Patent Publication Number: US-8534847-B2

Title: Projector and control method therefor to suppress flickering

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present invention contains subject matter related to Japanese Patent Application JP 2007-060440 filed in the Japan Patent Office on Mar. 9, 2007, the entire contents of which being incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a projector and a control method therefor, and more particularly to a projector and a control method therefor suitable for use where light is emitted from a lamp. 
     2. Description of the Related Art 
     In recent years, together with development of the image display technique, a projector which can be applied to the field of digital cinemas, that is, a projector which can be used for applications of screening of a movie in a movie theater, has appeared. One of projectors of the type described is disclosed, for example, in Japanese Patent Laid-Open No. Hei 5-260423. 
     SUMMARY OF THE INVENTION 
     In an existing projector, if a flicker phenomenon, that is, flickering of a screen image, occurs, then either the lamp is exchanged or the input power to the lamp is increased so that the luminance of the lamp becomes equal to or higher than a preset value. However, the existing projector has a problem in that the life of the lamp upon low input power driving when a flicker phenomenon occurs may not be assured sufficiently. 
     Therefore, it is demanded to provide a projector and a control method therefor by which a flicker which occurs upon low input power driving is suppressed so that a sufficient lamp life can be assured upon low input power driving. 
     According to an embodiment of the present invention, there is provided a projector for projecting an image to a screen, including a lamp configured to emit light, an elliptic reflecting mirror configured to reflect and condense the light from the lamp, a sensor configured to detect the amount of the light reflected and condensed by the elliptic reflecting mirror, a lamp power supply configured to supply power to the lamp to drive the lamp, and a control circuit configured to successively increase the power to be supplied from the lamp power supply to the lamp until after a variation value of the amount of the reflected light detected by the sensor becomes equal to or lower than a predetermined threshold value. 
     The projector may further include a position adjustment mechanism configured to adjust the position of the lamp so that the bright point of the lamp is displaced from a first focus of the elliptic reflecting mirror. In this instance, the projector may be configured such that the position adjustment mechanism adjusts the position of the lamp when the aspect ratio of the image displayed on the screen changes. Or, the projector may be configured such that the position adjustment mechanism moves the bright point of the lamp along an optical axis of the elliptic reflecting mirror or along a direction different from the optical axis. 
     The projector may further include a display section configured to display an alarm for urging for exchange of the lamp when the variation value exceeds the predetermined value while the power supplied from the lamp power supply to the lamp has a maximum value. 
     The threshold value may be a specified value determined in advance. 
     According to a different embodiment of the present invention, there is provided a control method for the projector described above. In particular, according to the different embodiment of the present invention, there is provided a control method for a projector for projecting an image to a screen, the projector including a lamp configured to emit light, an elliptic reflecting mirror configured to reflect and condense the light from the lamp, a sensor configured to detect the amount of the light reflected and condensed by the elliptic reflecting mirror, a lamp power supply configured to supply power to the lamp to drive the lamp, and a control circuit configured to control the lamp power supply, the control method including the step, executed by the control circuit, of successively increasing the power to be supplied from the lamp power supply to the lamp until after a variation value of the amount of the reflected light detected by the sensor becomes equal to or lower than a predetermined threshold value. 
     With the projector and the control method for a projector, the life of the lamp can be extended. Particularly, it is possible to sufficiently assure the life of the lamp upon low input power driving when a flicker phenomenon occurs thereby to extend the life of the lamp. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an example of a configuration of an information processing system applied to the field of digital cinemas; 
         FIG. 2  is a schematic view illustrating a vista size and a scope size; 
         FIG. 3  is a diagrammatic view illustrating adjustment ranges of the light amount of lamps; 
         FIG. 4  is a block diagram view showing a projector to which the present invention is applied; 
         FIG. 5  is a schematic view showing an internal configuration of a lamp house on which a lamp is mounted; 
         FIG. 6  is a schematic view showing an appearance of the lamp; 
         FIG. 7  is a diagrammatic view illustrating a manner of reflection of light by an elliptic reflecting mirror with respect to the position of a light source; 
         FIG. 8  is a graph illustrating the amount of movement of the lamp and the relative illuminance on different axes; 
         FIG. 9  is a block diagram showing a detailed configuration of the lamp house; 
         FIG. 10  is a flow chart illustrating a flicker detection process; and 
         FIG. 11  is a flow chart illustrating a lamp position adjustment process. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Before a preferred embodiment of the present invention is described in detail, a corresponding relationship between several features recited in the accompanying claims and particular elements of the preferred embodiment described below is described. The description, however, is merely for the confirmation that the particular elements which support the invention as recited in the claims are disclosed in the description of the embodiment of the present invention. Accordingly, even if some particular element which is recited in description of the embodiment is not recited as one of the features in the following description, this does not signify that the particular element does not correspond to the feature. On the contrary, even if some particular element is recited as an element corresponding to one of the features, this does not signify that the element does not correspond to any other feature than the element. 
     According to an embodiment of the present invention, there is provided a projector (for example, a projector  33  shown in  FIG. 4  which can be installed in movie theaters  11 A to  11 N shown in  FIG. 1 ) for projecting an image to a screen (for example, a screen  34  shown in  FIG. 1 ), including a lamp (for example, a lamp  83  shown in  FIG. 4  which has a shape shown in  FIG. 6 ) configured to emit light, an elliptic reflecting mirror (for example, an elliptic reflecting mirror  82  shown in  FIG. 4 ) configured to reflect and condense the light from the lamp, a sensor (for example, a light amount sensor  60  shown in  FIG. 4 ) configured to detect the amount of the light reflected and condensed by the elliptic reflecting mirror, a lamp power supply (for example, a power supply section  59  shown in  FIG. 4 ) configured to supply power to the lamp to drive the lamp, and a control circuit (for example, a CPU  51  shown in  FIG. 4 ) configured to successively increase the power to be supplied from the lamp power supply to the lamp until after a variation value of the amount of the reflected light detected by the sensor becomes equal to or lower than a predetermined threshold value. 
     The projector may further include a position adjustment mechanism (for example, the lamp position adjustment mechanism  91  composed of the CPU  51 , an I/O section  54 , a motor drive  55 , an encoder  56 , a motor  57 , an electric power section  81  and so forth shown in FIG.  4 ) configured to adjust the position of the lamp so that the bright point of the lamp is displaced from a first focus of the elliptic reflecting mirror. 
     In this instance, the projector may be configured such that the position adjustment mechanism adjusts the position of the lamp when the aspect ratio of the image displayed on the screen changes (for example, a lamp position adjustment process of  FIG. 11 ). 
     Or, the projector may be configured such that the position adjustment mechanism moves the bright point of the lamp along an optical axis of the elliptic reflecting mirror or along a direction different from the optical axis (for example, a process at step S 34  of  FIG. 11 ). 
     The projector may further include a display section (for example, a display section  72  shown in  FIG. 4 ) configured to display an alarm for urging for exchange of the lamp when the variation value exceeds the predetermined value while the power supplied from the lamp power supply to the lamp has a maximum value. 
     According to a different embodiment of the present invention, there is provided a control method for the control circuit of the projector described above (for example, a method corresponding to a flicker detection process of  FIG. 10  from among processes executed by the CPU  51  of the projector  33  of  FIG. 4 ). 
     In the following, a preferred embodiment of the present invention is described with reference to the accompanying drawings. 
       FIG. 1  shows an example of a configuration of an information processing system to which the present invention is applied wherein it is applied to the field of digital cinemas. 
     Referring to  FIG. 1 , the information processing system shown includes various apparatus hereinafter described which are installed in movie theaters  11 A to  11 N and a maintenance server  12  connected to each other by a predetermined network  13  such as the Internet. The maintenance server  12  here is an apparatus used by a person who provides maintenance of the apparatus installed in the movie theaters  11 A to  11 N as a service. 
     The movie theater  11 A includes a plurality of screening places  22   a  to  22   n  so that a plurality of movies can be shown concurrently. In order to collectively manage the screening places  22   a  to  22   n , a theater management (TM) apparatus  21  is installed in the movie theater  11 A. 
     Further, a screen management (SM) apparatus  31   a , a material server  32   a , a projector  33   a  and a screen  34   a  are provided in the screening place  22   a.    
     Similarly, a screen management apparatus  31   n , a material server  32   n , a projector  33   n  and a screen  34   n  are provided in the screening place  22   n . Also any other screening place  22   k  not shown includes a screen management apparatus  31   k , a material server  32   k , a projector  33   k  and a screen  34   k  not shown. Here, k is an alphabet of a small letter between a and n. 
     It is to be noted that, in the following description, where there is no necessity to individually distinguish the screening places  22   a  to  22   n  from one other, any of them is referred to simply as screening place  22 . Further, where the screening place  22   k  is referred to simply as screening place  22 , also the screen management apparatus  31   k , material server  32   k , projector  33   k  and screen  34   k  are individually referred to as screen management apparatus  31 , material server  32 , projector  33  and screen  34 , respectively. 
     The screen management apparatus  31  carries out management of the entire screening place  22  and controls the other apparatus in the screening place  22 , that is, the material server  32 , projector  33  and so forth. Further, the screen management apparatus  31  communicates with the theater management apparatus  21  to supply and receive various information to and from the theater management apparatus  21 . 
     The material server  32  provides digital data of a movie or material to be screened in the screening place  22  to the projector  33 . 
     The projector  33  projects an image corresponding to the digital data supplied thereto from the material server  32  to the screen  34 . The movie is screened on the screen  34  thereby. 
     Also the other movie theaters  11 B to  11 N have one or more screening places  22 , in each of which a screen management apparatus  31 , a material server  32 , a projector  33  and a screen  34  are provided. 
     The information processing system of  FIG. 1  is applied to the field of digital cinemas as described hereinabove. In the field of digital cinemas, standards called DCI Spec are defined by an organization called DCI (Digital Cinema Initiatives). According to the standards, it is written expressly that, as an image parameter to be referred to, “The white peak luminance should be 48 cd/m 2  (14 ft-L) at the center of the screen.” Since 14 ft-L=48 cd/m 2 , a brightness provided by approximately 48 candles is demanded per 1 m 2  at the center of the screen  34 . In other words, it is necessary to normally keep the luminance or brightness of an image projected on the screen  34  fixed. 
     On the other hand, the screen  34  may have a size selected from among various types of size depending upon the volume of the screening place  22  and so forth. 
     Therefore, it is necessary to adopt, as a light source of the projector  33 , an optimum lamp which can satisfy the DCT Spec such as, for example, a xenon lamp in accordance with the size of the screen  34  of an object of projection. 
     Also as regards the angle of field for a movie, various types which are different in aspect ratio such as, for example, scope and Vista are available. Accordingly, it sometimes becomes necessary to change over the angle of field for use in the same screening place  22 , that is, for use on the same screen  34 , from one to another one of the various angles of field. In this instance, it is necessary to change the magnification in zooming of the lens of the projector  33 . Further, it is necessary to change the power or input watt of the lamp in response to the change of the zooming magnification in order that the luminance or brightness of an image on the screen  34  may be kept fixed as described hereinabove. As a result, it is necessary to assure the light amount gain of the lamp at a fixed amount. 
     Referring to  FIG. 2 , the vista size is a horizontally elongated screen size having an aspect ratio of approximately 1:1.66, in the example of  FIG. 2 , an aspect ratio of approximately 1:1.85. As a representative one of such vista sizes, a vista size of 1:1.66 (European standards), another vista size of 1:1.85 (U.S. standards) and so forth are available. Meanwhile, the scope size is a horizontally elongated screen size having an aspect ratio of 1:2 or more, in the example of  FIG. 2 , an aspect ratio of 1:2.39. As a representative one of such scope sizes, the cinema scope size (registered trademark) having an aspect ratio of 1:2.35 and so forth are available. 
     Since the scope size is obtained, for example, by multiplying the vista size by 1.26 in both of the vertical direction and horizontal direction, the scope size has a magnitude equal to 1.6 times (≈1.26×1.26) the vista size. Accordingly, upon changeover from the vista size to the scope size, if the lamp power is increased to 1.6 times, then the luminance per unit area becomes fixed. For example, if the lamp power for the vista size is 50%, then 1.6 times the lamp power, that is, 80%, are requisite as the lamp power for the scope size. It is to be noted that, although upper and lower portions of the screen of the scope size indicated by slanting lines are not observable as seen in  FIG. 2 , as viewed from the lamp side, power including that for the slanting line portions is requisite. 
     Further, since it is necessary to keep the luminance or brightness of an image on the screen  34  fixed as described hereinabove, it is necessary to adopt a lamp which can cope with a change in power in terms of minimum watt and maximum watt as input ratings (such input ratings are hereinafter referred to as lamp size) and to carry out suitable setting also on the driving side for the lamp. In other words, there is the probability that the projector  33  may incorporate lamps of various lamp sizes. 
     For example, such three different lamps as seen in  FIG. 3  are incorporated in the projector  33 . Referring to  FIG. 3 , the lamp A is driven within a range between minimum watt of 2.1 kW and maximum watt of 2.4 kW. Similarly, the lamp B is driven within another range between minimum watt of 1.5 kW and maximum watt of 3.0 kW, and the lamp C is driven within a further range between minimum watt of 1.0 kW and maximum watt of 2.0 kW. 
     In particular, since a lamp is mounted on a predetermined lamp house, in the present embodiment, in a lamp house  58  shown in  FIG. 4 , the three lamps mentioned hereinabove have a same or similar shape in order to assure a function, for example, in the present embodiment, have such a shape as seen in  FIG. 6 . No particular prescriptions are available for the lamp size, and there is the possibility that lamps of various lamp sizes may be circulated on the market. Particularly in such a case that the movie theaters  11 A to  11 N are located discretely at remote distances, lamps of lamp manufactures or makers in the districts are adopted frequently. In such an instance, lamps of various lamp sizes different in different districts may be distributed on the market with higher possibility. Accordingly, even if the projector  33  projects an image to the screen  34  of the same size, lamps of different lamp sizes are adopted as the lamp to be incorporated in the movie theaters  11 A to  11 N. 
     In this manner, the lamp for use with a projector in the field of digital cinemas involves a situation unique to the field. As a result, a movie theater in which an existing projector is used suffers from such various problems as described below. 
     For example, even if changeover between the scope size and the vista size is carried out, it is necessary to always keep the luminance or brightness of an image projected on the screen  34  fixed. In this instance, in order to assure a fixed luminance, for example, it is necessary to assure the light amount gain of the lamp at 1.6 as described hereinabove. However, since only 2.0 (50% to 100%) is available as the input gain of a lamp in the past, it is necessary to normally use low input power, and therefore, there is a problem that a sufficient life has to be assured even where the input power is low. Further, a flicker phenomenon has a nature that it begins with low input power and ends if the power of the lamp is raised. For example, the flicker phenomenon begins with lower power of 50% and ends when the input power is raised to 60%. Therefore, if low input power is always used, then a flicker phenomenon is likely to occur. In words, lower power input is requisite in order to assure the light amount gain of the lamp at 1.6, and this gives rise to a problem of occurrence of a flicker phenomenon at lower input power. Such a problem as just described is hereinafter referred to as flicker phenomenon problem. 
     Further, while, for example, in order to keep the luminance or brightness of an image on the screen  34  fixed, it is necessary to adjust the amount of light to be emitted from the lamp, a method of adjusting the electric power amount of the light source is available as a method for the light amount adjustment. Where the electric power amount of the light source is adjusted, generally the adjustment is carried out between maximum power and approximately one half the maximum power. In particular, where the maximum value and the minimum value of the adjustment range of the light amount are represented by 100% and 0%, respectively, the adjustment range is given by 50% to 100%. For example, the adjustment range for such lamps as illustrated in  FIG. 3  is a range between 2.1 and 4.2 kW for the lamp A; another range between 1.5 and 3.0 kW for the lamp B; and a further range between 1.0 and 2.0 kW for the lamp C. Therefore, the lamp A, lamp B and lamp C may not emit light with power lower than 2.1 kW, 1.5 kW and 1.0 kW, respectively. In other words, there is a problem that each of the lamp A, lamp B and lamp C may not emit light of a brightness corresponding to power outside the adjustment range from 50% to 100%. Further, in addition to the method of adjusting the power amount of the light source, also a method of adjusting the light amount by opening/closing of an iris is known. However, although addition of an optical iris mechanism theoretically makes it possible to set the adjustment range of the light amount to a range from 0% to 100%, since the optical iris mechanism is newly mounted, it gives rise to a new problem that some physical restriction is caused by parts to be added and a rise of the cost is invited. 
     Therefore, in the information processing system of  FIG. 1  to which the present invention is applied, the projector  33  which can solve the various problems described above is installed in each screening place  22 . In other words, the projector  33  is a form of a projector to which the present invention is applied. An example of a configuration of the projector  33  is shown in  FIG. 4 . 
     Referring to  FIG. 4 , the projector  33  includes a central processing unit (CPU)  51 , a memory  52 , an inputting/outputting section  53 , an input/output (I/O) section  54 , a motor drive  55 , an encoder  56 , a motor  57 , a lamp house  58 , a lamp power supply section  59 , a light amount sensor  60 , an input/output interface  61 , a communication section  62  and a drive  63 . 
     The CPU  51  executes various processes in accordance with programs and so forth recorded in the memory  52 . The memory  52  suitably stores also data and so forth necessary for the CPU  51  to execute various processes. 
     Also the inputting/outputting section  53 , I/O section  54  and input/output interface  61  are connected to the CPU  51 . 
     The inputting/outputting section  53  includes an inputting section  71  formed, for example, from a touch panel for being operated by a user such as an operator, and a display section  72  formed from a display unit and so forth for displaying the substance of such operation and so forth. 
     The I/O section  54  repeats various kinds of information between the CPU  51  and the motor drive  55 , encoder  56 , lamp power supply section  59  or light amount sensor  60 . 
     The lamp house  58  for receiving a lamp  83  mounted thereon has an electric power section  81  provided for movement in three directions along X, Y and Z axes illustrated in  FIG. 4 . The motor  57  and the encoder  56  which generates a pulse in response to the rotational angle of a movable rotary shaft of the electric power section  81  are mechanically connected to the movable rotary shaft. An elliptic reflecting mirror  82  for suppressing spreading of light from the lamp  83  to irradiate the light to a remote plate is provided on the lamp house  58  in addition to the electric power section  81  and the lamp  83 . 
     The CPU  51  controls the motor drive  55  through the I/O section  54  to drive the motor  57 . When the motor  57  is driven, the electric power section  81  is moved in the three axis directions in  FIG. 4  so that also the lamp  83  mounted on the lamp house  58  is moved. At this time, a pulse signal is generated by the encoder  56  in response to the amount of movement of the electric power section  81  and read by the CPU  51  through the I/O section  54 . Consequently, the CPU  51  can acquire information regarding the position of the lamp  83 . 
     The light amount sensor  60  is provided at a position at which it can measure the amount of light emitted from the lamp  83  and detects the amount of light. The CPU  51  controls the light amount sensor  60  through the I/O section  54  to acquire information regarding the amount of light measured by the light amount sensor  60 . 
     The lamp power supply section  59  is a power supply which can drive a plurality of different kinds of lamps  83 . The lamp power supply section  59  provides appropriate driving power to the lamp  83  mounted on the lamp house  58  under the control of the CPU  51  through the I/O section  54 . 
     The communication section  62  and the drive  63  are connected to the input/output interface  61 . The communication section  62  controls communication carried out with a different apparatus such as the screen management apparatus  31  or material server  32  shown in  FIG. 1 . The form of communication in this instance is not limited particularly, but may be wired communication or wireless communication. Further, the communication may be carried out through direct connection or carried out through a network including the Internet. 
     Further, the communication section  62  may acquire a program from the outside under such communication control and store the acquired program into the memory  52 . 
     The drive  63  drives, when a removable medium  64  such as a magnetic disk, an optical disk, a magneto-optical disk or a semiconductor memory is loaded therein, the removable medium  64  to acquire a program, data and so forth recorded on the removable medium  64 . The acquired program and data are transferred to and stored into the memory  52  as occasion demands. 
     Incidentally, the lamp house  58  shown in  FIG. 4  has such an internal configuration as, for example, shown in  FIG. 5 . 
     Referring to  FIG. 5 , the lamp  83  serving as a light source is mounted on the lamp house  58  in such a manner as to be secured to the electric power section  81 . Consequently, if the electric power section  81  is moved in three directions indicated by X 81 , Y 81  and Z 81  in  FIG. 5 , then the lamp  83  is moved in the three axial directions of the X, Y and Z axes in  FIG. 5  corresponding to the directions of the movement of the electric power section  81 . 
     In the present embodiment, the lamp  83  has, for example, such a shape as seen in  FIG. 6 . In the present embodiment, any lamp which may possibly be incorporated as the lamp  83  in the projector  33  (exchangeability) has a shape same as that shown in  FIG. 6 . It is to be noted, however, that such lamps may possibly have various lamp sizes. Further, the shape of the lamp  83  shown in  FIG. 6  is a mere example but is not limited particularly only if it allows the lamp  83  to be mounted on the lamp house  58 . In other words, the lamp house  58  in the present embodiment casually has a structure which allows the lamp  83  of the shape shown in  FIG. 6  to be mounted on the lamp house  58 . 
     Referring back to  FIG. 5 , the elliptic reflecting mirror  82  is, for example, an elliptic reflecting mirror or elliptic mirror having an elliptic reflecting face which changes the advancing direction of a light beam from the lamp  83  and condenses light from a bright spot of the lamp  83  having a focus B as a first focus on the major axis of such an ellipse A as seen in  FIG. 5  on another focus C as a second focus which is on the major axis mentioned above. 
       FIG. 7  shows details of the ellipse A shown in  FIG. 5 . In other words,  FIG. 7  illustrates a manner of reflection of light by the elliptic reflecting mirror  82  with respect to the position of the lamp  83  serving as a light source. 
     Referring to  FIG. 7 , in the example shown, light outgoing from the focus B is condensed at the focus C. Further, as indicated by shorter broken lines in  FIG. 7 , light outgoing from the position of a point E is condensed at a point G, and as indicated by longer broken lines in  FIG. 7 , light outgoing from the position of a point F is condensed at a point H. 
     In particular, if it is assumed that the elliptic reflecting mirror  82  is designed such that, when the light source, that is, the bright point of the lamp  83 , is positioned at the focus B, if light is condensed at the focus C, then a maximum luminance is obtained, that is, a maximum luminance is approached, then if the position of the bright point of the lamp  83  is moved to the “+” side or the “−” side along the Z direction in  FIG. 7 , then the light condensing position varies and is displaced from the focus C at which the maximum luminance is obtained. Therefore, the light utilization efficiency drops. In particular, for example, if the position of the bright point of the lamp  83  positioned at the focus B is moved to the “+” side in the Z direction in  FIG. 7  to move the position of the bright point of the lamp  83  to the point E, then light outgoing from the point E is condensed at a point G. Therefore, the utilization efficiency of light emitted from the lamp  83  drops. Similarly, if the position of the bright point of the lamp  83  positioned at the focus B is moved to the “−” side in the Z direction, then light outgoing from the point F is condensed at the point H. Therefore, the utilization efficiency of the light emitted from the lamp  83  drops similarly. 
     In other words, by displacing the light condensing position intentionally from the position at which a maximum luminance is obtained, the utilization efficiency of light emitted from the lamp  83  can be dropped similarly. Consequently, for example, also outside the adjustment range of 50% to 100% in  FIG. 3  described hereinabove, light of brightness corresponding to power outside the range can be emitted by displacing the position of the lamp  83  to intentionally drop the utilization efficiency of light. In particular, in the example of  FIG. 3 , light of brightness corresponding to electric power lower than 2.1 kW for the lamp A, lower than 1.5 kW for the lamp B and lower than 1.0 kW for the lamp C can be emitted. 
     It is to be noted that, while, in the example described above, the position of the bright point of the lamp  83  serving as a light source is moved in the Z axis direction, even if the position of the bright point of the lamp  83  is moved in the X direction, Y direction, XZ direction, XY direction or the like, the brightness can be changed. The essential point is that only it is necessary for the condensing point of light from the light source to be displaced from the focus C at which a maximum luminance is obtained, and the light source may be moved in an arbitrary direction. 
       FIG. 8  is a graph illustrating a relationship between the amount of movement of the lamp  83  and the relative illuminance when the lamp  83  is moved in the three directions of the X, Y and Z axes. 
     Referring to  FIG. 8 , the axis of abscissa indicates the amount of movement of the lamp  83  and the axis of ordinate indicates the relative illuminance when the lamp  83  is moved in the axial directions of the X, Y and Z axes. From  FIG. 8 , it can be seen that, where the amount of movement of the lamp  83  is equal in the axial directions of the X, Y and Z axes, the utilization efficiency of light is comparatively high with the axis with regard to which the relative illuminance has a comparatively high value. Further,  FIG. 8  indicates curves indicative of the value of the relative illuminance when the bright point of the lamp  83  is moved in the three directions of the X, Y and Z. Among the curves, the curve when the lamp  83  is moved in the X direction is denoted by x; the curve when the lamp  83  is moved in the Y direction by y; and the curve when the lamp  83  is moved in the Z direction by z. 
     In  FIG. 8 , the position of a vertical line at the center indicates the position of the lamp  83  when the lamp movement amount is zero, that is, indicates the focus B at which the lamp  83  is positioned and light from the lamp  83  can be condensed at the focus C at which a maximum luminance is obtained. Accordingly, in this instance, since the utilization efficiency of light emitted from the lamp  83  is highest, the relative illuminance exhibits a maximum value with regard to all of the curves x, y and z. 
     In  FIG. 8 , if the lamp movement amount increases, that is, if the position of the lamp  83  is spaced away from the focus B, then the relative illuminance gradually decreases. However, the curve x is more moderate than the curve z, and the curve y is more moderate than the curve x. 
     In other words, where an equal lamp movement amount is considered, the relative illuminance increases in the order of the curve y, curve x and curve z. Therefore, if the lamp  83  is moved, for example, in the Z direction, then the illuminance can be decreased by a greater amount than where the lamp  83  is moved by the same lamp movement amount in the X or Y direction. In other words, if the lamp  83  is moved in the Z direction from among the three directions of the X, Y and Z axes, then the utilization efficiency of light can be decreased most efficiently with respect to the amount of movement of the lamp  83 . 
     In this manner, in the present embodiment, the adjustment range of the light amount can be expanded by moving the lamp  83  merely in any one of the three directions of the X, Y and Z axes without providing an additional part such as an iris mechanism to the optical system. Consequently, a physical restriction by an additional part or the like when an optical iris mechanism is attached newly can be eliminated, and increase of the cost can be suppressed to a minimum level. Further, since an existing mechanism having a function of moving the lamp  83  in the three directions of the X, Y and Z axes can be utilized, the functions mentioned can be implemented very readily. 
     It is to be noted that, in the present embodiment, by what amount the lamp  83  should be moved in any of the three directions of the X, Y and Z axes is determined depending upon by what amount the utilization efficiency of light should be dropped. 
     Incidentally, light emitted from the lamp  83  is reflected by the elliptic reflecting mirror  82  as seen in  FIG. 9  and emitted, through an illuminating system unit  92  which uniformizes the light, to a liquid crystal light valve apparatus  93  which modulates the light based on digital data of a movie or material to be screened from the material server  32 . Then, image data obtained by emitting the light to the liquid crystal light valve apparatus  93  is projected to the screen  34  through a projection lens  94 . Consequently, an image corresponding to the digital data provided from the material server  32  is projected from the projector  33  to the screen  34 . As a result, the movie is screened on the screen  34 . 
     In  FIG. 9 , a lamp position adjustment mechanism  91  is composed of, for example, the CPU  51 , I/O section  54 , motor drive  55 , encoder  56  and motor  57  shown in  FIG. 4  and adjusts the position of the lamp  83 . More particularly, the lamp position adjustment mechanism  91  moves the position of the lamp  83  in the three directions of the X, Y and Z axes in  FIG. 9  so that the bright point of the lamp  83  serving as a light source is displaced from the first focus of the elliptic reflecting mirror  82 , for example, from the focus B shown in  FIG. 5 , to decrease the effective light amount of the lamp  83 , that is, to displace the condensing point of light from the focus C shown in  FIG. 5 . In other words, the lamp position adjustment mechanism  91  moves the bright point of the lamp  83  in a direction of the optical axis of the elliptic reflecting mirror  82  or in a direction different from the optical axis of the elliptic reflecting mirror  82 . 
     The liquid crystal light valve apparatus  93  is an image display device such as a liquid crystal light valve apparatus of fixed pixels used for a projector of the light valve type. The image display device may be a liquid crystal panel of the reflection type such as a liquid crystal valve apparatus or a device which can use light emitted from the lamp  83  to display an image corresponding to digital data from the material server  32  such as a mirror device of the reflection type such as a digital mirror device (DMD). 
     The liquid crystal light valve apparatus  93  modulates light, that is, reflected light, from the lamp  83  reflected by the elliptic reflecting mirror  82  with digital data from the material server  32  to convert the light or reflected light into image light. 
     The projection lens  94  is used to project the image light from the liquid crystal light valve apparatus  93  to the screen  34  and is provided between the screen  34  and the liquid crystal light valve apparatus  93 . The image light from the liquid crystal light valve apparatus  93  is expanded by the projection lens  94  and emitted to the screen  34 . 
     It is to be noted that the projection lens  94  is formed as a group of one or more lenses having a zooming function. In this instance, while the magnitude of an image corresponding to the image light on the screen  34  can be changed by changing the position of the projection lens  94 , when the zooming condition is changed, the light of amount sometimes changes to make the luminance of the image on the screen  34  excessively bright. The situation that the image becomes excessively bright can be prevented by adjusting the position of the lamp  83  to lower the utilization efficiency of light. 
     Further, while the elliptic reflecting mirror  82  having a reflecting face in the form of an elliptic face is described in the description of the present embodiment, it is possible to use a parabolic mirror having a reflecting face in the form of a parabolic face in place of the elliptic reflecting mirror  82 . In this instance, since reflection light from the parabolic mirror is parallel light, a luminance variation may not be obtained by movement of the lamp  83  in the Z axis direction. Therefore, the lamp  83  is moved in the X direction or the Y direction to obtain an effect similar to that obtained by the elliptic reflecting mirror  82 . 
     Further, though not shown, a spherical mirror may be provided at a position confronting with the elliptic reflecting mirror  82 . In particular, this spherical mirror may be provided to collect overflowing light to raise the efficiency of light emission of the lamp  83 . 
     Now, an example of a process executed when a flicker phenomenon in a low input state occurs during execution of a calibration mode from among various processes executed by the projector  33  having such a configuration as described above is described with reference to a flow chart of  FIG. 10 . It is to be noted that the process mentioned is hereinafter referred to as flicker detection process. 
     It is to be noted that, while, in the projector  33 , the lamp input is normally set to 50 to 100%, the CPU  51  executes the flicker detection process of  FIG. 10 , for example, when a calibration mode is carried out. 
     At step S 11 , the CPU  51  controls the lamp power supply section  59  through the I/O section  54  to set the power lower limit value, for example, to 50%. For example, information of the power lower limit value set to 50 or the like is stored into the memory  52 . Consequently, the lamp  83  mounted on the lamp house  58  is turned on to emit light with the driving power of 50% supplied thereto from the lamp power supply section  59 . 
     At step S 12 , the CPU  51  decides whether or not the currently set power lower limit value is lower than 100%. If it is decided that the power lower limit value is 100%, then the CPU  51  controls the display section  72  to display an alarm for lamp exchange. Thereafter, the flicker detection process is ended. 
     In particular, if it is decided that the power lower limit value is 100%, then the power lower limit value may not be raised any more and the flicker phenomenon may not be suppressed any more. Therefore, an alarm for urging the user to exchange the lamp  83  is displayed on the display section  72  so that the user may exchange the lamp  83 . 
     In this manner, a flicker phenomenon is a significant rough estimate for lamp exchange, and if a flicker phenomenon is detected while the power lower limit value is set to 100%, then since an alarm for urging the user to exchange the lamp is outputted, it is possible to notify the user of an appropriate lamp exchanging timing so that otherwise possible failure by bursting of the lamp by normal use can be prevented. 
     On the other hand, if it is decided at step S 12  that the power lower limit value is lower than 100%, then the CPU  51  sets a counter N, for example, to 1 to initialize the counter N at step S 14 . 
     Then at step S 15 , the CPU  51  reads in a light amount sensor value measured by the light amount sensor  60  through the I/O section  54 . Then at step S 16 , the CPU  51  integrates data corresponding to the light amount sensor value thus read in. 
     At step S 17 , the CPU  51  decides whether or not the value of the counter N is equal to or higher than a predetermined number such as, for example, 10. If it is decided at step S 17  that the value of the counter N is lower than 10, then the CPU  51  increments the value of the counter N by one at step S 18 . Thereafter, the processing returns to step S 15 . 
     Consequently, the processes at steps S 15  to S 18  are repeated until after it is decided at step S 17  that the value of the counter N becomes equal to or higher than 10. In other words, the processes at steps S 15  to S 18  are repeated 10 times at fixed intervals until the value of the counter N becomes equal to or higher than 10 which is the predetermined number of times. Therefore, 10 integrated values are determined by the process at step S 16 . 
     After a predetermined number of integrated values such as 10 integrated values are determined, the CPU  51  calculates a variation value based on the integrated values at step S 19 . This variation value is calculated, for example, in accordance with the following expression (1):
 
variation value=(maximum value of integrated value−minimum value of integrated value)/average value of integrated value  (1)
 
     In particular, in the expression (1), maximum and minimum integrated values are selected from among, for example, 10 integrated values, and an average value of the 10 integrated values is calculated. Further, the difference between the selected maximum and minimum integrated values is divided by the calculated average value to calculate the variation value. 
     At step S 20 , the CPU  51  decides whether or not the calculated variation value is equal to or lower than a specified value determined in advance. 
     Here, the specified value is determined in advance, for example, by a manufacturer of the projector  33  or the like. In particular, according to the specification, a reference or threshold value for deciding occurrence of a flicker is determined, and if the calculated variation value exceeds the reference, then it is decided that a flicker phenomenon currently occurs. 
     If it is decided at step S 20  that the variation value is higher than the specified value, then the CPU  51  increases the power lower limit value by 10% at step S 21 . Then at step S 22 , the CPU  51  decides whether or not a predetermined interval of time such as one minute, elapses. Then, the deciding process at step S 22  is repeated until after it is decided at step S 22  that the predetermined interval of time elapses. 
     In particular, if it is decided that the variation value is higher than the specified value, then this indicates that a flicker phenomenon is currently proceeding. Since a flicker phenomenon has a nature that it stops if the power of the lamp  83  is raised as described hereinabove, the power lower limit value is changed from 50% to 60% to raise the power of the lamp  83  for 10%. 
     If it is decided at step S 22  that the predetermined interval of time such as one minute elapses, then the processing returns to step S 12  to repeat the processes described above. 
     Then, the processes at steps S 12  to S 22  described above are repeated until after it is decided at step S 22  that the predetermined interval of time such as one minute elapses. In particular, while the power lower limit value is increased successively by 10% like 60%, 70%, 80% and 90%, the variation value of the amount of light emitted from the lamp  83  which is turned on to emit light is successively calculated, and comparison between the calculated variation value and the specified value is carried out successively. 
     If it is decided at step S 20  that the variation value is equal to or lower than the specified value, then the CPU  51  sets the power lower limit value to a power lower limit value for the case wherein the variation value is equal to or lower than the specified value, for example, to 90% at step S 23 . Thereafter, the flicker detection process is ended. 
     As described above, when a flicker phenomenon which occurs upon low input power driving is detected, the power lower limit value or lamp input value is successively increased until the flicker phenomenon disappears. By this, a flicker which occurs upon low input power driving can be suppressed, and a sufficient lamp life upon low input power driving can be assured. In other words, the flicker phenomenon problem can be solved. 
     Further, to extend the lamp life upon low input power driving against a flicker provides also an effect that the lamp life is substantially extended. Furthermore, a flicker can be used as a significant rough estimate for lamp exchange, and to issue an alarm for urging the user for lamp exchange upon detection of a flicker with a 100% power input is significant from the point of view of prevention of bursting of the lamp by excessive use. 
     Now, a process of moving the lamp  83 , which is executed when the adjustment range of the amount of light emitted from the lamp  83  is expanded, from among the processes executed by the projector  33  having the configuration described hereinabove is described with reference to  FIG. 11 . It is to be noted that the process mentioned is hereinafter referred to as lamp position adjustment process. 
     As described hereinabove, it is prescribed that, when the size of an image to be projected on the screen  34  of the screening place  22  is changed over from the scope size to the vista size, the luminance of the image to be projected on the screen  34  is kept fixed between the two different angles of field, and in order to implement this, it is necessary to assure the light amount gain of the lamp  83  at 1.6. The CPU  51  thus executes the lamp position adjustment process of  FIG. 11 , for example, if it is necessary to keep the luminance of an image to be projected on the screen  34  whose image size is changed over to the vista size at a desired value after the flicker detection process of  FIG. 10  comes to an end. 
     At step S 31 , the CPU  51  reads in a light amount sensor value measured by the light amount sensor  60  through the I/O section  54  and decides whether or not the light emitted from the lamp  83  is excessively bright. In particular, the CPU  51  decides whether or not the light amount sensor value from the light amount sensor  60  for detecting, for example, the amount of light emitted to the screen  34  after changeover to the vista size, is equal to or higher than a value demanded for the vista size to decide whether or not the light from the lamp  83  is excessively bright. 
     If it is decided at step S 31  that the light emitted from the lamp  83  is not excessively bright, that is, that the light has a desired level of brightness, then since there is no necessity to adjust the position of the lamp  83 , processes at steps S 32  to S 35  are skipped and the lamp position adjustment process is ended immediately. 
     On the other hand, if it is decided at step S 31  that the light emitted from the lamp  83  is excessively bright, then the CPU  51  decides at step S 32  whether or not the position of the lamp  83  is within a limit range within which it is movable. If it is decided at step S 32  that the position of the lamp  83  is outside the limit range, then since the lamp  83  may not be moved any more, the lamp position adjustment process is ended. 
     On the other hand, if it is decided at step S 32  that the position of the lamp  83  is within the limit range, then since it is possible to move the lamp  83 , the CPU  51  acquires a light amount sensor value and position data from the light amount sensor  60  and the encoder  56 , respectively, through the I/O section  54 . 
     At step S 34 , the CPU  51  controls the motor  57  through the I/O section  54  and the motor drive  55  based on the light amount sensor value and position data acquired as described above to drive the electric power section  81  thereby to move the lamp  83  in one of the three directions of the X, Y and Z axes. 
     It is to be noted that, as a method of shifting the lamp  83  to adjust the position of the lamp  83 , for example, an optimum value of the position to which the lamp  83  is to be shifted is recognized by the encoder  56 , and every time the angle of field is changed over, the position of the lamp  83  is changed over based on the recognized optimum value so that the luminance of the image to be projected on the screen  34  can be kept fixed. 
     Further, in the present embodiment, the electric power section  81  has a movable amount with which the lamp gain of 1.6 can be implemented only by movement of the position of the lamp  83  while the input is kept at 100%. 
     At step S 35 , the CPU  51  decides based on the light amount sensor value from the light amount sensor  60  after the movement of the position of the lamp  83  whether or not the amount of light emitted from the lamp  83  is lower than the desired luminance. If it is decided at step S 35  that the amount of light emitted from the lamp  83  still remains equal to or higher than, for example, the value requisite for the vista size and the luminance on the screen  34  is equal to or higher than the desired luminance, then the processing returns to step S 32 . Consequently, the processes at steps S 32  to S 35  described above are repeated until after it is decided at step S 35  that the luminance on the screen  34  is lower than the desired luminance. 
     On the other hand, if it is decided at step S 35  that the luminance on the screen  34  is lower than the desired luminance, then the luminance is equal to or lower than the value demanded, for example, for the vista size, and since the luminance of the image projected on the screen  34  can be kept fixed, the lamp position adjustment process is ended. 
     As described above, the adjustment range of the light amount can be expanded only by moving the lamp  83  in any one of the three directions of the X, Y and Z axes to adjust the position of the lamp  83  without providing an additional part of an iris mechanism and so forth on the optical system. In other words, by moving the lamp  83  in any one of the three directions of the X, Y and Z axes to positively degrease the effective light amount of the liquid crystal light valve apparatus  93 , the adjustment range of the peak luminance can be expanded without damaging the gradation of the liquid crystal light valve apparatus  93 . In other words, the lamp adjustment range problem can be solved. 
     On the other hand, for example, if the angle of field or aspect ratio of the movie is changed, then in order to keep the luminance of the image on the screen  34  fixed, it becomes necessary to adjust the amount of light to be emitted from the lamp  83 . In this instance, after the flicker detection process of  FIG. 10  is executed, the lamp position adjustment process of  FIG. 11  is carried out to displace the position of the lamp  83  in a direction in which the image projected on the screen  34  becomes dark. By this, the luminance of the image can be kept fixed readily. Consequently, the flicker phenomenon problem and the lamp adjustment range problem can be solved simultaneously. For example, if adjustment of the light output of the lamp  83  within the range from 100% to approximately 50% by the flicker detection process of  FIG. 10  is carried out additionally, then a range of the luminance from 100% to approximately 30% of the maximum luminance can be made the adjustment range. 
     Further, while the lamp  83  may have any lamp size from among various lamp sizes as described above, since the adjustment range of the light amount can be expanded, the number of types of the lamp  83  can be reduced. 
     It is to be noted that, while, in the embodiment described above, the adjustment range of the light amount can be expanded by adjusting the position of the lamp  83 , similar effects can be anticipated also by moving or rotating the elliptic reflecting mirror  82  or the illuminating system unit  92  in place of the movement of the lamp  83 . 
     Further, in the projector  33  of  FIG. 4 , it is possible to use an external personal computer or like apparatus to input data or display data without providing the inputting/outputting section  53  including the inputting section  71  and the display section  72 . 
     Further, while, in the embodiment described above, changeover of the angle of field according to the DCI Spec is described, also changeover of the angle of field according to other standards can be applied effectively where screening involves changeover of the angle of field. 
     It is to be noted that, while the series of processes described above can be executed by hardware, it may otherwise be executed by software. Where the series of processes is executed by software, a program which constructs the software is installed from a recording medium into a computer incorporated in hardware for exclusive use or, for example, a personal computer for universal use which can execute various functions by installing various programs. 
     The recording medium is formed from the removable medium  64  shown in  FIG. 4  which may be a magnetic disc (including a flexible disc), an optical disc (including a CD-ROM (Compact Disc-Read Only Memory) and a DVD (Digital Versatile Disc)), or a magneto-optical disc (including an MD (MINI DISC) (Registered Trademark of Sony Corporation), or a semiconductor memory which has the program recorded thereon or therein and is distributed to provide the program to a user separately from a computer. Else, the recording medium is formed as a ROM, a recording section or the like in which the program is recorded and which is provided to a user in a state wherein the program is incorporated in a computer in advance. 
     Further, the program for causing the series of processes described hereinabove to be executed may be installed into a computer through an interface such as a router or a modem and further through a wired or wireless communication medium such as a local area network, the Internet or a digital satellite broadcast as occasion demands. 
     It is to be noted that, in the present specification, the steps which describe the program recorded in a recording medium may be but need not necessarily be processed in a time series in the order as described, and include processes which are executed in parallel or individually without being processed in a time series. 
     Further, in the present specification, the term “system” is used to represent an entire apparatus composed of a plurality of apparatus. 
     While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.