Abstract:
A zoom device for a lighting fixture has a first lens assembly of positive refractive power; a second lens assembly of negative refractive power; and a third lens assembly of positive refractive power. 
     The first lens assembly, second lens assembly, and third lens assembly are aligned along a longitudinal axis coincident with the axis of a light beam emitted by a light source of the lighting fixture, and are characterized by respective focal lengths, which are such as to effectively adjust the size of the images projected by the lighting fixture, while at the same time maintaining compactness of the zoom device.

Description:
[0001]    The present invention relates to a stage lighting fixture zoom device, and to a stage lighting fixture comprising said zoom device. 
       BACKGROUND OF THE INVENTION 
       [0002]    Known stage lighting fixtures comprise a main body extending along a longitudinal axis; a light source housed inside the closed end of the main body to emit a light beam substantially along the axis; and light beam filtering and/or modelling means positioned to intercept the light beam. 
         [0003]    The light beam filtering and/or modelling means are designed to produce special beam effects, and normally comprise light beam colouring assemblies; gobos; and a zoom device for adjusting the size of the image projected by the lighting fixture. 
         [0004]    The ever increasing need to reduce the size of stage lighting fixtures makes it necessary to minimize the size of the light beam filtering and/or modelling means and, therefore, also the zoom device. 
         [0005]    Known compact zoom devices, however, are invariably deficient in terms of quality and efficiency. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present invention to provide a zoom device designed to eliminate the above drawbacks of the known art, and which, in particular, is compact and efficient. 
         [0007]    According to the present invention, there is provided a zoom device as claimed in the attached Claims. 
         [0008]    Another object of the invention is to provide a lighting fixture that is compact and provides for efficiently adjusting the size of the projected image. 
         [0009]    According to the present invention, there is provided a lighting fixture as claimed in the attached Claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
           [0011]      FIG. 1  shows a schematic, partly sectioned view, with parts removed for clarity, of a lighting fixture in accordance with the present invention; 
           [0012]      FIG. 2  shows a schematic view, with parts removed for clarity, of the zoom device according to the present invention in a first operating position; 
           [0013]      FIG. 3  shows a schematic view, with parts removed for clarity, of the zoom device according to the present invention in a second operating position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Number  1  in  FIG. 1  indicates a stage lighting fixture comprising a main body  2 , a light source  3 , and light beam filtering and/or modelling means  5 . 
         [0015]    Main body  2  extends along a longitudinal axis A, and has a first end  7 , and a second end  8  opposite to the first end  7  along axis A. 
         [0016]    Light source  3  is housed inside first end  7  of main body  2 , and is designed to emit a light beam substantially along axis A. 
         [0017]    Light beam filtering and/or modelling means  5  comprise a carriage  9 , fitted with one or more elements to be projected, and a zoom device  10  in turn comprising a first lens assembly  13 , a second lens assembly  14 , and a third lens assembly  15 . 
         [0018]    More specifically, the elements to be projected fitted to carriage  9  may be a gobo assembly, a slide, a distorting glass, etc. In the non-limiting example described and illustrated, carriage  9  is fitted with a gobo assembly  12  comprising a gobo disk and a plurality of gobos (not shown for the sake of simplicity in annexed figures), which are disks typically made of stainless steel or glass, in which a pattern or shape is formed or drawn to produce a light pattern when the gobo intercepts the light beam. 
         [0019]    Carriage  9  is movable along axis A, and is positioned so that the distance D between the element to be projected (in the example shown, a gobo of gobo assembly  12 ) and the last lens in first lens assembly  13  to intercept the light beam is constant. In the non-limiting example described and illustrated, distance D is roughly 295 mm. 
         [0020]    First lens assembly  13  is located close to second end  8  of main body  2 , and is of positive refractive power. 
         [0021]    The refractive power of an optical element is the extent to which light travelling through the optical element changes direction. When refractive power is positive, the light issuing from the optical element converges; and when refractive power is negative, the light issuing from the optical element diverges. 
         [0022]    First lens assembly  13  comprises a convex-concave lens L 1 , a planoconvex lens L 2 , a convex-concave lens L 3 , and a frame  16  supporting lenses L 1 , L 2 , L 3 . Lenses L 1  and L 2  are joined, whereas lenses L 2  and L 3  are spaced apart, preferably by a distance of 0.5 mm. 
         [0023]    More specifically, lenses L 1 , L 2 , L 3  in first lens assembly  13  have the characteristics indicated in the Table below, in which lens “face a” and lens “face b” are intended to mean the light beam exit and entry face of the lens respectively. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 RADIUS OF 
                   
                   
               
               
                   
                   
                 CURVATURE 
                 THICKNESS 
                 DIAMETER 
               
               
                   
                 LENS 
                 (mm) 
                 (mm) 
                 (mm) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 L1 face a 
                 215.227 
                 3 
                 130 
               
               
                   
                 L1 face b 
                 105.768 
                   
                 130 
               
               
                   
                 L2 face a 
                 105.768 
                 26 
                 130 
               
               
                   
                 L2 face b 
                 infinite 
                   
                 130 
               
               
                   
                 L3 face a 
                 107.925 
                 19.80 
                 130 
               
               
                   
                 L3 face b 
                 500.781 
                   
                 130 
               
               
                   
                   
               
             
          
         
       
     
         [0024]    In the example described and illustrated, first lens assembly  13  is fixed. 
         [0025]    In a variation not shown of the present invention, frame  16  is fitted to a powered carriage movable along axis A to adjust the position of first lens assembly  13  with respect to the element to be projected fitted to carriage  9 , so that the distance D between the element to be projected and lens L 1  in first lens assembly  13  is constant. 
         [0026]    The diameter of lenses L 1 , L 2 , L 3  in first lens assembly  13  is preferably greater than or equal to the diagonal of the element to be projected (the gobo, in the example shown). 
         [0027]    Second lens assembly  14  is located between first lens assembly  13  and third lens assembly  15  along axis A, is of negative refractive power, and is movable along axis A. More specifically, second lens assembly  14  is movable between a first so-called wide-angle operating position, and a second so-called narrow-angle or telephoto operating position. 
         [0028]      FIG. 2  shows zoom device  10  with second lens assembly  14  in the first wide-angle position, in which second lens assembly  14  is positioned close to first lens assembly  13 , and the image projected by lighting fixture  1  is enlarged. 
         [0029]      FIG. 3  shows zoom device  10  with second lens assembly  14  in the second narrow-angle position, in which second lens assembly  14  is positioned close to third lens assembly  15 , and the image projected by lighting fixture  1  is made smaller. 
         [0030]    With reference to  FIG. 1 , second lens assembly  14  comprises a planoconcave lens L 4 , a double-concave lens L 5 , a negative meniscus lens L 6 , and a frame  17  supporting lenses L 4 , L 5 , L 6 . Lenses L 5  and L 6  are joined, whereas lenses L 4  and L 5  are spaced apart, preferably by a distance of 21.46 mm. 
         [0031]    Frame  17  is preferably fitted to a powered carriage (not shown for the sake of simplicity), the movement of which is controlled by a control device (not shown). 
         [0032]    More specifically, lenses L 4 , L 5 , L 6  in second lens assembly  14  have the characteristics indicated in the Table below, in which lens “face a” and lens “face b” are intended to mean the light beam exit and entry face of the lens respectively. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 RADIUS OF 
                   
                   
               
               
                   
                   
                 CURVATURE 
                 THICKNESS 
                 DIAMETER 
               
               
                   
                 LENS 
                 (mm) 
                 (mm) 
                 (mm) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 L4 face a 
                 2558.978 
                 2.00 
                 72 
               
               
                   
                 L4 face b 
                 35.984 
                   
                 55 
               
               
                   
                 L5 face a 
                 −143.637 
                 5.23 
                 55 
               
               
                   
                 L5 face b 
                 39.087 
                   
                 55 
               
               
                   
                 L6 face a 
                 39.087 
                 10.84 
                 55 
               
               
                   
                 L6 face b 
                 121.650 
                   
                 55 
               
               
                   
                   
               
             
          
         
       
     
         [0033]    Third lens assembly  15  is located between second lens assembly  14  and carriage  9 , is of positive refractive power, and is movable along axis A to adjust the focus of the projected image. 
         [0034]    Third lens assembly  15  comprises a double-convex lens L 7 , a negative meniscus lens L 8 , a double-concave lens L 9 , a double-convex lens L 10 , a negative meniscus lens L 11 , a planoconvex lens L 12 , and a frame  19  supporting lenses L 7 , L 8 , L 9 , L 10 , L 11 , L 12 . 
         [0035]    Lenses L 7 , L 8 , L 9 , L 10 , L 11  and L 12  are spaced apart, preferably by a distance of 0.2 mm between lenses L 7  and L 8 , 4.13 mm between lenses L 8  and L 9 , 14.42 mm between lenses L 9  and L 10 , 0.2 mm between lenses L 10  and L 11 , and 6.49 mm between lenses L 11  and L 12 . 
         [0036]    Frame  19  is preferably fitted to a powered carriage (not shown for the sake of simplicity), the movement of which is controlled by a control device (not shown). 
         [0037]    More specifically, lenses L 7 , L 8 , L 9 , L 10 , L 11 , L 12  in third lens assembly  15  have the characteristics indicated in the Table below, in which lens “face a” and lens “face b” are intended to mean the light beam exit and entry face of the lens respectively. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 RADIUS OF 
                   
                   
               
               
                   
                   
                 CURVATURE 
                 THICKNESS 
                 DIAMETER 
               
               
                   
                 LENS 
                 (mm) 
                 (mm) 
                 (mm) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 L7 face a 
                 93.321 
                 9.00 
                 50 
               
               
                   
                 L7 face b 
                 −225.250 
                   
                 50 
               
               
                   
                 L8 face a 
                 62.487 
                 6.01 
                 50 
               
               
                   
                 L8 face b 
                 673.000 
                   
                 50 
               
               
                   
                 L9 face a 
                 −75.264 
                 2.00 
                 46.40 
               
               
                   
                 L9 face b 
                 55.468 
                   
                 50 
               
               
                   
                 L10 face a 
                 93.321 
                 15.71 
                 62 
               
               
                   
                 L10 face b 
                 −60.582 
                   
                 62 
               
               
                   
                 L11 face a 
                 62.847 
                 2.00 
                 62 
               
               
                   
                 L11 face b 
                 35.294 
                   
                 60 
               
               
                   
                 L12 face a 
                 42.500 
                 14.25 
                 60 
               
               
                   
                 L12 face b 
                 2730.510 
                   
                 60 
               
               
                   
                   
               
             
          
         
       
     
         [0038]    Third lens assembly  15  preferably comprises a light beam reducing ring  20  for eliminating the aberration effect produced by the light beam travelling through the lenses of zoom device  10 . Ring  20  is preferably located between lenses L 7  and L 8 , and is smaller in diameter than lens L 8  which intercepts the light beam before ring  20 . 
         [0039]    In the non-limiting example described and shown, ring  20  is roughly 44 mm in diameter. 
         [0040]    Zoom device  10  as described satisfies the following conditions: 
         [0000]    
       
         
           
             2.12 
             &lt; 
             
               
                 F 
                 1 
               
               
                 F 
                 m 
               
             
             &lt; 
             
               2.80 
                
               
                 
 
               
               - 
               0.55 
             
             &lt; 
             
               
                 F 
                 2 
               
               
                 F 
                 m 
               
             
             &lt; 
             
               - 
               0.81 
             
           
         
       
       
         
           
             0.6 
             &lt; 
             
               
                 F 
                 3 
               
               
                 F 
                 m 
               
             
             &lt; 
             0.84 
           
         
       
       
         
           
             
               F 
               m 
             
             = 
             
               
                 ( 
                 
                   
                     F 
                     s 
                   
                   · 
                   
                     F 
                     l 
                   
                 
                 ) 
               
               
                 0 
                 , 
                 5 
               
             
           
         
       
     
         [0000]    where: 
         [0041]    F s  is the focal length of zoom device  10  when second lens assembly  14  is in the wide-angle position; 
         [0042]    F 1  is the focal length of zoom device  10  when second lens assembly  14  is in the narrow-angle position; 
         [0043]    F 1  is the focal length of first lens assembly  13 ; 
         [0044]    F 2  is the focal length of second lens assembly  14 ; 
         [0045]    F 3  is the focal length of third lens assembly  15 . 
         [0046]    Zoom device  10  as described provides for a so-called zoom ratio of 9:1, with a light beam exit angle ranging between roughly 6.5° and 60°. 
         [0047]    With the zoom device  10  according to the present invention, lighting fixture  1  can be used both as a diffused-light lighting fixture, also called washlight, and as a sharp-light lighting fixture, also called spotlight. 
         [0048]    Clearly, changes may be made to lighting fixture  1  and zoom device  10  as described herein without, however, departing from the scope of the accompanying Claims.