JP2003140044A - Zoom lens, video camera and digital still camera using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bright zoom lens having an F-number of >1.8, irrespective of a high power variation range up to a zooming ratio of about 10, and also, which is made small in size and provided with a high performance. SOLUTION: Provided that f1 denotes the composite focal distance of a 1st lens group 11, f2 denotes the composite focal distance of a 2nd lens group 12, f3 denotes the composite focal distance of the 3rd lens group 14, f4 denotes the composite focal distance of a 4th lens group 15 and fw denotes the composite focal distance of the whole system at a wide angle end, the following conditional inequalities are fetched in and satisfied; 5.0<f1/fw<6.0, 0.95<|f2/fw|<1.05, 2.5<f3/fw<3.5 and 2.5<f4/fw<4.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and a video camera and a digital still camera using the zoom lens. More specifically, it is suitable for video cameras and digital still cameras, and has a high zoom ratio of about 10 times, a high F-number of 1.8 or more, and a high resolution aspherical surface with a long back focus. The present invention relates to a zoom lens, and a video camera and a digital still camera using the zoom lens.

[0002]

2. Description of the Related Art In recent consumer video cameras,
With the widespread use of the DV format, it is essential to achieve both miniaturization and high image quality. Furthermore, since recent video cameras have a still image shooting function,
It also improves the image quality in the outermost part of the recordable range, and
There is a strong demand for a wider angle of view, which is to capture a wide area.

For example, Japanese Unexamined Patent Publication No. 9-281392 discloses a zoom lens having a high image quality, an angle of view of about 60 degrees at the wide end, and a zoom ratio of about 10 times.

[0004]

However, JP-A-9-2
In the zoom lens disclosed in Japanese Patent No. 81392, downsizing and high image quality are realized with a lens configuration of as few as 10 elements, but the angle of view is small and the image quality is greatly deteriorated at the outermost periphery of the photographic range. ing. In order to achieve a larger angle of view while maintaining high image quality, it is necessary to use 10 or more lenses or increase the total optical length, and it is difficult to realize a small zoom lens. It was

The present invention has been made in order to solve the above-mentioned problems in the prior art. The zoom ratio is as high as about 10 times, the F number is as bright as 1.8 to 1, and the size is small. An object is to provide a high-performance zoom lens, and a video camera and a digital still camera using the zoom lens.

[0006]

To achieve the above object, a zoom lens according to a first aspect of the present invention has a positive refracting power arranged in order from the object side to the image plane side. , A first lens group fixed with respect to the image plane, a second lens group having a negative refractive power and performing a zooming action by moving on the optical axis, and a second lens group perpendicular to the optical axis. Placed,
An aperture stop fixed with respect to the image plane, a third lens group having a positive refracting power and fixed with respect to the image plane, a third lens group having a positive refracting power, the second lens group and an object And a fourth lens group that moves on the optical axis so as to keep the image surface that varies with the movement of the object from the reference surface at a fixed position, wherein the first lens group is , A negative lens arranged in order from the object side, a positive lens, and a positive lens having a convex surface facing the object side, and the second lens group includes a negative lens arranged in order from the object side, and a negative lens. At least one surface of the lens group is an aspherical surface, and an optical element having a function of attenuating transmitted light by a certain amount is attached to the stop, and the optical element The element is placed at an angle to the diaphragm The third lens group is composed of a positive lens sequentially arranged from the object side and a cemented lens of a positive lens and a negative lens, and at least one surface of the lens group is an aspherical surface, and the fourth lens The group is composed of one positive lens having at least one aspherical surface, and the combined focal length of the first lens group is f1, the combined focal length of the second lens group is f2, and the combined focus of the third lens group. The distance is f3, the combined focal length of the fourth lens group is f4,
When the combined focal length of the entire system at the wide end is set to fw, the following conditional expressions (Formula 29) to (Formula 32) are satisfied. [Equation 29] 5.0 <f1 / fw <6.0

[0007]

[Equation 30]

[Equation 31] 2.5 <f3 / fw <3.5 [Equation 32] 2.5 <f4 / fw <4.0 According to the first configuration of the zoom lens, the aberration performance is improved. A high-resolution zoom lens can be made compact by cutting out ghosts and flares due to reflection from the lens surface and CCD face plate while adjusting.

In the first configuration of the zoom lens of the present invention, it is preferable that at least one negative lens in the second lens group has a refractive index of 1.85 or more.
According to this preferable example, the Petzval sum can be improved and a good image quality can be obtained in the outermost peripheral portion of the photographable range. Further, in this case, it is preferable that the aperture diameter gradually decreases from the wide end to the tele end. In this case, it is preferable that the following conditional expression (Formula 33) is satisfied, where Dw is the aperture diameter at the wide end and Dt is the aperture diameter at the telephoto end. [Equation 33] Dw / Dt <1.5 According to this preferable example, not only the F-number can be smoothly changed from the wide end to the tele end, but especially, the upper ray and the lower ray from the normal position to the tele end can be changed. It is possible to obtain an excellent image quality by cutting off unnecessary light rays. Further, in this case, when the angle formed by the diaphragm and the optical element is α, the optical element is preferably arranged so as to satisfy the following conditional expression (Formula 34). [Equation 34] 5 <α <15 According to this preferable example, it is not necessary to significantly increase the total lens length, and the third performance can be achieved without deteriorating the optical performance.
It is possible to cut ghosts and flares due to reflection from the lens surfaces of the lens group and the fourth lens group and from the CCD face plate. Therefore, the high-resolution zoom lens can be made compact. Further, in this case, in the aspherical surface of the second lens group, the local radius of curvature at a diameter of 10% of the lens effective diameter is r ₂₁ ,
The local radius of curvature at 90% of the lens effective diameter is r
_When it is set to ₂₉ , it is preferable that the following conditional expression (35) is satisfied. [Equation 35] 1.0 <r ₂₁ / r ₂₉ <1.3 Further, in this case, in the aspherical surface of the third lens group, the local radius of curvature at 10% of the lens effective diameter is r _31, when the local radius of curvature at 90% of the diameter of the lens effective diameter is r _39, preferably satisfies the following conditional expression (expression 36). [Equation 36] 0.4 <r ₃₁ / r ₃₉ <0.7 In this case, in the aspherical surface of the fourth lens group, the local radius of curvature at a diameter of 10% of the lens effective diameter is When r ₄₁ is a local radius of curvature at 90% of the lens effective diameter, r ₄₉ preferably satisfies the following conditional expression (Formula 37). [Equation 37] 0.4 <r ₄₁ / r ₄₉ <0.9 According to this preferable example, it is possible to obtain sufficient aberration performance for realizing high resolution of the zoom lens.

In this case, when the combined focal length of the entire system at the wide end is fw and the distance from the final lens surface in the air to the image surface is BF, the following (Equation 3)
It is preferable that the conditional expression (8) is satisfied. [Equation 38] 0.3 <BF / fw <1.0 According to this preferable example, a sufficient back focus for inserting an infrared cut filter or a low-pass filter such as a crystal can be secured. Further, since the back focus does not become larger than necessary, a compact zoom lens can be realized.

Further, in this case, the radius of curvature of the surface of the first lens group located closest to the image plane is the same as the radius of curvature of the surface of the second lens group located closest to the object. Is preferred. According to this preferable example, the surface distance between the surface of the first lens group that is closest to the image plane and the surface of the second lens group that is closest to the object side becomes smaller toward the lens periphery. Since this can be prevented, the lens barrel can be easily manufactured.

Further, in this case, it is preferable that an infrared cut filter is arranged between the fourth lens group and the image plane, and the infrared cut filter can be arbitrarily retracted from the optical axis. According to this preferable example, even in low illuminance such as at night, it is possible to obtain sufficient brightness for photographing without needing an auxiliary lamp or the like.

The second structure of the zoom lens according to the present invention is arranged in order from the object side to the image plane side,
A first lens group having a positive refracting power and fixed with respect to the image plane; a second lens group having a negative refracting power and performing a zooming action by moving on the optical axis; An aperture stop fixed with respect to the image plane, a third lens group having a positive refracting power and fixed with respect to the image plane, a third lens group having a positive refracting power, the second lens group and an object And a fourth lens group that moves on the optical axis so as to keep the image surface that varies with the movement of the object from the reference surface at a fixed position, wherein the first lens group is , A negative lens arranged in order from the object side, a positive lens, and a positive lens having a convex surface facing the object side, and the second lens group includes a negative lens arranged in order from the object side, and a negative lens. And a cemented lens with a positive lens, at least one surface of the lens group is an aspherical surface, The third lens group includes a positive lens sequentially arranged from the object side and a cemented lens of a positive lens and a negative lens, and at least one surface of the lens group is an aspherical surface, and the fourth lens group is A positive lens having at least one aspherical surface, and at least one positive lens of the third lens group and the fourth lens group is a lens having an infrared cut characteristic. .

According to the second configuration of this zoom lens,
By adding infrared cut characteristics to the lens while correcting aberration performance satisfactorily, an infrared cut filter becomes unnecessary, so a high-resolution zoom lens can be made compact and at low cost. .

In the second structure of the zoom lens of the present invention, the combined focal length of the first lens group is f.
1, the combined focal length of the second lens group is f2,
When the combined focal length of the lens group is f3, the combined focal length of the fourth lens group is f4, and the combined focal length of the entire system at the wide end is fw, the following conditional expressions (Formula 39) to (Formula 42) are given. It is preferable to be satisfied. [Equation 39] 5.0 <f1 / fw <6.0

[0016]

[Formula 40]

[Equation 41] 2.5 <f3 / fw <3.5 [Equation 42] 2.5 <f4 / fw <4.0 According to this preferable example, while properly adjusting the aberration performance,
It is possible to obtain a very compact zoom lens.
In this case, at least one of the second lens group
The refractive index of the negative lenses is preferably 1.85 or more. In this case, it is further preferable that the lens having the infrared cut characteristic has different transmittance characteristics inside and outside the arbitrary diameter within the lens effective diameter. According to this preferable example, good image quality can be obtained by suppressing color unevenness caused by different wavelength transmittance characteristics in the vicinity of the center of the lens and the peripheral portion. In this case, it is further preferable that the aperture diameter gradually decreases from the wide end to the tele end. Further, when the aperture diameter at the wide end is Dw and the aperture diameter at the tele end is Dt, the following (Formula 43) is obtained. It is preferable that the conditional expression (4) is satisfied. [Equation 43] Dw / Dt <1.5 According to this preferable example, not only the F number can be smoothly changed from the wide end to the tele end, but also unnecessary light from the normal position to the tele end is particularly cut. Therefore, good image quality can be obtained. Furthermore, in the aspherical surface of the second lens group, the local radius of curvature at 10% of the lens effective diameter is r ₂₁ , and the local radius of curvature at 90% of the lens effective diameter is r ₂₉ . In this case, it is preferable that the following conditional expression (Formula 44) is satisfied. [Equation 44] 1.0 <r ₂₁ / r ₂₉ <1.3 Furthermore, in the aspherical surface of the third lens group, the local radius of curvature at a diameter of 10% of the lens effective diameter is r ₃₁ , the lens is When the local radius of curvature at 90% of the effective diameter is r ₃₉ , it is preferable to satisfy the following conditional expression (Formula 45). [Equation 45] 0.4 <r ₃₁ / r ₃₉ <0.7 Furthermore, in the aspherical surface of the fourth lens group, the local radius of curvature at a diameter of 10% of the lens effective diameter is r ₄₁ , and the lens is When the local radius of curvature in 90% of the effective diameter is r ₄₉ , it is preferable to satisfy the following conditional expression (Equation 46). [Equation 46] 0.4 <r ₄₁ / r ₄₉ <0.9 Furthermore, the combined focal length of the entire system at the wide end is f
w, where BF is the distance from the final lens surface to the image surface in air, it is preferable to satisfy the following conditional expression (Formula 47). [Formula 47] 0.3 <BF / fw <1.0 Furthermore, the radius of curvature of the surface of the first lens group located closest to the image plane and the surface of the second lens group located closest to the object side. Is preferably the same as the radius of curvature of.

Further, a face plate of the image pickup device is arranged between the fourth lens group and the image plane, and
An optical low pass filter is preferably formed on the face plate of the image pickup device. According to this preferable example, the back focus, which has been long due to the insertion of the optical low-pass filter, can be shortened, so that the zoom lens can be further downsized.

In the zoom lens according to the third aspect of the present invention, the zoom lens is arranged in order from the object side to the image plane side.
A first lens group having a positive refracting power and fixed with respect to the image plane; a second lens group having a negative refracting power and performing a zooming action by moving on the optical axis; An aperture stop fixed with respect to the image plane, a third lens group having a positive refracting power and fixed with respect to the image plane, a third lens group having a positive refracting power, the second lens group and an object And a fourth lens group that moves on the optical axis so as to keep the image surface that varies with the movement of the object from the reference surface at a fixed position, wherein the first lens group is , A negative lens arranged in order from the object side, a positive lens, and a positive lens having a convex surface facing the object side, and the second lens group includes a negative lens arranged in order from the object side, and a negative lens. And a cemented lens with a positive lens, at least one surface of the lens group is an aspherical surface, The third lens group includes a positive lens and a negative lens arranged in order from the object side, at least one surface of the lens group is an aspherical surface, and the fourth lens group is arranged in order from the object side. The lens group is composed of a cemented lens of a negative lens and a positive lens, at least one surface of the lens group is an aspherical surface, and at least one positive lens of the third lens group and the fourth lens group has an infrared cut characteristic. It is a lens that has.

According to the third configuration of this zoom lens,
By adding infrared cut characteristics to the lens while correcting aberration performance satisfactorily, an infrared cut filter becomes unnecessary, so a high-resolution zoom lens can be made compact and at low cost. .

In the third structure of the zoom lens of the present invention, the combined focal length of the first lens group is f
1, the combined focal length of the second lens group is f2,
When the combined focal length of the lens group is f3, the combined focal length of the fourth lens group is f4, and the combined focal length of the entire system at the wide end is fw, the following conditional expressions (Formula 48) to (Formula 51) are given. It is preferable to be satisfied. [Equation 48] 5.0 <f1 / fw <6.0

[0022]

[Equation 49]

[Equation 50] 2.5 <f3 / fw <3.5 [Equation 51] 2.5 <f4 / fw <4.0 According to this preferable example, while properly adjusting the aberration performance,
It is possible to obtain a very compact zoom lens.
In this case, at least one of the second lens group
The refractive index of the negative lenses is preferably 1.85 or more. In this case, it is further preferable that the lens having the infrared cut characteristic has different transmittance characteristics inside and outside the arbitrary diameter within the lens effective diameter. In this case, it is further preferable that the aperture diameter gradually decreases from the wide end to the tele end. Further, when the aperture diameter at the wide end is Dw and the aperture diameter at the tele end is Dt, the following (Equation 52) is obtained. It is preferable that the conditional expression (4) is satisfied. [Equation 52] Dw / Dt <1.5 In this case, further, in the aspherical surface of the second lens group, the local radius of curvature at 10% of the lens effective diameter is r ₂₁ , and the lens effective diameter is When the local radius of curvature at 90% of the diameter is r ₂₉ , it is preferable to satisfy the following conditional expression (Equation 53). [Equation 53] 1.0 <r ₂₁ / r ₂₉ <1.3 In this case, further, in the aspherical surface of the third lens group, the local radius of curvature at 10% of the lens effective diameter is r _It is preferable that the following conditional expression (Equation 54) is satisfied, where r ₃₉ is the local radius of curvature at 90% of the lens effective diameter. [Equation 54] 0.4 <r ₃₁ / r ₃₉ <0.7 In this case, further, in the aspherical surface of the fourth lens group, the local radius of curvature at 10% of the lens effective diameter is r ₄₁ , It is preferable that the following conditional expression (Equation 55) is satisfied, where r ₄₉ is the local radius of curvature at 90% of the lens effective diameter. [Equation 55] 0.4 <r ₄₁ / r ₄₉ <0.9 In this case, further, the combined focal length of the entire system at the wide end is fw, and the distance from the final lens surface in the air to the image surface is BF. Then, it is preferable that the following conditional expression (Equation 56) is satisfied. [Equation 56] 0.3 <BF / fw <1.0 In this case, further, the radius of curvature of the surface of the first lens group located closest to the image surface and the radius of curvature of the surface closest to the object side of the second lens group It is preferable that the radius of curvature of the surface on which it is located is the same.

In this case, the face plate of the image pickup device is further arranged between the fourth lens group and the image plane, and the optical low-pass filter is formed on the face plate of the image pickup device. Is preferred.

Further, the structure of the video camera according to the present invention is a video camera provided with a zoom lens, wherein the zoom lens of the present invention is used as the zoom lens.

According to this video camera structure, it is possible to realize a high resolution video camera which is excellent in downsizing and weight saving.

The configuration of the digital still camera according to the present invention is a digital still camera including a zoom lens, wherein the zoom lens of the present invention is used as the zoom lens.

According to the structure of this digital still camera, the size and weight are excellent, and the magnification is high,
It is possible to realize a high resolution digital still camera.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to embodiments.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.
FIG. 6 is a layout diagram showing a configuration of a zoom lens in the embodiment.

As shown in FIG. 1, first from the object side (left side in FIG. 1) toward the image plane 17 side (right side in FIG. 1).
A lens group 11, a second lens group 12, a diaphragm 13, a third lens group 14, a fourth lens group 15, an infrared cut filter, a crystal cut filter, a flat plate glass 16 that is optically equivalent to a face plate of an image sensor, and the like. The zoom lenses are arranged in order, and a zoom lens is configured by this. The flat glass 16 is specifically configured by an infrared cut filter, an optical low-pass filter, and a face plate of an image sensor, which are sequentially arranged from the object side toward the image plane 17 side.

The first lens group 11 has a positive refractive power,
It is fixed with respect to the image plane 17 even during zooming and focusing. The second lens group 12 has a negative refracting power and moves on the optical axis to perform a zooming action. The diaphragm 13 is arranged perpendicularly to the optical axis, and is in a state of being fixed to the image plane 17 even during zooming and focusing. The third lens group 14 has a positive refractive power, and is in a state of being fixed with respect to the image surface 17 even during zooming and focusing. The fourth lens group 15 has a positive refracting power, and moves along the optical axis so as to keep the image plane 17, which varies with the movement of the second lens group 12 and the object to be photographed, at a constant position from the reference plane. By moving, the image movement due to zooming and the focus adjustment are performed at the same time.

The first lens group 11 is composed of a negative lens 1a, a positive lens 1b, and a positive lens 1c having a convex surface facing the object side, which are sequentially arranged from the object side. The second lens group 12 includes a negative lens 2a arranged in order from the object side.
And a cemented lens of a biconcave lens (negative lens) 2b and a positive lens 2c, and at least one surface of the lens group is an aspherical surface. An optical element having a function of attenuating the transmitted light by a certain amount is attached to the diaphragm 13, and the optical element is arranged to be inclined with respect to the diaphragm 13. The third lens group 14 is composed of a positive lens 3a arranged in order from the object side, and a cemented lens of a positive lens 3b and a negative lens 3c, and at least one surface of the lens group is an aspherical surface. . The fourth lens group 15 is composed of one positive lens 4a, and at least one surface thereof is an aspherical surface.

In the zoom lens according to the present embodiment, the combined focal length of the first lens group 11 is f1, and the second lens group 1 is
F2 is the combined focal length of the second lens group 14, f3 is the combined focal length of the third lens group 14, and f4 is the combined focal length of the fourth lens group 15.
When the combined focal length of the entire system at the wide end is fw, the following conditional expressions (57) to (60) are satisfied. [Equation 57] 5.0 <f1 / fw <6.0

[0035]

[Equation 58]

[Equation 59] 2.5 <f3 / fw <3.5 [Equation 60] 2.5 <f4 / fw <4.0 The above (Equation 57) is a condition relating to the refractive power of the first lens group 11. It is an expression. If the lower limit of the conditional expression (Equation 57) is exceeded, the refracting power of the first lens group 11 becomes large, and it becomes difficult to correct spherical aberration on the long focus side and coma aberration off-axis. On the other hand, if the upper limit of the conditional expression (Equation 57) is exceeded, the total lens length becomes long, making it difficult to make the zoom lens compact.

The above expression (58) is a conditional expression regarding the refractive power of the second lens group 12. When the value goes below the lower limit of the conditional expression (Equation 58), the Petzval sum of the entire system becomes large, and it becomes difficult to correct the field curvature. On the other hand, the above (Equation 5)
If the upper limit of the conditional expression 8) is exceeded, the Petzval sum will be small, but the amount of movement of the second lens group 12 during zooming will be large, and as a result, the entire system will be long, and therefore the zoom lens will be compact. Becomes difficult.

The above (Equation 59) is a conditional expression regarding the refractive power of the third lens group 14. When the value goes below the lower limit of the conditional expression (Equation 59), the refracting power of the third lens group 14 becomes large, and it becomes impossible to secure a back focus for inserting a crystal cut filter or the like, and spherical aberration Correction is also difficult. On the other hand, if the upper limit of the conditional expression (Equation 59) is exceeded, the Petzval sum becomes large, and it becomes difficult to correct the field curvature.

The above (Formula 60) is a conditional expression regarding the refractive power of the fourth lens group 15. When the value goes below the lower limit of the conditional expression (Equation 60), the entire lens system becomes large, and downsizing becomes difficult. On the other hand, if the upper limit of the conditional expression (Equation 60) is exceeded, it becomes difficult to satisfactorily correct off-axis aberrations at the time of short-distance photography and at the time of long-distance photography.

Further, in the zoom lens according to the present embodiment, it is desirable that at least one negative lens in the second lens group 12 has a refractive index of 1.85 or more. If the refractive index is less than 1.85, the Petzval sum may be deteriorated, the optimum image forming positions of the central portion and the outermost peripheral portion of the photographable range may be different, and the optical performance may be deteriorated.

Further, in the zoom lens of the present embodiment, the diaphragm diameter gradually decreases from the wide end to the tele end, and when the diaphragm diameter at the wide end is Dw and the diaphragm diameter at the tele end is Dt, It is desirable that the following conditional expression (Equation 61) is satisfied. [Equation 61] Dw / Dt <1.5 The above (Equation 61) is a conditional expression regarding the diaphragm. If the upper limit of the conditional expression (Equation 61) is exceeded, the degree of change in the F number increases from the wide end to the tele end, and the brightness balance in the entire zooming region is lost. FIG. 15 shows the aperture diameter that changes from the wide end to the tele end.

Further, in the zoom lens according to the present embodiment, the diaphragm 13 is provided with an optical element having a function of attenuating the transmitted light by a certain amount. Here, the optical element is obliquely attached to the diaphragm 13. In this case, when the angle formed by the diaphragm 13 and the optical element is α, it is desirable that the following conditional expression (Formula 62) is satisfied. [Equation 62] 5 <α <15 The above (Equation 62) is a conditional expression regarding the arrangement of the diaphragm 13. If the lower limit of the conditional expression (Equation 62) is exceeded, the aperture 1
The angle formed by 3 and the optical element becomes small, and it becomes difficult to remove ghost and flare. On the other hand, if the upper limit of the conditional expression (Equation 62) is exceeded, the angle formed by the diaphragm 13 and the optical element becomes large, making it difficult to make the zoom lens compact. Further, the focal length of the third lens group 14 becomes long and the balance of aberration performance deteriorates, so that it becomes difficult to secure good optical performance.

In the zoom lens of the present embodiment, the local radius of curvature of the aspherical surface of the second lens group 12 at a diameter of 10% of the lens effective diameter is r ₂₁ , and at 90% of the lens effective diameter. When the local radius of curvature is r ₂₉ , it is desirable that the following conditional expression (Equation 63) is satisfied. [Equation 63] 1.0 <r ₂₁ / r ₂₉ <1.3 Further, in the zoom lens according to the present embodiment, in the aspherical surface of the third lens group 14, a local area of 10% of the lens effective diameter is locally generated. It is preferable that the following conditional expression (Equation 64) is satisfied, where r _{31 is} a radius of curvature and r ₃₉ is a local radius of curvature at 90% of the lens effective diameter. [Equation 64] 0.4 <r ₃₁ / r ₃₉ <0.7 Further, in the zoom lens according to the present embodiment, in the aspherical surface of the fourth lens group 15, the local area is reduced to 10% of the lens effective diameter. It is desirable that the following conditional expression (Equation 65) be satisfied, where r _{41 is} a radius of curvature and r ₄₉ is a local radius of curvature at 90% of the lens effective diameter. [Equation 65] 0.4 <r ₄₁ / r ₄₉ <0.9 By satisfying the conditional expressions of (Equation 63) to (Equation 65), sufficient aberration performance for realizing a high resolution of the zoom lens is obtained. Can be obtained.

The above (Equation 63) is a conditional expression relating to the amount of aspherical surface of the aspherical lens forming the second lens group 12.
When the value goes below the lower limit of the conditional expression (Equation 63), spherical aberration is undercorrected, and sufficient aberration performance cannot be obtained.
On the other hand, if the upper limit of the conditional expression (Equation 63) is exceeded, spherical aberration, particularly spherical aberration during short-distance shooting, will be undercorrected, and sufficient aberration performance will not be obtained.

The above (Equation 64) is a conditional expression regarding the amount of aspherical surface of the aspherical lens forming the third lens group 14.
When the value goes below the lower limit of the conditional expression (Equation 64), spherical aberration is undercorrected, and sufficient aberration performance cannot be obtained.
On the other hand, if the upper limit of the conditional expression (Equation 64) is exceeded, spherical aberration is overcorrected and coma flare is likely to occur.

The above (Equation 65) is a conditional expression regarding the amount of aspherical surface of the aspherical lens forming the fourth lens group 15.
If the lower limit or the upper limit of the conditional expression (Equation 65) is exceeded or exceeded, the total aberration balance from the wide end (wide-angle end) to the tele end (telephoto end) is lost, and sufficient aberration performance is obtained. I will not be able to.

Further, in the zoom lens of the present embodiment, when the combined focal length of the entire system at the wide end is fw and the distance from the lens final surface to the image surface in air is BF, the following (Equation 66) is obtained. It is desirable that the conditional expression of is satisfied. [Equation 66] 0.3 <BF / fw <1.0 By satisfying the conditional expression of (Equation 66), a sufficient back focus for inserting an infrared cut filter or a low-pass filter such as a crystal is secured. can do. If the lower limit of the conditional expression (Equation 66) is exceeded, it is not possible to secure a sufficient back focus for inserting an infrared cut filter or a low-pass filter such as a crystal. On the other hand, if the upper limit of (Equation 66) is exceeded, the back focus becomes larger than necessary, and a small zoom lens cannot be realized.

Further, in the zoom lens according to the present embodiment, the radius of curvature of the surface of the first lens group 11 closest to the image surface 17 and the curvature of the surface of the second lens group 12 closest to the object side. It is desirable that the radius is the same. According to this configuration, the surface distance between the surface of the first lens group 11 located closest to the image plane 17 and the surface of the second lens group 12 located closest to the object becomes smaller toward the lens periphery. Since it is possible to prevent the movement, it is easy to manufacture the lens barrel.

Further, in the zoom lens according to the present embodiment, the infrared cut filter which is a part of the flat glass 16 arranged between the fourth lens group 15 and the image plane 17 is arranged on the optical axis. It is desirable to be able to evacuate arbitrarily. According to this configuration, it is possible to obtain sufficient brightness for photographing without needing an auxiliary lamp or the like even in low illuminance such as at night.

The zoom lens according to the present embodiment will be described below in more detail with reference to specific examples.

Example 1 The following (Table 1) shows specific numerical examples of the zoom lens according to the present embodiment.

[0052]

[Table 1]

In the above (Table 1), rd (mm) is the radius of curvature of the lens, th (mm) is the thickness of the lens or the air gap between the lenses, nd is the refractive index of each lens with respect to the d-line, and ν is the lens. Shows the Abbe number for the d-line (the same applies to Examples 2 and 3 described later). A surface having an aspherical surface (marked with * next to the surface number in the above (Table 1)) is defined by the following (Equation 67) (the same applies to Examples 2 and 3 described later). .

[0054]

[Equation 67]

However, in the above (Formula 67), y is the height from the optical axis, Z is the distance from the tangent plane of the aspherical aspherical vertex whose height from the optical axis is y, and c is the aspherical surface. The curvature of the vertex, k is a conic constant, and D, E, F, and G are aspherical coefficients.

The following Table 2 shows the aspherical coefficients of the zoom lens in this embodiment.

[0057]

[Table 2]

Further, the following (Table 3) shows the air gap (mm) that can be varied by zooming when the object point is at a position of 2 m measured from the tip of the lens. The standard position in the following (Table 3) is the third lens group 14 and the fourth position.
This is the position where the lens group 15 is closest. Below (Table 3)
Medium, f (mm), FNo. , Ω (degree) are the focal length, the F number, and the incident half angle of view (the same applies to Examples 2 and 3 described later).

[0059]

[Table 3]

2 to 4 are aberration performance diagrams of the zoom lens of the present embodiment at the wide end (FIG. 2), the normal position (FIG. 3) and the tele end (FIG. 4). In each figure, (a)
Is a diagram of spherical aberration (mm). (B) is astigmatism (m
It is a figure of m), a solid line shows sagittal field curvature, and a broken line shows meridional field curvature. (C) is a figure which shows a distortion aberration (%). (D) is a diagram of axial chromatic aberration (mm), where the solid line is the d line, the short broken line is the F line, and the long broken line is the C line.
The value for the line is shown. (E) is chromatic aberration of magnification (m
m), in which the short broken line indicates the value for the F line and the long broken line indicates the value for the C line (the same applies to Examples 2 and 3 below).

As is clear from the aberration performance charts shown in FIGS. 2 to 4, it can be seen that the zoom lens of this embodiment exhibits good aberration performance.

[Second Embodiment] FIG. 5 shows a second embodiment of the present invention.
FIG. 6 is a layout diagram showing a configuration of a zoom lens in the embodiment.

As shown in FIG. 5, from the object side (left side in FIG. 5) toward the image plane 27 side (right side in FIG. 5), the first side
A lens group 21, a second lens group 22, a diaphragm 23, a third lens group 24, a fourth lens group 25, an infrared cut filter, a crystal cut filter, a flat plate glass 26 which is optically equivalent to a face plate of an image pickup device, and the like. The zoom lenses are arranged in order, and a zoom lens is configured by this. The flat glass 26 is specifically composed of an infrared cut filter, an optical low-pass filter, and a face plate of an image sensor, which are sequentially arranged from the object side toward the image plane 27 side.

The first lens group 21 has a positive refractive power,
It is fixed with respect to the image plane 27 even during zooming and focusing. The second lens group 22 has a negative refracting power, and performs a zooming action by moving on the optical axis. The diaphragm 23 remains fixed with respect to the image plane 27 during zooming and focusing. Third lens group 24
Has a positive refractive power, and is in a state of being fixed with respect to the image plane 27 even during zooming and focusing. The fourth lens group 25 has a positive refractive power, and moves along the optical axis so as to keep the image plane 27, which varies with the movement of the second lens group 22 and the object to be photographed, at a constant position from the reference plane. By moving, the image movement due to zooming and the focus adjustment are performed at the same time.

The first lens group 21 is composed of a negative lens 5a, a positive lens 5b, and a positive lens 5c having a convex surface directed toward the object side, which are sequentially arranged from the object side. The second lens group 22 includes the negative lenses 6a arranged in order from the object side.
And a cemented lens of a biconcave lens (negative lens) 6b and a positive lens 6c, and at least one surface of the lens group is an aspherical surface. Third lens group 24
Is composed of a positive lens 7a arranged in order from the object side, and a cemented lens of a positive lens 7b and a negative lens 7c, and at least one surface of the lens group is an aspherical surface. The fourth lens group 25 is composed of one positive lens 8a, and at least one surface thereof is an aspherical surface. Further, at least one positive lens of the third lens group 24 and the fourth lens group 25 is composed of a lens having an infrared cutoff characteristic.

In the zoom lens according to the present embodiment, the combined focal length of the first lens group 21 is f1 and the second lens group 2 is
F2 is the combined focal length of the second lens group 24, f3 is the combined focal length of the third lens group 24, and f4 is the combined focal length of the fourth lens group 25.
When the combined focal length of the entire system at the wide end is fw, the conditional expressions (57) to (60) are satisfied.

Also in the zoom lens according to the present embodiment, as in the first embodiment, the second lens group 2
It is desirable that the refractive index of at least one negative lens of 2 is 1.85 or more.

Further, in the zoom lens according to the present embodiment, it is desirable that the lens having the infrared cut characteristic has different transmittance characteristics inside and outside the arbitrary diameter within the lens effective diameter. According to this configuration, it is possible to suppress color unevenness caused by different wavelength transmittance characteristics in the vicinity of the center of the lens and in the peripheral portion, and obtain good image quality.

Also in the zoom lens of this embodiment, as in the first embodiment, the aperture diameter gradually decreases from the wide end to the tele end, and the aperture diameter at the wide end is Dw, The aperture diameter at the tele end is Dt
Then, it is desirable that the conditional expression (Equation 61) be satisfied.

Also in the zoom lens according to the present embodiment, as in the first embodiment, the second lens group 2
In the aspherical surface of No. 2, when the local radius of curvature at 10% of the lens effective diameter is r ₂₁ and the local radius of curvature at 90% of the lens effective diameter is r ₂₉ , the condition of the above (Equation 63) is satisfied. It is desirable that the formula be satisfied.

Also in the zoom lens according to the present embodiment, as in the first embodiment, the third lens group 2
In the aspherical surface of No. 4, when the local radius of curvature in the diameter of 10% of the lens effective diameter is r ₃₁ , and the local radius of curvature in the diameter of 90% of the lens effective diameter is r ₃₉ ,
It is desirable that the conditional expression 4) is satisfied.

Also in the zoom lens according to the present embodiment, as in the first embodiment, the fourth lens group 2
In the aspheric surface of No. 5, where r ₄₁ is the local radius of curvature in the diameter of 10% of the lens effective diameter and r ₄₉ is the local radius of curvature in the diameter of 90% of the lens effective diameter,
It is desirable that the conditional expression 5) is satisfied.

Also in the zoom lens of this embodiment, as in the first embodiment, the combined focal length of the entire system at the wide end is fw, and the distance from the final lens surface to the image surface in air. Where BF is
It is desirable that the conditional expression 6) be satisfied.

Also in the zoom lens according to the present embodiment, the first lens group 2 is used as in the first embodiment.
It is desirable that the radius of curvature of the surface of No. 1 closest to the image surface and the radius of curvature of the surface of the second lens group 22 closest to the object side are the same.

Further, in the zoom lens according to the present embodiment, it is desirable that the optical low pass filter is formed on the face plate of the image pickup device. With this configuration, the back focus, which has been lengthened due to the insertion of the optical low-pass filter, can be further shortened, so that the zoom lens can be further downsized.

Hereinafter, the zoom lens according to the present embodiment will be described in more detail with reference to specific examples.

Example 2 The following (Table 4) shows specific numerical examples of the zoom lens according to the present embodiment.

[0078]

[Table 4]

Further, (Table 5) below shows aspherical coefficients of the zoom lens in the present embodiment.

[0080]

[Table 5]

Further, the following (Table 6) shows the air space (mm) that can be changed by zooming when the object point is at the infinite position.

[0082]

[Table 6]

6 to 8 are aberration performance diagrams at the wide end (FIG. 6), the normal position (FIG. 7) and the tele end (FIG. 8) of the zoom lens of this embodiment. As is clear from the aberration performance charts shown in FIGS. 6 to 8, it is understood that the zoom lens of the present embodiment exhibits good aberration performance.

[Third Embodiment] FIG. 9 shows a third embodiment of the present invention.
FIG. 3 is an arrangement diagram showing a configuration of a zoom lens in the embodiment of FIG.

As shown in FIG. 9, from the object side (left side in FIG. 9) toward the image plane 37 side (right side in FIG. 9), the first side
A lens group 31, a second lens group 32, a diaphragm 33, a third lens group 34, a fourth lens group 35, an infrared cut filter, a crystal cut filter, a flat plate glass 36 that is optically equivalent to a face plate of an image sensor, and the like. The zoom lenses are arranged in order, and a zoom lens is configured by this. The flat glass 36 is specifically composed of an infrared cut filter, an optical low-pass filter, and a face plate of an image sensor, which are sequentially arranged from the object side toward the image plane 37 side.

The first lens group 31 has a positive refractive power,
It is in a state of being fixed with respect to the image plane 37 even during zooming and focusing. The second lens group 32 has a negative refracting power and moves on the optical axis to perform a zooming action. The diaphragm 33 remains fixed with respect to the image plane 37 during zooming and focusing. Third lens group 34
Has a positive refractive power, and is in a state of being fixed with respect to the image plane 37 even during zooming and focusing. The fourth lens group 35 has a positive refracting power, and moves along the optical axis so as to keep the image plane 37, which varies with the movement of the second lens group 32 and the object as the subject, at a constant position from the reference plane. By moving, the image movement due to zooming and the focus adjustment are performed at the same time.

The first lens group 31 is composed of a negative lens 9a, a positive lens 9b, and a positive lens 9c having a convex surface directed toward the object side, which are sequentially arranged from the object side. The second lens group 32 includes the negative lenses 10 arranged in order from the object side.
a, a biconcave lens (negative lens) 10b, and a positive lens 10c
And a cemented lens with a cemented lens, and at least one surface of the lens group is an aspherical surface. The third lens group 34 is composed of a positive lens 11a and a negative lens 11b arranged in order from the object side, and at least one surface of the lens group is an aspherical surface. 4th lens group 3
Reference numeral 5 denotes a cemented lens of a negative lens 12a and a positive lens 12b arranged in order from the object side, and at least one surface of the lens group is an aspherical surface. Further, at least one positive lens of the third lens group 34 and the fourth lens group 35 is composed of a lens having an infrared cut characteristic.

In the zoom lens according to the present embodiment, the combined focal length of the first lens group 31 is f1 and the second lens group 3 is
F2 is the combined focal length of the second lens group 34, f3 is the combined focal length of the third lens group 34, and f4 is the combined focal length of the fourth lens group 35.
When the combined focal length of the entire system at the wide end is fw, the conditional expressions (57) to (60) are satisfied.

Also in the zoom lens according to the present embodiment, the second lens group 3 is used as in the first embodiment.
It is desirable that the refractive index of at least one negative lens of 2 is 1.85 or more.

Also in the zoom lens according to the present embodiment, as in the second embodiment, the lens having the infrared cut characteristic is used for the inside and outside of an arbitrary diameter within the lens effective diameter. It is desirable to have different transmittance characteristics.

Also in the zoom lens of this embodiment, as in the first embodiment, the aperture diameter gradually decreases from the wide end to the tele end, and the aperture diameter at the wide end is Dw, The aperture diameter at the tele end is Dt
Then, it is desirable that the conditional expression (Equation 61) be satisfied.

Also in the zoom lens according to the present embodiment, the second lens group 3 is used as in the first embodiment.
In the aspherical surface of No. 2, when the local radius of curvature at 10% of the lens effective diameter is r ₂₁ and the local radius of curvature at 90% of the lens effective diameter is r ₂₉ , the condition of the above (Equation 63) is satisfied. It is desirable that the formula be satisfied.

Also in the zoom lens according to the present embodiment, the third lens group 3 is used as in the first embodiment.
In the aspherical surface of No. 4, when the local radius of curvature in the diameter of 10% of the lens effective diameter is r ₃₁ , and the local radius of curvature in the diameter of 90% of the lens effective diameter is r ₃₉ ,
It is desirable that the conditional expression 4) is satisfied.

Also in the zoom lens according to the present embodiment, as in the first embodiment, the fourth lens group 2
In the aspheric surface of No. 5, where r ₄₁ is the local radius of curvature in the diameter of 10% of the lens effective diameter and r ₄₉ is the local radius of curvature in the diameter of 90% of the lens effective diameter,
It is desirable that the conditional expression 5) is satisfied.

Also in the zoom lens of this embodiment, as in the first embodiment, the combined focal length of the entire system at the wide end is fw, and the distance from the final lens surface to the image surface in air. Where BF is
It is desirable that the conditional expression 6) be satisfied.

Also in the zoom lens according to the present embodiment, the first lens group 3 is used as in the first embodiment.
It is desirable that the radius of curvature of the surface of No. 1 closest to the image surface and the radius of curvature of the surface of the second lens group 32 closest to the object side are the same.

Also in the zoom lens according to the present embodiment, it is desirable that the optical low pass filter is formed on the face plate of the image pickup device as in the second embodiment.

Hereinafter, the zoom lens according to the present embodiment will be described in more detail with reference to specific examples.

Example 3 The following (Table 7) shows specific numerical examples of the zoom lens according to the present embodiment.

[0100]

[Table 7]

Further (Table 8) below shows the aspherical surface coefficients of the zoom lens in the present embodiment.

[0102]

[Table 8]

Further, the following (Table 9) shows the air space (mm) which can be changed by zooming when the object point is at a position of 2 m measured from the lens tip.

[0104]

[Table 9]

10 to 12 are aberration performance diagrams of the zoom lens of this embodiment at the wide end (FIG. 10), the normal position (FIG. 11) and the tele end (FIG. 12). As is clear from the aberration performance charts shown in FIGS. 10 to 12, the zoom lens of the present embodiment exhibits good aberration performance.

[Fourth Embodiment] FIG. 13 is a layout showing the structure of a video camera according to the fourth embodiment of the present invention.

As shown in FIG. 13, the video camera according to the present embodiment has a zoom lens 100, an infrared cut filter 101, a low-pass filter 102, an image sensor 103, a signal processing circuit 104, and a liquid crystal viewfinder. 105, a recording system 106, a liquid crystal monitor 107,
And a housing 108. Here, the zoom lens 10
As 0, the zoom lens according to the first embodiment is used. In addition, as the zoom lens 100, the second
Alternatively, when the zoom lens according to the third embodiment is used, the infrared cut filter 101 is unnecessary.

As described above, if a video camera is constructed using the zoom lens of the present invention, it is possible to realize a small and highly functional video camera with a high zoom ratio of about 10 times. Even when the zoom lens according to the second or third embodiment is used,
It is possible to realize a compact and highly functional video camera while having a high zoom ratio of about 10 times.

[Fifth Embodiment] FIG. 14 is a layout showing the structure of a digital still camera according to the fifth embodiment of the present invention.

As shown in FIG. 14, the digital still camera according to the present embodiment includes a zoom lens 110,
Infrared cut filter 111 and low pass filter 112
The image sensor 113, the signal processing circuit 114, the optical viewfinder 115, the recording system 116, the liquid crystal monitor 117, and the housing 118. Here, the zoom lens of the first embodiment is used as the zoom lens 100. If the zoom lens of the second or third embodiment is used as the zoom lens 100, the infrared cut filter 111 is unnecessary.

As described above, when a digital still camera is constructed using the zoom lens of the present invention, the zoom ratio is 1
It is possible to realize a small and highly functional digital still camera with a high magnification of about 0. In addition, the second
Alternatively, even when the zoom lens according to the third embodiment is used, similarly, it is possible to realize a compact and highly functional digital still camera with a high zoom ratio of about 10 times.

[0112]

As described above, according to the zoom lens of the present invention, the zoom lenses are arranged in order from the object side to the image plane side, have positive refracting power, and are fixed with respect to the image plane. A first lens group, a second lens group having a negative refracting power and performing a zooming action by moving on the optical axis, and is arranged perpendicular to the optical axis, and with respect to the image plane. A fixed diaphragm, a third lens group having a positive refracting power and fixed with respect to the image surface, and a second lens group having a positive refracting power and moving an object to be an object. To select an appropriate power arrangement and an optimum aspherical shape in a zoom lens including a fourth lens group that moves on the optical axis so as to keep the image plane that fluctuates with the reference plane at a constant position. As a result, the zoom ratio is as high as 10x and the F number is 1.8- , Moreover, it is possible to realize a high-performance zoom lens compact. Further, since this zoom lens is suitable for constituting a video camera, by constructing a video camera using the zoom lens, a compact and highly functional video camera having a high zoom ratio of about 10 times can be obtained. Can be realized. Further, since this zoom lens is suitable for constructing a digital still camera, by constructing a digital still camera using this zoom lens, the zoom ratio is as high as about 10 times, but it is small and highly functional. A digital still camera can be realized.

[Brief description of drawings]

FIG. 1 is a layout diagram showing a configuration of a zoom lens according to a first embodiment of the present invention.

FIG. 2 is an aberration performance diagram at the wide end of the zoom lens according to the first embodiment of the present invention.

FIG. 3 is an aberration performance diagram of the zoom lens according to the first embodiment of the present invention at a normal position.

FIG. 4 is an aberration performance diagram at a telephoto end of the zoom lens according to the first embodiment of the present invention.

FIG. 5 is an arrangement diagram showing a configuration of a zoom lens according to a second embodiment of the present invention.

FIG. 6 is an aberration performance diagram at the wide end of the zoom lens according to the second embodiment of the present invention.

FIG. 7 is an aberration performance diagram of a zoom lens according to a second embodiment of the present invention at a normal position.

FIG. 8 is an aberration performance diagram at a tele end of a zoom lens according to a second embodiment of the present invention.

FIG. 9 is an arrangement diagram showing a configuration of a zoom lens according to a third embodiment of the present invention.

FIG. 10 is an aberration performance diagram at the wide end of the zoom lens according to the third embodiment of the present invention.

FIG. 11 is an aberration performance diagram of a zoom lens according to a third embodiment of the present invention at a normal position.

FIG. 12 is an aberration performance diagram at a tele end of a zoom lens according to a third embodiment of the present invention.

FIG. 13 is a layout diagram showing a configuration of a video camera according to a fourth embodiment of the present invention.

FIG. 14 is a layout diagram showing a configuration of a digital still camera according to a fifth embodiment of the present invention.

FIG. 15 is a graph showing how the aperture diameter changes with the focal length of the zoom lens in the embodiment of the present invention.

[Explanation of symbols]

11, 21, 31 First lens group 12, 22, 32 Second lens group 13, 23, 33 aperture 14, 24, 34 Third lens group 15, 25, 35 4th lens group 16, 26, 36 Flat glass 17, 27, 37 Image plane 100, 110 zoom lens 101,111 Infrared cut filter 102, 112 Low-pass filter 103, 113 image sensor 104, 114 Signal processing circuit 105,115 Viewfinder 106, 116, recording system 107,117 LCD monitor 108, 118 housing

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03B 17/12 G03B 19/02 5C022 19/02 H04N 5/225 D H04N 5/225 G02B 7/04 Z ( 72) Inventor Katsushi Yamada 1006 Kadoma, Kadoma City, Osaka Prefecture F-term within Matsushita Electric Industrial Co., Ltd. (reference) RA05 RA12 RA13 RA32 RA43 SA23 SA27 SA29 SA32 SA63 SA72 SA74 SB04 SB14 SB23 SB24 SB32 SB33 2H101 DD65 DD66 5C022 AA13 AB12 AB13 AB23 AB66 AC42 AC54 AC55

Claims (37)

[Claims] 1. A first lens group having a positive refractive power, which is arranged in order from the object side to the image surface side, and is fixed with respect to the image surface, and a negative refractive power, A second lens group that performs a zooming effect by moving on the optical axis, an aperture stop that is arranged perpendicular to the optical axis and is fixed with respect to the image plane, and has a positive refractive power, The third lens group fixed to the image plane, and the image plane having a positive refractive power and varying with the movement of the second lens group and the object to be photographed are set at a fixed position from the reference plane. A zoom lens including a fourth lens group that moves on the optical axis so as to keep the negative lens, wherein the first lens group includes a negative lens sequentially arranged from the object side, a positive lens, and a convex surface on the object side. The second lens group includes a negative lens sequentially arranged from the object side, and a negative lens. At least one surface of the lens group is an aspherical surface, and an optical element having a function of attenuating transmitted light by a certain amount is attached to the stop, and the optical element. Is tilted with respect to the diaphragm, and the third lens group includes a positive lens sequentially arranged from the object side and a cemented lens of a positive lens and a negative lens, and at least the third lens group One surface is an aspherical surface, and at least one surface of the fourth lens group is an aspherical surface. 1
The first lens group has a composite focal length of f1, the second lens group has a composite focal length of f2, the third lens group has a composite focal length of f3, and the fourth lens group has a composite focal length. F is the focal length
4. When the total focal length of the entire system at the wide end is set to fw, the following conditional expressions (1) to (4) are satisfied. [Equation 1] 5.0 <f1 / fw <6.0 [Equation 2] [Equation 3] 2.5 <f3 / fw <3.5 [Equation 4] 2.5 <f4 / fw <4.0 2. The zoom lens according to claim 1, wherein at least one negative lens of the second lens group has a refractive index of 1.85 or more. 3. The zoom lens according to claim 2, wherein the aperture diameter gradually decreases from the wide end to the tele end. 4. The zoom lens according to claim 3, wherein when the aperture diameter at the wide end is Dw and the aperture diameter at the tele end is Dt, the following conditional expression (5) is satisfied. [Equation 5] Dw / Dt <1.5 5. The zoom lens according to claim 2, wherein the optical element is arranged so as to satisfy the following conditional expression (6), where α is an angle formed by the stop and the optical element. [Equation 6] 5 <α <15 6. In the aspherical surface of the second lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₂₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. The zoom lens according to claim 2, wherein the following conditional expression (7) is satisfied, when ₂₉ is set. [Equation 7] 1.0 <r ₂₁ / r ₂₉ <1.3 7. In the aspherical surface of the third lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₃₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. The zoom lens according to claim 2, wherein, when set to ₃₉ , the following conditional expression (8) is satisfied. [Equation 8] 0.4 <r ₃₁ / r ₃₉ <0.7 8. In the aspherical surface of the fourth lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₄₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. The zoom lens according to claim 2, wherein the following conditional expression (9) is satisfied when ₄₉ is set. [Equation 9] 0.4 <r ₄₁ / r ₄₉ <0.9 9. The conditional expression of the following (Equation 10) is satisfied, where fw is the combined focal length of the entire system at the wide end and BF is the distance from the lens final surface to the image surface in the air. Zoom lens described in. [Equation 10] 0.3 <BF / fw <1.0 10. The radius of curvature of the surface of the first lens group that is located closest to the image plane and the radius of curvature of the surface of the second lens group that is located closest to the object side are the same. Zoom lens. 11. The zoom lens according to claim 2, wherein an infrared cut filter is arranged between the fourth lens group and the image plane, and the infrared cut filter can be arbitrarily retracted from the optical axis. 12. A first lens group having a positive refracting power, which is arranged in order from the object side toward the image plane side, and is fixed with respect to the image plane, and a negative refracting power, A second lens group that performs zooming by moving on the optical axis, an aperture stop fixed to the image plane, and a third lens group having a positive refractive power and fixed to the image plane. A lens unit, which has a positive refractive power and moves on the optical axis so as to keep the image plane, which varies with the movement of the second lens unit and an object as an object, from a reference plane at a constant position. A zoom lens including four lens groups, wherein the first lens group includes a negative lens arranged in order from the object side, a positive lens, and a positive lens having a convex surface facing the object side. The second lens group includes a negative lens sequentially arranged from the object side, and a cemented lens of a negative lens and a positive lens. At least one surface of the lens group is an aspherical surface, and the third lens group includes a positive lens and a cemented lens of a positive lens and a negative lens, which are sequentially arranged from the object side. At least one surface of which is an aspherical surface, and at least one surface of the fourth lens group is an aspherical surface.
A zoom lens comprising a positive lens, wherein at least one positive lens of the third lens group and the fourth lens group is a lens having an infrared cut characteristic. 13. The composite focal length of the first lens group is f
1, the combined focal length of the second lens group is f2,
When the combined focal length of the lens group is f3, the combined focal length of the fourth lens group is f4, and the combined focal length of the entire system at the wide end is fw, the following conditional expressions (11) to (14) are given. The zoom lens according to claim 12, which is satisfied. [Equation 11] 5.0 <f1 / fw <6.0 [Equation 12] [Equation 13] 2.5 <f3 / fw <3.5 [Equation 14] 2.5 <f4 / fw <4.0 14. The zoom lens according to claim 13, wherein at least one negative lens of the second lens group has a refractive index of 1.85 or more. 15. The zoom lens according to claim 14, wherein the lens having the infrared cut characteristic has transmittance characteristics different inside and outside of an arbitrary diameter within the lens effective diameter. 16. The zoom lens according to claim 14, wherein the aperture diameter gradually decreases from the wide end to the tele end. 17. The zoom lens according to claim 16, wherein the following conditional expression (15) is satisfied, where Dw is the aperture diameter at the wide end and Dt is the aperture diameter at the telephoto end. [Equation 15] Dw / Dt <1.5 18. In the aspherical surface of the second lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₂₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. 15. The zoom lens according to claim 14, wherein the following conditional expression (16) is satisfied when ₂₉ is set. [Equation 16] 1.0 <r ₂₁ / r ₂₉ <1.3 19. In the aspherical surface of the third lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₃₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. _15. The zoom lens according to claim 14, wherein the following conditional expression (17) is satisfied, when set to ₃₉ . [Equation 17] 0.4 <r ₃₁ / r ₃₉ <0.7 20. In the aspherical surface of the fourth lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₄₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. _15. The zoom lens according to claim 14, wherein the following conditional expression (18) is satisfied when ₄₉ is set. [Equation 18] 0.4 <r ₄₁ / r ₄₉ <0.9 21. When the combined focal length of the entire system at the wide end is fw and the distance from the final lens surface in the air to the image surface is BF, the following conditional expression (19) is satisfied. Zoom lens described in. [Formula 19] 0.3 <BF / fw <1.0 22. The radius of curvature of the surface of the first lens group located closest to the image plane and the radius of curvature of the surface of the second lens group located closest to the object are the same. Zoom lens. 23. The face plate of the image pickup device is arranged between the fourth lens group and the image plane, and an optical low-pass filter is formed on the face plate of the image pickup device. Zoom lens. 24. A first lens unit having a positive refracting power, arranged in order from the object side toward the image plane side, and fixed to the image plane; and having a negative refracting power, A second lens group that performs a zooming effect by moving on the optical axis, an aperture stop fixed to the image plane, and a third lens group having a positive refractive power and fixed to the image plane. A lens unit, which has a positive refractive power and moves on the optical axis so as to keep the image plane, which varies with the movement of the second lens unit and an object as an object, from a reference plane at a constant position. A zoom lens including four lens groups, wherein the first lens group includes a negative lens arranged in order from the object side, a positive lens, and a positive lens having a convex surface facing the object side. The second lens group includes a negative lens sequentially arranged from the object side, and a cemented lens of a negative lens and a positive lens. In addition, at least one surface of the lens group is an aspherical surface, the third lens group includes a positive lens and a negative lens sequentially arranged from the object side, and at least one surface of the lens group is an aspherical surface. The fourth lens group is composed of a cemented lens of a negative lens and a positive lens arranged in order from the object side, and at least one surface of the lens group is an aspherical surface, and the third lens group and the fourth lens group At least one of the positive lenses is a lens having an infrared cut characteristic, wherein the zoom lens is a zoom lens. 25. The combined focal length of the first lens group is f
1, the combined focal length of the second lens group is f2,
When the combined focal length of the lens group is f3, the combined focal length of the fourth lens group is f4, and the combined focal length of the entire system at the wide end is fw, the following conditional expressions (Formula 20) to (Formula 23) are given. The zoom lens according to claim 24, which is satisfied. [Equation 20] 5.0 <f1 / fw <6.0 [Equation 21] [Equation 22] 2.5 <f3 / fw <3.5 [Equation 23] 2.5 <f4 / fw <4.0 26. The zoom lens according to claim 25, wherein at least one negative lens in the second lens group has a refractive index of 1.85 or more. 27. The zoom lens according to claim 26, wherein the lens having the infrared cut characteristic has transmittance characteristics different inside and outside of an arbitrary diameter within a lens effective diameter. 28. The zoom lens according to claim 26, wherein the aperture diameter gradually decreases from the wide end to the tele end. 29. The zoom lens according to claim 28, wherein the following conditional expression (24) is satisfied, where Dw is the aperture diameter at the wide end and Dt is the aperture diameter at the telephoto end. [Equation 24] Dw / Dt <1.5 30. In the aspherical surface of the second lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₂₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. The zoom lens according to claim 26, wherein the following conditional expression (25) is satisfied when ₂₉ is set. [Equation 25] 1.0 <r ₂₁ / r ₂₉ <1.3 31. In the aspherical surface of the third lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₃₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. The zoom lens according to claim 26, wherein the following conditional expression (26) is satisfied, when set to ₃₉ . [Equation 26] 0.4 <r ₃₁ / r ₃₉ <0.7 32. In the aspherical surface of the fourth lens group, a local radius of curvature at a diameter of 10% of the lens effective diameter is r ₄₁ , and a local radius of curvature at a diameter of 90% of the lens effective diameter is r. when _49, zoom lens according to claim 26 which satisfies the following conditional expression (expression 27). [Equation 27] 0.4 <r ₄₁ / r ₄₉ <0.9 33. When the composite focal length of the entire system at the wide end is fw and the distance from the lens final surface to the image surface in air is BF, the following conditional expression (28) is satisfied. Zoom lens described in. [Equation 28] 0.3 <BF / fw <1.0 34. The radius of curvature of the surface of the first lens group located closest to the image surface and the radius of curvature of the surface of the second lens group located closest to the object are the same. Zoom lens. 35. The face plate of the image pickup device is arranged between the fourth lens group and the image plane, and an optical low-pass filter is formed on the face plate of the image pickup device. Zoom lens. 36. A video camera having a zoom lens, wherein the zoom lens according to any one of claims 1 to 35 is used as the zoom lens. 37. A digital still camera provided with a zoom lens, wherein the zoom lens is a digital still camera.
35. A digital still camera using the zoom lens according to any one of 35.