Re: Data reduction methodology for V-I colors

[Thomas Droege <tdroege2@earthlink.net>]

Scattered light was one of the reasons for installing flocked paper in all
the telescope tubes.  While I think this improved the faint magnitude
detection, it did not produce data with lower scatter.  A number of
different light shields have been tried also.  

Tom Droege


> [Original Message]
> From: Doug Welch <welch@physics.mcmaster.ca>
> To: Chris Albertson <chrisalbertson90278@yahoo.com>
> Cc: <tdroege2@earthlink.net>; <tass@listserv.wwa.com>
> Date: 8/31/2004 2:01:44 PM
> Subject: Re: Data reduction methodology for V-I colors
>
>
> If the correction is a function of magnitude, then scattered
> light may be a factor. This may be scattered light in the
> flat and not in an actual image.
>
> Cheers,
> Doug
>
> On Tue, 31 Aug 2004, Chris Albertson wrote:
>
> > 
> > Could it be that the zero point is really a function of
> > (x,y) on the frame and that using one "zero point" for the
> > entire frame is only a gross approximation of the true
> > "zero function".  It seems unlikely to me that the atmosphere
> > really is equally transparent over a degrees wide field.
> > 
> > Professionals may  have been using zero points for years but
> > how many of them use wide feild images?
> > 
> > One experiment might be to plot the difference between
> > instrumental and catalogged magnitutes and see if the differences
> > "clump" togeter.  If there were a cloud blocking
> > half the frame you would see it.  But more subtle effects
> > might also be detectable.
> > 
> > If the transpaarency does vary across a frame at the few percent
> > level then maybe you will have to compute some kind of "zero
> > function".
> > 
> > The "gradient" Tom talked about seems like it might headed in 
> > this direction.  "gradient" is a kind of fuction (a first order
> > one.) but I supect a tilted plain will not fit much better then
> > our current zeroth order function.  The physical atmosphere is
> > likey bumpy with sharp discontinuities.
> > 
> > 
> > 
> > 
> > --- Thomas Droege <tdroege2@earthlink.net> wrote:
> > 
> > > I will leave this for Michael.  I have just looked at data sets as a
> > > whole.
> > > Why not join in the fun?  There is lots of data.  Andrew, Michael and
> > > I
> > > have been working on this.   There is room for more clever minds to
> > > puzzle
> > > over the data.  As always, I stand willing to copy CDs for anyone
> > > willing
> > > to compute on the data.  
> > > 
> > > Tom Droege
> > > 
> > > 
> > > > [Original Message]
> > > > From: Michael Koppelman <lolife@bitstream.net>
> > > > To: <tdroege2@earthlink.net>
> > > > Cc: tass <tass@listserv.wwa.com>
> > > > Date: 8/31/2004 12:24:00 PM
> > > > Subject: Re: Data reduction methodology for V-I colors
> > > >
> > > > But aren't you getting a different zeropoint solution for every
> > > frame? 
> > > > Why not use a single zeropoint for the entire night?
> > > >
> > > > On Aug 31, 2004, at 12:20 PM, Thomas Droege wrote:
> > > >
> > > 
> > > 
> > > 
> > > 
> > 
> > 
> > =====
> > Chris Albertson
> >   Home:   310-376-1029  chrisalbertson90278@yahoo.com
> >   Cell:   310-990-7550
> >   Office: 310-336-5189  Christopher.J.Albertson@aero.org
> >   KG6OMK
> > 
> > 
> > 		
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>
> -- 
> ==================================================================
>  Douglas L Welch     | Res office/voicemail (905) 525-9140 x23186  
>  Physics & Astronomy | FAX                  (905) 546-1252 
>  McMaster University | 
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>  Canada L8S 4M1      | E-mail           welch@physics.mcmaster.ca
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