Initial focusing mechanism for zoom lens system

An initial focusing mechanism for a zoom lens system of rear focus type comprising:

• a cylinder cam contained within a barrel for rotational movement and slidable movement in the direction of an optical axis both with respect to said barrel;
• a variator and a compensator held by a variator frame and a compensator frame, respectively, which are, in turn, respectively supported by said cylinder cam by engagement with a pair of cam tracks formed in said cylinder cam;
• a relay lens located behind said variator and compensator;
• slide means adapted for slidably moving said cylinder cam with respect to said barrel along the optical axis and for adjustment of an amount by which said cylinder cam is slidably moved to achieve a desired initial focusing;
• means for rotating said cylinder cam with respect to the barrel to move said variator and compensator along the optical axis for continuous change of a focal distance;
• and
• means for moving said relay lens along the optical axis for focusing.

An initial focusing mechanism for a zoom lens system as recited in claim (1) or (2), wherein said means for rotating said cylinder cam includes:

• a ring gear normally bearing against one end of said cylinder cam;
• biasing means adapted for normally urging said cylinder cam against said ring gear;
• and
• said slide means slidably moving said cylinder cam along the optical axis against a restoring force of said biasing means as said ring gear is rotated around the optical axis.

An initial focusing mechanism for a zoom lens system as recited in claim (1) or (2), further comprising:

• an eccentric pin mounted on said barrel for swiveling around an axis extending diametrically of said barrel;
• one end of said cylinder cam bearing against a lateral surface of said eccentric pin;
• biasing means adapted for normally urging said cylinder cam against said eccentric pin;
• and
• said slide means slidably moving said cylinder cam along the optical axis against a restoring force of said biasing means as said eccentric pin is swiveled.

An initial focusing mechanism for a zoom lens system as recited in claim (1) or (2), further comprising:

• a circumferential slot formed in said cylinder cam;
• an eccentric pin rotatably extending through said barrel and inserted into said slot;
• and
• said slide means slidably moving said cylinder cam along the optical axis as said eccentric pin is rotated with respect to the barrel.