INNER-FOCUS OPTICAL SYSTEM

To provide an inner-focus optical system which has a light-weight focusing lens group, exhibits less image height variation when the focusing lens group is wobbled in an optical axis direction, and offers a bright F-number of 1.4 and a view angle corresponding to a 35 mm-equivalent focal length of 28-40 mm.SOLUTION: An inner-focus optical system disclosed herein comprises, in order from the object side to the image side, a first lens group G1 consisting of a negative single lens, an aperture stop S, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power, and is configured such that the third lens group G3 moves toward the object side when shifting focus from an object at infinity to an object at a short distance.SELECTED DRAWING: Figure 1 【課題】フォーカスレンズ群が軽量で、またフォーカスレンズ群を光軸に沿う方向へ微少振動（ウオブリング）させた際の像高変化率が小さく、Ｆ値が１．４と明るく、３５ｍｍ判換算焦点距離で２８～４０ｍｍ相当の画角を有するインナーフォーカス光学系を提供する。【解決手段】物体側から像側へ順に、負の単レンズからなる第１レンズ群Ｇ１と、開口絞りＳと、正の屈折力の第２レンズ群Ｇ２と、正の屈折力の第３レンズ群Ｇ３と、負の屈折力の第４レンズ群Ｇ４とからなり、無限遠物体側から近距離物体側へのフォーカシングをする際、前記第３レンズ群Ｇ３が物体側へ移動するインナーフォーカス光学系とする。【選択図】図１