These two series of images were taken to demonstrate the effect of aperture on the depth of field. Depth of field is the area of apparent sharpness in an image. With a vast depth of field, there is a large area both in front of and behind the subject that is in sharp focus and appears sharp in the image. With a narrow depth of field, only a thin band of apparent sharpness is present. Manipulating the depth of field is one of the creative techniques available to photographers.
As you may know, there are two determinants of depth of field: the proximity of the camera to the subject AND the aperture. As the distance between the subject and the camera increases, so does the depth of field. As the distance between the subject and the camera decreases, the depth of field decreases. For a given subject to camera distance, large apertures (f2.8) produce a narrow depth of field. As aperture decreases (f16), depth of field increases.
The following images were taken at the same subject-to-camera distance, with the camera on a tripod, so the only variable that changed in the images is the aperture. Note the narrow depth of field with the large apertures and the increased depth of field with the smaller apertures.
Hope this helps to illustrate the effect of changing apertures on depth of field.
At the suggestion of some of my forum members, I have added two animated GIF files, one for each series.
Excellent example of DOF providing a very useful reference. Surprising to me is that I seem to like shots at both extremes (f/20 & f/2.8) the best. Great job with this!