JP2007065514A - Optical system and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the manufacturing cost of a varifocal focal lens. <P>SOLUTION: The varifocal lens 1 includes, in the order starting from the object side, a first group 11 of negative refractive power, a second group 12 of positive refractive power and a third group of positive refractive power. A diaphragm 14, shifting integrally with the second group 12, is arranged on the object side of the second group 12. The focal distance is varied by changing distances between two of respective groups 11, 12 and 13. The third group 13 is comprises a single positive lens 41 made of resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical system and an image pickup apparatus including the optical system.

The optical system of the digital camera includes a first group having negative refractive power in order from the object side as a lens group, a second group having positive refractive power, and a third group having positive refractive power, There is known a variable focal length lens having an aperture that moves integrally with the second group on the object side of the second group. In the conventional variable focal length lens, an optical glass lens is also used for the third group.
JP 2003-131134 A

However, since the optical glass is expensive, it is desired to reduce the manufacturing cost by using a material other than the optical glass lens for the third group.
Further, as another problem, in a digital camera, it is necessary to make light rays as perpendicular as possible to an image pickup device (for example, a CCD), and conventionally, it has been difficult to widen a shooting angle of view. That is, if it is attempted to achieve both a wide angle of view and perpendicular incidence to the image pickup device, it becomes difficult to correct aberrations, and there are problems such as an increase in the number of lenses.
Therefore, an object of the present invention is to reduce manufacturing costs.
Another object of the present invention is to provide a compact photographic lens with good correction of various aberrations and a wide photographing range.

The invention according to claim 1 includes a first group having a negative refractive power in order as a lens group from the object side, a second group having a positive refractive power, and a third group having a positive refractive power. In the optical system having an aperture that moves integrally with the second group on the object side of the second group, and changing the focal length by changing the interval between the groups, the third group is a resin material lens. It is an optical system characterized by comprising one positive lens.
According to a second aspect of the present invention, in the optical system according to the first aspect, the first group includes a negative meniscus lens, a negative meniscus lens, and a positive lens in order from the object side, and the second group includes , Comprising a cemented lens composed of a positive lens and a negative lens and two positive lenses in order from the object, and the third group moves on the optical axis for focusing, and at least of the negative meniscus lens of the first group One surface and a surface closest to the object side of the second group have an aspherical surface.
According to a third aspect of the present invention, in the optical system according to the second aspect, the third group is a positive meniscus lens.
According to a fourth aspect of the present invention, in the optical system according to the second or third aspect, the radius of curvature of the third group on the object side is R1, the radius of curvature of the third group on the image side is R2, and the third group. When the refractive index of the group lens is N, a condition of −1.6 <(R1−R2) / (R1 + R2) × N <−0.8 is satisfied.
According to a fifth aspect of the present invention, in the optical system according to any one of the second to fourth aspects, the distance between the second group and the third group at the wide-angle end is D23w, and the focal point at the wide-angle end. When the distance is fw, the focal length of the third lens unit is f3, and the distance from the lens surface closest to the object side to the image plane at the wide-angle end is Lw, 0.005 <(D23w × fw) / (f3 × Lw) <0.01 is satisfied.
According to a sixth aspect of the present invention, in the optical system according to any one of the second to fifth aspects, the distance between the point where the principal ray having the maximum field angle intersects the aspheric surface and the optical axis is h, When the distance in the optical axis direction between the point where the spherical surface and the optical axis intersect with the point where the outermost ray of the maximum field angle intersects the aspherical surface is a, and the absolute value of the radius of curvature on the optical axis of the aspherical surface is R0 The third group has at least one aspheric surface, and satisfies the condition of 0.2 <(h ² + a ² ) / (2 × a × R 0) <1.2.

The invention according to claim 7 comprises a first group having negative refractive power in order from the object side as a lens group, a second group having positive refractive power, and a third group having positive refractive power. In the optical system having an aperture that moves integrally with the second group on the object side of the second group, and changing the focal length by changing the interval between the groups, the third group is used for focusing. Move the group on the optical axis, Wo is the angle formed by the principal ray with the largest field angle incident on the lens on the most object side at the wide-angle end, and the principal ray image with the largest field angle at the wide-angle end Satisfying the condition of 0 <(Wi × L) / (Wo × Y) <1.3, where Wi is the angle of incidence on the surface, L is the distance from the image plane to the exit pupil, and Y is the maximum image height. This is an optical system.
According to an eighth aspect of the present invention, in the optical system according to the seventh aspect, the first group includes at least two negative meniscus lenses and a positive lens in order from the object side.
The invention according to claim 9 is the optical system according to claim 8, wherein the focal length of the first group is f1, the focal length of the second group is f2, the focal length of the entire system at the wide angle end is fw, When the composite focal length of the negative meniscus lens of the first group is fN, the condition of 0.6 <(f1 × fw) / (fN × f2) <0.75 is satisfied.
According to a tenth aspect of the present invention, in the optical system according to the seventh aspect, the first group includes a negative meniscus lens, a negative meniscus lens, and a positive lens in order from the object side, and the second group includes The third lens unit is composed of a cemented lens of a positive lens and a negative lens and two positive lenses in order from the object, and the third lens group is composed of one positive lens.
The invention according to claim 11 is the optical system according to claim 10, wherein the focal length of the first group is f1, the focal length of the second group is f2, the focal length of the entire system at the wide angle end is fw, When the composite focal length of the negative meniscus lens of the first group is fN, the condition of 0.6 <(f1 × fw) / (fN × f2) <0.75 is satisfied.
According to a twelfth aspect of the present invention, in the optical system according to the tenth or eleventh aspect, at least one surface on the image side of the negative meniscus lens of the first group and the most object side surface of the second group. It has an aspherical surface.
A thirteenth aspect of the invention is an image pickup apparatus including the optical system according to any one of the first to twelfth aspects as a photographing lens.

According to the first aspect of the present invention, since the resin material lens is used in the third group which has conventionally used the optical glass lens, the manufacturing cost can be reduced.
According to the second aspect of the present invention, it is possible to realize a compact photographic lens in which three aberrations are positive and negative, the correction of various aberrations is wide, and the photographing range is wide (shortest photographing distance is short).
According to the invention described in claim 3, the image plane can be easily corrected.
According to the fourth aspect of the invention, particularly good correction can be performed.
According to the fifth aspect of the present invention, it is possible to perform good aberration correction while minimizing the increase in the total length.
According to the sixth aspect of the present invention, it is possible to suppress distortion as well as the correction of the image plane.
According to the seventh aspect of the invention, it is possible to realize a compact photographing lens in which various aberrations are corrected and the photographing range is wide.
According to the eighth and tenth aspects of the present invention, in the negative and positive three groups of variable focal length lenses, it is possible to realize a compact photographic lens that corrects various aberrations and has a wide shooting range (shortest shooting distance is short). it can.
According to the ninth and eleventh aspects of the invention, it is possible to correct aberrations satisfactorily while minimizing the increase in the total length.
According to the twelfth aspect of the present invention, it is possible to suppress distortion as well as the correction of the image plane.
According to invention of Claim 13, there exists the same effect as described in any one of Claims 1-12.

Hereinafter, the best mode for carrying out the present invention will be described.
[Embodiment 1]
FIG. 1 is a longitudinal sectional view of a variable focal length lens 1 that implements the optical system of the present invention. 1A shows the wide-angle end of the variable focal length lens 1, FIG. 1B shows the intermediate focal length, and FIG. 1C shows the telephoto end (c).
The variable focal length lens 1 includes a first group 11 having a negative refractive power, a second group 12 having a positive refractive power, and a positive refractive power in order from the object side (left side in FIG. 1) as a lens group. The third group 13 is provided, and a diaphragm 14 that moves integrally with the second group 12 is provided on the object side of the second group 12. The focal length can be changed by changing the distance between the groups 11, 12, and 13.
The first group 11 includes, in order from the object side, a negative meniscus lens 21 having a convex surface facing the object side, a negative meniscus lens 22 having a convex surface facing the object side, and a positive lens 23, and negative refraction as a whole. Has power. The second group 12 includes, in order from the object side, a cemented lens of a positive lens 31 and a negative lens 32 having an aspheric surface on the object side surface, and two positive lenses 33 and 34, and has a positive refractive power as a whole. . The third group 13 is composed of a single positive lens 41, and has a diaphragm 14 that can move with the second group 12 between the first group 11 and the second group 12, from the wide-angle end to the telephoto end. When the focal length is changed, the first group 11 moves so as to draw a concave locus toward the object side, the second group 12 moves monotonously toward the object side, and the focus from the infinity to the short distance object is the third group. 13 is moved to the object side on the optical axis. The parallel plate 15 arranged on the most image side is a filter such as a crystal low-pass filter or an infrared cut filter.
At least one surface of the negative meniscus lenses 21 and 22 of the first group 11 and the most object side surface of the second group 12 are provided with aspheric surfaces, and the positive lens 41 of the third group 13 is formed of a resin material lens. . Therefore, since the resin material lens is used for the third group 13 that has conventionally used the optical glass lens, the manufacturing cost can be reduced. Further, in the variable positive focal length lens 1 of the negative and positive three groups, it is possible to realize a compact photographing lens that corrects various aberrations and has a wide photographing range (shortest photographing distance is short).

Further, the positive lens 41 of the third group 13 has a meniscus shape. Therefore, the image plane can be easily corrected.
Further, when the curvature radius on the object side of the third group 13 is R1, the curvature radius on the image side of the third group 13 is R2, and the refractive index of the third group 13 is N,
−1.6 <(R1−R2) / (R1 + R2) × N <−0.8
Satisfy the condition. Under this condition, particularly good correction is possible.
In addition, the distance between the second group 12 and the third group 13 at the wide-angle end is D23w, the focal length at the wide-angle end is fw, the focal length of the third group 13 is f3, and the image is from the lens surface closest to the object at the wide-angle end. When the distance to the surface is Lw,
0.005 <(D23w × fw) / (f3 × Lw) <0.01
Satisfy the condition. This makes it possible to correct aberrations satisfactorily while minimizing the increase in the total length.
Here, the distance between the optical axis and the point where the principal ray with the maximum angle of view intersects the aspherical surface is h, the optical axis between the point where the aspherical surface and the optical axis intersect with the point where the outermost ray with the maximum angle of view intersects with the aspherical surface When the distance in the direction is a and the absolute value of the radius of curvature on the optical axis of the aspheric surface is R0, the third group 13 has at least one aspheric surface,
0.2 <(h ² + a ² ) / (2 × a × R 0) <1.2
Satisfy the condition. As a result, it is possible to reduce distortion as well as correction of the image plane.

[Embodiment 2]
FIG. 2 is a longitudinal sectional view of the variable focal length lens 1 that implements the optical system of the present invention. 2A shows the wide-angle end of the variable focal length lens 1, FIG. 2B shows the intermediate focal length, and FIG. 2C shows the telephoto end state.
The variable focal length lens 1 has a first group 11 having negative refractive power, a second group 12 having positive refractive power, and a positive refractive power in order from the object side (left side in FIG. 2) as a lens group. The third group 13 is provided, and a diaphragm 14 that moves integrally with the second group 12 is provided on the object side of the second group 12. The focal length can be changed by changing the distance between the groups 11, 12, and 13.
The first group 11 includes, in order from the object side, a negative meniscus lens 21 having a convex surface facing the object side, a negative meniscus lens 22 having a convex surface facing the object side, and a positive lens 23, and has a negative refractive power as a whole. It has. The second group 12 includes, in order from the object side, a cemented lens of a positive lens 31 and a negative lens 32 having an aspheric surface on the object side surface, and two positive lenses 33 and 34, and has a positive refractive power as a whole. Yes. The third group 13 includes a single positive lens 41, and has a diaphragm 14 that can move together with the second group 12 between the first group 11 and the second group 12, and the focal point from the wide-angle end to the telephoto end. When the distance changes, the first group 11 moves so as to draw a concave locus toward the object side, the second group 12 moves monotonously toward the object side, and the focusing from the infinity to the near object is the third group 13 Is moved to the object side on the optical axis. The parallel plate 15 arranged on the most image side is a filter such as a crystal low-pass filter or an infrared cut filter.
Then, Wo is the angle formed by the principal ray with the largest field angle incident on the lens on the most object side at the wide angle end and the optical axis, and the incident angle of the principal ray with the largest field angle at the wide angle end on the image plane is Wi. When the distance from the image plane to the exit pupil is L and the maximum image height is Y,
0 <(Wi × L) / (Wo × Y) <1.3
Satisfy the condition.
This conditional expression is in a range that allows both wide angle of view and normal incidence to the image sensor, and below the lower limit of the conditional expression, the exit pupil of the photographic lens is the object relative to the image sensor. It is located on the opposite side, and the loss of the light beam incident on the image sensor increases. If the upper limit of the conditional expression is exceeded, the position of the entrance pupil will be too close to the image sensor, and the loss of the light beam incident on the image sensor will be increased in the same way as when the lower limit is exceeded. Therefore, by satisfying this conditional expression, it is possible to realize a compact photographic lens with good correction of various aberrations and a wide photographing range.

The first group 11 includes at least two negative meniscus lenses 21 and 22 and a positive lens 23 in order from the object side. The second group 12 includes a positive lens 31 having an aspheric surface on the object side surface and a negative lens in order from the object side. Since it is composed of a cemented lens with the lens 32 and two positive lenses 33 and 34, and is composed of one positive lens 41, various aberrations are corrected in the variable focal length lens 1 of three negative positive and negative groups. And a compact photographing lens with a wide photographing range (shortest photographing distance is short).
In this case, the focal length of the first group 11 is f1, the focal length of the second group 12 is f2, the focal length of the entire system at the wide angle end is fw, and the combined focal length of the negative meniscus lens of the first group 11 is fN. And when
0.6 <(f1 × fw) / (fN × f2) <0.75
Satisfy the condition. This makes it possible to correct aberrations satisfactorily while minimizing the increase in the total length.
At least one surface on the image side of the negative meniscus lenses 21 and 22 of the first group 11 and the most object side surface of the second group 12 have aspheric surfaces. As a result, it is possible to suppress distortion as well as image surface correction.

[Embodiment 3]
Next, a digital camera 111 that is an imaging apparatus incorporating the variable focal length lens 1 of Embodiment 1 or 2 as a photographing lens will be described.
FIG. 3 is a block diagram of electrical connection of the digital camera 111, and FIG. 4 is an external perspective view of the digital camera 111.
The digital camera 111 has a photographing lens 112 (variable focal length lens 1) and a light receiving element (area sensor) 113, and is configured to read an image of a photographing object formed by the photographing lens 112 on the light receiving element 113. ing.
The output from the light receiving element 113 is processed by the signal processing device 115 under the control of the central processing unit 114 and converted into digital information. The image information digitized by the signal processing device 115 is subjected to predetermined image processing in the image processing device 116 controlled by the central processing unit 114 and then recorded in the semiconductor memory 117. An image being captured can be displayed on the liquid crystal monitor 118, and an image recorded in the semiconductor memory 117 can be displayed. The image recorded in the semiconductor memory 117 can be transmitted to the outside using the communication card 119 or the like.

When the digital camera 111 is carried, the photographing lens 112 is in a retracted state as shown in FIG. 4A. When the user operates the power switch 122 to turn on the power, the lens barrel 121 is shown in FIG. 4B. Is paid out. At this time, each group of the photographic lens 112 that is a zoom lens inside the lens barrel 121 has, for example, a short focal end arrangement, and the arrangement of each group changes by operating the zoom lever to the long focal end. Zooming can be performed. At this time, the viewfinder 120 also zooms in conjunction with the change in the angle of view of the taking lens.
Focusing is performed by half-pressing the shutter button 124. When the shutter button 124 is further pressed, shooting is performed, and thereafter, the processing described above is performed.
When the image recorded in the semiconductor memory 117 is displayed on the liquid crystal monitor 125 or transmitted to the outside using the communication card 119 or the like, the operation button 126 is used. The semiconductor memory 117 and the communication card 119 are inserted into dedicated or general-purpose slots 127 for use. Reference numeral 128 denotes a flash, and reference numeral 129 denotes a zoom lever.

<Example>
[Example 1]
This example corresponds to the first embodiment. FIG. 5A is an aberration diagram at the wide-angle end, FIG. 5B is an aberration diagram at the intermediate focal length, and FIG. 5C is an aberration diagram at the telephoto end.

[Example 2]
This example corresponds to the first embodiment. FIG. 6A is an aberration diagram at the wide-angle end of this example, FIG. 6B is an aberration diagram at an intermediate focal length, and FIG. 6C is an aberration diagram at the telephoto end.

[Example 3]
This example corresponds to the first embodiment. FIG. 7A is an aberration diagram at the wide-angle end, FIG. 7B is an aberration diagram at an intermediate focal length, and FIG. 7C is an aberration diagram at the telephoto end.

[Example 4]
This example corresponds to the first embodiment. FIG. 8A is an aberration diagram at the wide-angle end of this example, FIG. 8B is an aberration diagram at the intermediate focal length, and FIG. 8C is an aberration diagram at the telephoto end.

[Example 5]
This example corresponds to the second embodiment. FIG. 9A is an aberration diagram at the wide-angle end of this example, FIG. 9B is an aberration diagram at the intermediate focal length, and FIG. 9C is an aberration diagram at the telephoto end.

[Example 6]
This example corresponds to the second embodiment. FIG. 10A is an aberration diagram at the wide-angle end, FIG. 10B is an aberration diagram at the intermediate focal length, and FIG. 10C is an aberration diagram at the telephoto end.

[Example 7]
This example corresponds to the second embodiment. FIG. 11A is an aberration diagram at the wide-angle end of this example, FIG. 11B is an aberration diagram at the intermediate focal length, and FIG. 11C is an aberration diagram at the telephoto end.

2 is a longitudinal sectional view of a variable focal length lens according to Embodiment 1. FIG. 6 is a longitudinal sectional view of a variable focal length lens according to Embodiment 2. FIG. FIG. 6 is a block diagram illustrating electrical connections of a digital camera according to a third embodiment. 6 is an external perspective view of a digital camera according to Embodiment 3. FIG. FIG. 4 is an aberration diagram at the wide-angle end of Example 1. FIG. 6 is an aberration diagram at the wide-angle end of Example 2. FIG. 6 is an aberration diagram at the wide-angle end of Example 3. FIG. 6 is an aberration diagram at the wide-angle end of Example 4. FIG. 10 is an aberration diagram at the wide-angle end of Example 5. FIG. 10 is an aberration diagram at the wide angle end according to Example 6. FIG. 10 is an aberration diagram at the wide angle end according to Example 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical system 11 1st group 12 2nd group 13 3rd group 14 Diaphragm 111 Imaging device

Claims (13)

A first group having a negative refractive power in order from the object side as a lens group, a second group having a positive refractive power, and a third group having a positive refractive power are provided on the object side of the second group. In an optical system having a diaphragm that moves integrally with the second group and changing the focal length by changing the interval between the groups,
The third group includes one positive lens made of a resin material lens. The first group includes a negative meniscus lens, a negative meniscus lens, and a positive lens in order from the object side.
The second group includes a cemented lens of a positive lens and a negative lens and two positive lenses in order from the object,
The third group moves on the optical axis for focusing,
The optical system according to claim 1, wherein at least one surface of the negative meniscus lens of the first group and an object-side surface of the second group have aspheric surfaces.   The optical system according to claim 2, wherein the third group is a positive meniscus lens. When the radius of curvature on the object side of the third group is R1, the radius of curvature on the image side of the third group is R2, and the refractive index of the third group lens is N,
−1.6 <(R1−R2) / (R1 + R2) × N <−0.8
The optical system according to claim 2, wherein the following condition is satisfied. The distance between the second group and the third group at the wide angle end is D23w, the focal length at the wide angle end is fw, the focal length of the third group is f3, and from the lens surface closest to the object side to the image plane at the wide angle end. When the distance of is Lw,
0.005 <(D23w × fw) / (f3 × Lw) <0.01
The optical system according to any one of claims 2 to 4, wherein the following condition is satisfied. The distance in the optical axis direction between the point where the principal ray of the maximum field angle intersects the aspheric surface and the optical axis is h, and the point where the aspheric surface intersects the optical axis and the point where the outermost ray of the maximum field angle intersects the aspheric surface Is a, and the absolute value of the radius of curvature on the optical axis of the aspherical surface is R0,
The third group has at least one aspheric surface;
0.2 <(h ² + a ² ) / (2 × a × R 0) <1.2
The optical system according to claim 2, wherein the following condition is satisfied. A first group having a negative refractive power in order from the object side as a lens group, a second group having a positive refractive power, and a third group having a positive refractive power are provided on the object side of the second group. In an optical system having a diaphragm that moves integrally with the second group and changing the focal length by changing the interval between the groups,
Moving the third group on the optical axis for focusing;
The angle formed by the principal ray with the largest field angle incident on the lens on the most object side at the wide-angle end and the optical axis is Wo, and the incident angle on the image plane of the principal ray with the largest field angle at the wide-angle end is denoted by Wi. When the distance from the surface to the exit pupil is L and the maximum image height is Y,
0 <(Wi × L) / (Wo × Y) <1.3
An optical system characterized by satisfying the above condition.   The optical system according to claim 7, wherein the first group includes at least two negative meniscus lenses and a positive lens in order from the object side. When the focal length of the first group is f1, the focal length of the second group is f2, the focal length of the entire system at the wide-angle end is fw, and the combined focal length of the negative meniscus lens of the first group is fN ,
0.6 <(f1 × fw) / (fN × f2) <0.75
The optical system according to claim 8, wherein the following condition is satisfied. The first group includes a negative meniscus lens, a negative meniscus lens, and a positive lens in order from the object side.
The second group includes a cemented lens of a positive lens and a negative lens and two positive lenses in order from the object,
The optical system according to claim 7, wherein the third group includes a single positive lens. When the focal length of the first group is f1, the focal length of the second group is f2, the focal length of the entire system at the wide-angle end is fw, and the combined focal length of the negative meniscus lens of the first group is fN ,
0.6 <(f1 × fw) / (fN × f2) <0.75
The optical system according to claim 10, wherein the following condition is satisfied.   12. The optical system according to claim 10, wherein at least one surface on the image side of the negative meniscus lens of the first group and an object-side surface of the second group have aspheric surfaces.   An imaging apparatus comprising the optical system according to any one of claims 1 to 12 as a photographing lens.

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