Several minute delay before acquisition starts

Dear all -

I use Micromanager to acquire a time-lapse from a Sona-6 SCMOS camera, where the camera trigger is in “External Exposure” mode. I set it up to acquire 49,152 frames, where each frame is 200x200 pixels, and 12-bit, into a single image stack file of ~3.5 GB.

Strangely, there is a ~7 minute delay, after clicking “Acquire!”, until the first frame is acquired, after which the timelapse continues as expected. The delay until the first frame is only a couple of minutes if I switch the frame count value from 49,152 to ~10,000.

I checked and if I acquire this timelapse file, instead with Internal triggering, then there is no delay.

Screen shots from micromanager’s Multi-dimensional Acquisition window, and Device Property Browser window follow.

Please advise -

p.s., this is cross-posted on