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Take one cloudy night to do all your calibration frames

Acquisition Calibration Dark Frames Deep Sky
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Andy Wray avatar
Andy Wray avatar
I hate spending time taking calibration frames, but they are important.  In one cloudy evening tonight, I have:

Taken 16xdark frames at 30s, 90s, 180s and 300s each
Taken 20 flat frames for Lum, Red, Green, Blue, Ha, Oiii and Sii
Taken 20 dark flat frames for all the above flats
Processed the above into master darks and flats
Watched TV during most of that time

I tend to get lazy with darks and flats and use old ones, but it really is easy to use one cloudy night (and there are a lot of those) to do it properly.
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Andrea Alessandrelli avatar
Andrea Alessandrelli avatar
In the Netherlands clouds can last for so long that if I take darks during cloudy nights my library risks to become obsolete anyway. Jokes aside, I use my ASI1600MM since 5 years and I've noticed a certain consistency in Darks, so usually I put an expiration date which is one year while keep checking the calibrated frames for new hot pixels and if I see them I take new darks prior the expiration date.  

Concerning flats I tend to take them for each session (usually from 3 to 8 nights long). Dust is tricky and with a cooled chip you'll never know (micro ice cristals formation, dew etc.. can leave small signs on it). 

Clear Skies, 

Andrea
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Claudio Tenreiro avatar
Claudio Tenreiro avatar
Andrea Alessandrelli:
In the Netherlands clouds can last for so long that if I take darks during cloudy nights my library risks to become obsolete anyway


This year, in this part of Chile, latitude 35 south, we have now 5 months fully clouded, this month it seems to be also heading into that direction as well. I don´t remember such a thing before, so...I do agree with Andrea's comment. On the other side, making libraries, tests, upgrades of software and so on, oh ! and general maintenence stuff, avoid to get too bored. Nothing else to do , just waiting...
Michael avatar
Michael avatar
I had almost stopped astrophotography because I kept running into technical issues, forgetting calibration frames or not taking them correctly and so on.
This year, as we head into winter here (Scotland), I've been trying to read lots of forum posts looking for good ideas to help speed up my workflow and this has been one of them.  My setup has been working overnight producing 20 darks for various times between 15 and 300 seconds.  These were done indoors and the cooling struggled to hold my temperature of -20 degrees so I will redo them outside in a month or so.

Thanks for the post @Andy Wray 

Michael
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Fabiano R. Maioli avatar
Fabiano R. Maioli avatar
Hi Andy, don't we need to take flats in the same focus position of the lights? AFAIK it causes different artifact sizes in the flats for different focus positions.
Also rotation of camera, etc would move those in the image.
Those were the reasons I usually took after each sessions. But I would be interested if there is a better/easier way.
Did you consider those?

Thx.
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Andy Wray avatar
Andy Wray avatar
Fabiano R. Maioli:
Hi Andy, don't we need to take flats in the same focus position of the lights? AFAIK it causes different artifact sizes in the flats for different focus positions.
Also rotation of camera, etc would move those in the image.
Those were the reasons I usually took after each sessions. But I would be interested if there is a better/easier way.
Did you consider those?

Thx.

Yes, flats should be taken at same focus position as the lights and at same camera angle.  To be honest, as long as you haven't changed the camera angle, you can just re-focus prior to taking the flats.  Alternatively, over time you will get an idea of how far out the focus tube is when it is focussed at "infinity" and you can just eyeball it (i.e. set the focus tube to be sticking out as much as it always is).

If I'm spending several nights taking the same target and have not changed the camera rotation I would take my flats once only during the multi-night session.
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Andy Wray avatar
Andy Wray avatar
Michael:
These were done indoors and the cooling struggled to hold my temperature of -20 degrees so I will redo them outside in a month or so.


I tend to stick with -10 degrees rather than -20 as that works all year round for me and also saves on camera cool-down time.
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