In optics, a diffuser (also called a light diffuser or optical diffuser) is any material that diffuses or scatters light in some manner to transmit soft light. Diffused light can be easily obtained by reflecting light from a white surface, while more compact diffusers may use translucent material, including ground glass, teflon, opal glass, and greyed glass.

Types

Perfect reflecting diffuser

A perfect (reflecting) diffuser (PRD) is a theoretical perfectly white surface with Lambertian reflectance (its brightness appears the same from any angle of view). It does not absorb light, giving back 100% of the light it receives. Reflective diffusers can be easily characterised by scatterometers.{{cite web, url=http://www.zebraoptical.com/roughnessviascatterometry.html, title=Page Title, website=www.zebraoptical.com

Diffractive diffuser/homogenizer

A diffractive diffuser is a kind of

diffractive optical element Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a ...

(DOE) that exploits the principles of

diffraction Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

and refraction. It uses diffraction to manipulate monochromatic light, giving it a specific spatial configuration and intensity profile. Diffractive diffusers are commonly used in commercially available LED illumination systems. Usually, the diffuser material is GaN or fused silica with processed rough surfaces. LED diffusers can be characterized online using scatterometry-based metrology.Walecki, Wojciech, and Peter Walecki. "Robust diffuser and roughness metrology tool for LED manufacturing." SPIE OPTO. International Society for Optics and Photonics, 2015.

Applications

Diffusion filters may be used to diffuse the light falling on the subject, or placed between the camera and the subject for a hazy effect.

Lighting diffusers, transmitting and reflecting

A flash diffuser (also called a speedlight diffuser, or shoot-through diffuser) spreads the light from the flash of a camera. A diffusion filter of this type may also be used in front of a non-flash studio light to soften the light on the scene being shot; such filters are used in still photography, in

film lighting Cinematography (from ancient Greek κίνημα, ''kìnema'' "movement" and γράφειν, ''gràphein'' "to write") is the art of motion picture (and more recently, electronic video camera) photography. Cinematographers use a lens to focus ...

, and in

stage lighting Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts.

. In the film and stage industry, a diffusion filter may also be called diffusion gel, or just diffusion. This is by analogy to a

color gel Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...

, which is another type of

lighting gel Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing dayli ...

. Shōji are diffusing window/doors. Reflecting diffusers for photography are generally called " reflectors". In effect, the light will not come from one concentrated source (like a spotlight), but rather will spread out, bounce from reflective ceilings and walls, thus getting rid of harsh light, and hard shadows. This is particularly useful for portrait photographers, since harsh light and hard shadows are usually not considered flattering in a portrait. File:Blitz Diffusor fcm.jpg, Diffuser on a camera flash. Made from a sheet of paper, a rubber band, and two staples. File:Silver bounce (4097154692).jpg, A more formal diffuser filter over a camera flash, flanked by reflectors File:Tools of the trade (6484757517).jpg, Flash diffuser to be mounted on a camera File:Elinchrom flash equipment DSCF2813.JPG, Softbox diffuser; a larger area spreads the light more File:Foreign Secretary's Ramadan message (4852950309).jpg, A lighting technician holds a reflector to diffuse the light falling on a politician File:DIY Lightbox.jpg, A home-made lightbox, designed to produce images with diffuse lighting from all angles File:WikiDACH 2019, Nürnberg (P1080060).jpg, Lightbox photography File:Wagashi Lighting for Japanese TV Program Recording.jpg, Both transmitting (softbox) and reflecting diffusors are used to light wagashi for a television program File:Studioleuchte 2012-04 by-RaBoe-05.jpg, Studio lights, one white, two metallized File:FSboomerang.JPG, Theatrical colour magazine or boomerang. Placed in front of a stage light, it gives quick changes in lighting gel, including a diffusion filter File:障子に映る影Img568.jpg, Shōji

Objective-lens filters

"Diffusion filter" may also refer to a translucent photographic filter used for a

special effect Special effects (often abbreviated as SFX, F/X or simply FX) are illusions or visual tricks used in the theatre, film, television, video game, amusement park and simulator industries to simulate the imagined events in a story or virtual wor ...

. When used in front of the

camera lens A camera lens (also known as photographic lens or photographic objective) 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 capab ...

, a diffusion filter softens subjects and generates a dreamy haze. This effect can also be improvised by smearing

petroleum jelly Petroleum jelly, petrolatum, white petrolatum, soft paraffin, or multi-hydrocarbon, CAS number 8009-03-8, is a semi-solid mixture of hydrocarbons (with carbon numbers mainly higher than 25), originally promoted as a topical ointment for its h ...

on a UV filter or shooting through a nylon stocking. Diffusion filters may be uniform or may have a clear center area to create a vignette of diffused area around the clear center subject.

Diffuser materials

Silk sheets can also be used as diffusers, and in fact were until the invention of translucent plastics. "Opal" is a common translucent or opalescent diffusion. Recently, photopolymers have been used for making holographic diffusers. Photopolymers offer better performance than other materials and have a large viewing angle. Also, the process of synthesizing photopolymers is much simpler.

References

Optical components Photography equipment Optical filters Photographic lighting Stage lighting