Not quite it ... if a star is focused on the slit and it moves up or down the length of the slit (as it can if the seeing disk is smaller than the slit length) then the image formed by the second lens (as described by you) will move up and down. Note: I said "an important aperture (perhaps a grating or camera mirror) is at that lens' focal point" so is this lens "focused on the slit"?

Hint #2: the astronomer in question also made important contributions to our knowledge of a layer of the Earth's atmosphere