View Single Post
  #4  
Old 09-04-2013, 08:42 AM
Geoff45's Avatar
Geoff45 (Geoff)
PI rules

Geoff45 is offline
 
Join Date: Jul 2006
Location: Sydney
Posts: 2,631
Multiple dark frames averaged should give you a better result that ICNR. This is because there is a statistical variation from one dark frame to the next, so we average many dark frames to get close to the "true" dark current. If you do ICNR, you are using only one dark frame per light frame, so once you have stacked your lights the net result will be a little noisier than if you had used multiple averaged dark frames. It's like using an autodark with a ccd camera. However (as usual) there are caveats. A DSLR does not have temperature control, so if you take lots of darks with a view to averaging them, then temperature changes during the acquisition could null out the theoretical advantage. Also, it depends on your sky.If you have a bright sky, you need fewer darks (because sky noise overwhelms residual noise in the dark current), and so ICNR will be good enough. However, you would be better off taking 3 or 4 darks at your subframe exposure time and using them--much quicker than using ICNR for 20 or 30 light frames.
Geoff
Reply With Quote