To convert Scheiner's subjective method into an objective optometer, we reverse the direction of light propagation. In other words, we put a spot of light on the retina which then becomes a point source which reflects light back out of the eye.

Next, drill some more holes in Scheiner's disk so it becomes a Hartmann screen. That way each aperture in the Hartmann screen isolates a narrow pencil of rays emerging from the eye through a specific part of the pupil. The rays then intersect a video sensor which tells us the horizontal and vertical displacement of the ray from the non-aberrated, reference position.

Thus we have a Hartmann aberrometer for objectively measuring the ray aberrations of the eye. Now fill the individual apertures of the Hartmann screen with tiny lenses and you have a Hartmann-Shack aberrometer, or as I would prefer to say, a Scheiner-Hartmann-Shack aberrometer.