ETC has two different 50 degree EDLT – Enhanced Definition Lens Tubes. The first one, Model 450EDLT, Part# 7060A2049 - 50 DEG S4 ED LENS TUBE BLK was designed for use with the standard incandescent Source Four fixture.
When tested with the Source Four LED fixtures, we found that the “regular” 50deg EDLT lens tube clipped off some light (called vignetting), because the beam has a somewhat wider cone angle than an incandescent Source Four.
To avoid this issue with LED fixtures, ETC designed a new 50 degree lens tube that is built more like the 70 and 90 degree lens tubes and uses 7 ½” accessories. This design does not clip off the beam. The LED-specific 50 degree lens tube is Model LED50LT, Part# 7460A2008 - S4 LED 50° EDLT LENS TUBE (BLK).
The 50deg LED lens tube should work fine with an incandescent Source Four, but the increase in light output may cause gel to burn out more quickly. ETC has not specifically tested this behavior.
When using a 50 degree lens with a Source 4WRD, ETC recommends using the 7460A2008.