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The fine structure and the variations of the optical pulse shape and phase ofthe Crab pulsar are studied on various time scales. The observations have beencarried out on 4-m William Hershel and 6-m BTA telescopes with APD photoncounter, photomultiplier based 4-channel photometer and PSD based panoramicspectrophotopolarimeter with 1$\mu$s time resolution in 1994, 1999, 2003 and2005-2006 years. The upper limit on the pulsar precession on Dec 2, 1999 isplaced in the 10 s - 2 hours time range. The evidence of a varying from set toset fine structure of the main pulse is found in the 1999 and 2003 years data.No such fine structure is detected in the integral pulse shape of 1994, 1999and 2003 years.  The drastic change of the pulse shape in the 2005-2006 years set is detectedalong with the pulse shape variability and quasi-periodic phase shifts.Comment: 4 pages, 6 figures. To appear in ApSS, in the proceedings of the  conference "Isolated Neutron Stars: from the Interior to the Surface",  London, April 2006; eds. D. Page, R. Turolla and S. Zan

Short time scale pulse stability of the Crab pulsar in the optical band