  Pointlike systems coupled to quantum fields are often employed as toy models
for measurements in quantum field theory. In this paper, we identify the field
observables recorded by such models. We show that in models that work in the
strong coupling regime, the apparatus is correlated with smeared field
amplitudes, while in models that work in weak coupling the apparatus records
particle aspects of the field, such as the existence of a particle-like time of
arrival and resonant absorption. Then, we develop an improved field-detector
interaction model, adapting the formalism of Quantum Brownian motion, that is
exactly solvable. This model confirms the association of field and particle
properties in the strong and weak coupling regimes, respectively. Further, it
can also describe the intermediate regime, in which the field-particle
characteristics `merge'. In contrast to standard perturbation techniques, this
model also recovers the relativistic Breit-Wigner resonant behavior in the weak
coupling regime. The modulation of field-particle-duality by a single tunable
parameter is a novel feature that is, in principle, experimentally accessible.
