Darks for Atik 383L+

[rubecula]

Since I recently aquired a used Atik 383L+ I have been scouring this site for info on calibration frames.  This thread  answered most of my questions but I'm still not sure about darks.

With my DSLR I followed Mr Penrice's excellent advice to dither between images and use Bias frames as darks thus avoiding the need to waste valuable imaging time taking darks.

I understand that with a cooled CCD I can take darks at any convenient time, but I'm left wondering if there's any need to bother with them and just continue to use Bias as darks?

If the advice is to take darks then I have another question?

Do you image the year round with the same cooling setting i.e. -10C or -20C? Or do you use different cooling temperatures in the winter and summer?

And finally (for the time being anyway) How many darks do you take?  I'm assuming that you can take a set of darks and use them for several subsequent imaging sessions.  Before I started using Bias as darks I'd been taking the same number of darks as lights. But from night to night I'm sure that the number of lights I'm able to take will vary.

Thanks

[wxsatuser]

I do darks and bias every year and new flats if I take anything apart.

My flats last ages as I only do Ha and never take the gear apart.

I have Artemis set to -20 and never change it, just once, one hot summer night it could not
get there or maintain it, it was 22C in the obsy at the time.

I use 36 of each calibration frame, have darks for 600secs and 900secs and my flats are about 4secs but
find that is no problem.

[wxsatuser]

Just to point out.

Once I use the calibration files on one target, in PI there will be a master dark, bias and flat which is all that is needed for the next target.

[carastro]

I do use darks, I tried using a bias as a dark like you and Olly and got some very weird results.  With my Sony chip I probably don't need darks so much except they will remove hot pixels.

Flats I re-take every time I move the camera and you need separate flats for all filters if you have a mono camera (unless your system is clean/closed and you have checked that flats for one filter will do all).  

Be aware for an Atik383L you will get shutter shadow so you need to expose for about 3 secs to avoid that.  This means you need to dim the light source down in order to reach the correct ADU.

As regards number of calibration frames, I tend to only do about 12 - 15 of each regardless of how many images I took.

I tend to do -15 all year round so that I can use the same darks.  I have had the odd occasion when the camera struggles to get down to that in a hot summer. 

Also, if you have a mono camera and are planning any binned images you will also need to bin the calibration frames too. 

HTH

Carole 

 

 

[tooth_dr]

Just to add, with my 383L+, I've tried with and without darks, and haven't noticed any difference.  So I sometimes use darks, and sometimes I don't.  I take around 30-50 calibration files (bias, flats, darks), and create master frames from those.  I have tried using a single flat for all my filters, but it hasn't worked properly, so I will need to shoot a full set of flats for each filter, which is a PITA but once done, should be good for the season.  Also as Carole has pointed out, you need a complete set of calibration data if binning!

[ollypenrice]

If you use darks you must temperature-match them to your lights but you could do sets at a couple of different temperatures. It certainly helps the Kodak chips to run them as cool as possible, or nearly so. All that freezing cold might as well be put to good use!

Personally I don't use darks any more either with my Sony or Kodak chipped cameras. I use a master bias as dark and apply a defect map. I stack and calibrate in AstroArt and simply followed the developers' instructions on how to do this. I feel I get better results but these things are often variable from person to person. The standard method is fine.

With CCD you can use a master bias as a dark for your flats. This is a good idea.

Remember that your new camera has a shutter so you need to make flats using a low brightness source which will allow exposures to be long enough (maybe 3 seconds?) not to show the 'shutter wipe' effect.

Olly

PS I'm not going to admit to the age of my calibration files on here. I'd get thrown off. But they still work...

[Thalestris24]

7 minutes ago, ollypenrice said:

If you use darks you must temperature-match them to your lights but you could do sets at a couple of different temperatures. It certainly helps the Kodak chips to run them as cool as possible, or nearly so. All that freezing cold might as well be put to good use!

That's interesting, Olly. I set my 383l+ to -18 deg. Do you think it would be better to set it lower?

Thanks

Louise

[ollypenrice]

27 minutes ago, Thalestris24 said:

That's interesting, Olly. I set my 383l+ to -18 deg. Do you think it would be better to set it lower?

Thanks

Louise

I think it might, yes, if you can manage it. Shouldn't be too hard in Glasgow!!!  It's an easy experiment. In my case, not using darks, I can just go as cold as possible on the night.

Olly

[rubecula]

You are all BRILLIANT, thank you for such helpfull, precise and needed advice.

[rubecula]

Sorry, but your replies have prompted a couple of further questions:

I planned to bin R, G and B images 2x2 and use 1x1 for the rest, does that make sense?

How is a defect map created?

Thanks

[carastro]

You can also bin Oiii and Sii if you wish.  Just make sure Ha and Luminance are NOT binned.

I don't even know what a defect map is, unless it's a bad pixel map and I don't know how to create one of those either.  Would be interested to know.

Lol

Carole