Compact follow spot

Abstract

A theatrical follow spot utilizes elliptic reflective optics to achieve compact size and non-astigmatic projection. A source lamp is situated in front of the mirror, sufficiently offset to one side thereof so as to be out of the path of reflected light. The mirror has the shape of an ellipsoid of revolution, the mirror section being entirely on one side of a meridian plane of the ellipsoid. The axis of light from the source lamp is coincident with a line through the near focus of the ellipsoid and the center of the mirror. This insures that an image in the near focal plane, such as the circular opening of an iris, will be projected at the distant focal plane of the ellipsoid, without distortion of shape.

Intending to claim all novel, useful and unobvious features shown or described, the applicant claims: 
     
       1. A compact follow spotlight comprising: a housing having one end that is optically transparent,   an elliptic mirror mounted within said housing near the other end thereof, the reflecting surface of said mirror comprising a .[.section.]. .Iadd.segment .Iaddend.of an ellipsoid of revolution, said .[.section.]. .Iadd.segment .Iaddend.being offset to one side of a meridian plane including the axis of revolution of said ellipsoid, and   a light source mounted within said housing near said one end remote from the near focus of said ellipsoid of revolution and offset to one side thereof so as to be substantially out of the path of light reflected from said mirror, said light source being arranged to project light past an object to be imaged placed at the near focus of said ellipsoid of revolution and toward said mirror, light from said source being reflected by said mirror through said transparent end and focused by said elliptic mirror in a distant focal plane coinciding with the far focus of said ellipsoid of revolution.   
     
     
       2. A follow spotlight according to claim 1 wherein said light source comprises a lamp and an associated reflector for projecting a beam of light toward said elliptic mirror, the central axis of the light beam from said lamp passing through the near focus of said ellipsoid of revolution and impinging on said mirror near the center thereof. 
     
     
       3. A follow spotlight according to claim 1, wherein said object to be imaged comprises an iris interposed in the light path between said source and said mirror at said near focus. 
     
     
       4. A follow spotlight according to claim 2 wherein said mirror is angularly oriented within said housing so that the peripheral point of said mirror .[.section.]. .Iadd.segment .Iaddend.nearest said ellipsoid axis of revolution is in a plane including said near focus and the central axis of light reflected from said mirror, on the same side of said housing as said source. 
     
     
       5. A follow spotlight according to claim 2 wherein said mirror .[.section.]. .Iadd.segment .Iaddend.subtends an angle of about twice the angle between said light beam central axis and said ellipsoid axis of revolution. 
     
     
       6. A follow spotlight according to claim 1, wherein said mirror is mounted for limited linear movement, without rotation, parallel to a normal through the center of said mirror, said limited movement permitting adjustment of the focus of said spotlight for different throw distance. 
     
     
       7. A follow spotlight according to claim 2, wherein said mirror is mounted for limited linear movement, without rotation, parallel to said light beam central axis, said limited movement permitting adjustment of the focus of said spotlight for different throw distance. 
     
     
       8. A follow spotlight according to claim 2 wherein said lamp-associated reflector is elliptic, and wherein said light source includes an annular reflector at the open end of said lamp-associated reflector for limiting the size of said light beam so that said beam is completely encompassed by said mirror, and further comprising a pattern mask interposable in said light beam adjacent the near focal plane of said ellipsoid of revolution. 
     
     
       9. A follow spotlight according to claim 8 further comprising a mounting for said housing that permits both vertical and axial pivoting of said housing, and wherein said housing one end is open and said light source is mounted near the bottom of said housing open end, so that when the housing one end is pivoted downward, heat from said lamp will rise through said annular reflector and through said open end to accomplish draft ventilation of said lamp. 
     
     
       10. A follow spotlight according to claim 2 further comprising a flood or spread lens interposed in the light path between said source and said mirror to increase the effective magnification of the spotlight image. 
     
     
       11. A light projection system comprising: an elliptic reflector, the reflective surface of which is a .[.section.]. .Iadd.segment .Iaddend.of an ellipsoid of revolution on one side of a meridian plane of said ellipsoid, and   a light source situated in front of said reflector and remote from the near focus thereof for directing a beam of light onto said reflector through said near focus, said reflector thereby projecting an image, focused in the remote focal plane of said ellipsoid, of an object situated in the path of said beam at the near focal plane of said ellipsoid, said light source being offset to one side of said reflector so as to be substantially out of the path of light reflected from said elliptic reflector.   
     
     
       12. A theatrical follow spot comprising the light projection system according to claim 11 together with a pivotally mounted housing containing said light projection system and an iris situated in the path of said beam at said near focal plane of said ellipsoid. 
     
     
       13. A follow spot according to claim 11 wherein said reflective surface is the front surface of said reflector, said light projecting system thus being characterized by a single reflective surface. 
     
     
       14. A light projection system comprising an elongated housing having one open end,   an ellipsoidal mirror mounted within said housing opposite said open end, the reflecting surface of said mirror comprising a .[.section.]. .Iadd.segment .Iaddend.of an ellipsoid of revolution, said .[.section.]. .Iadd.segment .Iaddend.being offset to one side of a meridian plane including the axis of revolution of said ellipsoid,   light source means comprising an elliptical reflector for projecting a beam of light,   means for mounting said light source means within said elongated housing adjacent said open end, offset to one side thereof and remote from the near focus of said ellipsoidal mirror so as to direct said beam of light through said near focus onto said ellipsoidal mirror, and,   iris means interposed in said beam of light at said near focus, whereby an image of said iris means is caused to focus in the far focal plane of said ellipsoidal mirror.   
     
     
       15. The light projection system of claim 14, further comprising means for mounting said ellipsoidal mirror for linear movement parallel to the central axis of said beam of light whereby the throw of said system may be adjusted. 
     
     
       16. The light projection system of claim 15, further comprising an annular reflector means mounted about the open end of said elliptical reflector for selectively limiting the size of said beam of light. .Iadd. 17. A compact follow spotlight comprising: housing having one end that is optically transparent, a projecting mirror mounted within said housing near the other end thereof, the reflecting surface of said mirror comprising an offset segment of a revolved conic section having a near focus and a distant focus both on the same side of the mirror,   a light source mounted within said housing near said one end remote from the near focus of said revolved section and offset to one side thereof so as to be substantially out of the path of light reflected from said mirror, said light source being arranged to project light past an object to be imaged placed at said near focus of said revolved section and toward said mirror, light from said source being reflected by said mirror through said transparent end and focused by said mirror in a distant focal plane. .Iaddend. .Iadd. 18. A follow spotlight according to claim 17 wherein said light source comprises a lamp and an associated reflector for projecting a beam of light toward said mirror, the central axis of the light beam from said lamp passing through the near focus of said revolved section and impinging on said mirror near the center thereof. .Iaddend..Iadd. 19. A follow spotlight according to claim 17 wherein said object to be imaged comprises an iris interposed in the light path between said source and said mirror at said near focus. .Iaddend..Iadd. 20. A follow spotlight according to claim 18 wherein said mirror is angularly oriented within said housing so that the peripheral point of said mirror section nearest said axis of revolution is in a plane including said near focus and the central axis of light reflected from said mirror, on the same side of said housing as said source. .Iaddend..Iadd. 21. A follow spotlight according to claim 17 wherein a plurality of shutters interposed in the light path between said source and said mirror to comprise said object to be imaged; and means to move said shutters into operative position at said near focal plane. .Iaddend..Iadd. 22. A follow spotlight according to claim 17 wherein said mirror is mounted for limited linear movement, without rotation, parallel to a normal through the center of said mirror, said limited movement permitting adjustment of the focus of said spotlight for different throw distance. .Iaddend. .Iadd. 23. A follow spotlight according to claim 18 wherein said mirror is mounted for limited linear movement, without rotation, parallel to said light beam central axis, said limited movement permitting adjustment of the focus of said spotlight for different throw distance..Iaddend..Iadd. 24. A follow spotlight according to claim 18 wherein said lamp-associated reflector is elliptic, and wherein said light source includes an annular reflector at the open end of said lamp-associated reflector for limiting the size of said light beam so that said beam is completely encompassed by said mirror, and further comprising a pattern mask interposable in said light beam to the near focal plane of said revolved section. .Iaddend..Iadd. 25. A follow spotlight according to claim 24 further comprising a mounting for said housing that permits both vertical and axial pivoting of said housing, and wherein said housing one end is open and said light source is mounted near the top of said housing open end, so that when the housing one end is pivoted downward, heat from said lamp will rise through said annular reflector and through said open end to accomplish draft ventilation of said lamp. .Iaddend..Iadd. 26. A follow spotlight according to claim 18 further comprising a flood or spread lens interposed in the light path between said source and said mirror to increase the effective magnification of the spotlight image. .Iaddend. .Iadd. 27. A light projection system comprising:   a reflector, the reflective surface of which is an offset segment of a revolved conic section having a near focus and a remote focus both on the same side of the mirror,   a light source situated in front of said reflector and remote from the near focus thereof for directing a beam of light onto said reflector through said near focus, said reflector thereby projecting an image focused in a remote focal plane of an object situated in the path of said beam at the near focal plane of said section, said light source being offset to one side of said reflector so as to be substantially out of the path of light reflected from said reflector. .Iaddend. .Iadd. 28. A theatrical follow spot comprising the light projection system according to claim 27 together with a pivotally mounted housing containing said light projection system and an iris situated in the path of said beam at said near focal plane of said revolved conic section. .Iaddend..Iadd. 29. A follow spot according to claim 27 wherein said reflective surface is the front surface of said reflector, said light projecting system thus being characterized by a single reflective surface. .Iaddend. .Iadd. 30. A light projection system comprising an elongated housing having one open end, a projecting mirror mounted within said housing opposite said open end, the reflecting surface of said mirror comprising an offset segment of a revolved conic section, having a near focus and a far focus both on the same side of the mirror,   light source means comprising an elliptical reflector for projecting a beam of light,   means for mounting said light source means within said elongated housing adjacent said open end, offset to one side thereof and remote from the near focus of said mirror so as to direct said beam of light through said near focus onto said projecting mirror, and   iris means interposed in said beam of light at said near focus, whereby an image of said iris means is caused to focus in a far focal plane of said mirror. .Iaddend. .Iadd. 31. The light projection system of claim 30 further comprising means for mounting said mirror for linear movement parallel to the central axis of said beam of light whereby the focus of said system may be adjusted. .Iaddend..Iadd. 32. A light projecting system of claim 30 comprising means for mounting said iris for linear movement parallel to the central axis of said beam of light from said light source whereby the focus of said system may be adjusted. .Iaddend.