[Aavso-photometry] Light Box- from what error to report in WebObs

[Michael Koppelman]

I don't understand what the color of the sky has to do with anything. 
The flat field is correcting pixel-to-pixel variations as a function of 
color. The flat field would be useful even if you were not taking 
pictures of the sky, for example terrestrial imaging or other 
laboratory imaging. That is why, to my naive understanding, you just 
want a nice blackbody as your light source so you have a continuum 
across all wavelengths. Incandescent bulbs work perfectly, although 
because of the temperature you need longer exposures on the blue end.

Cheers,
Michael Koppelman
http://www.lolife.com/astronomy/



On Dec 26, 2004, at 9:08 AM, BailyHill at aol.com wrote:

> Hello Brad
>
> I agree its a small error, but when you are trying to get everything as
> correct as possible, and detect these exo solar planets, I try to work 
> all error
> sources.
>
> Each filter is taking a flat across the bandwidth of the filter--being
> aproximately 1000 angstroms wide.  So if the lite box has a color 
> balance different
> from the sky, then that will be recorded by the filter bandwidth.  If 
> we were
> taking 10 angstrom filtered slices, it would be much less important.  
> The sky
> is about 4-5000 angstroms, so 1000 is a large slice.  The effect would 
> be
> largest with incandescent lites, particularly for those folks using a 
> reostat to
> adjust the intensity, driving the color balance strongly into the red.
>
> The color of the nite sky may also vary, with seeing, clouds, moon, 
> etc.
> Have not looked at this yet.  Just matched lite box to a non moon, 
> clear nite.
>
> Gary
>
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