Patent Publication Number: US-2020301092-A1

Title: Lens unit and method for manufacturing lens unit

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Application No. 2019-052252 filed on Mar. 20, 2019, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     Field of the Invention 
     At least an embodiment of the present invention relates to a lens unit that includes a plurality of lenses and a lens barrel accommodating and fixing the plurality of lenses, and a method for manufacturing a lens unit. 
     Description of the Background Art 
     A lens unit in which a plurality of lenses are arranged from an object side to an image side (image pickup element side) in an optical axis (optical axis of the image pickup apparatus) direction has been used as an optical system used in an image pickup apparatus mounted on, for example, an automobile, a monitoring camera and the like. This lens unit is designed so as to make the imaging of an image of an object by visible light on an image pickup element good. Therefore, it is necessary that the positional relationship among each lens, the positional relationship between each lens and a lens barrel, and the positional relationship between the lens unit and the image pickup element is fixed with a high accuracy. 
     In this case, the lens barrel is constituted by a resin material having a high weatherability. Further, there are two types of materials that serve as the material for constructing the lens in this kind of small image pickup apparatus: glass and resin material. In case of glass, the mechanical strength is high, but glass is expensive, and in the latter case of a resin material, the mechanical strength is low, but the resin material is inexpensive. The coefficient of thermal expansion of glass is generally lower than a resin material, thus, the lens in which the influence on the imaging characteristics (change in focal point and the like) becomes large due to minute changes in the shape and position caused by thermal expansion at high temperatures is preferably made of glass (glass lens). On the one hand, lenses made of a resin material (plastic lens) are inexpensive, and furthermore, aspherically-shaped lenses are relatively inexpensive to manufacture. Weatherability is specifically necessary for the resin material for a lens barrel, whereas optical characteristics (light transmittance and the like) are necessary for the resin material for a lens, thus, different resin materials are used for the lens barrel and the lens, and crystalline plastic can be used for the lens barrel, while amorphous plastic can be used for lenses. 
     Even when forming lens surfaces of the same shape, different techniques can be used for plastic lenses and glass lenses, and in the case of plastic lenses, resin molding can be used, whereas in the case of glass lenses, a polishing process can be used. On the one hand, with regards to the thickness of the lens, an accuracy of several μm or less is achieved in the case of a plastic lens manufactured by resin molding, whereas in the case of a glass lens, the accuracy is roughly several tens of μm which is coarser than that of the plastic lens. Therefore, in order to precisely set an interval between the glass lens and the lens adjacent to the glass lens in the optical axis direction, it is necessary to consider the variation of the thickness of this kind of glass lens. 
     Therefore, Japanese Unexamined Patent Application Publication No. 2018-54922 describes the technique which makes it possible to finely adjust the interval between the glass lens and the lens adjacent to the glass lens in a lens unit in which a glass lens is used in a part. Herein, the glass lens is fixed to a lens holder made of a resin material, a plurality of protrusion parts protruding to the adjacent lens side are provided in the lens holder, and the interval between this lens and the lens holder (glass lens) is determined by the protrusion amount of the protrusion parts. This protrusion part is constructed of a resin material. thus, the protrusion amount may be adjusted by heating and melting processing in accordance with the measured thickness of the glass lens. The aforementioned lens interval can be finely adjusted thereby, and the lens unit having good imaging characteristics can be obtained regardless of the thickness of the glass lens. 
     In the technique described in Japanese Unexamined Patent Application Publication No. 2018-54922, the accuracy of the lens interval is determined by the accuracy of the protrusion amount, which is determined by the heating and melting processing, thus, the accuracy is not high, or expensive equipment is necessary in order to perform this processing at a high accuracy. Therefore, it is difficult to obtain an inexpensive lens unit in which the interval between the lenses with could be adjusted with a high accuracy. 
     It is an object of the present invention, in consideration of the above circumstances, to provide an inexpensive lens unit in which the intervals between the lenses are adjusted with a high accuracy and a method for manufacturing the lens unit. 
     SUMMARY 
     A lens unit according to at least an embodiment of the present invention may include a first lens arranged furthest on an object side along an optical axis, a plurality of lenses arranged on an image side relative to the first lens, and a lens barrel accommodating the first lens and the plurality of lenses. The plurality of lenses may include a glass lens that is made of glass, supported by a lens holder outside as viewed from the optical axis, and accommodated in the lens barrel. The lens holder may be provided, on one side in an optical axis direction, with a plurality of protrusion parts locally protruding toward the one side, and the plurality of protrusion parts are divided into a plurality of protrusion part groups in accordance with a protrusion amount. The plurality of lenses may also include a one side lens that is adjacent to the glass lens on the one side in the optical axis direction and is locked by protrusion parts belonging to one of the plurality of protrusion part groups to allow a positional relationship between the one side lens and the glass lens to be determined in the optical axis direction. 
     In this configuration, a lens body in which the glass lens may be integrated with the lens holder is accommodated in the lens barrel. The lens body (lens holder) and the one side lens may abut against the plurality of protrusion parts formed in the lens holder, and the interval in the optical axis direction between the glass lens and the one side lens may be determined by the protrusion amount of the protrusion parts. Since the protrusion amount of the protrusion parts can be precisely determined for each protrusion part group during the formation of the lens holder, the interval can be finely adjusted by selecting a protrusion part group. As a result, the imaging characteristics of the lens unit can be improved even when there is variation in the thickness, etc., of the glass lens. 
     The plurality of lenses may include an other side lens that is adjacent to the glass lens on another side of the lens holder. An engagement structure formed in the other side lens and an engagement structure formed in the lens holder may engage with each other to allow a positional relationship between the other side lens and the lens holder to be fixed in at least the optical axis direction or a direction perpendicular to the optical axis. The plurality of protrusion parts and the engagement structures formed in the other side lens and in the lens holder may have overlapping regions when viewed in the optical axis direction. 
     In this configuration, the positional relationship between the other side lens adjacent to the glass lens on the other side of the glass lens and the lens holder may be determined by the engagement structures. The positional relationship between the one side lens, the glass lens (lens body) and the other side lens may be determined thereby. In this case, causing the engagement structures and the protrusion parts to overlap each other when viewed from the optical axis direction suppresses distortion produced in the lens barrel or the plastic lenses (one side lens and other side lens) when installing the other side lens after the lens body or installing the lens body and the one side lens after the other side lens in the lens barrel. 
     Further, the plurality of lenses may include two lenses that are adjacent to each other in the optical axis direction and are joined together to form a cemented lens serving as the one side lens. 
     In this configuration, the one side lens may be the cemented lens. Such a configuration increases the degrees of freedom of the configuration of a lens system. 
     Further, a thin-film infrared cut filter that blocks light of a longer wavelength than light as a target for imaging may be formed on a surface on the image side of the glass lens. 
     By using the thin-film infrared cut filter, specifically, near-infrared light that is not necessary as a target for imaging and does not yield good imaging characteristics is prevented from reaching the image surface, and it becomes unnecessary to provide the infrared cut filter as a separate component. While the interval between the glass lens on which the infrared cut filter has been formed and the one side lens may influence the occurrence of ghosting and flaring, such adverse effects can be suppressed by finely adjusting the interval using the aforementioned protrusion parts. 
     A lens unit manufacturing method according to at least an embodiment of the present invention may be a method for manufacturing the lens unit as above and may include arranging the glass lens in a lens installation hole made by digging a region around the optical axis of the lens holder down in the optical axis direction, fixing the glass lens to an inner surface of the lens installation hole with an adhesive agent, measuring a thickness along the optical axis direction of the glass lens after fixing, selecting a protrusion part group from among the plurality of protrusion part groups in accordance with the thickness, processing protrusion parts that belong to another protrusion part group and have a larger protrusion amount than protrusion parts belonging to the protrusion part group as selected, to allow the protrusion parts belonging to the protrusion part group as selected to lock the one side lens, and arranging a lens body that includes the glass lens fixed to the lens holder in the lens barrel after the processing of protrusion parts. 
     In this lens unit manufacturing method, the lens body may be produced by the arranging and the fixing of the glass lens. Then, protrusion parts (protrusion part group) abutting to the one side lens may be determined by the selecting of a protrusion part group and the processing of protrusion parts to make the interval between the one side lens and the glass lens appropriate before the lens body is arranged in the lens barrel. In the processing of protrusion parts, processing may be performed on the protrusion parts having a larger protrusion amount than the selected protrusion part group, which does not need a high accuracy. Therefore, the fine adjustment of the lens interval is possible, and the manufacturing of the lens unit is easy. 
     A projection part, which protrudes to a side opposite to a side where the lens installation hole is dug down along the optical axis direction, may be formed in a periphery of the lens installation hole in the lens holder as viewed from the optical axis. In that case, the lens unit manufacturing method includes, between the arranging and the fixing of the glass lens, swaging to bend the projection part toward the optical axis while keeping the projection part in a non-contact state with the glass lens. 
     By providing the projection part in the lens holder in this way, the placement of the glass lens within the lens installation hole is easy, and the glass lens is fixed to the lens holder after the fixing, even in the location where there is a projection part. Further, the glass lens is prevented from moving from the lens holder prior to solidification of the adhesive agent. 
     The lens unit manufacturing method may include, between the fixing of the glass lens and the arranging of the lens body, installing an aperture on a surface on another side of the lens holder. 
     In that case, not only the glass lens but also the aperture is fixed to the lens holder. Therefore, the positional relationship between the glass lens, the one side lens, the other side lens, and the aperture is fixed through the lens holder. 
     According to at least an embodiment of the present invention, an inexpensive lens unit in which the intervals between lenses are adjusted with a high accuracy and a method for manufacturing the lens unit are obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which: 
         FIG. 1  is a cross-sectional view of a lens unit according to an embodiment of the present invention; 
         FIG. 2A  is a cross-sectional view of a lens barrel used in the lens unit according to the embodiment; 
         FIG. 2B  is a perspective view of the lens barrel used in the lens unit according to the embodiment; 
         FIG. 3  is an exploded view of the lens unit according to the embodiment; 
         FIG. 4  is a perspective view of a lens holder in the lens unit according to the embodiment as viewed from an image side; 
         FIG. 5  is a plan view of the lens holder in the lens unit according to the embodiment as viewed from an object side, illustrating the lens holder in which a fifth lens has been arranged; 
         FIG. 6A  is a plan view of the lens holder alone in the lens unit according to the embodiment as viewed from the image side; 
         FIG. 6B  is a plan view of the lens holder in the lens unit according to the embodiment as viewed from the image side, illustrating the lens holder in which the fifth lens has been arranged; 
         FIG. 7  is a cross-sectional view along the optical axis of a fifth lens body in the lens unit according to the embodiment; 
         FIG. 8  is a perspective view illustrating the relationship between the fifth lens body and an aperture in the lens unit according to the embodiment; 
         FIGS. 9A through 9C  are cross-sectional views describing a process for manufacturing the fifth lens body in the lens unit according to the embodiment; and 
         FIG. 10  is a cross-sectional view illustrating the positional relationship between a protrusion part in the lens unit and a stepped part and the like on an upper side relative to the protrusion part in the lens unit according to the embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will be described below using the drawings. 
       FIG. 1  is a cross-sectional view along an optical axis A of a lens unit  1  according to the present embodiment. Herein, an object (Ob) side is the upper side in the drawing, an image (Im) side is the lower side in the drawing, and an image pickup element  100  is positioned in the lowest part of the drawing. Each of lenses L 1  to L 7  is directly or indirectly fixed to a lens barrel  10 . In  FIG. 1 , the configuration for fixing each lens and an aperture  20 , or between each lens and the lens barrel  10  is mainly described, and the configuration for actually fixing the positional relationship of the image pickup element  100  and the lens barrel  10  is also provided, but the description thereof is omitted. 
     The image pickup element  100  is a 2-dimensional CMOS image sensor, each pixel is arranged two-dimensionally in a surface perpendicular to the optical axis A, and the image pickup element  100  is actually covered with a cover glass (not shown in the drawing). In  FIG. 1 , the lens unit  1  comprising the first lens L 1  to the seventh lens L 7  is configured. The lens unit  1  is configured so as to image a visible light image which is the target for imaging on the image pickup element  100  (image surface) with a desired field of view and a desired form. 
     In  FIG. 1 , the first lens L 1  provided furthest on the object side (upper side in the drawing) is a fish-eyed lens, and mainly determines the field of view and the like of the image pickup apparatus. A second lens L 2 , a third lens L 3 , a fourth lens L 4 , a fifth lens L 5 , a sixth lens L 6  and the seventh lens L 7  are sequentially arranged on the image pickup element  100  side (image side). Each lens has a substantially symmetrical shape around the optical axis A. Further, an aperture  20  for controlling the light flux is provided between the fourth lens L 4  and the fifth lens L 5 . Further, a light shielding plate to remove unnecessary light can be appropriately provided between the second lens L 2  and the third lens L 3 , but a description thereof has been omitted in  FIG. 1 . 
     Further,  FIG. 2A  is a cross-sectional view along the optical axis A of only the lens barrel  10 , and  FIG. 2B  is a perspective view of the lens barrel  10  viewed from the oblique upper side (object side) in  FIG. 1 . A first accommodation part  10 A in which the inner peripheral surface is a hollow part having a substantially cylindrical shape is provided on the object side (upper side in the drawing) of the lens barrel  10 , and the bottom surface of the image side of the first accommodation part  10 A is a first placement part  11  abutting against the first lens L 1 . Further, the image side (lower side in the drawing) is more coaxial to the first accommodation part  10 A than the first placement part  11 , a second accommodation part  10 B which is a hollow part having a substantially cylindrical shape with a smaller diameter than the first accommodation part  10 A is provided, and the bottom surface of the image side of the second accommodation part  10 B is a second placement part  12  abutting against a cemented lens L 60  (the image side lens which is described later). The center axis of the first accommodation part  10 A and the second accommodation part  10 B are common, and are equivalent to the optical axis A. Further, as illustrated in  FIG. 2A , the inner peripheral surface of the second accommodation part  10 B actually becomes gradually smaller from the object side toward the image side. 
     In  FIG. 1 , the lens surfaces (surfaces through which the light forming the image passes) on the object side and the image side of each lens are appropriately subjected to curved surface (convex surface and concave surface) processing so as to provide the lens unit  1  with the desired imaging characteristics. Below, the lens surface of the object side in each lens is referred to as the first surface R 1 , and the lens surface of the image side is referred to as the second surface R 2 . Further, as the shape (convex surface or concave surface) of the lens surface, the shape of the first surface R 1  means the shape viewed from the object side, and the shape of the second surface R 2  means the shape viewed from the image side. 
     Generally, there are two types of material that serve as the material for constructing the lens in this kind of small image pickup apparatus: glass and resin material. In case of glass, the mechanical strength is high, but glass is expensive, and in the latter case of a resin material, the mechanical strength is low, but the resin material is inexpensive. Further, the coefficient of thermal expansion of glass is smaller than that of a resin material, thus, the lens in which the influence on the imaging characteristics (change in the focal point and the like) becomes large due to minute changes in the shape and position caused by the thermal expansion at high temperatures is preferably made of glass. Therefore, in order to make a high performance and inexpensive lens unit  1 , lenses (glass lenses) made of glass are the only lenses which are preferable, and other lenses are preferably lenses (plastic lenses) made of a resin material. 
     From this point of view, in the embodiment, the first lens L 1  arranged furthest on the object side is located on the outermost surface of the lens unit  1 , and is therefore, a glass lens which does not easily become scratched. Further, since the lenses (fourth lens L 4  and fifth lens L 5 ) adjacent to the aperture  20  show significant changes in the focal length due to temperature changes, either lens (in the present embodiment, the fifth lens L 5 ) is a glass lens. Inexpensive plastic lenses can be used as the other lenses. 
     The first lens L 1  is a negative lens in which a lens surface L 1 R 1  of the object side is a convex surface and a lens surface L 1 R 2  of the image side is a concave surface. The lens surface L 1 R 1  occupies almost the entirety of the upper surface side of the first lens L 1 . On the lower surface side (image side) of the first lens L 1 , a first lens first lower surface L 1 A constituted by a flat surface perpendicular to the optical axis A is provided on the outside of the lens surface L 2 R 2 . A first lens second lower surface L 1 B parallel to the first lens first lower surface L 1 A and located on the object side (upper side in the drawing) relative to the first lower surface L 1 A can be provided further outside of the first lens first lower surface L 1 A. Further, the outermost peripheral part of the first lens L 1  forms a cylindrical shaped first lens outer peripheral surface L 1 C having the optical axis A as the center axis. Among these surfaces, the lens surfaces L 1 R 1  and L 1 R 2  are used optically, and the other surface can be used to fix the first lens L 1  to the lens barrel  10 . 
     In  FIG. 1 , the upper end side of the lens barrel  10  constitutes a first lens locking part  13  which is curved toward the optical axis A (center) side so as to suppress the movement to the object side of the first lens L 1 . Further, the first lens first lower surface L 1 A abuts against the first placement part  11  of the lens barrel  10 . Therefore, the positional relationship in the optical axis A direction relative to the lens barrel  10  of the first lens L 1  is determined by the first lens locking part  13  on the object side (upper surface in the drawing), and is determined by the first placement part  11  on the image side (upper surface in the drawing). In this case, a waterproof function on the inside of the lens barrel  10  can be obtained by arranging a ring shaped O-ring  30  that is compressed and elastically deformed in the direction perpendicular to the optical axis A direction in a gap between the first lens second lower surface L 1 B and the first placement part  11  further outside relative to the first lens first lower surface L 1 A. Note that, the shape of the aforementioned first lens locking part  13  is the shape after processing (heat swaging) in order to fix the first lens L 1  to the lens barrel  10 , and the shape of the upper end side of the lens barrel  10  prior to fixing is such that the first lens L 1  can be inserted into the lens barrel  10  as illustrated in  FIG. 1  from the upper side as illustrated in  FIG. 2A . 
     Further, the first lens outer peripheral surface L 1 C abuts against the inner peripheral surface of the first accommodation part  10 A in the lens barrel  10 . The positional relationship between the first lens L 1  and the lens barrel  10  in the direction perpendicular to the optical axis A is determined thereby. That is, the first lens L 1  is fixed to the lens barrel  10  by the aforementioned configuration. 
     The second lens L 2  is a negative lens in which a lens surface L 2 R 1  of the object side is a convex surface and a lens surface L 2 R 2  of the image side is a concave surface. A second lens first upper surface L 2 A which is perpendicular to the optical axis A and which is a flat surface positioned on the image side (lower side in the drawing) relative to the lens surface L 2 R 1  is provided on the outside of the lens surface L 2 R 1  on the object side (upper side in the drawing) of the second lens L 2 . Further, a stepped part (engagement structure) L 2 B constituted by a surface parallel to and a surface perpendicular to the optical axis A is provided outside relative to the lens surface L 2 R 2  on the image side (lower side in the drawing) of the second lens L 2 . A second lens outer peripheral surface L 2 C which is the surface constituting the outermost periphery of the second lens L 2  abuts against the inner peripheral surface of the second accommodation part  10 B. The second lens outer peripheral surface L 2 C is formed into a substantially conical surface shape so that the inner diameter around the optical axis A gradually decreases toward the image side. The positional relationship between the second lens L 2  and the direction perpendicular to the optical axis A of the lens barrel  10  is determined thereby. 
     Further, an elastic member  40  constituted by an elastic body between the second lens first upper surface L 2 A and the first lens second lower surface L 1 B and thin in the optical axis A direction is arranged in the region inside (side near the optical axis A) relative to the first placement part  11  and outside relative to the lens surface L 1 R 2  and the lens surface L 2 R 1 . That is, the first lens L 1  and the second lens L 2  are not in direct contact in the direction along the optical axis A, and the elastic member  40  is provided therebetween. 
     The third lens L 3  is a positive lens in which a lens surface L 3 R 1  of the object side is a concave surface and a lens surface L 3 R 2  of the image side is a convex surface. A stepped part (engagement structure) L 3 A formed on the object side (upper surface in the drawing) of the third lens L 3  so as to engage with the stepped part L 2 B in the second lens L 2  is provided on the outside of the lens surface L 3 R 1 . Further, a stepped part (engagement structure) L 3 B constituted by a surface parallel to and a surface perpendicular to the optical axis A is provided outside relative to the lens surface L 3 R 2  on the image side (lower surface in the drawing) of the third lens L 3 . Further, a third lens outer peripheral surface L 3 C which is a surface having a substantially cylindrical shape constituting the outermost periphery of the third lens L 3  is not in contact with the inner peripheral surface of the second accommodation part  10 B. 
     The fourth lens L 4  is a positive lens in which a surface L 4 R 1  of the object side is a concave surface and a surface L 4 R 2  of the image side is a convex surface. A stepped part (engagement structure) L 4 A formed on the object side (upper surface in the drawing) of the fourth lens L 4  so as to engage with a stepped part L 3 B in the third lens L 3  is provided on the outside of the lens surface L 4 R 1 . Further, a stepped part (engagement structure) L 4 B constituted by a surface parallel to and a surface perpendicular to the optical axis A is provided outside relative to the lens surface L 4 R 2  on the image side (lower surface in the drawing) of the fourth lens L 4 . Further, a fourth lens outer peripheral surface L 4 C which is a surface having a substantially cylindrical shape constituting the outermost periphery of the fourth lens L 4  is not in contact with the inner peripheral surface of the second accommodation part  10 B. That is, the third lens L 3  and the fourth lens L 4  are not in contact with the lens barrel  10 . 
     As stated above, the fifth lens L 5  is made of glass, and is a positive lens in which the surface L 5 R 1  of the object side is a convex surface and the surface L 5 R 2  of the image side is a convex surface. However, unlike the other lenses, the fifth lens L 5  is accommodated in the lens barrel  10  in a state in which the fifth lens L 5  is press-fit and integrated in a lens holder  51  made of a resin material to provide a fifth lens body L 50 . That is, the fifth lens L 5  is treated as a lens in the same manner as the third lens L 3  and the fourth lens L 4 , which are made of a resin material, in the form of the fifth lens body L 50  which includes the fifth lens L 5 . 
     A stepped part (engagement structure) L 50 A formed on the object side (upper surface in the drawing) of the fifth lens body L 50  so as to engage with a stepped part L 4 B in the fourth lens L 4  is provided on the lens holder  51  on the outside of the fifth lens L 5 . Further, a protrusion part L 50 B which protrudes locally from the periphery toward the image side (lower surface in the drawing) is provided outside relative to the fifth lens L 5  on the image side (lower side in the drawing) of the fifth lens body L 50 . The details of the protrusion part L 50 B will be described later. Further, a fifth lens body outer peripheral surface L 50 C which is a surface constituting the outermost periphery of the fifth lens body L 50  abuts against the inner peripheral surface of the second accommodation part  10 B. The fifth lens body outer peripheral surface L 50 C is formed to a substantially conical surface shape such that the inner diameter around the optical axis A gradually decreases toward the image side. The positional relationship in the direction perpendicular to the optical axis A between the fifth lens body L 50  (fifth lens L 5 ) and the lens barrel  10  is determined thereby. 
     Further, an IR cut coating layer (infrared cut filter)  52  is formed on the lens surface L 5 R 2  of the image side of the fifth lens L 5 . Due to the IR cut coating layer  52 , near-infrared light which is a component other than visible light toward the image pickup element  100  side can be removed. When the imaging characteristics of the lens unit  1  are optimized for visible light, since the characteristics are not optimal for the near-infrared light, it is preferable that the near-infrared light does not reach the image pickup element  100  in order to obtain a good image. The IR cut coating layer  52  prevents the near-infrared light from traveling toward the image pickup element  100  side, so that only visible light images in which good imaging characteristics can be obtained are obtainable by the image pickup element  100 . The IR cut coating layer  52  is formed, for example, by vapor deposition, to a thin film as a multilayer film which transmits light having a wavelength shorter than the cut-off wavelength and does not transmit light of a longer wavelength. This kind of IR cut coating layer  52 , specifically, can be adequately formed on a glass lens, and thus, can be easily formed on the lens surface L 5 R 2 . 
     The sixth lens L 6  is a negative lens in which a surface L 6 R 1  of the object side is a concave surface and a surface L 6 R 2  of the image side is a concave surface. The seventh lens L 7  has a smaller outer diameter than the sixth lens L 6 , and is a positive lens in which a surface L 7 R 1  of the object side is a convex surface and a surface L 7 R 2  of the image side is a convex surface. Further, the sixth lens L 6  and the seventh lens L 7  are set so as to form a cemented lens (image side lens) L 60  on the outermost image side by fitting and joining with the opposite lens surface. In short, the image side lens which is the lens that is the closest to the image side is substantially the cemented lens L 60  in which the lens surface L 6 R 2  of the image side of the sixth lens L 6  is fitted and joined with the lens surface L 7 R 1  of the object side of the seventh lens L 7 . 
     The cemented lens upper surface L 6 A which is a flat surface which abuts against the protrusion part L 50 B in the fifth lens body L 50  on the outside of a lens surface L 6 R 1  is provided on the object side (upper surface in the drawing) of the cemented lens L 60  (sixth lens L 6 ). Note that,  FIG. 1  describes, for the sake of convenience, that the protrusion part L 50 B abuts against the cemented lens upper surface L 6 A on both sides which sandwich the optical axis A, and herein, the position of the protrusion part L 50 B as described later is not precisely reflected. The actual configuration and the precise position of the protrusion part L 50 B will be described later. 
     Further, the cemented lens lower surface L 6 B which is a flat surface perpendicular to the optical axis A is provided outside relative to the lens surface L 7 R 2  on the image side (lower side in the drawing) of the cemented lens L 60  (sixth lens L 6 ). The cemented lens lower surface L 6 B abuts against the second placement part  12 . The sixth lens outer peripheral surface L 6 C which is the surface constituting the outermost periphery of the cemented lens L 60  (sixth lens L 6 ) abuts against the inner peripheral surface of the second accommodation part  10 B. The sixth lens outer peripheral surface L 6 C is formed in a substantially conical surface shape so that that inner diameter around the optical axis A gradually decreases toward the image side. Therefore, the position in the direction along the optical axis A of the cemented lens L 60  is controlled by the lens barrel  10  (second placement part  12 ) on the image side. 
     In this case, the fifth lens body L 50  (protrusion part L 50 B) is locked by the cemented lens L 60  on the image side, thus, the position in the direction along the optical axis A of the fifth lens body L 50  is controlled by the second placement part  12  (lens barrel  10 ) via the cemented lens L 60  on the image side. 
     Further, according to the configuration, the position in the direction along the optical axis A of the fourth lens L 4  is controlled by the lens barrel  10  via the fifth lens body L 50  and the cemented lens L 60  on the image side as a result of the engagement of the stepped part L 4 B and the stepped part L 50 A with each other. On the one hand, the position in the direction perpendicular to the optical axis A of the fourth lens L 4  is determined by the inner peripheral surface of the second accommodation part  10 B via the fifth lens body L 50  by the stepped part L 4 B engaging with the stepped part L 50 A. Similarly, the position in the direction along the optical axis A of the third lens L 3  is controlled by the lens barrel  10  via the fourth lens L 4 , the fifth lens body L 50  and the cemented lens L 60  on the image side by engaging the stepped part L 3 B with the stepped part L 4 A. On the one hand, the position in the direction perpendicular to the optical axis A of the third lens L 3  is determined by the inner peripheral surface of the second accommodation part  10 B via the fourth lens L 4  and the fifth lens body L 50  by the stepped part L 3 B engaging with the stepped part L 4 A. 
     Further, according to the configuration, the position in the direction along the optical axis A of the second lens L 2  is controlled by the lens barrel  10  via the third lens L 3 , the fourth lens L 4 , the fifth lens body L 50  and the cemented lens L 60  on the image side by engaging the stepped part L 2 B with the stepped part L 3 A. On the one hand, the position in the direction perpendicular to the optical axis A of the second lens L 2  is, as stated above, determined by the inner peripheral surface of the second accommodation part  10 B. 
     That is, in the aforementioned configuration, among the second lens L 2  to the cemented lens L 60  (seventh lens L 7 ), the second lens L 2 , the fifth lens L 5  (fifth lens body L 50 ) and the cemented lens L 60  are the contact lenses of which the outer peripheral parts abut against the inner peripheral surface of the second accommodation part  10 B in the lens barrel  10 . These contact lenses have a fixed positional relationship between the lens barrel  10  in the direction perpendicular to the optical axis A thereby. On the one hand, the third lens L 3 , the fourth lens L 4  are non-contact lenses which are not in direct contact with the inner peripheral surface of the second accommodation part  10 B. The non-contact lens are fixed in a positional relationship between the lens barrel  10  in the orthogonal direction by fixing the positional relationship in the direction perpendicular to the optical axis A between the contacts lenses by directly or indirectly engaging with the contact lenses on the object side and the image side via the aforementioned stepped part (engagement structure). All of the second lens L 2  to the cemented lens L 60  (seventh lens L 7 ) are in a positional relationship fixed between the lens barrel  10  in the direction perpendicular to the optical axis A thereby. 
     On the one hand, the outer peripheral surfaces of the third lens L 3  and the fourth lens L 4  are not in contact with the inner peripheral surface of the second accommodation part  10 B. Therefore, a force caused by the thermal expansion difference between the third lens L 3 , the fourth lens L 4  and the lens barrel  10  and applied to the third lens L 3 , the fourth lens L 4  (lens system) and the lens barrel  10  is suppressed. Therefore, the distortion, etc., of the lens caused by the thermal expansion difference is suppressed, and the adverse effects of temperature changes on the imaging characteristics are reduced. 
       FIG. 3  is an exploded perspective view of the lens unit  1 , and herein, also describes a light shielding plate  21  of which the description in  FIG. 1  omitted. Herein, the cemented lens L 60 , the fifth lens body L 50 , the aperture  20 , the fourth lens L 4 , the third lens L 3 , the light shielding plate  21 , the second lens L 2 , the elastic member  40 , the O-ring  30  and the first lens L 1  are installed in order to the lens barrel  10  from the upper side (object side) in the drawing. As illustrated in the drawings, the elastic member  40  and the O-ring  30  are annular. 
     A crystalline plastic (polyethylene, polyamide, polytetrafluoroethylene) excellent in weatherability is preferably used as the material of the lens barrel  10 . On the one hand, the second lens L 2 , the third lens L 3 , the fourth lens L 4 , the sixth lens L 6  and the seventh lens L 7  are constituted by an amorphous plastic (polycarbonate and the like) excellent in performance (light transmission and moldability) as the lens. Further, the lens holder  51  is constituted with the same amorphous plastic as the fourth lens L 4 , thus, the fifth lens body L 50  can, as a whole, be handled as a plastic lens in the same manner as the fourth lens L 4 . As stated above, the first lens L 1  and the fifth lens L 5  are made of glass. 
     In the lens unit  1 , the interval between the fifth lens L 5  adjacent to the aperture  20  on the image side and the cemented lens (image side lens) L 60  adjacent to fifth lens L 5  on the image side has a large effect on the imaging characteristics, thus, it is necessary that this interval is precisely determined. Further, in the fifth lens L 5 , the infrared cut coating layer  52  is formed in L 5 R 2  which is the lens surface of the cemented lens L 60  side. In this case, if this interval is not optimized, flaring and ghosting may occur. 
     On the one hand, errors in the thickness along the optical axis A direction such as in the fourth lens L 4  which is a plastic lens are, for example, in a range of several μm or less, whereas the errors in the thickness of the fifth lens L 5  which is a glass lens manufactured by the polishing process is roughly larger in the range of several tens of μm which is coarser than that of the plastic lens. This lens unit  1  is constituted so as to be able to compensate for the influence of variations in the thickness of this kind of fifth lens L 5  with respect to the interval between the fifth lens L 5  and the cemented lens L 60 . This point is described below. 
       FIG. 4  is a perspective view of the lens holder  51  constituting the fifth lens body L 50  viewed from the image side.  FIG. 5  is a plan view of the lens holder  51  (fifth lens body L 50 ) in which a fifth lens L 5  has been arranged.  FIGS. 6A and 6B  are each a plan view of the lens holder  51  as viewed from the image side ( FIG. 6A  illustrating the lens holder  51  alone;  FIG. 6B  illustrating the lens holder  51  with the fifth lens L 5  arranged therein). Note that, the above description is mainly based on the assembled structure in  FIG. 1 , whereas in the following, each constituent element is described prior (before assembly) to the state in  FIG. 1 . In this case, the optical axis A, the object side, the image side and the like mean the state when each constituent element is arranged in  FIG. 1 . 
     As illustrated in  FIG. 4 , the protrusion part L 50 B is formed into 21 equal intervals in the circumferential direction, and each interval is divided into a group (protrusion part group) consisting of L 50 B 1  to a group consisting of L 50 B 7  constituted by three protrusion parts L 50 B in accordance with the protrusion amount to the image side. This protrusion amount is set so as to increase from L 50 B 1  to L 50 B 7 . Therefore, when manufacturing this lens unit  1 , the protrusion part L 50 B actually abutting against the cemented lens upper surface L 6 A can be selected from among the aforementioned L 50 B 1  to L 50 B 7  in accordance with the measured thickness of the fifth lens L 5  after being joined to the aforementioned lens holder  51  so that the interval between the fifth lens L 5  and the cemented lens L 60  is an appropriate value. In this case, the protrusion part L 50 B of the protrusion part group having a larger protrusion amount than the selected protrusion part group can be made to have a smaller protrusion amount than the selected protrusion part group by mechanical or heating and melting processing. 
     The point that processing is performed on the protrusion part L 50 B is the same as the technique described in Japanese Unexamined Patent Application Publication No. 2018-54922. However, in the technique described in Japanese Unexamined Patent Application Publication No. 2018-54922, since the accuracy of the protrusion amount after the processing reflects the accuracy of the lens interval, a high processing accuracy is necessary. With respect thereto, since the processing used in the case of this lens unit  1  is performed only to make the protrusion amount lower than the selected protrusion part group, a high processing accuracy is not necessary. On the one hand, the lens interval is determined only by the protrusion amount of the protrusion part L 50 B of the selected protrusion part group independent of this process and is determined by the accuracy of the manufacturing (molding) of the lens holder  51 , thus, the accuracy is higher than the processing accuracy. 
     Further, if the three protrusion parts L 50 B 1  to L 50 B 7  are provided as illustrated in the drawing, since the fifth lens body  50  (lens holder  51 ) can be supported at three points on the cemented lens L 60 , the interval between the fifth lens L 5  and the cemented lens L 60  can be determined with a high accuracy after compensating for the variation in the thickness of the aforementioned fifth lens L 5 . The same is true not only for the variation in the thickness of the fifth lens L 5 , but also for the variation during the manufacturing of the cemented lens L 60  and the lens barrel  10 . Therefore, a high accuracy processing is not necessary, and it is possible to make fine adjustments to the lens interval. 
     Further, since the fifth lens body L 50  is supported on the image side by the cemented lens L 60  (cemented lens upper surface L 6 A) in the protrusion part L 50 B, the force is specifically applied to the cemented lens L 60  at the three protrusion parts L 50 B during the installation (press-fitting) of the fifth lens body L 50 . If this force is not uniform, the force acting to cause deformation (distortion) to the lens barrel  10  may act on the lens barrel  10  via the cemented lens L 60 . Due to the aforementioned configuration, since the three protrusion parts L 50 B belonging to each protrusion part group are arranged at equal intervals (phase: 120°) in the circumferential direction symmetric around the optical axis A as illustrated in  FIG. 4 , the force acting to deform the lens barrel  10  is suppressed in this way. 
     Next, the relationship between the lens holder  51  and the fifth lens L 5  will be described. As illustrated in  FIG. 4 , a lens installation hole  51 C which is a hole part for accommodating the fifth lens L 5  from the image side is formed in the lens holder  51 , and the fifth lens L 5  is locked on the object side by a lens fixing surface  51 D which becomes the bottom surface on the object side of the lens installation hole  51 C. That is, the fifth lens L 5  is locked by the lens fixing surface  51 D on the object side and fixed to the lens holder  51  in the optical axis A direction. As illustrated in  FIG. 6A , the lens fixing surface  51 D is formed along the outer peripheral part of the fifth lens L 5 , but is divided into three parts in the circumferential direction. 
     Further, in the lens installation hole  51 C, the outer peripheral part of the fifth lens L 5  abuts against ribs  51 E protruding locally to the optical axis A side as illustrated in  FIG. 4 . The ribs  51 E are formed at three positions at equal intervals in the circumferential direction where the lens fixing surface  51 D is not provided. That is, in the direction perpendicular to the optical axis A, the fifth lens L 5  is fixed to the lens holder  51  with the periphery locked by the three ribs  51 E. 
     Further, in  FIG. 4 , three small claw-shaped projection parts  51 F curved to the optical axis A side in the same manner as the first lens locking part  13  are provided in the circumferential direction. As stated above, the shape of a projection part  51 F changes during the manufacturing process, and herein, the state in which the fifth lens body L 50  has been formed is illustrated. 
     Further, as illustrated in  FIGS. 6A and 6B , a first adhesive agent groove  51 H which is a portion (groove) dug down to a lens holder bottom surface  51 G as the bottom surface perpendicular to the optical axis A is formed outside of the lens installation hole  51 C in a portion on the image side of the lens holder  51  where the ribs  51 E and the projection part  51 F are not formed in the circumferential direction. Six first adhesive agent grooves  51 H are formed at equal intervals in the circumferential direction so as to connect with the lens installation hole  51 C. Further, as illustrated in  FIG. 5 , a second adhesive agent groove (recessed part)  51 J which is the portion (groove) dug down to an aperture placement surface  51 B as the bottom surface perpendicular to the optical axis A is formed outside of the lens installation hole  51 C on the object side of the lens holder  51 . The aperture placement surface  51 B will be described later. Three second adhesive agent grooves  51 J are formed at equal intervals in the circumferential direction in a portion where the ribs  51 E are formed in the circumferential direction so as to connect with the lens installation hole  51 C. 
       FIG. 7  is a cross-sectional view along the optical axis A in the B-B direction of  FIG. 5  in the fifth lens body L 50 . In  FIG. 7 , the left side on the optical axis A illustrates a cross-section of the portion which has the lens fixing surface  51 D, and is without the ribs  51 E and the second adhesive agent groove  51 J. The right side of the optical axis A illustrates a cross-section of the portion which does not have the lens fixing surface  51 D, and has the ribs  51 E and the second adhesive agent groove  51 J. The fifth lens L 5  and the lens holder  51  are fixed to each other by the adhesive agent between them. Unlike  FIG. 5 ,  FIG. 7  also illustrates the adhesive agent layer  200  after fixing. 
     On the one hand,  FIG. 8  is a perspective view viewed from the object side of the aperture  20  and the fifth lens body L 50 . As illustrated in  FIG. 8 , three projections  51 A having a circular cross-sectional shape perpendicular to the optical axis A are formed at equal intervals in the circumferential direction on the object side of the lens holder  51 . Further, the periphery of the projections  51 A is a flat surface (aperture placement surface  51 B) perpendicular to the optical axis A. On the one hand, three positioning holes  20 A penetrating the thin flat aperture  20  in the optical axis A direction are formed so as to correspond with the projections  51 A outside a center opening  20 B. Therefore, the positioning holes  20 A can engage with the projections  51 A, and the aperture  20  can be fixed in a state placed on the aperture placement surface  51 B. In this case, the aperture  20  can be fixed to the lens holder  51  (fifth lens body L 50 ) by, for example, melting the projections  51 A protruding from the positioning holes  20 A to the object side after the placement of the aperture  20  and welding to the periphery. 
     In  FIG. 1 , the aperture  20  is provided perpendicular to the optical axis A, and if this angle fluctuates, ghosting may occur in the image pickup apparatus. With respect thereto, the aperture  20  is fixed in an appropriate manner to the fifth lens body L 50 , and the fluctuation of the angle relative to the optical axis A of the aperture  20  is suppressed by such a configuration. 
     In this case, as illustrated in  FIG. 8 , the positioning hole  20 A is formed longer in the circumferential direction around the optical axis A than in the radial direction of the optical axis A. As a result, with the aperture  20  in a mounted state, since the aperture  20  can be rotated around the optical axis A by a small amount, the installation on the fifth lens body L 50  of the aperture  20  is particularly easy. On the one hand, if the opening  20 B of the aperture  20  is considered to be a circle centered on the optical axis A, since the condition of the opening  20 B does not change during the aforementioned rotation, the imaging characteristics are not adversely affected even if the aperture  20  rotates in this manner. Therefore, by this configuration, the aperture  20  can be fixed to the lens holder  51  in a highly accurate positional relationship with good reproducibility. In the aforementioned example, the projections  51 A have a circular shape, but can include the case when the shape is not circular, and more generally, the length of the positioning hole  20 A along the circumferential direction around the optical axis A may be set longer than the length of the projections  51 A along the same direction. Therefore, the operation to install the aperture in the lens holder becomes easy, and does not cause an adverse effect to the imaging characteristics. 
     As illustrated in  FIGS. 5 and 7 , the lens fixing surface  51 D which supports the fifth lens L 5  and the aperture placement surface  51 B which is fixed to the aperture  20  are formed so as to overlap when viewed in the optical axis A direction. As a result, by constituting so that the region abutting against the fifth lens L 5  on the lens fixing surface  51 D overlaps with the region abutting against the aperture  20  on the aperture placement surface  51 B when viewed in the optical axis A direction, the positional relationship of the lens holder  51 , the fifth lens L 5 , and the aperture  20  in the optical axis A direction can be precisely determined. 
     A method (method for manufacturing of the lens unit) for forming the fifth lens body L 50  in this manner, and then installing the fifth lens body L 50  on the lens barrel  10  will be described below. 
       FIGS. 9A through 9C  illustrate a process for manufacturing the fifth lens body L 50  and are each a cross-sectional view corresponding to  FIG. 7 . In the actual manufacturing, since the fifth lens body L 50  is considered to be in a state which is vertically inverted compared to the state illustrated in  FIGS. 1 and 7 , herein, the configuration in  FIG. 7  is illustrated rotated 180°. First,  FIG. 9A  illustrates the situation prior to press-fitting the fifth lens L 5  in the lens holder  51 . Herein, the projection part  51 F is not a shape which is curved toward the optical axis A side as illustrated in  FIGS. 4  and  7 , but is a shape protruding toward the image side. Therefore, the projection part  51 F does not become an obstacle when the fifth lens L 5  is accommodated in the lens installation hole  51 C from the image side (upper surface in the drawing). Further, the aforementioned IR cut coating layer (infrared cut filter)  52  is formed in the lens surface L 5 R 2  of the fifth lens L 5 . 
     Next, as illustrated in  FIG. 9B , the fifth lens L 5  is press-fit into the lens installation hole  51 C from the image side (lens arranging process). In this case, as stated above, the position of the fifth lens L 5  in the optical axis A direction is determined by the lens fixing surface MD, and the position in the direction perpendicular to the optical axis A is determined by the ribs ME. 
     In this case, the ribs ME are formed so that the outer peripheral surface of the fifth lens L 5  abuts the three ribs ME. Since the lens holder  51  is made of a resin material, there is the risk that, in this case, a small chip is specifically discharged toward the object side. As stated above, when the second adhesive agent groove (recessed part)  51 J is provided so as to overlap the ribs ME, the second adhesive agent groove (recessed part)  51 J can be provided in place of the lens fixing surface MD locking the fifth lens L 5  on the object side in the position where the ribs ME are present. Therefore, the chip is prevented from being disposed between the lens fixing surface  51 D and the fifth lens L 5 , and the chip falls from the lens holder  51 , or is accommodated in the second adhesive agent groove  51 J. Therefore, this reduces the influence of the chip on the positional relationship with the lens holder  51  of the fifth lens L 5 , and subsequently, the positional relationship between the fourth lens L 4  and the lens holder  51 . 
     Next, as illustrated in  FIG. 9C , a process (swaging process) is performed (swaging step) so that the projection part  51 F is bent toward the optical axis A side (inside). However, in this case, the projection part  51 F is not in contact with the fifth lens L 5 . Therefore, the positional relationship between the fifth lens L 5  and the lens holder  51  is not influenced by this swaging process. 
     In this state, the fifth lens L 5  is fixed in the lens installation hole  51 C by the adhesive agent (fixing process). In this case, by providing the adhesive agent prior to solidification in the first adhesive agent groove  51 H and the second adhesive agent groove  51 J in  FIGS. 4 to 6 , the adhesive agent is filled specifically in the gap between the outer peripheral part of the fifth lens L 5  on the left side in  FIG. 9C  and the inner surface of the lens installation hole  51 C. Then, by solidifying the adhesive agent, a solidified adhesive agent layer  200  is formed as illustrated in  FIG. 7 , and the fifth lens L 5  is fixed to the lens holder  51 . In this case, by processing the projection part  51 F as stated above, the fifth lens L 5  can be prevented from moving prior to the solidification of the adhesive agent. Furthermore, as illustrated in  FIG. 7 , since the adhesive agent also accumulates in the gap between the projection part  51 F and the fifth lens L 5  prior to solidification, the fifth lens L 5  is fixed to the lens holder  51  even in this portion, and the fifth lens L 5  can be joined more firmly to the lens holder  51 . 
     When performing the aforementioned operation, if there are locations where excess solidified adhesive agent abuts against the cemented lens L 60 , the fourth lens L 4  or the lens barrel  10  in the fifth lens body L 50 , the accuracy of the positioning of the fifth lens L 5  itself and the fourth lens L 4  deteriorates thereby. With respect thereto, by supplying the adhesive agent during the fixing process prior to solidification in the first adhesive agent groove  51 H and the second adhesive agent groove  51 J which are both locally dug down, the adhesive agent prior to solidification is prevented from existing in other locations. Further, the excess adhesive agent which leaked to the image side during the joining of the fifth lens L 5  and the lens holder  51  is accommodated in the first adhesive agent groove  51 H, and the excess adhesive agent which leaked to the object side is accommodated in the second adhesive agent groove  51 J. As stated above, the fifth lens body L 50  having the cross-sectional structure illustrated in  FIG. 7  can be obtained. 
     Then, in the state illustrated in  FIG. 7 , the thickness of the fifth lens L 5  in the optical axis A direction is measured. The measurement is performed by a method for measuring the shape of each type of contact or non-contact lens. Then, as stated above, it is recognized which protrusion part group among the protrusion part groups L 50 B 1  to L 50 B 7  is used so as to obtain the optimal lens interval in accordance with the measured thickness (selection process). 
     Then, all of the protrusion parts L 50 B belonging to the protrusion part group having a larger protrusion amount than the selected protrusion part group are subjected to a mechanical or heating and melting processing, and processing is performed so that the protrusion amount of these protrusion parts L 50 B becomes lower than the selected protrusion part group (protrusion part machine processing). As stated above, in this case, since it is sufficient if only the protrusion part L 50 B of the selected protrusion part groups can be abutted against the cemented lens upper surface L 6 A, and it is not necessary to precisely control the protrusion amount, a high processing accuracy is not necessary for this processing. 
     Further, as illustrated in  FIG. 8 , the aperture  20  is installed (aperture arranging process) in the object side of the fifth lens body L 50  formed as stated above by engaging the projection  51 A in the positioning hole  20 A. Then, the projection  51 A which protrudes from the positioning hole  20 A to the object side is subjected to heating and melting processing to fix the aperture  20  to the fifth lens body L 50  (lens holder  51 ). 
     Then, after the aforementioned processing of the protrusion part, the fifth lens body L 50  is arranged (lens body arranging process) on the lens barrel  10  after the cemented lens L 60  is arranged. Then, the constituent elements of the object side relative to the fourth lens L 4  in  FIG. 3  are installed on the lens barrel  10  in order. Therefore, the aforementioned lens unit  1  can be easily manufactured in a state in which the positional relationships between the fifth lens L 5 , the cemented lens L 60 , the fourth lens L 4 , the lens barrel  10  and the aperture  20  are precisely determined. 
     As stated above, the cemented lens L 60 , the fifth lens body L 50 , the fourth lens L 4 , the third lens L 3  and the second lens L 2  are press-fit into the lens barrel  10  (second accommodation part  10 B). In this regard,  FIG. 10  illustrates the configuration, corresponding to  FIG. 1 , when the lens barrel  10  has up to the first lens L 1  in  FIG. 3  set therein. Herein, specifically, the positional relationship of the protrusion part L 50 B and stepped parts L 4 B(L 50 A), L 3 B(L 4 A) and L 2 B(L 3 A) and the elastic member  40  positioned on the object side relative to the protrusion part L 50 B is emphasized in the drawing. 
     As stated above, since the fifth lens body L 50  is locked with the protrusion part L 50 B by the cemented lens L 60  which has already been arranged on the lens barrel  10 , a force that deforms the lens barrel  10  may be applied to the lens barrel  10  side depending on the balance with the force applied to the cemented lens L 60  side during the press-fitting of the fifth lens body L 50 . As stated above, the selected protrusion part L 50 B is symmetric around the optical axis A, thus, the aforementioned situation is suppressed. However, the force which acts on the lens barrel  10  side in this way is the same as when the constituent elements of the object side are installed relative to the fourth lens L 4  in  FIG. 3 . Alternatively, as a result, the distortion may occur in each plastic lens (fourth lens L 4  to second lens L 2 ) on the side where each plastic lens is to be installed. 
     Herein, in the case when the constituent elements of the object side are installed relative to the fourth lens L 4 , specifically, in  FIG. 10 , a force is applied to the stepped parts L 4 B (L 50 A), L 3 B (L 4 A), and L 2 B (L 3 A) and the elastic member  40  from the image side. A region (load region X) illustrated by the dashed line in  FIG. 10  illustrates the range to which the protrusion part L 50 B extends in the optical axis A direction. As illustrated herein, the aforementioned stepped parts L 4 B (L 50 A), L 3 B (L 4 A), L 2 B (L 3 A) and the elastic member  40  are either in the load region X, or overlap with the load region X. Therefore, when press-fitting the fourth lens L 4 , the third lens L 3  and the second lens L 2 , or when press-fitting the first lens L 1  via the elastic member  40 , the force applied to the image side is transmitted directly below the protrusion part L 50 B, and the distortion occurring in the lens barrel  10  and each lens is suppressed by this force in the same manner as when the fifth lens body L 50  is press-fitted. Therefore, the occurrence of distortion in the lens barrel  10  and the like is suppressed when manufacturing the lens unit  1 . Therefore, the lens unit  1  having good imaging characteristics can be easily manufactured. In this case, if the stepped part L 50 A (L 4 B) is formed as a circumference as illustrated in  FIG. 8 , and the plurality of protrusion parts L 50 B are arranged on the circumference as illustrated in  FIG. 4 , the aforementioned positional relationship is maintained regardless of which protrusion part group is selected. The same is true for the stepped parts L 3 B (L 4 A) and L 2 B (L 3 A). 
     Note that, in the aforementioned example, the fifth lens L 5  (image side adjacent lens) is a glass lens, the fifth lens L 5  and the cemented lens L 60  adjacent to the image side (one side) abut against the protrusion part L 50 B in the lens holder  51 , and the fifth lens and the fourth lens L 4  adjacent to L 5  on the object side (other side) engage with the stepped part L 4 B (L 50 B). However, when a precise adjustment of the interval between the glass lens and the lens of the object side is necessary, the sides on which the protrusion part and the stepped part (engagement structure) are respectively provided in the lens holder may be reversed from the aforementioned example to carry out the same method for manufacturing. That is, the sides on which the protrusion part or the stepped part (engagement structure) in the lens holder which holds the glass lens is formed with are appropriately designed in accordance with the configuration of the lens system. 
     First, in the configuration of  FIG. 1 , the second lens L 2 , the fifth lens L 5  (fifth lens body L 50 ) and the cemented lens L 60  are the contact lenses whose outer peripheral parts abut against the lens barrel  10 , and the third lens L 3  and the fourth lens L 4  are designated as non-contact lenses which only contact the lens barrel  10  via other lenses. However, which among the plurality of lenses is designated as the contact lens and the non-contact lens is appropriately set, and in any case, the aforementioned configuration can determine the positional relationship between the lenses adjacent to the glass lens (lens holder). 
     Primary Characteristics of the Present Embodiment 
     The brief summary of the characteristics of the present embodiment is as follows. 
     (1) A lens unit  1  comprises a first lens L 1  arranged furthest on an object (Ob) side along an optical axis A, a plurality of lenses (second lens L 2  to seventh lens L 7 ) arranged on an image (Im) side relative to the first lens L 1 , and a lens barrel  10  which accommodates the first lens L 1  and the plurality of lenses, wherein a glass lens (fifth lens L 5 ) which is one lens among the plurality of lenses and is made of glass is supported by a lens holder  51  on the outside viewed from the optical axis A and is accommodated in the lens barrel  10 . A plurality of protrusion parts L 50 B protruding locally toward one side are formed in the lens holder  51  on one side (image side) in the optical axis A direction divided into a plurality of protrusion part groups (L 50 B 1  to L 50 B 7 ) in accordance with the protrusion amount, and the positional relationship between the one side lens (cemented lens L 60 ) which is a lens adjacent to the glass lens (fifth lens L 5 ) on the one side in the optical axis A direction and the glass lens (fifth lens L 5 ) in the optical axis A direction is determined by locking the one side lens by the plurality of protrusion parts L 50 B belonging to one of the protrusion part groups. 
     In this configuration, the fifth lens body L 50  in which the fifth lens L 5  is integrated with the lens holder  51  is accommodated in the lens barrel  10 . The fifth lens body L 50  (lens holder  51 ) and the cemented lens L 60  abut against the plurality of protrusion parts L 50 B formed in the lens holder  51 , and the interval in the optical axis A direction between the fifth lens L 5  and the cemented lens L 60  is determined by the protrusion amount of this protrusion part L 50 B. Herein, since the protrusion amount of the protrusion part L 50 B can be precisely determined during the formation of the lens holder  51  in each protrusion part group (L 50 B 1  to L 50 B 7 ), the interval can be finely adjusted by selecting the protrusion part group. Even when there is variation in the thickness, etc., of the fifth lens L 5 , this variation can be compensated for, and the imaging characteristics of the lens unit  1  can be improved. 
     (2) The positional relationship of an other side lens (fourth lens L 4 ) which is the lens adjacent to the fifth lens L 5  on the other side (object side) in a lens holder  51  and the lens holder  51  is fixed in at least one of the optical axis A direction and the direction perpendicular to the optical axis A by engaging engagement structures (L 4 B, L 50 A) formed together. Herein, when viewed from the optical axis A direction, the protrusion part L 50 B and the engagement structures (L 4 B, L 50 A) have overlapping regions. 
     In this configuration, on the object side of the fifth lens L 5 , the positional relationship between the fifth lens L 5 , the fourth lens L 4  adjacent to the fifth lens L 5 , and the lens holder  51  is determined by the engagement structures (L 4 B, L 50 A). The positional relationship between the cemented lens L 60 , the fifth lens L 5  (the fifth lens body L 50 ), and the fourth lens L 4  is determined. At this time, when viewed from the optical axis A direction, the engagement structure (L 4 B, L 50 A) and the protrusion part L 50 B are connected. By overlapping, when the fourth lens L 4  is incorporated into the lens barrel  10  after the fifth lens body L 50 , the occurrence of distortion in the lens barrel  10  and the plastic lens (the fourth lens L 4 ) is suppressed. 
     (3) A cemented lens L 60  in which two adjacent lenses (sixth lens L 6  and seventh lens L 7 ) in the optical axis A direction are joined together constitutes the one side lens. 
     In this configuration, the one side lens is the cemented lens L 60 . Such a configuration increases the degrees of freedom of the configuration of a lens system. 
     (4) A thin-film infrared cut filter  52  which blocks light of a wavelength longer than the light which is the target for imaging is formed on a lens surface L 5 R 2  on the image side in the fifth lens L 5 . 
     By using the thin-film infrared cut filter  52 , specifically, near-infrared light that is not necessary as a target for imaging and does not yield good imaging characteristics is prevented from reaching the image surface (image pickup element  100 ), and it becomes unnecessary to provide the infrared cut filter as a separate component. While the interval between the fifth lens L 5  on which the infrared cut filter  52  has been formed and the image side lens L 60  may influence the occurrence of ghosting and flaring, such adverse effects are suppressed by finely adjusting the interval using the aforementioned protrusion part L 50 B. 
     (5) A method for manufacturing a lens unit  1  comprises, a lens arranging process which arranges a fifth lens L 5  in a lens installation hole  51 C which is a hole part dug down in the optical axis A direction in a region around an optical axis A in a lens holder  51 , a fixing process in which an adhesive agent is fixed between the arranged fifth lens L 5  and the inner surface of the lens installation hole  51 C, a selection process which measures the thickness along the optical axis A direction of the fifth lens L 5  after fixing and selects one protrusion part group in accordance with the thickness, a protrusion part machine process which processes a protrusion part L 50 B belonging to another protrusion part group having a larger protrusion amount than the selected protrusion part group so that the protrusion part L 50 B belonging to the selected protrusion part group can lock a cemented lens L 60 , and after the protrusion part machine process, a lens body arranging process which arranges, in the lens barrel  10 , the lens holder  51  in which the fifth lens L 5  is fixed. 
     In the method for manufacturing, the fifth lens body L 50  is manufactured by the lens arranging process and the fixing process. Then, the fifth lens body L 50  is arranged in the lens barrel  10  by the lens body arranging process after it was determined that the protrusion part (protrusion part group) which abuts against the cemented lens L 60  has an appropriate interval between the cemented lens L 60  and the fifth lens L 5  by the selection process and the protrusion part machine processing. In the protrusion part machine processing, processing is performed to the protrusion part L 50 B having a larger protrusion amount than the selected protrusion part groups, but a high accuracy is not necessary for this processing. Therefore, the fine adjustment of the lens interval is possible, and the manufacturing of the lens unit  1  is easy. 
     (6) A projection part  51 F protruding to the side opposite (image side) the side (object side) where the lens installation hole  51 C is dug down is formed along the optical axis A direction in the periphery of the lens installation hole  51 C in the lens holder  51  viewed from the optical axis A. A swaging step for bending the projection part  51 F to the optical axis A side in a non-contact state with the fifth lens L 5  is provided after the lens arranging process and prior to the fixing process. 
     By providing the projection part  51 F in the lens holder  51  in this way, the operation for accommodating the fifth lens L 5  within the lens installation hole  51 C is easy, and the fifth lens L 5  is fixed to the lens holder  51  after the fixing process, even in the location where there is a projection part  51 F. Further, after the swaging step, the fifth lens L 5  is prevented from moving from the lens holder  51  prior to solidification of the adhesive agent. 
     (7) An aperture arranging process which installs an aperture  20  on the surface (aperture placement surface  51 B) of the other side (object side) of the lens holder  51  is provided after the fixing process and prior to the lens body arranging process. 
     By this method for manufacturing, not only the fifth lens L 5 , but also the aperture  20  is fixed to the lens holder  51 . Therefore, the fifth lens L 5 , the cemented lens L 60 , the fourth lens L 4 , and the positional relationship between these and the aperture  20  are fixed by the lens holder  51 . 
     Note that, other than the aforementioned example, it is possible to construct a lens system including the aforementioned glass lenses, and one side thereof, an image side, or specifically, an aperture. In this case, the number of other lenses in the lens system is arbitrary. 
     The present invention is explained based on the embodiment and modifications; however, it is understood by a person skilled in the art that, as the embodiment is presented as an example, various modifications may be made with respect to the combination of components, or the like, and those modifications are also within the scope of the present invention.