a zoom lens system is provided including a flat cam for driving the zoom lens mechanism . in one particular embodiment , the same flat cam used by the zoom lens system is used to correlate the effective focal length of the zoom lens to the viewfinder . additional particular embodiments of a viewfinder adjustment mechanism are provided wherein the viewfinder adjustment mechanism includes a diopter adjustment mechanism to adjust the ocular lens of the viewfinder to compensate for imperfections in the user &# 39 ; s sight .