Archived posting to the Leica Users Group, 2003/06/09

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Subject: Re: [Leica] Any thoughts on this flare problem?
From: Henning Wulff <henningw@archiphoto.com>
Date: Mon, 9 Jun 2003 23:08:23 -0700
References: <260932B2-9AEA-11D7-AF0F-000A9578C446@ncable.net.au>

At 12:20 PM +1000 6/10/03, Alastair Firkin wrote:
>Interesting thought: it was very dusty, and I did not clean the lens 
>between  takes. Never noted dust to do this, but with longer 
>exposures etc, maybe, but then, they were not in the same place all 
>the time.
>
>Hmm
>
>anyone know if dust can do this ?
>On Tuesday, Jun 10, 2003, at 11:54 Australia/Melbourne, Mike Durling wrote:
>
>>Could these be from dust on the lens surface that the light is 
>>hitting?  With a lens that wide they might be just out of focus.
>>
>>Mike D

These are lens design/coating parameter conditions, and dust wouldn't 
be enough of a factor. Also, dirt, dust and fingerprints would only 
produce 'fuzzy' diaphragm images. Under very contrasty images with 
multi-element lenses, you'll always get ghost diaphragm images with 
any lens, even the best.

It's mostly a matter of coatings. What's required is a coating that 
will absorb all visible or recoradable wavelengths on a surface of a 
given refractive index. If you where recording a single wavelength at 
a fixed angle of incidence, you could eliminate reflections entirely, 
but not with a wide range of wavelengths at a wide range of incident 
angles. Compromises are necessary. Since the refractive index is a 
constant, and the wavelengths aren't, you can't get complete 
absorbtion with the present technology. If the contrast is high 
enough, you'll get ghosts.

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    *            Henning J. Wulff
   /|\      Wulff Photography & Design
  /###\   mailto:henningw@archiphoto.com
  |[ ]|     http://www.archiphoto.com
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In reply to: Message from Alastair Firkin <firkin@ncable.net.au> (Re: [Leica] Any thoughts on this flare problem?)