Using NINAs DIYTrigger Plugin to Correct for Autofocus-Induced Pointing Error

[@nickhardy9651]

Hi James, Great to see the DIYTrigger being used. Exactly what it was meant for. ;) I created it for a system that has a real small fov and use it to slew to a starcluster before autofocus. Simliar kind of thing. In Nina 3.x it has been added to the power-ups plugin that Marc created. Seemed appropriate. Anyway, love your videos. Keep up the good work.

[@Aero19612]

Hey Nick. Thanks for watching and commenting. Your plug-in works great. It’s got me thinking of all sorts of other applications. That’s a good idea to slew to a star cluster for long focal length focus - I may have to try that myself.

[@HeavenlyBackyardAstronomy]

Hi James, Good tutorial. I am getting quite comfortable with the advanced sequencer and will certainly implement this code in it. It appears to be very useful.

[@Aero19612]

Hey Pat. I’m a big fan of the Advanced Sequencer. I know a lot of people have fallen in love with the ASI Air system, but I don’t think I’ll ever leave NINA. So many excellent plugins to consider as well. Thanks for watching!

[@tostativerdk]

As always great, thorough and insightful videos! I wonder why the “Center after drift” trigger does not actually do the recursive centering? I can’t seem to figure out why you would not want that always?

[@Aero19612]

Thanks for watching! I’m guessing that it’s the time commitment that they’re trying to avoid with Center After Drift. The Slew and Center instruction takes an exposure (6 sec or so), performs a plate solve, moves the scope ( 2 sec plus a settle time[?]), takes a second picture to confirm (another 6 sec), plate solves, and maybe repeats again. The Center After Drift just makes a blind move, which is ok If you don’t have backlash. Saves maybe 20 to 40 sec which is great…if it works. It doesn’t for me.

[@mleslie1080]

Jame does the triger also work for "AF After HFR Increase" and "AF After Temp Change” or is it needed for those?

[@guyjordan8201]

Love the programming logic shown here. Bravo. As you scrolled through images here 12:59 there were a few horizontal jumps. Can you ascribe cause to these?

[@Aero19612]

Thanks for watching! Not sure. If I had to guess, I'd say the apparent horizontal shift is just the leftover error mostly in the DEC axis. In the first Blink session (before the DIYTrigger), we were seeing error in RA and DEC.

[@guyjordan8201]

@@Aero19612 - OK thanks. Your DIYTrigger sequence improved repeatability very well.

[@jimwaters304]

Useful video James. Keep making them. Thanks

[@Aero19612]

Thanks for watching, Jim!

[@gregmckay666]

James, I enjoy how thorough you are in your investigation of this problem but find it extremely hard to believe the cause of this drift is torque from the focus motor. You did mention that you stop auto-guiding during your focus routines. Are you 100% positive it is not just drift during the focus routines? Maybe your polar alignment is off just a bit. One way to tell would be to time how long a focus routine takes, then do an unguiding sub for that period and see if there is drift in the same direction.

[@speppino]

I think that drift is caused by the focuser itself. These stock focusers have very lousy tolerances and the motor focuser will cause a small tilt in the imaging train and consequential drift. see it during focusing of my sharpstar scopes all the time. These focuser do not have bearings like moonlites focuser, but only some sort of shims opposed to the rack and pinion side and this is very prone to tilt and drift.

[@Aero19612]

Hey Greg. Haha. I’m not 100% sure of ANYTHING! But I agree with you. Some potential causes: (1) the forces/torques acting on a mechanical system with mechanical free play in the gears, (2) “Normal” drift due to polar mis-alIgnment, and (3) forces/torques acting on the focuser gear train as noted in the comment to your comment. Plus any number of other causes I haven’t thought of. I polar align each night before imaging, but I will investigate this more. Good question!

[@Aero19612]

@@speppino Very good comment. Several possible issues (including mirror flop with an SCT). Nice to know that the DIYTrigger plug-in solves all of these which means I don’t have to be that smart! Thanks for watching!

[@Spaced_Out_Bill]

I'm a little confused. It looks like you are not dithering. I always have stacking artifacts like you described but I thought it was from dithering. Maybe I should look again. How do you avoid walking noise in your stacked image if you don't dither? Thanks James, I always enjoy your videos.

[@Aero19612]

I rarely see walking noise. It was more common when I imaged with a DSLR combined with my Celestron CGEM. I suspect the CGEM was the culprit - more of a guiding issue than fixed pattern noise from the camera. As for stacking artifacts resulting from dithering - I think dithering radius should be within 10 pixels and should not produce noticeable stacking artifacts. Stacking artifacts like I'm seeing result from large (~50 pixels) jumps in the same direction. Dithering is random and much smaller in amplitude. Try out this DIYTrigger in your autofocus and see if the artifacts disappear. Good luck!

[@nathanielcharbonneau1726]

What reducer do you use? I have the 102fcd and have always had trouble getting a flat field. The ES FFFR isnt made for the 102 (which i found out after buying) so now use the stellarvue 0.8 SFFR25, but finding the right backfocus is a big challenge for seemingly no good reason.

[@Aero19612]

I’m using the Hotech field flattener (just a flattener, not a reducer). It works well. Thanks for watching!

[@dalepowell7353]

Are you dithering ?

[@Aero19612]

Hey Dale. No, I'm not dithering in this session.

[@MegaMichaeltodd]

Did you dithert in ths sessions where the focuser is throwing off the pointing accuracy?

[@Aero19612]

@@MegaMichaeltodd No. I don't dither. Dither does 2 things: (a) reduces fixed pattern noise and (b) improves resolution for under sampled images when combined with drizzle integration. I don't see fixed pattern noise and this scope/camera are not under sampled.