Who does darks with CCD?

[kirkster501]

I always did them with my DSLR.  However, I've never done them since I got a CCD.  However, why not create a darks library at my CCD imaging temperature and exposure length and create a master dark?  As long as this is refreshed every few months this should be good to go?  I've some dead and hot pixels on the CCD chip and this the way to get rid of them?

Steve

[gnomus]

This is what I do Steve.  I have a library of 5, 10 and 20 minute darks and I use them over and over.  (Since I don't take the camera off the scope, I can reuse flats too).  Another option (described to me and others by Olly) is to use a master bias as a dark and then a bad pixel map for pre-processing.

[ollypenrice]

Yes, I use BPM and bias as dark. It has the disadvanage that it doesn't kill amp glow in one corner on very long subs but that's a two click Ps fix. Since I have to reduce industrial quantities of data some mornings the fact that any sub length gets the same calibration data is a tasty bonus. I also find that it works better on my setups than 'proper' darks, but these things are very user-specific.

Olly

[Alien 13]

I always thought dark's are useful for ccd but a waste of time for DSLR but perhaps the new gen of cooled CMOS can use them to an advantage.

Alan

[D4N]

Yep BPM for me too, there really is very little dark current on my subs even at 30 minute exposures.  

[swag72]

I always do darks with the KAF8300 chip. I also started doing darks with the Sony chip as after trying it for an amp glow problem, I found that it really did helpr educe the noise, despite everything I was reading that said otherwise. For the time it takes during a cloudy night, it's worth running a library of darks and trying a process with and without them.

[RichLD]

I use bias as dark and Cosmetic Correction in PI to remove hot/cold pixels on both the KAF 8300 and Sony ICX413AQ.  

[steppenwolf]

I use Bias, Darks and Flats with my 8300 sensor images but the real kicker is dithering between subframes to remove hot pixels.

I have a library of Bias frames and a library of Darks captured at 300, 600, 900, 1200 and 1800 seconds and I refresh these every three to six months. All my images are taken at either 0° or 90° orientation so I sometimes use 'library' Flats but prefer to take them per session.

For some time, I just relied on dithering with no Darks but carried out a set of tests recently that indicated to me that my backgrounds were somewhat smoother when I subtracted dark frames so now I always use them.

[kirkster501]

Thanks everyone.  Please tell me about this "bias as dark" technique...... I confess, I've never heard of that. I need to research into it.

Steve

[D4N]

Basically using a master bias as your dark frame will subtract only the read noise which is very stable over a long period.

Then use a bad pixel map, dithering and stacking settings to deal with everything else