<P> For a given subject framing and camera position , the DOF is controlled by the lens aperture diameter , which is usually specified as the f - number , the ratio of lens focal length to aperture diameter . Reducing the aperture diameter ( increasing the f - number ) increases the DOF because the circle of confusion is shrunk directly and indirectly by reducing the light hitting the outside of the lens which is focused to a different point than light hitting the inside of the lens due to spherical aberration caused by the construction of the lens ; however , it also reduces the amount of light transmitted , and increases diffraction , placing a practical limit on the extent to which DOF can be increased by reducing the aperture diameter . </P>
to control depth of field and amount of light what should be adjusted
the lens aperture diameter