This gave us an interference figure for the polyester film fully filling the rear focal plane or exit pupil of the objective as shown in Figure 22. The ray diagram in Figure 23 explains why opening the aperture diaphragm did not illuminate the outer portion of the rear focal plane of the 60X objective when the condenser height was previously established to give best Koehler illumination with the 10X objective. The high NA rays converged below the object focal plane because of uncorrected spherical aberration and diverged without passing through the field of the 60X objective. Figure 24 illustrates what happened when the condenser was raised.  The intermediate NA rays now passed around the field of the objective and converged above.  The axial rays still go through the object field. Figure 25 illustrates what happened when the field diaphragm was opened fully so that the intermediate NA rays could pass through the object focal plane along with the high and low NA rays. Figure 26 illustrates the situation for an aplanatic condenser without spherical aberration. Lonert indicated the same behavior for an Abbe condenser but provided no examples or ray diagrams⁸.

Figure 23

Figure 24

Figure 25

Figure 26