Timed bulb exposures
I take astronomical pictures with exposure times typically around 5-15 minutes, with typically series of 5-50 such exposures. Darktable's tethering feature only supports using a number of predefined exposures up to 30 seconds (at least with my camera). There is the bulb mode, but it's not feasible to keep the button pressed for 15 minutes, or even to start and stop the exposures manually. Typically, I need to long sequences of shots, and sitting by the computer holding the mouse for hours is simply not feasible.
I haven't yet found any other tethering application for Linux that would fit that purpose specifically, so it would be nice if Darktable supported this very important feature.
There is #8899 earlier, but I'm not entirely sure if the ticket was only about time counter with bulb exposures. Apparently, the reported had a similar need.
The exposure time in bulb mode should perhaps be set in the sequence photography settings, as that's how it is in the camera remote controllers that I've seen.
Actually, the bulb mode doesn't seem to work for me at all with my Canon EOS 40D. Other tethered shots with fixed exposure times seem to work.