The technical determination of Depth of Field in photography involves measuring the “circle of confusion” created by out of focus points. As points get more and more out of focus they get larger. When they are above a certain size they are defined as out of focus, though the actual degree of sharpness decreases gradually.
The property of out of focus spots getting larger can be used creatively as I tried to do with the image below that I took yesterday in Foley Park just across the “ball bridge” in Norwich. I set my aperture fully open and used a lens and focus combination that gave me a lot of magnification–the two things that will result in shallow depth of field. I got one dew drop sharp and let the others grow into larger and larger circles of confusion.
The following blog has a slide show with 4 photos taken the same morning. I had my lens wide open for minumum depth of field for all of the images except the apple tree branches. However, the image of the blue jay has a lot of not-very-out-of-focus clutter behind the bird since the branches and blossoms were close to the jay. The background behind the house wren is better because it is farther from the wren. For the image of the apple blossoms in front of Tracy Hall I created a splash of colors using the very out of focus tulips in the background.