Sony Venice Cinema cameras offer Dual ISO and while Sony officially states that Sony a7S III does not have dual ISOs, there is a point 4-stops above the base ISO where a7S III boosts the signal to the analog digital converter resulting in lower noise. This effectively creates a second base ISO.
Philip Bloom put Sony A7S III Dual Base ISO to the test and found they vary depending upon the picture profile selected. Here’s what he found:
S-Log 2 / S-Log 3
Low Base ISO 640 / High Base ISO 12,800
Low Base ISO 100 / High Base ISO 2000
Low Base ISO 50 / High Base ISO 1000
No Picture Profile
Low Base ISO 80 / High Base ISO 1600
In other words, when shooting still with no picture profile you’ll get less noise at ISO 1600 than you would at ISO 1280 and the same is true in cine profiles meaning S-Log 3 has less at ISO 12,800 than at 10,000.
Because base ISO depends on the picture profile the ISOs will vary depending upon profile selected – but they are always 4-stops apart.
Bloom exaggerates noise by pushing up shadow detail in this video to show the point where noise drops: