Ah but Peter there are more advantages to super cooling than merely noise.
As you know the STL11 KAI11002 chip along with others in the KAI family suffer from vertical lines caused by hot pixels. Now theoretically these should dark subtract out or a bias frame should remove it etc but often they do not. They then become a real pain to remove if you can during processing.
Richard Crisp - the arguer, has demonstrated clearly in a paper that high cooling gets rid of these lines. They don't fade out until you hit -30C and beyond.
Merely going down to -10C will not and they will be a pesk when you process your images.
I know from long experience the STL11 ideally is operated at -35C. It is quite noisy at -10 and even -20C isn't ideal. It starts to shine at -35C.
Yes dark subtraction works but it now becomes critical that it is done excellently with lots of darks sigma reject combined and with accurate matching temps and exposure times.
Cold chips have practically no noise in the first place, dark subtraction almost becomes only if you want to and certainly less critical and exact matching of darks is less important and use of adaptive darks is feasible with little or no difference to exact matching.
In my opinion excellent cooling is important and gets rid of a lot of problems that complex processing requires otherwise having used different cameras with different cooling abilities.
Of course a dark site is more important again but if you had 2 cameras and all other things were equal then the one with the superior cooling should be your choice.
Greg.
Quote:
Originally Posted by Peter Ward
For those with further interest in this thread, Steve Cannistra has done some excellent work in this area. You can also download an excel spreadsheet from his site that helps you play around with some real world values
His take?
CCD cooling beyond -15 to -20 C produces minimal gains in the functional dynamic range for most imaging sites, because the sky flux becomes the limiting factor in this situation.
Roughly translated.....a dark site is way more valuable than a super cold chip! (Why do I have a backyard observatory again?? Doh! ) |