Gobo (lighting)

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Projected light shines through a Gobo and onto a screen for decorative, informational or dramatic effect.

A gobo, also called template or pattern, is a thin circular plate with holes cut in it to create patterns of projected light. The name may be derived from go between, or from Goes Before Optics. Go between refers to the its position between the lamp and the lens. Gobos are similar in use to cookies, flags and cucalorus, which are placed farther from lighting instrument between the lens and subject.

1 Use
2 Mechanics / Optics
3 Other meanings
4 Manufacturers
5 References

[edit] Use

A gobo in a gobo holder, which goes in a stage lighting instrument. The discolored portion is burned, but the gobo is still usable.

Gobos control light by blocking, coloring, or diffusing some portion of the beam before it reaches the lens. Because the light is shaped before it is focused, hard edged images can be projected over short distances. Most Ellipsoidal Reflector Spotlights (ERS) have moveable lenses to allow sharp or soft focusing.

A theatrical gobo may be made from either sheet metal or borosilicate glass, depending upon the complexity of the design.

Glass gobos can include colored areas (much like stained glass windows), made of multiple layers of dichroic glass, one for each color glued on an aluminium or chrome coated black and white gobo. New technologies make it possible to turn a color photo into a glass gobo.

In low budget theater, discarded soda cans or pie plates can be used and patterns cut out with any cutting tool. The latest commercial technology enables finely dithered patterns which give the illusion of shading. In the UK, printer's Lithoplate was widely used as an inexpensive gobo substitute. However, these gobos tend to wear quickly due to the heat produced by a stage lighting instrument and are not viable for most venues.

Plastic gobos—which are generally custom made—are available when a pattern is needed in color and glass does not suffice. However, these thin plastic films generally need to be used with special cooling elements to prevent melting them. A lapse in the cooling apparatus, even for just a few seconds, can cause an expensive gobo to be ruined.

A number of simple and complex stock patterns are manufactured and sold by various theatrical and photographic supply companies, or custom gobos from customer-created images can be manufactured for an additional fee. Generally the lighting designer chooses a pattern from a catalogue or small swatch book provided by the manufacturer. Because of the large number of gobos available, they are generally referred to by number, not name. For example, most manufacturers offer a gobo of a window, but they are all slightly different. So instead of calling it window, it would be identified as gobo 77143 [1]

[edit] Mechanics / Optics

The gobo is placed in the focal plane of the lantern (generally an ellipsoidal reflector spotlight). The gobo is inserted upside-down and back-to-front. The desired pattern is then projected by the lantern onto whatever surface it is pointed at such as a wall or dance floor.

Gobos can provide everything from abstract dappled light effects to complex night-time cityscapes. They are commonly used in stage lighting, television, and film production to create texture, mood, or set a scene. Specialized attachments are available to rotate multiple gobos in different directions and rates to create an illusion of motion, such as that of light reflected off of moving water.

For example using a gobo with the pattern below

would produce this effect with red light.

This effect allows the lighting designer to produce effects to help portray the scene. For example, a gobo with a cloud pattern may be used to suggest a scene is outdoors.

[edit] Other meanings

The derivation Goes Before Optics" is from motion picture production, where gobo is an antiquated term for a what is now called a "flag". Flags are manufactured in a variety of sizes and shapes, are most commonly made of opaque black fabric stretched over a steel frame, but flags can also be made of sheet steel or wood for specialised use. Flags are placed in the beam of a light source in order to create shadows.

The support system used to position and hold these flags in the light beam has, as its core component a fully rotatable, adjustable clamp called a gobo head. [2] Gobo heads are mounted at the top of C-Stands and on the ends of 30" long aluminum bars, called Gobo arms or Grip arms.