On-Camera Guide Output Axes Crossed?


#1

I have been working to improve the guiding with my setup (described below) and have found a very surprising behavior. When connecting to the mount through pulse-guide I get the expected motions but when connected using the on-camera relays the motions are wrong. I believe that RA motions commanded from PHD2 result in Dec motions from the On-Camera guide outputs.

My mount is a Celestron CGE. I am using the NexRemote connection to the mount through the PC port (as opposed to using the port on the Hand Controller). My Windows PC runs Vista (fully updated).

My camera is SBIG STT-8300M with filter wheel and the built-in tracking camera.

My camera software is Sequence Generator Pro v2.3.13 (latest available). I use the SGP API Guider v1.2.0 which is an interface that allows PHD2 to use the STT guide camera through the SGP software and also use the on-camera guide outputs.

I am using PHD2 v2.2.2a.

My autoguide cable has the pinouts reversed from one end to the other, i.e., 1-6. 2-5, 3-4, 4-3, 5-2, 6-1

For calibration of the camera-mount-NexRemote I did the following. I have the camera mounted to the refractor telescope with the top of the camera (the side opposite the cable connections) aligned with the top of the telescope, that is it is up when the scope is at its initial position, pointed to the North with the counterweight bar down. The calibration (and all of this discussion) is with the telescope pointed to the east. Using the RA DEC display on the NexRemote controller I found that the Right button on the NexRemote moved the telescope to the West (RA-) and the observed motion on the image from SGP and also in PHD2 was Up. The Up button moved the telescope North (DEC+) and the star moved Left on the image. The Left and Down buttons are the opposite. Note that if the telescope was pointed to the West, the Declination directions would be reversed, but I cannot view west from my site.

The first setup I tried connected PHD2 to the mount using the Celestron Telescope Driver (ASCOM) selecting the CGE telescope. This connected to the NexRemote controller on the PC which then connected to the mount. When I do the calibration procedure in PHD2 I get the following motions. When the calibration begins with motions to the West as noted in the PHD2 status bar, the star moves to the Down on the image and then moves back up when moving to the East. When calibrating to the North, the star moves to the Right on the image and then returns. Note that these directions are the opposite of those determined in the above calibration. But this is OK, because the purpose of the calibration in PHD is to determine the direction and amount of motion from the commands. But it is proper that the RA commands move the mount in the same axis as the NexRemote buttons, even if the direction is reversed, and similarly for DEC.

The second setup I tried used the on-camera guide connection using an ST4 cable from the camera to the guide port on the CGE mount. When I do the calibration procedure in PHD2 I get the following motions. When the calibration begins with motions to the West as noted in the PHD2 status bar, the star moves to the Right on the image and then moves back when moving to the East. When calibrating to the North, the star moves Up on the image and then returns. This is a problem because PHD2 calibration output in the West direction causes motion in the direction resulting from the Dec buttons on the NexRemote. That is, RA commands give Dec motions and visa-versa. This can be a problem because by default PHD2 used a different control algorithm for RA guiding than it does for Dec. PHD2 will allow the user to switch these control algorithms through the brain controls, but the user must know that this is necessary. PHD does not allow these algorithms to be switched.

I believe that there is an error in SGP that crosses the RA and Dec corrections when passing them from PHD2 to the on-camera guide output.

More evidence for this conclusion is from the PHD2 autoguide logs for these two tests, included below. Note that in these logs, the x direction is to the right, while the y direction increases down from the top. The first log is for using the pulse-guide connection through NexRemote and the second uses the on-camera connection.

Fred Klein

PHD2 version 2.2.2, Log version 2.3. Log enabled at 2014-07-10 22:15:34

Calibration Begins at 2014-07-10 22:15:58
Camera = SGP ASCOM Guider
Mount = Celestron CGE 4.21
Lock position = 193.717, 276.609, Star position = 193.647, 278.551
Direction,Step,dx,dy,x,y,Dist
West,1,-0.007,-0.197,193.654,278.748,0.197
West,2,-0.120,-2.316,193.767,280.867,2.319
West,3,-1.008,-6.120,194.656,284.672,6.203
West,4,-1.058,-9.471,194.706,288.023,9.530
West,5,-1.740,-12.379,195.388,290.931,12.501
West,6,-1.921,-14.966,195.569,293.517,15.088
West,7,-2.404,-18.102,196.052,296.654,18.261
West,8,-2.834,-21.669,196.481,300.220,21.853– Note that west corrections result in an increase in the x value which is right in the image
West calibration complete. Angle = -1.690, Rate = 0.0042
East,4,-2.987,-24.982,196.634,303.533,25.160
East,3,-2.159,-20.564,195.806,299.115,20.677
East,2,-1.367,-15.789,195.015,294.340,15.848
East,1,-1.035,-12.661,194.683,291.212,12.703
Backlash,1,0.257,-8.097,193.391,286.648,0.000
Backlash,2,-0.135,0.781,193.525,285.868,0.792
Backlash,3,-0.446,0.142,193.837,286.506,0.468
Backlash,4,-0.727,-0.967,194.118,287.615,1.210
Backlash,5,-1.756,-1.378,195.146,288.026,2.232
North,1,-3.690,-1.001,197.080,287.649,0.000
North,2,-3.006,0.181,200.087,287.468,3.012
North,3,-5.830,-0.654,202.910,288.303,5.866
North,4,-9.180,-0.464,206.261,288.114,9.192
North,5,-11.770,-0.729,208.850,288.378,11.792
North,6,-14.902,-0.278,211.983,287.927,14.905
North,7,-17.976,-0.118,215.057,287.767,17.977
North,8,-21.360,-0.423,218.440,288.072,21.364
North calibration complete. Angle = 0.022, Rate = 0.0041
South,6,-24.880,-0.544,221.960,288.193,24.886
South,5,-23.444,-0.787,220.525,288.436,23.457
South,4,-23.199,-0.621,220.279,288.270,23.207
South,3,-23.288,-1.496,220.368,289.146,23.336
South,2,-22.938,-1.962,220.018,289.611,23.022
South,1,-21.967,-1.617,219.048,289.266,22.027
Calibration complete, mount = Celestron CGE 4.21.


PHD2 version 2.2.2, Log version 2.3. Log enabled at 2014-07-10 22:50:50

Calibration Begins at 2014-07-10 22:51:18
Camera = SGP ASCOM Guider
Mount = On Camera
Lock position = 85.385, 221.804, Star position = 85.214, 222.501
Direction,Step,dx,dy,x,y,Dist
West,1,-0.178,-0.510,85.392,223.012,0.541
West,2,-1.091,-1.581,86.305,224.082,1.921
West,3,-3.702,-1.835,88.916,224.336,4.132
West,4,-7.038,-2.420,92.252,224.921,7.443
West,5,-10.122,-2.340,95.336,224.841,10.389
West,6,-13.480,-1.896,98.694,224.397,13.613
West,7,-16.356,-2.509,101.570,225.010,16.547
West,8,-19.503,-2.037,104.717,224.538,19.609
West,9,-22.712,-2.080,107.926,224.581,22.807 – Note that west corrections result in an increase in the y value which is down in the image
West calibration complete. Angle = -3.056, Rate = 0.0038
East,5,-25.465,-2.196,110.679,224.697,25.559
East,4,-27.170,-2.345,112.384,224.847,27.271
East,3,-26.689,-2.826,111.903,225.327,26.838
East,2,-26.453,-2.791,111.667,225.293,26.600
East,1,-26.338,-3.039,111.552,225.540,26.513
Backlash,1,-26.519,-3.878,111.733,226.379,0.000
Backlash,2,1.076,-0.137,110.657,226.516,1.085
Backlash,3,1.280,1.613,110.452,224.766,2.060
North,1,1.713,3.767,110.019,222.612,0.000
North,2,0.503,2.166,109.516,220.447,2.223
North,3,1.144,4.354,108.875,218.258,4.502
North,4,1.613,6.868,108.407,215.744,7.055
North,5,1.831,8.476,108.188,214.136,8.671
North,6,2.461,10.485,107.558,212.127,10.770
North,7,2.809,11.895,107.210,210.717,12.223
North,8,3.215,14.018,106.804,208.594,14.382
North,9,3.751,16.073,106.268,206.539,16.505
North,10,4.215,18.187,105.804,204.426,18.669
North,11,4.460,20.179,105.560,202.433,20.666
North,12,5.242,21.950,104.777,200.662,22.567
North calibration complete. Angle = -1.792, Rate = 0.0027
South,9,5.371,23.916,104.648,198.696,24.512
South,8,5.394,24.203,104.625,198.409,24.797
South,7,5.294,20.455,104.725,202.158,21.129
South,6,4.600,15.930,105.420,206.682,16.581
South,5,3.983,12.067,106.036,210.545,12.707
South,4,3.439,7.906,106.581,214.706,8.622
South,3,2.597,3.981,107.422,218.631,4.754
South,2,2.436,0.447,107.584,222.165,2.476
South,1,1.955,-3.474,108.064,226.086,3.987
Calibration complete, mount = On Camera.



#2

Hi Fred,

This issue has been seen before and was recently diagnosed to be an issue with the SGP API Guider. I believe Jared has already implemented a fix that will be available in the next 2.3 and/or 2.4 SGP release.

Andy

P.S. BTW, you should upgrade to PHD2 v2.3.0, or newer as those versions have some important improvements in the reliability of interactions with SGP, solving problems with intermittent failure of SGP starting the auto guider.


#3

Exactly, I was the one who did the on sky tests to diagnose this and it is my understanding that this will be fixed quite soon, it was only found last week. I had not noticed it during calibration (I probably should have) but the real operational problem shows up after a meridian flip when using the ST4/cable since that causes the RA to move in the wrong direction after the flip, which brings imaging to a screeching halt, so to speak.

FYI, I am also using the self-guide STT but with a Paramount ME.


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