Re: Elmarit 90mm

["Dan Post" <dwpost@email.msn.com>]

Back when I had an M2, I checked the engraving on the inner brass barrel of
the lenses; I had heard that Leitz actually put each lens on an optical
bench and measured the true focal length of each lens. They then engraved
the true focal length and f value on the inner barrel. It was there on all
three lenses I had. It would explain somewhat the fabled quality control
under which they are made ( and the reason for the outrageous cost! :) ).
They could then calculate the actual true f ratio- I suppose so that if you
wanted to use the lens for any photogrametric purpose, you would have the
lens' actual values. My assumption always was that when the lens was
assembled, that whatever variations in interelement (?) distances were
checked, and validated before the lens was released. Anyone heard of any
lore similar to this??
- -----Original Message-----
From: Paul Schliesser <paulsc@eos.net>
To: Leica User's Group <leica-users@mejac.palo-alto.ca.us>
Date: Friday, 31 October, 1997 4:41 PM
Subject: Re: Elmarit 90mm

>>Does anyone know if the Elmarit 90mm/f2.8 (the one with the detactable
>>lens head for use on the Visoflex 1958-1974?) was ever recomputed during
>>it's lifetime?  If so, which serial numbers correspond to the old and
>>new formulae?  Also, is there a book (preferably in English) which
>>would contain information such as this on this and other lenses?
>
>Dan,
>
>You know those little numbers after the distance scale, which tell you
>what the actual focal length is? When I was photographing stuff for the
>Photo Techniques article, at one point I examined two of these lenses at
>the same time, (both chrome), and happened to notice that one was marked
>00 and the other 90. This means that the second one was nearly 100mm.
>This made me wonder if there was not something different going on here as
>far as optical formula. Both lenses looked identical.
>
>None of the books I've seen mention a change in formula.
>
>Jim Lager's books have the most detail about lenses of any books that I
>am aware of. His _Leica An Illustrated History, Volume II-Lenses_ covers
>all of the thread mount, M and R lenses, up until 1994. Volume I is on
>cameras, volume III will be accessories, but is not out yet. You can
>order it from Tamarkin, http://www.tamarkin.com
>
>The other books I've seen either cover lenses superficially or cover only
>modern lenses in any detail.
>
>The one I own, in chrome, is marked 00. The serial number is 1735706.
>Maybe you could poll the list and find out what is out there.
>
>- Paul