This paper examines the influence of the construction of the optical component on the recording and evaluation of thermal radiation signals in order to determine the particle parameters precisely. The test correlation is carried out by means of plasma spraying from Mo. It is observed that only the signals with a trapezoidal shape, which has a saturated platform, can provide information about particle velocity, temperature, size, and volume distribution. Further analysis shows that the reliability and accuracy of measured particle parameters through the thermal radiation method are strongly dependent on the design of optical components geometry. Paper includes a German-language abstract.