If you want to monitor the global expression of the FP, a low
magnification objective with high N.A. and long distance correction will
be suitable to see the fluorescent cells with ease. If you need to
visualize the subcellular distribution pattern of th FP, it is always
better to grow the cells on coverslips and to use a high N.A. immersion
objective. EBFP is a bit critical due to high background signals of the
plastics at low wavelength excitation light.
Greetings, Michael Schaefer