Part of an ERS containing lens(es) and incorporating a colorframe holder. Hard or soft focus is achieved by moving the lens tube forward or back within the barrel. On many modern instruments, the lens tubes are interchangeable and available in 5°, 10°, 14°, 19°, 26°, 36°, 50°, 70°, and 90° sizes.
A 19° lens tube for an ETC SourceFour.
https://www.fullcompass.com/prod/082297-etc-419lt-19-degree-source-four-lens-tube
A 19° lens tube for an ETC SourceFour.
https://www.fullcompass.com/prod/082297-etc-419lt-19-degree-source-four-lens-tube