The ETC Source Four 19 Degree Lens Tube is a precision optical component designed for use with the industry-standard ETC Source Four ellipsoidal reflector spotlight (ERS). This specific lens tube provides a fixed, narrow beam angle of 19 degrees, making it an essential tool for lighting designers who require a tight, controlled pool of light to highlight specific subjects or scenic elements with sharp focus and defined edges. The lens tube houses a sophisticated optical system comprising two plano-convex lens elements arranged in a specific configuration to collect and project light from the lamp and reflector assembly with high efficiency and minimal aberration. This design ensures a bright, even field with consistent intensity from the center to the edge of the beam, which is critical for creating clean, professional looks in theatrical, television, and architectural lighting.

Installing the 19-degree lens tube transforms the versatile Source Four fixture into a dedicated narrow-angle spotlight. The fixed focal length necessitates adjusting the position of the entire fixture (via its yoke) to change the size of the illuminated area—moving the light closer to the subject creates a smaller, more intense pool, while moving it farther away enlarges the circle of light. This lens is particularly valued for its ability to throw light over long distances with minimal spread and intensity loss, making it ideal for front-of-house positions in large theaters, for isolating performers on deep stages, or for lighting architectural details from a remote location. The sharp cutoff of the beam allows for precise shaping with the fixture's integrated framing shutters and iris.

Constructed with durable, heat-resistant glass and a robust aluminum barrel, the lens tube is built to withstand the high temperatures generated by the fixture's HPL-type lamp. It is designed for quick and secure attachment to the Source Four body via a rotating collar and locking mechanism, allowing for easy swapping with other lens tubes (such as 26°, 36°, or 50° options) to change the fixture's field angle as needed. As a genuine ETC component, it is engineered to maintain the optical integrity and performance characteristics that the Source Four series is known for worldwide. The 19-degree lens tube remains a fundamental choice in a lighting designer's toolkit for creating dramatic focus, strong specials, and long-throw applications where beam control is paramount.