The microscope : its construction and management : including technique, photo-micrography, and the past and future of the microscope (1893)
Heurck, Henri van, 1838-1909 · London : C. Lockwood ; New York : D. Van Nostrand Co. · leaf 72
d the part of the object shown at any timeapproximate to a mathematical plane. It is necessary that the angleof aperture of an objective be made proportional to its power; itwould be absurd to give a very great angle to a low power, for itwould thus be made to give details, which the eye could not… … J2 THE OBJECTIVES aperture was subject to various interpretations, Professor Abbe thoughtof the happy idea of replacing this measure by another, which is calledNumerical Aperture. This quantity is represented by the expression:O = n sin uwhere n represents the index of refraction of the surrounding…
Microscopy
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