I finally got my Mark IV version of the light box built and operational. Procedurally it works well; ACP can change between two brightness settings to account for the dimmer filters. It is kind of huge (2.5 feet cube) so it takes a lot of room in my small observatory.
Unfortunately, the flats produced are poor. It looks like the Tak can detect lighter/darker zones from the bulbs depending on where the OTA is pointed; I don’t get a nice even flat. Also, I can’t position the box well so the OTA is orthogonal to the lighted panel so I think that also leads to a gradient across the flat (top to bottom).
So, I am back to doing dusk or dawn flats. Tricky doing dusk flats because it is so hot outside (95 degrees at dusk, only going to get hotter here in Arizona) so the camera can’t get cool. I am trying for -10C, but 0 degC may be more in reach. I could water cool the ST2000, I may test that out. The STF8300 does not have water cooling available.