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Old 04-05-2019, 10:37 AM
Startrek (Martin)
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Auto or Manual select guide star

I find that 9 times out of 10 if I manually select a guide star around 40 to 60 SNR on PHD2 in lieu of the auto select option it results in better guiding
Does anyone else find thatís the case ?
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Old 05-05-2019, 10:15 AM
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NorthernLight (Max)
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I have been using the auto selection function recently and find that if anything appears changed, then perhaps that the calibration process is marginally faster. But in reality, I have no data to back that up. Guiding is still around 1“RMS.

How is the effect on your graph? Or do you get eggy stars?
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Old 05-05-2019, 11:16 AM
Startrek (Martin)
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Iím set up for auto calibration so after selecting a guide star Iím guiding in a few seconds
Depending on seeing conditions my best guiding has been 0.74arc sec and usually averaging around 1.2 to 1.5 arc sec
I have taken 5 minute exposures with round stars but I do use a Baader coma corrector which helps using an 8Ē f5 newt
My guiding seems to improve a bit if I manually select a guide star with a higher SNR say between 45 and 60
In lieu of PHD2 selecting one for me which usually has a lower SNR around 29 to 40
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Old 05-05-2019, 05:08 PM
Karlzburg (Karl)
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I auto select stars well SGP does but always hit the brain and redo the guiding calc. My errors are around the 0.2 to 0.3 arc sec.
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Old 05-05-2019, 10:55 PM
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Wish I could get that sort of guiding accuracy Karl. I'm usually 0.7-1arcsec error (worse if seeing not so good). I just go with the SGP autoselect. I'm not getting up at 2-4am to manually pick a star!! And I usually only get guide star snr of 20-35
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Old 06-05-2019, 06:47 AM
Startrek (Martin)
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Most sessions Iím guiding around or just above 1 arc sec when seeing isnít that good or thereís a bit of wind around or Iím starting my image capture at low altitudes say 25 to 30 degrees. My guiding also improves when heading up towards higher altitudes too
Iíve imaged M83 with round stars when shooting 5 minute subs and my guiding is averaging out at say 1.3 arc sec and after a dither it can go up to 1.5 or 1.8 arc sec
If your guiding at sub arc minute numbers then according to my images you have nothing to worry about. Guiding figures of 0.2 and 0.3 arc sec error are absolutely astonishing !!!
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Old 07-05-2019, 07:14 PM
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Im not sure if one normally cannot expect round stars in longer exposures but I’m hardly doing anything under 500sec and for some applications up to 15 min. Once it guides, it guides. I thought that’s what it’s for?
Besides, I am curious about those 0.2 arc sec RMS values. Is that a permanent mountentop observatory?
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Old 08-05-2019, 03:48 PM
Startrek (Martin)
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Come to think of it Iíve never heard or seen anyone getting down to 0.2 arc sec error for guiding, even OAG,s on amateur equipment
Thatís almost absolute perfection in sync with earths rotation at round the pole inclusive of atmospheric disturbances and optical / chromatic aberrations etc...
Has anyone else heard or seen or produced those astonishing guiding numbers from basic amateur equipment ??
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Old 13-05-2019, 12:46 PM
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I got 0.65"rms the other night. That's a world record for my mount!!! But mind you, it went to over 1" when I went to a different part of the sky - back to normal ...
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Old 13-05-2019, 05:06 PM
Startrek (Martin)
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I was imaging the Sombrero last night and using auto select guide star in PHD2 had me guiding around 1.50 to 1.70 arc sec error ( SNR was 36)
I then reset PHD2 and manually selected a guide star at around 52 SNR and my guiding improved slightly to around 1.30 to 1.50 arc sec error
In the PHD2 manual it recommends to let PHD2 find a guide star in lieu of manually selecting one but I have found on many occasions manually selecting an unsaturated guide star at between 45 to 60 SNR gives better guiding through the night
Any comments ??
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