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Analyzing phd2 guide logs Analyzing PHD Guiding Results ?? A Basic Tutorial Introduction At some point most imagers want to analyze the guiding performance they ? re getting They may be trying to identify and ?x particular problems or perhaps just trying

Analyzing PHD Guiding Results ?? A Basic Tutorial Introduction At some point most imagers want to analyze the guiding performance they ? re getting They may be trying to identify and ?x particular problems or perhaps just trying to get the best performance they can from their set-up Either way the PHD guide logs are the best source of data and using them is far better than trying to look at the guiding graph in real-time The latter is useful as a quick check on how things are going but any serious problem diagnosis or tuning requires a longer time window than what is available in the real-time graph In this document I ? ll be using Andy Galasso ? s PHDLogViewer application as a way to show common problems and guiding behaviors This is the tool we most often use for helping PHD users and it is likely to serve you well What I ? ll discuss in this document is simply the result of my own personal experience and research I don ? t claim to be an expert on telescope mount mechanics and I still encounter guiding behavior that I can ? t explain But I ? ve been using some version of PHD since and I ? ve analyzed hundreds of guide logs in the ensuing years both my own and those from other PHD users Hopefully what I ? ve learned can help you understand your guiding results or can at least accelerate your learning curve a bit Basics ?? A Big Picture View Summary Statistics When looking at these graphs and statistics you want to look at the measurements in units of arc-secs a-s If this isn ? t obvious to you take a look at ??Image Scale and Measurements in Arcsecs ? in the Appendix To get a big picture view of your guiding start by looking at the RMS numbers that appear to the lower right of the graph CWhen PHDLogViewer loads a guiding session the ??RMS ? value is the standard deviation of all the star movements in that session In this example about of the movements were below a-s the remainder were larger Just as a rough starting point you probably want to see your total RMS value be a-s or lower How much lower will depend on many things especially your seeing conditions and the quality of your mount Now look at the individual RMS values for RA and Dec to see how they compare With most mounts I ? ve seen it ? s common for the RA value to be somewhat higher than the Dec value probably because the RA gear system is always running while the Dec gear system is not There are also some seeing-related things that can tend to make the RA displacements a bit larger and more frequent However if the RA and Dec RMS values di ?er by a large amount for example - X you are likely to see elongated stars