Proceedings PaperNearby Object Radiometry
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It is frequently desired to measure the flux exiting from a small aperture, using a radiometer that must be positioned near to that source. Such conditions arise, for instance, in determining the absolute output of a spectrometer or in measuring the throughput of an optical device. Since most radiometers are designed to have the sensor located in the focal plane of the fore-optics, a portion of the radiation collected under these circumstances will not fall onto the detector. This situation is considered here to indicate the relationship of the flux discerned to the radiance of the object as a function of the object distance involved. Accurate measurements of the radiance of nearby objects is a far more complex procedure than is that of distant objects. Those conditions for attaining the more accurate measurements are described.