Imaging in fluorescence direct-view microscopy

We derive a general theory of imaging for the fluorescence direct-view microscope (DVM) in terms of the system's incoherent optical transfer function. Particular attention is given to both the form of the in-focus transfer function and the optical sectioning capability of the instrument in the presence of (i) a spatially incoherent source and (ii) a spatially coherent (laser) source. Unlike its brightfield counterpart, the imaging properties of the fluorescence DVM are shown to be relatively insensitive to the source coherence, provided the pinhole spacing-to-radius ratio is kept sufficiently large. This suggests that the use of a laser source in fluorescence direct-view microscopy could prove to be extremely beneficial as regards increased light throughput and cost-effectiveness. (C) 1998 Elsevier Science B.V. All rights reserved.