Archived posting to the Leica Users Group, 1996/11/24

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Subject: 23 microns, was Re: It really IS 26tpi!
From: "C.M. Fortunko" <fortunko@boulder.nist.gov>
Date: Sun, 24 Nov 1996 18:17:05 -0700

Jan 
To put things in optical terms, 0.023mm is 23 microns. This will cause
binding and other awful phenomena. In other words, this is what you pay
$2795 for.

Best regards,

Chris


At 03:04 AM 11/25/96 +0000, you wrote:
>On 24 Nov 96 at 16:11, Marc James Small wrote:
>
>> At 09:22 PM 11/24/96 +0000, you wrote:
>> 
>> >Shoot. 39mm by 26 tpi is as much a collision of imperial/metric 
>> >worlds as using 255/75R16 for tire size.
>> >It hurts my eyes. Awful!....:-))
>> 
>> 
>> But that is EXACTLY the point.  It is NOT 39x1mm, it is 39mm by 26tpi.
>> Canon made this mistake, too, and that's why they never quite got it right.
>> See Dechert's CANON RF CAMERAS for a discussion.  Some of the early FED
>> cameras show the same mistake.  
>> 
>> There was a US ad campaign back in the '60's about a 'silly millimeter' but
>> that's really the case here.
>> 
>> It IS 39mm wide by 26 turns per inch.  Why Barnack mixed Imperial and
>> metric, ich weisse ist nicht.  But he did.
>
>Shoot^2....:-))
>Aside from the nomenclatura: how on earth can 1mm pitch cause 
>problems where 26tpi doesn't? 
>26tpi equals 0.977mm pitch (25.4/26), so there is only 0.023mm
>difference pro rotation between the systems. Even with a thread
>thickness of 1cm, there wouldn't be problems with binding or
>whatever. Heck, with a little stubbornness, one can even jam an M42
>male mount all the way down in a T2 female mount (0.25mm difference
>pro rotation). 
>
>Truely flabbergasted!....8-))
>
>--
>Bye,
>
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><w.j.markerink@a1.nl>
>[note: 'a-one' & 'en-el'!]
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