Anamorphic attachment is a Galileo tube, or the well-known theater binoculars, through which you look from the other side.
As is known, a feature of such an optical system is that the parallel beam entering it is parallel and exits, since the focal point of the negative lens coincides with the focus of the positive one.
In the anamorphic system, the lenses are not spherical, but cylindrical.
In other words, in one section these are all the same circles, and in the other plane-parallel plates.