Ioptron CEM70EC

[Daniel]

I have a new CEM70EC set up and running.  I guide with an OAG.  I am looking for the best settings to start with for this mount.  I have read that the corrections should be more infrequent than what I have been used to.  Any other advice for a good starting point for various settings would be appreciated.

[Tv-Home]

Daniel input all your imaging train inf into ChatGPT  tell it exactly what equipment your using mount , imaging camera , guide camera, telescope focal length, guide scope fl /OAG and ask chat gpt to recommend best parameters this will give you a good starting base before running guiding assistance, once guiding you can also take a screenshots chat gpt will give assistance, that goes to screen shots of setting tabs etc such as algorithm to use , I found it very useful and have had my best guiding in a while.

Dave 

Sent from my iPhone

On 31 Aug 2025, at 06:16, Daniel <daniel....@gmail.com> wrote:

I have a new CEM70EC set up and running.  I guide with an OAG.  I am looking for the best settings to start with for this mount.  I have read that the corrections should be more infrequent than what I have been used to.  Any other advice for a good starting point for various settings would be appreciated.

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[Dale Ghent]

Why not just use the provided tool for this. 5 minutes of running Guiding Assistant will give you exactly what you need without ChatGPT pooping out some numbers that have zero assurance of being grounded in reality. 

On Aug 31, 2025, at 04:58, Tv-Home <bottlet...@gmail.com> wrote:

Daniel input all your imaging train inf into ChatGPT  tell it exactly what equipment your using mount , imaging camera , guide camera, telescope focal length, guide scope fl /OAG and ask chat gpt to recommend best parameters this will give you a good starting base before running guiding assistance, once guiding you can also take a screenshots chat gpt will give assistance, that goes to screen shots of setting tabs etc such as algorithm to use , I found it very useful and have had my best guiding in a while.

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/5703C9FD-8A13-448C-9BA0-9896CF516853%40gmail.com.

[Bryan]

Daniel

Set u a new profile with the wizard and accept ALL the defaults.  Run Calibration Assistant, then Guiding Assistant, per Dale.  

If you are not happy with the results, share your logs here using the built-in log uploader.  https://openphdguiding.org/getting-help/

Good luck!

Bryan

[Bruce Waddington]

PHD2 is designed to work well out-of-the-box assuming you configure the profile correctly and follow recommended procedures.  I think the question you might want to be asking is, what are the capabilities of the new mount and does it meet expectations?   No two mounts - even two of the same models - are identical because of variations in manufacturing, assembly, and shipping history.  Over the years, I’ve observed that the delivered quality of iOptron mounts can be hit-or-miss, and we’ve seen many that have mechanical problems of one kind or another.  So in your position, I would be wanting to know if I got a “good one” and if not, what needs to be done to it.  The attached document described a procedure for getting a baseline measure of the mount’s capabilities and that would be a good place to start.  When you configure the PHD2 profile, don’t check the box for ‘has high-precision encoders’ – your mount doesn’t have them on the Dec axis as far as I know.  I would perform tests on both sides of the meridian to be thorough.  Keep in mind that guiding performance is often degraded by things other than the basic mount performance.  Poor cable routing and loose or flexing guide scope arrangements are a very common source of problems as well.

Good luck,

Bruce

[Daniel]

https://openphdguiding.org/logs/dl/PHD2_logs_fmgd.zip

There is the link to the log files.

I started out the evening following the Baseline Measurement document provided.  I started with the wizard, did the calibration and let it run on Assistant for four minutes I think.  Apparently, I am having a problem with polar alignment.  I will have to tackle that.  Once I got what I think was pretty good alignment, the tracking was acceptable, not great, but acceptable.   When I slewed from near the meridian and equator to my target NGC7000, the guiding got worse.  Much worse in my opinion.

Then I had a series of disconnects that I will need to figure out.  But got back to trying again near the end of the log.  Again, i calibrated near the meridian and equator and it guided ok.  When I did the slew again to NGC7000 the guiding sucked.  So I shut it down.

Not sure where to go from here, but it the CEM70EC doesn't perform better than this, it will be returned.

[Bruce Waddington]

Well, there was a lot going on here so it's a little hard to sort if all out.  It's particularly hard when you're only doing very short guiding sessions.  That said, there are some things that seem to be identifiable:

1.  You did a lot of unnecessary calibrations which led to very mixed results.  If you use the Calibration Assistant and get a good or acceptable result (you did), you should keep using that calibration.  The only reason to repeat it is if you make mechanical changes to the setup such as rotating the guide camera.  In your case, some of the guiding sessions were using poor calibrations which makes the results difficult to interpret.

2.  I think the problem you had when you slewed to a target at Dec=45 is probably caused by poor cable routing.  Here's what that looked like (RA in red, Dec in green):

You can see the guide commands were never able to move the guide star back to the target position.  This can be caused by cables that are pulling or binding and interfere with the movement of the mount.  This showed up multiple times even when the guiding sessions near Dec=0 looked ok.  The problem occurred on both sides of the pier at the Dec=45 pointing position.

3.  One of the Guiding Assistant runs shows some native RA tracking behavior that is concerning:

Keeping in mind that this is being done without guiding, the rapid oscillations in RA are a problem and I think you should ask iOptron about it.  It looks like the seeing wasn't very good based on the unguided Dec behavior, with excursions of about 1 arc-sec.  But the RA oscillations are more frequent and have amplitudes more like 1.5 to 2.0 arc-sec, and the repetition rate suggests to me it's coming from the RA drive system.

Hope this helps,

Bruce

[Daniel]

I understood part of that.

There are no cables to snag.  The rig has no cables running between the dovetail and the rest of the mount.  All internal.  I can move the mount anywhere within limits and no cable is anywhere near a snag point.

I did do a rotation on target that seems to have affected guiding.  But, I have the rotator as part of he PHD2 setup and I thought that was supposed to compensate.

Several of the calibrations were unsolicited.  When it did a slew and capture, it immediately went into calibration mode.  I thought that running the wizard initially would set a "master' calibration file.  It does not seem to be so, or it is not finding that, or I messed something up.  Probably the latter.

I have already contacted iOptron regarding the guiding.  It sounds like you are suggesting I send them the guide log?  Or part of it?  Can they even understand that stuff?

Regards,

Dan Jonas

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From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Bruce Waddington <bw_m...@earthlink.net>
Sent: Monday, September 1, 2025 11:00 AM
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: Re: [open-phd-guiding] Ioptron CEM70EC

 

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[Bruce Waddington]

Internal cabling doesn't mean there can't be cable tangles and snags - it just means you can't see them.  Moving the scope around by slewing or by hand doesn't prove anything about that because the forces used in guiding are many orders of magnitude smaller.  But the problem, at least, is pretty clear.  If it isn't a cabling problem, you'll have to figure out what else it is.  What it isn't is a guiding problem

It looks to me like you started some of the guiding sessions yourself from the keyboard.  For example, the one that started at 22:47:57 wasn't initiated by your imaging app (NINA, I guess) so that means you must have done it.  The calibration was explicitly cleared at that point, probably because you did a shift-click on the guiding icon rather than just a click.  PHD2 doesn't spontaneously discard calibrations, it does that only when it's specifically told to do so.  Many of us are using calibrations that are months old.  Of course, I don't really understand doing testing and measurement with an imaging app banging away in the background also talking to PHD2.  If you want to really evaluate the mount, you should be doing the guiding operations manually with nothing else going on.

I missed the fact that you're using a rotator on the rig.  That's fine but you'll have to be sure the polarity settings are correct for that to work right.  There's a section in the User Guide that describes a procedure for getting it right (Basic Use/Rotator selection).  But again, if you strips things down to the essentials during testing, there are fewer things to go wrong operationally.  Obviously, the rotator has no bearing on mount performance.

In my experience, the iOptron people are accustomed to looking at PHD2 graphs and have provided useful assistance to other users.  So I would say show them the graph and give them a chance to react.

Bruce

[Georg Albrecht]

Hi Daniel,

If I may ask, did you buy the mount directly from iOptron in the US? And how much time do they allow for a return (in the worst scenario)?
The CEM70EC is my second mount and I was going to poke this forum with questions as well.

The difference between your's and mine is that I do not use a rotator and we have different OTAs (focal length).
My guiding exposures are set at 4.5sec. Hysteresis for RA and Resist Switch for DEC were the settings I got when using the wizard for the initial set-up.
The only help I got from iOptron was - " In normal condition, EC mount prefers long cadency guiding, e.g. long exposure time and time laps"

I am keeping an eye on this thread. Once I have done more testing and fine tuning, I will post my logs and questions as well.
My mount is actually 2 years old, bought new at that time. But due to circumstances I don't want to elaborate here on this platform, I was only able to start freshly this past month. 
You are welcome to reach out to me directly if you are interested in the backstory. 

I hope after this next period of cloudy skies, I can gather more info and post my logs.

Cheers - Georg

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[Daniel]

Sorry, I did not answer your first question.  I bought it from Agena Astro.  My understanding is the return policy is 30 days.  I'm feeling a bit rushed to make a decision because of my own schedule.  I have had it for about four days and I leave in a week for a three week trip.  I have just a few days to figure out if I keep it or return it unless I can get them to bend on the policy.  I have an email out to them, but it is labor day and I don't expect a response until tomorrow.

Dan

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From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Georg Albrecht <gga...@gmail.com>
Sent: Monday, September 1, 2025 1:11 PM
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[Daniel]

Bruce,

I hope I got this in the right place.  I did as you suggested, and polar aligned and just ran tracking on several targets over several hours.  The PHD2 log is here:

https://openphdguiding.org/logs/dl/PHD2_logs_4V6r.zip

I am going to include the notes that I took during the run.  They are:

I had some trouble with the first few attempts at calibration.  I had polar aligned with the iPolar scope.  When the calibration did not work very well, I went back and used the 3 point alignment process in NINA.  It only reported a 1'25" error at the start.  I worked that down to about 40'.  After that, I got a good calibration.

Letting it run for about an hour.  During that time, got the following errorL

After 19.0 seconds the camera has not completed a 4.0 sec exposure, so if has been disconnected to prevent other problems.....PHD will attempt to reconnect.  

Apparently if did as it kept running.  Normal?

About an hour in, running Guiding Assistant.  Ran it for 4 minutes.  Showed a 4.8 arc-min alignment error  Dec drifter off quite a but after several minutes.  RA stayed pretty tight.

I'm not sure taking the recommendations of Guiding Assistant made the guiding any better.  Maybe a little bit worse.

11:05 pm switch connection lost along with rotator and focuser.  All equipment connected through the Pegasus Switch failed.  Restarting Unity only the focuser and the filter wheel were restored.  Unplugging the USB 3 from the Mount and reinserting the plug allowed everything to restart.

Slew to NGC 6960
 11:22 restarted guiding.  It took several tries to restart guiding.  had to pick a star manually.  Guiding appears worse.  Large divergence between the dec and RA lines.  No rotation of rotator in the target acquisition.  But I did loose the Pegasus Switch as noted.  I never lost PHD2 but the guide camera would have reset.

11:38, ran autofocus.

Stopped guiding at 12:00 am.

The notes about the loss of the switch has nothing to do with the guiding I think, but is a separate problem I may need to work on with iOptron.  I am cuious what your thoughts are on this log and what additional problems I might need to deal with.

Regards,

Dan J.

[Bruce Waddington]

This does look better and I don't see anything here that points to problems with the mount.  I see you've switched to variable-delay exposure times which may have helped to calm things down with the RA tracking.  I don't know how long it takes for the encoder system on your mount to stabilize but the slow-cadence guiding produced some good results.  The 50-minute guiding run at 21:50 had an overall guiding RMS of 0.6 arc-sec which is probably as good as the conditions would allow.  I'm really wondering about all the polar alignment problems you're having and if you're not getting mount adjusters tight enough when you finish the polar alignment.  I say that because you're still getting the apparent increase in drift when you slew away from Dec=0.  At Dec=35, the guiding looked like this:

We're again seeing the "offset" in RA tracking.  This isn't caused by polar alignment error, alignment error only affects Dec as you saw in the GA graph - and now we know it isn't related to the rotator.  RA drift can be caused by things like cables as I mentioned before, by a loose clutch, or by other payload problems like substantial weight imbalance.  You were working from the east side of the pier here and the guide corrections were to the east, which is what you would see if the payload was nose-heavy, dropping "down" toward the western horizon.  The spikes in Dec also suggest some kind of problem external to the mount such as cables.  At the time of each large Dec excursion, the Dec motor wasn't even running so it would be hard to blame the mount.

You will have to sort out all the problems with USB connections and whatever else it going wrong with power - these are killers for guiding and imaging, not something you can just hope to live with.  PHD2 will automatically try to recover camera connections but it will eventually stop trying - and in the meantime, it isn't sending guide corrections to the mount.

Good luck,

Bruce

[Brian Valente]

Dan

Just to clarify

>>>After 19.0 seconds the camera has not completed a 4.0 sec exposure, so if has been disconnected to prevent other problems.....PHD will attempt to reconnect.  Apparently if did as it kept running.  Normal?

it's not normal to have a camera disconnect, it is normal that PHD attempts to keep things going, attempting to reconnect to the camera. As Bruce said you need to hunt down the reason for this disconnect. Are you running it through the internal mount cables? 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/f18ba503-3c1f-488c-a9af-183e1b4b4b02n%40googlegroups.com.

--

Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Daniel]

Bruce,

Thanks.  That all helps.  As I said, no external cables but I may have to dig into the mount to see if something is going on there.  I thought I was pretty well balanced, but maybe making some adjustments might help.  Since the nose is dropping, I could slide it back a bit and see if that creates any improvement.  Another question might be the distance of the counterweight from the axis.  I have one large weight about halfway down the counterweight arm.  I could add a smaller and move the large one much closer to the axis?  Probably all good experiments.

I'm curious about the Dec excursions.  I have noticed that just walking up to the mount to look at something and then walking away, I see spikes in the guiding graph.  I have a good pier tripod that sits on a concrete patio.  I don't recall seeing this with the GEM28, but it seems consistent with the CEM70.  It is almost like it is sending me a warning to stay clear.  Could it be that much more sensitive?  I know wind can do it too, but we were pretty much calm winds during last evening's test.

One other thing I noticed was that the sharpness of the guide camera focus did not seem as good at the higher target as it did at the calibration target.  This is an OAG, so focus, once set, is controlled by the main image train focuser.  Could that have created the spread on the DEC and RA showing up in the later guiding?

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From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Bruce Waddington <bw_m...@earthlink.net>

Sent: Tuesday, September 2, 2025 8:39 AM

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[Daniel]

Yes, everything runs through the CEM70 mount internally.  That was one reason for the purchase (to get rid of all wires between the dovetail and the ground).  There is a USB 3.0 port on the back of the mount and three at the Dovetail.  I plug the mini computer into the USB 3 on the mount and then the main camera directly into one of the dovetail 3.0 sockets.  Through the 2600 that runs the OAG camera and filter wheel.  Another 3.0 goes to a Pegasus switch which supplies USB to the rotator, focuser and Deep Sky Dad flat panel.  Power also goes through the mount.  That is powered with a Pegasus 10 amp - 12 volt power supply to the mount connection.  From the dovetail then to the Pegasus Switch which supplies power to the Main camera and the Deep Sky Dad flat panel and one dew heater.

I don't think I have seen much more than 2 amps on the Pegasus power graph.  Usually runs under 1 amp.

Power for the CEM70 is supplied by a separate power supply which was provided with the CEM70.  The mini computer running NINA is AC powered with its own internal power supply and sits under the tripod.

---

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Brian Valente <bval...@gmail.com>
Sent: Tuesday, September 2, 2025 8:45 AM

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[Daniel]

I've never used that particular option.  I polar align, calibrate prior to running the sequence.  My command in the sequence is simply to start guiding.

---

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Mike Ales <mike...@gmail.com>
Sent: Monday, September 1, 2025 12:07 PM
To: open-phd...@googlegroups.com <open-phd...@googlegroups.com>
Cc: open-phd...@googlegroups.com <open-phd...@googlegroups.com>

Subject: Re: [open-phd-guiding] Ioptron CEM70EC

 

Daniel if you are using Nina as Brian speculated turn off the calibration option on Nina start guiding instruction in the sequencer

That option in Nina is for folks that want to do the initial slew near Zenith and calibrate PHD2 via sequencer instruction instead of the preferred PHD2 calibration asssistant which slews to near Zenith

Sent from my iPhone

On Sep 1, 2025, at 1:23 PM, Daniel <daniel....@gmail.com> wrote:



I understood part of that.

There are no cables to snag.  The rig has no cables running between the dovetail and the rest of the mount.  All internal.  I can move the mount anywhere within limits and no cable is anywhere near a snag point.

I did do a rotation on target that seems to have affected guiding.  But, I have the rotator as part of he PHD2 setup and I thought that was supposed to compensate.

Several of the calibrations were unsolicited.  When it did a slew and capture, it immediately went into calibration mode.  I thought that running the wizard initially would set a "master' calibration file.  It does not seem to be so, or it is not finding that, or I messed something up.  Probably the latter.

I have already contacted iOptron regarding the guiding.  It sounds like you are suggesting I send them the guide log?  Or part of it?  Can they even understand that stuff?

Regards,

Dan Jonas

---

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Bruce Waddington <bw_m...@earthlink.net>
Sent: Monday, September 1, 2025 11:00 AM
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: Re: [open-phd-guiding] Ioptron CEM70EC

 

Well, there was a lot going on here so it's a little hard to sort if all out.  It's particularly hard when you're only doing very short guiding sessions.  That said, there are some things that seem to be identifiable:

1.  You did a lot of unnecessary calibrations which led to very mixed results.  If you use the Calibration Assistant and get a good or acceptable result (you did), you should keep using that calibration.  The only reason to repeat it is if you make mechanical changes to the setup such as rotating the guide camera.  In your case, some of the guiding sessions were using poor calibrations which makes the results difficult to interpret.

2.  I think the problem you had when you slewed to a target at Dec=45 is probably caused by poor cable routing.  Here's what that looked like (RA in red, Dec in green):

<Guiding_Dec45.jpg>

You can see the guide commands were never able to move the guide star back to the target position.  This can be caused by cables that are pulling or binding and interfere with the movement of the mount.  This showed up multiple times even when the guiding sessions near Dec=0 looked ok.  The problem occurred on both sides of the pier at the Dec=45 pointing position.

3.  One of the Guiding Assistant runs shows some native RA tracking behavior that is concerning:

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[Bruce Waddington]

When you're trying to nail down performance, it's best to "make sure" whenever you can instead of hoping things are ok.  So there should be no question about balance - the mount payload needs to be well-balanced in both RA and Dec.  For RA, that means having the counterweights adjusted  to null out movement when the clutch is released.  As I said, I think you should be sure that everything is tightened down after you're done with polar alignment.  The Guiding Assistant has been making pretty consistent recommendations about improving the focus on the guide camera.  I agree with that, I think the star sizes looks too large for the image scale you have on this rig.  But that doesn't have anything to do with the apparent RA drift at Dec-35-40 degrees.  I remain suspicious of the through-the-mount cabling because I've seen numerous cases where that proved to be the problem.

Good luck,

Bruce

[Dale Ghent]

> On Sep 1, 2025, at 15:07, Mike Ales <mike...@gmail.com> wrote:
>
> Daniel if you are using Nina as Brian speculated turn off the calibration option on Nina start guiding instruction in the sequencer
>
> That option in Nina is for folks that want to do the initial slew near Zenith and calibrate PHD2 via sequencer instruction instead of the preferred PHD2 calibration asssistant which slews to near Zenith

Well, not quite. The purpose of the "Force Calibration" option on the "Start Guiding" instruction is for people who use old ST4-based guiding systems where PHD2 must be calibrated after every slew. However it could be used for other purposes, such as when a manual rotator being used. But, if you have a mount that is guiding via ASCOM pulse guiding (no ST4 cable in use) then yes the correct way to calibrate is to do it once as close to the meridian/equator as possible and then not worry about it unless the guide camera's mechanical angle changes.

[Brian Valente]

Building from Dale's comments

>>>if you have a mount that is guiding via ASCOM pulse guiding...) then yes the correct way to calibrate is to do it once as close to the meridian/equator as possible and then not worry about it unless the guide camera's mechanical angle changes

The ideal calibration sky area is the intersection of the meridian and the celestial equator. It does not refer to the Zenith

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[Daniel]

https://openphdguiding.org/logs/dl/PHD2_logs_bCVB.zip

Bruce,

The above is the guiding log for last night into this morning.  I polar aligned using NINA 3 point and alignment was reported as within .13'.  I did a calibration using the slew function of the calibration assistant.  The calibration was reported as good and looked good to me.  I allowed it to guide from there until about 10pm.  I then provided it a slew command (not centered) to SH2-129.  The reason I did not center is that SH2-129 may or may not be out of the trees on the east side of my property.  And it wasn't.

I waited until the target was clear and then started a sequence which slewed, centered, focused, started guiding and acquiring images.  There was a meridian flip around 11:35 that went as expected.  Additional imaging occurred until about 3:30am and the sequence ended as expected.  No apparent disconnects, although there was a message in PHD2 again about no image for 19 seconds like I got before.  My previous disconnects seem to be from Microsoft power saving options within the properties of individual USB ports and corrected.  Thank you Microsoft.  But to be sure, I also did not run the Pegasus Unity software along side NINA for this evenings effort.  Other than the PHD2 message above, I had absolutely no irregularities running the sequence from just after 10pm until 3:30am.

Before last evening, I took the dovetail plate off enough to get my fingers down around the mount internal wires.  I carefully swung both axis and I could feel no resistance associated with the wires.  If the above log still leaves you suspicious about possible snags, I will work with iOptron to guide me in further disassembly or consider having them do it.  I did a very careful balancing of both axis prior to this run.  I could disconnect the worm at any location, and nothing would move.  Both axis.  If I physically moved in either axis the movement stopped when I stopped applying any effort.  I'm not sure how I could make the balance more accurate.

If you would look at the log, I want to know your opinions.  Or anyone else who wants to chime in.  As I said, the calibration reported and seemed good.  I ran the Assistant as well and incorporated all recommendations.  I did not think that the guiding was too bad initially (while still on the calibration guide star) or later on SH2-129.  I don't know how to read the PHD2 logs.  All I have to understand what is going on is the graph references.  I understand that seeing will compromise guiding accuracy.  My other evaluation tool is comparison (to my GEM28) with the same payload.

While the guiding was "good enough" for my pixel scale, I'm not sure it was much better than my GEM28 would do.  Perhaps .2' RMS better.  I remain concerned that the DEC excursions are excessive.  If the graphing is accurate, they exist throughout the guiding from after the calibration all the way to the end of the SH2-129 sequence.  They are better at the start of the sequence than at the end.  I think those excursions are the source of your concern about a possible snag.  I want to complete a conversation with iOptron either accepting that this is as good as this mount should do, or effectively communicatee what needs to be reviewed, repaired, replaced, etc.

iOptron was ready to send me new cards for the mount and I asked them to hold off until the testing was farther along.  I can't see the wisdom of throwing parts at a problem without narrowing down what the problem(s) are.  I think the communication issues are resolved (although this is just one test).  My iPolar will not initialize unless the USB cords plugged into the dovetail are removed.  Not a PHD2 problem but remains an open item with iOptron.  The guiding accuracy remains a concern for me.  My expectations might be unrealistic and if so, please feel free to be candid, but I was expecting .5' RMS or better.

I know this is a PHD2 forum and some of the above is irrelevant to PHD2.  But I want to accurately present the facts as I know them in case anything lurking in there might be affecting the guiding.  No use sending the mount in or replacing parts if all I have is an elusive snag.  Thaks for taking the time to help.

Regards,  Dan

[Brian Valente]

Dan

that sounds like good progress, i agree re: don't have ioptron throwing fixes when you don't know what it is

Regarding dec excursions, an example is below that leads me to believe you have significant polar misalignment. Note the pattern of drift downward, followed by a series of guidepulses to bring it back to lock position. All the guidepulses are in one direction, this is all pointing to polar misalignment.

 If you believe polar alignment was spot on at the start, then it could be something else creating issues (something is loose, the ground is sagging, etc.). However on opposite side of pier (beginning of session) it shows the same issue but opposite direction, so that confirms for me the polar misalignment.

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[Daniel]

Brian,

Thanks.  That gives me something to work on.  And points to the more likely culprit with much in astrophotography....user error.  The mount is on a pier tripod on a concrete slab that has not developed a crack since I personally installed it 32 years ago.  Pretty stable.

I'm a little confused about the reliability of various ways to achieve polar alignment.

When I started using my GEM28 I was using the Three Point Polar Alignment in NINA (plugin I think).  After a bit, I figured out the iPolar and started using it.  I found that to be very reliable with consistent results.

WIth the CEM70, my iPolar is only working if I remove all other USB attachments from the dovetail.  iOptron and I are working on that fix.

But assuming I do an iPolar with the CEM70 and then follow it with a Three Point Polar Alignment the Three Point indicates a starting error of 1.25' to over 4.0'.  It does not seem like there should be a discrepancy?

I tried doing a drift alignment with PHD2 and I think I got lost.  I have since watched an instruction video and I think that might be the next process to toss into this testing effort.

But the question remains, what is the best way to confirm that polar alignment is accurate?  It seems like waiting for guiding results is not very efficient.

I do have some constraints based on my observation location.  I have nothing available to the east more than 10 degrees from the meridian.  My house obstructs to the west at pretty much anything over 30 degrees up from the horizon.  I'm good to the north and can run sequences that go up to 5-6 hours.  Pointing south, I'm only good for about 3 hour sequences.

Reading posts by others in various forums, I'm not the only guy who is shooting in a restricted environment.  In fact, many are more restricted than I am.

Even in PHD2 there are numerous paths for polar alignment.  Are some better than others?  Are some better depending on constraints?

Thanks again for the help.

Regards,  Dan

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From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Brian Valente <bval...@gmail.com>
Sent: Thursday, September 4, 2025 7:27 AM
To: open-phd...@googlegroups.com <open-phd...@googlegroups.com>

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[Jim Bachesta]

The way I confirm my polar alignment accuracy is via PHD Guiding Assistant. I would like confirmation if this if there are better ways to confirm alignment. 

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[Georg Albrecht]

Daniel,

When using 3PPA in NINA, you might want to repeat the procedure at least 3 times always starting from Zero position. Also check in the plugin page where in the quadrants to point and what areas to avoid. In the first attempt I get just below 1', then slew back to zero (home) 2nd attempt I get PA under 0.5' and back home. On the 3rd I dial PA in below 0.2' and let it run for at least 6-8 additional exposures. Also you mentioned previously that when you walk onto the concrete slab, that the mount (PHD2) picks up vibrations. Doublecheck that when you stand behind the mount, you have equal PA numbers then when you're off the slab. One third thing you may want to check is for cone error. I had quite a bit on my CEM70EC rig with 1000fl. You can double check that during the day on a far object.

Hope you can sort this all out in time.

Cheers - Georg

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[Brian Valente]

Dan

The gold standard is drift alignment, but i'm not sure that's always needed. 

I think you there are two possibilities to potentially investigate: Either a bad initial polar alignment, or something slipping/moving, or possibly a combination

For polar alignment, I don't know much about iPolar, but presumably that should work just as well as anything else. I would pick one one approach and stick with it rather than try to combine approaches. It sounds like you've had some questionable issues with iPolar, so maybe 3ppa?

as mentioned, i would measure the final PA with a guiding assistant run of about 5-10 minutes. That should give you some idea of the PA. It doesn't have to be perfect. If you see Dec spikes again, you can stop and do another guiding assistant run at that sky position to see if your PA has changed.

Brian 

On Thu, Sep 4, 2025 at 8:06 AM Daniel <daniel....@gmail.com> wrote:

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[Bruce Waddington]

I think we've probably reached our limit on trying to figure out what's wrong, to the extent that anything is actually wrong.  First of all, it's not reasonable to arbitrarily assume you should be getting 0.5 arc-sec guiding.  That's going to be constrained by seeing conditions from hour to hour and day to day.  I guess we don't know where you're imaging from but we do know the gear is on a concrete slab.  So if you're in a hot environment, you will get a lot of heat convection that is going to degrade your observing conditions.  As you know, I'm not convinced that you have a polar alignment problem but I certainly can't say that you don't.  I would just caution that you could spend a lot of time chasing your tail on this by trying to "micro-tune" your polar alignment, something that is largely a waste of time unless you are trying to image un-guided.   I think we should come back to the peculiar Dec excursions which, in my view, have nothing at all to do with polar alignment.  All of this assumes that you don't have high-resolution encoders on the Dec axis.  In other words, that you have an "EC" model and not an "EC2" model.  If you do have an EC2 model, then that's a whole different situation.  Assuming you don't, let's look at a magnified view of a series of Dec excursions:

Look at the points where the guide star starts to make a Dec excursion.  In each case, there was no guide command involved as shown by the rectangular guide pulse indicators.  So we know at those points in time, there was no guiding active and the Dec axis motor was idle. Now look at a wider view and notice the somewhat periodic behavior:

What would cause this?  A common cause is the one I brought up before which is cable pulling.  If you have cables intertwined or dragging across a stationary surface. you can often see a "catch and release' behavior.  There's a static resistance that has to be overcome and once that's accomplished, there's a release of stored energy that causes a quick reactive movement back to the intended position.  This is particularly true when there are cable ties involved.  But there can certainly be other causes.  One question would be whether there is anything going on with your imaging operations that happen every 6-7 minutes.  Filter changes, automatic re-focusing based on temperature changes, etc?  Going even further afield, you've mentioned that the imaging rig seems rather "bouncy" on the concrete pad.  In the past, people have reported that weird problems like this were being caused by non-astro equipment located nearby, things like cycling of air conditioners or pool equipment.  And believe me, even weirder things have been reported, but we won't go there. <LOL>

Regards,

Bruce

[Daniel]

Bruce,

I agree.  I want to thank you for all the help.  It can be difficult to troubleshoot when multiple issues require attention.  I appreciate your perseverance and patience.  I am including a guide log from last night.  I was able to finally get what I think was an accurate and acceptable polar alignment.  I did a calibration and let the assistant run for 240 seconds and it stayed pretty tight.  Then I adopted the settings with an alteration to guide camera exposure.  I did an image run on the North American Nebula and saw some really nice guiding number initially moving to more average as the session progressed.  I still see that DEC spike showing up and I made a request to iOptron for some specific guidance in disassembling enough to check for any internal snags.  The spike seems repetitive at set intervals and then just about when you think you see the pattern, it alters.  I'm going to look for the snags first, then worry about what might be next.  Also, I'm traveling for the next three weeks so won't have an opportunity to revisit testing until end of September.

https://openphdguiding.org/logs/dl/PHD2_logs_6Kuq.zip

I did change my guide camera exposure to 6 seconds.  That is more than the assistant suggested but I think if smoothed things out.  Again, thank you for the help and all you do for the PHD2 users.

Regards,

Dan J.

---

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Bruce Waddington <bw_m...@earthlink.net>

Sent: Thursday, September 4, 2025 2:52 PM

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[Bruce Waddington]

You're welcome, Dan.  This one has been a puzzler and I don't think Brian or I can feel like we've necessarily gotten to the bottom of it.  That said, the two long guiding sessions in your most recent log showed very good guiding results, presumably good enough to produce nice images.  So you may not want to invest a lot more time and effort in chasing the Dec excursions because they don't seem to be hurting you at this point.  The better results produced by the long guide exposure times are interesting.  That usually means there were higher-frequency components to the tracking errors that were averaged out by the longer exposures.  We usually see this with seeing-induced movements but the same would apply for any sort of mechanical sources such as vibration.  If you get further insight after talking to iOptron, please let us know.

Good luck,

Bruce