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 from the abstract to the literal.While fixtures from Martin such as the MAC Viper Profile or MAC Axiom Hybrid come with a great selection of stock gobos, many LD's prefer to load custom gobos. Care must be taken when changing and handling gobos and certain rules should be followed to help ensure the proper life of both the gobo and the lighting fixture.
Rule #1: Gobo Handling
Most automated luminarires utilize glass gobos, although a few also may use metal gobos. No matter the material, there are basics that are required when handling these tiny pieces of art.
- Always treat gobos with the upmost care; store them in a dust free environment and make sure they don't rub or scratch each other.
- It is best to wear gloves when handling gobos as this will eliminate fingerprints and other oils from transferring to the glass or metal.
- Always ensure the gobo is clean of dust, oil, or other contaminants before placing 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 then you have found the coated side. The un-coated or "glass" side will appear 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 towards 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.
Rule #3: Consider the Optics
The optics of your automated lighting fixture will 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 always 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 will be glued into the carrier from the gobo manufacturer, while others such as the MAC Viper series will use a retaining ring along with the carrier.
Most carriers will have an orientation mark (or magnet) that ensures the carrier can be placed back into the wheel in the same orientation for each fixture (see A below). You will want to also check that your gobos are all aligned with this marking within each carrier and inserted into the fixture with proper alignment; otherwise each gobo might be at a different angle within each fixture.
Gobos can create many dynamic and interesting looks on stage or in the air. By shaping the light output, creative images are easy to achieve. 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.
