[vsnet-chat 1718] Re: [AAVSO-DIS] Re: CCD's Lumpy flat field?

[Lew Cook <lcoo@yahoo.com>]

- William S G Walker <astroman@voyager.co.nz> wrote:
> Arne & Lew,
> Greetings,
> 
> How real is this 'few parts in a thousand' value? Or
> what is a few? Just at
> the moment I'm having trouble getting better than
> 2-4% with CCD BVRI
> measures but these are across 20-30 degrees between
> images. 

Anyone doing 0.05 mag all-sky CCD photometry is doing
really well. What I did was to take the prior night's
"dome" flat and treat it as an image - I flattened it
with tonight's flat. The resultant individual pixel
values were all 285xx with xx being 10-60 or so, except
for the very edge column/rows. All it demonstrated was
that the lumpiness was not due to a generic error in
the flat field technique. My image of X Leo (not
posted) 2 degrees from the moon clearly shows out of
focus dust, not just lumpiness, verifying Arne's
explanation. 
===
Regards, Lew 
- Visit http://home.pacbell.net/cookl 
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