[Aavso-photometry] RE: Crud on Filters

[Michael Koppelman]

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?
>