referring more specifically to the drawings , fig1 illustrates schematically , in plan view , a first form of the invention comprising a motion picture two - camera arrangement which may be employed to photograph , and thus record , on motion picture film , left and right views of a visual scene to be subsequently projected for viewing in stereopsis . as seen , a three - dimensional visual scene , indicated generally at 10 , is simultaneously photographed by two standard motion picture cameras 12 , 14 positioned with their lens axes 16 , 18 in common plane and at right angles to each other . positioned on the lens axis of each camera and at a 45 ° angle thereto is a standard two - way mirror 20 of the type which reflects a portion of the light received on its surface , while transmitting the remaining portion therethrough . typically , the mirror may be constructed to reflect 50 % light while transmitting 50 % light such that the lens of each camera receives a view of the visual scene with equal intensity . each of the cameras are suitably supported on a base ( not shown ) to ensure that their lens axes are directed at all times in a common plane . camera 14 is adjustably mounted for incremental movement along an axis parallel to the lens axis 16 of camera 12 . by incrementally positioning camera 14 through a distance d along the axis of sight to the scene of camera 12 , the effective lens base separation d of the two cameras may be varied . thus , as shown , the lens of camera 12 receives a left view of the visual scene 10 which passes through the mirror , while the lens of the camera 14 receives a right view of the visual scene which is reflected by the mirror . obviously , other means may be devised for similarly obtaining an effective lens base separation between the lenses of the two cameras , such as prisms , angular mirrors , or the like . preferably , the lenses of the cameras are positioned to provide parallel lines of sight 16 &# 39 ;, 18 &# 39 ; to the visual scene to be recorded . the support base for the two cameras is , in turn , adjustably supported in suitable manner so that the cameras 12 , 14 may be moved simultaneously in any direction to record a visual scene while maintaining the lens axes of the cameras in their proper relationship , as described . to record a visual scene on photographic film , the dual cameras 12 , 14 are synchronized , frame for frame , and simultaneously operated at a 24 frame per second filmspeed to take corresponding left and right view pictures of the scene . as previously indicated , for proper reproduction of the recorded scene in stereopsis , the effective lens base separation , d , of the cameras must be maintained at all times at a distance of no more than about 1 inch , with about a 1 / 2 inch lens base separation being employed for recording most visual scenes . experimentation has indicated that the lens base separation may be varied between from about 1 / 8th inch to 1 inch , depending on the distance from the recording camera system to the nearest non - moving objects , as will be explained . it has been found that lens base separations of less than about 1 / 8th inch do not show sufficient depth in the projected scene , while separations of greater than 1 inch cause the projected picture solidarity to be broken . as further indicated in fig1 the live visual scene 10 may typically contain a nearest non - moving object , such as bush 21 , an intermediate moving object or objects such as live actors 22 , a more distant non - moving object , such as a house 23 , and extremely distant non - moving objects , such as mountains 24 . in such case , and with a fixed - position camera system , the object of principal concern in establishing control parameters of the recording cameras 12 , 14 , is the nearest non - moving object in the scene , or bush 21 . the actual or approximate distance f from the recording cameras 12 , 14 to the bush 21 is determined and the lens base separation d between cameras selected in accordance with chart recommendations set forth in fig7 as will be explained . the center of focus of the lens system of camera 12 is adjusted in known manner to a central focal point distance which is two - thirds of the distance f to bush 21 , while the lens system of camera 14 is set at a central focal point distance which is one and one third of the distance f . thus the central focus of the two recording cameras are set respectively to fall in front of and beyond nearest non - moving object 21 by approximately one - third of its distance from the cameras . assuming that distance f is 12 feet , focus of camera 12 would be set at 8 feet while focus of camera 14 would be set at 16 feet . the scene is then simultaneously recorded by both cameras . after recording the visual scene , the filmstrips from the left and right cameras 12 , 14 are developed , and a single filmstrip containing left and right camera film frames is obtained . as illustrated in fig2 the left and right view filmstrips 25 , 26 from the respective left and right cameras 12 , 14 of fig1 are combined to produce a single filmstrip 27 which may be projected on a two - dimensional surface for viewing in stereopsis . as illustrated , the developed left and right view filmstrips 25 , 26 are arranged , frame for frame , and sequential groups of frames of left views and right views are alternately combined to form the single filmstrip 27 for projection . in the example illustrated in fig2 the single filmstrip 27 is composed of the three consecutive right view frames r - 1 , r - 2 , r - 3 , followed by the three consecutive left view frames l - 4 , l - 5 , l - 6 . this alternating sequence of groups of consecutive right and left view frames is continued , i . e ., l - 7 , l - 8 , l - 9 , r - 10 , r - 11 , r - 12 ( not shown ), throughout the preparation of the single filmstrip 27 to provide a resultant filmstrip which , upon projection at 24 frames per second , produces a screen image of groups of alternating left and right views , each group visible to the eye of a viewer for approximately 1 / 8th of a second . the unused frames on the left and right filmstrips obviously may be similarly combined to form another filmstrip for stereoptic viewing , if desired . to insure minimum flicker or jump of the scene as right and left view images are alternately projected on the screen , it is desirable that the right and left frames be carefully positioned on the composite filmstrip so that the predominant non - moving objects in the record scene will appear as closely superimposed on the screen , as possible . the exact manner in which frame views of the left and right filmstrips are combined to form a single filmstrip , physically or by photographic reproduction , may vary , and conventional equipment well known in the motion picture industry which do not require actual cutting and splicing of the left and right view filmstrip frames may be employed . such equipment is well known and details thereof will not be described . the single composite filmstrip of sequenced left and right view frames is thereafter projected by a standard motion picture projector onto a two - dimensional screen , and the resultant pictures may be viewed in stereopsis by the unaided eye of the viewer . in the production of a motion picture film , the composite filmstrip may be edited to provide special effects or achieve desired continuity , as may be done with conventional two - dimensional motion picture films . although , in the example illustrated , alternating groups of three frames of left view followed by three frames of right view have been described , it has been found , through experimentation that variations may be made within a camera lens base separation of 1 / 8 inch to 1 inch , as well as within the 1 / 24 to 1 / 4 second image duration range of left and right view images on the projection screen , to obtain optimum stereoptic effect in certain situations . for example , if the closest non - moving object in the scene to be recorded is relatively close to the cameras , then the lateral lens base separation may be decreased to as low as about 1 / 8 inch without loss of stereoptic effect in the projected image . similarly , if the closest non - moving object is at relatively far distance , such as a mountain range , and no non - moving objects are nearer the point of recordation , the effective lens base separation of the two cameras can be increased to as much as 1 inch , with satisfactory stereoptic results on the projected image . it has been found that for normal filming of normal size objects within a 10 - 30 foot range , the best workable lens base separation for maximum depth without annoying disparate jump in the projected image is from about 1 / 4 to 3 / 4 inches , with 1 / 2 inch being preferred . if an extremely close non - moving object is to be recorded and projected in depth , the number of right and left frame views in each group of the composite film may be decreased to as low as 1 frame right , 1 frame left ( using a 24 frame per second camera and projector speed ) for a visual image duration of about 1 / 24 of a second per view on the projection screen . similarly , if the nearest non - moving object in the scene is a far distant object , it has been observed that the number of frames in each group may be increased to as much as 5 to 6 right or left views per group with satisfactory stereoptic effect in the reproduced image . thus as can be seen from the foregoing explanation , the optimum stereoptic effect in reproduction of a visual scene may be obtained for a particular distance and / or size of nearest non - moving object by maintaining a &# 34 ; tempo &# 34 ; within a range , that is , by slightly varying the lens base separation and the duration of observation of the right and left views on the projection screen , and by focus variations within the limits hereinbelow described . although the duration of visible observation of alternating left and right view images of the projection screen are preferably maintained equal for the same scene reproduction , it may be possible to slightly vary the durations between right and left views for a given scene without appreciably losing the stereoptic effect in the viewed scene . although the foregoing description has been directed to motion picture production with camera and projector speeds of 24 frames per second , the same lens base separation range of the camera , range of focus disparity between left and right views , and the same range of duration of visual observation of left and right views applies if camera and projector speeds are varied , as in slow motion , fast motion , or special effect situations . the number of film frames in each group would only be varied to maintain the time duration for visualization described . in the television field , dual television cameras may be employed , in a similar manner as described for motion picture cameras , and the electronic transmissions therefrom ( in the case of video tape or live television reproduction ) transmitted in alternating sequence of right and left view groups to provide the desired visual duration time between right and left views on the television receiver set . fig3 - 5a and 5b illustrate a modified form of the invention from that shown in fig1 and 2 wherein a single camera may be employed to alternately record predominantly left and right views of a three - dimensional visual scene on a single recording surface , or filmstrip , which may be projected onto a two - dimensional surface for stereoptic viewing by the unaided eye . fig3 illustrates diagrammatically in plan view the paths of light rays passing from a three - dimensional visual scene 30 through a single lens system 32 onto a single recording surface or filmstrip 34 . positioned in front of lens system 32 is a light blocking element , or opaque shutter 36 , which covers the entire left half of the lens system and precludes the passage of light rays r l from the left side of visual scene 30 from passing directly through the left side of the lens system onto the recording surface . the right half of the lens system remains unobstructed to permit passage of light rays r r and r l from the visual scene onto the recording surface . light rays r l from the left half of the visual scene are illustrated in broken lines , while the light rays r r from the right half of the scene are illustrated in solid lines . thus it can be seen that the total recording surface 34 receives a greater amount of light rays r r from the right half of the visual scene to produce a more predominant right view of the visual scene than the left view . correspondingly , when the blocking shutter 36 is moved to the position 36 &# 39 ; indicated by broken lines to cover the right half of lens system 32 , the recording surface will receive a greater amount of light rays from the left half of the visual scene and thus a predominant left view of the scene . the effect of the use of the blocking shutter on the lens system of a single lens camera with respect to lateral effective lens base separation of predominant right and left views is best illustrated by references to fig4 . when no blocking shutter is employed with the single lens system 32 , the effective functioning center of the lens system as to light rays passing therethrough is the actual geometric center 40 of the lens . however , when the left half of the lens system is blocked by the shutter 36 the functioning center of the lens system as to light rays passing therethrough becomes located at point 42 , in the center of the right half of the lens . correspondingly , when shutter 36 is located at 36 &# 39 ; to cover the right half of the lens system , the effective functioning center of the lens system as to light rays passing therethrough is located at point 44 , in the center of the left half of the lens . thus , by alternately blocking right and left halves of the lens system , as indicated in fig3 and 4 , the recorded scenes of alternating predominant left and right views have their respective virtual centers spaced by the lateral distance d between the effective center points 42 and 44 . in this manner , the alternating predominant right and left views are laterally spaced at a sufficient interocular distance , or effective lens base separation , to produce the necessary disparity therebetween , i . e ., less than about 1 inch , as in the two - camera system of fig1 and 2 , to record the desired three - dimensional effect on the recording surface or filmstrip . thus , it can be appreciated that a single lens motion picture camera with movable blocking shutter as illustrated in fig3 may be employed to record laterally spaced , predominantly right and left views of a visual scene on a single recording surface or filmstrip in accordance with the basic teachings of the present invention . by use of a single camera and lens system with single filmstrip recording surface , it is not necessary to edit film frames from two filmstrips , as in the two - camera system of fig1 and 2 , to obtain a single filmstrip for a three - dimensional projection and viewing in stereopsis . additionally , because the single lens system is employed to alternately record right and left views of the visual scene , the single lens and camera system eliminates the problem of focal length differences of the two lens systems of a two - camera arrangement and would give identical sizes at the image plane of the three - dimensional recording and would reduce shake or &# 34 ; keystoning &# 34 ; of the projected picture to a negligible amount . fig5 a and 5b illustrate , in side and front elevation view , respectively , a single lens motion picture camera apparatus which may be employed in carrying out the aforementioned modified embodiment of the present invention shown in fig3 and 4 . as shown , the visual scene 30 is photographed by the camera through a reciprocating shutter mechanism 50 comprising a support frame 52 having a generally rectangular shutter 54 slidably mounted for vertical movement in frame 52 by means of a variable speed motor 56 having a speed - control knob 57 and an eccentric crank arm 58 attached to the shutter 54 . shutter 54 comprises two diagonally opposed , opaque sections 60 , 62 and two corresponding clear sectons 64 , 66 ( fig5 b ). the camera 68 is supportably positioned such that the opaque shutter sections 60 , 62 during reciprocation of the shutter by variable speed motor 56 alternately block opposite halves of the lens to provide predominant right and left views of the visual scene being recorded . by adjusting the speed of the drive motor in reference to the film speed of the camera , one or more alternating frame groups of predominant left and right views of the visual scene are recorded on the single filmstrip of the camera . thus , depending upon the frame groupings selected to achieve optimum three - dimensional reproduction , as hereinbefore explained , the single camera and lens system may be effectively varied to record the three - dimensional visual scene for stereoptic viewing . the effective lens base separation , or disparity , of predominant right and left views from the single lens camera may be varied in accordance with the size and distance of the nearest non - moving object in the scene from the camera , as aforementioned , by means of the conventional light - control , variable diameter shutter located in the lens system of the camera . as is well known , the variable diameter shutter or stop setting adjustment 69 of motion picture camera 68 may be manually adjusted to correspondingly vary the effective diameter of the camera lens to allow more or less light to enter the camera and expose the film . thus by increasing or decreasing the effective diameter of the lens system , it can be appreciated that the distance d between the effective centers 42 , 44 of the predominant right and left views , as illustrated in fig4 is correspondingly varied to provide the optimum disparity between the views ( between about one - eighth inch and one inch ) for stereoptic viewing . to compensate for light changes in the recorded film images when the variable diameter shutter is adjusted , filters may be employed in known manner to provide the lighting desired . with a single lens system camera set - up as shown and illustrated in fig3 , 5a and 5b , focus disparity between right and left spaced views of the scene being recorded may be varied as hereinbefore described , with respect to the nearest non - moving object , by suitable electrical or mechanical focus control means employed during the recording of the scene to alternate the focus of the lens system in sequence timed with the blocking shutter mechanism 50 of the camera . the provision of such focus control means are believed to be well within the skill of the art and details thereof are not included herein . fig6 illustrates in plan view a further modified form of apparatus which may be employed in practicing the present invention . the apparatus comprises a two - camera system with two - way mirror having 50 % reflectivity and 50 % transmission characteristics as the mirror of fig1 . two cameras with single lens systems 70 , 72 are positioned at right angles with their central lens axes 74 , 76 directed to a common point on mirror 77 positioned at a 45 ° angle to the lens axes to direct the central lens axes along a common axis toward visual scene 78 . thus , light rays from visual scene 78 pass directly to the lens of camera 70 through the mirror and are correspondingly reflected to the lens system of camera 72 by the mirror . one - half of the lens system of camera 70 is permanently blocked by a fixed blocking element or shutter 80 , while corresponding half of the lens system of camera 72 is blocked by a fixed shutter 82 . thus , it can be seen that light rays r l predominantly from the left side of the visual scene 78 pass directly into the lens system of camera 70 while light rays r r predominantly from the right side of the visual scene are reflected into the lens system of camera 72 . the filmstrip of camera 70 thus records a predominantly left view of the visual scene while the flimstrip of camera 72 records a predominantly right view of the visual scene . the two filmstrips are thereafter edited , as described in the embodiment of the invention illustrated in fig1 and 2 , to produce a composite single filmstrip of alternating right and left view groups which may be projected to permit three - dimensional stereoptic viewing on a two - dimensional surface . the chart of fig7 illustrates graphically the range of synchronization between right and left view film frame groupings , and the variable distance between right and left views which may be controlled by a camera operator to provide optimum stereoptic recording , depending upon the size of and distance of the nearest non - moving object in the visual scene to be recorded . as previously mentioned , depending upon the size and distance of the nearest non - moving object , the alternating number of frame groups of left and right views as well as the lens base separation therebetween , may be increased or decreased within specified limits within the visio - psychological alternation rate between right and left views of the visual apparatus to achieve optimum stereopsis . as illustrated in fig7 for prominent non - moving objects of close regard , optimum stereoptic reproduction may be achieved with a conventional motion picture camera having a film speed of 24 frames per second by utilizing a frame group alternation rate of from about 1 left , 1 right to 2 left , 2 right at a 1 / 8 &# 34 ; to 1 / 4 &# 34 ; lens base separation between left and right views . for intermediate distance non - moving objects , the frame group rate may vary from about 2 left , 2 right to 3 left , 3 right with a lens base separation between right and left views of from about 1 / 4 &# 34 ; to 1 / 2 &# 34 ;. similarly , best stereoptic recording of far non - moving objects may employ from about a 3 left , 3 right , to a 4 left , 4 right frame grouping at a lens base separation of from about 1 / 2 &# 34 ; to 7 / 8 &# 34 ;. non - moving objects at infinity may be recorded with a frame grouping of 3 left , 3 right , to 5 left , 5 right at a lens base separation of from about 7 / 8 &# 34 ; to one inch . correspondingly , focus disparity between right and left views of the scene also may be varied in accordance with the aforementioned range of distances set forth hereinabove . thus , it can be appreciated that the camera operator , in recording the visual scene for stereoptic reproduction , whether with a dual camera arrangement as shown in fig1 and 6 , or with the single camera arrangement of fig3 - 5 , may control the frame grouping ratio and the lens base separation distance of left and right views within the limits illustrated in fig7 to obtain optimum stereoptic reproduction effect in the recorded scene . keystoning can also be further minimized by utilizing focus differentiation of the left and right views . it is contemplated that a basic concept of the present invention , i . e ., the simultaneous recording of predominant left and right views of a visual scene from laterally spaced positions less than one inch apart may be employed to convert conventional two - dimensional motion pictures for visualization in stereopsis . as shown in fig8 a conventional two - dimensional motion picture may be projected by a projector 90 through a shutter mechanism 92 of the type described in fig5 a and 5b onto a translucent receiving surface or screen 94 . the scene on the screen is continuously recorded by a conventional motion picture camera 96 located behind the screen . by coordination of the speed of operation of the blocking shutter mechanism to the degree of motion of objects in the scene , the projector operator may create a visual stereoptic effect for recording by camera 96 . in the embodiment of fig8 the disparity , i . e ., the distance between lens bases , of predominant left and right views is not varied , as in the embodiments of fig1 - 7 . instead the motion picture projector operator depends upon the movement of objects of regard in the two - dimensional motion picture film to create the necessary disparity between left and right views to create the stimulus for stereoptic recording . for example , the blocking shutter mechanism 92 is controlled and regulated by observation of the particular scene and movement therein being projected on the translucent screen 94 . if the scene being projected on the screen has fast action or if the camera is moving and the nearest movement in the scene is close , the film frame group alternation to achieve stereopsis may be from about one left , one right to about two left , two right . if the same conditions in the scene exist except that movement in the scene is at intermediate distance , then a two left , two right to three left , three right film frame group alternation may be employed . for far movement in scenes , three left , three right to four left , four right may be employed , while at infinity , the alternation of the shutter between about four left , four right to five left , five right may provide best stereoptic reproduction . it can be understood that blocking shutter apparatus other than that shown in fig5 a and 5b may be employed to alternately block left and right halves of the camera lens of the motion picture projector lens . for example , a rotating disc shutter may be utilized to create the blocking effect , so long as the shutter may be regulated by the operator to provide the film frame right left tempo groupings desired for stereoptic reproduction .