Soft focus

A soft focus lens deliberately introduces spherical aberration which blurs fine texture in the image while retaining sharp edges across areas of high contrast; it is not the same as an out-of-focus image, and the effect cannot be achieved simply by defocusing a sharp lens.

For example, a front-focusing technique was suggested for the Kodak Portrait, in which the point of focus was placed closer to the camera than the actual subject.

[2] Unlike typical camera lenses, which have a generally symmetric depth of field characteristic extending both in front of and behind the point of focus, the uncorrected spherical aberration results in a depth of field which extends past (behind) the point of focus, but not in front.

Specifically, highlights in an image are blurred, but the bokeh effects of soft focus cannot be reproduced[citation needed].

For example, the two-element cemented meniscus lens fitted to early Vest Pocket Kodak cameras had a dish-shaped hood[11] which controlled spherical aberration by reducing the effective aperture to f/11; when the hood is removed, the resulting uncorrected images have a strong soft focus effect.

[20] As an alternative to variable element spacing, some soft focus lenses such as the Rodenstock Imagon use interchangeable sieve aperture "grid" or "diffusion" discs which have a perforated annular shape to control the balance of light recorded between the relatively well-corrected center of the lens and the uncorrected periphery.

It was supplied with a special filter to block light through the center of the lens, resulting in the image being formed by relatively uncorrected aberrations through the periphery.