For applications that require imaging scene temperature ranges higher than 550 C, it is necessary to reduce the signal coming into the camera sensor in order to avoid image saturation. This is typically done by using an external filter to attenuate the signal and put it in a range that the camera can handle. Neutral density (ND) filters work well for this purpose. For example, an ND 1.0 filter has a transmittance of 10%, which it accomplishes using a combination of absorption and reflection.
Using an ND 1.0 filter, it should be possible to image scene temperature ranges up to ~2,800C, since the 10% transmittance would attenuate the radiance signal within the Low Gain limit of 550 C.
A filter holder has been designed that screws onto the front of the lenses for Tau lenses that are threaded. It holds 1 inch diameter filters. Spectrogon is one source of LWIR ND filters.
Note that some FLIR cameras are specially calibrated to provide radiometric (temperature) data on a per-pixel basis, and use of external optics such as filters will invalidate the temperature results. A separate radiometric calibration would be required with a filter in place for better accuracy.Keywords: Tau2, Quark2