RE: [Leica] I eat crow

["Austin Franklin" <darkroom@ix.netcom.com>]

Johnny,

> > The plane of focus is an arc with the "anchor" point at the center of
> > the
> > film plane, and the radius the distance to the subject.  As long as
> > you KNOW
> > that and use that to focus, there is NO changing of focus to
> > accommodate
> > this.
>
> actually that is not true, Austin.

I certainly didn't use very good terminology.  But, with respect to what I
was talking about it is true.

> The plane of focus is indeed generally a plane, or close to it. (What
> you are describing is not an arc but a hemisphere).

(Sure what I am describing is an arc.  Arc is merely "something shaped like
a curve", "segment of a circle".  A hemisphere is "half a sphere", and
certainly wasn't what I was talking about)

When you are using a focusing "aid" to get a focus, you need that "aid" to
be the same distance from you as the subject.  In order to do so, you need
to use an arc, not a line parallel with the film plane.  If you use a
focusing aid that is planar with (in the same plane as) the subject, your
focus will be off, as the distance from the film to the focusing aid is not
the same as the distance from the subject to the film.

Regards,

Austin

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