Diffusers

Diffusers are used for a variety of purposes: to hide a light source or to eliminate the image of its filament; to broaden the angular range over which a signal transmitted through the air is detectable; to make the appearance of a viewing screen more uniform; or to spread the light from a source into a defined angle.

Diffusion occurs because of small lenslets or prisms on the surface of a refractive medium. Snell's law can be used to determine the directions in which rays will travel upon leaving the features. Steep surfaces, which exhibit total internal reflection, must be avoided to preserve as many rays as possible.

The ideal diffuser from the standpoint of efficiency is a hexagonally close-packed array of identical lenslets, all "slower" than f/2 or so. A diffuser of this type spreads an incident collimated beam (large compared to the lenslets) uniformly over a predictable angle. Virtually no light appears outside this angular range. Examples include the Canon "Lasermatte" focusing screen and our #300 and #360 hexagonal conventional lens arrays. Unfortunately, regular structures of this type show strong moiré patterns against other periodic structures.

At the other extreme is a refractive medium molded against a typical sandblasted or etched surface. In this case, a large percentage of the surface area is beyond the angle for total internal reflection, and many rays are lost. Furthermore, a large number of rays are refracted into very large angles, and therefore lost in many applications. There are no artifacts to annoy the viewer, but rays scattered into large angles make the diffuser appear "bright" when illuminated from within, "frosted" when illuminated from without.

Between these extremes is a randomly spaced array of identical lenslets. Unfortunately, this type of diffuser is limited in the maximum diffusion angle which may be produced. This limitation is due to the fact that the mean lenslet spacing must be small compared to the target lenslet diameter, in order to ensure complete coverage. The randomness of the spacing produces a randomness in the lenslet mean diameter (and shape). This results in a more or less Gaussian distribution of rays with angle, rather than the sharp distribution of the hexagonally packed array. The available set of randomly patterned Gaussian diffusers is listed here.

All the microlens arrays which we currently provide from stock are well suited for use as diffusers. Some of them are also suited for one type of 3D photography and for moiré pattern work. All of the available microlens and lenticular arrays are normally supplied with positive focal length lenslets, but can be supplied with negative focal length lenslets upon request. Data for the available arrays of spherical conventional lenses, when made from acrylic, are available in our Fresnel Lenses brochure; the microlens arrays are among the #3xx and #6xx items. The lenticular arrays are items #2xx. We have not formally catalogued the random diffusers, so please inquire if you need this type of item. Please also see our Fresnel Lenses brochure for other available materials and for the properties of those materials.