I am often asked in my Beginner Photography classes how to take a photo where the background is blurred at which point I start to discuss the camera’s Aperture. Aperture (Depth of Field or DOF) is just a fancy term for how much of the space between your camera and the horizon, or “infinity,” will be in focus in your photograph.
Your DOF is LARGE (DEEP) if lots of your scene is in focus; it is NARROW (SHALLOW), if there is only a small range of space that is in focus. Look at the photo of the young girl and pay attention to the background; This was shot with an aperture of 1.6. Many lenses do not open up to 1.6 so you have to see which is the maximum aperture your lens will open.

More to come on this…