Image Number 3 for United States Patent #6531698.
The invention relates to a particle-optic illuminating and imaging system with a condenser-objective single field lens (5) and a simple illuminating system which has only two condenser lenses (3, 4). The variation of the size of the illuminated field takes place exclusively by a change of the excitation of the source-side condenser lens (3). The objective-side second condenser lens (4) always has a constant excitation in the TEM mode. The excitation of the source-side condenser lens (3) is the greatest for maximum illuminating field diameter, and on the contrary is reduced for smaller illuminating field diameters. In TEM operation, two crossovers always exist in the illuminating beam path, of which the second is situated between the focal plane of the condenser-objective single field lens and the specimen plane (6).