(Photography: Brian Spady)

Hard edge, spot, profile, performance and other terms are used to describe automated fixtures that can project a sharp image. Most of these units also make use of gobos for projecting images that range from the abstract to the literal.

While fixtures from Martin, such as the MAC Viper Profile and MAC Axiom Hybrid, come with a great selection of stock gobos, many lighting designers prefer to load custom gobos. But they must take care when changing and handling gobos, and follow certain rules to help ensure the proper life of both the gobo and the lighting fixture.

Rule #1: Gobo Handling

Most automated luminaires use glass gobos, although a few may use metal gobos. No matter what material they are made of, there are basic protocols that are required when handling these tiny pieces of art.

  • Always treat gobos with the utmost care; store them in a dust-free environment, and make sure they don’t rub or scratch each other.
  • It’s best to wear gloves when handling gobos, as this eliminates fingerprints and other oils from transferring onto the glass or metal.
  • Always ensure the gobo is clean of dust, oil or other contaminants before placing it in a fixture. Use a soft, lint-free cloth or compressed air to clean any dirty gobos.

Rule #2: Gobo Placement

Glass gobos are typically made from a borosilicate with an aluminum coating on one side. You MUST ensure that the coated side is facing away from the lamp or source. Otherwise, it could cause the gobo to crack. In addition, improper placement could cause unwanted reflections within the luminaire.

To determine which side of the glass is the coated side, use the “pencil test.” Simply place the tip of a pencil or other small object near the edge of the glass. If the reflection is right next to the object, you have found the coated side. The un-coated or “glass” side appears with the reflection a small distance from the object. Be careful, though, and ensure you do not scratch or mark the gobo with your object.

 

Some gobos are not coated and instead are made from a unique textured glass. Always be sure to place the textured side toward the lamp or source. The only exception would be if the textured glass has also been coated for color or effect. In this case, you still want the coated side away from the light source.

 

Texture

 

Rule #3: Consider the Optics

The optics of your automated lighting fixture cause images to project “backwards” from what you may think. Always consider this when inserting gobos that have a specific look or direction required of them. This is especially important with gobos that are based on words or logos.

 

Rule #4: Understand the Carrier

Many rotating gobos use a carrier that includes the gobo as well as the gears for rotation. This makes it easy to change out the gobo, but you must consider how the gobo gets into the carrier. With some fixtures, the gobo is glued into the carrier from the gobo manufacturer. Others, such as the MAC Viper series, use a retaining ring along with the carrier.

 

 

Most carriers have an orientation mark (or magnet) that ensures the carrier is placed back into the wheel in the same orientation for each fixture (see A below.) You want to check that your gobos are all aligned with this marking in each carrier and inserted into the fixture with proper alignment. Otherwise, each gobo might be at a different angle in each fixture.

5-Carrier Marker

Gobos can create many dynamic and interesting looks on stage or in the air. Creative images are easy to achieve by shaping the light output. Ensure that you understand the methods for changing gobos on your fixtures. Martin has a wide range of hard-edge fixtures that make use of gobos, each with their own set of imagery. Be sure to read the user manual for each fixture for specific gobo changing information.

This post was originally published on Brad Schiller’s “In The Know” blog.

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