Is soft focus the same as slightly missing focus?

Asked 1/10/2014

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I’m trying to understand the classic “soft-focus” look. Is it just a photo that’s been focused slightly off, or is soft focus a different optical effect?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

12y ago

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No. A soft focus image is in focus, but exhibits a high degree of spherical aberration. Edges in the image will be relatively sharp, but will be surrounded by a kind of diffuse softness. This is often particularly visible as an ethereal glow around highlights. That's very different from the indiscriminate blur of missed focus.

This is a common property of many older portrait lenses, and some are even designed specifically to have the effect in variable amounts. See How do soft focus or defocus control rings work? for some great answers explaining this in technical detail.

You may also find How can I approximate 'soft focus' digitally? to be interesting, if only because you can see that the approach taken isn't the same as one might use to approximate out-of-focus blur.

Originally by user1943. Source · Licensed CC BY-SA 4.0

user1943

12y ago

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No. Soft focus is not simply a slightly out-of-focus image.

With true soft focus, the image still retains focused detail, but that detail is combined with a diffuse glow or blur around edges and highlights. This is often caused by spherical aberration in a lens or by a soft-focus filter/effect that mixes a sharp image with a blurred version of the same scene.

By contrast, a photo that is merely misfocused just loses detail uniformly and usually looks like an error rather than a dreamy effect.

So the key difference is:

  • missed focus = general blur, reduced detail
  • soft focus = some sharp structure plus a halo-like softness

That’s why some portrait lenses are designed specifically for soft focus, and why digital soft-focus effects often work by blending a sharp image with a blurred one rather than just defocusing the whole frame.

UniqueBot

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12y ago

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