NINA Autofocus fails after meridian flip

[david_taurus83]

Have posted this to the NINA Discord channel but no harm putting in here as well. On the outset it looks like a software issue but I'm not exactly sure so have posted in this thread as could also be mechanical, atmospherical issue etc

Hi all, I have been having issues the last couple of nights with focusing after meridian flips. Never had an issue before and when I start my sequence everything looks perfect. Went to check my subs from a few nights ago and realised most if not all subs after the flip, auto focus had failed miserably. I kept an eye on this last night and sure enough, issues started after the flip. See below screenshot of my focus graphs. Imaging Witches Broom in Oiii, Esprit 100, Astronomik 6nm filters and DSD AF3. First few focus routines are perfect and results of 300s subs tending to be 1.7/1.8 HFR.

 

 

These are my typical focus curves and yield good results. These are in fact from last night before meridian flip. Notice the final position doesn't change too much. To be expected as temperature cools. However, after meridian flip, things change.

 

 

First one at 00.55 I let it take the first post flip sub. HFR jumps from 1.8 to almost 3. I stop sequence and run auto focus myself. There's a huge difference in final focus position and these were only taken minutes apart. I thought maybe focuser is slipping but doesn't explain why everything was fine before meridian flip? I left it to run overnight anyway and HFR values throughout the night are tending to be 2.2 or there abouts. Inspecting the subs today in Blink and its noticeable to my critical eyes that they are below standard and I can't use them. Any ideas? We have a few rare clear nights here in the UK this week so was hoping to jump to Ha this week with the full moon but this could be a significant stumbling block if I can't figure it out! TIA

Edited August 8, 2022 by david_taurus83

[Fegato]

I'll start by saying that I'm no expert, but I've never seen this with NINA and meridian flips. It doesn't feel like a software issue - the curve suggests NINA has done its best to find the optimum focus position available, it's just not close to where it was before. One would think something has moved or changed in the optical train after the flip. Are the stars uniform across the field after the flip? Any other clues?

[david_taurus83]

Something isn't right. It appears something is shifting slowly and the AF3 is compensating to keep up. It could well be that it is getting good focus at the time but shifting over the course of 20 minutes or so until the next focus run. I've just checked back on months of focus routines and the average focuser position is roughly a stable 510500 steps. Just looking back 4 days ago and the steps were reading 510089 and last night ended up on 505776. That's 4313 steps in 4 days! Something must be slipping.

[david_taurus83]

Its not NINA or the AF3. Its the Esprit fine focus. I can move the coarse focus knob fairly easily while the fine focus is held firm.

Will start another thread elsewhere as its not a software issue.

Edited August 9, 2022 by david_taurus83