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“OPTICAL MEMBRANES”: A COMMON ARTEFACT
Author(s) -
Oettlé A. G.
Publication year - 1950
Publication title -
journal of the royal microscopical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0368-3974
DOI - 10.1111/j.1365-2818.1950.tb04432.x
Subject(s) - contrast (vision) , object (grammar) , phase (matter) , optics , phase contrast microscopy , oblique case , physics , diffraction , phase change , artificial intelligence , computer science , philosophy , linguistics , engineering physics , quantum mechanics
SYNOPSIS. A common group of optical artefacts is described in which regions of phase or amplitude change in the object appear in sharp outline in the image, where they may be misinterpreted and regarded as evidence of the presence of actual membranes. It is shown that these appearances are always encountered with dark‐ground illumination, of both types, oblique and central, provided the object is large enough to be resolved. Similar effects can also be obtained with bright‐ground illumination and various phase‐contrast methods. With phase‐retarding objects in positive phase‐contrast, the appearance of a black outline to image detail is seen when reversal of contrast occurs. This is seen when the object produces higher phase change than the optimum for the particular system. This optimum depends on the ratio of direct to diffracted light: the less direct light is transmitted, the lower is the optimum range of phase change in the object.