OBSERVATION APPARATUS

To provide an observation apparatus that can perform changing of an observation range while maintaining required observation image performance, quickly and using a wide change width.SOLUTION: An observation apparatus comprises: an objective lens that is an objective lens 2a focusing light from a sample in the observation device observing the sample, that is composed of a group of lenses including, from an object side, a single lens L1, in which concave surface is facing to the object side, and a variable aperture diaphragm changing an emission side numerical aperture of the objective lens, and in which magnification of the objective lens is more than or equal to 4 and less than or equal to 20; a camera that converts a sample image imaged by the objective lens to an image signal; an observation range change device that performs observation range change processing which changes an observation range by performing electronic variable magnification on the basis of the image signal obtained by the camera; and a control device that controls the variable aperture diaphragm according to the observation range change processing, and a conditional expression of 3≤|fa/fGS|≤10 is satisfied by defining a focal distance of the single lens as fa and defining a focal distance of the group of lenses from an object surface to the variable aperture diaphragm as fGS.SELECTED DRAWING: Figure 3 【課題】観察範囲の変更を、必要な観察像性能を維持しつつ高速且つ広い変更幅で実行することができる観察装置を提供する。【解決手段】観察装置は、標本を観察する観察装置において、標本からの光を結像する対物レンズ２ａであって、物体側から順に、物体側に凹面を向けた単レンズＬ１と、対物レンズの射出側の開口数を変更する可変開口絞りと、を含む正の屈折力を有するレンズ群から構成され、対物レンズの倍率が４倍以上２０倍以下である対物レンズと、対物レンズにより結像された標本の像を画像信号に変換するカメラと、カメラで得られた画像信号を元に電子変倍を行うことによって観察範囲を変更する観察範囲変更処理を行う観察範囲変更装置と、観察範囲変更処理に応じて可変開口絞りを制御する制御装置と、を含み、単レンズの焦点距離をｆａ、物体面から可変開口絞りまでのレンズ群の焦点距離をｆＧＳとして、３≦｜ｆａ／ｆＧＳ｜≦１０の条件式を満たす。【選択図】図３