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The isolation of the directions-image of small objects

Published online by Cambridge University Press:  14 March 2018

John William Evans
John William Evans*
Affiliation:
Imperial College of Science and Technology, and Birkbeck College
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Extract

There are two distinct kinds of image which are the subject of optical investigation: object-images, in which the form of the object is reproduced, and directions-images, in which every point represents a direction followed by light before reaching the objective. An instrument that shows a directions-image may be described as a hodoscope. It is focused not on the object but on infinity, so that parallel rays are collected at the same point in the image.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 18 , Issue 83 , November 1916 , pp. 45 - 51
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1916

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References

page 45 note 1 This term, from , a path, was first suggested by the author in Journ. Quekett Micx~scopieal Club, 1915, vol. xii, p. 618. The instrument has also been called a konoseope, but this is misleading, for it is the individual directions, not the cone that includes them, which are studied.

page 48 note 1 The position will vary according to the objective employed, the eye of the observer, and the part of the field under investigation.

page 49 note 1 This is not, of course, a real image, though it would become real if the direction of the transmission of the light were reversed.

page 50 note 1 See also Souza-Brandao, V., Zeits Kryst. Min., 1908, vol. xlv, pp. 331, 382Google Scholar.