58 



PROGRESS IN MICROSCOPY 



on while ground. The effects are not marked with an apochromatic 

 objective but, conversely, are significant with an achromatic one. 



Chart 1.1 



y =- distance between two points 



r ^ disk radius 



e — width of thin line 



p = distance between two bright or two 

 opaque lines. 



CiiAKi 1.2. Chromatic kffecis on iiii; imagh conirasi of a small black 



DISK ON WHHE GROUND 



(coherent illumination for each wave-length) 



