PHD2 plus AO magic

[ChrisR Oz]

I know this forum is mostly dealing with issues and problems. But I thought I’d share a good news story of how well PHD2 is performing on my (upgraded) system. PHD2 is a brilliant program and mostly “simply works”. Here’s another success case you mostly don’t hear, because we’re too busy out using PHD2 for imaging …

My system is a Celestron EdgeHD 800 w/ 0.7x reducer (only 105 mm back-focus to play with), ZWO 294MC pro camera, ZWO 120MM (bin 2x2) on OAG and AVX mount. Recently, “tuned” the AVX to reduce backlash. After that, using a better algorithm in PHD2 (Periodic PEC) and doing PEC training in CPWI, RA tracking was then about 1” RMS. Now I have upgraded to a Starlight Xpress Active Optic (AO) plus compact filter wheel and OAG (overall optical length just 80 mm) and have seen my best tracking ever at 0.47" RMS total. Not bad on an AVX! Haven't fully explored short exposures (ZWO 120MM bin 2x2) but get good tracking results at 0.5s so far.

And the best part was how painless it was to integrate and calibrate all this using PHD2. After some judicious choices (bin OAG camera 2x2, PHD search region 40 pixels, AO travel range tweaked back to 40, AO bump percentage back to 75%, dithering trigged by SharpCap) and calibrating twice (PHD2 does AO first, then mount) it simply works brilliantly. You’d think I’d have problems with the relative move directions between AO, mount and camera axes. But PHD handles all that. However, for some reason, it always seems to need two forced calibrations to juggle all that into place.

Very happy with how PHD2 performs. Well done team!

Cheers, Chris.

[Bruce Waddington]

Great work on this, Chris, congrats and thanks for posting.  Would you mind uploading your log files for this, I would like to have data that represent an AO use-case when things are setup correctly.  You can use the Help/Upload logs feature and then post the link here.  You will need to be very careful trying to reduce the exposure times below your current 0.5 sec level, you're very likely to just chase the seeing.

Thanks,

Bruce

[ChrisR Oz]

Hi Bruce,

Here's the whole log file for the tests that evening. Wind came up layer, so the session I posted was earlier (screen grab). 

Can't say I've tweaked it up fully. Notice that I still have quite large MinMo for both RA and DEC, which is more of a hangover from driving the AVX directly. May do better with a bit less (until the window appears, perhaps). Only obtained good data at 0.5s exposure. I did try shorter exposures a week earlier down to 0.1s (bin 2x2 helps). But at that time I did not have a good match between imaging and OAG camera focus, so it's all over the place. But it was working fundamentally. Must get back to try more of that, if this cloudy-wet weather gives me a break.

I had looked at the log file in the Log Viewer. But grabbing it now to send, I notice that the debug file is large. Seems a lot going on, not all good. I attached that as well, in case it proves useful (excerpts from it to reduce file size to attach). It starts in the afternoon with many connects and disconnects.  But later shows errors. Once I was guiding, I don't recall any disconnects/ USB issues at all - seldom have any issues. Did not seem to stop it working at the time.

Cheers, Chris.

P.S. Seems it's still too large to post. Will try another way ...  Uploaded from PHD2.

[ChrisR Oz]

forgot link:   https://openphdguiding.org/logs/dl/PHD2_logs_dTwB.zip

[ChrisR Oz]

Later when a light breeze started up, the total RMS grew to over 0.7". But it kept the peak from growing too much, which is new ...

[Bruce Waddington]

Thanks for posting this, it's quite instructive to see how an AO setup should work with a mount in this performance class.

Regards,

Bruce