At 04:54 6/16/02, you wrote:
Hi!
First TOPE 10 is great! Thanks to Olaf and the participators.
Entry 9 of TOPE 10, got me thinking of math and linear algebra, sorry if
this disturbs anyone. Anyway, the d.o.f. must be a 3D-space, where the exact
focus is a plane more or less in the center, and by tilting the camera, much
like on a large format camera, one could more or less get at horizontal or
at least tilted focus?
Tilt and shift, also called "adjustments" in the world of large format, are
covered in detail by Ansel Adams in _The_Camera_. Both require an image
circle at the film plane that is larger than the image that will be made on
film.
Shift is used primarily to keep the film plane parallel to a plane in
space, a classic example being the front of a building. It provides the
ability to control perspective lines and keep desired parallel lines in
space parallel in the image (e.g. the vertical lines of the
building). There are other uses as well, some more subtle, but it's always
an adjustment of perspective and the convergence of perspective lines.
Tilt is used primarily to change the critical focus distance across the
film plane, a classic example being landscapes in which the flowers no more
than 3 feet from the camera are in critical focus along with the mountain
peaks 20 miles from the camera. With rectilinear lenses, critical focus is
in a plane parallel to the film plane. Tilting the lens to the film plane
tilts the plane of critical focus. As with shift, there are other, more
subtle uses, but it's always an adjustment of the orientation of critical
focus plane to the film plane.
-- John
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