（聚焦区）无限远与光学系统（如照像镜头）有关的一个范围，表示距离是如此之远，以至于从在这一距离的物体上反射回来的光可以视为平行光线

• A range in relation to an optical system, such as a camera lens, representing distances great enough that light rays reflected from objects within the range may be regarded as parallel.