[Aavso-photometry] V filter only - transforms possible?

[Michael Newberry]

No, not possible.

Michael Newberry

----- Original Message ----- 
From: "Tom Krajci" <tom_krajci at tularosa.net>
To: <aavso-photometry at aavso.org>
Sent: Thursday, December 18, 2008 3:48 PM
Subject: [Aavso-photometry] V filter only - transforms possible?


>I have a CCD/scope rig with only a V filter screwed into the CCD nosepiece. 
>No filter wheel, no other filters.
>
> Here's the $64 question.  Is it possible to determine transformation 
> coefficients for this setup with only a V filter?
>
> If I do differential photometry of a Henden calibrated field (V magnitudes 
> and color indices are known for the comps, *and* the target), can I 
> transform to V magnitudes?
>
> What if I take images of ye-olde standard field, M67, and compare my 
> instrumental magnitudes with the catalog magnitudes?  What sort of 
> correlation/transformation coefficient will that give me?  (If it's not a 
> true transformation coefficient, then what is it called - a pseudo 
> transform?)
>
> (I know that if I use this V-filter-only rig on uncalibrated comps and 
> targets, i.e. V mags and color indices are unknown,...then there is no way 
> I can transform.  Therefore I'm looking for 'easy' target fields that I 
> can work to higher precision...hopefully with a proper transform to V 
> magnitudes.)
>
> I'm just trying to get the most out of this V-filter-only system.  (And if 
> I can't transform to V with this setup...how close can I get?  How do I 
> report the magnitudes?...as untransformed?)  (And if I can't transform to 
> V with this setup...what do I need to acquire?...a B or R filter?)
>
> Thanks in advance.
>
> -- 
> -------------------------------------------
> Tom Krajci
> Cloudcroft, New Mexico
> http://picasaweb.google.com/tom.krajci
>
> Center for Backyard Astrophysics (CBA)
> http://cbastro.org/ CBA New Mexico
>
> American Association of Variable Star
> Observers (AAVSO): KTC http://www.aavso.org/
> -------------------------------------------
>
>
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