Why is this?
ThermaCAM Researcher tries to detect changes of lenses in order to make the camera use proper calibration data.
However, sometimes this detection fails and ThermaCAM Researcher causes the camera to use the data of the previous lens. Changing the temperature range after having changed a lens can thus make the image quality and temperature accuracy degrade. If this happens, you need to both disconnect ThermaCAM Researcher and restart the camera to solve the matter.
Work-around
To avoid this, disconnect FLIR SC6x0 and FLIR SC6x5 cameras within ThermaCAM Researcher while changing the lens. (You do not need to unplug the cable or close the program.)