[Aavso-photometry] RE: Crud on Filters--Solvent Found??

[bailyhill at aol.com]

Hello All;

  This sounds a little too good to be true, but I may have found the 
solvent to get rid of the crud on B and V filters.

  I have been so busy with the AAVSO annual meeting, that I have not 
taken my filters out and looked at them, after all the discussion on 
this list. Well tonight we are having a Northeaster, courtesy of 
Hurricane Wilma, so I can't observe. When I last observed on Friday 
night, I did notice that TU CAS was very bloated, and could not be 
brought to focus. I have noticed this before, but only when imaging a 
bright star at the edge of the field. Thought it might be some artifact 
of the microlensing. This night, it seemed to be everywhere, not just 
at the extreme edge.

  So I took the filter wheel out, and there was a whitish coating on one 
side of the B and V filter. I went to the medicine cabinet to see if 
alcohol would touch it, expecting that it would not, based on the 
feedback from others on the list. Well, there was no alcohol, but I did 
have some 3% Hydrogen Peroxide. So I tried it, and much to my surprise, 
it cleaned right off.

  Well I do not know if your crud is the same as mine, but I do have 
Schueler filters and it looked the same. Try this and let me know if 
you have the same good fortune that I did. My filter is clean as a 
whistle. I used a pure cotton swab and some pure cotton cue tips. Clean 
like any other optic.

  I will check with some Chemist friends of mine, but I suspect that it 
has something to do with polar and non-polar solvents, and the H2O2 is 
the right one.

 Clear Skies and Clear Filters

 Gary Walker



 -----Original Message-----
 From: Michael Koppelman <lolife at bitstream.net>
 To: Richard Miles <rmiles.btee at btinternet.com>
 Cc: AAVSO CCD Discusion Group <aavso-photometry at mira.aavso.org>
 Sent: Sat, 22 Oct 2005 09:59:54 -0500
 Subject: Re: [Aavso-photometry] RE: Crud on Filters

  I'm using a normal 1.5" filter. I'm not sure of the thickness but the 
rest of my filter are the Schuler filters so parfocal with that would 
be good. It sounds like a good solution. 
  
  I sort of wonder, though, whether it would be worth it in general to 
have the AR coatings. The price difference, although not insignificant, 
amortized over time is not a huge deal. 
  
 Michael 
  
 On Oct 21, 2005, at 5:01 PM, Richard Miles wrote: 
  
  > AR-coating will certainly be an improvement but how stable they > 
remain depends on a lot of factors; layer thickness, composition, > 
absence or otherwise of pinholes, relative humidity in the filter > 
environment, BG39/BG40 batch, etc. 
 > 
  > As I mentioned, Norman Walker can produce an optically-flat V > 
filter with a 1mm silica plate cemented to the BG39 component. > Cost 
for the complete filter about 100 UK Pounds. 
 > 
 > What is the diameter and thickness of the V filter you need? 
 > 
  
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