Requirements for the design and production of high numerical aperture objectives for 4Pi confocal microscopy

We discuss the requirements on design and production regarding geometric and chromatic aberrations for objectives used in 4Pi confocal microscopy. We show that even the selection of a category 1/1 glass will not automatically assure that these requirements are met. due to residual variations in the Abbe number nu within the manufacturers tolerances. Consequently, the optical design has to take into consideration the possibility of balancing chromatic aberrations by varying selected air spacings in the final assembly of each individual objective. We also demonstrate. that for analyzing the influence of aberrations on the intensity distribution along the optical axis. a scalar diffraction theory is still applicable and very useful.