[Aavso-photometry] R: sky flats

[Papini Riccardo]

-----Messaggio originale-----
Da: Tom Krajci [mailto:tom_krajci at tularosa.net] 
Inviato: venerdì 16 maggio 2008 18.27
A: aavso-photometry at mira.aavso.org; paprika at inwind.it
Oggetto: Re: sky flats

>If your CCD is temperature regulated, you don't need to take new dark
frames every night.

You are right. I could sleep half an hour longer. But generally my
brain-built-in-alarm goes off half an hour earlier than my alarm-clock. I
don't know why but it happens quite often. So I go in front of desktop and
take darks until it is bright enough for flats.

>Question:  what do you do if there are clouds in the sky during this
crucial time window?  (This is why I use a flat light box, and why >you may
want to consider using dome flats or other 'artificial' method of making
flats.)

I take flats aiming the scope at a white cloth hanging on the observatory
wall. But I have to go outside home because mass-market mounts are beatiful
toys and sometime behave as a toy ;-)))

>Have you analyzed your CCD to see how linear it is?...and at what high ADU
level it deviates from linear?  

I have never checked the linearity of the CCD I presently own. In the past I
tested the SLXP MX916 which deviated from linearity even around 20.000 ADU
because of the ABG. I am so happy with the SBIG ST9 that I never desidered
to test it. But I must admit I am emotional not scientific here ... Thank
you for the interesting link.

>Also, does your software normalize the sky flats?  This can be important
when average values change significantly between flats, which is the case
with sky flats.

Can you explain what you mean here? I use MaxImDL.

>I hope this helps.

A lot! Thank you again Tom. The key point of my question was: is it correct
to average flats with different signal level? Flats are a topic of this list
but it seeems to me that each person take flats his/her way.

Riccardo Papini