The 0.5 gain should correspond to a UGF of a few Hz.
Given that below 10Hz the filter is just a simple integrator, reducing the gain by a factor 500, should reduce the bandwidth by 500 down to ~10mHz, so that the galvo loop can be closed but also the DC signal be used for ITF control. While reloading the SDB2 quadrant configuration I broke the lock, as I forgot that many parameters are set by Metatron via cm commands for quadrant processes.
Figure 1, the loop closes properly (here in recombined at half fringe) and the integration time constant is indeed of the order of 100 seconds (corresponding to 10mHz).
