Abstract: A thermal imaging device (10) receives thermal infrared radiation from a viewed scene and responsively provides a visible image replicating the viewed scene. The imaging device (10) has a main housing with an optical aperture (16) at which a lens assembly (12) is attached. The lens assembly (12) has a number of lenses (200, 204, 208, 212, 216) sequentially mounted within a cylindrical housing (146), and defining an optical axis (199). A field-of-view-change mechanism (228) allows a user to select a wide field of view or a narrow field of view. The field-of-view-change mechanism (228) includes a rotatable field-of-view (FOV) ring (226) which rotates a tumbler (210) with a pair of lenses (208, 212) mounted therein. The tumbler (210) is positioned between a first position providing a wide field of view and a second position providing a narrow field of view.

Abstract: A thermal imaging device (10) provides for its use with a variety of accessory telescopic lenses (12). Each of the accessory telescopic lenses (12) and the thermal imaging device (10) include cooperating physical features allowing the lenses (12) to be mated with the device (10) in a single relative position. Each lens (12) also carries a uniquely positioned magnet (176), and the thermal imaging device (10) includes a plurality of magnetically-responsive sensors (178) responding to the magnets (176) of the various lenses (12) to identify which (if any) of the accessory lens (12) is installed on the device (10). Some of the accessory lenses (12) also include a variable-power feature. These variable-power lenses (12) have an additional magnet (182) moving between an effective position and an ineffective position in response to a user-selected power setting for the lens (12).

Abstract: A thermal imaging device (10) includes a housing (130) defining a battery compartment, and carrying a door portion (166) closable over this battery compartment to provide environmental protection. The battery compartment door (166) includes a spring-loaded latching device (170) which will maintain the door (166) sealingly closed under normal use conditions of the device (10). However, in the event that a battery (124) received in the compartment should vent gasses sufficient to pressurize the compartment to a selected level, the latching device (170) will yield to allow a slight opening of the door (166) and a controlled venting of these gasses to ambient. Controlled venting of the battery gasses additionally occurs at a location of the device (10) remote from the user, and the battery compartment door (166) is itself interposed between the user and the venting battery (124).