fig1 - 3 shows generally a visual fields testing system including a projector - camera housing 10 in which is mounted the mirror mechanism 12 . the housing 10 includes a front wall 14 and a rear wall 16 , having apertures 18 , 20 respectively which can be opened or closed by a projection shutter indicated diagrammatically at 22 and film shutter indicated diagrammatically at 24 . the mirror mechanism 12 includes a double faced mirror 26 having a front face 28 and a rear face 30 . the mirror 26 is arranged so that it will reflect a collimated light beam 32 from a projection light 34 , mounted to a sidewall 36 of the housing 10 through the projection shutter 22 and onto the projection screen 38 . the opposite sidewall 40 of the housing 10 supports a second light source 42 which directs a beam of light 44 toward the rear face 30 of the mirror 26 along the same axis as that of the light beam from the projection light 34 . the beam from the recording light source 42 is reflected from the mirror surface 30 in a direction which is opposite that of the reflected projection beam 32 from the front face 28 of the mirror 26 . the recording light beam 44 is directed toward a film plane , indicated diagrammatically at 46 and disposed at the rear of the housing 10 by any of a variety of well - known film holding devices 48 . the double faced mirror 26 thus directs the projection beam 32 to a selected location on the screen and simultaneously directs the recording beam 44 to a corresponding location in the film plane 46 , depending on the attitude of the mirror 26 . the mirror 26 is mounted for adjustable movement by the mirror mechanism 12 in which the mirror 26 is rotatable about each of a pair of perpendicular axes . the mirror mechanism includes a support block 50 which is secured to the interior of the housing 10 . the mirror mechanism 12 includes a driven bevel gear segment 52 . the mirror 26 is secured with respect to and across the diameter of gear 52 by a bracket 54 and lies in a plane perpendicular to that of the gear 52 and which coincides with the axis of rotation of the gear 52 . the mirror 26 and gear 52 are supported for rotation in unison about the rotational axis of the gear 52 by means of a yoke 56 having low friction bearings 58 , 60 which support the upper edge of the mirror , by bracket 62 , and the opposite face of the gear 52 , by bracket 54 , to enable the mirror 26 and gear 52 to rotate in unison about the common axis defined by the bearings 58 , 60 . the yoke 56 is mounted for rotation about a horizontal axis perpendicular to the axis defined by bearings 58 , 60 to rotate the mirror 26 and gear 52 bodily about that horizontal axis . to this end the yoke 56 is secured to the end of an outer cylinder 64 which is rotatably mounted within a cylindrical cut - out 61 formed along one side of the block 50 as by ball bearings 63 which are securely mounted to the cut - out 61 . the cylinder 64 has a worm gear 66 secured thereto which is driven by a worm 68 which is driven , in turn , by a stepping motor 80 mounted to the block 50 . the worm 68 is disposed within a bore 69 formed in the block 50 and may be supported by bearings 71 . the mirror 26 and gear 52 are driven with respect to the yoke 56 by means of an inner cylinder 72 which extends through the outer cylinder 64 . an end of the inner cylinder 72 extends into and is journaled to the yoke at bearing 73 . the other end of the inner cylinder 72 extends rearwardly beyond the end of the outer cylinder 64 . the rear , protruding end of cylinder 72 has a collar 75 secured thereto and the collar 75 is rotatably mounted within cut - out 61 of the block 50 by bearing 77 . a bevel gear 74 is secured to the end of the inner cylinder 72 which projects into the yoke 56 and meshes with the driven beveled gear 52 to which the mirror is mounted . the inner cylinder 72 is rotated by means of a worm gear 76 secured to the collar 75 . gear 76 is driven by a worm connected to the drive shaft 78 of stepping motor 70 in the same manner as described above with regard to worm 68 . the stepping motors 70 , 80 are operated in response to appropriate electrical signals from the controlling electronic circuitry to pulse the motors incrementally to their intended positions . the motors 70 , 80 may be selected from a wide variety of commercially available devices and preferably are reversible . the recording light 42 is mounted in the housing and extends into the rearward end of the cut - off 61 in the block in alignment with the axis of rotation of the cylinders 64 , 72 . the recording light thus passes axially through the hollow inner cylinder 72 and , if desired , suitable lenses , such as suggested at 79 may be mounted within the hollow inner cylinder 72 to maintain the light beam collimated . the projection light source 34 is mounted to the opposite side wall of the housing , also in substantial alignment with the axis of rotation of the cylinders so that both light beams will be directed substantially along the same horizontal axis and will be reflected in substantially opposite directions . it may be noted that the axis of rotation of the mirror defined by the bearing 58 , 60 is a movable axis in that it intersects , perpendicularly , and is rotatably about the horizontal axis of the cylinders 64 , 72 . it may be noted further that operation of one of the step motors 70 , 80 usually will result in movement of the mirror in a compound direction , e . g ., rotation of the yoke alone usually will also cause some rotation of the mirror about the axis defined by its bearings 58 , 60 . when such compound motion is not desired , it may be corrected by operating the other of the stepper motors in a reverse direction to compensate and drive the inner cylinder to return the mirror to its desired position about the movable axes . this may be accomplished by suitable electronic control of the stepping motors 70 , 80 and reference is made to an application of marvin e . jernigan filed of even date herewith for a description of one such control system . similarly , the operation of the projection and recording lights as well as the projection and recording shutters may be controlled electronically as described in said application . the invention is illustrated as being employed in connection with a visual fields testing system which may also include a partially reflective plate 82 mounted above and forwardly of the housing 10 so as to be directly in front of the subject &# 39 ; s view when his head is properly placed in the head rest and chin support 84 . plate 82 is adapted to enable the subject to view the screen 38 and is disposed at an angle to his general line of sight to enable a light source 86 , preferably infrared , to reflect from the plate 82 and illuminate the subject &# 39 ; s eyes . the image from the subject &# 39 ; s eyes is , in turn , reflected from the plate 82 toward an imaging arrangement 88 which includes a ground glass screen 90 on which the reflected image of the subject &# 39 ; s eye may be focused , employing the technique described in the aforementioned u . s . patent . as described in that patent a pair of vertically spaced photoelectric cells 92 and horizontally spaced photoelectric cells 94 are located on or adjacent the screen 90 and are aligned with selected regions of the image of the subject &# 39 ; s eye on the screen 90 . variations in the output signals from the photocells 92 , 94 are dependent on the direction and magnitude of the subject &# 39 ; s eye movements and their signals may be electronically processed . imaging arrangement 88 preferably is mounted for adjustment to the housing 10 to facilitate initial alignment of the photocells 92 , 94 with the subject &# 39 ; s eye image on the screen 90 . this may include a bracket 96 pivoted for horizontal movement to the housing 10 and a vertical elevation screw 98 carried by the bracket 96 and in engagement with the end of the barrel 100 , the other end of the barrel 100 being pivoted to the bracket at trunnions 102 . while the invention has been described primarily for use in a visual fields testing system , it may be employed in other environments where it is desirable to control the direction of a beam of light . it should be understood that the foregoing description of the invention is intended merely to be illustrative thereof and that other modifications and embodiments may be apparent to those skilled in the art without departing from its spirit .
an apparatus for measuring and evaluating a subject &# 39 ; s visual field includes a projector for presenting a target image , consisting of a spot of light , at a series of selected locations within the subject &# 39 ; s visual field . a mirror is mounted for movement about a pair of axes and is rotated to a desired attitude by step motors which control the position of the mirror about the respective axes . a light beam is directed toward the mirror and is reflected in a direction dependent on the attitude of the mirror as controlled by the step motors .