And another very nice one,
with Canon.
Canon 70D - 10 x 120 seconds (20 Minutes) - ISO 3200
http://www.waa.at/bericht/2014/05/20...8api-n6087.jpg
From
http://www.waa.at/bericht/2014/05/20...fen/index.html
It is not absolute, but we can say that:
120 sec ISO 3200 = 4 min ISO 1600 = 8 min ISO 800 = 16 min ISO 400 = 32 min ISO 200
As he did with only 20 minutes, we can stop on ISO 400. I don't know if his Canon is modified.