FLAT DARKS

[gio24]

Hello everybody,
I have a very short question but I don't know if the solution is so simple.
I've read ,after searching, that the flats darks must be put together with the darks during the batch processing.
Is it ok?
The problem is that the exposure time is recognized only for some of that while in other cases the program put the dark of the flats tighter.
For example I have a duration of the dark flat with L filter of 4 seconds, a duration of the dark flat with blue filter of 20 seconds and the program associates them together under 4 seconds.
Anyone could help me?
many thanks
giorgio

[jkmorse]

Giorgio,

I am not a fan of batch processing since you surrender lots of control over the process and your issue is a good example.  It will take a bit longer, but a good solution is to use the ImageCalibration and ImageIntegration tools to create each Master Dark and Master Flat separately and in doing so then you can point to just the right Dark Master for each flat set (after you have created separate dark masters, of course).

In the event you are not sure exactly how to do that for flats and darks using ImageCalibration and ImageIntegration, here is a copy of my cribsheet which will walk you through the process.  I am posting this from work (shh, don't tell anyone) so this is an older version of my cribsheet (if you want the latest version in Word format so you can tweak it to your own needs, just drop me an email) but the workflow on creating dark and flat masters with ImageCalibration and ImageIntegration has not changed so that should work for you.  The information you need is on pages 3 and 4.

I hope that helps.

And, by the way, if no one has welcomed you to the forum yet, Welcome Aboard!!

Best,

Jim   

[gio24]

Jim,
many thanks for your kindness.
The file attached it's perfect I think.
I will try to follow your suggestions.
Just a short questions: after creating each master flat dark for each channel of the master flat and after creating the master darks and the master bias, could I move to batch processing by putting all the master darks under darks column and all the master flats under flats column?
Do you suggest to perform all the process manually or with the help of batch processing after creation of each master flat, master flat dark,master dark and master bias?
many many thanks for your help
Giorgio

[Phil Leigh]

Why bother with flat darks? - what's wrong with dark scaling? - I thought "the Pi way" was to not use flat darks?

[pfile]

with 1800s darks i'm not sure it makes sense to scale all the way down to 2s. at least i've never had good luck with that; i calibrate my flats with bias frames only. otherwise my flats are not properly calibrated and they overcorrect the lights.

i think if you add some shorter darks to BPP (not necessarily the same length as the flats, but shorter than those for your lights) that BPP will pick them up for use against the flats, but i'm not 100% sure of that.

rob

[gio24]

Hi Rob,
I'm a little bit confused. Do you suggest to add only some short exposure darks and the BPP will use them to calibrate the flats or to avoid to add any short dark and put only the one with the same exposure time of the lights?
Would it not be better to create all the master dark-flats and then begin the process with BPP by adding all the masters?
any suggestion?

Giorgio

[Phil Leigh]

with 1800s darks i'm not sure it makes sense to scale all the way down to 2s. at least i've never had good luck with that; i calibrate my flats with bias frames only. otherwise my flats are not properly calibrated and they overcorrect the lights.

i think if you add some shorter darks to BPP (not necessarily the same length as the flats, but shorter than those for your lights) that BPP will pick them up for use against the flats, but i'm not 100% sure of that.

rob

I agree and that's what I do too. I never use darks because dithering removes my bad pixels and anyway my super-cooled cameras are derived from DSLR's which do not do darks "correctly" anyway. I just use a superbias and flats. Seems to work just fine.

IMO the scaling only works for linear CCD darks (whenever I've tried it with various DSLR darks it always made things worse).
With DSLR's, a flat that takes a few seconds at most has very little thermal noise in it (unless the sensor is very hot).