Patent ID: 7542213

Claim:
A projecting zoom lens comprising: a plurality of lens group, wherein: at least two lens groups out of the plurality of lens groups are moved to perform a power varying operation, a reduction side of the zoom lens is constructed as a substantially telecentric system, at least one lens out of lenses of the plurality of lens groups is formed of an aspheric lens having at least one aspheric surface, and the following Conditional Expressions (1) to (5) are satisfied: 1.2≦ bf/fw (1) | fa/fw|≦ 4.5 (2) φ a/φim≦ 1.0 (3) | ffaw/fw|≦ 1.5 (4) E≦ 300×10 −7 (/° C.) (5) where bf denotes an overall system back focus on the reduction side in air, fw denotes an overall system focal length at a wide angle end, fa denotes a focal length of the aspheric lens whose effective aperture is smallest, φa denotes a maximum effective aperture of the aspheric lens whose effective aperture is smallest, φim denotes a maximum diameter of an image circle in a conjugate position on the reduction side, ffaw denotes a distance, on an optical axis, between (i) a surface on a magnification side of a surface of the aspheric lens whose effective aperture is smallest and (ii) a focal position, on the magnification side, of a complex lens that consists of the aspheric lens whose effective aperture is smallest and all lenses located on the reduction side of the aspheric lens whose effective aperture is smallest, at the wide angle end, and E denotes a coefficient of a linear expansion of the aspheric lens whose effective aperture is smallest.