ZOOM LENS FOR PROJECTION, AND PROJECTION-TYPE DISPLAY DEVICE

WIPO Patent Application WO/2014/076923

A1

[Problem] To provide a zoom lens for projection in which a high magnification ratio is maintained, the numerical aperture is fixed across the entire magnification range, and a sufficiently long back focus is maintained. [Solution] A zoom lens for projection comprising at least two mobile lens groups (G2-G5) that move during changes in magnification, and an aperture stop (St), wherein a variable stop, the aperture diameter of which varies such that the numerical aperture of the zoom lens is fixed across the entire magnification range, is used for the aperture stop (St). Furthermore, conditional expressions (1) and (2) are satisfied, where Bf is the reduction side back focus (air-equivalent distance) of the entire system at the wide angle end, Imφ is the maximum effective image circle diameter (image circle diameter) on the reduction side, and L is the distance, along the optical axis, from the lens surface furthest to the enlargement side when the zoom distance is infinity to the lens surface furthest to the reduction side. 2.5