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Curvature of Field in Camera Lenses
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A lens that projects an image as a
portion of a sphere demonstrates the aberration called curvature of
field. The center can be sharply focused but not the edges, or vice
versa.
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Although curvature of field is not
correctable, its effects can be minimized when photographing a flat
subject (where it will be most noticeable) by focusing the image at a
point a little out from the center, thus taking best advantage of the
depth of focus of the camera.
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Flat subjects are best photographed with
a "flat-field" lens, which has been corrected in manufacture to be free
of this aberration. Most macro lenses, and some wide-angle lenses
designed for architectural photography, are especially well corrected
for this fault.
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