Old 19-10-2017, 01:56 AM
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Location: Perth, Australia
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PHD2 calibration and drift alignment

A question regarding the PHD calibration and drift alignment. My usual setup is:
1. First do the calibration so PHD knows which way the camera is pointing.
2. Then do the drift alignment and change the mount's azimuth and altitude.
3. Start imaging...

My question is if the changes of azimuth and/or altitude invalidate the calibration? Or are these "inaccuracies" in calibration insignificant?

For example, placing the mount on the ground and doing the initial rough alignment with a compass will likely result in a polar alignment that is few degrees out. Should we then do:
1. calibration
2. drift alignment
3. calibration again
4. check the drift alignment again
5. and probably finish with another calibration before imaging?

Haven't really seen anyone talking about this, is it all insignificant?

Thanks for your thoughts
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Old 19-10-2017, 02:30 AM
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billdan (Bill)
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Hi Luka,

You do not need to re-calibrate after doing the drift alignment.

If your chosen target is a long way from the meridian (or DEC=0) then you should re-calibrate.

However if you're using the ASCOM driver for the mount it will report the change in DEC to PHD and a re-calibration is not necessary.

Also if you do a meridian flip you will need to reverse the DEC settings in the mount tab. The ASCOM driver should report which side of the pier the scope is and then its automatic. Or just do another re-calibrate for peace of mind, which is what I do.

To re-calibrate press the shift key on the keyboard while you click the guide button.


Last edited by billdan; 19-10-2017 at 03:05 AM.
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Old 19-10-2017, 10:22 AM
phomer (Paul)
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There is no point doing two polar alignments, however, I always do a second calibration, as it only takes a minute to do.

As far as polar alignment is concerned, the nearer the pole you are imaging, the more accurate it needs to be.


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Old 19-10-2017, 10:26 AM
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multiweb (Marc)
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I always do a calibration run in the area I'm going to image the DSO. I also redo calibration when slewing to a new area of the sky (including meridian flip). Calibration takes a few minutes anyway. Tracking/balance issues can last for a whole night. Not worth the hassle.
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calibration, drift alignment, phd

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