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Alex
Another handy visual aid in PHD2 is the Guide Star Profile Tool
I started using it only a month ago after guiding for nearly 3 years and it’s a very useful tool
Some info below -
PHD2 Guide Star Profile Tool
This tool is accessed in the main screen via the “View” drop down menu
Star Profile Tool displays both
FWHD ( Full Width Half Diameter)
HFD ( Half Flux Diameter)
measurements
HFD is a more stable measure of a stars size and shape and more reliable than FWHM
A HFD measurement of between 2.0 and 4.0 generally means excellent to good seeing conditions
A HFD measurement of between 4.0 and 5.0 generally means good to average seeing conditions
A HFD measurement above 5.0 generally means poor to bad seeing conditions
When selecting a guide star either using “Auto Select Star” from Tools or manual selection, make sure your Star Profile graph shows a sharp peak or tapered peak not a flat or sloped peak
When selecting your guide star ensure the “Signal to Noise Ratio” SNR is generally between 20 and 40 depending on seeing conditions
Don’t select a bright guide star as it will be saturated and will show a very high SNR ( say +50 SNR )You cannot guide on a saturated star
Don’t select a guide star to dim ( say below SNR of 20 ) as you may lose the guide star during guiding
Cheers
Martin
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