Patent ID: 8223435
Filing Date: 2012-07-17
Classification: G02B

Abstract:
1. A zoom lens for projection comprising: a lens group having a negative refractive power that is arranged farthest to a magnification side of the zoom lens; a lens group having a positive refractive power that is arranged farthest to a reduction side of the zoom lens; and at least one lens group that is arranged between the lens groups, and moves when the magnification of the zoom lens is changed, wherein the reduction side of the zoom lens forms a telecentric system, and wherein the lens group that is arranged farthest to the reduction side is fixed when the magnification of the zoom lens is changed, and is composed of a negative aspheric lens made of a plastic material having at least one aspheric surface and a positive lens, and wherein at least one positive lens arranged on the reduction side of a lens having the smallest effective diameter among lenses composing the zoom lens satisfies the following formula (1): where νa: Abbe number of the at least one positive lens arranged on the reduction side of the lens having the smallest effective diameter among lenses composing the zoom lens for d-line, and dn/dt: a change in the refractive index of the material forming the at least one positive lens arranged on the reduction side of the lens having the smallest effective diameter among lenses composing the zoom lens for d-line when temperature changes from 20° C.