Abstract:
An improved motion picture film projector ( 100 ) comprises a Geneva Mechanism ( 120 ), which intermittently drives a film ( 114 ). A light source ( 116 ) projects light through the film ( 114 ) and a shutter ( 106 ) periodically interrupts the light source ( 116 ). The shutter ( 106 ) has a blade with a shaped edge, which matches the frame shape on the film ( 114 ) thus, increasing the amount of light that is transmitted through the film ( 114 ). A second edge of the blade also matches the frame shape on the film ( 114 ) further increasing the amount of light transmitted through the film ( 114 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned copending U.S. patent application Ser. No. 09/329,841, filed Jun. 11, 1999, entitled GENEVA MECHANISM AND MOTION PICTURE PROJECTOR USING SAME, by Kirkpatrick et al., the disclosure of which are incorporated herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to the design of light shutters as used in motion picture film projectors. More particularly, the present invention relates to improved shutter designs, which can be used in cinema projectors of standard design, as well as in projectors with improved Geneva Mechanisms and improved illumination systems. 
     BACKGROUND OF THE INVENTION 
     Generally speaking, the state of the art motion picture film projector is little changed from those produced in the 1950&#39;s, when the advent of robust color films and xenon arc lamps encouraged the manufacturer&#39;s to make design changes. The most basic mechanisms within film projectors, such as the intermittent drive, the shutter, and the projection lens, can be seen in the earliest patents; such as U.S. Pat. No. 93,594 (O. Brown, 1869). Although at present, some manufacturers are producing re-designed projectors with modularity, stepper and servo motor drives, and modern control circuitry, the basic system design is still relatively unchanged. Thus, there continue to be opportunities to make design improvements to a classic opto-mechanical system like the motion picture film projector. 
     In a standard projector, the film is intermittently advanced by a Geneva Mechanism, also known as a “Maltese Cross,” until an image frame is in alignment with the projection aperture. The film is then held stationary for a discrete time period during which light is passed through the aperture, film frame, projection lens, and onto a screen. This intermittent frame-by-frame motion of the film is enabled by the Geneva Mechanism, which comprises one portion, the driver, which rotates continuously, and which causes intermittent rotation of a second portion, the star wheel. In a motion picture projector the star wheel is mounted on a central shaft with a sprocket, the teeth of which are engaged with perforations in the film. Therefore, when the driver moves the star wheel, both the star wheel and the film experience a resulting intermittent motion. As motion picture film is typically projected at a rate of 24 frames per second, a new film frame is positioned in the projection aperture every {fraction (1/24)} second, or approximately 42 ms. The standard Geneva Mechanism used in cinema, much as described is U.S. Pat. No. 1,774,789 (Dina), moves each film frame into the projection aperture with an indexing time of one-fourth of the frame period, or approximately 10.5 ms. 
     It is necessary to block or shutter the light to the screen during these indexing times to prevent the perception of image smearing or travel ghost by the audience. The typical shutter used in a motion projector is a simple sheet metal disc, which has two blades whose edges extend radially from a center hub, which is mounted to a drive shaft. The shutter is typically positioned between the light source and the film gate, and periodically blocks the light incident to the film through the projection aperture. Shutter design involves a set of trade-off&#39;s around light efficiency, the perception of flicker, and the perception of travel ghost. It happens that human perception of flicker or strobing peaks near the 24 Hz operating frequency of film projectors. To prevent the perception of flicker, the typical shutter has two blades, thereby blocking the light twice per frame (one blockage corresponding to the film indexing time), which raises the apparent illumination frequency to 48 Hz, where flicker perception is significantly reduced. Some systems have even employed three bladed shutters, to yield an effective frequency of 72 Hz, where flicker is barely perceptible. In either of the above cases, these shutters operate at the same 24 Hz rate as the intermittent film driver, and indeed are typically directly linked to the film drive mechanism by a series of worm gears and drive shafts. Alternately, a single bladed shutter driven at 48 Hz or 72 Hz could be employed. Indeed, single bladed shutters are optimal relative to the maximization of screen light and the minimization of travel ghost. However, since single bladed shutters must rotate faster, they generate design, balance, and safety issues, such that they are rarely used. Shutter performance can also be improved by using a shutter disc with a larger diameter, or by positioning the shutter as close as possible to the film plane. In the first case, the shutter blade edges move faster to block the light than is the case for a smaller diameter shutter blade operating at the same speed, and the shutter closure time is reduced. However, size constraints within projector heads typically limit shutters to approx. 4 to 12 inches in diameter. Likewise, physical constraints usually cause the shutter to be positioned an inch or more back from the film gate. Alternately, a shutter with a conical profile has been used as the shutter blade can be positioned closer to the film gate, and the blade velocity across the aperture is more uniform. However, conical shutters have not been widely adopted. 
     It is a further requirement in shutter design that the multiple blades must be nearly the same size (within a few percent), or else perceptible flicker will be present. Thus, in a cinema projector system employing a standard Geneva mechanism which indexes the film in ¼ the frame time, the standard two bladed shutter then blocks 50% of the available light from reaching the screen. Thus, rather than make the shutter blades overly large to avoid the appearance of even the slightest amount of image smear, or “travel ghost,” projector manufacturers will use blades which are barely large enough, and then tolerate a small amount of travel ghost. 
     The perception of travel ghost is a function of both the rate of actual motion of the film as well as the amount of light available to illuminate the film during this motion. It is left to the projectionist to control travel ghost by carefully synchronizing the rotation of the shutter blade with the intermittent action of the Geneva mechanism film driver. For example, travel ghost image smear will appear at the top of the frame when the shutter is late in closing, and will appear at the bottom of the image when the shutter opens too early. Visible travel ghost can occur simultaneously at both the top and bottom of the projected image if both the shutter openings are too large and the shutter is mis-timed with both the beginning and end of the film movement. 
     A variety of improved shutter designs have been proposed to attempt to maximize light efficiency to the screen while minimizing flicker. For example, the improved shutter described in U.S. Pat. No. 1,700,513 (Porter) has secondary blades, which are mounted to the primary shutter blade disc, and which can be positioned to adjust the size of the shutter openings. By controlling the openings between the radially extending blades in this manner, this shutter is intended to allow both tuning of the light efficiency as well as adjustment for vari-speed projector operation. The shutter described in U.S. Pat. No. 1,884,605 (Dina) also uses a combination of two shutter discs, each with two radially extending blades, whose positions relative to one another can be adjusted to alter the size of the shutter openings, and thus tune available screen light and flicker. In comparison, U.S. Pat. Nos. 3,773,412 and 3,784,293 (Yang) respectively describe shutters with five and four irregularly spaced radially extending blades, where the designed variations in blade position and width are intended to allow maximization of screen light while minimizing flicker. 
     An alternate approach, described in U.S. Pat. No. 6,014,198 (Baumann) uses a moving plane parallel plate optical compensator, synchronized with the intermittent film movement, to remove the travel ghost effect during shuttering. Accordingly, the screen image of the film appears stationary during a small initial period of time in which the film is actually in motion out of the gate. As during this same initial time period, the shutter blade is already cutting through the illuminating beam, the effective shutter closure time is reduced, although the actual physical closure time is not. 
     Given these various prior art shutter and projector arrangements, it can be seen advantageous to provide new shutter designs which either reduce the shutter closure time to block light from the projection aperture, or which reduce the time to reach a low light threshold of travel ghost imperceptibility. As a result of reducing either the actual shutter closure time or the travel ghost perception time, the openings of improved shutter can be widened relative to those of the prior art, allowing more light to reach the screen. Furthermore, these improved shutter designs can be combined advantageously with the improved Geneva Mechanism described in the related pending patent application, to further increase screen light. Finally, the improved shutter can be combined with alternate designs for projector illumination systems, to further shorten either the actual shutter closure time or the travel ghost perception time. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to provide shutter blades for a motion picture film projector which reduce shutter closure time and other problems identified above. 
     It is the further object of the present invention to provide a shutter blade shaped to meet the edge of the projecting aperture, or the aperture edge as projected back into the incident beam, so that the edge is nearly parallel to the aperture edge, or projection thereof. 
     It is the further object of the present invention to provide a shutter blade shaped to meet the edge of the projecting aperture, or the aperture edge as projected back into the incident beam, while the shutter axis is not located at the traditional position relative to the illumination aperture, which is at 3 o&#39;clock as viewed as the face of a clock, but is shifted relative to the center of shutter rotation. 
     According to one aspect of the present invention an improved shutter for a motion picture film projector comprises a Geneva Mechanism which intermittently drives a film. A light source projects light through the film and a shutter periodically interrupts the light source. The shutter has a blade with a shaped edge, which matches the frame shape on the film thus, increasing the amount of light that is transmitted through the film. A second edge of the blade also matches the frame shape on the film further increasing the amount of light transmitted through the film. 
     According to one embodiment of the invention an altered shape, such that the blade edge at the portion of the shutter which cuts through the actual light beam, does not lie along a radial line through the center of curvature of the shutter, but is shaped to meet the edge of the projecting aperture, or the aperture edge as projected back into the incident beam. 
     Other embodiments include shaping the blade edged to affect the transition times. For example, the leading and trailing edge transition time can be shaped differently. Likewise, the transition can be shaped to not necessarily follow a single slope in time. Also, this blade edge shaping techniques is not limited to two blade shutters, but can be used with one or three blade shutters for example. Also, for example with a two bladed shutter, the two blades may be shaped differently; if one blade is synched with the movement of the intermittent and the film (and is tuned to help with travel ghost), the other blade could be shaped in a different manner, so long as flicker is controlled. Finally, a shaped blade shutter could be constructed with a small blade and servo motor driver instead of as a rotating disc. 
     An advantage of the present invention is that the combination of blade shaping and aperture/beam shifting results in a faster transition of the shutter as it cuts through the light beam as compared to the standard shutter of the same size. 
     The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art projector, including light source, shutter, projection aperture, film, projection lens, screen, and Geneva mechanism and sprocket. 
     FIG. 2 is a top view of a prior art Geneva mechanism. 
     FIGS. 3 a - 3   c  are timing diagrams for the motion of the Geneva mechanism and the film. 
     FIGS. 4 a  and  4   b  are views of a standard shutter and projection aperture. 
     FIGS. 5 a  and  5   b  illustrate the relationship of the standard shutter to the aperture and the light passing through it. 
     FIG. 6 illustrates a first embodiment of a shutter according to the present invention. 
     FIG. 7 illustrates the improvement in shutter response of the first and second embodiment shutters. 
     FIG. 8 illustrates a second embodiment of a shutter according to the present invention. 
     FIG. 9 illustrates a third embodiment of a shutter according to the present invention. 
     FIG. 10 illustrates the improvement in shutter response of the third embodiment shutter. 
     FIG. 11 illustrates an improved Geneva Mechanism. 
     FIGS. 12 a-c  illustrate the timing diagram for the new Geneva Mechanism. 
     FIG. 13 illustrates an alternate projector illumination optics and shutter positions. 
     FIG. 14 illustrates a fourth embodiment of a shutter according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The traditional prior art motion picture film projector  100  is illustrated in FIG. 1, where a beam of light  116  generated by arc lamp  102 . A Projector uses elliptical reflector  104  as beam shaping optics to focus light beam  116  past shutter  300  and through aperture plate  108  to illuminate a frame of the film  114 . Said film frame is then imaged by projection lens  110  onto screen  112 . Each frame is sequentially moved through the film gate (not shown) and past the aperture plate  108  by sprocket  122 , which is driven by Geneva Mechanism  120 , whose main components are star wheel  140  and driver  130 . 
     The conventional Geneva Mechanism  120  is shown in greater detail in FIG.  2 . Geneva Mechanism  120  comprises a driver  130  and a star wheel  140 , which together drive a load (such as film) in a controlled intermittent fashion, while driver  130  itself is driven continuously with essentially constant rotary motion. The angular motion of star wheel  140  includes an index followed by a dwell for each revolution of driver  130 . 
     Driver  130  typically includes a drive shaft  132 , a restraining cam  134 , and a drive arm bearing a drive pin  136 . Driver  130  is typically attached to a flywheel (not shown) and a drive motor or gear train (not shown), which provide a constant angular velocity input to driver  130 . 
     Star wheel  140  comprises a shaft  146 , which is attached at one end to star wheel  140 , and at the other end to a load to be driven. In the case of a motion picture projector, a sprocket (not shown) is attached to the shaft  146 , and the sprocket in turn engages with the perforations of the film, thereby transferring the intermittent drive motion to the film (not shown). In the typical Geneva Mechanism, the star wheel  140  comprises a number of straight slots  142 , the center lines of which extend radially outward from the center of rotation, and where straight slots  142  are positioned at equal angles about the center of rotation. In between straight slots  142  are a number of concave surfaces  144 . Concave surfaces  144  and straight slots  142  alternate around the periphery of star wheel  140  and are equal in number. 
     During an indexing motion, drive pin  136  enters one of straight slots  142 , and then angularly accelerates star wheel  140  about its center of rotation. This acceleration continues until the midpoint of the indexing motion, where drive pin  136  crosses the line joining the centers of rotation of star wheel  140  and driver  130 . At this point star wheel  140  begins an angular deceleration which continues until drive pin  136  exits straight slot  142 . The star wheel  140  attains its maximum angular velocity at the mid-index position, while both at the beginning and end of index in its angular velocity is zero. As the star wheel  140  depicted in FIG. 2 has four straight slots, its complete motion for one index from rest to peak velocity and back to rest corresponds to 90° of rotation. 
     Following the indexing motion there occurs a dwell period, during which drive pin  136  is not in engagement with star wheel  140 . Driver  130  then rotates to complete one revolution such that it subsequently returns to a position of initial engagement with the next straight slot  142  of star wheel  140 . During the dwell period, the star wheel  140  is restrained from any rotation by the engagement of one of its concave surfaces  144  with convex surface of restraining cam  134  of driver  130 . 
     FIGS. 3 a , and  3   b  are plots of angular acceleration  160  and angular velocity  162  of star wheel  140  versus angular displacement of driver  130 , for a conventional Geneva Mechanism with four straight slots as shown in FIG.  2 . For the approximately first 15° of driver rotation, out of 90°, the star wheel displacement is minimal, and the magnitudes of the acceleration  160  and velocity  162  are relatively low. A similar period of relatively little motion occurs in the final 15° of driver rotation. The motion is slow to start and just as slow stop, however, in a motion picture projector the shutter must be closed during much of this time, because the film is moving. Failure to blank the screen during this period of film motion results in vertical smear, also known as “travel ghost.” Thus, as shown in FIG. 3 c , the first blanking period  164  of the shutter corresponds to the action of the Geneva Mechanism, as well as the attached sprocket and film. 
     As shown in FIGS. 4 a  and  4   b , a standard two blade shutter  200  consists of two opposed opaque blades  202  and  204 , each occupying 90° of arc, with their blade edges  212  extending radially from the center of rotation  205 . Likewise, there are two opposed shutter apertures,  206  and  208 , each of which also occupies 90° of arc, and through which light is transmitted. The shutter  200  is shown with an optional support  210 , which enhances the mechanical rigidity of the entire shutter. The arrow indicates the direction of shutter rotation. Specifically, light passes through rectangular aperture  230  and is incident on the film, unless the light is first obstructed by one of the opaque blades  202  or  204 . The center line of the aperture  230  lies on a radial line bisecting the shutter. Both the shutter  200  and the rectangular aperture  230  are scaled to representative dimensions for actual cinema equipment. The shutter  200  has a 4.0 inch outside radius, while the aperture  230  is centered approx. 3.11 inches from the center of rotation  205 , and it has approximate dimensions of 17.5×20.9 mm. The leading blade edge  212   a  is shown to be just in coincidence with a near corner of the aperture  230 . To entirely obstruct the aperture  230 , the leading blade edge  212   a  would have to sweep through the angular subtense occupied by the aperture  230 , which equals 14.56° for this geometry. At 24 fps operation, this angle corresponds to a closure time of 1.68 ms. Although the typical illumination at the film is typically non-uniform, with a 20+% fall off from screen center to edge not uncommon, it is a fair approximation to assume the total light falling first on the film, and then on the screen, is proportional to the area of the aperture  230 . 
     It should be noted that a very slight improvement in closure time can be obtained by shifting the shutter  200  about the center of the aperture  230 , such that the center of rotation  205  is further from the aperture and the subtended angle is minimized. In this example, if the shutters center of rotation is rotated by 0.354 inches the subtended angle is reduced to 14.34°, which equates to a 1.66 ms closure time. In this new configuration, shown in FIG. 4 b , the shutter rotation axis is coincident with the bottom of the aperture  230 . This minor shift gives potential total 0.1% increase in the available screen light when all four blade edge transitions across the aperture  230  are accounted for. 
     While FIGS. 4 a  and  4   b  shows the relationship of the shutter to the aperture, and the blade edge and the subtended angle, FIGS. 5 a  and  5   b  shows a more complete picture, which includes the relationship of the shutter to the film aperture, the film plane, and the projection lens. In reality, in most real projectors, the shutter  106  is offset some distance Z 1  from aperture  109 , and a distance Z 1 +Z 2  from the film plane. The projection lens collects a finite angular range of light, which typically corresponds to an F/2.3 cone. When light rays are projected back to the shutter plane, it can be seen that the effective aperture  109   a  filled with imaging light is much larger than the linear dimensions of aperture  109  itself. This means that the angle subtended by the aperture as seen by the shutter, and thus the total closure time required for the shutter to block all light passing through the aperture, increases as the distance Z 1  between aperture  109  and shutter  106  is increased. The total shutter closure time can be restored to the original time if the shutter dimensions are increased in like proportion with the increase in the area of the effective beam aperture (effective aperture  109   a ). 
     The time it takes for the leading blade edge to block both the upper and lower marginal light rays is the total closure time, during which the aperture is blocked and the screen is darkened. This is also known as the “gray time”. The perception of travel ghost depends primarily on the amount of the frame that is blocked when the film motion begins. However, it also depends on how well the shutter is synchronized with the film motion, the motion profile of the intermittent pull down mechanism (the Geneva), the distance Z 1  between shutter and aperture, the diameter of the shutter, and finally, the shutter configuration used. While the threshold for travel ghost imperceptibility is not an absolute, there are empirical standards used in the field. One such condition applied to the projector operation with a two bladed shutter is that the leading edge of the shutter blade should be at least half way across the aperture when motion begins. This standard, which equates to a 50% light level, will be used to judge the effectiveness of the design improvements described in this application. 
     FIG. 6 shows a first embodiment of the present invention, in which the shutter  300  has been shaped such that the outer leading edge  320  is parallel to the top edge of the aperture  330  when the inner leading edge  315  reaches the inner upper corner  335  of the aperture  330 . To accomplish this, the blade  310  is shaped such that the outer portion of the leading edge  320  does not extend along the radius of the shutter, as does the inner portion  315  of the leading edge, but rather protrudes from it. In this configuration, the center line of aperture  330  does cross through the center of rotation  305  of the shutter  300 . Likewise, the outer trailing edge  340  of the shutter blade  310  is shaped in mirror image to effect the shutter closure, but rather with material removed. As shown in the plot of FIG. 7, although addition of this material to shape the outer leading edge  320  does not reduce the total closure time, the shutter transition is still accelerated over much of the shutter motion. Thus, it still takes 14.56° of motion, or 1.68 ms in time, to block the aperture. However, at the start of closure, the shutter provides a greater initial blockage than does the standard shutter with a radially extending leading edge. The improved shutter continues to be advantaged for much of its motion relative to the standard shutter, with a larger percentage of the aperture area covered. Thus the flicker imperceptibility threshold of 50% light level is reached more quickly than is the case with the standard shutter. Indeed, the improved shutter has blocked ˜7.25% more of the aperture area than has the standard shutter when the standard shutter has reached the point of 50% blockage. Alternately, the improved shutter reaches 50% blockage more quickly, corresponding to an angle of ˜6.55°, vs. ˜7.28° for the standard shutter. 
     This improvement of ˜0.73 degrees at the leading edge (including portions  315  and  320 ) is also provided by shaping the trailing edge (including portion  340 ). Thus the shutter opening can be changed so that the opening is larger and the leading edge starting to cut through the aperture 0.73° later in its motion. As shown in FIG. 6, blade  310  would be reduced by having its trailing edge, as defined edges  340  and  345 , shifted radially by 0.73°, to become edges  340   a  and  345   a . The leading edge of blade  310 , which is defined by edges  315  and  320 , would likewise by shifted to reduce blade  310  by 0.73°, for simplicity this is not shown in FIG.  6 . Blade  312  would be similarly reduced in size, such that both shutter openings, apertures  306  and  308 , would be increased to ˜91.46°. This means that when both blades  310  and  312  of shutter  300  have both the leading and trailing edges reshaped accordingly, the total shutter opening time per frame expanded by (4*0.73 degrees)/360 degrees, to gain 0.8% additional light to the screen as compared to the standard shutter of the same size. This is equivalent to the shutter radius being increased to 3.43 inches, vs. the 3.11 inches in the original case. 
     A second embodiment for the improved shutter  400  is shown in FIG.  8 . As in the prior embodiment, the center line through the aperture passes through the center of rotation  405 . Likewise, the outer portion of the leading edge  420  has been shaped to be parallel to the top edge of the aperture  430  when a radial line extending from the center of rotation  405  reaches the inner upper corner  425  of the aperture  430 . However, the blade is additionally shaped so that the inner portion of the leading edge has a blade extension  435  parallel and in proximity to the inner side edge of the aperture  430 . It is also shown that the outer portion  440  of the trailing edge of blade  410  has been shaped similarly, but with mirror image cut-outs of removed material. The inner portion  445  of the trailing edge of blade  410  was not shaped in this configuration, as the resulting geometry did not give a worthwhile improvement. This version of the improved shutter, having the added blade extension  435 , has slightly enhanced performance as compared to the improved shutter of the first embodiment which lacks blade extension  435 . More precisely, this second version of the improved shutter blocks ˜7.57% more of the aperture area than has the standard shutter when the standard shutter has reached the point of 50% blockage. Thus, this second shutter design reaches the 50% the travel ghost imperceptibility threshold with a rotation of ˜6.26°, which is ˜1.0° of rotation quicker than the standard shutter. When both blades  410  and  412  of shutter  400  have both the leading and trailing edges reshaped by enlarging the shutter openings  406  and  408 , as illustrated with exemplary new leading edges  420   a  and  435   a , and new trailing edges  440   a , the total shutter opening time per frame can be expanded by (4*1.0 degrees)/360 degrees, to gain 1.1% additional light to the screen as compared to the standard shutter of the same size. This is equivalent to the shutter radius being increased to 3.58 inches relative to the original 3.11 inches. 
     In a third embodiment, shown in FIG. 9, the shutter  500  has been pivoted relative to the aperture  530 , such that the diagonal through the aperture passes through the center of rotation  505 . In this configuration, aperture  530  is rotated about the shutters center of rotation  505  by 39.9° relative to the original position, where its center line crossed through the shutters center of rotation. As with the second embodiment, the outer portion of the leading edge  520  has been shaped to be parallel to the top edge of the aperture  530 , but the blade is additionally shaped so that the inner portion of the leading edge has a blade extension  535  parallel and in proximity to the inner side edge of the aperture  530 . Blade extension  535  begins at the inner upper corner  525  of aperture  530 , and then extends the width of the aperture. Thus, these leading edge blade extensions  520  and  535  are much larger than the comparable extensions provided for the second embodiment shutter. A standard shutter of with the same 4.0 inch radius, but positioned at an acute angle of ˜40° to the aperture  530  would actually require more angular motion (θ 2 =9.3°) and time to traverse the aperture to totally close it off. Likewise, this third embodiment shutter, which has the leading edge of blade  510  shaped with outer leading edge portion  520 , and inner leading edge portion  525  also requires a greater angle of rotational motion (θ 1 =17.22°) to provide total closure than does the standard shutter. Thus, as shown in FIG. 10, the required time for total closure with the improved third embodiment shaped shutter is ˜20% larger than the total closure time of the standard shutter. However, as shown in FIG. 10, the third embodiment shutter is advantaged relative to the standard shutter over much of its motion. That is, by positioning shutter  500  at an acute angle θ=39.9° and adding aggressive leading edge blade shaping, the rotational motion required to cover 50% of the area of aperture  530 , corresponding to the 50% travel ghost imperceptibility threshold is reduced to 5.6°. Thus, as compared to the standard shutter which reaches 50% closure with 7.28° motion, the third embodiment shutter requires ˜1.68° less rotational motion for the same effect. As before blade shaping can be applied to the leading and trailing edges of both blades of shutter  500 , for example as illustrated at the trailing edge of blade  510 , with an outer shaped edge  520   a  and inner shaped edge  535   a . With these changes, shutter  500  would have shutter blades  510  and  512  which would each be ˜86.6° wide, while shutter openings  506  and  508  each would be ˜93.4° wide. In order to minimize flicker, the blades and opening should be identical size, and spaced symmetrically about the axis of rotation  505 . In combination, with the leading and trailing edges shifted to expand the shutter openings and provide faster transition to 50% closure, the total shutter opening time per frame can be expanded by (4*1.7 degrees)/360 degrees. This is a gain 1.9% additional light to the screen as compared to the standard shutter of the same size. This is equivalent to the shutter radius being to 3.95 inches as compared to the original 3.11 inch radius. While the performance of improved shutter  500  is maximized with projection aperture  530  positioned such that the diagonal through the aperture passes through the center of rotation  505 , it should be understood that this angular position can be shifted modestly in either direction while realizing most of the cited improvements. 
     The design for an improved Geneva Mechanism, which is described in greater detail in co-pending patent application Ser. No. 09/329,841 shown in FIG.  10 . This new Geneva mechanism  120  is similar to the standard mechanism discussed previously (FIG.  2 ), except that the curved slots  152  in the mechanism are shaped. FIG. 11 shows the timing diagram for this new Geneva, relative to the acceleration and velocity profiles describing the motion of the star wheel  140  as it undergoes an index. According to the design principles developed for this new Geneva mechanism, the drive pin  136  enters the curved slots  152  than is the case with the standard mechanism. The curved slots  152  are shaped to produce a time period of prolonged near peak acceleration prior to mid index, and a similar prolonged period of deceleration after mid index, after which the deceleration is rapidly reduced to zero. FIG. 12 shows this characteristic acceleration profile, as well as the resulting velocity profile for the star wheel  140 . As compared to the standard mechanism, the new mechanism produces an index of the star wheel  140 , and also for the attached sprocket and film, which is considerably quicker than the standard mechanism, without also requiring great increases in the peak acceleration experienced by the star wheel, sprocket, and film. As described in the related application, proper shaping of the curved slots  152  produces controlled acceleration enhancements, yielding ˜30% more light to the screen per film frame. Comparison of the timing diagram for the standard Geneva mechanism (FIG. 3) and the improved Geneva mechanism (FIG. 12) shows that the acceleration and velocity motion profiles for the improved Geneva are shorter and more abrupt at the beginning and end of index. On the one hand, the faster initial motion experienced by the film when driven by this improved Geneva mechanism should reduce the potential for perception of travel ghost. On the other hand, a long shutter transition time to a light threshold for low travel ghost perceptibility means that screen light is being reduced significantly at a time when the film is stationary. Therefore the light efficiency of a motion picture projector employing the improved Geneva mechanism  120  with curved slots  152  would be further enhanced by the use of a shutter with either a faster closure time, or a faster transition time to a low travel ghost perceptibility threshold. 
     Any of the previous described embodiments for improved shutters with blade shaping of the leading and trailing edges could be used in a projector utilizing either the standard Geneva Mechanism, or the just described improved Geneva Mechanism. While the gains in screen light with shutter edge shaping are a modest few percent, as compared to the 30% or more improvements offered by the improved Geneva, the shutter gains are nonetheless useful, particularly as the gains are achieved without requiring an increase in shutter size, thus minimizing the impact on the projection design. While the third embodiment shutter, which provides the greatest gains, does not require an increase in the shutter size, it does not require a significant positional shift of the axis of rotation. Also, it should be understood that while shutter offset from the gate along the optical axis, as shown in FIGS. 5 a  and  5   b , increases the time for shutter closure to either 50% or 100% closure, the gains provided by blade shaping of the leading and trailing edges, still apply as long as the shutter cuts through an effective beam (as defined by the aperture and the projection lens) of largely rectangular profile. This condition holds as long as the shutter is located within a few inches of the film gate, as opposed to being near the lamp source (the lamp and reflector of FIG.  1 ), where the beam is round in cross-section. 
     Shutter effectiveness can also be improved by changing the relationship of the shutter to the illumination system. As illustrated in FIG. 1, motion picture projectors use a relatively simple illumination system, where elliptical reflector  104  serves as the beam shaping optics to collect and focus the light emitted by arc lamp  102  into a beam  116  which is then incident on the film  114 . Shutter  106  is basically positioned as close to the film gate or aperture  108  as is physically reasonable, but as discussed previously, relative to FIG. 5, the inevitable offset causes the time for the shutter to provide total closure to increase. However, design changes in the illumination optics, which could be considered simply for the improvements in light efficiency and uniformity to the screen, also offer opportunities to improve the shutter response. For example, in the optical system shown in FIG. 13, the light emitted by arc lamp  102  is focussed by elliptical reflector  104  onto plane a 1 . The light is then directed through beam shaping optics comprising a fly&#39;s eye integrator assembly consisting of field lens  172   a , lenslet arrays  170 , and field lens  172   b , such that a plane of very uniform illumination is created at plane b 2 . Lens  172   c  is a field lens relative to plane b 2 , and may be used to image light into the pupil of lens  172   d , boosting the system light efficiency going forward. In one example of use for this system, the film could be located in proximity to plane b 2 , and lens  172   d  would be the projection lens, which images the film at high magnification onto a screen located at plane b 3 . Optional diffuser  174  may be placed prior to the film, to diffuse the light onto the film for the purpose of suppressing scratches and dirt. The shutter could of course be placed in this system in the vicinity of plane b 2 , but before (closer to the lamp) the film. Depending on the details of the design, the shutter (not shown) may be placed either before or after field lens  172   c . As thus described, this layout offers few advantages relative to the shutter operation. Alternately, the shutter could be located elsewhere in the system, and most optimally in the vicinity of plane a 1 , where the beam is typically the smallest and generally circular in cross-section. As such a shutter, shown in FIG. 13 as shutter  106 , could likely be located closer to plane a 1 , than a similar shutter would be relative to a film gate near plane b 2 , the shutter near the a 1  plane would be further advantaged relative to cutting through a small beam. Furthermore, as shown in FIG. 14, a shutter  600 , which is intended for operation at the a 1  plane, where the beam has a nominally circular cross-section  630 , could be further optimized for reduced transition times for beam closure (to 50% closure for example) by shaping both the leading and trailing edges  620  and  625  of the blades to have curved profiles. Additionally, a shutter operating at or near plane a, would be further advantaged, relative to closure times and masking travel ghost, by the nature of the illumination system, which would cause the entire illuminated aperture at plane b 2  to transition from white to gray to black (no light), as the shutter is closed. As such, the shutter would act as a dimming shutter, rather than a progressive shutter, and make travel ghost more difficult to perceive. 
     The system of FIG. 13 could be used in yet another way to advantage the shutter operation. The Fly&#39;s Eye integrator assembly could be used to provide illumination to an intermediate illumination plane located at plane b 2 . The optics would be designed to provide a rectangular area of uniform illumination with the same aspect ratio as the film frame, but of smaller size. Lens  172   d  would then be used to magnify this area to be the proper size to illuminate the full film frame, with the film located at plane b 3 . Yet another lens (not shown), positioned beyond plane b 3 , would be used to project an image of the illuminated film at plane b 3  to the screen (not shown). The optional diffuser  174 , if used, would not be located near plane b 2 , but rather near plane b 3 , though preceding the film. The shutter, which could be based on any of the advantaged designs, from the first, second, or third embodiments, would be further improved by cutting through a smaller beam of light than is possible in the traditional system of FIG.  1 . In this case, the shutter would again act progressively across the aperture to block the light, rather than being a dimming shutter like the prior cases, where shutter  106  (either standard or shaped (FIG.  14 )) is located at the a 1  plane. 
     Other options include shaping the blade edges to affect the transition times. For example, the leading and trailing edge transition time can be shaped differently. Likewise, the transition can be shaped to not necessarily follow a single slope in time. Also, blade edge shaping techniques are not limited to two blade shutters, but can be used with one or three blade shutters. Also, for example with a two bladed shutter, the two blades may be shaped differently; if one blade is synched with the movement of the intermittent and the film and is tuned to help with travel ghost, the other blade, which shutters while the film is stationary, could be shaped in a different manner, so long as flicker is controlled. Finally, a shaped blade shutter could be constructed with a small blade and servo motor driver instead of as a rotating disc. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
       100 . Motion picture film projector 
       102 . Arc lamp 
       104 . Elliptical reflector 
       106 . Shutter 
       108 . Aperture plate 
       109 . Aperture 
       109   a . Effective aperture 
       110 . Projection lens 
       112 . Screen 
       114 . Film 
       116 . Beam of light 
       120 . Geneva Mechanism 
       122 . Sprocket 
       130 . Driver 
       132 . Drive shaft 
       134 . Restraining cam 
       136 . Drive pin 
       140 . Star wheel 
       142 . Straight slots 
       144 . Concave surfaces 
       146 . Shaft 
       152 . Curved slots 
       160 . Angular acceleration 
       162 . Angular velocity 
       164 . Blanking period 
       170 . Lenslet arrays 
       172   a . Field lens 
       172   b . Field lens 
       172   c . Field lens 
       172   d . Lens 
       174 . Optional diffuser 
       200 . Shutter 
       202 . Opaque blade 
       204 . Opaque blade 
       205 . Center of rotation 
       206 . Shutter aperture 
       208 . Shutter aperture 
       210 . Optional support 
       212 . Blade edge 
       212   a . Leading blade edge 
       230 . Aperture 
       300 . Shutter 
       305 . Center of rotation 
       306 . Aperture 
       308 . Aperture 
       310 . Blade 
       312 . Blade 
       315 . Inner leading edge 
       320 . Outer leading edge 
       330 . Aperture 
       335 . Inner upper corner 
       340 . Outer trailing edge 
       340   a . Edge 
       345 . Edge 
       345   a . Edge 
       400 . Improved shutter 
       405 . Center of rotation 
       406 . Shutter opening 
       408 . Shutter opening 
       410 . Blade 
       412 . Blade 
       420 . Outer leading edge 
       420   a . New leading edge 
       425 . Inner upper corner 
       430 . Aperture 
       435 . Blade extension 
       435   a . New leading edge 
       440 . Outer portion 
       440   a . New leading edge 
       445 . Inner portion 
       500 . Shutter 
       505 . Center of rotation 
       506 . Shutter opening 
       508 . Shutter opening 
       510 . Blade 
       512 . Blade 
       520 . Outer leading edge 
       520   a . Outer shaped edge 
       525 . Inner leading corner 
       530 . Aperture 
       535 . Blade extension 
       535   a . Inner shaped edge 
       600 . Shutter 
       620 . Leading edge 
       625 . Trailing edge 
       630 . Circular cross-section