Provided are lens optical systems. A lens optical system includes first to third lenses sequentially arranged in a direction from an object to an image sensor. The first lens may have a positive refractive power and an entrance surface convex toward the object. The second lens may have a negative refractive power and a meniscus shape convex toward the image sensor. The third lens may have a positive refractive power, and at least one of entrance and exit surfaces of the third lens may have an inflection point in a direction from a center region toward an edge thereof. The outer diameter D3 (in millimeters) of the exit surface of the third lens and the diagonal length ImgHMAX of a maximum pixel region of the image sensor may satisfy 2.6