Archived posting to the Leica Users Group, 2000/07/25

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Subject: Re: [Leica] Leica or B+W Filters
From: John Collier <>
Date: Tue, 25 Jul 2000 13:40:48 -0600

The coatings have to be a quarter wavelength thick so that the reflections
are exactly a half a wavelength out of phase and thus cancelled out by the
incoming light. Austin is, of course, referring to the width of the filter

John Collier

>>Austin Franklin wrote:
>> One of the advantages of the Heliopan 'Standard Coating' filters, is they
>> are SO thin.  I do not know if the multi-coated ones are thin also, they
>> may be...
>then Shel Belinkoff enquired:
>How thin are the Heliopan coatings?  B+W coatings are, according to
>the B+W catalog I have here, about 1/4 wavelength (and a chart is
>shown showing the wavelength in the 400nm - 700nm range).  I don't
>know what a "nm" is, but since we're discussing wavelengths of light,
>I'd imagine it to be very small.