Greetings,

As a new user of CCDAP4, I'm learning to walk before I run. I've encountered a problem which I can't resolve. It has happened more than once. After a MF, the rotator (Takometer) rotates 180 degrees normally, and the plate solve reports a similar PA to the pre-flip value. However, during a post-flip focus and subsequent return to the target, the rotator and PA change to a new value that results in post-flip images being rotated approximately 131 degrees (my best estimate) from the pre-flip images. I'm not sure what I am doing wrong. The setup has been initialized (no guiding used) and the Takometer has been calibrated. Any help would be appreciated. The log file is attached. The run was aborted several images after the MF due to clouds moving in.

Thanks,

Scott Schafer

ccdap20080909_230557.log (24 Kb, 25 downloads)

Hi Scott,

I suspect the problem is caused by bad plate solving. Look at:
01:52:32 Solved RA: 23 20 43.0, Dec: +61 13 31 PA: 24.2
immediately after the meridian flip. This is a correct solve, based on your target. However, you specified focus star centering and the plate solve there gave:
01:52:53 Solved RA: 23 26 11.9, Dec: +60 59 05 PA: 254.2
Note the vastly disparate PA. Since there was no rotator movement in slewing to the focus star, this indicates a specious plate solve. This bad solve got reflected back as a target PA. See:
01:55:38 Rotating to PA: 254.2w
I suggest you lengthen your plate solve exposure and/or increase your plate solve binning to increase your plate solve reliability.

I will look into what can be done in the code to prevent a bad plate solve from corrupting the target coordinates. I don't think you will see this problem with guided operation, due to the differences in guided and unguided operation.

John,

Thanks for your response and analysis. I will try your suggestions on the next clear night.

Best regards,
Scott

You're welcome, Scott. The next maintenance release will have code to prevent what happened in your case. A test version that addresses this issue is available at:
http://ccdware.infopop.cc/eve/forums/a/tpc/f/6131063691/m/6831049892