Soft focus is a photographic technique and aesthetic quality describing an image that has been intentionally rendered with a gentle, controlled diffusion that softens fine detail, reduces harsh contrast at edges, and envelops the image in a luminous glow or haze, while retaining an underlying sense of sharpness and structure that distinguishes it from a simply out of focus or unsharp image. The essential character of soft focus lies in this paradoxical combination of apparent sharpness and gentle diffusion - a soft focus image is not blurred in the conventional sense but rather appears simultaneously sharp and dreamily soft, with highlights blooming gently into surrounding areas and fine textures rendered with a flattering, smoothing quality that pure optical sharpness would reveal in unforgiving detail.
The distinction between soft focus and simple unsharpness is fundamental to understanding and appreciating the technique. An out of focus image is unsharp because the lens has failed to converge the light rays from the subject to a precise point at the film or sensor plane, producing a generalised blur that destroys both the structural definition and the fine detail of the subject equally. A true soft focus image retains the underlying structural sharpness of the subject - the broad forms, tonal relationships, and overall composition are defined with clarity - while a controlled diffusion overlays this underlying sharpness with a soft halo effect that is most pronounced in the highlight areas, where the blooming of bright tones into surrounding areas creates the characteristic luminous quality of soft focus rendering.
Soft focus can be achieved at several different stages of the photographic process, each producing subtly different qualities of diffusion with their own distinctive aesthetic character. At the camera stage, soft focus effects can be produced using a dedicated soft focus lens - a portrait or pictorial lens deliberately designed with residual spherical aberration that creates the characteristic halo and diffusion effect - or through the use of soft focus filter attachments placed over a standard lens. Soft focus filters are available in a wide range of designs and materials, including etched glass, mesh, diffusion coated optical elements, and stretched hosiery or similar translucent materials, each producing a slightly different quality of diffusion ranging from subtle and natural to pronounced and heavily diffused.
Improvised soft focus effects can be achieved at the camera stage using a variety of simple and inexpensive materials including petroleum jelly smeared lightly on a UV filter placed over the lens - leaving the centre clear for maximum central sharpness with diffusion increasing towards the edges - stretched nylon stocking material held or taped over the lens, or breathing condensation on a glass filter. Each of these approaches produces its own characteristic quality of diffusion that differs in subtle ways from the optical soft focus produced by a dedicated lens or commercial filter, and experimentation with different materials and application methods can produce a wide range of diffusion effects suited to different subjects and aesthetic intentions.
At the enlarging stage in the darkroom, soft focus effects can be introduced during the printing process by placing a soft focus or diffusion filter beneath the enlarger lens during part or all of the exposure, or by breathing on the enlarging paper or negative during exposure to create a temporary condensation based diffusion. The use of a diffusion filter during part of a split exposure - making a portion of the total exposure through the diffuser and the remainder without it - allows the degree of diffusion to be precisely controlled by varying the proportion of the exposure given through the diffuser, producing any degree of softness from barely perceptible to heavily diffused within a single print. Printing with soft focus at the enlarger stage rather than the camera stage offers the advantage that the diffusion can be applied selectively and in a controlled and reversible manner, allowing the printer to experiment with different degrees of softness without committing to the effect at the point of capture.
In digital photography, soft focus effects can be applied in post processing using a range of techniques and software tools, from the simple application of a Gaussian blur layer blended with the original sharp image at reduced opacity, to sophisticated plug-in filters specifically designed to simulate the optical characteristics of different soft focus lenses and filters with adjustable bloom, diffusion radius, and highlight glow parameters. While digital soft focus can produce convincing results, many photographers argue that optically produced soft focus - achieved through a lens or filter at the point of capture - has a more organic and natural quality than digitally applied diffusion, which can sometimes appear mechanically uniform and lack the subtle irregularities and tonal interactions that optical diffusion produces in the actual image forming process.
Soft focus has been used as a creative tool in photography since the pictorialist movement of the late nineteenth and early twentieth centuries, when photographers including Gertrude Käsebier, Edward Steichen, and Clarence White used soft focus and diffusion techniques as a means of asserting photography's claim to fine art status by distancing their work from the mechanical precision of sharp photography and aligning it with the painterly, impressionistic aesthetic of contemporary fine art. The technique has remained a valued tool in portrait, fashion, glamour, and fine art photography throughout the history of the medium, valued for its ability to flatter the human subject, create a romantic or dreamy atmosphere, and produce images of distinctive aesthetic beauty that the clinical precision of perfectly sharp photography cannot achieve.