The term gobo comes from Hollywood, in the entertainment world. When the director wanted dark on the scene he ordered:   "go black out". The operator then introduced a metallic coat in front of the projector to interrupt the bright bundle. With the passing of time the phrase changed in the most immediate "Go.B.O" and the needs wanted that the coat was drilled so that the bright bundle acquires the desired forms. From this come the first metallic gobos.

In the time the techniques to drill the coat were improved, in order to get more and more complex images. Today usually laser or chemical photogravure are used to make holes in the coat.

In 90s dichroic gobos appear that compared to the metallic one offer the possibility to project more complex coloured and also photographic images.The image is got removing the present covering from the filter. For images with more colours are added more filters one on the other.

The removal can happen both with laser and with chemical photogravure.

fig 7