This setting applies only to Advanced Bulb Ramping mode. If optionally set to "Yes", Promote Control Advanced Bulb Ramping logic will check if:
1.The current ISO is higher than the Lowest Auto ISO Promote Control Setup setting, and
2.The current Bulb Ramping exposure time is close to the shortest limit.
If both conditions above are true, then Promote Control will attempt to lower the camera ISO down to the Lowest Auto ISO Setup setting, while also making Bulb Ramping exposure time longer to keep the originally requested exposure. This serves two purposes:
1.Lowering total image noise - generally, the lower the ISO, the lower the noise is.
2.Making the current Bulb Ramping exposure time longer - the longer the exposure time is, the more precisely Promote Control can time it.
However, this logic may unexpectedly change exposure durations preset for Start and End in Bulb Ramping. If this behavior is not desired, leave this setting at the default value of "No".