[Aavso-photometry] crud on filters

[Michael Koppelman]

Thanks everybody. I will try to clean it with optical cleaner. (Yes,  
Gary, it was on the outside on one side only.)

I have another V filter but it is not par focal with the rest. That's  
OK for now while I work on this. Seems like a very unfortunate "bug"  
in the recipe, IMHO.

Michael

On Sep 20, 2005, at 2:26 PM, Michael Koppelman wrote:

> I think someone else had posted something similar at one point...
>
> My photometry went to hell in the V-band. Errors went way up, the  
> stars looked fuzzy. It was clear something was up. I took the CCD  
> and filter wheel off and the V filter and to a lesser extent the B  
> filter had a coat of crud on them. The R and I filters were fine.  
> The crud looked sort of like salt water had dried on the filter. It  
> was bumpy and translucent. It would not clean off. I tried pure  
> alcohol and lens tissue, then switched to pure cotton. I forewent  
> my better judgment and scrubbed it pretty hard. I couldn't get it  
> clean. I'm going to try to disassemble it and soak it or something  
> but I suspect it is ruined at this point.
>
> Although I doubt it is air tight, there is no way dust or  
> contaminants could get in there that I'm aware of. My observatory  
> goes through large temperature swings throughout the course of a  
> year, from -20F to +100F or so. I wonder if the heat made something  
> bubble up? Why just V and B and not the other filters?
>
> I'm a bit confused.
>
> Thoughts?
>
> Michael
>
>
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