#Circle Of Confusion
Circle of confusion is a term used in determining depth of field. Depth of field refers to how much of a scene is “sharp” with a given aperture, lens, and camera. What is “in focus” is the area of a scene in which a point of light is focused on the sensor or film plane at its smallest. To understand, imagine shooting at a very wide aperture where it’s easy to see what is in and what is out of focus and there are lights in the background. You can try this yourself with your camera for an example. Open the aperture as wide as you can and focus on something. The out-of-focus lights will expand and become “bokeh balls.” If you focus on the lights instead, they will become point-like. If you focus manually, you can see the lights grow as you focus past them in either direction. Long story short, circle of confusion is the out-of-focus area, and it is important to the determination of depth of field because, in order to define in-focus, we must define out-of-focus.