Archived posting to the Leica Users Group, 1996/09/14

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Subject: Re: numbers on Summicron focusing ring, again
From: Willem-Jan Markerink <w.j.markerink@a1.NL>
Date: Sat, 14 Sep 1996 13:32:55 +0000
Comments: Authenticated sender is <>
Priority: normal

On 14 Sep 96 at 15:51, D Khong wrote:

> My 90 summicron has "05" engraved.  Should the actual focal length be 90.5mm
> or 89.5mm?  There must be a simple way to decipher all these numbers.
> Dan

Assuming the deviation is within 5mm, 00-45 means a longer focal 
length, 55-95 means a shorter one. 
This raises another question: does anyone have a 00 lens, and what 
are the largest deviation numbers among members of this list?
The closer to 50, the more deviation, both shorter and longer. 

On a side note: this system is also used on projector lenses, and I 
believe more manufacturers than only Leica do this. Pretty sure Kodak 
does, since Kodak caroussels are often used in large dissolve 
In dissolve systems, the exact focal length is even more important 
than with camera systems; you'd never exactly match the screen with 
two dissolving projectors if you didn't pick two identical lenses.

Another very critical application is stereo-photography, for both 
taking lenses and projecting lenses.


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     _/  _/ illem    _/     _/ an    _/  _/  _/ arkerink

      The desire to understand 
is sometimes far less intelligent than
     the inability to understand

[note: 'a-one' & 'en-el'!]