Archived posting to the Leica Users Group, 2000/11/30

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Subject: Re: [Leica] Jupiter 3, 50mm f1.5, on Leica IIIa
From: Marc James Small <>
Date: Thu, 30 Nov 2000 12:04:49 -0500
References: <034801c059f3$5e895f40$4d02a8c0@neurosoft.lan>

At 12:27 AM 11/30/2000 +1100, A.H.SCHMIDT wrote:
>The pitch for Leica screw mount lenses was always 0.977mm.

To be precise, the pitch for LTM has always been 26 turns-per-inch
Whitworth, which equates to .977mm but the slope of the threads is not
metric but Whitworth, a carry-over from Leitz' microscope origins.

This has been bolluxed by a number of manufacturers, most notably FED in
the 1930's and Canon after the end of the Second World War, both of whom
thought the pitch ought to be 1.0mm even.  Thus, early FED and Canon gear
might not be completely compatible with true LTM.  Also, Canon got the
chamfer on the lens-mount wrong at first, though this had minimal effect on

Marc  FAX:  +540/343-7315
Cha robh bas fir gun ghras fir!

Replies: Reply from "Roland Smith" <> (Re: [Leica] Jupiter 3, 50mm f1.5, on Leica IIIa)
In reply to: Message from "Stanislaw B.A. Stawowy" <> (Re: [Leica] Jupiter 3, 50mm f1.5, on Leica IIIa)