[Edited Message Follows]
[Reason: Added image clarification of 'east heavy']

I have been having the most success with my EQ5, 130mm Newtonian and 50mm guidescope combination using all three of refraction compensation, OnStep PEC playback and Predictive Pec (PPEC) in PHD2. I have been recording and averaging my PEC curve over about 5 or 6 sessions and it seems to have smoothed out the transient errors to reflect the natural periodic error of my RA drive by now. Most nights I am averaging around 0.4-0.8 arc seconds in RA which isn't bad for a 130mm on an EQ5 in my opinion and well within my imaging scale of 1.81 arc sec / pixel.

Every system is different though, so do some PEC recordings over a few nights to average out the polar alignment errors, wind etc. and incrementally update the PEC accuracy as you go. I can definitely recommend PPEC over the default Hysteresis algorithm for an EQ5 though regardless, definitely give it a try.

I'd suggest an analytical approach on a multiple night basis, keep a little notepad or text file and ignore the graph, focusing on the RMS values and the images you capture. Sometimes my graph looks horrific but the RMS values are tight and the resulting images have good star shapes.

When you're dithering then even the RMS values aren't anything to go by as it ruins my stats, but provided you leave a long enough 'settle' time after each dither you won't affect the quality of your images once guiding stabilises itself before the next exposure begins.

My approach was this:

• Polar drift align the mount, get it to within 5 minutes of error to minimise the effects of polar alignment on your readings
• Set guide speed to 0.5x
• Choose a target with minimal atmosphere in the way to reduce that variable on your guiding as well, you can image at the same time but don't expect much usable data, this is more about the mount than imaging at this point
• Balance the RA axis East heavy so the worm drive stays engaged at all times during guiding, so that when it's commanding a West guide pulse the teeth aren't disengaging and falling due to gravity
• Enable the Hysteresis algorithm on RA
• Run the Guiding Assistant for just over one full worm rotation period, on my EQ5 with 144 tooth RA axis this is just under 600 seconds or 10 minutes, I'm not sure what that is on the CGE
• Fill the min-move with what the assistant tells you to, adjust your guide camera exposures as directed, I run 2.5sec exposures 90% of the time, 3sec the other 10%
• Keep OnStep PEC playback turned off, start guiding and start recording PEC data
• Guide through 4 or 5 worm periods to get a nice averaged RMS result, don't do any dithering!
• Note down your stats
• Turn PEC on and repeat, compare the stats for improvements
• Write PEC data to EEPROM
• Turn off PEC playback in OnStep Switch the algorithm to Predictive PEC, repeat the observation and note taking
• Turn PEC back on in combination with PPEC, take notes again
• Compare all your results and see what is working and what isn't

It's a right pain to sit through but it works out in the end, and it's how I settled on my current combination of Predictive PEC, OnStep's PEC playback averaged over multiple sessions and Refraction compensation turned on. The next few nights are perfect for it as it's a full moon and you're not going to be imaging much anyway, except maybe the moon itself.

Hope this helps!

EDIT - Clarification of 'East Heavy' if you're unfamiliar. Just in case - https://stargazerslounge.com/uploads/monthly_2018_08/Untitled-1.jpg.800c56d9d5bbb13847b3003d96a85b0e.jpg

On Tue, Apr 7, 2020 at 08:37 AM, Terry Fishlock wrote:

I will always be guiding as this rig is for long exposures. So what do you think the best tracking combo would be for that for best guiding. Is there a chance that one of the options might fight against the corrections being applied by the guiding program?

Yes, don't use dual axis & guiding unless you have a zero backlash Declination drive.

I totally missed any indication of changes to V3 I am reluctant to upgrade as my mount is performing pretty well right now. Is there an update list of changes from V1?

GitHub can browse the OnStep history, pick a branch and work your way back to see the comments/changes.

Generally speaking stability and solid bug free performance arrived in release-2.22.  Then release-3.16 added refinements, like its much improved configuration file format & configuration validation & more sophisticated command error checking/reporting, but deep down it's basically just like 2.22.  The current master branch (version 4.3) reworked the micro-step mode switching code (a fairly major low level change) and added a nice "auxiliary feature" control subsystem (for operating switches, dew heaters, intervalometer, etc.)

On Tue, Apr 7, 2020 at 11:37 AM, Terry Fishlock wrote:

I will always be guiding as this rig is for long exposures. So what do you think the best tracking combo would be for that for best guiding.

What is the best combo? I am no expert in autoguiding, since I am still working to learn it ..

But the main observation is that with autoguiding, lots of errors and mistakes are compensated for.
For example, the last session, I forgot to do a proper alignment, and still got decent results. That is
with no PEC at all (disabled it since I started guiding).

One caveat is that the mount has very low PE to begin with (Vixen SXD, about +/- 4"), so maybe
that is why guiding can do away without it. Don't know how a regular EQ5 with +/- 40" will do
without PEC, so that is the only difference to consider.

And I enabled the refraction compensation setting I mentioned earlier. The higher in the sky you go,
the less refraction offset there is, so if you image near the zenith, it matters less. But again, it cannot
be worse than regular sidereal and has advantages elsewhere, so why not make that the default?

Is there a chance that one of the options might fight against the corrections being applied by the guiding program?

There is no evidence that PEC and guiding fight each other in OnStep. But you may want to ignore PEC and see if autoguiding alone takes care of business. Or you can check Adaptive PEC in PhD2 and see if it improves things.

I totally missed any indication of changes to V3 I am reluctant to upgrade as my mount is performing pretty well right now. Is there an update list of changes from V1?

This is a recurring question, and the answer is check github, but it is a very long list. If Howard
would include the version changes in the commit messages, I would extract a change log from
there and edit to remove all the extra stuff (fixing comments, refactoring, ...etc.). But this is an
added task for Howard to do, and we can't be demanding on this time.

My recommendation is a solid go ahead and upgrade to 3.16. It has a much easier configuration
system, and breaks nothing. A few improvements here and there, but nothing earth shattering.
If you email me your configuration file (off list, as an attachment), I will create a 3.16 config file
for your