Cokin Dream filters, available in three different strengths, create halos around the high lights. The effect varies in intensity depending on the filter chosen, with A0093 having the greatest effect. This effect becomes extra-obvious when light subjects are set against a dark background. For example, white flowers against a dark curtain or streetlights against the evening sky. The great advantage of this type of diffusion is that even though the effect creates an overflow of highlights, the image remains sharp.
It is advisable not to use an overly large aperture, otherwise you get double contours instead of dreamy halos. When using this technique, it is also advisable to use bracketing, especially if the subject is exposed from behind.