Zoom lens and image pickup apparatus using the same

A zoom lens, which changes a magnification by properly changing distances between a plurality of lens components, has, in order from the object side, a first lens component with positive power, a second lens component with negative power, a third lens component with positive power, a fourth lens component with positive power, and a fifth lens component with positive power, and the first lens component has a reflecting member changing an optical path. The zoom lens satisfies the following conditions:1.6<β2(t)/β2(w)<10.03.3<β4(t)/β4(w)<10.0where β2(t) is a lateral magnification of the second lens component in a telephoto position in infinite focusing, β2(w) is a lateral magnification of the second lens component in a wide-angle position in infinite focusing, β4(t) is a lateral magnification of the fourth lens component in the telephoto position in infinite focusing, and β4(w) is a lateral magnification of the fourth lens component in the wide-angle position in infinite focusing.

This application claims benefits of Japanese Patent Application No. 2008-039164 filed in Japan on Feb. 20, 2008, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a zoom lens suitable for compact digital still cameras or digital video cameras (which are hereinafter generically called digital cameras) and an image pick up apparatus provided with this zoom lens and an image sensor.

2. Description of the Related Art

It has been required that the zoom lens adopted to the digital camera is wide in angle of view, high in magnification, and compact in design. As a zoom lens satisfying such requirements, a zoom lens which includes, in order from the object side, a first lens component with positive power, a second lens component with negative power, a third lens component with positive power, a fourth lens component with positive power, and a fifth lens component with positive power and in which the first lens component has a prism for changing an optical path is known, and an example of this zoom lens is disclosed in Japanese Patent Kokai No. 2004-347712. Use of such a zoom lens realizes a variable magnification ratio of about 3 and favorable optical properties, and makes it possible to attain a slim design of a digital camera provided with the zoom lens.

SUMMARY OF THE INVENTION

A zoom lens according to the present invention, which changes a magnification by properly changing distances between a plurality of lens components, is characterized in that the zoom lens comprises, in order from the object side, a first lens component with positive power, a second lens component with negative power, a third lens component with positive power, a fourth lens component with positive power, and a fifth lens component with positive power; the first lens component has a reflecting member of changing an optical path; and the zoom lens satisfies the following conditions (1) and (2):
1.6<β2(t)/β2(w)<10.0  (1)
3.3<β4(t)/β4(w)<10.0  (2)
where β2(t) is a lateral magnification of the second lens component in a telephoto position in infinite focusing, β2(w) is a lateral magnification of the second lens component in a wide-angle position in infinite focusing, β4(t) is a lateral magnification of the fourth lens component in a telephoto position in infinite focusing, and β4(w) is a lateral magnification of the fourth lens component in a wide-angle position in infinite focusing.

The zoom lens according to the present invention preferably satisfies the following condition (3):
0.3<|φ4/φ2|<0.7  (3)
where φ2is a power of the second lens component, and φ4is a power of the fourth lens component.

In the zoom lens according to the present invention, the reflecting member is preferably a prism, and the zoom lens preferably satisfies the following condition (4):
1<Dp/ihw<5  (4)
where Dpis a length of the prism on the optical axis, and ihwis an image height in a wide-angle position.

In the zoom lens according to the present invention, the first lens component preferably comprises, in order from the objective side, a first lens component with negative power, a reflecting member of changing an optical path, and a second lens component with positive power.

The zoom lens according to the present invention preferably satisfies the following conditions (5) and (6) when the first lens component has the first lens element with negative power located at the most object-side position:
1.95<nd1<2.1  (5)
18<vd1<30  (6)
where nd1is the refractive index of the first lens element with negative power in the first lens component, and vd1is the Abbe's number of the first lens element with negative power in the first lens component.

The zoom lens according to the present invention preferably satisfies the following conditions (7):
3.5<ft/fw<7.0  (7)
where fwis the focal length of the entire zoom lens system in a wide-angle position, and ftis the focal length of the entire zoom lens system in a telephoto position.

In the zoom lens according to the present invention, a positive lens element of the third lens component preferably comprises a single lens.

The image pickup apparatus according to the present invention is provided with the above zoom lens and a circuit electrically correcting distortion and/or chromatic aberration of magnification.

The present invention can offer a zoom lens which is small, has a high variable magnification ratio of about 5 to 7, and has excellent optical properties with respect to on-axis and off-axis aberrations. The present invention also offers an image pickup apparatus using the zoom lens.

These and other features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments when taken in conjunction with accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before undertaking the description of the embodiments of a zoom lens according to the present invention and an image pickup apparatus using the same, the function and effect by each constitution will be explained.

A zoom lens according to the present invention has, in order from the object side, a first lens component with positive power, a second lens component with negative power, a third lens component with positive power, a fourth lens component with positive power, and a fifth lens component with positive power. The zoom lens is designed in such a way that a magnification is changed by properly changing distances between the lens components, and the second and fourth lens components are mainly moved along the optical axis in changing the magnification.

In such an arrangement of the zoom lens, burdens on the second and fourth lens components in the magnification change must be properly related to each other. For example, when the burden on the second lens component is heavy in the magnification change, power and the amount of movement of the second lens component must be increased in order to secure a variable magnification ratio. However, such a large power of the second lens component is liable to mainly cause off-axis aberration. In addition, as a result of the increase of the amount of movement of the second lens component, air spacing between the second and third lens components must be increased in a wide-angle position, and the diameter of the first lens component becomes large.

Similarly, when the burden on the fourth lens component is heavy in the magnification change, power and the amount of movement of the fourth lens component must be increased in order to secure a variable magnification ratio. However, such a large power of the fourth lens component is liable to mainly cause on-axis aberration. In addition, as a result of the increase of the amount of movement of the fourth lens component, air spacing between the third and fourth lens components must be increased in the wide-angle position, and the total length also becomes large.

For this reason, a zoom lens according to the present invention is designed to satisfy the following conditions (1) and (2):
1.6<β2(t)/β2(w)<10.0  (1)
3.3<β4(t)/β4(w)<10.0  (2)
where β2(t) is a lateral magnification of the second lens component at a telephoto position in infinite focusing, β2(w) is a lateral magnification of the second lens component at a wide-angle position in infinite focusing, β4(t) is a lateral magnification of the fourth lens component at a telephoto position in infinite focusing, and β4(w) is a lateral magnification of the fourth lens component at a wide-angle position in infinite focusing.

The conditions (1) and (2) show a relation between lateral magnifications of the second and fourth lens components in changing a magnification from the wide-angle position to the telephoto position. If the zoom lens satisfies both of these conditions together, it is possible to avoid excessive burdens of the second and fourth lens components in a variable magnification. If the ratio β2(t)/β2(w) is below the lower limit of the condition (1) or the ratio β4(t)/β4(w) is below the lower limit of the condition (2), since burden sharing of one lens component in a variable magnification remarkably becomes light, the other lens component must be given a large variable magnification function. This case causes necessity to increase the amount of movement of the lens component given a large burden sharing in a variable magnification or to strengthen power of the lens component, and leads to an increase of the total length and occurrence of various off-axis or on-axis aberrations. Similarly, If the ratio β2(t)/β2(w) is beyond the upper limit of the condition (1) or the ratio β4(t)/β4(w) is beyond the upper limit of the condition (2), a variable magnification function of one lens component becomes too strong, causing an increase of the total length and producing various off-axis or on-axis aberrations. In addition, a diameter of a lens of the lens component becomes large.

The zoom lens according to the present invention is more preferably designed to satisfy the following condition (1)′ or (1)″ instead of the condition (1):
1.7<β2(t)/β2(w)<6.0  (1)′
1.9<β2(t)/β2(w)<3.0  (1)″

In addition, the upper limit or lower limit of the condition (1) may be replaced with the upper limit or lower limit of the condition (1)′ or (1)″, respectively. The upper limit or lower limit of the condition (1)′ may be replaced with the upper limit or lower limit of the condition (1) or (1)″, respectively.

The zoom lens according to the present invention is more preferably designed to satisfy the following condition (2)′ or (2)″ instead of the condition (2):
3.4<β4(t)/β4(w)<7.0  (2)′
3.5<β4(t)/β4(w)<5.0  (2)″

In addition, the upper limit or lower limit of the condition (2)′ may be replaced with the upper limit or lower limit of the condition (2) or (2)″, respectively. The upper limit or lower limit of the condition (2)″ may be replaced with the upper limit or lower limit of the condition (2) or (2)′, respectively.

The zoom lens according to the present invention is designed so that the first lens component has a reflecting member which change an optical path. The zoom lens according to the present invention is capable of changing an optical path in the first lens component, and is capable of attaining a slim design with respect to the direction along the optical axis of incidence even though the other lens components are moved to change the magnification, because such a constitution is adopted.

The zoom lens according to the present invention preferably satisfies the following condition (3):
0.3<|φ4/φ2|<0.7  (3)
where φ2is a power of the second lens component, and φ4is a power of the fourth lens component.

The condition (3) is a condition regarding a share of power between the second and fourth lens components which are responsible for a variable magnification. If |φ4/φ2| is below the lower limit of the condition (3) or beyond the upper limit of the condition (3), since power of one lens component becomes too increased, a large on-axis or off-axis aberration is easy to occur.

The zoom lens according to the present invention is more preferably designed to satisfy the following condition (3)′ or (3)″ instead of the condition (3):
0.35<|φ4/φ2|<0.65  (3)′
0.39<|φ4/φ2|<0.61  (3)″

In addition, the upper limit or lower limit of the condition (3)′ may be replaced with the upper limit or lower limit of the condition (3) or (3)″, respectively. The upper limit or lower limit of the condition (3)″ may be replaced with the upper limit or lower limit of the condition (3) or (3)′, respectively.

In the zoom lens according to the present invention, the reflecting member is preferably a prism, and the zoom lens preferably satisfies the following condition (4):
1<Dp/ihw<5  (4)
where Dpis a length of the prism on the optical axis, and ihwis an image height at a wide-angle position.

The condition (4) is a condition for arranging the prism, which changes an optical path, in the zoom lens without difficulty. If Dp/ihwis below the lower limit of the condition (4), the amount of ambient light remarkably decreases, which is unfavorable. On the other hand, if Dp/ihwis beyond the upper limit of the condition (4), the total length becomes long.

The zoom lens according to the present invention is more preferably designed to satisfy the following condition (4)′ or (4)″ instead of the condition (4):
1.5<Dp/ihw<4  (4)′
2.5<Dp/ihw<3.5  (4)″

In addition, the upper limit or lower limit of the condition (4)′ may be replaced with the upper limit or lower limit of the condition (4) or (4)″, respectively. The upper limit or lower limit of the condition (4)″ may be replaced with the upper limit or lower limit of the condition (4) or (4)′, respectively.

In the zoom lens according to the present invention, the first lens component preferably has, in order from the object side, a first lens element with negative power, a reflecting member which changes an optical path, and a second lens element with positive power. This constitution makes the effective diameter small, and an aberration, especially an off-axis aberration in wide-angle position, is easily corrected well with the first lens component having sufficient power.

The zoom lens according to the present invention preferably satisfies the following conditions (5) and (6):
1.95<nd1<2.1  (5)
18<vd1<30  (6)
where nd1is the refractive index of the first lens element with negative power in the first lens component, and vd1is the Abbe's number of the first lens element with negative power in the first lens component.

The conditions (5) and (6) define a condition for suppressing an aberration and for shortening the total length of the zoom lens while securing the power of the negative lens element located at the most object-side position in the first lens component. If nd1is below the lower limit of the condition (5), the radius of curvature of the negative lens element located at the most object-side position in the first lens component becomes small, and an off-axis aberration is easy to occur. On the other hand, if nd1is beyond the upper limit of the condition (5), it becomes hard to get a glass material for making the negative lens element located at the most object-side position in the first lens component, which leads to a raise in cost and deterioration of a mass productivity. If vd1is below the lower limit of the condition (6) or beyond the upper limit of the condition (6) with the condition (5) satisfied, it becomes hard to get a glass material for making the negative lens element located at the most object-side position in the first lens component, which leads to a raise in cost and deterioration of a mass productivity.

The zoom lens according to the present invention preferably satisfies the following conditions (7):
3.5<ft/fw<7.0  (7)
where fwis the focal length of the entire zoom lens system in a wide-angle position, and ftis the focal length of the entire zoom lens system in a telephoto position.

The condition (7) is a condition regarding a variable magnification ratio. If ft/fwis beyond the upper limit of the condition (7), the total length is apt to be increase in the wide-angle position and in the telephoto position. If ft/fwis below the lower limit of the condition (7), a desired variable magnification cannot be obtained. In the zoom lens according to the present invention, the lens element with positive power in the third lens component consists of a single lens. This constitution easily prevents increase of the total length of the third lens component and the zoom lens, and easily contributes to cost cut.

In the zoom lens according to the present invention, it is preferable that the total length dose not change and an aperture stop does not move in changing the magnification. Since such a constitution makes the number of driving parts in the zoom lens decrease, the zoom lens becomes easy to be produced.

An image pickup apparatus according to the present invention is designed to have the above zoom lens and a circuit electrically correcting a distortion and/or chromatic aberration of magnification. Such a constitution, which is capable of accepting a distortion in the zoom lens, reduces the number of lenses in the zoom lens and makes it easy to downsize the zoom lens. In addition, an electric correction of a chromatic aberration of magnification makes it possible to reduce color blur in a photographed image and makes an improvement in resolving power.

The embodiments 1 to 4 according to the present invention will be explained below with the diagrams referred to.

Subscript numerals in r1, r2, . . . and d1, d2, . . . in cross sectional views of the optical system in the diagrams correspond to surface numbers, 1, 2, . . . in numerical data, respectively. In views showing aberration curves, ΔM in views of astigmatism denotes astigmatism in a meridional surface, and ΔS in views of astigmatism denotes astigmatism in a sagittal surface. In this case, a meridional surface is a surface in which the optical axis of an optical system and a principal ray are included (, or a surface parallel to the surface of a paper sheet). A sagittal surface is a surface perpendicular to a surface in which the optical axis of an optical system and a principal ray are included (, or a surface perpendicular to the surface of a paper sheet).

In the numerical data for lenses in each of the following embodiments, R denotes the radius of curvature of each surface, D denotes spacing between the surfaces, Nd denotes the refractive index relating to the d line, vd denotes the Abbe's number relating to the d line, K denotes a conic constant, and A4, A6, A8, and A10denote an aspherical coefficient. In addition, the configuration of each aspherical surface is expressed by the following equation with aspherical coefficients for each embodiment:
Z=(Y2/r)/[1+{1−(1+K)(Y/r)2}1/2]+A4Y4+A6Y6+A8Y8+A10Y10+ . . .
where, Z is taken as a coordinate in the direction along the optical axis, and Y is taken as a coordinate in the direction perpendicular to the optical axis.

First Embodiment

FIGS. 1A,1B, and1C are cross sectional views showing optical arrangements, developed along the optical axis, in wide-angle, middle, and telephoto positions, respectively, in infinite object point focusing of the zoom lens according to the first embodiment of the present invention.FIGS. 2A-2D,2E-2H, and21-2L are diagrams showing aberration characteristics in wide-angle, middle, and telephoto positions respectively, in infinite objective point focusing of the zoom lens shown inFIGS. 1A-1C.

First, the optical arrangement according to the first embodiment will be explained withFIGS. 1A,1B, and1C. A zoom lens according to the present embodiment comprises, in order from the object side, a first lens component G1with positive power, a second lens component G2with negative power, a third lens component G3with positive power, a fourth lens component G4with positive power, and a fifth lens component G5with positive power, and the lens components are arranged on the optical axis Lc. An aperture stop S, which is integrated with the lens component G3, is arranged between the lens component G3and the lens component G4. A low-pass filter LF, a CCD cover grass CG, and a CCD with an imaging plane IM are arranged in this order from the object side on the image side of the fifth lens component G5.

The first lens component G1comprises: a first lens element L11which is a biconcave lens and has negative power; a prism P which is a reflecting member of changing an optical path; and a second lens element L12which has positive power and is a biconvex lens whose both surfaces are aspherical. The lens elements L11, the prism P, and the lens element L12are arranged in this order from the object side.

The second lens component G2comprises: a first lens element L21which has negative power and is a biconcave lens whose both surfaces are aspherical; and a cemented lens consisting of a second lens element L22which is a biconvex lens and has positive power and a third lens element L23which is a biconcave lens and has negative power. The lens elements L21, L22, and L23are arranged in this order from the object side.

The third lens component G3comprises only a lens element L3with positive power. The lens element L3is a meniscus lens whose both surfaces are aspherical and whose convex surface faces to the object side.

The fourth lens component G4comprises: a fourth lens element L41which has positive power and is a biconvex lens whose both surfaces are aspherical; and a cemented lens consisting of a second lens element L42which is a biconvex lens and has positive power and a third lens element L43which is a biconcave lens and has negative power.

The fifth lens component G5comprises only a lens element L5with positive power. The lens element L5is a meniscus lens whose convex surface faces to the object side.

In changing a magnification from the wide-angle position to the telephoto position, the first lens component G1does not move on the optical axis Lc. The second lens component G2moves to the image side on the optical axis Lc with a distance between the first lens component G1and the second lens component G2being widen. The third lens component G3does not move on the optical axis Lc. The fourth lens component G4moves to the object side on the optical axis Lc with a distance between the third lens component G3and the fourth lens component G4being narrowed. The fifth lens component G5moves on the optical axis Lc in such a way that a distance between the fourth lens component G4and the fifth lens component G5is widen. The aperture stop S does not move on the optical axis Lc because the aperture stop S is integrated with the lens component G3.

The lens arrangement and the numerical data of the first embodiment according to the present invention are as follows, where a unit of length used in the data is millimeter (mm), R denotes a radius of curvature, D denotes a spacing between surfaces, Nd denotes a refractive index, vd denotes the Abbe's number, K denotes a conic constant, and A4, A6, A8, and A10denote aspherical coefficients:

Subsequently, an image pickup apparatus having a zoom lens according to the present invention will be explained in the case that the apparatus has a circuit of electrically correcting distortion. In the zoom lens for the image pickup apparatus according to the present embodiment, barrel distortion occurs on a photoelectric conversion surface of a CCD in the wide-angle position. On the other hand, such a distortion does not occur too much around the middle position and in the telephoto position. For this reason, the image pickup apparatus with a zoom lens according to the present invention is designed in such a way that an effective imaging region is formed into a barrel shape in the wide-angle position and is formed into a rectangular shape around the middle position and in the telephoto position in order to correct distortion. Barrel-shaped image data obtained in the wide-angle position is converted into rectangle-shaped image information in which distortion is reduced, by an electric image processing, and the image information is recorded or indicated.

The image pickup apparatus according to the present invention is designed in such a way that the image height in the wide-angle position is smaller than the image height around the middle position and in the telephoto position. In addition, the image pickup apparatus according to the present invention is designed in such a way that the short sides of the photoelectric conversion surface are as long as the short sides of the effective imaging region, and the effective imaging region is defined in such a way that distortion of about −3% remains after an image processing. Naturally, an effective imaging region that is smaller than the above effective imaging region may be defined to use an image which is converted into rectangle as an image for record or a playback.

Numerical data in the first embodiment in the case that distortion is electrically corrected are as follows, where data which are not shown below have the same value as the above data in the case that distortion is not electrically corrected, and a unit of length used in the data is millimeter (mm):

Second Embodiment

FIGS. 3A,3B, and3C are cross sectional views showing optical arrangements, developed along the optical axis, in wide-angle, middle, and telephoto positions, respectively, in infinite object point focusing of the zoom lens according to the second embodiment of the present invention.FIGS. 4A-4D,4E-4H, and4I-4L are diagrams showing aberration characteristics in wide-angle, middle, and telephoto positions respectively, in infinite objective point focusing of the zoom lens shown inFIGS. 3A-3C.

First, the optical arrangement according to the second embodiment will be explained withFIGS. 3A,3B, and3C. A zoom lens according to the present embodiment comprises, in order from the object side, a first lens component G1with positive power, a second lens component G2with negative power, a third lens component G3with positive power, a fourth lens component G4with positive power, and a fifth lens component G5with positive power, and the lens components are arranged on the optical axis Lc. An aperture stop S, which is integrated with the lens component G3, is arranged between the lens component G3and the lens component G4. A low-pass filter LF, a CCD cover grass CG and a CCD with an imaging plane IM are arranged in this order from the object side on the image side of the fifth lens component G5.

The first lens component G1comprises: a first lens element L11which is a biconcave lens and has negative power; a prism P which is a reflecting member of changing an optical path; and a second lens element L12which has positive power and is a biconvex lens whose both surfaces are aspherical. The lens elements L11, the prism P, and the lens element L12are arranged in this order from the object side.

The second lens component G2comprises: a first lens element L21which has negative power and is a biconcave lens whose both surfaces are aspherical; and a cemented lens consisting of a second lens element L22which is a biconvex lens and has positive power and a third lens element L23which is a biconcave lens and has negative power. The lens elements L21, L22, and L23are arranged in this order from the object side.

The third lens component G3comprises only a lens element L3with positive power. The lens element L3is a meniscus lens whose both surfaces are aspherical and whose convex surface faces to the object side.

The fourth lens component G4comprises: a fourth lens element L41which has positive power and is a biconvex lens whose both surfaces are aspherical; a cemented lens consisting of a second lens element L42which is a biconvex lens and has positive power and a third lens element L43which is a biconcave lens and has negative power; and a lens element L44which has negative power, where the lens element L44is a meniscus lens whose convex surface faces to the object side.

The fifth lens component G5comprises only a lens element L5which is a biconvex lens and has positive power.

In changing a magnification from the wide-angle position to the telephoto position, the first lens component G1does not move on the optical axis Lc. The second lens component G2moves to the image side on the optical axis Lc with a distance between the first lens components G1and the second lens component G2being widen. The third lens component G3does not move on the optical axis Lc. The fourth lens component G4moves to the object side on the optical axis Lc with a distance between the third lens component G3and the fourth lens component G4being narrowed. The fifth lens component G5moves on the optical axis Lc in such a way that a distance between the fourth lens component G4and the fifth lens component G5is widen. The aperture stop S does not move on the optical axis Lc because the aperture stop S is integrated with the lens component G3.

The lens arrangement and the numerical data of the second embodiment according to the present invention are as follows, where a unit of length used in the data is millimeter (mm), R denotes a radius of curvature, D denotes a spacing between surfaces, Nd denotes a refractive index, vd denotes the Abbe's number, K denotes a conic constant, and A4, A6, A8, and A10denote aspherical coefficients:

Numerical data in the second embodiment in the case that distortion is electrically corrected are as follows, where data which are not shown below have the same value as the above data in the case that distortion is not electrically corrected, and a unit of length used in the data is millimeter (mm):

Third Embodiment

FIGS. 5A,5B, and5C are cross sectional views showing optical arrangements, developed along the optical axis, in wide-angle, middle, and telephoto positions, respectively, in infinite object point focusing of the zoom lens according to the third embodiment of the present invention.FIGS. 6A-6D,6E-6H, and6I-6L are diagrams showing aberration characteristics in wide-angle, middle, and telephoto positions respectively, in infinite objective point focusing of the zoom lens shown inFIGS. 5A-5C.

First, the optical arrangement according to the third embodiment will be explained withFIGS. 5A,5B, and5C. A zoom lens according to the present embodiment comprises, in order from the object side, a first lens component G1with positive power, a second lens component G2with negative power, a third lens component G3with positive power, a fourth lens component G4with positive power, and a fifth lens component G5with positive power, and the lens components are arranged on the optical axis Lc. An aperture stop S, which is integrated with the lens component G3, is arranged between the lens component G3and the lens component G4. A low-pass filter LF, a CCD cover grass CG, and a CCD with an imaging plane IM are arranged in this order from the object side on the image side of the fifth lens component G5.

The first lens component G1comprises: a first lens element L11which is a biconcave lens and has negative power; a prism P which is a reflecting member of changing an optical path; and a second lens element L12which has positive power and is a biconvex lens whose both surfaces are aspherical. The lens elements L11, the prism P, and the lens element L12are arranged in this order from the object side.

The second lens component G2comprises: a first lens element L21which has negative power and is a biconcave lens whose both surfaces are aspherical; and a cemented lens consisting of a second lens element L22which is a biconvex lens and has positive power and a third lens element L23which is a biconcave lens and has negative power. The lens elements L21, L22, and L23are arranged in this order from the object side.

The third lens component G3comprises only a lens element L3with positive power. The lens element L3is a meniscus lens whose both surfaces are aspherical and whose convex surface faces to the object side.

The fourth lens component G4comprises: a fourth lens element L41which has positive power and is a biconvex lens whose both surfaces are aspherical; a cemented lens consisting of a second lens element L42which is a biconvex lens and has positive power and a third lens element L43which is a biconcave lens and has negative power; and a lens element L44which has negative power, where the lens element L44is a meniscus lens whose convex surface faces to the object side.

The fifth lens component G5comprises only a lens element L5which is a biconvex lens and has positive power.

In changing a magnification from the wide-angle position to the telephoto position, the first lens component G1does not move on the optical axis Lc. The second lens component G2moves to the image side on the optical axis Lc with a distance between the first lens components G1and the second lens component G2being widen. The third lens component G3reciprocates on the optical axis Lc in such a way that the third lens component G3first moves to the image side with a distance between the second lens component G2and then the third lens component G3being narrowed and then the third lens component G3moves to the object side. The fourth lens component G4moves to the object side on the optical axis Lc with a distance between the third lens component G3and the fourth lens component G4being narrowed. The fifth lens component G5moves on the optical axis Lc in such a way that a distance between the fourth lens component G4and the fifth lens component G5is widen. The aperture stop S does not move on the optical axis Lc because the aperture stop S is integrated with the lens component G3.

The lens arrangement and the numerical data of the third embodiment according to the present invention are as follows, where a unit of length used in the data is millimeter (mm), R denotes a radius of curvature, D denotes a spacing between surfaces, Nd denotes a refractive index, vd denotes the Abbe's number, K denotes a conic constant, and A4, A6, A8, and A10denote aspherical coefficients:

Numerical data in the third embodiment in the case that distortion is electrically corrected are as follows, where data which are not shown below have the same value as the above data in the case that distortion is not electrically corrected, and a unit of length used in the data is millimeter (mm):

Fourth Embodiment

FIGS. 7A,7B, and7C are cross sectional views showing optical arrangements, developed along the optical axis, in wide-angle, middle, and telephoto positions, respectively, in infinite object point focusing of the zoom lens according to the fourth embodiment of the present invention.FIGS. 8A-8D,8E-8H, and81-8L are diagrams showing aberration characteristics in wide-angle, middle, and telephoto positions respectively, in infinite objective point focusing of the zoom lens shown inFIGS. 7A-7C.

First, the optical arrangement according to the fourth embodiment will be explained withFIGS. 7A,7B, and7C. A zoom lens according to the present embodiment comprises, in order from the object side, a first lens component G1with positive power, a second lens component G2with negative power, a third lens component G3with positive power, a fourth lens component G4with positive power, and a fifth lens component G5with positive power, and the lens components are arranged on the optical axis Lc. An aperture stop S, which is integrated with the lens component G3, is arranged between the lens component G3and the lens component G4. A low-pass filter LF, a CCD cover grass CG, and a CCD with an imaging plane IM are arranged in this order from the object side on the image side of the fifth lens component G5.

The first lens component G1comprises: a first lens element L11which has negative power and is a plano-concave lens whose image-side surface is aspherical and whose concave surface faces to the image side; a prism P which is a reflecting member of changing an optical path; and a second lens element L12which has positive power and is a biconvex lens whose both surfaces are aspherical. The lens elements L11, the prism P, and the lens element L12are arranged in this order from the object side.

The second lens component G2comprises: a first lens element L21which has negative power and is a biconcave lens whose object-side surface is aspherical; and a cemented lens consisting of a second lens element L22which is a biconvex lens and has positive power and a third lens element L23which is a biconcave lens and has negative power. The lens elements L21, L22, and L23are arranged in this order from the object side.

The third lens component G3comprises only a lens element L3with positive power. The lens element L3is a meniscus lens whose object-side surface is aspherical and whose convex surface faces to the object side.

The fourth lens component G4comprises: a fourth lens element L41which has positive power and is a biconvex lens whose both surfaces are aspherical; a cemented lens consisting of a second lens element L42which is a biconvex lens and has positive power and a third lens element L43which is a biconcave lens and has negative power.

The fifth lens component G5comprises only a lens element L5which is a biconvex lens and has positive power.

In changing a magnification from the wide-angle position to the telephoto position, the first lens component G1does not move on the optical axis Lc. The second lens component G2moves to the image side on the optical axis Lc with a distance between the first lens components G1and the second lens component G2being widen. The third lens component G3does not move on the optical axis Lc. The fourth lens component G4moves to the object side on the optical axis Lc with a distance between the third lens component G3and the fourth lens component G4being narrowed. The fifth lens component G5moves on the optical axis Lc in such a way that a distance between the fourth lens component G4and the fifth lens component G5is widen. The aperture stop S does not move on the optical axis Lc because the aperture stop S is integrated with the lens component G3.

The lens arrangement and the numerical data of the fourth embodiment according to the present invention are as follows, where a unit of length used in the data is millimeter (mm), R denotes a radius of curvature, D denotes a spacing between surfaces, Nd denotes a refractive index, vd denotes the Abbe's number, K denotes a conic constant, and A4, A6, A8, and A10denote aspherical coefficients:

Numerical data in the fourth embodiment in the case that distortion is electrically corrected are as follows, where data which are not shown below have the same value as the above data in the case that distortion is not electrically corrected, and a unit of length used in the data is millimeter (mm):

Although the zoom lens in each of the above embodiments consists of the five lens components, the zoom lens according to the present invention is not limited to these arrangement and may be designed in such a way that another lens component is arranged on the image side of the fifth lens component. Although the reflecting member is a prism in the zoom lens in each of the above embodiments, the zoom lens according to the present invention is not limited to such a constitution and a mirror may be used as the reflecting member.

The zoom lens according to the present invention may be designed as follows: the zoom lens according to the present invention is preferable designed so that focusing for focus adjustment is carried out by a lens component located at the most image-side position. A low load is added to a motor in focusing because the lens weight is light in the lens component located at such a position. In addition, it becomes easy to downsize an image pickup apparatus, because the total length of the zoom lens does not change in focusing and it becomes easy to arrange a driving motor in a lens frame. Although focusing for focus adjustment is preferable carried out by a lens component located at the most image-side position in this way, focusing may be carried out by the other lens component. In addition, focusing may be carried out by a plurality of lens components. Or, focusing may be carried out by moving the whole zoom lens or by partially moving lens elements of a lens component.

A decline in brightness of the periphery of an image (shading) may be reduced by shifting a micro lens of a CCD in the zoom lens according to the present invention. For example, a design for a micro lens of a CCD may be changed in accordance with an angle of incidence of light in each image height, or an amount of a decline in brightness of the periphery of an image may be corrected by an image processing.

A zoom lens according to the present invention may be designed to place a flare stop in addition to an aperture stop in order to cut off unwanted light such as ghost and flare. Also, the flare stop may be located at any of positions on the object side of the first lens component, between the first and second lens components, between the second and third lens components, between the third and fourth lens components, between the fourth and fifth lens components, and between the fifth lens component and the imaging plane. The flare stop may be constructed with a frame member or with another member. In addition, the flare stop may be constructed in such a way that it is printed directly on an optical member or that paint or an adhesive seal is used. The flare stop may have any of shapes of a circle, an ellipse, a rectangle, a polygon, and a contour surrounded by a function curve. The flare stop may be designed to cut off not only detrimental light beams but also light beams such as coma flare on the periphery of an image.

In the zoom lens according to the present invention, antireflection coat may be applied to each lens element so that ghost and/or flare is reduced. In this case, in order to lessen ghost and/or flare more effectively, it is desirable that the antireflection coat to be applied is a multi-coat. An Infrared-cutoff coat may be applied not to a low-pass filter but to the lens surface of each lens element, a cover grass and so on. Also, in order to prevent ghost and/or flare from occurring, it is generally performed that the antireflection coat is applied to the air contact surface of a lens element. On the other hand, the refractive index of an adhesive on the cementing surface of a cemented lens is much higher than that of air. Hence, the cementing surface of a cemented lens often has the refractive index originally equal to or less than a single layer coat, and thus the coat is not particularly applied in most case. However, when the antireflection coat is positively applied to the cementing surface of a cemented lens, ghost and/or flare can be further lessened and a more favorable image can be obtained.

In particular, high-refractive index grass materials by which the effect of correction for aberration is obtained have been popularized in recent years and have come to be often used in optical systems for cameras. However, when the high-refractive index glass material is used for the cemented lens, reflection at the cementing surface ceases to be negligible. In this case, the application of the antireflection coat to the cementing surface is particularly effective. Such effective use of the coat of the cementing surface is disclosed in each of Japanese patent Kokai Nos. Hei 2-27301, 2001-324676, 2005-92115 and U.S. Pat. No. 7,116,482. For the application of the coat, it is only necessary that a relatively high-refractive index coating substance, such as Ta2O5, TiO2, Nb2O5, ZrO2, HfO2, CeO2, SnO2, In2O3, ZnO, or Y2O3, or a relatively low-refractive index coating substance, such as MgF2, SiO2, or Al2O is properly selected in accordance with the refractive index of a lens for a substrate and the refractive index of the adhesive and is set to a film thickness such as to satisfy a phase condition.

As a matter of course, the coat of the cementing surface, like the coating on the air contact surface of a lens element, may be used as a multi-coat. In this case, a proper combination of a coat substance and a film thickness of each layer makes it possible to reduce more reflectance and to control the spectral characteristic and/or the angular characteristic of the reflectance.

An image pickup apparatus with the above zoom lens is preferably available for a digital camera, a personal computer and a mobile phone. The embodiments of the image pickup apparatus will be shown below.

First, one example of a digital camera having a zoom lens according to the present inventions is shown.FIG. 9is a perspective front view showing the appearance of an example of a digital camera into which the image pickup apparatus is incorporated.FIG. 10is a perspective rear view showing the digital camera shown inFIG. 9.FIG. 11is a schematic view showing the internal structure of the digital camera shown inFIGS. 9 and 10.FIG. 12is a block diagram showing the structure of the essential part of an internal circuit of the digital camera1.

First, the constitution of the digital camera1will be explained withFIGS. 9 to 11. The front of the digital camera1is provided with a photographing opening section101, a finder opening section102and a flash lamp button103. The upside of the digital camera1is provided with a shutter button104. The rear of the digital camera1is provided with a liquid crystal display monitor105and an information input section106. An image pickup apparatus107, a processing means108, a recording means109and a finder optical system110are provided inside the digital camera1. A cover member112is placed in the photographing opening section101, the finder opening section102, and an aperture111which is located on the exit side of the finder optical system110and is placed on the rear of the digital camera1.

The image pickup apparatus107incorporated into the digital camera1corresponds to the image pickup apparatus according to the present invention which is described above. The image pickup apparatus107comprises, in order from the object side, a zoom lens107ahaving a prism P, a low-pass filter LF, a CCD cover glass CG, and a CCD107b. The prism P of the zoom lens107achanges the direction of an optical path of light entering from the photographing opening section101from direction perpendicular to the front surface of the digital camera1to direction parallel to the front surface of the digital camera1in the inside of the digital camera1.

The finder optical system110comprises a finder objective optical system110a, a Porro prism110b, and an eyepiece optical system110c. Light entering from an object into the finder opening section102is led to the Porro prism P that is an image erecting member by the finder objective optical system110a, an objective image is formed in a field frame11b1as an erect image, and then, the objective image is led to an observer's eye E by the eyepiece optical system110c.

When the shutter button104on the upside of the digital camera1is pushed, the digital camera1is designed in such a way that image information is obtained through the image pickup apparatus107in response to the operation of pushing the shutter button104. The image information obtained by the image pickup apparatus107is recorded in the recording means109through the processing means108. In addition, it is also possible to take the recorded image information by the processing means108to make the liquid crystal display monitor105on the rear of the digital camera1display the information as an electronic image.

Such a constitution of the digital camera1can realize the compact design of the digital camera1, in particular, downsizing of the digital camera1in the direction of the depth of the digital camera1, as compared with a type of digital camera in which an optical path of light is not changed, because an optical path for obtaining image information is changed in the inside of the digital camera1. In addition, not only can the above constitution of the digital camera1realize high performance of the digital camera1, but also the above constitution can lower costs, because the image pickup apparatus107has the zoom lens107a: which has a wide angle of view and a high variable magnification ratio, is favorably corrected for aberration, is bright, and has a long back focus; and in which filters can be arranged.

Also, although in this example the optical path used to acquire the image information is changed in the lateral direction of the digital camera1, it may be changed in the longitudinal direction of the digital camera1. In the example, plane-parallel plates are used as the cover members102, but the most object-side lens of the zoom lens107aof the image pickup apparatus107, the most object-side lens of the finder objective optical system110a, and the most object-side lens of the eyepiece optical system may be fitted directly into the opening sections, without using the cover members112for the opening sections.

Next, in accordance withFIG. 12, reference is made to image information processing which is performed in the digital camera1. The digital camera1, as shown inFIG. 12, is provided with an image pickup dividing circuit113in addition to the image pickup apparatus107, the processing means108, and the recording section109. The processing means108has a control section108a, a CDS/ADC section108b, a temporary memory section108c, a set information memory section108d, an image processing section108e, an image display section108f, and memory medium section108g, and these sections are mutually connected so that the input and output of data are possible. Also, the processing means108is connected to the liquid crystal display monitor105, the information input section106, the image pickup apparatus107, the recording section109, and the image pickup driving circuit113through buses114connected to a signal input-output port of the processing means. The image pickup driving circuit113is such as to drive and control the zoom lens107aand the CCD107bof the image pickup apparatus107in accordance with a signal from the control section108aof the processing means108.

The control section108aof the control means108includes a central arithmetic processing unit such as CPU and houses a program memory, not shown. The control section108ais a circuit which controls the whole of digital camera1in accordance with a program stored in the program memory and instructions which are inputted by a user of the digital camera1through the information input section106having a input button and switch. The CDS/ADC section108bof the control means108is a circuit which amplifies an electrical signal inputted from the CCD107bof the image pickup apparatus107, performs analog-to-digital conversion, and outputs raw image data in which only the amplification and the analog-to-digital conversion are performed (or Bayer data, which are called RAW data) to the temporary memory section108c. The temporary memory section108cof the control means108is, for example, a buffer including a SDRAM and is a memory unit of temporarily memorizing the above RAW data which is outputted from the CDS/ADC section108b.

The set information memory section108dof the processing means108has a ROM section and a RAM section which are not shown in the figure. The information memory108dis a circuit that reads various image quality parameters which are stored in the ROM section in advance and that memorizes a image quality parameter which is selected from the read image quality parameters by the input operation of the information input section106of a user of the digital camera1in the RAM section.

The image processing section108eof the processing means108is a circuit that reads the RAW data memorized in the temporary memory section108cor a memory medium section108gto electrically perform various image processing processes, which include correction for distortion, in accordance with a image quality parameter designated by a user of the digital camera1.

The image display section108fis a circuit that is connected to the liquid crystal display monitor105to display an image, an operation menu, and so forth on the liquid crystal display monitor105. The memory medium section108gis a circuit that controls a unit which records and/or saves RAW data transferred from the temporary memory section108cand image data image-processed by the image processing section108e. In this embodiment, the unit which records and/or saves the data is the recording means109incorporated into the digital camera1. However, the unit which records and/or saves the data may be, for example, a recording medium, such as a flash memory, which can be removably fitted to the outside of the digital camera1.

Next, one example of a personal computer that is an information processing apparatus into which the image pickup apparatus according to the present invention is incorporated will be shown.FIG. 13is a perspective front view showing a personal computer whose cover is opened and into which the image pickup apparatus according to the present invention is incorporated.FIG. 14is a side view showing the personal computer shown inFIG. 13.FIG. 15is a cross sectional view showing the image pickup apparatus incorporated into the personal computer and the periphery of the image pickup apparatus. As shown inFIGS. 13 to 15, the personal computer2has a keyboard201for a user to input information from the outside of the personal computer2, and a liquid crystal display monitor202for displaying information to the user. An opening203for photographing is provided at the side of the liquid crystal display monitor202. An image pickup apparatus204for photographing the user himself and a surrounding image, and an information processing means and a recording means which are not shown in the figures are provided inside the personal computer2.

The image pickup apparatus204incorporated into the personal computer2corresponds to the image pickup apparatus according to the present invention explained in each embodiment mentioned above. The image pickup apparatus204comprises, in order from the object side, a zoom lens204ahaving a prism P, a low-pass filter LF, a CCD cover glass CG, and a CCD204bwhich is an imaging element chip. The optical path of light entering from the user himself and the periphery of the user into the opening203is changed from a direction perpendicular to the liquid crystal display monitor202of the personal computer2to a direction parallel to the liquid crystal display monitor202by the prism P of the zoom lens204ainside the personal computer2.

Because the image pickup apparatus204, which changes an optical path of light for obtaining image information inside the personal computer2, is used in the personal computer2, the personal computer2having such a constitution can easily realize the compact design as compared with a personal computer having an image pickup apparatus which does not change an optical path. Also, the personal computer2can easily realize high performance and low cost, because the image pickup apparatus204for obtaining an image has the zoom lens204awhich has a wide angle of view and a high variable magnification ratio, is favorably corrected for aberration, is bright, and has a long back focus in which filters can be arranged.

The cover glass CG is additionally cemented to the CCD204bwhich is an imaging element chip, and the cover glass CG and the CCD204bare integrally constructed as an imaging unit and can be placed in a lens frame205holding the zoom lens204aby fitting the cover glass CG and the CCD204binto the rear end of the lens flame205in a single operation. For this reason, alignment of the zoom lens104aand the CCD204band the adjustment of the face-to-face spacing are not required, and the assembly is simplified. A cover member206for protecting the zoom lens204ais placed at the front end of the lens frame205(which is not shown in the figure). A driving mechanism for the zoom lens204aprovided in the lens frame205is omitted from the figure. An object image received by the CCD204bis inputted into a processing means of the personal computer2through a terminal207, and is displayed as an electronic image on the liquid crystal display monitor202. Also, the image can be displayed on a personal computer of a remote communication partner from the processing means through the Internet or a telephone circuit.

Although the image pickup apparatus204is placed at the side of the liquid crystal display monitor202in this embodiment, the placement of the image pickup apparatus204is not limited to the above placement, and the image pickup apparatus204may be placed anywhere, for example, at a position except for the side of the liquid crystal display monitor202or in the periphery of the keyboard201. Although a transmission liquid crystal display element, which is illuminated from the rear side by a backlight, is used for the liquid crystal display monitor202in this embodiment, a reflection liquid crystal display element reflecting and displaying light from the front may be used. The liquid crystal display monitor202may be replaced with a display device such as a CRT display.

Next, one example of a mobile phone that is an information processing apparatus into which an image pickup apparatus according to the present invention is incorporated will be shown.FIG. 16Ais a front view showing the mobile phone into which the image pickup apparatus is incorporated.FIG. 16Bare a side view showing the mobile phone.FIG. 16Cis a cross sectional view showing an image pickup apparatus incorporated into the mobile phone and the periphery of the image pickup apparatus. As shown inFIGS. 16A to 16C, the mobile phone3has a microphone section301for inputting a user's voice as information, a speaker section302for outputting a voice of a communication partner, input keys303by which the user inputs information, a liquid crystal display monitor304for displaying information of photographed images of the user himself and the communication partner and telephone number, and antenna305for transmitting and receiving communication waves. An opening306for photographing is provided at the side of the speaker section302. An image pickup apparatus307for photographing the user himself and a surrounding image, and an information processing means and a recording means which are not shown in the figures are provided inside the mobile phone3. A liquid crystal display element is used in the liquid crystal display monitor304The placement of each constitution is not limited to such a constitution in the figures, and the placement may be suitably changed.

The image pickup apparatus307incorporated into the mobile phone3corresponds to the image pickup apparatus according to the present invention which is explained above. The image pickup apparatus307comprises, in order from the object side, a zoom lens307ahaving a prism P, a low-pass filter LF, a CCD cover glass CG, and a CCD307bwhich is an imaging element chip, and is placed on an optical path of light entering from an user himself and the periphery of the user into the opening306. For this reason, the optical path of light entering from the user himself and the periphery of the user into the opening306is changed from a direction perpendicular to the liquid crystal display monitor304of the mobile phone3to a direction parallel the liquid crystal display monitor304by the prism P of the zoom lens307ainside the mobile phone3.

Because the image pickup apparatus307, which changes an optical path of light for obtaining image information inside the mobile phone3, is used in the mobile phone3, the mobile phone3having such a constitution can easily realize the compact design as compared with a mobile phone having an image pickup apparatus which does not change an optical path. Also, the mobile phone3can easily realize high performance and/or low cost, because the image pickup apparatus307for obtaining an image has the zoom lens307awhich has a wide angle of view and a high variable magnification ratio, is favorably corrected for aberration, is bright, and has a long back focus in which filters can be arranged.

The cover glass CG is additionally cemented to the CCD307bwhich is an imaging element chip, and the cover glass CG and the CCD307bare integrally constructed as an imaging unit and can be placed in a lens frame308holding the zoom lens307aby fitting the cover glass CG and the CCD307binto the rear end of the lens flame308in a single operation. For this reason, alignment of the zoom lens307aand the CCD307band the adjustment of the face-to-face spacing are not required, and the assembly is simplified. A cover member309for protecting the zoom lens307ais placed at the front end of the lens frame308(which is not shown in the figure). A driving mechanism for the zoom lens307aprovided in the lens frame308is omitted from the figures. An object image received by the CCD307bis inputted into a processing means of the mobile phone3through a terminal310, and is displayed as an electronic image on the liquid crystal display monitor304. Also, when an image is sent to a communication partner, the processing means has a signal processing function of converting the image information into a transmittable signal.