Zoom lens barrel

A selectable assembling device of a zoom lens barrel, comprising:

• a stationary barrel having a female helicoid and linear guide grooves, said linear guide grooves being formed across said female helicoid extending parallel to the optical axis of said zoom lens barrel, said linear guide grooves spaced at 120 degree intervals about the axis of said stationary barrel, wherein a portion of each of said plurality of linear guide grooves includes an introducing groove formed by cutting a portion of said female helicoid;
• a cam ring which is provided on the outer peripheral surface thereof with a male helicoid which is engaged with the female helicoid of the stationary barrel, said cam ring including bottomed cam grooves provided at 120 degree intervals about the axis of said cam ring on the inner peripheral surface thereof, said cam ring being rotated with respect to said stationary barrel which does not rotate;
• a linear guide barrel which is provided with linear guide projections and linear guide slots spaced at 120 degree intervals about the axis of said linear guide barrel, said linear guide projections being engaged in the linear guide grooves of the stationary barrel, said linear guide barrel and said cam ring being coupled so that the linear guide barrel is rotatable relative to the optical axis and moveable in the optical axis direction together with the cam ring;
• and
• a plurality of lens frames which are provided with sliding projections, that are spaced at 120 degree intervals about the optical axis, which are engaged in said linear guide slots of the linear guide barrel, each of said sliding projections comprising a cam follower thereon which is fitted in a corresponding bottomed cam groove of the cam ring;
• wherein, upon assembly, a first relative angular position of assembly for the cam ring and the linear guide barrel can be selected from among three circumferential positions spaced at 120 degree intervals about common axes of said cam ring and said linear guide barrel.