Originally Posted by
Mark J
Sorry I missed your comment Alan.
Yes, this is the key to it. With shiny film base and glass on top you have two reflections of about 4% or 4.5% . The fringe pattern is only generated when the surfaces come to within 2 or 3 waves of light apart ( for white light illumination ) , however there is a faint fringe pattern generated, now I haven't got the maths to hand right now, it might only be about 10% brightness modulation, but it's visible.
If you coat ONE of these surfaces and have it only reflecting about 0.5%, then the fringe pattern contrast will drop AT LEAST by a factor of 10. It might actually be 100, I will check my 'book of important things' while i'm working this week, if i get chance.
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