Help with guiding

[John Hoogerdijk]

Generally I experienced good to very good guiding, but the last couple of nights out, my log files have left me scratching my head.  Guiding was ok (there are some issues that are related to cold temperatures and frozen cables, as well as poor seeing). Essentially DEC values are shifted by about 1.5 arcseconds.  Watching the star in PHD, it appears that the star is also shifted.  I've attached relevant log files.

TIA,

jmh

[ian]

Frost on guiding camera lens?

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[John Hoogerdijk]

I haven't had a heater on the guidescope, and I probably image at least 15 nights a year when its around -20 to -25 C, and haven't noticed this behaviour before.  My setup is in a SkyShed obs, so I'm sheltered somewhat.  

I checked the balance and it and it was a little out, but nothing significant - if it was balance, I would expect a constant correction which is not observable in the data.  How might frost on the lens generate the behaviour in the log?  

I've got an extra heater channel, so I will put a heater on and  test it (when the clouds disappear...)

Regards,

jmh

On Saturday, February 8, 2020 at 2:04:38 PM UTC-6, ian wrote:

Frost on guiding camera lens?

 

From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of John Hoogerdijk
Sent: 08 February 2020 20:00
To: Open PHD Guiding
Subject: [open-phd-guiding] Help with guiding

 

Generally I experienced good to very good guiding, but the last couple of nights out, my log files have left me scratching my head.  Guiding was ok (there are some issues that are related to cold temperatures and frozen cables, as well as poor seeing). Essentially DEC values are shifted by about 1.5 arcseconds.  Watching the star in PHD, it appears that the star is also shifted.  I've attached relevant log files.

 

TIA,

 

jmh

 

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[Andy Galasso]

jmh,

This is actually the expected behavior for when the Dec guide algorithm selection is Z-Filter. Although Z-Filter allows a constant offset of the guide star, this does not affect the result in the imaging camera.  For Z-Filter, you should also set the Dec MinMove value to zero to get the best results.

I noticed that your calibration is a bit off due to attempting to calibrate at high declination (69 degrees).   For best results, calibrate near declination zero.  Please check out PHD2 Best Practices.

Andy

[John Hoogerdijk]

Thanks Andy!

Regarding calibration, guilty ... and got the messages from phd as well.  But given there were clouds to the south, not much choice. 

jmh

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