Archived posting to the Leica Users Group, 1998/04/21

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Subject: Re: [Leica] M's and focusing
From: Eric Welch <ewelch@ponyexpress.net>
Date: Tue, 21 Apr 1998 20:03:53 -0500

At 08:10 AM 4/21/98 -0400, you wrote:

>You are correct but that is not the question.  The question is if you focus
>on A and then recompose to B (without refocusing) then, if you assume a
>flat field, A would be past the point of focus and B would be in front of
>the point of focus.  Because, assuming a flat field the point of focus is

No, actually, the point of focus would be behind both objects. Because the
distance to A is farther away than B. When you turn to B, the plane of
focus swings perpendicular to the line from camera to B. If the lens is
flat field, then the plane of focus is now farther than B, and thus behind
A too.

And most lenses are not terribly flat, but some of them are very flat. This
is an area where you will be better off with an SLR, because you can see
where the optimum plane of focus is, no matter where the subject is on the
screen. Thus SLRs are given to more contemplative photography, rangefinders
to more dynamic fast-happening situations. Of course, with notable
exceptions on all points.
==========

Eric Welch
St. Joseph, MO
http://www.ponyexpress.net/~ewelch

I exist as I am - that is enough.

- - Walt Whitman