Abstract: The mechanism for moving the lens assemblies mounted to support rods in a variation power microscope includes a crank shaft having a pair of opposed arms. The lens assemblies are connected to the crank arms by linkages. The lens assemblies are biased to the support rods by resilient member. At least one of the crank arms may incorporate a motion correcting surface which cooperates with a cam follower fixed to the associated linkage to vary the length of the linkage. The lens assemblies may further include arms for stabilizing guiding them along the support rods. Still further, the mechanism may include a device for controlling the rotation in either direction of the crank shaft. Additionally, the lens assemblies may be adjustably fixed to the linkages.

Abstract: An apparatus for counterbalancing the weight of the movable member in a precision instrument includes a resilient member which is coupled, by way of a non-elastic member, over an eccentric surface of a rotatable member to the movable member. Rotation of the eccentric member causes the resilient member to deform an amount proportional to the eccentricity of the member and a nearly constant counterbalancing force may be applied to the movable member.