[Aavso-photometry] sky flats

[Papini Riccardo]

Hi all,

I am writing to ask your advice about sky flats.

My observatory is semi-automated, that is, I open the roof after sunset and
aim the scope with the CCD to the target. When the CCD's temperature is
stable, I start a series of images which keeps on all the night. At dawn,
when the sun is -12 degrees below the horizon, I wake up and take dark
frames remotely being cozy in front of my desktop inside home.

At this point I switch the tracking mode from sidereal to terrestrial to
avoid round stars in the frame and start a sequence of flats for about
twenty-thirty minutes. The exposure of each flat is 10 seconds. Since the
sky brightness changes quickly I take flats with different signal intensity;
signal varies even from one picture to the next. 

Later (may be in the afternoon or the day after) I choose the flats with the
maximum signal in the pixels greater than 10.000 ADU and less than 60.000
ADU and average them creating a master flat.

I don't know if this is best way to take flats but it is definitely the way
that allows me to stay inside home and come back to the bed for another
short sleep. So far flats seem good enough. I wonder if there are
disadvantages I can't see.

Thank you,

Riccardo Papini

 <mailto:aavso-photometry at mira.aavso.org>