Diffusion filters

For a soft-focus effect

Diffusion or "soft focus" filter types are perhaps the most numerous of the special effect filters, with more than a hundred varieties available. The idea behind them is to obtain a soft look by bending (refracting) some of the light from the subject so it is defocused while the rest remains in focus. Highlights are actually dispersed onto adjacent areas. The image still looks properly-focused overall, but its components are just enough out-of-focus that they are softened. Lines are slightly fuzzy and small details seem to disappear.

The range of diffusion filters finds its main use in portraitwork, softening wrinkles, lending skin a more youthful, Georgia-peach appearance, softening hair and giving eyes a misty, romantic look. They are also used extensively to create a misty, dreamy atmosphere in landscapes and moody pictures. Technically, they are not really filters; they are lens attachments or devices placed between the lens and the subject, but since many are handled in the same manner as true filters, we refer to them as such.

THE FIRST DIFFUSERS WERE PROBABLY STOCKINGS

Early photographers discovered that a fine mesh stretched over the lens could achieve a similar softening effect. A nylon stocking is made from such material. Some portrait photographers today continue to use this time-tested technique with great success. We know of one who specifies a brand, color and style of nylon stockingette for ideal portrait softening. Tulle can also be used for this purpose.

The material has a greater effect on the small details (a person’s blemishes and facial lines) than it does on the overall image, which remains sharp, because so much of the light travels unchanged through the clear spaces of the mesh, while light that meets the fine lines of the material gets reflected, absorbed and refracted.

Black material minimizes highlights "halation" (the blurred effect at the edges of a light area) so that dark areas remain dark. White material increases halation, thereby lightening dark areas. A light-colored mesh can lower shadow contrast and even add its own color to the shadowed parts of the image, while the highlights remain unaffected.

WHY DOES A MESH OVER THE LENS WORK?

The edges of the net material refract light, bending it at an angle that changes its distance to the film so that the refracted light becomes out of focus. The amount of out-of-focus light is minimal in relation to the overall amount of light that travels in straight lines from the subject to the film, but it’s enough to blur wrinkle lines and soften facial blemishes. The result is an image that looks properly-focused, but is forgivingly soft and gives skin an appropriately “fuzzy” appearance for a more youthful-looking portrait.

If the mesh is particularly fine and the lines are closer together, there are more fiber lines covering the lens, which makes the diffusing effect even greater.

COMMERCIAL DIFFUSION FILTERS

Filter makers produce diffusion filters with fine lines engraved on them, based on the net-like material diffusion method. Such filters are sometimes called "pattern" filters because their wave or line patterns can usually be seen on the surface or sandwiched between the filter elements.

Also available are “haze effect” or “fog effect” filters, intended for landscape photography and some portrait work.

Diffusion filters are not all mesh-based. Other commercially-made soft-focus filters are manufactured from glass or plastic in several different types - dimpled, frosted, etched, etc. with differing degrees of diffusion. One type that has concentric grooves etched in glass increases diffusion as the aperture is widened.

DIMPLED FILTERS MAY BE THE BEST DIFFUSERS

A number of diffusion filters are optically clear except for a splattering of round or diamond-like dimples embedded in their surface. The better ones, which are covered with tiny droplets that act as lenses themselves, are considered to be an improvement on the mesh type of diffusion filter, mainly because the dimpled material is the same as the clear material, and therefore has a less-pronounced effect on shadow areas of the subject. They are said to be more effective in concealing facial flaws than mesh filters, too, because they refract light throughout their surfaces, not just at the edges. They also do not exhibit any change in the degree of softening with changes in aperture.

LENS CHOICE & APERTURE CAN AFFECT THE RESULTS

If you plan to use either a nylon stocking or a pattern filter, be sure to use a portrait lens (focal length can affect the results) and to keep your aperture sufficiently-wide so that depth of field doesn’t cause the mesh lines to begin to show in the picture. Changes in aperture setting can sometimes change the degree of softening of the filter. Increasing exposure by about a half-stop will compensate for light absorption by most diffusion filters.

If you use a stockingette or other stretchy diaphanous material, the degree of diffusion is altered by the amount it is stretched. Be sure it is held securely in place so it doesn't move during exposure of the film. A rubber band will usually do the trick. Increase exposure by 1/3 to 1 stop. Because the effect is so unpredictable, bracket exposures for insurance.

WATCH THE EYES

Ideally, your subject's eyes will take on a romantic, "melting" look when using soft focus attachments. The last thing you want from a diffusion filter is for it to dull a subject’s eyes, which can occur if the overall effect is too soft or if the eyes just happen to be in an area of high diffusion. While it involves trial-and-error with a stocking or net filter, a good-quality dimple diffuser seems to get around this problem quite nicely.

GIVE YOUR SUBJECTS A GENTLE GLOW WITHOUT A DIFFUSION FILTER

A form of soft focus that is said to surround your subjects with a gentle glow while keeping details sharp involves taking a double exposure.

Your camera must be mounted on a tripod and cannot be moved during this procedure. The first exposure is made using a small aperture (ƒ/16 or ƒ/22, for example) for good depth of field and sharp definition, and a shutter speed that is one stop faster than your light meter calls for. With your subject remaining in place and motionless, take a second exposure at a your widest aperture (e.g. ƒ/2.8) and a shutter speed that is one stop faster than you would normally use.