Calibration failed, star did not move enough

[macd...@yahoo.com]

PHD log: https://openphdguiding.org/logs/dl/PHD2_logs_jMoY.zip

I did search past threads, but don't see answers to my specific questions, so here's a new request for help with calibration failure.  Note: I have successfully calibrated and gotten good results from the Guiding Assistant in recent weeks.  This attempt was with a new guiding set-up: separate guide scope piggy-backed on my main scope.  Same guide camera.  New profile using the Wizard, but I did add a couple of things, such as my Dec backlash value from previous Guiding Assistant results (my mount didn't change).  I also rebalanced my mount and checked for cable snags before trying to calibrate.  My guide scope was focused and pointed at the same place as my main scope: a target star (Sirius, so there'd be no mistake :-) ) appeared on both imaging chips when I did "frame and focus" exposures.  

I have four questions:

1. What does, "settling failed" mean?  That is the result at the end of each of my calibration attempts.  
2. It looks to me, looking at the X and Y coordinates, that my mount is moving with each West Step.  If PHD doesn't think my mount moves enough, what do I do to change this?
3. The calibration movement is shown as 176, is that in arcseconds?  Does that mean PHD wants my mount to move 176 each time a signal is sent?  Or 176 over the course of the entire calibration "run"?
4. Any ideas about what I need to do to fix this?

You'll notice I made several attempts to calibrate.  The last two or three were made during deteriorating sky conditions, so I increase image length from 1s to 2s hoping to reduce lost stars and increase SNR.  That didn't help, so I quit for the night.

[Bruce Waddington]

Ok, you started with a configuration profile telling PHD2 that your guider focal length was 5250mm.  Then you decided that wasn't right and changed the focal length to 560mm, nearly a factor of 10x difference.  But you didn't re-run the new-profile-wizard so the guiding and calibrations parameters weren't adjusted properly.  When you do anything at all to change the guider image scale, you need to re-run the new-profile-wizard - always.  From there, it looks like you kept trying to adjust the calibration step-size and were making some progress but you gave up to soon. 

You need to start over.  Create a new configuration profile with the correct parameters, give it a new name, and use that one.   Use PHD2 manually to get the new configuration sorted out and working correctly.  Always do calibrations with the Calibration Assistant and let it run to completion.  Always follow its recommendations.  Then run the Guiding Assistant to determine appropriate min-move values and re-measure your declination backlash.  All of these properties will be different than before because your guider image scale is different by a factor of 3x.  By that time, guiding should work but there is very little likelihood that you will avoid elongated stars on the main camera unless you are just taking short exposures.  With a main scope of over 5m focal length, the differential flexure of a separate guide scope will probably be a big problem.

Good luck,

Bruce

[macd...@yahoo.com]

Thank you, Bruce.  Yes, I switched from an OAG to a separate guide scope, hence changing focal length of my guider.  I understand your comment about the profile Wizard.  I did edit an existing, but unused, profile.  April 12 was the first time that profile had been used.  However, I'll create a new profile and try again.  I didn't realize there are things going on in the background.

Now that I know about "background magic", are there any things in a profile which can be edited?  I sounds like guide scope focal length, pixel size and binning should not be changed.  Can anything/ everything else be changed?

[bw_m...@earthlink.net]

Good question.  As you said, the properties that affect guider image scale are pixel size, binning, and focal length.  Those shouldn’t be changed on-the-fly in Advanced Settings unless you are doing development work or are an expert in how PHD2 works.  On the camera tab, changing the gain setting on-the-fly isn’t a great idea either unless you are just experimenting.  Doing that is likely to screw up your dark library.  Properties associated with the guiding algorithms can be changed although that can obviously screw things up – but that’s not a behind-the-scenes activity.   I’m thinking that we may need to add some preventative measures about this stuff in the Advanced Settings dialog because we’re seeing an increasing number of these mistakes.  Years ago, there wasn’t any “background magic” so users just flailed away at these settings and then had to figure out for themselves how to restore guiding.  Since then, the new-profile-wizard was introduced and then enhanced over time in an effort to produce good guiding results out-of-the-box.

 

Let us know if you have any more problems,

Bruce

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[macd...@yahoo.com]

The sky was supposed to be clear last night, so I hightailed it to the country after work.  I made a new profile, using the Wizard with my gear connected.  After dark I fired up the Calibration Assistant.  My first attempt failed (but it did complete quickly), my second attempt was improved and my third attempt clouded out.  Rats.  That's actually the same behavior I got when I was trying to make my OAG work; I expected success on my fourth calibration attempt.

While I'm waiting for clear skies, would somebody help me with these questions?

1. What does, "settling failed" mean?  That is the result at the end of each of my calibration attempts.  

1. The calibration movement is shown as 176, is that in arcseconds?  Does that mean PHD wants my mount to move 176 each time a signal is sent?  Or 176 over the course of the entire calibration "run"?

[Bruce Waddington]

"Settling" is not associated with calibration at all, only with guiding.  The settling timeout is most likely to be coming from a start of guiding after a calibration. The calibration step-size is the duration of the guide pulse in units of ms.  All of the calibration-related stuff is pretty well covered in the User Guide, I think.  On your next try, be sure to run the Calibration Assistant every time and then forward us both your log files.

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

https://openphdguiding.org/man/Advanced_settings.htm#Guiding_Tab

Bruce

[macd...@yahoo.com]

Thank you again, Bruce.

[macd...@yahoo.com]

After nearly three straight months of clouds I was able to get some time in my observatory.  I used the new from-scratch profile I made weeks ago after Bruce educated me there are background things in PHD.  Calibration finished quickly and failed the first time, which didn't surprise me.  I got an acceptable result after the second calibration.  Then things started going wonky and I couldn't figure out why.  Soon it was late enough and close to the time clouds were forecast to return, so I closed down and headed home.  Halfway home it occurred to me I may have had dew on my guide scope lens.  Duh.  No log, since the outing was short and unsuccessful.  Just an update for those who have helped me along.

Using a guide scope instead of an OAG solved my lack of guide stars and SNR troubles.  Since I haven't tried any image capture yet I don't know if Bruce's prediction of differential flexure will come to pass or not.  I realize it's a distinct possibility, but I hope not.

I'm out again tonight and the forecast is much better, so I am hopeful I'll make some progress.  Even if is it progress toward a rotator...

[Brian Valente]

>>> No log, since the outing was short and unsuccessful

PHD always produces a log, which in your case would at least show the calibrations

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/6138867c-d867-4433-b0a9-874db6f14549n%40googlegroups.com.

--

Brian 

Brian Valente

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

nature portfolio brianvalentephotography.com 

other astronomy https://www.brianvalentephotography.com/astrophotography/ 

[macd...@yahoo.com]

What I meant was: I didn't post a log because last week's outing was short and wasn't successful.

This week, I do have a log to post: https://openphdguiding.org/logs/dl/PHD2_logs_AULJ.zip

As ill- advised as it is, using a guide scope solved some problems: I was able to find plenty of guide stars, calibration worked, and I was able to guide.  But shoot, I forgot to follow Bruce's / bw_m...'s recommendation to run Guiding Assistant again.  Maybe that will help.  Maybe next weekend...

It was good to have eight to ten guide star candidates in the field.  I had initial trouble with 2s exposures (low SNR) so I increased that to 3s.  I think somewhere between 1.5- 2.25s is the sweet spot.  I noticed in my log the word SATURATED came up.  

1. Does "saturated" mean the guide star's image was saturated?  Can that cause poor guiding, maybe causing incorrect calculation of the centroid location?
2. I also noticed my SNR was between 600-800.  Is there a correspondence between SNR and image saturation?  
3. Is there a target range for SNR which generally gives good results?

Calibration worked, even though I ran it a bunch of times.  My first attempt completed in less than five minutes, but failed: orthogonality error.  Since I've been there before, I ran Calibration again.  This time I got an acceptable result.  The other times I ran Calibration I had moved to different parts of the sky and once I had moved my guide camera.  When you run Calibration, does the new calibration data replace previous data, or does PHD perform some kind of "averaging" or otherwise "merge" data from multiple calibrations?  Should calibration data be "cleared" before performing another calibration?

As I said, I forgot to follow bw_m...'s recommendation to also run Guiding Assistant again.  Rats.

I was able to guide, and I was able to get PHD and SGP to work together fairly well.  What I see as my two big symptoms are:

• Settling: guiding never did settle down for very long, maybe 30s at a time with 60-90s intervals of oscillation.  I don't remember seeing this in the few previous times I've gotten guiding to work.
• RA oscillation: this behavior stumped me.  Declination axis guiding seems pretty well- behaved: +-1" most of the time with consistent corrections and pretty evenly split between north and south.  RA; however, was all over the place.  Most baffling of all, the measured displacement was sometimes in the opposite direction of the guide signal.  In other words, if my mount was drifting east and given a "west correction" it would sometimes continue drifting east.  That created a weird saw-tooth pattern in my graph.

I tried adjusting RA agressiveness, and the hysteresis setting to see if either would help.  I don't think either adjustment improved performance.  One of the big spikes in my guiding is caused by me turning PEC on (I didn't realize it was off).  Another was caused by me pulling my truss shroud down in case a breeze I couldn't feel was moving my scope.  I wanted to try longer intervals between corrections, but couldn't think of a way to do that other than longer guide camera exposures.  I chose not to try that because I already had bright, stable exposures.  I also thought of changing my minimum move, but I thought that would allow more error than I wanted to "accumulate" before a correction was sent to my mount.

I will keep my fingers crossed that somebody has ideas which aren't OAG :-).  I understand that may be the answer, but I don't want it to be, at least not yet.

[macd...@yahoo.com]

Several suggestions have been made in various forums I'm posting to recommending I change my guide camera and OAG.  QHY now offers their Pro versions, with 10mm x 14mm prisms, so that's a readily available option which may be a drop-in replacement for my current OAG.  I could try that with my current 485 binned 2x2, which at least gets me to 0.28"/pixel with an OAG.  I'm going to invent a focal reducer for OAGs.  :-)

Unfortunately, the only cameras I've seen with, say an IMX432 sensor (9um pixels) do not come in mini-housings.  The problem I had with my ASI290 is it's mushroom housing which I couldn't bring to focus.  I think I'd have the same trouble with the Player One and ZWO IMX432 cameras.  If an IMX432 camera becomes necessary I'll have to think about rearranging the spacers I have, I might be able to make that work.

[macd...@yahoo.com]

This weekend I confirmed I won't be able to use a Player One or ZWO IMX432 camera as a guider.  My focuser is nearly all the way racked in and I don't have any spacers between my focuser and OAG.  I won't be able to bring either of those cameras to focus.  Even though my current 485 is color, I can at least bin 2x2 and then maybe add one of the new Pro OAG to get a bigger prism.

[Brian Valente]

>>> IMX432 sensor (9um pixels)

Why are you looking for a guide camera with pixels that large? 432 cameras are mainly used for solar imaging 

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/198545bb-f863-41a8-b091-12fbf3f29e24n%40googlegroups.com.

[macd...@yahoo.com]

Because my image scale with my current camera and an OAG is 0.15"/pixel, 0.3"/pixel binned 2x2 which is what my current camera (and any other mini-camera I've looked at) supports.  9 um pixels get me to 0.45"/pixel.

[Brian Valente]

>>> Because my image scale with my current camera and an OAG is 0.15"/pixel, 0.3"/pixel binned 2x2 which is what my current camera (and any other mini-camera I've looked at) supports.  9 um pixels get me to 0.45"/pixel.

ah got it

Can you describe your setup? telescope, mount, cameras, etc. if you have a few pics at different angles that would help

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/95cf0614-1a46-4ade-9198-1c115070c980n%40googlegroups.com.

[macd...@yahoo.com]

Mountain Instruments MI-250 w/ Gemini I

CFF 350mm f/15 classical Cassegrain (5250mm focal length)

Feather Touch R&P focuser

Optec Third Lynx focus motor

QHY medium OAG (8mm prism) --not currently in use, experimenting with an 80mm f/7 guide scope)--

QHY 485 mini camera for guiding

QHY filter wheel

QHY 268M imaging camera

The attached photo is two imaging train generations ago when I was still trying to get a ZWO ASI290 to work as a guider.  Couldn't bring it to good focus.  I also have since re-installed my 80mm refractor as a guide scope.

[macd...@yahoo.com]

Last night my mount guided.  It didn't guide consistently or all that well, but it did guide.  I'm going to close this thread and start a new one.