measurement aperture

measurement aperture (In French diaphragme) opening through which optical measuring devices record the measured values, and also illuminate the sample when measurements are taken with reflected light. The larger the diameter, the more representative the value basis. Such an integral measuring principle is especially practical when the measured object is not homogeneous, e.g. a screened surface. For particularly narrow ink control strips in rotary offset printing, Techkon, for example, also offers small or even slit-shaped apertures for its spectrodensitometers.