Quality Criteria of Lenses

An ideal lens would be one which is able to produce an image which represents an object exactly. An ideal lens could transfer all of the details of the object to the image without any variations. An ideal lens, however, could only exist under ideal conditions, and in the real world ideal conditions can not be achieved. As such, we must deal with real lenses, and real lenses produce slight variations between the object and the image. In order to show this, we represent the ability of a lens to transfer information from the object to the image as a Modulation Transfer Function (MTF).