Yeah. That one had me stumped for a while. Seems that raspistill will go through several frames (around 7 of them) before it presents the final frame to the user. Each frame is the length of the exposure time that has been set. That is the very reason for implementing raspiraw in my driver after attempting to use raspistill.
For me, as written, the image is saved after about 1 second longer than the set exposure length. ie for a 5 second it takes 6.
If I remove the -bm, it gets a little longer.
if I remove -ex off, it does indeed get very much longer.
Just to make sure, when you say the image exposure does not change. You have turned of the stretch-button in the FITS-viewer then, otherwise the stretch function will normalize the exposure, with more or less noise as a side-effect.
I'm finding that if I start EKOS and go straight to the camera exposure tab, change gain first to anything 1 or higher, then change exposure to something long. It will give me a true long exposure straight away, and carry on doing so for the session.
Ive found you must not touch the exposure before the gain, as the moment exposure has been entered, a test image is captured automatically, which prevents future long exposures.
The command line I gave before still continues to be 'foolproof'.
I have the Pi HQ Camera and want to try it in an All Sky Camera. Previously I have been using ZWO cameras for this with RPi 3B, in particular the ASI178MC but this is a relatively old camera and needs quite a lot of cooling (using 60s exposures) to reduce thermal noise and hot pixels. This system has worked well with KStars/Ekos/INDI but cooling has produced a complicated setup - cooling the case of a non-cooled astro camera is inefficient. I have friends who would like to make an ASC too but ZWO astro cameras are expensive and would be interested if I can get it working with a cheaper camera.
My thinking is that the Pi HQ Camera is a much later addition to the Sony sensor range and could well be a lot more advanced and more sensitive in spite of smaller pixels.
To summarise, I'm looking to use the Pi HQ Camera with INDI and RPi, maybe the RPi Zero, using exposures of around 30s to 60s.
Its quite useable with the current indi driver if ones takes care to set the parameters in the right order. I'm able to get exposures up to 200 sec, both through indi, and direct RPi command line.
However, I've been running it alongside a ZWOASI 120MM-S in a plate-solving project to compare performances. The small pixels do seem to be an issue. To get anywhere near the same sensitivity as the ZWO camera I have to bin it 4x4.