The Tiffen Fog 1/4 Filter
simulates the effects of natural fog or mist by creating a soft glow
around highlights and lowering the overall contrast of the scene. There
can also be a softening effect due to how the light interacts with the
subject matter.
Tiffen filters are made using ColorCore technology, a process that involves laminating the filter substrate between 2 pieces of optical glass, grinding flat to a tolerance of 1/10,000th of an inch, and then mounting to precision metal rings.