[Aavso-photometry] Filters to minimize differential extinction effects

[arne]

Tom Krajci wrote:
> I'm slowly learning about filtered photometry, but for years my bread 
> and butter work has been unfiltered.
> 
> I know that my unfiltered data may capture lots of photons, compared to 
> ye olde V filter bandpass (or other Johnson-Cousins filter bandpass):
> http://www.astrodon.com/custom/_2e2a/content/files/SchulerUVBRIYel.jpg
> 
> But I can have significant problems with differential extinction for 
> comp and target stars with poor color match.
> 
> Is there a filter type (inexpensive, easy to obtain) that provides a 
> larger bandpass than Johnson-Cousins, that is considered scientifically 
> valid and useful in the amateur science/photometry community?  I want to 
> try and strike a balance between gathering lots of photons, and reducing 
> differential extinction problems.  (Some sort of minus-blue filter perhaps?)
> 
You can't have everything. Even the Johnson/Cousins filters are 1000A
wide, very poor spectral resolution, and differential extinction even
with these filters (just much better than unfiltered).  SDSS is narrower,
and then there are the narrow bandpasses such as the Stromgren system
(which often doesn't need transformation since the bandpass is set
by the filter).

A V filter reduces your throughput by about a factor of 4.  It is
the widest bandpass that I'd consider to be standard.  Just
work with brighter objects, Tom!
Arne