Weird Dec results

[James Morse]

Hey guys,

See the log files below that includes parts of last night’s log from PHD2.  I have been having this issue on a regular basis recently.  For info, I was shooting in the north at a target at 72 degrees north.  I have had my Dec 9guiding set to hysteresis rather than resist switch, which could be the problem.  I finally just turned Dec guiding off, but that created issues after the pier flip.

My equipment should not be the issue.  I image from Starfront Observatories and have around 30lbs of equipment on a CEM70 mount, with excellent polar alignment and no cable snags.  

I would appreciate any thoughts,

Thanks,

Jim

***Example of Dec being weird on dither***



INFO: SETTLING STATE CHANGE, Settling complete

58,177.493,"Mount",-0.751,0.533,0.276,0.886,0.224,0.718,477,W,456,S,,,169305,280.17,0

59,181.484,"Mount",-1.755,0.610,0.042,1.858,0.000,1.570,0,,998,S,,,169747,282.20,0

60,186.156,"Mount",-2.943,1.049,0.095,3.125,0.000,2.672,0,,1699,S,,,167625,279.12,0

61,190.847,"Mount",-2.894,0.973,0.038,3.052,0.000,2.713,0,,1724,S,,,175676,287.77,0

62,195.028,"Mount",-1.957,0.688,0.054,2.074,0.000,1.924,0,,1223,S,,,168305,280.45,0

63,198.755,"Mount",-1.016,0.474,0.139,1.116,0.000,1.077,0,,685,S,,,163674,276.78,0

64,201.991,"Mount",-0.333,0.239,0.125,0.394,0.000,0.416,0,,264,S,,,175783,286.29,0

65,205.076,"Mount",-0.144,0.125,0.075,0.178,0.000,0.181,0,,115,S,,,168165,279.32,0

66,208.553,"Mount",-0.231,-0.128,-0.193,0.175,-0.156,0.158,333,E,100,S,,,163619,275.35,0



***2d example of Dec weirdness on dither***



INFO: SETTLING STATE CHANGE, Settling complete

177,559.245,"Mount",-2.398,0.923,0.142,2.569,0.000,1.798,0,,1143,S,,,166200,278.13,0

178,564.318,"Mount",-3.775,1.396,0.170,4.024,0.115,2.851,245,W,1812,S,,,162354,275.25,0

179,569.005,"Mount",-3.532,1.134,-0.004,3.708,0.000,2.717,0,,1727,S,,,165704,277.33,0

180,573.316,"Mount",-2.680,0.882,0.017,2.820,0.000,2.108,0,,1340,S,,,172777,284.09,0

181176,555.123,"Mount",-1.215,0.391,-0.001,1.276,0.000,0.861,0,,548,S,,,160513,272.69,0

,577.069,"Mount",-1.552,0.364,-0.130,1.584,0.000,1.227,0,,780,S,,,171534,283.89,0

182,580.602,"Mount",-1.155,0.267,-0.101,1.178,0.000,0.887,0,,564,S,,,167757,279.54,0

183,583.848,"Mount",-0.462,0.237,0.084,0.514,0.000,0.414,0,,263,S,,,169261,281.00,0

184,586.940,"Mount",-0.208,0.071,0.003,0.220,0.000,0.179,0,,114,S,,,166070,277.83,0

185,590.032,"Mount",-0.278,-0.070,-0.152,0.238,0.000,0.174,0,,111,S,,,171579,283.04,0



***Example of Dec acting normal on dither***



INFO: DITHER by 0.331, -0.983, new lock pos = 305.327, 684.342

INFO: SETTLING STATE CHANGE, Settling started

346,1111.660,"Mount",-1.037,-0.013,-0.331,0.983,-0.331,0.983,705,E,625,S,,,153050,264.80,0

INFO: SETTLING STATE CHANGE, Settling complete

347,1114.576,"Mount",0.168,0.224,0.265,-0.084,0.000,0.000,0,,0,,,,157787,269.61,0

348,1117.502,"Mount",0.206,0.299,0.347,-0.094,0.000,0.000,0,,0,,,,155240,269.29,0

349,1120.414,"Mount",0.193,0.184,0.235,-0.120,0.000,0.000,0,,0,,,,151035,265.40,0

350,1123.333,"Mount",0.166,0.349,0.383,-0.040,0.000,0.000,0,,0,,,,155690,269.51,0

351,1126.244,"Mount",0.174,0.387,0.422,-0.035,0.000,0.000,0,,0,,,,159628,272.56,0

352,1130.002,"Mount",0.199,0.494,0.531,-0.023,0.358,0.000,764,W,0,,,,155617,269.25,0

353,1132.916,"Mount",0.180,0.128,0.177,-0.128,0.000,0.000,0,,0,,,,151414,264.64,0

354,1135.843,"Mount",0.278,0.196,0.272,-0.197,0.000,0.000,0,,0,,,,157770,270.94,0

355,1138.754,"Mount",0.203,0.324,0.370,-0.084,0.000,0.000,0,,0,,,,145649,259.79,0

356,1141.686,"Mount",0.235,0.276,0.335,-0.129,0.000,0.000,0,,0,,,,153967,268.29,0

357,1144.606,"Mount",0.247,0.224,0.289,-0.158,0.000,0.000,0,,0,,,,155779,268.77,0

358,1147.537,"Mount",0.256,0.290,0.355,-0.145,0.000,0.000,0,,0,,,,159330,272.60,0



***Example of Dec going off the rails mid-guide***



387,1234.773,"Mount",0.438,-0.078,0.060,-0.439,0.000,0.000,0,,0,,,,158512,270.74,0

388,1237.702,"Mount",0.411,0.059,0.182,-0.368,0.000,0.000,0,,0,,,,157914,271.29,0

389,1240.617,"Mount",0.520,-0.010,0.150,-0.493,0.000,0.000,0,,0,,,,154469,268.29,0

390,1243.545,"Mount",0.442,0.039,0.173,-0.404,0.000,0.000,0,,0,,,,155131,268.60,0

391,1246.458,"Mount",0.437,0.033,0.166,-0.401,0.000,0.000,0,,0,,,,158203,271.38,0

392,1249.658,"Mount",0.595,0.093,0.271,-0.529,0.000,-0.357,0,,227,N,,,151917,265.21,0

393,1253.168,"Mount",1.304,-0.013,0.388,-1.233,0.000,-0.859,0,,546,N,,,157653,270.69,0

394,1257.429,"Mount",2.926,-0.644,0.285,-2.974,0.000,-2.072,0,,1317,N,,,151841,264.86,0

395,1261.924,"Mount",3.282,-0.722,0.320,-3.335,0.000,-2.406,0,,1530,N,,,134714,248.41,0

396,1266.308,"Mount",2.979,-0.725,0.224,-3.050,0.000,-2.239,0,,1423,N,,,139701,253.81,0

397,1270.308,"Mount",2.152,-0.320,0.356,-2.135,0.000,-1.609,0,,1023,N,,,143289,258.12,0

398,1274.084,"Mount",1.699,-0.077,0.448,-1.628,0.000,-1.220,0,,775,N,,,137873,251.85,0

399,1278.534,"Mount",1.403,0.142,0.566,-1.275,0.382,-0.952,814,W,605,N,,,134034,249.20,0

400,1281.943,"Mount",0.813,-0.332,-0.067,-0.877,0.000,-0.664,0,,422,N,,,145669,259.07,0

401,1285.250,"Mount",0.644,-0.235,-0.026,-0.685,0.000,-0.512,0,,326,N,,,149259,263.15,0

402,1288.165,"Mount",0.477,-0.060,0.089,-0.470,0.000,0.000,0,,0,,,,151989,265.80,0

403,1291.070,"Mount",0.438,-0.037,0.100,-0.425,0.000,0.000,0,,0,,,,158800,272.00,0

404,1293.989,"Mount",0.519,0.081,0.237,-0.462,0.000,0.000,0,,0,,,,150550,263.81,0

[Brian Valente]

Jim

Please submit your full logs via the built-in phd log uploader:

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

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Brian 

Brian Valente

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

[James Morse]

Uploaded!  Here's the link:  https://openphdguiding.org/logs/dl/PHD2_logs_aNNT.zip

I will also post it on the forum.

Thanks, 

Jim

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i5-Q%3DB9O5W34NzHfDXtMoc_UVd2-1UVbEFOJcfgu%2BLSjQ%40mail.gmail.com.

[Brian Valente]

Hi Jim

you have a lot of things going on here, not just one :

• Your Dec is wandering around quite a bit, the min move is quite high at around 1.75"? Depending on your image scale, you may want to consider a lower value.
  
  
• Yes, you should move to resist switch for dec, I'm not sure how or why you opted for hysteresis. The exact improvement here won't yet be clear, your polar misalignment is hiding your true dec performance (see next). Enable auto backlash compensation and start with a value around 250ms, it will adjust itself. 
  
  
• Despite the suggestion of 'excellent polar alignment', I think the data shows something different and you probably need better polar alignment. 
  I recommend you run a guiding assistant for a good 5-10 minutes and see what it shows.
  
  All of your dec movements are in one direction, which is typically the smoking gun for poor polar alignment. Here's one section of your guiding, you can see dec drifts upwards (north) until it hits the min move, then gets corrected back, repeats. I suspect it's bad enough that it's also impacting your RA, which consistently shows an inability to get back to the guidestar lock position.

once you do the above, you can send updated logs (including the unguided output of guiding assistant) and let's see what it looks like.

Brian 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAODyS0PVvpezW6sCm%3DxLO-sSKsAUZk1yHUQJ_pKWq14uQCVBTQ%40mail.gmail.com.

[James Morse]

Thanks for that but the huge dec errors go both ways, north and south and it is those I am trying to cure,  you can see those in the snippets I attached to the original post.  The guiding with those huge Dec jumps is actually more than sufficient given my image scale, but I will run the guiding assistant to see if we can’t tweak it a bit.  But it’s the huge jumps that are the problem.  They are ruining almost every image.

Jim

[James Morse]

Meant to say guiding without huge jumps is adequate.

[James Morse]

Example of both north and south errors are in the 1st snippet, versus the last snippet.

[Brian Valente]

Yes, we can get to that - but you may notice that most of them (not all, but certainly most) are directly related to dither. You made a huge offset on your dithers and without fast re-center (part of resist switch), you can see it takes many guild pulses to return. Related to this, your settle criteria is okay with Dec being that far off, so you should probably also look at that. 

So you still have a combination of a poor choice of dec algorithm, no fast re-center, poor polar alignment, and no backlash adjustment conspiring against you. 

My suggestion is still to fix those first, then see what that it looks like. 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/346fcb1c-d0ce-4066-af31-72f77ba76c64n%40googlegroups.com.

[James Morse]

Will test tonight, thanks!

[Michael Waring]

Couple of things not mentioned by the experts, they might be relevant ?

1.  Pixel scale = 10.07 arc-sec/px,

Way outside the envelope ?

2.  Mount setting of Guidespeed   RA Guide Speed = 7.5 a-s/s, Dec Guide Speed = 7.5 a-s/s,

But measured Guidespeed in Cal         Norm rates RA = 15.3"/s @ dec 0, Dec = 15.8"/s;

Michael

Wiltshire UK

[Jim Morse]

Thanks, will check those and see if it helps tonight.

Best,

Jim

Sent from my iPad

On Feb 23, 2026, at 7:37 AM, Michael Waring <treasurerb...@gmail.com> wrote:

Couple of things not mentioned by the experts, they might be relevant ?

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/9f6e1836-25ca-4670-b287-9b8639766951n%40googlegroups.com.

[Jim Morse]

Michael,

Actually those numbers are accurate.  10.07 is the image scale and the guide speed simply reflects the setting at 50% of the sidereal rate.

But thanks,

Jim

Sent from my iPad

On Feb 23, 2026, at 7:37 AM, Michael Waring <treasurerb...@gmail.com> wrote:

Couple of things not mentioned by the experts, they might be relevant ?

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/9f6e1836-25ca-4670-b287-9b8639766951n%40googlegroups.com.

[Brian Valente]

>>>  10.07 is the image scale 

Jim if 10.07 is your guiding setup image scale, what is your imaging setup image scale?  

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/E5C7ACE7-33BB-48AA-A7CD-6ADAD0321437%40gmail.com.

[Jim Morse]

Imaging scale is 1.8.  Been that way for a couple of years but my problem just arose in the last few months.

Jim

Sent from my iPhone

On Feb 23, 2026, at 11:47 AM, Brian Valente <bval...@gmail.com> wrote:



To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i4KcQuPWVUBYF7GDOzvYYwSOL%2BGtZdb_dfQ3T221uN2%2BA%40mail.gmail.com.

[Brian Valente]

>> Imaging scale is 1.8.  Been that way for a couple of years but my problem just arose in the last few months.

Understand, and unrelated to your recent problems, we really recommend no more than 3:1/4:1 for that image scale. you are 5:1 so aside from resolving your issues, it's a pretty rough scale for your likely desired rms.  

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/7F6CE575-3BDB-4669-8A4C-5AECD5E2ABCD%40gmail.com.

[Jim Morse]

Will consider a larger guiding scope.

Sent from my iPhone

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i7zPeEkmCRAPVoeNso24v%3DgN8UC_F5z5ObFtXWK3kf2iA%40mail.gmail.com.

[James Morse]

Ok,  here is the result of my guide assistant test.  Looks pretty good to me:

I also ran a new calibration but no improvement.  Finally, I simply hit reset on the declination algorithm.  For whatever reason, that seems to have fixed whatever was the issue.  Weird.

Thanks,

Jim

[Brian Valente]

Jim

Glad it's going better - resist switch should have resolved a lot of that. the measured backlash is over 3 seconds, that's quite large.and may cause issues for you. That's something you would want to investigate mechanically.

if you'd like more feedback, please upload your logs.

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAODyS0O-_eTszD%3Dh5H1QSe19C%2BQN7iTpwBEFYtS1amiajfjYcA%40mail.gmail.com.

[Michael Waring]

" the guide speed simply reflects the setting at 50% of the sidereal rate."

Adreed, the mount is set to 50% of sidereal rate =  7.5arcsec/s.

But why is the actual measured guide rate double that at 15.3arcsec/sec ?