Electrical camera focusing mechanism

Claim 1

In an optical instrument including a housing, focusable objective lens assembly having an optical axis and being supported by said housing, a motor for driving said lens assembly to focusing conditon, and normally incomplete circuit means including switch means connected to said motor and mounted for movement in response to the angular orientation of the optical instrument between a normally ''''open'''' position wherein the circuit means is incomplete and a ''''closed'''' position wherein said circuit means is complete for driving the lens assembly, the improvement in said switch means comprising: a mercury switch including an elongated enclosure mounted on said housing for movement relative thereto, liquid mercury received within said enclosure and contact means disposed within said enclosure for electrical contact by said mercury, wherein angular movement of said enclosure causes said mercury to move into and out of connecting engagement with said contact means defining said closed and open positions; a focusing ring rotatably mounted on said housing generally concentric with the axis of the objective lens assembly; cam means operatively associating said focusing ring and said enclousure for rotating the enclosure about an axis generally perpendicular to said optical axis in response to rotating said focusing ring, said cam means including a generally spiralshaped slot in said focusing ring and a pin on said enclosure protruding into said slot.