Soft focus was a popular effect with film cameras as it softened detail in the highlights, especially with skin. It was produced by using a special filter in front of the lens to slightly diffuse the highlights. It has gone out of fashion now that images are shot digitally, because it is now possible to edit skin tones directly and remove blemishes. However, the effect can still be useful.
I need to investigate this because in order to reproduce the effect of a soft focus filter on the camera only the highlights of an image need to be blurred in Photoshop, not the shadows. Here is the Google link to investigate further to recreate a David Hamilton look.
The Orton Effect
The original technique invented by Michael Orton was to overlay two or more images of an identical scene with very different exposures on slide film. One image is sharply focused and the others are very out of focus. Orton has also experimented with similar techniques, substituting one of the images in the composition for one of a different subject, such as a texture layer, or combining a multicoloured image and a monotone one. (Wikipedia).