PROBLEM TO BE SOLVED: To provide a lens unit in which plural lens are coaxially inserted, the lens unit being capable of allowing expanded air to escape from the lens tube when adhesive for fixing the lenses go through a heat treatment and capable of achieving high accuracy positioning of a small diameter lens.SOLUTION: At least one of lenses disposed at both ends in axial direction of plural lenses to be inserted coaxially into a lens tube includes a penetration part penetrating in the axial direction. Adhesive for fixing the lens is applied to an outer peripheral surface of the lens at least excluding the penetration part. When the lenses are coaxially inserted into the lens tube to configure an objective lens system, an inner diameter of the lens tube and outer diameters of the lenses defined with tolerances for preventing effects from decentering and declination of the lenses extremely narrow gaps between the lenses and the lens tube, which will worsen ventilation of air between lenses. When the adhesive is heated for hardening, expanded air between lenses may dislocate the lenses. The penetration part, however, allows air to escape.COPYRIGHT: (C)2015,JPO&INPIT【課題】鏡筒に同軸的に挿入された複数のレンズを固定する接着剤を加熱処理する場合に膨脹エアを逃がすとともに、小径レンズの位置決めを高精度化し得る。【解決手段】鏡筒に同軸に挿入する複数のレンズの軸線方向端に配置される少なくとも一方のレンズに、軸線方向に貫通する貫通部を設け、レンズを固定する接着剤をレンズの外周面の少なくとも貫通部を除いた部分に塗布する。複数のレンズを鏡筒に同軸に挿入して対物レンズ系を構成する場合にレンズの偏心及び偏角による影響を受けないようにするための公差で鏡筒の内径とレンズの外径とを規定すると、レンズと鏡筒との隙間が極めて狭くなることから、レンズ間に封入されるエアの抜けが悪くなり、接着剤を加熱して硬化させる場合に、レンズ間の封入エアが膨脹するとレンズが動く虞が生じるが、貫通部によりエアを逃がすことができる。【選択図】図7
