References: <ALEIKIMFDBDICIHJOPFECECGDBAA.tom_krajci
Date: Thu, 16 Mar 2006 08:17:28 +1100
Date: Thu, 16 Mar 2006 08:17:28 +1100

I have recently been discussing my B and V filter 'crud' problems with 
Astrodon's Don Goldman (the new Schuler filters owner). He was puzzled.about 
the B filter since the 'problem' BG39 glass is (currently) protected on one 
that my 2002 filter (before Schuler was taken over by Astrodon) was a 
different design.

He says the V filter, at this point, has no solution as It is made with only 
2 glasses and the BG39 is exposed and "even Schott Ph.D.'s don't know how to 
protect BG39".  He could put 1mm of a clear glass on it, but then it would 
not be parfocal with the others.  Thus, no current solution exists.

In response to my comment that A/R filters made by other manufacturers don't 
appear to suffer from this problem he was sceptical, pointing out that they 
only protect it by a MgF2 A/R coating which itself is hydroscopic. Astrodon 
could A/R coat one side of the V filter but that would add $20 to the price, 
with no guarantee it would cure the problem.

Bernard Heathcote


> Is it worth contacting the manufacturer about this?  Maybe he can offer a
> 'ruggedized' version of the filter sets...perhaps with a very thin layer 
> of
> chemically resistive glass cemented to the exposed layer of the vulnerable
> glass?  (About the thickness of a microscope cover slip?) 


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