PROBLEM TO BE SOLVED: To provide an optical unit which allows acquisition of stable optical characteristics and a reduction in size of an imaging apparatus.SOLUTION: An objective lens unit 40 includes: a lens frame 41 which has a first holding hole 51 having a preliminarily determined inside diameter dimension and having a front end opening 51h and a second holding hole 52 being a straight hole which has the same aperture axis as the first holding hole 51, has a diameter smaller than that of the first holding hole 51, and is constituted continuously to the first holding hole 51 via a step surface 51f so as to communicate with the first holding hole 51 a first lens 42 which is arranged in the first holding hole 51 and has a spherically concave portion 53 in the center on the side of the second holding hole 52 and a base end plane 54 provided on the outer periphery of the concave portion 53, wherein an inside diameter dimension of a circular edge part 55 of the concave portion 53 is set to be equal to or larger than that of the second holding hole 52 a second lens 44 arranged in the second holding hole 52 and a first diaphragm member 43 which is tabular and has, in the center, a diaphragm aperture 43m smaller than the inside diameter dimension of the second holding hole 52 and is arranged with a base end surface thereof in contact with the step surface 51f.COPYRIGHT: (C)2013,JPO&INPIT【課題】安定した光学特性を得られ、撮像装置の小型化を可能にする光学ユニットを提供すること。【解決手段】対物レンズユニット40は、予め定めた内径寸法で先端開口51hを有する第1の保持孔51、及び第1の保持孔51と開孔軸を同じくし、第1の保持孔51より小径なストレート孔で、第1の保持孔51に段差面51fを介して連設して連通して構成された第2の保持孔52を有するレンズ枠41と、第1の保持孔51内に配置される、第2の保持孔52側の中央に球形状凹部53、及び凹部53の外周に設けられた基端平面54を有し、凹部53の円形縁部55の内径寸法を第2の保持孔52の内径寸法以上に設定した第1のレンズ42と、第2の保持孔52内に配置される第2のレンズ44と、板状でその中央に第2の保持孔52の内径寸法より小径な絞り開口43mを有し、段差面51f上に基端面が当接して配置される第1の絞り部材43と、を具備している。【選択図】図4
