JP2005326743A - Zooming lens and information device having photographing function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a zooming lens which has a variable magnification ratio as high as ≥4.5 while having a sufficiently wide angle of view as ≥35° half angle of view in the wide-angle limit, and which has sufficient resolving power even for imaging an object image by a compact size pickup device having a 3- to 5-million pixel range. <P>SOLUTION: The zooming lens comprises, from the object side to the image side, first to third lens groups having positive, negative and positive refractive powers, respectively, and an aperture diaphragm disposed between the second lens group II and the third lens group III. When a scaling is changed from the wide-angle limit to the telescopic limit, the interval between the first and second lens groups is increased and the interval between the second lens group and the third lens group is decreased. In the zooming lens, the ratio Y'<SB>max</SB>/f<SB>w</SB>of the maximum image height Y'<SB>max</SB>to the focal length f<SB>w</SB>of the whole system in the wide-angle limit is in the range of (1): 0.70<Y'<SB>max</SB>/f<SB>w</SB><1.00. The second lens group II comprises three lenses: from the object side to the image side, a negative lens having a surface with a large curvature facing the image side, a positive lens having a surface with a large curvature facing the image side, and a negative lens having a surface with a large curvature facing the object side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an information device having a zoom lens and a photographing function. An information device having a photographing function can be implemented as a still camera, an electronic still camera, a camera device such as a digital camera or a video camera having a moving image photographing function, an information device having these as a photographing function unit, particularly a portable information terminal device.

  Devices having a function of capturing an object image are becoming common from a conventional still camera to an electronic still camera, a digital camera and a video camera having a moving image shooting function, and various information devices such as a portable information terminal device. As a lens used in these devices, a zoom lens is generalized, and its zooming region is required to have a higher zooming ratio, and there is a strong demand for higher performance.

  In particular, in the case of a zoom lens that forms an object image on an image sensor, it is necessary to have a resolution corresponding to an image sensor with 3 to 5 million pixels over the entire zoom range. Further downsizing, the diagonal size of the image sensor is about 6-9 mm being put into practical use, and when realizing 3 million to 5 million pixels with such a small image sensor, the pixel pitch is 3 μm or less, so that Advanced aberration correction is required.

  For example, if the pixel pitch is 2.5 μm, the Nyquist frequency is 200 lines / mm, and the diffraction limit is also a problem. Get smaller.

  Further, there is a strong demand for a wide angle of view with respect to the photographing lens, and it is desirable that the half angle of view at the wide angle end of the zoom lens is at least 35 degrees, preferably 38 degrees or more. Half angle of view: 38 degrees corresponds to a focal length of 28 mm in terms of a 35 mm silver salt camera (so-called “Leica version”). In such a wide angle of view, off-axis aberrations such as distortion and lateral chromatic aberration are likely to be generated, and the lens design is very difficult in combination with the small pixel pitch of the image sensor.

Regarding the zoom ratio, a zoom lens equivalent to 28 to 135 mm (about 4.8 times) with a “35 mm silver salt camera equivalent focal length” is considered to be able to handle most of the general photography. It is possible.
As a “type suitable for high zoom ratio” as a zoom lens, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens having a positive refractive power The lens unit is arranged, and has an aperture stop in the vicinity of the third lens unit on the object side. When zooming from the wide-angle end to the telephoto end, the distance between the first lens unit and the second lens unit is increased. There are known ones in which each group is moved or fixed so that the distance between the second lens group and the third lens group is small (Patent Documents 1 to 3, etc.).

  In addition to the above configuration, there is also known a lens having a “fourth lens group having a positive refractive power” on the image side of the third lens group (Patent Documents 4 to 7, etc.).

  These conventionally known zoom lenses have a zoom ratio of more than 5 times in any of the three-lens group configuration and the four-lens group configuration, but those whose half angle of view at the wide-angle end exceeds 35 degrees. Absent. In Patent Document 2 in which “an embodiment of the widest angle of view” is disclosed, the zoom ratio is about 3 to 5 times, the half angle of view is about 25 to 34 degrees, and the widest half angle of view is 34 degrees. In the embodiment which achieved the above, the zoom ratio is only 3 times, and it is difficult to say that it can sufficiently meet the recent demand for performance in terms of both wide angle of view and high zoom ratio.

JP-A-11-109236 JP-A-11-142733 JP 11-242157 A JP-A-62-024213 Japanese Patent Laid-Open No. 03-033710 JP 2001-56436 A Japanese Patent Laid-Open No. 06-094997

In view of the above-mentioned circumstances, the present invention has a zoom ratio of 4.5 times or more while the half angle of view at the wide angle end is sufficiently wide as 35 degrees or more, and has a zoom ratio of 4.5 times or more, and is small with 3 to 5 million pixels. An object of the present invention is to realize a zoom lens having sufficient resolving power even when an object image is formed on the image pickup element.
Another object of the present invention is to realize an “information device having a photographing function” having the zoom lens as a photographing optical system.

  According to the zoom lens of the present invention, “from the object side to the image side, the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the third lens group having a positive refractive power are described above. In addition to having an aperture stop between the second lens group and the third lens group, the distance between the first lens group and the second lens group is increased upon zooming from the wide-angle end to the telephoto end. This is a “zoom lens in which the distance between the second lens group and the third lens group is small”, and has the following characteristics (claim 1).

The ratio of the focal length of the entire system at the wide angle end: f _W and the maximum image height: Y ′ _max : Y ′ _max / f _W is the condition:
(1) 0.70 <Y ' _max / f _W <1.00
It is in the range.
The second lens group is a negative lens having a large curvature surface facing the image side from the object side to the image side, a positive lens having a convex surface having a large curvature toward the image side, and a concave surface having a large curvature toward the object side. Further, it is configured by arranging three negative lenses. In other words, the second lens group has a “configuration in which a positive lens is sandwiched between a negative lens on the object side and a negative lens on the image side”.

In the zoom lens according to claim 1, an image side surface (a surface closest to the image side in the second lens group) of the “image side negative lens” in the second lens group has a negative refractive power as the distance from the optical axis increases. Refractive index of the material of the “image side negative lens” in the second lens group: N _2I , “maximum effective ray height on the most aspherical surface on the image side” Of aspherical surface: X _2I (H _0.8 ), maximum image height: Y ′ _max , conditions:
(2) 0.0010 <(1−N _2I ) × X _2I (H _0.8 ) / Y ' _max <0.0500
Is preferably satisfied (claim 2).

3. The zoom lens according to claim 2, wherein an object side surface (most object side surface in the second lens group) of the “negative lens on the object side” in the second lens group is an aspherical surface. Refractive index of the material of the “negative lens on the object side”: N ₂₀ , Refractive index of the material of the “negative lens on the image side” in the second lens group: N _2I , “the most aspheric surface on the object side” of the second lens group Aspherical amount at 80% of the maximum effective ray height at X: X ₂₀ (H _0.8 ), aspherical amount at 80% of the maximum effective ray height at the image side aspherical surface of the second lens group: X _2I (H _0.8 ), maximum image height: Y ′ _max , conditions:
(3) -0.0500 <{(N _2O −1) × X _2O (H _0.8 ) + (1-N _2I ) × X _2I (H _0.8 )} / Y ′ _max <0.1500
Is preferably satisfied (Claim 3).

  “Aspheric amount: X (H)” is the difference between the sag amount (depth) at the height: H from the optical axis between the spherical surface defined by the paraxial curvature of the aspheric surface and the actual aspheric surface. The direction from the object side to the image side is positive.

The zoom lens according to any one of claims 1 to 3, wherein the refractive index and the Abbe number of materials of the i-th lens counted from the object side in the second lens group are N _2i and ν _2i :
(4) 1.75 <N ₂₁ <1.90, 35 <ν ₂₁ <50
(5) 1.65 <N ₂₂ <1.90, 20 <ν ₂₂ <35
(6) 1.75 <N ₂₃ <1.90, 35 <ν ₂₃ <50
Is preferably satisfied (claim 4).

5. The zoom lens according to claim 1, wherein three lenses constituting the second lens group are expressed as “a negative lens having a large curvature surface on the image side and a curvature on the image side in order from the object side”. A positive lens having a large convex surface and a negative lens having a concave surface having a large curvature on the object side ”, and the positive lens and the negative lens on the image side can be cemented. . In this case, the ratio between the radius of curvature of the “joint surface between the positive lens and the negative lens in the second lens group”: R _2C and the maximum image height: Y ′ _max is R _2C / Y ′ _max.
(7) -3.5 <(R _2C / Y ' _max ) <-1.0
Is preferably satisfied (claim 6).
Of course, in the second lens group, negative, positive, and negative lenses arranged in order from the object side may be configured separately.

The zoom lens according to any one of claims 1 to 6, wherein the first lens unit monotonously moves toward the object side upon zooming from the wide-angle end to the telephoto end, and the first and second lens units at the wide-angle end. The distance: D _12W , the distance between the first and second lens _{units at} the telephoto end: D _12T , the focal length of the entire system at the telephoto end: f _T , the condition:
(8) 0.50 <(D _12T −D _12W ) / f _T <0.85
Is preferably satisfied (claim 7).

The zoom lens according to any one of claims 1 to 7, wherein the third lens unit monotonously moves toward the object side upon zooming from the wide-angle end to the telephoto end, and the second and third lenses at the wide-angle end. The distance between the groups is D _23W , the distance between the second and third lens groups at the telephoto end is D _23T , and the focal length of the entire system at the telephoto end is f _T.
(9) 0.25 <(D _23W −D _23T ) / f _T <0.65
It is preferable that the configuration satisfies the above (claim 8).

The zoom lens according to any one of claims 1 to 8, wherein the focal length of the second lens group is f ₂ and the focal length of the third lens group is f _3.
(10) 0.5 <| f ₂ | / f ₃ <1.0
Is preferably satisfied.

The zoom lens according to any one of claims 1 to 9, wherein the focal length of the first lens group; f ₁ , the focal length of the entire system at the wide angle end: f _W is a condition:
(11) 6.0 <f ₁ / f _W <12.0
Is preferably satisfied (claim 10).

  The zoom lens according to any one of claims 1 to 10, wherein, as described above, "from the object side to the image side, the first lens group having a positive refractive power and the second lens group having a negative refractive power". The third lens group having a positive refractive power is provided in the above order. ”As such a configuration, the first lens group to the third lens group can be configured by three lens groups. .

  The zoom lens according to any one of claims 1 to 10, wherein a "fourth lens unit having a positive refractive power" is disposed on the image side of the third lens unit, and zooming from the wide-angle end to the telephoto end. At this time, at least the first lens group and the third lens group move to the object side so that the distance between the first lens group and the second lens group is increased and the distance between the second lens group and the third lens group is decreased. A configuration may also be adopted (claim 12).

  In the case of the three-lens group configuration of claim 11 or the four-lens group configuration of claim 12, a “fixed lens having weak negative power” may be further inserted on the image side of these groups. That is, the zoom lens according to any one of claims 1 to 10 has a degree of freedom to further add a lens group to the image side of the third lens.

  The zoom lens according to a twelfth aspect may be configured such that the fourth lens group does not move during zooming (Claim 13), or the fourth lens group when zooming from the wide angle end to the telephoto end. A configuration in which the group is displaced toward the image side can also be adopted.

  The zoom lens according to any one of claims 1 to 14 has an aperture stop between the second lens group and the third lens group, and the aperture stop and the second lens unit at the time of zooming from the wide-angle end to the telephoto end. It is possible to configure such that the distance from the three lens groups is “widest at the wide-angle end and narrowest at the telephoto end”.

  The “aperture diameter of the aperture stop” in the zoom lens according to any one of claims 1 to 15 can be constant regardless of the magnification (Claim 16), or the aperture diameter of the aperture stop can be changed according to the magnification. In other words, the opening diameter at the long focal end can be set larger than the opening diameter at the short focal end.

  An information apparatus having a photographing function according to the present invention is characterized in that the zoom lens according to any one of claims 1 to 17 "has as a photographing optical system" (claim 18). This information device can of course be implemented as a normal silver salt still camera.

The information device according to claim 18 may be configured such that “the object image by the zoom lens is formed on the light receiving surface of the image sensor” (claim 19). Such an information device can be implemented as an electronic still camera, a digital camera having a video shooting function, a video camera, or the like.
The information device according to claim 19 may be configured to use “an imaging element having a diagonal size of 9 mm or less and a number of pixels of 3 million pixels or more” (claim 20). Such an image sensor has, for example, a diagonal dimension of 9 mm and 5 million pixels, a diagonal dimension of 6 mm and 3 million pixels. The information device according to claim 19 or 20 can be configured as a “portable information terminal device” (claim 21).

  In a zoom lens having three lens groups of positive, negative, and positive in order from the object side, the second lens group is generally configured as a “lens group that bears a main zooming action (so-called variator)”. The composition of the group is important. In particular, in the “information device having a photographing function” using a small image pickup device of “diagonal dimension: 6 to 9 mm and 3 to 5 million pixels” as exemplified above, the pixel pitch of the image pickup device is small, so Since aberration correction is required and it is difficult to correct off-axis aberrations, the second lens group requires some unconventional ideas.

  Conventionally, a zoom lens having a positive, negative, and positive three-lens group configuration, in which the second lens unit is configured by three lenses, almost all of the second lens unit is arranged in order from the object side to the image side. In other words, a negative lens having a large curvature surface, a negative lens having a concave surface on the image side, and a positive lens having a convex surface on the object side are arranged. Such a configuration of the second lens group cannot be said to be an optimal configuration for realizing a zoom lens using a small image sensor as described above and having a half angle of view at the wide angle end exceeding 35 degrees.

  In addition, there is also known a configuration in which the second lens group is “a configuration in which four lenses of a negative lens, a negative lens, a positive lens, and a negative lens with a surface having a large curvature facing the image side are arranged in order from the object side”. However, if the number of lenses is increased, the second lens group becomes thick, the total length during storage becomes large, and compactness is hindered, resulting in an increase in cost.

In the present invention, the second lens group is suitable for use with a small-sized image sensor as described above under the “limit of the number of lenses: 3”, and the half angle of view at the wide angle end exceeds 35 degrees. This presents a “configuration of the second lens group” suitable for realizing a zoom lens.
That is, the second lens group in the zoom lens according to the present invention includes, as described above, “a negative lens having a large curvature surface facing the image side, a positive lens having a convex surface having a large curvature facing the image side, It is composed of three negative lenses having a concave surface with a large curvature on the side.

Condition (1) that the zoom lens of the present invention satisfies: When Y ′ _max / f _W is 0.70 or less, the half angle of view is 35 degrees or more at the wide-angle end when distortion is sufficiently corrected. Can not be realized. Parameter: When Y ′ _max / f _W is 1.00 or more, it is extremely difficult to correct off-axis aberrations at the wide-angle end, and the first lens group is enlarged to make the zoom lens more compact, and thus photography. It becomes difficult to downsize an information device having a function.

  In the state where the condition (1) is satisfied, the second lens group is arranged in order from the object side, as described above, with a negative lens having a large curvature surface on the image side and a positive lens having a convex surface having a large curvature on the image side. If the lens is composed of three negative lenses having a concave surface having a large curvature on the object side, off-axis aberrations at the wide-angle end, particularly chromatic aberration of magnification, can be favorably corrected.

  An important point in this configuration is that both the “image side surface of the second positive lens from the object side” and the “object side surface of the third negative lens from the object side” in the second lens group are both “convex shape on the image side”. It is in that. In such a configuration, the off-axis light beam near the wide-angle end is generally incident at “a large incident angle on the surface”, so that the off-axis aberration can be greatly changed even if the curvature radius of the surface is slightly changed. . For this reason, the “off-axis aberration to be canceled in the other surface of the second lens group and the other lens group” is determined according to the correction capability of the other surface and the other lens group. It can be generated with a high degree of freedom in the “convex shaped surface”), and a higher level of aberration correction than in the conventional second lens group configuration is possible.

  The second lens group consists of the three known lenses: a negative lens with a large curvature on the image side, a negative lens with a concave surface on the image side, and a positive lens with a convex surface on the object side Then, the image side surface of the second negative lens from the object side and the object side surface of the third positive lens from the object side both have a “convex shape on the object side”. When the “angle of the off-axis light beam with respect to the optical axis” increases, the incident angle of the off-axis light beam on these surfaces (surfaces convex toward the object side) decreases, and the “variable range of the amount of aberration to be generated” ”Is limited to a narrow range, and a sufficient effect for correcting off-axis aberration cannot be obtained.

  In order to realize “better aberration correction” in the zoom lens according to the present invention, as described in claim 2, the image side surface of the negative lens disposed closest to the image side of the second lens group is “ It is desirable that the aspherical surface has a shape in which the negative refractive power decreases as the distance from the optical axis increases. It is desirable that this aspherical surface satisfies the condition (2).

Condition (2) parameters: If (1−N _2I ) × X _2I (H _0.8 ) is 0.0010 or less, or 0.0500 or more, distortion, astigmatism and coma can be corrected in a well-balanced manner. In particular, this is an obstacle to ensuring “higher imaging performance” at the wide-angle end.

  In order to better correct distortion at the wide-angle end, as described in claim 3, in addition to the image side surface of the “negative lens disposed on the image side” of the second lens group, the second lens It is desirable that the object side surface of the “negative lens disposed on the object side” of the group is aspheric, and this aspherical surface satisfies the condition (3).

Condition (3) parameters: {(N _{2 O} −1) × X _{2 O} (H _0.8 ) + (1−N _{2 I} ) × X _2I (H _0.8 )} / Y ′ _max is −0.0500 or less, This is not preferable because the distortion at the wide-angle end is “undercorrected” or “unnatural with an inflection point”. If the above parameter is 0.1500 or more, not only will distortion be overcorrected, but it will also be difficult to satisfactorily correct other off-axis aberrations.
The aspheric amount of the aspheric surface is assumed to be “the absolute value increases monotonously from the optical axis toward the lens outer peripheral portion”, and at the position “80% of the maximum effective ray height”, the condition (2 If (3) and / or (3) is satisfied, good performance can be realized in the light receiving region of the small image sensor.

  Further, by selecting a glass type that satisfies the conditions (4) to (6), “better correction of chromatic aberration” becomes possible.

  6. A manufacturing error such as decentration by joining a “second positive lens and a third negative lens from the object side” that cause large aberrations in the second lens group as in the zoom lens according to claim 5. As a result, it is difficult to cause performance deterioration due to, and an interval ring is not required, so that the number of man-hours during assembly can be reduced. At this time, it is preferable that the joint surface satisfies the condition (7).

When the parameter of condition (7): (R _2C / Y ′ _max ) is −3.5 or less, the curvature of the joint surface becomes loose and the “degree of freedom to generate aberration at the joint surface” becomes small, and −1. If it is 0 or more, the curvature of the cemented surface becomes too strong, and the “off-axis aberration that occurs” becomes excessive, and it becomes difficult to cancel out aberrations on the other surfaces of the second lens group and the other lens groups.

  In order to achieve “higher zooming ratio” in the zoom lens of the present invention, when zooming from the wide-angle end to the telephoto end, “by moving the third lens unit to the object side, It is better to share the zooming action "and lighten the burden on the second lens group to ensure the degree of freedom of aberration correction. Also, when zooming from the wide angle end to the telephoto end, By moving the lens to the wide-angle end, the height of the light beam passing through the first lens unit can be reduced at the wide-angle end, and the enlargement of the first lens unit accompanying the wide-angle can be suppressed. A long focal length can be achieved by ensuring a large distance between the second lens group and the second lens group.

In this case, if the parameter (8): (D _12T −D _12W ) / f _T is 0.50 or less, the “contribution to the zooming of the second lens group” becomes small, and the zooming of the third lens group. Or the “refractive power of the first and second lens groups” must be increased, and in any case, “deterioration of various aberrations” is caused. In addition, the total lens length at the wide-angle end is increased, and the height of light passing through the first lens group is increased, leading to “upsizing of the first lens group”.

Parameter: (D _12T −D _12W ) / f When _{T is set} to 0.85 or more, the “total length at the wide angle end” becomes too short, or the total length at the telephoto end becomes too long. If the total length at the wide-angle end is too short, the “moving space of the third lens group” is limited, and the contribution of the third lens group to the zooming is reduced, making it difficult to correct the entire aberration. If the total length at the telephoto end becomes too long, it will not only hinder "downsizing in the total length direction", but also the manufacturing error such as the radial direction will be enlarged to secure the peripheral light quantity at the telephoto end, or the lens barrel will fall down. Degradation of image performance due to the image is likely to be caused.

The parameter: (D _12T −D _12W ) / f _T is more preferably the condition:
(8A) 0.60 <(D _12T −D _12W ) / f _T <0.75
It is good to satisfy.

On the other hand, when the parameter (9): (D _23W −D _23T ) / f _T that regulates the change in the distance between the second lens group and the third lens group is 0.25 or less, the third lens group changes. The contribution to the magnification is reduced and the burden on the second lens group for changing the magnification is increased, or the refractive power of the third lens group itself must be increased, and in any case, various aberrations are deteriorated. If the parameter is 0.65 or more, the “lens total length at the wide-angle end” becomes longer, and the height of the light beam passing through the first lens group increases, leading to an increase in size of the first lens group.

The parameter: (D _23W −D _23T ) / f _T is more preferably the condition:
(9A) 0.30 <(D _23W −D _23T ) / f _T <0.60
Is preferably satisfied.

As for aberration correction, it is preferable that the conditions (10) and (11) are satisfied. If the parameter (| f ₂ | / f ₃ ) of the condition (10) is 0.5 or less, the second lens group If the refractive power is too strong, on the other hand, if it is 1.0 or more, the refractive power of the third lens group becomes too strong, and in any case, “aberration fluctuation during zooming” tends to increase.

Parameter (11): When f ₁ / f _W is 6.0 or less, “the imaging magnification of the second lens unit approaches the same magnification and the zooming efficiency is improved, which is advantageous for high zooming”. However, each lens of the first lens group requires a large refractive power, and there is a detrimental effect such as deterioration of chromatic aberration particularly at the telephoto end. Also, the first lens group becomes thicker and larger in diameter, and is particularly housed. It is disadvantageous for miniaturization in the state. Conversely, if the parameter f ₁ / f _{W is set} to 12.0 or more, the contribution of the second lens group to the zooming becomes small, and it becomes difficult to achieve high zooming.

  As in the case of claim 15, the aperture stop is moved independently of the adjacent lens group so that the “interval between the aperture stop and the third lens group” is widest at the wide-angle end, so that at the wide-angle end. The aperture stop can be brought closer to the first lens group, and the “height of the light beam passing through the first lens group” can be made lower, so that further miniaturization of the first lens group can be achieved.

Hereinafter, conditions for performing “better aberration correction” within a range that does not hinder downsizing of the zoom lens will be described.
The first lens group is preferably “a configuration having at least one negative lens and at least one positive lens” from the object side. More specifically, it is composed of “a negative meniscus lens having a convex surface facing the object side in order from the object side and a positive lens having a strong convex surface facing the object side” or “object side in order from the object side” And a negative meniscus lens having a convex surface facing the surface, a positive lens having a strong convex surface facing the object side, and a positive lens having a strong convex surface facing the object side.

  When the entire system is composed of “only three lenses of positive, negative, and positive” (Claim 11), the third lens group is “four lenses of positive lens, positive lens, negative lens, and positive lens in order from the object side”. Is preferable. Here, the second lens and the third lens from the object side may be appropriately joined. In addition, when the entire system is composed of “four lens groups of positive, negative, positive, and positive”, the third lens group is composed of “three lenses of a positive lens, a positive lens, and a negative lens in order from the object side”. Is preferred. In this case, the second lens and the third lens from the object side may be appropriately joined.

  In the case where the entire system is configured with four positive, negative, positive, and positive lens groups, the fourth lens group is preferably configured with one positive lens. In “focusing to a finite distance”, the method of moving only the fourth lens group may have the smallest “weight of an object to be moved”. The fourth lens group has a small movement amount at the time of zooming, and there is an advantage that a moving mechanism for zooming can be used as a moving mechanism for focusing.

  An aspherical surface is indispensable for further downsizing while maintaining good aberration correction, but it is preferable that at least the third lens unit has at least one aspherical surface other than the second lens unit. The aspherical surface in the third lens group is mainly effective for correcting spherical aberration and coma aberration.

As an aspherical lens, optical glass or optical plastic molded (glass molded aspherical surface, plastic molded aspherical surface) or “a thin resin layer molded on the surface of the glass lens and the surface aspherical ( Hybrid aspherical surface, replica aspherical surface, etc.) ”can be used.
Considering the adoption of a glass mold aspherical lens on the most image side of the second lens group, if the lens on the most image side of the second lens group is a positive lens, a heavy flint system is used for chromatic aberration correction. Glass type is required, but there is a problem that few glass types of heavy flint type are suitable for molding. If the “lens closest to the image side of the second lens group” is a negative lens as in the present invention, a lanthanum crown type to tantalum flint type glass type is used for chromatic aberration correction, and many glass types are suitable for the mold.

  In addition, when considering using a hybrid aspherical surface for the “most image side surface of the second lens group (image side surface of the negative lens on the image side)”, it is convenient to apply a mold for molding the resin layer. In addition, a slightly larger lens outer diameter is required, but if the lens closest to the image side of the second lens group is a positive lens, the lens edge thickness may be reduced and processing may not be possible. If the lens on the most image side of the second lens group is a negative lens as in the present invention, the edge thickness is in the increasing direction, so that no processing problems occur.

  According to the sixteenth aspect of the present invention, it may be simplified in terms of the mechanism that “the opening diameter of the aperture is made constant regardless of zooming”. Further, as described in claim 17, “change in F number due to zooming” can be reduced by increasing the open diameter of the long focal end compared to the short focal end.

  If there is a need to reduce the amount of light reaching the image plane, the aperture may be made smaller. However, if the amount of light is reduced by "inserting an ND filter" without greatly changing the aperture diameter, diffraction is reduced. It is preferable because a reduction in resolution due to a phenomenon can be prevented.

As explained above, a novel zoom lens can be realized by the present invention.
As shown in the examples, this zoom lens has a zoom ratio of 4.5 times or more while having a sufficiently wide angle of view at a wide angle end of 35 degrees or more, and is small in size and 3 million to Resolving power corresponding to an image sensor with 5 million pixels. Therefore, by using such a zoom lens as a photographing optical system, an information device (digital camera, video camera, portable information terminal device) having a good photographing function can be realized. Of course, the zoom lens of the present invention exhibits good performance even when used in a silver salt still camera or the like.

With reference to FIGS. 17 and 18, an embodiment of an “information device having a photographing function” as a portable information terminal device will be described.
17A and 17B are views showing the front side and the upper surface, and FIG. 17C is a view showing the back side. The camera device 30 includes the zoom lens according to any one of claims 1 to 17 described above (more specifically, for example, an appropriate one in Examples 1 to 4 described later) as the photographic lens 31. It has as a “zoom lens for photographing”.

  In FIG. 17A, reference numeral 32 denotes a flash, and reference numeral 33 denotes a finder. The zoom lever 34 and the shutter button 35 are disposed on the upper surface side of the main body. FIG. 17B is a diagram illustrating a usage state of the photographic lens 31.

  When the photographing lens 31 is not used, it is housed in a “collapsed type” in the information device main body as shown in FIG. In each of the embodiments of the zoom lens described later, the number of lenses is as small as 9 to 10 and the thickness of the second group is small.

  As shown in FIG. 17C, the power switch 36, the operation button 37, and the liquid crystal monitor 38 are arranged on the back side of the information device main body, and the communication card slot 39A and the memory card slot 39B are arranged on the side surface of the main body. Has been.

  FIG. 18 is a diagram illustrating a “system structure” of the information device. The information device 30 is a “portable information terminal device”. As shown in FIG. 18, the information device 30 includes a photographing lens 31 and a light receiving element (area sensor) 45, and is configured to read an image of a photographing target formed by the photographing lens 31 by the light receiving element 45. The output from the light receiving element 45 is processed by a signal processing device 42 under the control of the central processing unit 40 and converted into digital information. That is, the information device 30 has a “function of converting a captured image into digital information”.

  The image information digitized by the signal processing device 42 is subjected to predetermined image processing in the image processing device 41 under the control of the central processing unit 40 and then stored in the semiconductor memory 44 (set in the memory card slot 39B). To be recorded. The liquid crystal monitor 38 can display an image being photographed, or can display an image recorded in the semiconductor memory 44. The image recorded in the semiconductor memory 44 can also be transmitted to the outside using the communication card 43 (set in the communication card slot 39A) or the like.

  As shown in FIG. 17A, the photographing lens 31 is in the “collapsed state” when the information device 30 is carried, and when the user operates the power switch 36 to turn on the power, as shown in FIG. The lens barrel is paid out. At this time, each group of the zoom lens inside the lens barrel is, for example, “arrangement of the short focal point”, and by operating the zoom lever 34, the arrangement of each group is changed to change the magnification to the long focal point. It can be performed. At this time, the viewfinder 33 also zooms in conjunction with the change in the angle of view of the taking lens.

  Focusing is performed by “half-pressing” the shutter button 35. Focusing can be performed by moving the first group, the third group, or the light receiving element. When the shutter button 35 is further depressed from the half-pressed state, photographing is performed, and thereafter, the above-mentioned “image information processing” is executed.

  When the image recorded in the semiconductor memory 44 is “displayed on the liquid crystal monitor 38” or “sent to the outside using the communication card 43”, the operation button 37 is operated.

  When any one of Examples 1 to 4 described later is used as the photographic lens 31, these have good performance, so that the light receiving element 45 has a diagonal dimension of about 6 mm to 9 mm, and has a class of 3 to 5 million pixels. It is possible to realize a small information device (portable information terminal device) with high image quality.

  Specific examples of the zoom lens are given below. The maximum image height: Y ′ is 3.50 mm in Example 1, and 3.70 mm in Examples 2 to 4.

  In each embodiment, the parallel plate disposed on the image plane side of the lens system is assumed to be various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of an image sensor such as a CCD. It is.

The lens materials are all optical glass except that the ninth lens (fourth lens group) of Example 3 is optical plastic.
In each embodiment, the aberration is sufficiently corrected, and it is possible to cope with an imaging element having a diagonal size of about 6 to 9 mm and a number of pixels of 3 to 5 million pixels.

The meaning of each symbol in the examples is as follows.
f: Focal length of the entire system
F: F number ω: Half angle of view (degrees)
R: radius of curvature
D: Surface spacing (including aperture surface)
Nd: Refractive index νd: Abbe number
K: Aspheric conical constant
A ₄ : Fourth-order aspheric coefficient
A ₆ : 6th-order aspheric coefficient
A ₈ : 8th-order aspheric coefficient
A ₁₀ : 10th-order aspheric coefficient An aspheric surface (marked with an asterisk (*) in the data of each example to indicate an aspheric surface) represents the reciprocal of the paraxial radius of curvature (paraxial curvature) as C The height from the optical axis is defined as H, and the shape is specified by giving values of a conic constant: K and a higher-order spherical coefficient: A _{4 to} A ₁₀ .
^{X = CH 2 / [1 +} √ {1- (1 + K) C 2 H 2}]
+ A ₄・ H ⁴ + A ₆・ H ⁶ + A ₈・ H ⁸ + A ₁₀・ H ¹⁰

f = 4.42 to 20.35, F = 2.89 to 4.62, ω = 39.55 to 9.62
Surface number RD Nd νd Remarks
01 56.183 0.90 1.84666 23.78 First lens
02 22.306 2.46 1.77250 49.62 Second lens
03 129.168 0.10
04 19.540 1.90 1.77250 49.62 Third lens
05 44.088 Variable (A)
06 * 31.255 0.84 1.83500 42.98 4th lens
07 3.826 2.10
08 143.581 2.45 1.76182 26.61 5th lens
09 -5.555 0.74 1.83500 42.98 6th lens
10 * -39.380 Variable (B)
11 Aperture variable (C)
12 * 8.333 1.80 1.58913 61.25 7th lens
13 -152.107 0.23
14 7.167 2.74 1.48749 70.44 Eighth lens
15 14.162 0.85 1.84666 23.78 9th lens
16 4.894 0.24
17 5.782 2.02 1.48749 70.44 10th lens
18 * -13.873 Variable (D)
19 ∞ 0.90 1.51680 64.20 Various filters
20 ∞.

Aspherical
6th page
K = 0.0, A ₄ = 1.84029 × 10 ^-4 , A ₆ = -4.83681 × 10 ^-6 , A ₈ = 1.03688 × 10 ^-7 ,
A ₁₀ = -1.32922 × 10 ^-9
10th page
K = 0.0, A ₄ = -5.53512 × 10 ^-4 , A ₆ = -2.57934 × 10 ^-5 , A ₈ = 1.05288 × 10 ^-6 ,
A ₁₀ = -1.31801 × 10 ^-7
12th page
K = 0.0, A ₄ = -2.23709 × 10 ^-4 , A ₆ = -8.77690 × 10 ^-7 , A ₈ = 3.19167 × 10 ^-7 ,
A ₁₀ = -1.93115 × 10 ^-8
18th page
K = 0.0, A ₄ = 8.00477 × 10 ^-4 , A ₆ = 2.50817 × 10 ^-6 , A ₈ = 5.14171 × 10 ^-7 ,
A ₁₀ = -1.09665 × 10 ^-7 .

Variable amount Short focal end Medium focal length Long focal end
f = 4.425 f = 9.488 f = 20.350
A 1.000 7.240 14.505
B 8.095 3.256 1.200
C 4.494 2.617 1.000
D 7.045 9.488 12.498.

Parameter value of conditional expression
Y ' _max / f _W = 0.791
{(1-N _2I ) × X _2I (H0.8)} / Y ' _max = 0.00732
{(N _2O -1) × X _2O (H0.8) + (1- N _2I ) × X _2I (H0.8)} / Y ' _max = 0.01593
R _2C / Y ' _max = -1.59
(D _12T -D _12W ) / f _T = 0.664
(D _23W -D _23T ) / f _T = 0.510
| f ₂ | / f ₃ = 0.689
| f ₁ | / f _W = 8.00
The lens configuration of the zoom lens of Example 1 is shown in FIG. FIG. 5 is an aberration diagram at the short focal point for Example 1, FIG. 6 is an aberration diagram at the intermediate focal length, and FIG. 7 is an aberration diagram at the long focal point.

  In the lens configuration diagram, I is the first lens group, II is the second lens group, III is the third lens group, F is “various filters”, and S is the stop. The same applies to FIGS.

  The broken line in the spherical aberration diagram indicates “sine condition”, the solid line in the astigmatism diagram indicates sagittal, and the broken line indicates meridional. Further, “g” and “d” represent the g line and the d line, respectively. The same applies to other aberration diagrams.

f = 4.74 to 21.55, F = 3.61 to 4.80, ω = 39.16 to 9.64
Surface number RD Nd νd Remarks
01 18.565 0.90 1.92286 20.88 First lens
02 12.194 3.90 1.72342 37.99 Second lens
03 58.393 Variable (A)
04 * 70.501 0.84 1.83500 42.98 Third lens
05 4.859 2.42
06 24.219 2.54 1.76182 26.61 4th lens
07 -9.529 0.74 1.83500 42.9 5th lens
08 * -247.508 Variable (B)
09 Aperture variable (C)
10 * 8.333 3.01 1.58913 61.25 6th lens
11 * -10.376 0.10
12 12.420 2.34 1.75500 52.32 7th lens
13 -7.111 1.35 1.68893 31.16 Eighth lens
14 4.591 Variable (D)
15 * 13.631 1.66 1.58913 61.25 9th lens
16 -45.606 Variable (E)
17 ∞ 0.90 1.51680 64.20 Various filters
18 ∞.

Aspherical
4th page
K = 0.0, A ₄ = 1.78565 × 10 ^-4 , A ₆ = -1.75390 × 10 ^-6 , A ₈ = 6.61261 × 10 ^-9 ,
A ₁₀ = 1.23143 × 10 ^-11
8th page
K = 0.0, A ₄ = -3.04000 × 10 ^-4 , A ₆ = -7.18126 × 10 ^-6 , A ₈ = 1.05398 × 10 ^-7 ,
A ₁₀ = -2.21354 × 10 ^-8
10th page
K = 0.0, A ₄ = -6.40609 × 10 ^-4 , A ₆ = -7.03343 × 10 ^-6 , A ₈ = 8.98513 × 10 ^-7 ,
A ₁₀ = -9.73391 × 10 ^-8
11th page
K = 0.0, A ₄ = 2.20124 × 10 ^-4 , A ₆ = -8.24086 × 10 ^-6 , A ₈ = 1.09927 × 10 ^-6 ,
A ₁₀ = -1.05069 × 10 ^-7
15th page
K = 0.0, A ₄ = -5.79936 × 10 ^-5 , A ₆ = 8.76394 × 10 ^-6 , A ₈ = -2.58155 × 10 ^-7 ,
A ₁₀ = 4.31238 × 10 ^-9 .

Variable amount
Short focal end Intermediate focal length Long focal end
f = 4.738 f = 10.103 f = 21.545
A 0.600 7.679 15.059
B 10.083 4.179 1.200
C 4.076 2.608 1.000
D 3.075 6.493 10.666
E 2.597 2.591 2.553.

Parameter value of conditional expression
Y'max / fW = 0.781
{(1-N _2I ) × X _2I (H0.8)} / Y ' _max = 0.00923
{(N _2O -1) × X _2O (H0.8) + (1- N _2I ) × X _2I (H0.8)} / Y ' _max = 0.02940
R _2C / Y ' _max = -2.58
(D _12T -D _12W ) / f _T = 0.671
(D _23W -D _23T ) / f _T = 0.555
| f ₂ | / f ₃ = 0.860
| f ₁ | / f _W = 9.35
The lens configuration of the zoom lens of Example 2 is shown in FIG. IV denotes a fourth lens group.
In addition, FIG. 8 shows an aberration diagram at the short focal point for Example 2, FIG. 9 shows an aberration diagram at the intermediate focal length, and FIG. 10 shows an aberration diagram at the long focal point.

f = 4.74 to 21.59, F = 3.32 to 4.98, ω = 39.14 to 9.55
Surface number RD Nd νd Remarks
01 23.330 1.00 1.84666 23.80 First lens
02 15.002 0.26
03 15.442 3.47 1.77250 49.60 Second lens
04 135.649 Variable (A)
05 * 91.446 0.84 1.83481 42.70 Third lens
06 4.439 1.77
07 15.704 2.67 1.74077 27.80 Fourth lens
08 -6.205 0.74 1.83481 42.70 5th lens
09 * 632.018 Variable (B)
10 Aperture variable (C)
11 * 8.333 2.78 1.58913 61.15 6th lens
12 * -8.607 0.10
13 15.588 2.42 1.83481 42.70 7th lens
14 -4.691 0.80 1.69895 30.10 Eighth lens
15 4.498 Variable (D)
16 * 12.500 2.21 1.54340 56.00 9th lens
17 -34.711 Variable (E)
18 ∞ 0.90 1.51680 64.20 Various filters
19 ∞.

Aspherical
5th page
K = 0.0, A ₄ = 2.42400 × 10 ^-4 , A ₆ = -2.92208 × 10 ^-6 , A ₈ = 9.40210 × 10 ^-9 ,
A ₁₀ = -4.16456 × 10 ^-11
9th page
K = 0.0, A ₄ = -5.16761 × 10 ^-4 , A ₆ = 1.81605 × 10 ^-6 , A ₈ = -1.01642 × 10 ^-6 ,
A ₁₀ = -1.75699 × 10 ^-8
11th page
K = 0.0, A ₄ = -1.08496 × 10 ^-3 , A ₆ = -2.17192 × 10 ^-5 , A ₈ = 5.79037 × 10 ^-6 ,
A ₁₀ = -5.25493 × 10 ^-7
12th page
K = 0.0, A ₄ = 4.85474 × 10 ^-4 , A ₆ = -4.49460 × 10 ^-5 , A ₈ = 8.98429 × 10 ^-6 ,
A ₁₀ = -5.68154 × 10 ^-7
16th page
K = 0.0, A ₄ = -5.46424 × 10 ^-5 , A ₆ = 1.80637 × 10 ^-5 , A ₈ = -9.17793 × 10 ^-7 ,
A ₁₀ = 2.09899 × 10 ⁻⁸ .

Variable amount
Short focal end Intermediate focal length Long focal end
f = 4.740 f = 10.131 f = 21.591
A 0.600 6.655 15.680
B 7.051 4.217 1.200
C 3.043 1.054 1.000
D 2.000 7.725 10.995
E 3.484 2.583 2.382.

Parameter value of conditional expression
Y'max / fW = 0.781
{(1-N _2I ) × X _2I (H0.8)} / Y ' _max = 0.00536
{(N _2O -1) × X _2O (H0.8) + (1- N _2I ) × X _2I (H0.8)} / Y ' _max = 0.01951
R _2C / Y ' _max = -1.68
(D _12T -D _12W ) / f _T = 0.698
(D _23W -D _23T ) / f _T = 0.366
| f ₂ | / f ₃ = 0.792
| f ₁ | / f _W = 8.44
The lens configuration of the zoom lens of Example 3 is shown in FIG. IV denotes a fourth lens group.
In addition, FIG. 11 shows an aberration diagram at the short focal point relating to Example 3, FIG. 12 shows an aberration diagram at the intermediate focal length, and FIG. 13 shows an aberration diagram at the long focal point.

f = 4.74 to 21.62, F = 3.42 to 4.99, ω = 39.12 to 9.50
Surface number RD Nd νd Remarks
01 96.656 0.90 1.84666 23.78 First lens
02 29.314 2.72 1.77250 49.62 Second lens
03 -219.341 0.10
04 20.153 1.80 1.77250 49.62 Third lens
05 33.538 Variable (A)
06 * 18.011 0.84 1.83500 42.98 4th lens
07 3.936 2.07
08 74.837 1.95 1.84666 23.78 5th lens
09 -9.146 0.74 1.80420 46.50 6th lens
10 * 759.807 Variable (B)
11 Aperture variable (C)
12 * 8.333 3.34 1.58913 61.25 7th lens
13 * -8.827 0.10
14 12.236 2.45 1.75500 52.32 Eighth lens
15 -7.054 0.80 1.69895 30.05 9th lens
16 4.892 Variable (D)
17 * 10.651 1.83 1.58913 61.25 10th lens
18 -261.223 Variable (E)
19 ∞ 0.90 1.51680 64.20 Various filters
20 ∞.

Aspherical 6th surface
K = 0.0, A ₄ = -8.08791 × 10 ^-5 , A ₆ = -2.03124 × 10 ^-6 , A ₈ = 6.26638 × 10 ^-9 ,
A ₁₀ = -6.12352 × 10 ^-11
10th page
K = 0.0, A ₄ = -7.52609 × 10 ^-4 , A ₆ = -1.24401 × 10 ^-5 , A ₈ = -9.65466 × 10 ^-7 ,
A ₁₀ = -8.33332 × 10 ^-8
12th page
K = 0.0, A ₄ = -7.07947 × 10 ^-4 , A ₆ = -1.16179 × 10 ^-6 , A ₈ = 6.72505 × 10 ^-8 ,
A ₁₀ = -2.53913 × 10 ^-8
Side 13
K = 0.0, A ₄ = 3.43658 × 10 ^-4 , A ₆ = -1.44022 × 10 ^-6 , A ₈ = -1.33484 × 10 ^-7 ,
A ₁₀ = -1.40822 × 10 ^-8
17th page
K = 0.0, A ₄ = -4.75410 × 10 ^-5 , A ₆ = 1.15429 × 10 ^-5 , A ₈ = -4.87258 × 10 ^-7 ,
A ₁₀ = 9.54084 × 10 ^-9 .

Variable amount
Short focal end Intermediate focal length Long focal end
f = 4.741 f = 10.112 f = 21.624
A 0.600 6.160 15.040
B 6.288 2.111 1.200
C 3.888 3.173 1.000
D 2.000 7.785 11.065
E 3.440 2.547 2.351.

Parameter value of conditional expression
Y'max / fW = 0.780
{(1-N _2I ) × X _2I (H0.8)} / Y ' _max = 0.00728
{(N _2O -1) × X _2O (H0.8) + (1- N _2I ) × X _2I (H0.8)} / Y ' _max = 0.00080
R _2C / Y ' _max = -2.47
(D _12T -D _12W ) / f _T = 0.668
(D _23W -D _23T ) / f _T = 0.369
| f ₂ | / f ₃ = 0.795
| f ₁ | / f _W = 8.14
The lens configuration of the zoom lens of Example 4 is shown in FIG. IV denotes a fourth lens group.
In addition, FIG. 14 shows aberration diagrams at the short focal point for Example 4, FIG. 15 shows aberration diagrams at the intermediate focal length, and FIG. 16 shows aberration diagrams at the long focal point.

3 is a diagram illustrating a lens configuration of a zoom lens according to Example 1. FIG. 6 is a diagram illustrating a lens configuration of a zoom lens according to Example 2. FIG. 7 is a diagram illustrating a lens configuration of a zoom lens according to Example 3. FIG. 6 is a diagram illustrating a lens configuration of a zoom lens according to Example 4. FIG. FIG. 4 is an aberration diagram at a short focal end of the zoom lens according to Example 1; FIG. 4 is an aberration diagram for the zoom lens of Example 1 at an intermediate focal length. FIG. 4 is an aberration diagram at the long focal end of the zoom lens according to Example 1; FIG. 6 is an aberration diagram at a short focal end of the zoom lens according to Example 2; 6 is an aberration diagram at an intermediate focal length of the zoom lens of Example 2. FIG. FIG. 6 is an aberration diagram at a long focal end of the zoom lens in Example 2; FIG. 10 is an aberration diagram at a short focal end of the zoom lens according to Example 3; FIG. 10 is an aberration diagram at an intermediate focal length of the zoom lens according to Example 3; FIG. 6 is an aberration diagram at a long focal end of the zoom lens in Example 3; FIG. 10 is an aberration diagram at a short focal end of the zoom lens according to Example 4; FIG. 10 is an aberration diagram at an intermediate focal length of the zoom lens according to Example 4; FIG. 10 is an aberration diagram at a long focal end of the zoom lens in Example 4; It is an external view showing one embodiment of a camera device (personal digital assistant device). It is a figure which shows the system structure of the camera apparatus of FIG.

Explanation of symbols

I First Group II Second Group III Third Group IV Fourth Lens Group S Aperture F Various Filters

Claims (21)

From the object side to the image side, the first lens group having positive refracting power, the second lens group having negative refracting power, and the third lens group having positive refracting power are arranged in the above order, and the first An aperture stop between the second lens group and the third lens group;
In zoom lenses in which the distance between the first lens group and the second lens group is increased and the distance between the second lens group and the third lens group is decreased upon zooming from the wide-angle end to the telephoto end,
The ratio of the focal length of the entire system at the wide angle end: f _W and the maximum image height: Y ′ _max : Y ′ _max / f _W is the condition:
(1) 0.70 <Y ' _max / f _W <1.00
In the range of
The second lens group includes, from the object side to the image side, a negative lens having a large curvature surface on the image side, a positive lens having a convex surface having a large curvature on the image side, and a concave surface having a large curvature on the object side. A zoom lens comprising three negative lenses facing each other. The zoom lens according to claim 1.
The image side surface of the negative lens on the image side in the second lens group is an aspherical surface having a shape in which the negative refractive power decreases as the distance from the optical axis increases.
Refractive index of the material of the negative lens on the image side in the second lens group: N ₂₁ , Aspheric amount at 80% of the maximum effective ray height on the most aspheric surface on the image side of the second lens group: X _2I (H _0.8 ) and the maximum image height: Y ′ _max , the condition:
(2) 0.0010 <(1−N _2I ) × X _2I (H _0.8 ) / Y ' _max <0.0500
A zoom lens characterized by satisfying The zoom lens according to claim 2.
The object side surface of the negative lens on the object side in the second lens group is aspheric,
Refractive index of the material of the negative lens on the object side in the second lens group: N ₂₀ , Refractive index of the material of the negative lens on the image side in the second lens group: N ₂₁ , the most object side of the second lens group Aspherical amount at 80% of the maximum effective ray height on the aspherical surface: X ₂₀ (H _0.8 ), Aspherical amount at 80% of the maximum effective ray height on the aspherical surface closest to the image side of the second lens group: X _2I (H _0.8 ) and the maximum image height: Y ′ _max , the condition:
(3) -0.0500 <{(N _2O −1) × X _2O (H _0.8 ) + (1-N _2I ) × X _2I (H _0.8 )} / Y ′ _max <0.1500
A zoom lens characterized by satisfying The zoom lens according to any one of claims 1 to 3,
In the second lens group, the refractive index and Abbe number of the i-th lens material counted from the object side are N _2i and ν _2i (i = 1 to 3):
(4) 1.75 <N ₂₁ <1.90, 35 <ν ₂₁ <50
(5) 1.65 <N ₂₂ <1.90, 20 <ν ₂₂ <35
(6) 1.75 <N ₂₃ <1.90, 35 <ν ₂₃ <50
A zoom lens characterized by satisfying The zoom lens according to any one of claims 1 to 4,
The three lenses constituting the second lens group are, in order from the object side, a negative lens having a large curvature surface facing the image side, a positive lens having a large curvature surface facing the image side, and a concave surface having a large curvature toward the object side. A zoom lens, wherein the positive lens is joined to the negative lens on the image side. The zoom lens according to claim 5.
In the second lens group, the radius of curvature of the cemented surface of the positive lens and the negative lens: R _2C and the maximum image height: Y ′ _max ratio: R _2C / Y ′ _max is the condition:
(7) -3.5 <(R _2C / Y ' _max ) <-1.0
A zoom lens characterized by satisfying The zoom lens according to any one of claims 1 to 6,
When zooming from the wide-angle end to the telephoto end, the first lens unit moves monotonously to the object side,
The distance between the first and second lens groups at the wide angle end: D _12W , the distance between the first and second lens groups at the telephoto end: D _12T, and the focal length of the entire system at the telephoto end: f _T :
(8) 0.50 <(D _12T −D _12W ) / f _T <0.85
A zoom lens characterized by satisfying The zoom lens according to any one of claims 1 to 7,
During zooming from the wide-angle end to the telephoto end, the third lens unit moves monotonously to the object side,
The distance between the second and third lens groups at the wide-angle end: D _23W , the distance between the second and third lens groups at the telephoto end: D _23T , and the focal length of the entire system at the telephoto end: f _T :
(9) 0.25 <(D _23W −D _23T ) / f _T <0.65
A zoom lens characterized by satisfying The zoom lens according to any one of claims 1 to 8,
The focal length of the second lens group: f ₂ and the focal length of the third lens group: f ₃ are the conditions:
(10) 0.5 <| f ₂ | / f ₃ <1.0
A zoom lens characterized by satisfying The zoom lens according to any one of claims 1 to 9,
The focal length of the first lens group; f ₁ , the focal length of the entire system at the wide angle end: f _W , the condition:
(11) 6.0 <f ₁ / f _W <12.0
A zoom lens characterized by satisfying The zoom lens according to any one of claims 1 to 10,
A zoom lens comprising a first lens group to a third lens group. The zoom lens according to any one of claims 1 to 10,
A fourth lens group having a positive refractive power is disposed on the image side of the third lens group;
At the time of zooming from the wide-angle end to the telephoto end, at least the first lens group and the second lens group are arranged so that the distance between the first lens group and the second lens group becomes large and the distance between the second lens group and the third lens group becomes small. A zoom lens characterized in that the three lens groups move toward the object side. The zoom lens according to claim 12, wherein
A zoom lens characterized in that the fourth lens group does not move during zooming. The zoom lens according to claim 12, wherein
A zoom lens, wherein the fourth lens unit is displaced toward the image side upon zooming from the wide-angle end to the telephoto end. The zoom lens according to any one of claims 1 to 14,
A zoom lens characterized in that, upon zooming from the wide-angle end to the telephoto end, the distance between the aperture stop and the third lens group is widest at the wide-angle end and narrowest at the telephoto end. The zoom lens according to any one of claims 1 to 15,
A zoom lens characterized in that the aperture diameter of the aperture stop is constant regardless of zooming. The zoom lens according to any one of claims 1 to 15,
A zoom lens, wherein an aperture diameter of an aperture stop changes depending on a magnification, and an aperture diameter at a long focal end is set larger than an aperture diameter at a short focus end.   An information device having a photographing function, comprising the zoom lens according to claim 1 as a photographing optical system. The information device according to claim 18,
An information device having a photographing function, wherein an object image formed by a zoom lens is formed on a light receiving surface of an image sensor. The information device according to claim 19, wherein
An information device having an imaging function, wherein the diagonal dimension of the imaging element is 9 mm or less and the number of pixels is 3 million pixels or more. The information device according to claim 19 or 20,
An information device having a photographing function, characterized by being configured as a portable information terminal device.

Images