Archived posting to the Leica Users Group, 2002/04/10

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Subject: Re: [Leica] Screw mount to M
From: SthRosner@aol.com
Date: Wed, 10 Apr 2002 15:38:51 EDT

In a message dated 4/10/02 2:44:43 PM Eastern Daylight Time, 
mginex@panynj.gov writes:

> Because I don't know any better, I guess. Just posed the question since I
>  have no experience with RF Leica's. 
>  

Sorry, Mike, I made an assumption I shouldn't have, that you did know about 
RF Leicas. M lenses have a cam whose curve activates a follower arm connected 
to a prism/mirror that determines the focus of the lens. The rangefinder base 
(the distance between the RF windows) determines the accuracy of the 
rangefinder - the wider the more accurate. That distance can be made more or 
less accurate by the magnification of the viewfinder itself. Leitz/Leica has 
found that 135mm lenses are the longest focal length that can be accurately 
focussed by M-cameras. In fact, in the 1960s, Leitz is believed to have made 
one or two prototypes of a 180mm f/2,8 Elmarit lens with "bugeyes" similar to 
those on the 135/2,8 Elmarit for M cameras. They found that this rig could 
not achieve adequate focussing accuracy.

Leica lenses of 65mm and longer can be used with adapters on Leica reflex 
cameras; their focus is simply determined by the mirror, prism and focussing 
screen.

Seth       LaK 9 
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Replies: Reply from alex olstein <alexolstein@comcast.net> (Re: [Leica] Screw mount to M)