Inlet Aperture is the image of the physical aperture in the lenses that can be seen when viewed from the front where light enters the optical system. The view of the same aperture from the back of the lens is called the exit aperture. As the optical design includes glass elements in front of the physical diaphragm, the diameter of the entrance opening will appear larger or smaller than it actually is. The diameter of the aperture is variable depending on the magnification of the lens and its location within the optical design. The location of the entrance opening is the perspective center of the lens. In other words, it is the point where the parallax effect is zero. From this point of view, it is important in panoramic photography. In cases where multiple frames are taken and finalized into a single photograph, the camera is rotated in the horizontal plane, keeping the point at which the entrance opening of the attached lens is fixed. In this way, usage eliminates perspective errors.