Hoya 52mm Misty Spot-Gradual Special Effects Glass Filter

Available in four types: Gradual, Breeze, Windmill and Halo.

They heve a sharp central image with a pleasant blurring of the outer field.

With Gradual, blurring that appears to emanate from the center.
Breeze has an unidirectional streaky blurring of background.

With Windmill, blurring that appears to swirl about the center,
and with Holo, blur that appears to radiate from a single point at the edge of the field.