Field-of-view frame switching device

A field-of-view frame switching device has a rectangular fixed field-of-view frame and a plurality of light-shielding members for covering portions of the rectangular fixed field-of-view frame so as to vary the size of the actual field-of-view frame. The light-shielding members are composed of a first pair of oppositely arranged light-shielding members and a second pair of oppositely arranged light-shielding members. The field-of-view frame switching device also has a coupling member for coupling the light-shielding members together in such relation that, when the first pair of light-shielding members are positioned closer to each other to narrow the actual field-of-view frame, the second pair of light-shielding members are positioned wide apart from each other and that, when the first pair of light-shielding members are positioned wide apart from each other, the second pair of light-shielding members are positioned closer to each other to narrow the actual field-of-view frame. The field-of-view frame switching device further has a moving member for moving at least a part of the light-shielding members in a direction substantially parallel to one side of the rectangular fixed field-of-view frame.

This application is based on applications Nos. H09-331479 and H09-331361
 filed in Japan, the content of which is hereby incorporated by reference.
 BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a field-of-view frame switching device,
 and more particularly to a device for switching the field-of-view frame of
 a viewfinder designed for the Advanced Photo System, which uses three
 picture formats.
 2. Description of the Prior Art
 In recent years, more and more products conforming to the Advanced Photo
 System (hereafter referred to as the "APS") have been introduced to the
 market. The APS uses three picture formats to allow an image to be taken
 in one of the following three different frame sizes: the wide format
 (hereafter referred to as the "H format") that offers an aspect ratio of
 9:16, the standard format (hereafter referred to as the "C format") that
 has the same vertical dimension as and a shorter horizontal dimension than
 the H format and offers an aspect ratio of 2:3, and the panorama format
 (hereafter referred to as the "P format") that has the same horizontal
 dimension as and a shorter vertical dimension than the H format and offers
 an aspect ratio of 1:3.
 Typically, a user's selection of a specific frame size causes the switching
 of the field-of-view frame of a viewfinder. Conventional field-of-view
 frame switching devices are disclosed, for example, in Japanese Laid-Open
 Patent Applications Nos. H6-273826 and H8-146493. How these conventional
 devices achieve the switching of the field-of-view frame is schematically
 illustrated in FIGS. 1A to 1C and in FIGS. 2A to 2C respectively. Of these
 figures, FIGS. 1A and 2A show the arrangement of the field-of-view frame
 for the H format, FIGS. 1B and 2B show the same for the C format, and
 FIGS. 1C and 2C show the same for the P format.
 Either of these devices has a fixed field-of-view frame 11 (indicated by
 broken lines) and two L-shaped movable masks 12 and 13. The vertical
 dimension of the C and H formats and the horizontal dimension of the H and
 P formats are determined by the fixed field-of-view frame 11. In each of
 the figures, the hatched area represents the frame size of the selected
 formats (H, C, or P).
 In the device shown in FIGS. 1A to 1C, the two L-shaped movable masks 12
 and 13 are individually moved horizontally (i.e. translated in the
 directions indicated by arrows C) to determine the horizontal dimension of
 the C format, and they are moved vertically (i.e. translated in the
 directions indicated by arrows P) to determine the vertical dimension of
 the P format. By contrast, in the device shown in FIGS. 2A to 2C, the two
 L-shaped movable masks 12 and 13 are individually moved obliquely (i.e.
 translated in the directions indicated by arrows C or P) to determine the
 horizontal dimension of the C format or the vertical dimension of the P
 format.
 However, allowing the movable masks to be moved in both horizontal and
 vertical directions requires not only a complicated driving mechanism but
 also an ample space for it. On the other hand, allowing the movable masks
 to be moved in oblique directions requires a simpler driving mechanism,
 since they need to be driven along only one axis, but requires them to be
 driven over a comparatively long movement stroke (see FIGS. 2B and 2C).
 Thus, both of these devices have been imposing various restrictions in the
 design of compact cameras.
 SUMMARY OF THE INVENTION
 An object of the present invention is to provide a device that makes it
 possible, in any photographing system including the APS, to select a
 field-of-view frame of a viewfinder from among a plurality of choices and
 that nevertheless requires only a minimal movement stroke of movable masks
 and a minimal space for a driving mechanism.
 To achieve the above object, according to one aspect of the present
 invention, a field-of-view frame switching device is provided with a
 rectangular fixed field-of-view frame and a plurality of light-shielding
 members for covering portions of the rectangular fixed field-of-view frame
 so as to vary the size of the actual field-of-view frame. Here, the
 light-shielding members are composed of a first pair of oppositely
 arranged light-shielding members and a second pair of oppositely arranged
 light-shielding members. This field-of-view frame switching device is
 provided also with a coupling member for coupling the light-shielding
 members together in such relation that, when the first pair of
 light-shielding members are positioned closer to each other to narrow the
 actual field-of-view frame, the second pair of light-shielding members are
 positioned wide apart from each other and that, when the first pair of
 light-shielding members are positioned wide apart from each other, the
 second pair of light-shielding members are positioned closer to each other
 to narrow the actual field-of-view frame. This field-of-view frame
 switching device is provided further with a moving member for moving at
 least a part of the light-shielding members in a direction substantially
 parallel to one side of the rectangular fixed field-of-view frame.
 According to another aspect of the present invention, a field-of-view frame
 switching device is provided with a rectangular fixed field-of-view frame
 and a plurality of field-of-view frame switching members for covering
 portions along the top, bottom, left-hand, and right-hand sides of the
 rectangular fixed field-of-view frame so as to vary the size of the actual
 field-of-view frame. This field-of-view frame switching device is provided
 also with a coupling member for coupling the field-of-view frame switching
 members together into a single unit.
 According to still another aspect of the present invention, a field-of-view
 frame switching device is provided with a rectangular fixed field-of-view
 frame and a field-of-view frame switching member for covering portions of
 the rectangular fixed field-of-view frame so as to vary the size of the
 actual field-of-view frame. Here, the field-of-view frame switching member
 is divided at least at one side thereof. This field-of-view frame
 switching device is provided also with a moving member for moving the
 field-of-view frame switching member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The structure of a camera incorporating the field-of-view frame switching
 device of a first embodiment of the invention is shown in FIGS. 3 and 4.
 FIG. 3 shows a sectional view and FIG. 4 shows a perspective view of the
 camera 1.
 The light beam coming from an object travels through a taking lens system
 2, and is then reflected by a quick-return mirror 3 so as to be focused on
 a focusing screen 4 and form an image thereon. Closely behind the focusing
 screen 4 along the beam path is disposed a field-of-view frame switching
 unit 5. The light beam having passed through the field-of-view frame
 switching unit 5 is then reflected by a pentagonal roof prism 6 and
 directed to an eyepiece lens 7 so that the user of the camera can observe
 an image of the object.
 When the user presses a release button 14, the quick-return mirror 3
 rotates so that the light beam from the object will be directed straight
 to a film 9, and a shutter 8 disposed in front of the film 9 is released
 to achieve exposure. Note that, instead of the pentagonal roof prism 6, a
 pentagonal roof mirror may be used.
 Although not shown, a fixed field-of-view frame is formed on the focusing
 screen 4. This fixed field-of-view frame determines the field-of-view
 frame for the H format. The field-of-view frame switching unit 5 is
 provided with a movable mask 12 having light-shielding wings 10 for
 shielding the field-of-view frame from four sides. When a field-of-view
 frame switching operation unit 15 is operated, appropriate ones of the
 light-shielding wings 10 are moved in an appropriate manner so that the
 field-of-view frame will be switched to that for the P or C format.
 In the APS, when the images recorded on the film 9 are printed on
 photographic paper, appropriate frame sizes are selected in accordance
 with the information recorded on the film 9. Thus, in principle, partial
 shielding of the film 9 is unnecessary in the APS. However, in other
 systems such as the 135 system, switching between a standard frame size
 and a panorama frame size, for example, cannot be achieved unless a
 special mechanism for switching the frame size is provided in front of or
 behind the shutter 8.
 Now, the movable mask 12 of the field-of-view frame switching device of the
 first embodiment will be described with reference to the drawings. FIGS.
 5A, 5B, and 5C illustrate the arrangement of the light-shielding wings for
 the H, C, and P formats respectively.
 The movable mask 12 includes four light-shielding wings, of which two will
 be referred to as the P light-shielding wings 21 and the other two as the
 C light-shielding wings 22. These P and C light-shielding wings 21 and 22
 each have a boss 19 or 20 formed thereon, and each boss 19 or 20 is guided
 along a slide guide groove 18 or 27 so that the P and C light-shielding
 wings 21 and 22 can move vertically and horizontally (as seen in the
 figures) respectively.
 The movable mask 12 as a whole is made of a flexible material, and is so
 shaped that the P and C light-shielding wings 21 and 22 are rigid enough
 to keep their field-of-view frame determining edges 29 and 30 straight at
 all times and simultaneously that the arm-like portions 23 connecting
 between the P and C light-shielding wings 21 and 22 are flexible enough to
 change their orientation freely. Alternatively, it is also possible to
 form the P and C light-shielding wings 21 and 22 out of one material and
 the arm-like portions 23 out of another material so that only the arm-like
 portions 23 may be made of a flexible material.
 The P and C light-shielding wings 21 and 22 each have a stopper 24 or 25
 formed thereon. The stoppers 24 and 25, by being struck against fixed
 members (not shown) provided near the corresponding sides of the fixed
 field-of-view frame 11, serve to position the field-of-view frame
 determining edges 29 and 30 in such positions where they determine the
 vertical dimension of the field-of-view frame for the P format and the
 horizontal dimension of the field-of-view frame for the C format
 respectively.
 Having the structure as described above, the movable mask 12 appears as
 shown in FIG. 5A when the H format is selected. At this time, the bosses
 19 and 20 are located substantially at the center of the slide guide
 grooves 18 and 27, and all of the P and C light-shielding wings 21 and 22
 are located outside the fixed field-of-view frame 11.
 When the frame size is switched from the H format to the C format, as shown
 in FIG. 5B, the bosses 20 are, by the action of a driving mechanism that
 will be described later, moved inward along the slide guide grooves 27,
 and thereby the C light-shielding wings 22, which are disposed opposite
 each other, are moved horizontally inward until the stoppers 25 strike
 against the fixed members (not shown) formed near the corresponding sides
 of the fixed field-of-view frame 11. Meanwhile, as the arm-like portions
 23 become more and more vertically oriented, the bosses 19 are moved
 outward along the slide guide grooves 18, and thereby the P
 light-shielding wings 21 are moved vertically outward. In this way, the
 field-of-view frame for the C format is determined.
 When the frame size is switched from the H format to the P format, as shown
 in FIG. 5C, the bosses 20 are, by the action of a driving mechanism that
 will be described later, moved outward along the slide guide grooves 27,
 and thereby the C light-shielding wings 22, which are disposed opposite
 each other, are moved horizontally outward. Meanwhile, as the arm-like
 portions 23 become more and more horizontally oriented, the bosses 19 are
 moved inward along the slide guide grooves 18, and thereby the P
 light-shielding wings 21 are moved vertically inward until the stoppers 24
 strike against the fixed members (not shown) formed near the corresponding
 sides of the fixed field-of-view frame 11. In this way, the field-of-view
 frame for the P format is determined.
 Next, the field-of-view frame switching device of a second embodiment of
 the invention will be described with reference to the drawings. FIGS. 6A,
 6B, and 6C illustrate the arrangement of the light-shielding wings for the
 H, C, and P formats respectively. Note that, in FIGS. 6A, 6B, and 6C, such
 components as are found also in FIGS. 5A, 5B, and 5C are identified with
 the same reference numbers.
 In FIGS. 6A, 6B, and 6C, the movable mask 12 includes an upper mask portion
 12a and a lower mask portion 12b, and these portions 12a and 12b are
 coupled together at two coupling portions 28 that are rotatably fitted
 around two slide shafts 26. The upper and lower mask portions 12a and 12b
 may be formed as two separate units that are later coupled together at the
 coupling portions 28, or alternatively may be formed as a single unit. The
 slide shafts 26 are guided along slide guide grooves 27 so that they can
 be moved, by a driving mechanism that will be described later,
 horizontally (as seen in the figures) in directions in which they recede
 from each other and approach each other.
 Two P light-shielding wings 21 are disposed opposite each other, and are
 coupled to C light-shielding wings 22a and 22b (here, the right-hand and
 left-hand C light-shielding wings are each divided into an upper and a
 lower portion) by arm-like portions 23b. The C light-shielding wings 22a
 and 22b are coupled to the coupling portions 28 by arm-like portions 23a.
 The P light-shielding wings 21 and the C light-shielding wings 22a and 22b
 each have a stopper 24 or 25 formed thereon. The stoppers 24 and 25, by
 being struck against fixed members (not shown) formed near the
 corresponding sides of the fixed field-of-view frame 11, serve to position
 the P light-shielding wings 21 and the C light-shielding wings 22a and 22b
 respectively, in appropriate positions.
 Having the structure as described above, the movable mask 12 appears as
 shown in FIG. 6A when the H format is selected. At this time, the slide
 shafts 26 are located substantially at the center of the slide guide 27,
 and all of the P and C light-shielding wings 21, 22a, and 22b are located
 outside the fixed field-of-view frame 11.
 When the frame size is switched from the H format to the C format, as shown
 in FIG. 6B, the slide shafts 26 move inward along the slide guide grooves
 27; meanwhile, the arm-like portions 23a and 23b are, as it were, folded
 up. As a result, the C light-shielding wings 22a and 22b move vertically
 away from each other, and meanwhile they move horizontally inward until
 the stoppers 25 strike the fixed members (not shown) formed near the
 corresponding sides of the fixed field-of-view frame 11. Even if the slide
 shafts 26 are moved further inward along the slide guide grooves 27, only
 the arm-like portions 23a change their rotation, and the C light-shielding
 wings 22a and 22b are kept in fixed positions by the stoppers 25.
 At this time, the field-of-view determining edges 30 of the C
 light-shielding wings 22a and 22b form straight lines. On the other hand,
 the P light-shielding wings 21 are moved vertically away from each other
 by the C light-shielding wings 22a and 22b and the arm-like portions 23b
 so as to be retracted out of the fixed field-of-view frame 11. In this
 way, the field-of-view frame for the C format is determined.
 When the frame size is switched from the H format to the P format, as shown
 in FIG. 6C, the slide shafts 26 move outward along the slide guide grooves
 27; meanwhile, the arm-like portions 23a and 23b are, as it were,
 unfolded. As a result, the C light-shielding wings 22a and 22b move
 vertically closer to each other, and meanwhile they move horizontally
 outward. This causes the P light-shielding wings 21 to move vertically
 inward until the stoppers 24 strike the fixed members (not shown) formed
 near the corresponding sides of the fixed field-of-view frame 11. At this
 time, the field-of-view determining edges 29 of the P light-shielding
 wings 21 determine the field-of-view frame for the P format.
 As shown in FIGS. 5A-5C and 6A-6C, coupling together the P light-shielding
 wings 21 and the C light-shielding wings by the use of flexible members
 (i.e. the arm-like portions 23) makes it possible to select a
 field-of-view frame from three or more choices by moving the oppositely
 arranged C light-shielding wings 22 in opposite directions along an axis
 substantially perpendicular to one side (11a) of the fixed field-of-view
 frame 11, with the C light-shielding wings 22 each driven at one point
 (i.e. the boss 20 or slide shaft 26) integral therewith.
 This can be achieved by the use of a simple driving mechanism that can
 drive the relevant members along only one axis and with a minimum of space
 secured to allow the movement of the light-shielding wings. This leads to
 a significant reduction in the size of the field-of-view frame switching
 device as a whole. Note that the first embodiment permits a modification
 in which the bosses 19 are moved vertically (as seen in the figures). Note
 also that the second embodiment permits a modification in which the P
 light-shielding wings 21 are each divided into a right-hand and a
 left-hand portion and the slide shafts 26 are disposed beside the outer
 edge of each P light-shielding wing 21 so as to be moved vertically.
 Moreover, in the second embodiment, in which the field-of-view determining
 edges 29 of the P light-shielding wings 21 are always straight, it is also
 possible to provide an additional stopper mechanism somewhere between the
 H-format and P-format positions so as to make available another
 field-of-view frame for a format other than the H, C, and P formats.
 In FIG. 5C, as the arm-like portions 23 become more and more parallel
 oriented with respect to the movement direction (indicated by arrows J) of
 the C light-shielding wings 22, the joint portions 23c between the C
 light-shielding wings 22 and the arm-like portions 23 shrink. Since the
 joint portions 23c are resilient, their shrinkage destabilizes the
 stoppers 24 for the P light-shielding wings 21 by predisposing them to
 move away from the fixed members (not shown), in the directions indicated
 by arrows K.
 In the second embodiment, the C light-shielding wings 22a and 22b are each
 divided into an upper and a lower portion, and these portions move
 vertically (as seen in the figures) in opposite directions. As shown in
 FIG. 6C, when the P format is selected, the arm-like portions 23a and 23b
 form large angles with respect to the movement direction (indicated by
 arrows J) of the C light-shielding wings 22, and this helps keep the
 stoppers 24 securely against the fixed members (not shown). As a result,
 it is possible to obtain stable and accurate field-of-view frames and also
 realize smooth movement of the P light-shielding wings 21. For these
 reasons, it is preferable that the C light-shielding wings 22a and 22b be
 each divided into an upper and a lower portion.
 Alternatively, as shown in FIG. 7, which illustrates the field-of-view
 frame switching device of a third embodiment of the invention, it is also
 possible to divide only one of the C light-shielding wings into two
 portions (22a and 22b). In this case, the arm-like portions 23a and 23b
 are made more rigid than the arm-like portion 23 or the joint portions 23d
 so as not to predispose the stoppers 24 to move away from the fixed
 members (not shown).
 Next, the driving mechanism used to drive the movable mask in the first to
 third embodiments will be described with reference to FIGS. 8A to 8C. FIG.
 8A is a perspective view illustrating the arrangement of the components of
 the driving mechanism 40 when the H format is selected, and FIGS. 8B and
 8C are front views illustrating the arrangement of those components when
 the P and C formats, respectively, are selected. Note that, in these
 figures, such components as are found also in FIGS. 5A and 6A are
 identified with the same reference numerals.
 In FIG. 8A, the movable mask 12 has its arm-like portions 23a rotatably
 fitted to the slide shafts 26, which are guided along the slide guide
 grooves 27 so as to be movable substantially parallel to the field-of-view
 determining edges 29 of the P light-shielding wings 21. The slide shafts
 26 are fitted with slide levers 41 and 42, which have slide grooves 41a
 and 42a and operation grooves 41b and 42b formed therein.
 Into the slide grooves 41a and 42a, slide guide bosses 43 are fitted so
 that the slide levers 41 and 42 are positioned appropriately in the
 direction perpendicular to the movable mask 12. Into the operation grooves
 41b and 42b, bosses 45a and 45b formed on an operation lever 44 are fitted
 so that, as the operation lever 44 rotates about its center of rotation
 44a, the slide levers 41 and 42 move in opposite directions as indicated
 by arrow J.
 In this structure, when the user rotates the operation lever 44, which is
 disposed outside the camera body, to a position marked [P] on an
 indication plate 46 as shown in FIG. 8B, the slide levers 41 and 42 move
 in directions in which they recede from each other. As a result, the
 distance between the right-hand and left-hand C light-shielding wings 22a
 and 22b increases, and the distance between the upper and lower P
 light-shielding wings 21 decreases. In this way, the frame size is
 switched to the P format.
 When the user rotates the operation lever 44 to a position marked [C] on
 the indication plate 46 as shown in FIG. 8C, the slide levers 41 and 42
 move in directions in which they approach each other. As a result, the
 distance between the right-hand and left-hand C light-shielding wings 22a
 and 22b decreases, and thus the frame size is switched to the C format. At
 this time, the P light-shielding wings 21 are retracted out of the fixed
 field-of-view frame 11. It is also possible to switch the field-of-view
 frame by driving the slide levers 41 and 42 electrically by the use of a
 motor, a cam, and other components instead of the operation lever 44.
 In this way, it is possible to select a field-of-view frame from three
 choices by the use of a simple driving mechanism 40 that drives the
 relevant members along only one axis and that therefore occupies a minimum
 of space. This helps make cameras compact.
 Next, the field-of-view frame switching device of a fourth embodiment of
 the invention will be described with reference to the drawings. FIGS. 9A,
 9B, and 9C show the arrangement of the movable mask 12 for the H, C, and P
 formats respectively. Note that, in these figures, such components as are
 found also in FIGS. 5A and 6A are identified with the same reference
 numerals.
 As shown in FIG. 9A, the movable mask 12 includes four L-shaped
 light-shielding wings 151 to 154, of which two 151 and 153, arranged
 opposite each other, have pin guide grooves 155a to 155d formed therein
 and the other two 152 and 154, also arranged opposite each other, have
 coupling pins 156a to 156d formed thereon. These four light-shielding
 wings 151 to 154 are, substantially at the center of each side of the
 fixed field-of-view frame 11, coupled together by the coupling pins 156a
 to 156d fitted into the pin guide grooves 155a to 155d in such a way that
 each of the light-shielding wings 151 to 154 is rotatable about their
 respective center of rotation 151a to 154a.
 Thus, this movable mask 12 has each of its four sides divided into two
 portions so that, as the distance between two opposite sides increases or
 decreases, the distance between the other two opposite sides decreases or
 increases. That is, when one of the coupling pins 156a to 156d is moved in
 a direction indicated by arrow J1, J2, K1, or K2, the light-shielding
 wings 151 to 154 each rotate about their respective center of rotation
 151a to 154a as shown in FIGS. 9B and 9C. The pin guide grooves 155a to
 155d guide the other three of the coupling pins 156a to 156d to move them
 along substantially straight axes until the field-of-view determining
 edges 30a and 30b or 29a and 29b form straight lines. In this way, the
 field-of-view frame is switched from the H format (FIG. 9A) to the C
 format (FIG. 9B) or to the P format (FIG. 9C).
 Instead of coupling together the light-shielding wings 151 and 152 by the
 coupling pin 156b and coupling together the light-shielding wings 153 and
 154 by the coupling pin 156d, it is also possible to use a driving
 mechanism like the one shown in FIG. 8A to drive the coupling pins 156a
 and 156c in opposite directions along one axis. Also this makes it
 possible to select a field-of-view frame from three choices. However, it
 is preferable to couple together the light-shielding wings 151 and 152,
 and the light-shielding wings 153 and 154, by the coupling pin 156b and
 156d respectively, because it is then possible to switch the field-of-view
 frame simply by driving only one of the coupling pins 156a and 156c . This
 leads to further simplification of the driving mechanism.
 Next, the field-of-view frame switching device of a fifth embodiment of the
 invention will be described with reference to the drawings. FIGS. 10A,
 10B, and 10C show the arrangement of the movable mask 12 for the H, C, and
 P formats respectively. Note that, in these figures, such components as
 are found also in FIGS. 5A and 6A are identified with the same reference
 numerals.
 As shown in FIG. 10A, the C light-shielding wings 22 each have a boss 20
 formed thereon. The bosses 20 are guided along slide guide grooves 27 so
 that the C light-shielding wings 22 can move horizontally (as seen in the
 figures, as indicated by arrows J). The C light-shielding wings 22 are
 coupled to the P light-shielding wings 21 by wires 52 and 53. Moreover,
 the P light-shielding wings 21 are fitted with pull springs 51 so as to be
 pulled in directions in which they recede from each other.
 The wires 52 and 53 change their direction by approximately 90.degree. at
 guide pins 54. As a result, when the two oppositely arranged C
 light-shielding wings 22 are moved in directions in which they recede from
 each other, the P light-shielding wings 21, pulled by the wires 52 and 53,
 move in directions in which they approach each other. By contrast, when
 the two oppositely arranged C light-shielding wings 22 are moved in
 directions in which they approach each other, the P light-shielding wings
 21, pulled by the pull springs 51, move in directions in which they recede
 from each other.
 How the wires 52 and 53 are used to achieve desired coupling is
 schematically shown in FIG. 11. The wires 52 and 53 change their direction
 at the guide pins 54. Thus, the upper (as seen in the figure) P
 light-shielding wing 21 is kept at a predetermined distance from the C
 light-shielding wings 22 by the wires 52a and 53a. On the other hand, the
 lower (as seen in the figure) P light-shielding wing 21 is kept at a
 predetermined distance from the C light-shielding wings 22 by the wires
 52b and 53b.
 Having the structure as described above, the movable mask 12 appears as
 shown in FIG. 10A when the H format is selected. At this time, the bosses
 20 are located substantially at the center of the slide guide grooves, and
 all of the P light-shielding wings 21 and the C light-shielding wings 22
 are located outside the fixed field-of-view frame 11.
 When the frame size is switched from the H format to the C format, as shown
 in FIG. 10B, the bosses 20 are moved, by a driving mechanism like the one
 shown in FIG. 8A, inward along the slide guide grooves 27, and thereby the
 C light-shielding wings 22 are moved horizontally inward until the
 stoppers 25 strike the fixed members (not shown) formed near the
 corresponding sides of the fixed field-of-view frame 11. At this time, the
 wires 52 and 53 tend to slacken, but this is prevented by the action of
 the pull springs 51, which pull the P light-shielding wings 21 and thereby
 retract them out of the fixed field-of-view frame 11.
 When the frame size is switched from the H format to the P format, as shown
 in FIG. 10C, the bosses 20 are moved outward along the slide guide grooves
 27, and thereby the C light-shielding wings 22 are moved horizontally
 outward. As a result, the P light-shielding wings 21, pulled by the wires
 52 and 53, move vertically inward until the stoppers 24 strike the fixed
 members (not shown) formed near the corresponding sides of the fixed
 field-of-view frame 11. In this way, the field-of-view frame for the P
 format is determined.
 In this way, by coupling together the P and C light-shielding wings 21 and
 22 by wires 52 and 53, it is possible to select a field-of-view frame from
 three or more choices by the use of a driving mechanism that can drive the
 oppositely arranged C light-shielding wings in opposite directions
 substantially parallel to one side of the fixed field-of-view frame, with
 each of the C light-shielding wings driven at one point integral
 therewith. This can be achieved by the use of a simple driving mechanism
 and with a minimum of space secured to allow the movement of the
 light-shielding wings, and thus helps make cameras compact.
 Alternatively, as shown in FIG. 12, which illustrates the field-of-view
 frame switching device of a sixth embodiment of the invention, the wires
 may be so arranged that each of the P light-shielding wings 21 is, at both
 ends, coupled to the two C light-shielding wings 22a and 22b. As shown in
 the figure, in this case, the right-hand C light-shielding wing 22a is
 coupled to the upper P light-shielding wing 21 by the wires 52a and 52c,
 and is coupled to the lower P light-shielding wing 21 by the wires 52b and
 52d.
 On the other hand, the left-hand C light-shielding wing 22b is coupled to
 the upper P light-shielding wing 21 by the wires 53a and 53c, and is
 coupled to the lower P light-shielding wing 21 by the wires 53b and 53d.
 The P light-shielding wings 21 and the C light-shielding wings 22b are
 each pulled outward by a spring 101 or 102.
 In this structure, when the right-hand C light-shielding wing 22a is moved
 straight rightward (as seen in the figure), the upper and lower P
 light-shielding wings 21 move in directions in which they are pulled by
 the wires 52a to 52d. At this time, the wires 53a to 53d coupling the
 left-hand C light-shielding wing 22b to the P light-shielding wings 21
 tend to slacken, but this is prevented by the action of the spring 102,
 which pulls the left-hand C light-shielding wing 22b outward and thereby
 causes the C light-shielding wings 22a and 22b to move in directions in
 which they recede from each other. In this way, the field-of-view frame
 for the P format is determined.
 When the right-hand C light-shielding wing 22a is moved straight leftward
 (as seen in the figure), the P light-shielding wings 21 are moved
 vertically outward by the action of the spring 101, just as in the case
 shown in FIG. 10B. At this time, as long as the pulling force of the
 spring 102 is set to be weaker than that of the spring 101, this movement
 of the P light-shielding wings 21 causes the left-hand C light-shielding
 wing 22b to move horizontally inward. In this way, the field-of-view frame
 for the C format is determined.
 In this way, it is possible to select a field-of-view frame from three or
 more choices by the use of a driving mechanism that can drive one point on
 the C light-shielding wing 22a along a straight line. This can be achieved
 with a simpler driving mechanism than in the fifth embodiment, and thus
 helps make cameras compact.
 Next, the field-of-view frame switching device of a seventh embodiment of
 the invention will be described with reference to FIG. 13. Note that, in
 this figure, such components as are found also in FIG. 10 are identified
 with the same reference numerals. Here, the P light-shielding wings 21 and
 the C light-shielding wings 22 are made of a flexible material, and are so
 arranged as to be movable in directions perpendicular to the focusing
 plate 4 while changing their direction as they pass light-shielding wing
 guides 162 and 164 that are disposed just outside the fixed field-of-view
 frame 11. The P and C light-shielding wings 21 and 22 are coupled together
 by wires 52 and 53 that are arranged in the same manner as in the fifth or
 sixth embodiment.
 At one end of each of the two oppositely arranged C light-shielding wings
 22, a rotary lever 161 is fitted by the use of a coupling pin 163 so as to
 be rotatable about a center shaft 161a. One of the rotary levers 161 has
 an operation lever portion 161b formed integrally therewith.
 In this structure, when the user rotates the operation lever portion 161b
 to a position marked [P], [H], or [C] on an indication plate 46, the P and
 C light-shielding wings 21 and 22 each move first straight parallel to the
 focusing plate 4 and then, outside the fixed field-of-view frame 11, in a
 direction perpendicular to the focusing plate 4, and thereby the
 respective field-of-view frame is determined. This structure is useful in
 cases where the space for the movement of the light-shielding wings 21 and
 22 cannot be secured within substantially the same plane as the focusing
 plate 4, because it even then allows the light-shielding wings to be
 retracted three-dimensionally. This contributes to efficient use of
 available space.
 Next, the field-of-view frame switching device of an eighth embodiment of
 the invention will be described with reference to the drawings. FIGS. 14A,
 14B, and 14C show the arrangement of the movable mask 12 for the H, C, and
 P formats respectively. On the other hand, FIG. 15 shows the driving
 mechanism 40 used in the eighth embodiment. Note that, in these figures,
 such components as are found also in FIGS. 5A and 8A are identified with
 the same reference numerals.
 As shown in FIG. 15, the movable mask 12 includes two C-shaped P
 light-shielding wings 21a and 21b that are disposed horizontally opposite
 each other and two I-shaped C light-shielding wings 22c and 22d that are
 also disposed horizontally opposite each other. Of these light-shielding
 wings, the left-hand P light-shielding wing 21a is coupled to the
 right-hand C light-shielding wing 22d by a slide lever 41, and the
 right-hand P light-shielding wing 21b is coupled to the left-hand C
 light-shielding wing 22c by another slide lever 42.
 Just as in the case shown in FIG. 8A, when the user rotates the operation
 lever 44, the slide levers 41 and 42 move in opposite directions as
 indicated by arrows J, and this causes the P and C light-shielding wings
 21a to 21d to move.
 As shown in FIGS. 14A to 14C, in this structure, it is possible to select a
 field-of-view frame from three choices by moving the C light-shielding
 wings 22c and 22d, on the one hand, and the P light-shielding wings 21a
 and 21b, on the other hand, along the same axis (in the directions
 indicated by arrows J) by the use of a driving mechanism that can drive
 the relevant members along only one axis. Moreover, this structure
 requires no vertical (as shown in the figures) movement, and therefore it
 is possible to realize a field-of-view frame switching device that
 occupies almost no space above and below the field-of-view frame.
 In this embodiment, it is also possible to form the P light-shielding wings
 21a and 21b as one continuous component. However, retracting such a P
 light-shielding wing, which would then be horizontally twice as long as
 otherwise, out of the fixed field-of-view frame 11 requires not only an
 unduly large retraction space but also an unduly long movement stroke in
 one of the directions indicated by arrows J. Moreover, then, the C
 light-shielding wings (22c and 22d) coupled thereto also need to be moved
 through an accordingly long movement stroke and thus require an unduly
 large retraction space. By contrast, by the use of the horizontally (as
 seen in the figure) divided P light-shielding wings 21a and 21b, it is
 possible to realize a field-of-view frame switching device that requires a
 minimum of space to the right and to the left of the field-of-view frame.
 Next, the field-of-view frame switching device of a ninth embodiment of the
 invention will be described with reference to the drawings. FIGS. 16A,
 16B, and 16C show the arrangement of the movable mask 12 for the H, C, and
 P formats respectively.
 As shown in FIG. 16A, the movable mask 12 includes four light-shielding
 wings 61 to 64, which are all designed to be rotatable about and together
 with their respective rotary shafts 65 to 68. These four rotary shafts 65
 to 68 are coupled to a driving shaft 70 by belts 69. As a result, when the
 drive shaft 70 is rotated in the direction indicated by arrow E, the
 rotary shafts 65 to 68, together with the light-shielding wings 61 to 64,
 rotate in the directions indicated by arrows F1 to F4 respectively, and
 thereby the field-of-view frame is switched to that for the C format as
 shown in FIG. 16B. Thereafter, when the drive shaft 70 is rotated further
 in the direction indicated by arrow E, the field-of-view frame is switched
 to that for the P format as shown in FIG. 16C.
 Also in this structure, dividing the movable mask into four light-shielding
 wings 61 to 64 and rotating in different directions these light-shielding
 wings thus divided at the center of each side of the movable mask helps
 reduce the retraction space for the light-shielding wings 61 to 64. In
 addition, this structure requires a driving mechanism that can simply
 rotate a target member about one point (i.e. the driving shaft 70), and
 thus helps reduce the space occupied by the driving system.
 In the field-of-view frame switching devices described heretofore,
 according as the distance between two opposite light-shielding wings is
 increased or reduced, the distance between the other two opposite
 light-shielding wings is reduced or increased. Thus, by driving one point
 on one of these light-shielding wings in a direction substantially
 perpendicular to one side of the fixed field-of-view frame, it is possible
 to select one among a plurality of field-of-view frames. This helps
 simplify the driving mechanism, minimize the space occupied by the driving
 mechanism, and minimize the retraction space for the light-shielding
 wings.
 Moreover, by appropriately coupling together the light-shielding wings that
 are disposed along the four sides of the movable mask, it is possible to
 increase or decrease the distance between two opposite light-shielding
 wings while decreasing or increasing the distance between the other two
 opposite light-shielding wings. Thus, by driving one point on one of these
 light-shielding wings in a direction substantially perpendicular to one
 side of the fixed field-of-view frame, it is possible to select one among
 a plurality of field-of-view frames. This helps simplify the driving
 mechanism, minimize the space occupied by the driving mechanism, and
 minimize the retraction space for the light-shielding wings.
 Moreover, when at least one of the light-shielding wings that are disposed
 along the four sides of the movable mask is divided into two portions, it
 is possible, simply by moving the thus divided light-shielding wing
 portions in opposite directions, to select one among a plurality of
 field-of-view frames accurately and smoothly. This is achieved by the use
 of a driving mechanism that can simply rotate a target member about one
 point or move it straight along one axis, and thus helps simplify the
 driving mechanism, minimize the space occupied by the driving mechanism,
 and minimize the retraction space for the light-shielding wings.
 The above descriptions deal only with cases where the field-of-view frame
 switching device is incorporated into a single-lens-reflex camera.
 However, the field-of-view frame switching devices of the above
 embodiments can be used also in LS cameras as shown in FIG. 17. In this
 case, the field-of-view frame switching unit 5 is disposed in a position
 within a camera where the light beam coming from the object forms an
 image. In cameras that employ a relay lens system, the field-of-view frame
 switching unit 5 may be disposed on the secondary imaging plane.
 The field-of-view frame switching devices of the embodiments may be used
 even in apparatuses other than cameras, for example slide projectors, to
 switch between a plurality of rectangular field-of-view frames. In FIG.
 17, reference numeral 72 represents an objective lens, reference numeral
 73 represents a Porro prism, and reference numeral 7 represents an
 eyepiece lens.