[Aavso-photometry] Differential transformation

[Radu Corlan]

> Radu, that's and interesting web page, I will have a closer look even
> though I am a happy Windows user ;-)

a happy windows user? isn;t that a contradiction in terms? (just kidding 
;-)).

Radu

> 
> Geir
> 
> On Tue, 28 Dec 2004 18:52:42 -0800, Chuck Pullen <cpullen at pacsafe.com> wrote:
> > Hi Radu - I think that Geir was trying to not have to do any
> > extinction/airmass calculations. Yes, you can use stars from all over the
> > sky for your transformation determinations, but if they are at different
> > airmass you'll have to calculate your extinction, and have a truly
> > photometic site and night.  Doing them from one field is nice for many of
> > us who don't have the best mountain top environments!
> > 
> > Thanks for sharing your web site.  I'll check it out.
> > 
> > Chuck
> > 
> > 
> > At 22:33 12/28/04 +0200, Radu Corlan wrote:
> > 
> > >On Tue, 28 Dec 2004, Chuck Pullen wrote:
> > >
> > > > Geir - in an ideal world, your approach would be perfect.  However, for
> > > > determining transformation coefficients, you want a wide range of color as
> > > > well as stars of about the same magnitudes so they have about the same
> > > > signal to noise across the color range.  And, of course, the stars need to
> > > > be non variable, and calibrated against a known data set, such as Landolt
> > > > fields.  So, the odds of finding all of these requirements in your 15' by
> > > > 15' image for a given part of the sky are pretty slim!
> > >
> > >Chuck - one can use Geir's approach and combine stars of different colors
> > >from different fields, they don't need to be all on one field. If you have
> > >enough stars with good photometry (for instance some of Arne's sequences,
> > >which are spread across the sky) the errors reduce pretty well.
> > >
> > >I use that approach (see http://astro.corlan.net/gcx/html/node9.html ) for
> > >a description and some example graphs.
> > >
> > >Radu
> > 
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> >
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-------------
Radu Corlan       Snail Mail: Bucuresti sect. 1, 
rcorlan at pcnet.ro  str. Argentina nr. 28, Romania

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