Wide-angle Soft Focus Photographic Lens

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 and wrinkles.