You are right, short exposures in alt az can give superb results as your image. Some astrophotographs are even going to lucky imaging below 1s to produce high resolution galaxy images to get rid of turbulences with the same technique as planetary imaging. The only limitation is that you can hardly image high in the sky where field rotation is strong.
Beautiful image indeed, Fr¨¦d¨¦ric?
Fr¨¦d¨¦ric Ruciak