Dark frame optimization and amp glow?

[magnusl]

Hi!

I'm wondering about the benefits and downsides of dark optimization. I'm using a DSLR, a Canon 350D, that shows substantial "amp glow". I take darks at the correct temperature and iso speed to try to compensate for this, and this is where the optimization plays in. It seems that the darks manage the amp glow better without dark optimization, than when it is turned on. But am I missing something here?

You find some subs and the master dark in the dropbox folder here. The *.fits file is the original sub, and then one with dark optimization (_c apendix) and one without (_c_wo_opt appendix). There is the master dark and the master flat. Which one should I use? Or should I produce another master dark in some way?

https://www.dropbox.com/sh/fs744ujp8oed79d/AACfnztnt-E98N8km8Tv2dUBa?dl=0

Magnus

[jkmorse]

Magnus,

Don't take this as gospel, but if you have matched the iteration times as well you don't ever need to use optimization.  I have found after lots of trial and error (lots of error) that I personally am better off having a suite of dark masters set at my typical iteration times for lights (my set includes 60, 120, 180, 300, 600, 900 and 1200 sec dark masters, the shorter ones needed for bloom correction since I don't have an antiblooming gate on my CCD).  Then I never need to use the optimization routine which for me results in some strange results (no correlation warnings).  Also, note, if you match the iteration times you do not need to include a bias frame since it is already built into the master dark.

Hope that helps,

Jim 

[magnusl]

Hi!

Thanks! Until now, I've always used optimimization, despite always having the same exposure time for the darks and the lights.

But I do use a bias anyway... hrm. Sure I don't need one?

Magnus

[jkmorse]

Mangus,

If you are using a Dark with the same iteration time there is no need to use the bias since it is already built into the dark.  At the same time, it wont hurt anything to include it since what the program will do is subtract the bias from the dark, then substitute the bias frame you included.  Still I prefer the simpler method of just using the Dark since using it alone eliminates one more place for read noise to sneak into your images. 

I have been doing it this way for years and I can assure you it works.

Jim