JP5387139B2 - Imaging lens, camera device, and portable information terminal device - Google Patents

Description

  The present invention relates to an imaging lens, a camera device, and a portable information terminal device.

With the expansion of the digital camera market, various types of digital cameras are required.
Although popular with digital cameras having a zoom function, many users like a “compact camera with a small image quality equipped with a high-performance single focal length imaging lens”.

  A user who likes this type of high-quality compact camera has a strong demand that the imaging lens with a single focal length is “high performance, small F number and large aperture”.

  In terms of "high performance" in the above compact camera, in addition to having a resolution corresponding to an image sensor of at least 10 million pixels to 20 million pixels, "From the full aperture to less coma flare, high contrast and the periphery of the angle of view" There is a demand for “no point image distortion”, “no chromatic aberration and no unwanted coloring even in a portion with a large luminance difference”, “a small amount of distortion and a straight line drawn”.

In terms of “large aperture”, there are many people who want F2.0 or “F number less than this” from the viewpoint of differentiation from a general compact camera equipped with a zoom lens.
The “field angle of the photographic lens” is preferably a half angle of view corresponding to 28 mm at a focal length converted to a so-called Leica plate which is a 35 mm silver salt camera: 38 degrees or more.

There are many types of imaging lenses for digital cameras. However, as a typical configuration of an “imaging lens with a wide angle and a single focal length” such as the imaging lens of the present invention, it has been conventionally applied to the object side. A so-called “retro focus type” in which a lens group having a negative refractive power and a lens group having a positive refractive power on the image side are provided.
Due to the characteristics of the area sensor that has a color filter and a micro lens for each pixel, the exit pupil position should be kept away from the image plane so that the peripheral luminous flux is “incident at an angle close to the light receiving surface of the area sensor”. Preferably, this is the main reason why the retro focus type is adopted.
However, since the retrofocus type has a large asymmetry in refractive power arrangement, correction of coma aberration, distortion aberration, lateral chromatic aberration and the like tends to be insufficient. Correction of these aberrations becomes more difficult as the diameter increases.
As a retrofocus type imaging lens having a relatively large aperture and a half angle of view of around 38 degrees, those described in Patent Documents 1 to 4 are known.

The imaging lens described in Patent Document 1 has a large aperture of F1.4, but has large astigmatism and curvature of field, and it is difficult to say that “sufficient performance up to the periphery” is achieved near the full aperture. .
The imaging lens described in Patent Document 2 is insufficient in F2.8 and “a surface having a large aperture” from the recent required level, and astigmatism, curvature of field, and lateral chromatic aberration are sufficiently corrected. It is hard to say that this imaging lens has also achieved “sufficient performance up to the periphery”.
Each of the imaging lenses described in Patent Documents 1 and 2 has a distortion aberration exceeding 2% in absolute value.

  In the imaging lens described in Patent Document 3, astigmatism, curvature of field, and distortion are corrected well. However, there is still room for improvement in terms of “large diameter and small size”.

  The imaging lens described in Patent Document 4 is insufficient in F2.9 and “a surface having a large aperture”, has a large curvature of field, and it is difficult to say that “a sufficient performance up to the periphery” is achieved. . In addition, there is room for improvement in that the number of lenses used is large and it is not easy to make it compact.

  The present invention has been made in view of the above-mentioned circumstances, and has a half field angle: a wide field angle of 38 degrees or more, an F number: a large aperture of about 2.0 or less, a relatively small size, astigmatism, The field of curvature, lateral chromatic aberration, coma color difference, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor with 10 to 20 million pixels, from wide open to high contrast and the periphery of the angle of view. It is an object of the present invention to realize a high-performance imaging lens that does not collapse a point image, does not cause unnecessary coloring even in a portion with a large luminance difference, and can draw a straight line without distortion.

The imaging lens of the present invention is a “single focal length imaging lens” and has the following configuration (claim 1).
That is, the imaging lens includes a first lens group located on the object side and a second lens group located on the image side with the aperture stop interposed therebetween. Therefore, the first lens group and the second lens group are defined by the “aperture stop”.

The “first lens group” is configured by arranging the first F lens group on the object side and the first R lens group on the aperture stop side. The first F lens group and the first R lens group are the first lens group. The widest air separation in the lens group.
The “first F lens group” is composed of two negative lenses, and the “first R lens group” is composed of one positive lens.
That is, the first lens group is composed of “three negative lenses, two negative lenses and one positive lens”.
The first F lens group has a negative refractive power, and the first R lens group has a positive refractive power.

  The “second lens group” includes a second F lens group and a second R lens group in order from the aperture stop side.

  The “second F lens group” has a positive refractive power, and includes a first positive lens, a first negative lens, a second negative lens, and a second positive lens in order from the aperture stop side. That is, the second F lens includes “four lenses of two positive lenses and two negative lenses” arranged in the order of positive, negative, negative, and positive.

The “second R lens group” includes at least one positive or negative lens.
The imaging lens described in claim 1 has the following characteristics in the above-described configuration.
That is, at least one of the two negative lenses (first negative lens and second negative lens) included in the second F lens group has an Abbe number: νdn and an anomalous dispersibility: ΔθgFn as a condition:
(1) 30 <νdn <41
(2) ΔθgFn <0
Satisfied. Of course, the materials of the two negative lenses included in the second F lens group may satisfy the conditions (1) and (2).

  Here, the Abbe number: νdn is given “n” in order to clarify that it is related to the material of the negative lens.

  Anomalous dispersibility: “n” in ΔθgFn is attached to clarify that it is related to the material of the negative lens.

Anomalous dispersibility: ΔθgF is defined as follows.
As is well known, the partial dispersion ratio: θgF is expressed by the following equation, using the refractive index of Fraunhofer line for g line: ng, the refractive index for F line: nF, and the refractive index for C line: nC:
θgF = (ng−nF) / (nF−nC)
Defined by

A two-dimensional coordinate with two orthogonal axes is assumed with the partial dispersion ratio defined as above: θgF as the vertical axis and Abbe number: νd as the horizontal axis.
On the two-dimensional coordinates, the reference glass type: K7 coordinate point (νd = 60.49, θgF = 0.5436) and the reference glass type: F2 coordinate point (νd = 36.26, θgF = 0.5828) The connected straight line is referred to as a “standard line”.
The “dispersion from the standard line” on the two-dimensional coordinates of the partial dispersion ratio of glass type: θgF is anomalous dispersion: ΔθgF.

  The above reference glass materials: K7 and F2 are both “glass materials manufactured by OHARA INC.” And the product names are “NSL7” and “PBM2”, respectively.

  The “deviation from the standard line”, when an arbitrary coordinate (νd, θgF) is considered on the above two-dimensional coordinate, is drawn from this coordinate to the standard line in parallel with the vertical axis (partial dispersion ratio: θgF). It is the length of the “straight line”, and “the length in the positive direction of the vertical axis” is plus and “the length in the negative direction of the vertical axis” is minus, as measured from the standard line.

The imaging lens according to claim 1 preferably satisfies the following condition with respect to the positive lens in the second F lens group (claim 2).
That is, at least one of the two positive lenses (the first positive lens and the second positive lens) in the second F lens group has an Abbe number: νdp and anomalous dispersion: ΔθgFp as a condition:
(3) 70 <νdp
(4) 0 <ΔθgFp
Is preferably satisfied.

  Of course, the materials of the two positive lenses included in the second F lens group may satisfy the conditions (3) and (4). “P” in Abbe number: νdp, anomalous dispersion: ΔθgFp is given to clarify that it is related to the material of the positive lens.

The imaging lens according to claim 1 or 2, wherein the focal length of the entire system is f and the focal length of the second F lens group is f2.
(5) 0.2 <f / f2 <0.5
Is preferably satisfied (Claim 3).

The imaging optical system according to any one of claims 1 to 3, wherein the focal length of the entire system is f and the focal length of the first lens group is f1.
(6) | f1 | / f> 8
Is preferably satisfied (claim 4).

The imaging lens according to any one of claims 1 to 4, wherein “at least one material” of the two negative lenses constituting the first F lens group has an Abbe number: νdn1, anomalous dispersion: For ΔθgFn1, the conditions:
(7) 70 <νdn1
(8) 0 <ΔθgFn1
Is preferably satisfied (Claim 5).

Of course, the materials of the two negative lenses constituting the first F lens group may satisfy the conditions (7) and (8).
“N1” in Abbe number: νdn1, anomalous dispersion: ΔθgFn1 is given to clarify that it is related to the material of the “negative lens in the first F lens group”.

The imaging lens according to any one of claims 1 to 5, wherein the material of the second negative lens among the two negative lenses of the second F lens group is:
(1) 30 <νdn <41
(2) ΔθgFn <0
Is preferably satisfied (claim 6).

  Of course, the first negative lens of the second F lens group can also be formed of a material that satisfies the conditions (1) and (2). That is, the sixth aspect of the first aspect of the present invention satisfies the “conditions (1) and (2)” among the two negative lenses (first negative lens and second negative lens) included in the second F lens group. “At least one” is preferably a second negative lens.

It is preferable that the imaging lens according to any one of claims 1 to 6 "the second negative lens and the second positive lens are cemented" in the second F lens group (claim 7).
In the imaging optical system according to any one of claims 1 to 7, the first negative lens in the second F lens group is preferably a “negative meniscus lens having a convex surface facing the image side” (claim 8). .

  The imaging lens according to any one of claims 1 to 8 can perform “focusing from infinity to a short distance by moving the whole or a part of the second lens group” (claim 9).

  The camera apparatus of this invention has the imaging lens according to any one of claims 1 to 9 as a photographing optical system (claim 10).

  As shown in the examples described later, according to the present invention, a high-performance imaging lens can be realized with a single focal length. Such a high-performance imaging lens can be used well as a photographing lens of a silver halide camera or an optical lens used for an optical sensor. However, “a camera device having a function of using a photographed image as digital information” That is, it can be suitably used for a digital camera (claim 11).

The camera device according to claim 11 can be used as a “camera function unit” of the portable information terminal device (claim 12).
The supplementary explanation will be given below.
As mentioned above, retrofocus type imaging lenses with negative refractive power on the object side and positive refractive power on the image side tend to cause distortion and lateral chromatic aberration due to the asymmetry of refractive power distribution. Therefore, the reduction of these aberrations is a big problem.
In addition, with the increase in diameter, it becomes difficult to correct “coma aberration and coma color difference”, and problems are accumulated.
The imaging lens of the present invention has been made by finding that the above-mentioned problem in correcting aberrations can be solved by the configuration as described above.

In the imaging lens of the present invention, it can be considered that the first lens group plays a role like “a wide converter added to the second lens group”.
The first lens group is configured to have negative refractive power (first F lens group) on the object side and positive refractive power (first R lens group) on the aperture stop side, and the interval between the positive and negative refractive powers ( By ensuring a relatively large distance between the first F lens group and the first R lens group on the optical axis (that is, the maximum distance in the first lens group), a sufficient field angle can be ensured and “spherical aberration can be started. "Various aberrations to be corrected".
The first R lens group faces the second F lens group of the second lens group through the aperture stop, and has the side of controlling coma aberration by the balance of “the positive refractive power of both of them”. ing.
What characterizes the imaging lens of the present invention the most is “the role and configuration of the second F lens group”.
The second F lens group in the imaging lens of the present invention has a “main imaging function” in the imaging lens, and is also the “most important lens group” in terms of aberration correction.
The second F lens group is based on the so-called triplet type of positive / negative / positive as the refractive power arrangement, and the negative refractive power at the center is divided into two negative lenses to obtain “positive / negative / negative / positive”. 4 sheets configuration ".
Since the aperture stop is disposed on the “object side of the second F lens group”, the “first positive lens and first negative lens pair” and “second negative lens and second positive lens pair” are off-axis. Since the heights of the light rays are different, it is possible to effectively reduce both the longitudinal chromatic aberration and the lateral chromatic aberration by utilizing this fact.
When the second F lens group is a normal positive / negative / positive triplet type, the positive power balance before and after the negative lens tends to directly affect the distortion, but with the imaging lens of the present invention, Since the aperture stop is disposed on the “object side of the second F lens group”, the positive power balance before and after the first negative lens in the second F lens group is less likely to directly affect distortion, and coma aberration. The degree of freedom for correction and reduction of eccentricity sensitivity is increasing.

The lens material satisfying the conditions (1) and (2) is “a glass type in which the refractive index change due to the wavelength is relatively linear in the wavelength range including the C-line and the g-line”. By adopting at least one of the negative lenses in the “second F lens group that is responsible for the main imaging function” in the system, the deterioration of chromatic aberration due to the secondary spectrum can be suppressed to a small extent, and “axial chromatic aberration and lateral chromatic aberration can be reduced. Correction "can be performed.
When the negative lens in the second F lens group does not include “which satisfies the upper limit of the condition (2)”, the lateral chromatic aberration due to the secondary spectrum, for example, “achromatization was performed with the F line and the C line” In some cases, the ability to correct the “g-line lateral chromatic aberration” may be insufficient.
When the negative lens in the second F lens group does not include the “negative lens made of a material that satisfies the lower limit” in the condition (1), the dispersion of the negative lens in the second F lens group becomes large, and F It becomes difficult to balance the correction of chromatic aberration of the line and the C line with correction of other aberrations such as spherical aberration, coma, astigmatism, and field curvature.

When the “negative lens made of a material that satisfies the upper limit” in the condition (1) is not included as a negative lens of the second F lens group, the axial chromatic aberration correction of the F line and the C line becomes insufficient, resulting in a result. It becomes easy to deteriorate the image quality of the entire image.
Insufficient correction of axial chromatic aberration will cause “color flare” over the entire image, which tends to reduce the contrast. If correction of lateral chromatic aberration is insufficient, It tends to deteriorate the image quality due to “blue-purple coloring called purple fringe” or color flare.

The second R lens group of the second lens group has a function of “balancing aberrations and controlling exit pupil distance”. Needless to say, if the second R lens group has a positive refractive power, it is effective to secure the exit pupil distance. However, if the exit pupil distance may be short, “the second R lens group has a negative refractive power. It is also possible to contribute to shortening the total lens length.
The second R lens group may be “a configuration having at least one positive or negative lens”.

  According to the configuration of the first aspect, as described above, it is possible to obtain a great effect in correcting the aberration of the imaging lens, and a half field angle: a wide field angle of about 38 degrees, and an F number: 2. It is possible to achieve very high image performance while satisfying the severe condition of a large aperture of about 0 or less.

  In order to achieve higher performance than the above, at least one “positive lens made of a material that satisfies the conditions (3) and (4)” is included in the second F lens group as described in claim 2. Is good.

The glass type that satisfies the condition (4) is “a relatively small change in refractive index depending on the wavelength in the wavelength range including the C line to the F line”, and the glass type that satisfies the condition (3) is “from the vicinity of the g line. The refractive index change is relatively large.
By adopting at least one positive lens made of a material satisfying these conditions (3) and (4) in the second F lens group, correction of “chromatic aberration due to secondary spectrum” is suppressed while suppressing the influence on chromatic aberration correction to be relatively small. Can be performed.
When the “positive lens made of a material that satisfies the lower limit of the condition (4)” is not included in the second F lens group, the glass types of the two positive lenses included in the second F lens group are “abnormal dispersion is negative”. Therefore, the ability to correct chromatic aberration due to the secondary spectrum, for example, “chromatic aberration of g-line when achromatic is performed with F-line and C-line”, tends to be insufficient.

  When the second F lens group does not include “a positive lens made of a material that satisfies the lower limit of the condition (3)”, the axial chromatic aberration correction of the F line and the C line is insufficient and the image quality of the entire screen is lowered. It becomes easy.

More preferably, in the second F lens group, the following conditions:
(3A) 80 <νdp
(4A) 0.02 <ΔθgFp
It is preferable to include at least one positive lens that satisfies the above.

  Of course, it is preferable that the two positive lenses in the second F lens group satisfy the conditions (3) and (4) or (3A) and (4A).

  The imaging lens can further improve performance by satisfying the condition (5) as described in claim 3.

When the lower limit of the condition (5) is exceeded, the positive power of the second F lens group with respect to the entire system becomes small, and “the influence of the image forming action of the second F lens group in the entire system” becomes relatively small. The effect of “the image lens includes the second F lens group” becomes small, and it may be difficult to maintain high performance while satisfying the strict condition of wide angle and large aperture.
When the upper limit of the condition (5) is exceeded, the positive power of the second F lens group with respect to the entire system becomes large, and the “effect of the image forming action of the second F lens group in the entire system” becomes relatively large, and the second F “Exchange of various aberrations including spherical aberration” in the lens group becomes excessive, and the required accuracy for lens decentration and air spacing tends to become extremely high.

When the first lens group has a positive refractive power and the parameter of the condition (6) of claim 4 exceeds the lower limit value, the positive refractive power of the first lens group becomes large and the second F lens group is connected. As the image action becomes relatively weak, the “role of aberration correction that the second F lens group plays in the entire optical system” becomes small, and it becomes difficult to effectively reduce both axial chromatic aberration and lateral chromatic aberration. There is a fear.
When the first lens group has a negative refractive power, if the parameter of the condition (6) exceeds the lower limit value, the negative refractive power of the first lens group increases, so that “on the axis passing through the second F lens group” The “marginal light” becomes too high, the effective diameter of the second F lens group becomes excessive, making it difficult to form a compact imaging lens system, and the aperture diameter tends to be large.
Furthermore, it is necessary to make the positive refractive power of the second lens group “relatively strong”, so that the curvature of the image surface becomes large and negative distortion is likely to occur greatly.
Regardless of whether the power of the first lens group is positive or negative, if the parameter of the condition (6) exceeds the lower limit value, “exchange of various aberrations including spherical aberration” in the first lens group becomes excessive, and the lens The required accuracy for the eccentricity and the air gap between them becomes too high.

  The numerator “f1” in the parameter “| f1 | / f” of the condition (6) can take a positive or negative value depending on whether the refractive power of the first lens group is positive or negative. If the refractive power of the second lens group is negative, it is necessary to relatively increase the positive refractive power of the second lens unit, and as described above, the curvature of the image surface becomes large and negative distortion aberration is greatly generated. It becomes easy to do.

  In each surface in the second F lens group, since each aberration is greatly exchanged in order to reduce the final aberration amount, when the refractive power of the first lens group is negative, the second F lens group The manufacturing error sensitivity tends to be high.

From this point of view, it is preferable that the refractive power of the first lens group is “positive”, in which case the condition (6) is
(6A) f1 / f> 8
In this case, the parameter: f1 / f is replaced with the condition (6A):
(6B) f1 / f> 10
Good to be satisfied.

  In order to achieve higher performance, as described in claim 5, at least one “negative lens made of a material satisfying the conditions (7) and (8)” is included in the first F lens group. Is good.

The glass type satisfying the conditions (7) and (8) is “a refractive index change with a wavelength is relatively small and a refractive index change is relatively large from the vicinity of the g line in a range including the C line to the F line”. Yes, by adopting such a glass type as “at least one negative lens” in the first F lens group having a relatively large refractive power, a “wide air gap (first air gap) between the first F lens group and the first R lens group”. When the aberration correction between the first R lens group and the other lens group is performed using the “maximum distance within one lens group”, an increase in chromatic aberration in the wavelength region including the C-line to the F-line is suppressed. On the other hand, it becomes possible to correct the “chromatic aberration near the g-line as the secondary spectrum” by the combination of the positive lens and the negative lens in the second F lens group described above, and “aberration correction in the first lens group”. Improve the ability of
In order to perform such aberration correction more satisfactorily, in the first F lens group, instead of the conditions (7) and (8), the condition:
(7A) 80 <νdn1
(8A) 0.02 <ΔθgFn1
It is preferable that the negative lens made of glass that satisfies the above conditions (1) and (2) includes “at least the second negative lens in the second F lens group”.

  In the second F lens group, the off-axis ray passing through the second negative lens far from the aperture stop is located higher than the off-axis ray passing through the first negative lens, and the second negative lens is in the condition (1). By satisfying the conditions (3) and (3), it is possible to satisfactorily correct lateral chromatic aberration by “a pair of the second negative lens and the second positive lens”.

In each surface of the second F lens group, “each aberration is greatly exchanged” in order to reduce the final aberration amount, and the manufacturing error sensitivity tends to be high. By joining the second negative lens and the second positive lens in the second F lens group, the manufacturing error sensitivity is substantially reduced, and stable performance is easily obtained.
In addition, it reduces the parts of the lens barrel that holds the lens.
By joining the “first positive lens and the first negative lens”, it becomes easy to obtain a stable performance by reducing the sensitivity of a substantial manufacturing error, which leads to further reduction of parts of the lens barrel. As in the case of the examples described later, the second negative lens and the second positive lens are cemented together and the “first positive lens and the first negative lens” are cemented to further increase the substantial manufacturing error sensitivity. It is easy to reduce and obtain stable performance.

If the first negative lens in the second F lens group is a “meniscus lens having a convex surface facing the image side” as in the eighth aspect, the “side surface of the first negative lens on the object side surface and the image side surface” The amount of change in the incident angle and the exit angle of the off-axis chief rays can be kept small, and the “role of axial chromatic aberration correction by the pair of the first positive lens and the first negative lens” in the second F lens group. It becomes possible to raise more.
In addition, by correcting the chromatic aberration of magnification by “mainly a pair of the second negative lens and the second positive lens”, the “role of axial chromatic aberration correction and chromatic aberration correction of magnification” is shared by the above two pairs. Thus, the degree of freedom for aberration correction is improved.
According to the ninth aspect of the present invention, by performing the focusing from infinity to a short distance by moving the whole or a part of the second lens group, the “focusing method by moving the entire imaging lens” is adopted. Compared with this, the weight of the moving part can be reduced, which is advantageous for speeding up focusing and power saving.
Further, when the imaging lens of the present invention is incorporated into a camera device as an optical system for photographing, when it is configured to have a `` mechanism for shortening the interval and back focus portion of each lens group when not in use and storing it in a compact manner '' There is an advantage that the mechanism for housing the second lens group can be shared with the focusing mechanism.

According to a fourth aspect of the present invention, by making the focal length of the first lens group relatively long , even if the air spacing between the first lens group and the second lens group changes, the second lens group is located closest to the object side. There is little change in the height of the on-axis marginal light passing through the surface, and performance degradation is unlikely to occur.

As described above, according to the present invention, a novel imaging lens, camera device, and portable information terminal device can be realized.
The imaging lens of the present invention has a half angle of view: a wide field angle of 38 degrees or more, a large aperture of F number: about 2.0 or less, a relatively small size, astigmatism and The field of curvature, lateral chromatic aberration, coma color difference, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor with 10 to 20 million pixels, from wide open to high contrast and the periphery of the angle of view. There is no distortion of the point image, no unnecessary coloring is generated even in a portion where the luminance difference is large, and a high performance capable of describing without distortion as a straight line can be realized.
Therefore, by using the imaging lens of the present invention as a photographing lens for a camera device or a portable information terminal device, a camera device or a portable information terminal device with good performance can be realized.

It is a figure which shows Example 1 of an imaging lens. It is a figure which shows Example 2 of an imaging lens. It is a figure which shows Example 3 of an imaging lens. FIG. 9 is a diagram illustrating a fourth example of the imaging lens. FIG. 9 is a diagram illustrating a fifth example of the imaging lens. It is a figure which shows Example 6 of an imaging lens. FIG. 6 is an aberration diagram for an object at infinity of the imaging lens according to Example 1; FIG. 6 is an aberration diagram for an object at infinity of the imaging lens of Example 2. FIG. 10 is an aberration diagram for an object at infinity of the imaging lens according to Example 3. FIG. 10 is an aberration diagram for an object at infinity of the imaging lens according to Example 4; FIG. 10 is an aberration diagram for an object at infinity of the imaging lens according to Example 5. FIG. 11 is an aberration diagram for an object at infinity of the imaging lens according to Example 6; It is a figure for demonstrating one Embodiment of a camera apparatus. It is a block diagram which shows the system structural example of the camera apparatus of FIG.

Embodiments relating to the imaging lens and the portable information terminal device will be described below.
1 to 6 show six examples of imaging lens embodiments.
In order to avoid complication, in FIG. 1 to FIG. 6, common parts are denoted by common reference numerals.

  FIG. 1 relates to Example 1 described later, and FIGS. 2 to 6 sequentially relate to Examples 2-6.

The imaging lens shown in FIGS. 1 to 6 has a first lens group G1 positioned on the object side (left side in the figure) and a first lens group positioned on the image side (right side in the figure) across the aperture stop S. It consists of two lens groups G2.
The first lens group G1 includes a first F lens group G1F having a negative refractive power on the object side, and has a widest air space in the first lens group, and a positive refractive power on the aperture stop S side. The first R lens group G1R having

  The first F lens group G1F has two negative lenses, and the first R lens group G1R has one positive lens.

  The second lens group G2 includes a second F lens group G2F and a second R lens group G2R in order from the aperture stop side.

The second F lens group G2F has a positive refractive power, and in order from the aperture stop S side, a first positive lens, a first negative lens, a second negative lens, and a second positive lens are arranged, and the second R lens group G2R has one positive or negative lens.
That is, in the examples shown in FIGS. 1, 2, and 6, one lens constituting the second R lens group G2R is a “positive lens”, and in the examples shown in FIGS. 3, 4, and 5, the second R lens group. One lens constituting the G2R is a “negative lens”.

  As shown in Examples 1 to 6 which will be described later, the imaging lenses of these embodiments have all the features specified by claims 1 to 9.

  In FIG. 1 to FIG. 6, the symbol F indicates that a composite system of various filters and a cover glass of the light receiving element is formed as one transparent parallel plate equivalent to this.

FIG. 13 is a diagram for explaining one embodiment of a “portable information terminal device”.
FIG. 13A shows the front side and the upper side, and FIG. 13B shows the back side.
In the portable information terminal device, the imaging optical system according to any one of claims 1 to 9 described above (specifically, appropriate ones of Examples 1 to 6 described later) is used as the photographing lens 1. .

FIG. 14 is a diagram showing a system configuration of the “portable information terminal device”.
As shown in FIG. 14, the portable information terminal device has a photographing lens 1 that is an “imaging lens” and a light receiving element 13, and reads the “image of the photographing object” formed by the photographing lens 1 by the light receiving element 13. It is configured as follows.
The output of the light receiving element 13 is processed by a signal processing device 14 under the control of the central processing unit 11 and converted into digital information. That is, the portable information terminal device has a “function of converting a captured image into digital information (claim 11)”.
The digitalized captured image can be displayed on the liquid crystal monitor 7 under the control of the central processing unit 11 and can be stored in the semiconductor memory 15. It can also be transmitted to the outside via a communication card 16 or the like.

  The portion excluding the “communication function by the communication card 16” constitutes a “camera device” which is a photographing function unit in the portable information terminal device.

  Note that the focusing method described in claim 9 may be configured to be “selectable from a menu screen”.

Six specific examples of the imaging lens are shown below.
The meanings of symbols in each embodiment are as follows.
f: Focal length of the entire system
F: F number
ω: Half angle of view
Y ': Maximum image height
R: radius of curvature
D: Surface spacing
Nd: Refractive index
νd: Abbe number
K: Aspherical conical constant
A4: Fourth-order aspheric coefficient
A6: 6th-order aspheric coefficient
A8: 8th-order aspheric coefficient
A10: 10th-order aspheric coefficient.

“Aspherical surface” means depth in the optical axis direction: X, reciprocal of paraxial radius of curvature (paraxial curvature): C, height from optical axis: H, conic constant: K, higher order aspherical coefficient: Using A4...
X = CH ² / [1 + √ (1- (1 + K) C ² H ² )] + A4 ・ H ⁴ + A6 ・ H ⁶ + A8 ・ H ⁸ + A10 ・ H ¹⁰
In the following data, the unit having a length dimension is “mm”.

Glass type is an optical glass type name of OHARA INC.
`` Example 1 ''
Focal length: 6.00 Fno: 1.96

Conditional calculation for Example 1

`` Example 2 ''
Focal length: 6.00 Fno: 1.95

Conditional calculation for Example 2

`` Example 3 ''
Focal length: 5.95 Fno: 1.96

Conditional calculation for Example 3

`` Example 4 ''
Focal length: 6.01 Fno: 1.96

Conditional calculation for Example 4

`` Example 5 ''
Focal length: 5.95 Fno: 1.96

Conditional calculation for Example 5

`` Example 6 ''
Focal length: 5.95 Fno: 1.95

Conditional calculation for Example 6

In the aspherical display, for example, “−2.6614E-08” means “−2.6614 × 10 ⁻⁸ ”.

  FIG. 7 to FIG. 12 sequentially show aberration diagrams of the imaging lenses of Examples 1 to 6 at an object at infinity.

  The broken line in the spherical aberration diagram indicates the “sine condition”, the solid line in the astigmatism diagram indicates “sagittal”, and the broken line indicates “meridional”. “D” indicates an aberration with respect to the d-line, and “g” indicates an aberration with respect to the g-line.

  In each of the examples, the aberration is sufficiently corrected, and the angle of view: a wide angle of view of 76 ° or more and a large aperture of about F2.0 or less, but it is sufficiently small and realizes a very good image performance. doing.

1 Shooting Lens 2 Finder 3 Flash 4 Shutter Button 5 Housing 6 Power Switch 7 LCD Monitor 8 Operation Button 9 Memory Card Slot

Japanese Patent Laid-Open No. 06-308385 JP 09-218350 A JP 2006-349920 A JP 2008-129403 A

Claims (12)

Consists of a first lens group located on the object side and a second lens group located on the image side across the aperture stop,
The first lens group includes a first F lens group having a negative refractive power on the object side, and has a positive refractive power on the aperture stop side with the widest air gap in the first lens group. The first R lens group is arranged,
The second lens group is configured by arranging a second F lens group and a second R lens group in order from the aperture stop side,
The first F lens group is composed of two negative lenses , the first R lens group is composed of one positive lens ,
The second F lens group has a positive refractive power, and in order from the aperture stop side, a first positive lens, a first negative lens, a second negative lens, and a second positive lens are arranged,
The second R lens group includes at least one positive or negative lens,
The refractive index of the Fraunhofer line with respect to the g line: ng, the refractive index with respect to the F line: nF, the refractive index with respect to the C line: nC, and the following formula:
θgF = (ng−nF) / (nF−nC)
On the two-dimensional coordinates of the orthogonal two axes with the vertical dispersion axis: θgF as the vertical axis and the Abbe number: vd as the horizontal axis defined by the coordinate point of the reference glass type: K7 (νd = 60.49, θgF = 0. 5436) and the reference glass type: F2 coordinate point (νd = 36.26, θgF = 0.5828) as a standard line, and the glass type partial dispersion ratio: θgF on the two-dimensional coordinate plane. When the deviation from the standard line is anomalous dispersion of the glass type: ΔθgF,
At least one negative lens included in the second F lens group has an Abbe number of the material: νdn and an anomalous dispersion: ΔθgFn.
(1) 30 <νdn <41
(2) ΔθgFn <0
A single focal length imaging lens characterized by satisfying The imaging lens according to claim 1.
At least one of the positive lenses in the second F lens group has an Abbe number: νdp and an anomalous dispersion: ΔθgFp as the condition:
(3) 70 <νdp
(4) 0 <ΔθgFp
An imaging lens characterized by satisfying The imaging lens according to claim 1 or 2,
The focal length of the entire system is f, and the focal length of the second F lens group is f2.
(5) 0.2 <f / f2 <0.5
An imaging lens characterized by satisfying The imaging optical system according to any one of claims 1 to 3,
The focal length of the entire system is f, and the focal length of the first lens group is f1.
(6) | f1 | / f> 8
An imaging lens characterized by satisfying The imaging lens according to any one of claims 1 to 4,
At least one of the two negative lenses constituting the first F lens group has an Abbe number of the material: νdn1, anomalous dispersion: ΔθgFn1, and conditions:
(7) 70 <νdn1
(8) 0 <ΔθgFn1
An imaging lens characterized by satisfying The imaging lens according to any one of claims 1 to 5,
Of the two negative lenses in the second F lens group, the material of the second negative lens is:
(1) 30 <νdn <41
(2) ΔθgFn <0
An imaging lens characterized by satisfying The imaging lens according to any one of claims 1 to 6,
An imaging lens, wherein a second negative lens and a second positive lens are cemented in the second F lens group. The imaging optical system according to any one of claims 1 to 7,
An imaging lens, wherein the first negative lens in the second F lens group is a negative meniscus lens having a convex surface facing the image side. The imaging lens according to any one of claims 1 to 8,
An imaging lens, wherein focusing is performed from infinity to a short distance by moving all or part of the second lens group.   A camera apparatus comprising the imaging lens according to claim 1 as a photographing optical system. The camera device according to claim 10.
A camera device characterized by having a function of using a captured image as digital information.   12. A portable information terminal comprising the camera device according to claim 11 as a camera function unit.

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