Optical system and camera module including same

A zoom optical system comprising a first lens group, a second lens group, a third lens group, and a fourth lens group which are sequentially arranged in a direction from a subject side to an image side,

• wherein the second lens group and the third lens group are movable,
• wherein an effective focal length (EFL) in a telephoto mode is defined by an expression below,
• 11.5
• <
• EFL
• tele
• H
• image
• ⁢
• D
• <
• 12.5
• ,
• here, EFLtele is the EFL of the zoom optical system in the telephoto mode, and HimageD is a half value of a diagonal length of a pixel area of an image sensor, and the pixel area of the image sensor is an area in which light-receiving pixels are arrayed in the image sensor which is located at an image plane behind the fourth lens group, and
• wherein a maximum diameter of a plurality of lenses included in the first lens group and the fourth lens group and a maximum diameter included in a plurality of lenses included in the second lens group and the third lens group are defined by an expression below,
• 1.1
• <
• APER
• fix
• APER
• mov
• <
• 1.45
• ,
• here, APERfix is the maximum diameter of the lens included in the first lens group and the fourth lens group which are fixed groups, and APERmov is the maximum diameter of the lens included in the second lens group and the third lens group which are moving groups.