Mechanism to maintain constant body tube length of binocular microscope

A mechanism to maintain a constant body tube length of a binocular microscope having a casing with two outer frames mounted thereon in a slidable manner in a width direction of the microscope, two ocular sleeves carried by said outer frames in a manner slidable in an axial direction thereof, oppositely slanted linear cam grooves bored on said casing with angles of 45.degree. relative to said axial direction, and pins connected to said ocular sleeves and fitted in said linear cam grooves respectively, said ocular sleeves being adapted to slide axially relative to the outer frames in response to symmetrical widthwise sliding of said outer frames relative to the casing so as to maintain said body tube length constant;

• said mechanism comprising slots bored through said outer frames so as to extend in the axial direction thereof and to slidably receive said pins connected to said ocular sleeves, and resilient means disposed between said casing and said ocular sleeves so as to apply axial forces to said two ocular sleeves in opposite directions.