Over on the Bird forum I put some advice on a thread about minimising camera shake saying to use 1/focal length as a general guide, not forgetting to put in the crop factor so for a Canon with a 400mm lens that would mean 1/640 sec. Postcardcv came back and said you did not have to allow for the crop factor so 1/400 would be sufficient even though the lens is effectually a 640. Who is right? Has anyone got any authoritative references?
