A diffusion filter is a translucent photographic filter used for a special effect

Special effect

The illusions used in the film, television, theatre, or entertainment industries to simulate the imagined events in a story are traditionally called special effects ....

. When used in front of the camera lens

Photographic lens

A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...

, a diffusion

Photon diffusion

Photon diffusion is a situation where photons travel through a material without being absorbed, but rather undergoing repeated scattering events which change the direction of their path. The path of any given photon is then effectively a random walk...

 filter softens subjects and generates a dreamy haze

Haze

Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic...

. This can also be improvised by smearing petroleum jelly

Petroleum jelly

Petroleum jelly, petrolatum, white petrolatum or soft paraffin, CAS number 8009-03-8, is a semi-solid mixture of hydrocarbons , originally promoted as a topical ointment for its healing properties...

 on a UV filter

UV filter

UV filters are individual compounds or mixtures to prevent ultraviolet light from getting through. UV filters are used in sunscreens to protect skin or in photography to reduce the level of ultraviolet light that strikes the recording medium....

 or shooting through a nylon

Nylon

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

 stocking

Stocking

A stocking, , is a close-fitting, variously elastic garment covering the foot and lower part of the leg. Stockings vary in color, design and transparency...

. Diffusion filters may be uniform or may have a clear center area to create a vignette

Vignetting

In photography and optics, vignetting  is a reduction of an image's brightness or saturation at the periphery compared to the image center. The word vignette, from the same root as vine, originally referred to a decorative border in a book. Later, the word came to be used for a photographic...

 of diffused area around the clear center subject.

Diffusion filters are also used in stage lighting

Stage lighting

Modern stage lighting is a flexible tool in the production of theatre, dance, opera and other performance arts. Several different types of stage lighting instruments are used in the pursuit of the various principles or goals of lighting. Stage lighting has grown considerably in recent years...

 (and likewise in photography

Photography

Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

 setups), where they may also be called diffusion gel, or just diffusion. This is a reference to color gel

Color gel

A color gel or color filter , also known as lighting gel or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to color light and for color correction...

, which is another type of lighting gel. Diffusion gels soften the light

Light

Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

 in order to reduce or diffuse shadow

Shadow

A shadow is an area where direct light from a light source cannot reach due to obstruction by an object. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the...

s or glare

Glare

Glare may refer to:* Glare is difficulty seeing in the presence of very bright light* A glare is a facial expression of squinted eyes and look of contempt* A call collision in telecommunications* GLARE, an advanced aerospace material...

.

Silk

Silk

Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...

 sheets can also be used in this manner, and in fact were until the invention

Invention

An invention is a novel composition, device, or process. An invention may be derived from a pre-existing model or idea, or it could be independently conceived, in which case it may be a radical breakthrough. In addition, there is cultural invention, which is an innovative set of useful social...

 of translucent plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

s. "Opal" is a common translucent or opalescent diffusion.