Abstract
Reflection characteristics of various rough surfaces are measured at large specular angles with a goniophotometer. A square-wave chart illuminated by a source is placed at the focal plane of the collimator lens. The chart is scanned and photocurrent generated in a photomultiplier tube placed behind a slit of receiver system is recorded. Relation between spatial frequency and the contrast of record is investigated and the k value of Jentzsch's equation,
2hcosθc=λ/k,
is determined, where h is the roughness of the sample, λ the wavelength of light, θc the critical angle of the so-called Sheen given as the angle at which the value of contrast becomes zero. The k value of ground glass is found independent of the wavelength of light or the roughness of the sample; it is 2_??_3 when h is taken as the central line average roughness.
