Title: Bright-field microscopy of transparent objects: a ray tracing approach,
Abstract: Formation of a bright-field microscopic image of a transparent phase object
is described in terms of elementary geometrical optics. Our approach is based
on the premise that image replicates the intensity distribution (real or
virtual) at the front focal plane of the objective. The task is therefore
reduced to finding the change in intensity at the focal plane caused by the
object. This can be done by ray tracing complemented with the requirement of
conservation of the number of rays. Despite major simplifications involved in
such an analysis, it reproduces some results from the paraxial wave theory.
Additionally, our analysis suggests two ways of extracting quantitative phase
information from bright-field images: by vertically shifting the focal plane
(the approach used in the transport-of-intensity analysis) or by varying the
angle of illumination. In principle, information thus obtained should allow
reconstruction of the object morphology.