Improving guiding performance

[matt_baker]

Always had some kind of trouble with guiding and I'm wondering how can I further improve it?

I have a HEQ5 Pro and my payload is around 7kg with everything attached.

I ran the guiding assistant in PHD2 and the backlash came back at an insane value of 9000ms, so my best guess is to only guide it in one direction. Just how do you know which direction to guide in?

I have the rowan belt mod and I've adjusted the worm on both RA and DEC and did tension the DEC a bit more as it did seem a bit loose.

This guide log is only after the worm adjustment and not the tensioning.

I'm going out tonight to see but I want to try and get the total RMS to be stable below 1 arc second if possible and was wondering if anyone could help?

The log isn't very long as it was a test run before things got cloudy the other night but should give a good idea

Matt

PHD2_GuideLog_2020-09-15_004500.txt

[blinky]

If you have the belt mod done, make sure you have the scope balanced perfectly.  I find some noghts I get sub arc second and some nights its maybe around 1.3, I put this down to the weather!

[johneta]

Ive got an EQ5 with around 11kgs on it. Very overloaded.  Backlash is a terrible 7secs.

Its a struggle and I need to upgrade some day, but I can still get OK results.
Gotta balance very well. Ive got a newt and Ive got to balance it for that nights imaging. So get the best compromise of balance for the few hours that I will be pointing at the object. So I estimate the travel the scope will cover and get the best balance (Newts have a twisted type of balance that requires balancing for the area of sky you will cover in that imaging session)
Make sure Polar alignment is really good. I use sharpCap for that.
I use 2.5 sec PHD exposure time to smooth out seeing.
I guide in both DEC directions and due to good polar alignment I can still get good results.
Also Predictive PEC mode on RA in PHD works well.

The EQ5 really isn't a great mount, and I guess the HEQ5 has similar mechanics?
Maybe spend more time on getting belts tight and adjusting worm mesh as I reduced the massive backlash I had with a good few hours of tweaking in the daytime. Its very fiddly. (yes my backlash was even worse before the tweaking)

I can get 0.6-0.9 total RMS on a good night. As hinted to above, weather and seeing is king. A stable night with good seeing and transparency will give good results.
More $$ would also help 😉

Edited September 21, 2020 by johneta

[michael8554]

A look at a PHD2 log with a Guide assistant run  would be interesting, as it would show the unguided RA behaviour, which looks very erratic on the supplied log.

Dec backlash is going to be tricky.

Usually you slightly unbalance in Dec so that the backlash is always taken up.

Then Dec guiding will only be needed to bring it back inside the MinMo setting, and not over to the other side of the axis , which will take ages to bring back.

And if your PA is good (5 arcmins or less), you can increase the MinMo setting above GA recommendation, and Dec will chug along with very few corrections.

You can leave it on Auto, PHD2 will still only guide in one direction if you have the balance right - but Dithering will take a long time to settle sometimes !

But blinky says balance must be perfect :-<

So looks like the Dec backlash will need adjusting.

Michael