Filters that produce a fog-like appearance in a scene are another type of diffusion filter. They are known as mist, fog, fog-effect or haze-effect filters (not to be confused with the haze filter that absorbs UV light.) The fog-like effect encompasses the entire scene, providing a soft, misty atmosphere over the whole picture. Contrast and sharpness are diminished, as with a more standard diffusion filter. Fog filters are especially applicable to landscape photography, but may be used quite successfully with many other subjects.
When shooting in a real fog, any light source shining towards the camera reflects off the water molecules suspended in the air, either creating a fuzzy path of light through the mist or glowing like a soft ball of illumination. With a fog filter, there is a similar effect when one or more light sources are placed in the picture, and doing so makes good use of this filter. When the subject is placed between a light source and the camera so that the subject is backlit, the effect can be quite mood-invoking, with the subject enveloped in a soft and hazy aura. If the light is colored (a neon sign, for example), the effect is even more enhanced – a softly-colored glow that wraps around the subject. (Different colored gels can be placed in front of white light sources to take advantage of this effect.)
Not only will fog filters soften lines, they tend to mute colors, too.
Fog filters are available in a variety of grades, with the stronger ones giving a more surreal, overall fantasy appearance to a scene that looks less like real fog than the effect produced by lighter grades. Their contrast is too high and they produce too much of an out-of-focus look. Almost all fog filters will lighten dark colors. We recommend you buy a weaker grade when starting out, unless you are certain of the effect you are seeking and the grade needed to produce it.
EXPOSURE CONSIDERATIONS
When using fog filters, exposure must be increased by 1/3 to one stop, depending on the filter's grade. Intentional overexposure or underexposure by one or one-and-a-half stops can produce interesting effects that sometimes improve the dream-like feeling of the image, so it is a good idea to bracket exposures.
Since stray light can affect the outcome, consistency is achieved through the use of a lens hood. Removing the lens hood in certain lighting conditions may add to the diffusion effect.
These scenes show the before and after results of using a light grade fog filter.
THE TIP OF THE ICEBERG
There are many variations of fog or mist filters on the market - some add more warmth to a scene; others produce greater or lesser fog effects. A few cause a large, halo-like flare around backlit subjects or where highlights appear in the scene.
Some filter makers produce what are called double fog filters (a soft fog effect combined with a heavy low contrast filter) that render close-up subjects more sharply (just as a real fog will do) and exhibit milder softening and less flare than standard fog filters.
Dream-effect filters (also known as low contrast filters) provide a scene with a soft, romantic ambience thanks to their pastel tints and their all-over diffused light, justifying their name by producing what many feel is a dream-like look.
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