[Aavso-photometry] Calibration Frames

[Jeff Hopkins]

Hi Bob,

You can take bias frames with any camera. Just set the exposure to 
the lowest setting and take a bunch. I twill only take a second or 
two.

While darks are important, when the outside temperature is in the 
40's F or colder, the dark frames become less significant. From where 
you are located (I'm from upstate NY) I know the night time 
temperatures this time of year hover around freezing. Taking one set 
of darks early (after the equipment has stabilized, should last 
through the evening. Since the darks contain a  bias frame, unless 
your are trying to make master darks (not really necessary) just take 
a set of darks before each observing session and do an automatic dark 
subtract on the images. I do that with my DSI Pro and it works well.

Jeff

At 11:54 -0700 01/06/2008, Bob Crumrine wrote:
>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

-- 
Jeff Hopkins
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Counting Photons
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