The influence of geometric factors on problems in the measurement of radiation fields is considered. Field sources and probes are often assumed to be point-shaped in problems of field physics. The probes correspond to certain measurable quantities. In many situations in which field source or/and probe (test object) are not point-shaped, we may assume that deviation of the measurements from the idealized case mentioned above depends exclusively upon geometric factors. In this paper approximate solutions are discussed and explicitly presented for several geometric configurations under said assumption.