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Old 20-11-2011, 02:44 PM
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ozstronomer (Geoff)
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Join Date: Jul 2007
Location: Brisbane
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Quote:
Originally Posted by multiweb View Post
A proper dark subtraction will reject those dots are they are hot pixels on your sensor. They trail because your frames are offset when registering and stacking them back. You can also make a BPM (Bad pixel map) in neb 2 I believe. Just subtract it from all your subs prior to registering.
Marc, I'll give Neb Bad Pix Map a go and see if that helps

Quote:
Originally Posted by RickS View Post
Geoff,

Best to get rid of the hot pixels as early as possible, as Marc suggested, but aren't you doing some form of data rejection when you stack? That should remove the hot pixels as well if it is working properly.

Cheers,
Rick.
Rick, I'm using the standard Neb dark subtraction which has worked ok in the past, always something to keep us on our toes

Quote:
Originally Posted by mldee View Post
I get the same thing, only I have a lot more hot pixels, to the point where I'm almost ready to ask Theo if it's normal to have so many. I made a bad pixel map in Neb2 last night that seems pretty good, I'll attach it.

As I want to make some reliable Darks and Flats now, I also did the Test as described in http://www.cool.id.au/astronomy/Neb_tut/ by Benko and Felix, which I think is also here on IIS if you do a search. My results were good apart from the unexplained drop in mean from ~64000 to 32742 at saturation (Gain 10). Any comments on this are welcome.

Anyway, my final settings appear to be G9, Offset 115, and they seemed to work OK last night, although still lots of hot pixels in my normal 5 minute exposures.

I was hoping to do a new set of bias, darks then flats at this setting this afternoon, but it's 42C in the obs and the poor old QHY9 will only hit -14C at the moment.

Hope this may assist the OP.
Thanks for all the suggestions.

I am taking another set of darks and will redo the processing again to see if that will clean it up.


Cheers Geoff
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