Archived posting to the Leica Users Group, 1998/04/20
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On Mon, 20 Apr 1998, TEAShea wrote:
> <<
> An open question regarding M's and lenses with good flatness of
> field--suppose
> I'm shooting wide-open with a wide angle lens and my subject is, say, a
> person
> who's pretty close, and I want the eyes to be sharp. I focus on the person's
> eyes in the center of the finder, but that's not what I want in composition,
> so I move that person close to the edge of the frame. Technically, it seems
> to
> me that if the field-plane is truly flat, that will back-focus the eyes of
> the
> person when I change the composition. >>
>
> If the distance from the lens to the person's eyes remains the same, the
> person's eyes should remain in focus if you are using a flat field lens (a
> lens with little or no curvature of field).
Not true.
A
|
|
|
|
|
|
Camera >----------------------B ---- center of view ( .i.e. camera is aimed
at B )
Distancace to A and B from the camera are different, but if the camera has a
flat field, then both will be in focus. If one recomposes to put A in the
center of the field and B on the edge, then A will behind the plane of focus
and B will be in front.
Duncan