Depth of Field and Subject Magnification
The focal length and the distance to subject have an influence on the Depth of Field, and this influence is simple to understand if it is explained with the notion of subject magnification. The subject magnification is a function of the focal length and the distance to subject. It is the parameter that influences the most the DoF, much more than the aperture. This articles explains what is the subject magnification and in which way it impacts the DoF.