JP2006058840A - Imaging optical system, imaging lens device and digital equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact imaging optical system of high optical performance while suppressing the increase of the cost, which can be loaded to a portable telephone and a portable information terminal. <P>SOLUTION: The imaging optical system is constituted by having a 1st reflection prism 1 having positive optical power as a whole, an optical diaphragm, a 1st lens 2 having positive optical power, a 2nd lens 3 having negative optical power and a 2nd reflection prism 4 having positive optical power as a whole on an optical axis in order from an object side. Regarding the 1st reflection prism 1, the incident surface has negative optical power, the exit surface has positive optical power, and a planar reflection surface RL1 is arranged on the optical path between the incident surface and the exit surface. Regarding the 2nd reflection prism 4, the incident surface has positive optical power, the exit surface has negative optical power and a planar reflection surface RL2 is arranged on the optical path between the incident surface and the exit surface. The reflection surfaces RL1 and RL2 bend the incident light at about 90 degrees and reflect the light toward the 1st lens 2 or a plane-parallel plate 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging optical system, an imaging lens device including the imaging optical system, and a digital apparatus equipped with the imaging lens device.

  In recent years, digital devices such as digital still cameras, digital video cameras, camera-equipped mobile phones and personal digital assistants (PDAs) have become widespread, and image sensors mounted on these devices have higher pixels and higher functions. Is progressing rapidly. For this reason, in order to make full use of the performance of an image sensor with an increased number of pixels and the like, a high optical performance is also required for an imaging optical system that guides an optical image of a subject to the image sensor.

  Each of the digital devices is also required to be portable, and the imaging optical system can be made compact as one means for reducing the size of the digital device. Conventionally, as a means for downsizing the imaging optical system, for example, a retracted structure of the imaging optical system is employed.

  However, in an imaging optical system with a retractable structure, the structure of the lens barrel becomes complicated, resulting in an increase in cost. In particular, when the lens is extended after the device is turned on, preparation for shooting is not possible. Since a predetermined time is required for completion, there is a problem that a photo opportunity is missed even if there is an object to be imaged during that time.

As another means for reducing the size of the image pickup optical system, a technique of providing a reflecting surface on the optical path of the image pickup optical system is known. Has been made. Patent Document 1 includes a first prism and a second prism formed of a medium having a refractive index greater than 1.3, and in order from the object side, a front group including the first prism, an aperture stop, An imaging optical system that includes a rear group including two prisms and does not form an intermediate image is described. Patent Document 2 proposes an imaging optical system in which a reflecting surface is arranged to fold an optical path for the purpose of reducing the size and thickness of the optical system. Patent Document 3 discloses a first refractive surface that is an incident surface, a convex mirror that is inclined with respect to a reference axis that is a first refractive surface, and a reference axis that is a second reflective surface in the order of incidence of light from an object. An optical system is disclosed that includes an optical element having an inclined concave mirror and a second refractive surface having negative power.
JP 2002-196243 A JP 2000-171716 A JP-A-9-212331

  Each of Patent Documents 1 to 3 has the following points to be improved. That is, in the imaging optical system of Patent Document 1, each prism is a decentered optical system in which the reflecting surface has optical power. Since decentration aberrations newly occur in the decentration optical system that did not occur in the axially symmetric optical system, conventional equipment cannot be used as equipment for manufacturing and evaluating the optical system. Need to be introduced. In this case, since many aberrations to be corrected are generated, the manufacturing difficulty of the imaging optical system is increased. Furthermore, theoretically, since there are two reflecting surfaces having decentration error sensitivity about four times that of the refractive optical system, high positional accuracy between the reflecting surfaces is required.

  Patent Document 2 devises the arrangement of the image pickup element in order to reduce the thickness of the imaging optical system. However, if sufficient space is required for the arrangement of the wiring or the like attached to the normal image pickup element, it is concluded. It is difficult to reduce the thickness of the image optical system. In Patent Document 3, as in Patent Document 1, there is a problem in the manufacturing difficulty of the prism, and since the optical system has only one reflecting prism having two reflecting surfaces, several hundred thousand pixels. Although it has optical performance corresponding to a certain degree of image pickup device, it cannot sufficiently handle an image pickup device having several million pixels. As described above, each of Patent Documents 1 to 3 has a problem of incurring an increase in cost and a problem that compactness is not sufficient.

  The present invention has been made in view of the above circumstances, and has a compact imaging optical system, an imaging lens device, and a high optical performance that can be mounted on a mobile phone or a portable information terminal while suppressing an increase in cost. An object of the present invention is to provide a digital device equipped with the imaging lens device.

  An imaging optical system according to claim 1 is an imaging optical system that forms an optical image of a subject on a light receiving surface of an imaging device that converts an optical image into an electrical signal, and each of incident light is bent by a predetermined angle. The two reflecting prisms that are reflected are arranged so that the incident surface of the reflecting prism arranged on the subject side on the optical path and the exit surface of the other reflecting prism are substantially parallel, and at least one of the reflecting prisms The incident surface or the exit surface of the light source has an optical power.

  An imaging optical system according to a second aspect is the imaging optical system according to the first aspect, wherein a bending angle of incident light by the reflecting prism is approximately 90 degrees.

  The imaging optical system according to claim 3 is the imaging optical system according to claim 1 or 2, wherein at least one of the incident surface and the exit surface of the two reflecting prisms has optical power. It is characterized by.

  An imaging optical system according to a fourth aspect of the present invention is the imaging optical system according to the first or second aspect, wherein each of the two reflecting prisms has optical power on both the entrance surface and the exit surface. It is characterized by that.

  The imaging optical system according to a fifth aspect is the imaging optical system according to any one of the first to fourth aspects, wherein an optical aperture is provided on the exit surface side of the reflecting prism disposed on the subject side on the optical path. In the above, at least the incident surface of the reflecting prism disposed on the subject side on the optical path has a negative optical power.

  An imaging optical system according to a sixth aspect is the imaging optical system according to any one of the first to fifth aspects, wherein the incident surface of the reflecting prism disposed on the subject side on the optical path and the exit surface of the other reflecting prism are arranged. An optical element having optical power including the reflecting prism is provided only on the optical path between them.

  An imaging optical system according to a seventh aspect is the imaging optical system according to any one of the first to sixth aspects, wherein a lens or a lens group is disposed between the two reflecting prisms.

  An imaging optical system according to an eighth aspect is the imaging optical system according to the seventh aspect, wherein the lens or the lens group is focused by moving the lens or the lens group substantially parallel to an incident surface of a reflecting prism arranged on the subject side in the optical path. It is characterized by performing.

  An imaging optical system according to a ninth aspect is the imaging optical system according to any one of the first to eighth aspects, wherein the reflecting prism is made of a resin.

  An imaging optical system according to a tenth aspect is the imaging optical system according to the ninth aspect, wherein a water absorption rate of a resin material constituting the reflecting prism is 0.01% or less.

  An imaging optical system according to an eleventh aspect is the imaging optical system according to any one of the first to eighth aspects, wherein the reflection prism is manufactured by a glass mold method.

  An imaging optical system according to a twelfth aspect is the imaging optical system according to any one of the first to eleventh aspects, wherein the other reflecting prism is provided with an infrared cut function for reducing an infrared component contained in incident light. It is characterized by that.

  An imaging lens device according to a thirteenth aspect includes the imaging optical system according to any one of the first to twelfth aspects, and forms an optical image of a subject on a light receiving surface of an imaging element that converts an optical image into an electrical signal. It is characterized by doing.

  A digital device according to a fourteenth aspect includes the imaging lens device according to the thirteenth aspect and an imaging element that converts an optical image into an electrical signal, and at least a still image shooting and a moving image shooting of the object on the object side. And a functional unit that executes one of the photographing operations.

  According to the first aspect of the present invention, the two reflecting prisms that reflect and bend the incident light by a predetermined angle are the incident surface of the reflecting prism disposed on the subject side on the optical path and the other reflecting prism. Since the arrangement is made so that the exit surface is substantially parallel, a compact imaging optical system can be realized while suppressing an increase in cost.

  According to the second aspect of the present invention, since the bending angle of the incident light by the reflecting prism is set to about 90 degrees, the most compact imaging optical system can be realized.

  According to the third aspect of the present invention, at least one of the entrance surface and the exit surface of the two reflecting prisms has optical power, and the reflecting prism has not only a reflecting function but also a lens function. Therefore, the number of parts can be reduced and the imaging optical system can be made more compact as compared with a configuration in which these functions are realized by separate optical elements.

  According to the invention of claim 4, the two reflecting prisms each have an entrance surface and an exit surface having optical power, and the reflecting prism has both a lens function and a reflecting function. Compared to a configuration in which these functions are realized by separate optical elements, the number of parts can be reduced, and the imaging optical system can be made more compact.

  According to the invention described in claim 5, it is possible to reduce the size of the reflecting prism itself. That is, in order to reduce the size of the reflecting prism, it is desirable that the light beam passing through the outermost peripheral part in the prism is close to the optical axis, but the exit of the reflecting prism in which the optical aperture is disposed on the subject side on the optical path. When arranged on the surface side, it is easy to ensure parallelism with the optical axis by providing the incident surface of the reflecting prism with a negative optical power. As a result, the size of the reflecting prism can be reduced, and as a result, the imaging optical system can be reduced in size.

  According to the invention described in claim 6, the optical power including the reflecting prism only on the optical path between the incident surface of the reflecting prism disposed on the subject side on the optical path and the exit surface of the other reflecting prism. The optical element is arranged on the object side on the optical path from the incident surface of the reflecting prism arranged on the object side on the optical path or on the image side on the optical path from the exit surface of the other reflecting prism. As compared with the case, the imaging optical system can be made compact.

  According to the seventh aspect of the present invention, since the lens or the lens group is disposed between the two reflecting prisms, aberration or the like can be corrected by the lens or the lens group, and the optical performance can be improved. it can.

  According to the eighth aspect of the invention, focusing is performed by moving the lens or the lens group disposed between the two reflecting prisms substantially parallel to the incident surface of the reflecting prism disposed on the subject side on the optical path. As a result, it is possible to reduce the driving force required for the driving unit for focusing as compared with the configuration in which the entire imaging optical system is driven. As a result, the driving unit can be made compact. Further, since the reflecting prism is not driven, it is possible to prevent or suppress problems such as the occurrence of a deviation of the optical axis and to secure the positional accuracy of the reflecting prism.

  According to the ninth aspect of the invention, since the reflecting prism is made of resin, a light-weight and inexpensive imaging optical system can be realized.

  According to the tenth aspect of the present invention, when the reflecting prism is made of resin, a resin material having a water absorption of 0.01% or less is used. Therefore, optical characteristics (refractive index, etc.) associated with moisture absorption for the reflecting prism. It is possible to realize an imaging optical system that is not affected by the fluctuations of the image.

  According to the eleventh aspect of the present invention, since the reflecting prism manufactured by the glass mold method capable of relatively easily obtaining a highly accurate and high refractive index reflecting prism is used, the optical path length can be shortened and the refractive surface can be reduced. It is possible to provide an imaging optical system that can easily reduce the occurrence of aberrations.

  According to the twelfth aspect of the present invention, when an optical image of incident light that has passed through the imaging optical system is picked up by an image pickup device, an infrared component that causes image deterioration is removed using an accompanying mechanism of a reflecting prism. As a result, the use of optical components for cutting infrared rays can be omitted. As a result, the configuration of the imaging optical system can be simplified, and further the downsizing of the imaging optical system can be achieved.

  According to a thirteenth aspect of the present invention, an optical image of a subject is provided on a light receiving surface of an image pickup device that includes the imaging optical system according to any one of the first to twelfth aspects and converts an optical image into an electrical signal. Since the imaging lens device to be formed is configured, it is possible to provide a compact and high-definition imaging lens device that can be mounted on a mobile phone or a portable information terminal.

  According to the fourteenth aspect of the present invention, the functional unit includes the imaging lens device according to the thirteenth aspect and an imaging element, and executes at least one of the still image shooting and the moving image shooting of the object on the object side. Therefore, it is possible to realize a compact and high-definition digital device such as a mobile phone or a portable information terminal.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Description of configuration of imaging optical system>
FIG. 1 is a diagram schematically showing a configuration of an imaging optical system 100 according to the present invention. The imaging optical system 100 forms an optical image of a subject H on a light receiving surface of an imaging element 105 that converts an optical image into an electrical signal, and each incident light is incident at a predetermined angle (approximately 90 degrees). Two reflecting prisms that are bent and reflected only, that is, a first reflecting prism 101 (referred to as “incident side prism 101” in this description) disposed on the subject H side on the optical path, and an imaging element 105 side on the optical path. A second reflecting prism 102 (referred to as “image plane side prism 102” in the description) is provided. A focusing lens 103 and an optical diaphragm 104 are disposed between the incident side prism 101 and the image side prism 102 as necessary.

  The incident surface 101a of the incident side prism 101 and the exit surface 102b of the image surface side prism 102 are arranged so as to be substantially parallel. That is, the optical axis AX from the subject H to the image sensor 104 is bent by 90 degrees by the reflecting surfaces 101c and 102c of the incident side prism 101 and the image side prism 102, respectively. Such an imaging optical system 100 is housed in a housing BD of various digital devices (for example, a mobile phone).

  In the imaging optical system 100 configured as described above, at least one of the incident surfaces 101a and 102a or the exit surfaces 101b and 102b of the incident-side prism 101 and the image-side prism 102 has an optical power. For example, either the entrance surface 101a or the exit surface 101b of the entrance-side prism 101 and / or the entrance surface 102a or the exit surface 102b of the image-side prism 102 may have optical power. it can. Alternatively, any of the incident surfaces 101a and 102a or the exit surfaces 101b and 102b of the incident-side prism 101 and the image-side prism 102 can be configured to have optical power. According to these configurations, since at least one of the entrance surfaces 101a and 102a or the exit surfaces 101b and 102b is utilized as a lens function surface, the use of a separate optical element can be omitted correspondingly, and imaging can be performed. The optical system 100 can be made compact.

  The image sensor 105 photoelectrically converts it into image signals of R, G, and B components according to the light amount of the optical image of the subject H imaged by the imaging optical system 100, and outputs it to a predetermined image processing circuit. Is. For example, as the image sensor 105, R (red), G (green), and B (blue) color filters are checkered on the surface of each CCD of an area sensor in which CCDs (Charge Coupled Devices) are two-dimensionally arranged. It is possible to use a single plate type color area sensor called a Bayer method that is attached in a shape. In addition to such a CCD image sensor, a CMOS image sensor, a VMIS image sensor, or the like can also be used.

  Here, when the optical stop 104 is located on the exit surface 101b side of the incident side prism 101, if the incident surface 101a of the incident side prism 101 has a negative optical power, the following is obtained. There are advantages. FIG. 2 is an optical path diagram showing the relationship between the incident side prism 101 (101 ') and the light beam. When a predetermined light beam width BT is emitted from the incident-side prism 101 (101 ′), in order to reduce the size of the prism itself, the light beam op-out of the light beam op that passes through the most peripheral side in the prism is used. Is preferably nearly parallel to the optical axis AX.

  That is, when the incident surface 101a ′ is a flat surface as in the incident side prism 101 ′ of FIG. 2A, the incident light beam op having the most peripheral angle θ1 among the light beams incident on the incident surface 101a ′. The light angle of −in cannot be reduced with respect to the optical axis AX, and as a result, the outgoing light beam op-out is emitted with a tilt angle with respect to the optical axis AX. Therefore, in order to obtain a predetermined light beam width BT, it is necessary to increase the entrance surface 101a 'and the exit surface 101b' in consideration of the tilt angle. For this reason, the size of the prism must be increased.

  On the other hand, when the incident surface 101a has a negative optical power (concave surface) as in the incident-side prism 101 of FIG. 2B, the angle θ1 on the most peripheral side of the rays incident on the incident surface 101a. The incident light ray op-in having a light beam angle becomes smaller with respect to the optical axis AX, and as a result, the outgoing light beam op-out is emitted in a state nearly parallel to the optical axis AX. Therefore, the size of the prism for obtaining the predetermined light beam width BT can be significantly reduced as compared with the case of FIG. 2A, and the imaging optical system 100 can also be made compact.

  Note that instead of providing the incident side prism 101 and the image plane side prism 102 as described above, an imaging optical system 100 provided with a reflecting mirror may be considered. In this case, a member for holding the reflecting mirror is separately provided. Therefore, it is desirable to use the two reflecting prisms as described above because the imaging optical system 100 increases in cost and size.

  Further, the bending angle of incident light by the reflecting surface is not limited to 90 degrees, but the size of the imaging optical system 100 increases in the direction of arrow A in FIG. Setting to 90 degrees is most desirable in order to achieve downsizing of the imaging optical system 100.

  Here, when the imaging element 105 is a rectangular shape having a long side and a short side, the bending direction thereof is the short side direction of the imaging element 105 (the width direction indicated by the arrow a in FIG. It is preferable to bend the light beam in the short side direction. Even if the light beam is bent in the long side direction of the image pickup element 105, the image pickup optical system 100 can be correspondingly thinned. However, it is more preferable to bend the light ray in the short side direction of the image pickup element 105. Can be made thinner.

  As in the imaging optical system 100 shown in FIG. 1, the object H side on the optical path from the incident surface 101a of the incident side prism 101 and the image side on the optical path (imaging element 105 side) from the exit surface 102b of the image side prism 102 are arranged. An optical element having refractive power is disposed only on the optical path between the incident surface 101a of the incident-side prism 101 and the exit surface 102b of the image-side prism 102 without arranging an optical element having refractive power (optical power). It is desirable to have a configuration to arrange. Thereby, the thickness (size in the direction of arrow A) of the imaging optical system 100 is reduced as compared with the case where an optical element having refractive power is arranged on the subject H side on the optical path from the incident surface 101a of the incident side prism 101. And an increase in the size of the imaging optical system 100 can be suppressed.

  In the imaging optical system 100, it is desirable to dispose a lens or a lens group between the incident side prism 101 and the image plane side prism 102. This is because correction of curvature of field, aberration, and the like can be performed by the lens, and the optical performance of the imaging optical system 100 can be improved. When a lens such as that described above is disposed, a lens that is smaller in the direction of arrow A than the reflecting prism is used as this lens, so that the problem of enlargement in the direction of arrow A due to the mounting of the lens does not occur. .

  It is preferable to perform focusing by driving this lens or lens group in the optical axis direction (direction substantially parallel to the incident surface 101a of the incident side prism 101). This is because when the entire imaging optical system including the reflecting prism is driven in the optical axis direction, an increase in the weight of the driven object causes an increase in the size of the motor, or the optical axis shifts due to the driving. Or the holding mechanism of each optical element of the imaging optical system becomes complicated, and by disposing a lens or a lens group between the two reflecting prisms, the reflecting prism and the optical diaphragm can be fixed, By driving the lens or the lens group in the optical axis direction, it is possible to solve the problems of increase in the size of the motor, occurrence of optical axis deviation, and complication of the holding mechanism.

  In the imaging optical system 100 shown in FIG. 1, a focusing lens 103 is disposed between the incident-side prism 101 and the image-side prism 102 in order to satisfy the above-described requirements. That is, focusing is performed by moving the focusing lens 103 in a direction parallel to the incident surface 101 a of the incident-side prism 101.

  In the imaging optical system 100, each optical surface of the imaging optical system 100 is symmetric about the optical axis AX from the viewpoint of ease of manufacturing the incident side prism 101, the image plane side prism 102, and the lens 103. It is preferable to use a plane (rotationally symmetric plane). An axially asymmetric optical system is not desirable because it not only increases the manufacturing difficulty level but also increases the difficulty level for evaluation and adjustment at the time of incorporation, which increases the cost. On the contrary, if the cost is allowed to be high, an axially asymmetric surface can be used as the reflecting surface.

  Next, a desirable arrangement relationship between the exit surface 102b of the image plane side prism 102 and the image sensor 105 will be described. The size of the imaging optical system 100 itself in the direction of arrow A can be reduced by adopting the optical configuration as described above. However, the imaging element 105 is disposed opposite to the exit surface 102b of the image side prism 102, and this is arranged. In order to reduce the thickness of the housing BD, it is desirable to shorten the distance between the exit surface 102b of the image plane side prism 102 and the image sensor 105 as much as possible.

Now, let d be the distance between the exit surface 102b of the image plane side prism 102 and the light receiving surface of the image sensor 105 (the physical distance includes the case where an optical component is interposed therebetween), and the imaging optical system 100 When the height of the light receiving surface of the image sensor 105 in the optical path bending plane (corresponding to the paper surface in FIG. 1) is defined as a (for example, the short side direction of the image sensor 105), the following relationship (1) is satisfied. Thus, setting the positional relationship between the exit surface 102b of the image-side prism 102 and the imaging element 105 is desirable from the viewpoint of reducing the thickness of the housing BD.
0.0 ≦ d / a <0.8 (1)

  In the above equation (1), if d / a is 0.8 or more, the distance d between the exit surface 102b of the image-side prism 102 and the image sensor 105 becomes too large, and is not suitable for thinning the housing BD. It becomes. That is, the large distance d means that the size of the image plane side prism 102 is large in order to form an image on the light receiving surface of the image sensor 105 in such an environment. (Thickening).

  On the other hand, when d / a = 0, the mode in which the exit surface 102b of the image plane side prism 102 and the light receiving surface of the image sensor 105 are in close contact with each other is a mode in which the size in the direction of arrow A can be minimized, which is called thinning. This is a desirable mode from the viewpoint. However, since the exit surface 102b and the light receiving surface of the image sensor 105 are in contact with each other, it is difficult to assemble, and a ghost is generated due to inter-surface reflection between the exit surface 102b and the light receiving surface of the image sensor 105. Concerned. In order to eliminate such inconvenience, it is desirable that the lower limit value of d / a is 0.1 or more.

As described above, not only the positional relationship between the exit surface 102b of the image plane side prism 102 and the image sensor 105 is set, but also the size (length) of the image plane side prism 102 is optimized, thereby further reducing the thickness. Can be achieved. Now, as shown in FIG. 3, the refractive index of the image plane side prism 102 is n, the principal ray distance on the optical axis AX passing through the image plane side prism 102 (thickness when the prism is expanded) is t, When the exit pupil distance is p, it is desirable to satisfy the relationship of the following equation (2).
-1.5 <(t * n) / p <1.0 (2)

  In the above equation (2), when (t * n) / p is 1.0 or more, the exit pupil distance p becomes longer with respect to the size of the prism, so that the optical system approaches telecentricity. Accordingly, the light beam width in the prism becomes large, and it is necessary to increase (longen) the size of the prism in order to turn back the light beam having such a light beam width. As a result, the imaging optical system 100 is compact. The tendency to become impossible to become more remarkable becomes remarkable.

  On the other hand, when (t * n) / p is −1.5 or less, the exit pupil distance p becomes shorter than the size of the prism. Therefore, contrary to telecentric, the optical system has an inclination with respect to the optical axis. Many large rays are included. In general, a microlens is disposed on the light receiving surface of the image sensor 105 for each pixel in order to increase the light collection efficiency. In the case of a telecentric optical system, it is only necessary to arrange the microlenses directly above each pixel, and the arrangement of the microlenses is relatively easy. However, when the exit pupil distance p is short and the light beam has an inclination, the microlens must be arranged with a predetermined amount shifted from each pixel in consideration of the inclination angle. Here, when the inclination angle of the light beam becomes large as below the lower limit value of the expression (2), it becomes difficult to arrange the microlens so as to ensure a predetermined light collection amount, and as a result, the light collection efficiency deteriorates. The tendency for the amount of ambient light to decrease becomes remarkable.

  Furthermore, a short exit pupil distance p results in a short distance between the optical aperture 104 and the image plane (the light receiving surface of the image sensor 105), but the image is more incident than the incident plane 102a of the image plane side prism 102. Since the optical diaphragm 104 cannot be disposed on the surface side (the diaphragm cannot be provided in the prism), the tendency that it is difficult to appropriately dispose the optical diaphragm 104 when the value is equal to or lower than the lower limit value of the expression (2). It becomes.

  By the way, when a CCD image sensor or a CMOS image sensor is used as the image sensor 105, an infrared component may be noise and deteriorate an output image. For this reason, in order to prevent the infrared component from being incident on the image sensor 105, conventionally, measures have been taken to arrange an infrared cut filter or the like at an appropriate location in the imaging optical system. However, since an optical component having such an infrared cut function is required separately, it has been an obstacle to downsizing the imaging optical system and suppressing the number of components.

  Therefore, it is desirable to provide the image plane side prism 102 itself with an infrared cut function for reducing or removing infrared components contained in incident light. FIG. 4 is a cross-sectional view showing an example of the image side prism 102 having an infrared cut function. FIG. 4A shows an example in which an infrared reflection film 102 d is integrally provided on the exit surface 102 b of the image side prism 102. As a result, the infrared component contained in the incident light is reflected by the infrared reflecting film 102 d and is not incident on the image sensor 105. As such an infrared reflection film 102d, for example, a dielectric multilayer coating layer that reflects light having an infrared wavelength is suitable. Such an infrared reflecting film 102 d may be provided on the incident surface 102 a of the image side prism 102.

  FIG. 4B shows an example in which an infrared absorption film 102e is integrally provided on the reflection surface 102c of the image surface side prism 102. As a result, the infrared component contained in the incident light is absorbed by the infrared absorption film 102 e and is not incident on the image sensor 105. As such an infrared absorption film 102e, for example, a coating layer of a dielectric multilayer film that absorbs light of an infrared wavelength is suitable. Instead of the infrared absorbing film 102e, an infrared transmitting film may be provided on the reflecting surface 102c so that only the infrared component is radiated from the image plane side prism 102.

  Next, materials and manufacturing methods of the incident side prism 101 and the image side prism 102 will be described. The material of these prisms is not particularly limited, and any optical material having a predetermined light transmittance, refractive index, etc. may be used, and various glass materials and resin (plastic) materials can be used. However, if a resin material is used, it is lightweight and can be mass-produced with an injection mold or the like. Therefore, compared to the case of manufacturing with a glass material, cost is reduced and the imaging optical system 100 is lighter. It is advantageous. Furthermore, when creating a reflecting prism having refractive power on the entrance surface and / or exit surface as described above, it is necessary to produce it through a polishing process according to a glass material. There is also an advantage that it can be easily manufactured by using.

  However, according to the injection mold, since some heat shrinkage is inevitable after molding, in the case of an optical component that requires high accuracy, the manufacturing difficulty may be increased. By the way, the degree to which high accuracy is required is higher for the incident-side prism 101 than for the image-side prism 102. This is because the image plane side prism 102 is closer to the image sensor 105 and has relatively low error sensitivity. Therefore, it is desirable that at least the image side prism 102 is made of a resin material, and whether the incident side prism 101 is made of a resin material or a glass material is selected according to the required accuracy.

  Here, when the incident side prism 101 and / or the image side prism 102 are made of a resin material, various optical resin materials such as polycarbonate and PMMA can be used as the resin material. Among these, it is desirable to select a resin material having a water absorption rate of 0.01% or less. The resin material has a hygroscopic action that combines with moisture in the air. If such moisture absorption occurs, optical characteristics such as refractive index may change due to moisture absorption even if a prism is manufactured as designed. Therefore, by using a resin material having a water absorption rate of 0.01% or less, the imaging optical system 100 that is not affected by moisture absorption can be constructed. As such a resin material, for example, ZEONEX (trade name of Nippon Zeon Co., Ltd.) can be used.

  Next, as a method of manufacturing a prism having optical power on the entrance surface and / or exit surface, for example, a method of bonding a lens having optical power to a predetermined prism, a method of polishing a curved surface of the prism, an injection mold, Examples thereof include a method using a glass mold. However, the method of bonding the lens to the prism and the method of polishing the curved surface of the prism require time-consuming alignment in order to adjust the positional relationship and inclination between the reflecting surface and the lens or the curved surface, which is difficult to manufacture. The degree will be relatively high. In contrast, an injection mold using a resin material is one of the preferable manufacturing methods because it is excellent in mass productivity as described above.

  When adopting the prism manufactured by the above injection mold, it is desirable to pay attention to the following points. When performing injection molding, a gate for injecting resin into the mold is required. Such a gate may be opposed to any surface of the prism, but is preferably disposed on a surface where light is not incident, emitted, or reflected on the prism. In general, birefringence is likely to occur due to resin flow traces remaining in the vicinity of the gate, which may affect the optical characteristics. Therefore, even if birefringence occurs, the influence can be reduced. Because.

  FIG. 5 is a perspective view illustrating the imaging optical system 100 shown in FIG. 1 in a three-dimensional manner. Referring to FIG. 5, the desirable configuration will be described. When the incident side prism 101 is formed by injection molding, a mold injection gate is arranged on the incident surface 101a, the exit surface 101b, and the reflecting surface 101c. Without, it arrange | positions to the unused surface 101m which is a side surface of these surfaces. In this case, since the normal gate has a rectangular column shape with a rectangular cross section, such a rectangular column-shaped gate mark Ge1 (gate mark Ge1 whose entrance surface 101a is parallel to the wide surface) remains on the unused surface 101m. (This gate mark Ge1 is exaggeratedly drawn). By arranging the gate in this way, even if birefringence occurs in the vicinity of the gate, the influence on the effective use area pw1 (hatched part in the figure; an area through which light rays can pass) of the incident side prism 101 is reduced. Can do.

  Similarly, in the image plane side prism 102, the mold injection gate is not disposed on the incident surface 102a, the exit surface 102b, and the reflection surface 102c, but is disposed on the unused surface 102m which is a side surface of these surfaces. In this case, a prismatic gate mark Ge2 (a gate mark Ge2 having a reflecting surface 102c and a wide surface in parallel) remains on the unused surface 102m. Similarly, even if birefringence occurs in the vicinity of the gate. The influence on the effective use area pw2 (hatched part in the drawing) of the image side prism 102 can be reduced.

  After injection molding, a method of pressing the molded product with an eject pin when removing the molded product (in this case, a prism) from a mold is widely used. Traces still remain at the contact portion of such an eject pin, and the optical characteristics may be disturbed also in this portion. Therefore, in the example shown in FIG. 5, with respect to the incident side prism 101, an eject pin is arranged at a portion corresponding to the unused area on the incident surface 101a so that the pin trace ep1 appears in the unused area. Further, with respect to the image surface side prism 102, an eject pin is arranged at a portion corresponding to the non-use area on the reflection surface 102c so that a pin trace ep2 appears in the non-use area. Of course, the eject pin may be arranged so that the pin traces ep1 and ep2 appear on the unused surfaces 101n and 102n on the opposite sides facing the unused surfaces 101m and 102m, respectively.

  Further, when the optical diaphragm 104 is disposed between the incident side prism 101 and the image side prism 102 as in the imaging optical system 100 (see FIG. 1), as shown in FIG. In addition, it is desirable to adjust the gate direction so that the gate traces Ge1 and Ge2 of the incident side prism 101 and the image plane side prism 102 exist in the same direction. This point will be described with reference to FIG.

  FIG. 6 is a schematic optical path diagram of the imaging optical system 100 shown in FIG. As shown in the drawing, the gate marks Ge1 and Ge2 for the incident side prism 101 and the image side prism 102 are formed on the unused surfaces 101m and 102m existing in the same direction. The other unused surfaces 101n and 102n facing the unused surfaces 101m and 102m are also flat surfaces (surfaces having a stable shape) where the gate traces Ge1 and Ge2 do not exist. And a prism holding member 106 (corresponding to a frame member of the housing BD) common to the image plane side prism 102. As a result, the prism can be assembled with high accuracy.

  Although the gate traces Ge1 and Ge2 are provided on the non-use surfaces 101m and 102m, the influence of birefringence and the like can be reduced, but it is difficult to completely remove the influence. Such regions that affect the optical characteristics in the vicinity of the gate traces Ge1 and Ge2 are shown as gate-affected regions Ge1m and Ge2m in FIG. 6 (corresponding to hatched portions in the figure).

  By the way, when the optical diaphragm 104 is disposed between the incident-side prism 101 and the image plane-side prism 102, the optical image is reversed before and after the optical diaphragm 104. Now, consider the optical path of a light beam op incident from the gate mark Ge1 side of the incident surface 101a of the incident side prism 101. In the incident side prism 101, the light beam op passes through the gate influence region Ge1m, and thus is affected by the birefringence index and the like. However, when passing through the optical aperture 104, the light beam op is refracted in a direction away from the gate mark Ge1 side. Then, when it enters the image side prism 102, it passes through a region away from the gate affected region Ge2m. Therefore, the light beam op does not pass through the gate-affected regions Ge1m and Ge2m of the incident side prism 101 and the image plane side prism 102 in a superimposed manner, and the influence of the residual birefringence is dispersed, and only one side of the screen is birefringent. Problems such as the uneven distribution of such effects will not occur.

  The injection molding method using the resin material as described above is suitable for mass production and has an advantage that a highly accurate concave surface can be formed on the entrance surface and the exit surface of the reflecting prism. A reflecting prism having a high refractive index cannot be manufactured. Therefore, when a high-precision and high-refractive-index prism is required, it is desirable to manufacture a high-refractive-index glass material by a glass mold method in which heat is applied using a prism-shaped mold. When a high refractive index prism is applied, the optical path length can be shortened and the occurrence of aberrations on the refracting surface can be reduced. As a result, the imaging optical system 100 can be downsized and the number of lenses can be reduced. Is advantageous.

<Description of digital equipment incorporating imaging optical system>
Next, a digital device incorporating the imaging optical system 100 as described above will be described. FIG. 7 is an external configuration diagram of a camera-equipped mobile phone 200 showing an embodiment of a digital device according to the present invention. In the present invention, the digital device includes a digital still camera, a video camera, a digital video unit, a personal digital assistant (PDA), a personal computer, a mobile computer, or peripheral devices (mouse, scanner, printer). Etc.). A digital still camera or digital video camera is an imaging lens device that optically captures an image of a subject, converts the image into an electrical signal using a semiconductor element, and stores the image as digital data in a storage medium such as a flash memory. is there. Furthermore, in the present invention, a mobile phone, a personal digital assistant, a personal computer, a mobile computer, or a peripheral device having a specification that incorporates a compact imaging lens device that optically captures a still or moving image of a subject. Contains.

  7A shows the operation surface of the mobile phone 200, and FIG. 7B shows the back surface of the operation surface, that is, the back surface. The mobile phone 200 has an antenna 201 on the top, a rectangular display 202 having a long side Lt1 in the vertical direction in the figure on the operation surface, an image switching button 203 for starting an image shooting mode and switching between still image and moving image shooting, A shutter button 204 and a dial button 205 are provided.

  The mobile phone 200 includes an imaging lens device (camera) 206 configured by the imaging optical system 100 according to the present invention and an imaging element 105 such as a CCD, and a photographing lens on which subject light of the imaging lens device 206 is incident. 207 is exposed on the back. The incident surface 101 a of the incident side prism 101 is disposed on the back surface of the photographing lens 207. That is, the subject light incident surface of the imaging lens device 206 and the display 202 are respectively disposed on the front and back surfaces (back surface and operation surface) of the mobile phone 200. As a result, it is possible to perform imaging while displaying an image acquired by the imaging lens device 206 on the display 202.

  Here, the image pickup device 105 is a device having a rectangular shape with an aspect ratio of the image pickup area of, for example, 4: 3. A general-purpose type image pickup device is generally such a rectangle, but the form of incorporation of the image pickup lens device 206 including such an image pickup device 105 into the mobile phone 200 is related to the rectangular display 202. It is desirable to adopt an embodiment as shown in FIG.

  That is, when the display 202 has the long side Lt1 in the vertical direction of FIG. 7A, the imaging element 105 is also configured to have the long side Lt2 in the vertical direction of FIG. Is desirable. In other words, it is desirable that the long side Lt1 of the display 202 and the long side Lt2 of the image sensor 105 are assembled so as to be in a parallel direction (the same direction). As a result, the subject light image that is incident from the photographing lens 207 and formed on the imaging element 105 having a rectangular imaging area is effectively displayed on the rectangular display 202 during imaging.

  That is, when the long side Lt1 of the display 202 and the long side Lt2 of the image sensor 105 are arranged in parallel, the long side direction of the image acquired by the image sensor 105 matches the long side direction of the display image. As a result, the display area of the display 202 can be used effectively, and the image can be displayed in a large size. That is, it is possible to display the area of the display 202 to the maximum, which is advantageous for confirming the composition at the time of shooting.

  The imaging lens device 206 may include a plane parallel plate corresponding to an optical low-pass filter or the like in addition to the imaging optical system 100 that forms an optical image of a subject. As an optical low-pass filter, for example, a birefringence low-pass filter made of quartz or the like whose predetermined crystal axis direction is adjusted, a phase-type low-pass filter that realizes a required optical cutoff frequency characteristic by a diffraction effect, etc. Is applicable.

  Note that the optical low-pass filter is not necessarily provided, and instead of the optical low-pass filter, an infrared cut filter is mounted in order to reduce noise included in the image signal of the image sensor 105 (in this case, the above-described case). As described above, it is desirable to provide the reflecting prism with an infrared cut function. Further, an infrared reflection coating may be applied to the surface of the optical low-pass filter, so that both filter functions can be realized by one.

  An imaging operation of the mobile phone 200 configured as described above will be described. When shooting a still image, first, the image switching mode 203 is pressed to activate the image shooting mode. Here, it is assumed that the video switching mode is switched to once by pressing the image switching button 203 once. When the still image shooting mode is activated, a subject image is periodically and repeatedly imaged by the imaging element 105 such as a CCD through the imaging lens device 206, transferred to the display memory, and then guided to the display 202. By looking through the display 202, it is possible to adjust the main subject so as to be in a desired position on the screen. By pressing the shutter button 204 in this state, a still image can be obtained. That is, the image data is stored in the still image memory.

  In addition, when performing moving image shooting, the still image shooting mode is activated by pressing the image switching button 203 once, and then the image switching button 203 is pressed again to switch to the moving image shooting mode. After that, as in the case of still image shooting, the display 202 is looked into and an image of the subject obtained through the imaging lens device 206 is adjusted so as to be in a desired position on the screen. By pressing the shutter button 204 in this state, moving image shooting is started. Then, when the shutter button 204 is pressed again, the moving image shooting ends. The moving image is guided to a display memory for the display 202 and is also stored in a moving image memory.

  In the above-described embodiment, the long side Lt1 of the display 202 and the long side Lt2 of the image sensor 105 are aligned in parallel in the vertical direction in FIG. 7, but the present invention is not limited to this, for example, the horizontal direction in FIG. It is desirable that they are aligned in one direction and parallel. Also in this case, the display that makes the best use of the area of the display 202 can be performed, so that the confirmation of the composition at the time of photographing can be performed effectively.

  This is the same in various digital devices having a display as a display element in addition to the mobile phone 200 as described above. For example, a foldable mobile phone, a digital still camera, a digital video camera, mobile information The same applies to terminals, personal computers, mobile computers, and peripheral devices.

  FIG. 8 is an external configuration diagram of the foldable mobile phone 300. FIG. 8A shows the operation surface of the mobile phone 300, and FIG. 8B shows the back surface of the operation surface, that is, the back surface. . This mobile phone 300 has a foldable structure in which a first casing 310 and a second casing 320 are connected by a hinge 330, and the operation surface of the first casing 110 is long in the vertical direction. A display 311 is provided. Further, the second housing 320 is provided with a key input unit 321 as an operation unit.

  In such a cellular phone 300, the first casing 310 includes the imaging lens device 206 and the imaging element 105 configured by the imaging optical system 100 described above, and the imaging lens 207 of the imaging lens device 206 is on the back surface. Is exposed. That is, the subject light incident surface of the imaging lens device 206 and the display 311 are respectively disposed on the front and back surfaces (back surface and operation surface) of the first housing 310. As a result, it is possible to perform imaging while displaying an image acquired by the imaging lens device 206 on the display 311. The long side Lt1 of the display 311 and the long side Lt2 of the image sensor 105 are assembled in a parallel direction (the same direction). Even with such a configuration, it is possible to effectively display on the rectangular display 311 the subject light image that is incident on the imaging lens 207 and formed on the imaging element 105 having a rectangular imaging area.

  9 is an external configuration diagram of the portable information terminal 400, FIG. 9A shows an operation surface of the portable information terminal 400, and FIG. 9B shows a rear surface. On the operation surface of the portable information terminal 400, a display 401 that is long in the left-right direction and a key input unit 402 as an operation unit are provided.

  In such a portable information terminal 400, the imaging lens device 206 and the imaging element 105 configured by the above-described imaging optical system 100 are provided, and the imaging lens 207 of the imaging lens device 206 is exposed on the back surface. That is, the subject light incident surface of the imaging lens device 206 and the display 401 are respectively disposed on the front and back surfaces (back surface and operation surface) of the portable information terminal 400. As a result, it is possible to perform imaging while displaying an image acquired by the imaging lens device 206 on the display 401. The long side Lt1 of the display 401 and the long side Lt2 of the image sensor 105 are assembled in a parallel direction (in this case, the horizontal direction). Even with such a configuration, it is possible to effectively display on the rectangular display 401 the subject light image that is incident on the imaging lens 207 and formed on the imaging element 105 having a rectangular imaging area.

  Hereinafter, the imaging optical system 100 as shown in FIG. 1, that is, the imaging that constitutes the imaging lens device 206 mounted in the camera-equipped mobile phone 200 or 300 or the portable information terminal 400 as shown in FIGS. A specific configuration of the optical system 100 will be described with reference to the drawings.

[Embodiment 1]
FIG. 10 is a cross-sectional view of the configuration of the imaging optical system 51 of Embodiment 1 with the optical axis (AX) cut longitudinally. As shown in FIG. 10, the imaging optical system 51 of the present embodiment includes, in order from the object side on the optical path, a first reflecting prism 1 having a positive optical power as a whole (corresponding to the incident side prism 101 in FIG. 1), An optical aperture (ST) for adjusting the amount of light, a first lens 2 having a positive optical power, a second lens 3 having a negative optical power, and a second reflecting prism 4 having a positive optical power as a whole (Corresponding to the image plane side prism 102 in FIG. 1). A plane-parallel plate 5 and an image sensor 6 are disposed at a position opposite to the second lens 3 with respect to the second reflecting prism 4.

  FIG. 10 and FIGS. 13 and 15 of the second and third embodiments to be described later show the arrangement of the optical elements in a state of being focused at infinity. 11, 14, and 16 are configured by replacing the reflecting prisms (first and second reflecting prisms) in FIGS. 10, 13, and 15 with lenses having functions substantially equivalent to the reflecting prisms. 17 is a diagram illustrating the configuration of the imaging optical system, and the direction of the arrow D illustrated in FIGS. 11, 14, and 16 corresponds to the diagonal direction of the imaging device 6. The imaging optical system shown in FIGS. 10, 13, and 15 is an imaging optical system in which a light beam is bent in the short side direction of the imaging element 6. The optical power described below is defined as the power when the medium on both sides of the optical surface is air. The image sensor 6 is an image sensor having an aspect ratio of, for example, 3: 4, and is, for example, an image sensor having a height of 1.8 mm and a width of 2.4 mm. The direction of the arrow A corresponds to the front and back direction of FIG.

  The first reflecting prism 1 has an incident surface 1a having a negative optical power and an exit surface 1b having a positive optical power. The first reflecting prism 1 is planar on the optical path between the entrance surface 1a and the exit surface 1b. A reflective surface RL1 is provided. The second reflecting prism 4 has a positive optical power at the incident surface 4a and a negative optical power at the exit surface 4b, and is flat on the optical path between the incident surface 4a and the exit surface 4b. A reflective surface RL2 is provided. In the present embodiment, the reflecting surfaces RL1 and RL2 provided on the first reflecting prism 1 and the second reflecting prism 4 bend the incident light at approximately 90 degrees and reflect it toward the first lens 2 or the plane parallel plate 5. It is something to be made.

  The first and second reflecting prisms 1 and 4 and the optical stop (ST) are fixed, and when performing focusing from the infinitely focused state to the close distance focused state, the lenses 2 and 3 are indicated by an arrow B in the figure. Move in the direction of.

  Hereinafter, in this specification, the terms “convex”, “concave”, and “meniscus” are used for the shape of the lens, which represents the lens shape in the vicinity of these optical axes (near the center of the lens). It does not represent the shape of the entire lens or the vicinity of the end of the lens. This is not a problem with a spherical lens, but with an aspherical lens, it should be noted that generally the shape near the center and the end of the lens is different. An aspheric lens is a lens having a paraboloidal surface, an elliptical surface, a hyperboloid, a quartic surface, or the like.

  The number ri (i = 1, 2, 3,...) Shown in FIG. 11 is the i-th optical surface when counted from the object side. The first lens 2 is a biconvex lens, and the second lens 3 is a negative meniscus lens convex on the image side. In FIG. 11, the first reflecting prism 1 ′ and the second reflecting prism 4 shown in FIG. 10 are replaced with lenses having functions substantially equivalent to those of the first reflecting prism 1 ′. And a second reflecting prism 4 '(the same applies to FIGS. 14 and 16 described below).

  Under such a configuration, light rays incident from the object side (subject side) in FIG. 10 are sequentially incident on the incident surface 1a of the first reflecting prism 1 and reflected by being bent by approximately 90 degrees on the reflecting surface RL1. After that, the light enters the first and second lenses 2 and 3 and the incident surface 4 a of the second reflecting prism 4. The reflection surface RL2 reflects the incident light by bending it by approximately 90 degrees, and exits from the exit surface 4b to form an optical image of the object there. Then, the optical image formed by these optical elements passes through the plane parallel plate 5 disposed adjacent to the second reflecting prism 4. At this time, the optical image is corrected so as to minimize so-called aliasing noise that occurs when the image pickup device 6 converts it into an electrical signal. The plane parallel plate 5 corresponds to an optical low-pass filter, an infrared cut filter, a cover glass of an image sensor, or the like.

  Finally, in the image sensor 6, the optical image corrected by the plane parallel plate 5 is converted into an electrical signal. This electric signal is subjected to predetermined digital image processing, image compression processing, and the like as necessary, so that the mobile phone 200, 300, the portable information terminal 400, etc. as shown in FIGS. It is recorded in a memory or transmitted to another digital device by wire or wireless. Note that a cover glass may be provided at a position closer to the subject side than the incident surface of the first reflecting prism 1 in order to prevent the imaging optical system, particularly the first reflecting prism 1 from being damaged.

  Hereinafter, the lens configurations of Embodiments 2 and 3 will be described in order as in Embodiment 1 with reference to the drawings. At this time, the meanings of the reference numerals in FIGS. 13 to 16 are the same as those in FIGS. 10 and 11.

[Embodiment 2]
FIG. 13 is a cross-sectional view of the configuration of the imaging optical system 52 of Embodiment 2 with the optical axis (AX) cut longitudinally. The imaging optical system 52 according to the second embodiment includes, in order from the object side on the optical path, an optical aperture (ST) for adjusting the amount of light, a first reflecting prism 7 having a positive optical power as a whole, a negative optical power. And a second reflecting prism 9 having a positive optical power as a whole.

  In the first reflecting prism 7, the incident surface 7a has a positive optical power, and the exit surface 7b also has a positive optical power. The first reflecting prism 7 has a planar shape on the optical path between the entrance surface 7a and the exit surface 7b. A reflective surface RL3 is provided. The second reflecting prism 9 has an incident surface 9a having a positive optical power and an exit surface 9b having a negative optical power, and has a planar shape on the optical path between the entrance surface 9a and the exit surface 9b. A reflective surface RL4 is provided.

  In this embodiment, the optical aperture (ST), the first reflecting prism 7 and the second reflecting prism 9 are fixed, and when focusing from the infinitely focused state to the close distance focused state, the first lens 8 is , Move in the direction of arrow C in the figure. The first lens 8 is a negative meniscus lens convex on the image side.

[Embodiment 3]
FIG. 15 is a cross-sectional view of the configuration of the imaging optical system 53 of Embodiment 3 with the optical axis (AX) cut longitudinally. The imaging optical system 53 according to the third embodiment includes, in order from the object side on the optical path, a first reflecting prism 10 having a positive optical power as a whole, an optical aperture (ST) for adjusting the amount of light, and a positive optical power. A first lens 11 having a negative optical power, a second lens 12 having a negative optical power, and a second reflecting prism 13 having a positive optical power as a whole.

  The first reflecting prism 10 has an incident surface 10a having a negative optical power and an exit surface 10b having a positive optical power. The first reflecting prism 10 has a planar shape on the optical path between the entrance surface 10a and the exit surface 10b. A reflective surface RL5 is provided. The second reflecting prism 13 has an incident surface 13a having a negative optical power and an exit surface having a positive optical power, and is reflected in a plane on the optical path between the entrance surface 13a and the exit surface 13b. Surface RL6 is provided.

  In the present embodiment, the first and second reflecting prisms 10 and 13 and the optical diaphragm (ST) are fixed, and when performing focusing from the infinite focus state to the close distance focus state, the lenses 11 and 12 are It moves in the direction of arrow B in the figure. The first lens 11 is composed of a biconvex lens having positive optical power, and the second lens 12 is composed of a negative meniscus lens (lens having negative optical power) convex to the image side. The second lens 12 is cemented.

  As in the imaging optical systems 51, 52, and 53 according to each of the embodiments described above, two reflecting prisms that reflect and bend the incident light by approximately 90 degrees are arranged on the object side on the optical path. By arranging the entrance surface and the exit surface of the other reflecting prism to be substantially parallel, the imaging optical system can be made compact.

  That is, for example, as shown in FIG. 11, without a reflecting prism (without providing any reflecting surface that reflects and reflects incident light by approximately 90 degrees), it is substantially equivalent to the imaging optical system 51 shown in FIG. When the imaging optical system 501 is configured and mounted on the mobile phone 200 or the like, the direction indicated by the arrow B corresponds to the thickness direction of the mobile phone 200 (front and back direction in FIG. 7). More than the total optical length of the system. In this configuration, the mobile phone 200 is very thick and large.

  Therefore, when an imaging optical system (an imaging optical system including the prism 1 instead of the lens 1 ′ shown in FIG. 11) having one reflecting surface is configured like the imaging optical system 502 shown in FIG. The direction of the arrow A can correspond to the thickness direction of the mobile phone 200, and the mobile phone 200 can be made thinner than in the case shown in FIG.

  However, the imaging device 6 is configured to include a package and electrical wiring, and has a large structure in a plane direction parallel to the light receiving surface due to the presence of these. Therefore, the thickness of the mobile phone 200 is equal to or greater than the length of the image sensor 6 in the surface direction (the length L or more shown in FIG. 12), and the mobile phone 200 is not sufficiently thin.

  Therefore, in the present embodiment, as shown in FIG. 10, the imaging optical system 51 having two reflection surfaces (the first and second reflecting prisms 1 and 4 instead of the lenses 1 ′ and 4 ′ shown in FIG. 11). In this case, the thickness of the imaging optical system corresponds to the width direction (arrow A direction) L ′ (<L) of the first reflecting prism 10. Thinning (compacting) can be achieved.

  Hereinafter, examples of the imaging optical system according to the present invention will be described more specifically with reference to construction (configuration) data, aberration diagrams, and the like.

  Tables 1 and 2 show construction data of each lens in the imaging optical system 51 of the first embodiment (Example 1).

  These are shown in order from the left of the table, the number of each optical surface, the radius of curvature of each surface (unit: mm), each optical surface on the optical axis in the infinitely focused state and the close distance focused state. (The distance between the upper surfaces of the axes, the unit is mm), the refractive index of each lens, and the Abbe number. The axial upper surface distance is a distance converted assuming that the medium existing in a region between a pair of opposing surfaces (including an optical surface and an imaging surface) is air. A blank in the close distance in-focus state in the axial upper surface interval indicates that it is the same as the value in the infinite focus state on the left. Here, the number ri (i = 1, 2, 3,...) Of each optical surface is counted from the object side on the optical path in the optical path diagram substantially equivalent to the optical path diagram of FIG. 10, as shown in FIG. The i-th optical surface, and the surface marked with * in ri is an aspherical surface (aspherical refractive optical surface or a surface having a refractive action equivalent to an aspherical surface).

  Further, since each surface of the optical diaphragm (ST), both surfaces of the plane parallel plate 5 and the light receiving surface of the image sensor 6 is a flat surface, the radius of curvature thereof is ∞.

  The aspherical shape of the optical surface is defined by the following mathematical formula using a local orthogonal coordinate system (x, y, z) in which the surface vertex is the origin and the direction from the object toward the image sensor is the positive z-axis direction. .

Where z is the amount of displacement in the z-axis direction at the height h (based on the surface vertex)
h: Height in the direction perpendicular to the z-axis (h ² = x ² + y ² )
c: Paraxial curvature (= 1 / radius of curvature)
A, B, C, D: 4th, 6th, 8th, and 10th-order aspheric coefficients k: Conic coefficients. As can be seen from the above equation (3), the radius of curvature for the aspheric lens shown in Table 1 shows a value near the surface vertex of the lens.

  The spherical aberration (LONGITUDINAL SPHERICAL ABERRATION), astigmatism (ASTIGMATISM), and distortion (DISTORTION) of the entire optical system in Example 1 under the lens arrangement and configuration as described above are shown from the left side of FIG. Shown in order. In this figure, the upper part represents each aberration in the infinite focus state, and the lower part represents each aberration in the close distance focus state. In addition, spherical aberration represents the focal position shift in mm, and the horizontal axis of the distortion represents the amount of distortion in% of the whole. The vertical axis of spherical aberration is shown as a value normalized by the incident height, while the vertical axis of astigmatism and distortion is expressed by the height of the image (image height, unit mm).

  Further, in the diagram of spherical aberration, red (broken wavelength: 656.28 nm) is indicated by a broken line, yellow (so-called d line; wavelength 587.56 nm) is indicated by a solid line, and blue (wavelength is 435.84 nm) is indicated by a two-dot chain line. The aberrations when two lights are used are shown. In the figure of astigmatism, the broken line (T) represents the tangential (meridional) image plane in terms of the deviation (horizontal axis, unit mm) in the optical axis (AX) direction from the paraxial image plane. The solid line (S) represents the sagittal (radial) image plane in terms of the amount of deviation (horizontal axis, unit mm) in the optical axis (AX) direction from the paraxial image plane. Further, the diagrams of astigmatism and distortion are the results when the yellow line (d line) is used.

  As can be seen from FIG. 17, in the imaging optical system 51 of the first embodiment, spherical aberration, astigmatism, and distortion are sufficiently suppressed in both the infinite focus state and the close distance focus state. And exhibits excellent optical properties. In addition, Table 7 shows the focal length (unit: mm), the F value, and the maximum image height in the infinitely focused state in Example 1. From these tables, it can be seen that a bright optical system can be realized in the present invention.

  Next, construction data of each lens in the imaging optical system 52 of Embodiment 2 (Example 2) are shown in Tables 3 and 4.

  Furthermore, the construction data of each lens in the imaging optical system 53 of Embodiment 3 (Example 3) are shown in Tables 5 and 6.

  The spherical aberration, astigmatism, and distortion of the entire optical system of Examples 2 and 3 under the lens arrangement and configuration as described above are shown in order from the left side of FIGS. In any of the imaging optical systems 52 and 53 in any of the embodiments, spherical aberration, astigmatism, and distortion are sufficiently suppressed in both the infinite focus state and the close distance focus state, and excellent optical characteristics. Is shown. Table 7 shows the focal length (unit: mm) and the F value in the infinitely focused state in Examples 2 and 3, respectively. From these tables, it can be seen that a bright optical system can be realized as in Example 1.

  In Examples 1 to 3, the arrangement relationship between the second reflecting prisms 4, 9, and 13 and the imaging element 6 was set as shown in Table 8 below in order to reduce the size of the imaging optical system. That is, the light receiving surface height a in the optical path bending surface of the image sensor 6 (the paper surface in FIGS. 10, 13, and 15), the exit surfaces 4 b, 9 b, 13 b of the second reflecting prisms 4, 9, 13 and the image sensor 6. The distance d from the light receiving surface (both in mm) and the value according to the above equation (1) were set as shown in Table 8.

  Further, in order to optimize the size (length) of the second reflecting prisms 4, 9, and 13, the second reflecting prisms 4, 9, and 13 having parameters shown in Table 9 in the first to third embodiments. It was adopted. That is, the refractive index n of the second reflecting prisms 4, 9, and 13, the principal ray distance t, the exit pupil distance p (all in mm), and the values obtained from the above equation (2) are set as shown in Table 9. did.

  By adopting the parameters shown in Table 8 and Table 9, the imaging optical systems 51 to 53 according to the first to third embodiments are sufficiently reduced in size in the thickness direction (the direction of the arrow L ′ in FIG. 10). Thinning is achieved.

  As described above, since the imaging optical system according to the present invention is small and light, it is suitable to be mounted on a digital device, particularly a mobile device such as the mobile phone 200. Furthermore, since the imaging optical system according to the present invention has high optical performance that can cope with a high-pixel imaging device (an imaging device of 2 million pixel class or higher), an electronic zoom system that requires interpolation is used. It is suitable for the imaging device to be employed.

  The first reflecting prisms 1, 7, 10 and the second reflecting prisms 4, 9, 13 correspond to the reflecting prisms in the claims, and the lenses 2, 3, 8, 11, 12 are It is an example of the lens or lens group in a claim.

In addition to the said embodiment, it can replace with the said embodiment and the deformation | transformation form demonstrated to the following form (a), (b) is also employable for this invention.
(A) The imaging optical system of each of the above embodiments may use a cam or a stepping motor for driving each lens group, diaphragm, or shutter, or if the amount of movement is small or the lens group to be driven is In the case of relatively light weight, it is possible to drive each lens group independently while suppressing the increase in the size of the drive unit and power consumption by using an ultra-small piezoelectric actuator. Can be achieved.

(B) In the above-described embodiment, the object-side surface of the first reflecting prism and the image-side surface of the second reflecting prism are arranged in the direction of the arrow A in consideration of the arrangement of components (compact imaging optical system). Although it is arranged so as to be the most separated in the direction, it is not limited to this, and the two surfaces are arranged so as to be closest to the direction of the arrow A (the same side region with respect to the first reflecting prism and the second reflecting prism). May be.

It is a figure which shows typically the structure of the imaging optical system concerning this invention. It is an optical path diagram which shows the relationship between an incident side prism and a light ray, (a) is a prism which does not have optical power, (b) has shown the optical path diagram about the prism which has optical power, respectively. It is explanatory drawing about an exit pupil distance. It is sectional drawing which shows the image surface side prism provided with the infrared cut function, (a) is an example in which an infrared reflecting film is integrally provided on the exit surface of the image surface side prism, and (b) is an image surface side prism. Each of the examples shows an example in which an infrared absorption film is integrally provided on the reflection surface. FIG. 2 is a perspective view illustrating the imaging optical system shown in FIG. 1 in a three-dimensional manner. FIG. 6 is a schematic optical path diagram for the imaging optical system shown in FIG. 5. BRIEF DESCRIPTION OF THE DRAWINGS It is an external appearance block diagram of the mobile telephone with a camera carrying the imaging optical system based on this invention, Comprising: (a) is an external appearance block diagram which shows the operation surface, (b) is an external appearance block diagram which shows the back surface of an operation surface. It is. It is an external appearance block diagram of a foldable camera-equipped mobile phone, (a) is an external view configuration diagram showing its operation surface, and (b) is an external configuration diagram showing the back surface of the operation surface. It is an external appearance block diagram of a portable information terminal, (a) is an external appearance block diagram which shows the operation surface, (b) is an external appearance block diagram which shows the back surface of an operation surface. It is a figure which shows arrangement | positioning of the optical element in the state focused on the infinity in Embodiment 1 of the imaging optical system which concerns on this invention. It is a figure which shows the structure of the imaging optical system comprised by replacing the reflecting prism in FIG. 11 with the lens which has a function substantially equivalent to this reflecting prism. It is a figure which shows the structure of the imaging optical system which replaced with the lens located in the object side on the optical path in FIG. 11, and provided the prism. It is a figure which shows arrangement | positioning of the optical element of the state focused on the infinity in Embodiment 2 of the imaging optical system which concerns on this invention. It is a figure which shows the structure of the imaging optical system comprised by replacing the reflective prism in FIG. 13 with the lens which has a function substantially equivalent to this reflective prism. It is a figure which shows arrangement | positioning of the optical element in the state focused on infinity in Embodiment 3 of the imaging optical system which concerns on this invention. FIG. 16 is a diagram illustrating a configuration of an imaging optical system configured by replacing the reflecting prism in FIG. 15 with a lens having a function substantially equivalent to the reflecting prism. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the lens group in the imaging optical system of Example 1. FIG. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the lens group in the imaging optical system of Example 2. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the lens group in the imaging optical system of Example 3.

Explanation of symbols

101 Incident-side prism 101a Incident-side prism incident surface 101b Incident-side prism exit surface 102 Image-side prism 102a Image-side prism incident surface 102b Image-side prism exit surface 103 Focusing lens 104, ST Optical aperture 105 , 6 Image sensors 1, 7, 10 First reflecting prism (incident side prism)
2,8,11 First lens 3,12 Second lens 4,9,13 Second reflecting prism (image surface side prism)
200 Mobile Phone 206 Imaging Lens Device (Camera)
210 Scaling Button 300 Folding Cell Phone 400 Portable Information Terminal AX Optical Axis RL1-RL6 Reflecting Surface H Subject

Claims (14)

An imaging optical system that forms an optical image of a subject on a light receiving surface of an image sensor that converts an optical image into an electrical signal,
Two reflecting prisms that bend and reflect incident light by a predetermined angle are arranged so that the incident surface of the reflecting prism arranged on the subject side on the optical path is substantially parallel to the exit surface of the other reflecting prism. An imaging optical system, wherein an incident surface or an exit surface of at least one of the reflecting prisms has optical power.   The imaging optical system according to claim 1, wherein a bending angle of incident light by the reflecting prism is approximately 90 degrees.   The imaging optical system according to claim 1 or 2, wherein at least one of the incident surface and the exit surface of the two reflecting prisms has optical power.   3. The imaging optical system according to claim 1, wherein each of the two reflecting prisms has an optical power on both the entrance surface and the exit surface. 4. In the case where an optical aperture is provided on the exit surface side of the reflecting prism arranged on the subject side on the optical path,
5. The imaging optical system according to claim 1, wherein at least an incident surface of a reflecting prism disposed on the subject side on the optical path has a negative optical power.   An optical element having an optical power including the reflecting prism is provided only on the optical path between the incident surface of the reflecting prism disposed on the subject side on the optical path and the exit surface of the other reflecting prism. The imaging optical system according to any one of claims 1 to 5, wherein   The imaging optical system according to claim 1, wherein a lens or a lens group is disposed between the two reflecting prisms.   The imaging optical system according to claim 7, wherein focusing is performed by moving the lens or the lens group substantially parallel to an incident surface of a reflecting prism disposed on the subject side in the optical path.   The imaging optical system according to claim 1, wherein the reflecting prism is made of a resin.   The imaging optical system according to claim 9, wherein the resin material constituting the reflecting prism has a water absorption of 0.01% or less.   9. The imaging optical system according to claim 1, wherein the reflecting prism is manufactured by a glass mold method.   The imaging optical system according to claim 1, wherein the other reflecting prism is provided with an infrared cut function for reducing an infrared component contained in incident light.   An imaging lens apparatus comprising the imaging optical system according to claim 1, wherein an optical image of a subject is formed on a light receiving surface of an imaging device that converts an optical image into an electrical signal.   A functional unit that includes the imaging lens device according to claim 13 and an imaging element that converts an optical image into an electrical signal, and that performs at least one of still image shooting and moving image shooting of the object on the object side. A digital device characterized by including:

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