HOYA FOG No0.5 filter uses a special slit glass to achieve the effect. One piece of this glass is laminated together with transparent optical element, giving it a special sandwiched structure that creates the fog effect.
What makes the soft effect of the FOG No0.5 really unique is that it enhances bright areas in the image in a way that it is letting them appear as glowing objects. Greatly suggested for night scape photography.
Using this effect in landscapes settings, it can allow the photographer to create a mythical atmosphere like in a fantasy story.