JP2007148051A - Photographing lens unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photographing lens unit which is made thin while having high optical performance, and also to provide an imaging device having the same. <P>SOLUTION: The photographing lens unit LU has a zoom lens system ZL which forms an optical image of a body and an imaging element SR which converts the optical image into an electric signal. The zoom lens system ZL has a plurality of lenses, an aperture stop ST disposed between the lenses, and a prism PR which bends an optical axis by nearly 90° on an object side of the open aperture ST. The aperture stop ST has an asymmetrical aperture shape about an image-side optical axis AX2 disposed on an image side of the prism PR. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photographic lens unit, for example, an imaging device such as a digital camera that captures an image of a subject with an imaging device, a digital device with an image input function, and a photographic lens unit that is suitable for reducing the thickness thereof.

In recent years, the spread of digital cameras has been remarkable, and there is a feeling that they have been replaced with silver halide cameras. Along with the widespread use of digital cameras, smaller digital cameras have been demanded, and further downsizing of the taking lens system has been demanded. In response to such demands, digital cameras that have achieved a significant reduction in camera thickness using bending means (for example, reflecting members such as prisms and mirrors) that bend the optical path in the taking lens system are on the market. . This type of digital camera takes advantage of features not found in silver halide cameras in order to make it thinner. In other words, a digital camera has a high degree of freedom in arrangement of an image sensor (e.g., a photoelectric conversion element) in the camera, and if it is a digital camera, an image reversed by the photographing lens system can be easily restored by electrical processing. is there. Therefore, it can be said that the bending of the optical path by the bending means is a technique for reducing the camera thickness that is possible because of a digital camera. In addition, there has also been proposed a photographing lens unit in which the mechanical configuration is simplified and the thickness is reduced by zooming the aperture stop while the shutter is fixed at a zoom position in a zoom lens system having a bending means (for example, Patent Documents). 1).
JP 2004-333721 A

When the bending means is adapted to the photographing lens system in order to reduce the camera thickness, the thickness of the photographing lens system is determined by one of the following sizes (i) and (ii) (in general, the size ( i) is determined by off-axis light, and size (ii) is determined by either on-axis light or off-axis light). Therefore, in order to further reduce the photographing lens system, it is necessary to make the sizes (i) and (ii) as small as possible. The size (i) can be reduced by increasing the power of the lens group. However, when the effective optical path diameter is reduced by such a method, the effective optical path diameter of the on-axis light increases conversely, that is, the size (ii) tends to increase. Becomes difficult.
(i): The sum of the thickness of the lens disposed on the object side from the bending position and the thickness of the bending means.
(ii): Effective optical path diameter of the lens arranged on the image side from the bending position.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a photographic lens unit that is thinned while maintaining high optical performance, and an imaging device including the photographic lens unit. is there.

  In order to achieve the above object, a photographic lens unit according to a first aspect of the present invention includes a photographic lens system that forms an optical image of an object, and an imaging device that converts the optical image into an electrical signal. The lens system includes a plurality of lenses, an aperture stop positioned between the lenses, and a reflecting member that bends the optical axis by approximately 90 ° on the object side of the aperture stop, the lens unit being more than the reflecting member. When the optical axis located on the image side is the image side optical axis, the aperture stop has an asymmetric aperture shape with respect to the image side optical axis.

  The photographic lens unit according to a second aspect of the present invention is characterized in that, in the first aspect, the aperture shape of the aperture stop is an elliptical shape.

  According to a third aspect of the present invention, there is provided the photographing lens unit according to the first aspect, wherein the aperture shape of the aperture stop is a rectangular shape.

  According to a fourth aspect of the present invention, there is provided the photographic lens unit according to the first aspect, wherein the aperture shape of the aperture stop is an oval shape.

  The photographic lens unit according to a fifth aspect of the present invention is the photographic lens unit according to any one of the first to fourth aspects, wherein an optical axis located on the object side relative to the reflecting member is an object side optical axis. The opening length in the direction parallel to the object-side optical axis is shorter than the opening length in the direction perpendicular to the object-side optical axis.

The photographic lens unit according to a sixth aspect of the present invention is characterized in that, in any one of the first to fifth aspects, the aperture stop satisfies the following conditional expression (1).
0.5 <LA / LB <0.9 (1)
However,
LA: the shortest distance from the image side optical axis on the aperture surface to the edge of the aperture stop,
LB: longest distance from the image side optical axis on the aperture surface to the edge of the aperture stop,
It is.

  According to a seventh aspect of the present invention, in the fifth or sixth aspect, at least one of the plurality of lenses positioned on the image side of the reflecting member is asymmetric with respect to the image-side optical axis. It has a lens shape, and the lens length in the direction perpendicular to the image side optical axis of the lens is shorter in the direction parallel to the object side optical axis than in the direction perpendicular to the object side optical axis. To do.

  The photographic lens unit of an eighth invention is characterized in that, in any one of the first to seventh inventions, a lens located closest to the object side among the plurality of lenses is a negative lens.

  An image pickup apparatus according to a ninth aspect includes the photographic lens unit according to any one of the first to eighth aspects.

  According to the present invention, since the aperture stop has an asymmetric aperture shape with respect to the image-side optical axis, it is possible to achieve a reduction in thickness while maintaining high optical performance in the photographing lens system. Therefore, it is possible to realize a thin and high-performance photographic lens unit and an image pickup apparatus including the same. If the photographic lens unit according to the present invention is used in an imaging device such as a digital camera or a portable information device, it can contribute to its thinness, light weight, compactness, low cost, high performance, high functionality, and the like. .

  Hereinafter, an imaging lens unit, an imaging apparatus and the like embodying the present invention will be described with reference to the drawings. The photographing lens unit according to the present invention is an optical device that optically captures an image of a subject and outputs it as an electrical signal, and constitutes a main component of a camera used for photographing a still image or moving image of the subject. It is. Examples of such cameras include digital cameras, video cameras, surveillance cameras, in-vehicle cameras, video phone cameras, door phone cameras, etc., and personal computers, portable information devices (mobile computers, mobile phones, mobile phones). Cameras that are built in or externally attached to information terminals (PDA: Personal Digital Assistant) and other small and portable information device terminals, peripheral devices (mouse, scanner, printer, memory, etc.), and other digital devices Can be mentioned. As can be seen from these examples, it is possible not only to configure a camera as an imaging device by using a photographing lens unit, but also to add a camera function by mounting the photographing lens unit on various devices. . For example, a digital device with an image input function such as a mobile phone with a camera can be configured as an imaging device.

  The term “digital camera” used to refer to the one that records optical still images exclusively, but digital still cameras and home digital movie cameras that can handle still images and movies simultaneously have also been proposed. In particular, it has become difficult to distinguish. Therefore, the term “digital camera” means a digital still camera, digital movie camera, or web camera (whether an open type or a private type, a camera that is connected to a network and connected to a device that enables image transmission / reception). , And the like, including those directly connected to a network and those connected via a device having an information processing function such as a personal computer.) All cameras including a photographic lens unit having an image pickup device or the like for converting a video signal into an electric video signal are included.

  FIG. 8 shows an appearance of a digital camera CU as an example of an imaging apparatus. 8A is a front view, and FIG. 8B is a rear view. The housing 1 of the digital camera CU has a substantially rectangular parallelepiped shape close to a flat plate. As shown in FIG. 8A, the photographing lens window 2 is located in the upper right part of the front, and the finder window 3 is located in the upper center of the front. A flash 4 is provided in the upper left part of the front. Also, as shown in FIG. 8B, an LCD monitor 11 is provided near the center of the back surface, and a shooting / movie / playback mode switching lever 8 is provided on the upper side of the LCD monitor 11 so as to be slidable to the left and right. Various operation buttons 10 are arranged in a horizontal row below the LCD monitor 11. Further, a substantially cross-shaped up / down / left / right lever 9 is provided at the upper right portion of the back surface, an optical finder 5 and an indicator 6 are provided at the upper left portion, and a battery compartment / card slot cover 12 is provided at the lower right portion of the rear surface. A shutter button 7 is provided on the upper surface.

  FIG. 9 is a schematic cross-sectional view showing a schematic optical configuration example of the digital camera CU. A photographic lens unit LU mounted on the digital camera CU sequentially corresponds to a zoom lens system ZL (corresponding to a photographic lens system, PR: prism, which forms an optical image of an object so as to be capable of zooming. RL: reflecting surface, ST: aperture stop) and parallel flat plate PT (corresponding to an optical filter such as an optical low-pass filter and an infrared cut filter arranged as necessary; a cover glass of the image sensor SR, etc.) And an image sensor SR that converts an optical image formed on the light receiving surface by the zoom lens system ZL into an electrical signal. A lens barrier LB for opening and closing the photographic lens window 2 (FIG. 8A) is disposed in the upper part on the front side in the housing 1, and the lens barrier LB is moved up and down as indicated by arrows. 2 is configured to open and close.

  In this digital camera CU, the photographic lens unit LU is vertically placed on the right side when viewed from the front side of the digital camera CU. The prism PR is located in the upper part of the housing 1 and the image sensor SR is located in the lower part of the housing 1 respectively. positioned. However, when realizing the camera function with the photographing lens unit LU, it is possible to adopt a form as necessary. For example, the photographic lens unit LU is placed on the front side of the digital camera CU so that the prism PR is located on the right side (or left side) in the housing 1 and the image sensor SR is located on the left side (or right side) in the housing 1. It may be placed horizontally in the center as seen from the top. Further, in this digital camera CU, the photographing lens unit LU is disposed inside the housing 1 constituting the camera body, but it is possible to adopt a form as necessary when realizing the camera function. It is. For example, the unitized photographing lens unit LU may be configured to be detachable or rotatable with respect to the camera body, and the unitized photographing lens unit LU may be configured to be detachable or rotatable with respect to the portable information device. May be.

  In the photographic lens unit LU shown in FIG. 9, a planar reflecting surface RL is arranged in the middle of the optical path in the zoom lens system ZL, and at least one lens is arranged on each of the front side and the rear side of the reflecting surface RL. Has been. The reflection surface RL bends the optical path for using the zoom lens system ZL as a bending optical system. At this time, the optical axis of the zoom lens system ZL is approximately 90 degrees (that is, 90 degrees or substantially 90 degrees). ) The light beam is reflected as if bent. If the reflection surface RL that bends the optical axis (that is, bends the optical path) is provided in the optical path of the zoom lens system ZL in this way, the degree of freedom of arrangement of the photographic lens unit LU is increased and the thickness direction of the photographic lens unit LU is increased. It is possible to achieve an apparent thinning of the photographic lens unit LU by changing the size of the photographic lens unit LU. In particular, as in the case of the photographic lens unit LU shown in FIG. 9, when one negative lens is disposed closest to the object side and the reflecting surface RL is disposed on the image side of the negative lens, a great effect of thinning is obtained. be able to. This is because the reflecting surface can be reduced by moving the pupil forward. The bending position of the optical path is not limited to the middle of the zoom lens system ZL, and may be further set on the front side or the rear side of the zoom lens system ZL as necessary. Appropriate bending of the optical path makes it possible to effectively reduce the apparent thickness and size of the digital camera CU on which the photographing lens unit LU is mounted.

  The reflection surface RL is constituted by a reflection member such as a prism (right angle prism or the like), a mirror (plane mirror or the like). In the photographing lens unit LU shown in FIG. 9, the prism PR is used as a reflecting member that bends the optical axis, but the reflecting member to be used is not limited to prisms. The reflection surface RL may be configured by using a mirror such as a plane mirror as the reflection member. In addition, the light beam is reflected by one reflecting surface RL so that the optical axis of the zoom lens system ZL is bent approximately 90 degrees, but the reflecting member may have two or more reflecting surfaces. That is, a reflecting member that reflects a light beam so that the optical axis AX of the zoom lens system ZL is bent by approximately 90 degrees with two or more reflecting surfaces may be used. The optical action for bending the optical path is not limited to reflection, and refraction or diffraction may be combined with reflection. That is, a reflecting member having a reflecting surface, a refracting surface, a diffractive surface, or a combination thereof may be used. Further, the prism PR used in the photographing lens unit LU shown in FIG. 9 does not have optical power (power: an amount defined by the reciprocal of the focal length), but is optically applied to a reflecting member that bends the optical path. You may give a certain power. For example, if some of the optical power of the taking lens system is borne by the reflecting surface of the prism, the light incident side, the light exit side, the mirror reflecting surface, etc., the optical performance is improved by reducing the power burden of the lens element. It becomes possible to make it.

  The zoom lens system ZL includes a plurality of lens groups. The plurality of lens groups move along the optical axis, and the zoom lens system ZL performs zooming by changing the lens group interval. The aperture stop ST included in the zoom lens system ZL is an asymmetric characteristic component of the aperture shape, as will be described in detail later. In this photographing lens unit LU, the aperture stop ST is also used as a shutter. However, the aperture stop and the shutter may be arranged independently, or the shutter may be fixed at the zoom position and the aperture stop may be moved in the zoom. . Note that the photographing lens system used for the photographing lens unit LU is not limited to the zoom lens system ZL. Instead of the zoom lens system ZL, another type of variable power optical system (for example, a variable focal length imaging optical system such as a multiple focal length switching type lens) or a single focus optical system may be used as the photographing lens system. .

  When an optical image to be formed by the zoom lens system ZL is converted into an electrical signal by passing through an optical low-pass filter having a predetermined cutoff frequency characteristic determined by the pixel pitch of the image sensor SR. The spatial frequency characteristics are adjusted so that the so-called aliasing noise that occurs is minimized. Thereby, generation | occurrence | production of a color moire can be suppressed. However, if the performance around the resolution limit frequency is suppressed, there is no need to worry about the occurrence of noise without using an optical low-pass filter, and the display system where the noise is not very noticeable (for example, the liquid crystal of a mobile phone) When a user performs shooting or viewing using a screen or the like, it is not necessary to use an optical low-pass filter in the shooting lens system. As the optical low-pass filter, a birefringence low-pass filter, a phase low-pass filter, or the like can be applied. Examples of the birefringent low-pass filter include those made of a birefringent material such as quartz whose crystal axis direction is adjusted to a predetermined direction, and those obtained by laminating wave plates that change the polarization plane. Examples of the phase type low-pass filter include those that achieve the required optical cutoff frequency characteristics by the diffraction effect.

  As the imaging element SR, for example, a solid-state imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor having a plurality of pixels is used. The optical image formed on the zoom lens system ZL (on the light receiving surface of the image sensor SR) is converted into an electrical signal by the image sensor SR. The signal generated by the image sensor SR is subjected to predetermined digital image processing, image compression processing, etc. as necessary, and recorded as a digital video signal in a memory (semiconductor memory, optical disk, etc.), or in some cases via a cable. Or converted into an infrared signal and transmitted to another device. In addition, an arithmetic device CA that performs image processing is electrically connected to the imaging element SR via a flexible substrate f.

  As in the above-described photographing lens unit LU, in a photographing lens unit that includes a photographing lens system that forms an optical image of an object and an image sensor that converts the optical image into an electrical signal, the optical axis is set on the reflecting surface. By using a bending optical system for bending as a photographic lens system, it is possible to achieve an effective thinning. However, there is a limit peculiar to a photographing lens unit having a bending optical system in reducing the thickness. That is, if the power of the lens group is increased to reduce the effective optical path diameter determined by off-axis light, the effective optical path diameter of the on-axis light tends to increase.

  From the viewpoint of reducing the effective optical path diameter determined by the on-axis light, the taking lens system includes a plurality of lenses, an aperture stop positioned between the lenses, and a reflecting member that bends the optical axis by approximately 90 ° on the object side from the aperture stop. It is preferable that the photographic lens unit has a configuration in which the aperture stop has an asymmetric aperture shape with respect to the image side optical axis (that is, the optical axis located on the image side relative to the reflecting member). According to this configuration, there is a degree of freedom to reduce the effective optical path diameter determined by the axial light beam, so that it is possible to achieve a reduction in thickness while maintaining high optical performance in the photographing lens system. Therefore, it is possible to realize a thin and high-performance photographic lens unit that can be used in an imaging device such as a digital camera or a portable information device, thereby reducing its thickness, weight, size, cost, and performance. This can contribute to higher functionality. Examples of the aperture shape of the aperture stop include an elliptical shape, a rectangular shape, and an oval shape. Among them, the oval shape is preferable from the viewpoint of effective use of the light beam.

  On the aperture surface of the aperture stop, the aperture length in the direction parallel to the object side optical axis is larger than the aperture length in the direction perpendicular to the object side optical axis (that is, the optical axis located on the object side of the reflecting member). Is preferably shorter. That is, it is preferable that the aperture length of the aperture stop in the direction perpendicular to the image side optical axis is shorter in the direction parallel to the object side optical axis than in the direction perpendicular to the object side optical axis. With this configuration, the effective optical path diameter determined by the axial light beam can be reduced. At this time, it is desirable that the aperture area of the asymmetric aperture stop having the aperture shape is the same as the aperture area of the aperture shape that should be a circle. Accordingly, it is possible to achieve a relatively thin thickness as compared with a photographing lens unit having the same F number. That is, it is possible to achieve both a reduction in the thickness of the photographing lens unit and achievement of a bright F number. In terms of reducing the thickness of the photographing lens unit, it is further preferable that the aperture length in the direction parallel to the object-side optical axis is the shortest on the aperture surface of the aperture stop. In other words, the direction parallel to the object-side optical axis is the direction of light incident on the photographic lens system. If the aperture length is minimized in this direction, the photographic lens unit can be thinned most effectively. Become.

It is desirable that the aperture stop satisfies the following conditional expression (1).
0.5 <LA / LB <0.9 (1)
However,
LA: the shortest distance from the image side optical axis on the aperture surface to the edge of the aperture stop,
LB: longest distance from the image side optical axis on the aperture surface to the edge of the aperture stop,
It is.

  If the upper limit of conditional expression (1) is exceeded, the effect of reducing the thickness cannot be obtained. On the other hand, if the lower limit of conditional expression (1) is exceeded, the asymmetry of the blurred image becomes conspicuous and there is a possibility of deteriorating the on-axis performance, which is not preferable. The aperture shape of the aperture stop is preferably plane-symmetric with respect to a plane that includes the image-side optical axis and is perpendicular to the object-side optical axis, and more preferably satisfies the conditional expression (1). By using an aperture stop having the above-described plane-symmetric opening shape, it is possible to more effectively improve the asymmetry of the blurred image, and further satisfying the conditional expression (1) provides a balance between thinning and optical performance. Even better.

  Of the plurality of lenses constituting the photographing lens system, at least one lens positioned on the image side of the reflecting member has an asymmetric lens shape with respect to the image side optical axis, and the image side optical axis of the lens is The lens length in the vertical direction is preferably shorter in the direction parallel to the object side optical axis than in the direction perpendicular to the object side optical axis. If the aperture length of the aperture stop is set as described above, the effective optical path diameter determined by the axial light beam can be reduced, so that the lens outer diameter on the image side than the reflecting member can be reduced. . Also, since the thickness of the photographic lens unit is affected by the outer diameter of the lens after bending the optical path, if the lens outer diameter is made smaller in a specific direction by actively cutting the area where the light beam used for imaging does not pass, It is possible to further reduce the thickness of the taking lens unit. Therefore, at least one lens positioned on the image side with respect to the reflecting member has a lens shape asymmetric with respect to the image-side optical axis, and the lens length in the direction perpendicular to the image-side optical axis of the lens is set to the object side. If the length is shorter in the direction parallel to the object side optical axis than in the direction perpendicular to the optical axis, the photographing lens unit can be made thinner.

  Of the plurality of lenses constituting the photographing lens system, the lens located closest to the object side is preferably a negative lens. Using a negative lens as the lens located closest to the object side is advantageous in reducing the size of the reflecting member. If this is a positive lens, the reflecting member will be increased in size. In order to reduce the thickness of the photographing lens unit, in order to reduce the sum of the thickness of the lens arranged on the object side from the reflecting surface and the thickness of the reflecting member, for example, the effective diameter of the lens positioned closest to the object side is reduced. It is effective to do. For this purpose, it is necessary to increase the negative power of the lens positioned closest to the object side. However, if the negative power of the lens positioned closest to the object side is increased, the effective optical path diameter of the on-axis light increases due to the negative power. In other words, increasing the negative power of the lens located closest to the object side is effective in reducing the front lens diameter, but the effective optical path diameter of the on-axis light in the lens arranged on the image side from the reflecting surface is reduced. It also causes an increase. However, if an aperture stop having an asymmetric aperture shape with respect to the image-side optical axis is used, the effective optical path diameter determined by the axial light beam can be reduced as described above. Therefore, using a negative lens as the lens located closest to the object side is effective for reducing the thickness of the photographing lens unit.

  FIG. 1 shows an embodiment of a photographic lens unit LU in which the aperture stop ST has an asymmetric aperture shape with respect to the image side optical axis AX2, and FIG. 6 shows an aperture shape in which the aperture stop ST is symmetric with respect to the image side optical axis AX2. An imaging lens unit LU as a comparative example is shown. The imaging lens unit LU shown in FIGS. 1 and 6 corresponds to the above-described imaging lens unit LU (FIG. 9), and only the lens configuration of the zoom lens system ZL is different (however, closest to the object side). It is the same in that it has a negative lens.) In the embodiment (FIG. 1) and the comparative example (FIG. 6), the lens configuration of the zoom lens system ZL is the same except that the outer shape of the lens and the aperture shape of the aperture stop ST are different.

  1A and 6B, (A) is an optical cross section (that is, a digital camera CU) on a plane that is parallel to the short side of the imaging region SS of the imaging element SR and includes the object side optical axis AX1 and the image side optical axis AX2. The cross section viewed from the side surface of the imaging area SS is shown, and the luminous flux is formed by the axial luminous flux that forms an image at the screen center of the imaging area SS and the end of the imaging area SS in the short side direction (that is, on the long side of the screen). The off-axis light beam to be imaged is shown. (B) is an optical cross section (that is, the front side of the digital camera CU) in a plane parallel to the long side of the imaging region SS of the imaging element SR (in other words, perpendicular to the short side) and including the image side optical axis AX2. A cross section viewed from the above), and the luminous flux includes an axial luminous flux that forms an image at the center of the screen of the imaging region SS and an axis that forms an image at the end in the long side direction of the imaging region SS (that is, on the short side of the screen). The external luminous flux is shown. FIG. 5 shows an imaging region SS (a shape when viewed along the image-side optical axis AX2 direction) of the imaging element SR. In the imaging region SS having a rectangular shape, the axial light beam forms an image at the point R (that is, the center of the screen through which the image-side optical axis AX2 passes), and the off-axis light beam in the short side direction of the screen forms an image at the point S (see FIG. 1 (A), FIG. 6 (A)), the off-axis light beam in the long side direction of the screen forms an image at a point T (FIG. 1 (B), FIG. 6 (B)).

  2 to 4 show three types of aperture stops ST used in the embodiment (FIG. 1) of the photographing lens unit LU, respectively. FIG. 7 shows a comparative example (FIG. 6) of the photographing lens unit LU. An aperture stop ST is shown. Both show the appearance when viewed along the image-side optical axis AX2 direction (the arrow Z direction in FIGS. 1A and 6A), and the shape of each aperture SA (that is, the aperture shape). Is plane-symmetric with respect to a plane including the image-side optical axis AX2 and perpendicular to the object-side optical axis AX1. That is, the aperture shape of the aperture stop ST shown in FIG. 2 is an elliptical shape, the aperture shape of the aperture stop ST shown in FIG. 3 is a rectangular shape, and the aperture shape of the aperture stop ST shown in FIG. The aperture shape of the aperture stop ST shown in FIG. 7 is circular.

  In order to make the F number the same in the embodiment (FIG. 1) and the comparative example (FIG. 6), the aperture area of the asymmetric aperture stop ST having the aperture shape is set to the aperture shape which should be essentially a circle. The area may be the same as the area. Since the aperture stop ST shown in FIG. 7 has a circular aperture shape, the aperture area is π × (D / 2) × (D / 2), where D is the diameter of the aperture surface. Since the aperture stop ST shown in FIG. 2 has an elliptical aperture shape, the aperture area is π × (a / 2) × (b / 2). Therefore, the relationship D × D = a × b may be satisfied. Since the aperture stop ST shown in FIG. 3 has a rectangular aperture shape, the aperture area is a ′ × b ′ when the lengths of the short side and the long side are a ′ and b ′, respectively. Therefore, the relationship of π × (D / 2) × (D / 2) = a ′ × b ′ may be satisfied.

The aperture stop ST shown in FIG. 4 has an oval shape. Assuming that the area of a circle of diameter D is S1, the short axis and long axis of the oval shape are a ″ and b ″, respectively, and the area of the oval shape is S2, the areas S1 and S2 are expressed by the following formula (I) , (II). Here, when θ = sin ⁻¹ (a / b) [deg], in order to satisfy S1 = S2, a ″ and b ″ may satisfy the following formula (III). Then, the F number of the design is determined by the diameter D, and the aperture shape a ″ for thinning is determined so that the same F number as that case is obtained, and aberration correction is performed up to the aperture diameter b ″. For example, if D = 5.508, a ″ = 4.486, b ″ = 6.111, (I): S1 = 24.701, (II): S2 = 24.700, the left side of (III) = 1.090 and the right side of (III) = 1.090. At this time, a ″ / b ″ = 0.734 (= LA / LB) satisfies the conditional expression (1).
S1 = π × (D / 2) ² (I)
S2 = π × b ″ ² × θ / 360 + a ″ × b ″ × cos θ / 2 (II)
b ″ /D=1.95×(a ″ / D) ² −3.96 × (a ″ /D)+3.01 (III)

  In the photographic lens unit LU shown in FIG. 1, the aperture stop ST is arranged so that the aperture length in the direction parallel to the object-side optical axis AX1 is the shortest on the aperture surface SA (FIGS. 2 to 4). . Further, the plurality of lenses positioned on the image side of the prism PR have an asymmetric lens shape with respect to the image-side optical axis AX2, and the lens length in the direction perpendicular to the image-side optical axis AX2 of the lens is It is the shortest in the direction parallel to the side optical axis AX1. Further, the negative lens G1 is used as the lens located closest to the object side. With these configurations, the photographing lens unit LU shown in FIG. 1 achieves thinning while maintaining high optical performance in the zoom lens system ZL.

  As can be seen by comparing FIG. 1 (A) and FIG. 6 (A), an embodiment using an asymmetric aperture stop ST (FIGS. 2 to 4) having an aperture shape with respect to the image-side optical axis AX2 (FIG. 1). Then, the photographic lens unit LU is shortened in the thickness direction of the digital camera CU (FIG. 9), compared to the comparative example (FIG. 6) using the aperture stop ST (FIG. 7) that is symmetrical with respect to the image side optical axis AX2. ing. On the other hand, as can be seen by comparing FIG. 1B and FIG. 6B, an embodiment using an asymmetric aperture stop ST (FIGS. 2 to 4) having an aperture shape with respect to the image-side optical axis AX2. In FIG. 1, the aperture stop ST in the left-right direction of the digital camera CU (FIG. 9) is larger than in the comparative example (FIG. 6) using the aperture stop ST (FIG. 7) that is symmetrical with respect to the image-side optical axis AX 2. The lens diameter in the vicinity is increasing. This is because the aperture area of the aperture stop ST in the embodiment (FIG. 1) is set to be the same as the aperture area of the aperture stop ST in the comparative example (FIG. 6). The photographic lens unit LU has been made thinner while maintaining the same.

  Note that when the photographing lens unit LU is arranged horizontally when viewed from the front side of the digital camera CU, due to the relationship between the vertical and horizontal orientations of the imaging area SS relative to the subject, the screen long side direction of the imaging area SS is the digital camera CU. Even in such a case, by using the aperture stop ST having an asymmetric aperture shape (for example, in the aperture surface SA of the aperture stop ST, the aperture length in the direction perpendicular to the object-side optical axis is larger than By shortening the opening length in the direction parallel to the object side optical axis), it is possible to obtain the same effect as in the case of the above-described vertical arrangement (FIG. 1 and the like).

FIG. 6 is an optical path diagram showing an embodiment of a photographing lens unit in which an aperture stop has an asymmetric aperture shape with respect to the image side optical axis. The top view which shows the aperture stop of the elliptical opening used for embodiment of FIG. The top view which shows the aperture stop of the rectangular-shaped opening used for embodiment of FIG. The top view which shows the aperture stop of the oval shape opening used for embodiment of FIG. The top view which shows the imaging area of the image pick-up element used for embodiment of FIG. 1 and the comparative example of FIG. FIG. 6 is an optical path diagram illustrating a photographing lens unit as a comparative example in which the aperture stop has an aperture shape that is symmetric with respect to the image side optical axis. The top view which shows the aperture stop of the circular opening used for the comparative example of FIG. The figure which shows the external appearance of the front side and back side of a digital camera. The side view which shows the example of a schematic optical structure of the digital camera carrying a photographic lens unit in a typical cross section.

Explanation of symbols

CU digital camera (imaging device)
LU Shooting lens unit ZL Zoom lens system (shooting lens system)
G1 negative lens PR prism (reflective member)
RL Reflecting surface ST Aperture stop SA Aperture surface SR Image sensor SS Imaging area AX1 Object side optical axis AX2 Image side optical axis

Claims (9)

An imaging lens system that forms an optical image of an object; and an imaging device that converts the optical image into an electrical signal, and the imaging lens system includes a plurality of lenses and an aperture stop positioned between the lenses; A photographic lens unit having a reflecting member that bends the optical axis by approximately 90 ° on the object side from the aperture stop,
An imaging lens unit, wherein the aperture stop has an asymmetric aperture shape with respect to the image side optical axis, where an optical axis positioned on the image side of the reflecting member is an image side optical axis.   2. The photographing lens unit according to claim 1, wherein the aperture shape of the aperture stop is an elliptical shape.   2. The photographing lens unit according to claim 1, wherein the aperture shape of the aperture stop is a rectangular shape.   2. The photographing lens unit according to claim 1, wherein the aperture shape of the aperture stop is an oval shape.   Assuming that the optical axis located on the object side of the reflecting member is the object side optical axis, the opening surface of the aperture stop has an opening length in the direction perpendicular to the object side optical axis, with respect to the object side optical axis. The photographic lens unit according to any one of claims 1 to 4, wherein an opening length in a parallel direction is shorter. The photographic lens unit according to claim 1, wherein the aperture stop satisfies the following conditional expression (1):
0.5 <LA / LB <0.9 (1)
However,
LA: the shortest distance from the image side optical axis on the aperture surface to the edge of the aperture stop,
LB: longest distance from the image side optical axis on the aperture surface to the edge of the aperture stop,
It is.   Among the plurality of lenses, at least one lens positioned on the image side with respect to the reflecting member has a lens shape asymmetric with respect to the image side optical axis, and a lens perpendicular to the image side optical axis in the lens 7. The taking lens unit according to claim 5, wherein the length is shorter in a direction parallel to the object side optical axis than in a direction perpendicular to the object side optical axis.   The photographic lens unit according to any one of claims 1 to 7, wherein a lens located closest to the object side among the plurality of lenses is a negative lens.   An imaging apparatus comprising the photographic lens unit according to claim 1.

Images