Zoom lens and image capturing apparatus having the same

A zoom lens system and an image capturing apparatus having the same. The zoom lens includes a first lens group having a positive refractive power; a second lens group having a negative refractive power; a third lens group having a positive refractive power; and a fourth lens group having a positive refractive power, wherein the first through fourth lens groups are sequentially arranged from an object side to an image side, and the third lens group includes a first positive lens, a doublet lens including a second positive lens and a third negative lens, and a fourth positive lens sequentially arranged from the object side.