Effective starting with the 6.4 beta firmware, RED cameras with the HELIUM sensor have a new ISO calibration to better match a light meter and improve overall exposure quality. HELIUM cameras will therefore depict a one stop brighter image compared to prior sensors (when set to an otherwise identical ISO, T-stop, and shutter speed). ISO 400 will now appear as bright as ISO 800 did before, for example.
To match exposure on HELIUM and non-HELIUM RED cameras, either reduce your HELIUM-based camera’s ISO speed by 1 stop compared to the other camera, or uncheck the box within “Menu>Image>ISO” labeled “Use new ISO calibration for HELIUM sensor” on your HELIUM-based camera. As usual, RED recommends using ISO 800 as a starting point for exposure, then adjusting the T-stop and lighting or ND filters to match.