US Patent 7375899 Compact zoom lens

A compact zoom lens includes, in order from an object side to an image side, a first lens group (1) of negative refractive power, and second, third, fourth and fifth lens groups (2, 3, 4, 5) of positive refractive power. The second, third and fourth lens groups are movable to effect zooming and focusing. During zooming from the telephoto end to the wide-angle end, the fourth lens group moves from the object side to the image side. The compact zoom lens has a long back focal length with various aberrations satisfactorily corrected, and a small F-number for enhanced image brightness.