  Homodyne tomography - i. e. homodyning while scanning the local oscillator
phase - is now a well assessed method for ``measuring'' the quantum state. In
this paper I will show how it can be used as a kind of universal detection, for
measuring generic field operators, however at expense of some additional noise.
The general class of field operators that can be measured in this way is
presented, and includes also operators that are inaccessible to heterodyne
detection. The noise from tomographical homodyning is compared to that from
heterodyning, for those operators that can be measured in both ways. It turns
out that for some operators homodyning is better than heterodyning when the
mean photon number is sufficiently small. Finally, the robustness of the method
to additive phase-insensitive noise is analyzed. It is shown that just half
photon of thermal noise would spoil the measurement completely.
