The following procedure can be used to obtain a spectrum of a filter illuminated by white light (i.e. at nonthermal wavelengths). It is presumed that the servo system is locked.
Note: not all filters can be scanned with the white light source. For broad band filters in the nonthermal infrared the detectors saturate, even with the light source set at minimum intensity, and in the thermal infrared the glass envelope of the white light source reduces the infrared radiation to impractical levels.