Archived posting to the Leica Users Group, 2003/07/31

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Subject: Re: [Leica] arggghhh... rant at Keeble & Shucat...
From: Eric Welch <eric@jphotog.com>
Date: Thu, 31 Jul 2003 18:43:59 -0700

No, that's not true. The longer the focal length the less accurate a 
rangefinder is. Because the base of the rangefinder (based on the 
distance between the two windows that make up its base) determines the 
accuracy of that rangefinder. It becomes smaller in proportion to the 
focal length as the latter increases. Thus less accurate in absolute 
terms. Why do you think Leica sells bodies with different viewfinder 
magnifications?

Why is an M6 more accurate than a CL? Because of the rangefinder base! 
It's wider on an M body. Why is it harder to focus accurately with a 75 
Summilux wide open than a 50 Summilux? It's in part because the depth 
of field is shallower. But it's also harder to place that plane of 
perfect focus where you want. Because the rangefinder is less accurate 
with that lens because the "base" is narrower for the 75 than it is for 
the 50 in proportion to the focal length.

This is basic physics. But you are right that the difference in 
relation to SLRs changes with focal lengths changes as focal length 
changes - more or less. An SLR becomes less accurate with wider lenses 
- - for the same reasons. The "base" of the focusing of an SLR lens is 
the width of the front element in proportion to its focal length.

Someone ask Erwin Puts to rule on this disagreement!

On Thursday, July 31, 2003, at 07:00  AM, Clive Moss wrote:

> I think he means "more accurate
> than SLRs" -- which is true. If he means "more accurate in the sense 
> of less
> deviation from the exact distance" - clearly untrue - the rangefinder 
> has no
> way of changing its measured distance based on the focal length of the 
> lens.

Eric Welch
Carlsbad, CA
http://www.jphotog.com

Always drink upstream from the herd. - Will Rogers

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Replies: Reply from "A. Lal" <alal@duke.poly.edu> (Re: [Leica] arggghhh... rant at Keeble & Shucat...)