Disclosed are an optical system for infinite image formation and a method for fabricating a camera module using the optical system. The optical system includes a first lens unit including at least one lens; a projection chart capable of partially allowing light to pass therethrough; a backlight unit capable of emitting light; and a first holder coupled with the first lens unit, the projection chart and the backlight unit. The first lens unit is exposed through an opening of the first holder. The method includes coupling the optical system with a camera module including a first lens unit, an image sensor and a printed circuit board, where the optical system is coupled to the first lens unit; and adjusting an effective focal length between the first lens unit and the image sensor by rotating the optical system and the first lens unit of the camera module.