The optical image forming system is equipped with a basic optical system, having an image-forming function as a single body, and a dome-type lens arranged on the object side of the basic optical system, turning its convex surface to the object side, and made variable in terms of its relative position in an optical axis direction to the basic optical system. 本発明の結像光学系は、単体で結像機能を持つ基本光学系と、前記基本光学系の物体側に配置され、物体側に凸面を向け、前記基本光学系に対する光軸方向の相対位置が可変のドーム型レンズとを備えたことを特徴とする。 - 特許庁