The canon ef 400mm f4 do is ii usm is a super telephoto prime lens for photographers on the move the lens incorporates a three mode image stabiliser is to allow the use of shutter speeds at up to 4 stops slower which is particularly useful when shooting handheld in dimly lit environments inside the lens is canons third generation diffractive optics do to ensure superb image quality with improved resistance to flare and coloured fringing power focus technology allows pull focus effects