just an update - had some unexpectedly cloud free skies this evening so was able to test again. By futzing with the low and high value settings in the solver settings it started solving and eventually landed on a low of about 570ish and a high of about 819ish. I was able to then run through the polar alignment process and complete it although there are a few snags to be wary of;
When you get to the actual alignment phase after the solving and you need to click refresh it defaults to a 1 second refresh and this seems to translate into a 1 second exposure (I imagine this isn't news to everyone more familiar with EKOS than I but it's not clear from the info on the screen) , this needs to be set to 0.5 or lower otherwise it crashes (and locks up) as I believe the V4L driver doesn't support beyond an exposure length beyond 0.5s. The other snag is that the image you use to align the star into the crosshairs has a _lot_ of noise on it (no idea if this is expected behaviour or not but the noise looks like what you see in the dark frame). It is, however, just about possible to make out the point you have selected although getting it super precise wouldn't be that easy.
In summary I had to ensure the following was set to make everything work;
Ensure in the indi control panel the iPolars image size is set to 1280x960 otherwise you will get strange images indeed.
Change the gain in the iPolars settings to a level suitable for your skies. This was in my back garden which is bortle 6/7 so I found I needed the gain at at least 160 to get solving to happen and right up at 192-288 to get it happening reliably.
I set the FOV in the alignment module to 780' x 585' and this seems to be happy.
I set the low and high values in the solver settings initially to around 400-900 and then it eventually homed in on about 571-819 after it solved the first image.
I used an exposure of 0.25s.
I used a refresh of 0.5 on the final screen.
With that in place it's then working for PA, with the noise issue mentioned above.
So I've successfully used it for alignment and I hope the info helps anyone else wanting to do the same.
Thanks you Jacqui! That was incredibly useful. I will try to check out the resolution issue on the INDI driver side. Regarding the noise, have you tried taking darks? Any setting in the V4L2 driver that would bring it down? was it mainly caused by the high gain?
The frames I was solving definitely had a 0.25s exposure dark frame but thinking about it there may not have been a 0.5s dark frame in the library for the refresh/alignment portion. It definitely looked like the dark frame wasn't being subtracted but I thought I had tried it with a 0.25 refresh as well and got the same result - this may not be the case and I'll try again next window I get (might get lucky tonight looking at weather).
In terms of the noise it doesn't show up much at all in the live view which is why it surprised me to see it at that point and so I'm not sure the V4L settings beyond gain and image size had much impact on it. That said I will do furthur experimentation with them to see what I get. Even when using the iOptron provided software on windows we typically had to crank the gain up to 2-4x to get solving to happen (it goes up in half step increments on their software so that's functionally equivalent to 192-288 ish on the V4L driver which is why I first played with that parameter).
That said, looking at the dark frames I do have it seems to be a pretty noisy device - the ioptron software dark frame seems to be a custom format so I've not been able to open that on my desktop to look.
Well, some more unexpected clear skies - did some more testing in the garden and definitely had dark frames in place and no change in the noise.
Even altering the gain had little impact on the noise tbh and I fiddled with various other settings in the driver but no real luck although changing the white balance seemed to be having some effect but fairly minimal.
However you can make out your target star from the noise (on the unit we have anyway) and I got the mount dialled in to what it told me was 1arcminute of alignment error so it is certainly viable to use the ipolar with the alignment module.
I can only throw wild guesses as to what is happening but it really looks like it's not subtracting the dark frame. Is it possible that because the refresh exposure has to be so low it doesn't have time to process it ?
Edit: sorry thinking out load but I don't see the noise on the live view which means logically there must be a setting to tone it down somewhere ...
It's been a while so I thought I'd add an update. Have been using the iPolar to do alignment successfully over the last 6 months - on a clear night with the right gain settings it just sails through alignment with the caveats previously mentioned even in a light polluted UK city suburb.
However just recently I thought that the indi libraries and kstars version should really be upgraded from the default raspbian repos I used initially so cloned the PIs flash card and ran some upgrades to indi 1.8.9 and kstars 3.5.2 from the astroberry repos in order to get the new polar alignment features and stellarsolver and it's fair to say the results were not positive.
The image now coming through from the ipolar is noisey as hell and solving fails completely against it, can't even get it to acknowledge there are stars in the image regardless of gain settings (solving works fine and super rapidly against the main camera although the image displayed in the solving screen is noisey).
So I recloned the old card, left the old version of INDI in place and only upgrade kstars - same problem! I haven't had time yet to go back and step through versions of kstars to see exactly where the problem occurs (There were a number of other oddities with kstars including the slew rate it tries to use on the iexos-100 mount we have) but right now I'd have to say that in terms of using the iPolar then all my comments previously about getting it working relate to Kstars version 3.0.0 and nothing newer at this time!
iOptron CEM120 EC2 and CEM25P
Celestron C11 EdgeHD and William Optics Star71
ASI 1600MM Pro, ASI 462MC
Moonlight Litecrawler (C11) and Motorfocus (WOStar71)
LodeStar X2 and ZWO OAG
Nextdome, AAG Cloudwatcher
I can't offer any more data at this point as I bgot stuck in a library mess after upgrading my pi so completely rebuilt it, however around the same time we acquired a guidescope with a QHY camera so we have been using that for polar alignment as it is one less USB cable to manage!
If we get some clear nights soon I'll do some testing with the ipolar and see if it's any better with my cleaner build of the libraries.