[Aavso-photometry] Re: Crud on filters

[Wolfgang Renz]

When I read this thread a question pops into my mind:

  Will this issue also occure with AR coated photometric filters ?

Or does the AR coating protect the BG39 filter glass good enough.
Does it also start at the circumfence when the AR coating doesn't
protect the sides too ?

Clear skies
  Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO



----- Original Message ----- 
From: "Richard Miles" <rmiles.btee at btinternet.com>
To: "Bill Goff" <b-goff at sbcglobal.net>
Cc: <aavso-photometry at aavso.org>
Sent: Wednesday, October 12, 2005 4:19 PM
Subject: Re: [Aavso-photometry] Re: Crud on filters

> Bill Goff wrote:
> 
> > I've begun to wonder if this is more of a preventative maintenance 
> > problem; a few times a year cleaning the filter with alcohol or something 
> > just to keep the crud from accumulating.
> >
> 
> I tend to agree Bill.  Although the BG39 filter glass effloresces (that's 
> the chemical term) in humid atmospheres, it does not seem to change the 
> colour of the glass when inspected visually.
> 
> So like you say, keeping it polished may be a good strategy but watch what 
> you use as the glass is quite soft - tin oxide is probably less hard than 
> alumina or rouge.  A soft lint cloth may be the best option.
> 
> The white surface layer might be soluble in a very weak acid such as lemon 
> juice - I'll give it a try and let you know.
> 
> Richard