  In recent proposals for achieving optical super-resolution, variants of the
Quantum Fisher Information (QFI) quantify the attainable precision. We find
that claims about a strong enhancement of the resolution resulting from
coherence effects are questionable because they refer to very small subsets of
the data without proper normalization. When the QFI is normalized, accounting
for the strength of the signal, there is no advantage of coherent sources over
incoherent ones. Our findings have a bearing on further studies of the
achievable precision of optical instruments.
