A zoom lens includes, in order from the enlarging side, a first lens group that has negative refractive power, is movable for focusing, and is stationary during zooming, second, third, fourth, and fifth lens groups that are movable for zooming, and a sixth lens group that is stationary during zooming....http://www.google.com.au/patents/US6801367?utm_source=gb-gplus-sharePatent US6801367 - Zoom lens and projection display device which uses same
