Guiding woes with an EQ6-R/ASI120MC/Ekos

[discardedastro]

Hi all,

I'm having some troubles with guiding my rig, and trying to work out how to fix it is driving me slightly mad. I've run with Ekos/KStars as well as SGP/PHD2, and I was doing okay but still seeing ~2-3 arcsecond RMS. I realised my guidescope was dewing up, but a Lacerta deltaT and heater strip on the guidescope appears to have completely cured that. However now I'm still getting fairly poor guiding performance - I can see drift artefacts in some frames, get lucky on others, but end up with diagonal oblong stars in a good % of my frames. I've most recently been using KStars/Ekos, mostly because I'm down a Windows box so all I have is Linux boxes.

My rig is:

• 200PDS on an EQ-6R
• ADM rail, clamps, Primaluce guidescope rings
• Primaluce 60mm guidescope
• ASI120MC camera

Obviously the ASI120MC isn't the perfect guide camera since it's fairly high noise and fairly low resolution.

I've tried tweaking the Ekos guide module and can achieve periods <0.5" RMS but not forever, and it seems like it's near-constantly nudging the mount around a small amount to the point where it causes these visible problems. Unguided performance I haven't really explored; I am a bit scared that I might've damaged the mount at some point in my learning (I had a couple of telescope/tripod collisions, one of which I didn't notice for >30 minutes).

I'm running out of ideas when it comes to debugging and diagnosing the root cause. Obviously I can throw money at it by swapping the 120MC for a better guide camera, or selling the guidescope and buying an OAG, or both, but I don't know if these are actually the cause of my problems and I don't know how to narrow it down. Where should I start?

[pete_l]

7 hours ago, discardedastro said:

it seems like it's near-constantly nudging the mount around a small amount

hysteresis settings? backlash compensation? too short guide update periods?
On a physical level, if you have swapped your computer out, are you seeing cable drag.

[david_taurus83]

Try running the guiding assistant and it will recommend some settings to try. Could be a number of things. Backlash, polar alignment, wind etc

[discardedastro]

I don't get hysteresis or backlash compensation knobs (as far as I can see) in Ekos/INDI. PHD2 seemed to work well, but I couldn't get it working happily with Ekos in the mix, with PHD2 guiding selected; every guide frame would pop up the FITS viewer window ? but perhaps the Ekos internal guiding isn't going to cut it.

I've tried update periods between 1 and 5 seconds. Also tried switching the guiding to RA+ or RA- only, disabling DEC, and neither of those seemed to improve matters. Tweaked proportional and integral gains up and down from 133 to 20 (on a .5x tracking rate).

[discardedastro]

OK, so I did a better job of cable management and loomed everything together off the mount to make sure there wasn't any snagging and reduce drag, and got PHD2 working properly with INDI/Ekos alright.

Now managing ~0.7" RMS with heavy clouds, but hard to test properly. I did go through the guiding assistant, ended up with .2 minmove and ~660ms dec backlash compensation, so I think that should help a whole bunch. Time will tell!