Depth of Field
Depth of Field is the distance between the closest object and the farthest object to be in the photograph with an acceptable focus. In simpler words, Depth of Field is the area in the picture which will be in focus. If most of the picture or the entire picture is in focus, it means the image has a greater Depth of Field. If, on the other hand, only one element (the closest to the camera) is in focus and the rest (farther from camera) is out of focus, the picture has little Depth of Field.
So, how does the diaphragm alter Depth of Field? When we use a wider (open) diaphragm (remember that wider diaphragms are the smaller f#: f/1.4, f/2, etc.) the Depth of Field decreases. When we are using a smaller (close) diaphragm (larger f#: f/16, f/22, etc.), the Depth of Field increases.
Let's see this in a couple of examples. All these pictures were taken using the same lens (70mm DX, at the same distance).
