  We discuss all possible fermion field renormalization prescriptions in
conventional field renormalization meaning and mainly pay attention to the
imaginary part of unstable fermion Field Renormalization Constants (FRC). We
find that introducing the off-diagonal fermion FRC leads to the decay widths of
physical processes $t\to c Z$ and $b\to s \gamma$ gauge-parameter dependent. We
also discuss the necessity of renormalizing the bare fields in conventional
quantum field theory.
