DHA's Metal Gobos

A gobo is useless without the right light. Important features are a small light source and an optical focusing system that will account for different throws (light-to-screen distances). In lighting terms, the best choice is a dedicated Profile Spot. In practical terms, it is common to fit a focusing accessory onto the front of a standard light and to use this as a gobo projector. Often, a zoom action is provided. This is not really needed in most photographic uses, having originated in theatre applications where the light is operated from a fixed position but may have to provide different areas of coverage. In studios, it is the norm for lights to be moved around as required.

Different lights take different size gobos. In the case of the ImageMaker, gobos are provided by the manufacturer, but in general they are obtained from independent sources. In the UK, the foremost of these is DHA Lighting, which supplies both photographic and theatre users and offers gobos in a wide range of sizes. Astute readers may recall that the company had a stand at Focus On Imaging earlier this year (as it has for the previous two years too).

DHA supports all the common photographic lights, including Bowens, Broncolor, Elinchrom and Multiblitz, as well as a host of tungsten units (including Photon Beard and Hedler). In addition, most other lights (such as the author's aged Courtenay Nova Twin Spot shown here) can be fitted with one of DHA's nine standard gobo sizes. Prices depend on the size chosen, but are most are around �6 each. Durability is excellent: the author has never yet suffered a broken DHA gobo in almost eight years of using them. Holders are also available, and can be made to suit special sizes if required. In some cases, it may prove cheaper to obtain a custom-made holder for stock-size gobos than to persevere with more expensive non-standard items. In all, DHA offers more than 700 designs, ranging from abstract patterns to specific items with recognisable scenes or words. As well as leaves, reflected water patterns and city skylines, there are pumpkins for Halloween pictures, holly and fir trees for Christmas, and a bunny with the words Happy Easter for, well, Easter! Custom designs can also be made if required. A free information pack, which includes a vast number of gobo diagrams, is available on request from DHA (tel: 0171 771 2900).

Lighting control is very much more critical when using gobos than at any other time. Under normal circumstances, small amounts of spill from one light into the illumination area of another has very little effect on the overall quality. Not so when gobos are used. Gobos are effective only when there are areas of darkness that can be selectively lit to reveal the projected pattern. Spill makes dark areas grey, reducing contrast and making the shadow pattern less clear.

There are three easy ways of helping to ensure optimum quality when gobos are used for projecting onto backgrounds.

1) Avoid poorly controlled broad lighting techniques. If softboxes are used, ensure that barndoors or grids are fitted to prevent spill. 2) Avoid placing general fill-in lights on, or close to, the lens axis. 3) Try to have as much separation as possible between the subject and the background. If subject lighting still reaches the background, use a darker background colour and boost the brightness of the gobo light.

Things are slightly different if the gobo is casting a shadow on the foreground (providing a dappled effect, for example). Here, contrast is usually lower, so spill is less of a problem (and may even be desirable). Conversely, there is no control over the 'screen' colour or brightness, so there is less room to vary the appearance of the shadow pattern.

As far as 'screens' go, shadow patterns can be projected onto paper background rolls (of any colour), walls, wallpapered flats, tables, or even naked bodies. For most uses, a flash head of 500J will perform adequately. If black paper backgrounds are used, more power will be required but better contrast will result. In the image shown here, for example, the gobo was projected onto white card using 300J of light, giving a modest low-contrast result.

A useful trick to determine lighting purity when using gobos is to check the effect of each light individually. Extracts from a b&w contact print show this for the example image. One frame shows the foreground lighting alone, another shows the gobo light alone, and the third shows the combined effect.

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