Seems reasonable, but if 720 is half a stop faster, and the ultimate downconversion is going to be comparable whether from 720 or 1080, then I'm sure people would want that half a stop. :thumbsup:
If you want that half stop, then simply use gain. That half stop of 720p itself just comes from implicitly added gain in the downconversion-process. So in terms of noise there won't be a difference.
You're right. I tested it. left is 1080 to SD, right 720 to SD.
