[vsnet-chat 1713] Re: [AAVSO-DIS] Re: CCD's Lumpy flat field?

["William S G Walker" <astroman@voyager.co.nz>]

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. Unfortunately
the ST6 with the filter wheel vignettes badly at f6.3 which may be a part
of the problem. But the values quoted by Lew seem to be very good for CCDs.
How are these determined?


Regards,
Stan

----------
> From: Lew Cook <lcoo@yahoo.com>
> To: aah@nofs.navy.mil; vsnet-chat@kusastro.kyoto-u.ac.jp;
aavso-discussion@physics.mcmaster.ca
> Subject: [vsnet-chat 1708] Re: [AAVSO-DIS] Re: CCD's Lumpy flat field?
> Date: Sunday, March 28, 1999 9:17 AM
> 
> Thanks to Arne Henden for the explanation of the lumpy
> field and the other tips. Yes, I knew working near the
> moon was difficult, but the point of my taking shots of
> SY Cnc (3 degrees from the moon) and X Leo last night
> (2 degrees from the moon!) was that NO ONE else
> observes there! I never observed there visually, and if
> I can fill a data gap with a mediocre quality
> observation, that is better than a gap. Getting down to
> 14th magnitude within 3 degrees of the gibbous moon
> would have been unthinkable for me before.
> 
> I think the 2 degrees may be too close!
> ===
> Regards, Lew 
> - Visit http://home.pacbell.net/cookl 
> _________________________________________________________
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