Re: Donut stars
Posted: Mon Mar 25, 2024 8:24 am
Thanks again, Ivo! An interesting discussion and of course upgrade, though I admit I am still trying to wrap my head around things. I will keep reading and thinking though.
And cool background on OptiDev. So it's scoring likely activity to determine how to curve things. Kind of explains why we can get a good starting point with much detail on hand, right away, when the same would take multiple (and subjective) iterations of histogram stretching.
I ran the graph out 10 more pixels on either side, and good grief I still didn't get down to background. Quite interesting just how far diffraction spreads out on a Mag 8 star! But not sure there's any new info here on the plateau.
Unless you were saying that OptiDev was sensing that stellar core (which would be a huge spike even if I had a bigger well I think), and so made sure it was still distinctly visible, and thus the surrounding shoulder pixels ended up compressed/plateaued as kind of an unfortunate byproduct -- again because it found the spike more worthy of interest?
The maxed pixels you noted was another interesting thing to chase down. I pulled another sub and things were a bit different, with only 3 pixels across overexposing instead of 4, and overall a softer shape. Kind of neat to zoom that deep into linear stars, and makes me believe there will be a great deal of variability. Clouds, transparency, focus drift, and most of all maybe seeing. Then of course the stacker will be trying to compute a star centroid based on what it has in front of it for each sub, which could have small variations as well.
Still, even with that sort of averaging I would have expected the results to be closer to 65535 than they were. So I checked another stack, the Horsehead, and even Alnitak wasn't maxed out. What is PI doing? Iin the end though I found the source to be the calibrated subs. Seems like that 65535 gets dropped due to darks subtraction and then I suppose flats division, and then afterwards probably gets played with by the possible variations in subs.
And cool background on OptiDev. So it's scoring likely activity to determine how to curve things. Kind of explains why we can get a good starting point with much detail on hand, right away, when the same would take multiple (and subjective) iterations of histogram stretching.
I ran the graph out 10 more pixels on either side, and good grief I still didn't get down to background. Quite interesting just how far diffraction spreads out on a Mag 8 star! But not sure there's any new info here on the plateau.
Unless you were saying that OptiDev was sensing that stellar core (which would be a huge spike even if I had a bigger well I think), and so made sure it was still distinctly visible, and thus the surrounding shoulder pixels ended up compressed/plateaued as kind of an unfortunate byproduct -- again because it found the spike more worthy of interest?
The maxed pixels you noted was another interesting thing to chase down. I pulled another sub and things were a bit different, with only 3 pixels across overexposing instead of 4, and overall a softer shape. Kind of neat to zoom that deep into linear stars, and makes me believe there will be a great deal of variability. Clouds, transparency, focus drift, and most of all maybe seeing. Then of course the stacker will be trying to compute a star centroid based on what it has in front of it for each sub, which could have small variations as well.
Still, even with that sort of averaging I would have expected the results to be closer to 65535 than they were. So I checked another stack, the Horsehead, and even Alnitak wasn't maxed out. What is PI doing? Iin the end though I found the source to be the calibrated subs. Seems like that 65535 gets dropped due to darks subtraction and then I suppose flats division, and then afterwards probably gets played with by the possible variations in subs.