JP2005208258A - Zoom lens and camera using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high performance zoom lens which is conveniently carried, having a high resolution and a small distortion aberration, and to provide a camera using the zoom lens. <P>SOLUTION: The zoom lens is composed of a first lens group having positive refractive power as a whole and a second lens group having negative refractive power as a whole from the object side, the first lens group being composed of a 1a lens group and a 1b lens group having a positive refractive power as a whole, the 1a lens group being composed of a negative first lens and a positive second lens, the 1b lens group being composed of a negative third lens, a positive fourth lens which is composed by being cemented to the third lens and a fifth lens, and the second lens group being composed of a positive or negative sixth lens, a negative seventh lens and a positive or negative eighth lens. The power variation of the zoom lens is performed by varying the distance between the first lens group and the second lens group. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a zoom lens apparatus having a zoom lens system with a low zoom ratio used for a small photographing optical system, and more particularly, a digital still camera and a digital video camera using an image sensor such as a CCD (charged coupled device). The present invention relates to a zoom lens apparatus having a compact and low zoom ratio zoom lens system suitable for a photographing optical system of a digital input / output device.

In recent years, digital input / output devices such as a digital still camera (DSC) or lower and a digital video camera have been actively developed, and have been actively published in photographing lenses (see Patent Document 1). ).
JP 2001-242379 A

  In terms of the construction of these photographic lenses, it can be considered that the photographic optical system for VTR has been developed. However, in particular, the DSC has higher performance and quality in terms of resolution and other image quality required. Therefore, the lens configuration is often complicated, and the DSC photographic lens is larger than the VTR photographic lens even when the CCD screen size is the same. Result. The following is a summary of features of conventional DSC photographing lenses.

1. High resolution Recently, with regard to the number of CCD pixels, a DSC employing a high pixel count of 3 to 4 million pixels has become common sense for general consumers. Since the screen dimensions are different from the 350,000-pixel class image sensor used in VTR, direct comparison does not make much sense, but if the screen dimensions are ignored, there is a difference of about 10 times. It will be a thing. That is, it is considered that the aberration correction level required for the taking lens also has a difference of about this difference.

  In order to increase the number of pixels of a CCD, currently, a method of increasing the number of pixels by reducing the pixel pitch without increasing the screen size as much as possible is used. For example, about two years ago. For example, in a CCD with 1.3 million effective pixels, the pixel pitch was about 4.2 μm, but further development has progressed, and currently there are many products in the 2 μm range. Therefore, if the minimum circle of confusion is assumed to be 2 times the pixel pitch when considered as 2 μm, the minimum circle of confusion of a 35 mm silver salt camera is considered to be about 33 μm. It can be said that the required resolving power is about 8 times that of a silver halide camera.

2. Since the dynamic range is small as a characteristic of the CCD that takes abundant amount of peripheral light, in order to maintain high quality image quality, there is a tendency to design a large amount of peripheral light in addition to the resolution described in the previous section. Although there is a relationship with the image processing system, it cannot be generally stated, but at least 40 to 50% is often targeted.

3. Image-side telecentricity is good Image-side telecentricity means that the principal ray of the beam bundle for each image point is almost parallel to the optical axis after exiting the final surface of the optical system, that is, the image It means that it intersects the surface almost perpendicularly. In other words, the exit pupil position of the optical system is sufficiently separated from the image plane. This is because, since the color filter on the CCD is located slightly away from the imaging surface, the effective aperture efficiency is reduced (called shading) when a light beam is incident obliquely. In many sensitivity type CCDs, a microlens array is arranged immediately before the imaging surface. Similarly, in this case, if the exit pupil is not sufficiently separated, the aperture efficiency is lowered in the vicinity.

4). A large back focus is required. In addition to the protective glass plate caused by the CCD structure and the subsequent space, a space for inserting several optical elements is generally required between the optical system of the taking lens and the CCD. It is said. The optical visual low-pass filter (hereinafter referred to as “OLPF”) inserted for the purpose of preventing the moire phenomenon that occurs due to the periodic structure of the CCD, or the relative visibility of the human eye by reducing the sensitivity in the infrared wavelength region of the CCD. This is an infrared absorption filter which is inserted between the optical system and the CCD for the purpose of getting close to.

  As described above, the conventional DSC photographing lens generally has four characteristics. Therefore, as a lens type, a single focus lens is a retrofocus type, and a low zoom ratio zoom lens is positive / negative / positive or negative. The positive / positive three-group type zoom lens or the negative / positive negative group-first type zoom lens type is selected even for the two-group type. Of these types, especially in the optical system of the preceding type with negative power, it is inevitable that the optical system becomes large, but on the other hand, the image circle can be made smaller compared to a camera for a film such as a 35 mm plate (1 By taking advantage of the great advantage of / 5 to 1/8), it is possible to make it a size that is not problematic for carrying. In recent years, development efforts for downsizing have become more active. For example, as disclosed in Japanese Patent Application Laid-Open No. 2002-365530 for a single-focus lens, as for telecentricity on the image side, a CCD is used. By specializing and developing, the color filter of the CCD and the arrangement of the microlens array are matched to the characteristics of the specific photographic lens, and the OLPF characteristics are also reviewed and the cover glass It has been reported that it is possible to adopt a lens type other than the retrofocus type by reviewing from a fundamental point of structure, such as the commonality of the lens, and to develop a more compact photographic lens Yes.

  As described above, when developing a zoom lens having a low zoom ratio of 2 to 3 times, it is common to select a zoom lens of the positive / negative / positive or negative / positive / positive three group type. Recently, as disclosed in Japanese Patent Application Laid-Open No. 2003-057542, by developing a specialized CCD, the telecentricity on the image side is reduced by matching the arrangement of the CCD color filter and microlens array. Although it has been reported that the negative lens type zoom lens type of the second group type is selected, in any case, from the viewpoint of compactness, the size when retracted, that is, when the lens is retracted is satisfactory. In actual use, it is necessary to take a collapsible structure with multiple stages of lens barrels, making the lens frame structure complicated, increasing the size of the lens unit, other operability and immediacy, and maintaining the front group If, which is a problem in terms of the degree and strength in many cases. Further, for example, in a positive group preceding type optical system as disclosed in Japanese Patent Laid-Open No. 7-128594, which has been known as a lens type of a zoom lens that is advantageous for miniaturization, the telecentricity is reduced by specializing the CCD. However, it cannot be adopted because it has an adverse effect on the image due to an increase in the incident angle on the CCD surface.

  In light of the circumstances described above, the present invention reduces the telecentricity by specializing the CCD, and at the same time adopts a zoom system of the front group advance type that is advantageous for compactness, so that it is compact and portable in the storage state. Of course, there is little difference in the size between the storage state and the usage state, and it can be realized by expanding and contracting the number of lens barrels even in actual use, thus simplifying the lens frame structure, downsizing the entire lens unit, and operability It is an object of the present invention to provide a high-performance, compact zoom lens and a camera using the same, with high resolution and low distortion, on the premise of improvement in reliability and immediacy and reliability such as strength.

The zoom lens according to the present invention includes, in order from the object side, a first lens group having a positive refractive power as a whole and a second lens group having a negative refractive power as a whole, and the first lens group in order from the object side. 1a lens group and 1b lens group having positive refractive power as a whole, the first lens group is a lens having negative refractive power (hereinafter, negative lens) in order from the object side. And a second lens that is a lens having a positive refractive power (hereinafter referred to as a positive lens), and the first b lens group is joined to the third lens that is a negative lens and the third lens in order from the object side. A fourth lens that is a positive lens and a fifth lens that is a positive lens, and the second lens group is a lens having a positive or negative refractive power in order from the object side. 6th lens, negative lens A zoom lens that includes seven lenses and an eighth lens that is a lens having a positive or negative refractive power, and is performed by changing the distance between the first lens group and the second lens group during zooming. The following conditional expression (1) is satisfied with respect to the dimension of the entire lens system in the optical axis direction at the wide angle end, and the following conditional expression (2) is satisfied with respect to the power of the second lens group. And (Claim 1)
(1) TL _w / f _w <2.2
(2) 1.0 <f _w / | f _II | <1.8 (because the absolute value is f _II <0)
However,
TL _w : Distance from the object side surface of the first lens to the image plane at the wide angle end
(However, parallel plane glass part is air equivalent distance)
f _w : Composite focal length of the entire lens system at the wide angle end f _II : Composite focal length of the second lens unit

  Conditional expression (1) defines the total lens length at the wide-angle end. That is, it is a condition related to downsizing of the lens of the present invention. Exceeding the upper limit is advantageous in terms of aberration correction, but contradicts the miniaturization that is a feature of the present invention. Conditional expression (2) relates to appropriate distribution of power to the second lens group having negative refractive power. This is a balance condition for appropriately correcting the size and various aberrations of the entire optical system. When the upper limit is exceeded, the negative power of the second lens group becomes large, and accordingly, the positive power of the first lens group must be increased, and it becomes difficult to balance various aberrations, and the performance deteriorates. The telecentricity on the image side is also adversely affected. On the other hand, if the lower limit is exceeded, the air gap from the first lens group must be increased, and the size of the entire optical system increases, making it unsuitable for use as a compact digital still camera.

The first lens that constitutes the first lens group, satisfies the following conditional expression (3) with respect to the power of the first a lens group that is disposed closest to the object side, and that constitutes the first a lens group: It is preferable that the following conditional expression (4) is satisfied with respect to the dispersion characteristics of the glass material used for the second lens, and further, the following conditional expression (5) is satisfied with respect to the shape of the object side surface of the second lens. . (Claim 2)
(3) _fw / | _f1a | <0.5 (because the absolute value includes the case of _f1a <0)
(4) 8 <ν ₁ −ν ₂
(5) 1.0 <f _w / r ₁₃ <2.0
However,
f _1a : Composite focal length of the 1a lens group ν ₁ : Abbe number of the first lens constituting the 1a lens group ν ₂ : Abbe number of the second lens constituting the 1a lens group r ₁₃ : 1a lens group Radius of curvature of the object side surface of the second lens constituting

Conditional expression (3) is a conditional expression regarding appropriate power distribution to the 1a lens group and the positive power 1b lens group of the first lens group. Since both lens groups are lens groups having positive power across the stop, it is important to balance the spherical aberration and coma aberration. Although the absolute value is taken, if f _1a is a positive value and exceeds the upper limit, the power given to the first lens group is excessive, which is advantageous for downsizing, but asymmetry with the aperture interposed therebetween. Becomes larger and it becomes difficult to balance spherical aberration and coma. Conversely, if the upper limit is exceeded with a negative value, that is, the power of the 1a lens group disposed closest to the object side becomes negative, the effective miniaturization means is lost. Conditional expression (4) relates to the distribution of the Abbe numbers of the positive lens and the negative lens used in the 1a lens group. That is, the achromatic condition is a condition for maintaining a balance with each aberration while satisfactorily correcting the chromatic aberration. If the lower limit is not observed, good chromatic aberration correction means will be lost, and even if chromatic aberration correction can be performed, the power of each lens will be increased, which will be disadvantageous for correcting spherical aberration and coma aberration. End up. Conditional expression (5) shows the condition regarding the shape of the object side surface of the second lens. Since the position where the second lens is arranged is immediately before or after the aperture stop, it is closest to the stop. Being one of the refracting surfaces and acting as a concentric surface, it is an important factor for the balance between spherical aberration and coma aberration correction. Beyond the upper limit, it is advantageous for spherical aberration correction. However, this is disadvantageous for coma aberration correction. On the other hand, exceeding the lower limit is advantageous as coma correction, but the spherical aberration becomes too under.

Further, the first lens group is configured, and the following conditional expression (6) is satisfied with respect to the power of the first b lens group disposed next to the first a lens group in order from the object side, and the first b lens group The following conditional expression (7) is satisfied with respect to the dispersion characteristics of the glass materials used for the third lens, the fourth lens, and the fifth lens constituting the lens, and the shape of the object-side surface of the third lens and the It is preferable that the following conditional expression (8) is satisfied with respect to the shape of the image side surface of the fifth lens. (Claim 3)
(6) 1.0 <f _w / f _1b <2.0
(7) 20 <(ν ₄ + ν ₅ ) / 2−ν ₃
(8) 1.5 <r ₁₅ / r ₁₉ <4.0
However,
f _1b : Composite focal length of the 1b lens group ν ₃ : Abbe number of the third lens constituting the 1b lens group ν ₄ : Abbe number of the fourth lens constituting the 1b lens group ν ₅ : 1b lens group Abbe number of the fifth lens constituting the lens r ₁₅ : radius of curvature of the object side surface of the third lens constituting the 1b lens group r ₁₉ : curvature of the image side surface of the fifth lens constituting the 1b lens group radius

  Conditional expression (6), together with conditional expression (3), is a conditional expression relating to appropriate distribution of power to the 1a lens group and the positive power 1b lens group of the first lens group. If the upper limit is exceeded, the power set as the 1b lens group becomes excessive, and the positive power of the 1a lens group becomes relatively small or negative power, which is disadvantageous for downsizing. On the other hand, if the lower limit is exceeded, it is advantageous for downsizing, but the positive group power applied to the 1a lens group becomes excessive, which is disadvantageous for each aberration correction. Conditional expression (7) relates to the distribution of the Abbe numbers of the positive lens and the negative lens used in the 1b lens group. That is, the achromatic condition is a condition for maintaining a balance with each aberration while satisfactorily correcting the chromatic aberration. If the lower limit is exceeded, the power of each lens increases for correcting chromatic aberration, which is disadvantageous for correcting spherical aberration and coma. Conditional expression (8) expresses the relationship between the shape of the object-side surface of the third lens and the shape of the image-side surface of the fifth lens. It is possible to balance the aberrations such as spherical aberration and coma aberration by taking a lick arrangement. Exceeding the upper limit is advantageous as coma aberration correction, but spherical aberration cannot be corrected, and exceeding the lower limit is advantageous for spherical aberration correction, but is disadvantageous for coma aberration correction.

Further, the following conditional expression (9) is satisfied with respect to the power of the seventh lens constituting the second lens group, and the following conditional expression (10) and conditional expression with respect to the power of the sixth lens and the eighth lens are respectively satisfied. (11) is satisfied, the following conditional expression (12) is satisfied regarding the shape of the seventh lens, and further, the following conditional expression (13) is satisfied regarding the dispersion characteristics of the glass material used for the seventh lens. It is preferable. (Claim 4)
(9) 0.9 <f _w / | f ₇ | <1.5 (because the absolute value is f ₇ <0)
_{(10) f w / | f} 6 | <0.5 ( for the absolute value including the case of _f 6 <0)
_{(11) f w / | f} 8 | <0.5 ( the absolute value including the case of _f 8 <0)
(12) 0.7 <f _w / | r ₂₃ | <2.2 (because the absolute value is r ₂₃ <0)
(13) 50 <ν ₇
However,
f ₆ : Focal length of the sixth lens constituting the second lens group f ₇ : Focal length of the seventh lens constituting the second lens group f ₈ : Focal length of the eighth lens constituting the second lens group r ₂₃ : Curvature radius of object side surface of seventh lens constituting second lens group ν ₇ : Abbe number of seventh lens constituting second lens group

  Conditional expression (9) is a conditional expression related to the power of the seventh lens, which is a negative lens constituting the second lens group. Conditional expression (10) and conditional expression (11) are conditional expressions relating to the power of the sixth lens and the eighth lens, respectively. This represents a state of an appropriate configuration of a large negative power of the seventh lens and a small positive or negative power of the sixth lens and the eighth lens, which are major characteristics of the second lens group of the zoom lens. The large negative power of the seventh lens represented by the conditional expression (9) is a power representative of the second lens group. If the upper limit is exceeded, it is advantageous for downsizing, but the power of the first lens group is also relative. The correction of each aberration becomes difficult. On the contrary, if the lower limit is exceeded, the air spacing of each group must be increased, which is contrary to the idea of downsizing. The purpose of the sixth lens and the eighth lens is to be aspherical. Rather, the power is limited to the range indicated by conditional expression (10) and conditional expression (11), so that costs and the like are taken into consideration. However, even if it is manufactured by resin molding, it is shown that image deterioration can be suppressed against changes in temperature and humidity. Therefore, in both types, if the limit value is exceeded, the influence of temperature and humidity cannot be guaranteed. Conditional expression (12) obtains good performance by placing the shape of the object side surface of the seventh lens having strong negative power concentrically with respect to the incident light beam. When the upper limit is exceeded, the surface power of the object side surface of the seven lenses becomes excessive, and the astigmatic difference increases. On the other hand, if the lower limit is exceeded, the surface power on the image side surface becomes excessive and telecentricity and coma aberration deteriorate. Conditional expression (13) relates to the restriction of the dispersion value of the seventh lens that takes charge of most of the negative power of the second lens group. Since the sixth lens and the eighth lens are small in terms of power, only the seventh lens is dominant in correcting the chromatic aberration of the second lens group, and the positional relationship with the first lens group is changed during zooming operation. In view of this, it is difficult to satisfactorily maintain chromatic aberration in the entire zooming range unless a certain limit is provided. The conditional expression (13) shows the limit.

  In addition, it is preferable that at least one of the object-side or image-side refractive surfaces of the second lens constituting the 1a lens group has an aspherical shape. (Claim 5)

  In addition, it is preferable that at least one of the refractive surfaces on the object side or the image side of the fifth lens constituting the first b lens group has an aspherical shape. (Claim 6)

  Further, in the sixth lens and the eighth lens constituting the second lens group, at least one of the object-side and image-side refractive surfaces is aspherical, and thus the formability and cost are considered. It is good to mold and manufacture with resin material. (Claim 7)

  As described above, by providing the zoom lens according to the present invention as a photographing lens of a camera, it is possible to provide a thin or small camera that has an optical zoom function but does not suffer even if it is always carried. (Claim 8)

  According to the present invention, it is possible to provide a high-performance, compact, low-magnification zoom lens that is easy to carry and has high resolution and low distortion.

  Hereinafter, the present invention will be described with respect to specific numerical examples. In the following first to ninth embodiments, the first lens group LG1 having a positive refractive power as a whole and a second lens group LG2 having a negative refractive power as a whole are configured, and the first lens group LG1 is an object. The first a lens group LG1a and the first b lens group LG1b having a positive refractive power as a whole are arranged in order from the side. The first a lens group LG1a is a lens having a negative refractive power in order from the object side (hereinafter, a negative lens). ) And a second lens L12 that is a lens having a positive refractive power (hereinafter, positive lens), and the first b lens group LG1b is a negative lens in order from the object side. The second lens group LG2 includes a third lens L13, a fourth lens L14 that is a positive lens configured to be joined to the third lens L13, and a fifth lens L15 that is a positive lens. Are arranged in order from the object side, a sixth lens L21 which is a lens having a positive or negative refractive power, a seventh lens L22 which is a negative lens, and an eighth lens L23 which is a lens having a positive or negative refractive power. Composed. A space for an aperture stop is provided between the second lens L12 and the third lens L13, which is represented by a stop front surface SF and a rear surface SR, and the second lens group LG2 and the image surface. A plane-parallel glass LPF is disposed between the air gaps. The parallel plane glass LPF is specifically composed of a CCD cover glass, a crystal filter, an infrared absorption filter, or the like, but there is no problem optically, so one parallel sheet equal to the total thickness thereof. Expressed in flat glass. The zooming operation is performed by changing the distance between the first lens group LG1 and the second lens group LG2. In the lens configuration diagrams in each embodiment, the arrangement at the wide-angle end and the telephoto end is shown. .

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 aspherical 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.

  Table 1 shows numerical examples of the first embodiment of the aspherical lens of the present invention. FIG. 1 is a diagram showing the lens configuration, and FIG. 2 is a diagram showing various aberrations thereof.

In the table and drawings, f is the focal length of the entire lens system, F _no is the total angle of view of F-number, 2 [omega lens, b _f is the back focus. The back focus b _f is an air equivalent distance of a distance from the side surface of the eighth lens image forming the second lens group to the image plane. In addition, R is the curvature radius, D is the lens thickness or distance between lens, N _d is the refractive index of the d line, [nu] d is the Abbe number at the d-line. D, g, and C in the various aberration diagrams are aberration curves at respective wavelengths. S represents sagittal and M represents meridional.

  Numerical examples of the second embodiment are shown in Table 2. FIG. 3 is a diagram showing the lens configuration, and FIG. 4 is a diagram showing various aberrations thereof.

  Numerical examples of the third embodiment are shown in Table 3. FIG. 5 is a lens configuration diagram, and FIG.

  Numerical examples are shown in Table 4 for the fourth embodiment. FIG. 7 is a lens configuration diagram, and FIG.

  Next, Table 5 collectively shows values corresponding to the conditional expressions (1) to (13) regarding the first to fourth embodiments.

  As is clear from Table 5, the numerical values related to the examples of Examples 1 to 4 satisfy the conditional expressions (1) to (13), and are also apparent from the aberration diagrams in the 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

Claims (8)

A first lens group having a positive refractive power as a whole and a second lens group having a negative refractive power as a whole are arranged in order from the object side. The first lens group includes a first a lens group and a first lens group in order from the object side. The first lens group is composed of a first lens group having positive refractive power as a whole, and the first lens group includes a first lens that is a lens having negative refractive power (hereinafter referred to as a negative lens) and a positive refractive power in order from the object side. A first lens that includes a second lens that is a positive lens, and the first b lens group is a positive lens that is formed by cementing the third lens that is a negative lens and the third lens in order from the object side. A fourth lens that is a lens, and a fifth lens that is a positive lens, and the second lens group is a lens having a positive or negative refractive power in order from the object side; a negative lens; 7th lens and positive or negative In a zoom lens configured by disposing an eighth lens, which is a lens having refractive power, and changing the distance between the first lens group and the second lens group during zooming, the entire lens at the wide-angle end is arranged. A zoom lens characterized in that the following conditional expression (1) is satisfied with respect to the dimension in the optical axis direction of the system, and the following conditional expression (2) is satisfied with respect to the power of the second lens group.
(1) TL _w / f _w <2.2
(2) 1.0 <f _w / | f _II | <1.8 (because the absolute value is f _II <0)
However,
TL _w : Distance from the object side surface of the first lens to the image plane at the wide-angle end (however, the parallel plane glass part is the air equivalent distance)
f _w : Composite focal length of the entire lens system at the wide angle end f _II : Composite focal length of the second lens unit The first lens group constituting the first lens group satisfies the following conditional expression (3) with respect to the power of the first a lens group arranged closest to the object side, and the first lens and the first lens constituting the first a lens group The following conditional expression (4) is satisfied with respect to the dispersion characteristics of the glass material used for the two lenses, and the following conditional expression (5) is satisfied with respect to the shape of the object side surface of the second lens. The zoom lens according to claim 1.
(3) _fw / | _f1a | <0.5 (because the absolute value includes the case of _f1a <0)
(4) 8 <ν ₁ −ν ₂
(5) 1.0 <f _w / r ₁₃ <2.0
However,
f _1a : Composite focal length of the 1a lens group ν ₁ : Abbe number of the first lens constituting the 1a lens group ν ₂ : Abbe number of the second lens constituting the 1a lens group r ₁₃ : 1a lens group Radius of curvature of the object side surface of the second lens constituting The first lens group is configured, and the following conditional expression (6) is satisfied with respect to the power of the first b lens group disposed next to the first a lens group in order from the object side, and the first b lens group is configured. The following conditional expression (7) is satisfied regarding the dispersion characteristics of the glass materials used for the third lens, the fourth lens, and the fifth lens, and the shape of the object-side surface of the third lens and the fifth lens The zoom lens according to claim 1, wherein the following conditional expression (8) is satisfied with respect to a shape of an image side surface of the lens.
(6) 1.0 <f _w / f _1b <2.0
(7) 20 <(ν ₄ + ν ₅ ) / 2−ν ₃
(8) 1.5 <r ₁₅ / r ₁₉ <4.0
However,
f _1b : Composite focal length ν _{3 of} the 1b lens group: Abbe number of the third lens constituting the 1b lens group ν ₄ : Abbe number of the fourth lens constituting the 1b lens group ν ₅ : 1b lens group Abbe number r _{15 of} the fifth lens constituting the first lens group: radius of curvature r ₁₉ of the object side surface of the third lens constituting the first b lens group: curvature of the image side surface of the fifth lens constituting the first b lens group radius The following conditional expression (9) is satisfied with respect to the power of the seventh lens constituting the second lens group, and the following conditional expression (10) and conditional expression (11) with respect to the power of the sixth lens and the eighth lens, respectively. ), The following conditional expression (12) is satisfied with respect to the shape of the seventh lens, and the following conditional expression (13) is satisfied with respect to the dispersion characteristics of the glass material used for the seventh lens. The zoom lens according to claim 1.
(9) 0.9 <f _w / | f ₇ | <1.5 (because the absolute value is f ₇ <0)
_{(10) f w / | f} 6 | <0.5 ( for the absolute value including the case of _f 6 <0)
_{(11) f w / | f} 8 | <0.5 ( the absolute value including the case of _f 8 <0)
(12) 0.7 <f _w / | r ₂₃ | <2.2 (because the absolute value is r ₂₃ <0)
(13) 50 <ν ₇
However,
f ₆ : focal length of the sixth lens constituting the second lens group f ₇ : focal length of the seventh lens constituting the second lens group f ₈ : focal length r _{23 of} the eighth lens constituting the second lens group : Radius of curvature ν ₇ of the object side surface of the seventh lens constituting the second lens group: Abbe number of the seventh lens constituting the second lens group   3. The zoom lens according to claim 2, wherein at least one of the object-side and image-side refractive surfaces of the second lens constituting the first-a lens group has an aspherical shape.   4. The zoom lens according to claim 3, wherein at least one of the object-side and image-side refractive surfaces of the fifth lens constituting the first b lens group is aspherical.   In the sixth lens and the eighth lens constituting the second lens group, at least one of the object-side and image-side refracting surfaces is aspherical and is molded and manufactured from a resin material. The zoom lens according to claim 4.   A camera comprising the zoom lens according to at least one of claims 1 to 7.

Images