This paper describes new techniques for self--calibration and for
recovering the motion from a projective reconstruction when the
calibration is known. We show that our approach deals with the
ambiguities in self--calibration produced by special motions.  We
extend our techniques to deal with varying calibration parameters.  In
passing, we prove convergence for the iterative
projective--reconstruction algorithm of Sturm/Triggs and
Berthilsson/Heyden/Sparr.