Re: [ATM] The standard aluminium coating: How much scatter?

["vladimir sacek" <vla@toast.net>]

Guntram Lampert wrote:

>However, I would be most interested in quantitative 
>data. How much light does a surface scatter before it is 
>put into the coating chamber, and how much does it 
>scatter when it comes out?

If we take surface micro-ripple as the main source of the 
off-glass scatter, and the Texereau's worst-case 
scenario figure of 1/100 wave RMS, it should be a 
fraction of 1% of the total light.

As for the off-coating scatter, some time ago I run into 
a Web article on the subject. Don't remember specifics, 
only that it contained results of a study conducted at a 
proffesional observatory. Relatively fresh, properly 
applied aluminum coating was measured as having less 
than 1% scatter, while coatings compromised either by 
improper application or years long "wear and tear" had 
significantly more of a scatter, some in excess of 10%. 

Obviously, it can be a significant factor. The problem, 
as usual, is that a number of variables - mostly unknown - 
determines what the figure is in every particular case.

Vlad

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