The state of focus makes a big difference to the beam convergence at any point on the specimen.

The convergence is defined as the angular range from which the electrons incident on a point appear to come. This is shaded blue in the diagram.

List in order of increasing convergence angle: focused, underfocused, overfocused.

What would be the maximum convergence angle for a system with a condenser aperture of 50 µm diameter and a C2-specimen distance of 20 mm? Express your answer in milliradians.