Hello, in the Arnold for Houdini documentation the following is said about "Extra roughness":
Adds some additional blurriness of refraction computed with an isotropic microfacet BTDF. The range goes from -1 to 1, where 0 means no roughness. It is computed as
transmission_roughness = specular_roughness + transmission_extra_roughness.
However, in Houdini (18.5.408) with Arnold 126.96.36.199 (HtoA 188.8.131.52) the "Extra Roughness" float parameter is locked between 0-1 and I cannot specify a value below 0.
Could this be a bug?