Alternative derivation of the Ruska/Langmuir reduced-brightness/spot-blurring formula, and some related comments

This conference poster present an alternative derivation of a well known formula that relates both to the concept of reduced brightness in a charge-particle (CP) beam and to the blurring of field-ion image spots. It is then argued that field ion images provide a practical illustration of some aspects of CP optics, including the issue of whether reduced brightness is always a conserved quantity.