Both "P" and "S" types of Minolta Portrayers are sophisticated phase filters applying state-of-the-art technology and wave optics. Each type consists of a special compound coated on a plain optical glass surface in scientifically determined patterns to precisely controlled microscopic thickness. Type "P" provides, for the first time ever, a primary-selective diffusion effect that is useful for smoothing human skins tones, etc. in colour photographs. Type "S" Portrayers, on the other hand, yield an overall diffusion effect while preserving basic image sharpness. Usable on either camera or enlarging lenses, both types are supplied in sets of filters grade-numbered to indicate the degree of effect, and in standard sizes of 55 or 72mm diameters. The filter effect remains the same no matter what aperture is used.