what I have learned about depth of field is that for a shallow picture you have to have your camera at a 55mm and the F at a 5.6 to get a close but blurry background. you want to make sure that your using your lens to focus in on the object and take the picture from a low angle. and if you are taking a good picture for depth of field you have you camera at a 18mm and the F at a 16 and stand back to get a wide look in the picture. Also depth of field is the zone within a photo that appears sharp and in focus, in every picture there is a point of focus where you focus your lens, Shallow depth of field photos are noticeable because the subject will remain steady while the background renders as a smooth, creamy blur.