Published online by Cambridge University Press: 06 November 2017
The 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 the 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 energy conservation. Despite major simplifications involved in such an analysis, it reproduces some results from the paraxial wave theory. In addition, 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.
The premature death of Anatoly Khitrin (1955–2017) took away from us a scientist of rare knowledge and imagination. His specialty was quantum physics and magnetic resonance, but he also had a unique ability to quickly get to the root of the most diverse problems, whether it was membrane biophysics, climate change, or trouble with a home furnace. He made original and useful inventions but never cared to patent them. Anatoly was a modest and gentle person, not seeking any special recognition, not jumping on bandwagons and “hot” topics. He thought about deep questions, achieved remarkable insights, helped colleagues and taught students – in other words, did what scientists are supposed to be doing.