Thanks for sharing info.
Arri uses a CMOS sensor in the Alexa and as far as I recall had superior DR in the Zacuto tests 2011.
I read about RED using some kind of HDR, found this on the Wiki: RED EPIC-X can capture HDRx images with a user selectable 1-3 stops of additional highlight latitude in the 'x' channel.
Here is RED's explanation:
"HOW DOES HDRX WORK?
In a single camera, HDRx simultaneously shoots two image tracks of whatever resolution and frame rate you have chosen. The primary track (A-track) is your normal exposure. The secondary track (X-track) is a "highlight protection" exposure that you determine in the menu settings. You select the amount of highlight protection you need in stops… 2,3,4,5, or 6. Each stop represents a stop less exposure in shutter speed. Example… if you select 2 and your primary exposure is 1/48th sec, the X-track will be two stops less exposure at 1/192 sec. The ISO and aperture remain the same for both exposures.
During recording, the two tracks are "motion-conjoined", meaning there is no gap in time between the two separate exposures. If they were two alternating standard exposures, there would be a time gap between the two tracks that would show up as an undesirable motion artifact. Both tracks (A & X) are stored in a single R3D. Since there are two exposures, the camera is recording double the amount of frames. For example, if you are shooting 24fps, the camera is recording 2-24fps tracks, the data equivalent of 48fps.* After combining the two tracks for playback you see only one 24fps motion stream."
So they say two frames combined using different exposures.