The present invention provides an optical system comprising, at least one lens group for projecting an image on an image sensing means, an optical path being defined between a light entrance of said optical system and said image sensing means, a reflective optical element having convergent or divergent optical power and being located in said optical path, and means for moving the reflective optical element in response to unwanted movement of the imaging system to eliminate or mitigate the negative imaging effect of the said unwanted movement.