After some experiments, the Dark Cube now works. A reducer was used in order to fit the whole solar disc into a single frame, given it has 5M pixels, making it a bit small is still fine enough. The reducer lens is just a 30mm binocular objective, dropped into the barrel of the BF10 so that it was sandwiched between the blocking filter and the camera. The focuser drawtube of my Ranger was fully retracted, and the fine helical focuser has enough travel.
Seeing 3/10, transparency 2-3/10 with cloud around, so I only got around 200 frames to stack. The T-max/RichView could be tuned more carefully if there was less cloud.
AR2458 on the left, a few small prominences around.
Taken at 1409 (GMT+8).