Patent Publication Number: US-2022230661-A1

Title: Optical element holder, optical element holding device, and vapor deposition apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to an optical element holder, an optical element holding device, and a vapor deposition apparatus. 
     BACKGROUND ART 
     In order to prevent reflection, scratches, etc., on an optical element such as a lens, a technique of forming a thin film on the surface of the optical element is conducted. For example, a vacuum vapor deposition method and sputtering film formation are known as the thin-film forming technique. In the vacuum vapor deposition method, in a state in which a vapor deposition material is vaporized within a vacuumized container, and a lens is held by a lens holding device, the vaporized vapor deposition material is adhered onto the surface of a glass substrate, while an ion beam is emitted thereinto, as needed, thereby forming a thin film. 
     As a lens-dedicated vapor deposition apparatus used for such various film forming methods, for example, the below-mentioned Patent Document 1 describes an apparatus comprising a plurality of lens holder units mounted in a circumferential direction, wherein each of the lens holder units comprises a lens holder having an opening, and further mentions a lens holding method using three elastically holding mechanisms provided, respectively, at three equally spaced positions around an opening-defining portion of the lens holder. In the method mentioned in the Patent Document 1, the lens holder is fixed to a base plate which is mounted to a frame by means of a pin and a screw (see paragraphs [0045] and [0047] of the Patent Document 1). 
     CITATION LIST 
     [Patent Document]
     Patent Document 1: JP-B 3084020   

     SUMMARY OF DISCLOSURE 
     Technical Problem 
     If a pin and a screw are used for mounting or demounting of the lens holder, it would take a lot of time and effort. Further, in the method using a pin and a screw during mounting of the lens holder, a vapor deposition material adhered onto these members can be scraped to generate dust, and the dust is likely to adhere onto a lens. 
     The present disclosure has been made in view of the above problems, and an object thereof is to, in a device for holding an optical element such as a lens to be subjected to a film forming process, make it possible to prevent dust generation, and demount an optical element holder of the device without taking a lot of time and effort. 
     Solution to Technical Problem 
     The present disclosure provides an optical element holder (hereinafter also referred to as “holder”) for holding an optical element, comprising: a holder body; an optical element holding part provided on the holder body and configured to hold the optical element; and a holder mounting part provided on the holder body and formed of one of a magnet and a magnet-attractable material, wherein the holder is attachable to a pallet comprising a pallet-side mounting part formed of other of the magnet and the magnet-attractable material, by a magnetic force between the holder mounting part and the pallet-side mounting part. 
     The present disclosure provides a method of forming a desired film on a surface of an optical element by using an optical element holding device, wherein the optical element holding device comprises: an optical element holder comprising a holder body, an optical element holding part provided on the holder body and configured to hold the optical element, and a holder mounting part provided on the holder body and formed of one of a magnet and a magnet-attractable material; and a pallet comprising a pallet-side mounting part formed of other of the magnet and the magnet-attractable material, the method comprising: an optical element mounting step of mounting the optical element to the holder by the optical element holding part; a first holder mounting step of mounting the holder to the pallet by a magnetic force between the holder mounting part and the pallet-side mounting part; and a first film forming step of applying film forming process to the optical element. 
     The above film forming process may be a vapor deposition process. 
     Effect of Disclosure 
     In the device for holding an optical element such as a lens to be subjected to a film forming process, the present disclosure makes it possible to prevent dust generation, and demount the holder without taking a lot of time and effort. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram showing the configuration of a vapor deposition apparatus according to a first embodiment of the present disclosure. 
         FIG. 2  is a perspective view showing the configurations of a pallet and a holder in the vapor deposition apparatus illustrated in  FIG. 1 . 
         FIG. 3  is a perspective view showing a pallet body of the pallet illustrated in  FIG. 2 . 
         FIG. 4A  is a perspective view enlargedly showing the holder illustrated in FIG.  2 . 
         FIG. 4B  is a side view enlargedly showing the holder illustrated in  FIG. 2 . 
         FIG. 5  is a flowchart showing the flow of the operation of subjecting a lens to a film forming process by the vapor deposition apparatus according to the first embodiment. 
         FIG. 6A  is a perspective view enlargedly showing a state in which a lens is attached to the holder illustrated in  FIG. 2 . 
         FIG. 6B  is a side view enlargedly showing the state in which the lens is attached to the holder illustrated in  FIG. 2 . 
         FIG. 7  is a perspective view showing how the holder is attached to the pallet in the vapor deposition apparatus according to the first embodiment of the present disclosure. 
         FIG. 8  is a plan view showing how the holder is demounted from the pallet in the vapor deposition apparatus according to the first embodiment of the present disclosure. 
         FIG. 9A  is a perspective view enlargedly showing a holder to be used in a vapor deposition apparatus according to a second embodiment of the present disclosure. 
         FIG. 9B  is a side view enlargedly showing the holder to be used in the vapor deposition apparatus according to the second embodiment. 
         FIG. 10  is a flowchart showing the flow of the operation of subjecting a lens to a film forming process by the vapor deposition apparatus according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     With reference to the drawings, a lens holder, a lens holding device and a vapor deposition apparatus according to a first embodiment of the present disclosure will now be described in detail. 
     The vapor deposition apparatus according to the first embodiment is designed to vacuum vapor deposit a protective layer (coating), an anti-reflection layer (coating) or a water-repellent layer (coating) onto a spectacle lens as an optical element.  FIG. 1  is a schematic diagram showing the configuration of the vapor deposition apparatus according to the first embodiment of the present disclosure. As shown in  FIG. 1 , the vapor deposition apparatus  1  comprises a chamber  2 , a vacuum pump  4  connected to the chamber  2 , an ion gun  6 , a material vaporization device  8 , and a lens holding device  10 . It should be noted that, in  FIG. 1 , the pallets of the pallet holding device  10  are illustrated less than actual in terms of number, for the purpose of illustration. 
     The chamber  2  is composed of a gastightly-formed housing. Although not illustrated, the chamber  2  is provided with an opening and a door for installing the holder to the lens holding device  10 . 
     The vacuum pump  4  is connected to a side portion of the chamber  2 , and configured to evacuate gas from the inside to the outside of the chamber  2 , thereby reducing the air pressure in the chamber  2  so as to approach nearly a vacuum state. This makes it possible to lower the vaporization temperature of a vapor deposition material (a material to be vapor deposited), and prevent collision of the vapor deposition material with gas molecules in the chamber  2 , which collision hindering the vapor deposition material from adhering to a lens. 
     The material vaporization device  8  is configured to heat the vapor deposition material, e.g., SiO 2  or Ta 2 O 5 , to vaporize (gasify or sublimate) the vapor deposition material. The vapor deposition material vaporized by the material vaporization device  8  fills the inside of the chamber  2 . As a method to vaporize the vapor deposition material in the material vaporization device  8 , it is possible to use, e.g., a method which comprises irradiate the vapor deposition material with an ion beam from an ion gun, thereby heating the vapor deposition material, or a method which comprises heating the vapor deposition material by a heater or the like. 
     The ion gun  6  is configured to emit an ion beam toward the after-mentioned pallets  16  of the lens holding device  10  through the vaporized vapor deposition material from the material vaporization device  8 . This makes it possible to allow the vaporized vapor deposition material from the material vaporization device  8  to tightly adhere to the surface of a lens  50  held by the lens holding device  10  and form a thin film made of the vapor deposition material. 
     The lens holding device  10  comprises a turning device  12  installed to a ceiling wall of the chamber  2 , a plurality of pallets  16  each held in the chamber  2  by the turning device  12 , and an inverting device  14  installed to the side portion of the chamber  2 . 
       FIG. 2  is a perspective view showing the configurations of the pallet and the holder in the vapor deposition apparatus illustrated in  FIG. 1 . As shown in  FIG. 2 , the pallet  16  comprises a pallet body  20  formed in an approximately isosceles triangular shape, a first shaft member  22  mounted to a vertex angle-side end of the pallet body  20 , and a second shaft member  24  mounted to the middle of the base of the pallet body  20 . A holder  30  for holding the lens  50  can be mounted to and demounted from the pallet  16 . 
       FIG. 3  is a perspective view showing the pallet body of the pallet illustrated in  FIG. 2 . As shown in  FIG. 3 , the pallet body  20  is a plate-like member formed in an approximately isosceles triangular shape, and made of, e.g., a non-magnetic material such as SUS 303. A first mounting part  20 A is formed at the vertex angle-side end of the pallet body  20 , and a second mounting part  20 B is formed in the middle of the base of the pallet body  20 . Each of the first mounting part  20 A and the second mounting part  20 B is a portion for allowing a respective one of the first shaft member  22  and the second shaft member  24  to be fixed thereto, and formed with an opening for allowing a bolt to penetrate therethrough. 
     Further, the pallet body  20  is formed with a first opening  20 C and a second opening  20 D each having a round shape. The first and second openings  20 C,  20 D may have the same diameter, or may have different diameters. Respective centers of the first and second openings  20 C,  20 D are located on a bisector of the vertex angle. 
     A peripheral edge region defining each of the first and second openings  20 C,  20 D of the pallet body  20  is formed with a pair of recesses  20 F at respective positions opposed to each other across the center of the opening, and a magnet  26  serving as a pallet-side mounting part is fixed to each of the recesses  20 F via bolted connection, adhesive bonding or the like. Each of the recesses  20 F has a rectangular parallelepiped shape, and the magnet  26  has a rectangular parallelepiped shape corresponding to the shape of the recess  20 F. As the magnet  26 , it is desirable to use a magnet having heat resistance to 100° C. or more, and it is possible to use, e.g., a neodymium magnet. The surface of the magnet  26  is flush with the surface of the pallet body  20 . 
     The first shaft member  22  is bolted to the first mounting part  20 A of the pallet body  20 . The first shaft member  22  comprises a shaft part  22 A. The first shaft member  22  is mounted such that a central axis of the shaft part  22 A is located on an extension of the bisector of the vertex angle passing through the through-thickness center of the pallet body  20  (the bisector will hereinafter be referred to as “axis”). 
     The second shaft member  24  is bolted to the second mounting part  20 B of the pallet body  20 . The second shaft member  24  comprises a gear part  24 A whose outer periphery is formed with teeth. The second shaft member  24  is mounted such that a central axis of the gear part  24 A is located on an extension of the axis of the pallet body  20 . 
       FIG. 4A  and  FIG. 4B  are, respectively, a perspective view and a side view each enlargedly showing the holder illustrated in  FIG. 2 . As shown in  FIGS. 4A and 4B , the holder  30  comprises a circular annular-shaped frame  32 , a pair of holder mounting parts  34 ,  35  each projectingly provided on a radially outer surface of the frame  32 , and a lens holding mechanism  42 . The holder  30  is formed of a magnetic material or a magnet-attractable material (material attractable by a magnet), such as SUS 430. It should be noted here that, although the holder  30  in this embodiment is entirely formed of a magnetic material, it is only necessary to form at least the holder mounting parts  34 ,  35  using a magnetic material. 
     The frame  32  is formed in a circular annular shape whose outer diameter is slightly less than the diameter of each of the first and second openings  20 C,  20 D of the pallet body  20 . In the case where the first and second openings  20 C,  20 D have different diameters, two types of holders each compatible with a respective one of the openings may be used. 
     The pair of holder mounting parts  34 ,  35  are provided on an outer peripheral surface of the frame  32  at respective positions opposed to each other across the center of the frame  32 . Each of the holder mounting parts  34 ,  35  has a flat portion  34 A,  35 A extending flatly in a radial direction of the frame  32 , and a manipulatable portion  34 B,  35 B standingly provided on a radially outward area of the flat portion  34 A,  35 A. The flat portion  34 A,  35 A is formed such that an upper surface (upper surface in  FIG. 4B ) thereof is flush with an upper surface of the frame  32 . The manipulatable portion  34 B,  35 B is formed by bending a radially outward end of the flat portion  34 A,  35 A vertically upwardly. Thus, in a state in which the holder  30  is mounted to the pallet  16 , the manipulatable portion  34 B,  35 B takes a posture where it extends in a direction intersecting a flat surface of the pallet body  20 . 
     The lens holding mechanism  42  comprises a first holding member  36 , a second holding member  38 , and a third holding member  40 . 
     The first holding member  36  and the second holding member  38  are provided on an inner peripheral surface of the frame  32  at respective positions corresponding to circumferential both sides of one 35 of the holder mounting parts. Each of the first and second holding members  36 ,  38  comprises an attachment part  36 A,  38 A formed in a curved shape along the frame  32 , and an engagement part  36 B,  38 B provided on a circumferential end of the attachment part  36 A,  38 A to project radially inwardly. Each of the first and second holding members  36 ,  38  has a thickness greater than that of the frame  32 , wherein each of the first and second holding members  36 ,  38  is attached to the frame  32  such that an upper surface thereof is flush with the upper surface of the frame  32 . A radially-inward end of the engagement part  36 B,  38 B is formed as an arc-shaped recess whose through-thickness center is concaved radially outwardly. The recess of the engagement part  36 B,  38 B is formed symmetrically with respect to a symmetrical axis passing through the center in thickness direction. Each of the first and second holding members  36 ,  38  is attached to the frame  32  such that, when the holder  30  is mounted to each of the first opening  20 C and the second opening  20 D of the pallet body  20 , the symmetrical axis of the engagement part  36 B,  38 B and the axis of the pallet body  20  are located on the same plane. 
     The third holding member  40  comprises a resilient part  40 A whose one end is fixed to the inner peripheral surface of the frame  32 , and an engagement part  40 B provided at the other end of the resilient part  40 A to project radially inwardly. The resilient part  40 A has a thickness greater than that of the frame  32 , and the engagement part  40 B has a thickness which is greater than that of the frame  32  and equal to that of each of the engagement parts  36 B,  38 B of the first and second holding members  36 ,  38 . An upper surface of the resilient part  40 A and an upper surface of the engagement part  40 B are flush with the upper surface of the frame  32 . The resilient part  40 A is formed in an arc shape whose diameter is less than that of the frame  32 . A radially-inward end of the engagement part  40 B is formed as an arc-shaped recess whose center in thickness direction is concaved radially outwardly. The recess of the engagement part  40 B is formed symmetrically with respect to a symmetrical axis passing through the center in the thickness direction. The third holding member  40  is fixed to the frame  32  such that the engagement member  40 B is located radially inward of the holder mounting part  35  opposed thereto. The third holding member  40  is attached to the frame  32  such that, when the holder  30  is mounted to each of the first opening  20 C and the second opening  20 D of the pallet body  20 , the symmetrical axis of the engagement part  40 B and the axis of the pallet body  20  are located on the same plane. Since the third holding member  40  has an arc shape, the engagement part  40 B can be displaced radially outwardly by bending the resilient part  40 A. 
     In this embodiment, the lens holding mechanism  42  is configured to hold a lens at three points by the first holding member  36 , the second holding member  38  and the third holding member  40 . Alternatively, the lens holding mechanism may be configured to hold a lens at four or more points. 
     As shown in  FIG. 2 , the frame  32  is placed inside each of the first opening  20 C and the second opening  20 D, while the pair of holder mounting parts  34 ,  35  are adjusted to come into contact with the magnets  26  as the pallet-side mounting parts, respectively. Thus, the holder mounting parts  34 ,  35  are attracted and held by the magnets  26 , so that the holder  30  can be demountably mounted to each of the first opening  20 C and the second opening  20 D. In this state, the through-thickness centers (symmetrical axes) of the engagement parts  36 B,  38 B,  40 B are located at the same height position as that of the axis of the pallet body  20 . 
     Returning to  FIG. 1 , the turning device  12  comprises a coupling part  12 A to be turned by a motor. The plurality of pallets  16  are arranged circumferentially side-by-side such that oblique sides of any adjacent two of the pallet bodies  20  extend parallel to each other, so as to form an umbrella shape (regular polygonal pyramid shape). In each of the pallets  16 , the shaft part  22 A of the first shaft member  22  is rotatably held by the coupling part  12 A. The turning device  12  is configured to turn the coupling part  12 A, thereby turning the plurality of pallets  16  arranged circumferentially side-by-side, about a central axis thereof. 
     The inverting device  14  is a device for inverting each of the pallets  16 . For example, the inverting device  14  may comprise a gear. In this case, the pallet  16  can be inverted by rotating this gear while meshing the gear with the gear part  24 A of the second shaft member  24  of the pallet  16 . The plurality of pallets  16  can be sequentially inverted by synchronizing the turning device  12  with the inverting device  14 . 
     Next, a method of subjecting a lens to a film forming process by the vapor deposition apparatus according to the first embodiment will be described.  FIG. 5  is a flowchart showing the flow of the operation of subjecting a lens to a film forming process by the vapor deposition apparatus according to the first embodiment. 
     In the operation of subjecting a lens to a film forming process, first of all, a lens (optical element) whose front and back surfaces are formed, respectively, in given shapes is mounted to the holder  30  (S 1 : optical element mounting step).  FIG. 6A  and  FIG. 6B  are, respectively, a perspective view and a side view each enlargedly showing a state in which the lens is mounted to the holder illustrated in  FIG. 2 . When mounting the lens  50  to the holder  30 , the engagement part  40 B of the third holding member  40  is first biased radially outwardly to bend the resilient part  40 A. In this state, a side surface of the lens  50  is brought into contact with the recesses of the engagement parts  36 B,  38 B of the first and second holding members  36 ,  38 . Then, the pressing or biasing force applied to the third holding member  40  is released. Thus, the engagement part  40 B of the third holding member  40  is brought into contact with the side surface of the lens  50 , so that the lens  50  is supported by the engagement parts  36 B,  38 B,  40 B of the first holding member  36 , the second holding member  38  and the third holding member  40 . On this occasion, the lens  50  is set in a posture where the through-thickness center thereof is located at centers in thickness direction of the engagement parts  36 B,  38 B,  40 B. 
     Subsequently, the holder  30  is mounted to the pallet  16  (S 2 : (first) holder mounting step).  FIG. 7  is a perspective view showing how the holder is mounted to the pallet in the vapor deposition apparatus according to the first embodiment of the present disclosure. As shown in  FIG. 7 , for the operation of mounting the holder  30  to the pallet  16 , it is only necessary to place the frame  32  inside each of the first opening  20 C and the second opening  20 D, while adjusting the pair of holder mounting parts  34 ,  35  to come into contact with the magnets  26 , respectively. Thus, the holder mounting parts  34 ,  35  are attracted and held by the magnets  26 , so that the holder  30  is mounted to each of the first opening  20 C and the second opening  20 D. In the state in which the holder  30  is mounted to the pallet  16  as just described, the axis of the shaft part  22 A of the pallet  16  is located on a through-thickness central plane of the lens  50 . The operation of mounting the holder  30  to the pallet  16  may be performed from above the pallet  16 , or may be performed from below the pallet  16 . 
     After mounting the holder  30  to each of the plurality of pallets  16 , a film is formed on a first one of the front and back surfaces of each of the lenses  50  by vacuum vapor deposition (S 3 : first film forming step). Specifically, the vapor deposition material is heated and vaporized by the material vaporization device, while the pallets  16  are turned circumferentially at a constant velocity by the turning device  12 . Then, an ion beam is emitted from the ion gun  6  toward the pallets  16  through the vaporized vapor deposition material. Thus, the vapor deposition material is adhered to the first surface of each of the lenses  50  held by the holders  30  mounted to each of the pallets  16 , so that a thin film is formed on the first surface of the lens  50 . 
     Subsequently, the pallets  16  are sequentially rotated 180 degrees (inverted) about the axis thereof by the inverting device  14  (S 4 : pallet inverting step). 
     After inverting all the pallets  16 , a film is formed on the other, second, surface of each of the lenses  50  by vacuum vapor deposition (S 5 : second film forming step). The film forming process for the second surface of the lens  50  may be performed in a similar manner to the film forming process (S 3 ) for the first surface of the lens  50 . 
     After completion of the film forming process for the second surface of each of the lenses  50 , the turning device  12  is stopped, and the holders  30  are demounted from the pallets  16  (S 6 ).  FIG. 8  is a plan view showing how the holder is demounted from the pallet in the vapor deposition apparatus according to the first embodiment of the present disclosure. As shown in  FIG. 8 , in the operation of detaching the holder  30  from the pallet  16 , the manipulatable portions  34 B,  35 B of the holder mounting parts  34 ,  35  are pushed in a circumferential direction of the frame  32  to turn the holder  30 . Thus, the pair of holder mounting parts  34 ,  35  of the holder  30  is separated from the pair of magnets  26 , and a magnetic attractive holding force therebetween weakens, so that the holder  30  can be demounted from the pallet  16 . That is, the demounting operation can be easily performed by turning the holder  30  to cause a relative displacement between the two magnetic materials so as to release the magnetic attractive holding force therebetween. Before the operation of detaching the holder  30  from the pallet  16 , the pallet  16  may be inverted by the inverting device  14 . This makes it possible to perform the demounting operation from the same side as that on which the operation of mounting the holder  30  to the pallet  16  is performed. 
     Since the magnetic attractive force is sufficient against the gravity during the film forming step, dropping of the lens holder can be suppressed. On the other hand, the detaching operation can be performed by a relatively small force, because the holder  30  is turned in a direction perpendicular to the vector of the magnetic attractive holding force. 
     Subsequently, the lens  50  is demounted from each of the holders  30  (S 7 ). In the operation of demounting the lens  50  from the holder  30 , it is only necessary to bias the engagement part  40 B of the third holding member  40  radially outwardly. Thus, the lens  50  is separated from the engagement parts  36 B,  38 B,  40 B, so that the lens  50  can be demounted. 
     The following advantageous effects are achieved by the first embodiment. 
     In the first embodiment, the holder  30  is mounted to the pallet  16  by attracting and holding the holder mounting parts  34 ,  35  of the holder  30  by means of magnetism of the magnets  26  of the pallet  16 . This makes it possible to easily and reliably mount the holder  30  to the pallet  16  just by placing the holder  30  in each of the first and second openings  20 C,  20 D of the pallet  16  in a given posture. Further, in the first embodiment, the holder  30  is mounted to the pallet  16  by means of magnetism as just described. Thus, this method is free from friction caused by screwing or deformation of a resilient member, so that it is possible to prevent dust generation due to foreign substances such as an adhered vapor deposition material. 
     In the first embodiment, the holder  30  comprises the manipulatable portions  34 B,  35 B each extending in a direction intersecting the surface of the pallet  16  in a state in which the holder  30  is mounted to the pallet  16 . Thus, the holder mounting parts  34 ,  35  can be separated from the magnets  26  by turning the manipulatable portions  34 B,  35 B, so that it is possible to demount the holder  30  easily in a short time without the need for large force. 
     In the first embodiment, the axis of the pallet  16  passes through the central plane in thickness direction of the lens  50  held by the holder  30 . Thus, supposing that the pallet  16  is inverted, a distance between the first surface of the lens  50  and the material vaporization device  8  or the ion gun  6  in the first vapor deposition step can be equalized to a distance between the second surface of the lens  50  and the material vaporization device  8  or the ion gun  6  in the second vapor deposition step, so that it is possible to subject the front and back surfaces of the lens  50  to a uniform film forming process. 
     Second Embodiment 
     In the first embodiment, the vapor deposition apparatus comprises the inverting device  14 , and is operable, after completion of the film forming process for one surface of a lens, to invert the pallet by the inverting device  14 , and subject the other surface of the lens to a film forming process. However, the present disclosure is not limited thereto. For example, the present disclosure is applicable even to a case where the vapor deposition apparatus is not equipped with the inverting device, i.e., is incapable of inverting the pallet. The following description will be made about a second embodiment in which the vapor deposition apparatus is not equipped with the inverting device, i.e., is incapable of inverting the pallet. It should be noted here that a similar element or component to that in the first embodiment is assigned with the same reference sign, and its detailed description will be omitted. 
     A vapor deposition apparatus according to the second embodiment is different from the vapor deposition apparatus  1  according the first embodiment, in that it is not equipped with the inverting device  14 . In connection with this, the second shaft member  24  of the pallet  16  becomes unnecessary, and the first shaft member  22  of the pallet  16  does not need to be rotatable with respect to the coupling part  12 A of the turning device  12 . 
     Further, the vapor deposition apparatus according to the second embodiment is different from the vapor deposition apparatus  1  according the first embodiment, in terms of the configuration of the holder.  FIG. 9A  and  FIG. 9B  are, respectively, a perspective view and a side view each enlargedly showing a holder to be used in the vapor deposition apparatus according to the second embodiment. As shown in  FIGS. 9A and 9B , in the holder in the second embodiment is different from the first embodiment in that each of the holder mounting parts does not have the manipulatable portion, i.e., is composed only of the flat portion. 
     Specifically, the holder  130  in the second embodiment comprises a circular annular-shaped frame  32 , a pair of holder mounting parts  134 ,  135  each projectingly provided on a radially outer surface of the frame  32 , and a lens holding mechanism  42 . The configurations of the lens holding mechanism  42  and the frame  32  are similar to those in the first embodiment. 
     The holder  130  is formed of a magnetic material or a magnet-attractable material (material attractable by a magnet), such as SUS 430. It should be noted here that, although the holder  130  in the second embodiment is entirely formed of a magnetic material, it is only necessary to form at least the holder mounting parts  134 ,  135  using a magnetic material. 
     The pair of holder mounting parts  134 ,  135  are provided on an outer peripheral surface of the frame  32  at respective positions opposed to each other across the center of the frame  32 . Each of the holder mounting parts  134 ,  135  consists of a flat portion  134 A,  135 A having a surface which extends flatly in a radial direction of the frame  32 . The flat portion  134 A,  135 A is formed such that an upper surface (upper surface in  FIG. 9B ) thereof is flush with an upper surface of the frame  32 . 
     Preferably, a distance between a lower surface (lower surface in  FIG. 9A ) of the flat portion  134 A,  135 A and a center in thickness direction of each engagement part  36 B,  38 B,  40 B is one half of the thickness of a pallet body  20  of each of a plurality of pallets  16 . Thus, irrespective of whether the holder  130  is mounted from above an upper surface of the pallet body  20  or mounted from below a lower surface of the pallet body  20 , a through-thickness center of a lens  50  will be located at the height position of a through-thickness center of the pallet body  20 . 
     Next, a method of subjecting a lens to a film forming process by using the vapor deposition apparatus according to the second embodiment will be described.  FIG. 10  is a flowchart showing the flow of the operation of subjecting a lens to a film forming process by the vapor deposition apparatus according to the second embodiment. 
     In the operation of subjecting a lens to a film forming process, first of all, a lens (optical element) whose front and back surfaces are formed, respectively, in given shapes is mounted to the holder  130  (S 11 : optical element mounting step). The operation of mounting the lens to the holder  130  may be performed in a similar manner to that in the first embodiment. 
     Subsequently, the holder  130  with the lens  50  is mounted to each of the pallets  16  (S 12 : first holder mounting step). For the operation of mounting the holder  130  to the pallet  16 , it is only necessary to place the frame  32  inside each of a first opening  20 C and a second opening  20 D, while adjusting the pair of holder mounting parts  134 ,  135  to come into contact with a pair of magnets  26 , respectively. Thus, the holder mounting parts  134 ,  135  are attracted and held by the magnets  26 , so that the holder  130  is mounted to each of the first opening  20 C and the second opening  20 D. In the state in which the holder  130  is mounted to the pallet  16  as just described, the axis of a shaft part  22 A of the pallet  16  is located on a central plane in thickness direction of the lens  50 . The operation of mounting the holder  130  to the pallet  16  may be performed from above the pallet  16 , or may be performed from below the pallet  16 . 
     After mounting the holder  130  to each of the plurality of pallets  16 , a film is formed on a first one of the front and back surfaces of each of the lenses  50  by vacuum vapor deposition (S 13 : first film forming step). Specifically, a vapor deposition material is heated and vaporized by a material vaporization device  8 , while the pallets  16  are turned circumferentially at a constant velocity by a turning device  12 . Then, an ion beam is emitted from an ion gun  6  toward the pallets  16  through the vaporized vapor deposition material. Thus, the vapor deposition material is adhered to the first surface of each of the lenses  50  held by the holders  130  mounted to each of the pallets  16 , so that a thin film is formed on the first surface of the lens  50 . 
     After completion of the film forming process for the first surface of each of the lenses  50 , the turning device  12  is stopped, and the holders  130  are demounted from the pallets  16  (S 14 : holder demounting step). In the operation of demounting the holder  130  from the pallet  16 , it is only necessary to turn the holder  130  with respect to the pallet  16 , as with the first embodiment. 
     Subsequently, after inverting the holder  130 , the inverted holder is mounted to the pallet  16  (S 15 : second holder mounting step). Thus, the holder  130  is mounted in a state in which the other, second, surface of the lens  50  faces downwardly. 
     After demounting and inverting all the holders  130 , a film is formed on the second surface of each of the lens  50  by vacuum vapor deposition (S 16 : second film forming step). The film forming process for the second surface of the lens  50  may be performed in a similar manner to the film forming process for the first surface of the lens (S 13 ). 
     After completion of the film forming process for the second surface of each of the lenses  50 , the turning device  12  is stopped, and the holders  130  are demounted from the pallets  16  (S 17 ). In the operation of demounting the holder  130  from the pallet  16 , it is only necessary to turn the holder  130  with respect to the pallet  16 , as with the first embodiment, 
     Subsequently, the lens  50  is demounted from each of the holders  130  (S 18 ). The demounting of the lens  50  may be performed in a similar manner to that in the first embodiment. 
     The following advantageous effects are achieved by the second embodiment. 
     In the second embodiment, the holder  130  is mounted to the pallet  16  by attracting and holding the holder mounting parts  134 ,  135  of the holder  130  by means of magnetism of the magnets  26  of the pallet  16 , as with the first embodiment, so that it is possible to easily mount the holder  130  to the pallet  16 , and prevent dust generation due to the vapor deposition material. 
     In the second embodiment, each of the holder mounting parts  134 ,  135  is formed as the flat portion  134 A,  135 A having a flat surface, so that it is possible to, after subjecting one surface of a lens  50  to a film forming process, invert the demounted holder  130 , and re-mount the inverted holder  130  so as to subject the other surface of the lens to a film forming process. This makes it possible to easily perform the operation of inverting the holder  130  even when using a vapor deposition apparatus equipped with no existing inverting device. 
     In the above embodiments, a magnet is used as the pallet-side mounting part, and the holder mounting part is formed of a magnetic material or a magnet-attractable material. Alternatively, the pallet-side mounting part may be made of a magnetic material, and the holder mounting part is composed of a magnet. In other words, the holder mounting part may be formed of one of a magnet and a magnetic material, and the pallet-side mounting part corresponding to the holder mounting part may be formed of a remaining one of the magnet and the magnetic material. 
     Although the above embodiments have been described based on an example where the holder and the lens holding device are used in vacuum vapor deposition, a vapor deposition method is not limited to vacuum vapor deposition. Further, a film forming method is not limited to vapor deposition, but the holder and the lens holding device may be applied to sputtering film formation. Further, a target of film formation is not limited to a lens, but the present disclosure may be applied to a wide variety of optical elements. 
     As used in this specification, the terms “one of a magnet and a magnet-attractable material” and “a remaining one of the magnet and the magnet-attractable material” mean that each of the one and the remaining one comprises a magnetic material, and includes a case where each of the one and the remaining one is a magnet 
     The present invention can be usefully applied to an optical element such as an optical lens. In particular, it is advantageous to an optical element made of plastic, such as a spectacle lens. For example, a film forming process using the present invention may be applied to a semifinished product after being formed preferably using a resin such as polycarbonate, thiourethane or methacrylate and before being formed in a frame shape. 
     In manufacturing of a spectacle lens, the curve of each of a convex surface and a concave surface of the lens varies a good deal according to a prescribed lens power, and the thickness and weight of the lens also vary according to selection of a material depending on refractive index. Although there are different types of lenses in terms of diameter or shape, the present invention can be suitably applied to any of them. 
     LIST OF REFERENCE SIGNS 
     
         
           1 : vapor deposition apparatus 
           2 : chamber 
           4 : vacuum pump 
           6 : ion gun 
           8 : material vaporization device 
           10 : lens holding device 
           12 : turning device 
           12 A: coupling part 
           14 : inverting device 
           16 : pallet 
           20 : pallet body 
           20 A: first mounting part 
           20 B: second mounting part 
           20 C: first opening 
           20 D: second opening 
           20 F: recess 
           22 : first shaft member 
           22 A: shaft part 
           24 : second shaft member 
           24 A: gear part 
           26 : magnet 
           30 : holder 
           32 : frame 
           34 : holder mounting part 
           34 A: flat portion 
           34 B: manipulatable portion 
           35 : holder mounting part 
           35 A: flat portion 
           35 B: manipulatable portion 
           36 : first holding member 
           36 A: attachment part 
           36 B: engagement part 
           38 : second holding member 
           38 A: attachment part 
           38 B: engagement part 
           40 : third holding member 
           40 A: resilient part 
           40 B: engagement part 
           42 : lens holding mechanism 
           50 : lens 
           130 : holder 
           134 : holder mounting part 
           134 A: flat portion 
           135 : holder mounting part 
           135 A: flat portion