[Aavso-photometry] Where do the professionals source their V and B filters from?

[arne]

Richard Miles wrote:

> Further to the troubles people are having with filter glass 
> degradation, it occurred to me that some professional observatories 
> carrying out V and B photometry may have solved the problem by finding 
> a supply of stable filters.  Does anyone know whether this is the case 
> or not?  If yes, then where do they source their filters from?
>
Most U.S. professionals get their filters from Custom Scientific.  We 
have filters that are 12 years
old at NOFS, with no degradation other than the usual scratches and AR 
pinholes.  Remember, though,
that Flagstaff humidity is extremely low most of the year.
  You will hear more about filters at the Fall AAVSO meeting.
Arne