The present invention relates to a multi-color gobo for the projection of a multi-color pattern, and to a method of manufacturing the gobo. On the basis of a multi-color pattern that is color-separated into single-color components, the single-color components are disposed to parallel planes in the gobo and at least two of these planes are mutually separated by means of a transparent substrate. The gobo may include a plurality of mutually superimposed disc-shaped and transparent substrates and each of the substrates may include a dichroic surface coating so as to form a color filter. Combinations of the color filters are able to reproduce the colors of the multi-color pattern and respective color-emitting surface coatings present a pattern that coincides with the pattern of corresponding color components in the multi-color pattern.

FIELD OF THE INVENTION 
The present invention relates to a multi-colour gobo. 
BACKGROUND OF THE INVENTION 
Gobos are used in theatres, TV studios, etc., to set desired light patterns 
and to project a pattern onto a surface. Gobos are a type of diapositive 
image placed in powerful projectors for projecting the pattern of the gobo 
onto a background to provide a light pattern or a light image thereon. In 
order to enable the light pattern to appear in a non-darkened surrounding, 
powerful projectors are required, these projectors generating a great deal 
of heat, partly in the form of IR radiation, meaning that the gobo must be 
heat-resistant. 
Because of the high temperatures that prevail, typical plastic diapositives 
or transparencies cannot be used and it is necessary to either cut or etch 
the contours of the patterns in metal sheets or in a metal-coated glass 
sheet. The most usual method of colouring a pattern at present is to mount 
a colour filter in front of or behind the pattern. This enables only one 
colour to be applied, however. A multi-colour picture or image can be 
produced by this method with the aid of several projectors, each having a 
colour-part of the image directed on one and the same surface, wherewith 
the overlapping projections reproduce the basic pattern in colour. 
It is known to produce a multi-colour image with the aid of a gobo by 
building-up a plurality of colour-emitting dichroic coatings on a glass 
plate. The colour-emitting coatings are built-up one at a time. Each 
coating corresponds to a colour in the image and consequently it is 
necessary to re-mask when one coating/colour has been built-up and the 
build-up of a new coating/colour shall commence. In turn, each coating 
involves a plurality of thin layers with alternate high and low refractive 
indexes. The coating is normally applied in a vacuum vapourization 
chamber. It is necessary to remove the glass plate from the chamber and 
re-mask between coatings, which is a time-consuming, expensive and 
irrational process. Furthermore, there is a risk of contamination each 
time the glass plate is masked or removed from the chamber. 
SUMMARY OF THE INVENTION 
An object of the present invention is to overcome the aforesaid drawbacks 
and to provide a multi-colour gobo. This object is achieved with a 
multi-colour gobo that have the characterizing features set forth in the 
following independent claim. 
Further features of the invention and advantages afforded thereby will be 
evident from the dependent claims and also from the following detailed 
description of a preferred, non-limiting embodiment of the invention. To 
facilitate an understanding of the description, the descriptive text 
includes references to the accompanying drawings, in which mutually 
equivalent or similar parts have been identified by the same reference 
signs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The multi-colour gobos shown in FIGS. 1 and 2 is circular in shape and can 
be used in a so-called profile projector to project a multi-colour 
pattern. 
The multi-colour pattern to be projected is colour-separated and rastered 
(or halftoned) in a manner known in the printing field, resulting in an 
array of single colour components. Colour separation is effected for 
instance in a computer that includes appropriate software. Those colours 
into which the image shall be separated are given and the separating and 
rastering operation is carried out. This results in what are designated 
here as single colour components, which is an array of patterns, one for 
each colour into which the original pattern is separated. The single 
colour components can normally be reproduced either positively or 
negatively. Whether positive or negative reproduction is preferred will 
depend on the following method steps. Colour strength or intensity is 
reproduced by varying the dot density in accordance with known rastering 
techniques. 
As will be evident from the drawing, the gobo includes a plurality of 
superimposed disc-shaped and transparent substrates 2, 3, 4. In the 
illustrated case, each substrate has a thickness of about 0.1 mm and is 
made of glass, although other transparent and heat-resistant substrate 
materials may be used. 
Applied to the surface of each of the substrates is a dichroic coating that 
forms a colour filter. Each colour-emitting surface coating presents the 
pattern of the single colour component and enables the colour strength to 
be reproduced through dot density. 
A contrast pattern is obtained with colour separation. A dichroic coating 
is inappropriate with respect to the contrast, and a totally blocking 
surface-coating is required instead. This surface coating, which in the 
illustrated case is deposited on substrate 1, gives the pattern component 
of the contrast in the finished multi-colour gobo. 
In order to stabilize the gobo and facilitate mounting of the gobo in the 
projector, the substrate 1 of the illustrated embodiment has a larger 
diameter and a greater thickness than the remaining substrates. 
With the intention of reducing the sensitivity of the gobo to external 
influences, the substrates may conveniently be orientated so that none of 
the substrates will have an outwardly directed surface coating when 
mounted in position. 
With reference to FIG. 1, the basic substrate 1 may present the contrast 
pattern on the surface thereof that faces towards the substrate 2. The 
substrate 2 may present its single-colour pattern in the surface coating 
that faces towards the substrate 3. The substrate 3 may present its 
single-colour pattern in the surface coating that faces towards the 
substrate 4. The substrate 4, however, will preferably be orientated so 
that the surface coating with the single-colour pattern faces towards the 
substrate 3, so as to avoid the surface coating of substrate 4 being 
scored or otherwise damaged. It will be observed, however, that if one of 
the substrates is turned so that the surface coating is located on another 
side than the remaining sides, which is the case of substrate 4, the 
pattern in the dichroic coating must be mirror-imaged so as to fit into 
the remaining pattern components in the correct manner. 
When multi-colour gobos are assembled, fitting marks--if these have been 
transferred to the substrates--can be used to align the substrates such 
that the pattern components will be congruent. According to one preferred 
embodiment of the invention, the substrates have mutually different 
diameters in accordance with the colour which the surface layer transmits. 
One reason for this is to facilitate fixation of the substrates on top of 
one another. The substrates are joined together one at a time subsequent 
to having aligned the pattern components one on the other. When the upper 
substrate has a smaller outer diameter than an underlying substrate and 
the substrates have been positioned correctly, the substrates can be 
readily glued around their edges and against the upper side of an 
underlying substrate. If the glue joint should project slightly above the 
edge of the substrate, this will not prevent the alignment of the 
next-following substrate when this substrate, in turn, has a slightly 
smaller outer diameter. The glue joint presents no great problem even when 
the substrates have mutually the same diameter and when the thickness of 
the substrate is greater than 1 mm, although the risk of a glue joint or 
some other affixation means is liable to obstruct a following substrate 
when the thickness of the substrates is decreased. 
In order to maintain a sharp projected image, the distance between the 
first and the last pattern component should not be too large. Trials have 
shown that the distance between the first and the last pattern-emitting 
surface coating will preferably lie beneath 1 mm. The distance is about 
0.2 mm in the illustrated case. The distance will depend on the thickness 
of the substrates 2 and 3 and of the dichroic layers. 
The basic substrate 1 with a material thickness of about 1 mm presents a 
total light-blocking coating of aluminium in the pattern of the contrast 
on its upper side. The surface coating has a thickness of about 0.40 m. 
Substrates 2 to 4 have a material thickness of about 0.1 mm and are coated 
with a surface coating that reflects a determined light wavelength 
interval. The light wavelength intervals reflected by the different 
surface coatings correspond to the complementary colours to those colours 
that are to be transmitted through the colour filter. Thus, when the 
substrate is to function as a colour filter and transmit yellow light for 
instance, i.e. allow yellow light to pass through, the surface coating 
shall be optimized to reflect light in the wavelength interval of the 
colour complementary to yellow light, which is blue. Correspondingly, the 
colour cyan is transmitted when the surface layer reflects red, while 
magenta is transmitted when the surface layer reflects green. 
In the illustrated embodiment, the colours cyan, magenta and yellow 
together with the contrast components constitute the colour pattern 
components into which the multi-colour pattern is separated. 
A multi-colour gobo is produced in accordance with the illustrated 
embodiment, by colour separating the multi-colour pattern in a computer 
equipped with appropriate software for instance, such as to divide the 
multi-colour pattern into a specified number of single-colour patterns. 
These single-colour patterns are then transferred to dichroic surface 
coatings on disc-shaped, transparent substrates, these dichroic surface 
coatings transmitting light with the colour that respective single-colour 
patterns shall reproduce. Finally, the substrates containing the 
single-colour patterns are disposed in line with each other so as to 
reproduce the multi-colour pattern 5 when light is projected therethrough. 
The colour-separated and rastered patterns are transferred onto films, one 
film per single-colour pattern. 
The single-colour patterns are preferably transferred to the surface 
coatings lithographically. According to one embodiment, the surface 
coating may be provided with a photoresist layer which is then exposed, 
e.g. by contact copying, with its respective films. Exposure may be 
effected by means of UV light or the like, depending on the photoresist 
chosen. Subsequent to developing the photoresist, the substrate may be 
placed in a bath and the surface coating etched away at those points where 
it is not protected by the photoresist. 
In another embodiment, an inkjet printer or plotter, or some like device, 
may directly print-out, apply, the pattern with an etch-protective 
substance directly on the dichroic surface coating of the substrate, 
therewith enabling the surface coating to be etched so as to create the 
single-colour pattern therein. 
In a further embodiment, a laser beam can be used to burn-out the 
single-colour pattern in the dichroic coating. 
The dichroic surface coating is built-up by alternating with layers of high 
and low refractive index. 
The first layer nearest the substrate will have a higher refractive index 
than the second layer, and the dichroic layers will have an optical 
thickness corresponding to a quarter of the light wavelength of the colour 
to be reflected. This last deposited layer in the surface coating, 
however, will preferably have an optical thickness corresponding to half 
the wavelength of the colour to be reflected. 
By higher refractive index is meant a refractive index above 2, and by 
lower refractive index is meant a refractive index below 1.6. 
The layers will normally include quartz and titanium dioxide, and the 
dichroic coating will normally include more than ten layers, preferably 
sixteen layers (i.e. eight layer pairs).