Patent ID: 6993256

Claim:
A method for controlling a lens group having a focus lens and a zoom lens group along an optical axis, where the zoom lens group includes at least one zoom lens, comprising: receiving input to change position of the focus lens; separately controlling positions of the focus lens and the zoom lens group along the optical axis such that the focus lens and the zoom lens approach no closer to one another than a selected minimum safe distance, for any selected magnification provided by the zoom lens group and the focus lens, said separately controlling comprising determining initial position of the at least one zoom lens, said separately controlling comprising determining a permissible working range; moving the focus lens to a best focus position within said permissible working range; wherein said moving the focus lens to the best focus position within said permissible working range comprises: selecting a focus figure of merit; moving the focus lens in one direction along the optical axis; tracking the position of the focus lens along the optical axis; if the focus figure of merit increases, moving the focus lens again in said one direction to a final position that is no further than a boundary of said permissible working range; and if the focus figure of merit decreases, moving the focus lens again in a direction opposite said one direction to a final position that is no further than a boundary of said permissible working range.