Archived posting to the Leica Users Group, 1996/07/28

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Subject: Re: IR marks on Leica lenses (2nd posting)
From: "joe b." <>
Date: Mon, 29 Jul 1996 00:03:45 +0100

In message <>, Willem-Jan Markerink
<w.j.markerink@a1.NL> writes
>Perhaps my previous subject line wasn't temping enough....;-))
>Hi gang,
>On the IR list, someone mentioned the fact that Leica, as Nikon, 
>recommends closing aperture instead of using the IR focus mark. 
>Assuming that most primes still have such an IR focus mark, this 
>surprised me. How is this subject treated in Leica manuals?
>[background: one of my technical IR books (written by Guenter 
>Spitzing, a well known German author of several camera books, I 
>assume about Leica as well(?)) clearly states that closing down to 
>minimum aperture is not recommended due to increasing diffraction 
>with increasing wavelengths (IR being longer waves than visible)]
>Can anyone shed some light on this subject?

Hi W-J, like all the best coincidences, I posted what is, in effect, a
rather voluminous answer to this question on the IR group and then found
your question here. Leica lenses don't have IR focusing marks nowadays,
and I think of the various Leica lenses I've got going back over many
years of manuafacture, I can't recall any of them having one. Maybe one
does, but I can't remember. To save bandwidth I won't post it here as
well unless somebody asks- I'll just leave this as a pointer to it (or
does the term "pointer" only refer to web pages....?)
joe b.

In reply to: Message from Willem-Jan Markerink <w.j.markerink@a1.NL> (IR marks on Leica lenses (2nd posting))