are disclosed. All of these are so-called rear focus types in which the fourth lens group on the image plane side corrects the movement of the focal position by zooming and performs focusing. On the other hand, Patent Document 5 discloses a focusing method of such a rear focus type zoom lens having a five-group configuration.

Here, when a zoom lens is mounted in a speed dome used in security systems, etc., the zoom magnification is 30 mm or more, but the zoom lens is designed so that the total lens length is approximately 85 mm or less. It is necessary to make the lens small and light. Specifically, the following conditions must be satisfied.
2.0 <L / Z <3.0
However,
L: Distance from the first lens on the object side to the image plane Z: Zoom magnification
Japanese Patent Laid-Open No. 4-13109 JP-A-5-224125 JP-A-4-301612 JP-A-8-327904 Japanese Patent Laid-Open No. 60-6914

  The rear focus type zoom lens has an advantage that the entire lens system can be made compact and compact compared to other types of zoom lenses. In addition, there is an advantage that a focusing mechanism that performs autofocusing can also be configured in a small size.

However, the conventional rear focus type zoom lens having a five-group configuration is focused by the fourth lens group on the image forming plane side or by the fourth lens group and the fifth lens group. In the case of this type, there is a tendency that the zoom magnification at finite distance tends to decrease compared to the zoom magnification at infinity, and there is a problem that it deviates from the nominal zoom magnification .

An object of the present invention is to provide a compact, lightweight zoom lens with a high resolution that can also ensure the same zoom magnification and when infinity at the time finite.

In order to solve the above-described problem, in the zoom lens having a five-group structure according to the present invention, the first lens group having a positive refractive power and the second lens having a negative refractive power from the object side toward the imaging surface side. Group, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power are arranged in this order. The zoom lens has a five-group configuration in which the first lens group, the third lens group, and the fifth lens group are fixed, and the second lens group and the fourth lens group are moved. with satisfied, among the lens surfaces of the lenses constituting said third lens group and the fourth lens group, is configured as at least one surface is an aspherical surface.
0.1 <| f2 / f1 | <0.18 (1)
1.36 <| f2 / FW | <1.75 (2)
3.7 <| f3 / FW | <10.0 (3)
1.2 <f3 / f4 <3.0 (4)
0.7 <(S) / (Z) <1.2 (5)
However,
FW: focal length at wide-angle end f1: focal length of first lens group f2: focal length of second lens group f3: focal length of third lens group f4: focal length of fourth lens group
(S): Amount of movement of the second lens unit during zooming from the wide-angle end to the telephoto end
(Z): Zoom magnification

In the present invention, for zooming, the first lens group, the third lens group, and the fifth lens group are fixed, the second lens group is moved in the front-rear direction along the optical axis, and the fourth lens group is moved. It is preferable to move the lens group in a direction to correct the fluctuation of the focal position.

The third lens group includes one convex lens and one concave lens, and at least one of the convex lens and the concave lens can be a plastic lens.

In this case, it is desirable that the third lens group satisfies the following conditions.
| F3Aνd−f3Bνd |> 20 (6)
However,
f3Aνd: Abbe number of convex lens
f3Bνd: Abbe number of concave lens

  Here, the conditional expression (1) is for determining the ratio of the focal lengths of the first lens group and the second lens group within an appropriate range. That is, this relates to the displacement of the first conjugate point with respect to the object point in the zooming range by the first lens group and the second lens group. If the lower limit of 0.1 of conditional expression (1) is not reached, the total length of the telephoto end is shortened relative to the wide-angle end, and the power of the second lens group is increased, ensuring stable performance in the zoom range. It becomes difficult. On the other hand, if the upper limit of 0.18 of conditional expression (1) is exceeded, the total length of the telephoto end becomes longer than the wide-angle end, and the focal position correction amount of the fourth lens group at the telephoto end increases abruptly. And it becomes difficult in terms of both performance.

  Conditional expression (2) relates to downsizing of the entire lens system and indicates the range of the focal length of the second lens group. If the lower limit of 0.36 of this conditional expression is not reached, the focal length of the second lens group becomes short, and it becomes difficult to correct aberrations generated by the second lens group. In addition, when the fourth lens group that corrects the focal position at the time of zooming is closest to the object side at the telephoto end and attempts to focus by the fourth lens group, the distance between the third lens group and the fourth lens group is Since it is necessary to increase the size, it is difficult to reduce the size of the entire lens system. On the other hand, if the upper limit of 1.75 in conditional expression (2) is exceeded, the focal length of the second lens group becomes too long and the amount of movement at the time of zooming increases, so that the entire lens system becomes longer and the first lens system becomes longer. The aperture of the lens group becomes large, and the entire lens system cannot be reduced in size. In addition, since the focal position correction amount of the fourth lens group at the time of zooming increases toward the image plane at the telephoto end, it is difficult to reduce the size of the lens system and correct aberrations.

  Conditional expression (3) is a condition for maintaining the range of the focal length of the third lens group appropriately. If the lower limit of 3.7 is not reached, the refractive power of the third lens group becomes too strong and spherical aberration or In addition to making it difficult to correct coma, it is difficult to secure bf (back focus). On the other hand, if the upper limit of 10.0 of the conditional expression (3) is exceeded, not only the lens system can be reduced in size, but also the amount of aberration accompanying focusing increases, and stable aberration correction from infinity to short distance cannot be obtained. .

  Conditional expression (4) is for maintaining an appropriate focal length between the third lens group and the fourth lens group, stably maintaining optical performance within a predetermined zoom, and the length of the entire lens system. It is also a condition for keeping small. If the lower limit of 1.2 of conditional expression (4) is not reached, the focal length of the third lens group and the fourth lens group is shortened, which is effective in shortening the overall length of the lens system. It becomes difficult to correct aberrations. In addition, it is difficult to secure bf. On the other hand, if the upper limit of 3.0 of the conditional expression (4) is exceeded, the focal length of the third lens group becomes long, which is not suitable for shortening the total length of the lens system.

  Conditional expression (5) is for shortening the entire lens system. If the lower limit of 0.7 of the conditional expression (5) is not reached, the total length of the lens system can be shortened, but spherical aberration and coma aberration in the entire zoom range while keeping the first lens group and the second lens group appropriate. It becomes difficult to maintain such aberrations as good. On the other hand, if the upper limit of 1.2 of the conditional expression (5) is exceeded, the refractive power of the first lens group and the second lens group can be weakened, but the total length of the lens system becomes long, so it does not meet the purpose of small size and light weight. .

  Conditional expression (6) is also for maintaining high chromatic aberration on the axis and chromatic aberration off axis in the entire zoom range, and for achieving high magnification while maintaining good correction of spherical aberration and coma aberration. . If it is out of the range of this conditional expression, it is necessary to make the focal length of either the convex lens or the concave lens extremely small in order to correct the axial chromatic aberration. Not only can it not be improved, but it is impossible to use inexpensive plastic lenses. Therefore, an inexpensive and compact high-power zoom lens cannot be obtained. However, the third lens group can be constituted by a glass lens.

The zoom lens according to the present invention is configured with a lens number substantially the same as that of a conventional zoom lens having a zoom ratio of about 5 to 10 times while having a high zoom ratio of 30 times or more, and good aberration correction can be achieved. It is possible to realize. Here, in a zoom lens having a five-group configuration, when focusing is to be performed by the fourth lens group, the fourth lens group is largely moved toward the object side. At this time, the focal length on the telephoto side is significantly reduced when the object position is finite compared to when it is at infinity, and deviates from the effective magnification. On the other hand, in the present invention, focusing is performed by moving the second lens group and the fourth lens group. Compared with the case where focusing is performed only by the fourth lens group, the moving amount of the lens group can be reduced, and the focal length at the finite distance at the telephoto end can be prevented from being shortened. Therefore, it is possible to provide a high-power zoom lens that is lightweight, compact, and inexpensive while maintaining high optical performance in the entire zooming area and the entire focusing area.

Furthermore, according to the zoom lens of the present invention, since the zooming and focusing movable lenses are the same, it is convenient in terms of mechanism.

In the zoom lens of the present invention, focusing is performed by moving the second lens group and the fourth lens group. Compared with the case where focusing is performed only by the fourth lens group, the moving amount of the lens group can be reduced, and the focal length at the finite distance at the telephoto end can be prevented from being shortened. Therefore, it is possible to provide a high-power zoom lens that is lightweight, compact, and inexpensive while maintaining high optical performance in the entire zooming area and the entire focusing area.

  Embodiments of a zoom lens to which the present invention is applied will be described below with reference to the drawings.

[Embodiment 1]
FIG. 1 is a configuration diagram illustrating a zoom lens according to Embodiment 1 of the present invention. The zoom lens 10 of the present example has a first lens group 1 having a positive refractive power, a second lens group 2 having a negative refractive power, and a first lens having a positive refractive power from the object side toward the image plane 8. The three-lens group 3, the fourth lens group 4 having a positive refractive power, and the fifth lens group 5 having a negative refractive power have a five-group configuration arranged in this order.

  The first lens group 1 includes, in order from the object side, a negative meniscus first lens G1 having a convex surface facing the object side, a biconvex second lens G2, and a positive meniscus first lens having a convex surface facing the object side. 3 lenses G3. The second lens group 2 is a cemented lens including, in order from the object side, a negative meniscus fourth lens G4 having a convex surface facing the object side, a biconcave fifth lens G5, and a biconvex sixth lens G6. is there. The third lens group 3 includes, in order from the object side, a biconvex seventh lens G7 having a strong convex surface facing the object side, and a negative meniscus eighth lens G8 having a convex surface facing the image surface side. The fourth lens group 4 is a cemented lens including, in order from the object side, a negative meniscus ninth lens G9 having a convex surface facing the object side and a biconvex tenth lens G10. The fifth lens group 5 includes a negative meniscus eleventh lens G11 with a strong concave surface facing the image surface side.

  In the third lens group 3, the lens surface on the image plane side of the seventh lens G7 and the lens surface on the object side of the eighth lens G8 are aspheric surfaces. In the fourth lens group 4, the tenth lens G10 has an aspheric lens surface on the image side.

  Here, in the zoom lens 10 of this example, when zooming from the wide-angle end to the telephoto end, the first lens group 1, the third lens group 3, and the fifth lens group 5 are fixed, and the second lens group 2 is It moves in the front-rear direction on the optical axis 10a from the object side to the image plane side. On the other hand, the fourth lens group 4 draws a convex curve on the object side toward the object side so as to correct the difference in focal position during zooming caused by the movement of the second lens group 2. Move along the trajectory. Thereby, on the imaging plane 8, the imaging position is flat from the wide-angle end to the telephoto end.

  In the distance adjustment in the zoom lens of this example, when the imaging magnification after the second lens group 2 is β, the second lens group 2 is moved to the imaging side from the time when β exceeds −1. The four lens group 4 is moved to the object side to focus on a short distance. As a result, it is possible to prevent a reduction in magnification that occurs during distance adjustment using only the fourth lens group 4. In addition, since the movable lens is specified for the second lens group 2 and the fourth lens group 4, it is convenient in terms of structure.

  Further, at the telephoto end, it is possible to photograph an object within 1 m even though the focal length exceeds 100 mm.

  In this example, a diaphragm 6 is disposed between the second lens group 2 and the third lens group 3, and an IR cut filter 7 and a cover glass (cover glass (between the fifth lens group 5 and the imaging surface 8)). Etc.) are arranged.

The lens data of the entire optical system of the zoom lens 10 of Embodiment 1 is as follows.
(Wide-angle end) (Normal) (Telephoto end)
F-number: 1.83 2.61 4.75
Focal length: 3.85 37.79 123.17 (mm)
Focal length f1: 40.560 mm of the first lens group
Focal length f2 of the second lens group: −5.598 mm
Focal length f3 of the third lens group: 25.818 mm
Focal length f4 of the fourth lens group: 14.427 mm
Movement amount at the time of zooming from the wide-angle end to the telephoto end of the second lens group (S): 28.638 mm
Zoom magnification (Z): 31.992

  Table 1A shows lens data of each lens surface of the zoom lens 10, and Table 1B shows aspheric coefficients for defining the aspherical shape of the aspherical lens surface. In Table 1A, i represents the order of the lens surfaces counted from the object side, R represents the radius of curvature of the lens surfaces, d represents the distance between the lens surfaces, Nd represents the refractive index of each lens, and νd represents Represents the Abbe number of each lens. In addition, the lens surface having the number i with an asterisk represents an aspherical surface.

  The aspherical shape adopted for the lens surface is given by the following equation, where X is the axis in the direction of the optical axis 10a, H is the height in the direction orthogonal to the optical axis 10a, K is the conic coefficient, and A and B are the aspheric coefficients. Can be represented by

  The meaning of each symbol and the expression representing the aspherical shape are the same in Embodiments 2 to 5 described later.

FIG. 2 is an aberration diagram showing various aberrations of the zoom lens 10 of the first embodiment. In the figure, W represents wide (wide angle), N represents normal, T represents tele (telephoto), SA represents spherical aberration, OSC represents sine conditions, AS represents astigmatism, and DIST represents distortion. In the AS, T represents tangential, and S represents sagittal .

In addition, the zoom lens 10 according to Embodiment 1 satisfies the following conditional expressions (1) to (6).
0.1 <| f2 / f1 | <0.18 (1)
1.36 <| f2 / FW | <1.75 (2)
3.7 <| f3 / FW | <10.0 (3)
1.2 <f3 / f4 <3.0 (4)
0.7 <(S) / (Z) <1.2 (5)
| F3Aνd−f3Bνd |> 20 (6)
However,
FW: focal length at wide-angle end f1, f2, f3, f4: focal length of each lens group f3Aνd: Abbe number of convex lens of third lens group f3Bνd: Abbe number of concave lens of third lens group

  That is, | f2 / f1 | = 0.138, | f2 / FW | = 1.45, | f3 / FW | = 6.71, f3 / f4 = 1.79, (S ) / (Z) = 0.895, | f3Aνd−f3Bνd | = 37.5, which satisfies the conditional expressions (1) to (6).

[Embodiment 2]
FIG. 3 is a block diagram showing a zoom lens according to Embodiment 2 of the present invention. Since the basic configuration of the zoom lens 20 of this example is the same as in the case of FIG. 1, the corresponding parts are denoted by the same reference numerals.

  The zoom lens 20 according to the present embodiment sequentially moves from the object side back and forth on the optical axis in the first lens group 1 which is fixed at the time of zooming having a positive refractive power and at the time of zooming having a negative refractive power. A second lens group 2; a third lens group 3 fixed at the time of zooming having a positive refractive power; a fourth lens group 4 moving in a direction for correcting a change in focal position that occurs at the time of zooming having a positive refractive power; Further, the fifth lens group 5 fixed at the time of zooming having a negative refractive power has a five-group configuration in which they are arranged in this order.

  The first lens group 1 includes, in order from the object side, a cemented lens including a negative meniscus first lens G1 and a biconvex second lens G2 having a convex surface facing the object side, and a positive lens having a convex surface facing the object side. It comprises a meniscus third lens G3. The second lens group 2 is a cemented lens including, in order from the object side, a negative meniscus fourth lens G4 having a convex surface directed toward the object side, a biconcave fifth lens G5, and a biconvex sixth lens G6. . The third lens group 3 includes, in order from the object side, a biconvex seventh lens G7 having a strong convex surface facing the object side, and a negative meniscus eighth lens G8 having a convex surface facing the image surface side. The fourth lens group 4 is a cemented lens including, in order from the object side, a negative meniscus ninth lens G9 having a convex surface facing the object side and a biconvex tenth lens G10. The fifth lens group 5 includes a negative meniscus eleventh lens G11 having a convex surface directed toward the object side.

  In the third lens group 3, the eighth lens G8 is a plastic lens, and both surfaces are aspheric. In the fourth lens group 4, the tenth lens G10 has an aspherical second surface on the image plane side.

  In the zoom lens 20 of the present example, zooming from the wide-angle end to the telephoto end and distance adjustment are the same as those in the first embodiment, and thus description thereof is omitted.

The lens data of the entire optical system of the zoom lens 20 according to the second embodiment is as follows.
(Wide-angle end) (Normal) (Telephoto end)
F number: 1.73 2.22 4.33
Focal length: 3.764 36.657 118.80 (mm)
f1: 41.359mm
f2: -5.996 mm
f3: 28.735mm
f4: 14.222mm
(S): 28.601 mm
(Z): 31.562

  Table 2A shows lens data of each lens surface of the zoom lens 20, and Table 2B shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface.

  FIG. 4 is an aberration diagram showing various aberrations of the zoom lens 20 of the second embodiment.

  In this example, | f2 / f1 | = 0.145, | f2 / FW | = 1.59, | f3 / FW | = 7.638, f3 / f4 = 2.02, (S) / (Z) = 0.91, | f3Aνd−f3Bνd | = 40.5, which satisfies the above conditional expressions (1) to (6).

[Embodiment 3]
FIG. 5 is a block diagram showing a zoom lens according to Embodiment 3 of the present invention. Since the basic configuration is the same as that in FIG. 1, the corresponding parts are denoted by the same reference numerals. The zoom lens 30 includes, in order from the object side, a first lens group 1 having a positive refractive power, a second lens group 2 having a negative refractive power, a third lens group 3 having a positive refractive power, and a positive refractive power. And a fifth lens group 5 having negative refractive power and having a five-group configuration arranged in this order. In zooming from the wide-angle end to the telephoto end, the first lens group 1, the third lens group 3, and the fifth lens group 5 are fixed, the second lens group 2 moves in the front-rear direction on the optical axis, The four lens group 4 is moved in a direction for correcting the fluctuation of the focal position.

  The first lens group 1 includes, in order from the object side, a cemented lens including a negative meniscus first lens G1 and a biconvex second lens G2 having a convex surface facing the object side, and a positive lens having a convex surface facing the object side. It comprises a meniscus third lens G3. The second lens group 2 is a cemented lens including, in order from the object side, a negative meniscus fourth lens G4 having a convex surface directed toward the object side, a biconcave fifth lens G5, and a biconvex sixth lens G6. . The third lens group 3 includes, in order from the object side, a biconvex seventh lens G7 and a negative meniscus eighth lens G8 with the convex surface facing the image surface side. The fourth lens group 4 is a cemented lens including, in order from the object side, a negative meniscus ninth lens G9 having a convex surface facing the object side and a biconvex tenth lens G10. The fifth lens group 5 includes a negative biconcave eleventh lens G11.

  In the third lens group 3, the seventh lens G7 is a plastic lens, and both surfaces are aspherical surfaces. In the fourth lens group 4, the tenth lens G10 has an aspherical second surface on the image plane side. Note that an IR filter 7 and a cover glass are disposed between the fifth lens group and the imaging plane 8.

The lens data of the entire optical system of the zoom lens 30 according to the third embodiment is as follows.
(Wide-angle end) (Normal) (Telephoto end)
F number: 1.70 2.28 4.51
Focal length: 3.842 37.9 122.93 (mm)
f1: 41.239 mm
f2: −5.721 mm
f3: 26.642 mm
f4: 14.053 mm
(S): 28.737 mm
(Z): 31.996

  Table 3A shows lens data of each lens surface of the zoom lens 30, and Table 3B shows aspheric coefficients for defining the aspherical shape of the aspherical lens surface.

  FIG. 6 is an aberration diagram showing various aberrations of the zoom lens 30 according to the third embodiment.

  In this example, | f2 / f1 | = 0.139, | f2 / FW | = 1.490, | f3 / FW | = 6.934, f3 / f4 = 1.896, (S) / (Z) = 0.898, | f3Aνd−f3Bνd | = 32.4, which satisfies the above-described conditional expressions (1) to (6).

[Embodiment 4]
FIG. 7 is a block diagram showing a zoom lens according to Embodiment 4 of the present invention. Since the basic configuration is the same as that in FIG. 1, the corresponding parts are denoted by the same reference numerals. The zoom lens 40 includes, in order from the object side, a first lens group 1 having a positive refractive power, a second lens group 2 having a negative refractive power, a third lens group 3 having a positive refractive power, and a positive refractive power. And a fifth lens group 5 having negative refractive power and having a five-group configuration arranged in this order. In zooming from the wide-angle end to the telephoto end, the first lens group 1, the third lens group 3, and the fifth lens group 5 are fixed, the second lens group 2 moves in the front-rear direction on the optical axis, The four lens group 4 is moved in a direction for correcting the fluctuation of the focal position.

  The first lens group 1 includes, in order from the object side, a cemented lens including a negative meniscus first lens G1 and a biconvex second lens G2 having a convex surface facing the object side, and a positive meniscus third lens G3. Consists of. The second lens group 2 is a cemented lens including, in order from the object side, a negative meniscus fourth lens G4 having a convex surface directed toward the object side, a biconcave fifth lens G5, and a positive meniscus sixth lens G6. is there. The third lens group 3 includes, in order from the object side, a biconvex seventh lens G7 and a negative meniscus eighth lens G8 with the convex surface facing the image surface side. The fourth lens group 4 is a cemented lens including, in order from the object side, a negative meniscus ninth lens G9 and a positive meniscus tenth lens G10. The fifth lens group 5 includes a negative meniscus eleventh lens G11 having a convex surface directed toward the object side.

  The seventh lens G7 and the eighth lens G8 constituting the third lens group 3 are both plastic lenses, and each of these lens surfaces is aspheric. In the fourth lens group 4, the tenth lens G10 has an aspherical second surface on the image plane side.

The lens data of the entire optical system of the zoom lens 40 according to the fourth embodiment is as follows.
(Wide-angle end) (Normal) (Telephoto end)
F number: 1.77 2.40 4.48
Focal length: 3.837 38.652 122.726 (mm)
f1: 41.736 mm
f2: −5.714 mm
f3: 28.207mm
f4: 13.902 mm
(S): 28.737
(Z): 31.985

  Table 4A shows lens data of each lens surface of the zoom lens 40, and Table 4B shows aspheric coefficients for defining the aspherical shape of the aspherical lens surface.

  FIG. 8 is an aberration diagram showing various aberrations of the zoom lens 40 of the fourth embodiment.

  In this example, | f2 / f1 | = 0.137, | f2 / FW | = 1.490, | f3 / FW | = 7.35, f3 / f4 = 2.03, (S) / (Z) = 0.898, | f3Aνd−f3Bνd | = 26.3, which satisfies the above conditional expressions (1) to (6).

[Embodiment 5]
Since the zoom lens according to the fifth embodiment has basically the same configuration as the zoom lens 10 according to the first embodiment, the configuration will be described with reference to FIG. 1 showing the zoom lens 10 according to the first embodiment. The zoom lens 50 includes, in order from the object side, a first lens group 1 having a positive refractive power, a second lens group 2 having a negative refractive power, a third lens group 3 having a positive refractive power, and a positive refractive power. And a fifth lens group 5 having negative refractive power and having a five-group configuration arranged in this order. In zooming from the wide-angle end to the telephoto end, the first lens group 1, the third lens group 3, and the fifth lens group 5 are fixed, the second lens group 2 moves in the front-rear direction on the optical axis, The four lens group 4 is moved in a direction for correcting the fluctuation of the focal position.

  The first lens group 1 includes, in order from the object side, a negative meniscus first lens G1 having a convex surface facing the object side, a biconvex second lens G2, and a positive meniscus first lens having a convex surface facing the object side. 3 lenses G3. The second lens group 2 includes, in order from the object side, a negative meniscus fourth lens G4 having a convex surface facing the object side, a biconcave fifth lens G5, and a positive meniscus sixth lens having a convex surface facing the object side. This is a cemented lens including the lens G6. The third lens group 3 includes, in order from the object side, a biconvex seventh lens G7 and a negative meniscus eighth lens G8 with the convex surface facing the image surface side. The fourth lens group 4 is a cemented lens including, in order from the object side, a negative meniscus ninth lens G9 having a convex surface facing the object side and a biconvex tenth lens G10. The fifth lens group 5 is composed of one negative meniscus eleventh lens G11 having a convex surface facing the object side.

  In the third lens group 3, the eighth lens G8 is a plastic lens, and both surfaces are aspheric. In the fourth lens group 4, the tenth lens G10 has an aspherical second surface on the image side.

The lens data of the entire optical system of the zoom lens 50 according to the fifth embodiment is as follows.
(Wide-angle end) (Normal) (Telephoto end)
F number: 1.88 2.67 4.70
Focal length: 3.815 39.28 121.975 (mm)
f1: 40.75mm
f2: -5.598 mm
f3: 27.102 mm
f4: 14.74 mm
(S): 28.638 mm
(Z): 31.972

  Table 5A shows lens data of each lens surface of the zoom lens 50, and Table 5B shows aspheric coefficients for defining the aspheric shape of the aspheric lens surface.

  FIG. 9 is an aberration diagram showing various aberrations of the zoom lens 50 according to the fifth embodiment.

  In this example, | f2 / f1 | = 0.14, | f2 / FW | = 1.5, | f3 / FW | = 7.1, and f3 / f4 = 1.84. (S) / (Z) = 0.9, | f3Aνd−f3Bνd | = 51.7, which satisfies the above-described conditional expressions (1) to (6).

It is a block diagram which shows the zoom lens which concerns on Embodiment 1 and 5 of this invention. FIG. 6 is an aberration diagram illustrating various aberrations of the zoom lens according to the first embodiment. It is a block diagram which shows the zoom lens which concerns on Embodiment 2 of this invention. 6 is an aberration diagram illustrating various aberrations of the zoom lens according to Embodiment 2. FIG. It is a block diagram which shows the zoom lens which concerns on Embodiment 3 of this invention. FIG. 10 is an aberration diagram illustrating various aberrations of the zoom lens according to Embodiment 3; It is a block diagram which shows the zoom lens which concerns on Embodiment 4 of this invention. FIG. 6 is an aberration diagram illustrating various aberrations of the zoom lens according to the fourth embodiment. FIG. 10 is an aberration diagram illustrating various aberrations of the zoom lens according to Embodiment 5.

Explanation of symbols

10, 20, 30, 40, 50 Zoom lens 1 First lens group 2 Second lens group 3 Third lens group 4 Fourth lens group 5 Fifth lens group 6 Aperture 7 Filter 8 Imaging plane G1 First lens G2 First 2 lens G3 3rd lens G4 4th lens G5 5th lens G6 6th lens G7 7th lens G8 8th lens G9 9th lens G10 10th lens G11 11th lens

Claims (4)

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 positive refractive power from the object side toward the imaging plane side The fourth lens group and the fifth lens group having a negative refractive power are arranged in this order, and the first lens group, the third lens group, and the fifth lens group are fixed during zooming. A zoom lens having a five-group configuration in which the second lens group and the fourth lens group are moved,
A zoom lens having a five-group structure, wherein the following conditional expression is satisfied, and at least one of the lens surfaces of the lenses constituting the third lens group and the fourth lens group is an aspherical surface. .
0.1 <| f2 / f1 | <0.18 (1)
1.36 <| f2 / FW | <1.75 (2)
3.7 <| f3 / FW | <10.0 (3)
1.2 <f3 / f4 <3.0 (4)
0.7 <(S) / (Z) <1.2 (5)
However,
FW: focal length at wide-angle end f1: focal length of first lens group f2: focal length of second lens group f3: focal length of third lens group f4: focal length of fourth lens group
(S): Amount of movement of the second lens unit during zooming from the wide-angle end to the telephoto end
(Z): Zoom magnification In claim 1,
In zooming, the first lens group, the third lens group, and the fifth lens group are fixed, the second lens group is moved in the front-rear direction along the optical axis, and the fourth lens group is focused. A zoom lens, wherein the zoom lens is adapted to move in a direction for correcting a change in position. In claim 1 or 2,
The third lens group includes one convex lens and one concave lens,
A zoom lens, wherein at least one of the convex lens and the concave lens is a plastic lens. In claim 3,
The zoom lens according to claim 3, wherein the third lens group satisfies the following conditions.
| F3Aνd−f3Bνd |> 20 (6)
However,
f3Aνd: Abbe number of convex lens
f3Bνd: Abbe number of concave lens