Abstract:
A single-lens-reflex camera includes means for virtually eliminating vibration, noise, and motion caused by mirror movement, resulting in a higher resolution image being recorded on a light-sensitive surface at the rear of the camera. A pair of bi-parting mirrors are smoothly and noiselessly slid from a position adjacent each other, reflecting an image upward to a viewing screen for focusing and viewing, to a separated position. When mirrors are separated they are clear of the image, so the image can then fall upon the shutter and light-sensitive surface at the rear of the camera. After the image is recorded on the light-sensitive surface, the mirrors return to their original adjacent position. The mirrors are symmetrically arranged, so their inertial masses oppose and cancel each other during mirror movement, thereby eliminating camera movement from this source. This allows larger and heavier mirrors to be used in large format cameras. Space does not have to be allowed for the arc of a pivoted mirror to clear the objective lens, so the camera body can be reduced in size, and a larger mirror can be used. The mechanism for the mirror moving means is simple and rugged. Most usual camera features can be incorporated into a camera utilizing this system. The quietness of this mirror moving means makes its use advantageous for cameras used in wildlife and candid photography.

Description:
FEDERALLY SPONSORED RESEARCH 
     None 
     SEQUENCE LISTING OR PROGRAM 
     None 
     BACKGROUND 
     1. Field of Invention 
     This invention relates to a camera, specifically to a mirror apparatus for the viewfinder of a single-lens-reflex camera. 
     2. Description of Prior Art 
     Typical single-lens-reflex (SLR) cameras have an optical system comprised of an objective lens, a pivoted movable mirror to reflect an inverted image upward to a viewing screen, and optics (a pentaprism) to erect the inverted image and direct it to an eyepiece. The user can then compose and focus the image on the viewing screen. The typical SLR camera also includes hardware to pivot the mirror out of the path of the image so the image can pass through the camera to a focal plane shutter and fall upon a light-sensitive surface at the back of the camera, and thereafter to reposition the mirror back to its original position for subsequent camera operations. The advantages of this system, compared to a rangefinder type camera, are that parallax misalignment is eliminated, and focusing and composing are easier. 
     However, the SLR camera system has serious disadvantages: 
     a) The hardware to pivot or otherwise move the mirror is complex and space-consuming. The mirror must be pivoted so its moving arc clears the objective lens, which means the mirror must be smaller, or the camera larger than would ideally be the case 
     b) The rapid and abrupt manner in which the mirror must pivot up and then down causes shock and vibration as the mirror impacts its hardware. This vibration makes it difficult to get a high resolution image on the film. 
     c) The noise generated by the mirror impacting its hardware makes wildlife and certain other types of photography difficult. 
     Some solutions of these problems have been proposed by the following: Ochai and Kato (U.S. Pat. No. 3,757,661, granted Sep. 11, 1973), Ohmori (U.S. Pat. No. 3,911,454, granted Oct. 7, 1975), and Kanno (U.S. Pat. No. 5,715,003, granted Feb. 3, 1998), have devised a mechanism for sliding the mirror horizontally out of the picture frame. Waaske (U.S. Pat. No. 3,967,290, granted Jun. 29, 1976), Schiff and Rikis (U.S. Pat. No. 3,785,270, granted Jan. 15, 1974), Sadre-Marandi et al. (U.S. Pat. No. 4,659,202, granted Apr. 21, 1987), and Lindenfelser (U.S. Pat. No. 4,750,012, granted Jun. 7, 1988), have devised a mechanism for sliding the mirror vertically out of the picture frame. Celenze (U.S. Pat. No. 4,758,853, granted Jul. 19, 1988) has a combination flexible mirror/shutter, which reflects the image to a viewfinder, then displaces to present a slot through which the image reachs the film. Although these mechanisms solve some of the problems mentioned above, none solve the problems of vibration and noise, and they are generally complicated, bulky and space consuming. 
     Also, a camera using a fixed, half-silvered pellicular mirror has been sold by Canon under the trademark Pelix. This camera solves the vibration problem, but at the expense of a compromised image brightness on the viewfinder screen and on the film surface. 
     OBJECTS AND ADVANTAGES 
     Accordingly, one object of this invention is to overcome the shortcomings and disadvantages of the typical single-lens-reflex camera by: 
     a) virtually elilnating vibration and noise in the mirror moving mechanism of an SLR camera, making higher resolution images possible, 
     b) providing an SLR camera with a simple mirror moving apparatus which is very rigid and rugged, with few moving parts, which will keep the mirrors in alignment under the most severe conditions, assuring increased reliability and trouble-free service, and 
     c) providing an SLR camera in which the mirror is close to the rear of the objective lens, allowing a larger mirror, and a brighter image on the viewing screen, as well as a smaller and more compact camera. 
     Other advantages will become apparent from reading the following sections and perusing the accompanying drawings. 
     SUMMARY 
     A simple and rugged mirror system for an SLR camera virtually eliminates camera movement, noise, and vibration caused by mirror action. It utilizes a pair of dynamically balanced bi-parting sliding mirrors, which, in a contiguous (normal) position reflect an undistorted image to the viewing screen, and which slide apart to allow the image then to pass through an aperture to the rear of the camera to record the image. Thereafter they return to their contiguous position. 
    
    
     DRAWINGS 
     FIG. 1 is a simplified isometric view of the optical components of an SLR camera according to my invention, illustrating its basic operation. 
     FIG. 2 is a vertical section through the SLR camera. 
     FIG. 2 a  is an enlarged detail through the mirror moving apparatus of FIG. 2, taken along the line  2   a—   2   a  of FIG.  7 . 
     FIG. 3 is an elevation of the mirror moving apparatus of the camera, taken along line  3 — 3  of FIG. 2, with mirrors in closed position. 
     FIG. 4 is a horizontal section through the apparatus of FIG. 3, taken in the direction indicated by line  4 — 4  in FIG.  3 . 
     FIG. 5 is an elevation similar to FIG. 3, with mirrors in open position. Mirrors in an intermediate position are shown by dashed lines. 
     FIG. 6 is a horizontal section through the apparatus of FIG. 5, taken in the direction indicated by line  6 — 6  in FIG.  5 . 
     FIG. 7 is an enlarged elevational view of principal mirror moving components, with the supporting pylon indicated by ghost lines. 
     FIG. 8 is an enlarged sectional view of a mirror and its guidance system. 
     FIG. 9 is a view of mirror and housing taken along line  9 — 9  of FIG. 8, 
     FIG. 10 is an enlarged detail of meeting edges of the mirrors. 
     FIG. 11 is an enlarged cross section of the mirror operating bar and its drive system taken on line  11  of FIG. 4 (moving the bar to the right). 
     FIG. 12 is an enlarged cross section of the bar and its drive system taken on line  12  of FIG. 6 (moving the bar to the left). 
     FIG. 13 is an elevation of a pawl and escapement wheel used to position a cam in the drive system which controls the lateral movement of the bar. 
     FIG. 14 is an enlarged plan view of a drive system for the bar. 
     FIG. 15 is an enlarged elevation of the drive system. 
     FIG. 16 is a section taken along line  16 — 16  of FIG. 11, showing a spring, a spring winding gear, and a spring housing of the mirror moving mechanism. 
    
    
     REFERENCE NUMERALS 
       14  camera body 
       16  image path 
       18  lens 
       19  diaphragm 
       20  mirrors 
       22  viewfinder screen 
       24  field lens 
       26  pentaprism 
       28  eyepiece 
       30  mirror moving app. 
       32  mirror upper guide 
       33  aperture 
       34  mirror lower guide 
       36  shutter 
       38  film 
       40  bar 
       42  gear 
       44  flanged support wheel 
       46  geared boss 
       48  wheel 
       50  connecting rod 
       52  mirror flange 
       54  pylon 
       56  eyepiece cap 
       58  sliding strip 
       60  resilient spacer 
       62  mirror housing 
       64  light seal 
       66  bar  40  drive system 
       68  pawl 
       70  pinion gear 
       72  shaft 
       74  bar  40  rack for g&#39;r  42   
       76  lower rack for gear  70   
       78  upper rack for gear  70   
       80  driving spring 
       82  spring housing and bearing 
       84  winding gear 
       86  compresson spring 
       88  spring retainer cap 
       90  cam 
       92  attachment bracket 
       94  shutter lever 
       96  camshaft 
       98  escapement wheel 
       100  winding gear 
       104  spring housing and bearing 
       106  wind&#39;g gear pawl 
       108  camera gear train 
     DETAILED DESCRIPTION 
     Description—FIG.  1 . 
     FIG. 1 is a simplified isometric view showing the main optical components and their relationship in my SLR camera. The components are a lens  18 , a viewing screen  22 , an aperture  33 , and a film strip  38 . Also indicated is a mirror moving apparatus  30 , which comprises two mirror housings  62  and coplanar left and right mirrors  20  mounted within upper and lower guides  32  and  34  in a position to reflect an image from lens  18  to the viewing screen. The components parts of apparatus  30  are shown in FIG. 2, and are described below. 
     Operation—FIG.  1 . 
     Prior to picture taking, mirrors  20 , in closed position (as shown), reflect an image from lens  18  to viewing screen  22 . After the shutter button (not shown) is depressed, the mirrors slide apart and into housings  62 , (as shown by the arrows), allowing the image to pass through aperture  33  and to be recorded upon film  38 . The mirrors then return to their closed position. Since the mirrors are balanced, and their motions are opposed to each other, and since there is no abrupt impacting of any hardware, the mirror moving sequence is quiet and vibration-free. 
     Description of mirror moving apparatus  30 —FIGS. 2-16. 
     FIG. 2 is a cross section through the camera showing apparatus  30 , which is rigidly fixed within a camera body  14 , and other usual elements of an SLR camera, such as a viewing screen, a pentaprism, a shutter, an eyepiece, etc. 
     Apparatus  30 , the essence of the mirror system, comprises a bar  40 , gears  42 , support wheels  44 , wheels  48  with bosses  46 , connecting rods  50 , mirrors  20 , aperture  33 , housings  62 , pylons  54  and a drive system  66 . FIG. 2 a  shows the apparatus in greater detail, and FIGS. 3-6 show the relationships of the parts more clearly. The parts will now be described in detail: 
     Bar  40  (FIGS. 11-12) is in the general shape of a channel with unequal legs. Rack gears  74  are situated on the upper face of its shorter upper leg, in positions to mesh with gears  42  at either end (FIG.  7 ). The lower face of its upper leg contains an upper rack  78 , and the upper face of its lower leg contains a lower rack  76 , situated to mesh alternately with a pinion gear  70  of drive system  66 , which drives the bar laterally, and will be described later. 
     Gears  42  (FIG. 7) are situated between bar  40  and the geared bosses  46  on wheels  48 , and are meshed with each. They translate the lateral motion of bar  40  to a rotary motion of the wheels. 
     Support wheels  44  (FIG. 7) are situated below bar  40  to keep bar  40  meshed with gears  42  and drive system  66 . Flanges on the wheel rims keep bar  40  aligned. 
     Wheels  48  (FIG. 7) are provided with geared bosses  46 , which engage gears  42 . As mentioned above, gears  42  also engage racks  74  on bar  40  (FIGS. 3,  6 , and  7 ) to translate a lateral motion of the bar to a rotary motion of bosses  46  and wheels  48 . The wheels are sized so that the connecting rods  50 , in a first position (FIGS.  3 - 4 ), extend to hold mirrors  20  in a closed position, and in a second position (FIGS.  5 - 6 ), after the wheels have rotated 180°, the rods separate the mirrors and move them into housings  62 , clear of aperture  33 . 
     Connecting rods  50  (FIGS.  3 - 6 ). are pivotally connected to mirrors  20  and wheels  48 , and translate the rotary motion of wheels  48  to a lateral, sliding motion of mirrors  20 . 
     Pylons  54  (FIGS. 2,  2   a  and  3 - 6 ) are structures rigidly attached to camera body  14 , and hold support wheels  44 , gears  42 , and wheels  48 , which are pivotally connected to the pylons, and drive system  66 , which is rigidly attached to the right-hand pylon, in the correct relationship. 
     Mirrors  20  (FIGS. 8-9) are sized to provide a light seal within guides  32  and  34 . Resilient spacers  60  are attached to mirrors  20  to assure that, because of their spring action, the mirrors are in planar alignment when adjacent and stationary, and do not bind on guides  32  and  34  or housings  62  when moving. When in the adjacent and stationary position they reflect an undistorted image to viewing screen  22 . A projecting sliding strip  58  is provided at the tops and bottoms of mirrors  20 , (FIG. 8) to assure that mirrors  20  will not be scratched or damaged while sliding. The meeting edges of mirrors  20  have flanges  52  (FIG.  10 ), which reinforce the meeting edges and provide operating clearance for connecting rods  50 , to which they are pivotally connected. Flanges  52  also include a light seal  64  (FIG.  10 ). Because the mirrors only reflect divergent rays of the image to be focused upon viewing screen  22 , the line of their meeting edges will not appear on the screen. 
     Aperture  33  is formed by top and bottom guides  32  and  34  and the inboard edges of housings  62  (FIG.  5 ). 
     Housings  62  (FIGS. 1,  6 , and  8 - 9 ) are enclosures which receive and protect mirrors  20  when the mirrors are in their retracted (open) position. 
     Drive system  66  (FIGS. 11-16) initiates and controls the lateral motion of bar  40 , and is comprised of two parts. A first part (FIGS. 11-12) includes pinion gear  70 , a shaft  72 , a driving spring  80 , a winding gear  84 , a compression spring  86 , and a spring retainer cap  88 . A spring housing  82  is rigidly attached to the right-hand pylon  54  by a mounting bracket  92 . (FIG.  16 ). The assembly of gear  70 , shaft  72 , and spring retainer cap  88  is urged by spring  80  to rotate clockwise. It also slides laterally to enable gear  70  to engage alternately racks  76  or  78  of bar  40 , as positioned by a cam  90  (described below), in conjuction with compression spring  86 . 
     When shifting between racks  76  and  78 , gear  70  momentarily meshes with both racks, thereby locking bar  40  and preventing gear  70  from rotating. The edges of racks  76  and  78 , and gear  70  are beveled so as to mesh smoothly during the changeover. 
     A second part of system  66  (FIGS. 14-15) includes an escapement wheel  98  and a pawl  68  (FIG.  13 ), cam  90 , a camshaft  96 , a spring  102 , and a spring winding gear  100 . A spring housing  104  is rigidly mounted on camera body  14 . The assembly of wheel  98 , camshaft  96 , and cam  90  rotates counterclockwise to position gear  70  laterally so as to engage racks on bar  40  alternately as described above (FIGS.  11 - 12 ). 
     Escapement wheel  98  (FIG. 13) is in the shape of two half-circles, offset so as to create two flat faces on the rim, separated by 180°. When pawl  68  is lifted, wheel  98  is allowed to rotate 180°, at which point the pawl, spring-loaded to ride against the wheel, drops into the next notch and the rotation is arrested. 
     Cam  90  is in the shape of an ellipse with an eccentric shaft so located that in a first position it causes pinion gear  70  to engage lower rack  76  of bar  40  (FIG. 12) and in a second position it causes gear  70  to engage upper rack  78  (FIG.  11 ). 
     Spring housings  82  and  104  include low-friction shaft bearings to assure proper alignment of the shafts. 
     Operation of mirror moving apparatus  30  (FIGS. 3-16) 
     To start the mirror moving sequence, pawl  68  (FIG. 13) momentarily lifts from one notch of escapement wheel  98  to allow the wheel, urged by spring  102 , (FIGS. 14 and 15) to rotate counterclockwise. It then follows the wheel and drops to engage the approaching opposite notch to prevent further rotation. This rotates the assembly of escapement wheel  98 , camshaft  96 , and cam  90  180°. In this first position (FIG.  12 ), cam  90 , by rotating against spring retainer cap  88 , (now a cam follower), urges gear  70  to engage lower rack  76  of bar  40 . 
     Pinion gear  70  is urged by spring  80  to rotate clockwise. Now engaged with lower rack  76  of bar  40 , it moves the bar to the left (FIG.  7 ). As bar  40  moves to the left, gears  42 , rotating clockwise, translate this lateral motion into a counterclockwise rotation of wheels  48  through geared bosses  46 . Through connecting rods  50 , which connect wheels  48  to mirrors  20 , the mirrors separate and retract into housings  62  (FIGS. 5-6) 
     Shutter  36  then opens and thereafter closes to expose film  38 . After this the mirror movements are reversed. Pawl  68  again lifts and drops to permit the assembly of escapement wheel  98 , camshaft  96 , and cam  90  to rotate counterclockwise 180°. From this first position (FIG.  12 ), the rotation of cam  90  allows gear  70  to disengage from lower rack  76  and to engage upper rack  78  of bar  40  (FIG.  11 ). Gear  70 , always rotating clockwise, then moves the bar to the right. As bar  40  moves to the right, gears  42  rotate counterclockwise to translate this lateral motion into a clockwise rotation of wheels  48  through geared bosses  46 . Through connecting rods  50 , the mirrors are then drawn from housings  62  and returned to their original adjacent position (FIGS.  3 - 4 ). 
     Driving spring  80  has a residual tension to keep pinion gear  70  acting on upper rack  78  (FIG.  11 ). Gear  70  urges rack  78  to the right to maintain the position of bar  40  in a mirrors closed position (FIG. 3) at all times that mirrors  20  are not open. 
     As wheels  48  rotate (FIGS.  3 - 6 ), the velocity of mirrors  20  follows a sinuous curve, gradually starting from zero when they are at their adjacent (closed) position, to a maximum when partialy separated, and back to zero at their fully separated (open) position. As mirrors  20  return to their adjacent position, this process reverses. Because of this gradual starting and stopping, there will be no sudden impacts or noise caused by the movement of mirrors  20 . Since mirrors  20  move in opposite directions, their inertial forces cancel each other, resulting in substantially noiseless and vibration-free operation. 
     Description and operation of spring winding gears  84  and  100  (FIG.  16 ). 
     Winding gear  84  engages gear  108  (a part of a film advancing mechanism, not shown). As gear  108  rotates, gear  84 , through shaft  72 , creates tension in driving spring  80 . Through this energy, spring  80  rotates pinion gear  70  to drive bar  40 . A pawl  106  is located on winding gear  84  to prevent the gear from rotating in a counter-winding direction. In a similar manner, winding gear  100  (FIGS. 14-15) tensions spring  102  to rotate the assembly of escapement wheel  98 , camshaft  96 , and cam  90 . 
     Detailed Operation—FIGS. 1-16 
     The above descriptions cover the component systems and their operation. The overall operation of the entire camera will now be covered. 
     By a known mechanism (not shown), generally by rotating a lever or knob, film  38  (FIGS. 1 and 2) is advanced to present an unexposed segment of film properly aligned to receive an image from lens  18 . This film advancing action, through well known systems of gear trains and other linkages (not shown), is also used to create tension in driving spring  80  (FIGS. 11,  12  and  16 ) and cam spring  102  (FIGS.  13  and  14 ). Springs for other camera functions, such as shutter operation, eyepiece cap operation, stopping of a diaphragm to a pre-set position, a self timing operation, etc., are also tensioned by this action. 
     As shown in FIG. 2, an image travels along path  16  through lens  18  and is reflected upward to viewing screen  22  for focusing and composing the image. The image, now inverted, passes through field lens  24  and pentaprism  26 , which erects and redirects the inverted image, and the user views the image through eyepiece  28 . The user positions the camera to align the image as desired in the viewfinder. 
     When the user is satisfied with the image, the user presses a conventional shutter release button (not shown). This action, (through a mechanism not shown), lifts pawl  68  (FIG. 13) from the upper notch on escapement wheel  98  and then immediately releases it so that it rides against the wheel. The assembly of wheel  98 , camshaft  96 , and cam  90 , freed from the restraint of pawl  68 , and urged by spring  102 , then rotates in a counterclockwise direction. After 180° of rotation its movement is arrested by pawl  68  engaging a second notch on escapement wheel  98 . 
     This 180° rotation of cam  90  causes pinion gear  70  to disengage from upper rack  78  on bar  40  (FIG.  11 ), and urged by compression spring  86 , to engage lower rack  76  (FIG.  12 ). As can best be seen in FIG. 7, gear  70 , rotating in a clockwise direction, then drives bar  40  to the left. 
     As shown in FIGS. 3-6, and in more detail in FIG. 7, as bar  40  moves to the left, gears  42 , meshed with rack  74 , rotate clockwise. Since gears  42  also engage geared bosses  46  on wheels  48 , the wheels then rotate in a counterclockwise direction. Because of this, connecting rods  50 , which are pivotally connected to wheels  48  and flanges  52  on mirrors  20 , cause the mirrors to separate and slide within guides  32  and  34  until they are moved fully into housings  62 . This leaves an unobstructed passage through aperture  33  for the image to fall upon shutter  36  (FIG.  2 ). 
     Mirrors  20  are dynamically balanced. As stated, their velocity is controlled by wheels  48  (FIG.  5 ), so that they move smoothly from a zero velocity to a maximum and then back to zero. This virtually eliminates any noise or vibration from the mirror movement. 
     As bar  40  nears its most leftward position (FIG.  6 ), with mirrors  20  in their open positions, it strikes and deflects shutter lever  94 . By known means (not shown), this causes shutter  36  to open and then close for a pre-set time to allow the image to be recorded on film  38  (FIG.  2 ). As shutter  36  closes, a further known mechanism (not shown) is activated to causes pawl  68  (FIG. 13) to be lifted again from the upper notch on escapement wheel  98 . The assembly of wheel  98 , camshaft  96 , and cam  90 , now freed from the restraint of pawl  68 , and urged by spring  102 , rotates counterclockwise another 180°. After this the movement is again arrested by pawl  68  engaging with the second notch on escapement wheel  98 . 
     Cam  90 , in this new position (FIG.  11 ), has urged pinion gear  70  to disengage from lower rack  76  on bar  40  and to engage upper rack  78 . Gear  70 , always rotating clockwise, now moves bar  40  to the right, causing wheels  48  to rotate clockwise. Mirrors  20 , pivotally connected to wheels  48  through connecting rods  50  (FIG.  5 ), now move smoothly from housings  62  back to their original (mirrors closed) position (FIG.  3 ). 
     A known mechanism (not shown) causes eyepiece cap  56 , (FIG.  2 ), to be closed when mirrors  20  are open. This prevents ambient light from entering the camera through the eyepiece and deleteriously affecting film  38  as a photographic exposure is made. 
     Thus, when the user depresses the shutter button, mirrors  20  move swiftly, smoothly and noiselessly out of the way of the image so it can then pass through aperture  33  (FIGS. 56) and fall upon shutter  36  and film  38  (FIG.  2 ). The lack of vibration and shock will result in a higher resolution image being recorded on the film. The return of mirrors,  20  to their closed and reflecting positions (FIGS. 1 and 3) is accomplished similarly with virtually no noise or vibration. 
     CONCLUSION 
     As will be understood from the above discussions and drawings, my camera mirror system has numerous advantages over today&#39;s typical single-lens-reflex systems, namely, 
     1) Its simplicity makes it less costly and easier to manufacture. 
     2) Most prior-art features of today&#39;s single-lens-reflex cameras, such as shutters, interchangeable and zoom lenses, built-in exposure meters, flash, exposure control devices and the like can be incorporated with little or no modification into a camera using my system. 
     3) Its noiseless performance will make it especially suitable for wildlife and candid photography. 
     4). It is adaptable to any size camera. 
     5). Its simple and rugged design makes it especially valuable for situations where a camera is subject to hard treatment. 
     6). The light weight and dynamic balance of the mirrors will allow faster mirror action with virtually no noise or vibration. 
     7) It can be used with any type of image recording medium. 
     RAMIFICATIONS 
     While the above description contains many specificities, these should not be considered limiting, but rather exemplary. Many ramifications are possible. 
     For example, the apparatus can be used in the type of camera in which the reflected image is viewed directly on the viewing screen The reflected image may be electronically recorded and viewed remotely. The apparatus can be used with any type of SLR camera using any type of recording medium, including 35 mm and larger and smaller film sizes, and digital cameras. Many different types of shutters can be employed, and methods other than a shutter release mechanism can be used to operate the camera. Many methods can be used to synchronize the various camera functions with my mirror moving system. A counterbalancing device can be introduced to eliminate any camera movement caused by lateral movement of bar  40 . Wheels  48  can be in the form of a lever. While mirrors  20  and aperture  33  are shown as rectangular, they can also form a trapezoid to more closely approximate the pattern of the image falling upon the oblique surface of apparatus  30 . 
     The above descriptions show a 35 mm single-lens-reflex camera using film, However, this method of moving the mirror out of the image path is particularly suitable for medium and large format single-lens-reflex cameras with their larger and heavier mirrors. It is also suitable for miniature cameras, where the compactness of this mirror moving system is advantageous, and for cameras using digitalized computer processing techniques rather than film. 
     Although what is shown is an apparatus mechanically driven by known means, such as springs tensioned by a film advancing operation, many other known techniques, such as electronically controlled electric circuits and motors, pneumatic devices, etc., can be employed to open and close the mirrors and operate the other camera functions with the same results. 
     SCOPE 
     Therefore, the scope of the invention should be determined by the following claims and their legal equivalents, rather than by the examples given.