Abstract:
An optical element mounting and demounting device for bringing an optical element ( 26 ) into an optical path of an optical lens system and removing it from the optical path includes a holder frame ( 28 ) for holding the optical element ( 26 ) that is supported for pivotal movement on a stationary shaft ( 30 ) so as to move the optical element ( 26 ) between a rest position and a working position, an urging member ( 40, 50, 60 ) for applying urging force against the holder frame during pivotal movement of the holder frame ( 28 ) between the rest position and the working position, the urging member being secured to a stationary member so as to invert the direction of urging force against the holder frame between the rest position and the working position, and a manually operable member elements for causing pivotal movement of the holder frame between the rest position and the working position.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a device for mounting and demounting an optical element, and more specifically, for inserting an optical element into an optical lens system, such as an image forming lens system of, in particular, a broadcasting television camera and removing the same from the optical lens system. 
   2. Description of Related Art 
   It is required so often for broadcasting television cameras such as electronic news gathering cameras (ENG cameras) to provide magnified images. An image forming lens system, namely a taking lens system, for such an ENG camera is provided with an optical element switch device for inserting an optical element such as a converter or extender lens into an optical path of the taking lens system for altering the focal length of the taking lens system and removing the optical element from the taking lens system. One of extender switching devices that is disclosed in, for example, Japanese Unexamined Patent Publication No. 9-171135 includes first and second extenders pivotally mounted on a common pivot shaft so as to be moves between a working position and rest positions independently through operation of a manual operation lever. The extender switching device is provided with urging means such as a tension spring for retaining an extender lens in a stationary state in a predetermined position and a damper mechanism for preventing generation of hitting sound and/or vibrations when the extender lens is moved from the rest position to the working position or vice versa. 
   However, the extender switching device disclosed in the publication needs a number of constituent parts for the retainer spring and the damper mechanism and increases the number of man-hour for fabrication in consequence. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a device for moving an optical element between a working position in an optical axis of a lens system and a rest position out of the optical axis of the lens system that is simple in structure and is smoothly operative. 
   The foregoing object is accomplished by an optical element switch device for bringing an optical element such as, for example, am extender lens, a ratio converter lens, or an optical filter for transmitting light according to wavelengths, into an optical path of an image forming lens system and removing it from the optical path that comprises a holder frame for fixedly holding the optical element which is movable between a rest position in which the optical element is put out of the optical path of the image forming lens system and a working position in which the optical element is put in the optical path of the image forming lens system, operating means for causing movement of the holder frame between the rest position and the working position, and urging means in the form of a leaf spring fixedly supported on a stationary part such as a housing of the device for applying urging force against the holder frame during movement of the holder frame between the rest position and the working position and inverting the urging force in direction with respect to the holder frame between the rest position and the working position. 
   According to the optical element switch device of the present invention, the urging means keeps itself applying urging force against the holder frame in a direction of movement and reverses directions of urging force with respect to the holder frame between the rest position and the working position. In consequence, the holder frame, and hence the optical element held by the holder frame, is firmly retained in an intended position, either the rest position or the working position, and prevented from generating hitting noises when reaching the rest position or the working position and causing cranky movement between the rest position and the working position. The directional inversion of urging force is distinctly recognizable, so that the optical element switch device is improved in operationality. Furthermore, the optical element switch device of the present invention eliminates installation of a tension spring and a damper mechanism and, in consequence, is simple in structure. 
   The urging means may comprise a leaf spring that is secured at one or both of opposite ends thereof to the stationary part, for example the housing, of the optical element switch device so as to be elastically bendable or deformable during movement of the holder frame between the rest position and the working position. In more detail, the leaf spring secured at one end thereof has a generally V-shaped form so that the leaf spring allows another end section to be bent by a projection or a rim of the holder frame. The leaf spring secured at both one ends thereof comprises bent and straight sections so that the leaf spring allows itself to be deformed by a rim of the holder frame. 
   The optical element switch device is especially suitably embodied as an extender switch device for inserting an extender lens into an optical lens system of, for example, a broadcasting television camera such as an electronic news gathering camera and removing the same from the optical lens system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and features of the present invention will be clearly understood from the following detailed description when reading with reference to the accompanying drawings, wherein the same reference signs have been used to denote same or similar parts throughout the drawings, and in which: 
       FIG. 1  is an external plane view of a zoom lens for an electronic news gathering camera which is equipped with an extender switch device according to an embodiment of the present invention; 
       FIG. 2  is a rear view of the extender switch device; 
       FIG. 3  is a rear view of an interior structure of the extender switch device which is in a rest position; 
       FIG. 4  is a rear view of an interior structure of the extender switch device which is in a working position; 
       FIG. 5  is a rear view of an interior structure of an extender switch device according to another embodiment of the present invention which is in a rest position; 
       FIG. 6  is a rear view of an interior structure of the extender switch device which is in a working position; 
       FIG. 7  is a rear view of an interior structure of an extender switch device according to a further embodiment of the present invention which is in a rest position; and 
       FIG. 8  is a rear view of an interior structure of the extender switch device which is in a working position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the accompanying drawings in detail, and in particular, to  FIGS. 1 and 2  showing a zoom lens  10  that is capable of being detachably mounted to portable TV cameras such as electronic news gathering (ENG) cameras (not shown), the zoom lens  10  comprises a zoom lens part  12  and an extender part  20  having a switch lever  22  for manually switching an extender lens between working and rest positions. Zoom lenses generally comprise at least a focusing lens system and a zooming lens system arranged in order from the object side to the image side. Such a zoom lens is known in various types and takes any type well known in the art. Details of the zoom lens will not be set out in detail since their construction and operation can be easily arrived at by those skilled in the art. 
   As shown in  FIG. 2 , the extender part  20  includes a housing  24  in which an extender lens  26  and a switch lever  22  are incorporated. The switch lever  22  is manually operated to switch the extender lens  26  between a rest position (see  FIG. 3 ) in which an extender lens  26  is out of the zoom lens system and a working position (see  FIG. 4 ) in which the extender lens  26  is put in the zoom lens system through a switching mechanism which will be described later. 
     FIGS. 3 and 4  show details of the switching mechanism for switching the extender lens  26  between the rest position and the working position, respectively. The extender lens  26 , which has a magnifying power of, for example X 2 and may consists of single or a plurality of lenses, is fixedly held in a holder frame  28  having a hub ring  28 A through which the holder frame  20  is pivotally mounted on a pivot shaft  30  fixed to the housing  24 . The holder frame  28  has circumferential locating faces  28 B and  28 C disposed at substantially diametrically opposite positions thereof. The locating face  28 B is brought into abutment with a stopper stud  32  fitted in a threaded hole  24 A formed in the housing  24  so as to retain the holder frame  28  in the rest position shown in  FIG. 3  when the extender lens  26  is moved out of the zoom lens system. The locating face  28 C is brought into abutment with a stopper stud  34  fitted in a threaded hole  24 B formed in the housing  24  so as to position the holder frame  28  in the working position shown in  FIG. 4  when the extender lens  26  is moved into the zoom lens system. These stopper studs  28 B and  28 C can be adjusted in threaded position for fine adjustment of the rest position and the working position, respectively. The switch lever  22  has a shaft  31  having an external gear  38  integrally formed therewith and pivotally mounted to the housing  24 . On the other hand, the hub ring  28 A of the holder frame  28  has an external gear  36  and a projection  44  integrally formed therewith. The switch lever  22  and the holder frame  28  are operationally coupled to each other through engagement between the external gears  36  and  38 . 
   The switching mechanism includes urging means comprising, for example in this embodiment, a generally V-shaped leaf spring  40  for preventing the holder frame  28  from generating hitting noises when the holder frame  28  hits the stopper studs  28 B and  34  and causing cranky movement between the rest position and the working position. The V-shaped leaf spring  40  is made from a steel strip having a predetermined width and comprises a pressure arm section  40 A, a base section  40 C and a bent section  40 B by which the pressure arm section  40 A and the base section  40 C are connected as an integral piece. The leaf spring  40  is fixed to the housing  24  by a fixing stud  42  fitted in a threaded hole  24 C formed in the housing  24 . The pressure arm section  40 A cooperates with the projection  44  of the hub ring  28 A of the holder frame  28  so as to urges the holder frame  28 . More specifically, when operating the switch lever  22 , the holder frame  28  is turned through engagement between the external gear  36  of the hub ring  28 A and the external gear  38  of the shaft  31  of the switch lever  22 . During movement of the holder frame  28  from the rest position to the working position and vice versa, the leaf spring  40  is elastically bent downward by the projection  44  as depicted by a broken line so as thereby to keep itself applying urging force against the projection  44  of the holder frame  28 . When the holder frame  28  is put in the rest position shown in  FIG. 3 , the leaf spring  40  urges the projection in a counterclockwise direction so as thereby to retain the holder frame  28  in the rest position. Similarly, when the holder frame  28  is put in the working position shown in  FIG. 4 , the leaf spring  40  urges the projection in a clockwise direction so as thereby to retain the holder frame  28  in the working position. In this manner, urging force against the holder frame  28  is inverted in direction according to the moved positions, namely the rest position and the working position, of the holder frame  28 . 
   In operation of the extender switching device thus structured, while the extender lens  26  is in the rest position as shown in  FIG. 3 , the holder frame  28  is retained with the circumferential locating face  28 B abutted against the stopper stud  32  due to urging force applied against the projection  44  of the hub ring  28 A of the holder frame  28  in a counterclockwise direction by the leaf spring  40 . When operating the switch lever  22  in a counterclockwise direction, the holder frame  28  is moved in a counterclockwise direction through engagement between the external gear  36  of the hub ring  28 A and the external gear  38  of the shaft  31  of the switch lever  22  so as thereby to put the extender lens  26  into an optical path of the zoom lens system as shown in  FIG. 4 . As a result, when the locating face  28 C is brought into abutment with the stopper stud  34 , the extender lens  26  is stationarily put in the optical axis of the zoom lens, and the holder frame  28  is retained in the working position by the leaf spring  40  shown in  FIG. 4 . On the other hand, when operating the switch lever  22  in a clockwise direction when the extender lens  26  is in the optical path of the zoom lens system, the holder frame  28  is moved in a clockwise direction through engagement between the external gear  36  of the hub ring  28 A and the external gear  38  of the shaft  31  of the switch lever  22  so as thereby to remove the extender lens  26  out of the optical path of the zoom lens system as shown in  FIG. 3 . As a result, when the locating face  28 B is brought into abutment with the stopper stud  32 , the extender lens  26  is completely removed out of the optical axis of the zoom lens, and the holder frame  28  is retained in the rest position by the leaf spring  40  shown in  FIG. 4 . 
   The urging force applied against the projection  44  of the hub ring  28 A of the holder frame  28  is inverted before and after an intermediate point of the movement of the holder frame  28  from the rest position to the working position and the vice versa. While it is necessary to operate the switch lever  22  with excess force in order to cause the holder frame  28  to pass through the intermediate point of the movement against the leaf spring  40 , operation of the switch lever  22  becomes easy after the intermediate point of the movement because the leaf spring  40  applies urging force to the holder frame  28  in the same direction as movement of the holder frame  28 . In consequence, an inversion point of urging force is distinctly recognizable, and operationality of the switch lever  22  is improved. Furthermore, because the holder frame  28  is always urged by the leaf spring  40  during movement from the rest position to the working position and the vice versa, the holder frame  28  is prevented from dashing against the stopper stud  32  or  34  with the locating surface  28 B or  28 C, respectively, and hence, from generating hitting noises when the holder frame  28  reaches the rest position or the working position, besides prevented from causing cranky movement between the rest position and the working position. 
     FIGS. 5 and 6  show an extender switching device  20  according to another embodiment of the present invention in which alternative urging means is employed. As shown, the urging means for preventing the holder frame  28  mounting an extender lens  26  therein from generating hitting noises and causing cranky movement comprises an integral piece of leaf spring  50 . The leaf spring  50  is made from a steel strip having a predetermined width and has a generally U-shaped sections  50 A between opposite end legs  50 B. The generally U-shaped section  50 A comprises a plurality of straight segments joined together at certain angles as an integral piece. The leaf spring  50  at the end legs  50 B is fixed to the housing  24  by fixing studs  52  fitted in threaded holes  24 D formed in the housing  24  so as to allow the U-shaped sections  50 A to be elastically flatly deformable with external force. The holder frame  28  has a rim  28 D formed on a rear surface thereof against which the leaf spring  50  is forced. 
   The leaf spring  50  keeps itself pushing the rim  28 D of the holder frame  28  in a circumferential direction with the while the holder frame  28  is moved between a rest position shown in  FIG. 5  and a working position shown in  FIG. 6 . More specifically, the leaf spring  50  is deformed when the holder frame  28  moves between the rest position and the working position so that the urging force applied against the rim  28 D of the holder frame  28  is inverted before and after an in-between position between the rest position and the working position. As a result, the holder frame  28  is urged in a counterclockwise direction while the holder frame is in the rest position and, on the other hand, in a clockwise direction while the holder frame  28  is in the working position. 
   While the extender lens  26  is out of the zoom lens system, the holder frame  28  is urged by the U-shaped section  50 A of the leaf spring  50  so as to be retained in the rest position through abutment of the locating face  28 B against the stopper stud  32 . When operating the switch lever  22  so as to move the extender lens  26  into the zoom lens, the locating face  28 C of the holder frame  28  is brought into abutment against the stopper stud  34 , so as to retain the holder frame  28  in the working position. Because the holder frame  28  is always urged by the leaf spring  50  during movement from the rest position to the working position and the vice versa, the holder frame  28  is prevented from dashing against the stopper stud  32  or  34  with the locating surface  28 B or  28 C, respectively, and hence, from generating hitting noises when the holder frame  28  reaches the rest position or the working position, besides prevented from causing cranky movement between the rest position and the working position. 
     FIGS. 7 and 8  show an extender switching device  20  according to a further embodiment of the present invention in which alternative urging means is employed. As shown, the urging means for preventing the holder frame  28  mounting an extender lens  26  therein from generating hitting noises and causing cranky movement comprises a cantilever type of leaf spring  60 . The leaf spring  60 , that is made from a steel strip having a predetermined width, has a generally V-shaped distal sections  60 A and  60 B directed inversely to each other and is fixed at an end leg  60 C to the housing  24  by a fixing stud  62  fitted in a threaded hole  24 D formed in the housing  24  so as to allow the V-shaped sections  60 A and  60 B to be elastically bendable with external force. The holder frame  28  has a rim  28 D formed on a rear surface thereof against which the leaf spring  60  is forced. 
   The leaf spring  60  keeps itself pushing the rim  28 D of the holder frame  28  in a circumferential direction with the V-shaped sections  60 A or  60 B while the holder frame  28  is moved between a rest position shown in  FIG. 5  and a working position shown in  FIG. 6 . More specifically, the leaf spring  50  is deformed when the holder frame  28  moves between the rest position and the working position so that the urging force applied against the rim  28 D of the holder frame  28  is inverted before and after an in-between position between the rest position and the working position. As a result, the holder frame  28  is urged in a counterclockwise direction while the holder frame is in the rest position and, on the other hand, in a clockwise direction while the holder frame  28  is in the working position. 
   While the extender lens  26  is out of the zoom lens system, the holder frame  28  is urged in a counterclockwise direction by the V-shaped section  60 A so as to be retained in the rest position through abutment of the locating face  28 B against the stopper stud  32 . When operating the switch lever  22  so as to move the extender lens  26  into the zoom lens, the holder frame  28  elastically bends the leaf spring  60  and brings the rim  28 D into engagement with the V-shaped section  60 B. Then, when the locating face  28 C of the holder frame  28  is brought into abutment against the stopper stud  34 , the leaf spring  60  urges the holder frame  28  in a clockwise direction by the V-shaped section  60 B so as thereby to retain the holder frame  28  in the working position. In this manner, urging force against the holder frame  28  is inverted in direction at a point of movement of the holder frame  28  where engagement of the leaf spring  60  with holder frame  28  changes from the V-shaped section  60 A to the V-shaped section  60 B. Also in this embodiment, because the holder frame  28  is always urged by the leaf spring  60  during movement from the rest position to the working position and the vice versa, the holder frame  28  is prevented from dashing against the stopper stud  32  or  34  with the locating surface  28 B or  28 C, respectively, and hence, from generating hitting noises when the holder frame  28  reaches the rest position or the working position, besides prevented from causing cranky movement between the rest position and the working position. 
   Although the optical element switch device of the present invention has been described as to the extender switch device embodied in a zoom lens for an ENG camera by way of example, the optical element switch device may be incorporated in various types of image forming optical lens systems. 
   It is to be understood that although the present invention has been described with regard to a preferred embodiments thereof, various other embodiments and variants may occur to those skilled in the art, which are within the scope and spirit of the invention, and such other embodiments and variants are intended to be covered by the following claims.