Quote:
Originally Posted by g__day
Short answer (from Cloudy Nights 2013- 2014, MaximDL V5.0 plug-in and I think Criag Stark's analysis) is 50% improvement in guiding when using 3-6 spread guide stars - as averaging 5-6 stars' centroid movement tends to remove very localised seeing fluctations thereby reducing the number of false positive guide commands.
Basically if your guide camera is seeing star movement that is heavily attributable to seeing conditions - you want to remove this. It happens to me a fair bit so I tend to lengthen the duration of my guide shots from 1 - 1.5 seconds up to 2.5 - 4.0 seconds and increase how much drift I must see before a guide pulse is sent. I have found over the years at my location and on my equipment this gives me excellent, long duration, long focal length guiding.
Craig Stark wrote one or two notes over the years that basically had the theme of don't chase the seeing! It hadn't occured to me that in a guide camera's very localised frame that several stars in the frame may move in an unusual manner in relation to each other. Say you had four stars in the frame in a perfect square - well if a frame shows the four stars in a different configuration I take it that one or more of the stars are effected by seeing! So statsistically these changes in geometry (the length and direction of the guide stars from each other) can be identified and used to modify the algorithm of what drift is actually occuring!
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Interesting. that kind of 'error correction' is the same as Trellis Encoding for high speed faxes ( 114.4kbaud upwards ). A pattern of voltage pulses plotted on a sinusoidal AC waveform. Basis being one spot of of kilter does not invaildate the data. Never thought my old expertise would come back to haunt me ...
