Curious about how this is happening.

[Kenn Hopkins]

Each time I run the Guiding Assistance I start by checking ‘Clear mount calibration’ then I calibrate on a star that is close to Meridian and 0 declination – East side of Meridian.

On the 3^rd of September I performed a Drift Alignment until there was no star movement for DEC and RA for 15 minutes. I then did a PHD2 Guiding Assistance and received a Polar Alignment Error of 3.4 arc-min with Right Ascension RMS of 0.18 arc-sec and Declination RMS of 0.10 arc-sec. guiding was OK.

September 6 I again ran a Drift Alignment until there was no star movement for DEC and RA for 30 minutes. I then did a PHD2 Guiding Assistant and received a Polar Alignment Error of 1.4 arc-min with Right Ascension RMS of 0.32 arc-sec and Declination RMS of 0.13 arc-sec.

I would have thought the guiding would be better with a longer Drift Alignment, but it seems to of produced result that were not as good. Even the guiding was poor with oblong stars. I use a Losmandy Titan Mount with a C-8 HD imaging scope and 80mm guide scope.

Kenn

[Brian Valente]

Kenn

Please upload your logs for the timeframe you are asking about

https://openphdguiding.org/getting-help/

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Brian Valente

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[Kenn Hopkins]

Following is the link for the log files: https://openphdguiding.org/logs/dl/PHD2_logs_FrX6.zip

Kenn

[Brian Valente]

Kenn

If polar alignment was the issue, then I would expect improving PA would result in improved guiding. However looking at your logs, the constraint to guiding performance is really in the periodic error of your mount

Your overall guiding RMS is low, but RA is higher than Dec. 

Here are a few things I see can can improve your guiding:

1. I would change your PPEC period to 159 seconds, increase your control gain to 0.7 and your prediction gain to 0.8. I realize you have it currently set to 32sec. I don't see anything that suggests it's an issue, but keep an eye on it

2. enable dec backlash compensation. start with a value of 600 and set the max value to 1200ms

I am not sure what version of the Gemini 2 controller you are on, but that 159 second period shoudl be easily addressed by using PEMPro for a mount-based PE correction and the latest L6 firmware 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/c871f957-07b4-4cba-89f9-e7b091047707n%40googlegroups.com.

[Kenn Hopkins]

10,000 years ago you assisted me with PemPro for my Titian mount and also suggested the following.

I regret but I do not see  PPEC period to 159 seconds, increase your control gain to 0.7 and your prediction gain to 0.8

Kenn

[Brian Valente]

Kenn

yes, you seemed familiar ;)

that 31.9 second error may have worked itself out, but it's worth testing some new settings

Look at this suggestion for revised PPEC

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/d8c567a8-7272-48ef-8958-17e338f242b4n%40googlegroups.com.

[Kenn Hopkins]

Weather will not cooperate for the next few nights but I will try as soon as it is clear to try these different settings.

You have a different setting for Declination, should I try those also?

I ran the Train PEC last night but will also need to wait until a clear night.

Last time I ran PemPro all I received was error messages because of  PemPro not working with ZWO Products, according to PemPro.

I need to install the latest version.

Anyway I will let you know what happens next imaging session.

Appreciate your time.

Kenn

[Brian Valente]

Kenn

do not make any other changes to PPEC or anything else on that screen other than what's pointed out

ZWO products absolutely do work with PEMPro, and you should use PEMPro for high quality PEC.

Just recording it via keypad is probably not going to produce a good PEC for precision imaging. You probably just need to bin your camera in PEMPro, but please take that up over at the PEMPro support forum

Brian

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/d2786ce1-82d8-4483-8666-98f7e96df58fn%40googlegroups.com.

[Kenn Hopkins]

If I may ask a question:

Back in 2018 you suggested I change the Period Length (in the Predictive PEC) to 31.9 but now in 2025 you are suggesting I change it to 159. Has something changed from 2018 to 2025?

I had a 1.5 hours window (9/10/2025) the other night and I entered the changes you suggested and ran the Guide Assistance in PHD2. I did get a better RA RMS of 0.14 px arc-sec and DEC of 0.06 but the Polar Alignment Error was 5.2. On the 7^th having the Period Length of 31.9 the RA RMS was 0.19 and DEC of 0.08 with a Polar Alignment Error of 1.4 arc-min. I have my Titan tripod embedded in cement and I cover it with a Telegizmo cover.

I’ve noticed that even when I run Guide Assistance on the same night the Polar Alignment Error changes each time, even on the same night. Is this normal?

I need to somehow get the RA RMS closer to the DEC RMS in order to obtain round stars. Would PEMPro help with that?

As soon as I get a clear night, I will run PEMPro and see what happens. I will try and update this posting with the results.

Again I really appreciate your time.

Kenn

[Brian Valente]

Hi Kenn

>>>Has something changed from 2018 to 2025?

based on your last logs, it appears yes

>>>>I had a 1.5 hours window (9/10/2025) the other night and I entered the changes you suggested...

please upload those logs, i would need to look at the details

>>>I’ve noticed that even when I run Guide Assistance on the same night the Polar Alignment Error changes each time, even on the same night. Is this normal?

yes, although keep in mind PA in PHD is an estimate. there are other factors that can change it such as flexure. I would not stress about PA too much unless it shows up as negatively affecting your guiding. your Dec RMS is lower, so it's not a constraint or issue

>>>I need to somehow get the RA RMS closer to the DEC RMS in order to obtain round stars. Would PEMPro help with that?

A lower periodic error (e.g., using PEMPro) will likely reduce RA RMS if it's periodic, and iirc yours has a good bit of that. Remember you will need the latest Gemini L6 firmware to get a good PEC

Brian

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/b9db1639-b460-4ae5-81c7-96bc651f43a0n%40googlegroups.com.

[Kenn Hopkins]

Guiding September 19, 2025

On the 15^th I was able to obtain a good PEMPro curve and uploaded it to the Gemini II, the following is an imaging session from last night. Gemini II, Hand controller, and mount itself were all worked on my Losmandy a little over a month ago so all software ‘should’ be up to date and the mount reworked and proper gaging established by Scott.

Scope on the West side of mount imaging Eastern sky object.

PHD2 Log entries:

1^st entry was calibration

2^nd entry is guiding on a star but changing the exposure time from 1.5 to 3 then 2 seconds.

Rest of the entries have guiding at 2 seconds sometimes stopping guiding to recenter star in main image.

Final entry: Same object being imaged but with scope on the East side of mount imaging in Western sky.

Observation:

The closer the object gets to the Meridian the better the imaged star gets. When starting an imaging session, the stars are very elongated but as the object gets closer to the Meridian the better the star gets. With the RA RMS being almost twice the DEC RMS even if I got an OAG the results would probably be similar. Overall tracking looks to be very good with an overall low RMS. I understand that with my C-8 HD the RMS ‘should be’ under 0.5 arc seconds.

Link of the PHD2 Log File

https://openphdguiding.org/logs/dl/PHD2_logs_KNmC.zip

Any suggestions on how to get the RA RMS closer to the DEC RMS?

Kenn

[Bruce Waddington]

I don't know what your image scale is on the main scope but my first reaction is that you shouldn't be getting substantially elongated stars with these guiding results.  I think it's pretty likely you have a differential flexure problem considering the size of the main scope and the length of an 800mm focal length guide scope.  It's also a pretty easy explanation for why the problem is sensitive to hour angle. Before you continue trying to squeeze out any more mount performance,  I think you should test for differential flexure.  That topic was just covered again in this post which includes a detailed method of testing:

https://groups.google.com/g/open-phd-guiding/c/tLltXqsfoKM

Good luck,

Bruce

[Kenn Hopkins]

AS soon as I have a clear night I will try the process on page 65 of the PHD2 Help. 

Kenn

[Kenn Hopkins]

Experimenting

Last night I experimented with PHD2 and balancing. The goal was to get the RA RMS to be closer to the DEC RMS since the difference between the two was over 10 points difference.

Using PHD2 Guide Assistance I watched the RA and DEC lines in the Display Graph option. I timed each balancing iteration for 3 minutes; I take 3-minute sub for any object I’m imaging.

Started with RA at 0.20 and DEC at 0.10 after moving the bottom weight down about 1.5 inches the RA was 0.26 and the DEC was 0.08. I thought that was interesting. I then slowly started moving the bottom weight up (though many iterations) until I obtained a RA RMS of 0.16 and DEC RMS of 0.13. I thought that with them being closer together the stars would be more ‘round’. With this value the RA and DEC lines in the Graph were almost on top of each other.

Did a PHD2 star calibration and slewed to a star near where I usually start my imaging of an object; usually 3- or 4-hours East of meridian. Unexpected as the Total RMS was 3.45 I thought the RMS would be vastly superior but boy was I wrong. Over the next hour I adjusted the bottom weight, recalibrated, recentered a star – 3 hours East of Meridian, until I was able to get a Total RMS of 0.48. With this I was able to obtain stars that looked ‘round’ and this seems to of solved my oblong, sometimes double star, images.

The scope I’m using is a C8 with a focal length reported at 2032mm and I heard that I needed an RMS of under 0.55 to get nice stars.

I may be wrong in thinking this solved my problem, but for now it looks promising -- to me.

Kenn