[Aavso-photometry] Calibration Frames

[Bob Crumrine]

Hi Gary,

I'm just getting into this, have a Meade DSI Pro (V filtered but 
uncooled), and a portable setup, so darks & flats generally eat into 
observing time.  I don't think I can take bias frames with that camera. 

I keep a thermometer near the telescope and take darks whenever the temp 
changes by more than a degree or two, but certainly every 30 min or so.  
Each time, I take five darks at the exposure I plan to use next and this 
usually doesn't take much time.  Is five OK?  BTW, I wait at least 15 
minutes for the camera to cool down after turning it on before I do 
anything, and keep the camera in the garage, taking it outside as soon 
as it gets dark on clear nights.

I build a light box and right now take my flats partially into the 
observing session when I'm sure everything is working right (cables, 
focus, camera orientation, etc.).  Since the flats (and flat darks) take 
time from observing, I have been taking just a few flats, say 5-7 and a 
similar number of flat darks.  Sounds like I should be taking more flat 
frames but what's a minimum number in this situation?

Bob Crumrine (CRR)
Rochester, NY

bailyhill at aol.com wrote:
>  Hello Derek;
>
> Here is what I do.? I take 100 bias' because they are fast to do.? No reason to cheap out on them.
>
> I take 50 darks because my setup is permanent, my camera is thermally stable, and I can reuse them for many nights--like maybe a month or so.? I take them in the day or on cloudy nights.? Makes good use of cloudy nights.
>
> When doing twilight flats, I take 3-5 in each color.? This is the maximum I can get between saturation and seeing stars.? I plan to combine flats from several nights, but have not done that.? 
>
> When doing lite box flats, I do 50 again--can do them on cloudy nights.
>
> Remember that the Noise of the cal frame goes down as the square root of the number of frames.? So 16 frames improves noise about a factor of 4, while 50 frames improves it by 7.? It takes 3 times as long and gives twice the result.? But if its down time, whats the difference.
>
> If you are not permanently setup, things are different.? You have to do flats each night.? If you camera is not well thermally controlled, you have to do darks each night.? 
>
> Even with my setup, I can see the best results the first night with new cal frames.? They go off a bit afterthat, but still work well.? I use them until I see the "Bah Relief" donuts start to appear.
>
> Clear Skies
> Gary
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> -----Original Message-----
> From: Derek C Breit <breit_ideas at hotmail.com>
> To: aavso-photometry at mira.aavso.org
> Sent: Sun, 6 Jan 2008 1:49 am
> Subject: [Aavso-photometry] Calibration Frames
>
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> >From various sources (People, Books, and the Internet) I am getting answers
> with a very large sigma to this question..
>  
> ( I know the answers will include "It depends on the target".. Please don't
> confuse me, unless it is essential because I am completely off base. 
> I of course would like to know, but try and separate the response into Part
> one and Part Two.. :-)   )
>  
> How Many Calibration frames do you use to make Master Calibration Frames??
>  
> I have heard anywhere from 4 to 20, though 16 seems to be a common answer..
>  
> Then I heard take twice as many Flats as darks.. Then I heard 3x the Flats..
>  
> So.. What do YOU do and Why??? 
>  
> Thanks in advance..
>  
> Derek
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