Blue Crane Digital Understanding The Canon 1D Mark IV Training DVD (zBC134)

the only way to ensure that your camera focuses on the correct subject is to select the AF point yourself earlier we demonstrated how to choose a focus point while looking through the viewfinder or looking at the function settings screen as you are choosing an AF point remember this not all focus points are created equal 39 of the 45 AF points are called across type points that means the AF point uses both vertically and horizontally oriented sensors to determine the correct focus focusing will be faster and more accurate in contrast these six AF points are not cross types they only have vertical sensors these sensors work best when focusing on subjects that are situated along the horizontal plane for example a vertical sensor would have no problem focusing on the horizon in this scene but it might not achieve focus on this candle this camera's horizontal sensors work faster and are twi