Archived posting to the Leica Users Group, 2000/11/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Thanks Marc. I am still puzzled that the lens will not mount all the way on a IIIa while it easily mounts on my IIIc and one of my IIIfs. I have not tried my other LTMs. All other lenses that I have. including my Jupiter 9 mount easily on the IIIa. The inconsistency between mounting on the others and not on the IIIa puzzles me. Can you explain it? Best regards, Roland Smith - ----- Original Message ----- From: "Marc James Small" <msmall@roanoke.infi.net> To: <leica-users@mejac.palo-alto.ca.us> Sent: Thursday, November 30, 2000 9:04 AM Subject: Re: [Leica] Jupiter 3, 50mm f1.5, on Leica IIIa > 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 > compatibility. > > Marc > > msmall@roanoke.infi.net FAX: +540/343-7315 > Cha robh bas fir gun ghras fir! > >