I’m trying to use iPolar with Astroberry and KStars 3.5.0 stable. I’m able to acquire images and videos, both at 1280x960 and 640x960, but apparently there is no way to change exposure and gain. The image has always the same appearance. Interestingly, 1280x960 has a brighter exposure than 640x960. I see no particular issue in the log, attached. I also enabled stacking in Indi panel, and played with Auto/Manual exposure settings, with no results.
Yes, 0.5s seems to be an hardware limit (which is recognized by Indi v4l2 driver), however in iOptron software it is possible to change the exposure time (but apparently no more the gain with the latest release...), whereas in Indi the exposure seems fixed (decreasing below 0.5s does not have any effect, and also changing the gain). Interestingly, from an indoor test, I get roughly the same exposure of Indi by setting 31ms in iOptron software. If this is true, it may be too low for actual use (sorry, I cannot test outside, completely cloudy)
Changing the exposure within the capture routine appeared to have an effect for myself and changing the gain under the V4L options certainly has an effect on the image captured. Having popped the back off the iPolar since I wrote in the thread you reference it's basically a Sonix SN9C camera controller coupled to a low light sensor, specifically an SN9C6287 which I don't seem to be able to find any data for but some code for earlier sonix drivers does reference registers that can be used for exposure control so it's reasonable to assume that it can be controlled to a point, if only coarsely, but without reading the V4L code for the drivers it's using couldn;t be sure but the maximum exposure definitely seems to be limited to 0.5.
We use the iPolar routinely (and sucessfully) with the Ekos PAA so it certainly does work. (typically a 0.25s or 0.5s exposure time with a gain of 288-384 works fine in my bortle 7 garden and much lower gain when in darker skies.)
Thought it might be useful to add my own update here - I was/am using a very old version of kstars/ekos (3.0.0) which I can make work with the iPolar for PAA happily. Recently I have been trying to upgrade to 3.5.2 and cannot make the iPolar work with it at all (the image it takes is deemed unsolvable). I know it's Ekos as I made sure every other driver was the same on the system (indi, kernel etc) but as yet don't know at what point between 3.0.0 and 3.5.2 it stops working.