Re: APCC, Sequence Generator Pro, and Automated Imaging Software

Andy Galasso

>>> bigeastro wrote: I have been using PHD2 with SGP.  It picks a faint star.

Although it may seem contrary to intuition, the brightest star is not always the best choice for the guiding on.  If a star is saturated, the centroid cannot be calculated with certainty.  PHD2's automatic histogram stretch can also make excellent guide stars appear dim on the screen when there are saturated stars present elsewhere in the frame. PHD2 does a histogram stretch based on the brightest and dimmest pixels in the frame, so a bright saturated star can make other stars appear dim. The actual guiding processing is done using the raw un-stretched image data. If you slide the gamma stretch slider to the left, your faint star will appear brighter (no effect on guiding). The important thing is to find a star that has a high SNR value but is not saturated, and we believe PHD2 does a pretty good job automatically selecting good guide stars.

That being said, we can't rule out a possibility that PHD2 is not handling your guide cam/scope combination optimally. We'd be glad to look into it in detail if you post your information (PHD2 debug log and sample camera frame File => Save Image) over in the PHD2 forum.


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