Date: Wed, 15 Mar 2006 09:44:38 -0800

> There was a recent thread on this, I think on this mail list, and also 
> apparently some discussion at the last AAVSO meeting.  Basically, one 
> of the glass layers in the filter composite is affected by moisture 
> and develops a tough, thin film.  It's easiest to detect the film by 
> appear even before the film is visible when just looking at the 
> polishing it off is the best approach.  I don't know if anyone has 
> done any analysis to see if there's any substantial color shift as the 
> glass deteriorates.
>
> Shawn
>

I was surprised that the Custom Scientific filters were showing a 
similar problem.  I've used Schuler's for 4 or 5 years and after the 
recent discussion looked at them and found a haze after close 
inspection.  In fact, I had to reflect a bright light off the surface 
to see it.  Alcohol, hydrogen peroxide didn't touch it, but a very 
light slurry of cerium oxide and 'finger tip polisher' took it right 
off.  It probably would also have taken off any coatings had there been 
any, so it might not be a fix for an AR coated filter.

Bill

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