GB2239938A

GB2239938A - Variable colour spotlight

Info

Publication number: GB2239938A
Application number: GB9000836A
Authority: GB
Inventors: Peter Roger Pierce-Harvey
Original assignee: PIERCE HARVEY PETER ROGER
Current assignee: PIERCE HARVEY PETER ROGER
Priority date: 1990-01-15
Filing date: 1990-01-15
Publication date: 1991-07-17
Anticipated expiration: 2010-01-15
Also published as: GB9000836D0; GB2239938B

Abstract

The spotlight includes two discs 15, 17 around the periphery of which are arranged a plurality of different coloured filters which may be selectively interposed into the beam at an antifocus, preferably close to the light source 1. Which and how many filters are interposed and what portion of the beam they intercept determines the hue and saturation of the output beam. Because the filters are at an antifocus of the system the projected spot will be uniformly coloured but will have an admixture of white light dependent on the amount of the beam not intercepted by the filter. As an alternative the apparatus may project an image of the filter plane so that a spot divided into coloured and non-coloured regions can be produced using a filter partly intercepting the beam. The filters used are preferably dichroic and reflect that portion of the light incident on them that they do not transmit. <IMAGE>

Description

VARIABLE COLOUR SPOTLIGHT The present invention relates to spotlights, particularly for use in theatres and film work etc, and is particularly concerned with the provision of a light capable of projecting a spot of variable colour, shape and size as desired by the operator.

In theatre lighting applications, it is often desirable to project a spot onto a stage or the like and it is advantageous to be able to control the colour, size and shape of the spot. In the past the colour of the projected spot can only be varied by the insertion of one or more filters with the light output being that which passes through the filter or filters. The light unit can thus only produce a limited number of colours corresponding to the filters that have been provided beforehand. Many previous designs have also been slow in changing from one colour to another and have produced undesirable effects while doing so, for example, the spot might be blacked out or go white between colour changes.

The present invention aims to provide a light capable of projecting a spot whose colour may be varied rapidly and easily over a wide range and with which a number of additional effects can be obtained.

According to the present invention there is provided a lighting apparatus comprising: a light source adapted to emit light in a divergent beam; at least one filter support means having a plurality of coloured filters mounted thereon; and condensing lens means for projecting the light emitted from the aperture in a beam; wherein said filter support means is adapted to interpose a selected one of said filters a selected extent into the path of the light emitted from said light source towards said lens means.

Preferably the filters are mounted on the filter support means around the circumference of a circle, the filter support means being rotatable so that different ones of the filters may be placed selectively in the path of the light, the filter support means also being capable of being translated perpendicular to the optical axis of the system in order to intersect the beam to a greater or lesser extent.

Preferably there are two filter support means each carrying a plurality of differingly coloured filters, the filter support means being arranged so that a selected filter on each may be positioned to an independently selectable extent in the beam. With this arrangement the filter support means are ideally positioned so that the selected filters on the two supports may be capable of moving to a position in which they can overlap.

It is advantageous for the filter support means to be motor driven; if the filters are arranged on the support in a circular fashion then a simple rotary motor may be provided to rotate the support while a lead screw arrangement may be provided to translate the filter support linearly.

Preferably also an adjustable aperture is provided after the condensing lens means in the direction of travel of the light beam, the condensing lens being arranged so as to uniformly illuminate the adjustable aperture, and second lens means are provided to project an image of said adjustable aperture. Further, preferably, the condensing lens means and the second lens means may be movable so as to project an image of the plane of said filter means.

The present invention will be further explained hereinafter with reference to the following exemplary embodiment and the accompanying schematic drawings, in which: Fig. 1 shows a section of the lighting apparatus along its optical axis; Fig. 2 is a plan view of a filter support means; and Figs. 3 and 4 are used explaining the frequency dependence of the output of the lighting apparatus.

As seen in Figure 1 the light emitted from a filament 1 is reflected by a parabolic mirror 3 to produce an image of the filament at a focal point 5. The light diverging from the point 5 then passes through filters 7 and 9, which may be moved perpendicular to the optical axis, as indicated by arrows 8, so that they intersect the diverging beam to a greater or lesser extent. Having passed through the filters, the light beam is collimated by lens 11 which may be moved along the optical axis as indicated by arrow 12. Lens 11 may be mounted on a wheel, so that it can be moved into or out of the path of the beam or so that lenses of different characteristics, e.g. focal length, may be substituted.

The collimated beam then passes through an iris 13 which, normally, is used to vary the diameter of the projected spot 25. Adjacent the iris 13 a gobo disc 15 may be provided to allow the projection of shaped and/or patterned spots. The iris 13 and gobo disc 15 are normally close together.

After the iris 13 and gobo disc 15 a further, or effect disc 17 may be provided. This may hold a variety of masks and/or filters, in particular it is advantageous to provide filters on the effects disc 17 which can correct the overall colour temperature of the light to ensure that the desired effect is produced correctly on television or film.

In some circumstances, particularly the previous example, it may be desirable to ensure that the filter on the effects disc 17 is always correctly aligned with the lens 11. In this case a simple solution is to link the discs bearing the lens 11 and the effects disc 17 so that they revolve in unison. While this limits the number of combinations of lens and effects filter available, this would not usually produce a problem.

The beam then passes through a telephoto-type lens system comprising lenses 19 and 21 which project a spot 25 of light onto the target as desired. A dimming iris 23 may be provided close to lens 21. Opening or closing iris 23 does not alter the size of the projected spot, provided it remains close to the lens 21, but instead effects its intensity. Lenses 19 and 21 may be moved independently over a wide range. As their separation is varied their combined focal length changes while moving them in unison has the effect of moving their focal point.

Figure 2 shows a filter disc which may be used for filters 7 and 9. The filter disc comprises a hub 29 onto which are mounted a number of filters 27. The filters 27 are of the dichroic reflector type in which dielectric films of particular thicknesses are deposited on glass or plastic plates. The dielectric constants and thicknesses of films are selected so that a particular band of frequencies is transmitted while others are reflected. The filter acts as a band pass filter, the location and width of the band pass can be selected as desired. This form of filter reflects almost all of the light that is not transmitted, little light is absorbed, so that the filters do not get too hot and may be placed close to the lamp. This is advantageous in this application. The disc may be made up from a number of filters of appropriate shape or may be a single glass disc onto which differing dielectrics are deposited in differing thicknesses in different areas to produce the desired effect. The different coloured filters may be arranged around the disc in the manner of a colour circle so that there is a gradual change of hue as the disc is rotated, or may be placed so that complementary colours are adjacent enabling a rapid transition from one colour to another.

With this arrangement a number of different effects may be obtained and the light switched rapidly from one format to another.

If it is desired to project a simple coloured spot then the lens 11 is positioned so as to colimmate the light diverging from the image of the bulb at 5 and evenly illuminates the aperture defined by the iris 13. The telephoto lens system, comprising lenses 19 and 21, is arranged so as to project an image of the aperture of iris 13 onto the desired location, for example, a stage, with a desired magnification. The width of the aperture of iris 13 together with the magnification of the telephoto lens system determines the size of the projected spot 25. Changing the size of the iris aperture causes the spot to change size correspondingly with uniform brightness. If the magnification of the telephoto lens system is changed then the brightness of the spot will vary, increasing as the spot size decreases, since the telephoto lens system projects the same amount of light into a varying area.Iris 23 may also be used to vary the brightness of the image.

The colour of the projected spot is determined by the filters 7 and 9. The colour of the emitted light may be defined by two factors, hue and saturation. Hue may be measured in terms of the wave length of the dominant component of the beam while saturation is a measure of the portion of white light to coloured light in the beam. If only one filter is interposed into the beam then the hue of the output of the light is determined by the characteristics of the pass band of that filter, while the saturation of the output is determined by the extent to which it intercepts the beam. If the entire beam passes through the filter the output beam will have a frequency distribution corresponding to the characteristics of the pass band of the filter.If only part of the beam passes through the filter then the frequency distribution of the output of the light will correspond to a sum of the frequency characteristics of the pass band and the frequency distyribution of the (assumed to be white) light emitted by the bulb in a proportion determined by the extent to which the filter intercepts the beam. This is shown in Figure 3 in which graph a shows the transmissivity, T1 of the filter as a function of frequency V to produce a bell curve centred about the V1. Graph b shows the frequency distribution of a pure coloured beam and graph c that of a beam with a certain proportion of white light.

The situation is more complex if two or more filters are interposed into the beam, it will be explained using the situation where two filters are employed as an example.

If the filters do not overlap such that no light which has passed through one passes through the other, then the output is simply a sum of the light which passes through each filter, having frequencies V1 and V2 respectively, possibly with an admixture of white light. This is illustrated in Figure 4 in which graph a shows the transmissivity of two filters and graph b shows the frequency distribution of an output beam comprising a mixture of the light which is passed through each filter.

This corresponds to a sum of the two curves in graph a, if the pass bands of the two filters are narrower or further apart the central plateau may have a dip in it, or, in extreme cases, the frequency distribution of the output may have two separate peaks.

If both filters completely intercept the beam such that all the light in the output has passed through both filters, then the output will correspond to the product of the two transmissivity functions. This is shown in Figure 4c.

Between these two extremes a variety of effects can be obtained; almost any combination of sums and products of the transmissivities of the filters and an admixture of white light may be obtained in the output.

If the telephoto lens system, lenses 19 and 21, is moved so that it is focused on, and projects an image of, the gobo disc 15, then a shaped or patterned spot may be thrown. Iris 13 and gobo disc 15 are close together so that both can be evenly illuminated by the lens 11 and so that the telephoto lens system does not have to be moved far to project an image of one rather than the other.

As described above, the lenses 19 and 21 may be positioned to project an image of the plane of the iris 13 or the gobo disc 15 as desired, which are evenly illuminated by the lens 11. In this arrangement, the light passing through one filter is mixed with that passing through the other filter or passing through neither. This occurs because the filters are at an antifocus of the composite system. The same effect may be obtained by placing the filters at other antifocal positions, for example, near or at the position of iris 23. The latter position the beam is much wider so larger filters would be necessary, with consequent added bulk and slower response time, however the heating problem would be lessened and a cheaper gell-type filters, which absorb the light and do not transmit, could be used.

By varying the position of the focal point of the combined system of lenses 11, 19 and 21, various other effects may be obtained.

If the lenses are positioned such that an image of the plane of filters 7 and/or 9 is projected, then, if one or both of the filters is partially intercepting the beam, the resultant spot will be circular with blurred edges but will be sharply divided into coloured or non-coloured portions corresponding to the parts of the beams intercepted or not by the filters. As the lenses move back towards the arrangement described first, various combinations of sharp or blurred spots with sharp or blurred colour divisions and partial colour mixing may be obtained.

A further possibility is the projection of a very small, very bright, "pencil spot". This is accomplished by moving lens 11 very close to the filters 7 and 9. In this position the light from the image of the filament 5 is directed onto a small portion of the iris 13, perhaps a spot 10 millimetres in diameter compared to the maximum of 46 millimetres, which is stopped down correspondingly. Lens 19 and 21 then project an image of the aperture in the iris 13.

Filters 7 and 9 may be used to colour the spot as desired.

Given the enormous potential of flexibility of the system it is desirable to be able to control the position of each of the movable elements - filters 7 and 9, lenses 11, 19 and 21, irises 13 and 23, gobo disc 15 and effects disc 17, independently of the others, in order to take full advantage of the potential formats of the system. This, however, results in highly complex controls. The system can best be exploited by providing electric drives for the various moving components and an electronic or computerized interface with which the user can specify the desired effect, while the interface calculates the appropriate arrangement of elements to produce that desired effect and then moves the elements to that arrangement.

In a preferred embodiment the elements which are to be translated along the optical axis are mounted on three lead screws which are driven by a simple dc electric motor via a central ring gear. A potentiometer is also provided to indicate the position of the various parts. Elements such as the filter discs, gobo disc and effects disc which are rotated may be driven simply by dc electric motors, again with potentiometers to indicate their position. The filter discs 7 and 9 may be moved perpendicular to the optical axis with further lead screw arrangements driven by dc electric motors.

Stepper motors with appropriate counters might also be used to move the elements and keep track of their location. However, in practice dc motors have a much higher power to weight ratio and the potentiometers provide a more accurate indication of the position of the element.

Rack and pinion mechanisms or worm gears might be used instead of the lead screws, but the latter tend to have less play and allower greater control.

Claims

1. A lighting apparatus comprising; a light source adapted to emit polychromatic light in a divergent beam; at least one filter support means having a plurality of coloured filters mounted thereon, each filter being adapted to pass only light of selected wavelengths; condensing lens means for collecting light from said divergent beam and projecting it in a beam; at least one control means for controlling the or each filter support means to interpose a selected one of said filters a selected extent into the beam of light.

2. An apparatus according to claim 1, wherein the filter supporting means are positioned so as to interpose the selected filter into an anti-focal plane of the system.

3. An apparatus according to claim 1 or 2, comprising a plurality of filter support means each having a plurality of filters mounted thereon, and wherein said control means is adapted to control each filter support means so that an independently selected filter of each support means may be interposed into the beam to an independently selectable extent.

4. An apparatus according to claim 3, wherein said control means are adapted such that filters from different ones of said filters support means may be overlapped in the path of the beam.

5. An apparatus according to claim 1, 2, 3 or 4, wherein the or each filter support means supports a plurality of filters in positions around the circumference of a circle and said control means comprises rotation means for rotating the or each filter support means to select a filter for interposition in the beam and translation means for translating the or each filter support means to interpose the selected filter to a greater or lesser extent in the beam.

6. An apparatus according to claim 5, wherein said rotation means comprises at least one electric motor connected to the or each filter support means.

7. An apparatus according to claim 5 or 6, wherein said translation means comprises at least one lead screw driven by an electric motor and a nut threaded on the lead screw and connected to the or each filter support means.

8. An apparatus according to any one of the preceding claims, wherein the filters are interposed in the beam between a light source and the condensing lens means.

9. An apparatus according to claim 8, further comprising an adjustable aperture after the condensing lens means in a direction of travel of the light beam; the condensing lens means being arranged to substantially uniformly illuminate the aperture.

10. An apparatus according to claim 9, further comprising additional lens means after the aperture in the direction of travel of the light beam, the additional lens means being adapted to project an image of the aperture.

11. An apparatus according to claim 10, wherein the focal length and position of said additional lens means is adjustable so that the additional lens means can also project an image of the plane of the or each filter support means.

12. An apparatus according to any one of the preceding claims, wherein the filters are dichroic.

13. A lighting apparatus constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.