“We’re no longer exposing for middle gray and letting the rest “roll off.” […] Through all of these techniques, it’s important to recognize that our old friend and exposure aid, middle (18%) gray, will be of limited usefulness, as middle gray will shift with the audience’s adaptation to brightness changes. It may be possible for a cinematographer to “chase” middle gray with a light meter, but they’ll likely need to find their new middle gray value by sitting in front of an HDR monitor long enough that their vision adapts to the brighter or darker image in the same manner as the intended audience. The cinematographer can then visually identify a new middle gray value in the scene and adjust their light meter accordingly.” – Art Adams
“Conventional exposure theory would suggest that with a camera like the Alexa that is ISO 800 it will reproduce a mid-grey as a mid-grey but if you set up for that in HDR then you are going to find objects in the frame over exposed. Candle flames, for example, tend to lose their color and can clip out very quickly and look unnatural. So, what I came up with as a solution, specifically because there are candles in every shot, was to expose from the top down. My starting point was not to over expose the candles in the HDR grade and let everything fall in underneath that. Since candles are usually the brightest object in the scene and I wanted to retain detail in them I began by setting the exposure so that the candles weren’t clipping with everything else being lit up to those levels.” – John Brawley on The Great
Where you decide to place middle gray is really scene dependent, as can be seen in the recommendations for live production above. In the image of the chessboard pattern, squares A and B have identical luminance.
The Daejeon Chronicles 
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