[Aavso-photometry] Mixing filter brands and transformations

[Shawn Dvorak]

Gerald Bokowy wrote:
> I just changed from a manual filter wheel to one that is motorized.
>
>  While doing so I noticed that my V filter has a bad case of crud.
>
> All of my current bvri filters are Schuler.
>
> I am considering getting a custom scientific V filter to replace the
> corroded one.
>
> Will mixing this new V filter with the anti reflective coatings and
> different thickness, with the remainder of my schuler filters.
>
> cause problems when doing transformations?
>
> I intend to slowly move to all custom scientific filters in time but not
> immediately.
>
>  
>
> Do I 
>
> 1)      Replace the crud coated schulerV filter with a new one and wait to
> buy a full set in the future.
>
> 2)      Or slowly convert from schuler to custom scientic as funds are
> available one filter at a time
>
>  
>
> Does everyone use a matched set of filters? Does it matter beyond focusing
> differences?
>
> My biggest concern is will there be any systematic problems for color
> transforms using a mixed set
>
>  
>
> G Bokowy
>
>  
>
>  
>
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>
>   
You might try cleaning off the crud as a stop-gap solution.  Here in 
Florida my Schuler filter lasts about 8-10 months before noticeable 
degradation occurs.  I've had reasonably good luck removing the film 
using mirror polishing powder and a little water, gently worked with my 
thumb.  Either cerium oxide or red rouge works, but go with the cerium 
if you have a choice since it's much less messy.  I've not done any 
exhaustive testing but the quality of photometry and the transformation 
coeffs are appreciably the same between a new filter and the cleaned one.

Shawn Dvorak