Influence of aperture position and size on infrared lens spectral transmittance measurements

In the infrared spectroscopic transmittance testing apparatus based on the retro-reflective method, the position and size of the aperture will affect the measurement of the spectral transmittance of the infrared lens during measurement. To address this issue, a vignetting model was established to analyze the vignetting of the measurement beam in the testing apparatus. The vignetting formula generated by placing apertures and other components at different positions was derived. Experimental results demonstrate that maintaining consistency in relative vignetting between the empty and actual measurements effectively reduces the impact of vignetting variations on the measurement of spectral transmittance of the infrared lens.