JP4687223B2 - Zoom lens - Google Patents

Description

  The present invention relates to a high-performance zoom lens of about 3 times that is used in a small-sized imaging device using an image sensor such as a CCD (charged coupled device) to be mounted mainly in a digital still camera or the like.

  The so-called pixel number competition of image sensors used in digital still cameras, which has been unfolding at an unusual speed for a while, has come to an end. It can be said that there is a tendency. The mainstream is the competition for miniaturization of cameras, and many of the popular types of so-called compact camera-type small cameras have been marketed with "card size". In the camera with the card size as a specification, it is natural that the size when viewed from the front is almost the size of a credit card etc. Naturally, the thickness (thinness) of the camera body is also thin with impact. This is an important factor in determining whether the product itself will be successful. In many cases, the size of the photographing lens in the optical axis direction is the biggest obstacle to designing a thin camera body. In other words, when taking the arrangement of general camera components, the optical axis of the product and the optical axis of the photographic lens are perpendicular to each other, so the dimension of this optical axis becomes the factor that determines the thickness of the camera body. In other words, reducing the product thickness means shortening the dimension of the direct photographing lens in the optical axis direction, which is difficult. For this reason, in the initial stage of a card-size digital still camera, a single focus lens that is a condition that the dimension in the optical axis direction becomes as small as possible is adopted, and as means for solving this problem, for example, disclosed in Patent Document 1 As a result, it was commercialized by creating unique lens types including a review of the telecentricity unique to image sensors such as CCDs. However, there is a strong demand for mounting a zoom lens on a camera, and as a result, at present, even in card-sized digital still cameras, the mainstream product is a camera with a zoom lens (see Patent Document 1).

  Even though a digital still camera of card size is equipped with a zoom lens that tends to be longer than the total length of the single focal length lens, there are currently two technologies for thinning the entire camera. It is thought that the technology can be classified. The first technique is represented by, for example, what is disclosed in Patent Document 2, and is a technique called a so-called bending type. In the bending type, a reflecting element such as a mirror or a prism is provided in the vicinity of the front and rear of the front lens of the optical system, and the lens portion is prevented from becoming large (thick) by bending the optical axis by 90 degrees. Flex-type reflective elements are often placed before and after the front lens as mentioned above due to the contribution to the thinness of the camera, the loss of space as an optical system, and the problem of sensitivity. On the other hand, there is no complicated structure such as a retracting operation or a lens barrel to which external force is applied, so there is no need for mechanical consideration of external strength, and the optical design limits the total length in the optical axis direction. Has a feature such as relaxation. It can also be said that the larger the zoom ratio, the more effective means. However, the bending type technically has excellent features as described above. However, when evaluated as a camera product, there is no lens barrel in the appearance, and only the lens near the front lens can be seen. A problem in product planning that it is difficult to express values as a camera lens has been pointed out (see Patent Document 2).

  The second technique is represented by, for example, a technique disclosed in Patent Document 3, and is a so-called sliding type technique. The sliding type can be said to be an advanced technology of the retractable storage system for zoom lenses, which has been adopted in conventional compact cameras using film. In this method, a part of the lens group constituting the zoom lens is slid (shifted) away from the optical axis when the lens is stored, and moved to a position where it does not interfere with other optical elements and stored to move from the optical axis. The total length of the lens group is shortened by the thickness of the lens group. Usually, a lens group that is advantageous in terms of mechanism or a lens group having a large size in the optical axis direction is often retracted in the middle lens group instead of the front group or the rear group. The problem with this method is that it is based on a complicated retractable structure. In addition to inheriting the problems of conventional retractable methods such as ensuring the required accuracy and adapting to external forces, the sensitivity of the retracting lens group is particularly high. It is necessary to set a low value, which is an important factor for stable production. In principle, it is possible to reduce the product thickness by performing a plurality of sliding operations. However, it turns out that there is not much meaning for the following reason (see Patent Document 3).

  In zoom lens optical systems based on the assumption that the retracted state is retracted, the total sum of the thicknesses of each lens group is reduced to shorten the total length during storage, while the air between the lens group and the lens group is reduced. A design method is used in which a wide interval is taken into consideration so-called sensitivity. Therefore, the sliding zoom lens is designed to reduce the total thickness of the lens group excluding the sliding group. It will not be established. Therefore, although related to the specifications of the optical system, the optical system designed according to such a policy is compact when stored, it is several times larger than the stored size during actual use. The result will be a size. Normally, in order to realize such an optical system, a structure in which a plurality of collapsible lens barrels are stacked is adopted. However, as the number of steps is increased, a lens disposed in front of the zoom lens. It becomes difficult to ensure the placement accuracy for the group. At present, the number of collapsible stages that is practically established is about three, and a larger number of stages is not practically established for the reasons described above, even if the design is possible. Therefore, there is actually a close relationship between the total length of the optical system during storage and the total length during actual use, and can only be taken within the range where the retracting mechanism is established. Therefore, it can be understood that it is not meaningful to reduce the total length during storage with a plurality of sliding objects. Furthermore, when the sliding method is adopted, it is easy to think of the lens storage state as determining the product thickness in order to reduce the thickness, but it is necessary to design an optical system that will be thinned in the storage state. However, depending on the size in use, it is essential to have a structure in which a plurality of lens barrels that perform the retracting operation are stacked, and it becomes impossible to guarantee the arrangement accuracy of the optical system. In other words, in order to achieve a thin product thickness, the dimension in the optical axis direction during storage is important, but this can be dealt with by sliding a group of zoom lens groups. However, it can be said that the obstacle in optical design is the size in the optical axis direction during actual use.

Therefore, in digital still camera products with a card size with a zoom ratio of about 3 times, the retractable method or sliding method is used to express the commercial values of the lens while giving priority to thinness. There is a demand for an optical design solution that can reduce the length of storage and use.
JP 2002-228922 A JP 2004-056362 A JP 2004-004765 A

  In the present invention, in view of the circumstances described above, in a zoom lens of about 3 ×, a first lens group having a negative power, which is composed of at least two conventional negative lenses, is followed by a first lens group having a negative power. By dividing the lens group into two independent lens groups of the weak power second lens group, aberration correction can be performed more rationally, and the total length during use can be shortened. It is also possible to shorten the distance by utilizing the air gap between the first lens group and the second lens group, and to provide a zoom lens and a camera using the same.

The zoom lens according to the present invention includes, in order from the object side, a first lens group, a second lens group, and a third lens group. The first lens group has a negative refractive power as a whole, and has a meniscus shape on the object side. The first lens is a lens having negative refractive power (hereinafter, negative lens), and the second lens group has a weak negative or weak positive refractive power as a whole, and has a positive refractive power ( A second lens that is a positive lens) and a third lens that is a negative lens on the image plane side of the second lens with a cemented or air space therebetween, and the third lens group as a whole is positively refracted. A fourth lens that is a positive lens, a fifth lens that is also a positive lens, a sixth lens that is a negative lens disposed in combination with the fifth lens, and has a weak negative or weak positive refractive power A seventh lens having the first lens In a zoom lens that is zoomed by moving the positions of the lens group, the second lens group, and the third lens group, the following conditional expression (1) is satisfied with respect to the power of the first lens group: The following conditional expression (2) is satisfied with respect to the power of the second lens group, and further, the following conditional expression (3) is satisfied with respect to the dimension in the optical axis direction of the entire lens system. . (Claim 1)
(1) 0.4 <f _w / | f _I | <0.7 (because the absolute value is f _I <0)
_{(2) f w / | f} II | <0.15 ( absolute value f _II <0,
Because there are cases where both f _II > 0)
(3) 4.2 <TL / f _w <6.1
However,
f _w : Composite focal length of the entire lens system at the wide angle end f _I : Composite focal length of the first lens group f _II : Composite focal length of the second lens group TL: From the object side surface to the image plane of the first lens at the wide angle end Distance (however, parallel plane glass part is air equivalent distance)

  Conditional expression (1) relates to appropriate distribution of power to the first lens group having negative power. This is a balance of conditions for appropriately correcting the size of the entire optical system and various aberrations. If the upper limit is exceeded, the negative power of the first lens group becomes large, and accordingly, the positive power of the third lens group and the fourth lens group must be increased, making it difficult to balance various aberrations. As a result, performance decreases. On the other hand, if the lower limit is exceeded, the air distance from the positive power third lens group must be increased, resulting in an increase in the size of the entire optical system and a loss of compactness. Conditional expression (2) relates to appropriate distribution of power to the second lens group having weak negative or weak positive power. The second lens group moves and corrects chromatic aberration due to movement of the first lens group in response to the first lens group, and when the power is set to a small value, fluctuations in other aberrations due to movement are smaller. . The condition is conditional expression (2), and if a large amount of power is applied beyond this upper limit, fluctuations in various aberrations during zooming operations increase. Conditional expression (3) defines the total lens length at the wide-angle end. That is, it is a condition that serves as a measure for downsizing the lens of the present invention. If the upper limit is exceeded, it is advantageous in terms of aberration correction, but it becomes impossible to provide a compact zoom lens that is an object of the present invention. On the other hand, if the lower limit is exceeded, the power of each lens must be increased, leading to deterioration of various aberrations and deterioration of sensitivity, making it practically difficult to manufacture.

In addition, it is preferable that an image side surface of the first lens constituting the first lens group has an aspherical shape, and the following conditional expression (4) is satisfied with respect to the radius of curvature. (Claim 2)
(4) 0.7 <f _w / r ₂ <1.4
However,
r ₂ : radius of curvature of the image side surface of the first lens

  Conditional expression (4) is for reducing the occurrence of off-axis aberrations such as coma and distortion by forming a concentric shape with respect to the entrance pupil under the condition of negative power applied to the first lens. It is a condition. That is, the first lens has a meniscus shape with strong negative power. If the lower limit of conditional expression (4) is exceeded, the occurrence of coma and distortion cannot be sufficiently suppressed. On the contrary, if the upper limit is exceeded, it is effective to suppress the occurrence of aberration, but the curved shape of the meniscus negative lens becomes too strong, which makes it difficult to manufacture. In order to effectively correct off-axis aberrations such as distortion and astigmatism, the shape of the image side surface of the first lens may be an aspherical shape. An aspheric surface, a composite aspheric surface with a resin material, and the like are preferable, but are not particularly limited.

In addition, the following conditional expression (5) is satisfied with respect to the power of the second lens constituting the second lens group, and dispersion by the materials used for the second lens and the third lens constituting the second lens group is satisfied. It is preferable that the following conditional expression (6) is satisfied with respect to the distribution of characteristics. (Claim 3)
(5) 0.4 <f _w / f ₂ <1.2
(6) 0 <ν ₃ −ν ₂
However,
f ₂ : Focal length ν _{3 of} the second lens: Abbe number of the third lens ν ₂ : Abbe number of the second lens

  As described above, the second lens group plays a role of correcting variations in chromatic aberration due to the movement of the first lens group, and conditions corresponding to the chromatic aberration correction conditions therefor are conditional expression (5) and conditional expression (6). Conditional expression (5) shows the power for color correction, and conditional expression (6) shows the characteristics of each lens constituting the second lens group with respect to the color of the glass material. If the lower limit of conditional expression (5) is exceeded, the achromatic condition becomes insufficient, and the change in chromatic aberration becomes large. Conversely, if the upper limit is exceeded, it becomes an advantageous condition for correcting chromatic aberration. Will increase. Similarly, when the lower limit of conditional expression (6) is exceeded, the power as the second lens group for achromaticity becomes excessive, and monochromatic aberration excluding chromatic aberration increases.

Moreover, the following conditional expression (7) is satisfied with respect to the power of the fourth lens constituting the third lens group, and the fourth lens, the fifth lens, and the sixth lens constituting the third lens group. It is preferable that the following conditional expression (8) is satisfied with respect to the distribution of dispersion characteristics depending on the material used for each of the lenses. (Claim 4)
(7) 0.7 <f _w / f ₄ <1.2
(8) 25 <(ν ₄ + ν ₅ ) / 2−ν ₆
However,
f ₄ : focal length of the fourth lens ν ₄ : Abbe number of the fourth lens ν ₅ : Abbe number of the fifth lens ν ₆ : Abbe number of the sixth lens

  Conditional expression (7) is a conditional expression related to the power of the fourth lens arranged closest to the object side in the third lens group. Although the power of the fourth lens is related to the power of the first lens group, it plays the most role in correcting spherical aberration, and can basically be rephrased as a conditional expression for correcting spherical aberration satisfactorily. It is. That is, in the conditional expression, if the lower limit is exceeded, it is easy to correct off-axis aberrations such as coma and astigmatism, but spherical aberration is overcorrected. On the contrary, if the upper limit is exceeded, the spherical aberration is undercorrected, and at the same time, it is difficult to correct off-axis aberrations well. Conditional expression (8) relates to the distribution of the Abbe numbers of the positive lens and the negative lens used in the third lens group. In the conditional expression (8), the term of the seventh lens is omitted because the power of the seventh lens described below is small, and the positive power that practically controls the power of the third lens group. The expression uses a fourth lens, a fifth lens, and a sixth lens having a negative power, and is a condition for maintaining a balance with each aberration while satisfactorily correcting the chromatic aberration of the entire lens system. When the upper limit is exceeded, that is, when the Abbe number of each positive lens in the third lens group becomes large, the respective refractive index becomes low, and the Petzval sum becomes large, which makes it difficult to correct field curvature. . On the other hand, when the lower limit is exceeded, the power of each lens increases for correcting chromatic aberration, which is disadvantageous for correcting spherical aberration and coma.

The following conditional expression (9) is satisfied with respect to the shape of the object side surface of the fourth lens disposed on the most object side of the third lens group, and the shape of the object side surface of the fourth lens is: It is preferable that the following conditional expression (10) is satisfied with respect to the relative characteristics of the shape of the image side surface of the sixth lens. (Claim 5)
(9) 0.9 <f _w / r ₇ <1.4
(10) 0.8 <r ₇ / r ₁₁ <2.0
However,
r ₇ : radius of curvature of the object side surface of the fourth lens r ₁₁ : radius of curvature of the image side surface of the sixth lens

  Conditional expression (9) is a conditional expression related to the shape of the fourth lens object side surface. Since the fourth lens object side surface is arranged immediately after the aperture stop, it plays an important role in correcting spherical aberration. In connection with the negative power of the first lens group, this is a condition for satisfactorily correcting spherical aberration. If the upper limit of conditional expression (9) is exceeded, off-axis aberrations such as coma and astigmatism will be easily corrected, but spherical aberration will be overcorrected. On the contrary, if the lower limit is exceeded, the spherical aberration is insufficiently corrected, and at the same time, it is difficult to correct off-axis aberrations well. Conditional expression (10) is a conditional expression related to the shape of the image side surface of the sixth lens. The object side surface of the fourth lens expressed by the conditional expression (9) is a surface arranged on the most incident side of the third lens group, and the image of the sixth lens expressed by the conditional expression (10). The side surface is a surface disposed on the most exit side of the optical element that effectively controls the power of the third lens group. That is, moderate negative spherical aberration and coma aberration generated on the object side surface of the fourth lens are corrected by generating positive aberration on the image side surface of the sixth lens. Therefore, if the upper limit is exceeded, the positive spherical aberration becomes excessive, and conversely if the lower limit is exceeded, the negative spherical aberration becomes excessive, and in any case, spherical aberration and coma cannot be corrected well.

Further, the seventh lens having a weak negative or weak positive refractive power constituting the third lens group is manufactured of a resin material, and at least one refractive surface on the object side or the image side has an aspherical shape, It is preferable that the following conditional expression (11) is satisfied with respect to the power of the seventh lens. (Claim 6)
(11) f _w / | f ₇ | <0.4 (the absolute value is f ₇ <0,
Because there are cases where both f ₇ > 0)
f ₇ : Focal length of the seventh lens

  The seventh lens is often arranged with a slightly larger air gap from the image side surface of the sixth lens, and therefore has an aspherical surface for correcting off-axis aberrations rather than the power applied to the lens. This is very important. Therefore, it is effective to use a resin material having a high degree of freedom in terms of cost and shape for the seventh lens. However, when introducing a lens made of a resin material into an optical system such as a digital camera that requires high resolution, it is important to keep the power of the resin lens small. Since the refractive index is easily affected by changes in the environment, it is related to whether or not the camera has an autofocus function, but the ideal is to design it so that it does not have refractive power. Normally, a considerable amount of power is allowed depending on the specification application for the reasons mentioned above, and by using resin materials, the advantages such as the ability to have a variety of aspheric shapes, which are their characteristics, are actively utilized. Conditional expression (11) defines the upper limit of the power of the seventh lens for that purpose. If the upper limit is exceeded, it is natural that environmental effects such as temperature and humidity affect the image quality due to the change in the refractive index of the resin material.

  As described above, by mounting the zoom lens according to the present invention as a photographing lens of a camera, a thin or small card-sized camera that has an optical zoom function and does not cause trouble even if it is always carried is provided. Is possible. (Claim 7)

  According to the present invention, the conventional first lens group having negative refractive power is divided into two independent group configurations of the first lens group and the subsequent second lens group, thereby making aberration correction more rational. In addition, it is possible to store more efficiently during storage, thereby providing a compact zoom lens.

  Hereinafter, specific numerical examples relating to the present invention will be described as Examples 1 to 8. In the following first to eighth embodiments, the first lens group LG1, the second lens group LG2, and the third lens group LG3 are sequentially arranged from the object side, and the first lens group LG1 has a negative refractive power as a whole. A first lens L1 that is a meniscus negative lens on the object side (the object side surface of the first lens L1 is S1, and the image side surface is S2. The image side surface S2 has an aspheric shape, In the case of a composite aspherical surface in which a resin material is formed in a thin film shape, the surface thereof is indicated by HB), and the second lens group LG2 as a whole has a weak negative or weak positive refractive power and is positive. A second lens L2 that is a lens (the object side surface of the second lens L2 is S3, and an image side surface is S4) and a third lens that is a negative lens with a cemented or air space on the image surface side of the second lens L2. L3 (the object side surface of the third lens L3 is The third lens group LG3 has a positive refractive power as a whole, and a fourth lens L4 that is a positive lens (the object side surface of the fourth lens L4 is defined as S7). The fifth lens L5, which is also a positive lens (the object side surface of the fifth lens L5 is S9, the image side cemented surface is S10), and the fifth lens L5 are disposed. A sixth lens L6 that is a negative lens (the image side surface of the sixth lens L6 is S11) and a seventh lens L7 that has a weak negative or weak positive refractive power (the object side surface of the seventh lens L7 is S12, and the image side surface is S13). Further, an air gap is provided between the seventh lens L7 and the image plane for protecting the quartz optical filter LPF (the object side surface of the quartz optical filter LPF is S14 and the image side surface is S15) and the imaging part of the CCD. Cover glass CG (S16 is the object side surface of the cover glass CG and S17 is the image side surface). Infrared light cut, which is usually required when handling an image sensor such as a CCD, is dealt with by applying an infrared reflective coating on one surface of the refractive surface of the quartz optical filter LPF.

  In each embodiment, focus adjustment for an object of a finite distance is performed by moving the first lens group LG1 in the direction of the optical axis toward the object side. However, the present invention is not limited to this method.

Furthermore, as is well known, the aspherical surface used in each embodiment has an aspherical formula when taking the Z axis in the optical axis direction and the Y axis in the direction orthogonal to the optical axis:
Z = (Y ² / r) [1 + √ {1- (1 + K) (Y / r) ² }]
+ A ・ Y ⁴ + B ・ Y ⁶ + C ・ Y ⁸ + D ・ Y ¹⁰ +
Is a curved surface obtained by rotating the curve given by around the optical axis, and the shape is defined by giving paraxial curvature radius: r, conic constant: K, and higher-order aspheric coefficients: A, B, C, D To do. In the notation of the conic constant and the higher-order aspheric coefficient in the table, “E and the number following it” represent “power of 10”. For example, “E-4” means 10 ⁻⁴ , and this numerical value is multiplied by the immediately preceding numerical value.

[Example 1]
Table 1 shows numerical examples of the first embodiment of the zoom lens according to the present invention. FIG. 1 is a diagram showing the lens configuration, and FIG. 2 is a diagram showing various aberrations thereof. In the tables and drawings, f is the focal length of the entire lens system (hereinafter, the values are shown at the wide-angle end, intermediate range, and telephoto end from the left side), F _no is the F number, 2ω is the full angle of view of the lens, and b _f is the back focus. Represents. The back focus b _f is an air-converted distance that is the distance from the side surface of the seventh lens image constituting the third lens group to the image plane. R is a radius of curvature, D is a lens thickness or a lens interval, N _d is a refractive index of d-line, and ν _d is an Abbe number of d-line. In the spherical aberration diagrams in the various aberration diagrams, d, g, and C are aberration curves at the respective wavelengths. S. C. Indicates a sine condition. In the astigmatism diagram, S indicates sagittal and M indicates meridional.

[Example 2]
Table 2 shows numerical examples of the second embodiment of the zoom lens according to the present invention. FIG. 3 is a diagram showing the lens configuration, and FIG. 4 is a diagram showing various aberrations thereof.

[Example 3]
Table 3 shows numerical examples of the third embodiment of the zoom lens according to the present invention. FIG. 5 is a diagram showing the lens configuration, and FIG. 6 is a diagram showing various aberrations.

[Example 4]
Table 4 shows numerical examples of the fourth embodiment of the zoom lens according to the present invention. FIG. 7 is a diagram showing the lens configuration, and FIG. 8 is a diagram showing various aberrations.

[Example 5]
Table 5 shows numerical examples of the fifth embodiment of the zoom lens according to the present invention. FIG. 9 is a lens configuration diagram, and FIG. 10 is a diagram showing various aberrations.

[Example 6]
Table 6 shows numerical examples of the sixth embodiment of the zoom lens according to the present invention. FIG. 11 is a diagram showing the lens configuration, and FIG. 12 is a diagram showing various aberrations.

[Example 7]
Table 7 shows numerical examples of the seventh embodiment of the zoom lens according to the present invention. FIG. 13 is a lens configuration diagram thereof, and FIG. 14 is a diagram showing various aberrations thereof.

[Example 8]
Table 8 shows numerical examples of the eighth embodiment of the zoom lens according to the present invention. FIG. 15 is a lens configuration diagram, and FIG. 16 is a diagram showing various aberrations.

  Next, Table 9 shows values corresponding to the conditional expressions (1) to (11) for the first to eighth embodiments.

  As is clear from Table 9, the numerical values related to the respective examples from Example 1 to Example 8 satisfy the conditional expressions (1) to (11), and are also apparent from the aberration diagrams in the respective examples. Each aberration is corrected well.

1 is a lens configuration diagram of a first embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the first example The lens block diagram of 2nd Example of the zoom lens by this invention. Various aberration diagrams of the lens of the second example 3 is a lens configuration diagram of a third embodiment of a zoom lens according to the present invention. FIG. Various aberration diagrams of the lens of the third example 4 is a lens configuration diagram of a fourth embodiment of a zoom lens according to the present invention. FIG. Various aberration diagrams of the lens of the fourth example 5 is a lens configuration diagram of a fifth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the fifth example 6 is a lens configuration diagram of a sixth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the sixth example 7 is a lens configuration diagram of a seventh embodiment of the zoom lens according to the present invention. Various aberration diagrams of the lens of the seventh example The lens block diagram of 8th Example of the zoom lens by this invention. Various aberration diagrams of the lens of the eighth example

Claims (7)

In order from the object side, a first lens group, a second lens group, and a third lens group are included. The first lens group has a negative refractive power as a whole, and has a meniscus shape and a negative refractive power on the object side. The second lens group has a weak negative or weak positive refractive power as a whole and is a lens having a positive refractive power (positive lens). 2 lenses and a third lens which is a negative lens with a cemented or air space on the image plane side of the second lens, and the third lens group as a whole has a positive refractive power and is positive. A fourth lens which is a lens, a fifth lens which is also a positive lens, a sixth lens which is a negative lens disposed in combination with the fifth lens, and a seventh lens having a weak negative or weak positive refractive power. The first lens group and the second lens group. In the zoom lens that is zoomed by moving the positions of the lens group and the third lens group, the following conditional expression (1) is satisfied with respect to the power of the first lens group, and the second A zoom lens characterized in that the following conditional expression (2) is satisfied with respect to the power of the lens group, and further the following conditional expression (3) is satisfied with respect to the dimension in the optical axis direction of the entire lens system.
(1) 0.4 <f _w / | f _I | <0.7 (because the absolute value is f _I <0)
_{(2) f w / | f} II | <0.15 ( absolute value f _II <0,
Because there are cases where both f _II > 0)
(3) 4.2 <TL / f _w <6.1
However,
f _w : Composite focal length of the entire lens system at the wide angle end f _I : Composite focal length of the first lens group f _II : Composite focal length of the second lens group TL: From the object side surface to the image plane of the first lens at the wide angle end Distance (however, parallel plane glass part is air equivalent distance) 2. The image-side surface of the first lens constituting the first lens group has an aspherical shape, and the following conditional expression (4) is satisfied with respect to the radius of curvature thereof. The described zoom lens.
(4) 0.7 <f _w / r ₂ <1.4
However,
r ₂ : radius of curvature of the image side surface of the first lens The following conditional expression (5) is satisfied with respect to the power of the second lens constituting the second lens group, and the dispersion characteristic of the second lens and the third lens constituting the second lens group depends on the materials used. The zoom lens according to claim 1, wherein the following conditional expression (6) is satisfied with respect to the distribution.
(5) 0.4 <f _w / f ₂ <1.2
(6) 0 <ν ₃ −ν ₂
However,
f ₂ : Focal length ν _{3 of} the second lens: Abbe number of the third lens ν ₂ : Abbe number of the second lens Regarding the power of the fourth lens constituting the third lens group, the following conditional expression (7) is satisfied, and each of the fourth lens, the fifth lens, and the sixth lens constituting the third lens group is satisfied. The zoom lens according to claim 1, wherein the following conditional expression (8) is satisfied with respect to distribution of dispersion characteristics depending on a material used for the lens.
(7) 0.7 <f _w / f ₄ <1.2
(8) 25 <(ν ₄ + ν ₅ ) / 2−ν ₆
However,
f ₄ : focal length of the fourth lens ν ₄ : Abbe number of the fourth lens ν ₅ : Abbe number of the fifth lens ν ₆ : Abbe number of the sixth lens The following conditional expression (9) is satisfied with respect to the shape of the object side surface of the fourth lens arranged on the most object side of the third lens group, and the shape of the object side surface of the fourth lens and the 5. The zoom lens according to claim 4, wherein the following conditional expression (10) is satisfied with respect to the relative characteristics of the shape of the image side surface of the six lenses.
(9) 0.9 <f _w / r ₇ <1.4
(10) 0.8 <r ₇ / r ₁₁ <2.0
However,
r ₇ : radius of curvature of the object side surface of the fourth lens r ₁₁ : radius of curvature of the image side surface of the sixth lens The seventh lens having a weak negative or weak positive refractive power constituting the third lens group is made of a resin material, and at least one refractive surface on the object side or the image side has an aspherical shape, 6. The zoom lens according to claim 5, wherein the following conditional expression (11) is satisfied with respect to the power of the lens.
(11) f _w / | f ₇ | <0.4 (the absolute value is f ₇ <0,
Because there are cases where both f ₇ > 0)
f ₇ : Focal length of the seventh lens   A camera equipped with the zoom lens according to any one of claims 1 to 6.

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