Variable focus flashlight

In a variable focus flashlight, the combination comprising:

• a switch housing of generally cylindrical configuration, having an external thread on its forward end, and having a seal ring groove formed at the rearward extremity of said thread;
• a switch module disposed within said switch housing in fixed relationship thereto, said switch module having a bulb receptacle projecting forwardly from the transverse center thereof, and also having an annular flat surface on its forward end surrounding said bulb receptacle;
• a bulb received within said bulb receptacle, so that its operation may be controlled by said switch module;
• a flashlight head which is of larger diameter than said switch housing, the rearward end portion of said flashlight head having an interior cylindrical wall surface which is disposed about said seal ring groove in spaced relationship thereto, said flashlight head also having an interior thread positioned forwardly of said seal wall, said interior thread of said flashlight head engaging said exterior thread of said switch housing;
• a seal ring occupying said seal ring groove, said seal wall of said flashlight head acting to radially compress said seal ring;
• a reflector of generally parabolic configuration disposed within said flashlight head with the larger end of said reflector being secured to the forward end of said head, said reflector at its rearward extremity having a central opening through which said bulb projects;
• whereby said flashlight head may be rotated relative to said switch housing for selecting a desired focus of the flashlight beam;
• and
• a longitudinally compressed helical spring disposed partly within said switch housing and partly within said flashlight head, the rearward end of said spring engaging said annular flat surface of said switch module, and the forward end of said spring engaging the exterior and rearward surface of said reflector;
• said spring being rather freely rotatable relative to said switch module, and serving to create a substantial frictional force between said interengaged threads so as to retain whatever rotational position of said flashlight head has been selected.

A variable focus flashlight comprising, in combination:

• a flashlight body of cylindrical configuration, its external surface being threaded at its forward end, and near its forward end containing means providing a flat transverse annular support surface;
• means supporting a flashlight bulb extending forward from the center of said annular support surface in fixed relation to said flashlight body;
• a flashlight head of generally cylindrical configuration but larger diameter than said flashlight body, the interior surface of said flashlight head near its rearward end being threaded, said flashlight head being supported upon said flashlight body by interengagement of its threads with the external threads of said flashlight body;
• a reflector of generally parabolic configuration disposed within said flashlight head, said reflector having an opening at its apex through which said bulb projects into the interior of said reflector;
• a lens covering the otherwise open forward end of said reflector;
• a face cap removably secured to the forward end of said flashlight head, said face cap normally holding both said lens and the forward circumferential edge of said reflector in fixed relation to said flashlight head;
• said flashlight head being rotatable upon the threads of said flashlight body so as to vary the longitudinal position of said reflector relative to said bulb, and hence to adjust the focus of the flashlight beam;
• and
• an elongated helical compression spring of tapered configuration, the last turn on the smaller end of said spring occupying a single plane and being pressed against said annular support surface about said bulb, the larger end of said spring surrounding and engaging the rearward outer surface of said reflector;
• the interengaging threads of the body and head having relatively high friction surfaces, and the expansive force of said spring thus biasing the threads together in a direction lengthwise of said flashlight body so that the frictional force holding said flashlight head in a selected rotational position is a function of the spring force and the surface friction of the two sets of threads, but is essentially independent of the amount of wear which has occurred in said threads.