The ETC Source Four 26 Degree Lens Tube is a precision optical assembly that defines the beam angle and quality of light for the industry-standard Source Four ellipsoidal reflector spotlight (ERS). This specific tube houses a meticulously engineered lens system designed to produce a medium-wide field of light with a beam spread of 26 degrees. When installed into the yoke of a compatible Source Four fixture body, it transforms the raw light from the lamp into a controlled, sharp-edged beam that is the cornerstone of theatrical, television, and architectural lighting. The lens tube is not a standalone lighting instrument but a critical, interchangeable component that allows lighting professionals to reconfigure their fixtures for different purposes by swapping tubes with different beam angles.

The optical performance of the 26-degree tube is characterized by its ability to produce a beam with excellent field flatness, minimal chromatic aberration, and even intensity distribution from center to edge. This ensures that gobos projected through the fixture remain sharp and undistorted across the entire beam. The lens assembly within the tube is a multi-element system, typically comprising two or more glass lenses arranged in a specific configuration to collimate and focus the light. This design allows for a smooth, adjustable beam edge via the fixture's internal shutter system and provides a long throw distance, making the 26-degree angle particularly versatile for general area lighting, key lighting for performers, and projection applications in mid-sized venues.

Constructed from durable aluminum with a matte black finish to minimize light spill and internal reflections, the lens tube is built for the rigors of professional use. It features a secure, tool-free locking mechanism that allows for quick and safe changes on a hanging fixture. The 26-degree angle sits in the middle of the Source Four lens tube range, offering a balance between beam width and intensity—wider than a 19-degree or 10-degree for more area coverage, but narrower and more intense than a 36-degree or 50-degree. This makes it one of the most commonly used and essential tools in a lighting designer's inventory, providing reliable, high-quality light shaping for a vast array of staging and highlighting applications.