Zoom lens system and a zoom lens barrel therefor

A zoom lens system comprising a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, in this order from an object;

• wherein upon zooming from the short focal length extremity towards the long focal length extremity, all of said lens groups move towards said object so that the distance between said first lens group and said second lens group increases, the distance between said second lens group and said third lens group decreases, and the distance between said third lens group and said fourth lens group decreases;
• wherein a lens group other than said first lens group comprises a lens group for focusing;
• wherein a ratio K of traveling distance of said first lens group to that of said second lens group is made constant in any part of the focal length range defined by the short focal length extremity and the long focal length extremity;
• and
• wherein said zoom lens system satisfies the following condition:
• 0.16<K<0.50
• wherein
• K=ΔX2/ΔX1;
• ΔX1 designates the traveling distance of said first lens group, upon zooming, from the short focal length extremity to the long focal length extremity;
• and
• ΔX2 designates the traveling distance of said second lens group, upon zooming, from the short focal length extremity to the long focal length extremity.