JP2008310133A - Variable power optical system, imaging apparatus and digital equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable power optical system which achieves reduction of cost by using a plastic lens and lessens deterioration of imaging performance caused by temperature change while securing a large aperture ratio, optical performance and compactness equal to or above those of the conventional one, and an imaging apparatus equipped therewith and digital equipment. <P>SOLUTION: The variable power optical system satisfies a predetermined condition to suppress the deterioration of imaging caused by the temperature change while securing the large aperture ratio and the compactness, and is equipped with, in order from an object side, first and second lens groups 11 and 12 having negative and positive optical power, and a diaphragm 13 between them. When varying power from a wide angle end to a telephoto end, the first and the second lens groups 11 and 12 move so that space between the first and the second lens groups 11 and 12 may be narrow, and the diaphragm 13 is fixed. The second lens group 12 includes at least one plastic lens having positive optical power and at least one plastic lens having negative optical power, and at least one surface of the plastic lens is an aspherical surface satisfying the predetermined condition to achieve the large aperture ratio and high optical performance by correcting spherical aberration. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a variable magnification optical system suitably used for a video camera, an electronic still camera, and the like, and particularly to a small and wide-angle variable magnification optical system suitable for a surveillance camera, an image pickup apparatus including the same, and an image pickup apparatus therefor It relates to the installed digital equipment.

  In recent years, the demand for surveillance cameras has increased. A variable power optical system for a surveillance camera is desired to be bright with a large aperture ratio so that it can be used even in a low illuminance environment, and to have a wide angle so that a wide range can be photographed. On the other hand, downsizing and cost reduction are also desired. In recent years, the number of pixels of the image sensor has been increasing year by year, and higher optical performance has been required.

Examples of such variable magnification optical systems include those described in Patent Document 1 and Patent Document 2 below. These are variable-magnification optical systems having a two-group configuration in which a negative first lens group, a fixed stop during zooming, and a positive second lens group are arranged from the object side. Such a configuration preceded by a negative lens group is suitable for widening the angle and is characterized by relatively easy back focus. Also, by fixing the diaphragm independently of the moving group, the zooming and focusing mechanism can be simplified, and the diaphragm diameter can be compared even if the F-number at the wide end is small (larger aperture). Can be made smaller.
JP 2002-277737 A JP 2006-251437 A

  However, in such a configuration, the incident height of the light beam to the second lens group (the passing height of the marginal light beam of the axial light beam) becomes high, and a large aberration tends to occur in the second lens group. Therefore, conventionally, when the configuration of the second lens group is only a spherical lens, the number of components increases, and the total thickness of the second lens group is large (long) (Patent Document 1).

  On the other hand, some lenses have been made compact by using an aspheric surface for the second lens group, but the glass is made an aspheric surface, and the cost is high (Patent Document 2). Aspherical lenses include glass-molded aspherical lenses with glass aspherical surfaces and ground aspherical glass lenses, as well as composite aspherical lenses in which aspherical resin is formed on spherical glass lenses, and aspherical resins. There is a plastic mold aspheric lens. In terms of cost, plastic molded aspheric lenses are much cheaper. However, the plastic lens has a larger refractive index change and volume change due to a temperature change than a glass lens, and image formation performance (image surface position change and aberration change) is likely to occur. In particular, surveillance cameras are often used in environments with large temperature changes such as outdoors, and conventionally, it has been considered difficult to use plastic lenses.

  The present invention has been made in view of the above circumstances, and its purpose is to achieve a reduction in cost by using a plastic lens while ensuring a large aperture ratio, optical performance and compactness comparable to or higher than conventional ones. An object of the present invention is to provide a variable magnification optical system capable of reducing deterioration in imaging performance due to temperature change, an imaging apparatus equipped with the same, and a digital device.

In order to solve the above technical problem, the present invention provides a variable magnification optical system, an imaging device, and a digital device having the following configurations. Note that the terms used in the following description are defined as follows in this specification.
(A) A refractive index is a refractive index with respect to the wavelength (587.56 nm) of d line | wire.
(B) Abbe number is determined when the refractive index for d line, F line (486.13 nm) and C line (656.28 nm) is nd, nF, nC and Abbe number is νd, respectively.
νd = (nd−1) / (nF−nC)
The Abbe number νd obtained by the definition formula
(C) The notation regarding the surface shape is a notation based on the paraxial curvature.
(D) When the notation “concave”, “convex” or “meniscus” is used for the lens, these represent the lens shape near the optical axis (near the center of the lens) (based on the paraxial curvature) Notation).

A variable magnification optical system according to an aspect of the present invention includes, in order from the object side to the image side, a first lens group having a negative optical power, a diaphragm, and a second lens group having a positive optical power. The first lens group and the second lens group move so as to narrow each other, and the stop is fixed, and the second lens unit is changed in zooming from the wide-angle end to the telephoto end. The group includes at least one first plastic lens having a positive optical power and at least one second plastic lens having a negative optical power, and the first and second plastic lenses are provided. At least one surface has an aspherical surface satisfying the following (1), and satisfies the following conditional expressions (2) and (3).
−6 <dφp × f2 <−0.8 (1)
0.6 <Z / (Fnw ² ) <4.5 (2)
−2.4e-4 <BFt × φ2pA <2.4e-4 (3)
However,
f2: Focal length of the second lens group dφp = φpm−φp0
φp0: optical power on the optical axis in the meridional section (plane including the optical axis),
When the curvature on the optical axis in the meridional section (plane including the optical axis) is C0, and the refractive indexes before and after the surface are N and N '
φp0 = C0 × (N′−N)
φpm: optical power at the passing position in the meridional section (plane including the optical axis) of the marginal ray (most peripheral) of the axial light beam (light beam converging on the optical axis at the image plane),
When the curvature at the passing position in the meridional section (plane including the optical axis) is Cm, and the refractive indexes before and after the surface are N and N ′
φpm = Cm × (N′−N)
Z: zoom ratio (a value obtained by dividing the telephoto end focal length by the wide angle end focal length)
Fnw: F number at wide angle end BFt: Back focus at telephoto end φ2pA = Σki / (fpi × (1-Ni))
i is an index representing each plastic lens in the second lens group, and Σ means taking the sum of these,
ki: Temperature coefficient of refractive index of each plastic lens in the second lens group in visible light having a wavelength of 400 nm to 700 nm in a normal temperature range of −30 ° C. to 70 ° C. (change amount of refractive index per 1 ° C.)
fpi: focal length of each plastic lens in the second lens group
Ni: Refractive index of each plastic lens in the second lens group

  In this configuration, the second lens group includes at least one positive optical power plastic lens and at least one negative optical power plastic lens, and has an aspherical surface satisfying conditional expression (1). . For this reason, it is possible to correct aberrations satisfactorily by adopting an aspherical surface satisfying conditional expression (1) while achieving cost reduction by employing a plastic lens.

  The conditional expression (1) is such that at least one surface of the plastic lens of the second lens group has a shape in which the optical power in the meridional section (plane including the optical axis) becomes loose as it moves away from the optical axis, that is, optical When the power is positive, the curvature of the meridional section (plane including the optical axis) becomes gentler. When the optical power is negative, the curvature of the meridional section (plane including the optical axis) is tight. This indicates that the shape becomes a shape, and thereby spherical aberration is corrected well, and high performance optical performance can be achieved with a large aperture ratio. If the lower limit of conditional expression (1) is not reached, the spherical aberration is excessively corrected, which is not preferable. Exceeding the upper limit of conditional expression (1) is not preferable because of insufficient correction.

The aspherical surface further preferably satisfies the following conditional expression (1 ′).
−5 <dφp × f2 <−0.9 (1 ′)

  In addition, a plastic lens usually has a larger change in refractive index and volume due to a temperature change than a glass lens. In an optical system for a surveillance camera, a complicated mechanism such as high-cost autofocus is not employed, and a simple configuration in which an imaging element is fixed at an image plane position is often employed. In such a case, a change in back focus when the temperature changes becomes a problem. Here, in the above configuration, since the variable magnification optical system satisfies the conditional expression (3), it is possible to suppress a change in back focus when the refractive index of the plastic lens changes due to a temperature change.

  Further, when only one plastic lens is used, it is necessary to make the optical power of the plastic lens as small as possible, and the degree of freedom of aberration correction is reduced. Here, in the above configuration, the first plastic lens having a positive optical power and the second plastic lens having a negative optical power are used in combination so as to satisfy the conditional expression (3), thereby causing a temperature change. Therefore, it is possible to increase the degree of freedom of the optical power of the first and second plastic lenses.

It is even more preferable that the variable magnification optical system satisfies the following conditional expression (3 ′).
−1.8e−4 <BFt × φ2pA <1.8e−4 (3 ′)

  In addition, the first plastic lens having a positive optical power and the second plastic lens having a negative optical power may be constituted by a cemented lens joined to each other. With this configuration, it is possible to suppress aberration deterioration due to the relative decentration of the first and second plastic lenses. In this case, the focal lengths fpi (i = 1, 2) of the first and second plastic lenses at φ2 pA in the conditional expression (3) are values in a state where they are not joined.

  If the lower limit of conditional expression (2) is not reached, a sufficient zoom ratio and brightness cannot be secured, which is not preferable. If the upper limit of conditional expression (2) is exceeded, it will be difficult to satisfactorily correct aberrations (particularly spherical aberration) while maintaining a large aperture ratio and compactness.

It is even more preferable that the variable magnification optical system satisfies the following conditional expression (2 ′).
0.8 <Z / (Fnw ² ) <3.0 (2 ′)

In the variable magnification optical system having the above-described configuration, it is preferable that the following conditional expression (4) is satisfied.
2.8 <f2 / fw <6.0 (4)
However,
fw: focal length of the entire system at the wide-angle end In this configuration, if the lower limit of conditional expression (4) is not reached, the power of the second lens group becomes too strong, and the generation of spherical aberration in the second lens group becomes large. It is not preferable. Exceeding the upper limit of conditional expression (4) is not preferable because the total length becomes too large.

Further, it is even more preferable that the variable magnification optical system satisfies the following conditional expression (4 ′).
3.0 <f2 / fw <4.5 (4 ′)

In the variable magnification optical system having the above-described configuration, it is desirable that the following conditional expression (5) is satisfied.
−1e-4 <BFt × φ2pB <1e-4 (5)
However,
φ2pB = Σαi / fpi
i is an index representing each plastic lens in the second lens group, and Σ means taking the sum of these,
αi: Linear expansion coefficient of each plastic lens in the second lens group in a normal temperature range of −30 ° C. to 70 ° C.

  In this configuration, since the conditional expression (5) is satisfied, it is possible to suppress a change in back focus when the plastic lens expands or contracts due to a temperature change. Similar to the conditional expression (3), when only one plastic lens is used, it is necessary to make the optical power of the plastic lens as small as possible, and the degree of freedom of aberration correction is reduced. Here, in the above configuration, the first plastic lens having a positive optical power and the second plastic lens having a negative optical power are used in combination so as to satisfy the conditional expression (5), thereby causing a temperature change. Therefore, it is possible to increase the degree of freedom of the optical power of the first and second plastic lenses.

Further, it is even more preferable that the variable magnification optical system satisfies the following conditional expression (5 ′).
−0.7e−4 <BFt × φ2pB <0.7e−4 (5 ′)

  An imaging apparatus according to another aspect of the present invention includes any of the above-described variable power optical systems and an image sensor that converts an optical image into an electrical signal. An optical image of an object can be formed on a light receiving surface of the image sensor.

  A digital apparatus according to another aspect of the present invention includes the imaging device having the above-described configuration, and a control unit that causes the imaging device to perform at least one of shooting a still image and a moving image of a subject, The variable power optical system of the apparatus is assembled so that an optical image of the subject can be formed on the light receiving surface of the image sensor.

  According to the present invention, while ensuring a large aperture ratio, optical performance, and compactness that are equal to or higher than those of conventional ones, the plastic lens is used to achieve cost reduction and to reduce deterioration of imaging performance due to temperature change. Therefore, it is possible to provide a variable magnification optical system, an imaging device, and a digital device.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

<Description of configuration of variable magnification optical system>
FIG. 1 is a lens cross-sectional view schematically illustrating the configuration of the variable magnification optical system in the embodiment.

  In FIG. 1, a zoom optical system 1 forms an optical image of an object (subject) on a light receiving surface (image surface) of an image sensor 15 that converts an optical image into an electrical signal. In order from the object side to the image side, a first lens group 11 having a negative optical power, a diaphragm 13, and a second lens group 12 having a positive optical power are provided, and change from the wide-angle end to the telephoto end. When the magnification is doubled, the first lens group 11 and the second lens group 12 move so that the distance between the first lens group 11 and the second lens group 12 becomes narrow, and the diaphragm 13 is located between the first lens group 11 and the second lens group 12. The second lens group 12 includes at least one first plastic lens having a positive optical power and at least one second plastic lens having a negative optical power. This is a variable magnification optical system. The variable power optical system 1 illustrated in FIG. 1 has the same configuration as the variable power optical system 1A (FIG. 3) of Example 1 described later.

  In FIG. 1, the first lens group 11 includes, in order from the object side, a negative meniscus lens (negative lens having a concave surface facing the image side) 111 convex to the object side, a biconcave negative lens 112, and a convex side toward the object side. The second menscus lens 113 includes, in order from the object side, a positive meniscus lens 121 convex to the object side, a biconvex positive lens 122, a biconcave negative lens 123, and an object. The positive meniscus lens 124 and the positive lens 125 are composed of a negative meniscus lens 124 that is convex to the side and a positive lens 125 that is biconvex. The positive lens 122 and the negative lens 123 are fixedly integrated. Are examples of plastic lenses having both aspheric surfaces. On the object side of the second lens group 12, an optical aperture 13 (aperture stop) is fixedly disposed. The variable magnification optical system 1 is a so-called negative lead optical system having two components of “negative / positive” in order from the object side.

  Note that the number of lenses in the cemented lens is not represented by one for the entire cemented lens, but by the number of single lenses constituting the cemented lens.

  The first lens group 11 includes, in order from the object side, a negative meniscus lens 111 having a concave surface facing the image side, a negative lens 112, and a positive lens 113. For this reason, a large negative optical power can be arranged where the light beam is relatively small (the incident height of the light beam is low), and it is possible to suppress the occurrence of aberrations (especially spherical aberration and coma aberration). In addition, it is possible to suppress the occurrence of aberration by sharing a large negative optical power between the negative meniscus lens 111 and the negative lens 112.

  In the second lens group 12, a negative meniscus lens 124, which is a plastic lens with negative optical power, and a positive lens 125, which is a plastic lens with positive optical power, are arranged on the most image side. . For this reason, it is desirable that the most image side of the second lens group 12 has a relatively low incident height of light rays (passing height of the marginal light beam of the axial light beam) and small error sensitivity with respect to the aspherical shape. This is preferable because the variation of spherical aberration in the case of temperature change is also suppressed.

The aspherical surface of the positive lens 125 and the aspherical surface of the negative meniscus lens 124 in the second lens group 12 have a focal length f2 of the second lens group and an axial luminous flux (converged on the optical axis at the image plane). The difference between the optical power φpm at the passing position in the meridional section (plane including the optical axis) of the marginal ray (most peripheral) of the luminous flux) and the optical power φp0 on the optical axis is defined as dφp (= φpm−φp0). In this case, the following conditional expression (1) is satisfied.
−6 <dφp × f2 <−0.8 (1)

The optical power φpm at the passing position in the meridional section (plane including the optical axis) of the marginal ray of the on-axis light beam is expressed by Cm as the curvature at this passing position and N and N ′ as the refractive indices before and after the surface. In this case, the optical power φp0 on the optical axis in the meridional section (plane including the optical axis) is expressed by the following formula (A), and the curvature on the optical axis in the meridional section (plane including the optical axis) is Is represented by the following formula (B), where C0 is the refractive index before and after the surface is N, N ′.
φpm = Cm × (N′−N) (A)
φp0 = C0 × (N′−N) (B)

  In the variable magnification optical system 1 of the present embodiment, the second lens group 12 includes a positive lens 125 and a negative meniscus lens 124 that are plastic lenses, and has an aspheric surface that satisfies the conditional expression (1). . For this reason, aberration can be favorably corrected by adopting an aspherical surface that satisfies the conditional expression (1) while achieving cost reduction by employing a plastic lens. In addition, the plastic lens is lighter than the glass lens.

The conditional expression (1) is a shape in which the optical power in the meridional section (plane including the optical axis) becomes weaker as at least one surface of the plastic lenses 125 and 124 of the second lens group 12 moves away from the optical axis. This indicates that the spherical aberration is corrected well, and high performance optical performance can be achieved with a large aperture ratio. If the lower limit of conditional expression (1) is not reached, the spherical aberration is excessively corrected, which is not preferable. Exceeding the upper limit of conditional expression (1) is not preferable because of insufficient correction. Further, from the viewpoint of achieving higher performance optical characteristics with a large aperture ratio while correcting spherical aberration better, it is more preferable that the aspherical surface satisfies the following conditional expression (1 ′).
−5 <dφp × f2 <−0.9 (1 ′)

The zoom optical system 1 has a zoom ratio Z that is a value obtained by dividing the focal length at the telephoto end (t) by the focal length at the wide-angle end (w), Fnw at the wide-angle end, and Fnw at the telephoto end. The focus is BFt, and the focal length fpi, the refractive index Ni, and the refractive index of the first and second plastic lenses in the second lens group 12 (in this embodiment, the positive lens 125 and the negative meniscus lens 124 are examples thereof). When the predetermined value based on the temperature coefficient ki of Ni is φ2 pA, the following conditional expressions (2) and (3) are satisfied.
0.6 <Z / (Fnw ² ) <4.5 (2)
−2.4e-4 <BFt × φ2pA <2.4e-4 (3)

Note that, as described above, the predetermined value φ2pA is the focal length of the first and second plastic lenses in the second lens group 12 as fpi, the refractive index thereof as Ni, and the temperature coefficient of the refractive index Ni as ki. Is represented by the following formula (C).
φ2pA = Σki / (fpi × (1-Ni)) (C)
Here, i is an index representing the first and second plastic lenses in the same manner as described below, and Σ means the sum of these. The temperature coefficient ki of the refractive index Ni is a change amount of the refractive index per 1 ° C., and is a value in a visible temperature range of −30 ° C. to 70 ° C. and a wavelength of 400 nm to 700 nm.

If the lower limit of the conditional expression (2) is not reached, a sufficient zoom ratio and brightness cannot be ensured, which is not preferable. On the other hand, if the upper limit of the conditional expression (2) is exceeded, a large aperture ratio and compactness are reduced. It is difficult to satisfactorily correct aberrations (especially spherical aberration) while maintaining them. Therefore, in the variable magnification optical system 1 configured to satisfy the conditional expression (2), the aberration is favorably corrected while maintaining a large aperture ratio and compactness while ensuring a sufficient zoom ratio and brightness. In addition, from the viewpoint of better correcting aberrations while maintaining a large aperture ratio and compactness while ensuring a sufficient zoom ratio and brightness, the variable magnification optical system 1 satisfies the following conditional expression (2 ′). It is more preferable.
0.8 <Z / (Fnw ² ) <3.0 (2 ′)

  In addition, a plastic lens usually has a larger change in refractive index and volume due to a temperature change than a glass lens. In an optical system for a surveillance camera, a complicated mechanism such as high-cost autofocus is not employed, and a simple configuration in which an imaging element is fixed at an image plane position is often employed. In such a case, a change in the back focus BFt when the temperature changes becomes a problem. Here, in the variable magnification optical system 1 having the above configuration, since the conditional expression (3) is satisfied, the first and second plastic lenses (in this embodiment, the positive lens 125 and the negative meniscus lens 124 are examples thereof due to a temperature change. The change in the back focus BFt when the refractive index changes is small.

  Further, when only one plastic lens is used, it is necessary to make the optical power of the plastic lens as small as possible, and the degree of freedom of aberration correction is reduced. Here, in the variable magnification optical system 1 of the present embodiment, a first plastic lens having a positive optical power and a second plastic lens having a negative optical power are used in combination so as to satisfy the conditional expression (3). As a result, the change in the back focus BFt caused by the temperature change can be canceled out, so that the degree of freedom of the optical power of the first and second plastic lenses can be increased.

Further, from the viewpoint of suppressing the change in the back focus BFt caused by the temperature change to be smaller, it is more preferable that the zoom optical system 1 satisfies the following conditional expression (3 ′).
−1.8e−4 <BFt × φ2pA <1.8e−4 (3 ′)

  Further, the negative meniscus lens 124 and the positive lens 125 in the present embodiment are composed of cemented lenses that are cemented with each other. For this reason, it is possible to suppress aberration deterioration due to relative decentration in the negative meniscus lens 124 and the positive lens 125. In this case, the focal lengths fp of the negative meniscus lens 124 and the positive lens 125 at φ2pA in the conditional expression (3) are values in a state where they are not joined.

  Further, since the diaphragm 13 is fixedly disposed between the first lens group 11 and the second lens group 12, the second lens group 12 is moved to change the magnification, and the first lens group 11 is moved. The focusing mechanism can be configured independently, and the zooming and focusing mechanisms can be simplified.

  On the image side of the variable magnification optical system 1, an image sensor 15 is disposed via a filter 14. The filter 14 is a parallel plate-shaped optical element, and schematically represents various optical filters, a cover glass of an image sensor, and the like. An optical filter such as a low-pass filter or an infrared cut filter can be appropriately disposed according to the use application, imaging device, camera configuration, and the like. The image sensor 15 performs photoelectric conversion into image signals of R (red), G (green), and B (blue) components in accordance with the amount of light in the optical image of the subject imaged by the variable magnification optical system 1. This element outputs to a predetermined image processing circuit (not shown). As a result, the object optical image on the object side is guided to the light receiving surface of the image sensor 15 at an appropriate magnification ratio along the optical axis AX by the variable magnification optical system 1, and the optical image of the subject is captured by the image sensor 15. Is done.

  The variable magnification optical system 1 having such a configuration achieves a reduction in cost by using a plastic lens while ensuring a large aperture ratio, optical performance, and compactness that are equal to or higher than those of the conventional one, and image formation by temperature change. It is possible to provide a variable magnification optical system, an imaging device, and a digital device that can reduce deterioration in performance.

In the variable magnification optical system 1 having such a configuration, the focal length of the second lens group 12 is set to f2 and the focal length of the entire system at the wide angle end is set to fw from the viewpoint of spherical aberration and the total length of the second lens group 12. In this case, it is desirable that the following conditional expression (4) is satisfied.
2.8 <f2 / fw <6.0 (4)

  If the lower limit of conditional expression (4) is not reached, the optical power of the second lens group 12 becomes too strong, and the occurrence of spherical aberration in the second lens group 12 becomes large, which is not preferable. Exceeding the upper limit of conditional expression (4) is not preferable because the total length becomes too large.

Further, from the viewpoint of shortening the overall length while reducing the occurrence of spherical aberration in the second lens group, it is more preferable that the variable magnification optical system 1 satisfies the following conditional expression (4 ′).
3.0 <f2 / fw <4.5 (4 ′)

In the variable magnification optical system 1 having such a configuration, the focal points of the first and second plastic lenses in the second lens group 12 (in this embodiment, the positive lens 125 and the negative meniscus lens 124 correspond to an example thereof). When the predetermined value based on the distance fpi and the linear expansion coefficient αi is φ2 pB, it is desirable that the following conditional expression (5) is satisfied.
−1e-4 <BFt × φ2pB <1e-4 (5)

As described above, the predetermined value φ2pB is expressed by the following equation (D) when the focal lengths of the first and second plastic lenses in the second lens group 12 are fpi and their linear expansion coefficients are αi. It is represented by
φ2pB = Σαi / fpi (D)
Here, the linear expansion coefficient αi is a value in a normal temperature range of −30 ° C. to 70 ° C.

  Since the variable magnification optical system 1 having such a configuration is configured to satisfy the conditional expression (5), the first and second plastic lenses (in this embodiment, the positive lens 125 and the negative meniscus lens) are changed by temperature change. 124 corresponds to an example thereof), and the change in the back focus BFt can be suppressed to a small extent when it expands or contracts. As in the case of the conditional expression (3), when only one plastic lens is used, it is necessary to reduce the optical power of the plastic lens as much as possible, and the degree of freedom of aberration correction is reduced. Here, in the variable magnification optical system 1 of the present embodiment, a first plastic lens having a positive optical power and a second plastic lens having a negative optical power are used in combination so as to satisfy the conditional expression (5). As a result, the change in the back focus BFt caused by the temperature change can be canceled out, so that the degree of freedom of the optical power of the first and second plastic lenses can be increased.

Further, from the viewpoint of suppressing the change in the back focus BFt due to the temperature change to a smaller value, the zoom optical system 1 more preferably satisfies the following conditional expression (5 ′).
−0.7e−4 <BFt × φ2pB <0.7e−4 (5 ′)

In the variable magnification optical system 1 having such a configuration, it is desirable that the following conditional expression (6) is satisfied when the focal length of the first lens unit is f1.
−1.2 <f1 / f2 <−0.6 (6)

  If the lower limit of conditional expression (6) is not reached, the optical power of the second lens group 12 becomes too strong, and the occurrence of spherical aberration in the second lens group 12 becomes large, which is not preferable. Exceeding the upper limit of conditional expression (6) is not preferable because the negative optical power of the first lens group 12 becomes too strong and distortion at the wide-angle end increases.

The zoom optical system 1 satisfies the following conditional expression (6 ′) from the viewpoint of further suppressing the occurrence of spherical aberration in the second lens group 12 and further suppressing the occurrence of distortion at the wide-angle end. It is more preferable.
−1.1 <f1 / f2 <−0.7 (6 ′)

<Description of digital equipment incorporating variable magnification optical system>
Next, a digital apparatus in which the above-described variable magnification optical system 1 is incorporated will be described.

  FIG. 2 is a block diagram illustrating a configuration of the digital device according to the embodiment. The digital device 3 includes an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a driving unit 34, a control unit 35, a storage unit 36, and an I / F unit 37 for the imaging function. Composed. Examples of the digital device 3 include a digital still camera, a video camera, a surveillance camera (monitor camera), a mobile phone, a personal digital assistant (PDA), a personal computer, and a mobile computer. Equipment (eg, a mouse, scanner, printer, etc.) may be included.

  The imaging unit 30 includes an imaging device 21 and an imaging element 15. The imaging device 21 includes a variable magnification optical system 1 as shown in FIG. 1 and a lens drive device (not shown) for driving the lens in the optical axis direction to perform variable magnification and focusing. The light beam from the subject is imaged on the light receiving surface of the image sensor 15 by the variable magnification optical system 1 and becomes an optical image of the subject.

  As described above, the imaging device 15 converts the optical image of the subject formed by the variable magnification optical system 1 into an electrical signal (image signal) of R, G, B color components, and each color of R, G, B To the image generation unit 31 as an image signal. The imaging device 15 is controlled by the control unit 35 for imaging operations such as imaging of either a still image or a moving image, or reading (horizontal synchronization, vertical synchronization, transfer) of an output signal of each pixel in the imaging device 15. .

  The image generation unit 31 performs amplification processing, digital conversion processing, and the like on the analog output signal from the image sensor 15, and determines an appropriate black level, γ correction, and white balance adjustment (WB adjustment) for the entire image. Then, known image processing such as contour correction and color unevenness correction is performed to generate image data of each pixel from the image signal. The image data generated by the image generation unit 31 is output to the image data buffer 32.

  The image data buffer 32 is a memory that temporarily stores image data and is used as a work area for performing processing described later on the image data by the image processing unit 33. For example, the image data buffer 32 is a volatile storage element. It is composed of a RAM (Random Access Memory).

  The image processing unit 33 is a circuit that performs image processing such as resolution conversion on the image data in the image data buffer 32. It is also possible to configure the image processing unit 33 to correct aberrations that could not be corrected by the variable magnification optical system 1 as necessary.

  The drive unit 34 drives the plurality of lens groups of the variable magnification optical system 1 so as to perform desired variable magnification and focusing by a control signal output from the control unit 35.

  The control unit 35 includes, for example, a microprocessor and its peripheral circuits, and includes an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a drive unit 34, a storage unit 36, and an I / F unit. The operation of each part 37 is controlled according to its function. In other words, the imaging device 21 is controlled by the control unit 35 to execute at least one of the still image shooting and the moving image shooting of the subject.

  The storage unit 36 is a storage circuit that stores image data generated by still image shooting or moving image shooting of a subject. For example, a ROM (Read Only Memory) that is a nonvolatile storage element, a rewritable nonvolatile memory, or the like. It comprises an EEPROM (Electrically Erasable Programmable Read Only Memory) that is a storage element, a RAM, and the like. That is, the storage unit 36 has a function as a still image memory and a moving image memory.

  The I / F unit 37 is an interface that transmits / receives image data to / from an external device. For example, the I / F unit 37 is an interface that conforms to standards such as USB and IEEE1394.

  Next, the imaging operation of the digital device 3 having such a configuration will be described.

  When taking a still image, the control unit 35 controls the imaging device 21 to take a still image, and drives the lens driving device (not shown) of the imaging device 21 to perform focusing. As a result, the focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 15, converted into R, G, and B color component image signals, and then output to the image generation unit 31. . The image signal is temporarily stored in the image data buffer 32, and after image processing is performed by the image processing unit 33, an image based on the image signal is displayed on a display (not shown). The photographer can adjust the main subject so as to be within a desired position on the screen by referring to the display. When a so-called shutter button (not shown) is pressed in this state, image data is stored in the storage unit 36 as a still image memory, and a still image is obtained.

  In this case, when zoom shooting is performed because the subject is at a position away from the image sensor or a close subject is to be enlarged, the control unit 35 executes lens driving for zooming and zooming optics. Let the system 1 continuously zoom. As a result, by adjusting the enlargement ratio even for a subject far from the photographer, the main subject can be adjusted to fit in the desired position on the screen, and enlarged An image can be obtained.

  In addition, when performing moving image shooting, the control unit 35 controls the imaging device 21 to perform moving image shooting. After that, as in the case of still image shooting, the photographer refers to the display (not shown) so that the image of the subject obtained through the imaging device 21 is placed at a desired position on the screen. Can be adjusted. In this case, similarly to still image shooting, the enlargement ratio of the subject image can be adjusted, and moving image shooting is started by pressing the shutter button (not shown). It is also possible to change the magnification rate of the subject at any time during the photographing.

  At the time of moving image shooting, the control unit 35 controls the imaging device 21 to take a moving image and drives the lens driving device (not shown) of the imaging device 21 to perform focusing. As a result, the focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 15, converted into image signals of R, G, and B color components, and then output to the image generation unit 31. . The image signal is temporarily stored in the image data buffer 32, and after image processing is performed by the image processing unit 33, an image based on the image signal is displayed on a display (not shown). Then, when the shutter button (not shown) is pressed again, the moving image shooting is completed. The captured moving image is guided to and stored in the storage unit 36 as a moving image memory.

  In such an imaging device 21 and the digital device 3, while achieving a large aperture ratio, optical performance, and compactness that are equal to or higher than those of the conventional one, cost reduction is achieved by using a plastic lens, and imaging by temperature change is achieved. Since the variable magnification optical system 1 capable of reducing the deterioration of performance is provided, it is possible to reduce the size and the cost. In particular, since the variable magnification optical system 1 is small, it is suitable for a mobile phone. Particularly, since the variable magnification optical system 1 is small and has a wide angle, it is suitable for a surveillance camera.

<Description of More Specific Embodiment of Variable-Magnification Optical System>
A specific configuration of the variable power optical system 1 as shown in FIG. 1, that is, the variable power optical system 1 provided in the imaging device 21 mounted in the digital device 3 as shown in FIG. This will be described with reference to FIG.

  FIG. 3 is a cross-sectional view illustrating the arrangement of lens groups in the variable magnification optical system according to the first embodiment. FIG. 3 also shows lens arrangements at the wide-angle end (W) and the telephoto end (T) of the variable magnification optical system 1A.

  The variable magnification optical system 1A of Example 1 includes a first lens group (Gr1) in which each lens group (Gr1, Gr2) has negative optical power as a whole in order from the object side to the image side, an optical aperture stop ST, and the like. , A negative / positive two-component zoom configuration comprising a second lens group (Gr2) having a positive optical power as a whole, and during zooming, as shown in FIG. 3, the first lens group (Gr1) ) And the second lens group 12 move, and the optical aperture stop ST is fixed and does not move.

  More specifically, in the variable magnification optical system 1A of Example 1, each lens group (Gr1, Gr2) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a negative meniscus lens convex to the object side (first lens L1), a negative biconcave lens (second lens L2), and a positive meniscus lens convex to the object side (third lens L3). Consists of. The second lens group (Gr2) includes a positive meniscus lens convex to the object side (fourth lens L4), a positive biconvex lens (fifth lens L5), a negative biconcave lens (sixth lens L6), and an object side. Convex negative meniscus lens (seventh lens L7) and biconvex positive lens (eighth lens L8). The fifth lens L5 and the sixth lens L6 are cemented lenses, and the seventh lens L7 and the eighth lens L8 are plastic lenses having both aspheric surfaces.

  In this embodiment, for example, the product name “OKP4” manufactured by Osaka Gas Chemical Co., Ltd. can be used for the seventh lens L7. “OKP4” is a fluorene-based polyester having a refractive index fp = 1.607, a refractive index temperature coefficient k = −1.3e-04 (/ K), and a linear expansion coefficient α = 7.2e-05 (/ K). The seventh lens L7 of Example 2, Example 3 and Example 6 to be described later is also made of the same glass material.

  In the present embodiment, for example, the product name “ZEONEX E48R” manufactured by Nippon Zeon Co., Ltd. can be used for the eighth lens L8. “ZEONEX E48R” is a cycloolefin polymer having a refractive index fp = 1.53048, a refractive index temperature coefficient k = −1.0e-04 (/ K), and a linear expansion coefficient α = 6.0e-05 (/ K). . The eighth lens L8 of Example 2, Example 3 and Example 6 to be described later is also made of the same glass material.

  An optical aperture stop ST is fixed and arranged on the object side of the second lens group (Gr2), and a light receiving surface of the image sensor (SR) is arranged on the image side via a parallel plate (FT) as a filter. ing.

  In FIG. 3, the number ri (i = 1, 2, 3,...) Given to each lens surface is the i-th lens surface when counted from the object side (however, the cemented surface of the lens is 1). It is assumed that a surface marked with “*” in ri is an aspherical surface. The optical diaphragm (ST), both surfaces of the parallel plate (FT), and the light receiving surface of the image sensor (SR) are also handled as one surface. The meaning of such handling and symbols is the same for Examples 2 to 7 described later (FIGS. 4 to 9). However, it does not mean that they are exactly the same. For example, in FIGS. 3 to 9 of the first to seventh embodiments, the lens surface arranged closest to the object side is denoted by the same reference numeral (r1). However, this does not mean that these curvatures are the same throughout the first to seventh embodiments.

  Under such a configuration, light rays incident from the object side sequentially pass through the first lens group (Gr1), the optical aperture stop ST, the second lens group (Gr2), and the parallel plate (FT) along the optical axis AX. Passes and forms an optical image of the object on the light receiving surface of the image sensor (SR). In the image sensor (SR), the optical image is converted into an electrical signal. This electrical signal is subjected to predetermined digital image processing as necessary, and is recorded as a digital video signal in a memory of a digital device such as a digital camera, or transmitted to another digital device by wired or wireless communication. To do.

  In the variable magnification optical system 1A of the first embodiment, at the time of zooming from the wide angle end (W) to the telephoto end (T), as shown in FIG. 3, the first lens group (Gr1) moves away from the object. The second lens group (Gr2) is moved linearly in a direction approaching the object, and the optical aperture stop ST is always fixed and does not move. Thus, in zooming from the wide-angle end (W) to the telephoto end (T), the first lens group (Gr1) and the second lens group (Gr2) move so that the distance between them decreases, The optical aperture stop ST disposed in is fixed.

  The construction data of each lens in the variable magnification optical system 1A of Example 1 is shown below.

Numerical example 1
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 17.569 0.800 1.80420 46.49
2 6.547 4.430
3 -49.85 0.600 1.80420 46.49
4 11.064 0.909
5 11.579 1.897 1.92286 20.88
6 30.944 Variable 7 (Aperture) ∞ Variable 8 10.366 1.916 1.80420 46.49
9 26.770 0.100
10 7.506 2.594 1.49700 81.61
11 -82.373 0.700 1.84666 23.78
12 30.104 0.539
13 * 12.830 1.000 1.60700 27.10
14 * 4.611 0.508
15 * 5.719 2.261 1.53048 55.72
16 * -21.029 Variable 17 ∞ 2.750 1.51680 64.20
18 ∞ 1.00
Image plane ∞
Aspheric data 13th surface
K = 0.000e + 000, A4 = -2.3830e-003, A6 = 2.9325e-005, A8 = 4.4734e-006, A10 = -1.6248e-007
14th page
K = 0.0000e + 000, A4 = -2.5422e-003, A6 = -2.5197e-004, A8 = 2.6829e-005, A10 = -1.1942e-006
15th page
K = 0.0000e + 000, A4 = 8.5315e-004, A6 = -3.2936e-004, A8 = 3.6416e-005, A10 = -1.7321e-006
16th page
K = 0.0000e + 000, A4 = 1.4388e-003, A6 = -6.8817e-005, A8 = 2.1306e-005, A10 = -1.2959e-006
Various data zoom data Zoom ratio 3.60
Wide angle Medium telephoto focal length 2.803 5.316 10.083
F number 1.353 1.735 2.708
Angle of view 47.014 24.251 12.735
Image height 2.250 2.250 2.250
Total lens length 48.368 37.749 36.095
BF 7.023 9.905 15.371
d6 13.742 3.123 1.469
d7 9.348 6.466 1.000
d16 4.210 7.092 12.558
Zoom lens group data group Start surface Focal length 1 1 -8.356
2 8 9.583
In the above surface data, the surface number corresponds to the number i of the symbol ri (i = 1, 2, 3,...) Given to each lens surface shown in FIG. The surface marked with * in the number i indicates an aspherical surface (aspherical refractive optical surface or a surface having a refractive action equivalent to an aspherical surface).

  Also, “r” is the radius of curvature of each surface (unit is mm), “d” is the distance between the lens surfaces on the optical axis in the infinite focus state (axis upper surface distance), and “nd” is The refractive index “νd” of each lens with respect to the d-line (wavelength 587.56 nm) indicates the Abbe number. In addition, since each surface of the optical diaphragm (ST), both surfaces of the plane parallel plate (FT), and the light receiving surface of the image sensor (SR) are flat surfaces, their radii of curvature are ∞ (infinite).

The above-mentioned aspheric surface data includes the quadric surface parameter (cone coefficient K) and the aspheric surface coefficient Ai (i = 4, 6, 6) of the surface that is an aspheric surface (the surface with the number i added to * in the surface data). 8 and 10). The aspherical shape of the optical surface is defined by the following equation using a local orthogonal coordinate system (x, y, z) in which the surface vertex is the origin and the direction from the object toward the image sensor is the positive z-axis direction. is doing.
z (h) = ch ² / [1 + √ {1− (1 + K) c ² h ² }] + ΣAi · hi
However, z (h): Amount of displacement in the z-axis direction at the position of height h (based on the surface vertex)
h: height in a direction perpendicular to the z-axis (h ² = x ² + y ² )
c: Paraxial curvature (= 1 / radius of curvature)
Ai: i-th order aspheric coefficient
K: quadratic surface parameter (cone coefficient)
The spherical aberration (sine condition), astigmatism, and distortion in the variable magnification optical system 1A of Example 1 under the lens arrangement and configuration as described above are shown in FIGS. 10, 11, and 12, respectively. . 10 shows each aberration at the wide angle end (W), FIG. 11 shows each aberration at the intermediate point (M), and FIG. 12 shows each aberration at the telephoto end (T). The horizontal axis of spherical aberration and astigmatism represents the deviation of the focal position in mm, and the horizontal axis of distortion aberration represents the actual image height as a percentage (%) with respect to the ideal image height. The vertical axis of spherical aberration is shown as a value normalized by the incident height, but the vertical axis of astigmatism and distortion shows the image height in mm.

  In the diagram of spherical aberration, the three lines of light aberration are shown as a solid line d line (wavelength 587.56 nm), a dash-dot line g line (wavelength 435.84 nm), and a broken line C line (wavelength 656.28 nm). is there. Moreover, in the figure of astigmatism, the broken line represents the result on the tangential (meridional) surface, and the solid line represents the result on the sagittal (radial) surface. The diagrams of astigmatism and distortion are the results when the d-line (wavelength 587.56 nm) is used. The above handling is the same in the construction data according to Examples 2 to 7 shown below and FIGS. 13 to 30 showing the respective aberrations.

  FIG. 4 is a cross-sectional view illustrating an arrangement of lens groups in the variable magnification optical system according to the second embodiment. FIG. 4 also shows lens arrangements at the wide-angle end (W) and the telephoto end (T) of the variable magnification optical system 1A.

  The variable magnification optical system 1B of Example 2 includes a first lens group (Gr1) in which each lens group (Gr1, Gr2) has negative optical power as a whole in order from the object side to the image side, an optical aperture stop ST, and the like. , A negative / positive two-component zoom configuration comprising a second lens group (Gr2) having a positive optical power as a whole, and during zooming, as shown in FIG. 4, the first lens group (Gr1) ) And the second lens group 12 move, and the optical aperture stop ST is fixed and does not move.

  More specifically, in the variable magnification optical system 1B of Example 2, each lens group (Gr1, Gr2) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a negative meniscus lens convex to the object side (first lens L1), a negative biconcave lens (second lens L2), and a positive meniscus lens convex to the object side (third lens L3). Consists of. The second lens group (Gr2) includes a positive meniscus lens convex to the object side (fourth lens L4), a positive biconvex lens (fifth lens L5), and a negative meniscus lens convex to the image side (sixth lens L6). And a biconcave negative lens (seventh lens L7) and a biconvex positive lens (eighth lens L8). The fifth lens L5 and the sixth lens L6 are cemented lenses, and the seventh lens L7 and the eighth lens L8 are plastic lenses having both aspheric surfaces.

  An optical aperture stop ST is fixed and arranged on the object side of the second lens group (Gr2), and a light receiving surface of the image sensor (SR) is arranged on the image side via a parallel plate (FT) as a filter. ing.

  In the zoom optical system 1B of the second embodiment, when zooming from the wide-angle end (W) to the telephoto end (T), as shown in FIG. 4, the first lens group (Gr1) moves away from the object. The second lens group (Gr2) is moved linearly in a direction approaching the object, and the optical aperture stop ST is always fixed and does not move. Thus, in zooming from the wide-angle end (W) to the telephoto end (T), the first lens group (Gr1) and the second lens group (Gr2) move so that the distance between them decreases, The optical aperture stop ST disposed in is fixed.

  The construction data of each lens in the variable magnification optical system 1B of Example 2 is shown below.

Numerical example 2
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 17.981 0.800 1.77250 49.65
2 6.678 4.373
3 -64.561 0.600 1.71300 53.94
4 8.700 1.156
5 9.772 1.917 1.84666 23.78
6 19.755 Variable 7 (Aperture) ∞ Variable 8 10.174 2.067 1.78590 43.93
9 31.278 0.100
10 7.823 3.640 1.49700 81.61
11 -15.383 0.700 1.84666 23.78
12 -74.793 0.200
13 * -36.891 1.000 1.60700 27.10
14 * 9.437 0.407
15 * 7.952 1.967 1.53048 55.72
16 * -20.880 Variable 17 ∞ 2.750 1.51680 64.20
18 ∞ 1.00
Image plane ∞
Aspheric data 13th surface
K = 0.0000e + 000, A4 = -7.1948e-005, A6 = -5.2555e-005, A8 = 9.5460e-006, A10 = -2.8620e-007
14th page
K = 0.0000e + 000, A4 = -5.7725e-004, A6 = -2.7425e-004, A8 = 2.5152e-005, A10 = -8.2176e-009
15th page
K = 0.0000e + 000, A4 = -1.1252e-003, A6 = -3.1791e-004, A8 = 1.9294e-005, A10 = 1.6241e-007
16th page
K = 0.0000e + 000, A4 = 6.7821e-004, A6 = -1.0120e-004, A8 = 8.6757e-006, A10 = -3.1906e-007
Various data zoom data Zoom ratio 3.59
Wide angle Medium telephoto focal length 2.803 5.314 10.070
F number 1.354 1.790 2.881
Angle of view 47.020 24.283 12.754
Image height 2.250 2.250 2.250
Total lens length 48.368 38.761 37.926
BF 7.025 10.121 15.985
d6 12.456 2.849 2.014
d7 9.960 6.864 1.000
d16 4.212 7.308 13.172
Zoom lens group data group Start surface Focal length 1 1 -7.819
2 8 9.641
The spherical aberration (sine condition), astigmatism, and distortion in the variable magnification optical system 1B of Example 2 under the above lens arrangement and configuration are shown in FIGS. 13, 14, and 15, respectively. . 13 represents each aberration at the wide-angle end (W), FIG. 14 represents each aberration at the intermediate point (M), and FIG. 15 represents each aberration at the telephoto end (T).

  FIG. 5 is a cross-sectional view illustrating the arrangement of lens groups in the variable magnification optical system according to the third embodiment. FIG. 5 also shows lens arrangements at the wide-angle end (W) and the telephoto end (T) of the variable magnification optical system 1C.

  The variable magnification optical system 1C of Example 3 includes a first lens group (Gr1) in which each lens group (Gr1, Gr2) has negative optical power as a whole in order from the object side to the image side, an optical aperture stop ST, and the like. A negative / positive two-component zoom configuration comprising a second lens group (Gr2) having a positive optical power as a whole, and during zooming, as shown in FIG. 5, the first lens group (Gr1) ) And the second lens group 12 move, and the optical aperture stop ST is fixed and does not move.

  More specifically, in the variable magnification optical system 1C of Example 3, each lens group (Gr1, Gr2) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a negative meniscus lens convex to the object side (first lens L1), a negative biconcave lens (second lens L2), and a positive meniscus lens convex to the object side (third lens L3). Consists of. The second lens group (Gr2) includes a positive meniscus lens convex to the object side (fourth lens L4), a negative meniscus lens convex to the object side (fifth lens L5), and a positive biconvex lens (sixth lens L6). And a biconcave negative lens (seventh lens L7) and a biconvex positive lens (eighth lens L8). The fifth lens L5 and the sixth lens L6 are cemented lenses, and the seventh lens L7 and the eighth lens L8 are plastic lenses having both aspheric surfaces.

  An optical aperture stop ST is fixed and arranged on the object side of the second lens group (Gr2), and a light receiving surface of the image sensor (SR) is arranged on the image side via a parallel plate (FT) as a filter. ing.

  In the variable magnification optical system 1C of Example 3, at the time of zooming from the wide angle end (W) to the telephoto end (T), as shown in FIG. 5, the first lens group (Gr1) moves away from the object. The second lens group (Gr2) is moved linearly in a direction approaching the object, and the optical aperture stop ST is always fixed and does not move. Thus, in zooming from the wide-angle end (W) to the telephoto end (T), the first lens group (Gr1) and the second lens group (Gr2) move so that the distance between them decreases, The optical aperture stop ST disposed in is fixed.

  The construction data of each lens in the variable magnification optical system 1C of Example 3 is shown below.

Numerical Example 3
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 26.559 0.800 1.83400 37.35
2 6.975 5.624
3 -22.228 0.700 1.69680 55.48
4 17.998 0.156
5 15.233 2.421 1.92286 20.88
6 124.669 Variable 7 (Aperture) ∞ Variable 8 11.096 1.599 1.83481 42.72
9 21.558 0.100
10 7.942 0.809 1.84666 23.78
11 5.655 3.058 1.62041 60.35
12 -174.706 0.673
13 * -22.432 0.800 1.60700 27.10
14 * 8.140 0.507
15 * 9.342 2.025 1.53048 55.72
16 * -10.575 Variable 17 ∞ 2.750 1.51680 64.20
18 ∞ 1.00
Image plane ∞
Aspheric data 13th surface
K = 0.0000e + 000, A4 = -5.3482e-004, A6 = -5.2327e-005, A8 = 8.2507e-006, A10 = -2.4108e-007
14th page
K = 0.0000e + 000, A4 = -2.3024e-004, A6 = -3.0865e-004, A8 = 2.2524e-005, A10 = -3.1902e-007
15th page
K = 0.0000e + 000, A4 = -6.1738e-004, A6 = -3.4543e-004, A8 = 1.4686e-005, A10 = -1.0619e-007
16th page
K = 0.0000e + 000, A4 = 1.2331e-004, A6 = -1.2353e-004, A8 = 7.0591e-006, A10 = -2.4473e-007
Various data zoom data Zoom ratio 3.40
Wide angle Medium Telephoto focal length 2.873 5.295 9.758
F number 1.350 1.590 2.454
Angle of view 65.290 32.751 17.559
Image height 3.000 3.000 3.000
Total lens length 51.057 39.214 36.256
BF 14.337 10.152 15.067
d6 15.918 4.075 1.117
d7 8.382 5.715 0.800
d16 4.672 7.339 12.254
Zoom lens group data group Start surface Focal length 1 1 -9.097
2 8 10.018
The spherical aberration (sine condition), astigmatism, and distortion in the variable magnification optical system 1C of Example 3 under the lens arrangement and configuration as described above are shown in FIGS. 16, 17, and 18, respectively. . 16 shows each aberration at the wide-angle end (W), FIG. 17 shows each aberration at the intermediate point (M), and FIG. 18 shows each aberration at the telephoto end (T).

  FIG. 6 is a cross-sectional view illustrating the arrangement of lens groups in the variable magnification optical system according to the fourth embodiment. FIG. 6 also shows lens arrangements at the wide-angle end (W) and the telephoto end (T) of the variable magnification optical system 1D.

  The variable magnification optical system 1D of Example 4 includes a first lens group (Gr1) in which each lens group (Gr1, Gr2) has negative optical power as a whole in order from the object side to the image side, an optical aperture stop ST, and the like. , A negative / positive two-component zoom configuration comprising a second lens group (Gr2) having a positive optical power as a whole, and during zooming, as shown in FIG. 6, the first lens group (Gr1) ) And the second lens group 12 move, and the optical aperture stop ST is fixed and does not move.

  More specifically, in the variable magnification optical system 1D of Example 4, each lens group (Gr1, Gr2) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a negative meniscus lens convex to the object side (first lens L1), a negative biconcave lens (second lens L2), and a positive meniscus lens convex to the object side (third lens L3). Consists of. The second lens group (Gr2) includes a positive meniscus lens (fourth lens L4) convex toward the object side, a biconvex positive lens (fifth lens L5), a biconcave negative lens (sixth lens L6), and a biconvex lens. Positive lens (seventh lens L7). The sixth lens L6 and the seventh lens L7 are plastic lenses having both aspheric surfaces.

  In the present embodiment, as the material of the sixth lens L6, for example, the product name “OKP4” manufactured by Osaka Gas Chemical Co., Ltd. can be used as in the seventh lens L7 of the first embodiment. In the present embodiment, as the material of the seventh lens L7, for example, the product name “ZEONEX E48R” manufactured by Nippon Zeon Co., Ltd. can be used, as in the eighth lens L8 of the first embodiment. .

  An optical aperture stop ST is fixed and arranged on the object side of the second lens group (Gr2), and a light receiving surface of the image sensor (SR) is arranged on the image side via a parallel plate (FT) as a filter. ing.

  In the variable magnification optical system 1D of Example 4, at the time of zooming from the wide angle end (W) to the telephoto end (T), as shown in FIG. 6, the first lens group (Gr1) moves away from the object. The second lens group (Gr2) is moved linearly in a direction approaching the object, and the optical aperture stop ST is always fixed and does not move. Thus, in zooming from the wide-angle end (W) to the telephoto end (T), the first lens group (Gr1) and the second lens group (Gr2) move so that the distance between them decreases, The optical aperture stop ST disposed in is fixed.

  The construction data of each lens in the variable magnification optical system 1D of Example 4 is shown below.

Numerical Example 4
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 20.951 0.902 1.80420 46.49
2 7.519 5.919
3 -27.843 0.820 1.48749 70.45
4 9.130 1.301
5 10.793 1.711 1.92286 20.88
6 16.757 Variable 7 (Aperture) ∞ Variable 8 10.302 2.080 1.62041 60.35
9 46.470 0.100
10 8.991 3.405 1.49700 81.61
11 -19.029 0.858
12 * -9.148 0.801 1.60700 27.10
13 * 9.814 0.524
14 * 8.684 2.272 1.53048 55.72
15 * -8.369 Variable 16 ∞ 2.750 1.51680 64.20
17 ∞ 1.00
Image plane ∞
Aspheric data 12th surface
K = 0.0000e + 000, A4 = -1.1234e-004, A6 = -7.0695e-005, A8 = 8.3176e-006, A10 = -2.1112e-007
13th page
K = 0.000e + 000, A4 = -4.6373e-004, A6 = -3.0640e-004, A8 = 2.0562e-005, A10 = -2.5697e-007
14th page
K = 0.0000e + 000, A4 = -8.9260e-004, A6 = -3.44674e-004, A8 = 1.6462e-005, A10 = -1.8223e-007
15th page
K = 0.0000e + 000, A4 = 5.1365e-004, A6 = -1.1528e-004, A8 = 6.2732e-006, A10 = -1.9115e-007
Various data zoom data Zoom ratio 2.04
Wide angle Medium Telephoto focal length 2.873 4.100 5.854
F number 1.229 1.377 1.632
Angle of view 62.398 42.304 29.322
Image height 3.000 3.000 3.000
Total lens length 49.076 41.850 37.816
BF 10.467 8.843 10.868
d6 16.714 9.488 5.454
d7 4.242 2.825 0.800
d15 4.613 6.030 8.055
Zoom lens group data group Start surface Focal length 1 1 -8.475
2 8 9.784
The spherical aberration (sine condition), astigmatism, and distortion in the variable magnification optical system 1D of Example 4 with the above lens arrangement and configuration are shown in FIGS. 19, 20, and 21, respectively. . 19 shows each aberration at the wide-angle end (W), FIG. 20 shows each aberration at the intermediate point (M), and FIG. 21 shows each aberration at the telephoto end (T).

  FIG. 7 is a cross-sectional view illustrating the arrangement of lens groups in the variable magnification optical system according to the fifth embodiment. FIG. 7 also shows lens arrangements at the wide-angle end (W) and the telephoto end (T) of the variable magnification optical system 1E.

  The variable magnification optical system 1E of Example 5 includes a first lens group (Gr1) in which each lens group (Gr1, Gr2) has negative optical power as a whole in order from the object side to the image side, an optical aperture stop ST, and the like. , A negative / positive two-component zoom configuration comprising a second lens group (Gr2) having a positive optical power as a whole, and during zooming, as shown in FIG. 7, the first lens group (Gr1) ) And the second lens group 12 move, and the optical aperture stop ST is fixed and does not move.

  More specifically, in the variable magnification optical system 1E of Example 5, each lens group (Gr1, Gr2) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a negative meniscus lens convex to the object side (first lens L1), a negative biconcave lens (second lens L2), and a positive meniscus lens convex to the object side (third lens L3). Consists of. The second lens L2 and the third lens L3 are cemented lenses. The second lens group (Gr2) includes a positive meniscus lens convex to the object side (fourth lens L4), a negative meniscus lens convex to the object side (fifth lens L5), and a positive biconvex lens (sixth lens L6). And a biconcave negative lens (seventh lens L7) and a biconvex positive lens (eighth lens L8). The fifth lens L5 and the sixth lens L6 are cemented lenses, the seventh lens L7 and the eighth lens L8 are cemented lenses, and the fourth lens L4 and the seventh lens L7 are object lenses. The side surface is an aspheric plastic lens, and the eighth lens L8 is an aspheric surface plastic lens.

  In the present embodiment, as the material for the seventh lens L7, for example, the product name “OKP4” manufactured by Osaka Gas Chemical Co., Ltd. can be used as in the seventh lens L7 of the first embodiment. In the present embodiment, as the material for the fourth lens L4 and the eighth lens L8, for example, the product name “ZEONEX E48R” manufactured by Nippon Zeon Co., Ltd., as in the eighth lens L8 of the first embodiment. Can be used.

  An optical aperture stop ST is fixed and arranged on the object side of the second lens group (Gr2), and a light receiving surface of the image sensor (SR) is arranged on the image side via a parallel plate (FT) as a filter. ing.

  In the variable magnification optical system 1E of Example 5, at the time of zooming from the wide angle end (W) to the telephoto end (T), as shown in FIG. 7, the first lens group (Gr1) moves away from the object. The second lens group (Gr2) is moved linearly in a direction approaching the object, and the optical aperture stop ST is always fixed and does not move. Thus, in zooming from the wide-angle end (W) to the telephoto end (T), the first lens group (Gr1) and the second lens group (Gr2) move so that the distance between them decreases, The optical aperture stop ST disposed in is fixed.

  The construction data of each lens in the variable magnification optical system 1E of Example 5 is shown below.

Numerical Example 5
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 20.838 0.900 1.83481 42.72
2 7.271 6.428
3 -16.912 0.817 1.51680 64.20
4 12.840 2.165 1.92286 20.88
5 43.102 Variable 6 (Aperture) ∞ Variable 7 * 11.751 1.811 1.53048 55.72
8 69.676 0.381
9 16.404 0.800 1.84666 23.78
10 9.541 4.946 1.77250 49.65
11 -15.388 0.108
12 * -21.981 0.800 1.60700 27.10
13 8.641 2.814 1.53048 55.72
14 * -16.818 Variable 15 ∞ 2.750 1.51680 64.20
16 ∞ 1.00
Image plane ∞
Aspheric data 7th surface
K = 0.0000e + 000, A4 = -2.4067e-004, A6 = -2.0899e-006, A8 = -5.4515e-008, A10 = -1.1719e-009
12th page
K = 0.0000e + 000, A4 = -3.5563e-005, A6 = 8.6413e-006, A8 = 1.1682e-007, A10 = -2.1243e-009
14th page
K = 0.0000e + 000, A4 = 3.8830e-004, A6 = 1.2755e-005, A8 = -7.6967e-008, A10 = 1.2276e-008
Various data zoom data Zoom ratio 2.54
Wide angle Medium telephoto focal length 3.076 4.900 7.810
F number 1.030 1.170 1.503
Angle of view 60.333 35.631 21.928
Image height 3.000 3.000 3.000
Total lens length 51.032 41.479 37.233
BF 11.137 9.236 12.132
d5 16.130 6.576 2.331
d6 5.512 3.696 0.800
d14 4.607 6.423 9.319
Zoom lens group data group Start surface Focal length 1 1 -9.715
2 7 9.668
The spherical aberration (sine condition), astigmatism, and distortion in the variable magnification optical system 1E of Example 5 under the above lens arrangement and configuration are shown in FIGS. 22, 23, and 24, respectively. . FIG. 22 shows each aberration at the wide-angle end (W), FIG. 23 shows each aberration at the intermediate point (M), and FIG. 24 shows each aberration at the telephoto end (T).

  FIG. 8 is a cross-sectional view showing the arrangement of lens groups in the variable magnification optical system in the sixth embodiment. FIG. 8 also shows lens arrangements at the wide-angle end (W) and the telephoto end (T) of the variable magnification optical system 1E.

  The variable magnification optical system 1F of Example 6 includes a first lens group (Gr1) in which each lens group (Gr1, Gr2) has negative optical power as a whole in order from the object side to the image side, an optical aperture stop ST, and the like. A negative / positive two-component zoom configuration comprising a second lens group (Gr2) having a positive optical power as a whole, and during zooming, as shown in FIG. 8, the first lens group (Gr1) ) And the second lens group 12 move, and the optical aperture stop ST is fixed and does not move.

  More specifically, in the variable magnification optical system 1F of Example 6, each lens group (Gr1, Gr2) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a negative meniscus lens convex to the object side (first lens L1), a negative biconcave lens (second lens L2), and a positive meniscus lens convex to the object side (third lens L3). Consists of. The second lens group (Gr2) includes a biconvex positive lens (fourth lens L4), a negative meniscus lens convex to the image side (fifth lens L5), and a positive meniscus lens convex to the object side (sixth lens L6). And a negative meniscus lens (seventh lens L7) convex to the object side and a positive biconvex lens (eighth lens L8). The fourth lens L4 and the fifth lens L5 are cemented lenses, the seventh lens L7 and the eighth lens L8 are cemented lenses, and the seventh lens L7 has a non-object-side surface. The eighth lens L8 is a plastic lens having an aspheric surface on the image plane side.

  An optical aperture stop ST is fixed and arranged on the object side of the second lens group (Gr2), and a light receiving surface of the image sensor (SR) is arranged on the image side via a parallel plate (FT) as a filter. ing.

  In the variable magnification optical system 1F of this embodiment, when the magnification is changed from the wide angle end (W) to the telephoto end (T), as shown in FIG. 8, the first lens group (Gr1) is curved in a direction away from the object. The second lens group (Gr2) is moved linearly in a direction approaching the object, and the optical aperture stop ST is always fixed and does not move. Thus, in zooming from the wide-angle end (W) to the telephoto end (T), the first lens group (Gr1) and the second lens group (Gr2) move so that the distance between them decreases, The optical aperture stop ST disposed in is fixed.

  The construction data of each lens in the variable magnification optical system 1F of Example 6 is shown below.

Numerical Example 6
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 57.998 0.914 1.80420 46.49
2 7.626 5.183
3 -18.979 0.800 1.48749 70.45
4 20.670 0.112
5 17.415 1.839 1.92286 20.88
6 66.365 Variable 7 (Aperture) ∞ Variable 8 17.171 4.228 1.49700 81.61
9 -9.771 2.490 1.83400 37.35
10 -24.391 0.100
11 10.150 3.191 1.80420 46.49
12 78.807 0.980
13 * 9281.921 0.813 1.60700 27.10
14 5.953 3.404 1.53048 55.72
15 * -19.385 Variable 16 ∞ 2.750 1.51680 64.20
17 ∞ 1.00
Image plane ∞
Aspheric data 13th surface
K = -6.0664e + 017, A4 = -1.1777e-004, A6 = 6.7396e-006, A8 = -7.3477e-008, A10 = 4.2721e-010
14th page
K = -3.2715e + 001, A4 = -7.3041e-005, A6 = 3.4192e-005, A8 = -9.0841e-007, A10 = 2.3023e-008
Various data zoom data Zoom ratio 2.54
Wide angle Medium Telephoto focal length 3.077 4.900 7.806
F number 1.030 1.231 1.584
Angle of view 64.283 36.213 22.048
Image height 3.000 3.000 3.000
Total lens length 53.043 43.206 38.923
BF 11.181 9.453 12.583
d6 15.606 5.770 1.487
d7 5.893 3.929 0.800
d15 4.676 6.640 9.770
Zoom lens group data group Start surface Focal length 1 1 -9.519
2 8 10.251
FIG. 25, FIG. 26, and FIG. 27 show the spherical aberration (sine condition), astigmatism, and distortion in the variable magnification optical system 1F of Example 6 under the lens arrangement and configuration as described above. . 25 shows each aberration at the wide-angle end (W), FIG. 26 shows each aberration at the intermediate point (M), and FIG. 27 shows each aberration at the telephoto end (T).

  FIG. 9 is a cross-sectional view showing the arrangement of lens groups in the variable magnification optical system in the seventh embodiment. FIG. 9 also shows lens arrangements at the wide-angle end (W) and the telephoto end (T) of the variable magnification optical system 1E.

  The variable magnification optical system 1G of Example 7 includes a first lens group (Gr1) in which each lens group (Gr1, Gr2) has negative optical power as a whole in order from the object side to the image side, an optical aperture stop ST, and the like. , A negative / positive two-component zoom configuration comprising a second lens group (Gr2) having a positive optical power as a whole, and during zooming, as shown in FIG. 9, the first lens group (Gr1) ) And the second lens group 12 move, and the optical aperture stop ST is fixed and does not move.

  More specifically, in the variable magnification optical system 1G of Example 7, each lens group (Gr1, Gr2) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a negative meniscus lens convex to the object side (first lens L1), a negative biconcave lens (second lens L2), and a positive meniscus lens convex to the object side (third lens L3). Consists of. The second lens group (Gr2) includes a biconvex positive lens (fourth lens L4), a negative meniscus lens convex to the image side (fifth lens L5), a positive lens convex to the image side (sixth lens L6), and It consists of a negative meniscus lens (seventh lens L7) convex to the image side. The sixth lens L6 and the seventh lens L7 are plastic lenses having both aspheric surfaces.

  In the present embodiment, as the material of the sixth lens L6, for example, the product name “ZEONEX E48R” manufactured by Nippon Zeon Co., Ltd. can be used as in the eighth lens L8 of the first embodiment. In the present embodiment, the material of the seventh lens L7 is, for example, the same as that of the eighth lens L8 of Embodiment 1, and the material thereof is, for example, the same as that of the seventh lens L7 of Embodiment 1. The product name “OKP4” manufactured by Osaka Gas Chemical Co., Ltd. can be used.

  An optical aperture stop ST is fixed and arranged on the object side of the second lens group (Gr2), and a light receiving surface of the image sensor (SR) is arranged on the image side via a parallel plate (FT) as a filter. ing.

  In the variable magnification optical system 1F of the present embodiment, at the time of zooming from the wide angle end (W) to the telephoto end (T), as shown in FIG. 9, the first lens group (Gr1) curves in a direction away from the object. The second lens group (Gr2) is moved linearly in a direction approaching the object, and the optical aperture stop ST is always fixed and does not move. Thus, in zooming from the wide-angle end (W) to the telephoto end (T), the first lens group (Gr1) and the second lens group (Gr2) move so that the distance between them decreases, The optical aperture stop ST disposed in is fixed.

  The construction data of each lens in the variable magnification optical system 1G of Example 7 is shown below.

Numerical Example 7
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 29.308 0.900 1.80420 46.49
2 6.899 5.689
3 -24.434 0.800 1.80420 46.49
4 20.800 0.209
5 16.980 4.916 1.92286 20.88
6 760.053 Variable 7 (Aperture) ∞ Variable 8 7.843 3.790 1.62041 60.35
9 -16.888 0.632
10 -11.482 0.800 1.84666 23.78
11 -25.272 0.100
12 * 19.119 2.391 1.53048 55.72
13 * -6.438 0.300
14 * -3.687 1.593 1.60700 27.10
15 * -6.493 Variable 16 ∞ 2.750 1.51680 64.20
17 ∞ 1.00
Image plane ∞
Aspheric data 12th surface
K = 0.0000e + 000, A4 = -8.7544e-004, A6 = 9.4527e-007, A8 = -2.1325e-006, A10 = 0.0000e + 000, A12 = 0.0000e + 000
13th page
K = 0.0000e + 000, A4 = 1.0295e-003, A6 = -5.1602e-007, A8 = -9.0464e-007, A10 = 0.0000e + 000, A12 = 0.0000e + 000
14th page
K = -2.8192e + 000, A4 = 1.1281e-003, A6 = 5.8607e-007, A8 = -1.0495e-007, A10 = -2.5945e-008, A12 = 1.9276e-009
15th page
K = 0.0000e + 000, A4 = 4.2546e-003, A6 = -1.2032e-004, A8 = 7.3900e-006, A10 = -3.8270e-007, A12 = 1.0851e-008
Various data zoom data Zoom ratio 2.54
Wide angle Medium Telephoto focal length 2.854 4.737 7.862
F number 1.232 1.497 1.958
Angle of view 66.164 36.762 21.684
Image height 3.000 3.000 3.000
Total lens length 51.081 40.983 37.090
BF 11.120 9.720 13.158
d6 15.002 4.905 1.011
d7 6.309 4.238 0.800
d15 4.836 6.907 10.345
Zoom lens group data group Start surface Focal length 1 1 -8.913
2 8 9.805
FIG. 28, FIG. 29 and FIG. 30 show the spherical aberration (sinusoidal condition), astigmatism and distortion in the variable magnification optical system 1G of Example 7 under the above lens arrangement and configuration, respectively. . 28 shows each aberration at the wide angle end (W), FIG. 29 shows each aberration at the intermediate point (M), and FIG. 30 shows each aberration at the telephoto end (T).

  Table 1 shows numerical values when the above-described conditional expressions (1) to (6) are applied to the variable magnification optical systems 1A to 1G of Examples 1 to 7 listed above.

  As described above, the variable magnification optical systems 1A to 1G in Examples 1 to 7 satisfy the requirements according to the present invention, and as a result, have a large aperture ratio, optical performance, and compactness that are equal to or higher than those in the past. In addition to achieving a reduction in cost by using a plastic lens, it is possible to reduce deterioration in imaging performance due to temperature changes.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Accordingly, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

FIG. 2 is a lens cross-sectional view schematically showing the configuration for explaining the variable magnification optical system in the embodiment. It is a block diagram which shows the structure of the digital device in embodiment. 3 is a cross-sectional view illustrating an arrangement of lens groups in a variable magnification optical system in Embodiment 1. FIG. 6 is a cross-sectional view illustrating an arrangement of lens groups in a variable magnification optical system in Example 2. FIG. 6 is a cross-sectional view illustrating an arrangement of lens groups in a variable magnification optical system in Example 3. FIG. 6 is a cross-sectional view illustrating an arrangement of lens groups in a variable magnification optical system in Example 4. FIG. 10 is a cross-sectional view illustrating an arrangement of lens groups in a variable magnification optical system according to Example 5. FIG. 10 is a cross-sectional view illustrating an arrangement of lens groups in a variable magnification optical system in Example 6. 10 is a cross-sectional view illustrating an arrangement of lens groups in a variable magnification optical system in Example 7. FIG. 4 is an aberration diagram of the lens unit at the wide angle end according to Example 1. FIG. 6 is an aberration diagram of a lens group at an intermediate point in Example 1. FIG. 4 is an aberration diagram of the lens unit at the telephoto end according to Example 1. FIG. 6 is an aberration diagram of the lens unit at the wide angle end according to Example 2. 6 is an aberration diagram of a lens group at an intermediate point in Example 2. FIG. 6 is an aberration diagram of a lens group at a telephoto end according to Example 2. FIG. 10 is an aberration diagram of a lens unit at a wide angle end according to Example 3. FIG. 10 is an aberration diagram of a lens group at an intermediate point in Example 3. FIG. 10 is an aberration diagram of a lens group at a telephoto end according to Example 3. FIG. FIG. 6 is an aberration diagram of a lens unit at a wide angle end according to Example 4. 10 is an aberration diagram of a lens group at an intermediate point in Example 4. FIG. 10 is an aberration diagram of a lens group at a telephoto end according to Example 4. FIG. 10 is an aberration diagram of a lens unit at a wide angle end according to Example 5. FIG. 10 is an aberration diagram of a lens group at an intermediate point in Example 5. FIG. 10 is an aberration diagram of a lens group at a telephoto end according to Example 5. FIG. 10 is an aberration diagram of a lens unit at a wide angle end according to Example 6. FIG. 10 is an aberration diagram of a lens group at an intermediate point in Example 6. FIG. 10 is an aberration diagram of a lens group at a telephoto end according to Example 6. FIG. 10 is an aberration diagram of a lens group at a wide angle end according to Example 7. FIG. 10 is an aberration diagram of a lens group at an intermediate point in Example 7. FIG. 10 is an aberration diagram of a lens unit at a telephoto end according to Example 7. FIG.

Explanation of symbols

AX Optical axis 1, 1A to 1G Variable magnification optical system 3 Digital equipment 11, Gr1 first lens group 12, Gr2 second lens group 13, ST aperture 15, SR imaging device 21 Imaging device

Claims (5)

In order from the object side to the image side, a first lens group having negative optical power, a diaphragm, and a second lens group having positive optical power,
In zooming from the wide-angle end to the telephoto end, the first lens group and the second lens group move so as to narrow the distance between each other,
The diaphragm is fixed,
The second lens group includes at least one first optical lens having a positive optical power and at least one second plastic lens having a negative optical power,
At least one surface of the first and second plastic lenses has an aspheric surface satisfying the following (1), and satisfies the following conditional expressions (2) and (3): .
−6 <dφp × f2 <−0.8 (1)
0.6 <Z / (Fnw ² ) <4.5 (2)
−2.4e-4 <BFt × φ2pA <2.4e-4 (3)
However,
f2: Focal length of the second lens group dφp = φpm−φp0
φp0: optical power on the optical axis in the meridional section,
When the curvature on the optical axis in the meridional section is C0, and the refractive indices before and after the surface are N and N '
φp0 = C0 × (N′−N)
φpm: optical power at the passing position in the meridional section of the marginal ray of the axial beam,
When the curvature at the passing position in the meridional section is Cm, and the refractive indexes before and after the surface are N and N ′
φpm = Cm × (N′−N)
Z: zoom ratio Fnw: F number at the wide-angle end BFt: back focus at the telephoto end φ2pA = Σki / (fpi × (1-Ni))
i is an index representing each plastic lens in the second lens group, and Σ means taking the sum of these,
ki: Temperature coefficient of refractive index of each plastic lens in the second lens group in visible light with a wavelength of 400 nm to 700 nm in a normal temperature range of −30 ° C. to 70 ° C.
fpi: Focal length of each plastic lens
Ni: Refractive index of each plastic lens in the second lens group The zoom lens system according to claim 1, wherein the following conditional expression (4) is satisfied.
2.8 <f2 / fw <6.0 (4)
However,
fw: focal length of the entire system at the wide angle end The zoom lens system according to claim 1 or 2, wherein the following conditional expression (5) is satisfied.
−1e-4 <BFt × φ2pB <1e-4 (5)
However,
φ2pB = Σαi / fpi
i is an index representing each plastic lens in the second lens group, and Σ means taking the sum of these,
αi: Linear expansion coefficient of each plastic lens in the second lens group in a normal temperature range of −30 ° C. to 70 ° C. A variable magnification optical system according to any one of claims 1 to 3,
An image sensor that converts an optical image into an electrical signal,
An imaging apparatus, wherein the variable magnification optical system is capable of forming an optical image of an object on a light receiving surface of the imaging element. An imaging device according to claim 4,
A controller that causes the imaging device to perform at least one of still image shooting and moving image shooting of a subject;
A digital apparatus, wherein a variable magnification optical system of the imaging device is assembled on a light receiving surface of the imaging device so as to form an optical image of the subject.

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