JP2005250285A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost and high-performance zoom lens by miniaturizing a lens system which has 1.05 to 1.2 F number and has a large diameter of about 15 variable magnifications and has high variable magnifications. <P>SOLUTION: The zoom lens comprises a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a positive refracting power in order from the object side, and the first and third lens groups are fixed. The third lens group consists of one positive lens and has at least one aspherical surface. The second lens group is moved in one direction to vary the magnification, and the fourth lens group is moved non-linearly to compensate movement of an image surface, which is caused by varying the magnification, and is moved to the object side to focus the zoom lens on an object at infinity to a close object. The fourth lens group consists of two positive lenses and one negative lens and has no aspherical surfaces, The zoom lens consists of 10 lenses in total. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a zoom lens, and more particularly to a zoom lens that employs a high-magnification, bright, and large-aperture-ratio master focus method suitable for a still camera, a video camera, a broadcast TV camera, and the like.

  There is a so-called four-group zoom lens as a zoom lens having a relatively high zoom ratio and a large aperture ratio used in a still camera, a video camera, or the like. In general, the four-group zoom lens includes, in order from the object side, a first lens group for focusing, a second lens group for zooming, a third lens group for correcting image plane movement accompanying zooming, and all The fourth lens group is used to balance the focal length and aberration correction of the system.

  This type of four-group zoom lens is a front focus (front lens extension) type zoom lens that moves the first lens group for focusing in addition to the two lens groups for zooming. In the front focus method, since the focal length of the first lens group is large, the amount of extension is large, and usually the angle of view variation tends to be large. Further, when focusing on a short-distance object, if a sufficient off-axis light beam is to be secured, the front lens diameter increases, which leads to an increase in the size and complexity of the lens configuration.

  Therefore, recently, various zoom lenses using a so-called master focus (rear focus) method using the rear lens group for focusing have been proposed (see, for example, Patent Documents 1, 2, 3, and 4).

  That is, in the conventional zoom lens described in Patent Document 1, the first lens group and the third lens group are fixed in the four-group zoom lens, the second lens group is moved in one direction, and zooming is performed. The group is moved non-linearly to correct the image plane movement accompanying zooming, and the fourth lens group is moved to the object side to focus from an infinite object to a close object.

  Further, in the conventional zoom lens described in Patent Document 2, in the same four-group zoom lens, the fourth lens group is composed of at least two positive lenses and one negative lens, and one of these is a plastic doublet (1 One positive lens and one negative lens). This Patent Document 2 discloses a zoom lens having a high zoom ratio and a low cost, including an example in which an F number is 1.2, 14 times, and 11 lenses including 6 aspherical surfaces have 5 plastic lenses. doing.

  Patent Document 3 discloses a four-group zoom lens as in Patent Documents 1 and 2. In the conventional zoom lens described in Patent Document 3, the fourth lens group is composed of two sets of doublets in which a positive lens and a negative lens are combined, and one set of these doublets is a plastic doublet. In this Patent Document 3, as Example 2, a zoom lens having a 12-lens configuration including 12 aspherical surfaces at 12 times the F number of 1.2 is disclosed.

  Further, the conventional zoom lens described in Patent Document 4 has a simple and compact configuration in which the fourth lens group is composed of at least one positive lens and one negative lens in the four-group zoom lens as described above. .

Japanese Patent No. 2901144 JP-A-9-311272 JP-A-8-320434 JP 2003-121737 A

  However, since the conventional zoom lens described in Patent Document 1 is composed of spherical lenses, the zoom lens is configured even when the F-number is as bright as 1.2 and the magnification is about 6 times. This requires 12 to 13 lenses, and as a result, there is a problem in that the diameter and overall length of the zoom lens increase and the size increases.

  Moreover, since the conventional zoom lens described in Patent Document 2 includes many plastic lenses, the aperture and the total length of the lens inevitably increase. In the example of the 11-sheet configuration described above, there are problems that the total length is as long as 77 mm, and birefringence occurs to impair image quality.

  In addition, the conventional zoom lens described in Patent Document 3 includes five plastic lenses and is low in cost. However, similar to the conventional zoom lens described in Patent Document 2, the aperture and the total length of the zoom lens resulting from the plastic lens are included. Increase (total length of about 83.5 mm). In addition, deterioration of image quality is inevitable due to the occurrence of birefringence. Furthermore, the conventional zoom lens described in Patent Document 4 has a magnification of only 10 and further includes two aspherical balls, so that it is compact but expensive and low in productivity.

  The present invention has been made in view of the above points, and has a F-number of 1.05 to 1.2, a large-aperture lens with a variable magnification of about 15 times, and a high-magnification lens system that has been downsized and is inexpensive and expensive An object is to provide a high-performance zoom lens.

  In order to achieve the above object, a zoom lens according to a first aspect of the 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, and a third lens group having a positive refractive power. The fourth lens group has a positive refractive power, the first lens group and the third lens group are fixed lens groups, and the third lens group is a zoom lens composed of one fixed positive lens. The fourth lens group is movable in a non-linear manner, has two positive lenses and one negative lens, and does not include an aspherical surface.

  In the present invention, the first lens group and the third lens group are fixed, the second lens group is moved in one direction to perform zooming, and the fourth lens group corrects image plane movement accompanying zooming. In a zoom lens for focusing from an object at infinity to a close object by moving in a non-linear manner, all the lenses constituting the fourth lens group are lenses that do not include an aspheric surface, and are integrated with the third lens group. The color is erased.

  In order to achieve the above object, a zoom lens according to a second aspect of the 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, and a third lens having a positive refractive power. The zoom lens includes a lens group, a fourth lens group having a positive refractive power, the first lens group and the third lens group are fixed lens groups, and the third lens group is composed of one fixed positive lens. The lens is characterized in that a fixed stop for limiting peripheral rays outside the second lens group at the telephoto end is provided between the first lens group and the second lens group.

  In the present invention, a fixed stop is provided between the first lens group and the second lens group so as to limit the peripheral rays outside the second lens group at the telephoto end. Deterioration of aberration can be prevented.

  Here, the positive lens constituting the third lens group may have an aspheric surface on at least one surface. Further, the first to fourth lens groups in the present invention are composed of a total of ten lenses. Furthermore, the zoom lens of the present invention has a magnification of 12 to 15 times, and an F number of 1.05 to 1.2.

  According to the present invention, a four-group master focus zoom with a bright F-number of about 1.05 to 1.2 and high optical performance over the entire zoom range with a high zoom ratio of 12 to 15 times. A lens that does not include an aspheric surface as a lens that constitutes the fourth lens group, and is achromatic with the third lens group, thereby realizing a high-quality zoom lens. Since an aspheric lens is not included in the lens group, cost reduction and productivity can be improved.

  In addition, according to the present invention, a fixed stop is provided between the first lens group and the second lens group, and the peripheral rays outside the second lens group at the telephoto end are limited, so that the outer side of the second lens group is limited. Since the deterioration of aberration due to peripheral rays is prevented, image quality deterioration due to peripheral rays at the telephoto end can be prevented, and the peripheral rays are not limited by the fixed aperture at the wide-angle end or in the middle range, so the fixed aperture reduces the darkness. Can also be prevented.

  Furthermore, according to the present invention, the total number of lenses can be reduced to ten, so that the overall length of the zoom lens can be reduced and the size can be reduced. Cost reduction can be achieved.

(First embodiment)
FIG. 1 is a schematic configuration diagram showing a first embodiment of a zoom lens according to the present invention together with surface numbers, and FIG. 2 shows a schematic configuration and a zoom trace curve of the first embodiment of the zoom lens according to the present invention. FIG. As shown in FIGS. 1 and 2, the zoom lens according to the first embodiment of the present invention includes, in order from the object side, a first lens group I having a positive refractive power and a second lens group II having a negative refractive power. And a third lens group III having a positive refractive power and a fourth lens group IV having a positive refractive power.

  As shown in FIG. 2, the first lens group I includes one negative lens 101 and two positive lenses 102 and 103 in order from the object side, and the second lens group II is formed from the object side. The two negative lenses 201 and 202 and one positive lens 203 are arranged in this order, the third lens group III is constituted by one positive lens 301, and the fourth lens group IV is two sheets in order from the object side. It comprises positive lenses 401 and 402 and a single negative lens 403. The positive lens 301 of the third lens group III is a double-sided aspheric meniscus lens. An optical LPF 601 is provided adjacent to the image side of the fourth lens group IV. The optical LPF 601 is precisely a combination of the thickness of the optical LPF and the CCD face plate.

  As described above, the zoom lens according to the present embodiment can shorten the overall length of the zoom lens by configuring the zoom lens with a total of ten lenses. The present embodiment is characterized in that the three lenses 401 to 403 constituting the fourth lens group IV do not have an aspheric surface.

  Zooming is performed by moving the second lens group II and the fourth lens group IV in the direction of the arrow in FIG. When the second lens group II is moved from the wide-angle end (W) to the telephoto end (T), the fourth lens group IV moves according to the zoom trace curve of FIG. At this time, the first lens group I and the third lens group III are fixed. In FIG. 2, a curve INF indicates a zoom trace curve for an object at infinity, and a curve NEAR indicates a zoom trace curve for a close object.

  The second lens group II mainly performs zooming, and the fourth lens group IV corrects image plane movement accompanying zooming. As shown in the zoom trace curve of FIG. 2, the fourth lens group IV moves non-linearly along a locus convex toward the object side. By moving the fourth lens group IV further toward the object side, focusing from an object at infinity to a close object is performed.

  As described above, the second lens group II having the negative refractive power disposed between the first lens group I having the positive refractive power and the third lens group III corresponding to the relay lens group is moved in one direction. As a result, image formation and zooming of the first lens group I to the third lens group III are performed. At the time of zooming, as described above, the fourth lens group IV is moved nonlinearly toward the third lens group III (object side) to correct the image plane movement, and the third lens group III and The space between the fourth lens group IV is effectively used to shorten the overall length of the zoom lens.

  During focusing, the first lens group I is always fixed without being extended. As a result, an increase in the lens diameter caused by feeding forward is prevented. When focusing, instead of the first lens group I, the fourth lens group IV, which is a part of the imaging system, is moved to reduce the number of movable lens groups, thereby simplifying and miniaturizing the entire zoom lens. I am trying.

  In the first lens group I and the second lens group II, chromatic aberration is corrected inside each lens group, and the third lens group III and the fourth lens group IV correct chromatic aberration as a unit of both groups. In addition, the first lens group I corrects mainly spherical aberration on the telephoto side, and the second lens group II mainly corrects astigmatism and distortion on the wide-angle side.

  In the present embodiment, as shown in FIGS. 1 and 2, the diaphragm 501 having the surface number 12 is located in or near the third lens group III. This arrangement is suitable for reducing aberration fluctuations due to the movable lens group and maintaining the lens diameters of the first lens group I and the fourth lens group IV in a well-balanced manner.

  Furthermore, in the present embodiment, the third lens group III is constituted by a single aspheric meniscus lens 301, and the fourth lens group IV does not include an aspheric surface. The third lens group III and the fourth lens group IV are integrally achromatic.

(Second Embodiment)
FIG. 3 is a schematic configuration diagram showing a second embodiment of a zoom lens according to the present invention together with surface numbers, and FIG. 4 is a schematic configuration diagram of a second embodiment of the zoom lens according to the present invention. In both figures, the same components as those in FIG. 1 or FIG. As shown in FIGS. 3 and 4, the second embodiment of the zoom lens according to the present invention includes a first lens group I having a positive refractive power and a second lens group II having a negative refractive power in order from the object side. The third lens group III having positive refractive power and the fourth lens group IV having positive refractive power are the same as in the first embodiment, but this embodiment is shown in FIG. As described above, by providing the fixed diaphragm 502 between the first lens group I and the second lens group II, the image quality at the telephoto end is improved.

  The effect of the fixed stop 502 will be described together with the ray tracing diagram of the second embodiment of the zoom lens of the present invention shown in FIG. 5A shows a middle angle WM on the wide-angle end side of the zoom lens, FIG. 5B shows a ray tracing diagram of the intermediate area M, and FIG. As shown in FIG. 5C, at the telephoto end T of the zoom lens in which the second lens group II is closest to the third lens group III, the peripheral rays outside the second lens group II are fixed among the peripheral rays 703. Since it is limited by the diaphragm 502, it is possible to prevent an adverse effect on the aberration caused by the peripheral light beam outside the second lens group II, and thereby improve the image quality at the telephoto end T.

  On the other hand, as shown in FIGS. 5A and 5B, the second lens group II is intermediate between the first lens group I and the third lens group III in the wide-angle end side intermediate area WM and the intermediate area M of the zoom lens. Since it is located closer to the first lens group I than the position, the peripheral rays 701 and 702 are not limited by the fixed aperture 502, so even if the fixed aperture 502 exists, the peripheral rays do not become dark. In this way, by providing the fixed stop 502 at a position that restricts the peripheral rays outside the second lens group II at the telephoto end T, the image quality at the telephoto end T is not affected without affecting the peripheral rays at other positions. Can be improved.

Next, examples of the present invention will be described. In the present invention, in order to reduce aberration variation due to zooming and reduce the size, the focal lengths of the first to fourth lens groups I to IV shown in FIGS. If the focal length at the end is fw,
6.08 <f1 / fw <7.03 (1)
1.35 <| f2 / fw | <1.54 (2)
6.66 <f3 / fw <8.19 (3)
1.89 <| f4 / f2 | <2.15 (4)
It is preferable to configure so as to satisfy the following conditions. The technical meaning of each conditional expression is as follows.

  Conditional expression (1) relates to the refractive power of the first lens group. If the refractive power of the first lens unit becomes too strong beyond the lower limit, it is difficult to correct axial aberrations and astigmatism on the telephoto side. If the refractive power of the first lens group becomes too weak beyond the upper limit value, the distance between the first lens group and the third lens group becomes too wide than the amount of movement of the second lens group, resulting in wasted space. This is not preferable.

  Conditional expression (2) relates to the refractive power of the second lens group. When the refractive power of the second lens unit is increased beyond the lower limit, it is desirable for downsizing, but the field curvature becomes large. On the other hand, if the refractive power of the second lens unit is weakened beyond the upper limit, the aberration variation associated with zooming is reduced, but the amount of movement of the second lens unit is increased to obtain a predetermined zooming ratio, and zooming is performed. The total length of the lens becomes longer.

  Conditional expression (3) relates to the refractive power of the third lens group. When the refractive power of the third lens group becomes strong beyond the lower limit, the spherical aberration on the wide angle side becomes insufficiently corrected, and accordingly, the refractive power of the fourth lens group must be weakened. As a result, the amount of movement of the fourth lens group increases. On the other hand, if the refractive power of the third lens unit becomes too weak beyond the upper limit, the spherical aberration on the wide angle side becomes overcorrected, which is not preferable.

  Conditional expression (4) represents the refractive power ratio between the second lens group and the fourth lens group. If the refractive power of the fourth lens unit becomes strong beyond the lower limit, it becomes difficult to correct aberration fluctuations during zooming. If the refractive power of the fourth lens unit becomes weaker beyond the upper limit, the movement amount increases, the back focus becomes longer, and the optical total length becomes too long, which is not preferable.

  According to the above conditional expressions (1) to (4), the first to fourth examples described below are examples of the first embodiment, and the fifth example is that of the second embodiment. This is an example. In each embodiment, r represents the radius of curvature of each lens surface, d represents the lens thickness and air spacing, and nd and νd represent the refractive index and Abbe number of the lens material. The aspherical surface is indicated by * and the aspherical coefficient is described. The aspherical surface is expressed by the following equation when the x-axis is in the optical axis direction, the y-axis is in the direction perpendicular to the optical axis, and k, a, b, c, d, and e are aspherical coefficients.

  The zoom lenses of the following examples each have 10 lenses as in the first and second embodiments described above. Among these, as shown in FIGS. 2 and 4, the negative lens 202 and the positive lens 203 are separated as a variator, and the fixed master as the third lens group is constituted by a meniscus double-sided aspheric glass lens 301. The moving master, which is the fourth lens group, has a three-lens configuration including convex and concave lenses 401 to 403, of which a convex lens (positive lens) 402 and a concave lens (negative lens) 403 are cemented lenses. No aspheric lens is used in the fourth lens group. The optical LPF 601 has a total thickness of 0.88 mm, which includes an optical LPF having a thickness of 0.38 mm and a CCD face plate (seal glass) having a thickness of 0.5 mm.

(First embodiment)
The first embodiment is a zoom lens having an F number F of 1.26 to 2.20, a focal length f of 2.692 mm to 30.862 mm, and an angle of view 2ω = 59.2 ° to 5.68 °. Lens data is shown in Table 1, and aspheric coefficient and position data are shown in Table 2. The surface numbers in Tables 1 and 2 are those shown in FIG.

また、この第１実施例の広角端Ｗ、中間域Ｍ及び望遠端Ｔにおける収差図は、それぞれ図６、図７及び図８に示される。また、本実施例の条件式の値は、ｆ１／ｆｗ＝６.５０９、｜ｆ２／ｆｗ｜＝１.４２５、ｆ３／ｆｗ＝７.７０７、｜ｆ４／ｆ２｜＝２.０４５である。このように、本実施例のズームレンズは、Ｆナンバーが１.２であり、かつ、１０枚構成としている。従来の１２〜１４枚構成のズームレンズに比較して、ズーム全長が短縮されると共に、画像が明るく、各収差が良好な高変倍（12倍）のズームレンズが実現される。

In addition, aberration diagrams of the first embodiment at the wide-angle end W, the intermediate region M, and the telephoto end T are shown in FIGS. 6, 7, and 8, respectively. Further, the values of the conditional expressions of the present embodiment are f1 / fw = 6.509, | f2 / fw | = 1.425, f3 / fw = 7.707, and | f4 / f2 | = 2.045. Thus, the zoom lens of the present embodiment has an F-number of 1.2 and a 10-lens configuration. Compared with a conventional zoom lens having 12 to 14 lenses, a zoom lens having a high zoom ratio (12 times) is realized in which the entire zoom length is shortened, the image is bright, and each aberration is favorable.

(Second embodiment)
The second embodiment is a zoom lens having an F number F: 1.155 to 2.807, a focal length f: 2.687 mm to 39.308 mm, and an angle of view 2ω = 59.3 ° to 4.46 °. Lens data is shown in Table 3, and aspherical coefficient and position data are shown in Table 4. The surface numbers in Tables 3 and 4 are as shown in FIG.

また、この第２実施例の広角端Ｗ、中間域Ｍ及び望遠端Ｔにおける収差図は、それぞれ図９、図１０及び図１１に示される。また、本実施例の条件式の値は、ｆ１／ｆｗ＝６.５２５、｜ｆ２／ｆｗ｜＝１.４２９、ｆ３／ｆｗ＝７.００６、｜ｆ４／ｆ２｜＝２.０４５である。このように、本実施例のズームレンズは、Ｆナンバーが１.１であり、かつ、１０枚構成としている。従来の１２〜１４枚構成のズームレンズに比較して、ズーム全長が短縮されると共に、画像が明るく、各収差が良好な高変倍（15倍）のズームレンズが実現される。

Aberration diagrams of the second embodiment at the wide-angle end W, the intermediate range M, and the telephoto end T are shown in FIGS. 9, 10, and 11, respectively. Also, the values of the conditional expressions in this embodiment are f1 / fw = 6.525, | f2 / fw | = 1.429, f3 / fw = 7.006, | f4 / f2 | = 2.045. Thus, the zoom lens of the present embodiment has an F-number of 1.1 and a 10-lens configuration. Compared with a conventional zoom lens having 12 to 14 lenses, a zoom lens having a high zoom ratio (15 times) is realized in which the entire zoom length is shortened, the image is bright, and each aberration is favorable.

(Third embodiment)
The third embodiment is a zoom lens having an F number F: 1.10 to 2.69, a focal length f: 2.618 mm to 37.643 mm, and an angle of view 2ω = 60.6 ° to 4.66 °. Lens data is shown in Table 5, and aspheric coefficient and position data are shown in Table 6. The surface numbers in Tables 5 and 6 are shown in FIG.

また、この第３実施例の広角端Ｗ、中間域Ｍ及び望遠端Ｔにおける収差図は、それぞれ図１２、図１３及び図１４に示される。また、本実施例の条件式の値は、ｆ１／ｆｗ＝６.６９７、｜ｆ２／ｆｗ｜＝１.４６６、ｆ３／ｆｗ＝７.１９、｜ｆ４／ｆ２｜＝１.９９である。このように、本実施例のズームレンズは、Ｆナンバーが１.１であり、かつ、１０枚構成としている。従来の１２〜１４枚構成のズームレンズに比較して、ズーム全長が短縮されると共に、画像が明るく、各収差が良好な高変倍（15倍）のズームレンズが実現される。

Aberration diagrams of the third embodiment at the wide-angle end W, the intermediate range M, and the telephoto end T are shown in FIGS. 12, 13, and 14, respectively. Also, the values of the conditional expressions in this embodiment are f1 / fw = 6.697, | f2 / fw | = 1.466, f3 / fw = 7.19, | f4 / f2 | = 1.99. Thus, the zoom lens of the present embodiment has an F-number of 1.1 and a 10-lens configuration. Compared with a conventional zoom lens having 12 to 14 lenses, a zoom lens having a high zoom ratio (15 times) is realized in which the entire zoom length is shortened, the image is bright, and each aberration is favorable.

(Fourth embodiment)
The fourth embodiment is a zoom lens having an F number F: 1.26 to 2.81, a focal length f: 2.739 mm to 39.299 mm, and an angle of view 2ω = 58.4 ° to 4.46 °. Lens data is shown in Table 7, and aspheric coefficient and position data are shown in Table 8. The surface numbers in Tables 7 and 8 are shown in FIG.

また、この第４実施例の広角端Ｗ、中間域Ｍ及び望遠端Ｔにおける収差図は、それぞれ図１５、図１６及び図１７に示される。また、本実施例の条件式の値は、ｆ１／ｆｗ＝６.４０２、｜ｆ２／ｆｗ｜＝１.４２４、ｆ３／ｆｗ＝７.５８１、｜ｆ４／ｆ２｜＝２.０１２である。このように、本実施例のズームレンズは、Ｆナンバーが１.２であり、かつ、１０枚構成としている。従来の１２〜１４枚構成のズームレンズに比較して、ズーム全長が短縮されると共に、画像が明るく、各収差が良好な高変倍（15倍）のズームレンズが実現される。

In addition, aberration diagrams at the wide-angle end W, the intermediate region M, and the telephoto end T of the fourth embodiment are shown in FIGS. 15, 16, and 17, respectively. Further, the values of the conditional expressions of the present embodiment are f1 / fw = 6.402, | f2 / fw | = 1.424, f3 / fw = 7.581, | f4 / f2 | = 2.12. Thus, the zoom lens of the present embodiment has an F-number of 1.2 and a 10-lens configuration. Compared with a conventional zoom lens having 12 to 14 lenses, a zoom lens having a high zoom ratio (15 times) is realized in which the entire zoom length is shortened, the image is bright, and each aberration is favorable.

(5th Example)
The fifth embodiment is a zoom lens having an F number F: 1.26 to 2.86, a focal length f: 2.662 mm to 38.178 mm, and an angle of view 2ω = 59.8 ° to 4.59 °. Lens data is shown in Table 9, and aspherical coefficients and position data are shown in Table 10. The surface numbers in Tables 9 and 10 are shown in FIG.

また、この第５実施例の広角端Ｗ、中間域Ｍ及び望遠端Ｔにおける収差図は、それぞれ図１８、図１９及び図２０に示される。また、本実施例の条件式の値は、ｆ１／ｆｗ＝６.６９３、｜ｆ２／ｆｗ｜＝１.４４１、ｆ３／ｆｗ＝７.８００、｜ｆ４／ｆ２｜＝２.０４５である。このように、本実施例のズームレンズは、Ｆナンバーが１.２であり、かつ、１０枚構成としている。従来の１２〜１４枚構成のズームレンズに比較して、ズーム全長が短縮されると共に、画像が明るく、各収差が良好な高変倍（15倍）のズームレンズが実現される。

Aberration diagrams of the fifth embodiment at the wide-angle end W, the intermediate region M, and the telephoto end T are shown in FIGS. 18, 19, and 20, respectively. Also, the values of the conditional expressions in this embodiment are f1 / fw = 6.693, | f2 / fw | = 1.441, f3 / fw = 7.800, and | f4 / f2 | = 2.045. Thus, the zoom lens of the present embodiment has an F-number of 1.2 and a 10-lens configuration. Compared with a conventional zoom lens having 12 to 14 lenses, a zoom lens having a high zoom ratio (15 times) is realized in which the entire zoom length is shortened, the image is bright, and each aberration is favorable.

  The present invention is not limited to the above embodiments and examples. For example, in the above embodiments and examples, the fourth lens group is composed of three lenses. Even when three lens groups are made up of one positive lens and the fourth lens group is made up of one positive lens and one negative lens, some aberrations remain, but the same degree as in the above embodiments and examples. F value and variable magnification can be achieved.

  In the second embodiment whose schematic configuration is shown in FIGS. 3 and 4, the fourth lens group IV includes two positive lenses and one negative lens. However, in the present invention, for example, the fourth lens group disclosed in Japanese Patent Application Laid-Open No. 2003-121737 is composed of two positive lenses and one negative lens. And a configuration in which the fixed stop 502 according to the second embodiment is applied to a configuration including at least one aspherical surface, and further, the fourth lens group described above. Can be applied to a lens composed of one positive lens and one negative lens.

It is a schematic block diagram which shows the 1st Embodiment of this invention with a surface number. It is a figure which shows schematic structure and zoom trace curve of the 1st Embodiment of this invention. It is a schematic block diagram which shows the 2nd Embodiment of this invention with a surface number. It is a schematic block diagram of 2nd Embodiment of this invention. It is a ray tracing figure of the 2nd Embodiment of this invention. It is an aberration diagram at the wide angle end W of the first embodiment of the present invention. It is an aberration diagram in the intermediate range M of the first embodiment of the present invention. It is an aberration diagram at the telephoto end T of the first embodiment of the present invention. It is an aberration diagram at the wide angle end W of the second embodiment of the present invention. It is an aberration diagram in the intermediate range M of the second embodiment of the present invention. It is an aberration diagram at the telephoto end T of the second embodiment of the present invention. It is an aberration diagram at the wide angle end W of the third embodiment of the present invention. It is an aberration diagram in the intermediate range M of the third embodiment of the present invention. It is an aberration diagram at the telephoto end T of the third embodiment of the present invention. It is an aberration diagram at the wide angle end W of the fourth embodiment of the present invention. It is an aberration diagram in the intermediate range M of the fourth embodiment of the present invention. It is an aberration diagram at the telephoto end T of the fourth embodiment of the present invention. It is an aberration diagram at the wide-angle end W of the fifth example of the present invention. It is an aberration diagram in the intermediate range M of the fifth embodiment of the present invention. It is an aberration diagram at the telephoto end T of the fifth embodiment of the present invention.

Explanation of symbols

I First lens group
II Second lens group
III Third lens group
IV Fourth lens group 101, 201, 202, 403 Negative lens 102, 103, 203, 301, 401, 402 Positive lens 501 Diaphragm 502 Fixed iris 601 Optical LPF

Claims (6)

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 fourth lens group having a positive refractive power in order from the object side; The lens group and the third lens group are fixed lens groups, and the third lens group is a zoom lens including a single fixed positive lens,
The fourth lens group is movable in a non-linear manner, has two positive lenses and one negative lens, and does not include an aspherical surface. 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 fourth lens group having a positive refractive power in order from the object side; The lens group and the third lens group are fixed lens groups, and the third lens group is a zoom lens including a single fixed positive lens,
A zoom lens, wherein a fixed stop for limiting peripheral rays outside the second lens group at a telephoto end is provided between the first lens group and the second lens group.   3. The zoom lens according to claim 1, wherein the positive lens constituting the third lens group has an aspheric surface on at least one surface. 4.   3. The zoom lens according to claim 1, wherein each of the first to fourth lens groups includes a total of ten lenses.   The zoom lens according to claim 1 or 2, wherein a magnification of the zoom lens is 12 to 15 times. The zoom lens according to claim 1 or 2, wherein an F number of the zoom lens is from 1.05 to 1.2.

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