EngineeringOptometryBiomedical OpticsOpticsOptoelectronicsLight SourcesLinear MeasurementPhotometric SystemsDetector Linearity CorrectionIllumination LevelsLight MeteringPhotometric AnalysisPhotometric CorrectionPhotometric MeasurementPhotometric SensitivityPhotometry
An apparatus with nine pairs of apertures can be used to test photometer linearity. The device employs aperture pairs whose areas double successively, selected via a rotatable disk, to measure photometer readings at each level and compare the sum of separate readings with the combined reading, enabling the ratio to correct the photometric scale. The apparatus offers a simple illumination selection method, a wide illumination range, and easy setup.
Illumination provided by an apparatus with nine pairs of apertures may be used conveniently to test the linearity of photometers. The apertures increase in area from one pair to the next by a factor of two. Thus the range covered is 512 to 1. The apertures are selected individually or in pairs by holes in a rotatable disk. The photometer reading on each illumination level in a pair is determined, and the numerical sum of these is compared with the reading on the two together. The ratio can be used to correct the photometric scale of the receiver. The advantage of this apparatus is the straightforward method of selecting illumination levels, the wide range of illumination, and the easily arranged equipment.