J. Brian Caldwell
When a lens designer sets out to
design a photographic objective
the usual goal is to produce the
sharpest possible lens by optimally minimizing all aberrations. However, this is not the case with lenses intended
for portrait photography. A
well-corrected lens will ruthlessly reveal all facial blemishes and wrinkles, and many people find this disturbing.
As Arthur Cox put it, "portrait
work, especially commercial or
professional portrait work, is as
much subtle flattery as photography." The best alternative is to use a special soft focus lens having a large
amount of spherical aberration. A
point image produced by such a lens will consist of a fairly small core surrounded by a large halo. And, since this effect is stable in the presence of
moderate amounts of defocus, the
depth-of-field is larger than that of a well-corrected lens. The small core ensures that high-contrast, fine detail
remains visible, while the large
halo tends to blend away blemishes
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Publish Date: 01 January 1999
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