Quote:
Originally Posted by gregbradley
Not sure what the advantage of a 30 minute sub with Ha - with S11 for sure. Even O111 is reasonably bright.
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Depends on the QE of the chip. If you're an narrowband enthusiast, you'd probably be nuts if you didn't go with an NABG cam. Unless of course, you want to do fast lens work where blooms are guaranteed.
Quote:
Originally Posted by gregbradley
A
On another point I havn't found that outlier data rejection of CCDstack to be that useful. Perhaps I am doing it wrong. How do you get it to select satellite trails or even hot pixels or odd shaped stars? It seems to not pick them up at all or pick "everything up" to be corrected. Also median combine gets rid of satellites fairly well.
Any tips there Jase? I have the Adam Block DVDs but seem to have misplaced the CCDstack one.
Greg.
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Could be a few things Greg...
Do you perform normalisation manual i.e. select the highlight and background of the image manual? Normalisation is critical for good data rejection. I don't use auto (may once in a while). If you're not happy with the image weightings, you can always re-normalise. Sub weights determine the preference of the subs in the stack (specifically the data it will use to build the master frame).
When it comes to registration, Nearest Neighbor is the go as it preserves pixels, thus the noise statistics therefore making the outlier detection easier. Though it only works well with large stacks. For all others, go with Bi-Linear if the subs only need shifting or B-Cubic if they need to be rotated or scaled. In your image processing routine, avoid double registrations...particularly with luminance data as it will lower the resolution by skewing, rotating, etc the image data again.
As for the rejection algorithm, either STD Sigma Reject or Poisson Sigma Reject. The latter is preferred as it work very well on small or large stacks. Based on stack size and data quality, you'll need to tweak the sigma multiplier. Anywhere between 1.5 to 2 works well, lower if the data is bad as this will make the algorithm more aggressive. Blink the subs to see what has been rejected. If you still see "nipples" as mike put it on stars or a satellite/aeroplane trail not highlight in red (rejection marker), the sigma value is not low enough or the sub weightings need to be recalculated (re-normalise them again).
Apologies for this off-topic post...umm, yes, Ha filters...they're great!
