JP2006309049A - Imaging apparatus using zoom lens system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of preventing the deterioration of image quality caused by dust such as dirt while keeping miniaturization and high performance. <P>SOLUTION: In the imaging apparatus equipped with a zoom lens system including a movable lens group, a positive lens and an imaging device unit are arranged in order from an object side on the image side of the movable lens group. The positive lens and the imaging unit are in hermetic structure through a member constituting the imaging apparatus, and a lens group having negative power is arranged on the object side of the positive lens by inserting air space in between. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image pickup apparatus using a zoom lens system that prevents the image quality from being deteriorated by dust by devising the image pickup system part and realizes downsizing.

  In recent years, cameras equipped with a photographing optical system having an electronic image pickup device such as a digital camera have been reduced in size and increased in pixels. There is also an increasing demand for mobile phones equipped with such cameras. Accordingly, there is a demand for downsizing and high performance of the photographing optical system used in these cameras. In such a photographing optical system, a combination of optical elements is devised in order to shorten the overall length of the optical system and reduce the outer diameter of the lens.

As a general configuration, a three-group configuration including a first lens group having negative power, a second lens group having positive power, and a third lens group having negative power ( For example, refer to Patent Documents 1 and 2), or a three-group configuration including a first lens group having negative power, a second lens group having positive power, and a third lens group having negative power. Further, there is a four-group configuration (for example, see Patent Documents 3, 4, 5, and 6) in which lens groups having positive power are arranged. In such an optical system, it is desirable to suppress the variation in the angle of the peripheral ray as much as possible by the movable lens group for zooming in order to reduce the outer diameter of the lens.
JP-A-5-93866 JP 2004-294910 A JP-A-9-179026 JP-A-11-109230 JP 2004-131130 A JP 2004-240464 A

  For example, in the zoom lens described in Patent Document 1 and the bifocal lens described in Patent Document 2, a first lens group having negative power, a second lens group having positive power, and a third lens having negative power. A three-group configuration consisting of groups is adopted. In such a configuration, since the third lens group can have a relatively strong zooming action, it is very effective for reducing the overall length of the optical system and the outer diameter of the lens. However, in these configurations, the incident angle of the imaging light beam with respect to the imaging surface normal line is large within the image height, and when an electronic image sensor is used, the influence of shading is strong, and a good image cannot be obtained.

  In the variable power optical system described in Patent Document 3, the video photographing optical system described in Patent Document 4, the zoom lens described in Patent Document 5, and the optical system described in Patent Document 6, the first lens having negative power A four-group configuration is employed in which a lens group having a positive power is arranged on the basis of a three-group configuration including a second lens group having a positive power and a third lens group having a negative power. However, in these configurations, a positive lens group has to be further arranged on the image side of the third lens group, and the optical system is optically compared with the optical system having the three-group configuration as described in Patent Documents 1 and 2. There is a problem that the total length of the system becomes large.

  In the field using an electronic imaging system such as a digital camera, dust such as dust adheres to the cover glass of an electronic imaging device such as a CCD, and the image appears on the imaging device and the image quality deteriorates. May occur.

  The present invention has been made in view of the above-described problems of the prior art, and its object is to prevent image quality deterioration due to dust such as dust while maintaining downsizing and high performance. An object of the present invention is to provide an imaging apparatus capable of

  In order to achieve the above object, an imaging apparatus according to the present invention is an imaging apparatus including a zoom lens system including a movable lens group, and in order from the object side to the image side of the movable lens group, a positive lens, An image sensor unit is disposed, and the positive lens and the image sensor unit are in a sealed structure via a member constituting the image pickup device, and negative power with an air gap is provided on the object side of the positive lens. Are arranged.

  In the imaging apparatus according to the present invention, it is preferable that the positive lens has a low-pass function or an infrared cut function.

In the imaging device according to the present invention, it is preferable that the lens group having the negative power satisfies the following conditional expression (1).
0.6 ≦ DL / IH ≦ 1.5 (1)
However,
DL: Distance from the object side surface of the field lens to the image plane
IH: Maximum photographed image height.

  In the imaging device according to the present invention, it is preferable that the lens group having the negative power is included in the movable lens group.

In the imaging apparatus according to the present invention, it is preferable that the positive lens satisfies the following conditional expression (2).
−3.7 ≦ (R1 + R2) / (R1−R2) ≦ −0.3 (2)
However,
R1: radius of curvature of object side surface of positive lens
R2: radius of curvature of the image side surface of the positive lens.

  In the imaging apparatus according to the present invention, the movable lens group includes a first lens group having negative power in order from the object side, a second lens group having positive power, and a third lens group having negative power. In the image pickup apparatus according to the present invention, it is preferable that the positive lens is disposed on the image side of the third lens group with an air gap therebetween.

  In the imaging apparatus according to the present invention, it is preferable that the positive lens has a rectangular outer shape.

  In the imaging apparatus according to the present invention, it is preferable that the positive lens is made of plastic.

  Furthermore, in the imaging apparatus according to the present invention, it is preferable that the imaging apparatus includes a field stop, and the field stop, the positive lens, and the imaging element unit are integrally attached to a member constituting the imaging apparatus. .

  Further, in the image pickup apparatus according to the present invention, it is preferable that a planar contact portion capable of contacting the field stop is formed in the lens peripheral portion of the plastic positive lens.

  In the imaging apparatus according to the present invention, it is preferable that the positive lens and the imaging element unit are at least partially in contact with each other.

  Furthermore, in the imaging apparatus according to the present invention, it is preferable that a contact surface is formed outside the effective diameter of the plastic positive lens, and the positive lens and the imaging element unit are in contact with each other through the contact surface.

  In the imaging apparatus according to the present invention, it is preferable that a wavelength band limiting coat is applied to the image side surface of the positive lens.

  In the imaging apparatus according to the present invention, it is preferable that the positive lens is a convex flat positive lens having a convex surface facing the object side.

In the image pickup apparatus according to the present invention, when the zoom lens system is zoomed from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is reduced in the second lens group. Moving to the object side, the third lens group moves so that the distance between the second lens group and the third lens group changes, and one negative lens among the lenses constituting the first lens group The second lens group includes at least one positive lens and at least one negative lens, and the following conditional expressions (3), (4), and (5) It is preferable to satisfy.
4.0 ≦ W_L / IH ≦ 12.0 (3)
1.7 ≦ | ΔD12 | /IH≦4.6 (4)
52.0 ≦ PAνd (5)
However,
W_L: Total length of the optical system at the wide-angle end
IH: Maximum image height
ΔD12: Amount of change in the distance between the first lens unit and the second lens unit upon zooming from the wide-angle end to the telephoto end
PAνd: Abbe number of the positive lens in the second lens group (in the case of multiple lenses, all positive lenses)
It is.

Furthermore, it is preferable that the imaging apparatus according to the present invention further satisfies the following conditional expression (6).
0.45 ≦ D23W / IH ≦ 3.0 (6)
However,
D23W: Distance between the second lens group and the third lens group at the wide-angle end.

Furthermore, it is preferable that the imaging apparatus according to the present invention further satisfies the following conditional expression (7).
0.38 ≦ (f2 / fw) × (IH / fw) ≦ 0.95 (7)
However,
f2: focal length of the second lens unit
fw: Total focal length at the wide-angle end.

Furthermore, it is preferable that the imaging apparatus according to the present invention further satisfies the following conditional expression (8).
2.7 ≦ W_L / fw ≦ 10.0 (8)
However,
fw: Total focal length at the wide-angle end.

Furthermore, it is preferable that the imaging apparatus according to the present invention further satisfies the following conditional expression (9).
3.7 ≦ | ΔD12 / ΔD23 | (9)
However,
ΔD23: an amount of change in the distance between the second lens unit and the third lens unit upon zooming from the wide-angle end to the telephoto end.

In the image pickup apparatus according to the present invention, it is preferable that the first lens group includes a negative lens and a positive lens in order from the object side, and satisfies the following conditional expression (10).
0.6 ≦ G1Σd / IH ≦ 1.3 (10)
However,
G1Σd: the total thickness of the first lens group.

Furthermore, in the imaging apparatus according to the present invention, the second lens group includes one negative lens and at least one positive lens, and at least one of the positive lenses satisfies the following conditional expression (11). It is preferable.
75.0 ≦ Pνd (11)
However,
Pνd: Abbe number of the positive lens in the second lens group (in the case of multiple lenses, any one positive lens)
It is.

Furthermore, it is preferable that the imaging apparatus according to the present invention further satisfies the following conditional expression (12).
45.0 ≦ Pνd−Nνd (12)
However,
Nvd: Abbe number of the negative lens in the second lens group.

  Furthermore, in the image pickup apparatus according to the present invention, it is preferable that the first lens group is movable between the wide-angle end and the telephoto end so that the total length of the optical system is the shortest during zooming.

Furthermore, it is preferable that the imaging device according to the present invention further satisfies the following conditional expressions (13-1), (13-2), (13-3), and (13-4) at the wide-angle end.
7.0% ≦ | DTW_ × 1.0 | (13-1)
3.5% ≦ | DTW_ × 0.7 | ≦ 15.0% (13-2)
7.0% ≦ | DTW_ × 1.0 | ≦ 25.0% (13-3)
| ΔDTW | ≦ 15.0% (13-4)
However,
DTW_ × 0.7: Length distortion at the position of 0.7 × of the maximum image height at the wide-angle end
DTW_ × 1.0: Length distortion at% position at the wide-angle end maximum photographed image height of 1.0
ΔDTW: the length at the position of x0.7 of the maximum image height at the wide-angle end and x1. Is the difference in% representation of distortion from the length at position 0,
Y′0: paraxial imaging height,
Y ′: When the actual imaging height is assumed,
Distortion amount = (Y′−Y′0) / Y′0 × 100 (%)
It is.

  Furthermore, it is preferable that the imaging apparatus according to the present invention performs focusing by moving the third lens group in the optical axis direction.

  Furthermore, in the imaging apparatus according to the present invention, the first lens group includes two negative lenses and a positive lens in order from the object side, and the second lens group includes a positive lens, a negative lens, a positive lens, and a negative lens in order from the object side. It is preferable that three lenses and the third lens group include one negative lens.

  According to the present invention, while maintaining good performance, image quality deterioration due to the influence of shading and imprinting of dust etc. on the imaging surface can be prevented, and miniaturization and diameter reduction of the optical system can be achieved. An imaging device having a zoom lens system that can be obtained can be obtained.

An imaging apparatus according to the present invention is an imaging apparatus including a zoom lens system including a movable lens group, and a positive lens and an imaging element unit are arranged in order from the object side on the image side of the movable lens group. The imaging element unit is in a sealed structure via a member constituting the imaging device, and a lens group having negative power is arranged on the object side of the positive lens with an air gap therebetween.
In this way, by adopting a configuration in which a lens having a positive power is arranged without arranging a low-pass filter or the like immediately before the imaging element, the imaging system can be reduced in size. Also, the positive lens can focus the light beam diverged from the negative lens group and reduce the incident angle of the light beam with respect to the image plane normal to the image plane, thus reducing the influence of shading. Can do. Furthermore, since the positive lens and the image sensor unit have a sealed structure, dust such as dust does not adhere to the image sensor, and it is possible to prevent image quality deterioration due to the dust appearing on the image sensor. it can. In addition, by arranging a lens group having negative power immediately on the object side of the positive lens, the beam height of the light beam emitted from the negative lens group to the object side can be kept low. The diameter can be reduced.

  In the present invention, the “sealed structure” means a structure in which dust of about φ0.02 (mm) or more does not enter between the positive lens and the image sensor unit. This sealed structure may be formed by one member constituting the imaging apparatus or may be formed by combining a plurality of members.

The positive lens preferably has a low-pass function or an IR cut function.
By arranging such a positive lens, it is possible to realize further higher image quality without increasing the number of members.

In addition, it is preferable that the lens group having the negative power satisfies the following conditional expression (1).
0.6 ≦ DL / IH ≦ 1.5 (1)
However,
DL: Distance from the object side of the positive lens to the image plane
IH: Maximum photographed image height.
Conditional expression (1) is an expression that defines the distance from the object-side surface of the positive lens disposed on the object side of the image sensor unit to the imaging surface. Exceeding the upper limit of conditional expression (1) is not preferable because the total length of the optical system increases and the apparatus becomes larger. Below the lower limit of conditional expression (1), for example, when dust such as dust adheres to the object side surface of the positive lens arranged on the object side of the image sensor unit, the dust is reflected on the image sensor. This is not preferable.

The lens group having negative power is preferably included in the movable lens group.
By making the lens group having negative power movable, it becomes possible to enhance the zooming effect, and correction by the negative lens group and the positive lens, particularly correction of astigmatism, is performed well in each zoom state. be able to.

In addition, it is preferable that the positive lens satisfies the following conditional expression (2).
−3.7 ≦ (R1 + R2) / (R1−R2) ≦ −0.3 (2)
However,
R1: radius of curvature of object side surface of positive lens
R2: radius of curvature of the image side surface of the positive lens.
The conditional expression (2) is an expression that defines the lens shape of the positive lens. If the upper limit of conditional expression (2) is exceeded, when applying a wavelength band limiting coat such as an IR cut coat to the image side surface of the positive lens, the angle of the light beam of each image height with respect to the image plane incident on that surface Since the change becomes large, uniform wavelength cut characteristics cannot be obtained over the entire image plane. If the lower limit of conditional expression (2) is not reached, the curvature of the object side surface of the positive lens becomes too strong, making it difficult to correct various aberrations with the positive lens alone, and the incident angle with respect to the image plane is sufficiently large. It cannot be corrected and is easily affected by shading, making it difficult to ensure performance.
The conditional expression (2) is
−1.5 ≦ (R1 + R2) / (R1−R2) ≦ −0.7 (2 ′)
If this condition is satisfied, better performance can be maintained.

The movable lens group includes a first lens group having negative power in order from the object side, a second lens group having positive power, and a third lens group having negative power. It is preferable that a positive lens is disposed on the image side of the third lens group with an air gap therebetween.
Such a three-group configuration is generally advantageous for downsizing. In addition, by placing the negative lens group immediately on the object side of the positive lens, the light rays are gradually bent in the order of negative, positive, negative, and positive. It becomes possible to reduce the diameter of the optical system. Such a configuration is particularly effective for a zoom lens system having the above-described three-group configuration that is advantageous for downsizing.

The outer shape of the positive lens is preferably rectangular.
This is because, when the positive lens disposed in the vicinity of the image sensor unit is formed in such a shape, the positive lens and the image sensor unit can be easily sealed.

The positive lens is preferably made of plastic.
By using a plastic lens, it is possible to reduce the cost and weight. In addition, since plastic has a higher degree of freedom of molding than glass, it can be produced in a desired shape as necessary, and the degree of freedom of design can be increased.

Furthermore, when the positive lens is made of plastic, it is preferable that the imaging device includes a field stop, and the field stop, the positive lens, and the imaging element unit are integrally attached to a member constituting the imaging device.
This configuration not only suppresses dust from entering the vicinity of the image plane, but also vibrates the integrated part at the same time when camera shake occurs, making it easy to correct blur and prevent blur using the image sensor. Can be performed. In addition, since the integrated part can be moved simultaneously in the optical axis direction, focusing can be easily performed.

Further, when the positive lens is made of plastic, it is preferable that a planar contact portion that can contact the field stop is formed around the lens of the positive lens.
By providing such a contact portion on the periphery of a plastic lens having a large degree of freedom in molding, the field stop can be easily arranged.

Moreover, it is preferable that the positive lens and the image sensor unit are in contact with each other at least partially.
By comprising in this way, while being able to form a sealing structure easily, it becomes possible to further raise a sealing degree.

Furthermore, when the positive lens is made of plastic, it is preferable that a contact surface is formed outside the effective diameter of the positive lens, and the positive lens and the image sensor unit are in contact with each other via the contact surface.
By providing a contact surface that contacts the image sensor unit on a plastic lens with a large degree of freedom of molding, in addition to cost reduction and weight reduction, it is possible to easily form a sealed structure and to further increase the sealing degree It becomes possible.

Further, it is preferable that a wavelength range limiting coat is applied to the image side surface of the positive lens.
For example, by using a film that can limit the wavelength range in this way, it is possible to limit the desired wavelength range without adhering dust such as dust to the wavelength range limiting coat. .

The positive lens is preferably a convex flat positive lens having a convex surface facing the object side.
By using a convex positive lens having a flat image-side surface on the positive lens, it becomes possible to easily apply a wavelength range limiting coat such as an IR cut coat to the image side surface of the positive lens. In addition, it is easy to make light rays incident on the image side surface of the positive lens, that is, the surface on which IR cut coating is applied, at an angle substantially parallel to the optical axis, and uniform wavelength cut characteristics can be obtained over the entire image plane. It becomes possible.

Further, when the movable lens group is composed of three lens groups, and a positive lens is arranged on the image side of the third lens group with an air gap therebetween, the second lens is used when zooming from the wide angle end to the telephoto end. The group moves to the object side so that the distance between the first lens group and the second lens group decreases, and the third lens group moves so that the distance between the second lens group and the third lens group changes, It is preferable that only one negative lens is included in the lenses constituting the first lens group, and the second lens group has at least one positive lens and at least one negative lens.
In this way, when the second lens group is moved to the object side so that the distance between the first lens group and the second lens group is reduced when zooming from the wide-angle end to the telephoto end, the entire length of the optical system is obtained. Although the height of the incident light is kept low, the incident angle on the imaging surface is made smaller than the normal to the imaging surface, and the influence of shading by the image sensor when using an electronic image sensor can be reduced. it can. Further, the third lens group having a negative power is disposed with a space from the second lens group, and is movable with respect to the second lens group at the time of zooming. It can have a variable power action. As a result, the outer diameter of the first lens unit can be kept small while shortening the entire system even when a zoom ratio exceeding 2.5 times is secured, and the half angle of view at the wide angle end is 28 °. The configuration described above (that is, conditional expression (14) “0.53 ≦ IH / fw”, where fw is the focal length of the entire system at the wide-angle end) can be employed.

In addition, when the movable lens group is composed of three lens groups and a positive lens is arranged on the image side of the third lens group with an air gap therebetween, each lens group of the movable lens group operates as described above. When the three-group configuration is used, it is preferable that the following conditional expression (3) is satisfied.
4.0 ≦ W_L / IH ≦ 12.0 (3)
However,
W_L: Length from the lens surface closest to the object side to the imaging surface of the first lens unit at the wide-angle end
IH: Maximum photographed image height.
Conditional expression (3) is a condition for shortening the overall length of the optical system, maintaining the light beam exit angle to the image plane at an appropriate angle, and obtaining a good image. If the lower limit of conditional expression (3) is not reached, the total length of the optical system becomes too short, so that the angle of the incident light beam entering the imaging plane emitted from the optical system can be kept small with respect to the normal to the imaging plane. Even if the size can be reduced, a good image cannot be obtained due to the influence of shading. If the upper limit of conditional expression (3) is exceeded, the total length of the optical system becomes too long, and it becomes impossible to achieve downsizing.

In addition, at this time, it is preferable to satisfy the following conditional expression (4).
1.7 ≦ | ΔD12 | /IH≦4.6 (4)
However,
ΔD12: Amount of change in the distance between the first lens unit and the second lens unit upon zooming from the wide-angle end to the telephoto end
IH: Maximum photographed image height.
By satisfying the conditional expression (4), there is no need to increase the power of the first lens group and the second lens group or increase the zooming action of the third lens group, and the overall length of the optical system can be shortened. A zoom ratio exceeding 2.5 times can be secured without impeding realization, and good performance can be obtained while shortening the overall length of the optical system. In order to obtain a zoom ratio of 2.5 or more in a state where the lower limit of conditional expression (4) is not reached, the power of the first lens group and the second lens group are increased, or the zoom ratio of the third lens group is increased. It is necessary to enhance the action. When the powers of the first lens group and the second lens group are increased, since the powers are too strong to obtain a required zoom ratio, good performance due to zooming cannot be obtained. When the zooming action of the third lens group is enhanced, if the number of lenses in the third lens group is two or less, aberration fluctuation due to zooming cannot be suppressed, and as a result, the thickness of the lenses constituting the third lens group And the total distance between the lenses increases, making it impossible to shorten the entire length of the entire optical system or shorten the total length of the lens frame when retracted. If the upper limit of the conditional expression (4) is exceeded, it is easy to obtain a high zoom ratio, but it becomes difficult to shorten the entire length of the optical system, and for example, a stop that moves integrally with the second lens group is used as the second lens. For example, when the lens is disposed on the object side of the group, the entrance pupil enters the image plane side too much from the most object side surface of the first lens group. As a result, the outer diameter of the first lens group required for off-axis rays to pass through the center of the entrance pupil becomes large, and the lens diameter cannot be reduced.

  In addition, at this time, it is preferable to adopt a configuration in which only one negative lens is included in the lenses constituting the first lens group. By adopting such a configuration, the total thickness of the first lens group can be shortened, the total length of the entire optical system or the total length of the lens frame when retracted can be shortened, and the outer diameter of the first lens can be reduced. Is possible.

In addition, at this time, it is preferable that the second lens group has a positive lens and a negative lens, and satisfies the following conditional expression (5).
52.0 ≦ PAνd (5)
PAνd: Abbe number of the positive lens in the second lens group (in the case of multiple lenses, all positive lenses)
By satisfying the conditional expression (5), it is possible to effectively correct the axial chromatic aberration and the chromatic aberration of magnification at the time of zooming even if the number of components of the second lens group is small, and the zooming ratio is 2.5. Even if it is twice or more, good performance can be obtained in the entire region. If there are a plurality of positive lenses in the second lens group, it is preferable that all of them satisfy the conditional expression (5).

In addition, the said conditional expression (3) and (4) is 5.5 <= W_L / IH <= 10.5 ... (3 ')
2.2 ≦ | ΔD12 | /IH≦4.6 (4 ′)
If this condition is satisfied, the above effect can be further enhanced.

Further, in the case where the movable lens group includes three lens groups and a positive lens is disposed on the image side of the third lens group with an air gap therebetween, it is preferable that the following conditional expression (6) is further satisfied. .
0.45 ≦ D23W / IH ≦ 3.0 (6)
However,
D23W: Distance between the second lens group and the third lens group at the wide-angle end
IH: Maximum photographed image height.
By satisfying the conditional expression (6), it is possible to obtain a good aberration correction effect and a zooming action by the third lens group even when the third lens group has a small number of lenses of two or less. If the lower limit of conditional expression (6) is not reached, it will be difficult to correct aberrations at the wide-angle end, and it will be difficult to ensure a half field angle of 28 ° or more at the wide-angle end. In addition, it becomes difficult to secure the amount of movement of the third lens group with respect to the second lens group, and it becomes difficult to maintain performance at the middle or at the telephoto end. If the upper limit of the conditional expression (4) is exceeded, when the angle of the light beam emitted from the third lens group is made small as a shading countermeasure, the power of the third lens group becomes too weak, and a zooming effect is obtained. As a result, it becomes difficult to shorten the overall length of the optical system.
In addition, the said conditional expression (6) is 0.7 <= D23W / IH <= 2.5 ... (6 ')
If this condition is satisfied, the above effect can be further enhanced.

Further, when the movable lens group includes three lens groups, and a positive lens is disposed on the image side of the third lens group with an air gap therebetween, it is preferable that the following conditional expression (7) is further satisfied. .
0.38 ≦ (f2 / fw) × (IH / fw) ≦ 0.95 (7)
However,
f2: focal length of the second lens unit
fw: Total focal length at the wide-angle end
IH: Maximum photographed image height.
By satisfying the conditional expression (7), it is possible to obtain a small and good performance while ensuring a zoom ratio and a half angle of view of 28 ° or more at the wide angle end. If the lower limit of conditional expression (7) is not reached, the second lens group having a large zooming action can be obtained when a zoom ratio of 2.5 or more is maintained while maintaining the performance in the entire zooming region. Since it is necessary to make the power weaker, it becomes difficult to secure a half field angle of 28 ° or more at the wide angle end and a good performance. If the upper limit of conditional expression (7) is exceeded, the power of the second lens group will be weakened, and the zoom ratio will be 2.5 times or more and 28 ° at the wide-angle end while maintaining the performance in the entire zoom range. In order to ensure the above half angle of view, it is necessary to move the second lens group greatly. Therefore, it is necessary to take a large space for the second lens group to move, and the total length of the optical system tends to be long.
In addition, the said conditional expression (7) is 0.38 <= (f2 / fw) * (IH / fw) <= 0.95 ... (7 ')
If this condition is satisfied, the above effect can be further enhanced.

Further, in the case where the movable lens group includes three lens groups and a positive lens is disposed on the image side of the third lens group with an air gap therebetween, it is preferable that the following conditional expression (8) is further satisfied. .
2.7 ≦ W_L / fw ≦ 10.0 (8)
However,
W_L: Length from the lens surface closest to the object side to the imaging surface of the first lens unit at the wide-angle end
fw: Total focal length at the wide-angle end.
By satisfying the above conditional expression (8), it is possible to obtain a good image with a wide angle of view, a shortened total length of the optical system, and an incident angle of the light beam on the imaging plane with respect to the imaging plane normal. It can be maintained at an appropriate angle. If the lower limit of conditional expression (8) is surpassed, the incident angle of the light beam on the imaging plane with respect to the imaging plane normal becomes too large when trying to secure a half angle of view of 28 ° or more at the wide-angle end. Therefore, a good image cannot be obtained. If the upper limit of conditional expression (8) is exceeded, when attempting to ensure a half angle of view of 28 ° or more at the wide-angle end, the total length of the optical system at the wide-angle end becomes too long, and thus miniaturization cannot be achieved.

In addition, when the movable lens group includes three lens groups, and a positive lens is disposed on the image side of the third lens group with an air gap therebetween, the imaging apparatus according to the present invention further satisfies the following conditional expression: It is preferable to do.
3.7 ≦ | ΔD12 / ΔD23 | (9)
However,
ΔD12: Amount of change in the distance between the first lens unit and the second lens unit upon zooming from the wide-angle end to the telephoto end
ΔD23: an amount of change in the distance between the second lens unit and the third lens unit upon zooming from the wide-angle end to the telephoto end.
By satisfying the conditional expression (9), it is possible to ensure good performance over the entire zooming area even if the third lens group is configured with a small number of two or less. If the lower limit of conditional expression (7) is not reached, the positional fluctuation of the third lens group with respect to the second lens group becomes too large, so that when the number of third lens groups is two or less, aberrations are maintained well over the entire zooming region. Becomes difficult. Although the performance variation due to zooming can be suppressed by using three or more third lens groups, the total thickness of the third lens group is increased, and the total length of the optical system or the retracted length of the lens frame is increased. Shortening becomes difficult.

Further, when the movable lens group includes three lens groups, and a positive lens is disposed on the image side of the third lens group with an air gap therebetween, the first lens group is arranged in order from the object side with a negative lens. It is preferable that the lens is composed of two positive lenses.
With this configuration, even when the zoom ratio exceeds 2.5, fluctuations due to the change in axial chromatic aberration and lateral chromatic aberration can be satisfactorily secured with a small number of lenses.

In addition, at this time, it is preferable that the following conditional expression (10) is satisfied.
0.6 ≦ G1Σd / IH ≦ 1.3 (10)
However,
G1Σd: Total thickness of the first lens group
IH: Maximum photographed image height.
By satisfying conditional expression (10), it is possible to satisfactorily ensure aberration fluctuations while shortening the overall length of the optical system. If the lower limit of conditional expression (10) is not reached, the degree of freedom for correcting aberrations, that is, the lens thickness and the radius of curvature are limited, so when the zoom ratio exceeds 2.5 times, It is difficult to ensure a good off-axis aberration over the entire zooming region. When the upper limit of conditional expression (10) is exceeded, it becomes difficult to shorten the total length of the optical system or the total length of the lens barrel when retracted. Further, the lens outer diameter of the first lens group becomes large, and miniaturization cannot be achieved.

In addition, when the movable lens group is composed of three lens groups and a positive lens is arranged on the image side of the third lens group with an air gap therebetween, the second lens group has at least one negative lens and at least one lens. In addition, it is preferable that at least one of the positive lenses satisfies the following conditional expression (11).
75.0 ≦ Pνd (11)
However,
Pνd: Abbe number of the positive lens in the second lens group (in the case of multiple lenses, any one positive lens)
It is.
By configuring the second lens group having a large zooming action in this way, it is possible to keep good fluctuations in axial chromatic aberration due to zooming.

Further, the movable lens group is composed of three lens groups, a positive lens is arranged on the image side of the third lens group with an air space therebetween, and the second lens group is composed of one negative lens and the above conditional expression ( In the case of having at least one positive lens that satisfies 11), it is preferable that the following conditional expression (12) is further satisfied.
45.0 ≦ Pνd−Nνd (12)
However,
Pνd: Abbe number of the positive lens in the second lens group (in the case of multiple lenses, any one positive lens)
Nvd: Abbe number of the negative lens in the second lens group.
By satisfying the conditional expression (12), it is possible to satisfactorily ensure a change in axial chromatic aberration due to zooming and further improve performance.

In addition, when the movable lens group is composed of three lens groups and a positive lens is disposed on the image side of the third lens group with an air gap therebetween, the first lens group has a wide-angle end and a telephoto end during zooming. In the meantime, it is preferable that the entire length of the optical system is movable.
With such a configuration, it is possible to increase the amount of change in the distance due to zooming from the first lens group to the second lens group, and to efficiently correct aberrations in the first lens group and the second lens group. Can be done. In other words, the first lens group can be effectively provided with the field curvature correction effect in the intermediate magnification range, and the overall length of the optical system can be further shortened in view of its performance.

Further, in the case where the movable lens group includes three lens groups and a positive lens is disposed on the image side of the third lens group with an air gap therebetween, the following conditional expression (13-1) may be satisfied. preferable.
7.0% ≦ | DTW_ × 1.0 | (13-1)
However,
DTW_ × 1.0:% display of the distortion aberration of length at the position of the maximum photographed image height at the wide angle end at × 1.0 at the time of focusing on infinity.
If a configuration that satisfies the conditional expression (13-1), that is, a configuration that generates distortion to some extent, it is possible to reduce the burden on the first lens group for correcting distortion, particularly at the wide-angle end. Therefore, the degree of freedom of aberration correction in the first lens group in which distortion occurs most at the wide angle end can be greatly increased. As a result, the total thickness of the first lens group can be reduced, and the total length of the optical system or the total length of the lens frame when retracted can be further shortened.

In addition, at this time, a good image can also be obtained by correcting the distortion of the photographed image using electrical processing after photographing. In that case, it is desirable to satisfy the following conditional expressions (13-2), (13-3), and (13-4).
3.5% ≦ | DTW_ × 0.7 | ≦ 15.0% (13-2)
7.0% ≦ | DTW_ × 1.0 | ≦ 25.0% (13-3)
| ΔDTW | ≦ 15.0% (13-4)
However,
DTW_ × 0.7:% distortion aberration of length at the position of 0.7mm of the maximum captured image height at the wide-angle end when focusing on infinity
DTW_ × 1.0:% display of length distortion at the position of 1.0mm of the maximum captured image height at the wide-angle end when focusing on infinity
ΔDTW: The difference in% display of the distortion at the position of x0.7 of the maximum captured image height at the wide-angle end and the length of distortion at the position of x1.0 when focused at infinity.
In conditional expressions (13-2) and (13-3) below the lower limit of each, that is, if the amount of distortion is too small, the burden on the lens system for correcting distortion becomes large. Therefore, it is difficult to reduce the total thickness of the first lens unit. Further, if distortion aberration correction is performed by electrical processing of an image exceeding the respective upper limits in the conditional expressions (13-2) and (13-3), the resolution is remarkably lowered and a good image cannot be obtained. In order to prevent the resolution from being lowered due to electrical correction, it is preferable to satisfy the conditional expression (13-4).

In addition, when the movable lens group is composed of three lens groups, and a positive lens is arranged on the image side of the third lens group with an air space therebetween, focusing is performed by moving the third lens group in the optical axis direction. It is preferable to carry out.
Since the third lens group can be reduced in diameter by adopting the above-described three-group configuration, it can be reduced in size and weight. Therefore, if focusing is performed by moving the third lens group, it is easy to reduce the size of the drive actuator, and the lens frame can be reduced in size.
At this time, if the conditional expression (6) is satisfied, the distance from the second lens group to the third lens group can be adequately secured, and a sufficient driving margin for focusing due to manufacturing variations is secured. can do. Further, by satisfying the conditional expression (9), it is possible to suppress aberration fluctuations due to focusing, and it is possible to ensure good performance even at a close distance.

In addition, when the movable lens group is composed of three lens groups, and a positive lens is arranged on the image side of the third lens group with an air gap between them, the first lens group is arranged in order from the object side with a negative lens and a positive lens. 2 lenses, 2nd lens group in order from the object side, 3 lenses of positive lens, negative lens, positive lens, 3 lenses of positive lens, negative lens, negative lens, 3rd lens group, 1 negative lens It is preferable to consist of.
With this configuration, the total thickness of each lens group can be reduced, and better performance can be ensured while further shortening the overall length of the lens frame when retracted. In addition, the second lens group can be composed of two lenses, a positive lens and a negative lens in order from the object side, by making the most object side surface and the most image side surface aspherical. By doing so, the total length of the lens barrel when retracted can be further shortened.

  Hereinafter, the present invention will be described in detail based on illustrated embodiments.

In the following examples, R is the radius of curvature of each lens surface, d is the thickness or spacing of each lens, Nd is the refractive index of each lens at the d-line, Vd is the Abbe number of each lens at the d-line, K is a conical coefficient, A ₄ , A ₆ , A ₈ , and A ₁₀ are aspherical coefficients, f is the focal length of the entire system, Fno is the F number, 2ω is the full angle of view, and D1, D2, and D3 are variable intervals, respectively. ing.
Each aspheric shape is expressed by the following equation using each aspheric coefficient. However, the coordinate in the optical axis direction is Z, and the coordinate in the direction perpendicular to the optical axis is Y.
Z = (Y ² / r) / [1+ {1− (1 + K) · (Y / r) ² } ^1/2 ]
+ A ₄ Y ⁴ + A ₆ Y ⁶ + A ₈ Y ⁸ + A ₁₀ Y ¹⁰
In the aspheric coefficient, for example, the value of A _{4 in} the aspheric surface 4 of Example 1, −5.6343e−4, can be displayed as −5.6343 × 10 ^−4, but in this numerical data, All are displayed in the former format.

  FIG. 1 is a diagram illustrating the configuration of the imaging apparatus according to the present embodiment, where (a) shows a state at the wide-angle end, (b) shows an intermediate state, and (c) shows a state at the telephoto end. FIG. 2 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration when the zoom lens according to the present embodiment is focused on an object point at infinity, (a) is a wide angle end, (b). (C) shows the state at the telephoto end. FIG. 3 is a cross-sectional view specifically showing a configuration example of a sealing structure of the positive lens and the image sensor unit of the present embodiment.

As shown in FIGS. 1A to 1C, the imaging apparatus according to the present exemplary embodiment has a first lens group G ₁ having a negative power, a second lens group G ₂ having a positive power, and a negative power. a movable lens group comprising a third lens group G ₃ and having a positive lens L ₄ is a field lens, is composed of a cover glass CG, and the solid-state imaging device CCD as an electronic image pickup element, the second lens group G ₂ An aperture stop S is disposed on the object side. However, the solid-state imaging device CCD shows its imaging plane.

In the lens group constituting the movable lens group, the first lens group G ₁ has a biconcave negative lens L _11, a surface on the image side has a double-convex positive lens L ₁₂ are aspherical. The second lens group G ₂ includes, in order from the object side, a biconvex positive lens L ₂₁ having an aspheric surface on the object side, a biconcave negative lens L _22, and an aspheric surface on the image side, in the vicinity of the optical axis. in a cemented lens and the positive lens L _23, consisting of a double convex. The third lens group G ₃ is composed only of a biconcave negative lens L ₃ having an aspheric object side surface. The positive lens L ₄ that is a field lens is a convex flat lens having a convex shape facing the object side having a rectangular outer shape as shown in FIG. 4, and is known as a wavelength band limiting coat on the image side surface. Infrared cut coat is applied.

In the thus configured imaging optical system of the present embodiment, upon zooming from the wide-angle end to the telephoto end, on the optical axis Lc, the re object side after the first lens group G ₁ is moved to the image side The second lens group G ₂ moves so as to approach the first lens group G ₁ , and the third lens group G ₃ moves to the object side.

A specific configuration from the positive lens L ₄ to the solid-state imaging device CCD will be described with reference to FIG. On the image side of the third lens group, a positive lens L ₄ that is a convex flat lens, a cover glass CG, and a solid-state imaging device CCD are arranged in this order from the object side. The cover glass CG and the solid-state image sensor CCD constitute the image sensor unit 1 by being attached to the support frame 11. The imaging element unit 1 is attached to a holding member 2 which is a part of a member constituting the imaging apparatus together with the positive lens L ₄ , and the space between the two is sealed. In this embodiment, by adopting such a configuration, dust such as dust does not adhere to the surface of the cover glass CG, and deterioration of image quality can be prevented.

Note that the structure for sealing the positive lens and the imaging element unit is not limited to such a configuration. For example, as shown in FIG. 5, the positive lens L in which a field stop 3 and a planar contact portion L ₄₁₁ that contacts the field stop 3 are formed in the holding member 2 ′ in order from the object side, and in the periphery of the lens. ₄₁ , an annular frame 4 made of an elastic material such as rubber, and a metal that is electrically connected to the solid-state image pickup device CCD by disposing an image pickup device unit 1 ′ made up of a cover glass CG, a solid-state image pickup device CCD, and a support frame 11 ′. A sealed structure in which the plate 5 is attached to the holding member 2 ′ with screws 6 may be used. Thus, with the configuration to integrate the field stop 3 and the positive lens L ₄₁ and the image sensor unit 1 ', not only suppress the entry of dust to the imaging plane near, when the camera shake occurs The integrated part can be vibrated at the same time, and it is possible to easily perform blur correction and blur prevention by the image sensor. In addition, since the integrated part can be moved simultaneously in the optical axis direction, focusing can be easily performed. In this embodiment, since the positive lens L ₄₁ is made of plastic, it is advantageous for cost reduction.

Further, as shown in FIG. 6A, the positive lens L ₄ may be in direct contact with the image pickup device unit 1 on the entire surface on the image side plane. With such a configuration, it is possible to effectively prevent dust such as dust from adhering. Further, a shape in which a contact portion L ₄₂₁ is provided like a positive lens L ₄₂ shown in FIG. 6B, and the image sensor unit 1 may be partially contacted. If the positive lens L ₄₂ is formed in such a shape, it is possible to secure the sealing property, and it is easy to integrate with the image pickup device unit 1 using an adhesive, and the assembly becomes easier.

  Next, numerical data of lenses constituting the photographing optical system according to the present example are shown.

Surface R d Nd Vd
1 -47.518 1.000 1.88300 40.76
2 5.169 1.376
3 23.251 1.900 1.79491 25.63
4 * -20.455 D1
5 (Aperture) ∞ 0.000
6 * 4.172 2.300 1.58913 61.14
7 -13.092 0.700 1.90366 31.31
8 13.883 2.400 1.49700 81.54
9 * -17.320 D2
10 * -24.216 1.000 1.69350 53.21
11 26.122 D3
12 20.000 1.200 1.52542 55.78
13 ∞ 0.400
14 ∞ 0.500 1.51633 64.14
15 ∞ 0.700
16 (imaging plane) ∞
*: Aspherical surface

Aspherical coefficient surface RDY K A ₄ A ₆ A ₈ A ₁₀
4 -20.455 0.0000 -5.6343e-4 -3.2087e-5 2.2662e-6 -1.4938e-7
6 4.172 0.0000 -3.0725e-4 5.3126e-6 5.8987e-7 0
9 -17.320 0.0000 3.6809e-3 4.1838e-4 -6.7426e-5 1.2679e-5
10 -24.216 -9.3274 -1.9976e-4 3.4609e-5 -1.4306e-5 1.5505e-6

Zoom data
Wide angle end Medium telephoto end f 6.388 11.022 18.400
Fno 3.160 4.326 5.800
2ω (°) 63.1 36.5 21.9
D1 10.078 4.714 0.612
D2 5.349 5.022 7.310
D3 1.938 6.155 8.565

The data related to the above conditional expressions is
Conditional expression (1): DL / IH = 0.78
Conditional expression (2): (R1 + R2) / (R1-R2) = − 1.00004
Conditional expression (3): W_L / IH = 8.57
Conditional expression (4): | ΔD12 | /IH=2.63
Conditional expression (5): PAνd = 61.14 (lens L ₂₁ )
PAνd = 81.54 (lens L ₂₃ )
Conditional expression (6): D23W / IH = 1.49
Conditional expression (7): (f2 / fw) × (IH / fw) = 0.78
Conditional expression (8): W_L / fw = 4.90
Conditional expression (9): | ΔD12 / ΔD23 | = 4.83
Conditional expression (10): G1Σd / IH = 1.19
Conditional expression (11): Pνd = 61.14 (lens L ₂₁ )
Pνd = 81.54 (lens L ₂₃ )
Conditional expression (12): Pνd−Nνd = 31.31
Conditional expression (13-1): | DTW_ × 1.0 | = 8.17
Conditional expression (13-2): | DTW_ × 0.7 | = 4.27
Conditional expression (13-3): | DTW_ × 1.0 | = 8.17
Conditional expression (13-4): | ΔDTW | = 3.9
Conditional expression (14): IH / fw = 0.57
It is.

  FIG. 7 is a diagram illustrating the configuration of the imaging apparatus according to the present embodiment, where (a) illustrates a state at the wide-angle end, (b) illustrates an intermediate state, and (c) illustrates a state at the telephoto end. FIG. 8 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration when the zoom lens according to the present embodiment is focused on an object point at infinity, (a) is a wide angle end, (b). (C) shows the state at the telephoto end.

As shown in FIGS. 7A to 7C, the imaging apparatus according to the present exemplary embodiment has a negative power with a first lens group G ₁ having a negative power, a second lens group G ₂ having a positive power. a movable lens group comprising a third lens group G ₃ and having a positive lens L ₄ is a field lens, is composed of a cover glass CG, and the solid-state imaging device CCD as an electronic image pickup element, the second lens group G ₂ An aperture stop S is arranged on the front side. However, the solid-state imaging device CCD shows its imaging plane.

In the lens group constituting the movable lens group, the first lens group G _1, the surface on the image side and a biconcave negative lens L ₁₁ which is a non-spherical surface, which is a double-convex positive lens L _12,. The second lens group G ₂ includes, in order from the object side, a biconvex positive lens L ₂₁ having an aspheric object side surface, a negative meniscus lens L ₂₂ having a convex surface facing the image side, and a non-image side surface. a negative meniscus lens L ₂₃ with a convex surface facing the located image side spherical surface, a cemented lens consisting of. The third lens group G ₃ is composed only of a biconcave negative lens L ₃ whose surfaces on both sides are aspheric. Further, the positive lens L ₄ that is a field lens is a convex flat lens having a convex shape facing the object side having a rectangular outer shape as in the first embodiment. Note that the image side surface of the positive lens L ₄ has a low-pass filter function and an IR cut function, for example, by a method described in Japanese Patent Laid-Open No. 9-211206.

In the photographic optical system of the present embodiment configured as described above, when zooming from the wide-angle end to the telephoto end, the first lens group G ₁ moves to the image side on the optical axis Lc, and the second lens group G ₂ moves so as to approach the first lens group G ₁ , and the third lens group G ₃ moves to the object side.

Also in the present embodiment, as in the first embodiment, the positive lens L ₄ and the image sensor unit 1 have a sealed structure.

  Next, numerical data of lenses constituting the photographing optical system according to the present example are shown.

Surface R d Nd Vd
1 -36.131 1.000 1.80610 40.92
2 * 4.971 1.063
3 8.286 1.900 2.00069 25.46
4 20.764 D1
5 (Aperture) ∞ 0.000
6 * 3.551 2.500 1.49700 81.54
7 -7.800 0.500 1.80810 22.76
8 -16.330 1.350 1.49700 81.54
9 * -21.673 D2
10 * -31.090 0.800 1.52542 55.78
11 * 9.948 D3
12 16.945 1.200 1.52542 55.78
13 ∞ 0.270
14 ∞ 0.500 1.51633 64.14
15 ∞ 0.700
16 (imaging plane) ∞
*: Aspherical surface

Aspherical coefficient surface RDY K A ₄ A ₆ A ₈ A ₁₀
2 4.971 0.0000 -6.4942e-4 -9.0006e-6 -1.3803e-6 -4.5550e-9
6 3.551 0.0000 -4.4733e-4 2.5140e-5 1.6854e-6 0
9 -21.6730 0.0000 5.1327e-3 4.1441e-4 1.0422e-5 1.4336e-5
10 -31.090 171.5492 -2.2956e-3 9.2140e-4 -1.8915e-4 2.0037e-5
11 9.948 0.0000 -2.0877e-3 3.9956e-5 -3.9926e-5 0

Zoom data
Wide angle end Medium telephoto end f 6.093 10.637 17.596
Fno 3.384 4.484 5.958
2ω (°) 66.7 37.3 22.6
D1 10.450 4.272 0.440
D2 3.094 3.400 4.735
D3 3.211 5.997 8.474

The data related to the above conditional expressions is
Conditional expression (1): DL / IH = 0.74
Conditional expression (2): (R1 + R2) / (R1-R2) = − 1.00003389
Conditional expression (3): W_L / IH = 7.93
Conditional expression (4): | ΔD12 | /IH=2.78
Conditional expression (5): PAνd = 81.54
Conditional expression (6): D23W / IH = 0.86
Conditional expression (7): (f2 / fw) × (IH / fw) = 0.70
Conditional expression (8): W_L / fw = 4.68
Conditional expression (9): | ΔD12 / ΔD23 | = 6.10
Conditional expression (10): G1Σd / IH = 1.10
Conditional expression (11): Pνd = 81.54
Conditional expression (12): Pνd−Nνd = 22.76
Conditional expression (13-1): | DTW_ × 1.0 | = 10.164
Conditional expression (13-2): | DTW_ × 0.7 | = 4.92
Conditional expression (13-3): | DTW_ × 1.0 | = 10.164
Conditional expression (13-4): | ΔDTW | = 5.244
Conditional expression (14): IH / fw = 0.59
It is.

  Specific examples of the imaging apparatus of the present invention as described above are shown below.

  9, 10 and 11 are conceptual diagrams showing the configuration of a digital camera using the present invention. 9 is a front perspective view showing the appearance of the digital camera 40, FIG. 10 is a rear front view thereof, and FIG. 11 is a schematic perspective plan view showing the configuration of the digital camera 40. However, FIGS. 9 and 11 show the photographing optical system 41 when it is not retracted.

  In this example, the digital camera 40 includes a photographing optical system 41 disposed on the photographing optical path 42, a finder optical system 43 disposed on the finder optical path 44, a shutter 45, a flash 46, a liquid crystal display monitor 47, a focal point. A distance change button 61, a setting change switch 62, and the like are provided. Further, when the photographing optical system 41 is retracted, the cover 60 is slid to cover the photographing optical system 41 and the finder optical system 43.

  When the cover 60 is opened and the digital camera 40 is set to the photographing state, the photographing optical system 41 is in the non-collapsed state shown in FIG. In this state, when the shutter 45 disposed on the upper part of the digital camera 40 is pressed, photographing is performed through the photographing optical system 41, for example, the photographing optical system as described in the first embodiment of the present invention. The object image formed by the photographing optical system 41 is formed on the imaging surface of the CCD 49 that is a solid-state image sensor via the cover glass CG. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the processing means 51. Further, by connecting the recording means 52 to the processing means 51, it is also possible to record a photographed electronic image. The recording means 52 may be provided separately from the processing means 51, or may be configured to perform recording and writing electronically using a floppy (registered trademark) disk, memory card, MO, or the like.

  Further, a finder objective optical system 53 is disposed on the finder optical path 44. The finder objective optical system 53 includes a plurality of lens groups (three groups in the figure) and two prisms, and the focal length changes in conjunction with the photographing optical system 41. The object image formed by the finder optical system 53 is formed on the field frame 57 of the erecting prism 55 that is an image erecting member. Behind the erecting prism 55, an eyepiece optical system 59 for guiding the erect image to the observer eyeball E is disposed. A cover member 50 is disposed on the exit side of the eyepiece optical system 59.

  In the digital camera 40 configured in this manner, the photographing optical system 41 is high-performance and compact, and can be retracted, so that good performance is ensured and the digital camera 40 is miniaturized. be able to.

As mentioned above, although the Example of this invention was described, this invention is not limited to these Examples, A various deformation | transformation is possible in the range which does not deviate from the summary of this invention. For example, in the first embodiment, the positive lens L ₄ is provided with an infrared cut function, and in the second embodiment, an infrared cut function and a low-pass filter function are provided. However, the present invention is not limited to these, and the function can be appropriately changed according to desired performance, such as the positive lens L ₄ having only a low-pass filter function. Further, the surface having these functions (infrared cut function and / or low-pass filter function) is not limited to the image side surface of the positive lens L ₄ , and may be another lens surface.
Note that it is not always necessary to provide the positive lens L ₄ with these functions (infrared cut function and / or low-pass filter function).

In addition to the description of the scope of claims, the imaging apparatus of the present invention described above can be configured as follows, for example.
(1) In an imaging apparatus including a zoom lens system including a movable lens group,
A positive lens and an image sensor unit are arranged on the image side of the movable lens group in order from the object side.
The imaging apparatus, wherein the positive lens and the imaging element unit are in a sealed structure via a member constituting the imaging apparatus.

1 is a diagram illustrating a configuration of a zoom lens according to Example 1 of the present invention, where (a) shows a state at a wide angle end, (b) shows an intermediate state, and (c) shows a state at a telephoto end. FIG. 4A is an aberration curve diagram of the zoom lens according to Example 1 of the present invention, where FIG. 5A illustrates a state at a wide-angle end, FIG. 5B illustrates an intermediate state, and FIG. It is sectional drawing which shows the specific example of the sealing structure of a positive lens and an image pick-up element unit. It is a perspective view which shows the shape of the positive lens concerning the Example of this invention. It is sectional drawing which shows the other specific example of the sealing structure of a positive lens and an image pick-up element unit. It is sectional drawing which shows the other specific example of the sealing structure of a positive lens and an image pick-up element unit. FIG. 5 is a diagram illustrating a configuration of a zoom lens according to Example 2 of the present invention, where (a) shows a state at a wide angle end, (b) shows an intermediate state, and (c) shows a state at a telephoto end. FIG. 6A is an aberration curve diagram of the zoom lens according to Example 2 of the present invention, where FIG. 5A illustrates a state at the wide-angle end, FIG. 5B illustrates an intermediate state, and FIG. It is a front perspective view which shows the external appearance of the digital camera to which this invention is applied. FIG. 10 is a rear perspective view of the digital camera of FIG. 9. FIG. 10 is a perspective plan view showing the configuration of the digital camera of FIG. 9.

Explanation of symbols

G ₁ first lens group G ₂ second lens group G ₃ third lens group S Brightness stop CG Cover glass CCD Solid-state image sensor Lc Optical axis L ₄ , L ₄₁ , L ₄₂ positive lens L ₄₁₁ , L ₄₂₁ contact part 1, 1 ′ Image sensor unit 11, 11 ' Support frame 2, 2 ' Holding member 3 Field stop 4 Annular frame 5 Metal plate 6 Screw 40 Digital camera 41 Imaging optical system 42 Optical path for shooting 43 Viewfinder optical system 44 Optical path for viewfinder 45 Shutter 46 Flash 47 LCD monitor 49 CCD
50 Cover member 51 Processing means 52 Recording means 53 Objective optical system for viewfinder 55 Erecting prism 57 Field frame 59 Eyepiece optical system 60 Cover 61 Focal length change button 62 Setting change switch

Claims (26)

In an imaging apparatus including a zoom lens system including a movable lens group,
On the image side of the movable lens group, in order from the object side, a positive lens and an image sensor unit are arranged,
The positive lens and the imaging element unit are in a sealed structure via members constituting the imaging device, and a lens group having a negative power is disposed on the object side of the positive lens with an air gap therebetween. An imaging apparatus characterized by that.   The imaging apparatus according to claim 1, wherein the positive lens has a low-pass function or an infrared cut function. The imaging apparatus according to claim 1, wherein the lens group having the negative power satisfies the following conditional expression.
0.6 ≦ DL / IH ≦ 1.5 (1)
However,
DL: Distance from the object side surface of the positive lens to the image plane
IH: Maximum photographed image height.   The imaging apparatus according to claim 1, wherein the lens group having the negative power is included in a movable lens group. The imaging apparatus according to claim 1, wherein the positive lens satisfies the following conditional expression.
−3.7 ≦ (R1 + R2) / (R1−R2) ≦ −0.3 (2)
However,
R1: radius of curvature of object side surface of positive lens
R2: radius of curvature of the image side surface of the positive lens. The movable lens group includes, in order from the object side, a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a negative power.
6. The image pickup apparatus according to claim 1, wherein the positive lens is disposed on an image side of the third lens group with an air gap interposed therebetween.   The imaging apparatus according to claim 1, wherein an outer shape of the positive lens is a rectangle.   The imaging apparatus according to claim 1, wherein the positive lens is made of plastic. The imaging device includes a field stop,
The image pickup apparatus according to claim 8, wherein the field stop, the positive lens, and the image pickup element unit are integrally attached to a member constituting the image pickup apparatus.   10. The imaging apparatus according to claim 8, wherein a planar contact portion capable of contacting a field stop is formed in a lens peripheral portion of the plastic positive lens.   The image pickup apparatus according to claim 1, wherein the positive lens and the image pickup element unit are in contact with each other at least partially.   The contact surface is formed outside the effective diameter of the plastic positive lens, and the positive lens and the image pickup device unit are in contact with each other through the contact surface. The imaging device described.   The imaging apparatus according to claim 1, wherein a wavelength band limiting coat is applied to an image side surface of the positive lens.   The imaging apparatus according to claim 1, wherein the positive lens is a convex flat positive lens having a convex surface facing the object side. When the zoom lens system zooms from the wide-angle end to the telephoto end, the second lens group moves to the object side so that the distance between the first lens group and the second lens group decreases, and the third lens group The lens group moves so that the distance between the second lens group and the third lens group changes,
Of the lenses constituting the first lens group, there is only one negative lens, and the second lens group has at least one positive lens and at least one negative lens,
The image pickup apparatus according to claim 6, wherein the following conditional expression is satisfied.
4.0 ≦ W_L / IH ≦ 12.0 (3)
1.7 ≦ | ΔD12 | /IH≦4.6 (4)
52.0 ≦ PAνd (5)
However,
W_L: Length from the lens surface closest to the object side to the imaging surface of the first lens unit at the wide-angle end
IH: Maximum image height
ΔD12: Amount of change in the distance between the first lens unit and the second lens unit upon zooming from the wide-angle end to the telephoto end
PAνd: Abbe number of the positive lens in the second lens group. The imaging apparatus according to claim 15, further satisfying the following conditional expression:
0.45 ≦ D23W / IH ≦ 3.0 (6)
However,
D23W: Distance between the second lens group and the third lens group at the wide-angle end. The imaging apparatus according to claim 15 or 16, further satisfying the following conditional expression:
0.38 ≦ (f2 / fw) × (IH / fw) ≦ 0.95 (7)
However,
f2: focal length of the second lens unit
fw: Total focal length at the wide-angle end. The imaging apparatus according to claim 15, further satisfying the following conditional expression:
2.7 ≦ W_L / fw ≦ 10.0 (8)
However,
fw: Total focal length at the wide-angle end. The image pickup apparatus according to claim 15, further satisfying the following conditional expression:
3.7 ≦ | ΔD12 / ΔD23 | (9)
However,
ΔD23: an amount of change in the distance between the second lens unit and the third lens unit upon zooming from the wide-angle end to the telephoto end. The image pickup apparatus according to claim 15, wherein the first lens group includes a negative lens and a positive lens in order from the object side, and satisfies the following conditional expression.
0.6 ≦ G1Σd / IH ≦ 1.3 (10)
However,
G1Σd: the total thickness of the first lens group. 21. The system according to claim 15, wherein the second lens group includes one negative lens and at least one positive lens, and at least one of the positive lenses satisfies the following conditional expression. The imaging apparatus of Claim 1.
75.0 ≦ Pνd (11)
However,
Pνd: Abbe number of the positive lens in the second lens group. The imaging apparatus according to claim 21, further satisfying the following conditional expression:
45.0 ≦ Pνd−Nνd (12)
However,
Nvd: Abbe number of the negative lens in the second lens group.   The first lens group is movable between the wide-angle end and the telephoto end so that the total length of the optical system can be the shortest at the time of zooming. Imaging device. The imaging apparatus according to any one of claims 15 to 23, further satisfying the following conditional expression at the wide-angle end.
7.0% ≦ | DTW_ × 1.0 | (13-1)
3.5% ≦ | DTW_ × 0.7 | ≦ 15.0% (13-2)
7.0% ≦ | DTW_ × 1.0 | ≦ 25.0% (13-3)
| ΔDTW | ≦ 15.0% (13-4)
However,
DTW_ × 0.7: Length distortion at the position of 0.7 × of the maximum image height at the wide-angle end
DTW_ × 1.0: Length distortion at% position at the wide-angle end maximum photographed image height of 1.0
ΔDTW: the length at the position of x0.7 of the maximum image height at the wide-angle end and x1. Is the difference in% representation of distortion from the length at position 0,
Y′0: paraxial imaging height,
Y ′: When the actual imaging height is assumed,
Distortion amount = (Y′−Y′0) / Y′0 × 100 (%)
It is.   The imaging apparatus according to any one of claims 15 to 24, wherein focusing is performed by moving the third lens group in an optical axis direction. The first lens group includes, in order from the object side, a negative lens and a positive lens,
The second lens group includes, in order from the object side, three positive lenses, negative lenses, and positive lenses, or positive lenses, negative lenses, and three negative lenses.
The imaging apparatus according to any one of claims 15 to 25, wherein the third lens group includes one negative lens.

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