Archived posting to the Leica Users Group, 1997/11/23

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Subject: Re: M6 range finder w/ lens longer than 75mm??
From: "Jacques Bilinski" <>
Date: Sun, 23 Nov 1997 20:51:08 -0800

> Focal length has a lot to do with the accuracy of focusing with a
> rangefinder. The longer the focal length, the less "width" the focusing
> base has. Read Gunter Osterloh's book "Leica M" for a decent explanation.
> The wider, the more accurate an M6 is. The longer (from 90+) the more
> accurate an SLR is.
> ==========

The difference between an SLR and a rangefinders w.r.t focusing accuracy is
that when a longer and/or faster lens is mounted on an SLR the focusing
accuracy is increased, but on a rangefinder the focusing accuracy is the
same regardless of which lens is mounted on the camera.	
If for example a Leica can focus to +/-1cm at 2 metres this will be much
more than adequate for any wide angle lens, but will less than adequate for
a 75mm lens at f1,4 where the depth of field is only 6mm. 
The depth of field figures come from the j'accuse Leica article at