Thermal imaging device with selectively replaceable telescopic lenses and automatic lens identification

A thermal imaging device comprising:

• a device housing sealingly defining a chamber therein, said device housing having at least a portion which is magnetically-permeable to allow penetration of an external magnetic field into said chamber;
• and said device housing defining an optical aperture allowing admission of infrared thermal radiation into said chamber, said optical aperture being sealingly closed by a window member which is transparent to thermal radiation;
• a lens assembly having an optical axis, and a respective lens housing removably attachable to said device housing at said optical aperture to align said optical axis with said optical aperture, thus to direct infrared thermal radiation from a viewed scene into said chamber via said optical aperture, said lens assembly including a movable power-adjustment portion movement of which changes a power of telescopic magnification for said lens assembly;
• a magnet fixedly positioned on said lens housing, when said lens housing is attached to said device housing said magnet being in juxtaposition to said magnetically-permeable portion of said device housing;
• a second magnet moving between a first position and a second position dependent upon position of said power-adjustment portion, said second magnet in only one of said first and second positions providing a magnetic field which penetrates into said chamber via said magnetically-permeable portion of said device housing;
• a magnetically-responsive sensor disposed within said chamber in juxtaposition to said magnetically permeable portion of said device housing;
• whereby said magnetically-responsive sensor indicates the presence of said lens assembly at said optical aperture;
• and
• another magnetically-responsive sensor responding to said magnetic field of said second magnet in said one of said first and second positions to uniquely identify the power setting of said lens assembly.